Modern container coatings

Modern Container Coatings

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Modern Container Coatings Robert C . Strand, EDITOR American Can Company

A symposiu the Division of Organic Coatings and Plastics Chemistry at the 174th Meeting of the American Chemical Society, Chicago, IL, August 2 9 September 2, 1977.

78

ACS SYMPOSIUM SERIES

AMERICAN

CHEMICAL

SOCIETY

WASHINGTON, D. C. 1978

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Library of Congress CIP Data Modern container coatings. (ACS symposium series; 78. ISSN 0097-6156) Bibliography: p. 124 + ix. Includes index. 1. Containers—Congresses. 2. Coatings—Congresses. I. Strand, Robert C., 1925. II. American Chemical Society. Division of Organic Coatings and Plastics Chemistry. III. Series: American Chemical Society. ACS symposium series; 78. TS198.3.C6M63 ISBN 0-8412-0446-2

621.7'57 ACSMC8

78-14801 78 1-124 1978

Copyright © 1978 American Chemical Society All Rights Reserved. The appearance of the code at the bottom of the first page of each article in this volume indicates the copyright owner's consent that reprographic copies of the article may be made for personal or internal use or for the personal or internal use of specific clients. This consent is given on the condition, however, that the copier pay the stated per copy fee through the Copyright Clearance Center, Inc. for copying beyond that permitted by Sections 107 or 108 of the U.S. Copyright Law. This consent does not extend to copying or transmission by any means—graphic or electronic—for any other purpose, such as for general distribution, for advertising or promotional purposes, for creating new collective works, for resale, or for information storage and retrieval systems. The citation of trade names and/or names of manufacturers in this publication is not to be construed as an endorsement or as approval by ACS of the commercial products or services referenced herein; nor should the mere reference herein to any drawing, specification, chemical process, or other data be regarded as a license or as a conveyance of any right or permission, to the holder, reader, or any other person or corporation, to manufacture, reproduce, use, or sell any patented invention or copyrighted work that may in any way be related thereto. PRINTED IN THE UNITED STATE OF AMERICA

American Chemical

Society Library

1158Container 16th St. N.W.Strand, R.; In Modern Coatings; ACS Symposium Series; American Chemical Washington, D. C. Society: 20036 Washington, DC, 1978.

ACS Symposium Series Robert F. G o u l d , Editor

Advisory Board Kenneth B. Bischoff

Nina I. McClelland

Donald G . Crosby

John B. Pfeiffer

Jeremiah P. Freeman

Joseph V . Rodricks

E. Desmond Goddard

F. Sherwood Rowland

Jack Halpern

Alan C. Sartorelli

Robert A . Hofstader

Raymond B. Seymour

James P. Lodge

Roy L. Whistler

John L. Margrave

Aaron Wold

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

FOREWORD The ACS SYMPOSIUM SERIES was founded in 1974 to provide

a medium for publishin format of the SERIES parallels that of the continuing ADVANCES IN CHEMISTRY SERIES except that in order to save time the papers are not typeset but are reproduced as they are submitted by the authors in camera-ready form. As a further means of saving time, the papers are not edited or reviewed except by the symposium chairman, who becomes editor of the book. Papers published in the ACS SYMPOSIUM SERIES are original contributions not published elsewhere in whole or major part and include reports of research as well as reviews since symposia may embrace both types of presentation.

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

PREFACE Containers—metal, glass, and more recently plastic—are an essential part of our food and beverage distribution system. The technology of these containers, particularly metal cans, has developed steadily over the past 75 years. A key to the success of the metal container has been the development and availability of organic coatings which offer a wide range of performance properties. Early coating materials such as C-enamel, which is used in corn cans, were relatively simple to manufacture and apply. They did not represent a high level o for a specific packaging need. Once a coating was developed, it tended to remain in use for many years because there generally was little reason to change it. With the advent of newer can-making technology such as the drawing-redrawing and the drawing and ironing processes, newer and more sophisticated coating materials were needed. Environmental concerns and energy conservation pressures also have contributed to the demand for new and different coating materials. This trend is seen also in the glass container industry where safety coatings for beverage bottles are now in use. Much of the change in coating technology has taken place within the past four to five years and brings the latest, most modern coating technology to the container industry. That segment of the coating industry which serves the packaging business is characterized by vigorous competition among suppliers and the use of extensive proprietary know-how. For these reasons it is difficult for coating chemists to discuss their company products or processes. For example, there are no papers in this symposium on the wash coating of two-piece beverage cans because the process involves proprietary technology on the part of several companies. Despite these problems, this symposium succeeds in surveying the main areas of coating development and analysis currently used in the rigid packaging industry. I would like to thank the authors whose time and effort contributed to the success of this symposium. American Can Company,

ROBERT C. STRAND

Barrington Technical Center, Barrington, IL May 31, 1978 ix In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

1 Waterborne Spray Can Coatings DAVID Ο. LAWSON PPG Industries, Delaware, OH 43015

In preparing to cove was difficult to determin coatings and the reasons for their increased interest in the industrial coatings field. Other presentations here have and w i l l mention some of the areas I wish to review. However, for understanding of water borne spray can coatings, we will explain the purpose of spraying the interior of metal cans, review why the various legislative actions of recent years have stimulated development of water borne sprays, give a general insight into coating formulations, and relate field experience with coating handling and equipment operation. From this, we will be able to have some feeling for the future of water borne spray can coatings. The metal can industry supplies the major share of its pro­ duction for the beer and soft drink markets. With calculations from various industry figures, this highly specialized business today is producing in the range of 45 to 50 b i l l i o n cans annually. The three-piece can is produced from decorated flat stock, which has undergone a number of coatings operations. Handling of sheets through the coating stages and subsequent can forming oper­ ations can be expected to damage the interior basecoat through abrasion and scratching. Complete protection and coverage must be achieved with the steel substrates used for three-piece cans, because of the delicate flavor properties of beer and the corrosiveness, as well as taste considerations, of carbonated soft drink products. The interior spray, then is actually a repair coating and is the last operation in coating of the can body. Two­ -piece cans are taking over the major share of the beverage can market and are produced in the integral form of the drawn cup. Both aluminum and tinplated steel substrates are used today, and again protection of beverages from the metal and of metal from the product to be packaged requires the inside spray coating. For some years, the interior sprays have been familiar or­ ganic coating types with organic solvents as the transport media. Reduction of organic solvent emissions from such coatings has 0-8412-0446-2/78/47-078-001$05.00/0 © 1978 American Chemical Society In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MODERN CONTAINER COATINGS

2

been a goal f o r some time and e f f o r t s i n c r e a s e d w i t h the advent of the famous Los Angeles Rule 66. Here i t was proposed to a l l o w s o l v e n t emissions i f s o - c a l l e d Rule 66 exempt s o l v e n t s were used. F i v e to s i x years l a t e r , other s e c t i o n s of the country had adopted Rule 66 and even added some more s t r i n g e n t requirements to attempt meeting governmental A i r Q u a l i t y Standards. Again, Los Angeles l e d the way w i t h a modified Rule 66, but we i n the coatings i n d u s t r y were given the opportunity to proceed w i t h water borne coatings which, along w i t h high s o l i d s c o a t i n g s , were made exempt from any requirements of i n c i n e r a t i o n of v o l a t i l e s . You should be aware that important progress was made i n the development and c o m m e r c i a l i z a t i o n of water r e d u c i b l e e l e c t r o c o a t ings i n the e a r l y 1960 s. This c o m m e r c i a l i z a t i o n and some b e t t e r understanding of how to formulate water r e d u c i b l e polymers to meet the demands of i n d u s t r i a l a p p l i c a t i o n s took p l a c e before the l e g i s l a t i v e pressures askin emissions. We were working c l o s e l y w i t h major can companies to see what place could be found f o r the e f f i c i e n t e l e c t r o d e p o s i t i o n process. This l e d to spray a p p l i c a t i o n s of the water r e d u c i b l e polymer systems that were e v o l v i n g f o r i n t e r i o r beer and s o f t d r i n k cont a c t . I t was recognized that the spray a p p l i c a t i o n area i n can p l a n t s i s a source of h i g h emissions, because of the spray opera t i o n and the use of low s o l i d s content c o a t i n g s . The i n d u s t r y was moved toward changing to water borne i n t e r i o r sprays because s o l v e n t emissions could be reduced by as much as 70 to 80% over the low s o l i d s , organic s o l v e n t c o n t a i n i n g c o n v e n t i o n a l systems. Remember, t h i s c o a t i n g o p e r a t i o n takes place f o r every beer and s o f t d r i n k can manufactured . As f u r t h e r i n c e n t i v e , the avenue of water borne spray o f f e r s continued use of e x i s t i n g equipment, which represents extremely high c a p i t a l investment i n the can industry. The f i r s t challenge from these m a t e r i a l s , then, i s to spray apply on the v a r i o u s types of a i r and a i r l e s s spray equipment i n the many can producing p l a n t s . The coatings are a l s o t a i l o r e d to meet cure c o n d i t i o n s d i c t a t e d by the v a r i o u s s u b s t r a t e s , s i d e seam c o n s t r u c t i o n , and oven designs i n use i n the i n d u s t r y . Of major importance, of course, i s meeting the h i g h e r temperature, s h o r t e r time c y c l e of the two-piece can cure. The f i n a l measure of a c c e p t a b i l i t y f o r a can l i n e r i n contact w i t h beer and s o f t d r i n k products i s to meet the performance and f l a v o r c h a r a c t e r i s t i c requirements expected. Much of the s u c c e s s f u l a p p l i c a t i o n to date i n v o l v e s a c r y l i c and epoxy chemistry, and we w i l l d i r e c t our b r i e f review f o r t h i s p r e s e n t a t i o n to those types of thermosetting m a t e r i a l s . These coatings are processed v i a an a d d i t i o n a l p o l y m e r i z a t i o n of monomers i n i t i a t e d by thermal decomposition of a f r e e r a d i c a l i n i t i a t o r . P o l y m e r i z a t i o n i n a batch r e a c t o r uses a c o u p l i n g s o l v e n t and chain t r a n s f e r s o l v e n t s to c o n t r o l molecular weight. Following proper p o l y m e r i z a t i o n , a p o r t i o n of the organic a c i d groups f

1

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

1.

LAWSON

Waterborne

Spray Can

Coatings

3

along the polymer backbone are converted to amine s a l t s , u s i n g an a p p r o p r i a t e amine, t o render the polymer r e d u c i b l e i n water. As i n many polymer systems, s t r i c t a t t e n t i o n i s given t o raw materi a l s , t h e i r p r o p o r t i o n s and a d d i t i o n r a t e s , times, temperatures, and s p e c i f i c process check p o i n t s . A m u l t i t u d e of p r o c e s s i n g f a c t o r s a f f e c t s u c c e s s f u l manufacture of product, and each i n t u r n would i n v o l v e d e t a i l e d study o f engineering parameters. I w i l l simply mention these f o r our purposes as: proper s e l e c t i o n and p r e p a r a t i o n o f equipment, c a r e f u l c o n t r o l o f p o l y m e r i z a t i o n c o n d i t i o n s , and m a i n t a i n i n g awareness o f how such f a c t o r s a f f e c t polymer molecular weight, p a r t i c l e s i z e , e t c . The performance of the water borne spray c o a t i n g so produced i s extremely dependent on p r o c e s s i n g procedures. As we work w i t h water borne spray c o a t i n g s , our b i g g e s t challenge comes from the rheology and s u r f a c e w e t t i n g c h a r a c t e r i s t i c s that are so predominantl Coated, as w e l l as bar problems. I n the area o f spray, of course, behavior o f the coating m a t e r i a l upon a t o m i z a t i o n through spray n o z z l e s has a great b e a r i n g on the w e t t i n g and coverage a l s o . Experience has been g e n e r a l l y good i n the h a n d l i n g o f these coatings through convent i o n a l equipment. Some reeducation i s r e q u i r e d i n the a c t u a l s e l e c t i o n o f spray nozzles because newer coatings cannot necessari l y have the exact same s o l i d s , v i s c o s i t y , and rheology propert i e s o f the c o n v e n t i o n a l coatings they r e p l a c e . O v e r a l l , recognize the f a c t t h a t l i n e c o n d i t i o n s vary w i d e l y i n the i n d u s t r y . Such f a c t o r s as temperature, type spray machine, can c o n f i g u r a t i o n , pressure a v a i l a b l e , can r o t a t i o n speeds, and many more can and must be d e a l t w i t h . To d i s c u s s these t o any degree would consume a great deal o f the time to which we are l i m i t e d f o r one p r e s e n t a t i o n . I b e l i e v e other speakers w i l l b e t t e r d e s c r i b e some equipment d e t a i l s . We are meeting these challenges and through experience the use of water borne spray coatings i s becoming more f a m i l i a r t o the i n d u s t r y . With these low s o l v e n t coatings h e l p i n g to meet A i r Q u a l i t y Standards, and the recognized s a f e t y aspects o f storage and h a n d l i n g , we can c e r t a i n l y expect t h i s technology t o enjoy a great growth p a t t e r n and a long and u s e f u l l i f e c y c l e . RECEIVED MAY 22, 1978.

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

2 Fast-Cure Epoxy Powders as Beer and Beverage Can Interior Lacquers PETER H. SCOTT, DONALD C. CLAGETT, and KENNETH V. FISCHER Dewey and Almy Chemical Division, W. R. Grace & Co., 55 Hayden Avenue, Lexington, MA 02173

The Clean Air Act the coatings industry t coatings (1, 2). These alternatives include waterborne coatings, powder coatings, non-aqueous dispersions, radiation cured total solids, and electrodeposition. Relative to coating the interior of beer/beverage cans with a solvent-free material, the Dewey and Almy Chemical Division of W. R. Grace & Co. has elected to pursue development of a powdered lacquer. Powdered coatings contain l i t t l e or no volatile effluents and require low energy consumption for application and cure. DISCUSSION Any acceptable beer/beverage can coating must meet several general requirements. It must be formulated exclusively of materials approved for this use by the FDA (3). It must not affect the taste of the beverage packed in the can. It must be coated at low film weights (thin films) to minimize coating expense, and when used in a two-piece can it must cure within two minutes at a maximum temperature of 400°F to meet existing line specifications. Other powder properties necessary to economically coat beer/beverage cans are: 1. Fine particle size powders on the order of 5-8 micron mean diameter. 2. Good bulk flow and fluidization such that the powder does not cake or cause blockage inside the application tubing. This is critical when dealing with very fine particle powders.

0-8412-0446-2/78/47-078-004$05.00/0 © 1978 American Chemical Society In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

2.

s e o i r ET AL.

Fast-Cure

Epoxy

Powders

3.

Minimal overspray and high t r a n s f e r e f f i c i e n c i e s .

4.

The powdered m a t e r i a l must be formulated such that i t does not b u i l d up (impact fuse) on moving machinery p a r t s i n s i d e the a p p l i c a t i o n device.

5

To meet the above requirements thermosetting epoxies and epoxy/phenolics were chosen f o r powder c o a t i n g development a t Grace. These r e s i n s have had a h i s t o r y of s u c c e s s f u l use as solvent base m a t e r i a l s and thus the p o t e n t i a l f o r o b t a i n i n g a powder w i t h the p r o p e r t i e s needed f o r an i n t e r i o r can c o a t i n g was high. T y p i c a l epoxy powder f o r m u l a t i o n s t e s t e d contained a b i s - p h e n o l A type epoxy r e s i n , c u r i n g agent ( a c i d i c or b a s i c ) , l e v e l i n g agent, w e t t i n g agent and c a t a l y s t (4, 5 ) . I n i t i a l t e s t r e s u l t s i n our l a b o r a t o r y showed that coatings w i t h acceptable p h y s i c a cure times a t 400°F wer (Table 1). This was a key problem s i n c e an oven residence time of two minutes or l e s s i s a n e c e s s i t y on a commercial beer^ beverage can l i n e . I n c r e a s i n g oven temperatures above 400 F was one obvious o p t i o n f o r reducing cure time, but that o p t i o n was r u l e d out because of increased energy consumption and other commercial c o n s t r a i n t s . Therefore, we screened a v a r i e t y of formulations to s e l e c t c u r i n g systems w i t h exotherms a t or below 400°F as determined u s i n g d i f f e r e n t i a l scanning c a l o r i m e t r y (DSC). Samples were prepared by m i c r o m i l l i n g raw m a t e r i a l m i x t u r e s , and DSC scans were made u s i n g a duPont 990 instrument. The sample s i z e was 17 -1 mg., and the samples were heated i n a n i trogen atmosphere at 0.3 mm p o s i t i v e pressure. Our i n i t i a l work showed that standard mixtures of epoxy and c u r i n g agent had exotherms a t or above 400°F (Figures 1 and 2 ) . Both a c i d and base c a t a l y s t , however, gave i n i t i a l exotherms s i g n i f i c a n t l y lower than obtained w i t h the uncatalyzed systems (Figure 3). U n f o r t u n a t e l y , many of these f o r m u l a t i o n s degraded other necessary p r o p e r t i e s , and some i n f a c t r e s u l t e d i n unstable powder f o r m u l a t i o n s . The survey revealed f i n a l l y that t r i m e l l i c t i c anhydride (TMA) cured epoxy powders could be c a t a l y z e d using e i t h e r stannous octoate (Figure 4) or dicyandiamide (DICY) (Figure 5 ) . Based on t h i s technology we have prepared epoxy powders w i t h small p a r t i c l e s i z e and narrow p a r t i c l e s i z e d i s t r i b u t i o n (Figure 6) which meet the requirements f o r an acceptable beer/ beverage can c o a t i n g . The p r o p e r t i e s of a t y p i c a l epoxy powder cured w i t h TMA and c a t a l y z e d w i t h stannous octoate a r e given i n Table I I . I t should be noted that both c a t a l y s t and c u r i n g agent a r e accepted by the FDA f o r use i n can c o a t i n g s as a r e s u l t of s u c c e s s f u l p e t i t i o n s by W. R. Grace & Co. and Sherwin W i l l i a m s Co.

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MODERN CONTAINER COATINGS

100

—I·— 150

Temperature Figure 1.

100

150

—h250

200

300

C

DSC scan of Τ M A/epoxy

200

250

300

Temperature °C Figure 2.

DSC scan of DICY/epoxy

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SCOTT ET AL.

Figure 4.

Fast-Cure

Epoxy

Powders

DSC scan of TMA/epoxy with stannous octoate catalyst

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MODERN CONTAINER COATINGS

Figure 5.

DSC scan of TMA/epoxy with DICY catalyst

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

2.

s e o i r ET AL.

Fast-Cure

Epoxy

9

Powders

TABLE I EFFECT OF CURING AGENT TYPE ON THE CURE: EPOXY/CURING AGENT RATIO = 1.5/1

AGENT

CURE TIME (minutes)

T r i m e l l i t i c Anhydride

4

P o l y a z e l a i c Polyanhydride

5

P h t h a l i c Anhydride

7

Dicyandiamide

8

XD 8038

1

C i t r i c Acid

Variable

Phosphoric A c i d

Variable

TABLE I I PROPERTIES OF DEWEY AND ALMY POWDERED CAN LACQUER FOR TWO-PIECE BEER/BEVERAGE CANS PROPERTY Cross Hatch Adhesion i n B o i l i n g Water

PERFORMANCE pass

Reverse Impact on Parker Panels (160 i n . l b . )

pass

P a s t e u r i z a t i o n Resistance (212°F/10 minutes)

pass

Flexibility (1/8 i n c h c o n i c a l mandrel)

pass

Beverage Pack Resistance (beer and s o f t d r i n k )

>1 month @ 100°F

Flavor P r o f i l e Testing

pass

Enamel Rater (WACO)

pass

I r o n Pick-up

pass

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MODERN CONTAINER COATINGS

10

As of now, equipment f o r a p p l y i n g Grace powders to twopiece can i n t e r i o r s i s i n commercial development a t Coors i n Golden,Colorado. We have succeeded i n powder c o a t i n g q u a l i t y cans at commercial l i n e speeds w i t h no impact f u s i o n and good transfer e f f i c i e n c i e s . SUMMARY In c o n c l u s i o n , W. R. Grace & Co. has succeeded i n develop­ ing a i r p o l l u t i o n - f r e e powdered epoxy can lacquers whose r e a c t i v i t y a l l o w s c u r i n g a t current commercial r a t e s using e x i s t i n g can-maker ovens and s e t t i n g s . I t i s very l i k e l y that these powdered coatings w i l l a l s o a l l o w r e d u c t i o n i n energy input as compared to that r e q u i r e d f o r solvent c o a t i n g s . Grace's developing powder technology represents an imme­ d i a t e s o l u t i o n to th emissions and conservin

REFERENCES CITED 1.

Gardon, J . L. and Prane, J . W., Non-polluting Coatings and Coatings Processes, Plenum Press, New York, New York, 1973, pp 1-13.

2.

Cole, J r . , G. E . , Plastics Raw Materials to End Products and Coatings, American Chemical Society, Division of Chemical Marketing and Economics, 1974, pp 168-9.

3.

Code of Federal Regulations, Title 21, paragraph 175.300.

4.

Talen, H. and Teringa, P. Μ., Powder Coating, Elsevier Sequoia Patent Report No. 4, Elsevier Sequoia, S. Α., Lausanne, Switzerland, 1974, pp 3-13.

5.

Miller, E. P. and Taft, D. D., Fundamentals of Powder Coating, Society of Manufacturing Engineers, Dearborn, MI, 1974, pp 16 and 162, 211-220.

6.

Zorll, Ü., Progress in Organic Coatings, 4, pp 124-125, (1976).

RECEIVED M A Y 22,

1978.

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

3 Waterborne Two-Piece Body Spray L. A. WATSON Technical Coatings Co., North & 25th Avenues, Melrose Park, IL 60160

The epoxy resins have served the container coatings industry well for many years. Solvent based epoxy systems have been designed for utilization in almost every segment of canclosure manufacture. If not as the basic backbone (component) of the coating system, the epoxy resin found merit as a modifier for other resinious materials. With the increased emphasis for ecologically acceptable coating, epoxy chemistry has been directed toward meaningful water borne systems. New water borne epoxy ester coatings have been developed in recent years which are fairly equivalent, in performance, to their solvent counterpart. Film integrity, such as fabrication, steam processing and moderate corrosion resistance can be maintained. Applied cost of the water borne systemVSi t s solvent counterpart is lower mainly because of the restricted use of expensive solvents. Recent developments have produced interior can coatings which meet the FDA requirements as per Regulation 121.2514, now 175.300. Formulating latitude with the water borne epoxy systems have allowed the chemist to circumvent the problems of taste, odor and turbidity when exposed to beer packaging. Application of spray linings can be tailored to provide adequate coverage over both steel and aluminum D&I containers. Commercial acceptance of epoxy water borne spray lining for the beer and beverage container is on the rise. This article w i l l relate to the interior spray application.

0-8412-0446-2/78/47-078-011$05.00/0 © 1978 American Chemical Society In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MODERN CONTAINER COATINGS

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DISCUSSION: Water borne epoxy i n t e r i o r c o a t i n g s can be c l a s s i f i e d i n t o three d i f f e r e n t groups: a) b) c)

Water D i s p e r s i b l e Epoxy Coatings Water Epoxy Emulsion Coatings Water Borne Epoxy C o a t i n g s - S o l u t i o n Type

From the above c l a s s i f i c a t i o n s the chemist must survey the known data f o r the necessary p h y s i c a l parameter conducive toward the proposed end use ( i n t e r i o r spray l i n i n g i n t h i s c a s e ) . Negative aspects sometimes p l a y the more aggressive r o l e i n the choice of v e h i c l e development GROUP A - WATER DISPERSIBLE EPOXY COATINGS In water d i s p e r s i b l e epoxy c o a t i n g s , the epoxy r e s i n i s d i s p e r s e d w i t h the a i d of a s u i t a b l e d i s p e r s i n g agent. These systems are heterogeneous i n nature and have s e v e r a l d i s t i n c t disadvantages : 1.

The d i s p e r s a n t must be h e l d to an a b s o l u t e minimum because of p o s s i b l e f l a v o r contamination i n packaged beer or beverage.

2.

Solvent t o l e r a n c e of dispersion i s rather extremely c r i t i c a l . factor separation i s

3.

Extended storage g e n e r a l l y produces s e t t l i n g w i t h i n the f i n i s h e d goods (product).

4.

Spray a p p l i c a t i o n of the epoxy d i s ­ p e r s i o n systems i s extremely d i f f i c u l t . (Poor s u b s t r a t e w e t t i n g ) .

the r e s u l t a n t l i m i t e d and Because of t h i s g e n e r a l l y noted.

GROUP Β - WATER EMULS IF TABLE EPOXY SYSTEMS 1.

S i m i l a r t o the epoxy d i s p e r s i o n f a m i l y , but much more complex.

2.

Need f o r an e m u l s i f y i n g agent and other s u r f a c e a c t i v e agents t o p r o t e c t the encapsulated p a r t i c l e .

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

3.

WATSON

Waterborne

Two-Piece

Body Spray

The n e c e s s i t y f o r such a d d i t i v e s , to maintain s i o n system, i n c r e a s e s b i l i t y of f l a v o r o f f the packed media.

13

additional the emulthe p o s s i notes of

3.

P o s s i b i l i t y of water s e n s i t i v i t y g e n e r a l l y caused by the presence of the v a r i o u s surface a c t i v e agents.

4.

Lowest g l o s s f a c t o r of the three v a r i a b l e s under c o n s i d e r a t i o n .

5.

Spray a p p l i c a t i o the epoxy d i s p e r s i o n system.

GROUP C - WATER BORNE EPOXY SOLUTION SYSTEMS The s o l u t i o n type water borne epoxy coatings a r e g e n e r a l l y epoxy r e s i n s e s t e r i f i e d w i t h d i f f e r e n t a c i d s . These e s t e r s a r e subsequently n e u t r a l i z e d w i t h amines. Water and a s u i t a b l e c o s o l v e n t a r e then added t o reduce the polymer t o the d e s i r e d n o n - v o l a t i l e content. Curing agents of v a r i o u s types (such as Melamines, Urea-Formaldehyde o r P h e n o l i c s ) may then be added t o optimize the system. The r e s u l t a n t epoxy system e x h i b i t s exc e l l e n t g l o s s , f l o w and f i l m formation. This type of c o a t i n g system i s very comparable t o s o l v e n t based epoxy coatings even i n product r e s i s t a n c e . Having resigned o u r s e l v e s to concentrate on the development of the s o l u t i o n type water borne epoxy, s e v e r a l major parameters must be s a t i s f i e d . These a r e : 1.

Taste and Odor P r o f i l e - (The c o a t i n g m a t e r i a l should n e i t h e r impart or d i s t r a c t any f l a v o r connotations from the packaged media).

2.

T u r b i d i t y Resistance - (Maintain the d e s i r e d c l a r i t y of the packaged goods).

3.

Application - (Sprayability).

4.

Shelf S t a b i l i t y - ( H y d r o l i t i c stability).

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

14

MODERN CONTAINER COATINGS

EXPERIMENTAL DETAILS A l l c o a t i n g systems were evaluated over the 12 oz. (211 χ 413) two p i e c e aluminum c o n t a i n e r (D&I). The treatment on these c o n t a i n e r s were both A l o d i n e 401-45 and 404. The s t e e l D&I can was a l s o i n c l u d e d i n our i n v e s t i g a t i o n . Dry f i l m depo­ s i t i o n f o r the aluminum c o n t a i n e r was 120-140 mgs./can and the s t o v i n g c y c l e 2 minutes @ 400 F. For the s t e e l c o n t a i n e r the f i l m weights were increased to 180-200 mgs./can and cured 2 minutes @ 400°F. The coated c o n t a i n e r s were evaluated f o r beer and water p a s t e u r i z a t i o n at 160 F. f o r 30 minutes. Taste and odor pro­ f i l e s were generated as w e l l as beer t u r b i d i t y d e f i n i t i o n . The attached dat water borne coatings evaluate TABLE I Having e s t a b l i s h e d a v a i l i d coatings candidate ( s o l u t i o n water borne epoxy) our next step was to d e f i n e r e p r o d u c i b i l i t y and s t o v i n g l a t i t u d e . TABLE I I I n d i c a t e s our f i n d i n g s w i t h System A - Laboratory Β - 1st P i l o t Batch.

Batch:

TABLE I I I Represents our t a s t e and odor c h a r a c t e r i z a t i o n s . Having s u c c e s s f u l l y demonstrated the v a l i d i t y of our approach u t i l i z i n g the s o l u t i o n type epoxy, one major h u r d l e remained: That being a p p l i c a t i o n . Because of v a r i o u s p r o f i l e s of the D&I c o n t a i n e r being used i n the i n d u s t r y , s p r a y a b i l i t y (uniform coverage) can be very e v a s i v e . A s s i s t a n c e from the spray equipment people was e n l i s t e d to maximize our e f f o r t s . C o l l e c t i v e l y , we were able to achieve good f i l m d i s t r i b u ­ t i o n of s i d e w a l l coverage from 3.0 to 3.5 mgs./4 i n . ^ and y i e l d enamel r a t e r readings of an average of 5 ma. Total f i l m weight i n the container was roughly 120 mgs. Temperature, pressure and s o l v e n t balance seemed to have more i n f l u e n c e on our m a t e r i a l than d i d i n i t i a l v i s c o s i t y . B e t t e r a t o m i z a t i o n at the lower f l u i d volume output seems to be the key.

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

ok

ok

Vinyl

Epoxy/ Acrylic Emulsion

Epoxy Disper­ sion

Epoxy Solu­ tion Type

Coating A

Coating Β

Coating C

Coating D

ok

ok

>100

>100

>50

10-15

SI.Blush

ok

MEK Rubs

Beer Past. 160°F. 30 Min.

ok

ok

ok

ok

ok

Excellent

ok

ok

ok

Satisfactory

Adhesion

ok

ok

Taste

Turbidity Resistance A f t e r 3 Mos. @ 105°F.

*Coating A & Β gave i n f e r i o r r e s u l t s on s t e e l cans compared to aluminum. However, coating C and Coating D has equivalent performance on both aluminum and s t e e l cans.

ok

SI.Blush

Type

System

Water Past. 160°F. 30 Min.

TABLE I. WATER BORNE COATINGS

ok

ok

Not Satis­ factory

ok

Flavor

ok

ok

ok

Not S a t i s f a c t o r y

Application Characteristic

ok

ok

ok

Satis­ factory

Stability 6 Months 9 77°F.

MODERN CONTAINER

16

COATINGS

TABLE I I

H 0 Past. 30 @ 160°F. X Scotch Tape 2

f

Beer P a s t . 30 @ 160°F. X Scotch Tape T

404 Alumn.

2

@ 360°F.

A

0-0

0-0

401 Alumn.

2' @ 360°F.

A

10-10

8-2

Steel

2' @ 360°F.

A

10-10

0-0

404 Alumn.

2

1

@ 360°F.

Β

10-8

9-8

401 Alumn.

2

f

@ 360°F

Steel

V

404 Alumn.

V

1

@ 360°F.

Β

@ 385°F.

A

10-10

10-9

401 Alumn.

2

@ 385°F.

A

10-10

10-8

Steel

2' @ 400°F.

A

10-10

10-10

404 Alumn.

2

@ 385°F.

Β

10-10

10-10

401 Alumn.

V

@ 385°F.

Β

10-10

10-10

Steel

2

@ 400°F.

Β

10-10

10-10

1

?

1

Lab Batch O r i g . A 1st P i l o t Batch - Β Legend:

0 - Complete F a i l u r e 10 - P e r f e c t

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

3.

WATSON

Waterborne

Two-Piece

17

Body Spray

TABLE I I I

A l l samples and the c o n t r o l were prepared u s i n g unpasteur­ i z e d beer. The samples were then p a s t e u r i z e d and h e l d f o r approximately 30 days before the f l a v o r e v a l u a t i o n was conducted. The t a s t e panel c o n s i s t e d of 8 p a n e l i s t s . CODE SHEET Lab Number C o n t r o l (Blank) Sample A Sample Β Sample C (Solvent base epoxy c o n t r o l )

C o l l e c t i v e Panel R a t i n g +1.3 +1.4

Distribution* 7/0/1 8/0/0

*In the r a t i n g d i s t r i b u t i o n , the f i r s t f i g u r e i n d i c a t e s how many panel members gave a p l u s (+) o p i n i o n ; the second f i g u r e i n d i c a t e s how many gave a zero ( 0 ) ; the t h i r d f i g u r e s i g n i f i e s how many gave a minus (-) r a t i n g . COMMENTS CONTROL SAMPLE D u l l aroma. Reasonably f r e s h . Rather f u l l i n body and f l a v o r . A t r a c e of harshness. The hop b i t t e r and a f t e r t a s t e are of average i n t e n s i t y . The f l a v o r i s moderately aromatic and malty, r a t h e r d r y and e s t e r y , s l i g h t l y a s t r i n g e n t w i t h a g r a i n y note. Good d r i n k i n g q u a l i t y . SAMPLE A S l i g h t l y f r e s h e r t a s t i n g and smoother p a l a t e than the Con­ t r o l Sample. Very good d r i n k a b i l i t y . SAMPLE Β Smoother p a l a t e and diminished d r y overtones. acceptance.

Good panel

SAMPLE C (Solvent Base Epoxy C o n t r o l ) A t r i f l e f r e s h e r t a s t i n g w i t h smoother p a l a t e and lessened dry notes. Reasonably good d r i n k i n g q u a l i t y .

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MODERN CONTAINER COATINGS

18

SUMMARY While other approaches d i r e c t e d toward the i n t e r i o r spray a p p l i c a t i o n of the D&I c o n t a i n e r have m e r i t , we f e e l that the water borne s o l u t i o n epoxy o f f e r s the best l a t i t u d e . Coating systems based on t h i s technology r e q u i r e very l i t t l e d e v i a t i o n from the norm w i t h r e s p e c t t o r e s i n manufacture and subsequent letdown. This i s a v e r y prominent f a c t o r t o consider because most of the previous knowledge of s o l v e n t type epoxy systems can be r e a d i l y a p p l i e d . I n d i c a t i o n s are that some energy cons e r v a t i o n and improved economics can a l s o be achieved. ACKNOWLEDGMENT Many thanks t o D opment input and Herb Goldt f o r h i s meticulous l a b o r a t o r y i n v e s t i g a t i o n . Thanks a l s o t o the Nordson people f o r t h e i r valuable contribution. RECEIVED JUNE 12,

1978.

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

4 Container Coatings Based on Dispersions of Epoxy Resins in Water FRANK N. JONES, THOMAS H. GLADNEY, WILLIAM T. SOLOMON, JOHN R. GREENWALD, JOHN E. MASTERS, and DAVID A. SHIMP Celanese Polymer Specialties Co., Technical Center, 9800E Bluegrass Parkway, Louisville, KY 40299

Coatings based o epoxy and beverage containers for over twenty-five years. These coatings are based on blends of resin (idealized structure in Fig.1) with a small proportion of crosslinker, usually an aminoplast which reacts predominately with the secondary hydroxyl groups along the backbone of the resin. Baking produces a film which has much of the toughness and chemical resistance of a thermoset coating yet retains considerable elasticity and is capable of excellent adhesion. These characteristics give epoxy coatings an outstanding combination of properties for container interiors - chemical inertness, physical damage resistance, little or no effect on flavor and the ability to protect metal from contents and vice versa.

Figure 1. Soon after the development of the two-piece drawn and ironed beverage can, epoxies were recognized as a preferred coating. In addition to adhesion and toughness, epoxy coatings are able to overcome a number of irregularities that occasionally arise during two-piece can production. They cover surface scratches well, they protect container contents from substances such as drawing lubricants which are occasionally left on the metal surface, and they are somewhat tolerant of variations in metal pretreatment, application and bake conditions. Most epoxy resins used in container linings are especially tailored for the purpose. Molecular weights are relatively high, ranging from 2500 to 8000 (n = 8 to 27 in Figure 1). 0-8412-0446-2/78/47-078-019$05.00/0 © 1978 American Chemical Society In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MODERN CONTAINER COATINGS

20

Lower molecular weights are usable, but molecular weights above 2500 impart superior elasticity to the film and are believed to reduce the potential for food or beverage contamination from traces of uncrosslinked substances in the cured film. Epoxy coating technology has not been static. In recent years "low-bake formulations based on specific resins, crosslinkers and solvent blends have been developed. Low-bake coatings can be cured at oven temperatures 20°C. to 40°C.lower than first generation epoxy coatings and they have broader bake latitude. Oven temperatures can vary over a 30°C. range without serious adverse effects. Historically the r e l i a b i l i t y of epoxy container coatings has been superb. Over 1QU cans have been coated, and the frequency of major coating-related problems has been very low. Epoxy coatings have established an excellent reputation among brewers for their abilit and among food canners aggressive contents. Container coatings are usually applied by rollcoating flat stock or by high-speed automatic spray into formed cans. Both methods require the resins to be used as dilute solutions in organic solvents to achieve low viscosity, substrate wetting and film-thickness control. Current formulations usually are sprayed at 20% to 23% solids by weight and are rollcoated at 28% to 42% solids. Application in this form causes air pollution and i t wastes solvents and energy. Therefore, new physical forms for epoxy coatings are needed. The industry is seriously examining coatings based on four technologies : (1) Water-dilutable epoxy resins (2) Emulsions of liquid epoxy resins in water (3) Dispersions of solid epoxy resins in water (4) Epoxy powders Each of these technologies has some attractive features, but each involves major technical problems. Our group has been exploring a l l of them for more than a decade. In recent years we have been working intensively with the third, epoxy dispersions. This paper is a generalized report on how this technology is progressing. CURRENT DISPERSION COATING FORMULATIONS. An epoxy dispersion container coating is based on a small particle size dispersion in water of solid resins and crosslinkers very similar to those used in solvent-borne coatings. Small amounts of dispersants are required to stabilize the dispersion, and other substances are usually added to adjust rheology for application. The total weight of non-volatile additives may be 2% to 8% of the weight of the film. Particle diameter is predominately 0.5^um to 3jam, although this may not be the optimum range. Spray formulations contain 25% to 30% 11

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

4.

JONES ET AL.

Container

Coatings

21

s o l i d s by weight; r e l a t i v e l y high s o l i d s are p o s s i b l e because the dispersed r e s i n adds l i t t l e t o the v i s c o s i t y o f the medium. The f o r m u l a t i o n complies w i t h a l l a p p l i c a b l e requirements of S e c t i o n 175.300 of T i t l e 21 of Code o f F e d e r a l Regulations f o r food contact coatings (1). Such coatings have been manufactured i n production equipment. O r i g i n a l l y i t was hoped that such d i s p e r s i o n s could be a p p l i e d on present-day spray equipment w i t h almost t o t a l p o l l u t i o n abatement. However, most c u r r e n t formulations i n c o r p o r a t e 18% to 20% by volume of organic s o l v e n t t o improve s p r a y a b i l i t y and to promote formation o f uniform f i l m s . FILM PROPERTIES OF DISPERSION COATINGS The r e s i n s used i n d i s p e r s i o n coatings a r e B i s p h e n o l - A / e p i c h l o r o h y d r i n types c r o s s l i n k e d w i t h amino r e s i n s , s i m i l a r t o those used i n solvent-borne epox coatings Ther i d reduce the molecular weigh bond s o l u b i l i z i n g groups to make t w a t e r - d i l u t a b l e . Molecula weight i s w i t h i n the 2500 to 8000 range p r e f e r r e d f o r f i l m p h y s i c a l p r o p e r t i e s and f l a v o r . This advantage i s being r e a l i z e d in practice. Industry requirements f o r p r o p e r t i e s such as s o l v e n t r e s i s t a n c e , adhesion, p a s t e u r i z a t i o n r e s i s t a n c e and absence of v o l a t i l e s i n the cured f i l m have been met or exceeded. For example, d i s p e r s i o n coatings r e s i s t the necking and f l a n g i n g of two-piece cans b e t t e r than current coatings based on watersoluble resins. Dozens of beer f l a v o r t e s t s o f v a r i o u s formulat i o n s have given c o n s i s t e n t l y good r e s u l t s , u s u a l l y e q u a l l i n g c o n t r o l s and sometimes surpassing them. Of course, s u b s t a n t i a l e f f o r t was r e q u i r e d to f i n d d i s p e r s a n t s and m o d i f i e r s which do not adversely a f f e c t c o a t i n g p r o p e r t i e s . Crosslinkable modifiers which meet t h i s requirement have been i d e n t i f i e d . METAL PRETREATMENT D i s p e r s i o n coatings have e x c e l l e n t adhesion t o detergentwashed aluminum, to aluminum t r e a t e d w i t h the standard p r e treatments and to most of the surfaces encountered i n s t e e l cans. However, i t i s recommended that i n c o n v e r t i n g to water-borne coatings of any type the i n d u s t r y should take e x t r a care w i t h washing and pretreatment procedures u n t i l the boundaries of acceptable p r a c t i c e can be d e f i n e d . Such care might prevent c o a t i n g f a i l u r e caused by adhesion l o s s o r poor w e t t i n g . Formulators of any water-borne c o n t a i n e r c o a t i n g face an inherent problem: the surfaces t o be coated are designed t o be e a s i l y wetted by solvent-borne coatings whose surface tensions u s u a l l y range from 26 t o 28 dynes/cm. Water has a very high surface t e n s i o n , 72 dynes/cm. at 25°C, and i t w i l l not wet low energy s u r f a c e s . A d d i t i v e s are a v a i l a b l e which are capable of reducing surface t e n s i o n t o about 32 dynes/cm. and which are acceptable f o r use i n food contact c o a t i n g s , but the i d e a l 26 dynes/cm. l e v e l i s d i f f i c u l t t o achieve. Even i f low surface

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

22

MODERN CONTAINER COATINGS

t e n s i o n i s achieved, i t i s d o u b t f u l that water-borne coatings can be as e f f e c t i v e as solvent-borne ones i n " b i t i n g " i n t o o i l contaminated s u r f a c e s . APPLICATION The most troublesome o b s t a c l e s to developing water d i s p e r s i o n coatings l i e i n the a p p l i c a t i o n area. The formulator i s faced w i t h the formidable task of a p p l y i n g a d i s p e r s i o n on equipment designed to s u i t the r h e o l o g i c a l c h a r a c t e r i s t i c s of a s o l u t i o n . The rheology of the d i s p e r s i o n i s g r o s s l y d i f f e r e n t . Further, the d i s p e r s i o n o f f e r s r e l a t i v e l y l i t t l e l a t i t u d e f o r a d j u s t i n g s o l v e n t evaporation r a t e s . In the e a r l y stages of development a p p l i c a t i o n d i f f i c u l t i e s c h a r a c t e r i z e d by poor s u b s t r a t e w e t t i n g , b l i s t e r i n g , poor atomizat i o n during spray, spray n o z z l e p l u g g i n g , i n s t a b i l i t y at elevated temperatures and poor flow during r o l l c o a t i n g were encountered. These problems have bee by a s e r i e s of s u c c e s s f u r e p r e s e n t a t i v e production c o n d i t i o n s . They were solved mainly by f o r m u l a t i o n refinements combined w i t h minor equipment changes. D i s p e r s i o n coatings having e x c e l l e n t a p p l i c a t i o n c h a r a c t e r i s t i c s have r e c e n t l y been formulated. Only minor set-up a d j u s t ments are needed to convert a two-piece can l i n e from s o l v e n t borne to aqueous d i s p e r s i o n spray c o a t i n g s . Beer f i l m weights (90-120 mg./can) can be achieved, and the r e l a t i v e l y high s o l i d s of d i s p e r s i o n coatings are advantageous f o r s o f t - d r i n k f i l m weights (160-220 mg./can). S p e c i a l spray n o z z l e s now being designed e s p e c i a l l y f o r water-borne coatings may o f f e r advantages. To prevent spray n o z z l e plugging a l l s o l i d p a r t i c l e s l a r g e enough to plug a 70 o r i f i c e have been s c r u p u l o u s l y e l i m i n a t e d . P a r t i c l e diameter i s under good c o n t r o l i n the 0.5 ^um to 3 jim range, and few i f any p a r t i c l e s as l a r g e as 10 jam are present i n current formulations. No i n s t a n c e of n o z z l e plugging has occurred i n more than two years of l a b o r a t o r y and production trials. D i s p e r s i o n coatings have s e v e r a l advantageous a p p l i c a t i o n characteristics : (1) Spray l i n e s t a r t up i s easy; the o p a c i t y of the wet c o a t i n g a l l o w s the operator to v i s u a l l y check u n i f o r m i t y of coverage. (2) Clean up i s e a s i e r than w i t h any other c o a t i n g type. (3) Less f i l t e r blockage occurs than w i t h other types of water-borne c o a t i n g s . A l s o , d i s p e r s i o n coatings o f f e r p o t e n t i a l energy savings. Baking temperatures are s i m i l a r to those of "low-bake" epoxy c o a t i n g s , and the cure r a t e i s such t h a t the f i r s t oven zone can be operated at reduced temperature. F u r t h e r , the low p r o p o r t i o n of s o l v e n t could reduce the amount of heated a i r which must be exhausted to stay s a f e l y below the lower e x p l o s i v e l i m i t .

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Type

borne,

borne,

borne,

Powder

Resin

dispersed

Water-borne,

dispersed

Water

dilutable

Water

dilutable

Water

resin

resin

resin

resin

Solvent borne, maximum s o l i d s

Solvent borne, standard s o l i d s

Coating

99

38.0

27.5

20.0

20.0

23.0

20.6

% Solids By W e i g h t

95:5

80:20

80:20

70:30

By Volume

Ratio of to O r g a n i c

96:4

83:17

83:17

74:26

By W e i g h t

0.066:1

0.45:1

0.68:1

1.04:1

3.35:1

3.85:1

Weight R a t i o Organic V o l a t i l e s to S o l i d s

99%

98%

88%

82%

73%

13%

Standard

Organic Solvent Reduction

OF SPRAY-TYPE EPOXY INTERIOR CAN COATINGS.

I.

Water Solvent

AIR POLLUTION ABATEMENT POTENTIAL

TABLE

MODERN CONTAINER COATINGS

24

Formulations for three-piece cans, end stock and side-seam stripe are not yet as well refined as those for two-piece cans, but we believe that dispersion technology w i l l soon find uses in these areas. AIR POLLUTION ABATEMENT Current dispersion coatings are formulated to meet a l l presert and proposed U.S. environmental regulations. The volatile portion contains at most 20% of organic solvent measured by volume. Current coatings based on water-dilutable epoxy resins are frequently formulated at a 70:30 water : organic solvent volume ratio to meet interim regulations. The proportion of solvent can be reduced, but technical problems multiply as coupling solvent is subtracted. An 80:20 ratio appears feasible, but i t may be near the limit of what can be accomplished without substantial trade off. In contrast, coating potential to far exceed current EPA regulations and to meet the very stringent regulations being proposed abroad. Coatings which are virtually solvent free are possible, and a formulation having a 95:5 water : organic solvent ratio shows considerable promise. However, such formulations cannot be properly applied to two-piece cans using presently available equipment. The application problems could probably be overcome with concentrated engineering effort. Even when formulated at an 80:20 water : solvent ratio, dispersion coatings are ecologically attractive because they can be applied in more concentrated form than water-dilutable types. The situation is summarized in Table I, from which i t can be seen that to apply a given weight of solids from a water-dilutable coating containing 20% solids by weight requires about 50% more solvent than to apply i t from a dispersion coating containing 27.5% solids. This factor is expected to increase in importance in future years. The trend in U.S. regulatory philosophy is toward controlling total organic effluent and away from the less fundamental approach of controlling water : solvent ratio. SUMMARY The feasibility of using epoxy dispersion coatings formulated at an 80:20 water :organic solvent volume ratio for two-piece cans has been firmly established. The technology is expected to be broadly applicable to other container interior uses. It offers a number of advantages including the potential for almost total pollution abatement. In the future, as environmental regulations tighten, the advantages of dispersion technology may become compelling. LITERATURE CITED (1) Title 21 was recently reorganized; the former section 121.2514 is now section 175.300. Federal Register 42, No.50, page 14545 (1977). RECEIVED MAY 23, 1978.

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

5 Coatings for Drawn Tinplate and Chrome-Coated Steel Food Containers G. W. GERHARDT, K. G. DAVIS, and J. R. HALL Mobil Chemical Co., Packaging Coatings Dept., 2000 Westhall St., Pittsburgh, PA 15233 Drawn container mad fro tinplat d chrome -coated steel are beginnin tration into the food containe market. U t i l i z a t i o n of these substrates for the production of a single draw or draw-redraw container has been prompted primarily by three factors: 1. The success of the drawn aluminum container in this market. 2. The increasing concern with the p o s s i b i l i t y of introducing trace quantities of lead into the packed product when lead-containing solders are used in making three-piece s o l dered side seam containers. 3· The continuing desire by industry to investigate whether better or lower cost containers than those already on the market can be made commercially. The manufacturer of a single or multiple draw container requires coatings which have much better fabr i c a t i o n properties than those commonly used on tinplate and chrome-coated steel three-piece containers where the coating must withstand only a simple forming, or is applied after fabrication of the container. The drawn container is fabricated from precoated metal to yield a container with a wall thickness essentially equal to the thickness of the bottom of the container and, in turn, equal to the thickness of the o r i g i n a l f l a t metal stock. There is very little thinning or thickening of the metal, but the metal is d r a s t i c a l l y reformed, p a r t i c u l a r l y on the sidewall near the top of the can. From a p r a c t i c a l standpoint, the industry would l i k e to form the container to the maximum capability of the metal being used. Thus, i t i s necessary that the coatings industry develop coatings which will perform under severe drawing conditions. Also,to 0-8412-0446-2/78/47-078-025$05.00/0 © 1978 American Chemical Society In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MODERN CONTAINER COATINGS

26

provide extra strength i n the w a l l of the container, many c a n s h a v e c i r c u m f e r e n t i a l b e a d s i n t h e b o d y . The b e a d i n g o p e r a t i o n i s done a f t e r d r a w i n g o f t h e c a n and thus adds f u r t h e r d e f o r m a t i o n . Coatings f o r food containers, by n e c e s s i t y , must have t h e u l t i m a t e i n p h y s i c a l p r o p e r t i e s . In addition t o t h e r e q u i r e m e n t t h a t t h e c o a t i n g n o t change t h e food I n a n y w a y , t h e c o a t i n g must p o s s e s s a m u l t i t u d e of other r e q u i r e m e n t s . S t e r i l e food packs are produced by p r o c e s s i n g t h e c o n t a i n e r a f t e r p a c k i n g of t h e food or by a s e p t i c a l l y p a c k i n g a s t e r i l e product i n a sterilized container. The e l e v a t e d t e m p e r a t u r e s to which the c o n t a i n e r i s exposed d u r i n g these processes r e q u i r e that the coatings perform under elevated temperatures as w e l l as at normal storage temperatures. The p a r t i c u l a r p r o p e r t i e s w h i c h t h e c o a t i n g s must possess are that the p r o c e s s i n g c y c l e , and t h e c o a t i n g on t h e e x t e r i o r o f the c o n t a i n e r must have e x c e p t i o n a l s c u f f resistance at elevated temperature since that coating i s In direct contact with the s t e r i l i z i n g equipment. A f t e r the container i s f i l l e d and processed, then the o r g a n i c c o a t i n g must p r o t e c t t h e f o o d p r o d u c t d u r i n g s t o r a g e p e r i o d s a s h i g h as 100°F. f o r p e r i o d s a s long as two or three years . Experimental The p r i m a r y p r o b l e m s i n t h e e v a l u a t i o n o f c o a t ings f o r drawn c o n t a i n e r s is to obtain meaningful test results i n a short period of time so that sign i f i c a n t p r o g r e s s c a n be a c h i e v e d rapidly. E a r l y i n o u r w o r k w e f o u n d t h a t we c o u l d n o t d u p l i c a t e the drawing of a c o n t a i n e r by any simple fabrication test. We t h e r e f o r e p r o c u r e d e q u i p m e n t f o r d r a w i n g a 202X200 c a n u t i l i z i n g a 44$ r e d u c t i o n I n t h e f i r s t d r a w a n d 22$ i n t h e s e c o n d d r a w . After we d i d c o n s i d e r a b l e w o r k w i t h t h i s s t r a i g h t - w a l l e d c o n t a i n e r , we f o u n d t h a t i t was n o t q u i t e as severe in f a b r i c a t i o n as commercial c o n t a i n e r s , s o we p r o c u r e d a s e t o f t o o l s w h i c h beads t h e c a n . A deep bead n e a r t h e f l a n g e a r e a g i v e s us a s e x t r e m e fabrication a s we h a v e s e e n o n m o s t c o m m e r c i a l c a n s . A f t e r f a b r i c a t i o n of the container, the cans are p a c k e d , seamed w i t h a n e n d w h i c h has a p r o d u c t resistant c o a t i n g on i t and p r o c e s s e d . We p r e f e r u s i n g a 90 m i n u t e a t 2 5 0 ° F . p r o c e s s , e v e n t h o u g h some p r o d u c t s do n o t r e q u i r e s u c h s t r i n g e n t s t e r i l i z i n g c o n d i t i o n s . After cooling of the containers, the e x t e r i o r and i n t e r i o r a r e examined f o r c o a t i n g performance a n d ,

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

5.

GERHARDT ET AL.

Coatings

for Food

Containers

27

presuming the coatings pass t h i s i n i t i a l screening, d u p l i c a t e c o n t a i n e r s a r e p l a c e d on s t o r a g e a t room t e m p e r a t u r e a n d a t 120°F. We r e c o g n i z e t h a t n o f o o d p r o d u c t s a r e s t o r e d a t 1 2 0 ° F . , b u t we u s e t h i s temperature t o a c c e l e r a t e breakdown of the coated c a n . The b e s t way o f d e v e l o p i n g a c o a t e d c a n f o r a p a r t i c u l a r p r o d u c t i s t o pack that p r o d u c t under commercial conditions. S i n c e we a r e n o t a l w a y s certain a s t o w h a t p r o d u c t s w i l l b e p a c k e d , we m u s t simulate pack c o n d i t i o n s . Quick tests f o r coating integrity a r e g e n e r a l l y r u n w i t h a s o l u t i o n c o n s i s t i n g o f 10 p a r t s h y d r o c h l o r i c a c i d / 2 0 p a r t s CuS04*5H20/70 p a r t s water. E x p o s u r e t i m e s t o t h i s t e s t s o l u t i o n may v a r y from several minutes t o several hours. This test is simply a screening t e s t t o determine whether the coating has f a b r i c a t e d p r o p e r l y and whether that system s h o u l d be p u t o n l o n t e s t pack r e p r e s e n t i n g v a r i o u s types of foods a r e shown i n T a b l e 1. We d o n o t p a c k f o o d s t h e w a y t h e y w o u l d be p a c k e d c o m m e r c i a l l y ; t h a t i s , from the basic food i n g r e d i e n t s . Our packs a r e a l l a c t u a l l y repacks. We f e e l , however, that by r e p a c k i n g a s t a n d a r d commerc i a l p r o d u c t , we c a n i n s u r e o u r s e l v e s g o o d c o n t r o l o f the c h a r a c t e r i s t i c s of that product without r e q u i r i n g extended food p r e p a r a t i o n time. Results E a r l y i n t h e t e s t w o r k we d e t e r m i n e d t h a t t h e c o a t i n g s w h i c h performed t h e best were those w h i c h showed t h e b e s t i n i t i a l f a b r i c a t i o n . Typical fabric a t i o n and process p r o p e r t i e s of coatings are presented i n Table 2. Of t h o s e w h i c h showed good fabricat i o n , a few were q u i c k l y e l i m i n a t e d because they d i d n o t have t h e r e q u i r e d h y d r o l y t i c s t a b i l i t y o r t h e r e s i s t a n c e t o s o f t e n i n g by f a t s and o i l s that a r e r e q u i r e d o f many f o o d s . The p r i m a r y development work then centered around the f o r m u l a t i o n of p o l y v i n y l d i s p e r s i o n type coatings and epoxy f o r m u l a t i o n s . S i n c e t h e d a t a i n T a b l e 2 shows t h a t t h e PVC d i s p e r s i o n v i n y l s as a r u l e have b e t t e r f a b r i c a t i o n than the epoxies, we t r i e d t o u s e t h e P V C d i s p e r s i o n s o n both the i n t e r i o r and the e x t e r i o r of the c a n . However, i n studying exterior coatings, we d i s c o v e r e d that t h e PVCd i s p e r s i o n s a r e n o t r e a l l y thermosetting; and, consequently, they w i l l resoften s l i g h t l y during processing of the f i l l e d container. A l s o , any movement i n t h e s t e r i l i z e r w i l l a b r a d e t h e P V C d i s p e r s i o n off of the metal. Epoxy coatings which thermoset duri n g t h e bake a r e n o t s u b j e c t t o t h i s t y p e o f a d h e s i o n

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MODERN CONTAINER COATINGS

28

TABLE

TEST

Type

of

Food

High

acid

1.

MEDIA

Product

or Lemon

Fatty

pudding

Vienna

Pea High

sulfur

aromatic

sausage

and

ham

soup

or

Tuna

Highly

Packed

in

Barbecue

brine

sauce

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

GERHARDT ET AL.

Coatings

for Food

Containers

Ο

pq

ι

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5H

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CO

I c Ο ·<-!

ÎH

CD CO

CO

Ο Ο Ρ,

•

> ΣΗ

Ο Ο

S

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< PH Ο CO

* OJ Ρ PQ

<

EH

M EH PS

Pi PH Ο

pc; PH H

PH

PH"

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In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

30

MODERN CONTAINER COATINGS

failure. To a s s u r e ourselves that these observations were based on sound t e c h n i c a l f a c t s , we r a n s o m e s c r a t c h t e s t s and c o e f f i c i e n t of f r i c t i o n v a l u e s on a number of c o a t i n g s a t 250°F. These r e s u l t s are shown i n Table 3 and c l e a r l y demonstrate the s u p e r i o r i t y of a t h e r m o s e t e p o x y t o t h e PVC d i s p e r s i o n s . Having decided that the thermosetting epoxy coati n g s a r e b e s t f o r use on the e x t e r i o r of the container, we h a d t o d e t e r m i n e w h a t l e v e l o f i n t e r n a l l u b r i c a n t was optimum f o r f a b r i c a t i o n . We a d v o c a t e t h e u s e of an e x t e r n a l l u b r i c a n t p r i o r t o f a b r i c a t i o n of the container, b u t we a l s o r e c o g n i z e t h a t a s m a l l a m o u n t of l u b r i c a n t i n c o r p o r a t e d i n t o the c o a t i n g (an Internal l u b e ) f a c i l i t a t e s good f a b r i c a t i o n . T y p i c a l data showing the e f f e c t of lube l e v e l are shown i n T a b l e 4. N o t e t h a t t h e o p t i m u m r a n g e i s 0.25 t o 0.75$ b a s e d on the c o a t i n g s o l i d s is g e n e r a l l y s u f f i c i e n t f o r most c o a t i n g s . One t h i n g we d o w a n t t o p o i n t o u t i s t h a t we h a v e n e v e r been s u c c e s s f u l i n a d d i n g a s u f f i c i e n t amount of internal l u b e s o t h a t e x t e r n a l l u b r i c a t i o n c a n be e l i m i n a t e d i n severe f a b r i c a t i o n s such as the d r a w - r e d r a w or t r i p l e draw c a n . A l s o , a t l e v e l s o f 3-5$ lubricant, the c o a t i n g s b e g i n t o t a k e on t h e c h a r a c t e r i s t i c s of t h e l u b r i c a n t and become s o f t and cheesy. A l t h o u g h the PVC d i s p e r s i o n s a r e n o t hard enough t o t a k e t h e s c u f f i n g on t h e e x t e r i o r of t h e container, they are p r e f e r r e d compositions f o r the interior. Since there i s no u n i v e r s a l p r e f e r e n c e for color of t h e i n t e r i o r c o a t i n g , we h a v e f o u n d i t n e c e s s a r y to f o r m u l a t e g o l d , b u f f , w h i t e and aluminum pigmented coatings. We a s f o r m u l a t o r s h a v e n o p a r t i c u l a r preference for c o l o r . We r e c o g n i z e b o t h a d v a n t a g e s and disadvantages to a p a r t i c u l a r c o l o r . For example, w h i t e w i l l hide any v a r i a t i o n s i n the appearance of the m e t a l s u r f a c e and have a n i c e c l e a n l o o k , but if t h a t w h i t e shows a p p r e c i a b l e v a r i a t i o n i n c o l o r due t o f i l m t h i c k n e s s or bake v a r i a t i o n s or i f i t absorbs any c o l o r a n t f r o m the f o o d , i t w i l l have l e s s chance of b e i n g a s u c c e s s f u l coating. B e c a u s e t h e l e v e l s o f c o l o r a n t m a y v a r y , we e x p e r i e n c e s l i g h t l y d i f f e r e n t p r o p e r t i e s among d i f f e r e n t c o l o r s depending upon c o a t i n g w e i g h t . Some general g u i d e l i n e s a r e shown i n T a b l e 5. Note that the gold and the a l u m i n u m c o a t i n g s g e n e r a l l y have good p e r f o r m a n c e i n t h e 6-8 mg/sq. i n . r a n g e , w h i l e the b u f f and w h i t e c o a t i n g s g e n e r a l l y r e q u i r e 8-10 mg/sq. i n . f o r good performance. H a v i n g e s t a b l i s h e d t h a t PVC d i s p e r s i o n s appear t o be b e s t f o r t h e i n t e r i o r o f t h e c o n t a i n e r a n d the

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

5.

GERHARDT ET AL.

Coatings

for Food

TABLE

HOT M A R R E S I S T A N C E

A l l

Scratch Resistance

Pencil Hardness

A

Good

Friction

made

at

Epoxy

Good

COATINGS

250°F.

Β

PVC Dispersion

Poor

2H

F

HB

0.2-0.25

0.2

0.35

Coefficient of

3.

OF E X T E R I O R

measurements

Epoxy

Containers

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

F

MODERN CONTAINER COATINGS

32

TABLE

4,

EFFECT COEFFICIENT

OF L U B R I C A N T L E V E L ON OF F R I C T I O N A N D F A B R I C A T I O N

Coating:

Internal Lube L e v e l ($)

Colorless

COF

Epoxy

C

Fabrication

0.45

P o o r - even when external lube

using

0.25

-

0.75

0.2

Optimum range f o r fabrication using external lube

good

0.75

-

3·0

--

No a d v a n t a g e level

lower

>3

Film

is

over

cheesy

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

5.

GERHARDT ET AL.

Coatings

for Food

TABLE

EFFECT

Containers

5.

OF L I N I N G C O A T I N G W E I G H T ON CONTAINER PERFORMANCE

PVC

Dispersion

Vehicle

Gold

Buff or White

Aluminum

4 ± 1

Marginal

Poor

Marginal

6 ± 1

Acceptable

Marginal

Acceptable

8 ± 1

Preferred

Acceptable

Preferred

Pigmentation:

Coating Weight (mg/sq i n )

10 ± 1 *Rating

Preferred

scale:

Preferred: Acceptable: Marginal:

Poor:

Will Will

hold hold

most

foods.

only

mildly

corrosive

W i l l h o l d some f o o d s , but at weight, i s on b o r d e r of good

Coating

too porous

to

hold

a

foods

this film continuity

liquid

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MODERN CONTAINER COATINGS

34

t h e r m o s e t t i n g epoxy best f o r the e x t e r i o r , our next t a s k was t o a s s u r e ourselves the coatings selected were, i n the terms of the can i n d u s t r y , "compatible." I n o t h e r w o r d s , c o u l d one c o a t i n g be a p p l i e d t o one s i d e of the p l a t e and the other c o a t i n g t o the other side. We d o n o t h a v e p r o b l e m s w h e n s h e e t s a r e coated, s i n c e the epoxy i s n o r m a l l y a p p l i e d and baked f i r s t and t h e n , the v i n y l d i s p e r s i o n i s a p p l i e d and b a k e d . The e p o x i e s g e n e r a l l y have s u f f i c i e n t l a t i t u d e to maintain t h e i r p r o p e r t i e s even a f t e r a double bake. H o w e v e r , when c o i l s t o c k i s c o a t e d , t h e c o a t i n g s are a p p l i e d i n t a n d e m a n d g i v e n one b a k e , a n d i t i s essent i a l that the epoxy c o a t i n g get i t s f u l l cure without overbaking the v i n y l d i s p e r s i o n . The m a t c h i n g of cure r a t e s has b e e n one o f o u r most d i f f i c u l t p r o b l e m s , a n d t h e p r o b l e m becomes p r o g r e s s i v e l y more d i f f i c u l t as t h e bake t i m e g e t s s h o r t e I n the d e v e l o p m e n t of c o a t i n g s f o r t i n p l a t e and TFS c o n t a i n e r s , we h a v e b e e n s u c c e s s f u l i n m a t c h i n g the i n t e r i o r and e x t e r i o r f o r m u l a t i o n s as shown on T a b l e 6. H e r e we s h o w t h a t , a l t h o u g h we h a v e t w o P V C d i s p e r s i o n s which cure at d i f f e r e n t temperatures on c o i l bake c y c l e s , one e p o x y c a n be u s e d w i t h b o t h dispersions . One q u e s t i o n t h a t is asked repeatedly is whether c o a t e d t i n p l a t e c a n be h e a t e d a b o v e t h e r e f l o w p o i n t of t i n and s t i l l g i v e s a t i s f a c t o r y p e r f o r m a n c e . Our experience is that temperatures above the r e f l o w p o i n t of t i n have n o e f f e c t on t h e c o a t i n g i f t h a t temperat u r e is needed t o cure the c o a t i n g . We d o r e c o g n i z e that i f the m e t a l i s n o t quenched i m m e d i a t e l y on e x i t from the oven, the t i n w i l l c r y s t a l l i z e i n a matte appearance rather than the shiny appearance normally associated with t i n . Actually, slow c o o l i n g generally gives a m o t t l e d , v a r i e d appearance t o the s h e e t . As to whether the h e a t i n g of the t i n p l a t e a f f e c t s the basic corrosion resistance of the t i n , t h i s i s a quest i o n w h i c h n e e d s t o be a n s w e r e d by t h e metallurgists. Our b e s t i n p u t i s t h a t t h e r e i s n o e f f e c t on c o r r o s i o n resistance under n o r m a l c o a t i n g and b a k i n g c o n d i t i o n s . For those o p e r a t i o n s where someone f e e l s t h e y cannot go above the r e f l o w p o i n t of t i n , t h e y w o u l d have to use the c o a t i n g d e s i g n a t e d PVC D i s p e r s i o n G in T a b l e 6. If metal temperature is not a r e a l factor, either o f t h e d i s p e r s i o n s l i s t e d i n t h e t a b l e c o u l d be used . T h e f i n a l c o n s i d e r a t i o n m u s t be w h e t h e r t h e cont a i n e r w i l l hold the p r o d u c t . I n T a b l e 7 we h a v e l i s t e d t y p i c a l p r o d u c t s and t y p i c a l r e s u l t s . W h i l e we f e e l t h a t m o s t p r o d u c t s c a n be p a c k e d i n l i n e d , drawl f

n

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

c

H

PVC D i s p e r s i o n

Epoxy

G

PVC D i s p e r s i o n

min

min

min

min

10 s e c

min

25 s e c

7.5

10 s e c

7-5

10 s e c

7-5

10 s e c

min

CYCLES

A t Peak

BAKE

6.

25 s e c

10

25 s e c

10

25 s e c

10

Total

Time

EQUIVALENT

TABLE

700-725

650-675

400

700-725

400

650-675

400

Ai r

Temperature

Metal

500

435

400

500

400

435

400

Peak

(°F)

MODERN CONTAINER COATINGS

36

TABLE

PERFORMANCE

Coating: Can:

OF

7.

COATED

CANS

PVC D i s p e r s i o n Draw/Redraw

TFS

(chrome

Substrate : Food

Low

acid

OK

OK

Fruits

OK

OK

Vegetables

OK

OK

Pickles

OK

Fails

High

High

acid

sulfur

Meats;

Milk

products

beans

Some

products

Products

*Unless chrome

in

brine

draw i s so s e v e r e layer occurs

staining

OK*

OK

OK

OK

OK

that

appreciable

cracking

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

of

5.

GERHARDT ET AL.

Coatings

for

Food

Containers

37

r e d r a w c a n s , we d o r e c o g n i z e t h e t r u e l i m i t a t i o n s i n T a b l e 7· No o r g a n i c c o a t i n g i s c o m p l e t e l y impervious t o the s u l f u r compounds p r o d u c e d d u r i n g the processing of meats, b e a n s , peas and so f o r t h . Consequently, some m e t a l s t a i n i n g may a p p e a r w i t h some p r o d u c t s . This is generally not objectionable unless the appearance of the c o n t a i n e r i s changed d r a s t i c a l l y or if the f a i l u r e i s so severe t h a t the i n t e g r i t y of the c o a t i n g is reduced t o the p o i n t where i t p e r m i t s metal ion transfer to the p r o d u c t . One o t h e r o b s e r v a t i o n we h a v e made i s t h a t t h e T F S c h r o m e - c o a t e d steel is not satisfactory for products with high acetic acid content. F o r t u n a t e l y , n o t many f o o d p r o d u c t s f a l l into this category. Conclusion C o a t i n g s s u i t a b l e f o r use on t i n p l a t e and TFS (chrome-coated s t e e l ) for making draw-redraw food containers have been d e v e l o p e d . Cans a r e i n commerc i a l p r o d u c t i o n w i t h a l i m i t e d number of p r o d u c t s . We p r e d i c t t h a t t h i s m a r k e t w i l l e x p a n d r a p i d l y in the n e x t few y e a r s as more e x p e r i e n c e is gained. RECEIVED MAY 31,

1978.

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

6 Photocurable Epoxide Coatings for Metal Containers DENNIS KESTER and W. A. TARWID American Can Company, 433 N. Northwest Hwy., Barrington, IL 60010

The curing of coating b u l t r a v i o l e t radiatio offer several significan thermally cured solvent and waterborne materials. Radiation curing units consume less energy and require less floor space than gas-fired ovens. Furthermore, UV cured coatings contain little or no solvent and therefore s i g n i f i c a n t l y reduce p o l l u t i o n . U l t r a v i o l e t radiation curable epoxide coating formulations contain a blend of epoxide monomers and oligomers and a photosensitive diazonium s a l t . When exposed to u l t r a v i o l e t radiation, photodecomposition of the diazonium s a l t occurs releasing a Lewis acid as shown i n Figure 1(1, 2, 3). When thermally decomposed, this reaction i s known as the Schiemann reaction(4). Among the Lewis acids that may be generated by this reaction are boron t r i f l u o r i d e (BF ), pentafluorophosphate (PF ), antimony pentafluoride (SbF ), and antimony pentachloride (SbCl ). Once generated, the Lewis acid complexes with the oxirane oxygen causing opening of the epoxide ring and thereby generating cationic polymerization of the blend as shown i n Figure 2. 3

5

5

5

An advantage of this system over the free radical i n i t i a t e d systems i s that cationic polymerization i s not inhibited by oxygen. A disadvantage i s that the cationic polymerization is inhibited whenever the epoxide blends are exposed to materials containing substances which can act as Lewis bases, e.g., nitrogen containing molecules. By properly blending epoxide monomers and oligomers, UV cured coatings with a wide variety of properties can be prepared. Coatings possessing good film 0-8412-0446-2/78/47-078-038$05.00/0 © 1978 American Chemical Society In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

KESTER AND TARwiD

Figure 1.

Photocurable

Epoxide

Coatings

Photodecomposition of diazonium salt

Initiation Θ

Figure 2.

Polymerization

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

40

MODERN CONTAINER

COATINGS

i n t e g r i t y , adhesion, f l e x i b i l i t y , hardness, chemical r e s i s t a n c e , and toughness a r e needed f o r end v a r n i s h e s where f l a t m e t a l p l a t e i s c o a t e d and then formed. A d d i t i o n a l p r o p e r t i e s such as g l o s s r e t e n t i o n and m o b i l i t y a r e needed f o r o v e r p r i n t v a r n i s h e s f o r con­ tainer labels. With the l a r g e number o f epoxide r e s i n s a v a i l a b l e , t h e s e p r o p e r t i e s may be a c h i e v e d by proper b l e n d i n g . Three epoxide monomers and one epoxide o l i g o m e r a r e shown i n F i g u r e 3. T a b l e I l i s t s a s e r i e s o f measure­ ments which were made on f o r m u l a t i o n s u s i n g t h e s e materials. These measurements were o b t a i n e d on prebaked t i n f r e e s t e e l p l a t e w i t h s e v e r a l d i f f e r e n t f o r m u l a t i o n s i n o r d e r t o i l l u s t r a t e the p r o p e r t y v e r s a t i l i t y o f UV c u r a b l T a b l e I I i l l u s t r a t e s how d i f f e r e n t r a t i o s o f two epoxide monomers, i . e . , CY-179 and RD-2, a f f e c t f i l m properties. I t might be e x p e c t e d t h a t the h i g h e r the epoxide v a l u e , the f a s t e r the b l e n d would c u r e o r become t a c k f r e e . However, as shown i n T a b l e I I , the epoxide v a l u e s f o r f o r m u l a t i o n s A t h r o u g h Ε a r e the same and f o r m u l a t i o n Β c u r e s t h e f a s t e s t . I t i s not c o m p l e t e l y u n d e r s t o o d why f o r m u l a t i o n Β c u r e s the f a s t e s t , however, i t may be r e l a t e d t o the f a c t t h a t f o r m u l a t i o n Β has a h i g h e r c y c l o a l i p h a t i c epoxide v a l u e than f o r m u l a t i o n s C, D and E. Cycloaliphatic e p o x i d e s t e n d t o be more r e a c t i v e than g l y c i d y l epoxides. By t h i s argument, f o r m u l a t i o n A would be e x p e c t e d t o c u r e the f a s t e s t , i . e . , h i g h e s t c y c l o ­ a l i p h a t i c epoxide v a l u e ; however, i t has the h i g h e s t viscosity. Cure r a t e tends t o d e c r e a s e a t h i g h v i s c o s i t y v a l u e s ( > 300 cps a t 2 5 ° C ) . I t can be seen t h a t t h e r e has t o be a f o r m u l a t i n g t r a d e - o f f between v i s c o s i t y and c y c l o a l i p h a t i c epoxide v a l u e s . The d a t a shown i n T a b l e I I i l l u s t r a t e t h a t a wide range o f s o f t e n i n g p o i n t s may be o b t a i n e d w i t h d i f ­ fering resin ratios. I t can a l s o be seen t h a t t h e s o f t e n i n g p o i n t almost always i n c r e a s e s when the UV cured f i l m i s given a thermal treatment. This i s p r o b a b l y the r e s u l t o f f u r t h e r p o l y m e r i z a t i o n and the p o s s i b l e v o l a t i l i z a t i o n o f u n r e a c t e d low m o l e c u l a r weight m a t e r i a l s p r e s e n t i n the f i l m . The a d h e s i o n grades shown i n T a b l e I I i n d i c a t e no d e f i n i t e trend with cure r a t e , s o f t e n i n g p o i n t s , e t c . However, the t h e r m a l postbake always improves the a d h e s i o n p r o p e r t i e s o f the f i l m s . Again, t h i s i s

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

KESTER AND TARwiD

Photocurable

Epoxide

î

CH OC(CH ) COCH 2

2

4

2

CY-178

(Ciba P r o d u c t s Co.)

CY-179

(Ciba P r o d u c t s Co.)

CH

RD-2

2

Coatings

χ»

CHCH 0(CH ) OCH CH 2

2

4

2

CH

2

(Ciba P r o d u c t s Co.)

Λ

CH

0

CH~

CHCHr

CH. A r a l d i t e 6004 (Ciba P r o d u c t s Co.) Figure 3.

Structures of material used in blends

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

42

MODERN" CONTAINER COATINGS

TABLE I, PARAMETERS AND PHYSICAL PROPERTY MEASUREMENTS 1. 2.

Tack Free Time - Number of seconds until tack free after exposure to two 170 watts/inch UV lamps at a belt speed of 110 feet/min. Viscosity - cps at 25°c.

3.

Epoxide Value - 100/epoxide equivalent weight

4.

Cycloaliphatic Epoxide Value - 100/cycloaliphatic epoxide eq. weight Softening Point - Determined by Perkin Elmer thermomechanical analyze afte UV Softening Poin mined after UV exposure and a thermal postbake of 380o f 9 minutes.

5. 6.

Fe

7.

8.

9.

10.

11.

12. 13. 14.

o r

Adhesion - Coating is scribed with an "x" and tested with #610 Scotch Tape. Number represents relative amount of loss (0 = no loss and 10 = 100% loss). Adhesion After Thermal Postbake - Same test as No. 7 after UV cured coating has been postbaked at 380OF. for 9 min. Pasteurization Adhesion - Same test as No. 7 after UV cured coating is exposed to 160°F. water for 20 minutes. Pasteurization Adhesion After Postbake - Same test as No. 8 after coating is exposed to 160θρ. water for 20 minutes. Reverse Impact Resistance - 30 inch-pounds - The number represents the relative amount of metal exposed after impact (0 = no metal exposure and 10 = 100% metal exposure). Reverse Impact Resistance After Postbake - Same test as No. 11 after UV cured coating has been postbaked at 380°F. for 9 minutes. Wedge-Bend "30 inch-pounds - The number repre­ sents the relative amount of metal exposed after impact. Wedge-Bend After Postbake - Same test as No. 13 after UV cured coating has been postbaked at 380°F. for 9 minutes.

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Properties^ 6 25 0.72 0.18 8 12 5 1 10 7 9 9 9 8

D 25 75

E x p l a n a t i o n s o f p r o p e r t y measurements g i v e n i n T a b l e I

2 47 0.72 0.36 44 56 3 1 10 7 9 5 7 5

C 50 50

2

1 100 0.71 0.53 74 89 8 0 10 2 3 3 5 6

Β 75 25

The p e r c e n t o f p h o t o i n i t i a t o r and s u r f a c t a n t s i s t h e same for a l l formulations.

- 346 - 0.71 - 0.71 - 64 - 74 0 0 1 0 - 10 - 10 8 9 -

8

A 100 0

BLENDS

1

Tack F r e e Time V i s c o s i t y - CPS @ 25°C. Epoxide V a l u e C y c l o a l i p h a t i c Epoxide V a l u e Softening Point S o f t e n i n g P o i n t A f t e r Postbake Adhesion A d h e s i o n A f t e r Postbake P a s t e u r i z a t i o n Adhesion P a s t e u r i z a t i o n A d h e s i o n A f t e r Postbake Reverse Impact R e s i s t a n c e Reverse Impact R e s i s t a n c e A f t e r Postbake Wedge Bend Wedge Bend A f t e r Postbake

Formulation CY-179 RD-2

PROPERTIES OF CY-179 AND RD-2

TABLE I I .

MODERN CONTAINER

44

COATINGS

p r o b a b l y t h e r e s u l t o f f u r t h e r r e a c t i o n s i n t h e UV c u r e d f i l m s and t h e v o l a t i l i z a t i o n o f t h e u n r e a c t e d m a t e r i a l s from t h e f i l m . Even though p a s t e u r i z a t i o n a d v e r s e l y a f f e c t e d most o f t h e f o r m u l a t i o n s , p o s t b a k i n g t h e f i l m s a l s o improved a d h e s i o n a f t e r pasteurization. Wide v a r i a t i o n s were a l s o o b s e r v e d w i t h t h e r e v e r s e impact and wedge bend t e s t s . F o r these t e s t s , postb a k i n g t h e UV c u r e d f i l m u s u a l l y does n o t s i g n i f i c a n t l y improve f i l m p r o p e r t i e s . T a b l e I I I shows t h e e f f e c t o f d i f f e r e n t r a t i o s o f CY-179 and CY-17 8 on f i l m p r o p e r t i e s . F o r t h e s e two monomers, t h e e p o x i d e v a l u e s and t h e c y l o a l i p h a t i c epoxide value that the cure r a t e c r e a s e s and as t h e epoxide v a l u e s d e c r e a s e . The s o f t e n i n g p o i n t s o f these formulations again u s u a l l y i n c r e a s e d a f t e r postbake. The a d h e s i o n o f f o r m u l a t i o n s A, F G, H and I i s q u i t e good, b o t h b e f o r e and after pasteurization. T h i s i s p r o b a b l y because b o t h o f t h e s e m o l e c u l e s a r e q u i t e p o l a r . As shown i n T a b l e I I , o n l y f o r m u l a t i o n A had good a d h e s i v e properties. When s u c c e s s i v e amounts o f t h e r e l a t i v e l y n o n - p o l a r RD-2 was added t o CY-179, t h e a d h e s i v e p r o p e r t i e s o f t h e c o a t i n g s were a d v e r s e l y a f f e c t e d . f

T a b l e IV shows t h e e f f e c t o f d i f f e r e n t r a t i o s o f CY-179 and A r a l d i t e 6004 on f i l m p r o p e r t i e s . I t c a n be seen t h a t A r a l d i t e 6004 c u r e s v e r y s l o w l y because o f i t s low epoxide v a l u e and h i g h v i s c o s i t y . The t r e n d s i n d i c a t e t h a t i n c r e a s i n g amounts o f A r a l d i t e 6004 d e c r e a s e t h e a d h e s i v e p r o p e r t i e s o f t h e f i l m and g e n e r a l l y i n c r e a s e f l e x i b i l i t y and impact r e s i s t a n c e . A l t h o u g h o n l y f o u r epoxide m a t e r i a l s and t h i r t e e n f o r m u l a t i o n s were i n v e s t i g a t e d , t h i s study i l l u s t r a t e s the parameters and f o r m u l a t i n g t r a d e - o f f s t h a t must be c o n s i d e r e d when b l e n d i n g u l t r a v i o l e t c u r e d e p o x i d e coatings. As w i t h any r e l a t i v e l y new t e c h n o l o g y , t h e s e experiments i n d i c a t e t h a t much i s n o t understood. F o r example, i t i s n o t r e a l l y known how t h e s e monomers and o l i g o m e r s c o p o l y m e r i z e o r which m a t e r i a l s p r e f e r t o homopolymerize and which p r e f e r t o c o polymerize. These q u e s t i o n s w i l l u l t i m a t e l y have t o be answered i n o r d e r t o f u l l y u t i l i z e t h e s e systems. However, c o a t i n g s f o r m u l a t e d u s i n g t h i s c h e m i s t r y a r e now b e i n g used c o m m e r c i a l l y . As p o l l u t i o n r e g u l a t i o n s and energy c o s t s i n c r e a s e , t h e s e t y p e s o f

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

19 545 0.53 0.53 47 47 0 0 1 1 2 2 3 1

25 75

E x p l a n a t i o n s o f p r o p e r t y measurements g i v e n i n T a b l e I .

2

the same

22 465 0.59 0.59 20 35 0 0 1 0 1 9 2 8 surfactants is

12 392 0.65 0.65 32 52 0 0 0 0 4 9 7 9

50

1

The p e r c e n t o f p h o t o i n i t i a t o r and for a i l formulations,

8 346 0.71 0.71 64 74 0 0 1 0 10 10 8 9

2 Properties Tack F r e e Time V i s c o s i t y - CPS @ 25°C. Epoxide V a l u e C y c l o a l i p h a t i c Epoxide Value Softening Point S o f t e n i n g P o i n t A f t e r Postbake Adhesion A d h e s i o n A f t e r Postbake P a s t e u r i z a t i o n Adhesion P a s t e u r i z a t i o n A d h e s i o n A f t e r Postbake Reverse Impact R e s i s t a n c e Reverse Impact R e s i s t a n c e A f t e r Postbake Wedge Bend Wedge Bend A f t e r Postbake

F 75 25

CY-178 BLENDS

1

A 100 0

Formulation CY-179 CY-178

PROPERTIES OF CY-179 AND

TABLE I I I .

19 685 0.47 0.47 28 29 0 0 0 0 1 1 1 1

100

S*

G

ο

n

S,

H

Ο

3 S

Ci

ο ο

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

9 3000 0.62 0.36 57 65 1 0 2 1 9 3 8 6

12 1187 0.67 0.53 56 62 0 0 1 0 10 8 10 8 8 346 0.71 0.71 64 74 0 0 1 0 10 10 8 9

Tack F r e e Time V i s c o s i t y - CPS @ 25°C. Epoxide V a l u e C y c l o a l i p a t i c Epoxide V a l u e Softening Point S o f t e n i n g P o i n t A f t e r Postbake Adhesion A d h e s i o n A f t e r Postbake P a s t e u r i z a t i o n Adhesion P a s t e u r i z a t i o n A d h e s i o n A f t e r Postbake Reverse Impact R e s i s t a n c e Reverse Impact R e s i s t a n c e A f t e r Postbake Wedge Bend Wedge Bend A f t e r Postbake

E x p l a n a t i o n s o f p r o p e r t y measurements g i v e n i n T a b l e I,

2

same

The p e r c e n t o f p h o t o i n i t i a t o r and s u r f a c t a n t s i s the for a l l formulations.

11 5500 0.58 0.18 55 72 5 1 10 0 4 3 7 6

75

L

1

Properties^

Κ 50 50

J "75 25

A TÏÏÏÏ 0

6004 BLENDS'

Formulation CY-179 6004

PROPERTIES OF CY-179 AND

TABLE IV.

120 6000 0.5 3 0.00 52 75 0 0 10 0 1 2 3 4

M 0 100

4^

Ο

H

ο >

w w ο

> S

H

8

S ο α w

os

6. KESTER AND TARwiD

Photocurable Epoxide Coatings

materials w i l l necessarily occupy a more prominent position among container coatings. References: (1)

S. I. Schlesinger, U.S. Patent 3,708,296

(2)

J . J. Licari and P. C. Crepeau, U.S. Patent 3,205,157

(3)

E. Fischer, U.S. Patent 3,236,784

(4)

For review, see Roe, Org. Reactions 5, 193-228 (1949)

RECEIVED MAY 22, 1978.

American Chemical Society Library 1155 16th St. N. W. Wuhtiftoi, L 6. 20038

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

7 High Solids Thermally Cured Systems Now, Forthcoming, and Future ROBERT W. JAMES, PAUL F. WESTFALL, K. L. PIERCE, and H. J. WRIGHT Cook Paint and Varnish Co., P. O. Box 389, Kansas City, MO 64141

This deliver higher solids, thermally cured systems and the position such coatings possess at the present, and will possess in the future, relative to the three "E" 's-environment, energy, and economics. High solids coatings are not novel--only the application of such systems to the container industry is relatively new. State and Federal environmental protection agencies thrust high solid systems to application reality faster than expected; however, regardless of regulations, economics would have forced the change. Conventional 30-60% solid coatings, in addition to being inefficient in the use of raw materials, are rapidly becoming too costly, due to the spiraling price of solvent. ENVIRONMENT : At the present point in time, billions of three-piece sanitary food cans have been commercially produced, beginning in August 1973, utilizing high solids coatings. High solids materials have been used as both interior and exterior protective coatings. The coating material, similar to an oleo resinous system, has a minimum 80% volume solids at a bake temperature of 10 minutes at 400°F. The coating contains approximately 15% by weight volatile exempt solvent. The system fulfills Ringleman II opacity requirements and, obviously, meet F.D.A. needs. Application problems associated with the above and similar high solid systems have been primarily substrate wetting. Plate wetting problems may be decreased or eliminated by the use of special flow agents, firm appli0-8412-0446-2/78/47-078-048$05.00/0 © 1978 American Chemical Society In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

JAMES ET AL.

High

Solids Thermally

Cured

Systems

49

c a t i o n r o l l s , and h e a t i n g t h e c o a t i n g d u r i n g rollcoat a p p l i c a t i o n . The u s e o f 45-55 d u r o m e t e r a p p l i c a t i o n r o l l s permits the c o a t e r o p e r a t o r to apply p r e s s u r e t o t h e s u b s t r a t e s h e e t w i t h o u t undue d i s t o r t i o n of p l a t e margins. C o n t r o l l e d h e a t i n g of the c o a t i n g t o 1 0 0 - 1 2 0 ° F . r e g u l a t e s v i s c o s i t y as w e l l as p r o m o t i n g s u b s t r a t e w e t t i n g and m i n i m i z e s f i l m weight v a r i a t i o n . High s o l i d s systems vary w i d e l y i n v i s c o s i t y response to h e a t i n g . The f o l l o w i n g c h a r t demons t r a t e s the v i s c o s i t y response of a t y p i c a l high s o l i d s oleo r e s i n o u s system to heat.

30 40 50 60 70 80 VIS.

90

#4 FORD CUP

Development problems p e r t a i n i n g to high s o l i d s c o a t i n g s have been d i s c o v e r i n g c u r e compositions which e x h i b i t reasonable three to four per cent fuming f a c t o r s a t d e s i g n e d bake s c h e d u l e s . T h i s has been p a r t i c u l a r l y t r u e o f melamine of u r e a c u r i n g a g e n t s , and t e n d s t o be a p r o b l e m w i t h any c o n d e n s a t i o n r e a c t i o n which emit a by-product other than carbon d i o x i d e or water. F u m i n g f a c t o r s may be g o v e r n e d t o an e x t e n t by c o n t r o l l e d m o l e c u l a r weight d i s t r i b u t i o n , s t a g e b a k i n g and r e d u c e d b a k i n g temperatures . Fuming f a c t o r s a r e not always o b j e c t i o n a b l e or unwanted. V o l a t i l a t i o n o f u n r e a c t e d monomer o r low m o l e c u l a r w e i g h t p o l y m e r s i s d e s i r a b l e and essential to e l i m i n a t e the p o s s i b i l i t y o f t h e s e p r o d u c t s being e x t r a c t e d i n t o the food. E x t r a c t i o n i n t o the food p r o d u c t c o u l d j e o p a r d i z e F.D.A. s t a t u s and p o s s i b l y cause " o f f f l a v o r " to the pack media. Volatilization o f t h e s e u n d e s i r a b l e s i s one a d v a n t a g e t h e r m a l l y cured c o a t i n g s d i s p l a y over " c o l d cure" u l t r a violet l i g h t , e l e c t r o n beam, e t c . , c u r i n g s y s t e m s t h a t u t i l i z e r e a c t i v e s o l v e n t s o r low m o l e c u l a r weight

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MODERN CONTAINER

COATINGS

polymers. The o b j e c t i v e o f h i g h s o l i d s a p p l i c a t i o n reduce s o l v e n t emission. The f o l l o w i n g c h a r t s t r a t e s t h e r e l a t i o n s h i p between volume s o l i d s s u r f a c e c o a t e d p e r pound o f s o l v e n t r e l e a s e d . enamel i n t h e c h a r t i s f o r m u l a t e d w i t h a 1 t o weight pigment-binder r a t i o .

i s to demonand The 1 by

HIGH

SOLIDS

COATINGS

SQUARE F E E T OF SURFACE COATED PER POUND OF SOLVENT RELEASED

VOLUME SOLIDS

% WT . GAL.

0 10 20 30 40 50 60 70 80 90 100

0 15. 6 29. 4 42 . 7 52. 7 62 . 5 71. 5 79. 6 87 . 0 93. 8 100. 0

SQ. F T .

LBS.

WT GAL.

DRY

OF

7. 52 8. 03 8. 53 9. 02 9. 53 10. 04 10. 54 11. 05 11. 55 12. 05 12 . 55

0 800 1600 2400 3200 4000 4800 5600 6400 7200 8000

1:1

FILM

OF

PAINT

SURFACE COATED

RELEASED

7. 52 6. 76 6. 01 5. 26 4 .51 3. 76 3. 00 2 .25 1. 50 75 0

Wt./Pigment B i n d e r

0 110 235 455 710 1065 1600 2485 4265 9600 00

Ratio

C h a r t #3 d e m o n s t r a t e s a c o m m e r c i a l l y a v a i l a b l e c o m p l i a n c e h i g h s o l i d s c l e a r and a c o m p l i a n c e waterbased c o a t i n g . The w a t e r - b a s e d c o a t i n g c o n t a i n s 20% exempt s o l v e n t i n t h e v o l a t i l e . HIGH

H.S. Water

SOLIDS

V S . WATER

SQ. F T . COVERAGE PER .2 MIL F I L M

SURFACE COATED PER L B . OF SOLVENT RELEASED

VOL. SOLIDS

WT. GAL.

80 26.75 Clear

7.98 6400 8.46 2140 unpigmented process

4010 1686 coatings

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

7.

JAMES ET AL.

is of

High

Solids Thermally

Cured

51

Systems

A n o t h e r way o f c o m p a r i n g p o l l u t i o n e f f i c i e n c y pounds o f s o l i d s v s . pounds o f s o l v e n t p e r g a l l o n coating. POUNDS OF SOLIDS V S . POUNDS OF SOLVENT CONTAINED IN ONE GALLON OF COATING LBS.

High S o l i d s Water Water-based

OF SOLIDS

L B S . OF SOLVENT

6.72 2.49 contains

1.26 1.19 2 0 % exempt

solution

RATIO 5.34:1 2.09:1

volatile

New d e v e l o p m e n t the s a n i t a r y c o a t i n fuming f a c t o r s , lowe , complianc with Ringleman I o p a c i t y requirements. F u t u r e c o a t i n g s w i l l q u i t e p o s s i b l y be h i g h e r t h a n 80% volume s o l i d s w o r k i n g toward t h e g o a l o f 100% v o l u m e s o l i d s . P o s s i b l y two-package system with g r e a t l y reduced cure response which approach zero emission. ENERGY H i g h v o l u m e s o l i d s exempt s o l v e n t s y s t e m s a l l o w m a n u f a c t u r e r s t o c o m p l y w i t h E.P.A. r e g u l a t i o n s i n c e r t a i n georgraphical areas without i n c i n e r a t i o n . This f a c t leads to s u b s t a n t i a l energy savings over c o n v e n t i o n a l s o l v e n t s y s t e m w h i c h must be i n c i n e r ated . Two-component h i g h s o l i d s s y s t e m s , r e q u i r i n g s h o r t e r bake c y c l e a t low t e m p e r a t u r e w i l l r e d u c e energy consumption drastically. ECONOMICS In g e n e r a l , h i g h s o l i d s s y s t e m s o f c o m p a r a b l e types d i s p l a y equal t o lower a p p l i e d c o s t s than conv e n t i o n a l o r w a t e r - b a s e d c o a t i n g s due t o t h e f o l l o w ing factors : 1. L e s s m a n u f a c t u r i n g expense p e r pound o f solids. 2. Less warehouse expense. 3. Lower e n e r g y e x p e n s e . 4. No r e d u c t i o n s o l v e n t . 5. Lower s h i p p i n g c o s t s .

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MODERN CONTAINER COATINGS

52

SUMMARY : High s o l i d s c o a t i n g s a r e b e i n g consumed i n l a r g e q u a n t i t i e s i n g e o g r a p h i c a l a r e a s r e q u i r e d t o meet E.P.A. r e g u l a t i o n s . H i g h s o l i d s s y s t e m s a r e economi c a l , e n e r g y s a v i n g , a n d c a n be a p p l i e d w i t h existing equipment. Future developments p o i n t e d toward h i g h e r t h a n 80% v o l u m e s o l i d s a n d l o w e r c u r e t e m p e r a t u r e s w i l l make h i g h s o l i d s e v e n more a t t r a c t i v e .

RECEIVED MAY 22, 1978.

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

8 Automated Dynamic Mechanical Testing: Application to Thermoset and Coatings Research and Development MARK B. ROLLER Edison Laboratory, Mobil Chemical Co., Edison, NJ 08817 JOHN K. GILLHAM Polymer Materials Program, Department of Chemical Engineering, Princeton University, Princeton, NJ 08540 The freely oscillating torsion pendulum and the vibrating reed are the simplest an namic mechanical propertie polymers; as early as 1950 (1). In 1970, ASTM issued the full standard D-2236-70, "Dynamic Mechanical Properties of Plastics by Means of a Torsional Pendulum." Table I summarizes the literature with respect to important events concerning Dynamic Mechanical Testing (DMT) and its use in the thermoset and coatings industries. In 1974 Gillham comprehensively reviewed (2) 12 years of development and application of Torsional Braid Analysis (TBA), which utilizes a polymer-impregnated glass braid as a specimen in a torsion pendulum. An automated (temperature controlled, signal initiated, data reduction with immediate time plotting) torsion pendulum system was introduced. This reduction in manual labor made DMT an attractive tool for industrial research and development. In 1976 and in early 1977, three other events occurred which were crucial to the acceptance of DMT to industrial research. First, in March 1976, at the Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Blaine and Woo reported (3) a Dynamic Mechanical Analysis attachment to du Pont's thermal analysis system. In it, a specimen is subjected to cyclic strain under forced resonance maintained at constant amplitude. The energy input required to maintain amplitude is a measure of mechanical loss; the natural frequency is a measure of modulus. Loss and frequency are recorded continuously. This instrument will expose DMT to a large number of chemically oriented personnel. The second event was the report at the San Francisco ACS meeting by Kenyon, et al. of an automated system providing control and data reduction for the Rheovibron (4) , in which the specimen is tested under forced tensile oscillation at definite frequencies. Commercial availability will make the Rheovibron more amenable to the requirements of industrial research. The third event was the report by Davis and Macosko (5), of a forced torsion pendulum with automatic data reduction. This is 0-8412-0446-2/78/47-078-053$09.25/0 © 1978 American Chemical Society In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

54

MODERN CONTAINER COATINGS

T a b l e I . - Development o f Dynamic M e c h a n i c a l T e s t i n g i n Thermoset and C o a t i n g s Reference (Yr.)

1

Author(s)

16,17

(1958)

Inoue and Kobataka

JLS

(1959)

11 2Ω

(1962)

Yoshino and Takayanagi Lewis and G i l l h a m

(1962)

Zorll

21

(1965)

Hansen

22

(1966)

Myers e t a l .

u

(1969)

Bender

24 25

(1970) (1971)

Takahashi e t a l . Myers

26.

(1971)

j_

(1971)

K o l l i n s k y and Markert G i l l h a m and Roller Naganuma e t a l .

27

(1972)

12_

(1973)

Babayevsky and Gillham

11973)

Massa

22

(1973)

Ikeda

10

(1973)

Heijboer

32.

(1974) (1975) (1975)

Gillham Shibayama Massa e t a l .

31 32

(1976)

3J.

(1976)

S e e f i r e d and Koleske Ginsberg e t a l .

-L

(1976)

B l a i n e and

4

(1976) (1977)

Kenyon e t a l . Davis and Macosko

(1977)

Gillham et a l .

(1978)

Gillham

A

ϋ

Woo

R&D

C O M M E N T S T o r s i o n Pendulum (TP) and V i b r a t i n g Reed. Coated A l F o i l i n TP. Reported e q u a t i o n s f o r p r o p e r t i e s o f c o a t i n g s from composite specimens and c o r r e c t i o n s f o r e f f e c t o f l o a d . "Rheovibron". E* and tano o f f r e e f i l m s measured under f o r c e d o s c i l l a t i o n i n t e n s i o n , semi-automatic. " T o r s i o n a l B r a i d A n a l y s i s " (TBA). Impregnated b r a i d as specimen i n TP. TP. Reported e q u a t i o n s f o r G' and tano o f c o a t i n g from c o a t e d f o i l . TP. I n v e s t i g a t i o n o f p l a s t i c i z e r s and d i f f u s i o n o f s o l v e n t s i n polymer specimens. " A t t n e u a t e d R e f l e c t i o n P u l s e s " (ARP). D r y i n g o f F i l m on a q u a r t z c r y s t a l m o n i t o r e d u s i n g

Rheovibron. Cure o f o i l - m o d i f i e d p h e n o l i c r e s i n . Review: " R e l a x a t i o n s d u r i n g the f o r m a t i o n o f films". Reference t o TBA and ARP. TP. Double Tgs r e v e a l phase s e p a r a t i o n i n random copolymerization. TP. E f f e c t o f cure and environment. Comparison o f TP & TBA d a t a . Non-drag t r a n s d u c e r . "Dynamic S p r i n g A n a l y s i s " (DSA). Coated s p r i n g used as specimen i n r h e o v i b r o n f o r study o f c u r e . G e n e r a l i z a t i o n o f t h r e e r e g i o n s o f temperature f o r c u r i n g b e h a v i o r , determined by the r e l a t i v e times f o r g e l a t i o n and v i t r i f i c a t i o n (using TBA). Rheovibron. Mathematical a n a l y s i s t o account f o r system and specimen compliance and i n e r t i a l e f f e c t s . Progreae in Organic Coatings A 1 s t review on dynamic v i s c o e l a s t i c i t y o f c o a t i n g f i l m s . Reference t o TP, v i b r a t i n g reed, f l e x u r a l v i b r a t i o n o f f r e e l y sus­ pended p l a t e , and r h e o v i b r o n . M o l e c u l a r assignments f o r t r a n s i t i o n s < Tg. Developed method f o r d e t e r m i n i n g frequency dependence o f these t r a n s i t i o n s from s i n g l e f r e ­ quency measurements. T o t a l l y Automated T o r s i o n Pendulum. Progreee in Organic Coatings: 2nd review. T o r s i o n pendulum c o n s i d e r e d more s e n s i t i v e than r h e o v i b r o n a t low l o s s l e v e l s . A p p l i c a t i o n s o f " B l o t t e r " (impregnated c e l l u l o s e specimen, f o r TP) and TP t e c h n i q u e s . Compared b l o t t e r TP t e c h n i q u e w i t h impregnated n y l o n f a b r i c i n r h e o v i b r o n t o study c u r e . "Dynamic M e c h a n i c a l A n a l y z e r " (DMA): A d d i t i o n t o Dupont's t h e r m a l a n a l y s i s equipment. T o t a l l y automated; specimen under c y c l i c o u t - o f - p l a n e s t r a i n i n f o r c e d resonance. T o t a l l y automated r h e o v i b r o n . Automated f o r c e d TP. F r e e TP p r o v i d e s h i g h e r r e s o l u t i o n than f o r c e d TP a t low l o s s . C o n t r o l o f morphology and p r o p e r t i e s by g e l a t i o n i n two-phase r e a c t i v e c r o s s l i n k i n g systems ( r u b b e r - m o d i f i e d e p o x i e s j [using TBA]. E s t a b l i s h e d e q u i v a l e n c e o f T ^ ' and t g as d e t e r m i n i n g l i m i t o f p r o c e s s i b i l i t y o f t h e r m o p l a s t i c s and thermosets [using TBA]. e l

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

8.

ROLLER AND GILLHAM

Dynamic

Mechanical

Testing

55

compatible with the Rheometrics Mechanical Spectrometer, which has been widely used to study f l u i d state v i s c o e l a s t i c i t y . In the l a s t three years, the methods of DMT, that have been for more than 25 years either tools of basic research or academic c u r i o s i t y , have come of age. Introduction of at least four d i s ­ t i n c t systems of automatic experimental control, data analysis, and display (2_ 3_ 4_ 5) have made DMT a viable i n d u s t r i a l tool akin to Gel Permeation Chromatography, Infrared Analysis, Nuclear Mag­ netic Resonance, and Thermal Analysis, i n terms of the require­ ments of human attention and intervention. The available DMT systems require specimens that are large relative to those which are normally encountered i n more f a m i l i a r thermoanalytical polymer characterization techniques. This, t o ­ gether with the low thermal conductivity of polymers, necessitates either slow (maximum l-2°C/min) or stepwise heating and cooling. Thermal lag problems can be monitored and the correct heating rates chosen by determinin ing and heating. The immediate future w i l l provide great advances i n applica­ tions of DMT, understanding of thermomechanical spectra, and cross correlation with other properties of bulk polymers. Reported here are examples of the authors experiences using one of these techniques, TBA, to provide insight into the behavior of thermosets and coatings. TBA and other techniques using sup­ ported specimens (16,17,20,22,27,32-38) are uniquely suited for the study of network-forming polymer systems. The a b i l i t y to study the systems before, during, and after cure on one specimen provides an e f f i c i e n t means to determine an unambiguous history of the transformation from tractable prepolymers to intractable, but useful products. The present a r t i c l e i s an expansion of a recent report which appeared i n the Journal of Coatings Technology (4£) . f

r

f

1

EXPERIMENTAL An automated, free-hanging, freely decaying torsion pendulum has been developed which permits monitoring of the changes which occur throughout cure and through load-limiting transitions (2^) . There are several distinguishing characteristics of a free-hanging, freely decaying torsion pendulum. These include:(1) accurate mea­ surement of low loss at low frequency—the state of the a r t of electronic data collection and analysis i n forced systems has less resolution of phase angle,δ,between stress and s t r a i n than i n free­ l y decaying systems (5_,31) ; (2) unlike forced o s c i l l a t i n g systems a free-hanging one tends to be s e l f - a l i g n i n g (under the influence of gravity); (3) s i m i l a r l y , free-hanging systems maintain a con­ stant load on the specimen without requiring adjustment for ther­ mal expansion; and (4) the major l i m i t a t i o n of resonance systems l i e s i n the d i f f i c u l t y i n obtaining the frequency dependence of relaxations. The method of Heijboer (10) provides an estimate, in many cases, of this dependence from single frequency measure-

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MODERN CONTAINER COATINGS

56

merits. The specimen i s made by impregnating a g l a s s f i b e r b r a i d with the r e a c t i v e system. The specimen can be cured e x t e r n a l l y or i n the apparatus. The pendulum i s i n t e r m i t t e n t l y s e t i n t o o s c i l l a ­ t i o n t o generate a s e r i e s o f f r e e l y damped waves. The frequency of o p e r a t i o n i s about 1 Hz. The c h a r a c t e r o f each o f these waves changes throughout cure t o p r o v i d e a monitor o f change. Similar­ l y , the dynamic mechanical s p e c t r a o f a "cured" polymer are p r o ­ v i d e d by the changing c h a r a c t e r o f the waves as a f u n c t i o n o f tem­ p e r a t u r e . Changes observed i n the thermomechanical s p e c t r a upon f u r t h e r h e a t i n g o f a "cured" polymer can be r e l a t e d t o cure l e v e l and/or degradation. The two mechanical f u n c t i o n s , r i g i d i t y and damping, are ob­ t a i n e d from the frequency and decay constants which c h a r a c t e r i z e each wave. The experiment p r o v i d e s p l o t s of r e l a t i v e r i g i d i t y (1/P , where Ρ i s the p e r i o ment [Δ = I n ( A i / A ^ i ) , wher l a t i o n of a f r e e l y damped wave]. The r e l a t i v e r i g i d i t y i s d i r e c t ­ l y p r o p o r t i o n a l t o the in-phase or e l a s t i c p o r t i o n o f the shear modulus (G ) , the l o g a r i t h m i c decrement i s d i r e c t l y p r o p o r t i o n a l t o the r a t i o o f the out-of-phase or v i s c o u s p o r t i o n of the shear modulus (G" ) t o G . [Δ - i\G"/G' = irtano. ] G' and G" are m a t e r i a l parameters o f the specimen which c h a r a c t e r i z e the storage and l o s s of mechanical energy on c y c l i c deformation; q u a n t i t a t i v e v a l u e s may be o b t a i n e d by u s i n g dimensions o f the specimen. A schematic diagram o f the automated pendulum i s shown i n F i g u r e 1. The photograph (Figure 2) shows the pendulum [enclosed i n a c a b i n e t , top r i g h t ; cabinet door open, bottom l e f t ] and the major components o f the assembly. An analog computer [top center] i s used f o r automatic c o n t r o l o f the experiment and data reduc­ tion. A p r i n t e r and d i g i t a l p a n e l meter p r o v i d e numerical values of the temperature (mV) or lapsed time (sec), l o g a r i t h m i c decre­ ment (Δ) and p e r i o d (P, sec) o f each damped wave [top c e n t e r ] . A monitoring s t r i p - c h a r t two-pen recorder p r o v i d e s a continuous r e c o r d o f the waves and temperature (mV) [below computer]. A temperature controller/programmer (range: -195°C t o 450°C, r a t e o f change o f temperature 0°C t o ± 5°C/min) i s shown above the com­ puter . An XY p l o t t e r p l o t s , immediately a f t e r computation, the r e l a ­ t i v e r i g i d i t y (1/P ) and l o g a r i t h m i c decrement versus temperature (mV) or l o g time (sec) [top l e f t ] . Switches permit s e l e c t i o n of o p t i o n s which i n c l u d e ON, OFF or REVERSE o f temperature program­ ming a t upper and lower s e t p o i n t s and s e l e c t i o n o f temperature or time as the running v a r i a b l e [top c e n t e r ] . Specimens, such as impregnated b r a i d and f i l m , are shown a t bottom r i g h t . A f i l m i s shown assembled w i t h lower and upper e x t e n t i o n rods ready f o r lowering i n t o the apparatus. The p o l a r i z e r d i s k of the transducer i s a l s o shown [bottom r i g h t ] . Dimensions o f specimens are se­ l e c t e d so as t o p r o v i d e p e r i o d s o f o s c i l l a t i o n i n the range 0.25 t o 15 seconds. 2

+

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In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

8.

ROLLER AND GILLHAM

Dynamic

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Testing

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A l C h E Journal

Figure 1. Automated TBA torsion pendulum (schematic) (2)

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MODERN CONTAINER COATINGS

58

A m e r i c a n C h e m i c a l Society, Preprints

Figure 2.

Automated torsion pendulum (13,)

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

8.

ROLLER AND GILLHAM

Dynamic

Mechanical

59

Testing

A key f a c t o r i n the instrumentation was the development o f a non-drag o p t i c a l transducer which produces an e l e c t r i c a l response t h a t v a r i e s l i n e a r l y w i t h angular displacement (7). As mentioned above, t h i s was implemented by the use o f a t w o - p o l a r i z e r l i g h t a t t e n u a t i o n system. A p o l a r i z e r d i s c i s employed as the i n e r t i a l member and a second s t a t i o n a r y p o l a r i z e r i s p o s i t i o n e d , i n the path o f a l i g h t beam, i n f r o n t o f a l i n e a r - w i t h - i n t e n s i t y vacuum photo tube (Figure 1). L i g h t t r a n s m i s s i o n through two p o l a r i z e r s i s a c o s f u n c t i o n of angular displacement. Over a u s e f u l range s y m e t r i c a l about the 45° p o s i t i o n , the t r a n s m i s s i o n f u n c t i o n approaches a s t r a i g h t line. The p o l a r i z e r system i s a l s o i n s e n s i t i v e to l a t e r a l o s c i l ­ l a t i o n s (7). As the p r o p e r t i e s o f the specimen change, t w i s t i n g may cause the transducer t o d r i f t out of t h i s l i n e a r range. The automation system d e s c r i b e d below i s designed t o compensate f o r this. The sequence o f event as f o l l o w s : S t r i p - C h a r t Recorder monitor (Figure 3, Top): I) Pre­ v i o u s wave decays, d r i f t d e t e c t e d and c o r r e c t i o n b e g i n s . II) Po­ l a r i z e r s c o r r e c t l y p o s i t i o n e d . I l l ) Wave i n i t i a t i n g sequence be­ gins. IV) Free o s c i l l a t i o n s begin. V) AB, f i r s t peak-to-peak amplitude l e s s than i n i t i a l boundary amplitude i s measured. VI) CD, f i r s t peak-to-peak amplitude
2

2

EXAMPLES OF DYNAMIC MECHANICAL ANALYSIS Influence of Water Vapor on Dynamic Mechanical Spectra The e f f e c t o f c o n t r o l l e d l e v e l s o f water vapor i n the atmos-

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MODERN CONTAINER COATINGS

60

I 2 CONTROLLER/DATA ANALYZER

3

4

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A l C h E Journal

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In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

8.

ROLLER AND GILLHAM

Dynamic

Mechanical

Testing

61

phere on a cured rubber-modified epoxy system has been r e p o r t e d (6). F i g u r e 4 compares a spectrum of a dry specimen i n a dry a t ­ mosphere and the same specimen a f t e r c o n d i t i o n i n g a t 15°C and 2800 ppm moisture (27% RH) f o r more than e i g h t hours. The c o n d i ­ t i o n e d m a t e r i a l d i s p l a y e d a water t r a n s i t i o n ("T Q") a t ^ -80°C, i n a d d i t i o n t o the Tg (-47°C) o f the rubber and the secondary t r a n s i t i o n (-140°C) o f the epoxy. P l a s t i c i z a t i o n by water r e ­ duced the Tg o f the epoxy t o 25°C from 37°C. The o r i g i n a l spec­ trum was regenerated on r e d r y i n g . Temperatures o f such waterinduced t r a n s i t i o n s depend on chemical composition (§_r]_r§) . T h i s example demonstrates the n e c e s s i t y f o r c o n t r o l o f the environment when u s i n g DMT techniques, e s p e c i a l l y w i t h p o l a r polymers which c o n s t i t u t e most thermoset f o r m u l a t i o n s . H

Comparison o f Chemically S i m i l a r Coatings In the c o a t i n g s i n d u s t r d i f f e r e n t coatings o f s i m i l a r chemistry. The l e f t s i d e s of F i g ­ ures 5-8 are s p e c t r a o f c r o s s l i n k a b l e water-dispersed a c r y l i c r e s i n s (A, B, C and C2). Specimens were prepared by h e a t i n g impregnated b r a i d s a t 191°C (375°F) f o r 2 min i n a f o r c e d a i r oven under 15g t e n s i o n (the weight o f the i n e r t i a l mass of the pendulum). They were then subjected t o the thermal treatment 120°C -> 0°C 204°C (400°F) + 0°C and simultaneous DMT i n the TBA apparatus. During the f i r s t cool/heat c y c l e , coatings A, C and C2 had s p e c t r a with Tg values at 78.5, 112 and 101°C; Β d i s p l a y e d two l o s s peaks, T a t 100°C and T a t 17°C. On h e a t i n g t o 204°C, A and C2 i n c r e a s e d t h e i r l e v e l s o f cure w i t h Tgs being r a i s e d t o 83°C and 112°C. In c o n t r a s t , the main Tg values o f Β and C were unchanged, although T of Β i n c r e a s e d t o 24 from 17°C which was accompanied by an i n c r e a s e i n the l e v e l of damping between T i and Tg2« The thermomechanical f i n g e r p r i n t s of these coatings r e ­ v e a l d i f f e r e n c e s due t o cure, p o s t - c u r e , and phase d i s t r i b u t i o n (B i s probably two-phased). The data a t the r i g h t of F i g u r e s 5-8 were generated from uncured specimens c y c l e d between 20 and 145°C a t 1.5°C/min. These simple experiments y i e l d i n f o r m a t i o n on the k i n e t i c s of cure. The Tg a f t e r each c y c l e to 145°C shown i n F i g u r e 9 p r o v i d e s a measure of the energy i n p u t r e q u i r e d t o a t t a i n a given Tg. More d e f i n i ­ t i v e approaches t o k i n e t i c s are d i s c u s s e d below. I t i s o f i n t e r e s t to note t h a t C and C2 were assumed to d i f ­ f e r only i n the s o l i d s l e v e l r e q u i r e d f o r d i f f e r e n t methods of application. I t was found t h a t although they had the same u l t i ­ mate g l a s s t r a n s i t i o n temperatures, C2 cured more s l o w l y . g l

g 2

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Accelerated-Aged Vs. Room Temperature-Aged Unreacted Prepolymers The supported specimens used i n TBA permit study of

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

8.

ROLLER AND GILLHAM

Dynamic

Mechanical

Testing

63

Journal of Coatings Technology

Figure 5. Water-dispersed Acrylic A. Left side: dynamic mechanical spectra 120°C -» 0°C -> 200°C —» 0°C at 2°C/ min in He of specimen cured 2 min in forced-air oven at 191°C. Right side: wet coating cycled from RT <—» 145°C, spectra generated during cycling (40)

Journal of Applied P o l y m e r Science

Figure 6. Water-dispersed Acrylic B. Left side: dynamic mechanical spectra 120°C -» 0°C -» 200°C -» 0°C at 2°C/min in He of specimen cured 2 min in forced-air oven at 191°C. Right side: wet coating cycled from RT <—> 145°C, spectra generated during cycling (12).

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MODERN CONTAINER COATINGS

64

WATER OISPERSEO ACRYLIC C

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Figure 7. Water-dispersed Acrylic C. Left side: dynamic mechanical spectra 120°C -» 0°C -> 200°C -> 0°C at 2°C/min in He of specimen cured 2 min in forced-air oven at 191°C. Right side: wet coating cycled from RT <—> 145°C, spectra generated during cycling (40).

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In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

ROLLER AND GILLHAM

Dynamic

Mechanical

Testing

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In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

66

MODERN CONTAINER COATINGS

coatings. Spectra o f two specimens o f the same water-based coating f o r m u l a t i o n are presented i n F i g u r e s 10 and 11: one a f t e r aging i n the c o n t a i n e r f o r two months at room temperature (RT), the other a f t e r aging i n the c o n t a i n e r f o r two months a t 49°C (HT). The HT aging r e s u l t e d i n cured coatings with s e r i o u s i n c r e a s e s i n water s e n s i t i v i t y (blushing) and decreases i n MEK r e s i s t a n c e . Spectra on the l e f t are from specimens d r i e d s i d e - b y - s i d e (10-20 mm Hg) f o r three days t o remove water and s o l v e n t . Data were then obtained during the c y c l e : 50°C -> -190°C -> 50°C. Spectra on the r i g h t were obtained a f t e r c u r i n g the same specimens i n the TBA apparatus a t 176°C f o r 5 min. The Tg value o f the d r i e d HT aged specimen was 24°C/ t h a t of the d r i e d RT specimen was 17°C. Note t h a t there i s a t r a n s i t i o n (Tsec) i n the RT specimen a t -73°C i n a d d i t i o n to the two i n both at -140 and -180°C. These data are taken as evidence of the d i s appearance upon HT agin i c a l loss responsible fo i n Tg with HT aging i s a t t r i b u t e d to an i n c r e a s e i n molecular weight o f the uncured r e s i n s . A f t e r c u r i n g , the s p e c t r a are s i m i l a r with Tg values of 57 and 60°C f o r both the RT and HT m a t e r i a l s . A Tsec t r a n s i t i o n occurred at -124°C i n both. On post c u r i n g t o 204°C, both RT and HT m a t e r i a l s i n c r e a s e d t h e i r Tg values to 119 and 112°C, respectively. The i n c r e a s e s of 60 and 52°C i n d i c a t e a s i g n i f i c a n t l e v e l of under cure. The higher temperature and narrower Tg regions of the RT specimen a f t e r the c o n t r o l l e d p o s t bake provide evidence of a lower and more uniform molecular weight between c r o s s l i n k s i n the post-baked RT specimen. T h i s concurs with an i n c r e a s e i n molecular weight o f the r e s i n during aging. Since these experiments were performed on specimens taken from a s i n g l e coating's batch, c o n d i t i o n e d s i d e by s i d e , c o n c l u s i o n s drawn r e l a t i n g the s m a l l d i f f e r e n c e s i n dynamic mechanical s p e c t r a to d i f f e r e n c e s i n aging, are considered t o be j u s t i f i e d . F a b r i c a b l e Cured Coatings Thermoset coatings f o r metal s u b s t r a t e s to be post-formed are o f t e n observed t o be hard and g l a s s y , y e t d u c t i l e m a t e r i a l s . The s p e c t r a o f F i g u r e s 12 and 13 were obtained f o r two varnishes cured 204°C/10 min. F i g u r e 12 i s f o r a c o n v e n t i o n a l commercial epoxybased c o a t i n g . F i g u r e 13 i s f o r an experimental c o a t i n g formul a t e d from lower molecular weight epoxy and c r o s s l i n k e r i n an a t tempt t o decrease s o l v e n t l e v e l s . The wedge bends (ASTM D3281-73) on t i n p l a t e were 85 (cracking)/80 (adhesion) and 85/75, respectively. T e s t i n g f a b r i c a t e d screw caps and can ends gave the conv e n t i o n a l c o a t i n g a r a t i n g o f 18 out o f 30 (perfect) and 18 out of 20 ( p e r f e c t ) , r e s p e c t i v e l y . The experimental c o a t i n g was r a t e d 9/30 and 0/20. A f t e r cure, the most f a b r i c a b l e ( i . e . , the conventional) coating had a higher Tg (110 v s . 82°C) than the experimental c o a t i n g .

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

8.

ROLLER AND GILLHAM

Dynamic

Mechanical

Testing

67

Journal of Coatings Technology

Figure 10. Room temperature-aged coating. Left: dynamic mechanical spectra from RT -> —180°C —» RT at 2°C/min in He of vacuum-dried specimen. Right: dynamic mechanical spectra, 120°C -> -180°C 204°C -» -180°C at 2°C/min of specimen cured in the TBA 5 min at 176°C in air (40).

T E M P E R A T U R E , (*C )

Journal of Coatings Technology

Figure 11. 49°C aged coating. Left: dynamic mechanical spectra from RT -> —180°C —> RT at 2°C/min in He of vacuum-dried specimen. Right: dynamic mechanical spectra, 120°C -» -180°C 204°C -+ -180°C at 2°C/min of specimen cured in the TBA 5 min at 176°C in air (40).

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MODERN CONTAINER COATINGS

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In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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70

The s i m i l a r i t y i n chemistry o f the two c o a t i n g s coupled with the r e s p e c t i v e Tg values suggests a h i g h e r c r o s s l i n k d e n s i t y f o r the conventional one. Examination o f the Τ < Tg r e g i o n s r e v e a l s low temperature t r a n s i t i o n s a t -100°C (conventional) and -108°C (ex­ perimental) with more skewness i n the l o s s towards higher temper­ ature f o r the more f a b r i c a b l e c o a t i n g . The d i f f e r e n c e s i n the sec i n h e r e n t i n behavior o f uncured epoxy r e s i n c o n s t i t u t e n t s . The q u e s t i o n a r i s e s whether the s u i t a b i l i t y of coatings f o r p o s t formable s u b s t r a t e s , which i s r e l a t e d to impact and adhesion, can be c o r r e l a t e d w i t h the shape and temperature o f these t r a n s i t i o n s . Survey (9) o f the l i t e r a t u r e on impact p r o p e r t i e s o f thermo­ p l a s t i c s r e v e a l s that m a t e r i a l s with low temperature t r a n s i t i o n s , which are r e l a t e d to polymer backbone motion, g e n e r a l l y d i s p l a y higher l e v e l s o f impact s t r e n g t h than do polymers without such transitions. Furthermore, i f the t r a n s i t i o n s are not due t o the presence of a phase-separate tance peaks a t a temperatur ence o f rubber p a r t i c l e s g e n e r a l l y r e s u l t s i n a s t e p - i n c r e a s e i n impact r e s i s t a n c e above the Tg o f the rubber. Consider the molecular motion o f a polymer backbone a t the temperature o f Tsec (at impact frequency), where a f r a c t i o n o f the groups r e s p o n s i b l e f o r Tsec i s moving. On impact, energy can be d i s s i p a t e d by i n i t i a t i n g motion of s t a t i o n a r y segments. I f a l l of the a v a i l a b l e groups are moving (T >> Tsec and Τ < Tg) there i s no mechanism ( r e l a t e d t o Tsec) a v a i l a b l e to absorb the impact. On the other hand, the presence of a damping peak due t o a g l a s s t r a n s i t i o n (Tg < T) o f a separate rubber phase can p r o v i d e mechanisms f o r energy d i s s i p a t i o n due t o flow (uncrosslinked rub­ ber) and/or l o c a l s t r e s s d i s s i p a t i o n ( c r o s s l i n k e d r u b b e r ) . A p p l i c a t i o n o f H e i j b o e r ' s method (10) f o r c a l c u l a t i n g the s h i f t o f Tsec w i t h frequency t o take Tsec t o impact f r e q u e n c i e s (10 - 1 0 Hz), r e s u l t s i n the i n t e n s i t y o f the damping o f the c o n v e n t i o n a l c o a t i n g a t room temperature being about double t h a t f o r the experimental c o a t i n g . Whether there i s a d i r e c t c o r r e l a t i o n between Tsec and f a b r i ­ c a t i o n remains t o be e s t a b l i s h e d by examining f u r t h e r samples of c r o s s l i n k e d systems. Determination o f whether the mechanism p r o ­ v i d i n g f a b r i c a b i l i t y i s r e l a t e d t o impact p r o p e r t i e s , adhesion (11) or a combination o f these and other f a c t o r s , must be l e f t to further studies. [Note t h a t these c o a t i n g s were a l s o undercured during the i n i t i a l bakes (see F i g u r e s 12 and 1 3 ) ] . T

a

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G e l a t i o n and V i t r i f i c a t i o n As Determinants o f Thermoset M a t e r i a l Behavior The three g e n e r a l i z e d temperature regions f o r cure d e s c r i b e d i n the f i r s t p a r t o f t h i s s e c t i o n stem from examinations o f sev­ e r a l epoxy systems (2_, 12^) . The experimental r e s u l t s f o r the cure of an epoxy system a t a s e r i e s of constant temperatures can be used t o o b t a i n the

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

8.

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apparent g e l a t i o n (onset o f i n f i n i t e network formation) time and the v i t r i f i c a t i o n (glass formation) time v s . cure temperature. These t r a n s f o r m a t i o n times correspond t o peaks i n the mechanical damping curves; they a l s o correspond t o p o i n t s o f i n f l e c t i o n i n the r i g i d i t y curves (see F i g u r e 14). Schematic r e s u l t s f o r i s o thermal cure o f a t y p i c a l system r e l a t i n g the time t o g e l a t i o n and the time t o v i t r i f i c a t i o n t o the temperature of cure are summari z e d i n F i g u r e 15. I t i s apparent from F i g u r e 15 t h a t there are three types of behavior depending on the temperature of cure. At h i g h temperatures the l i q u i d g e l s but does not v i t r i f y . At low temperatures the l i q u i d v i t r i f i e s as a r e s u l t of molecular weight i n c r e a s e s and need not g e l — i f r e a c t i o n s are quenched a t low chemical conv e r s i o n by v i t r i f i c a t i o n . At i n t e r m e d i a t e temperatures the l i q u i d f i r s t g e l s and l a t e r v i t r i f i e s (Figures 14 and 15) . The time t o g e l a t i o ture s i n c e the chemica constant. [ I t follows t h a t a p l o t o f l o g (time t o g e l a t i o n ) vs. 1/T (°K) p r o v i d e s an a c t i v a t i o n energy which can be used f o r obt a i n i n g g e l times a t experimentally i n a c c e s s i b l e temperatures.] On the other hand, i t i s noted t h a t the time to v i t r i f y passes through a minimum which occurs a t i n t e r m e d i a t e temperatures of cure. T h i s r e f l e c t s competition between the i n c r e a s e d r a t e cons t a n t s f o r r e a c t i o n and the i n c r e a s e d degree o f c r o s s l i n k i n g (and, t h e r e f o r e , o f r e a c t i o n ) r e q u i r e d f o r v i t r i f i c a t i o n a t higher temp e r a t u r e s . The temperature a t which g e l a t i o n and v i t r i f i c a t i o n occur together i s d e f i n e d as Tgg (Figure 15). V i t r i f i c a t i o n can occur before g e l a t i o n ( T < Tgg) simply by an i n c r e a s e of molecular weight. G e l a t i o n occurs without v i t r i f i c a t i o n when cure i s performed above the maximum s o f t e n i n g p o i n t o f the system, T o (Figure 15) . I t i s a l s o apparent t h a t i f r e a c t i o n s cease a t v i t r i f i c a t i o n , the s o f t e n i n g temperature (glass t r a n s i t i o n temperature, Tg) o f the system a f t e r cure w i l l equal the temperature o f cure. The v i t r i f i c a t i o n curve, t h e r e f o r e , gives the time t o reach the s o f t e n i n g temperature which the system can achieve by c u r i n g a t T . In p a r t i c u l a r , Tgg i s the g l a s s t r a n s i t i o n temperature o f the r e a c t i v e system a t i t s p o i n t of g e l a t i o n . A diagram, such as F i g u r e 15, summarizes much o f the behavior of the thermosetting process and i n p a r t i c u l a r shows t h a t i t i s c h a r a c t e r i z e d by two temperatures, Tgg and Tgoo. In c o n t r a s t , t h e r m o p l a s t i c m a t e r i a l s are c h a r a c t e r i z e d only by Tgoo s i n c e g e l a t i o n does not occur i n t h e i r formation. The temperatures Tgg and Tgoo are c r i t i c a l parameters which w i l l vary from system t o system. From the p r a c t i c a l p o i n t of view, the diagram (Figure 15) e x p l a i n s a number o f p r a c t i c e s i n the f i e l d of thermosets. Examples f o l l o w : • F i n i t e vs. i n f i n i t e s h e l f - l i f e : I f the storage temperature i s below Tgg, a r e a c t i v e m a t e r i a l w i l l convert t o a v i t r i f i e d s o l i d (prepreg or "B"-stage) which i s s t a b l e and can be l a t e r c u r e

go

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In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MODERN CONTAINER COATINGS

P o l y m e r Engineering a n d Science

Figure 14. Mechanical rigidity and mechanical damping vs. time during cure of an epoxy system at a constant temperature (Ί < T
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In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

8.

ROLLER AND GILLHAM

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Mechanical

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"melted" and processed; above Tgg the m a t e r i a l w i l l have a f i n i t e s h e l f - l i f e s i n c e g e l a t i o n w i l l occur b e f o r e v i t r i f i c a t i o n . • Post-cure: I f T < Tgoo a r e a c t i v e m a t e r i a l w i l l v i t r i f y and f u l l chemical conversion may be prevented; the m a t e r i a l w i l l then need t o be post-cured above T f o r development of u l t i m a t e p r o p e r t i e s . For the manufacture of o b j e c t s o f l a r g e s i z e , i t i s o f t e n necessary to go through a two-step process because of the exothermic nature o f the r e a c t i o n s . The process of g e l a t i o n can a c t a l s o to a r r e s t the development o f morphology, and, t h e r e f o r e , the time to g e l a t i o n can be used t o c o n t r o l mechanical p r o p e r t i e s . The g e l a t i o n time can be v a r i e d by c a t a l y s t s and temperature. T h i s i s p a r t i c u l a r l y import a n t d u r i n g the c u r i n g of rubber-modified-epoxy systems which o f ten i n v o l v e change from an i n i t i a l l y homogeneous s o l u t i o n t o a heterogeneous multiphase morphology (13). The e f f e c t o f c a t a l y s t a i n e d a f t e r "complete" system on g l a s s b r a i d supports i s made e v i d e n t by comparison of F i g u r e s 16 and 17. The rubber phase g l a s s t r a n s i t i o n i s most dominant i n the sample cured without c a t a l y s t (Figure 16). Curing without c a t a l y s t a t a lower temperature (120°C/16 hr) a l s o leads to a dominant rubber g l a s s t r a n s i t i o n but, on the b a s i s of the lower g l a s s t r a n s i t i o n temperature o f the epoxy, to inadequate cure. C u r i n g a t a lower temperature (120°C/16 hr) w i t h c a t a l y s t can g i v e r i s e t o a marked rubber g l a s s t r a n s i t i o n and y e t a cured system (13). These r e s u l t s suggest t h a t the i n t e n s i t y o f the rubber t r a n s i t i o n , the damping l e v e l between the t r a n s i t i o n s , and the s i z e o f the rubbery domains depend on the time a v a i l a b l e f o r the development o f morphology, which i s l i m i t e d by the process of g e l a t i o n . The h i g h e r g l a s s t r a n s i t i o n temperature o f the epoxy f o r the f u l l y cured sample, cured with long g e l a t i o n time, sugg e s t s more complete s e p a r a t i o n o f the two phases. The r e l a t i o n s h i p between cure temperature, g e l a t i o n time, and morphology i s summarized s c h e m a t i c a l l y i n F i g u r e 18, which demons t r a t e s how a s i n g l e chemical amorphous composition can produce d i s t i n c t l y d i f f e r e n t morphologies which i n t u r n are r e s p o n s i b l e f o r d i s t i n c t l y d i f f e r e n t macroscopic behavior. I t i s noted t h a t , although r e a c t i o n a t lower temperatures w i l l lengthen the time t o g e l , the i n c r e a s e d v i s c o s i t y a t lower temperatures can r e t a r d the development o f morphology. The e f f e c t o f temperature on s o l u b i l i t y i s another c o m p l i c a t i n g f a c t o r , i n crease o f which per se would i n h i b i t phase s e p a r a t i o n . c u r e

q o o

Emulsion Polymers/Gelation K i n e t i c s T h i s s e c t i o n compares two emulsion polymer-based c o a t i n g vehicles. F i g u r e 19 i s the spectrum o f an emulsion polymer cured 191°C/3 min w i t h 20% melamine c r o s s l i n k e r . F i g u r e 20 i s the spectrum o f a s i m i l a r l y cured commercially a v a i l a b l e emulsion polymer/ melamine c r o s s l i n k e r v e h i c l e . The obvious d i f f e r e n c e between the

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MODERN CONTAINER COATINGS

74

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Figure 16. Effect of catalyst level on the cure of rubber-modified epoxy: dynamic mechanical spectra, 170°C -> —180°C -> 170°C at 1.5°C/min in He. 0% catalyst. The temperature scale (MV) corresponds to that in Figure 12 (°C) (13).

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

8. ROLLER AND GILLHAM

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Figure 17. Effect of catalyst level on the cure of rubber-modified epoxy: dynamic mechanical spectra, 170°C ^> —180°C-*17()°C at 1.5°C/min in He. 0.5% catalyst. The temperature scale (MV) corresponds to that in Figure 12 (°C) (13).

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MODERN CONTAINER COATINGS

A m e r i c a n C h e m i c a l Society, Preprints

Figure 18. Development of a two-phase, rubber-modified thermosetting system vs. gelatin time. As polymerization progresses rubber precipitates in domains which grow in size with time. Gelatin is considered to arrest the growth process. Different morphohgies result from reaction at different temperatures (e.g., Tj and T ) (44). 2

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

8.

ROLLER AND GILLHAM

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Figure 19. Emulsion polymer cured with 20% melamine cross-linker: dynamic me­ chanical spectra, 120°C -> —180°C -> 204°C -* RT at 2°C/min in He of coating cured 3 min at 19ΓC (40)

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MODERN CONTAINER COATINGS

78

Journal of Coatings Technology

Figure 20. Commercial emulsion polymer/cross-linker: dynamic mechanical spectra, 120° -180 C -> 204 C -» RT at 2°C/min in He of coating cured 3 min at 191°C (40) e

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In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

8.

ROLLER AND GILLHAM

Dynamic

Mechanical

Testing

79

two systems l i e s i n the bimodel g l a s s t r a n s i t i o n r e g i o n (Tg = 26 and 52°C) o f the commercial product vs. the s i n g l e Tg (39°C) f o r the other. T h i s f e a t u r e has been r e l a t e d t o the presence of phase s e p a r a t i o n (14). S i m i l a r i t i e s i n the low temperature regions and simple c a l c u l a t i o n s o f an average Tg (39°C) f o r equal amounts of the two phases present i n the commercial m a t e r i a l a t t e s t t o these two c o a t i n g s being s i m i l a r i n monomer r e s i d u e composition. The technology r e q u i r e d to produce t h i s type of behavior v i a emulsion p o l y m e r i z a t i o n concerns i t s e l f w i t h the p r o d u c t i o n o f core and s h e l l emulsion p a r t i c l e s as has been d e s c r i b e d (14). The technique should provide rubber-modified, impact r e s i s t a n t c o a t i n g s , wherein the s o f t phase i s t o t a l l y encased i n the hard phase with the domain s i z e d e f i n e d by the p a r t i c l e . T h i s system, i n one c o a t i n g , would d i s p l a y a combination of impact r e s i s t a n c e , hardness, mar r e s i s t a n c e , and adhesion. I n v e s t i g a t i o n of th revealed the c a p a b i l i t q u i r e d c o a t i n g p r o p e r t i e s a t low baking temperatures. T h i s prompted a study of the g e l a t i o n k i n e t i c s of the two systems. F i g u r e 21 shows the Arrhenius s t r a i g h t l i n e p l o t s o f l o g (apparent g e l time) vs. 1/T°K f o r each system. Note t h a t the commercial system gels n e a r l y f o u r times as f a s t as the other at 204°C and n e a r l y 10 times as f a s t a t 100°C. Whether the source of the higher g e l a t i o n r a t e l i e s i n higher f u n c t i o n a l i t y of the r e s i n s and c r o s s l i n k e r s or more e f f i c i e n t c a t a l y s t systems has not been a s c e r tained. Note t h a t i n the case o f these two emulsion polymers the mechanical p r o p e r t i e s do not change a f t e r h e a t i n g to 200°C. Presumably, the room temperature toughness o f these m a t e r i a l s i s r e l a t e d to t h e i r low g l a s s t r a n s i t i o n temperatures. Emulsion p o l y mers develop t h e i r f i n a l Tg values b e f o r e c r o s s l i n k i n g as a consequence o f t h e i r very h i g h molecular weights. The r e l a t i v e l y l i g h t l e v e l s of c r o s s l i n k i n g i n t r o d u c e d t o these m a t e r i a l s p r o v i d e r e q u i r e d r e s i s t a n c e to c o l d flow and s o l v e n t s i n the v i c i n i t y of the g l a s s t r a n s i t i o n which i s c l o s e to room temperature. Comparison of the E f f e c t of C r o s s l i n k i n g Agents The nature of c r o s s l i n k e r s can d r a s t i c a l l y a f f e c t the propert i e s of cured thermosets. F i g u r e s 22-24 are the s p e c t r a of an a c i d f u n c t i o n a l a c r y l i c prepolymer and the same prepolymer cured with two monomeric hexamethoxymethyl melamine (HMMM)-type c r o s s l i n k e r s at the same c o n c e n t r a t i o n . One c r o s s l i n k e r had l e s s than 0.5% f r e e hydroxymethyl and the other had approximately 16% f r e e hydroxymethyl groups. The prepolymer i t s e l f d i s p l a y s a Tg o f 73°C and evidence of flow through both a r e d u c t i o n i n r i g i d i t y and a broad damping maximum above 100°C. The c r o s s l i n k e d systems show d i s t i n c t l y d i f f e r e n t behavior. The < 0.5% f r e e hydroxymethyl system d i s p l a y s a sharp Tg r e g i o n c e n t e r i n g about 79°C. The r i g i d i t y s t a r t s to decrease at 69°C and

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MODERN CONTAINER COATINGS

80

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In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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Figure 22. Acid functional acrylic polymer dried from solvent at 204°C for 2 min: dynamic mechanical spectra, 120°C -> 0°C -> 204°C at 2°C/min in He (40)

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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Figure 24. Acid junctional acrylic polymer and hexamethoxymethylmelamine with ~ 16% free hydroxymethyl; cured 204°C for 2 min: dynamic mechanical spectra, 120°C -> 0°C -> 204°C -> 77°C at 2°C/min in He (40)

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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84

and l e v e l s o f f near 91°C. The ^16% hydroxymethyl system d i s p l a y s a broad Tg r e g i o n c e n t e r i n g about 87°C. In t h i s case, the r i g i d ­ i t y begins t o decrease a t about 58°C and l e v e l s o f f near 110°C. T h i s behavior bears on the g e n e r a l p r o p e r t i e s o f the f i n a l prod­ ucts over a wide temperature range. The broad Tg r e g i o n o f the h i g h hydroxymethyl system presumably a r i s e s from the c o n t r i b u t i o n s o f the competing r e a c t i o n s o f the methoxymethyl groups w i t h both a c i d and hydroxymethyl groups which give r i s e t o molecular h e t e r o geneties. A f t e r h e a t i n g t o 204°C, the Tg o f the low hydroxymethyl HMMM i n c r e a s e d 6°C t o 85°C, whereas the Tg o f the 16% hydroxymethyl system i n c r e a s e d 7°C t o 94°C. T h i s behavior i s t y p i c a l o f the response t o f u r t h e r h e a t i n g o f most thermosetting m a t e r i a l s a f t e r t h e i r normal i n d u s t r i a l cure c y c l e s . In the i n t e r e s t o f economy o f time i n d u s t r y tends t o design i t s systems t o have acceptable p r o p e r t i e s i n an undercure Plasticization The a b i l i t y t o examine l i q u i d s by using supported samples permits study o f t r a n s i t i o n s i n the f l u i d s t a t e as w e l l as t r a n s ­ formation of l i q u i d t o s o l i d . The most complete example o f t r a n ­ s i t i o n s i n the f l u i d s t a t e i s the p l a s t i c i z a t i o n o f t h e r m o p l a s t i c p o l y s t y r e n e throughout the range o f composition (15). P o l y s t y r e n e (Mn = 37000, Mw/Mn < 1.1) was homogeneously p l a s t i c i z e d w i t h (Cg^OCgH^O) 2 6 + (which i s a low molecular weight analogue o f polyphenylene o x i d e ) . Dynamic mechanical s p e c t r a f o r the p l a s t i c i z e r / p o l y m e r system are d i s p l a y e d i n F i g u r e 25. Three t r a n s i t i o n s are made apparent, i . e . , Tg, T^£ and T ^ ' , a l l f o l l o w i n g the r e l a t i o n s h i p Τ = A A + B B KW^B is e m p i r i c a l constant, Τ r e p r e s e n t s the t r a n s i t i o n temperature o f the mixture (T) and o f the c o n s t i t u e n t s (^T and β Τ ) , and W and W r e f e r t o the r e s p e c t i v e weight f r a c ­ t i o n s o f the components. Corresponding t r a n s i t i o n s have been noted by us i n low molecular weight thermosetting prepolymers. These t r a n s i t i o n s , which r e l a t e t o flow, bear p a r t i c u l a r l y on p r o ­ c e s s i n g o p e r a t i o n s (see below). c

Hi

T W

T W

+

w

n

e

r

e

K

A

a

n

B

P r o c e s s a b i l i t y - The S i g n i f i c a n c e and Equivalence o f T ^ ' and t ^ (39) 1

Recent work has shown the c o i n c i d e n c e o f T j ^ obtained as a f u n c t i o n o f temperature w i t h the l o s s peak a t t r i b u t e d t o g e l a ­ t i o n ( t g e l = time o f g e l a t i o n ) observed during i s o t h e r m a l cure o f a thermosetting system (39). S i m i l a r l y i t has been shown t h a t T^£ corresponds t o a second maximum i n Δ observed a f t e r the "ap­ parent" g e l peak and b e f o r e v i t r i f i c a t i o n . The importance o f these l o s s maxima t o thermoset p r o c e s s i n g i s obvious s i n c e they occur d u r i n g the t r a n s f o r m a t i o n from f l u i d s t o i n t r a c t a b l e prod­ ucts. I t f o l l o w s from the c o i n c i d e n c e o f the i s o t h e r m a l t r a n s i -

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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o/ioo •0/90

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39.9/60.1

498/502 60/40 70/30 80/20 90 2/98 100/0 2

-2

4

6

8

12

10

TEMPERATURE, MV (IRON-CONSTANTAN) Polymer Engineering a n d Science

Figure 25. TBA. Dynamic mechanical spectra of a phsticized polystyrene: effect of composition (tvt % plasticizer / wt % polystyrene). Anionic polystyrene; A f / M < 1.1. Ffosticizer: (C H OC H O) C H/ Curves have been displaced vertically by arbitrary amounts for purposes of clarification. The temperature scale (MV) corresponds to the temperature scale demarcations of Figure 12 (°C) where the 0 MV and 0°C are taken as coincident (15). w

G

n

6

5

G

i

r

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t i o n s w i t h T^£ and T^^ t h a t the l a t t e r l o s s maxima observed i n t h e r m o p l a s t i c s should bear on t h e i r p r o c e s s i n g . I t has a l s o been observed t h a t the temperatures f o r T^£ and T ^ can be s u b s t r a t e (braid) m a t e r i a l and/or geometry dependent (41). D i f f e r e n t t h e r momechanical s p e c t r a have been observed a f t e r c u r i n g i s o t h e r m a l l y at d i f f e r e n t temperatures t o the peak o f the l o s s maximum which has been used t o approximate g e l a t i o n . I t f o l l o w s that t h i s l o s s maximum cannot correspond t o the t h e o r e t i c a l g e l p o i n t which i s d e f i n e d as an i s o c o m p o s i t i o n a l s t a t e . I t can be demonstrated t h a t i f t i as determined by t o r ­ s i o n a l b r a i d a n a l y s i s represents an i s o v i s c o u s s t a t e than an Arrhenius p l o t o f l o g t i v s . 1/T (°K) w i l l g i v e a s t r a i g h t l i n e over a s i g n i f i c a n t temperature range. T h i s has been done by ap­ p l y i n g an e m p i r i c a l time-temperature-viscosity model (42) t h a t has been used t o p r e d i c t the change i n v i s c o s i t y o f a c u r i n g system. This model reduce by many workers (42). The v i s c o s i t y model i s expressed f o r isothermal c u r i n g con­ d i t i o n s as f o l l o w s : 1

g

g

In where

e

e

n(t) = In ηoo + ΔΕη/RT + t k oo 7

A

E

k

/

/

R

T

e

η(t) = v i s c o s i t y o f time t (sec) η», = c a l c u l a t e d v i s c o s i t y o f the i n i t i a l m a t e r i a l a t Τ = , cps Τ = temperature °K ΔΕη = Arrhenius a c t i v a t i o n energy f o r the v i s c o s i t y , cal/mole R = gas constant = 1.987 cal/mole °K _^ ko, = c a l c u l a t e d k i n e t i c constant a t Τ = °°, sec ΔΕ]ς = "apparent" k i n e t i c a c t i v a t i o n energy, cal/mole. 00

I f a given i s o v i s c o s i t y l e v e l i s s e l e c t e d and the l o g o f p r e d i c t e d time t o t h a t v i s c o s i t y vs. 1/T (°K) i s p l o t t e d , the data can be f i t t e d w i t h a s t r a i g h t l i n e . Furthermore, the f i t becomes b e t t e r as the v i s c o s i t y range t r a v e r s e d (from zero time t o the end point) increases. This can be accomplished by choosing a higher cure temperature (lower i n i t i a l v i s c o s i t y ) o r a higher v i s c o s i t y end p o i n t . As the f i t improves, the a c t i v a t i o n energy o f l o g t i vs. 1/T curve approaches the "apparent" a c t i v a t i o n energy i n the v i s c o s i t y model. As the temperature f o r isothermal cure i s reduced, the zero time v i s c o s i t y approaches the i s o v i s c o u s l e v e l chosen and " t g i " goes t o zero. At h i g h e r temperatures, " t g i " goes through a maximum and then decreases. I t i s i n t h i s d e c r e a s i n g r e g i o n where the l i n e a r f i t h o l d s . From t h i s a n a l y s i s , i t appears t h a t i f t g ^ i s an i s o v i s c o u s s t a t e , l i n e a r A r r h e n i u s p l o t s can be obtained. Furthermore i f the v i s c o s i t y l e v e l detected f o r t l i s s u f f i c i e n t l y h i g h , i t i s c l o s e enough t o the t r u e g e l p o i n t t o be r e p r e s e n t a t i v e . As with g

e

e

e

g

e

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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all mechanical measurements of gelation, one depends upon a vis­ cosity measurement. Rising bubbles, tack tests and viscositytime measurements all provide similar approximations. As a matter of fact, the SPI Prepreg Reinforced Plastics Committee Test Method: Prepreg 3 - Measurement of Gel Time of Preimpregnated Inorganic Reinforcements (New York, May, 1960) was found to pro­ vide gel times corresponding to 120,000-140,000 cps (42). SUMMARY In this paper the history of dynamic mechanical testing and its past relationship to thermoset and coatings research and de­ velopment is reviewed. With the introduction of several fully automated systems, the study of thermosetting systems by these techniques will greatly increase. Provided are examples of the use of the technique a behavior of thermosettin of environment, comparison of similar materials, cure, aging of prepolymers, correlation with fabrication, monitoring of phase separation, apparent gelation kinetics, and the influence of gela­ tion and vitrification on material properties. The article con­ cludes with recent results which reveal the coincidence of transi­ tions in thermoplastics observed above the glass transition, and in thermosets during the transformation from fluid to intractible solids; these bear on processing. Now that the difficulties of data reduction have been elimi­ nated, the future applicability of dynamic mechanical techniques depends only upon the ingenuity of research and development per­ sonnel. ACKNOWLEDGMENT The authors wish to thank the management of Mobil Chemical Co. for permission to publish this paper. Plastics Analysis Con­ sultants Inc., P. O. Box 408, Princeton, New Jersey provided thermomechanical TBA plots. LITERATURE CITED (1) (2) (3) (4) (5)

Nielsen, L.E., ASTM Bulletin No. 165, p. 48, April (1950); Rev. Sci. Instr., 22, 690 (1951). Gillham, J.K., A.I.Ch.E. J., 20, 1066 (1974). Blaine, R.L. and Woo, L . , Am. Chem. Soc., Polymer Preprints, 17(2), 1 (1976). Kenyon, A.S., Grote, W. Α., Wallace, D. Α., and Rayford, M. J., ibid., 17(2), 1 (1976). Also J. Macromol. Sci.-Phys. B13(4), 553 (1977). Davis, W.M. and Macosko, C. W., Polymer Eng. Sci., 17(1), 32 (1977).

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(6) Gillham, J.K. and McPherson, C.A., Preprints of 32nd Annual Tech. Conf., Reinforced Plastics/Composites Institute, SPI, sect. 9-E (1977). (7) Gillham, J.K. and Roller, M.B., Polymer Eng. Sci., 11, 295 (1971). (8) Ozari, Υ., Chow, R. H. and Gillham, J.K., Am. Chem. Soc., Polymer Preprints 18(1), 649 (1977). (9) Roller, M.B., unpublished literature survey. (10) Heijboer, J., Publication P73/28, of Central Laboratories TNO, Delft, The Netherlands, 1973; also "Secondary Loss Peaks in Glassy Amorphous Polymers," presented at 4th Mid­ land Macromol. Meeting, Midland, Mich. Feb. (1975), Int. J. Polymer Material. 6, 11 (1977). See also Ann. N.Y. Acad. Sci., 279, 104 (1976). (11) Kaelble, D.H., "Physical Chemistry of Adhesion," Wiley Interscience, Ne (12) Babayevsky, P.G 17, 2067 (1973). (13) Gillham, J. K., Glandt, C. Α., and McPherson, C. Α., Am. Chem. Soc., Preprints, Div. Org. Coat. Plastics Chem., 37(1), 195 (1977); also "Chemistry and Properties of Crosslinked Polymers," S.S. Labana, Ed., Academic Press, New York, 1977, p. 491. (14) Manson, J.A. and Sperling, L.H., "Polymer Blends and Com­ posites," Plenum Press, New York, 1976, Chapters 3, 8 and 13. (15) Gillham, J. Κ., Benci, J.A., and Boyer, R.F., Polymer Eng. Sci., 16(5), 357 (1976). (16) Inoue, Y. and Kobatake, Υ . , Kolloid, Ζ., 159(1), 18 (1958). (17) Inoue, Y. and Kobatake, Υ . , ibid., 160(1), 44 (1958). (18) Yoshino, M. and Takayanagi, Μ., Zairyo Shiken,8, 330 (1959). (19) Lewis, A. F. and Gillham, J. Κ., J. Appl. Polymer Sci., 6, 422 (1962). (20) Zorll, U., Forschungsber. Landes Nordhein-Westfalen, No. 1361, Westdeutschen Verlag Omblt, Köln and Opladen (1962). (21) Hansen,C.M.,Official Digest, 37(480), 57 (1965). (22) Myers, R.R., Klimek, J., and Knauss, C.J., Journal of Paint Technology, 38(500), 479 (1966). (23) Bender, H.S., J. Appl. Polymer Sci., 13, 1253 (1969). (24) Takahashi, Y., Naganuma, S., Onozawa, Κ., and Kishi, Η., Proc. 5th Inter. Cong. Rheology, 1968, p. 485 (1970). (25) Myers, R. R., J. Polymer Sci., Part C 35, 3 (1971). (26) Kollinsky, F., and Markert, G., "Multicomponent Polymer Systems," Advances in Chemistry Series, No. 99, American Chemical Society, Washington, D. C., 1971, p. 175. (27) Naganuma, S., Sakurai, T., Takahashi, Υ . , and Takahashi, S., High Polymer Chemistry (Hobunski Kagaku), 29(322), 105, and (327), 519 (1972). (28) Massa, D. J., J. Appl. Phys., 44, 2595 (1973). (29) Ikeda, S., Prog. Org. Coatings, 1(3), 205 (1972/3). s

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(30) Shimbayama, Κ., ibid., 3(3), 245 (1975). (31) Massa, D. J., Flick, J . R., and Petrie, S.E.B., Am. Chem. Soc. Preprints, Div. Org. Coat. Plastic Chem., 35(1), 371 (1975). (32) Seefried, C.G., Jr. and Koleske, J.V., J. Testing Eval., 4(3), 220 (1976). (33) Ginsberg, T., Merriam, C.N., and Robeson, L.M., J. Oil Col­ our Chemists' Assoc., 59, 315 (1976). (34) Cowie, J.M.G., Am. Chem. Soc. Preprints, Div. Org. Coat. Plastic Chem., 38(1), 284 (1978). (35) Koleske, J.V. and Faucher, J.A., ibid, 38(1), 355 (1978). (36) MacKnight, W.J., Neuman, R.A. and Senich, G.A.,ibid, 38(1) 360 (1978). (37) Senich, G. A. and MacKnight, W.J., ibid, 38(1), 510 (1978). (38) Hill, D.R.J., ibid, 38(1) 590 (1978) (39) Gillham, J. Κ., Polymer Chem. Soc., Preprints, Org , 38(2), (1978). (40) Roller, M. B. and Gillham, J. Κ., J. Coatings Tech., 50, No. 636, 57 (1978). (41) Schwartz, Β., Ph.D. Thesis, Department of Chemical Engineer­ ing, Princeton University, 1979. (42) Roller, Μ. Β., Polym. Eng. Sci., 15, 406 (1975). (43) Gillham, J . Κ., Polym. Eng. S c i . , 16, 353 (1976). (44) Gillham, J . Κ., Am. Chem. Soc., Preprints, Div. Org. Coat. Plastics Chem., 38(1), 221 (1978). RECEIVED MAY 22, 1978.

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

9 Application of Electrochemical Techniques to the Evaluation of the Corrosion Barrier Properties of Modern Container Coatings R. E. BEESE American Can Co., 433 N. Northwest Highway, Barrington, IL 60010 J. C. ALLMAN M&T Chemicals, Inc., 26701

Introduction: Testing programs are required to evaluate the performance of materials considered for the development of new containers to preserve and store foods and beverages. Historically, testing was accomplished by packing fabricated containers with a representative product, storing the packed containers, and periodically evaluating to determine container performance. This lengthy procedure limits the number of variables to be considered and causes development delays. Experience has shown that electrochemical techniques can be used to evaluate the corrosion performance of new containers and coating materials. The electrochemical testing program permits one to evaluate a large number of variables in a short time. We have found that electrochemical tests can readily determine container failure caused by metal dissolution or corrosion for variables which perform poorly. In cases where measured corrosion rates are low, test packs are needed to establish whether or not long­ -term protection is provided. Application of Electrochemical Technique: We chose to measure the rate of iron dissolution by the slope-intercept technique identified by Stern(1) and formalized by ASTM(2) rather than the polarization resistance technique(3) 0-8412-0446-2/78/47-078-090$05.00/0 © 1978 American Chemical Society In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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which Kleniewski(4) employed t o measure the r e l a t i v e c o r r o s i o n b a r r i e r p r o p e r t i e s o f can c o a t i n g s . P o l a r i z a t i o n r e s i s t a n c e i s i n v e r s e l y p r o p o r t i o n a l t o c o r r o s i o n r a t e provided the nature of t h e anodic and cathodic r e a c t i o n s which account f o r t h e c o r r o s i o n process remain constant; however, t h i s i s not t h e case. Makrides(5) solved t h i s problem by measuring an average c o r r o s i o n r a t e by weight l o s s and then c a l c u l a t i n g an average p r o p o r t i o n a l i t y constant between p o l a r i z a t i o n r e s i s t a n c e and c o r r o s i o n r a t e . This procedure i s not a p p l i c a b l e because the c o r r o s i o n o f i r o n through can coatings cannot be monitored by weight l o s s . Mansfeld(6) p o i n t s out t h a t the IR drop i n the p o t e n t i a l measuring c i r c u i t causes e r r o r s i n t h e e v a l u a t i o n of c o r r o s i o n r a t e from p o l a r i z a t i o n r e s i s t a n c e data. Hausler(7) a l s o discusses f u r t h e r problems a s s o c i a t e d w i t h t h i s technique. The s l o p e - i n t e r c e p t techniqu an a c t u a l c o r r o s i o n r a t c o r r o s i o n performance. While problems a s s o c i a t e d w i t h e r r o r s caused by IR drops i n the p o t e n t i a l measuring c i r c u i t a r e s t i l l w i t h us, the data developed i n both beer and tomato j u i c e provide reasonable estimates o f i r o n c o r r o s i o n r a t e through organic enamel coatings o r a t d i s c o n t i n u i t i e s o r f r a c t u r e s i n organic enamel coatings on t i n p l a t e o r e l e c t r o l y t i c chromium coated s t e e l W h e t h e r the c o r r o s i o n r e a c t i o n occurs by i o n d i f f u s i o n through organic enamel coatings g e n e r a l l y or through coatings a t d i s c r e t e s i t e s caused by f o r e i g n m a t e r i a l as i n d i cated by Koehler(9) or through d i s c o n t i n u i t i e s such as cracks caused by mechanical damage t o the coatings depends on the system under study. Since the s l o p e - i n t e r c e p t technique f o r measuring c o r r o s i o n depends only on the anodic and cathodic r e a c t i o n s ; i . e . , the r a t e o f i r o n d i s s o l u t i o n and hydrogen e v o l u t i o n r e s p e c t i v e l y i n a i r - f r e e systems, the l o c a t i o n o f the r e a c t i o n s i t e s i s not important. Two other problems a s s o c i a t e d w i t h the e l e c t r o c h e m i c a l approach to c o n t a i n e r e v a l u a t i o n need t o be recognized. The b a r r i e r p r o p e r t i e s o f some coatings d i m i n i s h because the coatings a r e degraded by exposure t o aggressive media. This was i l l u s t r a t e d by L e i d h e i s e r 0 - 0 ) i n h i s work w i t h polybutadiene coatings i n aerated sodium c h l o r i d e s o l u t i o n s . Secondly, t h e metal area a t a pore or crack i n the c o a t i n g increases as c o r r o s i o n proceeds; thus, i t i s reasonable t o expect instantaneous c o r r o s i o n r a t e s to i n c r e a s e as c o r r o s i o n proceeds. Test procedures are d e v e l oped t o e s t a b l i s h reasonably steady s t a t e c o n d i t i o n s before making the c o r r o s i o n r a t e measurement. F o r example, c o r r o s i o n i n beer cans can be evaluated a f t e r a 15 minute immersion i n a 150° F water bath t o simulate a p a s t e u r i z a t i o n c y c l e . Tomato j u i c e cans are permitted t o stand two days b e f o r e e v a l u a t i n g c o n t a i n e r performance t o e s t a b l i s h a steady c o r r o s i o n r a t e .

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92 Instrumentation

and Test Procedure:

C o r r o s i o n r a t e can be estimated from a p o t e n t i o s t a t i c p o l a r i z a t i o n curve by the s l o p e - i n t e r c e p t technique. The l i n e a r p o r t i o n of the log c u r r e n t - p o t e n t i a l p l o t of a p o l a r i z a t i o n curve; i . e . , the T a f e l l i n e , i s e x t r a p o l a t e d t o the c o r r o s i o n p o t e n t i a l . The c u r r e n t at the i n t e r s e c t i o n of the T a f e l l i n e and the c o r r o s i o n p o t e n t i a l i s the r a t e of the c o r r o s i o n r e a c t i o n . Any q u a l i t y p o t e n t i o s t a t can be used t o c o n t r o l the p o t e n t i a l of a corroding metal sample. The log c u r r e n t - p o t e n t i a l r e l a t i o n s h i p i s a u t o m a t i c a l l y p l o t t e d w i t h an X-Y recorder. The p o t e n t i a l of the corroding metal i s measured w i t h respect t o a reference e l e c t r o d e on the Y a x i s of the r e c o r d e r . The log of the current flow between an a u x i l i a r y platinum e l e c t r o d e and the c o r r o d i n g metal i s recorded on the X a x i s . Examples of cathodic p o l a r i z a t i o Cans or can p a r t s are t e s t e d by f i l l i n g w i t h a r e p r e s e n t a t i v e product and measuring c o r r o s i o n r a t e . Beer i s the t e s t medium f o r beer cans. Tomato j u i c e i s used as a r e p r e s e n t a t i v e moderately c o r r o s i v e m i l d l y a c i d food product. Cans are c l o s e d by s e a l i n g a l u c i t e f i x t u r e t o the can or the can p a r t w i t h an O-ring. Cans f i l l e d w i t h beer are maintained under a carbon d i o x i d e atmosphere and can be given a simulated p a s t e u r i z a t i o n c y c l e by immersing the c l o s e d f i l l e d can i n a 150° F water bath f o r 15 minutes. The can i s s t o r e d overnight at 80° F before t e s t i n g . Cans to be t e s t e d w i t h tomato j u i c e are maintained under a n i t r o g e n gas atmosphere. They are f i l l e d w i t h 190° F tomato j u i c e and stored two days at 80° F before testing. C o r r o s i o n r a t e i s measured by i n s e r t i n g a platinum a u x i l i a r y e l e c t r o d e and a s a t u r a t e d calomel reference e l e c t r o d e i n a 1% sodium c h l o r i d e s a l t b r i d g e i n t o the product through a s i l i c o n e rubber gromet i n the l u c i t e c l o s u r e . The p o t e n t i o s t a t s reference p o t e n t i a l i s set at a p o t e n t i a l a few m i l l i v o l t s anodic t o the c o r r o s i o n p o t e n t i a l . The p o t e n t i o s t a t s reference p o t e n t i a l i s then permitted t o change i n the cathodic d i r e c t i o n ; i . e . , t o more negative p o t e n t i a l s at a r a t e of 5 t o 6 m i l l i v o l t s per minute t o generate the cathodic p o l a r i z a t i o n curve. It i s important t o p o l a r i z e at the slow r a t e t o o b t a i n r e p r o d u c i b l e data. The slow adsorbtion-desorbtion of the c o r r o s i o n i n h i b i t o r systems n a t u r a l l y o c c u r r i n g i n beer and tomato j u i c e on the c o r r o d i n g metal probably e x p l a i n s the need f o r the slow p o l a r ization rate. f

f

A p p l i c a t i o n of P o l a r i z a t i o n Measurements: The f o l l o w i n g three examples of i r o n c o r r o s i o n through organic enamel can coatings i l l u s t r a t e the v a r i o u s mechanisms by which

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

9. BEESE AND ALLMAN

Corrosion Barrier

Properties

93

AMPERES

Figure 2. Iron corrosion rate for experimental beer cans in 80°F beer: O , #1 211 X 413 cemented can; Δ , #2 211 X 413 cemented can; Q #3 207.5/209 X 504 D&Z can; X , #4 209/211 X 413 Dal can

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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c o r r o s i o n can occur through p r o p e r l y a p p l i e d can c o a t i n g s : A.

Iron C o r r o s i o n Through Breaks i n Coatings: The draw-redraw process f o r the manufacture of two-piece food cans i n v o l v e s the c o a t i n g of e l e c t r o l y t i c chromium coated s t e e l or t i n p l a t e w i t h an organic enamel c o a t i n g and mechanically forming the coated s t e e l i n t o a c y l i n d e r w i t h an i n t e g r a l end. Mechanical damage can occur t o the organic c o a t i n g during the drawing o p e r a t i o n . M i c r o s c o p i c t e a r s occur i n the v i n y l organosol c o a t i n g used on many draw-redraw cans. Draw-redraw cans have been evaluated w i t h tomato j u i c e t o determine the area of metal exposure through the damage t o the organic c o a t i n g of the c o n t a i n e r performanc T y p i c a l p o l a r i z a t i o n curves and c o r r o s i o n r a t e data f o r drawn cans are given i n F i g u r e 1 and i n Table I . The d i f ferences between the c o n t a i n e r s are r e l a t e d t o the area of i r o n exposed. I t should be p o i n t e d out t h a t Table I i n d i c a t e s t h a t the c o r r o s i o n r e a c t i o n through a 21 square i n c h area of v i n y l organosol coated s t e e l was very s m a l l . Since t h i s c o a t i n g provides an e x c e l l e n t b a r r i e r t o c o r r o s i o n before drawing, one must conclude t h a t the observed c o r r o s i o n occurs at s i t e s where the organic c o a t i n g was mechanically damaged by drawing.

B.

I r o n C o r r o s i o n Through a Thick P l a s t i s o l : Experimental easy-open beer ends made from organic enamel coated e l e c t r o l y t i c chromium coated s t e e l were made by p a r t i a l l y c u t t i n g two c i r c u l a r holes through the s t e e l and r e s e a l i n g the p a r t i a l l y cut c i r c l e w i t h a p l a s t i s o l f i l m approximately 10 m i l s t h i c k . The organic enamel coatings on the chromium coated s t e e l p r o v i d e an e x c e l l e n t b a r r i e r t o c o r r o s i o n . The p l a s t i s o l s e a l a n t was designed t o f i l l the crack between the d i s c and the end and t o p r o v i d e a mechanical s e a l . The p r o p e r t i e s of t h i s p l a s t i s o l are unique. I t must p r o v i d e a gas and l i q u i d s e a l and s t i l l be e a s i l y t o r n so t h a t the c o n t a i n e r can be opened. The p l a s t i s o l s e a l provided an e x c e l l e n t p h y s i c a l b a r r i e r ; however, beer t e s t packs i n d i c a t e d t h a t t h i s p l a s t i s o l was a poor b a r r i e r t o i r o n c o r r o s i o n . Reformulation of the p l a s t i s o l improved i t s c o r r o s i o n b a r r i e r p r o p e r t i e s , as i n d i c a t e d i n Table I I . T h i s example d e s c r i b e s an organic m a t e r i a l t h a t o r i g i n a l l y was formulated w i t h very poor c o r r o s i o n b a r r i e r p r o p e r t i e s .

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

9.

BEESE AND ALLMAN

Corrosion

Barrier

95

Properties

TABLE I Representative Iron C o r r o s i o n i n Drawn Cans Made From V i n y l Organosol Coated E l e c t r o l y t i c Chromium Coated S t e e l A f t e r Two Days i n 80° F Tomato J u i c e E l e c t r o c h e m i c a l Data C o r r o s i o n T a f e l C o r r . Iron C o r r . S t e e l P o t e n t i a l Slope Rate Rate Container D e s c r i p t i o n Code mV V jua/Can ppm Fe/Yr. 21 square inches o f enamel coated s t e e l

?

Β

<0.0003

<0.01*

404 χ 307 cans

A Β

-616 -623

0.20 0.20

0.038 0.093

0.46 1.13

307 χ 406 cans

A Β

-664 -658

0.26 0.26

0.36 0.29

5.4 4.4

C a l c u l a t i o n based on 307 χ 406 can i n t e r i o r s u r f a c e area and c o n t a i n e r volume

TABLE I I Rate o f Iron C o r r o s i o n Through P l a s t i s o l on Experimental S t e e l Easy-Open Ends i n 80° F Beer E l e c t r o c h e m i c a l Data Test Code

Plastisol Description

15-1 15-13 15-25

Initial

21-10 21-13 21-16

Reformulated Plastisol

formulation

Corr. Tafel Rate Iron Pickup Pot. Slope C o r r . Rate ppm Fe/3 Mos jua mV V -626 -609 -572

0.54 0.50 0.64

0.034 0.022 0.028

-659 -660 -664

0.17 0.23 0.25

0.00062 0.00007 0.00004

0.22 0.14 0.18 0.0040 0.0004 0.0003

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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MONTHS

Figure 1. Rate of iron corrosion through vinyl organoso-coated electrolytic chromiumcoated steel in drawn cans after 2d with 80°F tomato juice: A, 21 in. 2-coated steel surface; B, 404 X 307 can; C, 307 X 406 can

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

9.

BEESE AND ALLMAN

Corrosion

Barrier

97

Properties

D i f f u s i o n o f moisture, ferrous i o n s , hydrogen ions and hydro­ gen gas occurred e a s i l y . Reformulation improved the b a r r i e r p r o p e r t i e s , as measured by p o l a r i z a t i o n t e s t s and t e s t packs. This e l e c t r o c h e m i c a l technique permitted the e v a l u a t i o n o f a s e r i e s o f p l a s t i s o l formulations before one was s e l e c t e d f o r commercial t r i a l s . C.

Iron C o r r o s i o n Through D i s c r e t e S i t e s i n Coatings Experimental beer cans were c l o s e d , maintained under a carbon d i o x i d e atmosphere, f i l l e d w i t h beer, p a s t e u r i z e d , and s t o r e d a t 80° F. Iron c o r r o s i o n r a t e s were monitored p e r i o d i c a l l y over a 1.5 month t e s t p e r i o d . Measured cor­ r o s i o n r a t e s were expressed i n terms o f ppm i r o n pickup per month. T y p i c a l data are shown i n F i g u r e 2. C o r r o s i o n r a t e increases w i t can was c a l c u l a t e d by i n t e g r a t i n g the l e a s t square l i n e from time zero t o the time samples were taken f o r i r o n a n a l y s i s . The c a l c u l a t e d r e s u l t s from the c o r r o s i o n r a t e data are compared t o the measured i r o n pickup i n Table I I I . E x c e l l e n t agreement was found. TABLE I I I Measured Iron Pickup Compared t o Iron Pickup C a l c u l a t e d from C o r r o s i o n Rate Measurements

Experimental #1 #2 #3 #4

Beer Cans

211 χ 413 Cemented Can 211 χ 413 Cemented Can 207.5/209 χ 504 DSI Can 209/211 χ 413 D$I Can

Measured Iron Iron Pickup Test Pickup Caused P r e d i c t e d from P e r i o d by C o r r o s i o n P o l a r i z a t i o n Data ppm Fe ppm Fe Mo. 1.6 1.6 1.4 1.4

0.02 0.06 0.11 0.24

0.01 0.07 0.09 0.24

T h i s case i l l u s t r a t e s c o r r o s i o n through b a r r i e r coatings a t d i s c r e t e s i t e s . I n i t i a l l y , the organic c o a t i n g provides n e a r l y complete p r o t e c t i o n ; however, as time passes, d i f ­ f u s i o n through the c o a t i n g a t d i s c r e t e s i t e s permits cor­ r o s i o n . This mechanism i s described i n d e t a i l by K o e h l e r ^ ) Conclusion: The examples c i t e d i l l u s t r a t e the a p p l i c a t i o n o f e l e c t r o c h e m i c a l techniques t o the e v a l u a t i o n o f c o r r o s i o n through can c o a t i n g s . T h i s approach speeds the development o f new c o a t i n g m a t e r i a l s and the a p p l i c a t i o n o f these coatings t o new c o n t a i n e r s .

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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References: (1) M. Stern and A. L. Geary, "Electrochemical Polarization I. A Theoretical Analysis of the Shape of Polarization Curves," Journal of the Electrochemical Society, 104, 56 (1957). (2) ASTM Designation G3-74, "Standard Recommended Practice for Conventions Applicable to Electrochemical Measurements in Corrosion Testing." (3) M. Stern, "A Method for Determining Corrosion Rates from Linear Polarization Data," Corrosion 14, 440t, (1958). (4) A. Kleniewski, "Polarization Resistance Measurements as a Guide to the Performance of Lacquered Tinplate," Br. Corros. J., 10 (5) A. C. Makrides, "Corrosion in Dilute Acids Part I A Modified Linear Polarization Technique," Corrosion, 29, 148 (1973). 6

( ) F. Mansfeld, "The Effect of Uncompensated IR-Drop on Polarization Resistance Measurements," Corrosion, 32, 143 (1976). (7) R. H. Hausler, "Practical Experiences with Linear Polarization Measurements," Corrosion, 33, 117 (1977). (8) ASTM Designation A 657-74, "Standard Specification for Steel, Cold-Rolled, Single and Double Reduced Tin M i l l Black Plate Electrolytic Chromium Coated." (9) E. L. Koehler, "The Influence of Contaminants on the Failure of Protective Organic Coatings on Steel," accepted for publication in Corrosion (1977). (10) H. Leidheiser, J r . , and M. W. Kendig, "The Mechanism of Corrosion of Polybutadiene-Coated Steel in Aerated Sodium Chloride," Corrosion, 32, 69 (1976). RECEIVED MAY 22, 1978.

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

10 Detecting, Measuring, and Analyzing Visible Emissions from High Solids Coatings in the Laboratory P. G A N S E R and C . W .

HEIDEL

The O'Brien Corporation, 450 E . Grand Ave., South San Francisco, C A 94080

INTRODUCTION:

Odors and visible finishes have been a problem for many years and some container plants had i n s t a l l e d fume incinerators p r i o r to Rule 66.(1). With the enactment of t h i s r u l e , Regulation 3 (2) and others which have followed, all California metal decorating lines were forced to install after burners or control devices. These have been expensive to install, run and maintain not to mention the increased drain on our natural gas supply. National regulations which would have required similar control devices across the country would have been disasterous for the container industry and others. Fortunately, exemptions were provided for water borne and high solids coatings and the coatings industry has aimed its research and development programs toward these technologies. Exempt high solids coatings have been defined as 70, 80 or 95 percent nonvolatile by volume i n various regulations (1,2). The coatings industry i s attempting to move l e g i s l a t i o n toward 70 percent which is considered to be the state of the art today. Early attempts to supply exempt coatings l e d to many problems such as poor wetting of o i l y p l a t e , poor f l e x i b i l i t y and excessive v i s i b l e emissions. Most A i r Quality Control Regions l i m i t v i s i b l e emissions to less than No. 1 on the Ringleman scale (3) (20 percent opacity). Stack monitoring devices are not usually available on l i t h o lines and i n spectors are usually trained to observe smoke of various degrees of opacity against various sky conditions. I f you w i l l , they calibrate t h e i r eyes. As formulators of coatings for the container industry, we f e l t that a test procedure was required which would allow us to measure quantitatively and analyze the smoke given o f f during the bake cycle for various coatings i f we were to be successful i n supplying coatings exempt from incineration. The only test method available at the beginning of our program was a laser system which required about ho sq. f t . of plate to be baked i n 0-8412-0446-2/78/47-078-099$05.00/0 © 1978 American Chemical Society In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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a laboratory oven. A s l i p s t r e a m s a m p l i n g t u b e drew o f f p a r t o f t h e oven exhaust and a t t e n u a t e d i t t h r u a Τ t u b e . A laser beam was p r o j e c t e d t h r u t h e t u b e and r e c e i v e d b y a p h o t o c e l l , t h e s i g n a l was a m p l i f i e d and r e c o r d e d on a s t r i p c h a r t recorder. T h i s p r o c e d u r e has been u s e d i n s e v e r a l l a b s w i t h f a i r l y g o o d c o r r e l a t i o n t o p r o d u c t i o n o v e n s ; b u t i t has f a i l e d t o give correlation i n a l l cases. I t was c o n s i d e r e d t o o c u m b e r ­ some a n d t i m e c o n s u m i n g f o r o u r l a b o r a t o r y , as i t w o u l d b e q u i t e d i f f i c u l t t o u s e when many v a r i a b l e s w e r e t o b e c h e c k e d a n d t h e amount o f c o a t i n g a n d p l a t e u s e d w o u l d h a v e b e e n a problem f o r the c o a t i n g f o r m u l a t o r . PROCEDURE FOR MEASURING V I S I B L E OMISSIONS I n s e e k i n g an a l t e r n a t i v e l a b p r o c e d u r e , we c o n t a c t e d M o n i t o r T e c h n o l o g y (k) and determined t h a t t h e i r Model ΐ 6 θ / ΐ 3 1 t u r b i d i m e t e r was s e n s i t i v small area of coating a d a p t e d t o what we c a l l t h e 0 ' B r i e n / M o n i t e k M e t h o d o f measuring v i s i b l e emissions. The M o n i t e k s l i p s t r e a m t u r b i d i m e t e r was d e s i g n e d originally for liquids. I t u s e s an i n t e n s e c o l l i m a t e d beam o f white l i g h t p a s s i n g t h r u the stream. In u s i n g the instrument f o r a i r , we h a d t h e g l a s s t u b e u s e d f o r a q u e o u s measurements removed. The l i g h t p a s s i n g t h r u t h e s t r e a m i s m e a s u r e d b y t h e d i r e c t beam d e t e c t o r . The l i g h t s c a t t e r e d i n a f o r w a r d d i r ­ e c t i o n , by t u r b i d i t y i n the s t r e a m , i s measured by the s c a t t e r e d beam d e t e c t o r . These s i g n a l s are r a t i o e d to p r o v i d e the t u r b i d i t y measurement. The e f f e c t s o f c o l o r a n d s o u r c e d r i f t a r e t h e r e b y e l i m i n a t e d , p r o v i d i n g an a c c u r a t e a n d l i n e a r measurement o f o p a c i t y . I n THE 0 B R I E N / M O N I T E K METHOD we g e n e r a t e smoke b y b a r c o a t i n g a p p r o x i m a t e l y 20 s q . i n s . o f c o a t i n g on a t i n p l a t e p a n e l which i s cut to f i t our oven. The oven i s a c t u a l l y a c u r e h o t p l a t e w i t h shims t o h o l d t h e p a n e l above t h e h o t p l a t e s u r f a c e , a s p r i n g c l i p t o h o l d the p a n e l i n p l a c e , a hood t o c o l l e c t v a p o r s a n d fumes a n d a t u b e l e a d i n g t o t h e M o n i t e k u n i t . A small tube i n the t u r b i d i m e t e r presents the emissions j u s t b e l o w t h e l i g h t beam a n d a l a r g e r t u b e j u s t a b o v e t h e l i g h t beam c o l l e c t s t h e e m i s s i o n s w h i c h a r e drawn o f f b y an a i r pump. This design should minimize contamination o f the o p t i c s due t o t h e n e g a t i v e p r e s s u r e i n t h e l i g h t beam a r e a . The a i r f l o w t h r u t h e u n i t i s 35 c c . p e r m i n u t e a n d we h a v e d e t e r m i n e d t h a t b y s e t t i n g t h e c u r e h o t p l a t e a b o u t 50 d e g r e e s F h i g h e r t h a n t h e d e s i r e d m e t a l t e m p e r a t u r e , we g e t a p p r o x i ­ m a t e l y 2 m i n u t e s come up t i m e a n d b a k e s a r e n o r m a l l y h e l d 8 minutes at the d e s i r e d metal temperature. The M o n i t e k u n i t h a s s c a l e s o f 0 . 5 t o 500 ppm. The l o w e s t s c a l e w h i c h w i l l measure t h e e m i s s i o n s w i t h o u t o f f s c a l e r e a d i n g s i s used f o r each sample. R e s u l t s a r e r e c o r d e d on a n i n t e g r a t i n g s t r i p c h a r t r e c o r d e r a t 300 c o u n t s p e r m i n u t e . 1

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

10.

GANSER AND iiEiDEL

High

Solids

Coatings

101

The r e c o r d e r h a s a z e r o s u p p r e s s i o n a d j u s t m e n t w h i c h i s used t o blank out the background a i r r e a d i n g . T a r e d panels are c o a t e d , baked and reweighed t o determine t o t a l coating weight. The c o a t e d a r e a i s measured t o determine mgs. p e r s q . i n . o f d r y f i l m . In our comparison o f v a r i a b l e s o f a p a r t i c u l a r formulation we u s e t h e i n t e g r a t o r c o u n t s p e r mg. o f d r y f i l m b a s e d u p o n t h e 20 ppm. f u l l s c a l e s e t t i n g t o d e t e r m i n e t h e r e l a t i v e amount o f smoke f r o m e a c h v a r i a b l e . Formula I i s used t o c a l c u l a t e t h e c o u n t s p e r mg: I.

M =

C χ S 20 χ W M = C o u n t s p e r mg. o f d r y f i l m - 20 ppm. scale basis C = T o t a l i n t e g r a t o r counts f o r bake c y c l e . S = Ful readings W = T o t a l c o a t i n g d r y f i l m weight i n mgs. I f c o a t i n g o f d i f f e r e n t a p p l i c a t i o n weights and bakes a r e t o b e c o m p a r e d , we u s e t h e c o u n t s p e r s q u a r e i n c h o f c o a t i n g a s the b a s i s . Formula I I i s used to convert a l l data to the 20 ppm. s c a l e b a s i s . II. I = C χ S 20 χ A I = C o u n t s p e r s q . i n . o f c o a t i n s - 20 ppm. scale basis A = Area coated (sq. i n s . ) A c o m p a r i s o n o f some t y p i c a l c o a t i n g s i s shown i n T a b l e I . T h e s e r e s u l t s seem t o a g r e e w e l l w i t h o b s e r v e d e m i s s i o n s f r o m c o m m e r c i a l o v e n s ; b u t , a s s t a t e d e a r l i e r , no r e l i a b l e q u a n t i ­ t a t i v e d a t a has been a v a i l a b l e from t h e f i e l d t o d a t e .

O r g a n o s o l Non R e p a i r A c r y l i c White Enamel Oleoresinous Sanitary Conventional Alkydm e l a m i n e WI V a r n i s h H i S o l i d s WI V a r n i s h E p o x y - U r e a Enamel

TABLE I Dry F i l m Wt. M g s . / ε iq. i n . 10. 0 10. 0

Counts/Mg.

Counts, In

2k.9

2k9

k. 7

20.9 11.6

209 55

3. ,k 3. ,k 3. .9

11.8 3.8 2.8

13 11

ho

PROCEDURE FOR QUALITATIVE ANALYSIS OF EMISSIONS: A n o t h e r p r o c e d u r e w h i c h we h a v e f o u n d u s e f u l i n f o r m u l a t i n g in

c o n j u n c t i o n w i t h t h e O ' B r i e n Monitek Method i s

analysis

o f the emissions

from

infrared

bakes.

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MODERN CONTAINER COATINGS

102

The o r i f i c e o n an 8 mm. χ 10 cm. m e d i c i n e d r o p p e r i s p a r t i a l l y blocked with a " B o i l e z e " b o i l i n g stone. Approxi­ m a t e l y 100 mgs. o f I n f r a r e d G r a d e P o t a s s i u m B r o m i d e i s t r a n s ­ f e r r e d to the prepared dropper, which i s then attached to the exhaust l i n e o f the " o v e n " . C a r e must b e u s e d t o a v o i d l o s s o f K B r powder b y m e c h a n i c a l s i f t i n g a r o u n d t h e b o i l i n g s t o n e . A c o a t e d p a n e l i s i n s e r t e d i n t o t h e b a k i n g chamber a n d t h e fumes a r e drawn o f f t h r u t h e l i n e c o n t a i n i n g t h e K B r t r a p . An FMI L a b o r a t o r y ( 5 ) pump h a s b e e n u s e d s u c c e s s f u l l y i n t h i s p r o c e ­ dure. I t a l l o w s the a i r f l o w t o be r e g u l a t e d t o p r e v e n t the KBr from b e i n g b l o w n from t h e t r a p . A t t h e e n d o f t h e b a k e c y c l e , t h e pump i s s t o p p e d a n d t h e d r o p p e r removed w i t h c a r e t o a v o i d l o s s o f K B r . The K B r i s g r o u n d i n an a g a t e m o r t a r a n d p e s t l e t o r e d u c e p a r t i c l e s i z e , t h e n c h a r g e d i n t o a W i l k s M i n i - p r e s s . The t h r e e r e l e a s e c y c l e procedure i s used to form the p e l l e t . Recent s t u d i e s have r e v e a l e d t h a t b e t t e not ground p r i o r t o p r e s s i n g i n t o a p e l l e t . A f t e r r e m o v a l o f b o l t s , t h e p e l l e t i s mounted i n an i n f r a ­ r e d spectrophotometer and t h e scan i s r u n . We u s e a P . E . 297 (6) and r u n a t X I , 8 m i n s . s c a n t i m e , s l i t 2 p r o g r a m . I f t h e s p e c t r u m i s t o o weak f o r i n t e r p r e t a t i o n , t h r e e m o d i f i c a t i o n s o f t h e p r o c e d u r e can be u s e d : 1. I f the instrument used i s equipped f o r o r d i n a t e expan­ s i o n , a weak s p e c t r u m c a n b e e x p a n d e d s a t i s f a c t o r i l y . 2. The KBr t r a p can be exposed t o t h e v a p o r s o f a second p a n e l i n c r e a s i n g t h e amount o f v a p o r s t r a p p e d w h i c h w i l l give a stronger spectrum. 3. The u s e o f M i c r o K B r a c c e s s o r i e s w i l l p r o v i d e g o o d s p e c t r a f r o m s m a l l e r amounts o f v a p o r s o n p r o p o r ­ t i o n a t e l y s m a l l e r amounts o f K B r . We h a v e u s e d t h e Harshaw C h e m i c a l C o m p a n y ' s W i c k S t i c k ' method o f p r o c e s s i n g t h e v a p o r s i n t o a m i c r o 1 mm b y 3 mm pellet. When u s e d w i t h a beam c o n d e n s e r a c c e s s o r y , e x c e l l e n t s p e c t r a have been o b t a i n e d . M o d i f i c a t i o n s 1 & 3 a r e p r e f e r r e d t o #2 s i n c e t h e l a t t e r w i l l f r e q u e n t l y p r e s e n t p r o b l e m s due t o t r a p p i n g o f a t m o s p h e r i c m o i s t u r e on t h e K B r . T h i s causes a v e r y low p r o f i l e spectrum, the appearance o f s t r o n g water a b s o r p t i o n b a n d s , and o t h e r spectral abnormalities. These can be p a r t i a l l y a v o i d e d by d r y i n g t h e K B r powder a f t e r i t i s p l a c e d i n t h e W i l k s M i n i p r e s s (8) and b e f o r e i t i s p r e s s e d . T h i s i s done b y h e a t i n g f o r t h r e e o r more h o u r s a t 60 d e g r e e s C a n d 30 i n c h e s v a c u u m , p r e s s i n g i m m e d i a t e l y and r u n n i n g t h e s c a n . There i s always a p o s s i b i l i t y t h a t p a r t o f t h e c o n d e n s e d v a p o r s w i l l be v o l a t i l i z e d w i t h t h e m o i s t u r e , so t h i s p r o c e d u r e i s t h e l e a s t favored of the t h r e e . ff

1

A s an example o f how t h e s e p r o c e d u r e s h a v e "been u s e d t o develop a p r a c t i c a l h i g h s o l i d s c o a t i n g , a low m o l e c u l a r weight a l k y d was p r e p a r e d t o h a v e a m o l e c u l a r w e i g h t o f a b o u t 1150

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

10.

GANSER AND HEIDEL

High

Solids

CoatîUgS

103

(number a v e r a g e ) , f o r good g l o s s , f l e x i b i l i t y , l o w e m i s s i o n s and t h e l o w e s t v i s c o s i t y f o r r o l l c o a t a p p l i c a t i o n . Blends o f t h e a l k y d r e s i n l o w m o l e c u l a r w e i g h t m e l a m i n e r e s i n s were t h e n p r e p a r e d t o g i v e a r a t i o o f 75$ a l k y d t o 25% m e l a m i n e on a s o l i d s b a s i s . F l o w a d d i t i v e s a n d s o l v e n t s were a d d e d t o g i v e 70$ s o l i d s b y v o l u m e . The f i r s t v a r i a b l e u s e d a monomeric methoxy m e l a m i n e w i t h a m o l e c u l a r weight o f about 6 0 0 . T h i s r e s i n g i v e s t h e minimum v i s c o s i t y a n d m i g h t be r o l l c o a t e d a t room t e m p e r a t u r e . It gave a r e a d i n g 6 . 3 2 c o u n t s p e r mg. o f d r y f i l m . T h e IR s p e c t r u m o f t h e v a p o r s c o n d e n s e d on K B r i n d i c a t e d t h a t t h e e m i s s i o n s were p r e d o m i n a t e l y m e l a m i n e r e s i n . A s e c o n d v a r i a b l e was p r e p a r e d u s i n g a b u t o x y m e l a m i n e r e s i n w i t h a m o l e c u l a r weight o f about 1200. T h i s c o a t i n g gave a r e a d i n g o f 3 . 7 5 c o u n t s p e r mg. o f d r y f i l m a n d t h e IR s p e c t r a was a l m o s t e n t i r e l y f r e In formulating a minimum v i s c o s i t y w h i c h w o u l d b e a p p l i c a b l e a t t h e l o w e s t p o s s i b l e temperature, the O ' B r i e n - M o n i t e k procedure i n d i c a t e d t h a t t h e low m o l e c u l a r w e i g h t melamine s h o u l d not be u s e d . The b u t o x y m e l a m i n e was f o u n d t o c o n t r i b u t e l i t t l e t o v i s i b l e e m i s s i o n s a n d was c h o s e n f o r c r o s s l i n k i n g t h e a l k y d r e s i n . A wet i n k f i n i s h i n g v a r n i s h was f o r m u l a t e d w i t h t h e s e p r e f e r r e d r e s i n s and r u n c o m m e r c i a l l y w i t h o u t o b j e c t i o n a b l e v i s i b l e emissions. CONCLUSIONS: The 0 ' B r i e n - M o n i t e k s y s t e m o f m e a s u r i n g v i s i b l e emissions gives the coatings formulator a simple t o o l f o r measuring v i s i b l e emissions o f bake f i n i s h e s q u a n t i t a t i v e l y . S m a l l s a m p l e s c a n b e u s e d a n d many v a r i a b l e s c a n b e c o m p a r e d i n a r e l a t i v e l y short p e r i o d of time. The method c a n b e a d a p t e d t o t r a p v a p o r s o n K B r a n d s u b s e q u e n t l y s c a n n e d b y IR and i d e n t i f i e d . ACKNOWLEDGEMENTS : The a u t h o r s acknowledge t h e c o n t r i b u t i o n s o f c o l l e a g u e s i n p r e p a r i n g r e s i n s and d i s c u s s i n g p r o c e d u r e s and r e s u l t s . A s p e c i a l t h a n k s i s due t o o u r T e c h n i c a l D i r e c t o r , Mr. R . M . L e v i n e , f o r h i s e n t h u s i a s t i c support of t h i s program.

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MODERN CONTAINER COATINGS

104

REFERENCES: 1. Rule 66 County of Los Angeles APCD Amended 8/31/71 Currently Rule 442 Southern California APCD. 2. Regulations 3 Bay Area APCD San Francisco, CA. 3. Ringlemann Chart, U.S. Bureau of Mines. 4. Monitor Technology, 630 Price Avenue, Redwood City, CA 94063 5. FMI Model RPD-D Fluid Metering, Inc., Oyster Bay, Ν. Y. 6. Perkin Elmer Corp., Instrument Div. Norwalk, Conn. 7. Harshaw Chem. Co., Div. Kewauee Oil Co., Crystal & Electronics Prod. Dept. 6801 Cochran Rd., Solon, Ohio 44139. 8. Wilks Scientific Co., P.O. Box 449, So. Norwalk, Conn. 06856. RECEIVED MAY 22, 1978.

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

11 Polyethylene Powders for Glass Retentive Beverage Bottle Coatings S. E. HMIEL ARCO/Polymers, Inc., Research and Development Dept., Monaca, PA 15061 0

ARCO/Polymers commercialized SUPER DYLAN high densit polyethylene productio and currently operate a 150 million pound plant at Port Arthur, Texas. New production facilities are being constructed for completion in 1978 which will significantly add to present capacity. Ethylene feedstocks are supplied by our Houston and Channelview, Texas, olefin plants. These commitments have established ARCO Polymers as a reliable present and future source for high density polyethylene. The ARCO polymers polymerization process can be controlled to produce HDPE as a finely divided powder with 20-60 micron average particle diameter. These powders are particularly suitable for use in electrostatic powder spray (EPS) application equipment. SUPER DYLAN powders applied via EPS demonstrated considerable promise for coating glass, metals and other substrates. In the mid-1970's, the glass container industry had developed lightweight, non-returnable, resealable, family-sized soft drink bottles to compete with the ever increasing threat from cans. However, their increased usage by bottlers was accompanied by increasing consumer complaints due to injuries from glass fragments scattered when filled beverage bottles were accidentally broken. A survey of hospital emergency rooms, National Electronic Injury System (NEIS) by the U. S. Consumer Product Safety Commission (CPSC), Bureau of Epidemiology, confirmed an increase in reported cases and glass beverage bottles were considered for study by the CPSC. SUPER DYLAN powders, because of their low cost, availability, strength, and chemical resistance, were candidates for glass retentive beverage bottle coatings. ARCO Polymers initiated exploratory programs to establish their feasibility for electrostatic powder spray coating of glass bottles. These studies revealed that application, fusion, and cooling technique development would be required to maximize their performance as glass retentive coatings. The successful 0-8412-0446-2/78/47-078-105$05.00/0 © 1978 American Chemical Society In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MODERN CONTAINER COATINGS

106

development o f a coating process and c o r r e l a t i o n of powder p h y s i c a l p r o p e r t i e s vs. c o a t i n g performance r e s u l t e d i n the development o f a medium d e n s i t y ethylene copolymer powder f o r g l a s s r e t e n t i v e beverage b o t t l e c o a t i n g s . ARCO Polymers' commitment d i d not cease with t h i s development and the next generation of ethylene polymers being studied have demonstrated s i g n i f i c a n t improvements i n both strength and transparency. B o t t l e Coating Requirements A survey of the g l a s s c o n t a i n e r i n d u s t r y e s t a b l i s h e d the f o l l o w i n g d e s i r e d c h a r a c t e r i s t i c s f o r coatings and powders: A. Low Cost - A v a i l a b l e In Bulk B. Total Glass Containment And/Or Low Glass S c a t t e r When Broken C. Transparent D. A l k a l i Resistan E. Recyclable F. P o l l u t i o n Free - Air/Water. SUPER DYLAN HDPE powders had a l l these d e s i r e d c h a r a c t e r ­ i s t i c s with the exception o f transparency. Polymer P r o p e r t i e s Vs. Coatings The i n i t i a l program o b j e c t i v e was the establishment o f a c o r r e l a t i o n between p h y s i c a l p r o p e r t i e s and c o a t i n g p e r ­ formance on non-returnable g l a s s beverage b o t t l e s . Melt index and d e n s i t y as i l l u s t r a t e d in Figures 1 and 2 would i n f l u e n c e c o a t i n g performance. Our HDPE powders, 0.940-0.960 d e n s i t y , produced coatings with varying degrees of opaqueness and, t h e r e f o r e , low melt index powders would be more d e s i r a b l e to minimize haze or cloud i n the c o a t i n g s . However, a com­ promise in melt index, i . e . , 3.0 was necessary to achieve acceptable c o a t i n g smoothness and fragment r e t e n t i o n . TABLE I POLYMER AND COATING PROPERTIES Sample No. Property 1 2 3 Powder D e n s i t y ^ ) , q/cc Melt I n d e x l ) , g/10 Coating Transparency, %\ ) Glass R e t e n t i o n , Wt. % (4) (5) 2

ό

(1) (2) (3) (4) (5)

Min.

0.952 3.0 75 98

0.953 6.0 <70 86

0.958 16.0 <70 95

4 0.955 26.0 <65 95

ASTM D1505 ASTM 1238 L i g h t Transmission T h i c k n e s s > 1 0 M i l s , Wt. % Retained Within 3 Foot Diameter Drop Zone Bare Glass 30-50%

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

11.

HMiEL

107

Beverage Bottle Coatings

SMOOTHNESS

30.0

TRANSPARENCY STRENGTH IMPACT CHEMICAL RESISTANCE

0.0 MELT INDEX

Figure 1.

STRENGTH

formance—melt index

0.960

CHEMICAL RESISTANCE

IMPACT TRANSPARENCY 0.920

ELONGATION - TEAR DENSITY

Figure 2.

Polymer properties vs. coating performance—density

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

108

MODERN CONTAINER COATINGS

Coating Process E l e c t r o s t a t i c powder spray c o a t i n g technology was in i t ' s infancy and although more advanced f o r metal s u b s t r a t e s , c o a t ing g l a s s b o t t l e s r e q u i r e d c o n s i d e r a b l e process development to achieve uniform and r e p r o d u c i b l e c o a t i n g s . Electrostatic powder spray, dust c o l l e c t i o n , h e a t i n g , and c o o l i n g equipment were i n s t a l l e d in our Powder Laboratory and processing s t u d i e s initiated. A. Powder A p p l i c a t i o n A Model 720 GEMA EPS gun was used to manually apply powder to the r o t a t i n g g l a s s b o t t l e . Since g l a s s i s an i n s u l a t o r , i t was necessary to increase the c o n d u c t i v i t y o f the g l a s s by preheating. The r o t a t i o n , grounding v i a metal holder chuck, and b o t t l e surface temperature c o n t r o l ( 1 5 0 - 1 7 5 ° C . ) measured v i a powder d e p o s i t i o T h i s procedure was s u f f i c i e n t l y f l e x i b l e and permitted s e l e c t i v e powder d e p o s i t i o n to more c r i t i c a l areas i f d e s i r e d (Figure 3). B. Fusion The powder a p p l i e d to the heated b o t t l e would p a r t i a l l y fuse and f u r t h e r post heating was r e q u i r e d to achieve c o n t i n u i t y and melt "flow o u t . " Smooth and continuous coatings were obtained with f i n a l melt temperatures of 200-215°C. with f o r c e d a i r or i n f r a red heating equipment (Figure 4 ) . C. Cooling HDPE coated b o t t l e s cooled g r a d u a l l y in a i r or with fans were somewhat opaque or t r a n s l u c e n t . A "water quench" c o o l i n g procedure was developed to maximize c o a t i n g transparency. T h i s procedure was as f o l l o w s : 1. Molten coatings were fan cooled to a temperature s l i g h t l y above the 130°C. c r y s t a l l i n e melting p o i n t , i . e . , 145°C. (Figure 5). 2. Water was d i r e c t e d downward onto the r o t a t ing b o t t l e s l i g h t l y below the f i n i s h onto the shoulder f o r 10-20 seconds (Figure 6). The coatings provided an i n s u l a t i o n b a r r i e r and minimized thermal shock of the g l a s s . Once the c o a t i n g c r y s t a l l i z e d , the coated b o t t l e s could be handled mechanically without damage. This water quenching procedure formed smaller c r y s t a l s than those obtained by slower annealing r a t e s , in e f f e c t , lowered the d e n s i t y , and improved both transparency and s t r e n g t h .

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

HMiEL

Beverage

Bottle

Coatings

Figure 3.

Powder application—electrostatic powder spray

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

HO

MODERN CONTAINER COATINGS

Figure 4.

Powder fusion—melt transparency

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

HMiEL

Beverage Bottle Coatings

Figure 5. Melt temperature via IR—air cooling

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MODERN CONTAINER COATINGS

112

Figure 6.

Water cooling-coated bottle—transparency

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

11.

HMiEL

Beverage

Bottle

Coatings

113

Coated B o t t l e Performance The c o a t i n g - c o o l i n g process developed f o r HDPE coated bev­ erage b o t t l e s demonstrated improved strength and transparency. However, there was concern that heating and shock c o o l i n g might induce undetectable s t r e s s e s or s t r a i n s in the glass which might rupture under pressure on f i l l i n g l i n e s or in storage. Normally, g l a s s beverage b o t t l e s w i l l withstand thermal shock d i f f e r e n t i a l s up to 38°C. ( 1 0 0 ° F . ) ; our water quench procedure had a d i f f e r e n t i a l of 65-100°C. American Glass Research (AGR), a leader in glass technology, was commissioned to study the e f f e c t s of t h i s c o o l i n g procedure on g l a s s b o t t l e s t r e n g t h . They tested the coated b o t t l e s f o r i n t e r n a l burst (pressure ram), thermal shock, l u b r i c i t y , and other q u a l i t y t e s t s . AGR r e p o r t e d : "Coated ware ( b o t t l e s ) had higher i n t e r n a l burst strengths an scratched o Our c o a t i n g - c o o l i n g process d i d not adversely a f f e c t g l a s s b o t t l e strength c h a r a c t e r i s t i c s and coated b o t t l e s appeared safer even with minor flaws which might not be detected during manufacture. Cooperative g l a s s r e t e n t i o n studies of p r e s s u r i z e d bot­ t l e s were a l s o made with several g l a s s companies. The f o l l o w i n g procedure was used in our l a b o r a t o r y s t u d i e s : A. D i l u t e a c i d s o l u t i o n was charged to the b o t t l e s , volume a d j u s t e d , sodium bicarbonate added, and sealed. An i n t e r n a l pressure of 60 PSI was generated overnight at 72°F. B. B o t t l e s were dropped from 48" h o r i z o n t a l l y to impact on t h e i r s i d e w a l l s on an 18" χ 18" χ 2" r e i n f o r c e d concrete slab with a 12" χ 12" χ 1/4" steel p l a t e imbedded in the s u r f a c e . This s l a b was centered in a three (3) f o o t diameter circle. C. Glass s c a t t e r e d beyond the circumference of the c i r c l e was c o l l e c t e d and weighed. D. Glass r e t e n t i o n was expressed as wt. % g l a s s r e t a i n e d w i t h i n the three f o o t c i r c l e . Transparency was determined by the transmission of a monochromatic l i g h t beam through a water f i l l e d b o t t l e and measuring the transmitted l i g h t with a photo l i g h t meter. Polyethylene Fragment Retentive Coatings HDPE powders were s e l e c t e d to provide a range o f d e n s i t y (0.940-0.960) and melt index (0.2-30.0) to e s t a b l i s h a c o r ­ r e l a t i o n between polymer p r o p e r t i e s and coated b o t t l e per­ formance. The powders shown in Table I were the more promising of the many powders tested in t h i s p r e l i m i n a r y t e s t i n g program. Coating thickness >10 mils d i d contain fragments w i t h i n the impact zone. However, transparency was

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MODERN CONTAINER COATINGS

114

not acceptable and the economics w i t h > 1 0 mil coatings were borderline. To meet program o b j e c t i v e s , 6-8 mil coatings would be r e q u i r e d and low melt index - lower d e n s i t y powders were the obvious t a r g e t s . Several medium d e n s i t y ethylene copolymers produced v i a our v e r s a t i l e p o l y m e r i z a t i o n process e x h i b i t e d s i g n i f i c a n t l y improved transparency and strength with e x c e l l e n t g l a s s r e ­ t e n t i o n at nominal 6 mil coating t h i c k n e s s . SDP-531, a medium d e n s i t y ethylene copolymer, was s u c c e s s f u l l y produced meet­ ing the targeted p h y s i c a l p r o p e r t i e s : 0.935 d e n s i t y and 5-6 melt index. Beverage b o t t l e coatings obtained with SDP-531 e x h i b i t e d e x c e l l e n t g l a s s r e t e n t i o n , s t r e n g t h , and acceptable transparency: contact c l a r i t y with beverage was e x c e p t i o n a l l y good (Figure 7) and Tables II and III.

MEDIUM DENSIT POLYMER PROPERTIES Property Density, g/cc Melt Index, g/10 Min. Melting P o i n t , °C. (1)

Test Method ASTM-D1505 ASTM-1238 DSCU)

D i f f e r e n t i a l Scanning Elmer C o r p o r a t i o n .

SDP-531 0.935 5.5 122

C a l o r i m e t e r , DSC-1B, P e r k i n -

TABLE III MEDIUM DENSITY POLYETHYLENE GLASS BOTTLE COATING PROPERTIES Thickness, M i l s , Glass R e t e n t i o n , W t . % Transparency (2), % Appearance Coating Elongation ( ) , % Coating T e n s i l e Strength (3), PSI 1 λ

U j

3

(1) (2) (3)

5.5 98.0 91.0 Very S l i g h t Haze 800 3500

Wt. % Retained Within 3' Drop Zone. L i g h t Transmission, Water F i l l e d B o t t l e . ASTM D-638, Type IV M o d i f i e d .

SDP-531 was e x t e n s i v e l y evaluated i n l a b o r a t o r i e s and on p i l o t c o a t i n g l i n e s with the f o l l o w i n g r e s u l t s : A. Glass Retention - >95% @ 5.5 M i l s B. Transparency ->90% L i g h t Transmission C. A l k a l i Resistance - No Change i n Strength or Appear5% Caustic @ 80°C ance A f t e r 16 Hours Immersion

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

11.

HMiEL

Beverage Bottle Coatings

Figure 7.

Super Dylan SDP-531-coated glass beverage bottle— water cooling (left) vs. air cooling (right)

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

115

MODERN CONTAINER COATINGS

116

D.

Heat Resistance

- No Change in Strength or Appearance A f t e r 4 Hours @ 98°C. In Water E. U. V. S t a b i l i t y - 1000 Hours Fadeometer Exposure. NR g l a s s beverage b o t t l e s have h o t - c o l d end surface treatments to improve o n - l i n e handling and s c r a t c h r e s i s t a n c e . Studies were made varying these treatments as well as using bare ( p r i s t i n e ) g l a s s to determine t h e i r e f f e c t s . SDP-531 coatings performed comparably r e g a r d l e s s of s u r f a c e treatment. Production Coating and Market T r i a l s A s u c c e s s f u l production t r i a l on a commercial coating l i n e was made and the coated beverage b o t t l e s e x h i b i t e d performance c h a r a c t e r i s t i c s comparable to l a b o r a t o r y and p i l o t l i n e coated ware. Normal productio mended c o a t i n g and c o o l i n on a commercial b o t t l i n g l i n e and s u c c e s s f u l l y marketed. The contact c l a r i t y o f f i l l e d b o t t l e s was acceptable to b o t t l i n g and marketing personnel. Returnable Beverage B o t t l e s Glass r e t u r n a b l e b o t t l e s are designed to withstand normal abuse repeatedly through the washing, f i l l i n g , and consumer use c y c l e . The e x c e l l e n t a l k a l i r e s i s t a n c e of SDP-531 c o a t ings suggested p o s s i b l e use on r e t u r n a b l e b o t t l e s with c o r responding reduction i n g l a s s weight. Both l i g h t w e i g h t NR's and r e t u r n a b l e b o t t l e s were coated and tested on a commercial soft drink b o t t l i n g l i n e . The b o t t l e s were washed in a twostage c a u s t i c washer, f i l l e d with carbonated beverage, capped, and d i s t r i b u t e d to s e l e c t e d users. These coated b o t t l e s remained i n t a c t and f u n c t i o n a l through nine complete c y c l e s before a mechanical malfunction terminated the t e s t . These p r e l i m i n a r y r e s u l t s suggest that l i g h t e r weight coated g l a s s b o t t l e s f o r l i m i t e d t r i p r e t u r n a b l e s are a n e a r - f u t u r e possibility. Conclusion A medium d e n s i t y ethylene copolymer powder was s u c c e s s f u l l y developed and scaled up i n production equipment f o r fragment r e t e n t i v e non-returnable beverage b o t t l e coatings with acceptable transparency. T h i s R&D program e s t a b l i s h e d a c o r r e l a t i o n between polymer p r o p e r t i e s and c o a t i n g performance; developed procedures to maximize strength and transparency by water quenching molten coatings and s u c c e s s f u l l y a p p l i e d these c o a t i n g - c o o l i n g procedures on a commercial c o a t i n g l i n e . Current s t u d i e s with our v e r s a t i l e polymerization process are designed to f u r t h e r r e f i n e these " e t h y l e n e " powders f o r even b e t t e r performance as economical, fragment r e t e n t i v e beverage b o t t l e coatings with g l a s s - l i k e transparency. RECEIVED M A Y 31,

1978.

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

INDEX A Β Accelerator-aged coating 67 Bake cycles, equivalent Accelerator-aged vs. room tempera­ Basecoat, interior ture-aged unreacted prepolymers 61 Beading Acid functional acrylic polymer 81 Beer hexamethoxymethylmelamine with can interior lacquers < 0.5 % free hydroxymethyl ... 82 cans, corrosion in and hexamethoxymethylmelamine markets with ~ 16% free hydroxy methyl 8 Acids, Lewis 3 Acrylic bottle coatings, glass retentive A, water-dispersed 63 can interior lacquers B, water-dispersed 63 can market C, water-dispersed 64 Blends, structures of materials used in C2, water-dispersed 64 Blushing polymer Body spray, waterborne two-piece acid functional 81 Bottle coating requirements and hexamethoxymethylmelamine Bottles, returnable beverage with < 0.5% free hydroxy­ methyl, acid functional 82 C and hexamethoxymethylmelamine with ~ 16% free hydroxy­ methyl, acid functional 83 Can coatings, waterborne spray resins 61 cure, two-piece Adhesion grades 40 production, two-piece Adhesion, pasteurization 42 three-piece Air cooling, melt temperature via IR .... I l lCationic polymerization cooling, water cooling vs 115 Chemically similar coatings, com­ parison of pollution abatement 24 Chrome-coated steel food containers, potential of spray-type epoxy coatings for interior can coatings 23 Chrome-coated steel, TFS Almy powdered-can lacquer for twopiece beverage cans, properties of 9 Circumferential beads Alodine 401-45 14 Clean Air Act of 1970 Alodine 404 14 Coated bottle performance Aluminum D & I containers 11 bottles, cooling of Application 13 cans for particular products, of container coatings 20 development of problems of high-solid systems 48 cans, performance of Araldite 6004 44 Coating(s) ARCO polymers polymerization accelerator-aged process 105 based on four technologies Arrhenius plot for commercial emul­ chrome-coated steel food containers sion polymer/cross-linker 80 Arrhenius plot for emulsion polymer comparison of chemically similar .... cured with 2 0 % melamine crosscompatability linker 80 container Automated dynamic mechanical conventional epoxy testing 53 curing of 119 In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

35 1 26 4 91 1

105 4 1 41 66 11 106 116

1 2 19 1 38 61 25 36 26 4 113 108 27 36 67 20 25 61 34 19 68 38

MODERN CONTAINER COATINGS

120 Coatings (continued) epoxy 19, 27 experimental epoxy 69 exterior 27 fabricable-cured 66 food contact 21 glass retentive beverage bottle 105 high-solids 48 hot mar resistance of exterior 31 interior 27 low-bake 20 for metal substrates, thermoset 66 organic enamel 91 polyethylene fragment retentive 113 polymer properties vs 106 polyvinyl-dispersion-type 27 process 108 properties 106 repair 1 room temperature-aged 6 technology, electrostatic powde thermoset 19 thermosetting 30 vinyl organosol 94 waterborne 15 weight 30 Coefficient fabrication, effect of lubricant level on 32 friction, effect of lubricant level on 32 friction values 30 Cold cure curing systems 49 Colorant, levels of 30 Commercial emulsion polymer/crosslinker 78 Arrhenius plot for 80 Complete cure 73 Container(s) coating(s) 19 application of 20 epoxy dispersion 20 test procedure for 92 draw-redraw 25 drawn 25 and ironed (D&I) 14 linings 19 performance 33 effect of lining coating weight on 33 single-draw 25 Controller data analyzer sequence 60 Cooling of coated bottles 108 Coors 10 Corrosion barrter properties of modern container coatings, application of electromechanical techniques to the evaluation of 90 in beer cans 91 rate measurements 91

Cross-link density Cross-linking agents, comparison of the effect of Cure effect of curing agent type on the .... isothermal time reduction Cured coatings, fabricable Cured epoxy rubber system, effect of environment on the dynamic mechanical spectra of a Curing agent(s) melamine-of-urea type on the cure, effect of of coatings systems cold cure

Cycloaliphatic epoxides

70 79 9 86 5 66 62 13 49 9 38 5 49

40

D Decorated flat stock 1 Deformation 26 Density, polymer properties vs. coating performance 107 Determinants of thermoset material behavior 70 Dewey powdered-can lacquer for twopiece beer cans, properties of 9 D & I ( drawn and ironed ) can, twopiece 19 D & I (drawn and ironed) container .. 14 Diazonium salt, photodecomposition of 39 DICY (dicyandiamide) 5 Dicyandiamide (DICY) 5 epoxy, DSC scan of 6 Dispersion coating(s) 20 adhesion 21 application 22 characteristics 22 film properties of 21 formulations, current 20 Draw-redraw cans 94 Draw-redraw containers 25 Drawn containers 25 iron corrosion in 95 and ironed ( D&I ) container 14 -tinplate food containers, coatings for 25 DSC scan of dicyandiamide/epoxy 6 polyazelaic polyanhydride (PAPA)/ epoxy with dicyandiamide catalyst 7

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

INDEX

121

DSC scan of (continued) trimellictic anhydride/epoxy with dicyandiamide catalyst with stannous octoate catalyst .... Dynamic mechanical analysis, examples of spectra of a cured epoxy/rubber system, effect of environment on testing (DMT) automated in coatings, development of in thermoset, development of

6 8 7 59 62 53 53 54 54

Ε Electromechanical techniques to the evaluation of the corrosion barrier properties of modern containe coatings, application of 9 Electrocoatings 2 Electrodeposition process 2 Electrostatic powder spray coating technology 108 Electrostatic powder spray, powder application 109 Emissions, procedure for qualitative analysis of 101 Emulsion polymer(s) 73 cross-linker, commercial 78 cured with 20% melamine crosslinker 77 Arrhenius plot for 80 Epoxide coatings for metal containers, photocurable 38 monomers 38 parameters physical property measurements 42 oligomers 38 parameters physical measure­ ments on 42 resins 40 Epoxy chemistry 11 coating(s) 19,27 conventional 68 disadvantage of water-dispersible 12 experimental 69 technology 20 thermosetting 30 water-dispersible 12 control, solvent-base 17 dispersion container coating 20 ester coatings, waterborne 11 interior coatings groups, waterborne 12 powder(s) fast-cure 4 formulations, typical 5

powders (continued) prepared trimellictic anhydride ( TMA ) cured resins in water, dispersions of solution systems, parameters of waterborne solution systems, waterborne system ( s ) at a constant temperature, me­ chanical damping vs. time curing cure of an at a constant temperature, me­ chanical rigidity vs. time curing cure of an rubber-modified solvent-based water-emulsifiabl hot mar resistance of External lubrication

5 5 11 19 13 13

72 72 73 11 2 31 30

F Fabricable cured coatings Fabrication screening test Fast-cure epoxy powders Film integrity properties of coatings, relative properties of dispersion coatings .... Finite vs. infinite shelf-life Flat stock, decorated Flavor evaluation Food contact coatings containers, coatings for chromecoated steel containers, coatings for drawn tinplate packs, sterile Friction values, coefficient of Fuming factors

66 25 27 4 11 29 21 71 1 17 21 25 25 26 30 49

G Gelation 70 kinetics 73 temperature and 71 Glass beverage bottle, Super Dylan SDP-531-coated 115 bottle coating properties, mediumdensity polyethylene 114 retentive beverage bottle coatings .. 105 transition temperature (Tg) 71

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MODERN CONTAINER COATINGS

122 Glycidyl epoxides Grace powders

40 10 H

High solids application, objective of coatings in the laboratory, visible emis­ sions from oleo resinous system to heat, viscosity response of systems, application problems of .... thermally cured systems vs. water-based coating Hot mar resistance of exterior coatings Hydrogen evolution Hydroxymethyl system

50 48 99 49 48 48 50 31 91 84

Lubricant level on coefficient of friction, effect on Lubrication, external Lubrication, internal

32 30 30

M Materials used in blends, structures of Measured iron pickup Mechanical damping vs. time-curing cure of an epoxy system at a constant temperature Mechanical rigidity vs. time-curing cure of an epoxy system at constant temperature Medium-density ethylene copolymer, (SDP-513) polyethylene glass bottle coating properties

41 97 72 72 114 114

I Impact properties of thermoplastics .. Interior basecoat coatings groups, waterborne epoxy lacquers, beer can lacquers, beverage can sprays Internal lubrication IR analysis of the emissions from bakes Iron corrosion rate for experimental beer cans .. through breaks in coatings through discrete sites in coatings in drawn cans through organic enamel can coatings, examples of through plastisol, rate of through a thick plastisol dissolution measurement pickup calculated from corrosion rate measurements pickup, measured Isothermal cure Isoviscosity level

70 1 27 12 4 4 1 30 101 95 95 94 97 95 92 95 94 90 97 97 86 86

L Lacquer, powdered Lewis acids Line conditions Los Angeles Rule 66 Low-bake coatings Low-bake formulations Low-melt index powders Lubricant level on coefficient of fabrication, effect of

4 38 2 2 20 20 106 32

index polymer properties vs. coating performance temperature via IR-air cooling transparency, powder fusionMelamine(s) -of-urea curing agents Metal can industry containers, photocurable epoxide coatings for pretreatment substrates, thermoset coatings for .... Monitek slip-stream turbidimeter

106 107 Ill 110 13 49 1 38 21 66 100

Ν Non-drag optical transducer

59

Ο O'Brien/Monitek method of measur­ ing visible emissions Odor profile Opacity requirements, Ringleman I .... Opacity requirements, Ringleman II .. Optical transducer, non-drag Organic enamel can coatings, examples of iron corrosion through Organic enamel coatings

100 13 51 48 59 92 91

Ρ Particle-size distribution for pow­ dered-can lacquer Pasteurization adhesion beer water

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

8 42 14 14

123

INDEX Pencil hardness 31 Phenolics 13 Photocurable epoxide coatings for metal containers 38 Photodecomposition of diazonium salt 39 Plasticization 61, 84 Plastisol, rate of iron corrosion through 95 Plastisol sealant 94 Plate-wetting 48 Polarization measurements, applica­ tion of 92 Polarization resistance 91 Polyazelaic polyanhydride ( P A P A ) / epoxy with dicyandiamide catalyst 7 Polyethylene fragment retentive coatings 113 Polyethylene powders 105 Polymer(s) properties 106 medium-density polyethylene 114 vs. coating performance density 107 vs. coating performance-melting index 107 vs. coatings 106 emulsion 73 systems, water-reducible 2 Polymerization, cationic 38 Polymerization process, A R C O polymers 105 Polyvinyl dispersion-type coatings 27 Postbake, thermal 40 Post-cure 73 Potentiostatic polarization curve 92 Powder application 108 electrostatic powder spray 109 coating development 5 fusion 108 transparency 110 Powdered-can lacquer particle-size distribution for 8 for two-piece beer cans, properties of Dewey 9 for two-piece beverage cans prop­ erties of Almy 9 Powdered lacquer 4 Prepolymers, unreacted 66 Processability 84 Production coating and market trials .. 116 Properties of epoxy coatings 19 P V C dispersion G 34 P V C dispersion vehicle 33

R RD-2 blends, properties of Reflow point

43 34

Reformation Repair coating Resins, acrylic Rheometrics mechanical spectrometer Rheovibron Returnable beverage bottles Ringleman I opacity requirements Ringleman II opacity requirements .... Rollcoat application Rollcoating Room temperature-aged coating Rubber-modified epoxy, effect of catalyst level on the cure of Rubber-modified epoxy systems

25 1 61 55 53 116 51 48 49 202 67 74 73

S Schiemann reaction SDP-531 (medium-density ethylene

38

Shelf stability Sherwin-Williams Co. Single-draw container Slope-intercept technique Soft drink markets Softening points Softening temperature Solvent-base epoxy control Solvent-based epoxy systems Scratch tests Spray can coatings, waterborne nozzles plugging -type epoxy interior can coatings, air pollution abatement poten­ tial of Stannous octoate catalyst, D S C scan of trimellitic anhydride/epoxy with Steel D & I containers Sterile food packs Substrate wetting Super Dvlan high-density poly­ ethylene production ( H D P E ) .... Super Dylan SDP-531-coated glass beverage bottle

13 5 25 91 1 40 71 17 11 30 1 22 22 23 5 7 11 26 48 105 115

Τ Tack free time Tafel line Taste profile T B A , (torsional braid analysis) Temperature and gelation Test pack foods Testing programs for new containers T F S chrome-coated steel Tg, (glass transition temperature) ....

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

42 92 13 85 71 28 90 36 71

MODERN CONTAINER COATINGS

124 Thermal postbake 40 Thermoplastics, impact properties of .. 70 Thermoset coating(s) 19 for metal substrates 66 development of dynamic mechan­ ical testing on 54 material behavior, determinants of 70 Thermosetting 27 epoxy coatings 30 systems, time to gel vs. isothermal cure temperature for 74 system, time to vitrify vs. isothermal cure temperature for 74 Three-piece can 1 Three-piece food containers 48 Time to gel vs. isothermal cure temperature for thermosetting systems 74 Time to vitrify vs. isothermal cur temperature for thermosettin system 74 Torsion pendulum automated 58 free-hanging, freely decaying 55 torsional braid analysis 57 characteristics of an automated, free-hanging, freely decaying .. 55 mechanical function of 56 sequence of events of the automated 59 Torsional braid analysis (TBA) 53,85 torsion pendulum (automated) 57 Transparency, water cooling-coated bottle 112 Trimellictic anhydride (TMA) / epoxy with dicyandiamide catalyst, DSC scan of 8 DSC scan of 6 with stannous octoate catalyst, DSC scan of 7 -cured epoxy powders 5 Turbidimeter, Monitek slip-stream .... 100 Turbidity resistance 13 Two-piece beer cans, properties of Dewey powdered-can lacquer for 9 beverage cans, properties of Almy powdered-can lacquer for 9

Two-piece (continued) body spray, waterborne can cure can production D & I can

11 2 19 19

U

Unreacted prepolymers accelerated-aged vs. room tempera­ ture-aged Urea-formaldehyde UV radiation curing, advantages of V Vinyl organosol coating Viscosity response of high-solids oleoresinous system to heat Visible emission, procedure for measuring Vitrification

66 61 13 38 38 94 49

100 70

W

Water cooling-coated bottle transparency Water cooling vs. air cooling Waterborne coatings epoxy ester coatings interior coatings groups solution systems parameters of spray can coatings two-piece body spray Water-dispersed Acrylic A Β C C2 Water-dispersible epoxy coatings disadvantages of Water-emulsifiable epoxy systems Water pasteurization Water-reducible polymer systems W. R. Grace & Co

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

112 115 15 11 12 13 13 1 11 63 63 64 64 12 12 12 14 2 5