Paint & Coating Industry February 2011

February 2011 VOLUME 27, NUMBER 2

INSIDE Waterborne Technology

Paint

Coatings Industry

Molecular Weight Characterization of Polymers Focus on Marine Coatings

Globally Serving Liquid and Powder Formulators and Manufacturers

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CONTENTS PA I N T & C O AT I N G S I N D U S T RY , V O L U M E 2 7 , N U M B E R 2

February 2011

FEATURES 20 A Novel Mixed Mineral Thixotrope Technology for Industrial Coatings, Southern Clay Products 26 Low-Angle Light Scattering Detection for GPC – Why Closer is Better, Malvern Instruments 32 Focus on Marine Coatings, Bayer MaterialScience and Sherwin Williams

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ONLINE FEATURES w w w. pcimag.com Effective Cleaning With Light, The KRONOS Group New Coating Extends Truck Bed and Vehicle Protection for Owners, Burtin Polymer Laboratories PPG Reports Most Popular Vehicle Color/Introduces 66 New Exterior Shades, PPG Industries As the Economy Recovers, How Important is Employee Engagement? Rollins College

DEPARTMENTS 6 Viewpoint 8 Industry News

34 2K Waterborne Polyurethane Technology for Automotive Clearcoat Applications, Perstorp

12 Names in the News

40 Designing, Formulating and Measuring Coatings for Optimum Rheology, Brookfield Engineering

18 Products

42 Recent Advances in Photocuring and Stabilization of Waterborne Coatings, BASF Corp.

14 Company News 49 Classifieds 50 Advertiser Index

BUSINESS TOOLS 48 Supplier Showcases 48 Lab/Testing Showcases

PCI - PAINT & COATINGS INDUSTRY (ISSN 0884-3848) is published 12 times annually, monthly, by BNP Media, 2401 W. Big Beaver Rd., Suite 700, Troy, MI 48084-3333. Telephone: (248) 362-3700, Fax: (248) 362-0317. No charge for subscriptions to qualified individuals. Annual rate for subscriptions to nonqualified individuals in the U.S.A.: $115.00 USD. Annual rate for subscriptions to nonqualified individuals in Canada: $149.00 USD (includes GST & postage); all other countries: $165.00 (int’l mail) payable in U.S. funds. Printed in the U.S.A. Copyright 2011, by BNP Media. All rights reserved. The contents of this publication may not be reproduced in whole or in part without the consent of the publisher. The publisher is not responsible for product claims and representations. Periodicals Postage Paid at Troy, MI and at additional mailing offices. POSTMASTER: Send address changes to: PCI - PAINT & COATINGS INDUSTRY, P.O. Box 2145, Skokie, IL 60076. Canada Post: Publications Mail Agreement #40612608. GST account: 131263923. Send returns (Canada) to Pitney Bowes, P.O. Box 25542, London, ON, N6C 6B2. Change of address: Send old address label along with new address to PCI - PAINT & COATINGS INDUSTRY, P.O. Box 2145, Skokie, IL 60076. For single copies or back issues: contact Ann Kalb at (248) 244-6499 or [email protected].

Audited by BPA Worldwide

Associate Member

Printed in the U.S.A.

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Smart Coatings 2011 kicks off Feb. 23-25, in Orlando, FL. Coatings, polymers and related materials continue to be an innovative area in research and technology. Smart materials (adaptive, r e s p o n s ive , b io ac t ive , photonics and nanotechnology-based coatings) are becoming the norms of the industry. The objective of this symposium is to provide a forum to stimulate new ideas, present and discuss fundamental and applied science of smart coatings, identify critical problems, provide promising solutions, and assess possible roadmaps. The 38th Waterborne Symposium will be held Feb. 28-March 4 in New Orleans. Sponsored by the School of Polymers and High Performance Materials at The University of Southern Mississippi, this event has a reputation for excellent scientific presentations and discussions. Sixteen papers have been chosen as finalists for the Best Paper Award to be presented during the closing ceremonies of the symposium. Coming up in March is uv.eb West 2011, a two-day conference and exhibition providing presentations and demonstrations by leading industry suppliers and users targeting the environmental, economic, energy savings and performance benefits of UV and EB. The event will occur March 8-9 in Santa Clara, CA.

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By Kristin Johansson, Editor | PCI

FEBRUARY 2011 | W W W . P C I M A G . C O M

And many of us are gearing up for the European Coatings Show, which will be held March 29-31 in Nuremberg, Germany. The parallel European Coatings Congress will begin one day earlier, on the 28th, and run through the 30th. In 2009, 806 exhibitors from 42 countries offered the 19,756 trade visitors from 100 countries a world-class range of raw materials, laboratory and production equipment, testing and measuring equipment, and services. The Congress invites the global coatings community to learn about the most recent results and industrial developments, covering the full range of processes and raw materials for the formulation of coatings, inks, adhesives, sealants and construction chemicals. 150 selected papers in 25 sessions, and 14 equally interesting poster presentations, offer potential contributions that add value to the coatings industry. These are just a sampling of the many shows and conferences pertaining to the coatings industry that are taking place over the next several months. For a complete list of industry happenings, visit the Events section at www.pcimag. com. Make plans to attend as many as you are able, as they will introduce new ideas and technology that will help, motivate and inspire you. I’m looking forward to reporting on these events, and PCI will be publishing select papers from many of them throughout 2011.

I NDUSTRY NEWS

Growth Expected for Automotive Coatings, Adhesives and Sealants CLEVELAND – U.S. demand for coatings, adhesives and sealants used in the automotive industry is forecast to expand 9.4 percent annually to $5.6 billion in 2014. The U.S. motor vehicle industry was particularly hard hit by the weak global economy. As a result, vehicle output was cut in half between 2004 and 2009, reducing demand for coatings, adhesives and sealants at the original equipment manufacturer (OEM) level. Through 2014, however, this segment of the market will drive overall gains, as vehicle production expands rapidly from a depressed base. These and other trends are presented in “Automotive Coatings, Adhesives & Sealants,” a new study from The Freedonia Group Inc. The OEM segment has historically dominated the automotive coating, adhesive and sealant market. In 2009, however, vehicle output had fallen so low that the aftermarket

accounted for nearly three-fifths of demand. Going forward, the OEM segment will expand at a double-digit annual pace and once again take its place as the leading outlet for coatings, adhesives and sealants. Coatings will remain the leading product type, accounting for more than three-quarters of market value in 2014. Water-based, powder and radiationcurable coatings will provide the best gains, as their good environmental

USB Helps Soy-Based Products Come to Market ST. LOUIS, MO – Due in part to the United Soybean Board (USB) and the U.S. soybean research and promotion program known as The Soybean Checkoff, 32 new soy-based products hit the market in 2010. The USB provides funding to industrial partners to research, develop and commercialize products containing soy. The USB focuses its research on several target areas, including adhesives, coatings, printing inks, lubricants, plastics, fibers, solvents and emerging industrial products. While the products represent a diverse range of categories, all represent sustainable, bio-based alternatives to petrochemicals. Each new soy-based product represents the culmination of a three- to five-year process that began with researchers presenting their ideas for new soy technology to USB farmer-directors.

profile enables users to meet stricter VOC requirements. However, overall demand will advance at a below-average pace as efforts to improve paint-shop efficiency, reduce costs and limit waste will restrict gains in market volume. Sales will also be impacted by greater competition from alternative materials, such as in-molded colored plastics and paint films. More rapid growth will be achieved by the smaller adhesive and sealant segments. Advances will be promoted by cost-cutting measures and efforts to increase fuel efficiency by reducing vehicle weight, both of which favor the use of adhesives and sealants over welded joints, mechanical fasteners and gaskets. Adhesives will benefit from the rising use of plastics in motor vehicle manufacture, since plastics are compatible with adhesives and cannot be welded. For further details about the study, visit www.freedoniagroup.com.

coatings industry is heavily reliant on the end-use industries it serves. “Asia, being a developing industrial nation, has many key growth sectors that aid the growth of the market. Some of the key industrial sectors monitored are construction, steel, marine, automotive and furniture,” she said. Currently, China is witnessing high growth in its steel and furniture industries, while India is similarly experiencing positive growth in its construction and steel industries. ASEAN countries are witnessing growth in construction, marine, automotive and furniture industries. In terms of industry specifics, the coming year will see industry players creating a competitive edge by introducing innovative products in the market with enhanced sustainability features. Green-based technology will see high growth, particularly for powder and water-based coatings.

Asia-Pacific Paint and Coatings Market Expects Growth in 2011

Coatings Industry to Meet in Germany

SINGAPORE – The APAC paint and coatings market for 2010 is estimated to be approximately $48 billion, with a market size of 15 million metric tons (MT) and a growth rate of 8 to 11 percent. This was aided mainly by the strong driving forces of China and India as well as developing growth from key ASEAN countries (Association of Southeast Asian Nations) such as Indonesia and Vietnam. Industry players are optimistic about the prospect of seeing double-digit growth once again in 2011. According to Frost & Sullivan’s Program Manager of Chemicals, Material and Food Practice, Sheila Senathirajah, the paint and

HANNOVER, Germany – From March 29-31, 2011, Nuremberg will become the world’s hub for the coatings industry, when the European Coatings Show 2011 takes place. One of the highlights will be the comprehensive Congress program, which will take place from March 28-30. The Congress will feature 25 technical sessions on coatings development, printing inks, adhesives and sealants, construction chemicals, production technology and on raw material procurement issues. Two keynote speakers, representing both the coating university researchers and the industrial perspective, will give

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FEBRUARY 2011 | W W W . P C I M A G . C O M

I NDUSTRY NEWS their views on current challenges and trends in the coatings industry during the plenary session. The comprehensive Congress program can be viewed at www. european-coatings-show.com/en/congress/.

Call for Papers Issued for Sink or Swim Symposium

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AKRON, OH – Abstracts for podium and poster presentations are now being accepted for the 54th Annual Sink or Swim Technical Symposium, to be held May 24-25, 2011, at the University of Akron. The deadline for submission of abstracts is Feb. 15, 2011. This year’s symposium theme is “Advances in Coatings Technologies — the Future, Today.” For questions or to request speaker forms, contact Kathy Hogan, Cleveland Coatings Society, at [email protected].

12th International Coatings Congress Issues Call for Papers SÃO PAULO, Brazil – Technicians, professors, researchers and other professionals interested in presenting papers at the 12th International Coatings Congress may now submit their abstracts. The Congress will be held Nov. 21-23, 2011, at the Transamerica Expo Center in São Paulo, Brazil. It is held in conjunction with the 12th International Exhibition of Coatings Industry Suppliers, as part of ABRAFATI 2011. Those interested in presenting a lecture or participating in the poster session should submit an abstract by May 31, 2011, at www.abrafati2011.com.br. 䡲

AMAZING FINISHES DON’T JUST HAPPEN We’ve had years of practice to perfect ours. Few specialty chemical manufacturers can offer the same level of performance or experience in the coatings industry. That has given us plenty of practice at perfecting an extensive line of additives – from pigment dispersions and colorants to defoamers – to achieve that perfect finish. So don’t settle for anything less than a proven performer.

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N AMES IN THE NEWS 䡲 International Paint LLC

䡲 Archer Daniels Midland Co.

has named Paul Bloom Business Director, Industrial Chemicals. Bloom will be responsible for developing and commercializing renewable chemicals, and for managing the commercial activities of ADM’s industrial chemicals business.

䡲 Archway Sales Inc. has hired Mark Cowling as the Purchasing Inventory Control Analyst. He will be based out of St. Louis, MO.

has promoted Chris McMillan to Protective Coatings Senior Market Manager, and has appointed Karl Nollsch to dual positions as Water and Wastewater Market Manager, Americas, and Protective Coatings Distributor Program Coordinator. Martin Criado has been hired as Marine & Protective Coatings Manager, Latin America.

McMillan

䡲 Chemsultants International has promoted Berry Decker to Technical Project Manager and Cheryl Saqqa to Testing Project Leader. 䡲 Keystone Aniline Corp. has hired Kane Henneke as Business Manager, Inks and Coatings. 䡲 Deeks & Co. Inc. has announced the addition of Dennis R. James as an Account Executive responsible for eastern Georgia and South Carolina. The company also announced the addition of Edward B. Grey as Account Executive for western Georgia, Alabama and the Florida Panhandle. 䡲 BASF Automotive Refinish has named Nick Maloof its new Central Zone Manager.

Nollsch 䡲 Ulrich Steiner has been appointed Head of Group Communications & Investor Relations for Clariant. In addition, Steiner continues to lead Investor Relations. Ulrich Nies has been appointed Head of Corporate Communications in addition to his current role as Head of Communications EMEA.

䡲 E.T. Horn Co.

has hired Jay Umphrey as Senior Account Manager. He will develop and manage key accounts within the company’s Coatings and Building Materials group.

䡲 DSM NeoResins+ has appointed Martin Vlak to the position of Global Sales Director. Vlak replaces Ad Ernst, who will focus his energies on integration within the DSM Resins Business Group and helping grow the recently announced acquisition of a majority stake in AGI Corp. 䡲

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C O M PANY NEWS

Clariant Builds Innovation Center in Germany MUTTENZ, Switzerland – Clariant is pla n n i ng to ex pa nd its globa l research and development activities at its site in Frankfurt, Germany. The new, 23,000-square-meter Clariant Innovation Center is due to be completed by the end of 2012. It will provide space for 500 people.

The planned center will be located in the Frankfurt-Höchst Industrial Park and represents an investment of more than

Appleton to Microencapsulate Biocides for Troy Corp. APPLETON, WI – Encapsys®, the microencapsulation division of Appleton Papers, has entered into an exclusive strategic partnership with Troy Corp., Florham Park, NJ, to develop and supply a microencapsulated biocide to select marketplaces worldwide. Microencapsulation is the process in which solid, liquid or gaseous core materials are encased in “shells” or “capsules” that are one micron to several hundred microns in diameter. Among the many benefits of microencapsulation is the controlled release of a core

€50 million. The new innovation center will closely cooperate with all of the R&D satellite sites in Gendorf (near Munich, Germany), Lamotte (France) and Suzano (Brazil), as well as 40 application centers around the globe. Clariant invested well over CHF 130 million in research and development in 2010.

material. Through microencapsulation, Encapsys scientists were able to control the antimicrobial activity of a biocide to be used in paints, architectural coatings and mortar formulations.

Buhler Acquires Draiswerke Inc. UZWIL, Switzerland – The Buhler Technology Group has acquired Draiswerke Inc., Mahwah, NJ. Draiswerke Inc., which generated sales of about $5 million last year, will be integrated in the Buhler Grinding & Dispersion business unit. Integration will be completed

C O M PA N Y N E W S

by the end of 2011. Gisbert Schall, the current President and CEO of Draiswerke Inc., will retain his function up to mid2011, when a successor will be appointed.

Arkema Sees Growth in Green-Market Products CARY, NC – Arkema Emulsion Systems’ EnVia™ certification program, first introduced in 2009, now includes 10 products that meet specific standards set by the company related to regulatory compliance in finished products. Beginning in 2011, every new latex product introduced by Arkema Emulsion Systems will be EnVia certified.

Evonik to Expand Capacity in Isophorone Chemistry ESSEN, Germany – Evonik Industries intends to construct a new production plant for isophorone and isophorone diamine. A suitable site is being sought, and production is scheduled to start in 2013. According to Gerd Brand, head of the Crosslinkers

Business Line, the company will take into consideration attractive investment climates in Southeast Asia and China when making a final decision about the location of the plant. Evonik currently has production sites in Herne and Marl (Germany), Antwerp (Belgium), as well as Mobile, AL.

PETRONAS and BASF to Explore Joint Investment KUALA LUMPUR, Malaysia – BASF and PETRONAS have signed a Memorandum of Understanding to undertake a joint feasibility study to produce specialty chemicals in Malaysia, a move that would extend the two parties’ existing business collaboration in the country. The two parties will evaluate the technical, commercial and economic viability of jointly owning and operating worldscale facilities for the production of specialty chemicals including non-ionic surfactants, methanesulfonic acid and isononanol, as well as other C4-based specialty chemical products. The final scope

of the investments will be determined following the outcome of the study, which is targeted for completion in 2011.

LANXESS Receives National Performance Improvement Honor PITTSBURGH – The Society of Chemical Manufacturers and Affiliates (SOCMA) has awarded LANXESS Corp.’s operations in Baytown, TX, with a 2010 Silver Award for implementing a recognized environmental, health, safety and security (EHS&S) program. LANXESS’ Baytown facility, which manufactures maleic anhydride, is being recognized in the product stewardship category for developing and making available to all customers a guide and video on the safe handling and transportation of its product.

Ashland Dedicates HEC Facility in China NANJING, China – Ashland Inc. celebrated the grand opening of its new Natrosol™ hydroxyethylcellulose (HEC) production

The EnVia™ certification program from Arkema Emulsion Systems simplifies your sustainability efforts by providing a choice of coatings raw materials to meet your specific performance and regulatory benchmarks. Our range of EnVia™ certified products includes a variety of product chemistries – 100% acrylic, styrene acrylic, vinyl acrylic and vinyl acetate ethylene binders, and our new SNAP™ 720 Structured Nano-Acrylic Polymer – so you don’t have to compromise performance or value in your final product. And, with Arkema Emulsion Systems’ commitment to EnVia™ certification of all new products, there’s no time like the present to turn over a new leaf in your sustainability program.

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Visit www.arkemaemulsionsystems.com/EnVia to learn more about the EnVia™ certification program. At Arkema Emulsion Systems, we’re focused on your future.

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C O M PANY NEWS facility in Nanjing, China. Ashland’s largest single investment in China and the AsiaPacific region, the plant is located within the Nanjing Chemical Industry Park, a modern, highly integrated chemical manufacturing complex. The new facility is Ashland’s fourth HEC production facility.

Huber Enters Agreement with Almatis ATLANTA – Huber Engineered Materials (HEM), a division of J.M. Huber Corp., and Almatis Inc. (Almatis) have reached an agreement under which Almatis will toll produce for HEM certain specialty

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Rhodia Completes Acquisition of Feixiang Chemicals PARIS – Specialty chemical producer Rhodia has completed the acquisition of Feixiang Chemicals after receiving approval from Chinese authorities. Located in Zhangjiagang near Shanghai, China, Feixiang Chemicals is one of China’s leading producers of amines and surfactants.

OMNOVA Solutions Acquires ELIOKEM

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VANTAA, Finland – Tikkurila Oyj’s Swedish subsidiary, Dickursby Holding AB, is selling all the shares in OOO Tikkurila Powder Coatings, a Russian industrial coatings company, to Teknos Group Oy. With a production plant in St. Petersburg, Russia, OOO Tikkurila Powder Coatings sells and markets its products in Russia under the Ohtek brand. After the transaction, Tikkurila will have no powder coatings-related operations.

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A Novel Mixed Mineral Thixotrope Technology for Industrial Coatings

A

s regulations call for lower VOC levels, it becomes increasingly difficult to design coatings with appropriate rheology. Properties such as sag resistance and settling resistance become more difficult to balance with package viscosity. The use of Garamite® mixed mineral thixotropes (MMTs) can help with key properties such as sag resistance and settling resistance while maintaining a reasonable package viscosity. This article explains how and why Garamite works. MMTs are compared to various thixotrope technologies used in different types of industrial coatings, including highsolids epoxies, low-HAPs systems, high-solids alkyds, chainstopped alkyds and zinc primers. Also discussed are methods of incorporation and other processing considerations.

Mixed Mineral Thixotropes MMTs are a combination of two different morphologies; one being a plate, the other being a rod. They are off-white powders that are organically modified and have a specific

FIGURE 2 | How MMTs differ from organoclays.

Conventional Organoclay

Garamite

Easily Dispersible Organoclay MMT = Mixed Mineral Thixotrope gravity of about 1.6. If needed for very thin-film applications, there is a micronized version available [Garamite 2578 (8 μm d50 grain size)]. However, the primary product is Garamite 1958 (32 μm d50 grain size) for most applications (Table 1).

How MMTs Work TABLE 1 | Garamite properties.

General Color..............................................................Off White Form ..............................................................Fine Powder Moisture Content .....................................4% Bulk Density ...............................................130 kg/ m3 Specific Gravity..........................................1.5 - 1.7 Specifications % H20 (2.0 – 6.0) % LOI (29.0 – 33.0) V/R (0.75 – 1.3) FIGURE 1 | Thickening mechanism; hydrogen bonding forms a three-dimensional network.

= -OH.....HO ....HOhydrogen bonding

MMTs thicken systems similarly to the way in which organoclays work, using hydrogen bonding to form a three-dimensional network (Figure 1). However, MMT networks use different spacing than do traditional organoclays, due to the different particle shapes involved.

Garamite Compared to Organoclay There are a variety of organoclays, but for the purpose of this article we will stick to the basics and compare and contrast activated versus self-activating organoclays. A simple way to look at organoclay is to look at the level and type of quaternary amine modification on the clay. The lowest levels, considered to be traditional organoclays, have to be activated with some type of polar activator. These organoclays usually are more efficient for thickening, but can be more difficult to incorporate, and order of addition can be more critical. Self-activating organoclays tend to have a higher loading of quaternary amine on them. This higher level of quaternary amine typically makes them easier to incorporate, but slightly less efficient than traditional organoclays, all other things being equal. Also the type of quaternary amine modification determines which type of solvent system the organoclay will work best in. Certain quaternary amines work better in aliphatic vs. aromatic systems, for example. Organoclays are typically made from smectite and come in a form somewhat like a deck of cards, with clay particles

By Wes Huff, Technical Service Manager | Southern Clay Products, Louisville, KY 20

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stacked one upon another. As organoclay manufacturers we impart a lot of energy to break this naturally occurring layered mineral apart. But in the end, Mother Nature tries to return the clay back to its natural state. Including the other mineral type helps to prevent this from occurring. Garamite 1958 has a unique morphology of rods and plates as compared to conventional organoclays that use just a plate-like layered structure (Figure 2). This morphology plays a role in not only the ease of incorporation, but also in the efficacy of sag resistance and settling resistance over heat aging.

MMT Advantages In practical terms we have found that Garamite tends to build less package viscosity while providing more sag resistance than organoclays. The MMTs provide 50% or more increase in sag resistance at equal use levels versus organoclays. Not only is sag resistance increased, but runs are reduced or eliminated (Figure 3). This becomes more important as VOC goes down and solids go up. The trend for higher-solids coatings is to have excessive package viscosity without sufficient sag resistance. We also found that the quaternary amine does not play as important a role in determining efficiency in a specific solvent system, like with traditional organoclays. In recent studies we have seen the Garamite 1958 work across a very wide range of solvent systems. Does this mean it will work every time? Probably not. But it does mean MMTs are more flexible as compared to organoclays and have the ability to work in more systems. This flexibility could reduce the number of thixotropes needed. The morphology also plays a role in ease of incorporation. Unlike organoclays, Garamite is easily incorporated into the coating formulation without using a high level of quaternary amine. In part, we believe this has to do with the difference in having a combination of rods and plates and having more spacing, making it much more difficult for Mother Nature to put the clay back to its natural state. Another advantage of the MMTs is that in most systems polar activators are not necessary. If needed to gain a little more efficiency, one can use polar activators in a manner similar to traditional organoclays. Another key advantage to the coatings manufacturer is the ability to make high-solids premixes at pourable viscosities. Garamite 1958 can be used to make a pourable pregel as high as 20% solids. Typical pregels made from traditional organoclays are usually not pourable once they reach about 4 or 5% solids. Having the ability to make pourable high-solids pregels makes it easier to formulate in systems where one has low levels of solvents (Figure 4). When comparing MMTs to fumed silica, the big difference is in bulk densities. While the MMTs have a low bulk density compared to traditional organoclays, it is much higher than fumed silica, which has an extremely low bulk density. This leads to issues with dusting and incorporation for the fumed silica as compared to Garamite (Figure 5). When replacing fumed silica with Garamite, one can typically reduce the level of thixotrope by 40% or more to get equal sag resistance and eliminate runs. One advantage for fumed silica is clarity in the final film.

However, this property is not noticed in filled systems. Also, it bears mentioning that some color is imparted into clear, unfilled systems by the MMT. In unfilled systems, another shortcoming would be that the MMTs do not perform quite as well for sag resistance. It is as though the MMT needs to space something to work. When comparing Garamite to polyamides or castor derivatives, the MMT is much less sensitive to processing conditions. The comparison thixotropes need to achieve the correct temperature and dwell time to be activated and

FIGURE 3 | MMT typical effect on sag resistance.

Notice the elimination of runs or drips

0.3% Garamite

0.5% Fumed Silica

0.5% Organoclay

FIGURE 4 | Garamite 1958 can be used to make a pourable pregel as high as 20% solids.

20% Garamite in Exxsol D80

10% Organoclay in Exxsol D80*

stable, pumpable

* = including 3% activator, hectorite-based organoclay

FIGURE 5 | Bulk density of Garamite compared to fumed silica and organoclay.

Fumed Silica 50 g/L

Garamite 130 g/L

Organoclay 400 g/L

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A Novel Mixed Mineral Thixotrope Technology for Industrial Coatings

work properly, while Garamite does not. They also require the proper agitation during cooling in order to prevent the system from forming a false body. This can make the other thixotropes much more difficult to deal with in the long run. Also, it may be possible to use these products during manufacture without the ideal conditions, yet still pass QC. Then somewhere down the road the system may have seeding problems or lose stability. Stability can be lost in different areas, whether it be sag resistance falling off or package viscosity rising substantially. While polyamides in particular may be among the best at yielding that perfect buttery feel, they are much less forgiving during manufacture than MMTs.

FIGURE 6 | Garamite 1958 in 100% solids, edge-retentive epoxy.

60 50 Mils

40 30 20

Comparisons in Various Systems High-Solids Epoxy In the first system, we compared Garamite 1958 to a polyamide in a 100% solids, edge-retentive epoxy. This system was based on Epon 862, and the hardener was Cardolite’s NX-5079 (phenalkamine). The starting-point formula had 1% polyamide in Part A and 0.59% in Part B. Originally we used the Garamite 1958 only in Part A. While the efficiency was there we discovered that the sag resistance fell off during the pot life. We then realized that by splitting the Garamite 1958 50:50 in both Part A and Part B that not only did the coating have a reasonable sag resistance over the pot life, but that it was more stable during the shelf life during heat aging. Due to the lower viscosity of the phenalkamine, a 20% high-solids pregel was made in the phenalkamine, which was pourable, then added to the rest of the Cardolite NX-5079. As Figure 6 shows, Garamite 1958 is both efficient and stable. The table shows the pot life stability at 10 minutes and at 30 minutes, as well as heat age stability over a month at 140 °F. It also points to a stability issue for the polyamide, which dictates the end user would probably add solvent to cut viscosity, while that shouldn’t be necessary for the epoxy made with the Garamite 1958.

10

Epoxy Floor Coating

0

Polyamide

initial 10 mins 1 week 140 ºF 30 mins

Garamite 1958

initial 30 mins 4 weeks 140 ºF 10 mins

1 week 140 ºF 10 mins 4 weeks 140 ºF 30 mins

FIGURE 7 | Suspension of quartz sand in an epoxy floor coating.

Goal: Prevent Settling of Quartz Sand Epoxy Floor Coating with Quartz Sand Polypox E403 BYK 341 BYK 530 Quartz Sand GS 13 Plastorit O Polypox E403 BYK 530 Thixotrope BYK R605 (Enhancer)

36.0 0.16 0.5 36.8 12.0 14.0 0.5 0.4 0.04

Figure 7 highlights the suspension of quartz sand in an epoxy floor coating. Garamite 1958 outperforms fumed silica and significantly outperforms conventional organoclay. Notice the phase separation of the modification made with organoclay. This is also the first time in this article we use a rheological enhancer, the BYK R605. This class of material is used from time to time to boost or enhance the properties of the thixotrope.

Low-HAPs Primer Control blank of quartz sand Garamite Conventional Fumed 1958 Silica Organoclay

MMT eliminated settling of quartz sand

FIGURE 8 | Settling resistance in a low-HAPs primer.

10

The next study was of a low-HAPs primer based on a chain-stopped short oil alkyd. In this study we compared the MMT to a polyamide, both conventional and selfactivating organoclays, as well as a blank. Even though the polyamide yielded the highest viscosity, the Garamite at the lowest level, 2 pounds per 100 gallons, had a settling resistance that matched the higher loading level of polyamide (Figure 8). This allows for lower package viscosity, lower cost and increased ease of manufacture.

Industrial White Topcoat

2

The next study looked at an industrial white topcoat. As with the previous study, we compared the MMT to a polyamide, conventional and self-activating organoclays, and a blank. In this case the polyamide had the highest viscosity but did not do well for the prevention of settling during heat aging (Figure 9). This system turned out to be a little more difficult than the previous system, as it took the higher (4 pounds per 100 gallon) level of Garamite to eliminate the settling.

0

Zinc Primer

8 6 4

-2

22

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1 day 3 weeks

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T M

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k an bl initial 2 weeks

1 week 4 weeks

FEBRUARY 2011 | W W W . P C I M A G . C O M

The next study intended to find the level of Garamite needed to suspend zinc through the use of high-solids pregels. To totally suspend the zinc it took 1.7% of the Garamite 1958 that was done in a very high solids pregel of 18.9%. This pregel was both pourable and pumpable (Figure 10).

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A Novel Mixed Mineral Thixotrope Technology for Industrial Coatings

FIGURE 10 | Zinc-ethylsilicate anti-corrosive primer stability.

FIGURE 9 | Settling resistance in an industrial white topcoat. 10

Control 0.7% MMT 1% MMT 1.7% MMT blank (8.8% pregel) (12% pregel) (18.9% pregel)

8 6 4 2 0 5 .7

T5

7 .3

T2 weeks

5 .7 gin at 75 tiv -.3 Ac g lf in 5 Se at .7 ytiv cla Ac lf 75 lO .3 Se na yio cla nt lO ve na Co tio en 5 nv .7 Co eid am 75 ly .3 Po eid am

M

M

nk

ly Po

M

M

a bl 1 week

FIGURE 11 | Effectiveness of Garamite compared to organoclay in a

3 weeks

PU system.

2-Pack PU-Coating incl. Hardener (Synthalat A 077)

100 μm

4 weeks

Polyurethane Systems Other potential applications include polyurethanes, epoxy adhesives and grouts, unsaturated polyesters, metallic coatings and aerosol coatings. For polyurethanes, in particular the moisture-cured systems, it should be noted that Garamite contains 4% water. The water is adhering to the clay surface and is not automatically available for reaction with the isocyanate. But for reactivity and storage stability it should be tested to see if the water in Garamite causes issues in these watersensitive formulations. To overcome this, Garamite could be oven dried at 120 °C to lower the moisture content, or the use of moisture scavengers could be employed. Figure 11 evaluates the effectiveness of Garamite compared to organoclay in a PU system.

How to Use Garamite The use of Garamite is very similar to organoclays. In solvent-containing systems that can tolerate such processing, always add the Garamite to the solvent. The Garamite should be added at a percentage high enough to

300 μm 350 μm

Control

Organoclay

Garamite 1958

make a pregel that is still pourable. While not completely necessary, this will consistently yield the most efficient results. If solvent is not available, then add the Garamite to a reactive diluent or to the lowest-viscosity resin, with the first choice being the diluent. As you move from solvent to diluent to resin the efficiency will drop somewhat. However, the Garamite will still in most cases maintain an advantage over other competitive materials. Cowles-type shear will suffice in all applications for dispersing the MMTs. Other incorporation methods can also be used.



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FEBRUARY 2011 | W W W . P C I M A G . C O M

We will now recommend some starting use levels, keeping in mind that we are talking in generalities, and some systems have different demands than expected. When compared to fumed silica, a good starting point is at about 60% of the level of fumed silica used. Keep in mind that the viscosity may be lower, but the sag resistance should be greater. When replacing organoclay, start the bottom of your ladder study at 50% and work up. The 50% level is also a good place to start the replacement of either the polyamides or the castor derivatives. Always be mindful of the fact the actual rheology of the finished system may not match exactly. It is not unusual for the package viscosity to be lower and the sag resistance to be higher. When working with epoxies do not be afraid to try various combinations between Part A and Part B. In 100% solids epoxies, dispersing the Garamite directly into the epoxy itself or the hardener is fine. Be sure to test for compatibility and stability. Placement can be important to both pot life and shelf life and should be tested.

Conclusions

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As coating formulations move to lower VOCs and higher solids, the demand on the thixotrope becomes more difficult as it pertains to package viscosity, sag and settling resistance. The package viscosity tends to go higher and the sag and settling resistance trend lower, making it difficult for the end user to provide a uniform surface to protect the substrate. We have shown that Garamite 1958 fills this need in many cases as compared to conventional organoclays, polyamides and fumed silicas. Garamite 1958 has a unique morphology of rods and plates as compared to conventional organoclays that use just a plate-like layered structure. This morphology plays a role in not only the ease of incorporation, but also in the efficacy of sag resistance and settling resistance over heat aging. Garamite is significantly easier to incorporate when compared to polyamides and castor derivatives and does not have their temperature and dwell time limitations. Garamite provides the sag resistance and settling resistance at much lower use levels, as much as 60% lower, than these other thixotropes. 䡲 For more information, visit www.scprod.com. This paper was presented at the 2010 Coatings Trends and Technologies Conference, sponsored by the Chicago Society for Coatings Technology and PCI Magazine, in Lombard, IL.

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Low-Angle Light Detection for GPC

S

uccessful formulation of coatings demands consideration of both the ease of application and the final surface finish. This surface finish is, in very many cases, a thin polymeric film, making polymers a key constituent of coatings products. Acrylics, polyesters, epoxy resins, polyurethanes, alkyd polymers and latexes are just some of the polymer types routinely applied to a wide variety of substrates. The molecular weight and molecular weight distribution of these polymers are both key properties that influence ease of use and finish quality. The direct correlation of molecular weight with melting point, for example, means that for powder coatings, molecular weight must be optimized to achieve desirable flow and leveling properties during heating, without compromising the flow properties of the raw powder. Low-molecular-weight resins can soften or become sticky at relatively low temperatures, increasing the tendency to cake, which compromises spray application. With solvent-miscible and suspension-based paints, and with varnishes, higher-molecular-weight polymers tend to be associated with a more durable protective surface, while lower molecular weights may give higher gloss and better penetration of the substrate. With solvent-miscible products based on alkyd polymers, such as gloss paints for domestic use, the incorporation of high-molecular-weight polymers is problematic because their inclusion increases product viscosity to unacceptable levels. Here, a possible solution is to introduce branched polymers: for a polymer of equivalent molecular weight, branching reduces the associated solution viscosity.

Introducing GPC GPC (Gel Permeation Chromatography) is widely used for polymer molecular weight characterization across many industrial sectors. Traditional systems rely on a single refractive index (RI) detector and require suitable calibration standards. Such systems report relative molecular weight unless the calibration standards used are identical in nature to the polymer being analyzed, which is not always feasible. The major attraction of light scattering detectors is their ability to measure molecular weight directly. Cali-

bration remains necessary but is far simpler. There is no need for the specific calibration standards required with RI detection alone because the molecular weight measured is independent of polymer type or structure. Light scattering detectors therefore measure absolute, rather than relative, molecular weight. For applications where there are no suitable RI standards, such as measuring some of the extremely high-molecular-weight latexes used in water-based emulsion paints, this has an obvious and immediate benefit. Over and above this however, combining light scattering with other detectors increases experimental productivity and gives access to more detailed molecular information. For example, the common triple detector combination of RI, viscometer and light scattering detection enables the direct investigation of polymer branching and molecular structure via the construction of a Mark-Houwink plot (log molecular weight versus log intrinsic viscosity). The addition of UV detection to this triple system enables the detailed study of copolymers if one of the monomers has a suitable chromaphore. The technique allows the measurement of each monomer distribution as a function of molecular weight, enabling the more sensitive specification and development of polymers for a specific application. Comparing these capabilities with the needs of the coatings industry underlines the potential value of light scattering detection for this sector.

Light Scattering Theory A brief introduction to light scattering theory provides a secure foundation for assessing the relative merits of different light scattering detector designs. Light illuminating a molecule is scattered by that molecule across a range of angles at varying intensity. Scattered light intensity and the weight average molecular weight of the molecule are linked by the Rayleigh equation:

By Paul Clarke, Product Group Manager | Malvern Instruments, Worcestershire, UK 26

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FEBRUARY 2011 | W W W . P C I M A G . C O M

Scattering – Why Closer is Better where Rθ=0 is the scattering at a zero degree angle to the incident light, Mw is the weight average molecular weight, c is the concentration of the solution, K is an optical constant that includes dn/dc, the rate of change of refractive index with concentration, and A2 is the second virial coefficient. For dilute solutions, typical of those used for GPC, the concentration-dependent term can be ignored and the equation reduces to a simpler form:

This equation directly relates scattered light to molecular weight, however, it is important to note that the equation is expressed in terms of the scattered light measured at a zero degree angle, relative to the incident beam. In practice, it is impossible to measure the intensity of scattered light at a zero angle because of the intensity of the incident laser beam (Figure 1). Light scattering detectors must therefore measure at some other angle and determine scattered light intensity at zero degrees from this value. This is clearly a complicating factor. Unfortunately the intensity of scattered light produced by a molecule varies with both the scattering angle and the size of molecule being measured. For very small molecules, scattering intensity can be considered to be independent of measurement angle, but for molecules of any significant size, (>12 nm radius)1 the influence of angle on scattering intensity cannot be ignored. Figure 2 illustrates how scattering intensity may vary, but this variation is neither constant nor readily predictable. When measuring at angles other than zero, extrapolating to zero is not always straightforward.

Choices for Light Scattering Detector Design In the design of light scattering detectors there are three ways of overcoming the fundamental problems of having to measure an angle other than zero degrees to the incident beam. These are: • Multi-angle light scattering (MALS). Measure the scattered light at two or more angles and extrapolate the data back to estimate the scattered light intensity at zero degrees.

• Right-angle light scattering (RALS)/viscometry. Measure the scattered light at 90º and use viscosity data to estimate the scattered light intensity at zero degrees. • Low-angle light scattering (LALS). Measure at a very low angle, close enough to zero that the angular effects are negligible and no correction is needed. All three options are commercially available. Multi-angle detection avoids the technical difficulties of measuring close to the incident beam but doesn’t measure molecular weight directly. All multi-angle systems work in the same way but vary according to the number of detectors and the angles at which the light is measured. In each case measurements are taken at two or more angles and the results are then extrapolated. It is easy to believe when using a MALS system that you are directly measuring absolute molecular weight, but this is clearly not the case. All MALS detectors require calibration and detector normalization procedures but, most importantly, the molecular weight is derived from extrap-

FIGURE 1 | The incident laser beam passes straight through the flow cell, preventing measurement of scattered light at zero angle I0. The scattered light must be measured at an angle θ to the beam.

Scattered detector Laser Flowcell

Zero angle

FIGURE 2 | An illustration of how the intensity of light scattering can vary as a function of angle for larger molecules (>12 nm).

Laser

PA I N T & C O A T I N G S I N D U S T R Y

7º

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0º

27

Low-Angle Light Scattering Detection for GPC — Why Closer is Better

olated data, a plot of scattered light intensity against angle, extrapolated back to zero degrees. This is the inherent weakness of the MALS approach. The choice of extrapolation fit (e.g. Debye, Zimm, Berry, etc.) and the choice of order of fit (linear, 2nd order, etc.)

FIGURE 3 | Schematic showing optical pathway of a LALS detector (Viscotek) that measures at 7º to the incident beam.

Photodetector (7º scattering)

Sample cell

Right angle mirror (Hole in center)

Incident laser beam Cell window (2 ea.)

FIGURE 4 | Chromatography of two polymers showing difference in response with RALS and LALS: a) is polyethylene oxide and b) is hyaluronic acid. PEO (23 000 Da)

Response (mV)

12.5

LALS (7º) RALS (90º) C = 1.5 mg/mL

9.3 6.0 2.8

0.5 17.0 20.0 23.0 26.0 29.0 32.0

Retention Volume (mL)

Polysaccharide (106 Da)

(b) 60.0

Response (mV)

(a)

LALS (7º) RALS (90º) C = 0.5 mg/mL

44.8 29.5 14.3

1.0 12.0 15.0 18.0 21.0 24.0 27.0

Retention Volume (mL)

FIGURE 5 | Triple detector chromatogram of a nitrocellulose sample. (Red = Refractive index, Blue = Viscometer, Black = LALS) Conditions: Viscotek TDAmax system at 35 °C using 2x mixed bed columns with THF @ 1 mL/min. -75

Viscometer - DP

-100 -125 -150 -175 -200 -225 -250 -275 -300

2 4

6

8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40

Retention Volume (mL) 28

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FEBRUARY 2011 | W W W . P C I M A G . C O M

directly impacts the reported molecular weight, raising the question of which fit is optimal for any given sample. A broad size distribution exacerbates this problem. For small molecules a linear data fit yields the most accurate molecular weight value, but as molecules get larger a nonlinear, higher order fit is more appropriate.2 For samples containing both small and large molecules the order of fit chosen is therefore always a compromise. The accuracy and precision of MALS detectors is further hampered because they tend to lack quality data in the all-important low-angle region. MALS detectors are designed to collect data from many angles rather than high-quality data at a single low angle. However, the goodness of fit of the extrapolation plot is, in fact, highly dependent on how close to zero the lowest angle data point is and the quality of that signal.3 Measuring at many angles does not compensate for lower signal quality data at the smallest angles. RALS detectors are highly effective for small molecules when the intensity of scattered light is independent of angle. At 90º the signal-to-noise ratio is at a maximum so the quality of data measured with a RALS detector is high. However, as we have already seen, measuring larger molecules requires a correction to compensate for the variation of intensity with angle. This correction can be achieved using viscometry data where the GPC system has a viscometer as part of the detector array, but this compromises the accuracy of the Mark–Houwink plot. On the basis of the preceding discussion it is reasonable to argue that LALS is the only one of these three light scattering techniques that lives up to the claim of measuring molecular weight directly, across the molecular size range. After initial calibration, a LALS detector measures the molecular weight of all different types of polymers directly, avoiding the assumptions and data manipulations of the alternative two methods. It is an elegant solution but one that has taken a number of years to become a commercial reality.

Designing a LALS Detector The challenge of measuring scattering intensity close to the incident beam has slowed the commercialization of LALS technology. The benchmark commercial LALS detector was the Chromatix KMX-6, which was produced from the late 1970s to late 1980s. This detector was not developed further, and no new products were launched until 2001 when advances in optics and electronics allowed Viscotek to enter the market with a detector that measures at 7º to the incident beam (Figure 3). With this clever design the incident beam is separated from the scattered light to allow collection of the scattered light intensity signal at 7º.4 An excellent signal-to-noise ratio is achieved as demonstrated by Figure 4, which compares the LALS signal with that measured at 90º (RALS), the angle that gives the highest-quality data. The data presented in Figure 4 relates to two different molecules – polyethylene oxide and hyaluronic acid. With the low-molecular-weight polyethylene oxide both the RALS and LALS detectors give the same signal because the intensity of scattered light has no angular dependence. With the larger hyaluronic acid, on the other hand,

Low-Angle Light Scattering Detection for GPC — Why Closer is Better

there is a very high angular dependence of the scattered light, severely compromising the RALS data. In contrast, the LALS detector is able to precisely measure molecular weight without any need for extrapolation or data fitting.

TABLE 1 | Results obtained from the polyurethane sample shown in Figure 7 when processed with OmniSEC software.

Analyzing Polymers from Coatings The LALS detector and triple detection GPC can be employed for the full range of polymers used in coatings. Figures 5 to 7 and Table 1 show data for two of the more difficult-to-analyze molecules, nitrocellulose and polyurethane, to give an overview of the type of information produced. Nitrocellulose, a film-forming resin, is used widely in many applications including paper coating and printing inks, nail varnish and automotive refinish paints. It can be a challenging material to analyze as the nitrogen content affects the polymer solubility, particularly at high molecular weight. The determination of both the molecular weight and viscosity is important for all applications, and being able to plot the relationship of both parameters (Mark Houwink plot) helps to differentiate small performance differences. Figure 5 shows a typical triple detec-

FIGURE 6 | Mark-Houwink plot overlay of two nitrocellulose samples revealing a structural difference in the polymers. The x-axis values of molecular weight comes directly from the LALS detector and the y-axis intrinsic viscosity data from the viscometer detector. Log Intrinsic Viscosity

0.80 0.60 0.40 0.20 0.00 -0.20 -0.40 -0.60 4.20

4.40

4.60

4.80

5.00

5.20

5.40

5.60

5.80

Log Molecular Weight FIGURE 7 | Triple detector chromatogram of a polyurethane sample. (Red = Refractive index, Blue = Viscometer, Black = LALS). Conditions: Viscotek TDAmax system at 60 °C using 2x I-series columns with DMF+LiBr @ 1 mL/min.

-50

Viscometer - DP

2.3160

MW number average (Da)

63,578

MW weight average (Da)

179,576

MW Z-average (Da)

279,058

Intrinsic viscosity (d L/g)

1.1207

Hydrodynamic radius (w) (nm)

14.04

Mark Houwink Slope

0.636

Mark Houwink Intercept

-3.258

tion GPC chromatogram with LALS of a nitrocellulose sample, and Figure 6 is a Mark Houwink plot showing the structural comparison (viscosity to molecular weight) of two samples. The structural difference revealed here can be related to the product performance. Polyurethane is used in a variety of coatings, most noticeably in varnishes, where it helps to form a hard, abrasion-resistant, durable coating. Figure 7 shows a chromatogram of a polyurethane sample together with the calculated molecular parameters in Table 1, including molecular weight, intrinsic viscosity and molecular size.

Conclusion

1.00

The commercial availability of LALS detectors allows GPC practitioners to measure the molecular weight of a sample with certainty, avoiding any issues of data extrapolation or data fitting. This technology is inherently superior to extrapolation of data measured across multiple angles, back to an estimated value for zero degrees. Analysis of the principles underpinning both types of detector lays bare the perceived wisdom that more angles are better. In fact it is clear that when measuring molecular weight, closer (to the incident beam) is better (LALS). An additional important advantage of LALS detectors is that their size and simplicity facilitate inclusion in integrated multi-detector systems with, for example, viscometers, RI and/or UV detection. Multi-detector systems are a powerful option for the coatings industry, providing not only molecular weight data but also information about molecular structure and composition.5,6 This technology maximizes the productivity of GPC experimentation towards formulation goals. 䡲

References

-100

1 2

-150 -200

3

-250 -300

4

-350 5

-400 2 3

4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Retention Volume (mL) 30

Peak concentration (mg/mL)

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6

GPC Masterclass™, Viscotek (1998-2003). Mori, S. Barth, H. Size Exclusion Chromatography, SpringerVerlag Berlin, Heidelberg, Germany, 1999. Anderson, M.; Wahlund, K-G; Wittgren, Bengt. Separation and Characterization of Natural and Synthetic Macromolecules, Amsterdam, February 2003. Haney, M.; Stone, D. Waters International GPC Symposium, 2000. Walkenhorst, R. LC-GC Europe, October 2001. Clarke, P. LC-GC Europe Applications Book, September 2002, 37-39.

FOCUS ON

MARINE COATINGS Tiiny T Tiny T Tu Tubes Making Waves in Kayak Design Baytubes®, carbon nanotubes from Bayer MaterialScience, are now making waves in kayak design, marking a new chapter in the evolution of these popular boats, which were originally made by the Inuits using wood, bone and animal skin. Today’s kayaks are usually made from plastics and composite materials. Some new kayak prototypes have now been coated with an epoxy gelcoat modified with Baytubes that has been developed by Norwegian research company Re-Turn AS, based in Gamle Fredrikstad. “We are confident that these prototypes outperform standard models in a number of areas,” explains Stein Dietrichson, General Manager of Re-Turn AS. Reinforcing the outer skin of a kayak, the gel coat with carbon nanotubes makes it far more resilient to abrasion from a shingle beach (beach covered with gravel consisting of large, smooth pebbles unmixed with finer material) or contact with the edge of a river bank. In contrast, many conventional gel coats, especially those of particularly lightweight and sporty kayaks, are highly sensitive to external mechanical action. But that isn’t the only way that these tiny tubes in the solvent-free gel coat help to prolong enjoyment of the boat. They ensure that cracks appear less frequently over long-term use and reduce wear on the outer skin. They also absorb UV radiation, thereby minimizing the associated bleaching and embrittling effects. Re-Turn AS modified the outer shell of one of the prototypes with Baytubes. “This means that the kayak doesn’t get as dirty above or below the water line and is

easier to clean,” states Dietrichson. And he hopes that this innovative combination will result in another effect: “The flow resistance of the hull should also be lower.” This will enable the kayak to glide through the water faster without its occupant having to paddle harder – a fantastic advantage for any aspiring kayaker. And there are further advantages to the use of Baytubes in the epoxy base of the kayak, which the additive helps to make more stable and rigid. “This makes the boat easier to paddle and translates more of the kayaker’s muscle power into speed. The new gelcoat incorporates many advantages from the development of nanotube-reinforced marine paints, which are already commercial,” comments Dietrichson. Experts from the Norwegian company are already working closely with Bayer MaterialScience to develop further nanotube-reinforced materials that could find their way into the rotor blades for wind turbines. “More and more innovative companies are beginning to recognize that Baytubes have enormous potential to give established materials entirely new properties,” says Dr. Raul Pires, Head of Global Activities for nanotubes and nanotechnology products at Bayer MaterialScience. For more information, visit www.bayermaterialscience.com, www.baytubes.com and www.re-turn.no.

Coatings for the Historic Battleship Missouri Nearly 5,500 gallons of Sherwin-Williams coatings have been applied to the historic Battleship Missouri, which recently returned to her home pier near the USS Arizona Memorial at Pearl Harbor, Hawaii. The ex-USS Missouri, or “Mighty Mo,” is known as the site of Japan’s surrender to Allied Forces on September 2, 1945, ending World War II. The ship was launched in June 1944 and provided firepower in the decisive battles for Iwo Jima and Okinawa. On Sept. 2, 1945, the Missouri served as the site of Japan’s formal, unconditional surrender to Allied Powers while anchored in Tokyo Bay, Japan. The famous ship also saw action in the Korean Conflict and Persian Gulf during Operation Desert Storm. Today, the ship is under the care of the non-profit USS Missouri Memorial Association, which owns and operates the ship as the Battleship Missouri Memorial, a historic attraction and memorial in Pearl Harbor. Work on the $18 million refurbishment was under the guidance of BAE Systems at the U.S. Navy’s Pearl Harbor Naval Shipyard. The superstructure was pressure washed

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by memorial volunteers. BAE Systems and its subcontractors used power tools to remove remaining paint, spot-primed bare steel, airless sprayed the ship’s superstructure and freeboard, and plural component-sprayed the underwater hull. Sherwin-Williams products used on the 887-foot battleship included: • Dura-Plate® UHS Epoxy, SeaGuard® Vinyl Antifoulant (underwater hull); • Dura-Plate UHS Epoxy, Polysiloxane XLE-80 (freeboard); • Macropoxy® 920 Pre-Prime, Mil-PRF-24635 Silicone Alkyd (mast aloft black areas); • Macropoxy 920 Pre-Prime, SeaGuard 5000 HS Epoxy, Polysiloxane XLE-80 (superstructure); and • Dura-Plate MT, Dura-Plate UHS Epoxy (decks). Sherwin-Williams also provided technical expertise and worked closely with both the shipyard and contractor throughout the project. “It was an honor for Sherwin-Williams to provide coatings for one of the most renowned and historically significant ships in U.S. history,” said Brad Rossetto, Vice President Marketing, Sherwin-Williams Protective & Marine. According to Roger Kubischta, Director of Operations for BAE Systems’ Hawaii Shipyard, “There was a tremendous amount of marine growth stuck to the hull that needed to be removed before the team could start the preservation work. There was corrosion in spots of the hull, but it was mostly intact. In all, over eight acres of the boat’s surface needed to be preserved.”

Dave Herr, President of BAT Systems Support Solutions, said, “BAE Systems was honored to help lead the preservation effort on this historic vessel. With the hard work of our employees and subcontractors, and our trusted partnership with Pearl Harbor Naval Shipyard, one of our nation’s most treasured assets is back pierside today. We’re grateful for the opportunity to partner with the USS Missouri Memorial Association, whose passion for the project was inspiring and a testament to the historic significance of the Mighty Mo and the importance of bringing her history to life.” 䡲 For more information, visit www.sherwin-williams.com.

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2K Waterborne Polyurethane Technology for © GM Corp.

Automotive Clearcoat

P

olyurethane chemistry is well established for high-performance coatings. This success over the years comes from the outstanding properties brought by polyurethane backbones such as high solvent and mechanical resistance (hardness/flexibility compromise), very good adhesion on various substrates, fast film forming and drying at room temperature, and excellent weathering resistance, provided that aromatic structures are absent from the polymer composition. These characteristics have made polyurethane-based coatings ideal candidates in application fields requiring high film appearance and resistance as in automotive car refinishing and OEM. Over the last decades, solvent-based systems have dominated the market. However, more stringent regulations concerning VOC emissions in most countries have led paint manufacturers and raw material suppliers to develop alternative technologies to conventional solvent-based PUs, more respectful to the environment but offering the same level of performance. Thus, waterborne polyurethane coatings (1K and 2K systems) emerged at the end of the 1980s and are now being used in numerous applications.

2K Waterborne Polyurethanes: a Technical Challenge 2K WB PU systems truly represent a technical challenge which, 30 years ago, seemed unrealistic to overcome. In 2K waterborne polyurethane systems, an unblocked polyisocyanate hardener is dispersed in an aqueous medium containing an emulsion of a polyhydroxylated binder (polyol). The blend is applied by conventional tools (similar to solventborne systems), and the polymer network is developed after removal of water and (co)

TABLE 1 | Compared reactivity of isocyanate groups with OH groups.1 Primary OH

Secondary OH

Tertiary OH

Water

2-4

1

0.01

0.4

FIGURE 1 | Schematic representation of (a) the application and film formation of a 2K WB polyurethane system; (b) dispersion of the polyisocyanate hardener in the aqueous phase with polyol emulsion; (c) water and solvent evaporation with particle coalescence; (d) polymer network and film formation. (a)

isocyanate polyol

Emulsification of the polyisocyanate into polyol dispersion

(b)

(c)

(d)

Water evaporation and particle coalescence

Crosslinked polymer network

solvents (Figure 1). The challenge consists in avoiding significant side reactions between the polyisocyanate phase and water during a “reasonable” period of time, sufficient to let the applicator prepare the formulation and apply it. Luckily, with primary OH-functional polyols, the reactivity of the NCO groups is greater than toward water, as seen in Table 1, which limits this issue. The emulsification of the hardener can be obtained by high-shear mixing of a conventional hydrophobic polyisocyanate. However, this method requires specific equipment; a preferred alternative is to modify the polyisocyanate with an appropriate surfactant system to get a “spontaneous emulsification” when added into an aqueous medium. Spontaneous emulsification occurs when two immiscible liquids are put together and an emulsion is obtained without requiring additional energy (stirring and temperature), as shown in Figure 2. The knowledge of the mechanisms responsible for the spontaneous emulsification of an “oil” phase into water is not complete yet and there is still intensive research aimed at better understanding the processes and parameters involved. It is generally admitted that the spontaneous emulsification of an organic solution grows through the organization of the surfactant into bilayer structures (lamellar phase or vesicles), which leads to the formation of an emulsion when destabilized.2 Although waterborne coating technologies are now state-of-the-art in the automotive industry for primers and basecoats, they are still limited in use for clearcoat applications, and only a few commercial systems are available. This is partly due to limitations of the first systems developed: lower film building rate due to water evaporation, water sensitivity of the hardeners, surface defects (pinholes, microfoams), etc.3 However, new generations of raw materials and particularly hydrophilic polyisocyanates enable us now to overcome most of these weaknesses, and high-performance systems can be designed, which really compete with conventional solvent systems in terms of end-use properties. The objective of this paper is to compare the properties obtained with different generations of solventborne clearcoats used in the automotive coatings industry (acrylic melamine and 2K solventborne polyurethanes designed for OEM and car refinish applications) with those of a 2K waterborne system.

Experimental Formulation and Coating Preparation Table 2 describes the different clearcoat types studied as well as the curing conditions. Clearcoat A is a commercial acid-catalyzed acrylic/melamine system.

By Philippe Barbeau and Rolf Klucker | Perstorp, France; Jean-Luc Loubet and Sophie Pavan | Ecole Centrale de Lyon, France 34

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Applications Clearcoat B (high-bake system) and C (low-bake system) correspond to 2K solventborne PU systems designed respectively for OEM and auto refinish applications. In this study, Clearcoat B will be considered as a reference in terms of mar resistance: in fact, previous work in our lab showed that the loss of gloss after the car wash test in the case of Clearcoat B remained below 20% after 1500 h under accelerated weathering conditions (WeatherOmeter). Clearcoat D (low-bake system) is based on a 2K waterborne formulation specifically designed to fulfill car refinish requirements (viscosity, drying kinetics and end-use properties), as will be demonstrated in the following discussion. The polyisocyanate characteristics used for the polyurethane systems are presented in Table 3. Easaqua X D 401 is a hydrophilic polyisocyanate (hybrid structure based on HDI/IPDI derivatives) specifically designed to improve drying properties of 2K waterborne systems.4 For the 2K polyurethane clearcoat formulation, the NCO/OH ratio was adjusted to 1.05 for the solvent-based systems (Clearcoats B and C) and 1.2 for the Clearcoat D (waterborne system). All the clearcoats were applied using a conventional air spray gun (DeVilbiss SRI) onto a commercial “black Onyx” basecoat (dry film thickness = 12-14 μm). Paint systems were applied onto metallic substrates (aluminum panels from Q-panel) previously degreased and coated with a commercial 2K solventborne primer surfacer (DFT = 35 to 40 μm).

and after the scratch are collected. The penetration depth during the scratch is recorded after subtracting the topography of the undamaged coating. The remaining scratch is visualized afterwards by optical microscopy. In this study, nanoindentation and nanoscratch tests were performed on “fresh” systems (stored 1 month at 23 °C and 50% RH) and on aged systems (after 1500 h of accelerated weathering using a Weather-Ometer).

FIGURE 2 | Comparative emulsification of polyisocyanate hardener in water. On the left, conventional hydrophobic polyisocyanate; on the right, chemically modified polyisocyanate (“self-emulsifiable” system).

Hydrophobic polyisocyanate

Easaqua™

Experimental Techniques All cured systems were stored at 23 °C and at 50% relative humidity before testing. Tests performed were as follows: • Persoz hardness; • reverse impact; • gloss; • solvent resistance (MEK double rub); • nanoindentation and nanoscratch characterization; • weatherability under accelerated conditions (WeatherOmeter); and • acid etch resistance under Jacksonville conditions. procedure5

determines the The nanoindentation test mechanical characteristics of the material close to the surface (elastic modulus, hardness). The indenters used in this study are a diamond pyramid, Berkovich type, with a face angle of 115°. Both the nanoindentation and the nanoscratch tests were carried out with a Nano-Indenter XP from MTA. Nanoscratch tests were performed following a rampload procedure using the normal applied load increase from 20 μN to 160 mN, at scratch velocities of 1 μm/s, using a spherical indenter (R = 7 μm). The total scratch lengths were 500 μm. Classically, height profiles before

TABLE 2 | Clearcoat description and composition. Clearcoat A

Clearcoat B

Clearcoat C

Commercial 2K OEM 2K Refinish System acrylic solventborne solventborne description melamine polyurethane polyurethane Polyol nature

NA

Acrylic polyol Acrylic polyol

Hardener nature

Butylated melamine

HDI trimer (Tolonate HDT 90)

HDI trimer (Tolonate HDT 90)

Cure conditions

30 min at 140 °C

30 min at 140 °C

30 min at 60 °C

Clearcoat D 2K Refinish waterborne polyurethane Acrylic polyol (emulsion in water) Hydrophilic HDI/IPDI hybrid derivative (Easaqua X D 401) 35 min at 60 °C

TABLE 3 | Characteristics of the polyisocyanate hardeners used in the polyurethane formulations. Reference

Nature

Tolonate HDT 90 Easaqua X D 401

Hydrophobic polyisocyanate Hydrophilic polyisocyanate

Solid Content

% NCO

90% in butyl acetate

19.8

85% in butyl acetate

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2K Waterborne Polyurethane Technology for Automotive Clearcoat Applications

TABLE 4 | Mechanical, optical and chemical properties of the clearcoats measured 7 days after curing at 23 °C and 50% RH. Test

Clearcoat A Clearcoat B Clearcoat C Clearcoat D

Persoz hardness Reverse impact (in cm.kg) Gloss (20°) MEK double rub

230 <10

345 100

311 100

302 100

94 200

94 200

99 200

94 200

TABLE 5 | Clearcoat mechanical properties determined by nanoindentation before and after accelerated weathering. “Aged” Samples (after 1500 h Accelerated Weathering)

“Fresh” Samples

Clearcoat A Clearcoat B Clearcoat C Clearcoat D

E’* (GPa) 2.3 3.3 3.6 3.2

H (MPa) 81 142 163 141

E’* H (H/E) n (GPa) (MPa) 0.035 8.7 2.6 105 0.040 8 0.043 10.5 3.6 165 0.046 12.2 0.045 10.7 3.8 175 0.046 11.7 0.044 10.5 3.8 177 0.047 11.9 (H/E)

n

FIGURE 3 | Evolution of the H/E ratio for the four different clearcoats. 50 45

H/E (x 10-2)

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35 30 25 20 Clearcoat A Clearcoat B Clearcoat C Clearcoat D

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FEBRUARY 2011 | W W W . P C I M A G . C O M

Results and Discussion General Properties and Final Finish Good balance of mechanical properties (hardness/flexibility compromise), controlled finish smoothness and brightness, and high chemical resistance are key requirements for automotive clearcoats. Table 4 presents the mechanical and optical characteristics of the different clearcoat formulations, as well as their solvent resistance measured by a MEK double rub test. The results show that the three polyurethane clearcoat systems exhibit very similar performance in terms of mechanical hardness, flexibility (impact resistance), optical aspect and solvent resistance. In particular, no difference can be seen between solventborne and waterborne clearcoats. However, Clearcoat A (acrylic melamine system) leads to lower hardness/ flexibility. This behavior is characteristic of a heterogeneous crosslinking network in the case of Clearcoat A.

Mar/Scratch Resistance In automotive applications, the damage corresponding to mar/ scratch resistance is one of the most important perception problems from a customer point of view, which relates to durability performance of the coating. Mar/scratch resistance is clearly only ensured by the clearcoat layer. The behavior of the polymer material during scratching is a complex phenomenon, and specific tools, like nanoindentation, are

As demonstrated by Bertrand-Lambotte,6 n indicates the ability of the material to heal ductile scratches: the lower the value for n, the faster ductile scratches will heal. The resistance of the clearcoats to plastic deformation and their ability to heal ductile scratches (H/E and n factors) are reported in Figures 3 and 4 respectively. The results show that Clearcoat A (acrylic melamine system) exhibits lower elastic modulus and lower hardness, as well as

FIGURE 4 | Evolution of the viscoplastic index (n) for the four different clearcoats. 14

Viscoplastic index n

required to analyze and understand the overall performance. The mechanical properties of the four different clearcoats measured by nanoindentation tests, before and after accelerated weathering, are summarized in Table 5. In this table, E’* corresponds to the reduced elastic modulus of the coating given by E'* = 1 –E'υ2 where E’ is the elastic modulus of the material and i is the Poisson’s coefficient. H corresponds to the hardness value measured with the Berkovich indenter at a load rate of 3.10 -2 s-1. The values for E’* and H are given for an indented depth of 1 μm. The values for the ratio H/E are also reported. H/E represents the limit strain where plastic deformation is induced by the indenter. The higher the value of H/E, the better the material will resist plastic deformation during mechanical indentation and scratch. Finally, n is the viscoplastic index of the Norton-Hoff law relating hardness to (1/n) strain rate: H 1/n = 1: the material exhibits pure viscous behavior 1/n = 0: the material is purely plastic (no influence of the strain rate on the hardness determination).

12 10 8 Fresh samples Aged samples

6 4 2 0 Clearcoat A Clearcoat B Clearcoat C Clearcoat D

lower H/E and n values, than the polyurethane systems. The fact that Clearcoat A exhibits lower hardness and elastic modulus is consistent with the Persoz hardness values obtained previously. The low H/E value indicates that Clearcoat A exhibits poorer resistance to plastic deformation during scratching. On the other hand, the lower value for n (viscoplastic index) suggests a higher ability to heal ductile scratches. This behaviour is undoubtedly related to the motion of the macromolecular chains in the conditions of test and indicates a broad glass transition consistent with a more heterogeneous polymer network compared to polyurethanes.

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2K Waterborne Polyurethane Technology for Automotive Clearcoat Applications

Interestingly, all the polyurethane systems again exhibit similar mechanical properties as determined by nanoindentation. In the case of the “fresh” samples, Clearcoat C shows slightly higher hardness and elastic modulus than Clearcoats B and D, but similar values for n and H/E. After accelerated weathering, all clearcoats tend to harden slightly. This behaviour is probably due to physical aging of the polymer network. Clearcoats C and D present equivalent properties.

FIGURE 5 | Scratch morphology observed for the “fresh” clearcoats.

Clearcoat A

Clearcoat B

Clearcoat C

Clearcoat D

TABLE 6 | Plastic deformation length before first crack appearance during scratching (spherical indenter, R = 7 μm, 1 μm/s). “Aged” Samples (after 1500 h Accelerated Weathering)

“Fresh” Samples Clearcoat A

144 ± 34

62 ± 6

Clearcoat B

267 ± 34

145 ± 25

Clearcoat C

424 ± 27

181 ± 25

Clearcoat D

199 ± 22

141 ± 2

TABLE 7 | Clearcoat UV and acid etch resistance. Reference Gloss (20°) retention after 1500 h in WOM Gloss (20°) retention after 4 months in Jacksonville

Clearcoat A

Clearcoat B

Clearcoat C

Clearcoat D

<3

<3

<3

<3

NM

NM

-9

<3

The shape and morphology of the scratches performed on the different clearcoat systems before aging are shown in Figure 5. All the systems present at the beginning of the scratch (for low indentation forces/depths) a ductile-type behavior, which turns to brittle for higher indentation depths. Ductile/brittle transition is governed by both size and energy criteria: in other words, a crack will appear in the material if the energy brought to the material exceeds the energy required to develop a new surface (following Griffith’s approach), and will propagate if the characteristic size of the sample is at least twice the dimension of the plastic domain induced at the front of the deformation as demonstrated by Puttick.5-6 The ductile/brittle transition is clearly seen on the pictures with the first “fish bones” along the scratch groove. Brittle failure is obviously a key property in terms of scratch resistance since it will affect the protection role played by the clearcoats (points of failure will let chemical agents penetrate the whole coating system and may cause delamination, hydrolysis reactions, etc.). In order to quantify the performance of the clearcoat toward brittle scratching, we have reported in Table 6 the length in μm of the plastic scratch before the first crack appears for each clearcoat before and after aging. Before aging, the ranking of the different systems in terms of resistance to brittle failure is the following: Clearcoat C > Clearcoat B > Clearcoat D > Clearcoat A. After accelerated weathering, a decrease in terms of resistance to brittle failure for all the systems is observed. This phenomenon is consistent with the “hardening” observed by nanoindentation measurements and is particularly pronounced in the case of Clearcoats A and C. Whereas the results for Clearcoat A are to some extent expected and due to the lower stability of the acrylic/melamine network in accelerated weathering conditions (compared to polyurethanes), the drop in the case of Clearcoat C is more surprising. However, C still exhibits slightly better performance among the systems tested even after accelerated aging. Clearcoats B and D show the same performances, which is particularly interesting considering the excellent performance of Clearcoat B obtained by the car wash test.

Weathering and Acid Etch Resistance The interest for technical improvement on automotive clearcoats has been focused in the recent past on durability towards “environmental” conditions, and particularly

TABLE 8 | Jacksonville exposure – recorded atmospheric conditions. Temp. max (avg.) Temp. min (avg.) Temp. (mean) Relative humidity Sunshine -Sky cover -Fair -Partly cloudy -Cloudy Precipitation

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Exposure Period

Aug.

82.0 ºF [27.8 ºC] 63.8 ºF [17.7 ºC] 73.2 ºF [22.9 ºC] 39445 min. 55% 25 d 42 d 31 d 23.1" [587 mm]

88.8 ºF (-2.1) 86.2 ºF (-1.0) 78.5 ºF (-0.6) 69.7 ºF (-3.3) 73.2 ºF (+0.5) 69.5 ºF (-0.6) 57.4 ºF (-2.3) 45.7 ºF (-5.2) 81.0 ºF (+0.2) 77.9 ºF (+0.1) 68.2 ºF (-1.2) 57.7 ºF (-4.0) 78% 75% 70% 17350 min. 13572 min. 11193 min. 10257 min. 70% 61% 51% 54% 2d 4d 12 d 14 d 15 d 18 d 16 d 8d 14 d 8d 3d 8d 16.83" (+9.96) 5.84" (-2.06) 1.62" (-2.24) 1.01" (-1.33) (): Deviation compared to mean value of reference period 1971-2000

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Sept.

Oct.

Nov.

etching resistance (caused by both acid rain in industrialized regions and natural fallout in the form of bird droppings). Resistance to etching is highly linked to the crosslink density of the polymer network and also to the hydrolytic stability of the coating. In our study, resistance to weathering/ UV exposure of the different clearcoat systems was determined by recording the gloss retention after 1500 h in accelerated conditions (Weather-Ometer). As for acid etch resistance, samples were sent to Jacksonville, FL, for 14 weeks and gloss retention recorded accordingly (only Clearcoats C and D were tested). Results are reported in Table 7. Atmospheric conditions recorded at Jacksonville during the test are given in Table 8. As far as gloss retention is concerned, results obtained show good performance in terms of UV resistance for all systems studied (note that all systems contain UV light stabilizers). Concerning acid etch resistance, the performance of the two low-bake polyurethane systems (C and D) are obviously very good. Interestingly, Clearcoat D (waterborne) outperforms Clearcoat C since almost no visual degradation is observed after almost 4 months in an acidic environment.

E. European Coatings Journal 2005, 4. 5 Roche S.; Pavan S.; Loubet J.L.; Barbeau P.; Magny B. Progress in Organic Coatings 2003, Vol. 47, p. 37-48. 6 Bertrand-Lambotte P. “Sur les mécanismes de rayures des vernis de finition automobile”, PhD report (2001), 143.

This paper was presented at The Waterborne Symposium, Advances in Sustainable Coatings Technology, 2010. The symposium is sponsored by The University of Southern Mississippi School of Polymers and High-Performance Materials.

::: Intelligence in Rheometry

Rheometry Focusing on Solutions

Conclusion Waterborne 2K polyurethane systems have been available on the market for 10 years. The choice of raw materials especially designed for this technology has evolved to meet formulators’ and endusers’ needs. This study demonstrates that 2K waterborne polyurethane clearcoats can be a technology of choice in automotive clearcoat applications in order to combine high-demanding requirements (such as mar/scratch resistance, final finish, etc.) and sustainability development concerns. 䡲

References 1 “Waterborne & Solvent-Based Surface Coatings and their Applications”, ISBN 0471 078868, Volume III: Polyurethanes, chapter I, P. Ardaud, E.Charrière-Perroud, C.Varron, edited by P. Thomas, published in 1998 by SITA Technology Ltd. 2 Shahidzadeh N.; Bonn D.; Meunier J.; Nabavi M.; Airiau M.; Morvan M. Langmuir 2000, 16, 9703-9708. 3 Vandervoorde P., van de Watering P., Double liaison, n° 514, 25-30. 4 Olier P.; Dubecq M.; Barbeau P.; Charriere

Fully automated, robotically operated: The HTR High Throughput Rheometer from Anton Paar. ³ Automatic sample filling and cleaning of measuring systems ³ Processes up to 96 samples in a single run up to 24 hours

Anton Paar® USA

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800-722-7556 [email protected] www.anton-paar.com

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39

Designing, Formulating and Measuring Coatings for

Optimum Rheology

T

oday’s coatings are applied to a wide variety of substrates for both decorative and protective purposes. While the ability of the coating to deliver acceptable properties depends primarily on the performance of the dry film, the rheology of the coating plays a critical role in the actual process of applying the coating to the substrate. This process not only impacts the ease and cost of the application, but it may also affect the final decorative and protective properties of the dry paint film. Thus, it is critical that the coating have the correct rheology, and hence, selecting the right rheology modifier package is critical to formulating such coatings. The rheological needs of most coatings can be grouped according to the shear rate of the particular phenomenon. Shear rate is a measure of the severity of a coating’s flow during the process of interest, with that severity being a ratio of the speed of the flow to the thickness of the film. Thus, the shear rate of the processes range from very low for pigment settling (very low velocity and very thick film) to very high for brush drag (thin film under the brush

FIGURE 1 | Rheology profile. Mid Shear

High Shear

Log (Viscosity)

Low Shear

and rapid movement). Shear rate is expressed in units of reciprocal seconds (sec-1), with values ranging from as low as 0.001 sec-1 for pigment settling to 10,000 sec-1 or greater for brushing and spraying. By characterizing the coating’s rheology as a function of shear rate, a few simple measurements can provide good direction to the design of the optimum rheology package. Because an instrumental measurement is typically much quicker, easier and more objective than a real-world test, pushing this testing to later in the development cycle will save time and money. Virtually all coatings exhibit a non-Newtonian rheology profile, meaning that their viscosity is not the same at all shear rates. Typically, waterborne coatings exhibit shear-thinning behavior, i.e., they have lower viscosity at higher shear rates. However, this decrease in viscosity is not permanent. They are only thinner while the shear rate is high. When the shear rate is again low, the coating again exhibits a higher viscosity. To characterize the degree of this shear-thinning profile, it is useful to divide the shear rate spectrum into three regions; low-, mid- and high-shear (Figure 1). From such a three-point characterization, useful assessments can be made of whether a given change in rheology package will increase or decrease the performance of the coating in various rheological attributes, such as sag resistance and brush drag.

Developing a Rheology Profile

0.01

0.1

1

10 100 1,000 Shear Rate (sec-1)

10,000 100,000

In thinking about the design of a coating’s rheology, it is necessary to first determine the critical application properties, (e.g., high sag resistance and low brush drag), and then consider the shear rate of those processes, so that the right portion of the rheology vs. shear rate profile is optimized. In addition, because the viscosity of a coating is affected by the temperature, it is also important to measure the viscosity at temperatures reflective of those under

By Daniel Saucy, Ph.D., Technical Sales Service Leader for Rheology Modifiers and Dispersants, Dow Coating Materials; and Vinnie Hebert, Senior Sales Engineer | Brookfield Engineering, Middleboro, MA 40

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which the coating will be used. Hence, temperature control during testing, both instrumental and lab, can be critical. Fortunately, there is a wide range of rheology modifier products on the market and so it is almost always possible to achieve the desired rheology. The challenge is doing so quickly and efficiently. Typical coating properties that are controlled by the rheology are in-can appearance, brush or roller loading, film build, sag resistance, brush drag, spatter resistance, and pigment settling, to name just a few. In order to be efficient at creating the right rheological profile for a coating, it is necessary to have quick, lab-based methods for predicting the performance properties just mentioned.

FIGURE 2 | The Brookfield CAP2000 viscometer.

FIGURE 3 | The Brookfield KU-2 viscometer.

Thickeners During the development of a coating’s rheology profile, the formulator chooses from a large variety of available thickener choices. These vary by both their chemical type as well as their rheological effect on the coating. The three most-common chemical types are cellulosic thickeners, hydrophobically modified alkali swellable emulsions, often referred to as HASE, and the non-ionic PEG-based products, often referred to as HEUR. The cellulosics, such as CELLOSIZE hydroxyethylcellulose products, have the longest history of use. They are broadly applicable and still widely used for lower-sheen coatings. Two types of synthetic thickeners have been developed during the past 30 years to improve upon the performance of the cellulosics. The first of these is the hydrophobically modified alkali-swellable emulsion, or HASE, products, a common example of which is ACRYSOL TT-935 rheology modifier from Dow Coating Materials. This type of chemistry offers excellent efficiency and the benefits of a liquid product form. The second major type of synthetic product is the hydrophobically modified ethylene oxide urethanes, or HEUR, exemplified by ACRYSOL RM-845 rheology modifier. This type of chemistry maximizes flow and leveling, as well as gloss. Within these chemical classes, each manufacturer has developed a range of products, from those having a relatively flat viscosity vs. shear rate profile, often referred to as ICI-builders or Newtonian thickeners, to those that impart steeply shear-thinning rheology, often referred to as lowshear builders. A typical coating uses a combination of two to three thickeners to achieve a rheological profile delivering the performance necessary for a particular coating over the entire shear rate range. The formulator’s task is to determine which combination of products best meets these needs.

Measuring Viscosity Low-shear processes include pigment settling, brush and roller loading, in-can appearance, flow and leveling, and sag resistance. The low-shear viscosity of a coating can be measured with a low-speed rotational viscometer such as a Brookfield DV-II+ Pro and a Small Sample Adapter; shear rates as low as 0.1 sec-1 can be achieved. In order to adjust the low-shear viscosity of a coating, products that offer a steeply shear-thinning profile, such as ACRYSOL RM-12W, are added to the formulation. Phenomena such as brush drag, roller slip and back pressure in spray applications are examples of high-shear processes. In order to measure the viscosity at high shear rates, the viscosity measurement must be taken while a thin film

of the coating is being subjected to fast deformation. An easy-to-use instrument for this measurement is the Brookfield CAP2000 (Figure 2). This instrument is configurable for speeds of 5 rpm to 1000 rpm and low-temperature (5 °C - 75 °C) or high-temperature (50 °C - 235 °C) capability. A cone is selected to provide the correct film thickness. When used at a given rotational speed, the combination delivers the desired shear rate. A common shear rate value used for characterizing architectural coatings is 10,000 sec-1, this being representative of the condition under a brush. The viscosity values for typical coatings range from approximately 0.5 to 2.0 poise. To adjust the high-shear viscosity to the value needed for a particular formulation, rheology products such as ACRYSOL RM-5000 deliver viscosity even at high shear rates because they are specifically designed to offer a low degree of shear thinning. Proper selection of type and level of such products will allow the formulator to achieve the desired properties. Mid-shear processes include stirring, some types of pumping, and pouring. While these properties are typically not critical to a coating’s performance and thus may not be critical to its development, the mid-shear viscosity is still a common quality control measurement during manufacture. The mid-shear viscosity is particularly useful for QC because most common rheology modifiers have some degree of effect on the viscosity in the mid-shear range, thus making the KU measurement a good indicator of whether the correct type and level of thickeners were added during manufacture. A common instrument used in the coatings industry for measuring mid-shear is the Brookfield KU-2 (Figure 3). This instrument is based on the historical Stormer method of testing coatings. A paddle-type spindle is spun in a paint can at 200 rpm, and the resulting viscosity is reported in Krebs units, abbreviated KU. Architectural paints typically have mid-shear viscosities between 90 and 120 Krebs units, although the range of values extends from 50 to 140 KU. In summary, the rheological expectations on today’s coatings are very high, but with the proper approach and measurements, those expectations can be met. 䡲 PA I N T & C O A T I N G S I N D U S T R Y

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41

Recent Advances in Photocuring and Stabilization of

Waterborne

COATINGS

I

n recent years the field of waterborne UV-curable coatings has taken on greater significance as the coatings industry recognizes how it can help increase production efficiencies, lower volatile organic compounds (VOCs), and deliver high-end performance.1,2 In previous papers, BASF described how various waterborne urethane acrylate dispersions could be photocured and also photostabilized.3,4 We found a particularly effective strategy for photocuring was to use two or more photoinitiators. The individual photoinitiators target specific regions (surface and bottom) of the coating. Short-wavelength-absorbing photoinitiators were found to effectively cure the top coating surface. On the other hand, a long-wavelength-absorbing and photobleachable photoinitiator can be effective for deep through-curing. Examples of the common photobleachable, long-wavelength-absorbing photoinitiators are monoacylphosphine oxide (MAPO) and bisacylphosphine oxide (BAPO).

SCHEME 1 | Common photoinitiator type used for UV curing of light-stabilized waterborne acrylate coatings (AHK = α-hydroxyl ketone, BAPO = bisacylphosphine oxide). O OH R'

O O O P

R AHK

BAPO

Photoinitiators that work well to cure the surface are aromatic α-hydroxy ketones (AHK) and mixtures of benzophenone/AHK.5 To ensure good through-curing arylphosphine oxide photoinitiators were employed.6 Deep through cure was particularly critical for coatings that contained UV-blocking materials (light stabilizers and/or pigments/fillers). Water-dispersible benzotriazole (BZT) and polar hindered amine light stabilizers (HALS) were found to be useful in these early studies.3 These light stabilizers, however, do not necessarily offer the best performance for low wash-out and high photopermanence.

SCHEME 2 | Light stabilizers used in UV-curable waterborne acrylate coatings.

OR1 OH N N

HO

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R2

R3 R5 Hydroxyphenyl triazine (HPT)

N

Hydroxyphenyl benzotriazole (BZT)

R2

N R

R2

N N N

R2

N OR

"N-alkyl" "N-OR" Hindered Amine Light Stabilizer (HALS) Since that time, newer high-performance waterborne UV-curable resins have been introduced into the marketplace,7 and these in turn place more stringent requirements on the photoinitiator and light stabilizer packages. Further, the higher durability requirements often are not met with traditional light stabilizer packages. Part of solving the light stabilizer problem was trying to get high-performance and hydrophobic additives into the resin system. A new way to overcome this barrier was recently introduced to the coatings industry.8,9 The solution was to use an encapsulation technology for the highperformance additives. The so-called Novel Encapsulated Additive Technology (NEAT) was found to provide a way to easily incorporate the materials in aqueous paints without using co-solvents and without requiring high-energy dispersion equipment. The goal of this article is to explore the use of NEAT additives for a UV-curable waterborne resin, which yields a photostable coating. We found that stability, control over

By I. M. Spinu, E. V. Sitzmann, K. O. Sass and K. P. Milks, | BASF Corp., Wyandotte, MI 42

R1

R4

color and increased weatherability were achieved using NEAT light stabilizers with liquid-based photoinitiators.

Experimental Materials Ethylene glycol monobutylether (EB) from Acros Organics was used as an additive co-solvent for selected photoinitiators and/or light stabilizers. BASF photoinitiators were used as is, which included the α-hydroxyketones (AHK), mixtures of benzophenone and AHK, and mono and bisacylphosphine oxides. The AHK photoinitiators used were: Irgacure® 2959,12 which is a solid, water-soluble AHK, blended Irgacure 184 with EB, and an experimental liquid AHK (LAHK). The Irgacure 500 was a 1:1 liquid blend of benzophenone and Irgacure 184. The acylphosphine oxide photoinitiators included the monoacylphosphine oxide (MAPO) and the bisacylphosphine oxide (BAPO). The BAPO examined was in three forms: dispersion, liquid mixture with either MAPO or AHK. The Irgacure 819-DW is a water dispersion of BAPO. The liquid Irgacure 2022 is a blend of AHK/BAPO.6 The Irgacure 2100 is a liquid blend of BAPO/MAPO. 6 The BASF light stabilizers used consisted of UV absorbers (UVAs) and hindered amine light stabilizers (HALS). Tinuvin® 1130 (UVA-BZT) and Tinuvin 292 (HALS-292) were used as is. The Tinuvin 123-DW (HALS 123-DW) is a nonpolar HALS (Tinuvin 123), which uses the NEAT technology to render it 30% active in an aqueous solution. The Tinuvin 400-DW (UVA 400-DW) and Tinuvin 477DW (UVA 477-DW) are both hydroxyphenyl triazene UV absorbers. The UVA 400-DW and UVA 477-DW are both 20% active in an aqueous solution.

Polyurethane Dispersion (PUD) Formulation Laromer®

BASF 8949 was selected as the resin for the UV-curable aliphatic polyurethane dispersion. Laromer 8949, 38-42% active,12 is a waterborne, energy-curable aliphatic urethane dispersion with physical drying properties. This high-performance resin is intended for the production of coatings for paper, wood, wood-based materials, plastic and printing inks.7 A low-gloss, fast-curing formulation using Laromer 8949 as the base resin is given in Table 1. This formulation, hereafter referred to as PUD, is suitable as a coating for wood and/or for plastic. Photoinitiators were added by simple mixing to the formulation to make the resin UV curable. The light stabilizers were also added by simple mixing, and they were used to determine their effect on photodurability, color and photoresponse.

Formulation Stability Testing

convection oven at ~53 ºC for 10 minutes. The dried specimens were subsequently photo-cured in air at ambient temperature with a Fusion UV 600 watt gallium doped “V” lamp followed by an iron doped “D” lamp at various energy levels. The typical line speed was 20 feet per minute. A single pass under the lamps corresponded to a UVA energy of 3.8 J/cm². A radiometer UV Power Map® from EIT Inc. was used to measure UV light on the conveyer belt. The diode detector is sensitive to the following regions: UVV (395-445 nm), UVA (320-390 nm), UVB (280-320 nm), UVC (250-260 nm).

Xenon Accelerated Weathering The Xenon WOM measurements were performed with a Weather-Ometer ® from Atlas Electric Devices Company, following the SAE J1960 test protocol. To this end the

TABLE 1 | Polyurethane dispersion (PUD) UV-curable formulation. Type/Description

Parts

Aliphatic urethane dispersion (Laromer LR 8949) Thixotropic agent (Aerosil® 200)a Matting agent (Syloid® C 809, Syloid C 906)b Thickener (Optiflo® H 400)c Water Anti-foam DPM (Dipropylene glycol monomethyl ether) Leveling agent

77.3 0.6 2 0.3 13.2 0.8 2.1 0.3

a) Evonik Degussa Corp.; b) W.R. Grace & Co., c) Southern Clay Products, Inc.

TABLE 2 | Effect of various photoinitiators on the shelf life stability of PUD. Photoinitiator (in PUD Formulation) No photoinitiator Irgacure 819-DW (1%) Irgacure 819-DW (0.5%) Irgacure 819-DW (1%) + Irgacure 500 (1%) Irgacure 819-DW (0.5%) + Irgacure 500 (1%) Irgacure 819-DW (0.3%) + Irgacure 500 (1%) Irgacure 819-DW (1%) + Irgacure 525 (1%) Irgacure 819-DW (0.5%) + Irgacure 525 (1%) Irgacure 819-DW (0.3%) + Irgacure 525 (1%) Irgacure 819-DW (0.5%) + Irgacure 184/EB (1%) Irgacure 2022 (1%) LAHK (0.6%) Irgacure 184/EB (1.2%) Irgacure 184/EB (2%) LAHK (1.33%) Irgacure 184/EB (2%)

Days of Stability >96 >142 >142 >142 >142 >142 >142 >142 >142 >142 >98 >98 >98 >65 >148 >148

TABLE 3 | Effect of light stabilizers on the shelf life stability of PUD.

The formulations were prepared containing various additives and stored at 23 ºC. The samples were examined for any change in appearance over time, such as the development of phase separation, thickening and/or gelation.

Photocuring and Characterization Bird®

Samples were applied using a bar by Bird Film Applicators, Inc. onto white aluminum panels, dried at room temperature for 5 to 10 minutes, then placed in a

Light Stabilizer in PUD Formulation

Days of Stability

UVA-BZT/HALS-292, 2:1 (3%) UVA-BZT/HALS-292, 2:1 (3%) resin only without matting agents UVA-BZT/HALS-292, 2:1 (3%) + EB (3%) Control - no PI, no LS Tinuvin 400-DW (2%) + Tinuvin 123-DW (1%) Tinuvin 477-DW (2%) + Tinuvin 123-DW (1%)

PA I N T & C O A T I N G S I N D U S T R Y

1 2 > 63 > 96 > 125 > 96

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Recent Advances in Photocuring and Stabilization of Waterborne Coatings

xenon arc burner was equipped with a quartz inner filter and a “Type S” borosilicate outer filter. A Cam #180 also was installed. The light cycle used had an irradiance of 0.55 W/m² @ 340 nm, with black panel temperature at 70 ºC, wet bulb depression at 12 ºC and conditioning water at 45 ºC; dark cycle used: black panel temperature at 38 ºC, conditioning water at 40 ºC. The CAM #180 installed provided 120 minutes of light and 60 minutes of dark in the following cycle: 40 minutes of light followed by 20 minutes of light and front specimen spray, followed by 60 minutes of light, followed by 60 minutes of dark with back rack spray and repeating. The coated sample specimens were visually inspected after exposure and characterized for changes in color and/or solvent resistance.

FTIR Double Bond Conversion A Nicolet™ Avatar™ 370 DTGS spectrophotometer by Thermo Electron Corporation was used to obtain the FTIR/ATR spectra. The spectrophotometer was equipped with a diamond crystal and a smart orbit accessory. Data acquisition used a resolution of 4 cm-1 and data spacing of 1.929 cm-1; each spectrum was an average of 32 scans, taken from 4000 cm-1 to 400 cm-1 and referenced against an air background. The reported percent double bond conversion (% conv) was determined from ATR-FTIR spectra. The double bond conversion is expressed as % conv = 100*(Initial-Final)/Initial, where Initial and Final observables are integral ratios of (acrylate absorbance integral at 815 cm-1)/(carbonyl absorbance integral at 1704 cm-1). ATR-FTIR spectra were obtained from both top and bottom sides of the coating.

Solvent Resistance Solvent resistance, using methyl ethyl ketone (MEK) is a well-known method to determine cure. Double rubs are performed on the coating surface with a cloth soaked with MEK solvent.10

Coloristics Colorimetric measurements were performed with a Minolta® Spectrometer CM 3600d by Konica Minolta Sensing, Inc. The color values were specifically quantified by determining the CIE L*a*b* system, following ASTM E 308 methods.11 A higher positive number for the b* value indicates a stronger yellow color.

Results and Discussion The PUD formulation used the high-performing Laromer LR 8949, which is a waterborne, energy-curable aliphatic polyurethane dispersion for coatings for wood, wood-based materials, paper, plastic and printing inks. A generic structure of the resin is shown in Scheme 3.

SCHEME 3 | General structure of the water-dispersible urethane acrylate.

O

O

+ O O HNR3 H C 3 H H ON NO

H ON O

The substructures

O

O

O

O

O

H NO

represent oligomeric backbones.

Coatings based on the PUD formulation were tack-free after physical drying (evaporation of the water) and therefore are well-suited for three-dimensional substrates.

TABLE 4 | Effect of combining photoinitiators with light stabilizers on the shelf life stability of PUD. LS Package

44

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PI Package Tinuvin 477-DW

Irgacure 819-DW

Irgacure Irgacure 2022 2100

Irgacure 2959

Irgacure 500

Irgacure 184/EB

Time to Failure, Days

Tinuvin 400-DW

Tinuvin 123-DW

2

1

1

1

10

2

1

0.5

1

21

2

1

0.3

1

29

2

1

0.3

2

1

0.3

LAHK

1

21

1

29

1

2

1

1

2

1

1

1

10 15

1

2

0.5

1

21

1

2

0.5

1

2

0.3

1

2

1

0.2

2

1

0.2

2

1

2

1

1

21

0.6

>136 0.6

0.2

>136 1.2

1 2

0.2

1

2

0.2

1

2

0.2

1

2

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>136 >136

1

1

21

0.6

>136 0.6

>132 1.2

>132 >132

The UV-cure profile can be assessed by a number of ways, such as spectroscopically and/or through physical testing such as tensile analysis or solvent resistance. In this study we examined the double bond conversion and solvent resistance. FTIR analysis was used to determine the degree of conversion (measurement of the acrylate double bond). The results of how the UV exposure affects the conversion are shown graphically in Figures 2 and 3. From the FTIR analysis it was found that at the surface the double bond conversion was at best 60%. In contrast, excellent double bond conversion (90%) was seen for the bottom side of the coating. As shown in Figure 4, the exposure to UV lamps caused, in some cases, an increase in color. Without light stabilizers the coating becomes increasingly more yellow (6b*>0) with increasing UV lamp exposure. Adding in the LS reduces the effect. Thus, without a LS package, the b* increases on all samples. With the LS the color is more stable. Using the Tinuvin 477-DW as the light stabilizer,

FIGURE 1 | Transmission spectra of UV-cured PUD coating (2.2 mil dry thickness) containing various UV absorbers and BAPO (Irgacure 819) and BAPO/MAPO blend (Irgacure 2100) photoinitiators. 40

3 No light stabilizer

30 + T400-DW

20

+ T479-DW

10

Absorbance

As a first step in additive selection, it is necessary to determine their effect on stability of the waterborne formulation. Since this is a UV-curable PUD formulation, we needed to assess the stability of the individual photoinitiators (which are needed for curing), the light stabilizers (which are needed for photostabilization after curing and/ or color management) as well as their combination. It was found that the photoinitiators commonly used for waterborne coating2,4 systems showed excellent stability characteristics (Table 2). For example, good stability (>140 days) was observed for the dispersed BAPO (Irgacure 819-DW), for Irgacure 500 as well as for the liquid AHKs (LAHK and Irgacure 184/EB). The solution stability with the PUD was more greatly affected by use of the light stabilizers. As given in Table 3, the combination UVA-BZT/HALS-292 proved unusable, because the shelf life stability was less than 1 day. In an effort to see if a small amount of co-solvent could overcome some of the stability issue, we co-mixed EB with the UVA-BZT/HALS-292. This resulted in an improved shelf life, but the stability still remained too low to be useful. In contrast, the NEAT products were especially good, and the shelf life was up to greater than 90 days. Following the early work,4 we initially examined the use of Irgacure 819-DW in combination with the light stabilizers of the NEAT (Tinuvin DW) type. The results in Table 4 show without exception low stability (<30 days) resulted for all formulations containing Irgacure 819-DW. The stability was as low as only 10-15 days for formulations with higher Irgacure 819-DW content. The results indicate that for this particular PUD formulation the Irgacure 819-DW is not a good option. Prompted by these results, we investigated a variety of photoinitiator packages involving Irgacure 2022 or combinations of Irgacure 2100 with LAHK or Irgacure 500 or Irgacure 184/EB. Since the UV absorbers will block UV light below 375 nm (Figure 1), we will still need the BAPO or MAPO photoinitiators to ensure good through cure. The stability results for these formulations without Irgacure 819-DW also presented in Table 4 are very good; all formulations displayed stability in excess of 132 days. In summary, traditional additives caused stability issues with the resin system. UVA-BZT and HALS-292 were unusable; the Irgacure 819-DW by itself was acceptable but when combined with a light stabilizer caused major stability problems. Thus, the use of NEAT (Tinuvin DW)-based light stabilizers was critical for the formulation stability where the liquid photoinitiators combined with the Tinuvin DW light stabilizers gave the best overall stability.

Effect on Photocure Response

% Transmittance

Effect on Solution Stability

Having found the preferred photoinitiator/light stabilizer combinations, the next questions are how these additives affect the UV-curing profile and long-term weathering.

0 300 325 350 375 400 425 450

Irgacure 2100 (MAPO/BAPO blend) Irgacure 819 (BAPO)

2 1 0 300 325 350 375 400 425

Wavelength, nm

Wavelength, nm

FIGURE 2 | Conversion vs. energy. Top side of cured PUD. Light stabilizer package in the formulations was: 2% Tinuvin 400-DW + 1% Tinuvin 123-DW. Film thickness: 10 mil wet (2.2 mil dry). 100

Conversion, %

After curing with UV light, the cured films show excellent resistance to water and chemicals (such as MEK), and are also very scratch- and block-resistant. The methodology used to optimize the formulation with respect to selecting the photoinitiator and light stabilizer packages divided the screening work into three parts: 1) formulation stability, 2) photocure response, and 3) accelerated weathering.

80 60 0.2% Irgacure 2100+ 0.6% LAHK 0.2% Irgacure 2100+ 0.6% Irgacure 500

40

0.2% Irgacure 2100 + 1.2% Irgacure 184/EB (1/1)

20

1% Irgacure 2022

0 0

5

10 Energy, J/cm

15

20

2

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Recent Advances in Photocuring and Stabilization of Waterborne Coatings

FIGURE 3 | Conversion vs. energy. Bottom side of cured PUD. Light stabilizer package in the formulations was: 2% Tinuvin 400-DW + 1% Tinuvin 123-DW. Film thickness: 10 mil wet (2.2 mil dry). 100

Conversion, %

80 60 0.2% Irgacure 2100+ 0.6% LAHK

40

0.2% Irgacure 2100+ 0.6% Irgacure 500 0.2% Irgacure 2100+ 1.2% Irgacure 184/EB (1/1)

20

1% Irgacure 2022

0 0

5

10

15

20

Energy, J/cm2

FIGURE 4 | Effect of UV lamp exposure on color: b* function as of energy (J/cm2), for the PUD coating (2.2 mil dry). 9 8

1% Irgacure 2022

7

1.2% Irgacure 184/EB (1/1)

b*

6

0.2% Irgacure2100+ 1.2% Irgacure 184/EB (1/1) + 2% Tinuvin DW +1% Tinuvin 123 DW

5 4

1% Irgacure 2022 + 2% Tinuvin 400 DW + 1% Tinuvin 123DW

3

1% Irgacure 2022 + 2% Tinuvin 477DW +1% Tinuvin 123DW

2 1 0 0

5

10

15

20

UV Lamp Energy, J/cm2

Effect on Accelerated Weathering

FIGURE 5 | Effect on color (b*) after Xenon WOM accelerated weathering for various

Initial b* 500 Hours 1000 hours

As given in Table 5, coatings maintained their solvent resistance properties even up to 1200 hours Xenon WOM exposure. The question is whether their color also could be stabilized. As given in Figure 5, the light stabilizer package (which consisted of 2% Tinuvin 400-DW and 1% Tinuvin 123-DW) was critical in maintaining color. Indeed, as shown in the right side of Figure 5, with light stabilizers the 6b* was within 0.5 units over 1000 hours Xenon WOM. We also saw a general decrease in color when the light stabilizer package was used. In contrast, the 6b* shifted dramatically without light stabilizers (see left side of Figure 5). For example, during the first 500 hours of exposure the 6b* increased (from 0.5 to 1.5 units). In subsequent exposure the 6b* actually decreased (approximately 0.5 units). The lowest color without a light stabilizer package was with the photoinitiator Irgacure 184/EB (1:1).

1%

0.6 %

0.6 %

with LS

LA HK Irg ac u 1% re 1.2 20 Irg 22 % ac Irg Irg ur ac ac e2 ur ur 1.2 02 e1 e1 % 2 84 84 Irg 0.2 /E Irg / a E B 0 c B % ac u (1 .2 (1 re Irg ur /1 % /1 18 ac e 1 ) + Ir ) 4/ ur 84 ga T 0.2 i E e2 nu cu /E B % (1 vin re 10 B ( 0 Irg /1 0+ 1/1 .2% 40 210 ) ac 0.6 ) + I 0 ur Ti rga +1 0+ 1 % e2 n 2 LA 3- .2% uv cur 10 DW HK in e 0+ 0.6 +T 40 210 in 0+ 0+ % 1% uv 1 LA Irg in 23- 1.2% HK 40 DW ac +T u 0 +1 re in 1% uv 20 23 Irg in 22 -D ac 40 W + ur 0 T +1 in e2 uv 2 02 3in 2+ DW 40 Ti 0+ nu 1 23 vin -D 40 W 0+ 12 3DW

without LS

LA HK

b*

photoinitiators and light stabilizer combination for 2.2 mil thick PUD coatings. 5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0

we see that the coatings have a much higher initial b* (which is expected since the Tinuvin 477 is a super red shifted). The best results were seen with the use of Tinuvin 400-DW/Tinuvin 123-DW. The Tinuvin 477-DW light stabilizer blocks light up to 400 nm. Indeed, it is the most red shifted hydroxyphenyltriazene that is commercially available. Its ability to block light is exceedingly good. For thin coatings (<1.5 mil) the long wavelength absorption does not cause a problem in giving the coating a yellow colored appearance. At a higher thickness, i.e., 2 mil, it can add color to the coating, which may be unacceptable. As shown in Figure 4, the coatings containing Tinuvin 400-DW/ Tinuvin 123-DW have a b* of approximately 7 to 8. Thus, for color-sensitive applications the preferred UV blocker would be Tinuvin 400-DW. A further advantage in using Tinuvin 400-DW in a UV-curable system is that the acylphosphine oxide photoinitiators are easier to photo-excite, since the UV blocking is basically limited to <375 nm and these photoinitiators absorb at longer wavelengths. This condition allows good through curing (see Figure 3). The question now is at what light exposure is the coating considered well cured? As summarized in Table 5, it was found that a single pass under the lamps at 20 fpm (380 mJ/cm2) gave coatings with very high solvent resistance. From the MEK resistance test it was found that unexposed samples had poor solvent resistance (MEK double rubs <2). After a single pass under the lamps all the coatings had a MEK double rub >100, which indicated excellent cure. Based on these results we used a single pass exposure to prepare samples for accelerated weathering. We used the light stabilizer package consisting of Tinuvin 400DW and Tinuvin 123-DW.

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Conclusions The fast, UV-curable, water-based PUD resin exhibited very high solvent resistance and durability. It was found that the NEAT was necessary for introducing high-performance light stabilizers into the UV-curable PUD formulation. The best overall performance was obtained using the

TABLE 5 | Effect of UV exposure on MEK solvent resistance.

1

Coating/Cure Conditions for PUD at 2.2 mil dry (10 mil wet)

MEK Double Rubs

Dry coating after water flash off, before UV lamp exposure

<2

Produced By

After UV exposure using 3.8 J/cm² 2 (1 pass, 20 fpm)

> 100

After 1200 hours Xenon WOM of the UV-cured coatings

> 100

3

NEAT light stabilizer products and liquid photoinitiators based on acylphosphine oxide. The optimal combination of light stabilizers (UV absorber 1% Tinuvin 400-DW, and HALS 2% Tinuvin 123-DW) with photoinitiators (0.2% Irgacure 2100 plus 1.2% Irgacure 184/EB) proved crucial for formulation stability and fast photospeed curing. They were also keys to maintain low color even under accelerated weathering conditions. The outlook for the future in using this eco-friendly technology remains bright. We expect this formulation knowledge can be successfully applied to even more-demanding applications, such as ultra-thin protective coatings for high-end applications. 䡲

References 1

2

3

4

5

6

7

8

9

10

11

12

Lorinczova, I.; Decker, C. Chemical Technology of Wood, Pulp and Paper, Proceedings of the International Conference “Chemical Technology of Wood, Pulp and Paper”, Bratislava, Slovakia, Sept. 17-19, 2003 (2003), 487-490. Sitzmann, E.; Fuchs, A.; Wostratzky, D. Handbook of Coatings Additives (2nd Edition); Marcel Dekker, Inc., New York, NY; 2004; pp. 61-125. Kaspers, S.R.; Szewczyk, C; Megert, S.; Peter, W.; Cressy, L.; Rogez, D.; Sitzmann, E.V. Radtech 2002 North Am. UV/EB Conference Proceedings (2002). Peter, W.; Megert, S.; Rogez, D.; Sitzmann, E. European Coatings Journal 2002, 11, 14-18, 21. Crivello, J.V. Dietliker, K. Photoinitiators for Free Radical Cationic & Anionic Photopolymerization, John Wiley and Sons/ SITA Technology Ltd.: London, 1998. Sitzmann, E.V.; Peter, W.; Bramer, D.; Jankauskas, J.; Losapio, G.; Wolf, J.P.; Huguenard, S. Technical Conference Proceedings - UV & EB Technology Expo & Conference, Charlotte, NC, May 2-5, 2004 (2004), 874-891. Schwartz, M.; Menzel, K.; Bechert,B.; Beck, E.; Reich, W. Eur. Pat. Appl. (1999) EP 894780. Landuydt, T. Rogez, D. European Coatings Journal 2008, 4, 34, 36-38. Schaller, C.; Rogez, D.; Braig, A. J. Coatings Techn. and Research 2009, 6(1), 81-88. Lowe, C. Test Methods for UV & EB Curable Systems, Volume VI, John Wiley & Sons, in association with SITA Technology Limited: 1996; p. 76 ASTM E 308-06: Standard Practice for Computing the Colors of Objects by Using the CIE System. Tinuvin®, Irgacure®, Laromer ® are registered trademarks of BASF.

This paper was presented at the RadTech 2010 Technology Expo and Conference, Baltimore, MD, www.radtech.org.

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