New Waterborne Fluoropolymer Resins for Ultra-Weatherable

Winn Darden and

Bob Parker, AGC

Chemicals Americas;

and Naoko Sumi, New Waterborne Isao Kimura, Masakazu Ataku, and Fluoropolymer Resins Takashige Maekawa, Asahi Glass Co. Ltd. for Ultra-Weatherable Coatings

Editor’s Note: This article is based on a C (392 F) to form a film. In addition, the low surface energy of the resins impedes paper the authors presented at PACE acceptable adhesion to metals and other 2009, the joint conference of SSPC: The luoropolymers, substrates, a property needed in primers introduced in the and direct-to-metal coatings, for instance. Society for Protective Coatings and the F 1930s, are known for their excellent ther- Hence, fluoropolymers are not typically Painting and Decorating Contractors of mal, chemical, and weather resistance, used as primers. along with surface properties like water Among traditional fluoropolymers, America, held February 15–18, 2009, in and oil resistance, and optical properties. only polyvinylidene fluoride (PVDF) is New Orleans, LA. Because of their properties, fluoropoly- widely used in coatings. This resin is usu- mers have been used in coatings on a ally supplied as a dispersion in a high variety of substrates. For example, fluo- boiling solvent blend, and is used mainly ropolymers for coatings include aqueous in coil coatings, where it is processed at dispersions of polytetrafluoroethylene high temperatures. PVDF is employed (PTFE), tetrafluoroethyl- primarily in architectural markets due to ene/hexafluoroethylene copolymers its exceptional weatherability. (FEP), and TFE/perfluoroalkyl vinyl A fluoropolymer resin was developed ether copolymers (PFA). These materials in the 1980s in an attempt to overcome are used primarily in non-stick and anti- the difficulties found in using traditional corrosion coatings. fluoropolymer resins in coatings, while Unfortunately, the use of fluoropoly- still maintaining their advantages. These mers in coatings is limited due to their resins, known generically as fluoroethyl- physical properties. Fluoropolymers ene vinyl ether (FEVE) resins, are solvent have poor solubility in traditional sol- soluble, and can be made compatible with vents used in the coatings industry. water. This article describes solvent- Usually, fluoropolymer resins must be borne as well as two types of waterborne Above: Tokyo Edo Museum, with FEVE coating Photos courtesy of the authors heated to temperatures greater than 200 FEVE resins—emulsions, which have

www.paintsquare.com 32 JPCL December 2009 been around for some time, and new dis- FEVE Emulsion Polymers FEVE resins provide a way to meet such persions—and the potential for uses of for Coatings regulations, the resins still require the use the new FEVE dispersion resins in coat- The first waterborne FEVE polymers of solvents to produce coatings. There ings for field application where high were aqueous emulsions, manufactured thus appears to be a need for a water- weathering properties are needed. via emulsion polymerization. The resins borne FEVE resin that offers the same were developed to enable coating manu- performance as that of solvent-borne FEVE Resins facturers to meet VOC and HAPS regula- FEVE resins. FEVE water dispersion in Solvent-Borne Coatings tions, which restrict the amount and type resins, as demonstrated below, yield FEVE resins can be synthesized with of solvents used to formulate coatings. properties in cross-linked coatings reactive hydroxyl groups and can be approaching those obtained cross-linked with standard aliphatic iso- with solvent-grade FEVE cyanates to make fluorourethane coat- resins. ings. FEVE resins can be used at high temperatures to make coil coatings, or FEVE Water at room temperature for field-applied Dispersion Resins coatings. This versatility in use substan- Preparation of Resins tially broadens the types of applications FEVE water dispersions are where FEVE-based fluorourethane derived from FEVE solid coatings can be used. resins of varying molecular Fluorourethanes have the same out- weight, acid numbers, and standing weatherability as traditional flu- hydroxyl numbers. To be use- oropolymers but offer other advantages, Institute for Global Environmental Strategies, with FEVE coating ful as a coating raw material, as well. Fluorourethanes can be cured at a resin must first be stable either room temperature or elevated tem- Vinyl ether monomers substituted with enough in storage to impart a reasonable peratures, so they can be used as mainte- polyoxyethylene (EO) units were copoly- shelf life to the formulated coating. It was nance coatings, applied in the field. Using merized with the fluorinated monomer found that dispersion stability was influ- appropriate additives, FEVE-based coat- and other vinyl ethers to obtain stable enced by several factors, including molec- ings can be manufactured in a wide range emulsions and to maintain the structure ular weight, particle size, and acid value. of gloss, unlike other fluoropolymers of the FEVE copolymer. The resulting The most stable products were derived used for coatings. As solution polymers, polymers are high in molecular weight, so from lower molecular weight, moderate FEVE resins have better compatibility they can be used in single-component particle size, moderate acid value poly- with a wide range of pigments, enabling a coatings, or they can be cross-linked with mers. broader color palette. And because fluo- aliphatic isocyanate dispersions. The A FEVE water dispersion with proper- rourethanes are cross-linked polymers, emulsions have found use in blends with ties shown in Table 1 (p. 34) was prepared they tend to offer higher hardness and other waterborne resins to improve the and then formulated to make a fluo- better corrosion resistance than some weatherability of conventional coatings. rourethane topcoat. types of fluoropolymers commonly used Unfortunately, coating properties in coatings. Yet, fluorourethanes retain obtained from these FEVE emulsions are Preparation of Fluorourethane enough flexibility and toughness for use generally inferior to those obtained from Coatings for Testing as topcoats for military aircraft, where solvent-borne FEVE resins. This inferiori- Coatings were prepared from the select- flexibility and adhesion are required at - ty is believed to be due to residual emulsi- ed FEVE water dispersion, a two-part 40 C (-40 F) as well as at higher tempera- fier from the resin system in the cured water emulsion FEVE resin, and a sol- tures. FEVE coating, the presence of the EO vent-borne FEVE resin. Then, all three FEVE-based fluorourethane topcoats units in the polymer, and the high molec- types of coatings were applied to chro- can be formulated and applied to yield a ular weight of the resins. In general, water mate-treated steel panels, cured for 14 coating life exceeding 50 years. Based sensitivity of FEVE emulsions is higher days, and subjected to a variety of tests. on work done by several Japanese than that of solvent-borne FEVE resins, transportation authorities, engineering while weatherability is usually lower. Comparative Test Results organizations, and private parties, these The shortcomings in performance of for Physical Properties topcoats are required to be used on all the FEVE water emulsions have limited The resulting fluorourethane coatings, bridges in Japan, with an expected life of their usefulness as low VOC and low along with an unreacted FEVE emulsion 100 years in some cases. HAPS coatings in the U.S. While solid resin, were subjected to several standard www.paintsquare.com JPCL December 2009 33 u

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Table 1: Properties of FEVE Water Dispersion Property Value Appearance Milky White Liquid Solids, Wt. % 40% ±2% pH 7–9 Particle Diameter, nm 50–300 Minimum Film Forming Temperature, °C 27 Acid Value, mg KOH/g-polymer 15 Hydroxyl Value, mg KOH/g-polymer 85

Hydroxyl Equivalent Weight (HEW) 660 UV/Condensation Cabinet Cycle 8 hours UV at 70 C (158 F) and 4 hours Condensation at 50 C (122 F)

Fig. 1: QUV-B weathering testing of FEVE-based coatings tests for the coatings’ physical properties. that the dispersion-based fluorourethane of the emulsion film was irregular, and Of the results shown in Table 2, sever- weathers as well as the solvent-borne the coalesced portions of the film could al are noteworthy. First, the gloss of the coating (Fig. 1). be seen. These imperfections could dispersion-based fluorourethane is close reduce the performance of the emulsion to that of the solvent-grade coating, and SEM Comparison: film. higher than that of the cross-linked emul- FEVE Dispersion and Emulsion sion coating. Hardness, impact resis- Scanning electron micrography (SEM) Application Characteristics tance, and adhesion of the three coatings showed that the dispersion formed a uni- of FEVE Dispersions are about the same, although the cross- form, dense film with no surface defects FEVE dispersions are formulated as two- linked emulsion has slightly lower after cross-linking. Thus, water resis- component systems using water-dis- impact resistance. The FEVE emulsion tance in the dispersion was improved; persible isocyanates as cross-linkers. that is not cross-linked has far lower water could not penetrate the film. In They are combined with pigments and hardness and impact resistance, and contrast, the cross-linked emulsion had additives for control of flow, gloss, foam- poor adhesion compared to the other surface defects thought to adversely ing, and other application and physical three cross-linked coatings. While the affect physical properties such as gloss properties. These systems can be applied emulsion is high enough in molecular and water resistance. Also, the surface with air or airless spray equipment, by weight to form a film using a coalescent, without the isocyanate cross-linker, film Table 2: Comparative Performance of Various FEVE Coatings properties are poor. The biggest difference in performance FEVE FEVE EVE Emulsion (OHV=55) is in the water resistance of the three flu- Property Test Dispersion Solvent-Based (OHV=85) (OHV=52) orourethane coatings. The water dispersion and solvent-grade fluorourethanes Cross-linker Water- HDI-Based Water- None (NCO/OH=1) N/A dispersible polyisocyanate dispersible show excellent water resistance, while isocyanate isocyanate the cross-linked emulsion develops blis- Gloss, 60° ISO 2813 88 90 78 78 ters during the test. In this battery of tests, the FEVE dispersion offered per- Pendulum ASTM D 4366 79 80 75 19 Hardness formance equivalent to that of the solvent-borne coating. This means that zero DuPont Impact ASTM D 2794 >1.0 m >1.0 m 1.0 m 0.3 m (D=0.5”) VOC fluorourethane coatings with excellent properties can be formulated Cross-Cut ASTM D 3359 5B 5B 5B 0B Adhesion* using the FEVE dispersions. Water Adhesion, 4B 5B 3B 0B Resistance ASTM D 3359 Comparative Weathering ISO 2812 Blistering, No Blistering No Blistering <8, Medium 2, Dense Fluorourethane coatings were tested in 40 C, 24 hrs ASTM D 714 the ASTM D 53 accelerated weathering test. Accelerated weathering tests show *Cross-cut adhesion test performed after soaking in hot water for 24 hours.

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Click our Reader e-Card at paintsquare.com/ric Click our Reader e-Card at paintsquare.com/ric 36 htteueu o iei o exceeded. not is life pot useful the that ensure to measurements, gloss using probably performed, on-site be field, should the testing in use For maximum hours. a 4 is of F) (77 C 25 FEVE at the dispersion of life pot expected the that indicate results These life. pot 4 hours’ at degrade to began coatings cured the of resistance Solvent exceeded. was life pot the that indicating cracking, extensive showed coating cured the hours, 6 After coating changed. cured measurably the of gloss the hours, After 5 lives. pot different for test gloss examined. was coatings cured the of tance resis- solvent the addition, In was examined. coatings resulting the of gloss system. The the of life pot estimated the over intervals one-hour at applied then were Coatings 1.0. of ratio NCO/OH a at isocyanate water-dispersible a with achieved. is life pot certain a after coating finished the of properties physical in decline a and during application, gloss in decrease a namely, pot life, the determine to used Other are approaches. measures life pot its of end the as viscosity in substantially increase not does dispersion FEVE blended the coatings, solvent-borne sys- Unlike coating tem. blended the of life pot ful use- the of determination is FEVE dispersions using in difficulties the of one site. job the at environment the on depending brush, by or roller, aebreFluoropolymers Waterborne iue2sosterslso the of results the shows 2 Figure coatings, waterborne other with As h EEdseso a blended was dispersion FEVE The 9 0 0 2 r e b m e c e D L C P J i.2 hrei 0 ls essptlife pot versus gloss 60° in Charge 2: Fig. .S ueaa “Fluoropolymers as Munekata, S. 1. aerospace. and automotive, architectural, include dispersions FEVE for markets potential Other buildings. office as such a structure, of occupants affect can solvents of smell the where applications in coatings solvent-borne the replace addition, can In dispersions g/L. 100 is IM for limit VOC current the where California, in even towers, water and plants, process .P rigradP isn Industries, Wilson, P. and Greigger P. 5. Durable “Performance of Asakawa, A. 4. .N ui .Kmr,M tk,T. Ataku, M. Kimura, I. Sumi, N. 3. in “Progress Yamabe, Takayanagi, M. T. 2. Coatings,” otn Materials,”Coating nttt etn,20,Ciao IL. Chicago, 2004, Meeting, Institute SpecificationsConstruction the at Presented Coatings,” Performance Fluoropolymer“High Germany.Nurnburg, 2003, April, Show, Coatings European Congress, Nurnburg 7th the at Presented Coatings,” Fluoropolymer LA. Orleans, New 2008, 1, 30–February January on Symposium, borne Water- the at Presented Coatings,” for Dispersions “Fluoropolymer Maekawa, Dispersions,” Aqueous and Soluble Spirits Mineral of Development Applications: Coating for Fluoropolymers utial otn Technologies, Coating Sustainable Coatings,” www.paintsquare.com tutrssc sbridges, as such structures for coatings (IM) nance mainte- industrial as used be can they VOCs, ered consid- be may which cents, coales- without used be can dispersions FEVE Because today. used are products solvent-borne where tions applica- all for dispersions FEVE use to possible is It 0 8-9 (2000). 185-190 40, (1994). 113-134 16, References rgesi Organic in Progress akt o FEVE for Markets Dispersions dacsin Advances rgesi Organic in Progress Click our Reader e-Card at paintsquare.com/ric Click our Reader e-Card at paintsquare.com/ric 37 the Coatings best articles covering rchitectural Handbook A of a 237-page compilation of JAC’s all aspects of specifying and using architectural coatings Order the print version orat a http://www.paintsquare.com/jac_handbook PDF download Journal of Architectural Coatings (JAC) JPCL December 2009 • Roof Coatings • Air Barrier • Coatings forArchitecturalMetal • Decorative and Other Interior• Coatings Coatings and Waterproofing for• Concrete Generic Coating Types and• Their Fire-resistant Uses and other Special• Purpose Coatings Coatings forSchools and OtherHigh Buildings Performance New from the JPCL Winn Darden is busi- ness manager for AGC Chemicals Americas line of LUMIFLON® fluoropolymer resins. Involved in the sales and marketing of coatings and coating raw Fluoropolymer Resins for Long-Life Coatings,” Presented at the Paint and Coatings Expo PACE 2007, Tampa, FL. 6. W. Darden, “Advances in Takashige Maekawa is R & D manager for Asahi Glass Chemicals in Chiba, Japan. His background is in polymer and surface chemistry. Isao Kimura is currently assigned to the headquarters of Asahi Glass Chemicals in Tokyo, Japan. He was involved in developing and testing waterborne fluoropolymer resins for coatings at the AGC research lab in Chiba. Naoki Sumi is a research chemist with Asahi Glass Chemicals in Chiba, Japan. She worked to develop new fluoropolymer resins for the semiconductor industry and on the now involved withnew developing fluororesins for coatings. Masakazu Ataku is a research chemist with Asahi Glass Chemicals at its corpo- rate labs in Chiba, Japan. He was responsible for improving production methods for polymers used in ion exchange membranes. He is now work- ing on the development of new fluoropolymers for the coatings industry. Bob Parker is technical service chemist for AGC Chemicals Americas in Exton, PA. He has been involved in formulating paints and coatings for over 30 years.received He his BS in chemistry from Alvernia College. He is currently responsible for technical service for LUMI- FLON® fluoropolymer resins in the U. S. materials for over 20 years, he haslished widely pub- in the industry and hassented pre- papers for SSPC, NACE, and Mega Rust. He holds 12 U.S. Patents. www.paintsquare.com Click our Reader e-Card at paintsquare.com/ric