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Copyright # 2015 ASM InternationalWAll rights reservedasminternational.orgASM Handbook, Volume 5B, Protective Organic CoatingsK.B. Tator, editorFluoroethylene Vinyl Ether Resins forHigh-Performance CoatingsRobert Parker and Kristen Blankenship, AGC Chemicals Americas, Inc.THIS ARTICLE DISCUSSES THE TECHNOLOGY of organic coatings based on fluoroethylene vinyl ether (FEVE) resins. Theseresins entered the commercial market in 1982and have been used in coatings for architectural,industrial maintenance, aerospace, and marinemarkets. Many bridges in Japan are coated withan FEVE polyurethane-based topcoat, includingthe Akashi Strait Bridge (Fig. 1).The FEVE-polyurethane topcoats are alsoused in architectural applications.In the United States, one example of an industrial maintenance application of an FEVE-basedtopcoat is the Rosemont Water Tower in Rosemont, IL, near Chicago (Fig. 2).These structures need to function and maintain their aesthetic appeal for a long time. TheFEVE-based coatings offer this protection.The demand for longer-life coatings was thedriving force behind the development of FEVEresins. The original fluoropolymer resins wereknown for their superior properties, such asweatherability and chemical resistance, but theypossessed limited application capabilities due totheir high melting point, high melt viscosity,and insolubility in organic solvents. Several different types of fluoropolymer resins were studied before the FEVE resins were chosen as themost viable candidate. Some of the importantcriteria were solvent solubility, hydroxyl (–OH)functionality, reasonable glass transition temperature (Tg) properties, and an adequate presence of fluorine in the polymer backbone thatwould offer protection to the weaker bonds inthe polymer.The FEVE resin family consists of several different products that can be used in a wide varietyof coating systems. There are solvent-based solution resins, 100%-solid flake resins, water-basedemulsions, and a water-based dispersion. A moredetailed explanation of each of these productsis given later in this article. Also, formulationguidelines are covered as well as applicationtechniques and performance characteristics.Finally, a short segment on health and safety ispresented.The Chemistry of FEVE ResinsThe FEVE resins were developed in the late1970s in Japan. These resins are amorphouscopolymers consisting of a combination of fluoroethylene and substituted vinyl ether chemistryin a regular repeating, alternating pattern. TheFEVE polymers are not pure fluoropolymers;they have characteristics of both fluoropolymersand hydrocarbons. Pure fluoropolymers exhibitexcellent durability but require specific application conditions. They are not soluble in solventsand therefore cannot be used in liquid coatings.The incorporation of the vinyl ether monomerin the FEVE polymer transforms it from a traditional pure fluoropolymer to a copolymer that issoluble in solvents. The alternating pattern(Fig. 3) is critical for the extreme ultraviolet(UV)-resistance properties it possesses.Fig. 1Fig. 2Fluoroethylene vinyl ether polyurethane-basedtopcoat used on the Akashi Strait Bridge inJapan. Photo property of Asahi Glass Co. Ltd.FFHHFFHCCFXCCCCHOFXFluoroethyleneVinyl etherFig. 3R1Fluoroethylene vinyl ether-based topcoatused on the Rosemont Water Tower near theChicago O’Hare International Airport. Courtesy ofTnemec Company, Inc.HFFHHFFCCCCHOFXCCCCHOFXR2R3R1 –OHR2, R3 Proprietary, impact Tg and other propertiesAlternating structure of fluoroethylene vinyl ether resins. “X” is proprietary. Tg, glass transition temperature
Fluoroethylene Vinyl Ether Resins for High-Performance Coatings / 89Alternating Structure of FEVE ResinsThe solubility afforded by the vinyl ethermonomer is what allows FEVE resins to beused in a wide array of coating formulationsthat can be applied in the factory as baked coatings or in field settings where the coating is airdried. Another unique characteristic of FEVEpolymers compared to pure fluoropolymers istheir ability to achieve high gloss. The vinylether monomers not only provide solubility intosolvents, but they also increase the refractiveindex of the polymer, which increases gloss.Coatings for factory and field application canbe made with these soluble FEVE resins.Hydroxyl functionality is incorporated into manyFEVE resins, allowing them to be cross linkedvia polyisocyanates or amino resins. Lowhydroxyl-functional FEVE resins are availablefor one-component (i.e., 1K) coatings. Physicalproperties such as flexibility and chemical resistance are tailored by the R groups. CycloaliphaticR groups provide increased chemical resistance,while softer, lower-Tg linear aliphatic groupsprovide flexibility. Acid-functional R groupsimprove pigment wetting. Hydroxyl-functionalR groups allow for cross linking of FEVE resinswith cross linkers such as melamine formaldehyde and polyisocyanate. The FEVE resins areavailable as solution resins, solids resins for powder coatings, and waterborne resins.The fluoroethylene groups are the strength ofthe FEVE resin. These groups are what make thisclass of polymers so resistant to UV degradation.The carbon-fluorine bond is strong. The energyof this bond is 486 kJ/mol (Ref 1), while theenergy of UV radiation at 300 nm is 399 kJ/mol.Often, total fluorine content is used as a predictorof UV resistance, but this is not the case withFEVE resins. The alternating structure is of keyimportance. The chemically stable and UV-resistant fluoroethylene unit sterically and chemicallyprotects the neighboring vinyl ether unit (Ref 2).Typical properties of FEVE resins are shown inTable 1.In addition to the FEVE chemistry, whichthis article addresses specifically, there isanother type of fluorinated copolymer resin:fluoroethylene vinyl ester. Instead of a vinylether monomer, a vinyl ester monomer is usedto copolymerize with the fluoroethylene monomer. Debate regarding which performs betteris ongoing. For the purposes of this article, discussion is limited to FEVE technology.FEVE Resin TypesThe first iteration of the FEVE polymer wassynthesized as a solution polymer in organicsolvent. The molecular weight varied significantly, from as low as 2,000 to upward of80,000 (number average Mw 4000–150,000).The solution-grade resin was studied extensively. It was used in two-component (i.e.,2K) formulations with melamine-formaldehyderesins in bake systems and polyisocyanates inambient cure systems. A low –OH-functionalsolution resin was also synthesized for use in1K air-dry systems.As market demand increased, a method totailor the solvent in which the resin was supplied was developed. Depending on the application, the solution resin precursors were furtherprocessed to be diluted in different solvents.A step in this processing was the removal ofthe original carrier solvent. This yielded a solid,flakelike resin. This form was later marketedfor use in powder coating applications. The flakelike resins had a Tg slightly above room temperature and therefore remained solid instorage. For use in powder coating applications,the flakes were typically pulverized into fineparticles. The powder coating resins were formulated with blocked polyisocyanates andused in bake applications. The bake temperaturedepended on the unblocking temperature of thepolyisocyanate and usually was approximately195 C (380 F).As the “green” movement gained tractionglobally, another use was found for the flakegrade FEVE resins. Laboratory studies weredone to test the solubility of the various flakegrade resins in the major volatile organic compound (VOC)-exempt solvents. It was discovered that FEVE flake grades were soluble inall but one of the five major VOC-exempt solvents. The FEVE resins are soluble in acetone,Oxsol 100 (Makhteshim Agan Industries),t-butyl acetate, and dimethyl carbonate. Theyare not soluble in propylene carbonate. Thisability to be used in VOC-exempt solvents,coupled with the use of FEVE flake grades forpowder, elevated FEVE technology to the frontof the green-coatings movement.In the early 1990s, another step into the forefront of the environmental coatings movementwas made when the first FEVE waterborneemulsion was manufactured. Now formulatorshad three options for environmentally friendlycoatings: powder, low-VOC solution resins,and waterborne emulsions for water-based coatings. Part of the synthesis of waterborne emulsions enlisted the use of surfactants. Thesewater-sensitive surfactants remained in thesubsequent formulated coating film. It wasfound that the performance of the emulsionswas not quite at the level of the solution orflake-grade resins. It was theorized that if thesurfactant could be removed from the film, theperformance of the waterborne emulsion couldall but match that of the original solution-typeFEVE resins.In the early 2000s, this concept was studiedand developed into a viable resin product. In2012, a water-based FEVE resin dispersionwas presented to the market. The emulsiongrades are produced using emulsion polymerization, but the dispersion grade was made quitedifferently. The precursor used was a flake resindissolved in a polar solvent. A small portion ofthe hydroxyl groups are then modified to acidgroups and then stabilized by amine. At thispoint, the polymer was dispersed into water.The final dispersion included no surfactants tocompromise its water resistance. Instead of surfactant, stability in water was achieved by theneutralized acid groups. This new dispersionretained its low molecular weight (Mn 7000)and exhibited excellent film formation. The performance of this dispersion-grade FEVE resinsurpassed that of the emulsion FEVE resinsand did approach the performance of the solution resins.Methods of Formulation forFEVE ResinsThis section is divided into three separatesegments: solvent-based coating formulations,water-based coating formulations, and powdercoating formulations. The first two segmentsdiscuss both one-component and two-componentsystems, because both of these systems are possible with FEVE resins. The powder coatingsegment is limited to one-component bakingsystems.Solvent-Based Coating FormulationsThe first generation of FEVE resins were solutions of polymers that were cured by thehydroxyl-isocyanate reaction. Because this reaction can occur at ambient temperatures, thesesystems were either two-component in nature orthe isocyanate component had its functionalgroup chemically blocked to stabilize the coatinguntil its application. The basic formulationfor these FEVE resins consisted of threeingredients—FEVE resin, isocyanate resin, andtin catalyst—with solvent addition to adjust theviscosity. Because most formulations must havethe necessary robustness to conquer applicationissues, additives played a big part in makingthese coatings a success. The following are someof the important considerations that are helpfulwhen formulating these types of FEVE-basedcoatings.Choice of Isocyanate. Most FEVE-basedcoatings are used on exterior structures, so itis necessary to use aliphatic isocyanates asthe cross linker for the hydroxyl groups of theFEVE resin. Beyond this recommendation, theTable 1 Typical properties offluoroethylene vinyl ether resinsFluorine contentOH valueCOOH valueMolecular weightSpecific y parameter(calculated)(a) Tg, glass transition temperature25–30 wt%47–170 mg KOH/g0–15 mg KOH/gMn 2,000–80,0001.4–1.5Glassy (Tg 20–50 C, or70–120 F)(a)240–250 C (460–480 F)8.8
90 / Coating Materialschoice of isocyanate depends on the desiredproperties for the coating. Performance properties such as flexibility, speed of cure, and viscosity vary with each different isocyanate resin.Catalyst Choice. Historically, dibutyltindilaurate has been the workhorse catalyst forthe two-component systems since the beginningof the FEVE technology. It is suggested that thecatalyst level be kept at a much lower level thanthe standard 0.005% (based on resin solids)used in traditional two-component acrylic orpolyester polyurethanes. The suggested rangeof catalyst levels is 0.0002 to 0.001% (basedon resin solids). The reason for the loweramount is because the hydroxyl (OH) groupsare strictly primary in nature, causing a fasterreaction rate with the isocyanate groups.Solvent Choices. There are a wide variety ofsolvents that are compatible with the FEVEresins. As with a wide variety of organic resinsfor coatings, the FEVE resins show varyingdegrees of viscosity decrease, depending onthe polarity of the solvent. The lower-molecular-weight resin is used to manufacture coatingswith lower VOC content (Tables 2, 3).Pigment Choices. There are no restrictionswhen pigments must be chosen for an FEVEformulation. Because a majority of the coatingsthat use FEVE resins are expected to possesssubstantial weatherability characteristics, it isrecommended that any organic pigment chosenhave a high degree of lightfastness. The protection from UV degradation offered by the presence of the FEVE resin extends primarily tothe resin itself. Because it is transparent to UVlight, it cannot protect opaque organic pigmentsfrom absorbing UV light and suffering the consequences of chemical structure alteration,which will result in a color change. It is recommended that UV absorbers and hindered aminelight stabilizers be added to these types of pigmented formulations for additional protectionfrom color change. Mixed metal oxide pigments offer improved UV resistance comparedto organic pigments, so they should be usedwhenever possible. Extender pigments alsocan be used in FEVE resin-based formulationsfor the adjustment of the gloss level of the coating. Talc, nepheline syenite, calcium carbonate,barium sulfate, and fumed and precipitated silicas have been used in these formulations forgloss adjustment and for reduction in VOCcontent.Additive Choices. Several types of additiveshave been used in FEVE resin-based coatings.In pigmented coatings, the use of a pigment dispersant is highly recommended when dispersing dry pigments into the FEVE resin itself.The wetting ability of a typical FEVE resin islimited due to the presence of fluorine atomsin the structure. Also, flow and leveling aidsare sometimes used, depending on the application method and the desired appearance.Depending on the physical properties desiredin the coating, the additive choices will vary.Compatibility with Other Resins. Thedegree of compatibility possessed by all of theFEVE resins is quite high. This informationhas been discovered by extensive blending performed in the generation of a wide variety offormulation types. Both acrylic and polyesterpolyols of varying molecular weights have beenblended with the FEVE resins and tested forcompatibility by observing the clarity of themixture. This level of compatibility is important when specific properties of the coatingmust be improved by the use of non-FEVEresins in the formulation. The reason for addingnon-FEVE polyols to an FEVE formulation isto improve specific physical properties, suchas flexibility and abrasion resistance. Also, thefinal cost of the formulation can be decreasedby the addition of these polyols.Water-Based Coating FormulationsThis section is divided into two parts: formulating with FEVE emulsion resins and formulating with FEVE dispersion resins. The physicalproperties of the FEVE emulsion and the FEVEdispersion resins were presented in a previoussection. This discussion covers the appropriatemethods for creating successful coatings whenthese FEVE resins are in the formulation.Table 2 Percent solids and viscosity offluoroethylene vinyl ether high-molecularweight resin in various solventsSolventXylenet-butyl acetateAcetoneOxsol 100(a)Methyl acetateDimethyl carbonateMethyl ethyl ketoneMethyl n-amyl ketoneMethyl isoamyl ketoneEthyl 3-ethoxypropionatePropylene glycol monomethylether acetateMethyl propyl ketoneMethyl isobutyl ketonen-butyl acetatePropyl Cellosolve(b)Solids,wt%Brookfieldviscosity, 4961939(a) Makhteshim Agan Industries. (b) Dow Chemical CompanyThe FEVE emulsions have similar behaviorswhen compared to many acrylic or vinyl acrylicemulsions. They need assistance from coalescing solvents to form good films. They associatewith associative thickeners for viscosity adjustment of the coating. They can accommodate thepH range that is popular for most water-basedsystems. In summary, they can be treated similarly to the standard emulsions used in coatingstoday (2015). However, they are not shear stable, so they cannot be used as a grindingmedium for the dispersion of pigments.Choice of Coalescing Solvent. The standard coalescing solvents have been tested withthe FEVE emulsions to measure their effectiveness in facilitating film formation. Table 4 provides a list of solvents that can be used for thispurpose.Choice of Isocyanate Cross Linker. One ofthe FEVE emulsions has sufficient hydroxylfunctionality to permit additional cross linkingwith water-dispersible isocyanates. There are awide variety of these types of isocyanates fromwhich to choose for the final formulation. It isimportant to mention that catalysts are not necessary to initiate the hydroxyl-isocyanate reaction in these types of coatings.Choice of Pigments. As with the solventborne FEVE resin-based systems, there are nolimitations when choosing the appropriateTable 3 Percent solids and viscosity offluoroethylene vinyl ether low-molecularweight resin in various solventsSolventSolids,wt%Brookfieldviscosity, ylenet-butyl acetateAcetoneOxsol 100Methyl acetateDimethyl carbonateMethyl ethyl ketoneMethyl n-amyl ketoneMethyl isoamyl ketoneEthyl 3-ethoxypropionatePropylene glycol monomethylether acetateMethyl propyl ketoneMethyl isobutyl ketonen-butyl acetatePropyl CellosolveTable 4 Coalescing solvents for fluoroethylene vinyl ether emulsion (Tg 56 C, or 133 F)Coalescing solventsEthylene glycol monobutyl etherEthylene glycol monobutyl ether acetateDiethylene glycol monobutyl ether acetatePropylene glycol monophenyl etherPropylene glycol monomethyl ether acetateDipropylene glycol monopropyl etherDipropylene glycol monobutyl etherDipropylene glycol dimethyl etherTripropylene glycol monobutyl etherTexanol(a)Water solubility, %Coalescent amount onresin solids, %Infinite1.16.51191955330.91010710101010101010Tg, glass transition temperature. (a) Eastman Chemical CompanyTemperature of film formation C2712323421614201824 F815437731086157686475
Fluoroethylene Vinyl Ether Resins for High-Performance Coatings / 91pigment(s) for these coatings. Also, the samecautions apply when choosing organic pigments, due to the inability of the FEVE resinto absorb UV radiation from sunlight.Choice of Additives. Water-based formulations require a number of different additivetypes to overcome the limitations of this typeof coating technology. This fact is also truefor FEVE emulsion-based finishes. The standard commercial additives available in the market for properties such as pigment stabilization,surface tension reduction, and foam controlwork equally well in FEVE emulsion-basedsystems. Associative thickeners are effectivefor viscosity control; however, the degree ofassociation with FEVE emulsions is somewhatless than with typical acrylic and vinyl acrylicemulsions. Oftentim
©2015 ASM International. This article was published in ASM Handbook, Volume 5B: Protective Organic Coatings and is made available as an electronic reprint with the permission of ASM International. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via