Kurt A. Wood

Acrylic-fluoropolymer mixtures and their use in coatings

Fluoropolymer coatings, particularly those based on polyvinylidene fluoride (PVDF) resins, have a 35 year history of outstanding performance in outdoor applications. However, the chemical inertness of PVDF presents challenges to the paint formulator in that it prevents adhesion to substrates and makes it difficult to disperse pigments. To overcome these difficulties, an acrylic modifier resin is usually added to the PVDF resin. The acrylic modifier is traditionally physically blended with the PVDF resin to improve coating adhesion and enhance pigment dispersion. The physical blending results in a PVDF/acrylic mixture on a macro-molecular scale. ATOFINA Chemicals, Inc. has developed a novel approach to mix the fluoropolymer and acrylic on micro-molecular scale. Because of this intimate mixing, and the wide latitude of the acrylic and fluoropolymer monomers that can be utilized, a wide range of unique properties can be achieved in solvent-base dispersion coatings, and water-borne coatings. The unique properties of the solvent-base and water-borne coatings are discussed in this paper.

Predicting the exterior durability of new fluoropolymer coatings

Abstract Commercial coatings based on polyvinylidene fluoride (PVDF)/acrylic blends typically show minimal gloss loss or bulk chemical change even after many months of Florida or accelerated weathering testing. Because of this excellent weathering, better short term tests are needed to predict long term weatherability. We have recently found dramatic differences in the steady state weight loss rate for different fluoropolymer/acrylic coatings in a ‘QUV-B’ unit. For clear coats, steady state weight loss rates can be measured long before the coatings begin to lose gloss. Studies are now underway to understand the microscopic basis for these differences. For new fluoropolymer/acrylic blend compositions, the weight loss rate can be used as an early predictor of the blend’s weatherability.

Optimizing the exterior durability of new fluoropolymer coatings

The most demanding exterior paint applications typically require not only the coating gloss and color are maintained for 10 years or longer, but also the barrier properties are maintained during the same period. Service life prediction (SLP) theory looks at the microscopic antecedents of the failure modes which ultimately limit the service life of coatings. SLP theory can be used to help identify key material requirements for the coating, such as the photochemical stability of the paint binder, or its ability to maintain specific-tensile properties during outdoor exposure. New latex materials based on poly(vinylidene fluoride) copolymers offer the possibility of achieving these demanding performance requirements in air-dry paints, suitable as topcoats for architectural coatings on various substrates, and in industrial maintenance applications.

Patterns of erosion from acrylic and fluoropolymer coatings in accelerated and natural weathering tests

Commercial poly (vinylidene difluoride) (PVDF)/acrylic coatings show minimal gloss loss or bulk chemical change even after sustained Florida or accelerated weathering testing. Previously, we showed that “QUV-B” weight loss rates can be used as an early predictor of the weatherability of fluoropolymer/acrylic blend clearcoats. In this work, we study the microscopic basis for differences seen between various blends and pure acrylic coatings. Scanning electron microscopy (SEM) images reveal different characteristic patterns of degradation.

How Can We Effectively Use Accelerated Methods to Predict the Decorative Properties of PVDF-Based Coatings?: A Practical Approach

Poly(vinylidene fluoride) (PVDF) resins are the dominant component of some of the most weatherable commercially available decorative coatings. These coatings can have color retention and chalk resistance service lifetimes of decades. We have recently outlined a quantitative service life prediction model for the decorative properties of coatings of this type (Wood K (2009) A quantitative model for the prediction of gloss retention, color change, and chalking for poly(vinylidene fluoride)/acrylic blends. In: Proceedings of 4th European weathering symposium, Budapest, Hungary, Sept 2009). The model is based on the “contraction” theory of gloss loss and chalking, coupled with simple assumptions about the photochemical kinetics of two-resin hybrid systems where one resin (PVDF) is much more weatherable than the other (in this case, an acrylic). Because different mechanisms account for gloss loss, color change, and chalking, the relative rates of change for each of these properties can be different, in accordance with experimental observations. We outline a methodology that uses insights from the model, empirical data from accelerated tests, and long-term weathering test data from solvent-based baked PVDF coatings, to predict the service life of new waterborne no-bake PVDF coatings.

New Tools for Service Life Prediction and Risk Minimization for Exterior Building Product Finishes

This chapter considers two specific newer tools that can be useful in predicting the decorative service life of coatings. One tool is the newer accelerated weathering cycle, ASTM D7869-13. This xenon arc–based cycle with enhanced time-of-wetness was validated for automotive and aerospace coatings, but its relevance for premium architectural finishes has not yet been evaluated. The second tool is a simple data analysis method in which the evolution of the individual components of the coating color during a weathering experiment, relative to one another, can be used as a proxy measure of the relative rates of the underlying weathering processes. Individual color components may also be compared with the coating gloss in a similar fashion. This tool can be useful to compare different accelerated and natural weathering test cycles, to assess the degree to which the weathering test conditions affect the dynamics or “chemical balance” of the system during weathering. It may be particularly discriminating for coatings where several types of pigments are used, or where several important photodegradation mechanisms are operative.

Evaluation of the ASTM D7869-13 test method to predict the gloss and color retention of premium architectural finishes-I

A recently developed xenon arc-based accelerated weathering cycle, ASTM D7869-13, has been validated for automotive and aerospace coatings, but its ability to predict the gloss and color retention of premium architectural finishes has not yet been evaluated. We review new weathering data comparing the performance of poly(vinylidene fluoride) (PVDF) architectural finishes in south Florida exposure as well as several accelerated exposure methods including ASTM D7869-13. ASTM D7869 accurately reproduced Florida rank order gloss and color retention trends for coatings made with PVDF-acrylic blends and inorganic pigments, as well as the gloss and color changes seen in Florida for 70% PVDF masstone coatings made with a number of single organic pigments. However, the D7869 cycle has difficulty predicting the rank order of rutile TiO2 grades for the gloss retention of PVDF coatings in Florida, as well as the magnitude and direction of color fade from organic pigment degradation in organic pigment/inorganic pigment blends. One open question that remains is whether the ASTM D7869 cycle might have some utility for industry standard or specification purposes, if the test is limited to specific reference colors or more ideally to specific reference pigments.

Chapter 6:Commercial Synthesis and Applications of Poly(Vinylidene Fluoride)

Poly(vinylidene fluoride) (PVDF) was first introduced commercially in the 1960s for architectural coatings, followed shortly thereafter by additional grades for industrial applications with continued technology developments to service demand in other application areas. PVDF homopolymers and copolymers are synthesized commercially as stable aqueous latexes, or using suspension processes in which larger particle sizes are produced. Nearly all grades are melt and solution processable and are relatively low-cost fluoropolymers with excellent weatherability and resistance to chemical attack. They find application where excellent physical properties, coupled with ease of processability, are of critical importance. They are particularly useful in formulations for highly weatherable coatings, or processed for high-purity piping, porous membranes, binders for lithium ion batteries and photovoltaics, among others. PVDF, by volume, is the second-highest produced fluoropolymer worldwide, with the majority of demand from the USA, Europe, China and Japan. It continues to experience good market growth, and is projected to exceed a 5% volume increase per year for the foreseeable future.