Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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Page 75 of 331

coating materials LOW-VOC WATERBORNE COATINGS BY RON JOSEPH (1944 - 2011) RON JOSEPH & ASSOCIATES INC., SAN JOSE, CALIF. This article focuses on a comprehensive range of waterborne coating technolo- gies, which include water-reducible, dispersion, and latex formulations. Advan- tages and disadvantages of each of the resin systems are listed to serve as a guide to assist in the selection of a VOC-compliant coating. Metal fabricators and coating users located in areas that are considered to be in nonattainment with the ozone standard have already addressed the prob- lems of selecting VOC compliant coatings. However, the New Clean Air Act amendments of 1990 have more clearly defined when an area is in attainment with the standard. In fact, the implementation of VOC regulations for surface coat- ings will depend on whether an area has been designated extreme (only Los An- geles-Anaheim-Riverside), severe, serious, moderate, or marginal. Consequently, thousands of fabricators and other coating users who have not previously been affected by the VOC regulations, will soon be searching for low-VOC coatings. The predominant question people will need to resolve is whether to convert to low- VOC, solvent-based coatings or waterborne coating systems. Numerous papers have been published extolling both types of systems. Indeed, since the mid 1980s, high-quality compliant coatings have been available to meet even the stringent requirements of California and other state rules. This paper is devoted solely to compliant waterborne coatings, which are ap- plied by dip, flow, or one of the many types of spray equipment commonly used in coating facilities. The paper does not claim that waterborne coatings are bet- ter than their solvent-based cousins, or vice versa. On the contrary, both types of systems should be carefully considered before making the final selection. Before discussing the various waterborne resin systems, it must be pointed out that most VOC regulations limit the VOC content of a coating in terms of pounds per gallon or grams per liter, less water, and less exempt solvent. Exempt solvent-containing coatings are not discussed in this paper; therefore, only the less-water terminology will be explained. One gallon of a waterborne coating (water reducible, water dispersible, or la- tex) contains many ingredients, specifically, the resin or binder pigments, ex- tender pigments, coalescing agents, a small quantity of co-solvents, and usual- ly a fairly substantial amount of water. The volatile portion of the coating com- prises the co-solvents and water. In a one-gallon can, the co-solvents, which are considered to be the VOCs, may account for less than 1.0 lb. In other words, the VOC content of the coating may only be 1.0 lb/gal. The VOC regulations, how- ever, require that the VOC content of the coating be calculated as if no water were in the coating. Depending on the coating formulation, the VOC content, less wa- ter, may be considerably higher, such as 2.0 lb/gal or more. In this section all references to VOC content automatically assume the less-wa- ter values; therefore, when it is stated that a coating technology is commercial- ly available with a VOC content of, say, 2.3 lb/gal, it can be assumed that implies less water. For those who are not familiar with the EPA's differentiation between air- or force-dried coatings and those that cure by baking, a few words of clarification 74

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