Waterborne paints

PVC plastisols, i.e., poly(vinyl chloride) dispersed in plasticizers, are used in special applications such as underseals for automobiles or as sealing compositions. 

Waterborne (water-thinnable) paints were developed in the 1950s with the aim of replacing the common organic paint solvents by water, which has the obvious advantages of being noncombustible and nontoxic [3.39]. 

Waterborne paints provided the technological basis for electrodeposition paints (Section 3.8), in which negatively charged paint particles (anaphoresis, industrial introduction at the beginning of the 1960s), or positively charged paint particles (cataphoresis, industrial introduction at the end of the 1970s) are deposited from aqueous solution onto metallic substrates by application of an electrical field [3.40]. 

20 C and in millinewtons per meter) of water and other substances follow  

The high polarity of water is responsible not only for differences between the application behavior of waterborne paints and solvent-containing paints. It also means that the organic polymers used as binders for waterborne paints must have a different structure from those used in solventborne paints. 

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Prior to the 1990s phenyhnercuric acetate was the primary bactericide and fungicide in latex and waterborne paints. Because of the increasing concerns of mercury toxicity and the potential for high consumer and occupational exposures to mercury when present in paints, the U.S. Environmental Protection Agency (EPA) induced U.S. manufacturers of PMA and other mercury compounds to withdraw their registrations for use of these substances as biocides in paints (see AIercury). Mercury compounds are used only for very limited, specific purposes, such as the use of phenyhnercuric mXx.2LX.e[55-68-5] as a bactericide in cosmetic eye preparations (see Cosmetics). 

The coatings industry has developed waterborne paints and coatings that greatly reduce VOC emissions. Some applications include automotive coatings, interior latex paints, and polyurethane coatings (Sherman et al., 1998). 

Case studies illustrate that waterborne paints are indeed feasible for many applications ... 

Waterborne paints can reduce the amount of solvent used in vehicle painting from 42.4 to 7.3 kg (Clancy, 1994). 

Novel coating additives are also being studied as a way to ameliorate the disadvantages that have become synonymous with waterborne paints ... 

Possible combinations of red lead with various binder systems are listed in Table 39 [5.114]. Red lead is still used for heavy-duty anticorrosion applications, especially for surfaces bearing residual traces of rust. In waterborne paints, red lead has no advantages over zinc phosphate [5.149]. 

Clausen, P.A. (1993) Emission of volatile and semivolatile organic compounds from waterborne paints-the effed of the film thickness. Indoor Air, 3, 269-75. 

Hansen, M.K., Larsen, M. and Cohr, K.H. (1987) Waterborne paints. A review of their chemistry and toxicology and the results of determinations made during their use. Scandanavian Journal of Work and Environmental Health, 13, 473-85. 

Waterborne paints are usually emulsions of polymer-based binder particles. They are made by making an emulsion of droplets of monomers in water, after which the monomers are polymerized to form solid particles. When applied, the water and possibly other solvents evaporate, and the binder particles fuse to form a solid layer. 

Emulsions are dispersions of one fluid into another. Both oil-in-water and water-in-oil emulsions are encountered. Foams are similar to emulsions, but the dispersed phase is a gas. Emulsions are everywhere some examples of products that are based on emulsions are salad dressings, mayonnaise, egg yolk, milk, margarine, cream, ice cream, waterborne paints and bitumen. Emulsions are generally not stable, so they need to be stabilized against coalescence. One can use surfactants for that, or polymers, such as proteins and polysaccharides, or particles. 

Most household maintenance products contain mixtures of lipophiles and hydrophiles that can produce unanticipated toxic effects. Irritant-induced asthma is an example of such an effect. Solvent-based and waterborne paints contain solvents that are nonsensitizing irritants that are individually not known to induce asthma. Despite this, exposures to both types of paints have been shown to cause the asthma-like condition reactive airways dysfunction syndrome (RADS).I13 14 RADS is discussed in detail in Chapterl8. 

Exposure to waterborne paints is known to induce acute and chronic dermal, respiratory, and CNS effects. 11 All the chemicals listed in Table 12.4 are individually toxic 13 anc[ mixtures of many of these are known to induce unanticipated toxic effects in humans. 14 ... 

Table 12.4 Volatile Components Contained in Waterborne Paints...

Specific teratogens were not identified, but as previously discussed in Sections 12.5 and 13.5, both waterborne paints and oil-based paints contain mixtures of lipophilic and hydrophilic species. Exposures to both types of paints have been associated with low level unexpected effects. Accordingly, the teratogenic results reported in the Dutch study are not surprising. 

Clausen P.A., Wolkoff P. and Nielsen P.A. (1990) Long term emissions of volatile organic compounds from waterborne paints in environmental chambers. Proceedings of Indoor Air 93, Helsinki, Finland, Vol. 3, 557-562. 

Degussa Technical Information - Pigment Blacks in Waterborne Paint (TI 1227). 

Neutralizing agents are used in waterborne paints to neutralize binders and stabilize the product. Ammonia and various alkylated aminoalcohols are used, depending on the type of binder and method of application. On hardening, the amines mainly evaporate along with the water. 

Corrosion inhibitors are used to prevent the formation of corrosion products when waterborne paints are applied to metallic substrates (flash rust). They include oxidiz-... 

Thus, numerous low-emission paints have been developed, including high-solids paints, waterborne paints, aqueous dispersions for industrial use, powder coatings, and radiation-curing coatings. At the forefront in adopting these environmentally friendly products is heavy industry, in particular the automobile and household appliance industries. Medium-sized and smaller businesses will profit from this experience, adapting it for their own needs. 

The increasing importance of environmental considerations places new requirements on paint resins and has broadened the range of paint systems. Paints are now required that have a low solvent content (medium-solids, high-solids coatings) or are solvent-free (powder coatings), that can be adjusted by dilution with water (waterborne paints), and that are thermoplastic or capable of undergoing cross-linking. All of these properties must be obtained via the polymer structure of the binders. Important parameters are described below. 

COOH HOOC xAr COOH branched, low molecular mass, carboxy-functional 1000- 5000 triglycidylisocya-nurate, epoxy resins, melamine resins powder coatings, waterborne paints... 

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