© 2006 by Taylor & Francis Group, LLC
© 2006 by Taylor & Francis Group, LLC
© 2006 by Taylor & Francis Group, LLC
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3<br />
Waterborne Coatings<br />
Most of the important types of modern solvent-borne coatings — epoxies, alkyds,<br />
acrylics — are also available in waterborne formulations. In recent years, even<br />
urethane polymer technology has been adapted for use in waterborne coatings [1].<br />
However, waterborne paints are not simply solvent-borne paints in which the organic<br />
solvent has been replaced with water; the paint chemist must design an entirely new<br />
system from the ground up. In this chapter, we discuss how waterborne paints differ<br />
from their solvent-borne counterparts.<br />
Waterborne paints are <strong>by</strong> nature more complex and more difficult to formulate<br />
than solvent-borne coatings. The extremely small group of polymers that are soluble<br />
in water does not, with a few exceptions, include any that can be usefully used in<br />
paint. In broad terms, a one-component, solvent-borne coating consists of a polymer<br />
dissolved in a suitable solvent. Film formation consists of merely applying the film<br />
and waiting for the solvent to evaporate. In a waterborne latex coating, the polymer<br />
particles are not at all dissolved; instead they exist as solid polymer particles dispersed<br />
in the water. Film formation is more complex when wetting, thermodynamics,<br />
and surface energy theory come into play. Among other challenges, the waterborne<br />
paint chemist must:<br />
• Design a polymer reaction to take place in water so that monomer building<br />
blocks polymerize into solid polymer particles<br />
• Find additives that can keep the solid polymer particles in a stable, even<br />
dispersion, rather than in clumps at the bottom of the paint can<br />
• Find more additives that can somewhat soften the outer part of the solid<br />
particles, so that they flatten easier during film formation.<br />
And all of this was just for the binder. Additional specialized additives are<br />
needed, for example, to keep the pigment from clumping; these are usually<br />
different for dispersion in a polar liquid, such as water, than in a nonpolar organic<br />
solvent. The same can be said for the chemicals added to make the pigments<br />
integrate well with the binder, so that gaps do not occur between binder and<br />
pigment particles. And, of course, more additives unique to waterborne formulations<br />
may be used to prevent flash rusting of the steel before the water has<br />
evaporated. (It should perhaps be noted that the need for flash rusting additives<br />
is somewhat questionable.)<br />
<strong>©</strong> <strong>2006</strong> <strong>by</strong> <strong>Taylor</strong> & <strong>Francis</strong> <strong>Group</strong>, <strong>LLC</strong><br />
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