Foam in Waterborne Latex Paints and Varnishes

Control of Foam in Waterborne Latex Paints and Varnishes 

The industrial reaction to this situation is one of compliance, with an increasing use of waterborne paint formulations based on the use of synthetic latices as binders especially in paints for domestic application. Such latices are usually polymeric colloids, of volume fraction from 0.2 to 0.5, dispersed in aqueous surfactant solution, prepared by a process of emulsion polymerization. These dispersions have a slightly turbid appearance, often with a low viscosity of order 1 mPa s. The latices can be readily prepared as near-monodisperse colloids. 

FIGURE 9.1 Schematic illustration of model of emulsion polymerization by Harkins. 

FIGURE 9.2 Scanning electron micrograph of acidic styrene-acrylate block copolymer latex dispersed in aqueous 0.03 M aerosol OT solution. (Reprinted from Colloids Surf. A, 283, Garrett, P.R., Wicks, S.P., Fowles, E., 307. Copyright 2006, with permission from Elsevier.) 

Initial partial fusion of upper layer of latex a 

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In this chapter, we consider the foam and antifoam behavior of waterborne latex paints and varnishes, particularly with respect to the role of the latex polymer in this context. Oil-hydrophobed particle-based antifoams are often used in paints and varnishes. We briefly consider the difficulties associated with their incorporation in these products. However, even though they are introduced to eliminate the coating defects associated with foam bubbles, they are often the cause of other defects. The latter represents a key aspect of the application of antifoams in this context and therefore we consider the causes of such defects in some detail. 

It is clear that control of foam in the case of waterborne latex paints and varnishes is easily achieved nsing the well-known concepts realized in mixtures of hydrophobic oils and hydrophobic particles. Occasional references in the relevant patent and scientific literature to the oil component as a mere carrier does, however, suggest a failure to embrace modem nnderstanding abont the mode of action of such antifoams [18,24,25, 51]. This is snrprising since that nnderstanding is based on experimental evidence, carefully garnered over more than a qnarter of a century and published in respected, peer reviewed, scientific jonmals. 

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