| abstract |
Finely divided water insoluble solid particles free of ionic charges and ranging in size from about 0.01 to several hundred microns or higher, including but not limited to paint pigment particles, are given a generally uniform polymeric encapsulation by admixing such particles in an aqueous reaction medium with a water insoluble monomer polymerizable to form a generally water insoluble polymer free of ionic charges in the presence of a nonionic surface active stabilizing agent, preferably a polyethoxylated alkyl phenol containing at least about eight carbon atoms in the alkyl group thereof and preferably at least about 40-50 ethylene oxide groups per molecule, and polymerization of the monomer is then initiated, usually with heating, with a redox polymerization initiating system which is free of ionic groups and does not decompose to release ionic groups in the reaction medium. Naturally agglomerated particulate materials are effectively dispersed in situ during polymerization, eliminating the necessity for preliminary grinding and/or dispersion treatments. Monomers generally useful for emulsion polymerization and free of ionic groups are effective and reaction conditions are generally the same as employed in emulsion polymerization. The polymerization product is a suspension of generally discrete particles enveloped within a polymeric coating which exhibits remarkable stability against flocculation or settling. White paint pigments, e.g., titanium dioxide, encapsulated in this manner exhibit greatly increased hiding power, while colored pigments exhibit greater brilliance and depth of color in dried paint films, and the film in either case has much improved abrasion or scrub resistance, and much improved stain resistance due to reduced porosity, all compared to equivalent conventional latex paints. |