NOVEL COMPOSITE LATEX-PARTICLES FOR USE IN COATINGS

A novel emulsion Polymerization technique is described to produce core -shell latex particles comprising poly(vinyl acetate) cores inside vin yl-acrylic shells. In a variation, acrylic shells can be produced surr ounding poly(vinyl acetate) or vinyl acrylic cores. The latexes can be produced at commercial solids levels, with controlled, monodisperse p article sizes. The coatings formed from such core-shell particles exhi bit the properties expected of the shell polymers. Core monomers are l ess expensive than the shell monomers, resulting in significant saving s in raw material costs. The technique described is an inverted core-s hell process in which the second-stage polymer is engulfed by a previo usly formed first-stage material. In coatings formulations the less ex pensive second stage monomers are more hydrophilic than those used to make the first stage polymer. Nevertheless, an inverted core-shell mor phology can be made thermodynamically stable by appropriate choices of copolymerizable surfactants in the first-stage copolymer and nonionic initiator for the second-stage polymer. The resulting anchoring group s stabilize the desired particle structure.