Patent ID: 7094830

Claim:
A process for preparing an aqueous dispersion of particles, said particles comprising at least one addition polymer and at least one finely divided inorganic solid, said process comprising dispersing at least one ethylenically unsaturated monomer in an aqueous medium and polymerizing the monomer by free-radical aqueous emulsion polymerization with at least one free-radical polymerization initiator in the presence of at least one dispersely distributed, finely divided inorganic solid and at least one of each of an anionic, cationic and nonionic dispersant, wherein a) the at least one finely divided inorganic solid is present as a stable aqueous dispersion that when prepared at an original solids concentration of ≧1% by weight, based on the aqueous dispersion of said at least one finely divided inorganic solid, the dispersion contains in dispersed form one hour after preparation more than 90% by weight of the originally dispersed finely divided inorganic solid and the dispersed finely divided inorganic solid particles have a diameter ≦100 nm, and b) the dispersed particles of said at least one inorganic solid exhibit a nonzero electrophoretic mobility in an aqueous standard potassium chloride solution at a pH which corresponds to the pH of the aqueous reaction medium before the addition of the anionic, cationic or nonionic dispersants, said process further comprising c) adding at least one of each of an anionic, cationic and nonionic dispersant to the aqueous dispersion of the finely divided inorganic solid before beginning dispersing said at least one ethylenically unsaturated monomer therein, d) then adding from 0.01 to 30% by weight of the total amount of said at least one monomer to the aqueous dispersion and polymerizing to a conversion of at least 90%, and e) thereafter adding the remainder of said at least one monomer under polymerization conditions at the rate at which it is consumed.