Patent ID: 8304485

Claim:
A process for forming an opacifying pigment encapsulated in polymer comprising: (a) dispersing a pigment particle having an average particle diameter of from 150 to 500 nm and an index of refraction of at least 1.8 in a medium with from 0.1% to 10% by weight, based on the weight of said pigment particle, a first polymer, wherein the zeta potential of said dispersed pigment particle is less than −28 mV between pH 5 and pH 8; and (b) performing an emulsion polymerization in the presence of said dispersed pigment particle to provide from 10% to 200%, by weight, based on the weight of the pigment particle, of a second polymer that at least partially encapsulates said dispersed pigment particle, wherein the first polymer consists essentially of at least three sulfur acid moieties or a salt thereof and at least one other moiety selected from the group consisting of an amine functional monomer; styrene; vinyl toluene; vinyl acetate; vinyl versatate; acrylonitrile; (meth)acrylamide; C 1 -C 40 esters of (meth)acrylic acid; alcohol containing monomers; and ethylenically unsaturated mono-, di- and trialkyl esters of ethylenically unsaturated carboxylic acids and anhydrides and wherein the molecular weight of the first polymer is controlled by a chain transfer reagent consisting of an alkyl mercaptan or an alcohol or a halogenated compound.