Patent ID: 9546297
Date: 2017-01-17
CPC Classifications: C01P,C08K,C09C,C09D

Claim:
1. A method of preparing an aqueous dispersion of opacifying polymer particles containing inorganic pigment particles, the method comprising: i) dispersing an inorganic pigment in an aqueous medium in the presence of an anionic polymer dispersant of a weight average molecular weight (Mw) of at least 1000 Daltons, wherein the dispersant comprises acid moieties that are at least one of carboxyl, sulphur acid, or phosphorus acid functional moieties, and wherein the acid value of said anionic polymer dispersant is from 65 to 400 mg KOH/g non-volatile (non-vol.) dispersant, and wherein the pH during dispersion is greater than the pKa of the acid moieties and at least 0.25 pH units above or below the iso-electric point of the pigment particles, to form a stable aqueous dispersion of the pigment in the aqueous medium; ii) adjusting the pH of the stable aqueous dispersion to below the pKa of the acid moieties of a base swellable polymer while satisfying the pH criteria of i); iii) optionally polymerizing monomers to form first intermediate polymer layer having an acid value between 0 and 65 mg KOH/g polymer on the pigment; iv) forming a first layer of the base swellable polymer on the pigment particles or, if present, the first intermediate polymer layer, by polymerizing monomers comprising acid moieties; v) optionally polymerizing monomers to form a second intermediate polymer layer having an acid value between 0 and 65 mg KOH/g polymer on the first layer; vi) forming a second layer of a non-base swellable polymer on the first layer or, if present, the second intermediate polymer layer; vii) at least partially neutralizing the base-swellable-polymer, using a base, at a temperature above the Tg viii) cooling the dispersion of opacifying polymer particles to a temperature below the Tg wherein the polymerizations are free of RAFT agents.