A METHOD OF MAKING OPACIFYING POLYMER PARTICLES

摘要

A method of preparing an aqueous dispersion of opacifying polymer particles containing inorganic pigment particles therein comprising or consisting of the steps of: i.dispersing inorganic pigment in aqueous medium using a dispersant of acid value at least 65mg KOH/g of dispersant,the dispersant comprising acid moieties and the p H during dispersion is greater than the pKa of the acid moieties and also at least 0.25 pH units above or below the iso-electric point of the pigmentparticles, to form a stable aqueous dispersion of the pigment in the aqueous medium ii.adjusting the pH of the pigment dispersion to below the pKa of the acid moietiescomprising the base swellable polymer of step iii. whilst satisfying the pH criteria of step i. iii. forming a first layer of a base swellable polymer on the pigment particles by polymerising monomers comprising acid moieties iv. forming a second layer of non-base swellable polymer v.optionally polymerisingfurther monomers to form intermediate polymer layers having acid valuebetween 0 and 65mg KOH/g polymer between the pigment and the first layer and/or between the first and second layer vi. at least partially neutralisingthe base-swellable-polymer, using a base, at a temperature above the effective Tg of the non-base-swellablepolymer whereby the base-swellablepolymer is caused to swell vii.and cooling the dispersion of opacifying polymer particles to a temperature below the effective Tg of the non-base-swellable polymer.