Process for producing anti-blocking compositions

Abstract

There is disclosed a process for preparing a filler composition suitable for incorporation in a polyester film-forming material, which process comprises the following steps: (a) calcining a crude kaolin clay under conditions such that the calcined product comprises particles consisting of aggregates of fine kaolin platelets; (b) suspending the calcined clay product from step (a) in water containing a dispersing agent for the calcined clay, so as to form a suspension containing from 40% to 70% by weight of dry calcined clay; (c) subjecting the suspension formed in step (b) to comminution by attrition grinding with a particulate grinding medium for a time sufficient to reduce the average diameter of the aggregate particles to within the range from 0.3 .mu.m to 0.9 .mu.m, and to ensure that the calcined clay is substantially free of particles having an equivalent spherical diameter larger than 5 .mu.m; and (d) heating the suspension of comminuted calcined clay formed in step (c) to a temperature in the range from 80.degree. C. to 100.degree. C. to drive off water by evaporation, a liquid glycol being added at the same time as the water is driven off to keep the volume of the suspension substantially constant. The process produces a product which has good anti-blocking characteristics, making it useful for incorporation in organic polymer film materials.