Abstract: This disclosure describes a process for producing a surface-modified calcium carbonate, the process comprising contacting a calcium carbonate or precursor thereof with at least one amphiphilic copolymer comprising hydrophilic subunits and hydrophobic subunits, in which the hydrophilic subunits derive from at least one ethylenically-unsaturated compound comprising a carboxylic acid group or salt or derivative thereof; the hydrophobic subunits derive from at least one ethylenically-unsaturated compound comprising a hydrophobic group; and the amphiphilic copolymer has a hydrophilic-lipophilic balance ranging from about 1 to about 40. Surface-modified calcium carbonates obtained from the process are also described, as well as compositions containing the surface-modified calcium carbonates.

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.