Process for grinding minerals in aqueous dispersion using a dispersing agent comprising homopolymers and/or copolymers of (meth)acrylic acid

A process for producing a dispersion of mineral materials suitable for use as pigments, comprising the steps of:

• (A) preparing a mixture comprising water and a mineral be ground, comprising particles and said mixture having at least 75% solids content by weight, based on the total weight of the mixture;
• (B) introducing a fully neutralized dispersing agent into the mixture, in an amount of from 0.1% to 0.5% by weight, based on the dry weight of the mineral present in the mixture;
• (C) grinding the mixture to produce an aqueous dispersion;
• (D) introducing into said dispersion, during grinding, at least two portions of a partially neutralized dispersing agent, which has been at least 30% neutralized, based on equivalents of acid groups, wherein the total of said portions is from 0.2% to 1.0% by weight, based on the dry weight of the mineral present in the mixture, wherein said at least two portions of said introducing step comprise a plurality of portions, a first group of which comprises two separately introduced portions which total 0.3% by weight of the partially neutralized dispersing agent and a second group of which comprises four separately introduced portions which total 0.5% by weight of partially neutralized dispersing agent, based on the dry weight of the mineral present in the mixture;
• and
• (E) continuing grinding said dispersion until 95% or more of the mineral particles have a minimum dimension below 2 microns.