US RE38,301 E1 · Paper coating pigments, their production and use

Abstract

There is disclosed a method for the preparation of a precipitated calcium carbonate (PCC) for use as a pigment in paper coating compositions, the method comprising the steps of (a) carbonating an aqueous lime-containing medium to produce an aqueous suspension of a PCC predominantly in a selected crystal form, (b) at least partially dewatering the PCC-containing suspension; and (c) subjecting the PCC-containing suspension to comminution by high shear attrition grinding with an attrition grinding medium. Steps (b) and (c) may be applied in either order, ie. (b) followed by (c) or alternatively (c) followed by (b). The dewatering step (b) is preferably carried out using a pressure filter device operating at a pressure of at least 5 MPa, preferably at least 10 MPa. A pH reduction step may be applied after steps (b) and (c). Also disclosed are pigments produced by the method and pigment and paper coating compositions including such pigments.

Claims39

Dependent claims

A method for the preparation of a precipitated calcium carbonate (PCC) for use as a pigment in paper coating compositions, the method comprising the steps of (a) carbonating an aqueous lime-containing medium to produce an aqueous suspension containing a PCC in predominantly scalenohedral, rhombohedral, or aragonite crystal form, (b) at least partially dewatering the PCC-containing suspension;

and (c) subjecting the PCC-containing suspension in wet form to comminution by high shear attrition grinding with an attrition grinding mediums medium wherein the comminution step is carried out such as to dissipate in the aqueous suspension containing the PCC at least 100 kilowatt hours of energy per dry tonne of PCC and wherein the PCC product produced following steps (b) and (c) comprises particles having a particle size distribution such that at least 70% be by weight of the particles have an equivalent spherical diameter as measured by sedimentation of less than 1 μm and at least 50% by weight of the particles have an equivalent spherical diameter of less than 0.5 μm.

Dependencies are inferred from the claim text.

Paper coating pigments, their production and use

Life of this patent

Paper coating pigments, their production and use

Life of this patent

Abstract

Claims39