Treatment of calcium carbonate containing materials for increased filler load in paper

A self-binding pigment particle suspension obtained by the process comprising the following steps:

• a) providing an aqueous suspension comprising at least one calcium carbonate containing material,
• b) providing at least one acid or acid salt in an amount from 0.001 to 40 wt.-% based on the total weight of the dry calcium carbonate containing material, wherein the anion of the acid or acid salt is capable of forming water-insoluble calcium salts, and wherein the at least one acid or acid salt of step b) is selected from the group consisting of citric acid, oxalic acid, phosphoric acid, arsenic acid, iodic acid, acid salts thereof, and any mixture thereof,
• c) providing an anionic polymeric binder in an amount from 0.001 to 20 wt.-% based on the total weight of the dry calcium carbonate containing material, wherein the binder comprises at least one modified polysaccharide,
• d) providing at least one cationic polymer in an amount from 0.001 to 20 wt.-% based on the total weight of the dry calcium carbonate containing material,
• e) mixing the aqueous suspension of step a) with the at least one acid or acid salt of step b) to obtain a suspension of calcium carbonate containing material that is at least partially coated with a water-insoluble calcium salt formed from the anion of the acid or the acid salt, and
• f) mixing the suspension of step e), the anionic polymeric binder of step c) and the at least one cationic polymer of step d) to obtain an aqueous suspension of self-binding pigment particles, wherein the self-binding pigment particles so obtained comprise calcium carbonate containing material which is at least partially coated with a water-insoluble calcium salt formed from the anion of the acid or acid salt, the anionic binder comprising the at least one modified polysaccharide, and the at least one cationic polymer.