Process for the preparation of a mineral filler product

A process for the preparation of a mineral filler product, the process comprising the steps of:

• a) providing a calcium carbonate-containing material;
• b) providing water;
• c) providing at least one grinding agent;
• d) wet grinding the calcium carbonate-containing material in a mixture obtained by contacting:
• i) the calcium carbonate-containing material provided in step a), with
• ii) the water provided in step b), and with
• iii) the at least one grinding agent provided in step c) in any order in at least one grinding unit to obtain a wet ground mineral filler;
• e) optionally classifying the wet ground mineral filler of step d) to obtain a coarse fraction and a fine fraction, wherein the coarse fraction is removed or subjected to wet grinding step d) and the fine fraction represents a fine mineral filler;
• f) drying the wet ground mineral filler of step d) and/or the fine mineral filler of step e) to obtain a dried mineral filler having a total moisture content of less than or equal to 1.0 wt.-%, based on the total weight of said dried mineral filler;
• and
• g) treating the dried mineral filler of step f) with a hydrophobizing agent to obtain a surface-treated product having a treatment layer on at least part of the surface of said product;
• wherein the total moisture content in the mixture of step d) ranges from 15.0 to 50.0 wt.-%, based on the total weight of said mixture;
• the amount of the at least one grinding agent provided in step c) ranges from 0.01 to 10.0 wt.-%, based on the total dry weight of the calcium carbonate-containing material;
• the temperature in step d) ranges from 60° C. to 150° C.;
• and
• the at least one grinding agent is selected from the group consisting of styrene-maleic anhydride co-polymers and derivatives of styrene-maleic anhydride co-polymers, said derivatives being selected from styrene-maleic anhydride co-polymers having partially or fully hydrolyzed maleic anhydride units, wherein said grinding agent has a monomer unit ratio (styrene units:maleic anhydride units, S:MA) of from 1:2 to 5:1 and a molecular weight MW of from 500 to 40,000 g/mol.