Process of controlled chemical reaction of a solid filler material surface and additives to produce a surface treated filler material product

A surface treated filler material product comprising

• a) at least one calcium carbonate-containing filler material having
• i) a weight median particle size d50 value in the range from 0.1 μm to 7 μm,
• ii) a top cut (d98)≤15 μm,
• iii) a specific surface area (BET) of from 0.5 to 150 m2/g as measured by the BET nitrogen method, and
• iv) a residual total moisture content of ≤1 wt.-%, based on the total dry weight of the at least one calcium carbonate-containing filler material, and
• b) a treatment layer on the surface of the at least one calcium carbonate-containing filler material comprising (A) at least one mono-substituted succinic anhydride, (B) at least one mono-substituted succinic acid, and (C) optionally salty reaction product(s) of the at least one mono-substituted succinic acid and/or the at least one monosubstituted succinic anhydride,
• wherein the surface treated filler material product comprises the treatment layer in an amount of from 0.1 to 3 wt.-%, based on the total dry weight of the at least one calcium carbonate-containing filler material.