A process for preparing a surface treated filler material product with succinic anhydride(s), the process comprising at least the steps of: a) providing at least one calcium carbonate-containing filler material having i) a weight median particle size d 50 value in the range from 0.1 μm to 7 μm, ii) a top cut ( d 98) of ≤ 15 μm, iii) a specific surface area of from 0.5 to 150 m 2 /g as measured by the BET nitrogen method, and iv) a residual total moisture content of from 0.01 wt.-% to 1 wt.-%, based on the total dry weight of the at least one calcium carbonate-containing filler material, b) providing at least one mono-substituted succinic anhydride and optionally at least one mono-substituted succinic acid 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 of step a), c) contacting the surface of the at least one calcium carbonate-containing filler material of step a) under mixing, in one or more steps, with the at least one mono-substituted succinic anhydride and the optional at least one mono-substituted succinic acid of step b) such that a treatment layer comprising the at least one mono-substituted succinic anhydride and the optional at least one mono-substituted succinic acid and/or salty reaction product(s) thereof is formed on the surface of said at least one calcium carbonate-containing filler material of step a), wherein the temperature before and/or during contacting step c) is adjusted such that the temperature is at least 2°C above the melting point of the at least one mono-substituted succinic anhydride and the optional at least one mono-substituted succinic acid. a) providing at least one calcium carbonate-containing filler material having i) a weight median particle size d 50 value in the range from 0.1 μm to 7 μm, ii) a top cut ( d 98) of ≤ 15 μm, iii) a specific surface area of from 0.5 to 150 m 2 /g as measured by the BET nitrogen method, and iv) a residual total moisture content of from 0.01 wt.-% to 1 wt.-%, based on the total dry weight of the at least one calcium carbonate-containing filler material, i) a weight median particle size d 50 value in the range from 0.1 μm to 7 μm, ii) a top cut ( d 98) of ≤ 15 μm, iii) a specific surface area of from 0.5 to 150 m 2 /g as measured by the BET nitrogen method, and iv) a residual total moisture content of from 0.01 wt.-% to 1 wt.-%, based on the total dry weight of the at least one calcium carbonate-containing filler material, b) providing at least one mono-substituted succinic anhydride and optionally at least one mono-substituted succinic acid 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 of step a), c) contacting the surface of the at least one calcium carbonate-containing filler material of step a) under mixing, in one or more steps, with the at least one mono-substituted succinic anhydride and the optional at least one mono-substituted succinic acid of step b) such that a treatment layer comprising the at least one mono-substituted succinic anhydride and the optional at least one mono-substituted succinic acid and/or salty reaction product(s) thereof is formed on the surface of said at least one calcium carbonate-containing filler material of step a),