Method for producing a thermoplastic moulding compound containing: up to 40 wt.% of a graft copolymer A, containing 50-70 wt.% graft base A1 from an acrylic ester polymer and 30-50 wt.% of a graft shell A2, and 0-90 wt.% of a hard matrix B, wherein the reaction for producing the graft copolymer A is carried out in the presence of 0.01 to 4 times the molar amount of sodium carbonate, relative to the molar amount of initiator, wherein the reaction for producing copolymer A is carried out in the presence of 0.1 to 1 wt.% of an emulsifier relative to the amount of the respective monomers used, and wherein during the polymerisation reaction, during the post-polymerisation and/or after the polymerisation reaction, water or an aqueous alkali solution are added to the reaction mixture for producing the graft copolymer A.