Process for producing a thermoplastic molding composition comprising: 10% to 40% by weight of at least one graft copolymer A comprising: 50% to 70% by weight, based on A, of a graft base A1 made of an elastomeric, crosslinked acrylate polymer and 30% to 50% by weight, based on A, of a graft shell A2 made of a vinylaromatic monomer and of a polar, copolymerizable, ethylenically unsaturated monomer, in a ratio by weight of 80:20 to 65:35; 50% to 90% by weight of a hard matrix B made of one or more copolymers of styrene, α-methylstyrene, acrylonitrile, methyl methacrylate and/or phenylmaleimide; 0% to 40% by weight of at least one further graft copolymer C which differs from the graft copolymer A and which has an average particle diameter (weight average) in the range from 200 to 800 nm, comprising: 50% to 80% by weight, based on C, of an elastomeric, crosslinked acrylate polymer C1 which differs from A1, 2.5% to 25% by weight, based on C, of a first graft shell C2 made of a vinylaromatic monomer, and 10% to 45% by weight, based on C, of a second graft shell C3 made of a mixture of a vinylaromatic monomer C31 and of a polar, copolymerizable, ethylenically unsaturated monomer C32 in a ratio by weight of C31 to C32 of 90:10 to 60:40; and 0% to 15% by weight of one or more additives D, wherein the sum total of A and B, and optionally C and D, is 100% by weight, and wherein the reaction for production of the graft copolymer A and the reaction for production of the graft copolymer C is conducted in the presence of 0.01 to 4 times the molar amount of sodium carbonate, based on the total molar amount of initiator, especially PPS (potassium peroxodisulfate), used in the production of the graft base and graft shell; and wherein the reaction for production of the graft copolymer A and the reaction for production of the graft copolymer C is conducted in the presence of 0.1% to 1% by weight of an emulsifier, especially an alkali metal alkylsulfonate, based on the amount of the monomers used in each case; and wherein water or an aqueous alkaline solution is added to the reaction mixture for production of the graft copolymer A and the graft copolymer C during the polymerization reaction, during the postpolymerization and/or after the polymerization reaction. 10% to 40% by weight of at least one graft copolymer A comprising: 50% to 70% by weight, based on A, of a graft base A1 made of an elastomeric, crosslinked acrylate polymer and 30% to 50% by weight, based on A, of a graft shell A2 made of a vinylaromatic monomer and of a polar, copolymerizable, ethylenically unsaturated monomer, in a ratio by weight of 80:20 to 65:35; 50% to 70% by weight, based on A, of a graft base A1 made of an elastomeric, crosslinked acrylate polymer and 30% to 50% by weight, based on A, of a graft shell A2 made of a vinylaromatic monomer and of a polar, copolymerizable, ethylenically unsaturated monomer, in a ratio by weight of 80:20 to 65:35; 50% to 90% by weight of a hard matrix B made of one or more copolymers of styrene, α-methylstyrene, acrylonitrile, methyl methacrylate and/or phenylmaleimide; 0% to 40% by weight of at least one further graft copolymer C which differs from the graft copolymer A and which has an average particle diameter (weight average) in the range from 200 to 800 nm, comprising: 50% to 80% by weight, based on C, of an elastomeric, crosslinked acrylate polymer C1 which differs from A1, 2.5% to 25% by weight, based on C, of a first graft shell C2 made of a vinylaromatic monomer, and 10% to 45% by weight, based on C, of a second graft shell C3 made of a mixture of a vinylaromatic monomer C31 and of a polar, copolymerizable, ethylenically unsaturated monomer C32 in a ratio by weight of C31 to C32 of 90:10 to 60:40; and 50% to 80% by weight, based on C, of an elastomeric, crosslinked acrylate polymer C1 which differs from A1, 2.5% to 25% by weight, based on C, of a first graft shell C2 made of a vinylaromatic monomer, and 10% to 45% by weight, based on C, of a second graft shell C3 made of a mixture of a vinylaromatic monomer C31 and of a polar, copolymerizable, ethylenically unsaturated monomer C32 in a ratio by weight of C31 to C32 of 90:10 to 60:40; and 0% to 15% by weight of one or more additives D, wherein the sum total of A and B, and optionally C and D, is 100% by weight, and wherein the reaction for production of the graft copolymer A and the reaction for production of the graft copolymer C is conducted in the presence of 0.01 to 4 times the molar amount of sodium carbonate, based on the total molar amount of initiator, especially PPS (potassium peroxodisulfate), used in the production of the graft base and graft shell; and wherein the reaction for production of the graft copolymer A and the reaction for production of the graft copolymer C is conducted in the presence of 0.1% to 1% by weight of an emulsifier, especially an alkali metal alkylsulfonate, based on the amount of the monomers used in each case; and wherein water or an aqueous alkaline solution is added to the reaction mixture for production of the graft copolymer A and the graft copolymer C during the polymerization reaction, during the postpolymerization and/or after the polymerization reaction.