A process for producing a thermoplastic molding composition comprising: 10% to 40% by weight of a graft copolymer A comprising 50% to 70% by weight, based on A, of a graft base A1 formed from an elastomeric, crosslinked acrylic ester polymer and 30% to 50% by weight of a graft shell A2, 50% to 90% by weight of a hard matrix B formed from copolymers of styrene or α-methylstyrene and acrylonitrile, 0% to 50% by weight of a further graft copolymer C, 0% to 15% by weight of additives D, wherein the reaction for preparation of the acrylic ester polymer A and/or the reaction for preparation of C is conducted in the presence of 0.01 to 4 times the molar amount of sodium carbonate, based on the sum total of the molar amount of initiator used in the preparation of the graft base and graft shell, leads to lower coagulate formation.