The present invention relates to a process for producing a thermoplastic moulding composition comprising a thermoplastic copolymer A, a graft copolymer B and optionally a further polymer component C as well as optional further additives K, wherein the preparation of the graft copolymer B is carried out via emulsion polymerization, and wherein at least one surfactant S2 is used in grafting step of emulsion polymerization in a volume concentration in the range of 0.46 to 0.75 mol/m3, based on the volume of the graft copolymer B latex particles obtained; and wherein the mean particle diameter Dw of the latex particles of graft copolymer B is in the range of 60 to 800 nm.