ABS molding compound having a good property combination of processability and surface quality

A thermoplastic molding composition F consisting of:

• (a) from 5 to 50% be weight, based on the total thermoplastic molding composition F, of a mixture of graft rubbers P-I and P-II of:
• P-I:
• at least one graft rubber P-I obtained by emulsion polymerization with inorganic persalt initiation and polymerization of styrene and acrylonitrile in a styrene:acrylonitrile ratio by weight of from 95:5 to 50:50, where styrene can be replaced entirely or to some extent by alpha-methylstyrene, and where acrylonitrile can be replaced entirely or to some extent by methyl methacrylate or N-phenylmaleimide, in the presence of:
• at least one polybutadiene latex A with average particle diameter d50 from 230 to 330 nm and at least one polybutadiene latex B with average particle diameter d50 from 340 to 480 nm,
• where the polybutadiene latices A and B have been obtained by seed polymerization starting from at least one polybutadiene latex C with average particle diameter d50 from 10 to 220 nm (as seed latex);
• P-II:
• at least one graft rubber P-II obtained by emulsion polymerization with inorganic persalt initiation and polymerization of styrene and acrylonitrile in a styrene:acrylonitrile ratio by weight of from 95:5 to 50:50, where styrene can be replaced entirely or to some extent by alpha-methylstyrene, and where acrylonitrile can be replaced entirely or to some extent by methyl methacrylate or N-phenylmaleimide, in the presence of said at least one polybutadiene latex C with average particle diameter d50 from 10 to 220 nm;
• (b) from 50 to 95% by weight, based on the total thermoplastic molding composition F, of at least one rubber-free copolymer matrix P-III made of styrene and acrylonitrile in a styrene:acrylonitrile ratio by weight of from 95:5 to 50:50, where styrene can be replaced entirely or to some extent by alpha-methylstyrene,
• (c) optionally from 0 to 10% by weight, based on the total thermoplastic molding composition F, of one or more thermoplastic components T not composed of vinyl monomers;
• and
• (d) optionally from 0 to 5% by weight, based on the total thermoplastic molding composition F, of one or more additives D,
• where the graft rubbers P-I and P-II are prepared in separate steps and mixed with each other to obtain mixture of the respective emulsions comprising P-I and P-II,
• where the process of production of the graft rubbers P-I and P-II is completed via coprecipitation of the mixture of respective emulsions comprising 5 to 30% by weight of the graft rubber mixture of P-I and P-II in an aqueous electrolyte solution containing one or more salts, one or more acids, or a combination of one or more salts and one or more acids, and
• wherein the mixture of coprecipitated graft rubbers P-I and P-II is mixed with the at least one rubber-free copolymer matrix P-III and optionally the one or more thermoplastic components T and optionally the one or more additives D.