Improved process for producing thermoplastic abs molding compositions

A process for producing a thermoplastic ABS molding composition comprising:

• 30 to 80 wt.-%, based on the total weight of the thermoplastic ABS molding composition, of at least one thermoplastic copolymer matrix A comprising components A1, A2, and A3:
• A1:
• 50 to 80 wt.-%, based on the dry weight of A, of styrene, α-methylstyrene, and/or p-methylstyrene;
• A2:
• 20 to 40 wt.-%, based on the dry weight of A, of (meth)acrylonitrile;
• and
• A3:
• 0 to 20 wt.-%, based on the dry weight of A, of one or more co-polymerizable monomers;
• 19.99 to 60 wt.-%, based on the total weight of the thermoplastic ABS molding composition, of at least one ABS-copolymer B comprising components B1 and B2:
• B1:
• 30 to 90 wt.-%, based on the dry weight of B, of one or more rubber component(s) as graft basis, having a glass transition temperature of less than 0° C., comprising components B11 and B12:
• B11:
• 50 to 100 wt.-%, based on the dry weight of B1, of one or more of butadiene or isoprene;
• and
• B12:
• 0 to 50 wt.-%, based on the dry weight of B1, of further monomers;
• and
• B2:
• 10 to 70 wt.-%, based on the dry weight of B, of one or more graft stages, polymerized after the graft basis, comprising components B21, B22, and B23:
• B21:
• 50 to 90 wt.-%, based on the dry weight of B2, of styrene, α-methylstyrene, and/or p-methylstyrene;
• B22:
• 5 to 40 wt.-%, based on the dry weight of B2, of (meth)acrylonitrile;
• and
• B23:
• 0 to 40 wt.-%, based on the dry weight of B2, of one or more co-polymerizable monomers;
• 0 to 40 wt.-%, based on the total weight of the thermoplastic ABS molding composition, of one or more polymers C selected from the group consisting of polycarbonates, polyesters, polyestercarbonates, and polyamides;
• and
• 0.01 to 20 wt.-%, based on the total weight of the thermoplastic ABS molding composition, of one or more additives D,
• wherein the process for producing the thermoplastic ABS molding composition comprises the following steps:
• a) mixing the components A, B, and D and optionally C, by using at least one extruder comprising:
• a first feeding zone FZ1, wherein component B and at least part of component D are fed to the at least one extruder;
• a preheating zone PZ, wherein component B is heated to a temperature of 100° C. or below;
• a mechanical dewatering zone DZ, wherein component B, having a water content of more than 20 wt.-% based on the total weight of component B, is mechanically dewatered at a dewatering temperature Tdw in a range from 50° C. to 200° C., whereby the water content in component B is reduced by 10 wt.-% to 90 wt.-%, based on the water comprised in component B when fed to the first feeding zone FZ1, and wherein the mechanical dewatering zone DZ comprises at least one dewatering aperture;
• a second feeding zone FZ2, wherein at least part of component A and optionally part of component D are fed to the at least one extruder, wherein component A is brought in contact with component B;
• at least one degassing zone DG, wherein component A and/or component B are degassed;
• and
• an optional third feeding zone FZ3, wherein part of component A, component C, and/or part of component D are optionally fed to the at least one extruder together or separately from one another;
• and
• b) removing the thermoplastic ABS molding composition from a discharge zone CZ of the at least one extruder.