Impact-resistant thermoplastic resin composition

An impact-resistant thermoplastic resin composition comprising (a) a graft copolymer (II) prepared by polymerizing 10 to 1,000 parts by weight of a monomer or monomer mixture composed of 50 to 100% by weight of a monomer selected from the group consisting of methyl methacrylate and styrene and 50 to 0% by weight of a monofunctional or polyfunctional monomer copolymerizable therewith in the presence of 100 parts by weight (as solids) of a latex of an agglomerated rubber copolymer (I'), and (b) a heat-resistant rigid thermoplastic resin (III) comprising a member selected from the group consisting of a copolymer derived from 10 to 40% by weight of acrylonitrile, 90 to 60% by weight of .alpha.-methylstyrene, and 30 to 0% by weight of another monomer copolymerizable therewith and a copolymer derived from 5 to 40% by weight of a maleimide compound, 10 to 40% by weight of acrylonitrile, 85 to 30% by weight of at least one monomer selected from the group consisting of styrene and .alpha.-methylstyrene, and 30 to 0% by weight of another monomer copolymerizable therewith;

• the proportion of the graft copolymer (II) to the rigid thermoplastic resin (III) being such that the amount of the agglomerated rubber copolymer (I') is 1 to 70% by weight based on the total weight of the impact-resistant thermoplastic resin composition;
• said agglomerated rubber copolymer (I') being prepared by the steps of:
• emulsion-polymerizing a monomer mixture comprised of 51 to 99% by weight of an alkyl acrylate having 2 to 8 carbon atoms in the alkyl group, 49 to 1% by weight of 1,3-butadiene, and 10 to 0% by weight of at least one copolymerizable monomer selected from the group consisting of monofunctional monomers and polyfunctional monomers, to prepare a latex of a rubbery copolymer (I), and
• agglomerating the rubbery copolymer (I) to an extent such that the average particle diameter of the agglomerated rubbery copolymer is 0.12 to 0.4 .mu.m, by adding 0.1 to 5 parts by weight of an agglomerating agent to 100 parts by weight as solids of the latex of the rubbery copolymer (I);
• said agglomerating agent being selected from the group consisting of (A) an acid group-containing copolymer in a polymer latex formed by emulsion-polymerizing a monomer mixture comprised of 3 to 40% by weight of at least one unsaturated acid selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic acid, fumaric acid, cinnamic acid, sorbic acid and p-styrenesulfonic acid, 97 to 35% by weight of at least one alkyl acrylate having 1 to 12 carbon atoms in the alkyl group and 0 to 40% by weight of other monomer copolymerizable therewith.