Flame-retardant thermoplastic resin composition

A flame retardant for thermoplastic resins, which comprises:

• a polyorganosiloxane-containing graft copolymer (B) obtained by polymerizing, in at least one stage, monomer(s) (B-3) and a vinyl monomer (B-4) in the presence of polyorganosiloxane particles (B-1), wherein monomer(s) (B-3) comprises a polyfunctional monomer (B-2) containing at least two polymerizable unsaturated bonds within the molecule thereof,
• an alkali metal salt of a sulfur-containing organic compound, and
• a bivalent or further polyvalent metal salt of a sulfur-containing organic compound,
• wherein the polyorganosiloxane-containing graft copolymer (B) is produced by polymerizing, in at least one stage, 1.5 to 10 parts by weight, per 100 parts by weight of the whole copolymer, of monomer(s) (B-3) comprising 100 to 20% by weight of a polyfunctional monomer (B-2) containing at least two polymerizable unsaturated bonds within the molecule thereof and 0 to 80% by weight of another copolymerizable monomer (B-5) in the presence of 40 to 95 parts by weight of polyorganosiloxane particles (B-1) and further polymerizing, in at least one stage, 5 to 50 parts by weight of a vinyl monomer (B-4).

A method of producing flame retardant for thermoplastic resins,

• which comprises:
• emulsion-polymerizing, in at least one stage, monomer(s) (B-3) and/or a vinyl monomer (B-4) in the presence of polyorganosiloxane particles (B-1), wherein monomer(s) (B-3) comprises a polyfunctional monomer (B-2) containing at least two polymerizable unsaturated bonds within the molecule thereof,
• recovering the polyorganosiloxane-containing graft copolymer containing a bivalent or further polyvalent metal salt of a sulfur-containing organic compound by the coagulation method,
• adding an alkali metal salt of a sulfur-containing organic compound to the polyorganosiloxane-containing graft copolymer containing the bivalent or further polyvalent metal salt of the sulfur-containing organic compound, and blending them.