Method of producing composite foamed shaped articles from thermoplastic resins

A method of producing shaped articles of a thermoplastic resin having a non-foam layer and a foam layer, which consists essentially of mixing thermoplastic resin particles not containing a heat-decomposable blowing agent, said resin being selected from the group consisting of polyethylene, polypropylene resins, styrol resins, acrylonitrile-butadiene-styrene copolymers, vinyl chloride resins, methacrylic resins and acrylonitrile-styrene copolymers and thermoplastic resin particles containing a heat-decomposable blowing agent, said resin being selected from the group consisting of polyethylene resins, polypropylene resins, styrol resins, acrylonitrile-butadiene-styrene copolymers, vinyl chloride resins, methacrylic resins and acrylonitrile-styrene copolymers, said heat-decomposable blowing agent being at least one member selected from the group consisting of dinitropentamethylene-tetramine, dimethyl-dinitrosoterephthalazide, benzene sulfonyl-hydrazide, toluene sulfonylhydrazide, azobisisobutyronitrile, diazoaminobenzene, trihydrazine-triazine, paratoluenesulfonyl-semicarbazide, oxybisbenzenesulfonyl-semicarbazide and azodicarbonamide, and derivatives thereof, wherein the said thermoplastic resin particles not containing a heat-decomposable blowing agent and said thermoplastic resin particles containing said blowing agent have the following relationship:

• 1000 .ltoreq. C.sub.A /C.sub.B .ltoreq. 50
• wherein C.sub.A is the heat capacity of said thermoplastic resin particles containing a heat-decomposable blowing agent and C.sub.B is the heat capacity of said thermoplastic resin particles not containing a blowing agent;
• introducing the mixture thus obtained into a mold;
• heating the mold and, in the meantime, moving said particles in said mold to effect the heat-melting of said particles as well as the heat-decomposition of the blowing agent into a gas and thereby forming the non-foam layer derived from said thermoplastic particles not containing the blowing agent and the foam layer derived from said thermoplastic particles containing said blowing agent.