Production of foamed resins

1,148,119. Foamed thermoplastic resins. MONSANTO CHEMICALS Ltd. 20 Oct., 1967 [9 Dec., 1966], No. 55125/66. Headings C3C and C3P. A foamed thermoplastic resin is produced by extruding a heat-softened foamable thermoplastic resin containing a blowing agent (which is a volatile liquid or a gas) under pressure and a nucleating agent comprising a salt of a C 1-16 aliphatic carboxylic acid into a zone of lower pressure to allow foaming of the resin. The resin may be polyethylene or a copolymer of ethylene and vinyl acetate. The salt may be sodium, calcium, magnesium, aluminium, barium, lead or zinc palmitate, formate, acetate, butyrate, or lactate and may be used with silica, boric acid, a wax or talc as additional nucleating agents. The blowing agent may be butane or nitrogen. The resin may be formed into a foamed film.