| 摘要 |
A process for making foamed thermoplastic synthetic resin by extrusion comprises forming a plurality of separate strands of heat-softened foamable synthetic resin under a pressure sufficient to prevent the resin foaming, coalescing the strands while still under pressure and extruding the resulting coalesced mass so as to expand it into foamed thermoplastic synthetic resin. A foamable thermoplastic synthetic resin composition may be extruded through a die having at its inlet end a plurality of separate passages 2 communicating with a slit 3 at the outlet end of the die, the pressure within the die being sufficient to prevent the resin foaming before it leaves the slit and the dimensions of the passages 2 and of the slit 3 being such that the streams of resin issuing from the passages 2 fill the slit and coalesce whilst still in the unfoamed state. The resin may consist of a polymer or copolymer of a vinyl or vinylidene hydrocarbon monomer, e.g. ethylene, propylene, butadiene, styrene, vinyltoluene or a -methyl styrene, or a substituted monomer such as acrylonitrile, vinyl chloride or acetate, methyl acrylate or methacrylate, or ethyl acrylate. The foamable composition may contain as blowing agent a lower aliphatic hydrocarbon such as ethane, propane, butane, or pentane, a lower alkyl halide such as methyl chloride, trichloromethane or 1,2-dichlorotetrafluoroethane, an inorganic gas such as carbon dioxide or nitrogen, sodium or ammonium bicarbonate, or an organic nitrogen compound such as dinitrosopentamethylenediamine or barium azodicarboxylate.
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