METHOD OF MAKING FOAMED POLYOLEFIN SHEET MATERIAL

摘要

1519551 Foamed polyolefin sheet material FURUKAWA ELECTRIC CO Ltd 23 Feb 1976 [26 Feb 1975] 07080/76 Heading B5N A foamed polyolefin sheet material is produced by heating under atmospheric pressure a layer of polyolefin supported by a support member, the layer containing a thermally decomposable foaming agent and, if the polyolefin is not already cross-linked, a cross-linking agent therefor, to decompose the foaming agent and activate the cross-linking agent (if any), there being provided between the lower surface of the layer and the support member a film of a non- cross-linked thermoplastic resin free from crosslinking agent, the film being attached to the lower surface of the layer and preventing contact between the layer and the support member during the heating. The polyolefin base layer may be produced by mixing the foaming agent with a polyolefin, forming the mixture into a sheet, e.g. extrusion, and irradiating with ionizing radiation to effect cross-linking, or by mixing the foaming agent and cross-linking agent with the polyolefin and forming the mixture into a sheet. The polyolefin may be of ethylene, propylene or butene which may be copolymerized with vinyl acetate or acrylic acid. The polyolefin may contain rubber or other plastics material or a flame retardant, e.g. antimony oxide or chlorinated paraffin. The foaming agent may be p,p1oxybis(benzene sulphonyl hydrazide, azodicarbonamide, dinitroso pentaethylene tetramine or p-toluene-sulphonyl semicarbazide, and the cross-linking agent may be dicumyl peroxide, 1,10-decane-bis-sulphonazide, m-phenylene diazide, vinyltriethoxysilane, vinyl trimethoxysilane, dibutylatin dilaurate and dibutyl tin diacetate which may be used together with triallyl cyanurate or triallyl isocyanurate. The thermoplastic film which may have a thickness of 0À05-1 mm., may be of low or high density polyethylene or polypropylene. The film-fitted sheet may be conveyed on a wire net conveyer, e.g. of stainless steel, through a furnace to effect foaming. A film may be applied to both surfaces of the sheet. The film fitted surface of a foamed sheet may be bonded to the heated surface of an iron plate, the other surface of which is covered with an embossed sheet of vinyl chloride resin.