| 摘要 |
1327284 Extruding foamed vinyl BADISCHE ANILIN- & SODA-FABRIK AG 1 Jan 1971 [2 Jan 1970] 74/71 Heading B5A [Also in Division C3] A vinyl chloride polymer is melted at a temperature of 120‹ to 200‹C. during passage through the barrel of a screw extruder wherein it is mixed, at a pressure which prevents expansion, with solid decomposable, or liquid, or gaseous expanding agent, and discharged, via an outlet 5, into a water cooled cylinder 6 wherein it is cooled to a temperature of 80‹ to 120‹ C., (or maintained thereat if cooled at the extruder barrel end) and remains therein for at least 10 minutes at a shear gradient of not more than 10 sec<SP>-1</SP>, under a pressure which prevents expansion, prior to extrusion through an orifice 9 to expand at atmospheric pressure and temperature into a tube or sheet which may pass through a calibrating device. The extrudate density may be down to 30 g/l. The orifice 9 is preferably smaller than the outlet 5. The extruder screw may discharge intermittently or continuously respectively to one, or two or more, cylinders 6 from which, or each of, the melt is intermittently extruded through an intermittently opened orifice 9 by a piston 8. Alternatively, the melt may be pressurized within the cylinder 6 under a gas cushion, and extruded by a gear pump through the orifice 9 simultaneously with discharge from the extruder. The vinyl chloride polymer may comprise polyvinyl chloride, copolymers of vinyl chloride with 0À1 to 10% by weight of ethylene, propylene vinyl acetate, acrylates and methacrylates, and chlorination products of vinyl chloride polymers of 55 to 65% weight chlorine. A preferred copolymer comprises 95 to 99À8% by weight of vinyl chloride with 5 to 0À2% propylene. Liquid or gaseous expanding agents may comprise 4 to 40% e.g. 15 to 25%, by weight of the polymer of methyl, ethyl or vinyl chloride, or monofluorotrichloromethane or mixtures thereof. Solid decomposable expanding agents may comprise 0À2 to 6% by weight of azodicarbonamide, azodiisobutyronitrile, or carbonates. Nucleating agents may comprise aluminium hydroxide, silica gel, talc, or citric acid/sodium bicarbonate mixtures. In the examples, a vinyl chloride/ propylene co-polymer containing talc and either ethyl-2-hexyldibutyl tin thioglycolate, or barium and cadmium laurate, is respectively: (1) melted and mixed with methyl chloride by corotating twin screws of an extruder comprising successive hot water controlled barrel temperature zones of 160 degrees and 60 degrees, the barrel temperature being 80‹ C. during residence of the molten polymer in the cylinder 6 prior to piston extrusion therefrom into a sheet; (2) melted and mixed with methyl chloride/monofluorotrichloromethane in a single screw (provided with mixing means) similarly heated extruder which sequentially discharges to each of a pair of similar sheet extrusion cylinders. Comparative prior art examples are given. |
