GB1292971A - A method of producing expanded synthetic plastics products by the continuous extrusion of a thermoplastics containing an expanding agent - Google Patents

Abstract

1292971 Extruding foamed thermoplastics CHEMISCHE WERKE HULS AG 6 Nov 1969 [7 Nov 1968] 54425/69 Heading B5A [Also in Division C3] An expanded thermoplastics is produced by the screw extrusion of a mixture of thermoplastics and pore-regulating substance from hopper T, through zones A, B, and C, the zones A and B being heated by a jacket H and respectively comprising a zone in which a homogeneous melt is produced followed by a zone of increasing compression, and the zone C effecting an increasing pressure in the direction of the nozzle and being cooled by coolant circulated through a jacket K to prevent expansion, prior to the nozzle, of an expanding low-boiling liquid or a gas which is injected at E. The zone C is also provided with a heating jacket H which is employed at the commencement of extrusion. The thermoplastics may comprise polystyrenes, polyolefines or polyamides. The pore regulating substances may comprise carbonates and bicarbonates of alkali and alkaline earth metals, e.g. of sodium together with organic acids, e.g. citric or boric acid, or their acid salts, or crystalline inorganic compounds such as titanium dioxide, carbon black, talc, or kaolin. The liquid expanding agents may comprise aliphatic hydrocarbons, e.g. pentane, or hexane, or chlorohydrocarbons, e.g. monofluorotrichloromethane and trifluorotrichloroethane, and the gaseous agents may comprise propane or butane. Details are given of a preferred compression ratio between zones A and C, and of preferred zone length to diameter ratios.