GB745480A - A process for the production of cellular thermoplastic products - Google Patents

Abstract

<PICT:0745480/IV(a)/1> Hot thermoplastic polymer containing a normally gaseous agent dissolved therein is fed by an extruder 5 or by a gear pump to a vessel 11 where it is cooled and mixed and then extruded through a nozzle 14 into the atmosphere, where the gaseous agent expands the polymer to form a cellular body. The polymer and the gaseous agent are mixed in the extruder 5 under pressure at 120-220 DEG C. The temperature of the material as it enters the vessel 11 is 120-220 DEG C. or lower and as it leaves the extrusion nozzle it is at 60-130 DEG C. The material is mixed in vessel 11 by projections 16 on a revolving drum 15. The vessel is cooled by fluid in jacket 17 and the drum is cooled by fluid entering at 18 and leaving at 19. The extruder 5 includes a screw 3, heating jacket 7, cooling jacket 7a and discharge tube 9, 10 leading to the vessel 11. Normally gaseous agent is introduced into the extruder through a pipe 8, and to prevent the escape of this agent rearwardly a disc 6, which may be perforated, is provided on the screw. The agent may be supplied through pipe 12. The amount of the agent is 5 to 25 parts per 100 by weight of the polymer. In the examples the polymer is mixed with precipitated calcium silicate and barium stearate. The thermoplastic polymer may be polystyrene, polymers of para- or meta-chlorostyrene, ortho-, meta- or para-methylstyrene, ortho- or meta-ethylstyrene, para-isopropylstyrene, methyl methacrylate or vinyl acetate, or co-polymers of styrene and methyl methacrylate, styrene and alpha-methylstyrene or vinyl acetate and vinyl chloride. The normally gaseous agent may be ethyl chloride, methyl chloride, methyl ether, propylene, butylene, dichlorodifluoromethane or mixtures of any two or more of these. Specifications 661,002 and 679,761 are referred to.