GB679761A - Improvements in or relating to a method for dissolving normally gaseous agents in thermoplastic resins - Google Patents

Abstract

Homogeneous compositions of a thermoplastic resin and a normally gaseous agent which undergo expansion to form cellular products are continuously manufactured by feeding the molten resin through one or more restricted orifices into a mixing zone at an applied pressure so as to form within the inlet to said zone a plastic seal, feeding a resin soluble normally gaseous agent at super-atmospheric pressure into the mixing zone and agitating the mixture of the resin and the gaseous agent; the mixture is then forwarded under pressure through a temperature regulating zone where it is brought to a temperature below the critical temperature and boiling point of the gaseous agent, and the resulting composition is charged to a vessel where it is stored at a pressure sufficient to maintain the composition as a solution of the normally gaseous agent and resin; releasing the pressure converts the thermoplastic resins to the cellular form. Thermoplastic resins specified are polymers and copolymers of styrene, ortho and para chlorostyrenes, dichlorostyrene, meta and para methyl styrenes, alpha methylstyren, ortho and meta ethylstyrenes, para iso-propylstyrene, methyl methacrylate, and vinyl chloride. Suitable normally gaseous agents are methyl and ethyl chlorides, dichlorodifluoromethane, methyl ether, methyl ethyl ether and gaseous olefines such as propylene and butylene. The process is preferably put into operation by the addition of a small amount of high boiling solvent, such as ortho dichlorobenzene, diethylbenzene, 2-ethylxylene and iso-propylbenzene, to the molten resin in the mixing zone to form a plastic plug flowable at the lower temperatures employed in the heat exchanger; the normally gaseous agent is then fed under pressure to the molten resin. Specification 406,267, [Group XIII], is referred to.