Production of foamable vinyl aromatic resin compositions

Claim 1

IN A PROCESS FOR MAKING A LATENT-FOAMING POLYMERIC COMPOSITION COMPRISING A NORMALLY SOLID THERMOPLASTIC VINYL AROMATIC RESIN HAVING A VOLATILE ORGANIC COMPOUND HAVING A MOLECULAR WEIGHT OF A LEAST 58 AND A BOILING POINT NOT HIGHER THAN 95*C. AT ATMOSPERHIC PRESSURE, IN WHICH THE POLYMER IS INSOLUBLE, UNLIFORMLY DISTRIBUTED THROUGHOUT, WHEREIN A UNIFORM HOMOGENEOUSLY HEATPLASTIFIED MASS COMPRISING THE VINYL AROMATIC RESIN AND THE VOLATILE ORGANIC COMPOUND UNDER SUPERATMOSPHERIC PRESSURE IS EXTRUDED INTO A ZONE OF LOWER PRESSURE AND ALMOST IMMEDIATELY CONTACTED WITH A LIQUID COOLING MEDIUM AND COOLED TO A TEMPERATURE BELOW 50*C., WHEREBY THE COOLED EXTRUDED MATERIAL IS RIGIN NON-FOAMED MATERIAL AND CONTAINS THE SOLID POLYMR IN ORIENTED CONDITION, THE STEPS WHICH CONSIST IN CONTACTING THE SOLID POYLMER CONTAINING THE VOLATILE ORGANIC COMPOUND DISPERSED THROUGHOUT WITH AN AQUEOUS LIQUID HEAT TRANSFER MEDIUM AT TERMPERATURES BETWEEN 50*C. AND THE SOFTENING POINT OF THE POLYMER FOR A PERIOD OF TIME NOT GREATER THAN 180 MINUTES SUFFICIENT TO ANNEAL THE ORIENTED POLYMER AND INSUFFICIENT TO CAUSE APPRECIABLE SWELLING OF TEH JPOLYMER BY VAPORS OF THE VOLATILE ORGANIC COMPOUND CONTAINED THEREIN AND WITHOUT SUBSTANTIAL LOWERING OF ITS DENSITY, THEN COOLING THE SOTREATED POLYMER MATERIAL TO A TEMPERATURE BELOW SAID TREATING TEMPERATURE.