Method of making celluloar plastic articles from vinyl aromatic resins

Claim 1

A PROCESS FOR MAKING A CELLULAR THERMOPLASTIC POLYMER ARTICLE POSSESSING GOOD DIMENSIONAL STABILITY AT TEMPERATURES ABOVE THE HEAT-PLASTIFYING TEMPERATURE OF THE POLYMER, WHICH PROCESS COMPRISES IMPREGNATING A SOLID GLASS-LIKE COPOLYMER OF FROM 99.75 TO 99.99 PERCENT BY WEIGHT OF AT LEAST ONE MONOVINYL AROMATIC COMPOUND OF THE BENZENE SERIES AND FROM 0.01 TO 0.25 PERCENT BY WEIGHT OF A POLYVINYL AROMATIC HYDROCARBON, WITH A NORMALLY GASEOUS AGENT SELECTED FROM THE GROUP CONSISTING OF CARBON DIOXIDE, METHYL FLUORIDE, ETHANE, PROPANE, ETHYLENE AND PROPYLENE, BY SUBJECTING THE SOLID COPOLYMER TO CONTACT WITH THE NORMALLY GASEOUS AGENT UNDER PRESSURE AT A TEMPERATURE BELOW THE HEAT DISTORTION TEMPERATURE OF THE COPOLYMER UNTIL THE COPOLYMER ABSORBS AT LEAST 2 PERCENT BY WEIGHT OF SAID AGENT, RELEASING THE PRESSURE AND HEATING THE COPOLYMER CONTAINING THE DISSOLVED NORMALLY GASEOUS AGENT TO A TEMPERATURE ABOVE THE HEAT DISTORTION TEMPERATURE OF THE COPOLYMER, WHEREBY THE DISSOLVED NORMALLY GASEOUS AGENT EXPANDS THE COPOLYMER TO FORM A CELLULAR PRODUCT.