Preparation of high bulk density expansible thermoplastic materials

Claim 1

THE PROCESS FOR THE PRODUCTION OF A PARTICULATE, EXPANSIBLE, HIGH BULK DENSITY POLYSTYRENE WHICH COMPRISES HEATING A PARTICULATE POLYSTYRENE CONTAINING ESSENTIALLY BUTANES AS A HYDROCARBON EXPANDING AGENT IN AN UNCONFINED SPACE AT A TEMPERATURE IN THE RANGE OF FROM ABOUT 75* TO ABOUT 100*C., THEREBY OBTAINING A PARTIAL EXPANSION OF SAID POLYSTYRENE IN THE ABSENCE OF ANY AGGLOMERATION, COOLING THE RESULTING PARTIALLY-EXPANDED POLYSTYRENE TO SUBSTANTIALLY ATMOSPHERIC TEMPERATURE AND AGEING IT IN AIR FOR AT LEAST ONE-QUARTER HOUR, THEN SUBJECTING THE RESULTING PARTIALLY-EXPANDED, AGED POLYSTYRENE PARTICLES TO AN ELEVATED MECHANICAL PRESSURE IN THE RANGE OF FROM ABOUT 50 TO ABOUT 300 LBS./SQ. IN. AND MAINTAINING SAID ELEVATED PRESSURE UNTIL THE BULK DENSITY OF SAID PARTIALLYEXPANDED POLYSTYRENE HAS BEEN REDUCED TO A VALUE IN THE RANGE OF FROM ABOUT 5 TO ABOUT 20 LBS./CU. FT., WITHOUT ANY SUBSTANTIAL AGGLOMERATION OF SAID PARTICLES AND WITHOUT BURSTING ANY SUBSTANTIAL PROPORTION OF SAID PARTICLES AND OF ANY INTERCELLULAR WALLS THEREOF.