Foamed polymers and process for preparing same

Claim 1

A PROCESS FOR PREPARING A FOAMED THERMOPLASTIC POLYMER STRUCTURE WHICH COMPRISES EXTRUDING A FOAMABLE THERMOPLASTIC POLYMER COMPOSITION AT A TEMPERATURE OF ABOUT 250-400*F. AND AN EXTRUSION DIE PRESSURE OF ABOUT 150-3000 P.S.I.; SAID FORAMABLE THERMOPLASTIC POLYMER COMPOSITION COMPRISED OF A FREE-FLOWING UNIFORM BLEND OF (A) LARGE THERMOPLASTIC POLYMER PARTICLES HAVING AN AVERAGE PARTICLE SIZE OF 700-1500 MICRONS, AND (B) FINELYDIVIDED THERMOPLASTIC POLYMR PARTICLES HAVING AN AVERAGE PARTICLE SIZE OF LESS THAN 100 MICRONS AND HAVING ASSOCIATED THEREWITH A VOLATILE ORGANIC FOAMING AGENT IN THE AMOUNT OF ABOUT 10-50% BY WEIGHT; SAID VOLATILE ORGANIC FOAMING AGENT BEING SELECTED FROM THE GROUP CONSISTING OF (1) A NON-REACTIVE ORGANIC COMPOUND WHICH HAS AT MOST A SLIGHT SOLVENT ACTION ON THE LARGE THERMOPLASTIC POLYMER PARTICLES AND FINELY-DIVIDED THERMOPLASTIC POLYMER PARTICLES AND HAS AN ATMOSPHERIC BOILING POINT IN THE RANGE OF FROM ABOUT -10*C. TO ABOUT 80*C. AND (2) MIXTURES CONSISTING OF 70-99% BY WEIGHT OF (1) WITH, CORRESPONDINGLY, 30-1% BY WEIGHT OF AN ORGANIC COMPOUND HAVING A SOLVENT ACTION ON THE THERMOPLASTIC POLYMER PARTICLES EMPLOYED THEREIN; THE PROPORTIONS OF (A) AND (B) BEING SUCH THAT THE COMPOSITION CONTAINS ABOUT 5-12% BY WEIGHT OF THE VOLATILE ORGANIC FOAMING AGENT.