Method for making foamed polymeric structural materials

Claim 1

A PROCESS FOR PREPARING A FOAMED THERMOPLASTIC ARTICLE WHICH COMPRISES COMPLETELY FILLING A SEALABLE MOLD WITH SMALL PARTICLES OF A FOAMED THERMOPLASTIC RESIN HAVING DISPERSED THEREIN, AS A FOAMING AGENT, AN ORGANIC LIQUID WHICH BOILS BELOW THE SOFTENING POINT OF THE RESIN AND WHICH HAS AT MOST A SLIGHT SOLVENT ACTIONON THE THERMOPLASTIC RESIN, THE SURFACES OF SUBSTANTIALLY ALL OF SAID FOAMED THERMOPLASTIC RESIN PARTICLES BEING COATED WITH AN AQUEOUS SOLUTION HAVING DISSOLVED THEREIN ONLY AN IONIC SURFACE ACTIVE AGENT AND PASSING ELECTRIC WAVES OF HIGH FREQUENCY ALTERNATING CURRENT THROUGH THE SEALED MOLD FOR A PERIOD OF TIME SUFFICIENT TO CONVERT THE WATER OF THE AQUEOUS COATING CARRIED ON SAID FOAMED THERMOPLASTIC RESIN PARTICLES INTO STEAM AND FURTHER FOAM SAID FOAMED THERMOPLASTIC RESIN PARTICLES TO FORM A HOMOGENEOUS FOAMED THERMOPLASTIC RESIN ARTICLE; THE MOLD EMPLOYED IN THE PROCESS BEING FABRICATED FROM A MATERIAL SELECTED FROM THE GROUP CONSISTING OF POLYTETRAFLUOROETHYLENE, GLASS, QUARTZ, CERAMICS AND POLMETHACRYLATES.