Process of foaming a mixture of a thermoplastic resin and a binding agent

Claim 1

AN IMPROVED PROCESS FOR THE PRODUCTION OF A LIGHTWEIGHT EXPANDED MATERIAL WHICH COMPRISES: MIXING (A) 10 TO 90 PARTS BY WEIGHT OF EXPANDABLE INDIVIDUAL PARTICLES OF A THERMOPLASTIC RESIN SELECTED FROM THE GROUP CONSISTING OF POLYSTYRENE AND POLYMETHACRYLIC ACID METHYL ESTER, SAID RESIN CONTAINING A BLOWING AGENT CAPABLE OF EXPANDING SAID RESIN PARTICLES WHEN SOFTENED, WITH (B) 90 TO 10 PARTS BY WEIGHT OF A BINDING AGENT SELECTED FROM THE GROUP CONSISTING OF BITUMEN AND PARAFFIN WAXES HAVING A MELTING POINT BELOW THE SOFTENING POINT OF SAID RESIN PARTICLES; HEATING THE RESULTANT MIXTURE TO MELT SAID BINDING AGENT, SAID RESIN BEING INSOLUBLE IN SAID MOLTEN BINDING AGENT, WHEREBY SAID EXPANDABLE RESIN PARTICLES ARE UNIFORMLY COATED WITH SAID BINDING AGENT; FURTHER HEATING THE RESULTANT MIXTURE TO SOFTEN AND EXPAND SAID INDIVIDUAL COATED RESIN PARTICLES; AND PLACING SAID EXPANDED PARTICLES IN ADHERING CONTACT WITH EACH OTHER.