Method for forming articles comprising expanded thermoplastic resinous materials

Claim 1

METHOD FOR FORMING INTO A FOAMED STRUCTURE A THERMOPLASTIC RESINOUS MATERIAL IN DISCRETE GRANULAR FORM IN WHICH THERE IS INCORPORATED A BLOWING AGENT AND WHICH IS ADAPTED TO BE EXPANDED BY APPLICATION OF ADEQUATE HEAT TO THE MASS TO ATTAIN A FOAMING TEMPERATURE WITHIN THE MASS TO SUFFICIENTLY SOFTEN THE MASS AND CAUSE EXPANSION OF THE BLOWING AGENT IN THE DISCRETE PARTICLES THEREIN WHICH COMPRISES COATING THE DISCRETE PARTICLES OF EXPANDABLE THERMOPLASTIC RESINOUS MATERIAL WITH A MINOR PROPORTION OF BETWEEN ABOUT 0.05 AND 20 WEIGHT PERCENT, BASED ON THE WEIGHT OF SAID PARTICLES, OF A LOW MOLECULAR WEIGHT, NONVOLATILE, THERMOPLASTIC POLYMERIC BONDING AGENT THAT IS ADAPTED TO FLOW AT A TEMPERATURE WHICH IS BENEATH THE FOAMING TEMPERATURE OF THE EXPANDABLE MASS, SAID BONDING AGENT HAVING AN ADHESIVE EFFECT UPON THE THERMOPLASTIC RESINOUS MATERIAL WHEN IT IS IN AN EXPANDED CONDITION; MECHANICALLY PERFORMING THE MASS OF COATED DISCRETE PARTICLES OF EXPANDABLE THERMOPLASTIC RESINOUS MATERIAL INTO A COHERENT FURTHER EXPANDABLE FORM HAVING A DEPTH IN EXCESS OF THE DIAMETER OF THE LARGEST PARTICLE EMPLOYED AT A TEMPERATURE IN THE RANGE FROMM THE FLOW TEMPERATURE OF THE POLYMERIC BONDING AGENT TO THE FOAMING TEMPERATURE OF THE EXPANDABLE MASS; AND SUBSEQUENTLY HEATING THE PERFORMED MASS OF EXPANDABLE THERMOPLASTIC RESINOUS MATERIAL TO A FOAMING TEMPERATURE TO EXPAND IT TO A FOAM STRUCTURE.