Method of molding a foamed plastic structure having a smooth outside surface

Claim 1

A PROCESS FOR PREPARING A SHAPED STRUCTURE HAVING A FOAMED PLASTIC CORE COVERED WITH AN INTEGRAL SUBSTANTIALLY UNFOAMED PLASTIC LAYER HAVING A SMOOTH OUTSIDE SURFACE AS MOLDED, WHICH COMPRISES HEATING A COMPOSITION CONTAINING A THERMOPLASTIC RESIN AND A BLOWING AGENT TO A TEMPERATURE ABOVE BOTH THE SOFTENING POINT OF THE RESIN AND THE TEMPERATURE AT WHICH THE BLOWING AGENT FORMS BUBBLES, FILLING A CONSTANT-VOLUME MOLD WITH SAID COMPOSITION PRIOR TO COMPLETE FORMATION OF BUBBLES FROM THE BLOWING AGENT, SEALING THE MOLD, MAINTAINING THE INTERIOR SURFACE OF THE MOLD AT A TEMPERATURE ABOVE THE SOFTENING POINT OF THE PLASTIC AND BELOW THE TEMNPERATURE AT WHICH THE BLOWING AGENT FORMS BUBBLES UNTIL SOME PRESSURE FROM THE BLOWING AGENT BUILDS UP IN THE CENTRAL PORTION OF THE MOLD CAVITY, COOLING THE PLASTIC COMPOSITION IN THE MOLD TO SOLIDIFY THE PLASTIC AND REMOVING THE RESULTING SHAPED STRUCTURE FROM THE MOLD.