Preparation of molded plastic articles

Claim 1

THE PROCESS OFPRODUCING A MOLDED ARTICLE OF CROSSLINKED CELLULAR POLYPROPYLENE HAVING A UNIFORM CELL STRUCTURE IN WHICH AT LEAST 50% OF THE CELLS ARE CLOSED WHICH COPRISES SHAPING A MASS OF POLYPROPYLENE COMPOSITION BETWEEN THE MALE AND FEMALE MEMBERS OF A MATCHED MOLD BE APPLYING AN EXTERNAL MECHANICAL FORCE ON ONE OF SAID MEMBERS ONTO SAID POLYPROPYLENE COMPOSITION CONTAINED IN THE OTHER OF SAID MEMBERS, SAID POLYPROPYLENE COMPOSITION COMPRISING STEREOREGULAR POLYPROPYLENE, A BLOWING AGENT WHICH YIELDS AT LEAST ONE MOLE OF GAS PER MOLE OF BLOWING AGENT AT A TEMPERATURE WITHI N THE RANGE OF FROM THE SOFTENING TEMPERATURE OF THE COMPOSITION TO ABOUT 190*C., AND FROM ABAOUT 0.01% TO ABOUT 2%, BASED ON THE WEIGHT OF POLYPROPYLENE I THE COMPOSITION OF A POLY(AZIDOFORMATE) AS THE CROSS-LINKING AGENT, SAID COMPOSITION BEING AT A TEMPERATURE ABOVE THE SOFTENING POINT OF SAID COMPOSITION AND SUFFICIENT TO RELEASE GAS FROM SAID BLOWING AGENT AND TO EFFECT CROSS-LINKING OF SAID POLYPROPYLENE.