Process for making cellular polyethylene articles

Claim 1

IN A PROCESS FOR MAKING A POLYETHYLENE FOAM WHEREIN A FLOWABLE GEL COMPRISING ESSENTIALLY POLYETHYLENE HAVING A NORMALLY GASEOUS AGENT SELECTED FROM THE GROUP CONSISTING OF TETRAMETHYLMETHANE, MONOCHLORODIFLUOROMETHANE, MONOCHLOROTRIFLUOROMETHANE, DICHLORODIFLUOROMETHANE AND DICHLOROTETRAFLUORETHANE, INTIMATELY INCORPORATED THEREWITH UNDER PRESSURE IS EXPANDED BY SUDDENLY RELEASING THE PRESSURE BY EXTRUDING THE GEL INTO A ZONE OF LOWER PRESSURE SUFFICIENT TO CAUSE EXPANSION OF THE EXTRUDED MATERIAL WITH RESULTANT FORMATION OF A FOAM, THE STEP WHICH CONSISTS IN SUBJECTING THE GEL UNDER PRESSURE TO IONIZING RADIATIONS IN AMOUNT CORRESPONDING TO A TOTAL DOSE OF FROM 1 TO 20 MEGA-R.E.P.''S IN A FIELD HAVING AN INTENSITY OF AT LEAST 3 MEGA-R.E.P.''S PER SECOND AND SUFFICIENT TO BRING ABOUT AN INCREASE IN RESISTANCE TO FLOW OF THE POLYETHYLENE AT A TEMPERATURE OF 100*C. AND INSUFFICIENT TO PREVENT APPRECIABLE FLOW OF THE POLYETHYLENE AT SAID TEMPERATURE, AT A POINT JUST PRIOR TO EXTRUDING THE MATERIAL INTO THE ZONE OF LOWER PRESSURE.