Process for forming cross-linked polyethylene film

Claim 1

PROCESS FOR CONTINUOUS PRODUCTION OF SHRINKABLE POLYETHYLENE FILM WHICH COMPRISES FORMING A SUBSTANTIALLY HOMOGENEOUS MIXTURE OF A NORMALLY SOLID POLYETHYLENE AND FROM ABOUT 0.2 TO ABOUT 4.0 PERCENT BY WEIGHT, BASED ON THE WEIGHT OF THE POLYETHYLENE, OF A CROSSLINKING AGENT; SHAPING SAID MIXTURE INTO A TUBE BY EXTRUDING THE SAME AT TEMPERATURES BETWEEN THE MELTING POINT OF THE POLYETHYLENE AND THE GEL POINT OF THE MIXTURE; FEEDING THE EXTRUDED TUBE INTO A HEATED CURING ZONE MAINTAINED AT TEMPERATURES SUFFICIENT TO HEAT THE MIXTURE ABOVE THE DECOMPOSITION TEMPERATURE OF THE CROSSLINKING AGENT; PASSING SAID TUBE THROUGH SAID CURING ZONE AT A RATE SUFFICIENT TO PROVIDE A RESIDENCE TIME IN SAID ZONE AT LEAST EQUAL TO ABOUT THREE HALF-LIVES OF SAID CROSSLINKING AGENT; COOLING THE THUS CURED TUBING TO A TEMPERATURE BELOW THAT AT WHICH IT ADHERES TO ITSELF; REHEATING THE CURED, COOLED TUBING TO TEMPERATURES AT WHICH IT CAN BE EXPANDED AND EXPANDING SAID REHEATED UBE TO FORM TUBULAR FILM THEREFROM.