Method of making a thermoplastic receptacle having improved high temperature seal

Claim 1

A process for forming a heat shrinkable, flexible, thermoplastic receptacle having a gas barrier layer wherein food products or the like can be raised to pasteurizing temperatures comprising the steps of: (a) coextruding a tubular multi-layer film comprising a layer of hydrolyzed ethylene-vinyl acetate copolymer and an interior surface layer of a polyolefin which is cross-linkable by ionizing radiation, the layers of said multi-layer film being directly melt joined without an adhesive disposed therebetween; (b) irradiating said tubing with ionizing radiation to a first dosage level sufficient to allow continuous processing of said tubing by the trapped bubble technique, said dosage level being at least 0.5 MR; (c) heating said tubing to the orientation temperature of said polyolefin; (d) inflating and then cooling said tubing by the trapped bubble technique to stretch the tubing to film thickness and to orient it thereby producing a heat-shrinkable film; (e) sealing selected portions of said film to itself using heat and pressure and severing selected portions of said film to form a heat shrinkable receptacle having an opening; and, (f) irradiating the entire receptacle to impart a second and higher dosage level, said second dosage being at least 0.5 MR thereby producing a heat shrinkable receptacle in which a food product can be pasteurized.