Process for producing biaxially oriented thermoplastic tubular film

Claim 1

A METHOD OF PREPARING AN ORIENTED THIN THERMOPLASTIC RESINOUS FILM COMPRISING PROVIDING A TUBE OF AN ORIENTABLE THERMOPLASTIC RESINOUS MATERIAL AT A TEMPERATURE SUBSTANTIALLY BELOW THE TEMPERATUR AT WHICH SAID MATERIAL WILL STRETCH AND ORIENT, PREHEATING SAID TUBE TO A TEMPERATURE BELOW WHICH IT WILL ORIENT BY APPLYING EXTERNALLY THERETO RADIANT HEAT TIN A FIRST HEATING ZONE MECHANICALLY RESTRAINING SAID TUBE FROM TRANSVERSES MOTION, WHILE CONTINUOUSLY FORWARDING SAID TUBE THROUGH A FINAL HEATING ZONE, PASSING SAID TUBE INTO THE FINAL HEATING ZONE, HEATING THE TUBE BY EXTERNALLY APPLYING RADIANT HEAT TO AT LEAST THE TEMPERATURE AT WHICH IT IS ORIENTED BY THE APPLICATION OF INTERNAL GAS PRESSURE OF A TRAPPED VOLUME OF GAS WITHIN THE TUBE WHILE MECHNAICALLY RESTRAINING SAID TUBING FROM TRANSVERSE MOTION WHILE SIMULTANEOUSLY PREVENTING PASSAGE OF AIR TO OR FROM THE FINAL HEATING ZONE OVER THE EXTERNAL SURFACE OF THE TUBE, SAID INTERNAL GAS PRESSURE BING SUFFICIENT TO CAUSE SAID TUBE TO BE CIRCUMFERENTIALLY ORIENTED TO A DESIRED DEGREE, SIMULTANEOUSLY WITHDRAWING SAID TUBING FROM THE FINAL HEATING ZONE AT A RATE SUFFICIENT TO PRODUCE LONGITUDINAL ORIENTATION WITHIN THE TUBE, MAINTINING WITHIN SAID TUBING DURING THE ORIENTATION THEREOF A TEMPERATURE UNIFORMITY SUFFICIENT TO RESULT IN A SUBSTANTIALLY UNIFORM WALL THICKNESS AND SUBSEQUENTLY COLLAPSING SAID TUBING TO A FLAT SHEET.

Claim 2

A METHOD OF PREPARING AN ORIENTED THIN THERMOPLASTIC RESINOUS FILM COMPRISING PROVIDING A TUBE OF AN ORIENTABLE THERMOPLASTIC RESINOUS MATERIAL AT A TEMPERATURE SUBSTANTIALLY BELOW THE TEMPERATUR AT WHICH SAID MATERIAL WILL STRETCH AND ORIENT, PREHEATING SAID TUBE TO A TEMPERATURE BELOW WHICH IT WILL ORIENT BY APPLYING EXTERNALLY THERETO RADIANT HEAT TIN A FIRST HEATING ZONE MECHANICALLY RESTRAINING SAID TUBE FROM TRANSVERSES MOTION, WHILE CONTINUOUSLY FORWARDING SAID TUBE THROUGH A FINAL HEATING ZONE, PASSING SAID TUBE INTO THE FINAL HEATING ZONE, HEATING THE TUBE BY EXTERNALLY APPLYING RADIANT HEAT TO AT LEAST THE TEMPERATURE AT WHICH IT IS ORIENTED BY THE APPLICATION OF INTERNAL GAS PRESSURE OF A TRAPPED VOLUME OF GAS WITHIN THE TUBE WHILE MECHNAICALLY RESTRAINING SAID TUBING FROM TRANSVERSE MOTION WHILE SIMULTANEOUSLY PREVENTING PASSAGE OF AIR TO OR FROM THE FINAL HEATING ZONE OVER THE EXTERNAL SURFACE OF THE TUBE, SAID INTERNAL GAS PRESSURE BING SUFFICIENT TO CAUSE SAID TUBE TO BE CIRCUMFERENTIALLY ORIENTED TO A DESIRED DEGREE, SIMULTANEOUSLY WITHDRAWING SAID TUBING FROM THE FINAL HEATING ZONE AT A RATE SUFFICIENT TO PRODUCE LONGITUDINAL ORIENTATION WITHIN THE TUBE, MAINTINING WITHIN SAID TUBING DURING THE ORIENTATION THEREOF A TEMPERATURE UNIFORMITY SUFFICIENT TO RESULT IN A SUBSTANTIALLY UNIFORM WALL THICKNESS AND SUBSEQUENTLY COLLAPSING SAID TUBING TO A FLAT SHEET.