Apparatus and process for use in the expansion of tubular film

Claim 1

A PROCESS COMPRISING THE STEPS, IN SEQUENCE, OF EXTRUDING THERMOPLASTIC POLYMERIC MATERIAL IN THE FORM OF MOLTEN TUBING; ADVANCING THE TUBING OVER AND IN CONTACT WITH THE SURFACE OF A COOLING MANDREL; THEREAFTER, ADVANCING THE TUBING OVER A RESILIENTLY DEFORMABLE COLLAR PROJECTING FROM THE SURFACE OF SAID MANDREL, THE PROJECTING COLLAR IN ITS RELAXED POSITION MAKING AN OBTUSE ANGLE WITH THE UPSTREAM PORTION OF THE MANDREL; PASSING A GASEOUS MEDIUM INTO THE INTERIOR OF SAID TUBING AT A POINT DOWNSTREAM FROM SAID MANDREL AND SAID COLLAR; DEFLECTING SAID RESILIENT COLLAR INTO CONTACT WITH THE INNER SURFACE OF THE TUBING; AND WITHDRAWING GASEOUS MEDIUM AT SPACED INTERVALS AROUND THE SURFACE OF SID MANDREL AT LOCATIONS ADJACENT TO AND UPSTREAM FROM SAID COLLAR WHEREBY GAS IS PREVENTED FROM FLOWING BACK TO THE POINT OF EXTRUSION.