Process for producing thin walled tubes from normally crystalline polymers

Claim 1

IN A PROCESS FOR MAKING RESILIENT TUBING FROM A NORMALLY CRYSTALLINE VINYLIDENE CHLORIDE POLYMER, IN WHICH THE POLYMER IS FUSED, EXTRUDED IN TUBULAR FORM AND WITH A WALL THICKNESS OF AT LEAST 0.005 INCH DOWNWARD THROUGH AIR INTO A SUPERCOOLING BATH, AND THE SUPERCOOLED TUBE IS TAKEN AWAY FROM THE SUPERCOOLING BATH AT SUCH A RATE AS TO AVOID ANY MATERIAL STRETCHING OF THE SUPERCOOLED TUBE, THE IMPROVEMENT WHICH CONSISTS IN PASSING THE TUBE BETWEEN PINCH ROLLS IN THE SUPERCOOLING BATH, MAINTAINING A COLUMN OF INERT LIQUID WITHIN THE TUBE EXTENDING FROM THE SAID PINCH ROLLS BACK TOWARD THE POINT OF EXTRUSION BUT TERMINATING SHORT OF THAT POINT, SUBMERGING THE SUPERCOOLED TUBE IN AND LEADING IT THROUGH AN INERT LIQUID BATH MAINTAINED AT A TEMPERATURE ABOVE 60* C. BUT BELOW THE SOFTENING POINT OF THE POLYMER, MAINTAINING THAT PORTION OF THE TUBE WHICH IS IMMERSED IN SAID HOT LIQUID FILLED WITH MORE OF THE INERT LIQUID, AND WITHDRAWING THE TUBE FROM THE HOT BATH AT ESSENTIALLY THE SAME LINEAR RATE AS IT IS SUPPLIED THERETO.