Patent GB-849070-A (GB)
Title: Process and apparatus for the production of polymer tubing and films
IPC: B29C48/10
Filed: 1958-12-30
Abstract: <PICT:0849070/IV(a)/1> Orientated tubular films are made by continuously extruding a tube of molten, normally crystalline polymer, withdrawing the tube downwardly from the extruder die by a pair of nip rolls while maintaining a constant head of circulating cooling liquid within the tube between the nip of the nip rolls and the face of the die in order to supercool the tube, and immediately cold-working the tube to accomplish orientation.  The cooling liquid may contain material for coating the inside surface of the tube, preferably finely-divided solids in an aqueous phase, so as to prevent cohesion of the tube on flattening.  The normally crystalline polymer may be a polyurethane or a vinylidene chloride copolymer, and in the latter case the finely-divided solid may be polyvinyl chloride, talc or limestone.  The constant head of circulating cooling liquid may be maintained by using separate inlet and outlet means, the outlet means having a larger capacity than the inlet means.  Preferably the inlet means supplies the cooling liquid at a fixed rate and the outlet means removes the liquid from the tube at a relatively higher rate than the rate of supply, the constant head being determined by the location of the exit opening of the outlet means with respect to the face of the die. Apparatus as shown comprises an extruder die 12 with an annular orifice 11, means for feeding molten polymer to the die, nip rolls 14 located below the die, inlet and outlet pipes (18 and 26) for cooling liquid which pass through the die within the area bounded by orifice 11, the outlet pipe ending at a level higher than that of the inlet pipe, means for withdrawing cooling liquid through the outlet pipe (hose 28, pump 27) at a potentially greater rate than the rate of feed of the cooling liquid to the inlet pipe, and means for cold working the tube after it has passed nip rolls 14 comprising rolls 55 and means (not shown) for inflating the tube. Means for adjusting the height of the lower end of the outlet pipe above the nip rolls (adjusting screw 41) may be provided.ALSO:<PICT:0849070/III/1> Oriented tubes and tubular films are made by continuously extruding a tube of molten, normally crystalline polymer, withdrawing the tube downwardly from the extruder die by a pair of nip rolls while maintaining a constant head of circulating cooling liquid within the tube between the nip of the nip rolls and the face of the die in order to supercool the tube, and immediately cold-working the tube to accomplish orientation.  The cooling liquid may contain material for coating the inside surface of the tube, preferably finely-divided solids in an aqueous phase, so as to prevent cohesion of the tube on flattening.  The normally crystalline polymer may be a polyurethane or a vinylidene chloride copolymer, and in the latter case the finely-divided solid may be polyvinyl chloride, talc or limestone.  The constant head of circulating cooling liquid may be maintained by using separate inlet and outlet means, the outlet means having a larger capacity than the inlet means.  Preferably the inlet means supplies the cooling liquid at a fixed rate and the outlet means removes the liquid from the tube at a relatively higher rate than the rate of supply, the constant head being determined by the location of the exit opening of the outlet means with respect to the face of the die.  Apparatus as shown comprises an extruder die 12 with an annular orifice 11, means for feeding molten polymer to the die, nip rolls 14 located below the die, inlet and outlet pipes (18 and 26) for cooling liquid which pass through the die within the area bounded by orifice 11, the outlet pipe ending at a level higher than that of the inlet pipe, means for withdrawing cooling liquid through the outlet pipe (hose 28, pump 27) at a potentially greater rate than the rate of feed of the cooling liquid to the inlet pipe, and means for cold working the tube after it has passed nip rolls 14 comprising rolls 55 and means (not shown) for inflating the tube.  Means for adjusting the height of the lower end of the outlet pipe above the nip rolls (adjusting screw 41) may be provided.