Patent GB-941610-A (GB)
Title: Oriented tubular films from thermoplastic polymers
Inventor: UNDERWOOD WILLIAM FREDERICK
IPC: B29C48/10
Filed: 1960-07-27
Abstract: 941,610. Tubular films; laminates and laminating. UNION CARBIDE CORPORATION. July 27, 1960, No. 26160/60. Headings B5B and B5N. [Also in Division B8] Seamless tubing is made by melt extruding a thermoplastic polymer of low melt-viscosity through a first annular orifice, constricting the tubing at a point spaced from the first orifice and maintaining a bubble of a gaseous medium under pressure in the tubing between the first orifice and the point of constriction to cause distension of the tubing, the tubing being supported on a second concentric tubing of a thermoplastic polymer of high meltviscosity simultaneously melt-extruded through a second annular orifice adjacent to and concentric with the first orifice, constricted at the same point of constriction and distended by the same bubble of gaseous medium. Extrusion is preferably upwards, and the first orifice may be inside or outside the second orifice. Preferred low melt-viscosity polymers are polyethylene terephthalate and poly-m-xylyene adipamide. Others specified include polyhexamethylene adipate, polyhexamethylene sebacate, polycaprolactam and polyurethanes made by reaction of hexamethylene diisocyanate with diols, e.g. 1,4-butane diol. Polyethylene is the preferred high melt-viscosity polymer. Others specified include polystyrene, cellulose acetate, cellulose acetate-butyrate and polyvinyl acetals. The polyethylene terephthalate used may have a melt-viscosity less than 7000 poises at 350- 600 F., and the polyethylene may have a meltviscosity in the range of 10,000-200,000 poises at 350-600 F. Desirably, the extrusion temperature is at least 510 F. As shown, polymer melts are supplied via extruders 2, 4 to the inlets 1, 3 of annular extrusion nozzle 10, so constructed that the two melts converge to form two concentric tubes 16, 18, which emerge from the nozzle 9 and are inflated by gas supplied via 21. The tube is chilled and set by passage through cooling zone 12 and collapsed by squeeze rolls 20. The concentric seamless tubes can be used as such or further treated, or they can be separated by slitting and removing the outer tubing and the inner seamless tubing further treated. Thus, where a tube of polyethylene terephthalate or other low meltviscosity polymer is desired, it may be extruded as the inner tubing, using a polyethylene or other high melt-viscosity outer tubing. The concentric tubes after passing through squeeze rolls 20 are then passed through a slitting device 24 and the outer tubing 18 slit and separated from the inner tubing and wound up on a windup reel 26. The polyethylene terephthalate tubing 16 remaining is in the amorphous state and may be biaxially oriented by passing through squeeze rolls 28, heated to about its second order transition temperature by passage through radiant heater 34, and collapsed by passage through converging rolls 31 and squeeze rolls 32, longitudinal stretching being effected by rotation of rolls 32 at a higher rate than that of rolls 28, and transverse stretching by inflation of the tube between rolls 28 and 32. The oriented tubing 16A is heat shrinkable and may be reeled at this point. (For the use of this film in packaging, see Division B8 Abridgment). A heat stable film may be made by passing the oriented tubing 16A through squeeze rolls 38, diverging rolls 39, heating it by passage through radiant heater 42, and collapsing it by passage through converging rolls 43 and squeeze rolls 44. The rolls 38 and 44 are rotated at the same speed and the tubing is inflated to keep it taut while passing through heater 42. To stabilize the film against subsequent shrinkage, it is heated in this step to a temperature higher than its second order transition temperature but below the polymer melting point. In a modification, biaxial orientation and heatstabilization are effected in one operation. As shown (Fig. 4), the tubing 16 is passed through squeeze rolls 70, inflated, heated to a temperature for biaxial orientation by passage through heater 72, and further heated to effect crystallization and stabilization by passage through heater 74 before being collapsed by squeeze rolls 76. Seamless, crystalline, biaxially oriented tubing having a melt-viscosity at the extrusion temperature less than 7000 poises, and even as low as 500 poises, may be made by the method of the invention.