Patent GB-1071085-A (GB)
Title: Oriented thermoplastic film
Inventor: DYER GERALD BENJAMIN
IPC: B29C48/10
Filed: 1962-12-31
Abstract: 1,071,085. Films; laminates. E. I. DU PONT DE NEMOURS & CO. Dec. 31, 1963 [Dec. 31, 1962], No. 49074/62. Headings B5B and B5N. Apparatus for producing a monoaxially oriented tube of thermoplastic polymeric material such as polythene, polypropylene or other polyhydrocarbons comprises an extruder 26, and a rotating annular die 25 to which air is admitted to inflate the extruded tube 10, which is drawn upwardly over cooler 11 supplied with a liquid coolant. The cooler must have sufficient cooling capacity to reduce the temperature of the film to a temperature below that of the thermoplastic material in its formative state. Above cooler 11 is positioned a first set of draw rolls 12, 13 the outer driven rolls 12 engaging with the inner idler rolls 13. An internal heater 14 is located above this first set of draw rolls 12, 13, and this is followed by a second cooler 15. A second set of draw rolls 16, 17 is mounted above the second cooler. Draw rolls 16, 17 are driven at a speed 2-5¢ times greater than the speed of first set 12, 13 resulting in the film being stretched or oriented in the space between the two sets of rollers. Heater 14 raises the temperature of the film to the orientation temperature range. Cooler 15 cools and sets the film after it leaves this orientation zone. Cooler 11, draw rolls 12 and 13, heater 14, second cooler 15 and draw rolls 16 and 17 are all mounted coaxially with, and rotate at the same speed as the rotating annular die 25. The tube 10 rotates at the same speed and thus there is no relative rotational motion between any of these components and the thermoplastic tubing. Hence the tube becomes longitudinally oriented. The oriented thermoplastic tube is then slit on the bias by stationary knife 18 or by a pair of knives 18 and 19 to give two flat sheets 20, 21 which are wound on rolls 22, 23. Hence the flat films produced are oriented at an angle to their longitudinal direction, and this angle may be varied from approximately 1 degree to approximately 89 degrees. The theory of the method is illustrated by Fig. 1 (not shown). Where the direction of orientation of each of the sheets 20 and 21 is at approximately 45 degrees to the longitudinal direction and these two sheets are laminated together, the directions of orientation will be at right angles to each other and hence a relatively high tensile strength film will be obtained. In addition, the resultant film overcomes the low tear deficiencies of biaxially oriented films since any tear would always be in the high tear direction of one sheet. A similar laminated film may be made from two sheets, one of which has been oriented substantially at right angles to its new longitudinal direction and another sheet which has been oriented longitudinally. Apparatus for making a laminated film is shown in Fig. 3. The monoaxially orientated rotating tube 10 is drawn upwardly and cut on the bias by stationary knives 18 and 19 to form two sheets 20, 21 in which the direction of orientation 38 is at approximately 45 degrees to the longitudinal direction of the sheets. Sheet 20 is taken over the rolls 28 and 30 and sheet 21 over rolls 29 and 31. The two sheets are then brought into surface-to-surface contact at laminating means 32. The directions of orientation are approximately at right angles to each other. The biaxially oriented laminated sheet 35 is then taken through nip rolls 33, 34 over roll 36 and wound on roll 37. The lamination of the sheets may be effected by extrusion lamination, solvent coating or other similar means. The adhesive interlayered between the two sheets, may be used as a carrier for pigments, colour, ultra-violet stabilizers, carbon black or other additives. Biaxially oriented film may be readily produced by taking film which is monoaxially oriented substantially at right angles to its new longitudinal direction and stretching this sheet in its new longitudinal direction. Hence the necessity of transverse stretching is avoided. The direction of the orientation lines of the monoaxially oriented film may be varied over quite a large range, but acceptable film may be produced from a monoaxially oriented film in which the angle of the initial monoaxial orientation is in the range from 45 to 89 degrees to the longitudinal direction of the film.