GB1087156A - Thermoplastic articles, apparatus and process for their manufacture - Google Patents

Abstract

1,087,156. Film and sheet extrusion and conveying apparatus. MOBIL OIL CORPORATION. Feb. 11, 1965 [Feb. 17, 1964], No. 6594/64. Headings B5A and B5B. Apparatus for producing shaped articles, especially flat and tubular film and sheet material, comprises an extrusion die for forming a continuous shaped article having edge margins from molten thermoplastic material and means for restraining the article against substantial reduction in width and against substantial change in length, said restraining means being so disposed relative to said die that said means engage the edge margins while the extruded article is still at a temperature above the softening point of said thermoplastic material and so restrain the article. In Fig. 1, the cylinder 10 of a heated worm-screw extruder is connected by die feed conduit to the heated die 14, the face of which has a long slot of uniform width. Fig. 4 (not reproduced) shows a die suitable for extrusion of tubular materials having a central orifice 102 through which air is evacuated to flatten the extruded tube and an annular orifice 100 having ears 108 to provide beaded flanges along the length of the extruded film. The edge margins of the extrudate are gripped by the nip of coacting web guides 18 which may be in the form of endless belts, ropes, wires, cables, tapes or chains of metal, fibreglass, polytetrafluoroethylene, or polychlorotrifluoroethylene. Flat film or sheet material to be conveyed may be extruded with beaded edges to facilitate gripping but this is not essential. Members 20 and 22 may be sprockets, if the web guides 18 are chains, or may be flanged or grooved pulleys where other forms of web guides are used. The web guides move around the support plates 24 on a number of additional guiding devices, e.g. idler pulleys 32, 34, suitably mounted on slotted bases (not shown) bolted to plates 24 to provide means for adjusting the tension of web guides 18, fixed outer shoes 30 and adjustable inner shoes 26 and 28. Shoes 26 may be moved towards or away from shoes 28 by means of cams 74 operated by a lever mechanism 80 on the back of the plate (Fig. 3, not reproduced). The material is cooled on a chilled casting roll 46. Longitudinal stretching may be effected by variation of the speed of rotation of the roll relative to that of the web guides or alternatively by immersion in a liquid bath. If desired, cold air jets may be arranged to strike the material in the discharge end of the guides so as to cool it to below its softening point while still carried by the web guides. The web guides may be cooled during their return travel between shoes 30 by application of a spray of volatile liquid, e.g. ethanol, or by using internally cooled support plates 24. The assemblies 16 have brackets 36 affixed thereto, pivotally attached to box frame member 38 by pivot pins 40. Journal block 42 is adjustably fastened to frame 38 by bolts or other suitable means and is provided with an opening therethrough for slidable and rotatable engagement with the horizontal support rod 44 which is rigidly attached to die 14. Hence both web guide assemblies 16 are independently capable of several types of movement. Thus they may be moved back and forth horizontally on support rods 44 towards or away from the die, e.g. to accommodate materials of different width. They may also be pivotally swung around the rods 44 to any selected plane from the vertical to the horizontal, the box frame 38 being locked in the selected position by set screws (not shown). Each assembly 16 may be moved pivotally around pins 40 as centre enabling the guide assemblies to be brought into parallel or diverging relationship so as either to maintain or vary the width of the material carried by the guides, e.g. in transverse stretching. The assemblies are held in position by struts 96 which are connected to the rack of rack-andpinion assemblies. The assemblies may also be vertically raised or lowered to adjust the gap between the die orifice and the nips of the web guides by means of set screws (not shown) in box frame 38, which control the position of block 42 relative to frame 38. Desirably, means for simultaneously reversing both driving trains are fitted so as to facilitate reversal of the web guides to clear jams or torn films. Deckled edge films may be made by oscillating the web guide assemblies in small arcs by a suitable mechanism connected to struts 96 and centred on pivot pins 40. Multi-laminar materials may be processed by providing a plurality of extrusion dies as close as possible to the nips of the two pairs of converging web guides and directing the various extruded sheets or films into the nips. Tubular films may be handled using the extrusion die of Fig. 4 (not shown), the tubing being evacuated to deflate it and produce a two-layer laminar structure. Materials which may be processed using the apparatus include polymers and copolymers of polypropylene, polyethylene, polystyrene, polyvinyl and polyvinylidene chlorides, and polyethylene terephthalate.