Patent GB-1206322-A (GB)
Title: Method and apparatus for the preparation of biaxially oriented film
Inventor: SEDERLUND EDWARD RAGNER
IPC: B29C55/28
Filed: 1968-08-16
Abstract: 1,206,322. Tubular films. DOW CHEMICAL CO. 16 Aug., 1968 [21 Aug., 1967], No. 39397/68. Heading B5B. Apparatus for the biaxial stretching of a synthetic resinous film comprises in co-operative combination at least a first torus 17 and a second torus 22, the first torus having a lesser diameter than the second torus, each torus having (i) a surface 20, 24, (ii) an axis of generation and (iii) a circle of generation, the first and second tori having generally coaxial axes of generation, and means to rotate the surfaces of the tori about their respective circles of generation, wherein the rotation of the surface has a component of motion lying in a plane containing the axes of generation. A synthetic resinous film tube may be biaxially oriented using this apparatus, by forming a tube of the film, stretching the tube by expanding it in a generally radially outward path while mechanically supporting the tube about its periphery by a toroidal support 17 at a first location and applying a frictional force about its periphery, supporting the tube by a toroidal support 22 at a predetermined second location remote from the first location, applying a predetermined frictional force circumferentially to the tube, thereby increasing the diameter of the tube, and stretching it longitudinally and transversely to obtain a biaxially oriented synthetic resinous tube. Thus, in Fig. 1, tube 15 passes from the annular opening 13 of die 12 to the inner space 18 defined by torus 17. Tube 15 is then passed more or less radially outwardly from the axes of generation of the tori, over the surface 20 of torus 17 to the surface 24 of torus 22. Tube 15 then essentially reverses its original direction, contacting the slitting members 26 and 27 which slit the tube into a pair of separate sheets 32 and 33 which are wound up on take-up rolls 29 and 30. Fig. 2 shows the construction of the apparatus in more detail. A portion of tubular film 70 is heated as it passes upwardly and over tori 67 and 105 by heaters 108, 110, 111, and 112. Torus 67 is supported by a plurality of first torus support assemblies of which one, 49, is shown, comprising a support 50 secured to surface 48. Support 50 has rotatably mounted therein remote from surface 48 a rotatable idler support roll 51, and has pivotally mounted therein a bell-crank or drive roll support 53, adjustably supported on base 43 by an adjusting means 55 and a tension means 57. A second arm 60 of bell-crank 53 has rotatably fixed thereto a rotatable drive roll 62. A toroidal flexible drive shaft 64 is in operative engagement with drive roll 62 and connected to a plurality of further drive rolls (62), not shown, and disposed in generally radial arrangement about the axis of a tube passing upwardly through opening 45. Thus, torus 67 is in contact with drive roll 62 and idler roll 61, and has a centre of rotation 68 lying on the circle of generation of the torus. The angle formed by the centre of rotation 68, the drive roll 62 and the idler roll 51 is about 90 degrees and preferably somewhat greater. Oppositely disposed from the torus support assembly 49 is a first torus drive assembly 72, comprising a toroidal flexible shaft 64 to which is attached driving pulley 75 engaging belt 76 driven by motor 79. Rotation of the shaft 64 causes rotation of a plurality of radially spaced drive rolls 62 which are in frictional engagement with torus 67, so that frictional force causes at least the outer surface of the torus to rotate as indicated by the arrows. Thus, film 70 is frictionally engaged by the surface of torus 67 and urged in a generally radially outward direction. A plurality of second torus support assemblies 85 (one shown) are disposed on a circle outwardly from the first torus support assemblies 49. Second torus support assembly 85 comprises a support 86 carrying a rotatable idler roll 88, adapted to rotate in a plane passing through the axis of the tube 70, that is a radial plane. Support 86 carries a drive roll support arm 91, having a first end 92 having disposed therein a bearing 94 supporting a toroidal flexible drive shaft 95 which has concentrically mounted thereon a drive roll 97. The second end 98 of arm 91 has a positioning means 100 and a resilient tensioning means 101 adapted to force the second end 98 towards the body 42 and so tension drive roll 97 in a radially outward direction. A second torus 105 is in operative engagement with drive roll 97 and idler roll 88. Torus 105 has a centre 106 co-extensive of the circle of generation of the torus and at least the outer surface of second torus 105 is capable of rotating about its circle of generation indicated by reference numeral 106. The smallest angle formed by the centres of the rolls 97 and 88 and the centre 96 beneficially is slightly greater than 90 degrees. Thus tubular film 70 passes over the first torus 67 into a stretching region lying between the first and second tori 67 and 105, respectively. Film passes over second torus 105 still in tubular form. The film is heated by annular discoidal heaters 110, 111 and 112 disposed generally adjacent film 70a in the stretching zone lying between first torus 67 and second torus 105. Slitting assembly 115 is supported external to body 42. Fig. 4 (not shown) shows a sectional view of torus (105) illustrating its construction. Torus (105) comprises a rigid core (135) of a rigid material such as steel and forms a static mandrel. A plurality of bearings or rings (136) are disposed about (135) and are a free sliding fit thereon. A sheath (137) having the configuration of a hollow torus is disposed over core (135) and bearings or rings (136). Sheath (137) is made of an elastomeric material beneficially composed of one or more layers of rubber. Fig. 5 (not reproduced), illustrates the second torus drive assembly (131) in more detail. Fig. 6 shows a sectional view of an alternative embodiment of the invention comprising a first torus 151, a second torus 152 coaxial with and adjacent to torus 151, a third torus 153 coaxial with and adjacent to torus 152, and a fourth torus 154 coaxial with and adjacent to torus 153. The tori 151, 152, 153 and 154 are of successively increasing diameter and axially spaced from each other to form a generally bell-shaped configuration. Drive means, heaters &c. are omitted for clarity. The film tube 156 is thus stretched outwardly in a generally bell-shaped configuration, thereby providing zones of varying machine direction and transverse direction stretch between adjacent tori. Fig. 7 shows a further alternative arrangement of tori of the present invention. A first or small torus 165 is disposed coaxially with regard to a second torus 167, tori 165 and 167 being selectively positioned along the axes of generation as indicated by the arrows. This embodiment provides a means to vary the machine and the transverse direction orientation imparted to a tube being treated and to provide a longer temperature control zone. In operation of any of the embodiments illustrated, the surface speeds of the first and second tori are independently variable, so that the tube is caused to be stretched in a desired manner in the zone generally indicated by reference numeral 70a of Figure 2. Applying appropriate heat to the film from the heaters 108 to 112, stretching conditions are obtained which are optimum for obtaining the desired film characteristics and are independent of the melt strength of the tube being extruded. Apart from the arrangement of Fig. 4, tori suitable for the present invention may be made using a rotating mandrel rather than a static mandrel by utilizing a helical spring disposed within an elastomeric tube made, e.g., of neoprene rubber and/or polysiloxane or silicone rubber. The helical spring is bent to form a torus, the ends joined and subsequently formed into a batt joint by a suitable adhesive. Alternatively, bearings 136 may be replaced with a metal ring of generally toroidal configuration prepared of steel or brass and a suitable lubricant disposed within the elastomeric sheath prior to vulcanization or sealing of the ends. Advantageously, a mandrel that rotates with the outer sheath may be prepared from sheet metal bellows bent to form a generally toroidal configuration. When a bellows, helical spring or the like is employed, the number of turns in a helix or corrugations in the bellows relative to the diameter must be selected to provide adequate support for the outer sheath to maintain the torus of generally constant dimensions when under pressure from the film being stretched. Using the apparatus illustrated, extruded tubular films of polystyrene, polypropylene, a copolymer of 85% vinyl chloride and 15% vinylidene chloride, polyamides, a copolymer of 25% acrylonitrile and 75% styrene, and copolymer of 60% styrene and 40% acrylonitrile, polyethylene terephthalate, chlorinated polyethylene containing about 28% chlorine, high density or linear polyethylene and polyvinyl chloride may be oriented over a wide variety of conditions, many of such conditions not being feasible with the conventional trapped bubble process.