GB550106A - Improvements in or relating to the manufacture of non-fibrous web material - Google Patents

Abstract

550,106. Films. BRITISH CELLOPHANE, Ltd. June 17, 1941, No. 7663. Convention date, June 22, 1940. [Class 2 (ii)] In the production of non-fibrous web material by extrusion of a solution or melt, the web while in a condition susceptible to plastic deformation is caused to travel past one or more fixed convex guide members the convexity of which is directed towards the web and the convex side of which is arranged to contact the web. The curved guide members cause the middle portion of the plastic web to be displaced in its line of travel to a greater distance than the marginal portions and the web is thus stretched in the transverse direction. The process is applicable to the production of regenerated cellulose films from aqueous cellulosic solutions or dispersions, e.g. viscose, cuprammonium cellulose solutions, solutions of lowly substituted cellulose esters or ethers. It is also applicable to the production of films of cellulose esters or ethers from solutions in organic solvents, and to the production of films of nylon, polyvinyl acetals or butyrals, and phenol-formaldehyde resin. When producing regenerated cellulose films, e.g. from viscose, there may be used a single coagulating and regenerating bath or two separate baths. The curved guide rods may be used in coagulating or regenerating bath. The curved guide member may be made of nickel, stainless steel, or glass, or of a less acid-resistant material coated with rubber. It may be in the form of a rod or tube bent to the desired shape, or it may be fashioned from a slab so as to have a rounded edge of the desired curvature. The guide member need not be rigid but may be of flexible material with arrangements for adjusting the convexity. The guide member may be of constant or varying radius of curvature. As shown in Fig. 6, cellulosic solution is extruded from hopper 12 into coagulating bath 11. The extruded film 20 passes through the coagulating liquid and round a curved guide 15, a similar guide 16, and an intermediate straight guide 17. Guides 15, 16, can be rotated on an axis extending through their ends. The position of guide 15 is regulated by rod 31 sliding in block 33. Guide 16 may be rotated by a lever and fixed in any desired position by inserting a pin through one of the perforations 42 on disc 41 and perforation 44 in fixed member 43. The curved guides may have a flat central portion with fairly sharp curved portions at the sides so that the middle part of the film is transversely stretched to a greater extent than the margins. A straight support may be welded across the bowed part of the curved guide rod to increase its rigidity. As shown in Fig. 4, the guide member is a flexible tube 75 with a rubber sheath 76. At short distances along the guide, sustaining rods 77 are secured. These rods are adjustably fixed to the rigid member 71. Individual adjustments enable any desired contour in the guide member to be attained. The guide member 15, Fig. 6, may be clamped in such a position that the transverse stretching produced compensates for or exceeds the amount of shrinkage which occurs between the extrusion slit and the guide. The total transverse stretching produced by all the curved guides may be equivalent to the longitudinal stretch imposed after coagulation by the mechanism which forwards the web through the apparatus. Specifications 211,446, [Class 2 (iii)], 473,222 and 545,434 are referred to.