Patent GB-822681-A (GB)
Title: Film casting apparatus and method
IPC: B29C48/03
Filed: 1957-11-15
Abstract: <PICT:0822681/IV (a)/1> <PICT:0822681/IV (a)/2> <PICT:0822681/IV (a)/3> A film-casting apparatus comprises a coagulating bath, means for extruding into the bath a continuous web of film-forming material coagulable in the bath, a number of transverselydisposed fixed guide members, including a number of curved guide members, arranged in the bath to guide the web progressively through the bath in an alternately ascending and descending path, there being at least two descents whereby the web forms at least one upwardly extending pocket in its travel through the bath, the curved guide members being convex against the web and the guide members being so arranged that, with respect to at least two of the curved guide members, the edges of the web immediately approaching each curved guide member make an angle of not greater than 90 degrees with the edges of the web leaving the curved guide member.  As shown in Fig. 1, a continuous web F of filmforming material, e.g. viscose, is extruded from a conventional extruder 1 below the liquid level of the coagulating bath 2 contained in tank 3.  The freshly extruded web first passes downwardly in contact with conventional straight guide members 4, 5, 6 and thence around a curved guide member or rod 7 so positioned that the convex side of the curved portion of the rod contacts the film.  The straight guide 6 is in the plane of the curved guide 7.  The web just touches the guide 6 and is not deflected by it, so that the web approaches guide 7 with its plane parallel to the plane of the curved guide.  The web then passes upwardly and over a straight guide member 8, over the convex portion of a second curved guide member 9 positioned just below the surface of the bath, and downwardly under a straight guide-rod 9a and a third curved guide member 10.  From guide member 10 the web passes over and in contact with the convex side of a curved guide member 11, and out of the bath first to guide roll 11a and then to a conventional wiper rod 12 and a transfer roll 13.  The top of the or each upwardly extending pocket is preferably located at or near the bath surface to allow any accumulations of gas to vent easily to the atmosphere.  In order to control bath currents produced by the higher bath flow required to effect coagulation at the increased casting speeds rendered possible by the apparatus, a vertical baffle 20 is provided extending across the tank 3 and as far below bath level as possible without contacting the film.  Instead of a single curved rod an assembly of two or more curved rods 20, 211 and 212 welded to a reinforcing straight rod 22 (Figs. 5 and 6) may be used.  The curved guide member may be a slab or a relatively thick sheet of material having a rounded edge of the desired curvature or contour.  The radius of curvature of the curved guide members is preferably such that the centre of the web will be distended 3-7 inches from the straight line joining the edges of the web where they contact the member.  The ends or trunnions of the members may be mounted in bearings so that the effective curvature with relation to the path of travel of the web may be varied.  Specifications 211,446, [Class 2 (ii)], and 550,106, [Group IV], are referred to.