Patent GB-869404-A (GB)
Title: Method and apparatus for producing two or more films simultaneously
IPC: B29D7/00
Filed: 1959-10-12
Abstract: <PICT:0869404/IV (a)/1> <PICT:0869404/IV (a)/2> <PICT:0869404/IV (a)/3> Two or more flat self-supporting films are produced simultaneously by extruding filmforming material through two or more nozzles into a bath or baths of coagulating liquid, withdrawing the at least partially coagulated films from the coagulating liquid and positioning them together with their adjacent surfaces in contact with each other at a point above the level of the liquid, separating successive portions of the films from each other while advancing them above the level of the liquid, then positioning the films together again with their adjacent surfaces in contact with each other as the films are again passed into a bath or baths of coagulating liquid, withdrawing the films from the latter and then passing the films into and through an after-treating liquid with their adjacent surfaces maintained in contact with one another.  The film-forming material may be viscose, a solution of cellulose in an aqueous solution of zinc chloride or of cuprammonium or an organic amine, an aqueous solution of a water- or alkalisoluble cellulose ether, or an aqueous solution of gelatin, casein, vinyl acetate or polyvinyl alcohol.  As shown in Fig. 1, two films, A and B, are simultaneously formed by extruding, for example, viscose from hoppers 11 and 13 through nozzles 17 and 19 into heated coagulating liquid 15 contained in tanks 21 and 23.  The at least partially coagulated films are passed about the guide rods 35 and 37 and then withdrawn from the coagulating liquid 15 along vertical paths through wipers 45 by driven rollers 39.  From the rollers 39 the films travel over guide rollers 43 to a roller 41 where they are positioned together with their adjacent surfaces in contact with each other.  The films are then separated from each other by a series of rollers 47 along paths of equal length to facilitate the escape of gases and vapours from the films during a stage when the gases and vapours are being rapidly evolved.  The films are then again positioned together as they are passed over a roller 49, again separated from each other by being passed over spaced guide means 51 and 53 and brought together as they pass under a guide rod 55 immersed in a coagulating and/or regenerating liquid 25 contained in a series of tanks 57, 59, 61 and 63.  Within the liquid 25 the films are separated a number of times. Thus after leaving the rod 55 they are separated, the upper film passing over a roller 67 before passing over a roller 69, while the lower film travels directly to the roller 69 where it is again contacted with the upper film. The films then travel in contact together downwardly into the liquid 25 in tank 57 and about a guide rod 71, after which their paths are separated in the same manner as before.  After leaving the liquid 25 the films are passed in contact with one another through a series of after-treating liquids contained in tanks 99, 101, and 103 as shown in Fig. 3.  Tanks 105 contain a softening liquid and in passing through this liquid the films are separated twice in a manner similar to that shown in Fig. 2 in order to effect a faster and more complete plasticizing of the films.  The process and apparatus, of the invention reduces the tendency of the films to tear during their production.