Patent GB-241590-A (GB)
Title: Method of and means for the production of thin and very thin foils and film-like bands from soluble cellulose derivatives
IPC: B29C48/08
Filed: 1925-10-20
Abstract: Films and very thin foils down to 0.03-0.01 mm. in thickness, are prepared from cellulose derivatives such as nitrocellulose, cellulose acetate and cellulose ethers, by applying to a base consisting of a long endless band of flexible material, a highly viscous or highly concentrated or easily-solidifying solution of the cellulose derivative, conveying said band continuously, as a series of loops, without pulling or tensioning it, through drying devices and eventually stripping the film from the backing; by the use of such solutions, the layer on the band will no longer run off or be displaced thereon.  The thickness of the film is adjusted by varying the speed of the band and the outlet of the coating-device; generally the method permits of speeds of production much higher than those ordinarily employed.  Suitable materials for the band are cardboard, sheet metal (for example, hard or semi-hard aluminium), thick cellulose film, linoleum, rubberized material and cellulose acetate, and the base may be coated with gelatine, starch, rubber, albumen or cellulose derivatives.  The solution is applied to the band by a funnel with a very wide slot and adjustable with respect to the base, or by means of a roller or knife-spreader, and it is convenient that during coating the band should be horizontal, and after coating it should be led over a smooth surface on a drum until the coating has solidified, with or without the aid of heating or cooling; if both sides of the band are to be coated, the coating-devices operate on both sides thereof, the band travelling vertically. The coated material is then passed continuously through the drying-apparatus in the form of loops so as to accommodate an increased length of material, and the looping-apparatus preferably comprises a series of rollers or discs of substantial diameter mounted in fixed bearings and driven at the same peripheral speed as the coating-device, the band itself being positively moved forward by means of rotating discs, hollow rollers, toothed wheels, belts, &c. which contact only with its edgs and are arranged on opposite sides of the band.  After passage through the drying-apparatus, the strip or strips of film are removed from the backing and separately rolled up; the band is returned to be again coated.  Alternatively, the band after drying and without removal of the film, may be again coated, and the several coatings may be of the same composition if a thick film is desired, or the coating may be dissimilar, as, for instance, in the case of photographic films, the preliminary coatings of the film-backing or even the photographic emulsion being applied in a single working operation. The surface of the band may be polished, or it may be etched, stamped, printed &c., in which case the film will have a matt or ornamented surface.  Specifications 202,306 and 224,848 are referred to.  The Specification as open to inspection under Sect. 91 (3) (a) comprises also the following subject-matter:-the band need not be endless and is rolled up after the film is stripped therefrom; the thickness of the film is adjusted also by varying the distance of the band from the coating-device; the use of a loop-way for drying the film is optional, and the band may be subjected to successively different drying conditions, as by differential heating or cooling, or by the introduction or removal of air at one or more points; a number of pouring-devices may be used in series; and the endless band is preferably returned below the loops.  This subject-matter does not appear in the Specification as accepted.