Patent GB-407351-A (GB)
Title: Improvements in the manufacture of films, foils and the like containing cellulose derivatives
IPC: C08L1/08
Filed: 1932-09-09
Abstract: <PICT:0407351/IV/1> Films, foils, or sheets are obtained by forming a solution of a cellulose ester or ether into the required shape, passing the shaped material through an encompassing gaseous medium and then into a coagulating bath.  The gaseous medium is isolated from the surrounding atmosphere or alternatively vapours having a solvent or softening action on the cellulose derivative are introduced into the gaseous medium in addition to those arising from the evaporation of the film-forming solution.  After issuing from the shaping device and passing through the gaseous medium, the film may be received on a drum or band wholly or partially immersed in the coagulating bath.  The film may pass through the coagulating bath for some distance before being received on the drum and it may be surrounded with a protecting shield.  The shaping device may be placed within a casing the atmosphere in which is saturated with solvent vapour by the presence of a vessel containing solvent or a fabric or porous material such as pumice saturated with solvent. Alternatively, a current of evaporative medium may be passed through the casing.  The films may be stretched longitudinally and laterally continuously with their production. The film-forming solution may contain high or low boiling point solvents and diluents.  The coagulating baths may be aqueous, or organic, and may contain softening agents for the cellulose derivative.  The softening agents or solvents may be washed out before drying, or a residue of solvent may be left in the material to be removed by evaporation.  Drying may be carried out on the drum or other support on which the films are produced or in a separate drying apparatus.  In an example a solution of cellulose acetate is extruded through a shaping device contained in a casing and after passing through the gaseous medium enclosed therein, the film enters a strong solution of calcium chloride. After passing for a few inches through the bath, the film passes round a rotating drum.  It is then washed first with dilute calcium chloride solution and then with water, dried on a steam heated drum and wound. As shown in Fig. 2, film-forming solution is extruded from a shaping device 10 enclosed in a casing 12 which is placed over one end of a tank 5 containing coagulating liquid. The space within the casing 12 is saturated with solvent vapour by means of a strip of absorbent fabric 16 suspended from the top of the casing and dipping into solvent contained in a shallow vessel 15.  The extruded film passes through the casing into the coagulating bath and round a drum 6 from which it passes out of the bath to washing and drying devices.  The casing extends into the vessel 5 so that one edge almost touches the drum 6. Coagulating liquid enters and leaves through slotted pipes extending across the width of the vessel 5 In another construction, the casing 12 is provided with inlet and outlet pipes for a current of evaporative medium.  Specifications 177,868, 179,234, [both in Class 2 (ii)], 340,324, 340,325, 340,326, 340,436, 340,437, 343,062, 375,423, 378,858, 380,819, 400,589, 405,676, 405,692, 406,337, and 406,985 are referred to.