Patent GB-528107-A (GB)
Title: Improvements in the production of films or sheets of cellulose derivatives
IPC: B29D7/01
Filed: 1939-01-16
Abstract: 528,107. Cellulose derivative compositions ; films. KODAK, LTD. (Eastman Kodak Co.). Jan. 16, 1939, Nos. 1431, 2003, 2004, 2005, 2006 and 20682. [Class 2 (ii)] Films are produced by casting on to an endless film-forming surface a composition containing a volatile solvent and an organic cellulose derivative and such that the composition before casting is a readily flowable liquid which is convertible to a non-flowable self-supporting continuous clear gel by mere cooling. The composition is cooled to a temperature at which such conversion takes place while it is moving away from the casting position and, before or after removal of some of the solvent by evaporation, the cast material is stripped from the film-forming. surface, and any residual solvent is thereafter removed. The cast composition may be removed while it is still in the form of a non-flowing self-supporting continuous clear gel. The composition employed may be one which gives a clear liquid at temperatures above 50‹C. but which forms a self-supporting gel at a temperature between 10 and 50‹C. The cellulose derivative may be cellulose acetate, aceto propionate, aceto butyrate, or other ester. The solvents employed include ethylene, propylene, and butylene chlorides, and trichlorethylene, or mixtures of one or more of these. Propylene chloride or trichlorethylene may be used in admixture with a monohydric alcohol of 2-5 carbon atoms. A mixture of toluene or xylene and an aliphatic alcohol containing not more than 5 carbon atoms may be used for cellulose mixed organic esters. Acetone or other solvents may be used in limited amounts. There may be used a cellulose-acetate propionate or cellulose acetate-butyrate having a total acyl content of at least 43 per cent and a propionyl or butyryl content of 8-35 per cent dissolved in a liquid consisting of propylene chloride alone or with ethylene chloride or butylene chloride. The composition may be cellulose acetate, acetopropionate, or aceto-butyrate of a total acyl content of at least 39 per cent dissolved in propylene chloride and a monohydric alcohol e.g. 70 per cent of propylene chloride and 30 per cent of isopropyl alcohol. The composition may be cellulose aceto-propionate or butyrate of a total acyl content at least 40 per cent with propionyl at least 18 per cent or butyryl at least 13 per cent, dissolved in toluene and an aliphatic alchol. Suitable acetyl and propionyl or butyryl contents of cellulose acetate or cellulose mixed esters for use with particular solvent mixtures are represented graphically. The process is applicable to the production of films for wrapping or photographic purposes or of sheets for making laminated glass. The films produced are of low swell and shrink amplitude. Plasticizers such as triphenyl phosphate may be present. For making films there may be employed an apparatus comprising a pair of spaced drums, a movable band running over the drums, a hopper adapted to receive the warm fluid composition and to apply a thin layer of such liquid to the band, a heater to heat the band at the point of application of the liquid, and a cooling device to cool the band and congeal the applied layer of liquid. Alternatively, a drum casting surface may be employed. As shown in Fig. 1, the fluid composition passes from storage vessel 1 into the hopper 7 and is applied to the drum 12 provided with cooling means. A current of heated air is passed through the casing 14. The film in gel form containing all or a large proportion of the solvent is stripped from the drum and passed through a series of chambers 18-20 through which air at successively higher temperature is passed. The dried film is finally wound on spool 55. Specifications 12976/09, [Class 2 (ii)], 528,375, and 528,382 are referred to.