Patent GB-550560-A (GB)
Title: Improved method of making cellulose organic derivative films or sheets
IPC: B29D7/01
Filed: 1941-05-15
Abstract: 550,560. Cellulose derivative compositions and films. KODAK, Ltd. May 15, 1941, No. 6276. Convention date, Aug. 1, 1940. Addition to 528,107. [A Specification was laid open to inspection under Sect. 91. of the Acts, Nov. 17, 941.] [Class 2 (ii)] The process of the parent Specification, in which a cellulose derivative solution is cast on to an endless film-forming surface and converted by cooling to a non-flowable self-supporting con. tinuous clear gel which is stripped from the casting surface before or after removal of some of the solvent by evaporation and then treated for removal of residual solvent, is modified by employing a solution of cellulose propionate, cellulose butyrate, cellulose aceto-propionate, or cellulose aceto-butyrate, containing at least about 5 per cent. of propionyl or butyryl and not less than about 40 per cent. total acyl, in a solvent mixture comprising an alkylene chloride or a chloroalkylene compound having 2 or 3 carbon atoms in the molecule, a monohydric aliphatic alcohol having 1 to 5 carbon atoms, and an aliphatic or alicyclic hydrocarbon boiling within the range of 50À110C. The casting temperature is not in excess of the boiling point of the lowest boiling solvent or solvent combination present in the composition, and preferably it is not above 65C. Instead of converting the solution to a continuous gel by cooling, the gel may be formed by casting the solution on to a film-forming surface at a temperature sufficient to bring about selective evaporation of the more volatile components of the solvent mixture, but not above 65C. 'The ethylene or propylene chloride forms about 40-80 per cent. of the solvent composition. The aliphatic alcohol forms about 5-30 per cent. of the solvent mixture. The hydrocarbon forms about 10-50 per cent. of the solvent mixture. It may be an aliphatic hydrocarbon or a mixture of such hydrocarbons obtained from petroleum, e.g. ligroin or petroleum ether, or it may be cyclohexane or methyl cyclohexane. The cellulose. ester compositions are such that they are readily flowable liquids at temperatures above 50C. but are capable of gelation when the temperature is lowered e.g. to within the range of 10C. to 50C., and also capable of gelation by selective evaporation of one of the components of the solvent mixture. The range of suitable proportions of the constituents of the solvent mixture for any particular cellulose ester varies with the particular constituents selected. Suitable compositions are shown graphically in the Specification. Among the solvent mixtures used are :-ethylene chloride, n-butyl alcohol, cyclohexane ; trichloroethylene, n - butyl alcohol, cyclohexane ; ethylene chloride, methyl alcohol, ligroin; propylene chloride, n - butyl alcohol, cyclohexane ; cis-dichloro ethylene, n-butyl alcohol, cyclohexane. As shown in Fig. 1, the film-forming solution in tank 1 is heated by fluid circulating in coil 4 and thermostatically controlled. The solution is passed into hopper 7 which com. prises a V-shaped trough 10 provided with chambers 11, 12 through which heating fluid may be passed. The hopper has an adjustable blade 13 co-operating with fixed blade 14 to control the thickness of the issuing stream of dope. Solvent vapour may be fed into the space just below blades 13 and 14 on opposite sides of the dope stream through suitably placed inlets. The blades are raised some distance above the wheel surface so as to provide a baffled space for confinement of solvent vapours at the sides of the dope stream. In an alternative construction means are provided for supplying solvent in liquid form directly to the back blade of the hopper. The dope is cast on wheel 23 provided with cooling means and with a casing 25 through which a current of heated air may be passed in counterdirection to the wheel surface. The formed film is stripped at roller 28 and then passed through a drying chamber 29 comprising three sections each provided with inlet and outlet conduits for heated air and with guide rollers which are driven in such manner as to allow the film to shrink.