Improvements in the manufacture of films from cellulose derivatives

摘要

Films suitable for photographic purposes are obtained from solutions of a cellulose derivative in a solvent mixture of which the individual constituents are non-solvents and include one or more constituents miscible with water in all proportions, and one or more constituents insoluble in water or not miscible in every proportion, and the latter constituent is present in a quantity at least twice that of the constituent which is miscible with water in all proportions. The solution of the cellulose derivative is formed into a thin layer which is coagulated with an aqueous solution of an aliphatic alcohol miscible with water in all proportions. In an example, a solution of nitrocellulose with a small proportion of camphor in a solvent mixture of ether and alcohol is introduced, in the form of a thin layer, into a bath of aqueous alcohol at a slightly raised temperature. The film is stripped from the forming surface and washed. It may then be coated with gelatine. In another example, a solution of cellulose acetate with tripropylphosphate as plasticiser in a mixture of methylene chloride, methyl alcohol, and ethyl alcohol is formed into a film with the aid of a coagulating liquid consisting of aqueous methyl alcohol. In another example nitroethyl cellulose dissolved in a mixture of benzene and ethyl alcohol is formed into a film with the aid of n-propyl alcohol and water. The coagulating liquid may enter the bath at the place where the film is stripped from the drum or other forming surface, and flow in countercurrent to the film. The use of a drum or like surface may be dispensed with. As shown in the drawing, a cellulose derivative solution issues from a slot, into a flowing precipitating liquid 3 where it coagulates in the form of a sheet 2 which is carried with the liquid through the chamber 8 to the chamber 4. The film is then taken over rollers and passed through a washing tank 7 on its way to a drying chamber. The liquid from chamber 4 is pumped back to the supply tank 6. Specification 347,423 is referred to.