Patent GB-534719-A (GB)
Title: Improvements in and relating to a process for producing regenerated cellulose pellicles and the product produced
IPC: B29C71/00
Filed: 1939-11-06
Abstract: 534,719. Films. CELLULOSE HOLDINGS, Ltd. Nov. 6, 1939, No. 29504. Convention date, Nov. 7, 1938. [Class 2 (ii)] An aqueous dispersion of a coagulable cellulosic substance from which cellulose can be regenerated is formed into a continuous film which is conveyed by a moving body of liquid while being regenerated without being subjected to any substantial tension and the film is allowed to shrink both longitudinally and transversely. The film may also be allowed to shrink during purification treatment such as de-sulphuring by conveying it through the treatment apparatus under substantially no longitudinal tension. It may be conveyed through the treatment apparatus by a stream of liquid which may be the subsequent treatment liquid, e.g. the de-sulphuring liquid. The dispersion of coagulable cellulosic substance may be viscose, cuprammonium cellulose solution, or an aqueous solution of cellulose in zinc chloride, alkali metal thiocyanate, alkali perchlorate, sulphuric acid, or phosphoric acid. The film may be formed by extrusion as from a hopper or by casting as upon the surface of a drum. Preferably the cellulose solution is extruded through a slit-like orifice of a hopper, the slit being immersed in a coagulating liquid. The coagulated film is treated to regenerate the cellulose. It may then be passed through an acid bath to complete the regeneration. It is washed and neutralized, preferably while being substantially free from tension. In the case of viscose film, de-sulphuring may be effected with a hot solution of sodium hydroxide and sodium sulphide. The film may be washed, bleached, washed, and then treated with a plasticizer. It may then be dried under tension just sufficient to prevent wrinkling by passing it over a number of rollers rotating at an appropriate speed. The rollers may be heated or may be enclosed in a heated atmosphere. The cellulose solution may be extruded from the slit of a hopper on to a roller immersed in the coagulating liquid. The freshly coagulated film passes on to an endless belt which delivers the film to a long flat tank containing regenerating liquid which moves from one end of the tank to the other and conveys the film. From this tank the film is conveyed by a driven roller through several long flat tanks in which the treating liquid flows from end to end and conveys the film. To prevent gases from accumulating under the film there may be provided a plurality of rods with their tops just above the surface of the liquid so that entrapped gas may escape at the sides of the film as it passes over the rods. Films made by the process have substantially the same tensile strength and elongation longitudinally and transversely. Waterproof coatings applied to the films adhere tenaciously in view of the uniform properties of the films. Specification 376,278 is referred to. The Specification as open to inspection under Sect. 91 comprises also the production of cellulosic films from solutions of cellulose in organic solvents and it is not restricted to the use of a flowing liquid for conveying the films without tension. This subject-matter does not appear in the Specification as accepted.