GB545434A - Improvements in and relating to the manufacture and production of regenerated cellulosic film - Google Patents

Abstract

545,434. Films. BRITISH CELLOPHANE, Ltd. Nov. 22, 1940, No. 16813. Convention date, Dec. 1, 1939. [Class 2 (ii)] Films are obtained by shaping a cellulosic solution, treating it with a coagulating liquid, and passing the coagulated products through a gaseous environment while they are being converted to regenerated cellulose products by the action of an acid regenerating agent. The films are then subjected to washing and purifying treatments and are finally dried. Regeneration may take place immediately after the formation of the film by coagulation of the cellulosic solution. During passage of the film through the gas or vapour, it is preferably allowed to shrink freely in its longitudinal direction. The gaseous environment may be heated and the regeneration may be effected by the action of an acid medium. Regeneration may be effected in a chamber provided with rollers for guiding the film without stretching it. As shown in Fig. 1, viscose is extruded from a hopper 191 into a tank 193 containing coagulating liquid. The film passes over a roller 41 which applies regenerating liquid from a trough 43, and it then passes into a chamber 20 where it is conveyed and guided by rollers 21, 22. The chamber 20 contains a nozzle 25 supplied with a heated gas such as steam through a pipe 26. The gas strikes a spreader device 24. The nozzle may be of a flat triangular shape and may be made of lead sheets. The piping may be made of canvas impregnated with a phenol-formaldehyde resin. As shown in Fig. 2, the steam expander 24 may be lead tube mounted on a lead rod 88. The regenerated cellulose film leaves chamber 20 and passes through a series of tanks where it is subjected to liquid treatments such as washing, desulphurizing, bleaching, dyeing, and softening. It is then subjected to drying treatment. At the conclusion of the liquid treatments, the film may pass between squeeze rolls and the liquid so removed may flow down drainboards back to the tanks. The film is dried in a chamber 16 where it passes over rolls 51-54. Rolls 51, 52 and 53 are driven by belts which themselves are driven from a main shaft 64. In order that the film may be free to shrink, an adjustable drive is provided for rolls 21, 22 of the regenerating chamber 20. This drive is shown in Fig. 5. The film 100 passes round rolls 21, 22, which have shafts extending outside the chamber 20. Pulleys 121, -122, on these shafts are frictionally driven by a belt 90 which may be made up of a plurality of small belts each of trapezoidal crosssection. The belt 90 passes under adjustable guide rollers 91, 92, which maintain the frictional drive. The tension in the belt is maintained by fixed guide rollers 93, 95, and a swinging guide roller 94 mounted on an adjustably weighted, pivoted arm 96. The coagulating bath may be a solution of ammonium sulphate or of sulphuric acid and sodium sulphate, and the regenerating liquid, applied by roller 41, may be dilute sulphuric acid. The process is applicable also to the production of films by the cuprammonium process. Instead of steam, there may be used air, nitrogen, or hydrogen chloride gas in the regenerating chamber which may be heated by radiant heaters, or high frequency electric fields. The gas may be circulated and the vapours removed. The coagulating and regenerating liquids may be heated. The rolls 21 may have surface knobs or grooves to avoid slippage of the film. Specification 211,446, [Class 2 (ii)], is referred to.