GB510802A - Improvements in or relating to transparent closures and the like - Google Patents

Abstract

510,802. Cellulose derivative and synthetic resin films, eye-pieces, windows &c. DREYFUS, H. Feb. 8, 1938, No. 3947. [Classes 2 (ii) and 2 (iii)] Eye-pieces of respirators or goggles, or windows or windscreens of closed vehicles, aircraft, gun-turrets or other articles liable to be exposed on one side to a warm moist atmosphere and on the other side to a colder atmosphere comprise transparent closures of material obtained by saponifying sheet material of a cellulose organic ester or a polymerised ester of an unsaturated compound so as to provide at least one surface capable of absorbing moisture while maintaining transparency and resistance to the penetration of water and gases in the sheet material as a whole. The closure is arranged with an absorbent surface on the side of the article which in use is exposed to the moist damp atmosphere. The eye-piece discs or other closures may be cut or punched from the sheet material before or after the saponification treatment. The sheet material may be made by extrusion, casting, or blocking and slicing methods. It may contain one or more plasticisers which are not readily removable by the saponifying bath and which preferably have a slight affinity for water. Dimethyl phthalate, dimethoxyethyl phthalate, dioxyethyl phthalate, ethyl ethoxyethyl phthalate, or ethyl acetanilide may be used as plasticiser. Preferably saponfication is intense at the surface of the material, but does not extend far below the surface. Saponification may be on both sides or confined to one surface by coating the other side with wax. Saponification may be such that the sheet material has an affinity for cotton dyes extending from the surface to a depth of not more than onethousandth of an inch, but it may be deeper in the case of thick sheet material. The saponifying agent may be caustic soda or potash, barium hydroxide, alkali metal carbonate or phosphate, ammonia, guanidine, quaternary ammonium bases, alkylamines, alkylolamines, benzylamines, ethylene diamine, or cyclohexylamine. Agents which repress swelling, e.g., sodium acetate or sulphate, may be added to the saponifying medium, or swelling agents, e.g., dioxane or methanol, may be added. The saponified surface of the sheet material may be subjected to buffing or treatment with a strong jet of water. The sheet material may be made flat, curved, or flexible, according to the desired shape of the closure. The cellulose acetate or other ester is preferably made under conditions such as to avoid degradation of the cellulose molecule and, in the case of acetate, ripening is carried out to acetone solubility or even to a stage where the ester is soluble in acetone diluted to a considerable extent with water. The sheet material may be of cellulose acetate, propionate, propionate-nitrate, or oxyethyl cellulose nitrate, or it may be of polyvinyl acetate, chloride, or acetate-chloride, or of a polyacrylic or polyalkylacrylic ester, e.g., poly- (ethyl acrylate) or poly- (methyl methacrylate). Specification 503,834 is referred to.