Patent GB-550494-A (GB)
Title: Improvements relating to films, foils and the like
IPC: B29C48/08
Filed: 1941-07-07
Abstract: 550,494. Films ; compound sheet materials. CELLULOID CORPORATION. July 7,1941, No. 8545. Convention date, July 8, 1940. [Class 2 (ii)] [Also in Group VIII] Composite films or sheets are obtained by taking at least two thinner films of thermo. plastic material, preheating them, coating them with a hot plasticizer which is an active solvent for the thermoplastic material at the temperature of application, bringing them together with their coated surfaces in contact, uniting them under heat and pressure, and annealing the composite film by a heat treatment. In a modification of the process a sheet material such as cotton cloth, cotton mesh, cellulose derivative fabric, metal or wire cloth or mesh, or a film of a polyvinyl or polyacrylic ester resin, may be sandwiched between two coated thermoplastic films, e.g. two cellulose derivative films. A mandrel. cut sheet of thermoplastic material in continuous length may be surfaced on both sides with cast film or foil to obliterate objectionable knife-lines. The cellulose derivative or other films may carry printed designs or ornamentations. To facilitate bonding, the paper or other intermediate layer may be impregnated with a synthetic resin such as polyvinyl acetate. The component films may be of the same or of different thermoplastic substances. Cellulose derivatives specified are cellulose acetate, propionate, butyrate, aceto-butyrate or other ester, or methyl, benzyl, or other cellulose ether. The plasticizer may be dimethyl or diethyl phthalate, ethyl, phthallyl ethyl glycollate or triethylene glycol. The individual films to be united may be drawn from spools located in heated chambers, through a pre-heating chamber in which the films pursue a tortuous path, and after being coated with hot plasticizer, the coated surfaces are united by passage of the films together through the nip of a pair of hot rollers. The composite film is passed through a heated annealing chamber, and then cooled by passage through the air. On its way to the annealing chamber, the composite film may pass through the preheating chamber. The component films should be freed from dust and de-electrified before being coated with plasticizer. A wiper bar of sponge rubber may be used for removing dust. The hot plasticizer may be applied by means of a furnishing roll rotating in the opposite direction to the film and dipping into the heated bath of plasticizer. Heated air may be circulated through the annealing chamber. The plasticizer may be applied to the component films in slight excess, the excess exerting a washing action to remove dust when forced out at the nip of the uniting rolls. The uniting rolls may be pressed towards each other by a system of weights and levers or may be maintained at a fixed clearance which is less than the sum of the thicknesses of the films being united. Instead of using component films of cellulose derivatives, films of synthetic resins such as polyvinyl acetate, polymethyl methacrylate, or polystyrol may be used. The component films may be made by casting on a wheel and it is preferable to unite them so that the bond is between the wheel-to-wheel or air-to-air sides.