GB540567A - Improvements in or relating to projection screens - Google Patents

Abstract

540,567. Films. KODAK, Ltd. March 18, 1940, No. 5002. Convention date, March 18, 1939. Drawings to Specification. [Class 2 (ii)] [Also in Groups XX and VIII] A film for use as a translucent projection screen is made by forming a solution of an organic derivative of cellulose and a transparent material or synthetic resin incompatible therewith in a solvent or solvent mixture, so chosen as regards quantity and nature that on concentration by evaporation the cellulose derivative remains in solution but not the resin, casting the solution into sheet form and removing the solvent, whereby the resin is thrown out of solution in the form of small transparent particles and the cellulose derivative dries to form a continuous transparent phase. Cellulose organic acid derivatives such as cellulose acetate, propionate, butyrate, acetate-propionate and acetate-butyrate, and cellulose ethers such as ethyl and benzyl cellulose, may be used as the base material. Natural and synthetic resins which may be employed include coumarone-indene, polymerized methyl methacrylate, manila, rosin, sandarac, chlorinated rubber, the composition known under the Registered Trade Mark " Vinylite," and also "Nevillite " and " RH-35." The solvent may be a solution of ethylene chloride containing 3 to 15 per cent of methyl alcohol or acetone. In an example, the solution comprises 80 parts of cellulose acetate, 20 parts of Nevillite resin and 400 parts of a solvent consisting of 90 per cent. ethylene chloride and 10 per cent methyl alcohol. The solution is coated on a glass plate to form after evaporation of the solvent a sheet of 0.007 inches in thickness. A plasticizer may be added to the solution to form a flexible screen, and in an example, 15 parts of triphenyl phosphate are added to the solution above referred to. In other examples, the proportions of the constituents are varied and other resins are employed, and an example employing a natural resin is given in which a solution is formed of sandarac resin and cellulose acetate in acetone. The sheets may be formed on a roll-casting apparatus.