GB533789A - Improvements in or relating to sheet material and apparatus for the production thereof - Google Patents

Abstract

533,789. Film manufacture ; casting metals. DALY, A. J., and LOWE, W. G. Aug. 19, 1939, No. 23969. [Class 2 (ii)] (Also in Group XXII] Films, sheets, and the like are obtained by casting a solution of film-forming substance on to the flat polished surface of a solid metal alloy which has a melting point of about 100‹C. The film-casting support may be made by pouring the molten alloy on to a flat polished surface of a glass plate forming the bottom of a mould, cooling the alloy in position on the plate and removing the plate without damaging that surface of the alloy which was in contact therewith. The molten alloy may be rapidly chilled by immersing therein a base-plate of iron or other relatively high melting metal, adapted to adhere to but not to alloy with the low melting alloy, and the alloy may be allowed to set with the base-plate in position before removing the glass plate. Another method of chilling the molten alloy is to place the glass plate over a metal table from which it is separated by a thin filin of water. The alloy may comprise lead, tin, bismuth, and cadmium. A solution of film-forming substance is cast on the smooth surface of the alloy and preferably the sheet material is stripped from the surface while it still contains a considerable amount of volatile solvent, residual solvent being removed from the stripped sheet while it is held under tension. Several thin layers of film-solution may be applied in succession, the bulk of volatile solvent being removed from each layer before applying the next layer. The film-forming substance may be a cellulose ester or ether or a synthetic resin such as a polyvinyl ester, ether, or ketone, polystyrene, or a polymerized ester of the acrylic acid series. Plasticizers may be present in the film-forming solution. When multi-layer sheets are made, the individual layers may be of the same or different composition. Instead of stripping the formed sheet from the surface of the solid alloy, the assembly may be heated to a temperature sufficient to melt the alloy without damaging the sheet.