Patent GB-538024-A (GB)
Title: Improvements in the production of films and like sheet materials
IPC: B29C41/24
Filed: 1940-01-16
Abstract: 538,024. Films. HAWTIN, P. R., and GARDNER, C. Jan. 16, 1940, No. 923. [Class 2 (ii)]  A solution of a transparent organic filmforming substance in a volatile organic liquid is deposited on a surface of a water-soluble substance containing an aliphatic hydrophobe group of at least 12 carbon atoms and when a sheet has been formed by evaporation of solvent, the sheet is stripped from the surface. The water-soluble substance may be soap or soaplike substance. A block of hard soap or a thin layer of soft soap on a supporting plate or band of glass or metal may be used. The soap may be sodium palmitate or stearate. Other alkali metal salts of long-chain fatty acids may be used as may the corresponding salts of nitrogenous bases, e.g. ammonia and the alkylolamines. Triethanolamine stearate, palmitate, or oleate may be used. Sodium, potassium, ammonium, alkylamine and alkylolamine salts of cetyl naphthalene sulphonic acid, of sulphonated octyl, cetyl, lauryl, and oleyl alcohols, of sulphonated esters of higher alcohols such as the dihexyl and dioctyl esters of succinic acid, and of sulphated higher fatty alcohols, fatty acid amides, and fatty acid esters may be used. Partial esters of ether-alcohols containing at least two hydroxy groups with soap forming acids, e.g. mono-stearates and palmitates of diethylene glycol and triethylene glycol may be used. To avoid premature stripping there may be provided around the surface of soap a surface, e.g. of untreated glass or metal, to which the sheet material readily adheres. Thick sheets may be built up by application of several successive layers of solution. The film-forming substance may be cellulose acetate, propionate, butyrate, aceto-propionate, or other ester or mixed ester, or benzyl cellulose or other ether, mixed ether, or ether-ester. It may be a polymerized unsaturated compound such as polyvinyl alcohol, polyvinyl acetate, or other polyvinyl ester, or polymethyl methacrylate, or polystyrene. The film-forming composition may be applied to the soap surface by pouring, brushing, or spraying. The composition may contain plasticizers including those with fireretardant properties, e.g. trichloro-ethyl phosphate. In an example, a film-casting surface is produced by coating a glass plate having a flat highly polished surface with a solution of triethanolamine oleate in ethanol, drying, and polishing. A margin of uncoated glass is left around the coating and the edges of the plate are provided with detachable metal sides. In another example, molten diethylene glycol mono stearate is poured into a metal tray with detachable sides. Each side has a lower vertical portion, a horizontal portion, and an upper vertical portion. Sufficient of the molten material is poured in so that on cooling the upper surface of the block so formed is flush with the horizontal portions of the metal sides. Film-forming solution is applied and the sheet is stripped from the block by removing the side pieces. The sheet is then trimmed by cutting off the marginal portions adherent to the side pieces. Any soap or like material adhering to the stripped film or sheet may be removed by washing with water or with soap solutions of progressively decreasing concentration and finally with water.