Patent GB-327121-A (GB)
Title: Improved manufacture of strengthened glass
IPC: B32B17/08
Filed: 1928-12-24
Abstract: 327,121. Murray, H. D., and Spencer, D. A. Dec. 24, 1928. Compound transparent sheets.-In a composite glass of the type wherein a layer of flexible transparent material is mounted between glass elements, the flexible layer is formed of regenerated cellulose which is built up of two or more layers united by a binder (for example an emulsified colloid such as gelatine or water soluble gum), and impregnated with one or more plasticizing agents for example a neutral non- volatile viscous liquid such as glycerol or a solid such as glucose yielding from a solution a non- brittle residue. Preferably two or more plasticizing agents are used. The regenerated cellulose may be obtained from solutions of cellulose such as cellulose xanthate by decomposition thereof with a suitable acid or salt. The regenerated cellulose may be produced in situ on the glass elements. For example glass plates with a substratum of gelatine, water soluble gum &c. may be coated with viscose which is then decomposed, preferaby in the presence of a colloid or a sugar, to deposit the cellulose on the glass. Alternatively, films of regenerated cellulose may be rolled or otherwise applied to the glass elements in the presence of the impregnating solution, or a number of such films may be impregnated and consolidated to form a compound sheet which is then mounted between the glass elements. The impregnation is preferably effected at a temperature of from 40‹-60‹ C. which is maintained for 10-15 minutes. To prepare the cellulose films, a solution of cellulose xanthate ripened for 7-10 days is spread over a prepared glass surface coagulated with hot ammonium sulphate solution, washed with water, dried, and then stripped from the glass. The mounting of the elements of a composite glass is preferably effected in the presence of two liquids, one of which, such as glacial acetic acid, is capable of solvating the gelatine substrata on the glass and in the flexible element, and the other, such as ethyl alcohol, is capable of penetrating the substrata without causing them to swell or to dissolve. In one example a solution of cellulose xanthate which has ripened from 7-10 days is filtered, the concentration being such that the solution just flowed freely over a glass surface. The glass plates are covered with a 10 per cent solution of gelatine, dried, the xanthate solution applied, and the plates immersed in a coagulating medium consisting of an aqueous solution of 5 parts of hydrated di-sodium hydrogen phosphate, 10 parts of hydrated sodium sulphate, 15 parts of sodium chloride, 10 parts of glucose and 100 parts of water. When coagulation is complete the plates are washed, placed in a bath of 95 parts of water and 5 parts of concentrated hydrochloric acid, then in a bath containing 90 parts of water and 10 parts of sodium sulphate, then washed with water, dried sopernoially and immersed for five minutes at 40‹-50‹ C. in a bath composed of 85 parts of water, 15 parts of glycerine and 10 parts of gelatine. The plates are then removed, dried and mounted under a mixture of 15 parts of glacial acetic acid and 90 parts of alcohol (industrial spirit) the jointing being effected under pressure at a temperature of 40‹ C. In a second example a film of regenerated cellulose is spread on gelatine-coated glass plates under a mixture of 100 parts of glycerine, and 850 parts of glucose, 192 parts of glycerine, and 850 parts of water, at about 50‹-60‹ C., the operation being repeated until a film 5/1000 in. thick is formed on each plate. The plates are then dried and pressed together as before. In a further example, a number of films of regenerated cellulose giving a total thickness of 10/1000 in. are pressed together under a solution of the same composition as in the preceding example, and the compound sheet dried in air and mounted between gelatine coated glass plates under pressure and gentle heat in a bath of acetic acid and alcohol as in the first example. In another example the impregnated film is mounted between clean glass plates which are chemically etched in any known manner.