GB343962A - Improvements in or relating to the manufacture of films, sheets and the like from cellulose nitrate - Google Patents

Abstract

Homogeneous films or sheets are prepared by spreading on a suitable surface a solution in a volatile solvent of a cellulose nitrate of low viscosity and having a nitrogen content of less than 11,35 per cent, e.g. 10,7 to 11,35 and preferably 11 per cent. The viscosity is preferably 10,75 seconds, as determined by the fall of a steel ball 3/32" diameter through 11,44" of a solution formed by dissolving one part of the nitrate in 9 parts of a mixture of 199 DEG proof ethyl alcohol and acetone, the solution being maintained at 20 DEG C. The low viscosity nitrate is preferably prepared by treating cellulose nitrate with hot water under pressure with or without catalysts. Suitable solvents are acetone alone or mixed with ethyl or methyl alcohol, or a mixture of ethyl or methyl alcohol with ether. Plasticizers, e.g. camphor, diethyl phthalate or dibutyl phthalate may be added, e.g. 40-50 per cent; and stabilizers, e.g. urea may also be present. Concentrated solutions may be employed to obtain thick films, e.g. 0,015". The films or sheets may be moulded or embossed and are readily cemented to other surfaces. They are particularly applicable as photographic films and in the making of reinforced glass. In an example a solution is made up of cellulose nitrate, of 11 per cent nitrogen content and 15 seconds viscosity, 100 parts, camphor 50 parts, urea 1 part and acetone 400 parts by weight. The solution is flowed on to the rim of a slowly rotating large wheel and the acetone is caused to evaporate by exposure to the air.