GB696103A - Improvements in or relating to methods of producing superficially saponified films or the like of fatty acid cellulose esters - Google Patents

Abstract

A foil, film or the like of a fatty acid ester of cellulose which contains more than 1.5 but less than 3 molecules of combined fatty acid per glucose residue is subjected to superficial saponification in a bath containing an alkaline substance and an organic solvent, and when the saponification has proceeded to the desired depth the foil or other article is treated in one or more baths which terminate the saponification, at least one of these after-treatment baths being one which contains no aqueous solution of monobasic or dibasic acid but which is capable of reducing aqueous swelling of partially esterified cellulose having 0.5 to 1.5 molecules of combined fatty acid per glucose residue. Such an after-treatment bath may be a solution of a water-soluble sulphate, phosphate, sulphite, thiosulphate, carbonate, tartrate, citrate, acetate, lactate, fluoride or chloride. It may be an aqueous solution of a tribasic acid or of glycerol, glucose or a sugar. It may be a primary saturated alcohol having a straight chain of 4-11 carbon atoms, such as butanol-1. An after-treatment bath containing toluene, benzene, tetrahydronaphthalene or a liquid ether may be used. The treated films may be used for photographic purposes, e.g. the saponified layers may be impregnated with light-sensitive substances. If desired, plasticizers originally present in the films may be removed from the saponified layers by solvent treatment, e.g. by treatment with aqueous or alcoholic-aqueous solutions of dispersing agents such as salts of sulpho-ricinoleic acid, sodium oleate, sodium p-octylbenzene sulphonate, dodecylamine hydrochloride and lauryl ethers of polyethylene oxide. The substance for reducing aqueous swelling and the solvent for the plasticizer may be incorporated in a single treatment bath. In an example, a cellulose acetate tape is passed in succession through a solution of caustic potash in aqueous methanol, through two baths of butanol-1, through an aqueous solution of phosphoric acid and through two baths of circulating water.