Patent GB-543854-A (GB)
Title: Improvements relating to the production of photographic emulsions
IPC: G03C1/053
Filed: 1940-09-12
Abstract: 543,854. Polyvinyl acetals ; cellulose derivatives. KODAK, Ltd. (Eastman Kodak Co.). Sept. 12, 1940, No. 14135. Addition to 531,579. [Classes 2 (ii) and 2 (iii)] [Also in Group XX] A photographic silver halide emulsion has a binder consisting of a polyvinyl propionaldehyde acetal containing 45 to 60 per cent. hydroxyl, a polyvinyl butyraldehyde acetal containing 58 to 80 per cent. hydroxyl or a polyvinyl propionaldehyde-butyraldehyde acetal containing 45 to 80 per cent. hydroxyl, the hydroxyl content in each case being calculated as vinyl alcohol. Silver halide or a mixture of silver halides may be precipitated in an aqueous solution of a silver halide dispersing agent, and a solution of the polyvinyl compound added to the dispersion so formed. The dispersing agent and the polyvinyl, compound may be watersoluble or soluble in a mixture of water and an organic solvent. A polyvinyl butyraldehyde acetal may be prepared by adding to an aqueous solution of polyvinyl alcohol of molecular weight about 19,800, concentrated hydrochloric acid followed by butyraldehyde. A polyvinyl propionaldehyde acetal may be prepared by mixing an aqueous solution of polyvinyl alcohol with concentrated hydrochloric acid and propionaldehyde. The alcohol may have been prepared previously by hydrolysing a polyvinyl ester such as polyvinyl acetate, or may be formed in this way simultaneously with the aldehyde condensation. An acetal having part of the acetal groups derived from one or more other aldehydes, such as benzaldehyde may also be used. The acetal may also contain a residual acetate or other ester content. The emulsions can be prepared by running an aqueous solution of silver nitrate and an aqueous solution of one or more alkali metal halides into an aqueous solution of the polyvinyl acetal with stirring. An organic solvent such as ethyl alcohol, acetone, or the monomethyl or monoethyl ester of ethylene glycol may be added. In the alternative method using a dispersing agent, part of the acetal may be included in the dispersing agent solution. Suitable dispersing agents are the co-polymer of maleic anhydride and vinyl acetate and its derivatives, watersoluble natural resins such as gum arabic, and carbohydrate derivatives such as water-soluble starch acetate and ethanolamine cellulose acetate. The ethanolamine cellulose acetate may be prepared by causing cellulose acetate which has been hydrolysed to a low acetyl content such as 22 per cent. to react with ptoluenesulphonyl chloride in the presence of pyridine to form cellulose acetate-p-toluenesulphonate, and causing this to react with an ethanolamine. In example (1) polyvinyl propionaldehyde acetal having a hydroxyl content of 54.5 per cent. is dissolved in a mixture of ethyl alcohol and water, and after diluting with water and acetone, is heated to 80‹ F. Aqueous solutions of silver nitrate and of a mixture of potassium bromide, chloride, and iodide are added simultaneously with rapid stirring. A further quantity of acetal is added, and after stirring, the emulsion is sensitized with 2:3<SP>1</SP>- diethyl - 4<SP>1</SP> - methyloxathiazolo - carbocyanine iodide and coated on paper. In example (2) the procedure is similar using. polyvinyl butyraldehyde acetal containing 75.2 per cent. hydroxyl, except that acetone is added during the addition of the,silver nitrate and potassium halide solutions. In example (4) an aqueous solution of diethanolamine cellulose acetate is heated to 80‹ F., and aqueous solutions of silver nitrate and, potassium halides are added as in example (1). A polyvinyl butyraldehyde acetal solution in alcohol and water is added, followed by the monoethyl ether of ethylene glycol. The emulsion is dye-sensitized as in example (1) and coated on paper. In example (5) the procedure is similar, using gum arabic as the dispersing agent. The procedure is also similar in examples (6) and (7), using the co-polymer of maleic anhydride and vinyl acetate as the dispersing agent, polyvinyl butyraldehyde acetal being used in example (6) and polyvinyl propionaldehyde acetal in example (7). Specifications 542,704, [Group XX], and .543,855 are referred to.