GB542704A - Improvements relating to photographic emulsions - Google Patents

Abstract

542,704. Photographic emulsion. KODAK, Ltd. (Eastman Kodak Co.). July 19, 1940, No. 11909. [Class 98 (ii)] A photographic emulsion is prepared by forming silver halide or a mixture of silver halides in an aqueous solution of a silver halide dispersing agent other than gelatine, such as a watersoluble hydrolysed starch acetate, a water-soluble co-polymer of maleic anhydride and vinyl acetate, a water-soluble condensation product of such a polymer with aniline, a water-soluble cellulose ether such as methyl or ethyl cellulose or gum arabic, and a polyvinyl protective colloid is added to the dispersion so formed. The protective colloid may be polyvinyl alcohol or a polyvinyl ester such as polyvinyl acetate. A watersoluble polyvinyl compound may be used and a gelling agent incorporated in the emulsion. Polyvinyl acetate of acetate content (calculated as vinyl acetate) from 0.5 to 5 per cent may be added in aqueous solution, while polyvinyl acetate of acetate content from 59 to 71 per cent may be added in solution in a mixture of water and an organic solvent. Part of the polyvinyl compound may be present in the solution of the silver halide dispersing agent, and the remainder added subsequently, or in a modification all the polyvinyl compound may be present in the dispersing agent solution. Gelling agents such as # naphthyl-salicylamide, gallic acid, resorcinol, or #- naphthol may be added to the emulsion at a raised temperature (40-90‹ C.) and the emulsion gelled by cooling. An increase in the amount of dispersing agent used gives greater contrast in the resulting emulsion. The emulsions may be prepared by running aqueous solutions of silver nitrate and alkali metal halide into an agitated dilute aqueous solution of the dispersing agent, and then adding an aqueous solution of the polyvinyl compound and thoroughly mixing. The emulsion may be digested. An organic solvent may be added to the developing and fixing baths. With a paper support, the amount of sensitizing used should be insufficient to cause staining. The emulsions may be used in black-and-white or in colour processes. In an example (1), an aqueous solution of starch acetate is rapidly stirred together with an aqueous solution of silver nitrate and an aqueous solution of potassium bromide, potassium chloride, and potassium iodide at 80‹ F. An aqueous solution of polyvinyl acetate of acetate content less than 5 per cent is added and stirring continued. The resulting emulsion is sensitized with 2:3<SP>1</SP>-diethyl-4<SP>1</SP>-methyloxathiazolocarbocyanine. The procedure in examples (2), (3), (4), (5) and (6) is similar, with the use as dispersing agents of ethyl cellulose, methyl cellulose, gum arabic,' the co-polymer of maleic anhydride and vinyl acetate, and the condensation product of the co-polymer of maleic anhydride and vinyl acetate with aniline respectively. A plasticizer such as monoacetin may be added. Specifications 525,085, [Group IV], and 527,283 are referred to.