GB523661A - Improvements in or relating to the production of photographic silver halide emulsions - Google Patents

Abstract

523,661. Photographic silver halide emulsion. CZEIJA, O., and LIERG, F. Dec. 6, 1938, Nos. 35593 and 35594. Convention dates, Dec. 6, 1937 and June 20, 1938. [Class 98 (ii)] In the production of silver halide emulsions, the carrier colloid has added thereto or produced therein colloidal silver halide having a particle charge opposite to the charge of the carrier colloid without completely neutralizing the charge of the carrier colloid. The carrier colloid may be a cellulose derivative or a polymerization or condensation product such as polyvinyl alcohol or polyacrylic acid, or a mixture of one or more of such substances. If the carrier colloid has a negative particle charge, the components for forming the silver halide are so added that there is an excess of the silver compound over the halogen compound at each instant during the formation of the silver halide and the silver compound remains in excess at the completion of the operation. The excess controls the resulting gradation. Conversely, if the carrier colloid has a positive particle charge, the halogen compound is maintained in excess. Part of the silver compound may be replaced by a compound or compounds of another metal or metals, for example thallium, which impart a positive charge to the silver halide. Examples of carrier colloids are partially etherified cellulose or partially saponified cellulose esters. A negative charge may be increased by treatment with alkalis and a positive charge increased by treatment with acids. Suitable solvents in the case of cellulose acetate are methyl and other alcohols, acetone, diacetone alcohol, chlorinated hydrocarbons and mixtures of acetone and water. Positive charges may be reduced by addition of acid dyes or colloidal metals, and negative charges by the addition of basic dyes or colloidal oxides or hydroxides. The support may be glass, metal, paper, celluloid or cellulose acetate. No support need be employed. One or more emulsion layers and filter or other intermediate layers may be provided. A small amount of high-boiling solvent, for example, diacetone alcohol, may be added to promote adhesion of the emulsion to the supporting layer. The emulsion may be used for sound recording and may be colour sensitized. In an example, cellulose acetate is partially saponified with alkali and the emulsion either prepared directly from the saponification solution or after washing and re-solution.