Patent GB-729211-A (GB)
Title: Photographic emulsions
Inventor: HOWE DENNIS JOHN THOMAS
IPC: G03C1/10
Filed: 1952-03-11
Abstract: 729,211. Photographic emulsions. IMPERIAL CHEMICAL INDUSTRIES, Ltd. Feb. 23, 1953 [March 11, 1952], No. 6260/52. Class 98 (2). A light-sensitive non-colour-sensitized gelatino silver halide emulsion is divided into two or more parts, each of the parts is optically sensitized to the same wavelength of light by the addition of the same sensitizing dye or a mixture of the same sensitizing dyes which is irreversibly adsorbed on the silver halide, at least two of the parts being sensitized to different degrees, and subsequently mixing the parts to obtain an emulsion of improved latitude. One part of the emulsion may be sensitized with a quantity of a sensitizing dye which gives full sensitization and a second part either sensitized with the same dye in a quantity smaller than that required for full sensitization, or with the same dye either in a quantity giving full sensitization or in a lesser quantity together with a desensitizing substance reducing the sensitivity in a part or the whole of the spectrum. Alternatively, the first part of the emulsion may contain a supersensitizer. The desensitizer and the supersensitizer, when used, must also be irreversibly adsorbed on the silver halide. A test for irreversible adsorption is given. The differently sensitized parts of the emulsion are preferably kept at about 35‹ to 40‹ C. for ¢ to 1 hour to allow the dye to become completely adsorbed. A colour coupler may be added before or after the mixing step. The green and the red sensitized layers of multilayer colour photographic material may be prepared by the process according to the invention. In example 1, a melted gelatino silver iodobromide emulsion is divided into two equal parts. To one part is added 0.06 parts by weight of the red-sensitizer [3 - ethyl - 4 - keto - 5 - (3 - ethyl - 6 : 7- tetrahydrobenzbenzthiazolylidene - α - phenylethylidene) - thiazole] [3 - ethyl - 4 : 5 - diphenylthiazole]-methinecyanine iodide, and to the other part is added 0.003 parts by weight of the same dye. The two parts are maintained at 35 ‹ C. for 30 minutes, an alcoholic caustic soda solution of the cyan coupler 2-(1-hydroxy-2- naphthoyl) - amino - 1 - (N - methyl: N - octadecyl)-aniline-4-sulphonic acid is added to each part, and the two parts are'mixed and coated on a film support. In example 2, 0.006 parts by weight of the dye are added to the second part, and the final red-sensitized emulsion layer is successively overcoated with a green-sensitized emulsion layer containing a magenta colour coupler, a yellow colloidal silver filter layer, and a blue-sensitive emulsion layer containing a yellow colour coupler. In example 3, a silver iodobromide emulsion is divided into two parts, to one of which (one third) is added an alcoholic solution of 0.02 parts by weight of the greensensitizer 3 : 3<SP>1</SP> : 9 - triethyl - 5 : 5 - diphenyloxacarbocyanine thiocyanate and 0.015 parts by weight of 3 : 3<SP>1</SP>-diethyl-5-phenyl-4<SP>1</SP>: 5<SP>1</SP>: 9-trimethyloxathiacarbocyanine iodide. To the remainder of the emulsion is added 0.002 parts of the first dye and 0.0015 parts of the second. Both parts are maintained at 35‹ C. for 30 minutes and an alcoholic caustic soda solution containing 10 parts of 1-(4<SP>1</SP>-phenoxy-3<SP>1</SP>-sulphophenyl)-3-heptadecyl-5-pyrazolone is added to the first part of the emulsion and a similar solution containing 20 parts of coupler to the second. The two parts are mixed and coated on a film support. According to the Provisional Specification, the second part of the emulsion may be sensitized with a different dye which sensitizes over approximately the same band of wavelengths of light and with the maximum of sensitivity at about the same wavelength as the dye used for the first part. A desensitizer may be used in the second part or a supersensitizer may be used in the first part.