Patent GB-703029-A (GB)
Title: Photographic silver halide emulsions and the sensitizing thereof
IPC: G03C1/015
Filed: 1951-12-10
Abstract: 703,029. Photographic emulsions. KODAK, Ltd. Dec. 10, 1951 [Dec. 14, 1950], No. 28828/51. Class 98(2) A photographic emulsion comprises at least two sets of silver halide grains separately sensitized to the same spectral region with different optical sensitizing dyes producing different emulsion speeds, the emulsion having a greater latitude than emulsions containing either of the sets of grains alone before or after sensitization. A portion of an emulsion may be sensitized with one dye and another portion with another dye whose sensitizing maximum is not more than 25 mÁ from that of the first dye, and the two portions of emulsion, which may or may not have approximately the same gamma values, mixed. The mixture may contain more than two portions of emulsion sensitized with different dyes but the mixture should not contain less than about 25 per cent of any one emulsion. The emulsion may be a silver bromide or chlorobromide emulsion. In rare cases, the use of the pair of dyes may result in supersensitizing. The dyes, which should be relatively non-diffusing, may be 3: 31-dimethyl- 9-ethyl-4:5:4<SP>1</SP>:5<SP>1</SP>-dibenzthiacarbocyanine chloride, 3 : 3<SP>1</SP>-dimethyl-9-phenyl-4: 5 : 4<SP>1</SP> : 5<SP>1</SP>-dibenzthiacarbocyanine bromide, 3:3<SP>1</SP>:9-triethyl-4:5:4<SP>1</SP>:5<SP>1</SP>- dibenzthiacarbocyanine bromide, and similar dyes in which the nuclei may be substituted by halogen, alkyl, or alkoxy, in which the 3-alkyl groups may be replaced by hydroxyalkyl or carboxyalkyl groups, and in which the 9-substituent may be an aryl group substituted by alkyl, alkoxy, or halogen (red sensitizers); 9-alkyl- and 9-aryl thia- and selenacarbocyanines substituted in the benzene nuclei, e.g. 3: 3<SP>1</SP>: 9-triethyl-5: 5<SP>1</SP>-dichloroselenacarbocyanine bromide (red sensitizers); 3:3<SP>1</SP>-dimethyl-8:10-di-m-toloxythiacarbocyanine bromide (red sensitizer); 3:3<SP>1</SP>-dimethyl-8:10-di-m-toloxyoxacarbocyanine bromide (green sensitizer); 5- phenyl- and 5-(p-tolyl)-9-alkyl- and 9-aryl oxacarbocyanines, e.g. 3:3<SP>1</SP>:9-triethyl-5:5<SP>1</SP>-diphenyloxacarbocyanine bromide (green sensitizers); complex merocyanines as described in U.S.A. Specification 2,454,629; and merocyanines derived from 1-benzthiazolyl-5-pyrazolone, such as those described in U.S.A. Specification 2,211,762. In examples 1 and 2, speed, gamma, and latitude (the distance along the exposure axis between the projections of the points where the gamma of the characteristic curve was 0.3 in the toe and 0.6 in the shoulder) values are given for portions of a silver chlorobromide emulsion sensitized with 3: 3<SP>1</SP>-dimethyl-9-ethyl-4: 5:4<SP>1</SP>:5<SP>1</SP>-dibenzthiacarbocyanine chloride and with 3:3<SP>1</SP>-dimethyl-9-phenyl-4 : 5 : 4<SP>1</SP> : 5<SP>1</SP>-dibenzthiacarbocyanine chloride and digested at 50‹C and for an emulsion obtained by mixing the two portions of emulsion, and for two portions of a silver chlorobromide emulsion sensitized with 3: 3<SP>1</SP>: 9- triethyl-5 : 5<SP>1</SP>-diphenyloxacarbocyanine bromide and 1-(2-benzthiazolyl)-3-methyl-4-(1-methyl-2-#- naphthathiazolylidene - 1 - ethylethylidene)-5-pyrazolone respectively and for the emulsion obtained by mixing the two portions. In example 3, the two mixed emulsions of examples 1 and 2 are mixed, and after coating and drying are exposed to a colour chart. The material is hardened in a solution containing sodium hexametaphosphate, sodium bisulphite, formaldehyde, sodium carbonate, sodium sulphate, and potassium bromide, washed, developed in a black-and-white developer including metol, hydroquinone, sodium hexametaphosphate, sodium metaborate, sodium thiocyanate, and 6-nitrobenzimidazole, washed, re-exposed to red light, colour developed cyan in a developer including 2 - amino - 5 - diethylaminotoluene hydrochloride, sodium hexametaphosphate, 2:4-dichloro- 5-p-toluenesulphonamino-1-naphthol, 6-nitrobenziminazole, and sodium hydroxide, washed, developed in an auxiliary black-and-white developer not containing sodium thiocyanate, washed, reexposed to green light, colour developed magenta in a developer including 2-amino-5-diethylaminotoluene hydrochloride, 2 - cyanacetylcoumarone, sodium hexametaphosphate, 6-nitrobenzimidazole, and sodium hydroxide, washed, bleached in a potassium ferricyanide-potassium-bromide bath containing sodium hexametaphosphate, fixed in a hyposodium sulphite bath containing sodium hexametaphosphate, and washed. Specifications 378,870, [Group IV], 378,885, 408,277, [Group IV], 496,116, 533,425, 552,368 and 592,267 are referred to.