Patent GB-559201-A (GB)
Title: Improvements relating to photographic emulsions
IPC: C07C37/50
Filed: 1942-04-21
Abstract: 559,201. Photographic sensitive material. KODAK, Ltd., and KNOTT, E. B. April 21, 1942, No. 5346. [Class 98 (ii)] The tendency for a sensitizing dye to wander from a dye-sensitized silver salt emulsion to a sensitive silver salt emulsion with which it is mixed is reduced by mixing the emulsions at a temperature not exceeding the critical temperature (i.e. that temperature above which the degree to which the dye wanders from the first-mentioned emulsion is substantially increased as compared with the degree of wandering below it), and the mixed emulsion is coated on a support without its temperature having been allowed to exceed this critical value. The emulsions may be of the same or different silver salts, and can be gelatino silver bromide, chloride, chlorobromide, iodobromide, or iodochlorobromide emulsions. When a dye-sensitized gelatino silver bromide, chloride, chlorobromide, or iodobromide emulsion containing a dispersion of soft lac resin as described in Specification 540,451 is mixed with a gelatinosilver bromide or iodobromide emulsion also containing soft lac resin but not dye-sensitized, the critical temperature is about 33‹ C. and the mixing temperature is not allowed to exceed about 30‹ C. Where the dye-sensitized emulsion is mixed with a gelatino silver chloride or chlorobromide emulsion containing soft lac resin but not dye-sensitized, the critical temperature is about 28‹ C., and the mixing temperature is not allowed to exceed about 25 C. When a dyesensitized gelatino silver chloride or chlorobromide emulsion is mixed with a second dyesensitized emulsion of the same kind (both containing soft lac resin), the critical temperature is also about 28‹ C. The degree of wandering which occurs may be measured by maintaining the mixed emulsion in the liquid state for 30 minutes, coating, and drying, and inspecting the wedge-spectrogram of the coated emulsion. The critical temperature may be determined by measuring the gamma of the dye-sensitized emulsion (coated to a given thickness) at a wavelength to which the second emulsion is not sensitive, taking another specimen of the dye-sensitized emulsion, mixing with the second emulsion at a selected temperature, allowing the mixture to stand for 30 minutes at that temperature, and coating at the same temperature to a thickness such that the dye-sensitized emulsion is present to the same extent as before, and measuring the gamma of the mixed emulsion at the selected wavelength. If this gamma is the same as the first, and no augmentation of the toe of the curve has occurred, no appreciable dye-wandering has occurred. A series of measurements are made and the critical temperature estimated. Alternatively, the wedge-spectrograms of the two emulsions separate and mixed can be prepared using a series of temperatures for the mixing and coating operations in the case of the mixed emulsion, and the spectrograms inspected to estimate the degree of wandering. A dye having a low tendency to wander (e.g. as described in Specifications 524,552, [Group IV], and 532,098) may be used, and resins, resin salts, and inorganic substances dispersed in the dye-sensitized emulsion as described in Specifications 540,451, 540,464 and 544,134. The dye should be incorporated during the manufacture of the emulsion, and no more dye used than necessary. In example 1, a contrasty gelatino silver bromide emulsion is sensitized with [5-(1-phenyl-3-n-heptyl-2-thiohydantoin) - (2 - )3-ethylbenzoxazole]-dimethinemerocyanine and an alcoholic solution of soft lac resin is added. The emulsion is mixed at a temperature of 30‹ C. with a soft gelatino silver bromide emulsion also containing soft lac resin, and is coated at a temperature of 30‹ C. Alternative sensitizing dyes are 9-methyl-3-3'-diethyl- 4:5:4':5'-dibenzthiocarbocyanine iodide and 5:51- example 2, a contrasty gelatino silver chloride dichloro-3:3<SP>1</SP>:9- triethylcarbocyanine chloride. In emulsion is sensitized with the first dye of example 1 and soft lac resin added. A soft gelatino silver chloride is sensitized with [5-(3-nheptylrhodanine)] - [2-(3-methyl-4:5-benzbezoxazole)] merocyanine and resin is added. The emulsions are mixed at 252 and coated without the temperature being allowed to exceed this value. In example 3, a contrasty gelatino silver chloride emulsion is sensitized with (5-(1-phenyl-3-ethyl-2- thiohydantoin)] - [2 - (3 - ethylbenzoxazole)] - dimethine-merocyanine and soft lac resin is added. The emulsion is mixed at 30‹ C. with a soft gelatino silver iodobromide emulsion containing resin. Alternative dyes are [5-(3-n-heptylrhodanine)] - [2 - (3 - ethylbenzoxazole)] - dimethinemerocyanine, [5-(1-phenyl-3-n-heptyl-2-thiohydantoin)] - [ 2-(3-ethylbenzthiazole)] - dimethinemerocyanine, 1:1'-diethyl-2:2'-cyanine iodide, 3:3'- diethyl-4:5:4':5'-dibenzoxacarbocyanine iodide, and [5-(3-ethylrhodanine)]-[2-(3-ethylbenzoxazole)]-dimethinemerocyanine. In example 4, to one part of a high contrast gelatino silver iodobromide emulsion is added 1:1<SP>1</SP>-diethyl-2:2<SP>1</SP>- cyanine iodide, and the emulsion is mixed with a non-sensitized part of the same emulsion at 33‹ C., and coated at the same temperature. In example 5, the procedure of example 4 is repeated using [1:3:3-trimethyl-2-indolenine]-[4-(1-pheny)-3- methyl-5-pyrazolone)]-dimethinemerocyanine. The setting point or setting rate of the emulsion may be lowered by the use of emulsions of lower gelatino content by the use of degraded gelatines, or by adding urea, sodium nitrate, sodium chloride, or sodium dihydrogen phosphate. Specifications 450,958, 541,510, 541,511 and 541,514 also are referred to.