Patent GB-547883-A (GB)
Title: Improvements in or relating to photographic light-sensitive material
IPC: G03C1/035
Filed: 1941-03-11
Abstract: 547,883. Photographic multi-contrast material. RENWICK, F. F., and WALLER, C. March 11, 1941, No. 3339. [Class 98 (ii)] Light-sensitive multi-contrast material comprisea support coated with a mixture of a non-coloursensitized part of a gelatino-silver halide emulsion and at least one fully colour-sensitized part of the same emulsion, the sensitizing dye or dyes employed being present in total quantity less than would be necessary to impart optimum colour sensitivity to the whole of the mixed emulsion and being such that the resulting photographic material yields developed images of different contrast between wide limits according to the light used'for exposure. The ratio of the maximum to the minimum gamma value of the developed images obtainable from the photographic material is 5:4 or greater. The smaller the fraction of the mixed emulsion which is fully colour-sensitized, the wider are the extremes of contrast obtainable. Increase in the quantity of sensitizing dye raises the speed, but reduces the extremes of contrast obtainable. Exposure to blue light yields developed images of greater contrast. The original non-colour-sensitized emulsion should have high contrast characteristics. The sensitizing dye may be added before or after washing or before or after digestion. In example (1), sensitizing dye is added to a high-contrast gelatino-silveriodobromide emulsion which is then mixed with a non-sensitized portion. Tables are given of the results obtained on exposure to blue light and to yellow light, using as sensitizing dye (a) 1:3:3-trimethylindolylidene - 2:4<SP>1</SP>-ethylidene -1<SP>1</SP>- phenyl-3<SP>1</SP>- methyl - pyrazole - 5<SP>1</SP> - one ; (b) 1 : 3 : 3 : 5 - tetramethylindolylidene - 2 : 41 - ethylidene - 1<SP>1</SP>- phenyl - 3<SP>1</SP> methylpyrazole - 5<SP>1</SP> - one ; (c) 1:1<SP>1</SP> - diethylpseudocyanine iodide ; and (d) 2:1<SP>1</SP> - diethyl - 4 - chlorthiapseudocyanine iodide in various quantities. Example (2) is similar, using as sensitizing dye (a) 1:1<SP>1</SP>- diethylpseudocyanine iodide ; (b) 2:1<SP>1</SP>-diethyl-4-methylselenapseudocyanine iodide ; (c) 1:3:3:5-tetramethylindolylidene-2:4<SP>1</SP>-ethylidene-1<SP>1</SP>-phenyl-3<SP>1</SP>-methylpyrazole-5<SP>1</SP>-one ; (d) 1:3:3- trimethylindolylidene - 2:41 - ethylidene - 11 - m - tolyl - 3<SP>1</SP> - methylpyrazole - 5<SP>1</SP> one ; (e) 2:2<SP>1</SP> - diethyl - 5:6:5<SP>1</SP>:6<SP>1</SP>- dibenz - 7:7<SP>1</SP> ethylenethiacarbocyanine - p - toluenesulphonate ; (f) 1 - phenyl - 3 - methyl - 4 - (# - N - methyldihydrobenzthiazolylidene)- pyrazole - 5 - one ; and (g) 2 - thio - 3 - ethyl- 4-keto- 5 - (# - N - methyldihydrobenzoxazolylidene) - isopropylidenetetrahydrothiazole in various quantities. Example (3) is similar, using blue and red light and the panchromatic sensitizing dyes 2:2<SP>1</SP>-diethyl-8- methylthiacarbocyanine bromide and 2:21-8-triethyl- 4:41-d'ichlorthiacarbocyanine chloride. Example (4) is similar, using a silver chlorobromide emulsion and the sensitizing dyes 1:3:3:5-tetramethylindolylidene- 2:4<SP>1</SP>- ethylidene - 1<SP>1</SP> - phenyl - 3<SP>1</SP> - methylpyrazole - 5<SP>1</SP>- one and 2:1 - diethyl - 4 - chlorthiapseudocyanine iodide in various quantities. Specification 494,088 is referred to. According to the Provisional Specification, a colour sensitized emulsion may be mixed with a non-colour sensitized emulsion of the same or similar contrast.