Patent GB-541514-A (GB)
Title: Improvements in photographic light sensitive materials
IPC: G03C1/035
Filed: 1940-06-06
Abstract: 541,514. Photographic light-sensitive material. KODAK, Ltd., KNOTT, E. B., AMOR, A. E., and ROBINSON, A. June 6, 1940, Nbs. 7934/41, (divided out of 540,464) and 13997/40. [Class 98 (ii)] Photographic material comprises a single sensitive layer which comprises a mixture of two silver chlorobromide emulsions (containing over 10 per cent and less than 90 per cent, and preferably over 30 per cent and less than 70 per cent of silver chloride based on the total silver halide and including emulsions containing some silver iodide) of which one gives a gradation less than 1.8 and the other gives a gradation of at least 2.5 greater than that of the first and of which one has its maximum speed at least 60Á further towards the long wavelengths than the maximum speed of the other, the speed of the former measured at about the wavelength of the maximum speed of the latter being not greater than half the speed of the other measured at the same wavelengths, while measured at about the wavelengths of maximum speed of the former, the speed of the former emulsion is at least twice the speed of the latter. The gradation is measured using light of about the wavelength (including up to 40Á each side thereof) of maximum sensitivity of the emulsion concerned. Both emulsions should be preferably substantially insensitive to wavelengths above 600 Á. The layer is coated on a support of paper, film, or glass. The emulsions may comprise (a) a silver chlorobromide emulsion of between 30 and 70 per cent silver chloride and of relatively high gradation sensitized from 500-570Á but substantially insensitive above 600Á, and (b) a silver chlorobromide emulsion of between 30-70 per cent silver chloride and of relatively low gradation and not optically sensitized. On such a layer, high contrast negatives may be printed with blue light, medium contrast negatives with white light (or mixed blue and yellow to green light), and low contrast negative with minus-blue light. The blue speed of the non-optically sensitized emulsion should be at least 1.8 times (and preferably at least twice) the blue speed of the optically sensitized emulsion, while the green-to-yellow speed of the optically sensitized emulsion should be between 1/3 and 1“ (preferably between and 1“) times the blue speed of the non-optically sensitized emulsion, and the gradation of the non- optically sensitized emulsion in the blue portion should be between 0.8 and 1.8 (preferably between 1.0 and 1.6), while the gradation of the optically sensitized emulsion in the yellow to green region, should be at least 2.5 greater (preferably 3.5 greater). Both emulsions may be sensitized to have their maximum sensitivities outside the region of natural sensitivity, while substantially insensitive beyond 600Á, each being substantially insensitive at the wavelength of maximum sensitivity of the other. One or both may have a high silver chloride content between 80-90 per cent, and such an emulsion, giving a gradation of the violet between 0.8 and 1.8 (preferably 1.2-1.6) may be mixed with a similar emulsion optically sensitized from 430-570Á. and giving a gradation in the green to yellow of at least 2.5 (preferably 3.5) greater, the violet speed of the non-optically sensitized emulsion being at least 1.8 (preferably at least 2.5) times the violet-speed of the other emulsion, and the green-to-yellow speed of the latter being between 1/3 and 1“ (preferably ¥ and 1“) times the violet speed of the former. The higher gradation emulsion should be the one having the higher sensitivity at the higher wavelengths, and the speeds of the two emulsions should be about the same in the spectral regions used for printing. The exposure at one end of the range may be made with a filter transmitting light of a maximum of 390Á but little useful light above 480Á (e.g. a ''Wratten" (Registered Trade Mark) No. 35 filter), and at the other end with a filter transmitting light of a maximum 530Á but little useful light below 480Á (e.g. a " Wratten " (Registered Trade Mark) No. 5 filter). Intermediate gradations may be obtained by using either white light or mixed violet and yellow light. In another material, both emulsions have a silver chloride content of 80-90 per cent, and one is sensitized to a maximum in the region 420-490Á (e.g. 470Á) with little or no sensitivity above 500Á, the other not being optically sensitized. This material may be processed in yellow light (above 500Á). In a further material, both emulsions have a silver chloride content of 80-90 per cent, and one is sensitized to a maximum in the region 420-490Á (e.g. 470Á) and the other to a maximum in the region 500 to 570Á (e.g. 550-570Á), preferably without useful sensitivity above 600Á. Suitable speeds and exposure filters are specified. A formula for a standard developing solution is given. One or more sensitizing dyes are used for the optical sensitization. Non-wandering sensitizing dyes are specified. After incorporation of sensitizing dye in an emulsion, the latter is kept at an elevated temperature as long as possible, and then cooled to 30‹ C. before mixing. The emulsion may be kept at about 45‹ C. for half an hour at a pH below 7, (citric or hydrochloric acid being added). The material may be made with a greater gradation difference than necessary to compensate for loss due to dye-wandering. In an example, an amount of silver chlorobromide emulsion made from 200 grams of silver nitrate and containing 50 per cent silver chloride and 0 to ¢ per cent silver iodide is sensitized with 0.1 gram of the dye of Example 3 of Specification 532,098. After ripening and addition of more gelatine, the emulsion is set and washed, and has a blue-to-violet speed of 0.2, a green-to-yellow speed of 0.7, and a green-to-yellow gradation of 5.0. This is mixed at 30‹ C. with an equal amount of a non-optically sensitized emulsion of the same composition having a blue-to-violet speed of 0.8 and a gradation of 1.4. In a second example, an amount of silver chlorobromide emulsion made from 200 grams of silver nitrate and containing 85 per cent silver chloride and 15 per cent silver bromide is sensitized with 0.02 gram of the dye of Example 3 of Specification 532,098, and is ripened and washed. The emulsion has a violet speed of 0.1, a green-to-yellow speed of 0.7, and a green-toyellow gradation of 4.8. This is mixed at 30‹ C. with an equal amount of a like emulsion sensitized with 3-n-heptyl-5-(1-methyl-2-#-naphthoxazolylidene)-rhodanine ,and having a violet speed of 0.3, a blue speed of 1.0, and a blue gradation of 1.4. The emulsion layers of the examples are exposed by tungsten light through low-contrast negatives using a " Wratten (Registered Trade Mark) No. 5 filter, through medium-contrast negatives using no filter or a Wratten K1 filter, and through high-contrast negatives using a Wratten No. 47A filter. An emulsion having a bluesensitivity maximum may be mixed with an emulsion having a violet-sensitivity maximum. More than two emulsions may be mixed. Specifications 15054/12, [Class 98 (ii)], 450,958, 524,552 and 540,451 are referred to.