Patent GB-541515-A (GB)
Title: Improvements in photographic light sensitive materials
IPC: G03C1/46
Filed: 1940-06-06
Abstract: 541,515. Photographic light-sensitive material. KODAK, Ltd., and KNOTT, E. B. (Eastman Kodak Co.). June 6, 1940, Nos. 7935/41, (divided out of 540,464) and 16749/40. [Class 98 (ii)] Photographic material comprises two superimposed silver chlorobromide emulsion layers (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), the emulsion of one layer giving a gradation less than 1.8 and the other giving 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 first measured at about the wavelength of the maximum speed of the second 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 first, the speed of the first emulsion is at least twice the speed of the second. 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 600Á. The support may be of paper, film, or glass. The material may comprise one layer of 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 a second layer of silver chlorobromide emulsion of between 30-70 per cent silver chloride and of relatively low gradation and not optically sensitized. On such material, 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 negatives 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 region 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 in the violet between 0.8 and 1.8 (preferably 1.2-1.6) may be used in one layer, in conjunction with a second layer of 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- 570Á (e.g. 550-570Á), preferably without useful sensitivity above 600Á. Suitable speed, and exposure filters are specified. A formula for a standard developing solution is given. Non- wandering sensitizing dyes are specified. The material may be made with a greater gradation difference than necessary to compensate for loss due to dye-wandering. More than two emulsion layers may be used. A thin gelatine layer may be coated between the emulsion layers, and may contain a substance capable of reacting with or otherwise influencing the sensitizing dye or dyes to prevent wandering, and may also contain a decolorizable filter dye. The emulsion giving the higher gradation is preferably used for the lower layer, but may be used for the upper layer. Where an opaque support (e.g. white paper) is employed, density measurements are made with reflected light. In an example, both layers comprise silver chlorobromide emulsions of 50 per cent silver chloride and 0 to ¢ per cent silver iodide content. The emulsion for the lower higher-gradation layer is optically sensitized with 2:2<SP>1</SP>-diethyl-5:6:5<SP>1</SP>:6<SP>1</SP>dibenzoxacarbocyanine iodide and has a blue-to-violet speed of 0.2, a green-to-yellow speed of 0.7, and a green-toyellow gradation of 5.2. The non-optically sensitized emulsion for'the upper layer has a blueto-violet speed of 0.7 and a gradation of 1.5, In a second example, both layers comprise silver chlorobromide emulsions of 85 per cent silver chloride and 15 per cent silver bromide content. The emulsion for the lower higher-gradation layer is optically sensitized with 5-(2-ethyl-1-benzoxazylidene-ethylidene)-3-ethylrhodanine and has a violet speed of 0.1, a green-to-yellow speed of 0.7, and a green-to-yellow gradation of 4.9. The emulsion for the upper layer is optically sensitized with 3-ethyl-5-(1-methyl-2-#-naphthoxazylidene)-rhodanine and has a violet speed of 0.3, a blue-speed of 1.0 and a blue-gradation of 1.4. Specification 15054/12, [Class 98 (ii)], is referred to.