Patent GB-541510-A (GB)
Title: Improvements in photographic light sensitive materials
IPC: G03C1/035
Filed: 1940-04-15
Abstract: 541,510. Photographic light-sensitive material. KODAK, Ltd., DAVEY, E. P., AMOR, A. E., and KNOTT, E. B. April 15, 1940, Nos. 6240/41, (divided out of 540,451), 6244/41, (divided out of 540,464), and 13801/40. [Class 98 (ii)] Multi-contrast material comprises a single sensitive layer which comprises a mixture of two silver bromide emulsions (which consist of at least 90 per cent silver bromide based on the total silver halide, and may contain some silver iodide, and not more than 10 per cent silver chloride) of which one emulsion gives a gradation (measured at about the wavelength, including the range covering 40 Á on each side thereof, of the maximum speed of the emulsion concerned) less than 1.8, and the other emulsion gives a gradation of at least 2.5 greater than that of the first emulsion, and of which one emulsion (A) is sensitized to have its maximum speed at least 60 Á further towards the long wavelengths than the maximum speed of the other emulsion (B), the speed of emulsion (A) measured at about the wavelength of maximum speed of (B) being not greater than half the speed of (B) measured at the same wavelengths while measured at about the wavelength of maximum speed of (A) the speed of (A) is at least twice that of (B). Both emulsions should be substantially insensitive beyond 600 Á. The layer may comprise a mixture of a non-optically sensitized silver bromide emulsion (including an emulsion sensitized in the blue region only and substantially insensitive beyond 520 Á) giving a gradation in the blue between 0.8 and 1.8 (preferably between 1.2 and 1.6) and a silver bromide emulsion optically sensitized in the region 500-560 Á and giving a gradation in the green-to-yellow of at least 2.5 (preferably 3.5) greater, the blue-speed of the non-optically sensitized emulsion being at least 1.8 (and preferably at least 2.5) times the blue-speed of the optically sensitized emulsion and the green-to-yellow speed of the optically sensitized emulsion being between ¢ and 1“ (preferably and 1“) times the blue-speed of the non-optically sensitized emulsion. With an opaque support, such as white paper, density measurements are made with deflected light. A formula for a standard developing solution is given. The non-optically sensitized emulsion should be one having a characteristic H and D curve whose straight portion is as long as possible. One or more sensitizing dyes may be used for the optically sensitized emulsion, and such dyes are incorporated before mixing the emulsions, and in such a manner, as for example described in Specification 540,451 that the tendency of the dye or dyes to wander is avoided or minimized. The material may be made with a greater gradation difference than necessary to compensate for loss due to dye-wandering. In examples, (1) to an amount of a silver bromide emulsion containing 3 per cent silver iodide made from 200 grams of silver nitrate is added at 35‹C a mixture of 500 ccs. of ethyl alcohol containing 0.10 grams of soft lac and 200 ccs. of ethyl alcohol containing 0.03 grams of the dye made according to either example 2 or 3 of Specification 532,098. This optically sensitized emulsion has a bluespeed of 2.0, a green-to-yellow speed of 5.7, and a green-to-yellow gradation of 5.5. To an amount of a similar silver bromide emulsion having a blue-speed of 5.4 and a gradation of 1.5 made from 200 grams of silver nitrate is added 500 ccs. of ethyl alcohol containing 10 grams of soft lac at 35 ‹C. The emulsions are mixed at 35 ‹C and immediately coated on a paper support. In example (2) to an amount of a high-contrast pure silver bromide emulsion made from 200 grams of silver nitrate is added, immediately after formation of the silver bromide, 0.03 gram of the dye of example 3 of Specification 532,098, and the emulsion is ripened at 40‹C for 10 minutes, set and washed, and after addition of more gelatine digested at 55‹C for 30 minutes. This emulsion has a blue-speed of 1.0, a green-to-yellow speed of 2.7, and a green-to-yellow gradation of 4.4. A non-optically sensitized emulsion having a blue-speed of 4.7 and a gradation of 1.3 is mixed with this emulsion, and the mixture coated immediately on a paper support. In example (3), a similar mixture is used, except that the blue-speed of the non-optically sensitized emulsion is 3.0. In example (4), a high-contrast silver bromide emulsion containing the equivalent of 200 grams of silver nitrate is adjusted to a pH of 7 and sensitized with 0.05 gram of the dye of example 43 of Specification 450,958, and allowed to stand for 30 minutes at 35 ‹C. After the successive addition of a suspension of 30 grams of magnesium hydroxide, a 5 per cent alcoholic solution of 50 grams of soft lac resin, and 50 grams of potassium chloride, the product is kept at 35‹C for the requisite period (e.g. 90 minutes), and the resultant emulsion has a blue-speed of 1.5, a green-to-yellow speed of 3.0, and a green-toyellow gradation of 4.5. This emulsion is mixed with a silver bromide emulsion to which have been added the same quantities of magnesium hydroxide and resin and having a blue-speed of 4.0 and a gradation of 1.2, and the mixture is immediately coated on a paper support. Suitable exposure filters for various contrasts are specified. More than two emulsions may be mixed. Specifications 15054/12, [Class 98 (ii)], and 524,552 are referred to.