Patent GB-541513-A (GB)
Title: Improvements in photographic light sensitive materials
IPC: G03C1/46
Filed: 1940-04-15
Abstract: 541,513. Photographic light-sensitive material. KODAK, Ltd., and DAVEY, E. P. (Eastman Kodak Co.). April 15, 1940, Nos. 6243/41, (divided out of 540,451) and 16735/40. [Class 98 (ii)] Multi-contrast material comprises two superimposed light-sensitive layers, both consisting of silver chloride emulsions containing over 90 per cent of silver chloride and preferably free from silver bromide, but possibly containing some silver iodide, of which one gives a gradation (measured by light of about the wavelength, including the range 40Á on each side thereof, of maximum sensitivity of the emulsion concerned) less than 1.8, and the other a gradation of at least 2.5 greater, and of which one (A) is sensitized to have its maximum speed at least 60Á further towards the long wavelengths than the other (B), the sensitivity of (A) measured at about the wavelength of maximum sensitivity of (B) being not greater than half the sensitivity of (B) at that wavelength, while measured at about the wavelength of maximum sensitivity of (A) the sensitivity of (A) is at least twice that of (B). One layer may comprise a non-optically sensitized emulsion (including an emulsion sensitized within its natural sensitivity region and substantially insensitive above 430 Á) giving a gradation in the violet between 0.8 and 1.8 (preferably between 1.2 and 1.6), and the other an emulsion optically sensitized in the region 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 optically sensitized emulsion, while the green-to-yellow speed of the optically sensitized emulsion is between 1/3 and 1“ (preferably between ¥ and 1“) times the violet-speed of the non- optically sensitized emulsion. Each of the emulsions may be substantially insensitive at the wavelength of maximum sensitivity of the other. The material is substantially insensitive above 60011. Suitable exposure-filters for use in obtaining the various contrasts are referred to. The emulsion giving the lower gradation should be one having a characteristic H and D curve whose straight portion is as long as possible. The emulsion giving the higher gradation is preferably the under layer, especially with a paper support, but may be the upper layer. With an opaque support such as paper, density measurements are made with reflected light. The material may be made with a greater gradation difference than necessary to compensate for dye-wandering. A thin intermediate gelatine layer, which may contain a substance which is capable of reacting with or otherwise influencing the sensitizing dye or dyes used, and which may also contain a decolorizable filter dye, may be used to prevent wandering of the sensitizing-dye. A formula for a standard developing solution is given. 3-ethyl-5- (1-methyl-2-#-naphthoxazolylidene )-rhodanine may be used to sensitize to a maximum near 470Á. In example (1), an amount of silver chloride emulsion made from 1,000 grams of silver nitrate is sensitized with the above dye to have a maximum near 460Á, and has a blue-speed of 0.2 and a gradation of 1.4. This is coated on a paper support. A second silver chloride emulsion sensitized in a similar manner with 5-(2-ethyl-1-benzoxazylidene-ethylidene)-3-ethylrhodanine to have a maximum near 550Á and having a violetspeed of 0.04, a green-to-yellow speed of 0.15, and a gradation in the green-to-yellow of 4.8 is coated over the first emulsion. High-contrast is obtained using a " Wratten " (Registered Trade Mark) No. 12 filter and low-contrast using a No. 47 filter. In example (2), the first layer comprises a non-optically sensitized silver chloride emulsion having a violet-speed of 0.15 and a gradation of 1.4, and the second layer is the upper layer of example (1). An emulsion sensitized to have its maximum in the blue may be employed with a non-optically sensitized emulsion whose maximum is in the violet, either (but preferably the sensitized emulsion) being that giving the higher gradation. Specifications 15054/12, [Class 98 (ii)], 450,958 and 532,098 are referred to.