Patent GB-541512-A (GB)
Title: Improvements in photographic light sensitive materials
IPC: G03C1/46
Filed: 1940-04-15
Abstract: 541,512. Photographic light-sensitive material. KODAK, Ltd., DAVEY, E. P., AMOR, A. E., and ROBINSON, A. April 15, 1940, Nos. 6242/41, (divided out of 540,451) and 16944/41. [Class 98 (ii)] Multi-contrast material comprises two superimposed light-sensitive layers, one consisting of a silver bromide emulsion (which contains at least 90 per cent silver bromide, and which may contain up to a maximum of 10 per cent of silver chloride, and some silver iodide) which 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 of a silver bromide emulsion giving a gradation at least 2.5 greater than that of the other emulsion, and one emulsion (A) is sensitized to have its maximum speed at least 60Á further towards the long wavelengths that the maximum sensitivity of the other emulsion (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 silver bromide emulsion (including an emulsion sensitized in the blue region and substantially insensitive beyond 520Á) giving a gradation in the blue between 0.8 and 1.8 (preferably between 1.2 and 1.6) and the other a silver bromide emulsion optically sensitized in the region 500-560Á 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 (preferably at least 2.5) times the blue-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 blue-speed of the non-optically sensitized emulsion. The material may have substantially no sensitivity beyond 600Á. Suitable exposure-filters for use in obtaining the various contrasts are referred to. The non- optically sensitized emulsion 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 loss due to dyewandering. 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. In an example, both layers consist of gelatinosilver bromide emulsions containing 3 per cent silver iodide but free from chloride. The higher gradation emulsion for the under layer is sensitized with 2:21-diethyl-5:6:51:61-dibenzoxacarbocyanine iodide and has a blue-speed. of 2.0, a green-to-yellow speed of 5.6, and a gradation in the green-to-yellow of 5.4. The upper layer comprises a non-optically sensitized emulsion having a blue-speed of 5.4 and a gradation of 1.5. Highcontrast is obtained using a "Wratten" (Registered Trade Mark) No. 5 filter, low-contrast using a No. 47A filter, and medium contrast with no filter or a K1 filter. A formula for a standard developing solution is given. Specification 15054/12, [Class 98 (ii)], is referred to.