Patent GB-529041-A (GB)
Title: Improved photographic process and light-sensitive elements therefor
IPC: G03C1/76
Filed: 1939-02-04
Abstract: 529,041. Photographic reflex copying processes. KODAK, Ltd., MARRIAGE, A., SELMAN, R. F. W., and STEVENS, G. W. W. Feb. 4, 1939, No. 3720. Drawings to Specification. [Class 98 (ii)] In the reflex copying process, the light is passed in succession through a light-diffusing layer comprising a finely divided photographically innocuous reflecting material and then a light-sensitive layer and causing the light to be reflected from the material to be printed. The light-diffusing layer may be between the lightsensitive layer and the support or on the opposite side of the support, and has a colloid, for example, gelatin, binder. The support may be glass, film or paper. The light-sensitive layer may comprise a silver halide emulsion, such as silver bromide, chloro-bromide, or iodo-bromide emulsion, having a gamma as high as possible and in which the density at which the straight line portion of its characteristic curve is reached is as low as possible. The emulsion may be treated with a colour sensitizing dye in much smaller amount than the optimum. A thick emulsion layer may be superficially colour sensitized to provide an outer light-sensitive layer and an inner light-diffusing layer, light of the appropriate colour being used for copying. Alternatively, the emulsion layer may be coated with a thin gelatin or other layer containing a colour sensitizer. The support may be successively coated with a not specially colour sensitized silver halide emulsion layer, and then with either a more rapid not specially colour sensitized emulsion layer or with a colour sensitized emulsion layer. A strippable lightdiffusing layer, which may be carried by an additional support, or which may itself be similar to a support but contain a finely dispersed pigment, may be used. The binder for the light-diffusing layer may be readily watersoluble, soluble in the developer or fixing bath. The finely divided reflecting material may also be soluble in a processing or special bath. A dye may be incorporated in the light diffusing layer. Long or short wavelength light may be used in the exposure. An exposure filter layer, preferably decolorizable by a processing or special bath may be provided. Alternatively, a dye or colloidal silver may be incorporated in one of the other layers. A separate filter may be used. The finely divided pigment may be zinc oxide, cadmium carbonate, or lead oxalate. In an example, glass plates are coated with a gelatino silver bromide emulsion of low sensitivity and then with a contrasty gelatino silver chloro-bromide process emulsion. A yellow exposure filter and a process developer containing hydroquinone, potassium metabisulphite, potassium bromide, and caustic potash are used. In a second example, glass plates are coated with a gelatino silver chloride emulsion having a spectral sensitivity with a sharp cutoff between 400 mÁ. and 450 mÁ. and then with a contrasty process emulsion having a sensitivity curve with a more gradual cut-off from about 480 to 550 mÁ. The material is exposed and developed in a similar manner. In a third example, a thin cellulose acetate base is coated on one side with the silver chloro-bromide emulsion of example 1 and on the other with a gelatino suspension of titanium oxide. In a fourth example, glass plates are thickly coated with the silver chloro-bromide emulsion of example 1, and are then superficially colour sensitized with a solution of 2:2<SP>1</SP>-diethyl-3:4:3<SP>1</SP>-4<SP>1</SP>-dibenzoxacarbocyanine iodide. The exposure is through a selenium glass filter cutting off light of shorter wavelengths than 620 mÁ.