GB627719A - Improvements in and relating to photographs and to sensitive photographic materials - Google Patents

Abstract

627,719. Reducing light-scattering and halation in photographic materials. KODAK, Ltd. (Eastman Kodak Co., Nadeau, G. F., and Jelley, E. E.). Oct. 25, 1946, No. 31663. Drawings to Specification. [Class 98 (ii)] Light-scattering in photographic material having a transparent layer on a light-diffusing support or a translucent but light-diffusing layer on a transparent support, is reduced by providing between the transparent and the lightdiffusing layers a continuous solid layer having a thickness greater than that at which interference patterns appear but less than 0.005 inch, and having a refractive index at least 0.08 less than that of the transparent or translucent layer. The auxiliary layer, when between the support and an emulsion layer, functions as an antihalation layer, its thickness may be between 0.005 inch and 0.00005 inch, and may be constituted by a finely-dispersed fluoride such as cryolite or sodium fluosilicate in cellulose acetate or polymethyl methacrylate. The auxiliary layer may form a subbing layer, and since the solvent therefor attacks the support and reduces the sharpness of the interface, the thickness may be as low as 0.00002 inch. An additional low dye density antihalation layer, permitting exposure through the support, may be provided on the back of the support. Lithium, sodium, potassium, magnesium, rubidium, or ammonium fluorides or cryolite, cryolithiolite, fluosilicates, or fluoborates may be used. Over 30 per cent by weight (e.g. 50 per cent) of fluoride should be present, e.g. 0.8 per cent by weight sodium fluoborate in a 1 per cent by weight solution of cellulose nitrate in a suitable solvent gives a suitable layer. Over 50 per cent of the dispersed particles should be smaller than .2 micron in diameter and preferably about .1 micron. A photographic colour print may comprise a transparent multicolour image separated from a white light-diffusing support by a continuous solid layer of the general type defined containing more than 30 per cent by weight of fluoride in a transparent binder having a sufficiently low water permeability to prevent wandering of fluoride into adjacent layers during manufacture of the print. The refractive index of the intermediate layer may be at least 0.05 less than that of the image layer and the ratio of fluoride to binder greater than 1 : 2 by weight, more than 50 per cent of the dispersed particles being smaller than 0.2 microns in diameter. Specification 600,310 is referred to. According to the Provisional Specification, the emulsion may have a high refractive index and the other layers normal refractive indices, or the emulsion may have a high, the intermediate layer a low, and the support a normal refractive index.