Patent GB-717915-A (GB)
Title: Improvements in photographic processes involving physical development
IPC: G03C5/58
Filed: 1951-07-20
Abstract: 717,915. Photographic process using physical development. NAAMLOOZE VENNOOTSCHAP PHILIPS' GLOEILAMPENFABRIEKEN July 20, 1951 [July 25, 1950], No. 17232/51. Class 98(2) Photographic contrasts are made by increasing the intensifiability of a silver germ image, defined as a weak or imperceptible image obtained by reduction of soluble silver compounds by a firstformed light-reaction product (other than silver halide), and physical development of the silver germ image, characterized in that the starting material is an acid or neutral layer and that afterexposure and before physical development the pH in the layer is increased by treatment with alkaline vapour or liquid, thus likewise increasing the reducing power of the product, said reducing fewer prior to increasing the pH in the layer being not greater than about 0.8 volt and the reducing power at the pH of the medium which increases the pH in the layer being greater than about 0.2 volt. Soluble silver compounds for formation of the silver germ image may be present in the layer during exposure or may be introduced afterwards, and the first-formed light-reaction product may result from exposure of light-senitive materials such as diazonium, ferric or uranyl compounds, aromatic quinones such as benzoquinone; indophenols, indamines, indamilines, or azine, oxazine, thiazine or indigo dyes. Dye forming physical developers, with removal of the metal image, may be used for colour photography. Methods of determination of the reducing powers are referred to in the Specification together with theoretical considerations of the reactions involved In Example 1 superficially saponified cellulose acetate foil or gelatin coated paper is impregnated with a solution containing specified proportions of ferric nitrate, silver nitrate and citric acid, dried, exposed under a sensitometer, treated with a sodium lactate solution of pH 7.5, washed and physically developed with a solution containing metol, citric acid and silver nitrate, to show a 30 times gain in sensitivity as compared with a case in which the sodium lactate treatment is omitted. In Example II a similar foil is sensitized with methylene blue or other dye together with sulphuric acid, exposed, treated in a solution of sodium lactate and then in a solution of sodium lactate together with silver nitrate, and physically developed similarly, or use may be made of a bluegreen colouring physical developer containing dimethylamino, phenylamine nitrate, tartaric acid, silver nitrate and naphthol, with silver removal by a liquid containing potassium ferricyanide and thiosulphate. Example III specifies p-diethylaminobenzene-diazonium boron fluoride. with silver nitrate as sensitizer. treatment after exposure with a sodium lactate-silver nitrate solution and then with potassium thiocyanate to prevent fogging and physical development, to show sensitivity 200 times higher than that of the method of Specification 391,677 which does not use physical development. Of twelve further examples, example XI uses a diazo compound alone as sensitizer, with treatment after exposure with a solution containing sodium lactate and silver nitrate and then potassium thiocyanate and the physical developer; examples XIII and XV specify, respectively benzoquinone and uranyl nitrate with silver nitrate and acid, and.all other examples diazonium salts with silver nitrate. as sensitizers, with similar treatment for reduction of acidity after exposure, and physical development. Specification 511,816 also is referred to.