GB491586A - Improvements in and relating to the production of light sensitive printing papers - Google Patents

Abstract

491,586. Photographic blue -print processes. HALDEN & CO., Ltd., J., and HOLDEN, J. Dec. 4, 1936, No. 33273. [Class 98 (ii)] Blue-print papers are made by coating the paper with a solution of a ferric salt, a ferrocyanide with or without a ferricyanide and a suitable buffer salt in neutral or alkaline condition, drying the paper, and applying a fixing agent before or after exposure to light to render the ferrocyanide or ferricyanide insoluble when the paper is developed by aqueous contact. .The buffer salt inhibits the formation of the insoluble Prussian blue, due to the presence of the ferric salt and the ferrocyanide. Ferric ammonium oxalate, potassium ferrocyanide and potassium ferricyanide are included in the coating solution and may be buffered by alkaline oxalates, citrates or tartrates. The fixing agents which may be applied in whole or in part immediately after drying the paper include zinc, nickel and cobalt salts of aliphatic or aromatic acids such as zinc salts of naphthalene sulphonic acid or phenol sulphonic acids, metallic salts of sulphuric acid esters of high fatty alcohols, zinc, nickel and cobalt sulphates, and even insoluble or slightly soluble compounds such as oxides, carbonates &c. These fixing agents may also be applied in the form of a fine dry powder. Oxidizing agents are added as intensifying or stabilizing agents and examples include bichromates, persulphates, stabilized compounds of hydrogen peroxide, chloramines, hypochlorites, and salts of paradichlorosulphonamino-benzoic acid. Oxidizing agents which combine the properties of fixing and intensifying include metallic peroxides, persulphates, chromates and double salts of alkali persulphates and hypochlorites. Buffer salts are included for stabilization after exposure to light and may be acid or neutral phosphates of the alkali metals or ammonia, organic salts of phthalic and benzoic acids, and calcium and magnesium salts. Stabilizing agents may be added to the coating mixture or during subsequent development, examples being chlorates, bromates and persulphates. Wetting-agents may be added to the coating solutions and its effect destroyed at any stage by a barium salt. Four examples of the preparation of prints having yellow, cream or white lines on a stable blue background are described in the Specification. Specifications 418,976 and 424,976 are referred to.