Patent GB-954198-A (GB)
Title: Improvements in image reproduction
IPC: G03C1/73
Filed: 1960-04-21
Abstract: 954,198. Photographic materials. MINNESOTA MINING & MANUFACTURING CO. April 21, 1960 [April 30, 1959], No.14035/60. Heading G2C. A photographic light-sensitive sheet comprises an oxidizing agent and a reducing agent which, when initiated by electron transfer, will react together to form an image, and a catalyst which is activated into the transfer of electrons by radiation wave lengths below 5 microns to effect reaction between the oxidizing and reducing agents. Oxidizing agents specified are salts of silver, mercury, lead, gold, manganese, nickel, tin, chromium, platinum and copper, tetrazolium salts, genacryl red,' diphenyl carbazone, and silver saccharin. Reducing agents specified are alkali metal or alkaline earth metal oxalates and formates, hydroxylamine (which may have a phenyl or benzyl substituent), hydrazine, phenylhydrazine, ascorbic acid, metal, hydroquinone, catechol, polyvinyl pyrrolidone or polyamides (the latter two also may serve as binders). The catalyst may be zinc oxide, cadmium sulphide, selinium, titanium dioxide, antimony trioxide, aluminium oxide, certain photochromic complexes of cobalt, iron, manganese or chromium, or a fluorescent material such as zinc sulphide activated by silver, zinc oxide activated by zinc, zinc phosphate activated by manganese, a mixture of copper sulphide, antimony sulphide and magnesium oxide, cadmium borate, or zinc-8-hydroxyquinoline. The components may be mixed with binders and coated in one or two layers on a support, or a sheet containing the imageforming composition may be pressed against a sheet coated with the catalyst in a binder before exposure, in which case the sheets may be held together by means of a pressure-sensitive adhesive. The compositions may contain additional complexing agents such as formamide, acetamide or phytic acid, acids such as oxalic and stearic acids, bases such as ammonium hydroxide, sodium acetate and hexamethylene triamine, or stabilizers such as a benzene diazonium fluoroborate. The images formed on exposure are usually visible, but may be latent and require a development step. In many of the examples, a support is coated with a zinc oxide or titanium dioxide catalyst and the reducing agent (sodium oxolate, sodium format, metol or hydroquinone) in a butadiene/styrene copolymer binder, and then a coating of the oxidizing agent (silver nitrate, copper sulphate, gold chloride, nickel chloride or tetrazolium blue) in a binder of polyethylene glycol, polyamide, gelatin or polyvinylpyrrolidone is applied. After exposure, the top layer may be washed off with water to stabilize the image which is formed in the first layer. In Example III, the oxidizer is chromous chloride and diphenylcarbazone, and the material is heated to develop the image (which is stable). In Example IV the first layer contains p-(N-acetyl- N-methylamine benzene diazonium fluoroborate which is subsequently decomposed by heat to stabilize the image. Where gold chloride is used as the oxidizer, the image is developed by heating or by dipping in water or hydroquinone solution. In other examples, the components are coated on a support in a single layer with a binder of polyamide, polystyrene or a butadiene/styrene copolymer. These may be fixed by washing out the remaining oxidizer. Other methods of stabilizing the image include (i) incorporating in the material compounds which release acid on heating such as a mixture of m -nitro-benzene sulphonyl chloride and phloroglucinol, or p-toluene sulphonic acid/urea complex. p-acetamidobenzene diazonium fluoroborate or m -chlorobenzene diazonium fluorophosphate, or with water, such as diazonium fluoroborate, (ii) including in the material a chelating agent which reacts on heating such as the use of salicylaldoxime with a copper oxidizing agent or benztuazole with silver, (iii) by the application of pressure, or (iv) in the case of a laminate, by separating the layers.