Patent GB-440736-A (GB)
Title: Improvements relating to the production of photo-mechanical printing surfaces
IPC: G03F7/07
Filed: 1934-07-05
Abstract: 440,736. Producing photo-mechanical printing-surfaces. WEBB, K. W. C., 31, Colville Gardens, Notting Hill, London, and GALL, R. L. B., Westlake, Ootacamund, Nilgiris, South India. July 5, 1934, Nos. 19831, 23814, and 25557. [Class 98 (ii)] A process for the production of a photomechanical printing-surface comprises the application of a photographic image defined in a halide of silver or silver and mercury, in contact with a smooth metal surface, for example a polished copper plate, in the presence of a deposition agent, whereby a silver or a silver and mercury deposit corresponding to the image is obtained on the plate. The deposition agents may be hydrochloric acid, sodium or potassium chloride, sodium sulphite, sodium thiosulphate, sodium, potassium or ammonium ferrocyanide, potassium cyanide, ammonium sulphocyanide, ammonium hydroxide, pyridine or derivatives, thiocarbamide, allylthiocarbamide or allylcyanamide. The copper plate may be replaced by a zinc plate electrolytically coated with copper, a brass plate, a nickel-coated plate, a plate with an amalgamated surface or a zinc plate. A developed positive may be treated with a bleaching agent such as copper chloride to obtain the desired image. In one example the image is pressed into contact with a highly polished copper plate that has been wetted with dilute hydrochloric acid solution for from one to three minutes. The copper plate bearing the silver deposit is dipped into a solution of copper sulphate containing sulphuric and hydrochloric acid, forming cuprous chloride on the exposed copper. The plate is covered with printing ink by a roller, and the plate immersed in strong sodium thiosulphate solution, the cuprous chloride being dissolved off, and the ink which had adhered thereto being removed by a roller. The plate is then etched in the usual manner. Alternatively the silver is amalgamated by rubbing with mercury the cuprous chloride dissolved with strong sodium thiosulphate solution, and the plate inked up and etched. In another example the plate with the silver deposit is treated with ferric chloride solution to grain the copper and then inked up in a lithographic machine. Mercury or mercuric chloride may be applied to the plate, which may be employed for lithographic printing. For half-tone printing the plate is etched after inking. To obtain a positive printing surface from a negative image, the graining and inking up is followed by deposition of chromium on the copper, removal of the ink and etching with chromic acid to remove the silver and etch the copper. In another example the plate with the silver deposit is treated with dilute mercuric chloride solution containing free hydrochloric acid. The surface is inked, and the mercury deposit augmented by treatment with strong mercuric chloride solution or with an amalgamated copper or brass cylinder, and the plate re-inked and etched. In a further example, the plate with the silver deposit is amalgamated directly with metallic mercury or with dilute mercuric chloride solution containing free hydrochloric acid, the surface being gently rubbed. The surface is inked and treated with petrol or benzene to dissolve off the ink, and at the same time to remove the mercury on the copper. The plate is then re-inked, being attracted to the copper and repelled by the amalgamated silver, and etched. The wet ink resists may be dried by dusting over with bitumen and heating. The ink image may be transferred to a grained zinc or aluminium plate by the off-set process and the latter plate used for lithographic printing. In a process for obtaining an intaglio plate for rotogravure printing, a film is exposed under a rotogravure screen and the negative bleached and used to deposit the silver image on the copper plate. The plate is treated with stronger mercuric chloride solution containing free hydrochloric acid, and the copper is dissolved and mercury deposited. The action of the mercuric chloride on the copper is retarded according to the thickness of the silver image. The deposited mercury is evaporated by heating. In a still further modification the plate with the silver deposit is made the anode, and a plain copper plate the cathode, in an electrolytic cell containing copper sulphate solution with free sulphuric acid. The copper under the silver deposit is dissolved according to the depth of the deposit. In another modification, the plate with the silver deposit is treated with weak iodine solution and then with dilute sodium thiosulphate, ammonium or potassium cyanide. solution. The plate is then made the cathode in an electrolytic cell with a nickel anode and a nickel salt electrolyte; whereupon a black deposit of nickel is formed on the silver iodide according to the thickness therof. The plate is dried, and an electrotype or cast is made to give an intaglio plate. When the surface ultimately obtained is of cylindrical form, it can be employed or adapted for the transmission of the image by telegraph or wireless.