GB947479A - Improvements in or relating to the production of images of originals - Google Patents

Abstract

947,479. Printing and stencilling processes. GEVAERT PHOTO - PRODUCTEN N.V. March 2, 1960 [Dec. 2, 1958], No. 38813/58. Heading B6C. [Also in Division G2] In a process for forming on a support a fixed visible image from an electrostatic latent image a temporary powder image is formed by powder development on said support of the latent image, or by powder development elsewhere of the latent image and image wire transferring the powder or a layer of the powder to the said support, then without fixing the powder on said support the uncovered area or area of the powder-image bearing surface of the support is (are) rendered visibly distinct from the area or areas of such surface covered by the powder and the powder is subsequently removed. In one embodiment, the process comprises spraying a support bearing a powder-image, which image may be formed by any of the known direct or transfer methods, with a quickly drying ink or dye stuff solution, allowing the ink or dye stuff solution to dry, and removing the powder by brushing or wiping or in the case of ferromagnetic powders by magnetic means. The sprayed liquid may for example be a solution of printing ink in petrol or toluene or of aniline black in alcohol, and the said liquid may be given an electrostatic charge as it is sprayed by means of a corona discharge electrode placed adjacent to the spraying nozzle. In a second embodiment the powder image is formed on a support which incorporates a colour component and the process comprises spraying the said support with a colour developing solution to develop the said colour component in the uncovered areas, and finally of removing the powder as before. The colour component may be of the type which forms a colour dependent upon pH (in which case the developer solution may be either acid or alkaline), may be of the type which is oxidizable to a coloured form (in which case the developer solution is an oxidizer) or may be a compound which forms, a colour by the diazonium reaction. As an example of the oxidizable type the colour component may be a leucobase of a triphenyl methane dyestuff (example leuco malachite green) and the developer spray may be a solution of potassium permanganate in aqueous acetic acid. As an example of the diazonium type the colour component may be 2,5-diethoxy-4-benzylamine -benzene diazonium chlorozincate, and the developer a solution of phloroglucinol in alcohol and water. Alternatively a colour component and a colour developer which only react when a further substance is applied may be present together in the surface layer of the support and after establishing a temporary powder image thereon the whole area may be treated with the further substance. In a third embodiment the process comprises spraying a support bearing a powder image with a colourless solution, allowing the solution to dry, removing the powder, and rendering the image areas visible by treatment (for example heating) of the support as a whole. Multicolour images may be prepared from coloured originals by preparing colour separation powder images for the different colours in turn using filters, and by successively transferring and printing these powder images in the appropriate colour on the same support sheet by a process as described above. Examples of suitable powders for obtaining the powder image include various sawdusts, leather and rubber dust, potato flour, Indian meal, natural and synthetic resins such as polyvinyl alcohol, carboxymethyl cellulose, gelatin, polymethacrylic acid cellulose and a terpolymer of vinyl chloride vinyl acetate and maleic anhydride, silicic acid and derivatives such as sand, kieselguhr ,diatomaceous earth and talc,various metals, metalloids such as selenium and tellurium, metal oxides and other metal compounds such as iron carbonyl. The Specification also refers to the transfer of ferromagnetic powders to supports by magnetism. The Provisional Specification also refers to the formation of powder images by means other than electrostatic means (for example by using a support with magnetic properties) to changes in hydrophobic or hydrophilic properties in the areas of the support not covered by the powder, to the use of a bleaching spray to remove the colour from the said uncovered areas, and to the use of a powder (for example a sequestering compound such as ethylenediamine sodium tetraacetate) for destroying the colour of the ink which may comprise a compound of iron with gallic acid. Other methods of producing the multicolour images are disclosed in the Provisional Specification. For example successive colour separation powder images may be formed by using a line screen during exposure and by using a panchromatic photoconductive layer, the said screen having either transparent lines and twice as thick opaque lines, or successive blue and green and red lines of equal thickness. The screen may alternatively comprise an irregular multicolour screen. Specifications 658,699, 672,767, 772,873, and U.S.A. Specifications 1,818,760 and 2,143,214 are referred to.