SILVER IMAGE BLEACHING PROCESS

Abstract: A method for bleaching a silver image wherein the image is treated with a first solution comprising iodine and an iodide salt and then the iodine stain is removed by treating it with a second solution comprising ascorbic acid ans sulphite ions. The method is particularly useful for silver images formed by the silver salt diffusion transfer process.

Description: SILVER IMAGE BLEACHING PROCESS This invention relates to a method of bleaching silver images and to solutions therefor. The photographic silver halide image forming process is well known. Sometimes it is desirable to retouch the silver image formed thereby and, specifically, it is sometimes desired to remove parts of the image such as unwanted spots. It is known, for example from British specification 2 107 889 that a thickened solution containing, for example, iodine and an iodide can achieve the desired result. A problem with this approach is that a brown stain is produced which is unsightly. In addition the compositions of 2 107 889 are only suitable for printing plates which do not have any gelatin layers. It is therefore desirable to be able to delete the silver image without causing any stain and to delete the silver image in a gelatin- containing layer. The present invention provides a method of removing silver images without causing any stain. According to the present invention there is provided a method for bleaching a silver image wherein the image is treated with a first solution comprising iodine and an iodide salt and then the iodine stain is ..emoved by treating it with a second solution comprising ascorbic acid and sulphite ions. The image is bleached rapidly and permanently, there is no stain and the solutions have a long life. The silver image to be treated may be on an imagewise exposed and fully processed photographic film or paper or on a printing plate made by the photographic silver salt diffusion transfer process. Such materials are described in Research Disclosure Item 308119, December 1989 published by Kenneth Mason Publications, Emsworth, Hants, United Kingdom. In a preferred embodiment of the present invention the solutions are applied to the silver image using "felt tipped" pens, preferably ones with a fine tip to ensure accurate application. The first solution, used to delete the silver image preferably contains a mixture of water and butyrolactone. The ratio of aqueous to organic solvent is optimised to provide sufficient water for rapid penetration of the solute into the gelatin layer on the image-bearing material, together with sufficient butyrolactone to obtain high complexing power for silver iodide so that the image is removed in a conveniently quick time. The first may also contain other solvents used alone or in combination including alcohols eg ethyl or butyl alcohol. The iodide may be provided by an ammonium or alkali metal iodide, eg sodium or potassium iodide. The first solution preferably contains from 2 to 50g, especially from 20g to 45g, of iodine and from 50g to 250 g, especially from 150g to 200g, of iodide ions per litre. The solvent preferably comprises from 10 to 60% by weight of water, the exact figures being dependent on the considerations outlined above. Preferably the first solution also contains a wetting agent and an acid. The second solution preferably contains from 10 to lOOg, especially from 40 to 80g, ascorbic acid and from 10 to lOOg, especially from 30 to 70g, of potasium sulphite per litre. The solution is preferably aqueous. The invention further provides a deletion fluid kit comprising the first and second solutions as defined above. Preferably the solutions are each contained in a felt tip pen. The following Example is included for a better understanding of the invention. The words KODAK and PMT are trademarks. EXAMPLE The following solutions were made up: SOLUTION A Iodine 26 g Potassium iodide 170 g ETHOQUAD C25 (surfactant) 1 g Butyrolactone 510 g Water 270 g Acetic acid 18 g SOLUTION B Ascorbic acid 60 g Potassium sulphite 50 g Water 1 litre Each solution was filled into a felt tip pen. Images were produced using Kodak PMT3 KNP negative paper, exposed on a Kodak Imagemaker Camera and processed in a Kodak 43DT Imagemate Processor onto a variety of Kodak PMT receivers. Images were deleted successfully from the following receivers in an average time of 20 secc"ds. PMT 3 KRPM Matt receiver paper PMT 3 KRPT Thin receiver paper PMT 3 KRPTA Adhesive thin receiver paper PMT 3 KRPG Glossy receiver paper PMT 3 KRF Receiver film PMT 3 KRFT Thin receiver film PMT II Metal litho plates Other materials tried were Kodak PMT II Paper Litho plates and Kodak Pagiset Phototypesetting paper. Images could be successfully deleted from both, but the deletion time was greater than 1 minute.

Claims: CLAIMS : 1. A method for bleaching a silver image wherein the image is treated with a first solution comprising iodine and an iodide salt and then the iodine stain is removed by treating it with a second solution comprising ascorbic acid and sulphite ions. 2. A method as claimed in claim 1 in which the silver image to be treated is located on an imagewise exposed and fully processed photographic film or paper or on a printing plate made by the photographic silver salt diffusion transfer process. 3. A method as claimed in Claim 1 or 2 in which the solutions are applied to the silver image using felt tipped pens. . A method as claimed in any of claims 1 - 3 in which the first solution contains from 2 to 50g, preferably from 20g to 45g, of iodine per litre. 5. A method as claimed in any of claims 1 - 4 in which the first solution contains from 50 to 250 g, preferably from 150g to 200g, of potassium iodide per litre. 6. A method as claimed in any of claims 1 - 5 in which the solvent of the first solution comprises from 10 to 60% by weight of water. 7. A method as claimed in any of claims 1 - 6 in which the second solution comprises an aqueous solution containing from 10 to lOOg, preferably from 40 to 80g, ascorbic acid and from 10 to lOOg, preferably from 30 to 70g, of potassium sulphite per litre. 8. A deletion fluid kit comprising the first and second solutions as defined in any of claims 1 - 2 and 4 - 7. 9. A deletion fluid kit as claimed in claim 8 in which the solutions are each contained in a felt tip pen.

Inventors: BARNETT ANTHONY MALCOLM, HALLBERY DAVID ALAN, BARNETT, ANTHONY, MALCOLM, HALLBERY, DAVID, ALAN
Applicants: EASTMAN KODAK CO, KODAK LTD, EASTMAN KODAK COMPANY, KODAK LIMITED
Application year: 1991
Main classification: G03C11
IPC codes: G03C5, G03C11