| 摘要 |
1330955 Printing plate HOWSON-ALGRAPHY Ltd 2 Feb 1972 [9 Feb 1971] 4307/71 Heading B6C [Also in Divisions B2 G2] A sheet suitable for use in the production of a lithographic printing plate comprises a sheet of aluminium or aluminium alloy having an anodic layer formed thereon, the layer being impregnated with a composition comprising water-soluble polyvinyl alcohol and a further water-soluble colloid. The coating may comprise 1-20 parts by weight of polyvinyl alcohol per 20-1 parts by weight of the further water-soluble colloid. Said other colloid may be gum arabic, a carboxymethyl cellulose salt, e.g. the sodium salt, or dextrin. Additional materials such as a wetting agent and/or a colourant and/or a preservative may be present in the coating solution. The sheets are suitable for use both in the water-developed "deep etch" reversal process of plate making and in the acid-developed water wash and/or organic solvent wash deep etch reversal process. In a typical example an electrochemically grained and anodized aluminium sheet was washed and then immersed in a bath containing 60 grams gum arabic lumps, 60 grams polyvinyl alcohol in 8 litres water to impregnate the anodized surface. The sheet was then dried and coated with a dichromate light-sensitized layer of gum arabic, placed in contact with a line and dot structured photographic film positive transparency, and exposed to the light from a single phase open carbon electric arc. The exposed plate was then developed with an aqueous solution of calcium and zinc chlorides and the areas of the sheet thereby revealed were deep etched using a solution containing zinc chloride and hydrochloric acid. After cleaning and drying the etched areas were coated with a thin film of vinyl-based lacquer and when the lacquer was dry it was inked with a layer of black-pigmented greasy "inking in solution". The inked plate was then immersed in clean water, drained and flooded with a 2% solution of sulphuric acid to loosen the stencil constituted by the light struck areas of the lightsensitized coating. The stencil was then scrubbed off. The printing plate was completed by washing and applying a thin layer of gum arabie. |
