Patent GB-944276-A (GB)
Title: Improved light sensitive sheet
IPC: B41N1/14
Filed: 1959-11-26
Abstract: 944,276. Photosensitive sheet especially for lithographic procedure. MINNESOTA MINING & MANUFACTURING CO. Nov. 26, 1959 [Nov. 26, 1958], No. 40202/59. Drawings to Specification. Headings G2C and G2M. A light-sensitive sheet material comprises a support carrying a diazo resin layer which upon exposure becomes differentially soluble in the exposed and non-exposed areas, and overlaying the diazo resin layer a thin abrasion-resistant solvent-softenable resinous coating at least one millionth of an inch thick and containing 0 to 50% by weight of pigment, the diazo resin becoming insoluble in the exposed areas and firmly bound to the resinous coating while the unexposed portions of the diazo resin remain soluble and removable upon gentle rubbing with an aqueous solvent. In Example 1 a cleaned aluminium sheet is treated with aqueous silicate solution, washed free of soluble materials, coated with a #-diazodiphenylamine-formaldehyde resin solution and then with one of polyvinylformal resin in ethylene chloride containing a blue pigment. The sheet so prepared is imagewise exposed, rubbed with aqueous propanol and then wiped with acidified gum arabic solution, after which it is mounted in an offset litho press for printing. Instead of polyvinyl formal, there may be used polyvinylbutyral, polymethylmethacrylate, polystyrene, polyvinyl acetate, vinyl chloride-acetate copolymer, polythene, an expoxy, alkyd, polyamide, phenolaldehyde, silicone, or polyalkylene-polysulphide resin, cellulose acetate-butyrate, a natural or synthetic rubber, shellac, or compatible mixtures. Typical alternative processing solutions for different specified resin coatings are aqueous solutions of methyl ethyl ketone, acetonitrile, ethanol, and acetone, while for a coating of chlorinated rubber water alone may be used. Example 2 describes as a modification coating a vegetable parchment sheet with a methanol solution of the water-insoluble #-toluene sulphonate salt of the diazo resin of Example 1 to form the light-sensitive layer. Example 3 concerns the production of a printed circuit by coating a copper surface phenolic resin sheet with the light-sensitive resin of Example 2, overcoating this with a toluene solution of polystyrene and after exposure wiping with methanol to remove the unexposed diazo resin, the resin overcoat breaking cleanly away from the boundary of the exposed areas. In place of polystyrene, polyvinyl chloride or a synthetic rubber or chlorinated rubber may be used. Example 4 describes the preparation of a metal-backed label by the process of Example 1, the diazo resin on the aluminium sheet being overcoated with a solution of polyethylmethacrylate containing a green pigment. To produce accurate colour printing proofs, (Example 5), an oriented polyethylene terephthalate film coated with an invisible layer of silicon monoxide is coated with a diazo resin as in Example 2 and then overcoated with a polyvinylformal containing a transparent cyan, magenta or yellow pigment of the colour to be used in printing and colour separation records made with these materials. An opaque overlayer may be applied and exposure effected through the base for providing the black key print or for use in preparing a positive transparency from a negative transparency.