Patent GB-888935-A (GB)
Title: Stencil means and manufacture thereof
IPC: G03F7/12
Filed: 1958-08-08
Abstract: 888,935. Photochemical printing surfaces; printing frames. KENDALL, F. E. Aug. 8, 1958, No. 25518/58. Class 98(2). A stencil comprises a flexible sheet of pervious material coated with an impervious flexible coating of a .light sensitised synthetic resin the thickness of which is not less than the thickness of the pervious sheet, said coating having been exposed to light to render the exposed resin insoluble, and solvent-developed to expose the stencil design. The pervious support may be Yoshino long fibre paper which may be wet-strengthened, silk screen, fine woven glass fibre fabric, nylon, linen, cotton, wool, metal cloth, "Orlon" (Registered Trade Mark) or "Dacron" (Registered Trade Mark), and ¢-1 mil. thick. The artificial resin may be a photosensitised polymeric cinnamic ester such as cinnamic ester of polyvinyl alcohol with a sensitiser such as a nitro-aryl compound having a nucleus containing 6-10 carbon atoms, from 1-3 nitro groups attached to the nucleus, the mono-nitric compounds being free of amino, hydroxyl and formyl groups in a position ortho to the nitro group, and such nitro aryl compounds being free of an amino and a hydroxyl group in a position ortho to each other, and free of carboxyl and sulpho groups. The light sensitivity of the cinnamic esters may be enhanced by the inclusion of nitro compounds, anthrone compounds, quinone compounds, diaminophenyl carbinol, diaminophenyl methane, and diaminophenyl ketone compounds. The resin may also be a copolymer of styrene or 1- cinnamyl styrene, or a rubber hydrohalide or nitrocellulose sensitised with iso-cyclic and heterocyclic compounds containing at least three ring system such as anthracine, acridine and phenozine. The resin may be applied by resin coating, roll coating, immersion or spraying. The coating may be on one or both sides of the support. The support may be reinforced with a preliminary coating of the same resin used as the photosensitive coating, but having a solids content of less than 7% by weight, preferably 4-5% so as not to block the pores, which coating is then dried. A more concentrated solution may be used with an absorbent medium to absorb the excess, or suction may be employed. Alternatively, the reinforcing coating may be applied after development to the design areas only. For exposure, the coated support is placed on a rectangular metal operating area defined within a flat metal plate 1, Figs. 7 and 8, of a frame by a groove 2“ inch thick and “  inch deep milled in the plate parallel to its outer edge, which is 1/16 inch above the operating area. A photonegative or photopositive transparency 8 is placed on the coated support 7 and held thereon by a flexible transparent sheet 9 extending beyond the groove, in which vacuum is produced through a tube 4. The transparent sheet may be clamped to the outer border of the plate, which is mounted on a hollow metal base 5 having an inner chamber 6 through which cooling water is circulated. The .operating area is painted black or has a piece of non-reflective black paper placed thereon. The transparent sheet may be cellulose acetate, cellulose nitrate, cellulose propionate, cellulose butyrate, polyvinyl acetate, vinylidene chloride, melamine formaldehyde, methyl methacrylate, nylon, or other polymers or copolymers. After exposure the unexposed portions are washed out with a solvent, which may be dichlorethylene, trichlorethylene, ethylene glycol mono-methyl ether acetate, ethylene glycol mono-ethyl ether acetate, ethylene glycol mono-butyl-ether acetate, chlorobenzene, xylene or decahydronaphthalene. The photosensitive resin may have added thereto up to 20% by weight of solids, a plasticizer such as dimethyl phthalate, dibutyl phthalate, diamyl phthalate, dimethoxyethyl phthalate, dibutoxyethyl phthalate, tricresyl phosphate, triphenyl phosphate, or orthonitrophenyl. There may be mixed with the resin or with the solvent a dye such as malachite green, nigroxine black, wool fast blue, plasto blue or spirit blue.