Patent GB-780218-A (GB)
Title: Photographic process for preparing intaglio and relief images
IPC: G03F7/039
Filed: 1955-04-22
Abstract: 780,218. Photomechanical printing surfaces. DU PONT DE NEMOURS & CO., E. 1. April 22, 1955 [April 23, 1954], No. 11738/55. Class 98(2) Intaglio and relief images are made by exposing through a transparency a solid layer of a synthetic organic macromolecular addition polymer, optionally having a liquid layer thereon, and provided with a photo-polymerization catalyst, to degrade the polymer to lower molecular weight products in the light-exposed areas at least in the surface of the solid layer, and physically removing the degradation products without affecting the polymer in the non-exposed areas. Examples I to V use a liquid polymerizable layer over the solid layer and action of the exposing light appears to be polymerization in the liquid layer but depolymerization in underlying areas of the solid layer Examples VI to IX use a liquid hydrocarbon oil layer with similar effect, and Example X only commences with a solid layer; thus in Example I a viscous solution of liquid partially polymerized methyl methacrylate with benzoin as catalyst in liquid monomeric polyethylene glycol dimethacrylate is coated over a thick sheet of methyl methacrylate/polyethylene glycol dimethacrylate copolymer, a line process negative on a glass plate is placed in contact with the viscous liquid layer with the aid of spacers, and after 10 minutes exposure from a mercury vapour lamp 7 inches from the sheet the glass plate with negative and attached polymer formed from the liquid polymerizable layer under the clear areas of the negative is removed and remaining liquid layer is removed by brushing with an ethyl acetate/ethanol mixture to reveal a sharp, detailed, but shallow, intaglio image in the copolymer sheet. Examples II-V describe similar operations using a methanol solution of polyvinylacetate containing benzoin as liquid layer -on a polymethylmethacrylate sheet and methanol as developing solvent, using hydrogenated terphenyl with dibutyl phthalate and benzoin methyl ether as liquid layer on a solid sheet of polymerized polypropylene glycol maleate/phthalate/polyester/monomeric styrene mixture, using the latter sheet with unpolymerized mixture of similar composition as liquid layer, and using the latter sheet with polyvinyl acetate containing benzoin methyl ether as liquid layer respectively. Example VI describes coating the oil layer on a solid layer formed by evaporation of a chloroform solution of polymethyl methacrylate obtained with aid of benzoyl peroxide, benzoin methyl ether and omega, omega, omega-trichloroacetophenone for production of a relief image by methanol rinsing after exposure through a positive transparency, and Examples VII to IX somewhat similarly describe intaglio image production in solid sheets based on formaldehyde, polytetrahydrofuran and formaldehyde polymers respectively. The solid layer of Example X is obtained by flowing benzoin methyl ether solution in ethanol on to a polymethyl methacrylate sheet and evaporating the solvent, and this is exposed through a negative to produce an image directly by spontaneous evaporation of degradation products from the incised image, or preferably by treatment with methanol to remove residual products. Innumerable other polymers for the solid layers and catalysts and solvents therefore are described or indicated, such solid layers may be formed on supports as of cellulose derivatives, synthetic resins or metals and may incorporate antihalation materials, dyes or pigments. Diazo catalysts are used in some modifications. Specification 753,299 [Group IV(a)] is referred to.