Patent GB-741441-A (GB)
Title: Preparation of printing relief images and photographic elements therefor
IPC: C08F2/48
Filed: 1953-05-01
Abstract: 741,441. Photo-sensitive element and process for preparing printing relief images. DU PONT DE NEMOURS & CO., E. I. May 1, 1953 [Dec. 19, 1952], No. 12197/53. Addition to 741,294. Drawings to Specification. Class 98 (2). A film or impregnated paper is used as the permanent support for a layer of an ethylenically unsaturated photopolymerizable composition containing a catalyst for such photopolymerization, and which layer normally lies on an intermediate polymeric anchor layer absorptive of actinic light, instead of the permanent support as of metal of the main Specification. Exposure through a process transparency to polymerize the exposed portions of the layer to the insoluble state throughout its entire thickness and removal of unexposed portions as by solvent washing produces a printing relief image. The photopolymerizable layer may be liquid or may be solid or non-flowable as a result of addition of preformed polymer, conveniently of the same general type as the monomers of the layer, or of addition of immiscible polymeric or other transparent fillers such as silica, bentonite or powdered glass. A thin strippable protective film may be provided on the photopolymerizable layer, and the reverse surface of the permanent support may be provided with a pressuresensitive adhesive layer for attachment as to a base for use in printing, which adhesive layer may, however, be protected prior to such attachment by a further strippable film. A particular feature of the invention is the use of a broad light source for exposure, especially in conjunction with rotation of the assembly being exposed, whereby the resulting raised printing relief surfaces have tapered sides forming an inner angle with the support or the anchor layer of from 50 to 90 degrees and thereby acquire increased strength. Four specific examples all include this feature, thus in Example 1 a cellulose acetate film support is provided with a thin layer of vinyl chloride/vinyl acetate/maleic acid copolymer from xylene/methyl isobutyl ketone solution and then with a photo-sensitive layer of irradiated methyl methacrylate containing benzoin as catalyst and to which monomeric polyethylene glycol dimethacrylate is added, this layer being in the form of a thin syrup retained by spacing strips. A test process negative protected by a regenerated cellulose membrane is placed on the layer and the whole rotated on a horizontal turntable during offcentre exposure by a mercury vapour lamp 7 inches above the turntable, after which the negative is removed and the unpolymerized material removed by scrubbing with a carbon tetrachloride/acetone mixture and the result, having image areas with tapered sides, inked and used for printing. In Example II a polymeric methyl methacrylate sheet support is sensitized with a mixture of isobutyl methacrylate, styrene and a polypropylene glycol/ maleate/phthalate polyester containing benzoin methyl ether as catalyst, exposed under a positive during rotation and blotted with paper tissues to remove unpolymerized syrup and leave an intaglio printing plate. Example III specified a paper laminate support which is lightly sanded, sensitized with the mixture of Example II except that the isobutyl methaerylate is omitted, exposed in two stages under a line negative and treated with an ethyl acetate/ ethanol solvent to produce a plate suitable for letterpress printing. In Example IV a layer of the sensitive mixture of Example II is photopolymerized to make the support, and this is coated with the same mixture, exposed under a ruled negative and washed with ethyl acetate/ ethanol to produce a finished plate of the same size as the negative. In addition to the materials referred to above the Specification describes or indicates the use of innumerable other materials for the photo-polymerizable composition, for solidification thereof, for catalysts therefor, for inhibiting polymerization before desired, for making the antihalation layer when this is used, and for other similar purposes. Specifications 566,795 and 741,470 also are referred to.