| 摘要 |
741,470. Photographic process for preparing printing relief images. DU PONT DE NEMOURS & CO., E. I. May 1, 1953 [Dec. 19, 1952], No. 20708/54. Divided out of 741,441. Addition to 741,294. Drawings to Specification. Class 98 (2). The process of the parent Specification, in which a layer of an ethylenically unsaturated photopolymerizable composition containing a catalyst for such photopolymerization carried on a permanent metal support is exposed through a half-tone or line transparency to polymerize the exposed portion to the insoluble state and subsequently treated to remove unexposed areas and thereby leave a relief image, is modified by effecting the exposure so as to produce a tapered relief image the projection of the sides of which form in the case of a half-tone printing relief an inner angle with the support between 50 and 90 degrees and in the case of a line-printing relief a corresponding inner angle between 63.4 and 76 degrees. Such relief images have enhanced strength and minimize building up of ink on the printing areas; and the exposure therefor may be effected by a broad light source or an oblique light source arranged around the periphery of the area to be exposed. In Example I an aluminium base-plate is first provided with the antihalation anchor layer of Example IV of the parent Specification and then a clear anchor layer comprising methyl methacrylate, isobutyl methacrylate, polymeric methyl methacrylate, monomeric polyethyleneglycol dimethacrylate, benzoin and 1,11-azodicyclo-hexanecarbonitrile, which mixture is photopolymerized to form such anchor layer. Spacing strips are then placed at the edges of the layer and a photopolymerizable syrup comprising benzoin methyl ether, styrene and polypropylene glycol/maleate/phthalate is flowed thereon; a half-tone film negative mounted on a glass plate is lowered on to the syrup, excess of which is allowed to flow out until the negative rests on the spacing strips, and the assembly is exposed for 10 minutes while rotating on a turntable to three mercury vapour lamps, one above the assembly and the other two on opposite sides with their beam axes directed at 45 degrees to the assembly. After exposure the negative is removed and unpolymerized material washed away with an ethyl acetate/ethanol mixture to leave a relief image with printing areas having sides sloping at angles of about 58 degrees to the base. A somewhat corresponding procedure using a line negative and directed to the production of a printing relief of high dimensional fidelity to the negative is described in Example II. Seven further specific examples and descriptive matter usually referring to the original Specification 741,441 are concerned with other variations. Specification 566,795 also is referred to.
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