Patent GB-1042519-A (GB)
Title: Improvements relating to the production of photohardenable relief images
IPC: G03F7/36
Filed: 1963-06-27
Abstract: 1,042,519. Photopolymerizable materials and processes. E. I. DU PONT DE NEMOURS & CO. June 27, 1963 [June 27, 1962; June 7, 1963], No. 25698/63. Heading G2C. A process for producing images comprises image wise exposing a photohardenable (i.e. a material which increases its melting point or flow temperature on exposure) thermoplastic layer on a support, heating or maintaining the exposed material at a temperature at which the unexposed areas can flow, removing these areas either (a) by contact with a separate absorber layer which is at least 0. 002 inch thick and of a pore size not above 0.003 inch at least at the surface, until at least 80% of the unexposed areas are removed, or (b) by imposing a fluid pressure gradient across the support if this is porous. The invention also relates to a material comprising a porous support at least 0.005 inch thick in which the pores extend through the support coated with a photohardenable thermoplastic layer, either the layer or the support containing an infra-red absorbing material. The photohardenable layer preferably contains a polymeric binder, an ethylerically unsaturated comcompound, a photoinitiator and a thermal polymerization inhibitor; the first two components may be combined e.g. polyvinyl acetate/acrylate, cellulose acetate/acrylate or methacrylate, N-acryloxymethyl polyamide or acrylate or methacrylate copolymers of vinyl acetate and vinyl alcohol. Preferred ethylenically unsaturated compounds are tri- and poly-ethylene glycol diacrylates, acrylates and methacrylates of polyhydric alcohols and diacrylates and dimethacrylates of the esters of di-basic acids and ether glycols. Alternatively dichromated colloids and tinnable silver halide emulsions may be used. In the examples, polyethylene glycol diacrylate, a cellulose ester, a photo-initiator and a dye are coated on a temporary support, covered with an aluminium layer coated with an adhesive so that the photohardenable layer is transferred thereto. This layer is then laminated with a polyester layer to form a protective cover, imagewise exposed, the protective cover removed and the exposed layer contacted with a felted cotton filter layer, heated and pressure applied to remove the unexposed areas leaving a pointing plate. The felted cotton layer may be replaced by nainsook cloth, filter paper, clay plates, porous metal, sintered glass, latex or polyurethane foam. Half-tone plates may be produced by exposure through a screen. Instead of using an aluminium plate as a support, a porous support such as a cotton felt treated with carbon black may be used so that after imagewise exposure, the exposed material is heated and suction applied so that the unexposed areas are sucked into the support to leave a relief image on the support which may be used as a printing plate. Alternatively, the support may be contacted with a felt layer and pressure applied to transfer the unexposed areas from the support to the felt layer. The cover layer on the photohardenable layer is softened on heating and deforms into the shape of the relief image so that it may be pulled off and coated with wax and used as a mould. In a further example, polyvinyl-benzylphenone and benzylalcohol are coated on a support of felt containing an infra-red absorbent dye, imagewise exposed and the unexposed areas are sucked into the support leaving a relief image. Another variant is that the photohardenable layer is forced into the porous support, imagewise exposed, heated and pressure applied so that the unexposed areas are removed and these areas may then be inked up and the product used as a printing plate.