Use of photosensitive resin compositions for printing plate materials is known, and it is the main stream in the art of relief printing, lithographic printing, intaglio printing and flexographic printing.
With its photosensitive resin layer being contacted with a negative or positive original picture film, the printing plate material of the type is exposed to activated rays through the original picture film so as to form a solvent-soluble part and a solvent-insoluble part in its photosensitive resin layer, and then processed into a printing plate having a relief image thereon.
The printing plate material thus requires a negative or positive original picture film and requires development. Therefore, for forming one printing plate from it, the material requires many steps and much labor.
With the recent progress in computerization, proposed are methods of directly outputting the information having been processed by computer onto a printing plate material followed by processing the resulting material into a relief or flexographic printing plate not requiring a step of preparing an original picture film for it.
Concretely, proposed are method (1) which is a method of forming an image on a photosensitive resin layer or on a thin film layer provided on a photosensitive resin layer, with toner or liquid ink, not requiring an original picture film (Japanese Patent Publication No. 20029/1983, Japanese Patent Laid-Open Nos. 110164/1991, 10709/1998, 10710/1998); method (2) which is a method of directly obtaining a printing plate by exposing a porous material or a photosensitive layer to laser rays followed by dissolving or subliming the exposed part (Japanese Patent Laid-Open Nos. 56601/1977, 127005/1978, Japanese Patent Publication No. 40033/1981, Japanese Patent Laid-Open No. 106249/1986, International Patent Publication Nos. 505840/1995, 506780/1995, Japanese Patent Laid-Open Nos. 99478/1996, 90947/1996, 142050/1997, 254351/1997; and method (3) which is a method of forming a pattern on an IR-sensitive layer provided on the surface of a photosensitive resin layer, by exposing it to laser rays, not requiring an original picture film (Japanese Patent Laid-Open No. 52646/1983, Japanese Patent Nos. 2,773,847, 2,773,981, International Patent Publication No. 509254/1998, Japanese Patent Laid-Open Nos. 305007/1996, 305030/1996, 171247/1997, 166875/1997, 39512/1998, 73917/1998).
The method (1) requires toner or liquid ink for image formation; it is problematic in that fine images could not be formed therein. In the method (2), a porous material or a photosensitive layer is exposed to high-energy laser rays, and therefore this method is problematic in that sharp images are difficult to obtain therein since the relief edges of the porous material and the photosensitive layer melt down. In the method (3), the IR-sensitive layer formed is not transparent, and therefore it is problematic in that the photosensitive resin printing plate processed by method (3) is difficult to inspect. In this, even though the layer is transparent in some degree, it is still further problematic in that its UV-blocking ability is unsatisfactory.
In view of the above-mentioned problems, the present invention relates to a photosensitive resin printing plate material which is transparent and thereby able to accept virtual inspection and which can form an image thereon through exposure to light having a wavelength of from 450 to 1500 nm. Concretely, through the step of image formation thereon, the material enables a difference between the UV-transmissive portions and the UV-non-transmissive portions thereof to thereby reproduce even fine relief thereon, not requiring an original picture film.