Photosensitive compositions comprising an o-naphthoquinone diazide compound and a novolak type phenolic resin have been industrially used as very superior photosensitive compositions in the field of photoresists or in the production of lithographic plates.
However, since the novolak type phenolic resins are used as a main ingredient in such conventional photosensitive compositions, they have disadvantages in that adhesion to substrates is poor, films formed therefrom are brittle, their coatability is poor and wear resistance is low. Further, they have such problems that chemical resistance is low and printing durability is insufficient when used as lithographic plates, and printing durability is extremely poor, particularly when UV ink (a greasy ink for lithographic offset printings which cures upon exposure to ultraviolet light) is used. As a method for improving these performances, a burning-in treatment (after exposure and development, a heat-treatment is conducted) is generally carried out. When the burning-in treatment is conducted, however, there is posed the problem of that a low-molecular weight compound in a photosensitive layer is deposited from an image part on an non-image part, etc. and staining is liable to be caused during printing.
Various high-molecular weight materials have been proposed as binders to solve the problem. For example, JP-B-52-41050 (the term "JP-B" as used herein means an "examined Japanese patent publication") discloses polyhydroxystyrene or hydroxystyrene copolymers. Film forming properties are certainly improved by these copolymers. However, the photosensitive composition still has disadvantages in that wear resistance and chemical resistance are poor. Further, JP-A-51-34711 (the term "JP-A" as used herein means as "unexamined published Japanese patent application") discloses the use of high-molecular weight compounds having the structural unit of an acrylic acid derivative in the molecular structure as binders. However, such high-molecular compounds have such problems that the range of proper developing conditions is narrow and wear resistance is insufficient.
USPTO Backgrounds
USPTO Backgrounds