Electrophotographic lithographic printing plate precursor

Details Electrophotographic lithographic printing plate precursor Electrophotographic lithographic printing plate precursor

1994-09-12

1997-04-29

Rodee, Christopher D.

Radiation imagery chemistry: process, composition, or product th

Electric or magnetic imagery, e.g., xerography,...

Radiation-sensitive composition or product

430 49, G03G 505

Patent

active

056247770

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to an electrophotographic lithographic printing plate precursor for producing a printing plate through electrophotography and, more particularly, to an improvement in a composition for forming a photoconductive layer of the electrophotographic lithographic printing plate precursor.


TECHNICAL BACKGROUND

Various kinds of offset printing plate precursors for directly producing printing plates have hitherto been proposed, and some of which have already been put into practical use. A widely employed precursor is a light-sensitive material having a photoconductive layer comprising photoconductive particles such as zinc oxide particles and a binder resin provided on a conductive support. A highly lipophilic toner image is subsequently formed on the photoconductive layer surface by an ordinary electrophotographic process. The surface of the photoconductive layer having the toner image is then treated with an oil-desensitizing solution, called an etching solution, to selectively render the non-image areas hydrophilic thereby producing an offset printing plate.
In order to obtain satisfactory prints, an offset printing plate precursor must faithfully reproduce an original on the surface thereof; the surface of the light-sensitive material should have a high affinity for an oil-desensitizing solution so as to render non-image areas sufficiently hydrophilic and, at the same time, should be water resistant. When used as printing plate, the photoconductive layer having a toner image formed thereon should not come off during printing, and should be well receptive to dampening water so that the non-image areas can remain sufficiently hydrophilic to be free from stains, even after a large number of prints have been reproduced from the plate.
These properties are affected by the proportion of binder resin to zinc oxide in the photoconductive layer as already known. Specifically, when the proportion of binder resin to zinc oxide particles in the photoconductive layer is decreased, the oil-desensitivity of the photoconductive layer surface is enhanced and background stains are decreased. However, the internal cohesive force and mechanical strength of the photoconductive layer itself is lowered, resulting in the deterioration of the printing durability. On the contrary, when the proportion of resin binder is increased, the background stains are increased although the printing durability is heightened. Background stains are related to the oil-desensitivity of the photoconductive layer surface. Not only does the ratio of binder resin to zinc oxide in the photoconductive layer influence the oil-desensitivity of the photoconductive layer surface, but it has become apparent that the oil-desensitivity also depends greatly on the kind of the binder resin employed.
With respect to the offset master, the background stain resulting from insufficiency in oil-desensitization is a particularly serious problem. For the purpose of solving this problem, various binder resins for zinc oxide have been developed for improving the oil-desensitivity. Resins having an effect on improvement in oil-desensitivity of the photoconductive layer include those as follows: JP-B-50-31011 (the term "JP-B" as used herein means an "examined Japanese patent publication") discloses the combination of a resin which has a weight average molecular weight of from 1.8.times.10.sup.4 to 1.times.10.sup.5 and a glass transition point (Tg) of from 10.degree. C. to 80.degree. C. and which is prepared by copolymerizing a (meth)acrylate monomer and another monomer in the presence of fumaric acid, with a copolymer prepared from a (meth)acrylate monomer and a monomer other than fumaric acid; JP-A-53-54027 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") discloses a terpolymer comprising a (meth)acrylic acid ester unit having a substituent which contains a carboxylic acid group apart from the ester linkage by at least 7 atoms; JP-A-54-20735 and JP-A-57-202544 disclose a tetra- or penta

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