Method for making printing plates

Disclosed is a method for electrophotographically making a printing plate excellent in resolving power and having a high printing endurance by using a liquid developer containing a copolymer comprising an acrylate ester or methacrylate ester having an alkyl group of 4 or more and a styrene or a styrene derivative, preferably said copolymer additionally containing an acrylate ester or a methacrylate ester having an alkyl group of 3 or less carbon atoms, more preferably said binary or ternary copolymer additionally containing a vinyl monomer having a basic group or an acidic group.

BACKGROUND OF THE INVENTION 
This invention relates to a method for making a printing plate, wherein a 
toner image is electrophotographically formed by using a wet-type 
developer on an original printing plate comprising an electroconductive 
support and an organic photoconductive compound layer disposed thereon, 
then the image is fixed, and the non-image areas are removed by etching 
with an alkaline aqueous etching solution, leaving behind the toner image 
intact. 
It is known that as the photosensitive material of a printing plate using 
electrophotographic image forming, use is made of a photosensitive element 
comprising paper, film, or aluminum sheet and, provided thereon, a coating 
layer of an inorganic photoconductive powder, such as zinc oxide or 
cadmium sulfide, dispersed in a suitable binder. To form an image and to 
convert the element to a printing plate by the electrophotographic 
technique, the element is subjected to corona discharge, exposure, and 
toner development, the resulting toner image being receptive to a greasy 
printing ink and the non-image areas becoming hydrophilic after 
hydrophilizing treatment. Although the toner image is obtained by either 
dry development or wet development, the latter is generally preferred 
because of better resolution of the image. In such a printing plate, 
however, since a large quantity of an inorganic photoconductive powder 
together with a binder is coated on a support in order to increase the 
sensitivity, it follows that a certain limitation is posed upon the 
surface smoothness, strength of the coating film, and the adhesiveness 
between the coating film and the support; with respect to the retention of 
sufficient hydrophilicity of the non-image areas there is a problem 
arising from the strength of the coating film. For these reasons, the 
printing plate is unsuitable for the long-run printing exceeding 10,000 
copies, though it is satisfactory for the short-run printing. 
There are also known many printing plates carrying organic photoconductive 
compounds, which are adaptable to electrophotographic treatment. As 
examples of such printing plates, mention may be made of those disclosed 
in Japanese Patent Publication Nos. 17,162/62, 6,961/63, 2,426/66 and 
39,405/71; Japanese Patent application "Kokai" (Laid-open) Nos. 19,509/75, 
19,510/75, 145,538/79, 89,801/79, 34,632/79, 19,803/79 and 105,244/80. In 
the printing plates disclosed by these patents, the photosensitive 
elements comprise electroconductive supports such as aluminum sheet and, 
disposed thereon, a coating of photoconductive compounds using a binder 
soluble in alkalis and/or alcohols such as styrene-maleic anhydride 
copolymer, vinyl acetate-crotonic acid copolymer, vinyl acetate-maleic 
anhydride copolymer, or phenolic resin, and the toner images are formed by 
subjecting the photosensitive elements to corona discharge, exposure, and 
toner development, said toner images serving as a resist layer in the 
subsequent removal of the coating layer in non-image areas by treating 
with an etching solution containing an alkali or alcohol as major 
component, thereby to produce a printing plate comprising the unremoved 
image areas and the non-image areas of hydrophilic surface of the aluminum 
support. A commercial product based on this principle has been offerred 
for practical use under the trade name of "Elefasol" by Kalle Co. The 
Elefasol system, however, utilizes a dry developer in forming the toner 
image and, as a consequence, is insufficient in resolving power. Even if 
use is made of a dry developer of finely subdivided particles, there is 
obtained a printing plate having a resolving power of only 3-5 lines/mm. 
As contrasted, the toner image formed by a wet developer has a resolution 
of 15-20 lines/mm. Although the toner image formed by the dry developer is 
inferior in resolving power owing to a larger size of toner particles, it 
has an advantage in that owing to a larger amount of fixed particles the 
thick toner image acts as a resist in the etching of non-image areas with 
an alkali and/or an alcohol, thus preventing, in most cases, the image 
areas from being etched. To the contrary, although superior in resolution 
and sharpness, the toner image formed by the wet developer is considerably 
smaller in thickness than that formed by the dry developer, thus 
detracting much from the effectiveness of toner image as a resist. As a 
consequence, the resolving power of the printing plate before etching is 
no longer retained after the etching. Therefore, it is also difficult to 
obtain a printing master of high resolving power even by the wet 
development. 
Another problem generally accompanying the wet developer is the stability 
of dispersion. Since the wet developer is a dispersion of a resin, a dye 
or pigment, a charge regulator, and others in an organic solvent of low 
dielectric constant and high insulating property, the dispersion stability 
is an extremely important factor for the manufacturers of wet developers 
which requires utmost endeavor for the improvement. An especially 
difficult problem to be solved during the developmental stage of the 
present wet developer is to find a way of controlling such contradictory 
tendencies that a resin composition having an improved dispersion 
stability tends to be inferior in resist property, while that having an 
improved resist property tends to be inferior in dispersion stability. 
SUMMARY OF THE INVENTION 
The first object of this invention is to provide a wet developer which 
forms a toner image capable of exhibiting a high resistance to an alkaline 
etching solution in the aforementioned process for making a printing 
plate. 
The second object of this invention is to provide a wet developer for use 
in making the aforementioned printing plate, which is excellent in 
dispersion stability and withstands a long-term use or storage. 
The third object of this invention is to provide a method for making the 
aforementioned printing plate of the wet development type which has an 
excellent resolving power and a high printing endurance. 
DESCRIPTION OF THE INVENTION 
It was found by the present inventors that it is favorable to the 
achievement of the above objects to use as the resin component of the wet 
developer a copolymer containing (a) an acrylate ester or methacrylate 
ester having an alkyl group of 4 or more carbon atoms and (b) styrene or a 
styrene derivative. It is most preferable that the above copolymer 
contains a third monomeric unit having a basic or acidic group. The resin 
composition of the wet developer for use in the present printing plate is 
described below in detail. 
The wet developer of this invention is a dispersion of a resin, a dye or 
pigment, and, if necessary, a charge regulator and so on in a solvent 
having a low dielectric constant and a high insulating property, into 
which the resin of this invention is insoluble, swellable, or soluble to a 
limited extent. The methacrylate or acrylate ester component having an 
alkyl group of 4 or more carbon atoms (hereinafter referred to briefly as 
the first component) is a component which solubilize the resin, while 
styrene or a styrene derivative (hereinafter referred to briefly as the 
second component) is a component which insolubilize the resin. By 
dispersing a pigment or dye and a charge regulator together with a 
copolymer of these two components into the above solvent, it was possible 
to prepare a wet developer of a fairly good dispersion stability. However, 
the toner image formed by the wet developer containing the binary 
copolymer resin was found to exhibit, in some cases, a very low resistance 
against an alkaline aqueous etching solution. As a result of an extensive 
study, such a phenomenon was found to occur markedly when a copolymer 
resin containing about 30 mole % or less of the second component was used. 
Although the optimum amount of the second component varies depending upon 
the number of carbon atoms of the alkyl group of the first component, the 
resist property of the resin becomes better with the increase in the 
second component content, except for an extremely high content, in which 
case the dispersion stability of the wet developer becomes deteriorated 
and unsuitable for the long-term use or storage. Although depending upon 
the type of the first component, the content of the second component 
should not exceed 90% by weight. A suitable content of the second 
component is in the range of from 35 to 80% by weight. If a C.sub.4-8 
-alkyl ester or/and a third component alkyl ester (described later) are 
used, the lower limit can be decreased to about 30% by weight. 
It was further found that the resist property and the dispersion stability 
are improved by copolymerizing as a third component a methacrylate ester 
or an acrylate ester having an alkyl group of 3 or less carbon atoms. The 
third component is used in an amount in the range of from 5 to 40% by 
weight. It is difficult to obtain a wet developer with a sufficient resist 
property by using a homopolymer of the third component. The first 
component is used in an amount in the range of from 5 to 60% by weight. 
When the numbers of carbon atoms in the alkyl groups of the first and 
third components are very near to each other such as when the first 
component is butyl (C.sub.4) ester and the third component is propyl 
(C.sub.3) ester, the advantage of this invention is more fully exhibited 
by using butyl acrylate for the butyl ester and propyl methacrylate for 
the propyl ester. For the purpose of further improvement, it is possible 
without any loss in the resist property to incorporate into the above 
binary or ternary copolymer a third or fourth component of copolymerizable 
monomer so far as the resin characteristics are not injured. 
It was found that a printing plate of high resolving power and high 
printing endurance is obtained without any loss in the resist property by 
using as the copolymerizable monomer to be incorporated in the binary or 
ternary copolymer a vinyl monomer having an acidic group (e.g. carboxyl 
group) or a basic group as described later. It is desirable to incorporate 
such a monomer into the above ternary copolymer to obtain a quaternary or 
higher copolymer. 
It is possible, if necessary, to use as a comonomer component an acrylamide 
or methacrylamide, a vinyl monomer having a hydroxyl or epoxy group, vinyl 
acetate, or a monomer having a halogen atom such as chlorine or fluorine 
in preparing the resin used in this invention. 
As examples of alkyl groups of 4 or more carbon atoms in the acrylate 
esters or methacrylate esters as the first component of the resins for use 
in the present wet developers, mention may be made of n-butyl, isobutyl, 
tert butyl, n-amyl, pentyl, hexyl, 3-methylbutyl, 2-methylpentyl, 
2-ethylbutyl, sec-amyl, tert-amyl, heptyl, octyl, 2-ethylhexyl, nonyl, 
decyl, dodecyl, tetradecyl, hexadecyl, and halogen-substituted alkyls such 
as, for example, 1,1,5-trihydroperfluoropentyl. This first component may 
comprise one or two or more of the esters. When at least one of the esters 
has an alkyl group of 4 to 8 carbon atoms, excellent results are obtained. 
Examples of styrene and styrene derivatives used as the second component 
include alkyl-styrenes such as methylstyrene, ethylstyrene, and 
isopropylstyrene; halogenated styrenes such as chlorostyrene, 
bromostyrene, and fluorostyrene; alkoxystyrenes such as methoxystyrene, 
ethoxystyrene, and butoxystyrene; hydroxystyrenes such as p-hydroxystyrene 
and 3-methoxy-4-hydroxystyrene; carboxystyrenes and derivatives thereof 
such as vinylbenzoic acid and methyl vinylbenzoate; nitrostyrenes such as 
nitrostyrene and trinitrostyrenes; aminostyrenes such as m-aminostyrene 
and dimethylaminostyrene; sulfur-containing styrene derivatives such as 
ethyl p-vinylbenzenesulfonate; and .alpha.- and .beta.-substituted 
derivatives. These styrene derivatives are described in S. Murahashi et 
al. "Synthetic Polymer, II" (published by Asakura Publishing Co.). 
Examples of alcohol moieties of acrylate esters or methacrylate esters 
containing alkyl groups of 3 or less carbon atoms used as the third 
components include methyl, ethyl, n-isopropyl, and isopropyl, which may 
have halogen atoms as substituents, e.g. 1,1,3-trihydroperfluoropropyl. 
As copolymerizable monomers having acidic group, there may be added to the 
binary or ternary component, for example, acrylic acid, methacrylic acid, 
itaconic acid, crotonic acid, itaconic anhydride, maleic acid, maleic 
anhydride, half esters of maleic acid, fumaric acid, vinylsulfonic acid, 
and acrylamidopropanesulfonic acid. The monomer components having acidic 
groups are used preferably in an amount of 1 to 15% by weight. 
The monomers having basic groups include diethylaminopropyl methacrylate, 
dimethylaminopropyl methacrylate, 4-vinylpyridine, 2-vinylpyridine, 
vinylimidazole, p-dimethylaminostyrene, and aminostyrenes. These monomers 
are used in an amount of 15% or less, preferably 10% or less, by weight. 
Each of these components may comprise one or two or more monomers like the 
first component. 
From the foregoing description and the examples given later, it will become 
apparent that by using the resins of abovementioned compositions, there is 
obtained a wet developer for printing plate, which exhibits excellent 
dispersion stability and a high resistance against an alkaline aqueous 
etching solution. 
The solvents used in the present wet developer are organic solvents of low 
dielectric constant and high insulation resistance such as, for example, 
normal paraffin hydrocarbons, isoparaffin hydrocarbons, cycloaliphatic 
hydrocarbons, aromatic hydrocarbons, and halogenated aliphatic 
hydrocarbons. Of these hydrocarbons, especially preferred are 
isoparaffinic hydrocarbons such as, for example, "Shellsol 71 " (Shell 
Petroleum Co.), "Isopars G, H, K and L" (Esso Petroleum Co.), and "IP 
Solvent" (Idemitsu Petroleum Co.). 
Examples of electric charge regulators preferably used in the present wet 
developer include copper oleate, cobalt naphthenate, zinc naphthenate, 
manganese naphthenate, cobalt octylate, lecithin, sodium 
dioctylsulfosuccinate, and aluminum salt of staybelite rosin. 
The dyes or pigments preferably used in the present wet developer for the 
purpose of coloring are any of those known as colorants generally used in 
wet developers. As examples, mention may be made of oil-soluble azo dyes 
such as Oil Black and Oil Red; basic azo dyes such as Bismarck Brown and 
Chrysoidine; acid azo dyes such as Wool Black, Amido Black Green, and Blue 
Black HF; direct dyes such as Direct Deep Black E and Congo Red; 
anthraquinone dyes such as Sudan Violet and Acid Blue; carbonium dyes such 
as Auramine, Malachite Green, and Crystal Violet; rhodamine dyes such as 
Rhodamine B; and quinone imine dyes such as Safranine, Nigrosine, and 
Methylene Blue. Examples of pigments are Carbon black, Phthalocyanine 
Blue, Phthalocyanine Green, and Benzidine Yellow. Surface-treated pigments 
such as, for example, carbon black and graft carbon dyed with nigrosine, 
and silicon oxide fine powder dyed with Rhodamine B, Micro Lith Blue, 
etc., are also used. These dyes and pigments are used in a least possible 
amount, that is, 50% by weight or less based on the resin. The addition in 
an excessive amount causes deterioration in the dispersion stability and 
tends to decrease also the resist property. 
The present wet developer provides a positively charged or negatively 
charged toner as required, by selecting the charge regulator, dye or 
pigment which are used in preferred embodiments. 
It is desirable to add to the present wet developer a resin soluble in the 
solvent used in this developer, for the purpose of preparing, steadily and 
with desirable reproducibility, a developer suitable for the objects of 
this invention. The amount of the resin is generally about 10-200% by 
weight of said copolymer. 
When a copolymer with a monomer having a basic group is used, there is 
added a resin soluble in the solvent and having an acid value of 50 or 
below, such as, for example, lauryl methacrylate-acrylic acid copolymer, 
stearyl methacrylate-methacrylic acid copolymer, or 2-ethylhexyl 
acrylate-crotonic acid copolymer. When a copolymer with a monomer having 
an acidic group is used, there is added a resin soluble in the solvent and 
having a basic group, such as, for example, stearyl 
methacrylate-diethylaminopropyl methacrylate copolymer, lauryl 
acrylate-vinylpyridine copolymer, lauryl acrylate-vinylimidazole 
copolymer, 2-ethylhexyl acrylate-dimethylaminoethyl acrylate copolymer, 
lauryl methacrylate-dimethylaminoethyl methacrylate copolymer. 
For the purpose of improving the fixing property, a low-softening resin may 
be used in admixture with the resin of this invention. Examples of such 
low-softening resins include petroleum-based resins such as polybutadiene, 
polyisoprene, polyisobutylene, and polyethylene as well as those resins 
generally called rubbers, such as copolymers of styrene or acrylonitrile 
with monomers of said petroleum-based resins. 
There are known various preparative techniques for wet developers, such as, 
for example, a technique in which a mixture of a colorant and a resin is 
dispersed in a solvent such as petroleum-base aliphatic hydrocarbon or a 
small amount of an aromatic hydrocarbon or a halogenated hydrocarbon by 
means of an attritor, ball mill, or Kady mill and the resulting 
concentrated toner is diluted with a solvent of a low dielectric constant 
and a high electrical insulation, a method in which a concentrated mixture 
of a colorant, resin, and charge regulator is added dropwise into an 
isoparaffinic solvent, while applying ultrasonic vibration, to obtain a 
wet developer, or a method in which monomers are polymerized in a high 
electrical insulating solvent of a low dielectric constant containing a 
colorant and a charge regulator to obtain a wet developer. This invention 
is, of course, not limited to any particular preparative method. Examples 
of reference resins (the figures in parentheses indicate percentages by 
weight): 
A. Stearyl methacrylate/styrene (80/20) 
B. Lauryl methacrylate/methyl methacrylate (50/50) 
C. Styrene/n-butyl acrylate (95/5) 
D. Stearyl methacrylate/vinyltoluene/ethyl methacrylate (30/20/50) 
E. Lauryl methacrylate/styrene/diethylaminoethyl methacrylate (70/25/5) 
F. Butyl acrylate/.alpha.-methylstyrne/acrylic acid (70/20/10) 
Examples of the present resins (the figures in parentheses indicate 
percentages by weight): 
1. Butyl acrylate/styrene/ethyl methacrylate (25/60/15) 
2. Lauryl methacrylate/vinyl toluene/methyl methacrylate (10/70/20) 
3. Lauryl methacrylate/styrene/methyl acrylate (30/50/20) 
4. Ethylhexyl acrylate/styrene/methyl methacrylate (20/40/40) 
5. Ethylhexyl acrylate/.alpha.-methylstyrene/ethyl methacrylate (10/70/20) 
6. Stearyl methacrylate/styrene/isopropyl acrylate (20/50/30) 
7. Stearyl methacrylate/vinyltoluene/propyl methacrylate (40/50/10) 
8. Butyl methacrylate/vinyltoluene/methyl methacrylate (45/50/5) 
9. Isobutyl methacrylate/vinyltoluene/ethyl acrylate (30/40/30) 
10. Butyl acrylate/styrene/propyl methacrylate (35/40/25) 
11. Butyl acrylate/.alpha.-methylstyrene/isopropyl acrylate (30/60/10) 
12. Stearyl methacrylate/styrene/methyl methacrylate/diethylaminoethyl 
methacrylate (20/60/15/5) 
13. Lauryl methacrylate/vinyltoluene/ethyl acrylate/dimethylaminoethyl 
methacrylate (30/50/15/5) 
14. Butyl methacrylate/styrene/methyl acrylate/vinylpyridine (20/40/35/5) 
15. Butyl acrylate/.alpha.-methylstyrene/isopropyl acrylate/vinylimidazole 
(30/45/22/3) 
16. Stearyl methacrylate/styrene/ethyl methacrylate/hydroxyethyl 
methacrylate (20/50/20/10) 
17. Butyl acrylate/styrene/ethyl methacrylate/glycidyl methacrylate 
(20/55/20/5) 
18. Lauryl methacrylate/styrene/ethyl methacrylate/acrylic acid 
(20/60/15/5) 
19. Lauryl methacrylate/vinyltoluene/methyl methacrylate/crotonic acid 
(25/45/25/5) 
20. Stearyl acrylate/.alpha.-methylstyrene/methyl methacrylate/itaconic 
acid (40/40/15/5) 
21. Stearyl methacrylate/styrene/methyl acrylate/methacrylic acid 
(12/80/5/3) 
22. Butyl acrylate/styrene/propyl methacrylate/acrylic acid (25/55/15/5) 
23. Butyl methacrylate/styrene/methyl methacrylate/methacrylic acid 
(25/50/15/10) 
24. n-Butyl methacrylate/styrene (40/60) 
25. Ethylhexyl acrylate/.alpha.-methylstyrene (40/60) 
26. Ethylhexyl acrylate/n-butyl acrylate/styrene (30/20/50) 
27. Lauryl methacrylate/vinyltoluene/diethylaminoethyl methacrylate 
(40/50/1) 
28. Lauryl methacrylate/n-butyl acrylate/styrene/acrylic acid (25/10/60/5) 
29. Stearyl acrylate/ethylhexyl acrylate/styrene/itaconic acid 
(30/10/57/3). 
These resins are easily synthesized in a well-known manner by block 
polymerization, solution polymerization, or suspension polymerization 
using as polymerization initiator a peroxide or an azo compound. A resin 
having a molecular weight in the range of from 5,000 to 1,000,000 may be 
used. If a low molecular-weight resin is used the resistance against the 
etching solution tends to be inferior, whereas if a resin of excessively 
high molecular weight is used, difficulties will be encountered in 
preparing the wet developer. A most preferable molecular weight is in the 
range of from about 10,000 to about 300,000. The molecular weight can be 
easily regulated in a known manner by properly selecting the initiator 
concentration, molecular-weight regulator, polymerization temperature, and 
monomer concentration. The molecular weights of the above resin examples 
were about 100,000, as determined by gel permeation chromatography. 
The binder forming a photosensitive layer containing an organic 
photoconductive compound in the original printing plate which is developed 
by the wet developer of this invention should be soluble in the alkaline 
aqueous etching solution. It is also desirable that the binder may retain 
sufficient adhesiveness to the toner image formed by the wet development 
and subsequent fixing. Such binders for forming a photosensitive layer 
include styrene-maleic anhydride copolymer, styrene-maleic anhydride half 
ester copolymer, maleic acid resin formed by the reaction between rosin 
and maleic anhydride, vinyl acetatecrotonic acid copolymer, phenol resin, 
vinyl acetatemaleic anhydride copolymer, and acrylate or methacrylate 
ester resin having an acid value of about 50 or above. 
As examples of the organic photoconductive compounds used in the present 
printing plate, mention may be made of the following compounds: 
a. Aromatic tertiary amino compounds: triphenylamine, diphenylbenzylamine, 
di-(.beta.-naphthyl)benzylamine, and diphenylcyclohexylamine; 
b. Aromatic tertiary diamino compounds: 
N,N,N',N'-tetrabenzyl-p-phenylenediamine, N,N,N',N'-tetrabenzylbenzidine, 
1,1'-bis(4-N,N-dibenzylaminophenyl)ethane, 
2,2-bis-(4-N,N-dibenzylaminophenyl)butane, 
bis-[4-N,N-di-(p-chlorobenzylaminophenyl)]methane, 
3,3-diphenylallylidene-4,4'-bis-(N,N-diethyl-m-toluidine), and 
4,4'-bis(di-p-tolylamino)-1,1,1-triphenylethane; 
c. Aromatic tertiary triamino compounds: 
4,4',4'-tris(diethylaminophenyl)methane, 
4-dimethylamino-4',4"-bis(diethylamino)-2,2"-dimethyltriphenylmethane; 
d. Condensation products: condensation product of an aldehyde and an 
aromatic amine, reaction product of an aromatic tertiary amine and an 
aromatic halogen compounds, poly-p-phenylene-1,3,4-oxadiazole, reaction 
product of formaldehyde and a condensed polycyclic compound; 
e. Metal-containing compounds: 2-mercaptobenzothiazole zinc salt, 
2-mercaptobenzoxazole lead salt, 2-mercapto-6-methoxybenzimidazole lead 
salt, o-hydroxyquinoline aluminum salt, 2-hydroxy-4-methylazobenzene 
copper salt; 
f. Polyvinylcarbazole compounds: polyvinylcarbazole, halogen-substituted 
polyvinylcarbazole, vinylcarbazole-styrene copolymer, and 
vinylanthracenevinylcarbazole copolymer; and 
g. Heterocyclic compounds: 1,3,5-triphenylpyrazoline, 
1-phenyl-3-(p-dimethylaminostyryl)-5-(p-dimethylaminophenyl)pyrazoline, 
1,5-diphenyl-3-styrylpyrazoline, 1,3-diphenyl-5-styrylpyrazoline, 
1,3-diphenyl-5-(p-dimethylaminophenyl)pyrazoline, 
3-(4'-dimethylaminophenyl)-5,6-di-(4"-methoxyphenyl)-1,2,4-triazine, 
3-(4'-dimethylaminophenyl)-5,6-dipyridyl-1,2,4-triazine, 
2-phenyl-4-(4'-dimethylaminophenyl)quinazoline, 
6-hydroxy-2,3-di-(p-methoxyphenyl)benzofuran, and 
2,5-bis-[4-ethylaminophenyl(1')]-1,3,4-oxadiazole. 
A printing plate of good quality is obtained also by using as the organic 
photoconductive compound one of the pigments such as phthalocyanine 
pigments, quinacridone pigments, indigo pigments, cyanine pigments, 
perylene pigments, binsbenzimidazole pigments, quinone pigments, azo 
pigments. 
The base for the present printing plate may be any of the known bases for 
use in printing plates. Examples of such base materials include sheet 
metals such as aluminum sheet, zinc sheet, magnesium sheet, and copper 
sheet; film and synthetic paper materials of polyester, cellulose acetate, 
polystyrene, polycarbonate, polyamide, or polypropylene; and converted 
paper such as resin coated paper. Since the surface of the base of 
non-image areas produced after image formation and removal of the 
photoconductive compound together with the binder should be hydrophilic, 
it is necessary to subject the hydrophobic surface of the base to 
hydrophilization treatment. Metal sheets, especially aluminum sheets are 
most preferred, but the surface should preferably be subjected to surface 
treatments such as graining, alkali treatment, acid treatment, or anodic 
oxidation. Film materials are either coated with a polymer having a 
comparatively high hydrophilicity and subsequently crosslinked or applied 
with a metal coating by vapor coating or cladding. An insulating base 
material should preferably be subjected to an electroconductive treatment 
on the surface. 
The original printing plate is prepared by dissolving a photoconductive 
compound and the binder of this invention in a solvent (in case the 
photoconductive compound is not soluble in the solvent, a suspension is 
prepared by means of a colloid mill, homogenizer, or ultrasonic dispersion 
device), adding a sensitizing dye, applying the resulting mixture onto the 
above-mentioned support (base) at a coverage of 1 to 30.mu. in thickness, 
and drying. The support may have an undercoat removable by etching. It is 
possible to prepare an original printing plate of the separate function 
type comprising superposed charge carrier generating layer and charge 
carrier transport layer. 
The solvents suitable for use are those organic solvents which can dissolve 
the binder and the photoconductive compound or suspend the latter. As 
examples, mention may be made of alcohols such as methanol, ethanol, 
propanol, butanol, and hexyl alcohol; "Cellosolves" such as methyl, ethyl, 
or butyl "Cellosolves"; cyclic ethers such as dioxane and tetrahydrofuran; 
esters such as ethyl acetate, butyl acetate, and amyl acetate; ketones 
such as acetone, methyl isobutyl ketone, and methyl ethyl ketone; 
dimethylformamide, dimethyl sulfoxide, and halogenated hydrocarbons. In 
view of the solubility, cost, and safety, a mixture of 2 or more solvents 
is frequently used. 
The printing plate of this invention is prepared by electrophotographically 
forming a toner image on the original printing plate and etching the 
non-image areas with an aqueous alkali solution or an aqueous alkali 
solution containing an alcohol. Suitable alkalis include sodium hydroxide, 
potassium hydroxide, sodium carbonate, sodium silicate, sodium phosphate, 
potassium phosphate, and ammonia. Suitable alcohols are lower alcohols and 
aromatic alcohols such as methanol, ethanol, propanol, benzyl alcohol, 
phenethyl alcohols; ethylene glycol, diethylene glycol, triethylene 
glycol, polyethylene glycol, and "Cellosolves". 
Although the etching can be performed with an aqueous alkali solution 
alone, it is preferable to use an amino alcohol such as diethanolamine or 
triethanolamine in view of the rate of etching, safety, and hygiene. From 
the viewpoint of either resolution or image reproducibility, a combination 
of an amino alcohol and a simple alcohol is most preferable. When water 
washing treatment and a treatment with diluted aqueous acid solution are 
conducted after the etching treatment, printing plates causing no scumming 
during printing and excellent in image reproducibility are obtained. 
______________________________________ 
Examples of etching solution. 
______________________________________ 
1. EDTA-4H 3 g 
Benzyl alcohol 30 g 
Monoethanolamine 5 g 
Triethanolamine 50 g 
Potassium hydroxide 20 g 
Reaction product of formalin 
2 g 
and sodium sulfite 
Made up with water to 
1 liter 
2. Sodium hexametaphosphate 
3 g 
Phenethyl alcohol 30 g 
Monoethanolamine 50 g 
Reaction product of formalin 
2 g 
and sodium sulfite 
Made up with water to 
1 liter 
______________________________________

EXAMPLE 1 
Preparation of original printing plate 
(a) Into a mixture of 100 g of butyl acetate and 20 g of butanol, was 
dissolved 10 g of an ethyl methacrylate/butyl methacrylate/acrylic acid 
(50/30/20 in weight ratio) copolymer as a binder. Into the resulting 
solution, was dissolved 8 g of 1,3,5-triphenylpyrazoline as an organic 
photoconductive compound. After addition of 5 cc of a 1-% Rhodamine B (a 
sensitizing dye) solution in dimethylformamide, the mixture was made up to 
150 g with butyl acetate. The resulting composition was coated by means of 
a wire bar on an aluminum sheet, 250.mu. in thickness, which had been 
subjected to graining and anodic oxidation, at a coverage of 5 g/m.sup.2 
on solids basis and dried to obtain an original printing plate [A]. 
(b) Into a mixed solvent of 80 g of xylene, 20 g of butanol, and 20 g of 
tetrahydrofuran, was dissolved 10 g of an octyl half ester (acid value 
165) of styrene maleic anhydride as a binder and then dissolved therein 8 
g of 2,5-bis-(4'-diethylaminophenyl)1,3,4-oxadiazole as an organic 
photoconductive compound. After addition of 5 cc of a 1% Ethyl Violet (a 
sensitizing dye) solution in methanol, the mixture was made up to 150 g 
with xylene. The resulting composition was coated and treated in the same 
manner as in (a) above to obtain an original printing plate [B]. 
(c) A mixture of 10 g of m-cresol-formaldehyde resin as a binder, 2 g of 
.epsilon.-type copper phthalocyanine as an organic photoconductive 
compound, 40 g of xylene, and 140 g of butanol was treated in a ball mill 
for 3 hours. The resulting dispersion was coated and treated as in (a) 
above to obtain an original printing plate [C]. 
Preparation of wet developer 
(i) A mixture of 4 g of a copolymer resin example (8) enumerated 
hereinbefore for wet developer, 0.4 g of a carbon black surface treated 
with a colorant [nigrosine/MA-100 (Mitsubishi Chemical Co.) =1/10], 15 g 
of xylene, 13 g of Isopar G, and 0.04 g of cobalt naphthenate, a charge 
regulator, was treated in attritor for 2 hours to obtain a dispersion of 
concentrated toner. The concentrated toner was gradually added dropwise to 
1 liter of Isopar G and the resulting mixture was made up to 1.5-liters 
with Isopar G to obtain a wet developer (A). 
(ii) The following wet developers were prepared in the same manner as in 
(i) above, except that various resins and colorants were used. 
______________________________________ 
Wet developer Resin 
No. Colorant No. 
______________________________________ 
(B) The same as in (i) (4) 
(C) " (7) 
(D) " (10) 
(E) " (12) 
(F) " (14) 
(G) " (16) 
(H) " Reference (A) 
(I) " Reference (B) 
(J) The same as in Example (a) 
Reference (C) 
(K) " Reference (D) 
(L) " Reference (E) 
(M) Oil Black FS (7) 
(N) " (12) 
______________________________________ 
(iii) Below are shown examples wherein mixtures of two resins were used in 
order to further improve the dispersion stability and the fixing property. 
Each developer was prepared in a manner similar to that in (i) above. In 
each case, amount of the resin mixed with the numbered resin was 3 g and 
the colorant was Oil Black FS. 
______________________________________ 
Wet developer 
No. Resin 
______________________________________ 
(O) Resin example (12) and stearyl 
methacrylate/acrylic acid (95/5) 
copolymer 
(P) Resin example (13) and lauryl 
methacrylate/methacrylic acid 
(97/3) copolymer 
(Q) Resin example (15) and the same 
copolymer as used in (P) 
(R) Resin example (2) and polybutadiene 
resin 
(S) Resin example (6) and polyisoprene 
resin 
______________________________________ 
Each original printing plate obtained in (a), (b) and (c) was negatively 
charged in dark place under -6 kV corona discharge and exposed to a 
positive image under white light. The exposed plate was immediately 
developed with a wet developer obtained in (i), (ii) and (iii), and the 
image was thermally fixed in a fuser. The developed plate was dipped in 
the above-mentioned etching solution for about 30 seconds to remove the 
coating in non-image areas, thereby to obtain a printing plate. The resist 
property of the toner image areas was evaluated by measuring the resolving 
power. 
The same toners as those obtained in (i), (ii) and (iii) were prepared on 
an enlarged scale of each 3 liters. Each toner was tested for the 
dispersion stability by using the development section of a printing plate 
processor EP-11 of Mitsubishi Diafax Master (made by Mitsubishi Paper 
Mills Co.). Only the development section of EP-11 was operated and the 
toner was circulated at high speed for about one hour to observe the 
agglomeration. Another sample of the wet developer was left standing for 
one month to examine the change in dispersion stability with time. The 
results obtained are as shown in Table 1. 
TABLE 1 
______________________________________ 
Re- 
solving 
Etch- power 
Orig- Wet ing (number 
Dispersion stability 
Run inal devel- so- of lines 
of wet developer 
No. plate oper lution 
per mm) 
EP-11 Stationary 
______________________________________ 
1 [A] (A) (2) 15-17 Good Good 
2 " (B) " " " " 
3 " (D) " " " " 
4 " (F) " 12-14 " " 
5 " (M) " 15-17 " " 
6 " (N) (1) 18-20 " " 
7 " (O) " " " " 
8 " (P) (2) 15-17 " " 
9 " (J) " " Coarse Precipitate 
agglom. 
in large 
amount 
10 " (K) " 2-4 Good Good 
11 [B] (A) " 15-17 " " 
12 " (B) " " " " 
13 " (C) (1) " " " 
14 " (E) " 18-20 " " 
15 " (M) " 15-17 " " 
16 " (R) " 18-20 " " 
17 " (Q) (2) 15-17 " " 
18 " (H) " 2-4 " " 
19 " (I) " 1-2 Coarse Precipitate 
agglom. 
in large 
amount 
20 " (L) (1) 2-4 Good Good 
21 [C] (A) " 15-17 " " 
22 " (E) " " " " 
23 " (G) " 10-12 " " 
24 " (P) " 15-17 " " 
25 " (J) " " Coarse Precipitate 
agglom. 
in large 
amount 
______________________________________ 
From the results shown in Table 1, it is seen that when the reference 
resins were used, the resolving power is inferior due to a high resistance 
against the etching solution. Some of the reference resins showed a fair 
resolving power, but were too inferior in dispersion stability to be of 
any use in practice. Some resins other than those of this invention gave 
wet developers of good dispersion stability, but are poor in resist 
property and unsuitable for use in the present printing plate. 
EXAMPLE 2 
The procedure of Example 1 was repeated, except that the following wet 
developers were used. 
______________________________________ 
Wet developer 
No. Colorant Resin 
______________________________________ 
(A) The same as in (i) of 
(18) 
Ex. 1 
(B) The same as in (i) of 
(19) 
Ex. 1 
(C) The same as in (i) of 
(20) 
Ex. 1 
(D) The same as in (i) of 
(21) 
Ex. 1 
(E) The same as in (i) of 
(22) 
Ex. 1 
(F) The same as in (i) of 
(23) 
Ex. 1 
(G) The same as in (i) of 
Ref. (F) 
Ex. 1 
(H) Oil Black FS (18) 
(I) " (20) 
(J) " (22) 
______________________________________ 
Below are shown examples in which two resins were mixed for the purpose of 
further improving the dispersion stability and the fixing ability. Each 
developer was prepared in a manner similar to that in (i) of Example 1. In 
each case, amount of the resin mixed with the numbered resin was 3 g and 
the colorant was Oil Black SF. 
(K) Resin (18) and lauryl methacrylate/dimethylaminoethyl methacrylate 
(90/10) 
(L) Resin (20) and the same copolymer as used in (K) (90/10) 
(M) Resin (22) and the same copolymer as used in (K) (90/10). 
Each original printing plate obtained in Example 1 (a), (b) and (c) was 
negatively charged under the application of corona discharge at -6 KV in 
dark place and exposed to a positve image under white light. The exposed 
plate was immediately developed with a wet developer of (A) to (M) and 
thermally fixed in a fuser. The plate was dipped in the above-mentioned 
etching solution for about 30 seconds to remove the coating in non-image 
areas leaving behind the toner image, whereby a printing plate was 
obtained. The evaluation was performed as in Example 1. The results 
obtained are as shown in Table 2. 
TABLE 2 
______________________________________ 
Resolving 
power Stability of 
Wet (number of wet developer 
Original 
develop- Etching lines per Station- 
plate er solution mm) EP-11 ary 
______________________________________ 
[A] (A) (2) 15-17 Good Good 
" (B) " 13-15 " " 
" (C) " 12-14 " " 
" (D) " 15-17 " " 
" (E) " " " " 
" (F) " " " " 
" (G) " 2-4 " " 
" (H) " 15-17 " " 
" (I) " 12-14 " " 
" (J) " 15-17 " " 
" (K) " " " " 
" (L) " " " " 
" (M) " " " " 
" (A) (1) " " " 
" (C) " 12-14 " " 
" (E) " 15-17 " " 
" (I) " 12-14 " " 
" (L) " 15-17 " " 
[B] (A) " " " " 
" (C) " 12-14 " " 
" (I) " " " " 
" (L) " 15-17 " " 
[C] (A) " 14-16 " " 
" (I) " 12-14 " " 
" (L) " 14-16 " " 
______________________________________ 
From the results shown in Table 2, it is seen that when a reference resin 
was used, the printing plate became inferior in resolving power due to a 
low resistance to the etching solution. 
EXAMPLE 3 
The following wet developers were prepared in the same manner as in Example 
1 (i), except that other resins were used. 
______________________________________ 
Developer Resin 
______________________________________ 
1 (24) 
2 (25) 
3 (26) 
4 (27) 
5 (28) 
6 (29) 
7 (27) mixed with 1 g of SA* 
8 (28) mixed with 1 g of LA* 
______________________________________ 
Note: 
SA stands for stearyl methacrylate/methacrylic acid copolymer (95/5 by 
weight). 
LA stands for lauryl methacrylate/dimethylaminoethyl methacrylate 
copolymer (95/5 by weight). 
The evaluation results are as shown in Table 3. 
TABLE 3 
______________________________________ 
Resolving 
power 
(number of Stability of developer 
Developer lines per mm) EP-11 Stationary 
______________________________________ 
1 15-17 Good Good 
2 " " " 
3 12-13 " " 
4 13-15 " " 
5 15-17 " " 
6 " " " 
7 " " " 
8 " " " 
______________________________________ 
Although inferior in stability to the wet developers prepared in Examples 1 
and 2, those prepared in the present Example have sufficient stability and 
show good performance as a resist.