Photosensitive printing plate

The photosensitive printing plate of this invention features incorporation of an organic foaming agent in the photosensitive composition that constitutes the photosensitive layer, said organic foaming agent being thermally decomposed upon drying of said composition under heating to thereby roughen the surface of the photosensitive layer. According to this invention, no specific mechanical treatment is required for forming the photosensitive layer and also there is no need of remodeling the existing coating equipments, and further, the vacuum contact time can be appreciably lessened, so that this invention can greatly improve the working efficiency in plate making and markedly reduce the production cost.

DESCRIPTION 
Technical Field 
This invention relates to a photosensitive printing plate, and more 
particularly it relates to an improvement in the photosensitive printing 
plate having a photosensitive resin layer on a support made of metal or 
other like material. 
BACKGROUND ART 
Generally, photosensitive printing plate is manufactured by coating the 
surface of the support such as aluminum plate, zinc plate, etc., with a 
photosensitive resin composition after roughening and making hydrophilic 
the support surface so as to intensify its adhesion to the photosensitive 
resin composition. The thus manufactured and commercially sold 
photosensitive printing plate is generally called PS plate. 
Such photosensitive printing plate is smooth and flat on its surface, that 
is, the surface of the photosensitive layer formed from a photosensitive 
resin composition, so that when a flat original film is placed overlying 
said layer for effecting exposure and printing, it is found very difficult 
to purge air out of the space therebetween in a short period of time, and 
hence a long time would be required for bringing them into close contact 
with each other. Generally, the original film is placed on the 
photosensitive printing plate in a vacuum-type contact frame and the air 
trapped therebetween is sucked out by vacuum to bring them into close 
attachment. But since air usually stays in the form of independent cells 
in the non-peripheral areas of the two members, it would take long time to 
get rid of such air for ensuring close contact of said two members. If 
exposure is performed in an inperfect stage of contact, there can not be 
attained reproduction of a picture faithful to the original. For these 
reasons, reduction of the time required for attaining close contact has 
been a desideratum in the plate making industry. 
As a solution to this problem, it was proposed to provide an uneven layer 
on the surface of the photosensitive printing plate. For instance, 
Japanese Patent Laid-Open Nos. 111102/76 and 29302/77 and U.S. Pat. No. 
4,126,406 propose the methods for producing uneveness on the 
photosensitive layer surface by applying thereon a material which can be 
removed by a developing treatment. These methods, however, complicate the 
production process as one or more additional steps are involved, that is, 
the photosensitive composition is first applied on the support and, after 
drying thereof resin is printed thereon in an uneven pattern, followed by 
further drying. 
Disclosure of Invention 
The primary object of this invention is to provide, in an economically 
advantageous way, a photosensitive printing plate which allows reduction 
of the time required for effecting perfect attachment and detachment of 
the photosensitive printing plate and original film to greatly improve the 
working efficiency for plate making. 
The photosensitive printing plate according to this invention is 
characterized in that a photosensitive composition containing a 
photosensitive resin and an organic foaming agent is applied on a support 
to form a photosensitive layer and then said organic foaming agent is 
thermally decomposed to roughen the surface of said photosensitive layer. 
In a preferred form of photosensitive printing plate according to this 
invention, said organic foaming agent is at least one organic foamable 
compound selected from the nitroso, sulfonylhydrazine, azo and hydrazo 
compounds, and such organic foaming agent is contained in an amount of 
about 3 to 30% by weight based on the photosensitive resin. 
In another preferred form of photosensitive printing plate according to 
this invention, said organic foaming agent is composed of an organic 
foamable compound and a thermal decomposition assistant, said assistant 
being contained in the ratio of about 30 to 60% by weight to the organic 
foamable compound. 
A most salient advantage of this invention is that by merely incorporating 
an organic foaming agent in a photosensitive composition and without 
requiring addition of any extra step to the normal printing plate making 
process, there can be obtained a photosensitive printing plate which 
allows marked reduction of the time required for vacuum contact of the 
printing plate and original film and is also capable of reproducing a 
clear and sharp picture faithful to the original. 
The "photosensitive printing plate" provided according to this invention 
includes all types of printing plates used for lithoprinting, relief 
printing and intaglio printing.

BEST MODE OF CARRYING OUT THE INVENTION 
The organic foaming agent contained in the photosensitive composition used 
for forming a photosensitive printing plate according to this invention is 
one which is thermally decomposed to generate gas and roughens the 
photosensitive layer surface without giving any adverse effect to the 
properties of both photosensitive composition and photosensitive layer 
when said photosensitive layer formed from said photosensitive composition 
is dried under heating. 
The organic foaming agent used in this invention may be selected from the 
organic foamable compounds including nitroso compounds, sulfonylhydrazine 
compounds which are the hydrazine derivatives of organic sulfonic acids, 
azo compounds and hydrazo compounds, which may be added with a thermal 
decomposition assistant. 
Examples of the nitroso compounds usable as foaming agent in this invention 
include dinitrosopentamethylenetetramine, N, N'-dimethyl-N, 
N'-dinitrosoterephthalamide and trinitrosotrimethylenetriamine. Examples 
of the sulfonylhydrazine compounds include p-toluenesulfonylhydrazine, 
benzenesulfonylhydrazine, p, p'-oxybis (benzenesulfonylhydrazine), 
benzene-1, 3-disulfonylhydrazine, 3, 
3'-disulfonylhydrazinediphenylsulfone, toluene-2, 4-disulfonylhydrazine 
and p, p'-thiobis (benzenesulfonylhydrazine). Examples of the azo 
compounds are azobisisobutyronitrile, azodicarboneamide (azobisformamide), 
azoaminobenzene and azocarboxylic acid diethylester 
(diethylazocarboxylate), and the examples of the hydrazo compounds include 
hydrazodicarbonamide, N, N'-dibenzoylhydrazine, 
.beta.-acetylphenylhydrazine, Biurea and 1, 1-diphenylhydrazine. 
All of these organic foamable compounds are decomposed upon heating to 
generate nitrogen gas. Some of these compounds produce small quantities of 
other gases than nitrogen gas, such as carbon monoxide, carbon dioxide and 
steam, but at least 60% of the whole produced gas is nitrogen gas. The 
amount of gas produced is approximately 100 to 300 ml/g. 
The thermal decomposition temperature of these organic foamable compounds 
spans a wide range from about 80.degree. C. to about 300.degree. C. 
These organic foamable compounds are decomposed and foamed when the 
photosensitive composition is heated and dried. It is essential that 
decomposition of such organic foamable compound is not attended by 
deterioration of the physical properties of the photosensitive layer, and 
the decomposition temperature must not be so high as to affect the 
photosensitive property of the photosensitive resin. Therefore, it needs 
to select a suitable organic foamable compound in accordance with the type 
of the photosensitive resin used. It is also possible to use an organic 
foaming agent formed by adding a thermal decomposition assistant in said 
compound so as to lower the decomposition temperature of the compound. 
Preferred examples of thermal decomposition assistant usable in this 
invention are urea and urea derivatives, zinc white, lead carbonate, lead 
stearate and glycolic acids. Use of a metallic salt type assistant is 
undesirable as it may cause bleeding in the photosensitive layer surface. 
It is most desirable to use urea and its derivatives such as for example 
ureaethanolamine, guanylurea and aminoguanidine carbonates. 
In the case of the organic foaming agents composed of an organic foamable 
compound and a thermal decomposition assistant, the desired effect can be 
obtained by adding the thermal decomposition assitant in the ratio of 
approximately 30 to 60% by weight to the organic foamable compound. The 
foaming agents of such blend are available on the market and used in other 
fields of industry, too. These commercially available organic foaming 
agents can be effectively used in the present invention. 
As said before, the thermal decomposition temperature of the organic 
foamable compounds ranges from about 80.degree. to 300.degree. C. For 
example, the decomposition temperature of chemically pure azodicarbonamide 
is believed to be 230.degree. C. However, such decomposition temperature 
may be lowered to around 120.degree. C. by adding a thermal decomposition 
assistant. The decomposition temperatures of some examples of organic 
foaming agents composed of an organic foamable compound or such compound 
added with a thermal decomposition assistant are shown below:- 
dinitrosopentamethylenetetramine: 125.degree.-250.degree. C.; 
p-toluenesulfonylhydrazine: 90.degree.-95.degree. C.; p, p'-oxybis 
(benzenesulfonylhydrazine): 120.degree.-140.degree. C.; 3, 
3'-disulfonylhydrazinediphenylsulfone: 145.degree.-155.degree. C.; 
azobisisobutylonitrile: 100.degree.-115.degree. C.; azodicarbonamide: 
125.degree.-200.degree. C. 
All types of known photosensitive resins may be used for the photosensitive 
composition which forms the photosensitive printing plate according to 
this invention. For instance, there may be used negative photosensitive 
resins such as polyvinyl cinnamate shown in Japanese Patent Publication 
No. 1492/63, its derivatives shown in U.S. Pat. No. 2,725,372, partially 
saponified polyvinyl acetate such as p-azidobenzoate and polyazidostyrene 
shown in British Pat. No. 843,541 and U.S. Pat. No. 3,096,311, diazo resin 
and acryl copolymer shown in Japanese Patent Laid-Open No. 30604/75, diazo 
resin and shellac mixture shown in Japanese Patent Publication No. 
25841/75, and condensates of diethyl-p-phenylene diacrylate and 1, 
4-di-.beta.-hydroxyethylcyclohexane shown in U.S. Pat. Nos. 3,030,208, 
3,622,320 and 3,453,237. It is also possible to use a positive 
photosensitive resin such as for example o-naphtho-quinonediazide shown in 
U.S. Pat. No. 3,046,120 and Japanese Patent Publication No. 24361/74. 
The photosensitive composition forming the photosensitive layer of the 
photosensitive printing plate according to this invention contains a 
photosensitive resin and an organic foamable compound. In order to 
properly roughen the photosensitive layer surface, the organic foamable 
compound is preferably added in an amount of about 3 to 30% by weight, 
most preferably about 5 to 15% by weight, based on the photosensitive 
resin. The photosensitive composition coating build-up on the support is 
usually about 0.3 to 3 g/m.sup.2, preferably about 0.5 to 2 g/m.sup.2, 
based on dry weight. 
Usually, direct coater, reverse coater or fountain coater is used for 
coating the photosensitive composition on the support, and heat drying of 
the photosensitive composition which is attended by thermal decomposition 
of the organic foaming agent is performed under the conditions which don't 
cause deterioration of the photosensitive layer properties, that is, at a 
temperature of about 90.degree. to 250.degree. C. for the period of 2 to 5 
minutes. 
For attaining quick purge of air from the space between the photosensitive 
layer surface of the photosensitive printing plate and the original film 
for obtaining vacuum contact of the printing plate with the original film, 
the difference of elevation on the roughened photosensitive layer surface 
should preferably be about 1 to 10 .mu.m, the protuberance diameter about 
2 to 20 .mu.m and the inter-protuberance distance 0.1 to 1.5 mm. Such 
roughened surface can be obtained according to the photosensitive printing 
plate of this invention. When an organic foaming agent is used in an 
amount of about 5 to 15% by weight based on the photosensitive resin in 
this invention, there can be obtained a most favorable uneven rough 
surface with elevation difference of 2 to 4 .mu.m and inter-protuberance 
distance of 0.2 to 0.7 mm. 
The photosensitive printing plate according to this invention is described 
in further detail hereinbelow by way of embodiments thereof, but it is to 
be understood that these embodiments are by no means restrictive to the 
scope of the invention. 
EXAMPLE 1 
A 0.3 mm thick aluminum plate was degreased in a 55.degree. C. 10% caustic 
soda solution for 30 seconds and washed well with water. Then the surface 
was roughened by a brush abrader made by Fuller Brush Co. (U.S.), washed 
with water, immersed in a 85.degree.-90.degree. C. 3% sodium silicate 
solution for 2 minutes for a silicate treatment, washed well with water 
and then dried. 
The thus treated aluminum plate was coated with a photosensitive 
composition specified below by using a roll coater to provide a coating 
build-up of about 2 g/m.sup.2 by dry weight, followed by drying in a 
125.degree.-135.degree. C. atmosphere for 3 minutes by using a far 
infrared heater. 
______________________________________ 
Photosensitive composition 
______________________________________ 
Naphthoquinone-(1, 2)-diazido-5-sulfonyl chloride and 
phenol novolak condensate (photosensitive resin) 
5.0 gr 
Ethylene glycol monobutyl ether 
15 gr 
Oil Blue #603 (made by Orient Kagaku KK) 
0.05 gr 
Cellmic CAP (an azodicarbonamide foaming 
agent mfd. by Sankyo Kasei KK) 
0.5 gr 
______________________________________ 
The surface of the thus obtained photosensitive layer was measured by a 
surface roughness and configuration meter (Surfcom Type 4 mfd. by Tokyo 
Seimitsu KK), the results being shown by a diagram in FIG. 1. FIG. 1 is a 
graphic representation magnified 50 times horizontally and 2,000 times 
vertically. 
This photosensitive printing plate (800 mm.times.1,000 mm) was adapted in 
an automatic photo-composer (OTO Stepper KS-77 mfg. by OTOKO Machinery 
Corp.) in close contact with a positive original film and exposed by using 
a 2 kW ultra-high pressure mercury lamp. The vacuum contact time was set 
at 10 seconds. 
When this photosensitive printing plate was developed by a 3% sodium 
metasilicate solution, a clear positive picture faithful to the positive 
original appeared distinctly on the support. By applying a fatty ink 
thereto, there was obtained an aluminum printing plate for lithographic 
printing. 
By way of comparison, there was prepared a printing plate by following the 
completely same procedure as Example 1 except that no organic foaming 
agent was added to the photosensitive composition, but this printing plate 
was incapable of forming a clear picture faithful to the original. When 
plate making was performed by gradually increasing the time of vacuum 
contact between this comparative photosensitive printing plate and 
positive original film, a clear picture equal to that obtained in Example 
1 could be obtained only when the vacuum contact time was made longer than 
30 seconds. 
EXAMPLE 2 
A 0.3 mm thick photoengraving zinc plate was abraded and roughened on its 
surface with a nylon-made rotary brush by using abrasive sand, then washed 
with water and dried. 
This surface-roughened zinc plate was coated with a below-defined 
photosensitive composition by a roll coater and dried by heating in a 
120.degree.-130.degree. C. hot-air oven for 3 minutes to form a 3 
g/m.sup.2 photosensitive layer. 
______________________________________ 
Photosensitive composition 
______________________________________ 
Polyvinyl cinnamate (photosensitive resin shown 
in Japanese Pat. Pub. No. 1492/63) 
6 g 
Ethylene glycol monomethyl ether acetate 
25 g 
5-Nitroacenaphthene 0.5 g 
Phthalocyanine blue-s-10 (mfd. by Dainichi 
Seika Kogyo) 0.5 g 
Cellmic AN (a dinitrosopentamethylene- 
tetramine foaming agent mfd. by Sankyo Kasei) 
0.6 g 
______________________________________ 
The thus obtained photosensitive layer had the substantially same surface 
configuration as the photosensitive layer of Example 1. This 
photosensitive printing plate was vacuum contacted with a negative 
original film for 10 seconds by using the same machine as used in Example 
1 and then exposed by using a 2 kW ultra-high pressure mercury lamp. 
When this photosensitive printing plate was developed with a 
trichloroethylene solution, there was obtained a clear picture faithful to 
the original. This plate was then etched according to an ordinary Dow 
etching process to obtain a zinc relief. 
By way of comparison, there was prepared a similar printing plate in the 
same way as Example 2 except for non-addition of the organic foaming agent 
to the photosensitive composition, but no clear picture faithful to the 
original could be obtained with this plate. In order to obtain a picture 
faithful to the original, vacuum contact time must be made longer than 30 
seconds. 
EXAMPLE 3 
A 0.3 mm thick aluminum plate was surface-roughened after the manner of 
Example 1, then anodized in a 20% phosphoric acid solution, washed with 
water and dried. 
The thus treated aluminum plate was coated with a photosensitive 
composition specified below by a roll coater to a coating build-up of 1 
g/m.sup.2 and then dried in a 125.degree.-135.degree. C. atmosphere by a 
far infrared heater for 3 minutes. 
______________________________________ 
Photosensitive composition 
______________________________________ 
Azido group-containing polymer (photosensitive 
resin shown in Example 3 of British Pat. No. 
843,541) 10 g 
4-oxo-4a-Azanaphthalene 1.0 g 
Cyclohexanone 100 ml 
Cellmic S (p, p'-oxybis (benzenesul- 
fonylhydrazine foaming agent mfd. by 
Sankyo Kasei) 1.0 g 
______________________________________ 
The thus obtained photosensitive layer had the substantially same surface 
configuration as the photosensitive layer of Example 1. This 
photosensitive printing plate was vacuum contacted (vacuum contact time: 
10 seconds) with a negative original film in the completely same way as 
Example 1 and then exposed. 
This photosensitive printing plate was then developed with cyclohexanone 
and the picture portion of a swollen state was dyed with a cyclohexanone 
solution of Methyl Violet to obtain a clear picture faithful to the 
original. 
By way of comparison, there was prepared a similar printing plate in the 
same way as Example 3 except for non-addition of the organic foaming agent 
to the photosensitive composition, but no picture faithful to the original 
was obtained. Also, more than 30-second vacuum contact time was required 
for obtaining a faithful picture. 
EXAMPLE 4 
A 0.3 mm thick aluminum plate was surface-roughened after the manner of 
Example 1, anodized in a 15% sulfuric acid solution according to a known 
method, followed by washing with water and drying, then further immersed 
in a 70.degree. C. 1% zirconium potassium fluoride solution for 3 minutes, 
washed with water and dried to perform a hydrophilization treatment. 
The thus treated aluminum plate was coated with a photosensitive 
composition, shown below, by a roll coater to a coating build-up of 1 
g/m.sup.2 and then dried in a 120.degree.-135.degree. C. atmosphere by 
using a far infrared heater for 3 minutes. 
______________________________________ 
Photosensitive composition 
______________________________________ 
A 32% ethylene glycol monomethyl ether solution of 
poly (.beta.-hydroxyethyl methacrylate) (photosensitive 
resin solution) 24 g 
p-Toluenesulfonic acid double salt of condensation 
product of paradiazodiphenylamine and formaldehyde 
1.5 g 
Oil Blue #603 (made by Orient Kagaku) 
0.23 g 
Ethylene glycol monomethyl ether 
60 g 
Cellmic CAP-250 (an azodicarbonamide foaming 
agent mfd. by Sankyo Kasei) 0.23 g 
______________________________________ 
The thus obtained photosensitive layer had the substantially same surface 
configuration as the photosensitive layer of Example 1. This 
photosensitive printing plate was vacuum contacted (vacuum contact time: 
10 seconds) with a negative original film after the manner of Example 1 
and then exposed. 
When this photosensitive printing plate was developed with a developing 
solution of the following composition, there was obtained a clear picture 
faithful to the original. 
______________________________________ 
Developing solution 
______________________________________ 
Benzyl alcohol 20 g 
40% Sodium silicate solution 
10 g 
Monogen Y-100 (higher alcohol sufonic acid ester 
sodium mfd. by Daiichi Kogyo Seiyaku KK) 
30 g 
Water 940 g 
______________________________________ 
By way of comparison, there was prepared a similar printing plate in the 
same way Example 4 except that no organic foaming agent was added to the 
photosensitive composition, but no picture faithful to the original was 
obtained with this plate. For reproducing the picture true to the 
original, the vacuum contact time must be made longer than 30 seconds. 
EXAMPLE 5 
A 0.5 mm thick aluminum plate was subjected to a surface roughening 
treatment same as practiced in Example 1, then anodized in a 42% 
phosphoric acid solution, washed with hot water and dried. 
This anodized aluminum plate was coated with the following photosensitive 
composition to a coating build-up of 2 g/m.sup.2 and then dried in a 
120.degree.-130.degree. C. atmosphere by using a far infrared heater. 
______________________________________ 
Photosensitive composition 
______________________________________ 
Ester-substituted polyester of diethyl-p-phenylene 
diacrylate and 1,4-di-.beta. -hydroxyethoxycyclohexane 
(photosensitive resin) 4.0 g 
2-benzoylmethylene-1-methyl-.beta.-naphthothiazoline 
0.32 g 
Benzoic acid 0.16 g 
Hydroquinone 0.08 g 
Monochlorobenzene 100 ml 
Cyanine Blue S-10 (mfd. by Dainichi Seika Kogyo) 
0.8 g 
Cellmic CAP-149 (an azodicarbonamide foaming 
agent mfd. by Sankyo Kasei) 
0.4 g 
______________________________________ 
The thus obtained photosensitive layer had the substantially same surface 
configuration as the photosensitive layer of Example 1. The photosensitive 
printing plate was vaccum contacted (for 10 seconds) with a negative 
original in the same way as Example 1 and then exposed. 
When this photosensitive printing plate was treated with the following 
developing solution, a clear picture faithful to the original could be 
reproduced. 
______________________________________ 
Developing solution 
______________________________________ 
4-Butylolactone 250 ml 
Triethanolamine 25 ml 
Glycerol 25 ml 
Methylabietate 2.5 ml 
______________________________________ 
In the case of the printing plate containing no foaming agent, more than 30 
-second vacuum contact time was required for reproducing a clear picture 
faithful to the original. 
EXAMPLE 6 
A 0.3 mm thick aluminum plate was surface-roughened and anodized after the 
manner of Example 5, then coated with the following photosensitive 
composition to a coating buildup of 2 g/m.sup.2 and dried in a 200.degree. 
C. atmosphere for 2 minutes. 
______________________________________ 
Photosensitive composition 
______________________________________ 
Naphthoquinone-(1, 2)-diazido-5-sulfonyl chloride 
and phenol novolak condensate 
5.0 g 
Ethylene glycol monobutyl ether 
15 g 
Oil Blue #603 (mfd. by Orient Kagaku) 
0.05 g 
Cellmic No. 142 (a hydrazodicarbonamide 
foaming agent mfd. by Sankyo Kasei) 
0.5 g 
______________________________________ 
The thus obtained photosensitive layer had a surface configuration such as 
shown in FIG. 2. This photosensitive printing plate was vacuum contacted 
(vacuum contact time: 10 seconds) with a positive original film in the 
completely same manner as Example 1 and then exposed. 
When this photosensitive printing plate was developed with a 3% sodium 
metasilicate solution, there was obtained a clear and sharp picture 
faithful to the positive original, and it was found that no adverse effect 
was given to the photosensitive layer by the foaming agent and the foaming 
treatment. 
By way of comparison, there was prepared a similar printing plate in the 
completely same way as Example 6 except that no organic foaming agent was 
added to the photosensitive composition, but no clear picture faithful to 
the original was formed with this plate. When plate making was performed 
by gradually increasing the vacuum contact time between this comparative 
photosensitive printing plate and the positive original film, a clear 
picture same as provided in Example 6 could be obtained only when the 
vacuum contact time was set at 30 seconds. 
Industrial Applicability 
This invention makes it possible to roughen the surface of the 
photosensitive layer coated on the support in a PS plate with no need of 
any extra step in the plate making process. This allows completion of 
vacuum contact between photosensitive printing plate and original film in 
a short period of time and also makes it possible to obtain a clear and 
sharp picture faithful to the original. Thus, the plate making efficiency 
is markedly improved and the production cost is reduced. This invention, 
therefore, is of great value in the plate making industry.