Plate surface correcting solution for dry lithographic printing plate

A process of correcting a dry lithographic printing plate which comprises applying to an unwanted area of an ink-accepting area in the dry lithographic printing plate consisting of ink-repellent areas comprising a silicone rubber layer and ink-accepting area, a correcting solution comprising the following components: ______________________________________ amount (parts by weight) ______________________________________ (a) Linear organopolysiloxane having three 100 alkoxy groups at both terminal ends (b) Titanium based condensation catalyst 0.1 to 5 (c) Organic solvent. 100 to 5,000 ______________________________________ The plate surface retouching solution provides a coating which has a good adhesion to a light-sensitive layer and a good resistance to printing.

BACKGROUND OF THE INVENTION 
The present invention relates to a correcting solution for a dry 
lithographic printing plate in which a silicone rubber layer serves as an 
ink repellent layer. 
There have been proposed a variety of dry lithographic printing plates in 
which a silicone rubber layer serves as an ink repellent layer. Among 
these, those which comprise a substrate having provided thereon, in order, 
a light-sensitive resin layer and a silicone rubber layer are typical ones 
and examples thereof are, for instance, these disclosed in Japanese Patent 
Publication for Opposition Purpose (hereunder referred to as "J. P. 
KOKOKU") Nos. Sho 54-26923 (U.S. Pat. No. 3,894,873), Sho 56-23150, Sho 
55-22781 (British Pat. No. 1,419,643) and Japanese Patent Unexamined 
Publication (hereunder referred to as "J. P. KOKAI") No. Hei 2-226249. 
These lithographic printing plates have many advantages since they do not 
require dampening water. 
However, the silicone rubber layer is relatively liable to be damaged so 
that scratches will be made easily when the printing plate is handled. 
There have been proposed some correcting solutions for dry lithographic 
printing paltes which may delete scratches and defects in the form of a 
pinhole and defects due to film edges, accordingly. 
J. P. KOKOKU No. Sho 61-3417 describes a plate surface retouching solution 
comprising one pack hardening silicone rubber solution containing 
triacetoxysilane as a cross-linking agent. J. P. KOKAI No. Sho 62-299854 
describes a plate surface correcting solution comprising one-pack 
hardening silicone rubber solution containing vinyloxysilane compound as a 
cross-linking agent. 
The coating obtained by the conventional correcting solutions has 
insufficient adhesion to the surface of image portions and can not bear 
printing more than 50,000 sheets before beginning to peel off the coating 
from the plate surface when correcting solid image portions, though the 
strength and hardening rate of the coating reach an almost satisfiable 
level in view of the printing techniques. 
As a general method for strengthening the adhesion to image portions, it is 
conceivable that an appropriate silane coupling agent should be added to 
the correcting solution. However, the addition of such silane coupling 
agent influences the whole cross-linking reaction to lower the hardening 
rate and/or to lower the coating strength. Accordingly, even though the 
adhesion is strengthened, it does not lead to the increase of the 
resistance to printing. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to provide an improved 
correcting solution for a dry lithographic printing plate which may adhere 
to image portions strictly and may provide a coating having a good 
resistance to printing. 
The foregoing objects of the invention can effectively be achieved by 
providing a correcting solution for deleting an image portion to a 
non-image portion in a dry lithographic printing plate in which a silicone 
rubber layer serves as an ink repellent layer wherein the correcting 
solution is the silicone rubber solution having the following components. 
______________________________________ 
amount 
(parts by weight) 
______________________________________ 
(a) Linear organopolysiloxane having three 
100 
alkoxy groups at both terminal ends 
(b) Titanium based condensation catalyst 
0.1 to 5 
(c) Organic solvent 100 to 5,000 
______________________________________ 
DETAILED EXPLANATION OF THE INVENTION 
The linear organopolysiloxane having three alkoxy groups at each of both 
terminal ends used as component(a) according to the present invention is 
represented by the following general formula (I); 
EQU (R.sup.1 O).sub.3 Si--(OSi(R.sup.2).sub.2).sub.n --OSi(OR.sup.1).sub.3(I) 
In the above formula, R.sup.1 represents a methyl, ethyl or propyl group, 
preferably a methyl group in view of hardening property. R.sup.2 
represents a monovalent hydrocarbon group having 1 to 10 carbon atoms and 
include, for instance, an alkyl group such as a methyl, ethyl, propyl, 
butyl or hexyl group, an aryl group such as a phenyl group or an aralkyl 
group such as a .beta.-phenyl ethyl or .beta.-phenyl propyl group. R.sup.2 
is preferably a methyl group, because the component(a) in which R.sup.2 
represents a methyl group can be synthesized easily and has good 
repellency of printing ink. n is a number from 50 to 1000. If n is less 
than 50, the coating obtained tends to be made too hard and have a poor 
resistance to printing and ink repellency. If n exceeds 1000, the 
hardening property tends to be poor. 
The titanium based condensation catalyst as component(b) according to the 
present invention includes tetrabutyl titanate, tetra 2-ethyl hexyl 
titanate, triethanolamine titanate and tetraisopropenyloxy titanate. 
The titanium based catalyst has a better hardening property at room 
temperature and a better stability in a solution in combination with the 
component(a) as compared with the other tin, zinc or copper based 
catalysts. The amount of the component(b) used is 0.1 to 5.0 parts by 
weight per 100 parts by weight of the component(a). If the amount of the 
component(b) used is less than 0.1 parts by weight, the hardening property 
of the solution will be insufficient. If the amount of the component (b) 
exceeds 5 parts by weight, the storage stability of the solution will be 
made poor. 
The type of the organic solvent as component(c) is not limited as long as 
the component(a) and component(b) can dissolve in it, but those which may 
evaporate rapidly and have a good wetting property to the plate surface 
are desirable. 
Such organic solvents may include n-hexane, n-heptane, ethyl acetate, 
mineral spirits, toluene and xylene, etc. The amount of the organic 
solvent used to provide a good thickness of a coating is preferably 100 to 
5000 parts by weight, more preferably 500 to 1000 parts by weight per 100 
parts by weight of the component(a). 
The correcting solution for a printing palte of the present invention can 
provide a coating which has a good adhesion to a light-sensitive layer and 
a good resistance to printing. 
The correcting solution for a dry lithographic printing plate of the 
present invention will hereinafter be explained in more detail with 
reference to the following non-limitative working Examples and further the 
effects practically attained by the present invention will also be 
discussed in detail in comparison with comparative Examples.

EXAMPLE 1 
The following composition for a primer layer was applied to the surface of 
a smooth aluminum plate which had been degreased in a usual manner so that 
the amount of the composition coated was 2.0 g/m.sup.2 (on dry basis), and 
was heated to harden. 
______________________________________ 
amount 
Composition for Primer Layer 
(parts by weight) 
______________________________________ 
Epikote 1001 (made by Shell Chemical, Ltd. 
100 
bisphenol A based epoxy resin, 
epoxy equivalent is 450 to 500) 
Methyl tetrahydrophtalic acid anhydride 
36 
2,4,6-tris(dimethylaminomethyl)phenol 
10 
Methyl cellosolve acetate 
600 
Toluene 600 
Methyl ethyl ketone 600 
______________________________________ 
The following light-sensitive composition was applied to the surface of the 
primer layer provided on the aluminum plate so that the amount of 
light-sensitive composition coated was 0.25 g/m.sup.2 (on dry basis), and 
dried. 
______________________________________ 
amount (parts 
Light-sensitive Composition 
by weight) 
______________________________________ 
Light-sensitive unsaturated polyester made by 1:1 
10 
polycondensation of p-phenylene diacrylic acid 
ester and 1,4-dihydroxy ethyloxycyclohexane 
1-methyl-2-benzoylmethylene-.beta.-naphtothiazoline 
0.6 
Sumitone cyanine blue VH514 (made by Sumitomo 
2 
Chemical, Ltd. phthalocyanine blue pigment) 
Methyl cellosolve acetate 600 
Toluene 300 
______________________________________ 
The following silicone rubber composition was then applied to the 
light-sensitive layer so that the amount of the silicone rubber 
composition coated was 2.0 g/m.sup.2 (on dry basis), and dried to obtain a 
silicone rubber vulcanized layer. 
______________________________________ 
amount (parts 
Silicone rubber composition 
by weight) 
______________________________________ 
Dimethyl polysiloxane having OH groups at 
100 
both terminal ends (M.W. is about 600,000) 
Methylhydrogen polysiloxane having trimethyl- 
3.5 
silyl groups at both terminal ends 
(M.W. is about 2,500) 
1-Trimethoxy silylpropyl-3,5-diallylisocyanurate 
3.3 
Dibutyl tin dioctanoate 3.3 
Isopar G (made by Esso Chemical, ltd.) 
2000 
______________________________________ 
A single side matted polypropylene film having a thickness of 12 .mu.m was 
laminated on the silicone rubber layer thus obtained to produce a dry 
presensitized plate for use in making a a dry lithographic pringing plate. 
A positive transparency was overlaid on the dry presensitized plate, and 
was vacuum-contacted to the plate. The plate was then exposed to light 
using FT261V UDNS ULTRA-PLUS FLIP-TOP PLATE MAKER made by Nuarc, Ltd. for 
30 counts, and the laminated film was then peeled off. The plate was 
dipped in a developer comprising Isopar H (Esso Chemical, Ltd.) 90 parts 
by weight, diethylene glycol monobutyl ether 7 parts by weight, diethylene 
glycol monoethyl ether 3 parts by weight, and diethyl succinate 5 parts by 
weight for one minute, and was rubbed by a developing pad slightly to 
remove the light sensitive layer and the silicone rubber layer in 
unexposed areas. A dry lithographic printing plate was thus obtained. 
The correcting solution having the following components was applied to the 
pinholes, scratches, damages due to film edge produced on the developed 
printing plate and solid image portions using a brush, and was left to 
stand for ten minutes at room temperature to finish hardening. 
The coating after hardening was resistant to peeling off by the correcting 
shear generated at the time of printing. More than 50,000 good prints were 
produced. 
______________________________________ 
amount 
Correcting Retouching solution 
(parts by weight) 
______________________________________ 
(CH.sub.3 O).sub.3 Si--(OSi(CH.sub.3).sub.2).sub.700 --OSi(OCH.sub.3).sub. 
3 100 
Tetrabutyl titanate 1 
n-Hexane 450 
n-Heptane 450 
______________________________________ 
COMATIVE EXAMPLE 1 
A developed printing plate was prepared in the same manner as in Example 1. 
The following correcting solution comprising the silicone rubber 
composition was applied to solid image portions of the printing plate 
using a brush, and was left to stand at room temperature for ten minutes 
to complete hardening. 
______________________________________ 
amount (parts 
Correcting Retouching Solution 
by weight) 
______________________________________ 
Dimethyl polysiloxane having hydroxyl groups at 
100 
both terminal ends of the molecular chain 
(viscosity is 1500 cps (at 25.degree. C.) 
Vinyl tri(isopropenyloxy)silane 
4 
[(CH.sub.3).sub.2 N].sub.2 C.dbd.N--C.sub.3 H.sub.6 Si(OCH.sub.3).sub.3 
1 
3-aminopropyl triethoxysilane 
1.2 
Humed silica having a specific surface area of 
8 
200 m.sup.2 /g 
______________________________________ 
As a result of printing, the silicone rubber of the corrected portion was 
peeled off except the especially thick coated portion when 50,000 sheets 
were printed. 
EXAMPLE 2 
Positive working dry presensitized lithographic printing plate TAP (made by 
TORAY) was imagewise exposed to light. Then, the silicone rubber layer of 
the image portions was removed using gauze while dipping it in n-heptane 
to obtain a dry printing plate. The same correcting solution as used in 
Example 1 was applied to the solid image portions of the printing plate 
with a brush and was left to stand at room temperature for ten minutes to 
complete hardening. 
The coating after hardening was resistant to peeling at the time of 
printing, and the printing plate provided more than 50,000 good prints. 
COMATIVE EXAMPLE 2 
The correcting solution having the following components was applied to the 
solid image portions of the developed printing plate obtained in the same 
manner as in Example 2 using a brush and was left to stand at room 
temperature for ten minutes to complete hardening. 
As a result of printing, silicone rubber of the correcting portion was 
peeled off except the especially thick coated portions when 50,000 sheets 
were printed. 
______________________________________ 
amount 
Correcting Solution (parts by weight) 
______________________________________ 
Dimethyl polysiloxane (having OH groups 
100 
at terminal ends, number average molecular 
weight is about 20,000) 
Methyl triacetoxy silane 
20 
Dibutyltin octanoate 7 
n-Heptane 1000 
______________________________________ 
EXAMPLE 3 
The following primer composition was applied to the surface of a smooth 
aluminum plate which had been degreased in a usual manner so that the 
amount of the composition coated was 8.0 g/m.sup.2 (on dry basis) and was 
heated at 120.degree. C. for three minutes and dried. 
______________________________________ 
Primer Composition 
amount 
(parts by 
weight) 
______________________________________ 
Photographic Gelatine #680 
100 
(made by Nitta Gelatine, Ltd.) 
Dispersion comprising TiO.sub.2 : 30% by weight/ 
20 
photographic gelatine #680: 3% by weight/ 
pure water: 67% by weight 
Tartrazine (yellow dye) 2 
##STR1## 2 
______________________________________ 
The following hardening agent was applied to the surface of the primer 
layer thus obtained so that the amount of the agent coated was 1.04 
g/m.sup.2 (on dry basis) and heated for one minute at 100.degree. C., 
dried to harden the gelatine membrane. 
______________________________________ 
amount 
Hardening Agent (parts by weight) 
______________________________________ 
CH.sub.2 .dbd.CHSO.sub.2 CH.sub.2 CH(OH)CH.sub.2 SO.sub.2 CH.dbd.CH.sub.2 
2 
Methyl alcohol 70 
Pure water 30 
______________________________________ 
After the primer layer was dried and hardened, it was left to stand for one 
day at about 20.degree. C. The following light-sensitive composition was 
applied to the surface of the primer layer so that the amount of the 
composition coated was 1.0 g/m.sup.2 (on dry basis), and dried. 
______________________________________ 
Light-sensitive composition 
amount 
(parts by 
weight) 
______________________________________ 
Copolymer of allyl methacrylate and sodium 
100 
methacrylate (sodium methacrylate content: 
15 mol %) 
Epoxyacrylate monomer of 30 
HOCH(CH.sub.2 OCH.sub.2 CHOHCH.sub.2 OCOCHCH.sub.2).sub.2 
##STR2## 10 
Defensor MCF323 10 
(made by Dainippon Ink and Chemical Industries, 
Ltd.) 
Methyl ethyl ketone 350 
Propylene glycol monomethylether 
330 
______________________________________ 
The following silicone rubber composition was applied to the surface of the 
light-sensitive layer so that the amount of the composition coated was 1.7 
g/m.sup.2 (on dry basis), and dried to obtain a silicone rubber vulcanized 
layer. 
______________________________________ 
amount 
Silicone rubber composition 
(parts by weight) 
______________________________________ 
Dimethyl polysiloxane having vinyl groups 
100 
at both terminal ends 
(M.W.: about 35,000) 
Methylhydrogen polysiloxane having trimethyl 
3 
silyl groups at both terminal ends 
(M.W.: about 2,500) 
Olefin-chloroplatinate catalyst 
2 
(10% toluene solution) 
Isopar G (made by Esso Chemical, Ltd.) 
1800 
______________________________________ 
A single-side matted PET film having a thickness of 6.5 .mu.m was laminated 
on the surface of the silicone rubber layer thus obtained to form a dry 
presensitized plate. 
A positive transparency was overlaid on the surface of the dry 
presensitized plate thus obtained and was intimately contacted and was 
imagewise exposed to light using a usual vacuum frame. The laminated film 
was then peeled off. 
The silicone rubber layer and the light-sensitive layer in image portions 
were rubbed off using gauze while the dry presensitized plate was dipping 
in a developer having the following composition to obtain a dry 
lithographic printing plate. 
______________________________________ 
Developing Solution 
amount 
(parts by 
weight) 
______________________________________ 
Benzyl alcohol 8 
New Coal B4SN 9 
(made by Nippon Emulsifying Agnets, Ltd.) 
60% by 
weight 
##STR3## solution 
Triethanol amine 1 
Pure Water 82 
______________________________________ 
The correcting solution having the following composition was applied to the 
solid image portion of the printing plate using a brush and left to stand 
at room temperature for ten minutes to complete hardening. 
The coating after hardening was resistant to peeling. More than 50,000 good 
prints were produced. 
______________________________________ 
amount 
Plate Surface Retouching Solution 
(parts by weight) 
______________________________________ 
(CH.sub.3 O)Si--(OSi(CH.sub.3).sub.2).sub.500 --OSi(OCH.sub.3).sub.3 
100 
Tetrabutyl titanate 1 
n-Heptane 500 
______________________________________