Method for producing a steel lithographic plate

A method for producing a metal substrate for a lithographic plate is provided herein by treating the substrate having the thickness in the range of 50 to 400 .mu.m. The said substrate is electrochemically, chemically or mechanically treated in order to provide an average surface roughness in the range of 0.1 to 3 .mu.m, followed by a surface treatment such as plating or chemical treatment, and then followed by a conventional hydrophilic treatment.

FIELD OF THE INVENTION 
The present invention relates to the method for producing a metal substrate 
for a lithographic plate, whereby the substrate is electrochemically, 
chemically or mechanically treated in order to improve the surface 
roughness, corrosion resistance and hydrophilic quality of a metal 
substrate, the said product having excellent water holding ability, 
hydrophilic quality, adhesion of photoresist and printability. 
DESCRIPTION OF THE PRIOR ART 
Lithographic printing is usually based on the principle that water cannot 
mix with ink oil. In the printing process, the surface of the metal 
lithographic plate consists of an ink-receptive image area and a 
hydrophilic non-image area. The entire surface of the metal lithographic 
plate is first soaked with water and then the ink-receptive image area 
repels water. However, the hydrophilic non-image area holds water. 
Next, the surface of the metal lithographic plate is soaked with the 
printer's ink and the printer's ink only covers the ink-receptive image 
area. The said ink on the ink-receptive image area is transferred directly 
or through the blanket roll to the printing paper. 
The image area consisting of the ink-receptive organic material, for 
example, light sensitive diazo resin, thermosetting resin or ultraviolet 
curing resin is formed on the metal lithographic plate by means of the 
photography or printing. 
In the case of estimating the printability and the shelf life of the metal 
lithographic plate, it is important that the non-image area on the plate 
be hydrophilic. When the non-image area is poorly hydrophilic, the 
printer's ink causes stains, spots or scumming on the plate. When the 
non-image area becomes non-hydrophilic due to aging, the shelf life of the 
plate becomes short. 
Adhesion to the ink-receptive organic material is an important factor in 
estimating the printability. The poor adhesion to the ink-receptive 
organic material causes the amount of the printing to decrease. 
From these viewpoints, the various surface treatments are applied to the 
metal substrate for the lithographic plate. 
For example, a metal substrate for the metal lithographic plate mainly 
consisting of aluminum is grained mechanically or etched electrochemically 
and then is subjected to the conventional hydrophilic treatment. An 
aluminum sheet substrate is so expensive that a thin aluminum or aluminum 
alloy sheet substrate is used for the metal lithographic plate. But the 
thinner the aluminum or aluminum alloy sheet substrate, the weaker its 
strength. Therefore, an aluminum or aluminum alloy sheet substrate having 
a thickness of 0.3 mm is usually used for the metal lithographic plate. In 
the case of a thickness under 0.3 mm, an aluminum or aluminum alloy sheet 
substrate is used for small amount of printing. 
There are many inventions relating to processes for production of metal 
lithographic plates by using an aluminum or aluminum alloy sheet 
substrate. But these processes are so complicated, as described above, 
that the plates are expensive. 
Therefore, it is an object to the present invention to produce an 
economical metal substrate having excellent properties. 
BRIEF SUMMARY OF THE INVENTION 
A metal substrate for a metal lithographic plate having a thickness in the 
range of 50 to 400 .mu.m is electrochemically, chemically or mechanically 
treated in order to exhibit an average surface roughness in the range of 
0.1 to 3 .mu.m, and is subjected to a surface treatment such as plating or 
chemical treatment, and then to a conventional hydrophilic treatment. 
DETAILED DESCRIPTION OF THE INVENTION 
The detailed method according to the present invention will be described 
below. 
The metal substrate for the metal lithographic plate may include a steel 
sheet and steel foil, said metal substrate having a thickness in the range 
of 50 to 400 .mu.m. 
The average surface roughness of said metal substrate in the range of 0.1 
to 3 .mu.m (is suitable for improving the hydrophilic quality. The average 
surface roughness of more than 3 .mu.m) has a remarkably bad influence on 
the image produced. In order to roughen the surface, said metal substrate 
must be grained, etched chemically or electrochemically, or electroplated 
with iron. 
In order to improve the corrosion resistance of a metal substrate, after 
roughening the surface, the plating or the chemical treatment is applied 
on the metal substrate by the following methods: 
(1) Plating with a metal such as chromium, nickel, copper, tin or zinc, 
(2) Alloy plating with the alloys of said metals, 
(3) Plating with multi-layers of said metals, and 
(4) Chemical treatment (dipping or electrolysis) in the treatment solution 
containing chromate, phosphate, molybdate, silicate, borate, perborate or 
aluminate. 
The said surface treatment is improved not only in corrosion resistance but 
also in adhesion to the ink-receptive organic material. 
Also, in the case of electroplating, a suitable surface roughness for the 
metal lithographic plate is obtained by forming electrodeposited nuclei 
(or crystals). Therefore, it is necessary in the electroplating to impart 
roughness to the base substrate. 
The thickness of the electrodeposited material must be selected from the 
standpoint of economy and corrosion resistance of the metal substrate, in 
the case of electroplating with an expensive metal such as chromium or 
nickel. 
Even if the said metal substrate is suitable for the metal lithographic 
plate, its hydrophilic quality is deteriorated by aging. Therefore, a 
further hydrophilic treatment is performed on said metal substrate. The 
hydrophilic treatment is usually applied by a well-known method, for 
example, employing silicates, zircofluorides, organic titanium compounds, 
organic phosphoric acid, ferrocyanide, ferricyanide, organic polymer 
coating consisting of polyacrylic acid or carboxymethyl cellulose, gallic 
acid, phosphotungstate, or inorganic compound sol. 
The method employing a sol of an inorganic compound is especially suitable 
for the hydrophilic treatment, and is described in detail below. 
The water-dispersible sol of a metal compound, which is one of the main 
components, has the effect of improving the hydrophilic quality, the 
corrosion resistance and printability. The said hydrophilic treatment may 
be applied to one or both sides of a metal substrate. 
The water-dispersible sol may include a compound (oxide or hydroxide) of a 
metal such as aluminum, titanium, zirconium, silicon, chromium, nickel, 
zinc, tin, manganese, copper, cobalt, iron, lead, cadmium, magnesium or 
calcium and any metal compound which can positively charge the suspension. 
The diameter of the particle is 1 to 500 M.mu.. In order to stabilize the 
metal compound sol in the suspension, a stabilizing additive may also be 
included in the treatment solution. For example, an inorganic acid such as 
chromic acid or phosphoric acid, an organic acid such as citric acid or 
acetic acid, and a surface active agent may be employed. At least one sol 
of a metal compound may be added to the suspension. 
A concentration of metal compound sol in the range of 1 to 100 g/1 (as 
solid) is suitable for improving the hydrophilic quality. A concentration 
of less than 1 g/l has little effect on the hydrophilic quality and 
conversely, a concentration of more than 100 g/l has a very adverse effect 
on the appearance of the metal lithographic plate and is uneconomical. 
Said sol is positively charged in the suspension and is easily and strongly 
absorbed on said metal substrate. The hydrophilic treatment can be applied 
by dipping or electrolysis in the suspension containing the sol compound. 
In the case of electrolysis treatment, as the sol of the metal compound is 
positively charged in the suspension, the metal substrate is cathodically 
treated in said suspension. 
The sol absorbed by the electrolysis treatment is bonded to the metal 
substrate more strongly than that of sol absorbed by the dipping 
treatment. 
In order to stabilize the sol of a metal compound in the suspension, an 
agent such as chromic acid, phosphoric acid, acetic acid, chloric acid or 
sulphuric acid may be added. When chromic acid or phosphoric acid is 
added, the hydrophilic film layer formed on the metal substrate has 
excellent corrosion resistance. In the case of a steel substrate or steel 
foil substrate, said method is especially desirable. 
As the hydrophilic film layer formed is bonded strongly to a metal 
substrate, and does not contain an alkali compound, the ink-receptive 
organic material does not peel from the metal substrate during the 
printing. The presensitized plate according to the present invention has a 
higher printing capacity than the conventional lithographic printing 
plate.

Specific embodiments of the present invention are as follows: 
EXAMPLE 1 
A cold-rolled steel foil having a thickness of 100 .mu.m was treated by the 
method of the present invention. 
Treatment of the present invention: 
A. Graining treatment for improving the surface roughness. 
A cold-rolled steel foil was electroplated with iron (chloride bath) to 5 
.mu.m. The average surface roughness was 0.6 .mu.m. 
B. Surface treatment for improving the surface roughness, corrosion 
resistance and printability. 
A steel foil substrate treated by A was electroplated with chromium by 
treating for 20 seconds in a Sargent bath at a cathodic current density of 
40 A/dm.sup.2 and at a temperature of 45.degree. C. 
C. Hydrophilic treatment for improving printability and corrosion 
resistance. 
A steel foil substrate treated by A and B was dipped for 10 seconds in the 
suspension consisting of alumina sol (particle diameter: 50 .mu.m) of 30 
g/l (trade name: AS-200, Nissan Chemical Industries, Ltd.) and chromium 
trioxide of 5 g/l and then was dried. 
EXAMPLE 2 
A cold-rolled steel substrate having the thickness of 200 .mu.m was treated 
by the method of the present invention. 
Treatment of the present invention: 
A. Graining treatment for improving the surface roughness. 
One side of a steel substrate was etched in the solution of 40.degree. Be 
of FeCl.sub.3. The average surface roughness of the steel substrate formed 
was 0.8 .mu.m . 
B. Surface treatment for improving corrosion resistance and printability. 
A steel substrate treated by A was electroplated with zinc by using the 
sulfate bath at a cathodic current density of 5 A/dm.sup.2 and at a 
electrolyte temperature of 50.degree. C. The thickness of zinc deposit was 
4 .mu.m. 
C. Hyrophilic treatment for improving printability. 
A steel substrate treated by A and B was cathodically treated for 30 
seconds in the suspension consisting of the chromium compound sol of 20 
g/l and phosphoric acid of 10 g/l at a cathodic current density of 2 
A/dm.sup.2. After rinsing with water, the steel substrate was dried. 
EXAMPLE 3 
A cold-rolled steel substrate having the thickness of 300 .mu.m was treated 
by the method of the present invention. 
Treatment of the present invention: 
A. Graining treatment for improving the surface roughness. 
A cold-rolled steel substrate was electroplated with iron by treating for 8 
minutes in a solution consisting of ferrous sulfate of 400 g/l and 
ammonium sulfate of 100 g/l at a cathodic current density of 30 A/dm.sup.2 
and at an electrolyte temperature of 50.degree. C. The thickness of the 
iron deposit formed was 50 .mu.m. The average surface roughness of the 
iron plated steel substrate was 1.6 .mu.m. 
B. Surface treatment for improving printability and corrosion resistance. 
A said steel substrate treated by A was coated with nickel by treating for 
20 seconds in Watts bath at a current density of 20 A/dm.sup.2 and at a 
temperature of 40.degree. C. 
C. Hydrophilic treatment for improving printability. 
A steel substrate treated A and B was coated with gum arabic solution to 
the thickness of 5 .mu.m and was dried. 
EXAMPLE 4 
A cold-rolled steel foil substrate having the thickness of 100 .mu.m was 
treated by the method of the present invention. 
Treatment of the present invention: 
A. Graining treatment for improving surface roughness. 
A cold-rolled steel foil substrate was grained by sand. 
The average surface roughness was 2.5 .mu.m. 
B. Surface treatment for improving printability and corrosion resistance. 
Said steel foil substrate treated by A was electroplated with nickel by 
treating in a Watts bath at a current density of 5 A/dm.sup.2 and at a 
temperature of 50.degree. C. The thickness of nickel deposit was 0.2 
.mu.m. And then the said nickel plated steel foil substrate was 
electroplated with chromium by treating in a Sargent bath at a cathodic 
current density of 40 A/dm.sup.2 and at a electrolyte temperature of 
45.degree. C. The thickness of chromium deposit was 0.5 .mu.m. 
C. Hydrophilic treatment for improving printability. 
Said steel foil substrate treated by A and B was cathodically treated for 
30 seconds in the suspension consisting of phosphoric acid of 50 g/l and 
the sol of zirconium compound (the average particle diameter of 50 .mu.m) 
of 10 g/l at cathodic current density of 2 A/dm.sup.2 and then was rinsed 
with water and was dried. 
EXAMPLE 5 
The steel sheet substrate subjected to treatment A of Example 2 was 
electroplated with chromium by treating in a Sargent bath at a cathodic 
current density of 40 A/dm.sup.2 and at an electrolyte temperature of 
45.degree. C. The thickness of chromium deposit was 0.1 .mu.m. The said 
chromium plated steel sheet substrate was coated with gum arabic solution 
to 1 .mu.m thickness and dried. 
COMATIVE EXAMPLE 1 
The steel sheet substrate was treated by the same A treatment as described 
in Example 2. The average surface roughness was 0.8 .mu.m. B and C 
treatments, as described in the above Examples, were not applied to the 
said steel sheet substrate. 
COMATIVE EXAMPLE 2 
The steel sheet substrate having the thickness of 0.3 mm was treated to 
attain an average surface roughness of 0.05 .mu.m. B and C treatments, as 
described in the above Examples, were not applied to the said steel sheet 
substrate. 
COMATIVE EXAMPLE 3 
A commercial presensitized plate (aluminum sheet substrate: thickness of 
substrate . . . 0.3 mm, FUJI FILM PRESENSITIZED OFFSET PLATE, Fuji Film 
Co., Ltd., Japan). 
Evaluation: The metal substrates which were prepared in Examples 1, 2, 3, 4 
and 5, and in Comparative Examples 1, 2 and 3 were evaluated by the 
following text methods. The results were shown in Table 1. 
(1) Hydrophilic quality: Hydrophilic quality was evaluated by measuring the 
contact angle (water). 
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Contact angle &lt;30.degree. 
.circle. 
30.degree.-50.degree. 
.DELTA. 
&gt;50.degree. 
x 
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(2) Adhesion to the ink-receptive organic material. 
A piece of adhesive tape was applied firmly to the ink-receptive organic 
material (image area) and then was pulled off quickly. 
The image area was formed on the test pieces by curing a light-sensitive 
resin (a quick-wipe-on negative working, Ueno Chemical Industries, Ltd.). 
The said light-sensitive resin was cured by ultraviolet. 
means that no adhesion loss of the image areas was found. 
x means that adhesion loss of the image area was found. 
TABLE 1 
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Characteristics of treated sample 
Adhesion to the ink- 
receptive organic 
Hydrophilic quality 
material 
immediate- 
after aging 
immediate- 
after aging 
ly after for ly after 
for 
Sample producing 3 months producing 
3 months 
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Example 1 
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Example 2 
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Example 3 
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Example 4 
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Example 5 
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Comparative 
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Example 1 (red rust) 
Comparative 
x x x x 
Example 2 (red rust) 
Comparative 
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Example 3 
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The printing capacity of said Examples was determined by printing on a 
press. Each metal lithographic plate of Example 1, 2, 3, 4 and 5 can print 
forty thousand of the printing papers without problems such as stains, 
spots or scumming.