Support for a planographic printing plate and method for producing same

A support for a planographic printing plate support in which variations in the quality of the material of the aluminum support are reduced to thereby improve the yield in an electrolytic graining treatment and which is excellent in susceptibility to graining, has no stripe irregularities, and excellent appearance, and a method for producing such a planographic printing plate. An aluminum plate material is formed through a twin-roller continuous casting apparatus and subjected to cold rolling. Successively, the plate is subjected to heat treatment so as to form a surface portion of a depth of at least 15 .mu.m in the thickness direction having no recrystallization in the surface layer. If necessary, the plate may be subjected to cold rolling again as final rolling. Thereafter, the plate is subjected to correction.

BACKGROUND OF THE INVENTION 
The present invention relates to a method for producing a support for a 
planographic printing plate, and particularly relates to a method for 
producing an aluminum support having excellent electrolytic graining 
properties. 
Art aluminum plate (including aluminum alloy) is often used as a printing 
plate, particularly, a printing plate for use as an offset printing plate. 
In using an aluminum plate used as an offset printing plate support, it is 
generally necessary that the aluminum plate have a good adhesive property 
to a photosensitive layer and good water retentivity. For this purposes, 
the aluminum plate must be roughened to provide the aluminum plate with a 
uniform and finely grained surface. Because this toughening treatment has 
a remarkable influence on printing characteristics and durability during 
offset printing, the effect of the roughening treatment is an important 
factor in the production of the plate material. 
An AC electrolytic graining method is generally employed for roughening an 
aluminum support for a printing plate. For the waveform of the current 
used in such a method, an ordinary sinusoidal wave form alternating 
current or a special waveform alternating current such as a square 
waveform alternating current, etc., can be employed. Graining of an 
aluminum plate is performed using such an alternating current with a 
suitable electrode such as a graphite electrode as a counter electrode. 
The graining can generally be completed in one treatment, but in such a 
case the depth of the pits obtained by the graining is generally small, so 
that the resulting aluminum support is inferior in durability. Therefore, 
various methods have been proposed to obtain a suitable aluminum plate for 
use as a support for a printing plate having a grained surface in which 
pits having depths larger than their diameter are formed evenly. Examples 
of such methods are disclosed in Japanese Patent Unexamined Publication 
No. Sho. 53-67507, Japanese Patent Unexamined Publication No. Sho. 
54-65607, Japanese Patent Unexamined Publication No. Sho. 55-25381, and 
Japanese Patent Unexamined Publication No. Sho. 56-29699, etc. Further, a 
method using a combination of an AC electrolytic etching and mechanical 
graining treatments is disclosed, for example, in Japanese Patent 
Unexamined Publication No. Sho. 557-142695. 
A known method for producing an aluminum support includes steps of casting 
a slab (with a thickness of 400 to 600 mm, a width of 1000 to 2000 mm, and 
a length of 2000 to 6000 mm) by melting and holding an ingot of aluminum, 
applying a surface cutting to remove a thin portion (about 3 to 10 mm) 
from the surface of the slab to thereby remove the impurity-structure 
surface portion, evenly heating the slab in a furnace at a temperature of 
480.degree. to 540.degree. C. for 6 to 12 hours in order to remove stress 
inside of the slab and equalize the surface portions of the slab, and then 
hot-rolling the slab at a temperature of 480.degree. to 540.degree. C. 
After the slab is hot-rolled to a thickness of 5 to 40 nun, the slab is 
cold-rolled to a predetermined thickness at room temperature. Then, to 
homogenize the surfaces and to make the plate excellent in flatness, 
annealing is carried out to thereby homogenize the rolled structure and 
the like. Then, cold rolling is carried out to obtain a predetermined 
thickness, and finally correction is carried out. The aluminum support 
thus produced is used as a support for a planographic printing plate. 
An electrolytic graining treatment is apt to be affected by the 
characteristics and composition of the aluminum support subjected to the 
treatment. That is, in the production of an aluminum support through the 
steps of melting/holding, casting, surface cutting and soaking, there can 
arise variations of the components of the metal alloy in the surface 
layer, even in the case where not only heating and cooling are alternately 
carried out, but also surface cutting is employed, that is, a step of 
cutting away the surface layer is carried out. This causes a lowering of 
the yield rate of the aluminum support for a planographic printing plate. 
To reduce variations in the quality of the material of the aluminum support 
so as to improve the yield rate in the electrolytic graining treatment and 
to thereby produce a planographic printing plate excellent both in quality 
and in yield, there has been proposed a method for producing a support for 
a planographic printing plate including steps of forming a hot-rolled 
thin-plate coil by continuously carrying out casting from molten aluminum 
and hot rolling, applying cold rolling, a heat treatment and applying 
correction to the coil to thereby obtain an aluminum support, and then 
graining the aluminum support (see U.S. Pat. No. 5,078,805 which 
corresponds to Japanese Patent Unexamined Publication No. Hei. 3-79798). 
In such a method, however, there can still arise variations in the 
electrolytic graining treatment of the plate. In addition, stripe 
irregularities sometimes occur in the grained surface so that the external 
appearance of the plate is sometimes poor. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to provide a support for 
a planographic printing plate in which variations in the quality of the 
material of the aluminum support can be reduced to thereby improve the 
yield in the electrolytic graining treatment, which is excellent in its 
susceptibility to graining, and which has no stripe irregularities and is 
excellent in the external appearance. It is also an object of the 
invention to provide a method for producing such a support for a 
planographic printing plate. 
The foregoing and other objects of the invention have been met by a support 
for a planographic printing plate in the form of an aluminum plate having 
a surface portion to a depth of 15 .mu.m in the direction of thickness 
thereof which is not recrystallized, while remaining portions of the 
aluminum plate from the surface portion toward its center are 
recrystallized. 
The foregoing and other objects of the invention are also satisfied by a 
method for producing a support for a planographic printing plate in which, 
after molten aluminum is formed directly into an aluminum plate of a 
thickness of 4 to 30 mm through continuous casting using twin rollers, the 
plate is subjected to cold rolling to reduce its thickness by 60 to 95%, 
the plate is then subjected to a heat treatment and correction so that a 
portion of a thickness of at least 15 .mu.m in which no recrystallization 
takes place is formed in the surface of the aluminum plate, and the 
thus-prepared aluminum support is subjected to surface graining. 
To form a thin-plate coil by casting from molten aluminum to form an 
aluminum plate directly with use of twin rollers, as is performed in the 
method according to the present invention, thin-plate continuous casting 
techniques such as a Hunter method, a 3C method, etc., can be employed. 
Further methods of producing a thin-plate coil are disclosed in Japanese 
Patent Unexamined Publications Nos. Sho. 60-238001 and Sho. 60-240360. 
First, a thin plate having a thickness of 4 to 30 mm is formed through hot 
rolling, the thickness of the thin plate is reduced 60 to 95% through cold 
rolling, and then a heat treatment, cold rolling for finishing, and 
correction are performed on the thin plate to make the thin plate suitable 
as o a printing plate support. 
Another object of the present invention is the provision of a method for 
producing a support for a planographic printing plate in which variations 
in the quality of the material of the aluminum support are reduced to 
thereby improve the yield in the electrolytic graining treatment, which is 
excellent in its susceptibility to graining, produces no stripe 
irregularities, and is excellent in the external appearance. 
The foregoing object of the present invention can be achieved by a method 
for producing a support for a planographic printing plate in which, after 
molten aluminum is formed directly into an aluminum plate through 
continuous casting using a twin rollers, the aluminum plate is subjected 
to cold rolling, heat treatment and correction to thereby prepare an 
aluminum support, and the thus-prepared aluminum support is subjected to 
surface graining, characterized by the steps of: forming a thin plate of a 
thickness of 4 to 30 mm in the step of continuous casting, reducing the 
thickness of the thin plate by 60 to 95% in the step of cold rolling, 
annealing the thin plate at 260.degree. to 300.degree. C. for a time not 
shorter than 8 hours, and further reducing the thickness of the thin plate 
by 30 to 90% through finishing cold rolling. 
The above object of the invention is also achieved by a method for 
producing a support for a planographic printing plate in which, after 
molten aluminum is formed directly into an aluminum plate through 
continuous casting by using twin rollers, the aluminum plate is subjected 
to cold rolling, heat treatment and correction to thereby prepare an 
aluminum support, and the thus-prepared aluminum support is subjected to 
surface graining, characterized by the steps of: forming a thin plate of a 
thickness of 4 to 30 mm in the step of continuous casting, reducing the 
thickness of the thin plate to 0.3 mm to 3.0 mm in the step of cold 
rolling, performing two types of intermediate annealing on the 
thickness-reduced thin plate at 500.degree. C. to 660.degree. C. for 1 
second to 600 seconds and at 260.degree. C. to 300.degree. C. for 8 hours 
to 12 hours, and further reducing the thickness of the thin plate to 0.1 
mm to 1.0 mm. As in the previously described case, to form a thin-plate 
coil by casting from molten aluminum into the form of a plate directly 
with use of twin rollers, thin-plate continuous casting techniques such as 
a Hunter method, a 3C method, etc., can be used, as can the methods of 
producing a thin-plate coil disclosed in Japanese Patent Unexamined 
Publication Nos. Sho-60-238001 and Sho-60-240360, etc. 
First, a thin plate having a thickness of 4 to 30 mm is formed through hot 
rolling. Next, the thickness of the thin plate is reduced by 60 to 95% 
through cold rolling, the thin plate is annealed at 260.degree. to 
300.degree. C. for a time not shorter than 8 hours, then the thickness of 
the thin plate is finally reduced by 30 to 90% through the cold rolling 
again, and thereafter the thin plate is subjected to a correcting device 
to make the thin plate excellent in flatness. 
Alternatively, the thickness of the thin plate after continuous casting is 
reduced to 0.3 mm to 3.0 mm through cold rolling. The thin plate is then 
subjected to high temperature annealing at a temperature not lower than 
500.degree. C. for a 1 second to 600 seconds and low-temperature and 
long-time intermediate annealing at 260.degree. C. to 300.degree. C. for 8 
hours to 12 hours, and subjected to finishing cold rolling so that the 
thickness is reduced to 0.1 mm to 1 mm, and then subjected to a correction 
device. Either one of the two intermediate annealing conditions may be 
executed first, and rolling may be inserted between the two intermediate 
annealing conditions.

DESCRIPTIONS OF THE PREFERRED EMBODIMENTS 
A preferred embodiment of an aluminum support producing method in 
accordance with the present invention will be described more specifically 
with reference to the process schematic view of FIG. 1. Reference numeral 
1 designates a melting/holding furnace in which an ingot is melted and 
held. Molten aluminum is delivered from the furnace to a twin-roller 
continuous casting machine 2. That is, a hot-rolled thin-plate coil with a 
thickness of 4 to 30 mm is formed directly from the molten aluminum and 
taken up by a coiler 3. 
Thereafter, the thin plate is passed through a cold rolling mill 4, as 
shown in FIG. 2. Succeedingly, the thin plate is subjected to a heat 
treatment in the heat treatment step 5 depicted FIG. 3 under the condition 
that no recrystallization takes place in a region from the plate surface 
layer to a depth of at least 15 .mu.m in its thickness direction. In this 
case, the heat treatment may be performed after final rolling by again 
using the cold rolling mill 4. Thereafter, the material is subjected to a 
correction device 6 as shown in FIG. 4. The plate material thus obtained 
is subjected to a graining treatment. 
Considering the above process in more detail, it is necessary to hold the 
aluminum at a temperature not lower than the melting point thereof in the 
melting/holding furnace 1. The melting temperature varies according to the 
components of the aluminum alloy, but is generally 800.degree. C. or 
higher. 
Further, to suppress oxide of the molten aluminum and to remove alkaline 
metal impurities which are harmful to quality, there may be carried out 
inert gas purging, flux treatment, etc., if necessary. 
Then, casting is carried out using the twin-roller continuous casting 
machine 2. Although there are various casting methods available, the most 
commonly used methods in current industrially-running are a Hunter method, 
a 3C method, and the like. Although the casting temperature varies 
according to the system or the alloy, a temperature of about 700.degree. 
C. is generally used. In the case where a Hunter method or a 3C method is 
employed, rolling can be carried out between the twin rollers while the 
molten aluminum is solidified. Thereafter, the thickness of the aluminum 
is reduced through cold rolling, and the distribution of alloy components 
is made uniform through heat treatment. In this case, however, the state 
of the grained surface of the final product may sometimes become 
nonuniform. Accordingly, rolling is performed with the cold rolling mill 4 
so that the thickness of the continuously cast thin plate is reduced by 60 
to 95%. Thereafter, the heat treatment is performed under conditions such 
that no recrystallization takes place in a region from the surface to a 
depth of at least 15 .mu.m in the thickness direction of the plate. Cold 
rolling is performed again for finishing. 
Although the conditions for the heat treatment cannot be defined absolutely 
because they vary depending on the thickness of plate, it is generally 
suitable for the temperature to be in the range of 260.degree. to 
300.degree. C. in the case where the thickness of the plate is 0.4 to 0.7 
mm. In this case, there is no recrystallization in the surface portion to 
a depth 15 .mu.m or more. Then, correction is carried out by the 
correction device 6 to thereby impart a predetermined flatness to the 
resulting plate prior to its being grained. The correction may be carried 
out in conjunction with the final cold rolling step. 
As the method for graining the thin aluminum plate to form a support for a 
planographic printing plate in accordance with the present invention, 
there are available various methods such as mechanical graining, chemical 
graining, electrochemical graining and combinations thereof. 
With respect to the mechanical graining method, there are known, for 
example, a ball graining method, a wire graining method, a brush graining 
method, a solution honing method, etc. As for the electrochemical graining 
method, there is generally used an AC electrolytic etching method 
employing either an ordinary sinusoidal alternating current or an 
alternating current having a special waveform such as a square waveform, 
etc. Further, etching with caustic soda may be carried out as a 
pretreatment of the electrochemical graining. 
In the case of electrochemical graining, the surface is preferably grained 
with an aqueous solution mainly containing hydrochloric acid or nitric 
acid while applying an alternating current. A more detailed description 
will be given below. 
First, the aluminum support is alkali-etched. Examples of the preferred 
alkali agent include caustic soda, caustic potash, metasilicate soda, 
sodium carbonate, aluminate soda, gluconate soda, etc. The concentration, 
temperature and treatment time period are preferably selected to be 0.01 
to 20%, 20.degree. to 90.degree. C., and 5 seconds to 5 minutes, 
respectively. The preferred etching quantity is 0.1 to 5 g/m.sup.2. 
In the case of a support containing a particularly large amount of 
impurities, the etching quantity is preferably selected to be 0.01 to 1 
g/m.sup.2 (see Japanese Patent Unexamined Publication No. Hei-1-237197). 
De-smutting may be performed if necessary since alkali-insoluble smut may 
remain on the surface of the aluminum plate subjected to alkali-etching. 
The above-described pretreatment is followed by AC electrolytic etching in 
an electrolytic liquid mainly containing hydrochloric acid or nitric acid 
in the present invention. The frequency of the alternating electrolytic 
current is selected to be 0.1 to 100 Hz, more preferably, 0.1 to 1.0 or 10 
to 60 Hz. 
The solution concentration is selected to be 3 to 150 g/l, more preferably, 
5 to 50 g/l. The quantity of aluminum dissolution in the bath is selected 
to be not larger than 50 g/l, more preferably, 2 to 20 g/l. Although 
additives may be supplied if necessary, it becomes difficult to control 
the solution concentration and the like in the case of mass production. 
The current density is selected to be 5 to 100 A/dm.sup.2, more preferably, 
10 to 80 A/dm.sup.2. A suitable electric source waveform is selected in 
accordance with the components of the aluminum support to be used. 
Preferably, a special alternating waveform as described in U.S. Pat. No. 
4,087,341 (which corresponds to Japanese Patent Postexamination 
Publications Nos. Sho. 56-19280 and Sho-55-19191) is used as the waveform. 
Such waveform and solution conditions are selected suitably in accordance 
with the applied voltage and current, the quality required, the 
compositions of the aluminum support to be used, etc. 
The electrolytically grained is then immersed in an alkaline solution to 
thereby dissolve smuts. Although various kinds of alkali agents such as 
caustic soda can be used, it is preferable that the alkali treatment be 
performed in a very short time under the conditions of a pH of 10 or more, 
a temperature of 25.degree. to 60.degree. C., and an immersing period of 1 
to 10 sec. 
Then, the aluminum is immersed in a solution mainly containing sulfuric 
acid. As for the solution condition of sulfuric acid, there are preferred 
a concentration of 50 to 400 g/l, one-stage lower than the conventional 
case, and a temperature of 25.degree. to 65.degree. C. If the sulfuric 
acid concentration is not lower than 400 g/l or if the temperature is not 
lower than 65.degree. C., corrosion of the treating cells and the like 
becomes intense, and accordingly the electrochemically grained surface may 
be destroyed in the case of an aluminum alloy containing 0.3% or more of 
manganese. If etching is carried out in such a manner that the quantity of 
dissolution of the aluminum base is not smaller than 0.2 g/m.sup.2, 
durability during printing is lowered. Accordingly, the quantity of 
dissolution of the aluminum base is preferably selected to be not larger 
than 0.2 g/m.sup.2. An oxidized surface of the anode is preferably formed 
on the surface in an amount of 0.1 to 10 g/m.sup.2, preferably, in an 
amount of 0.3 to 5 g/m.sup.2. 
Although the anodic oxidation treatment conditions cannot be determined 
simply because it varies widely according to the electrolytic solution 
used, the electrolytic solution concentration, the solution temperature, 
the current density, the voltage and the electrolytic time are generally 
selected to be 1 to 80% by weight, 5.degree. to 70.degree. C., 0.5 to 60 
A/dm.sup.2, 1 to 100 V and 1 sec to 5 min, respectively. 
Because the thus-obtained grained aluminum plate coated with the oxidized 
surface of the anode is stable by itself and has an excellent hydrophilic 
property, a photosensitive film can be provided thereon directly. If 
necessary, a surface treatment can be further applied thereto. For 
example, a silicate layer made of alkali metal silicate as described above 
or an undercoat layer made of a hydrophilic polymer compound can be 
provided. The coating quantity of the undercoat layer is preferably 
selected to be 5 to 150 mg/m.sup.2. 
Subsequently, a photosensitive layer is provided on the aluminum support 
treated as described above. After plate making is performed through image 
exposure and development, the plate is set in a printer to start printing. 
EXAMPLES 
An aluminum plate material having a thickness of 7.3 mm was formed using a 
twin-roller continuous casting apparatus 2 as shown in FIG. 1, and then 
subjected to cold rolling through the cold rolling mill 4 so that the 
thickness thereof was reduced to 0.5 mm. Through the heat treatment device 
5, various samples in which the degree of recrystallization in the 
thickness direction was varied by suitably changing the condition of heat 
treatment as shown in Table 1 were obtained as an example of the present 
invention and comparative examples. With respect to the samples obtained 
in the example and comparative examples, observation was carried out on 
the crystal grain sizes in the section perpendicular to the casting 
direction as shown in FIG. 5. Comparative evaluation was carried out on 
samples which were subjected to cold rolling to 0.24 mm plate thickness 
after heat treatment with 0.5 mm plate thickness. 
TABLE 1 
______________________________________ 
Test State of Condition of 
No. Example Recrystallization 
Heat Treatment 
______________________________________ 
1 Example 1 Recrystallization 
280.degree. C., 10 hrs 
only in central 
portion 
2 Comparative No None 
Example 1 recrystallization 
3 Comparative Recrystallization 
600.degree. C., 1 hr 
Example 2 in entire 
thickness 
______________________________________ 
Each of the aluminum plates thus prepared was used as a support for a 
planographic printing plate as follows. The support was etched with an 
aqueous solution of 15% caustic soda at a temperature of 50.degree. C. 
with an etching quantity of 5 g/m.sup.2 and then washed with water. Then, 
the support was immersed in a solution of 150 g/l of sulfuric acid at 
50.degree. C. for 10 sec so as to be desmutted, and then was washed with 
water. Subsequently, in an aqueous solution of 16 g/l of nitric acid, the 
support was grained electrochemically using an alternating current as 
described in U.S. Pat. No. 4,081,341 (which corresponds to Japanese Patent 
Postexamination Publication No. Sho. 55-19191). An anode voltage V.sub.A 
=14 volts and a cathode voltage V.sub.c =12 volts were used as the 
electrolytic condition so that the quantity of electricity at the positive 
electrodes was selected to be 350 coulomb/dm.sup.2. An anode surface oxide 
coating of 2.5 g/m.sup.2 was formed on each of the supports in a 20% 
sulfuric acid, and then dried. 
Each of the substrate samples 1 to 5 thus prepared was coated with the 
following coating composition so that the weight of coating after drying 
was 2.0 g/m.sup.2 to thereby provide a photosensitive layer. 
______________________________________ 
Photosensitive Coating Compositions: 
______________________________________ 
N-(4-hydroxyphenyl) methacrylamide/2-hydroxyethyl 
5.0 g 
methacrylate/acrylonitrile/methyl methacrylate/ 
methacrylic acid (mole ratio 15:10:30:38:7) copolymer 
mean molecular weight 60000) . . . 
hexafluophosphate salt of a condensate of 
0.5 g 
4-diazophenylamine and formaldehyde . . . 
phosphorous acid . . . 0.05 g 
Victoria Pure Blue BOH (made by Hodogaya 
0.1 g 
Chemical Co., Ltd.) . . . 
2-methoxyethanol . . . 100.0 g 
______________________________________ 
Each of the photosensitive planographic printing plates thus prepared was 
exposed to a metal halide lamp of 3 kW at a distance of 1 m for 50 seconds 
through a transparent negative film in a vacuum printing frame, developed 
with a developing solution of the following composition and then gummed 
with an aqueous solution of gum arabic to thereby prepare a planographic 
printing plate. 
______________________________________ 
Developing Solution: 
______________________________________ 
Sodium sulfite. . . 5.0 g 
benzyl alcohol. . . 30.0 g 
sodium carbonate. . . 5.0 g 
isopropylnaphthalenesodiumsulfonate. . . 
12.0 g 
pure water. . . 1000.0 g 
______________________________________ 
Using the plenographic printing plates thus prepared, printing was 
performed in a general procedure. As a result, the data of Table 2 was 
obtained. 
TABLE 2 
______________________________________ 
Presence of 
Evaluation of 
Strip 
Test No. Printing Irregularities 
State of Pits 
______________________________________ 
1 good absent uniform 
2 poor present nonuniform 
3 poor present nonuniform 
______________________________________ 
With respect to the same samples as were subjected to the above-mentioned 
printing test, their surfaces grained before application of the 
photosensitive layer were observed with an electron microscope. It was 
found from the observation that Tests Nos. 2 and 3, which were classified 
as poor results in the printing test, had nonuniform pits formed in the 
graining process compared with the Test No. 1. 
As described above, the planographic printing plate produced by the support 
for a planographic printing plate producing method according to the 
present invention can improve the yield of electrolytic graining because 
variations in the quality of the aluminum support can be reduced. 
Furthermore, the planographic printing plate has excellent printing 
characteristics because it can be adapted to graining, and the 
planographic printing plate has no stripe irregularities and has an 
improved appearance. 
Further, the aluminum support producing process can be rationalized to 
thereby attain a reduction in the cost of raw materials. Particularly, the 
present invention greatly contributes to improvement in quality and 
reduction in cost of the support for a planographic printing plate. 
Another embodiment of the aluminum support producing method used in the 
present invention will be described more specifically again with reference 
to the process schematic view of FIG. 1. Reference numeral 1 designates a 
melting/holding furnace in which an ingot is melted and held. Molten 
aluminum is delivered from the furnace to a twin-roller continuous casting 
machine 2. That is, a hot-rolled thin-plate coil with a thickness of 4 to 
30 mm is formed directly from the molten aluminum and wound up by a coiler 
3. Thereafter, the thin plate is subjected to a cold rolling mill 4 to 
reduce the thickness thereof by 60 to 95%, succeedingly subjected to the 
heat treatment step 5 of FIG. 3 so as to be annealed at 260.degree. to 
300.degree. C. for a time not shorter than 8 hours, then subjected to 
final rolling through the cold rolling mill 4 again to thereby reduce the 
thickness by 30 to 90%, and thereafter the thin plate is subjected to the 
correction device 6. The thus-obtained plate material is subjected to a 
surface graining treatment. Although the heat treatment step of FIG. 3 is 
an example of the batch system, the invention is not limited to such an 
application, the coil material may be subjected to a heat treatment 
continuously using a gas furnace or so. 
As another method, the plate material can be subjected to the cold rolling 
mill 4 thereafter. After the cold rolling has been performed until the 
thickness of the material is reduced to 0.3 mm to 3.0 mm, the plate 
material is subjected to the heat treatment step illustrated in FIG. 3. In 
the heat treatment step, annealing at 500.degree. C. to 660.degree. C. for 
1 second to 600 seconds and annealing at 260.degree. C. to 300.degree. C. 
for 8 hours to 12 hours are carried out. Either annealing step may be 
carried out first. A step of rolling may be carried out between the two 
annealing steps. Further, either one of the two annealing steps may be 
carried out using a batch system and the other carried out using a 
continuous system. Thereafter, the plate material is subjected to the cold 
rolling mill 4 again as the final rolling step so that the thickness is 
reduced to a predetermined value of 0.1 mm to 1.0 mm. Subsequently, the 
plate material is subjected to the correction device 6 of FIG. 4. The 
thus-obtained plate material is subjected to surface graining. 
In more detail, it is necessary to hold the aluminum at a temperature not 
lower than the melting point thereof in the melting/holding furnace 1. The 
temperature varies according to the aluminum alloy components. The 
temperature is generally 800.degree. C. or more. 
Further, to suppress oxidation of the molten aluminum and to remove 
alkaline metals harmful to quality, there may be carried out inert gas 
purging, flux treatment, etc., if necessary. 
Then, casting is carried out using the twin-roller continuous casting 
machine 2. Although there are various casting methods available, the most 
commonly employed techniques are the Hunter method, the 3C method, etc. 
Although the casting temperature varies according to the system or the 
alloy, a temperature of about 700.degree. C. may be used. In the case 
where the Hunter method or the 3C method is employed, rolling can be 
carried out between the twin rollers while the molten aluminum is 
solidified. 
If the element distribution in section is observed using electronic probe 
microanalysis (hereinafter referred to as "EPMA") with respect to the 
plate material obtained in this stage, the element distribution will be 
found to be nonuniform in the thickness direction as well as in the 
widthwise direction, resulting in a disadvantage in that surface graining 
in the final product is nonuniform. Accordingly, the continuously cast 
plate material is rolled by the cold rolling mill 4 so that the thickness 
thereof is reduced by 60 to 95% or reduced to 0.1 mm to 1.0 mm. 
If the element analysis in the surface at this point of time is observed 
through EPMA, the thin plate will be found to have a shape elongated in 
the rolling direction so that the element analysis is nonuniform, and if 
the crystalline microstructure in the surface is observed, the crystal 
will be seen to have a shape elongated in the rolling direction, resulting 
in a disadvantage that stripe irregularities and streaking after treatment 
are generated. Accordingly, an annealing step is carried out at 
500.degree. C. to 660.degree. C. for 1 second to 600 seconds in order to 
make the crystalline grain size coincident, and another annealing step is 
carried out at 260.degree. C. to 300.degree. C. for 8 hours to 12 hours in 
order to make the element distribution uniform. Thereafter, the thickness 
of the plate material is reduced by 30% to 90% or reduced to 0.1 mm to 
1.0mm to thereby form a thin plate, and then the plate material is 
subjected to correction through the correction device 6. Other conditions 
may be as previously described. That is, the same techniques for casting, 
graining, etc., as previously described can be used. 
EXAMPLES 
Further examples according to the above-described embodiment will now be 
discussed. 
Example 2 
An aluminum plate material having a thickness of 7.3 mm was formed using a 
continuous casting apparatus 2 as shown in FIG. 1, and then subjected to 
cold rolling so that the thickness thereof was reduced to 0.5 mm. After 
annealing while varying the annealing conditions as shown in Table 3 
below, the plate material was further subjected to cold rolling so that 
the thickness was reduced to 0.24 mm to thereby form test materials. 
TABLE 3 
______________________________________ 
Plate thickness 
Conditions for 
Sample No. 
Example after annealing 
annealing 
______________________________________ 
1 Example 2 t = 0.5 mm 280.degree. C., 10 hrs 
2 Comparative t = 0.5 mm 280.degree. C., 1 hr 
Example 3 
3 Comparative t = 0.5 mm 600.degree. C., 10 hrs 
Example 4 
4 Comparative t = 3.5 min 280.degree. C., 10 hrs 
Example 5 
______________________________________ 
Each of the aluminum plates thus prepared was used as a support for a 
printing plate as follows. The support was etched with an aqueous solution 
of 15% caustic soda at 50.degree. C. with an etching quantity of 5 
g/m.sup.2, and then washed with water. The support was next immersed in a 
solution of 150 g/l of sulfuric acid at 50.degree. C. for 10 sec so as to 
be desmutted, and then was washed with water. 
Then, in an aqueous solution of 16 g/l of nitric acid, the support was 
grained electrochemically using an alternating current as described in 
U.S. Pat. No. 4,087,341 (which corresponds to Japanese Patent 
Postexamination Publication No. Sho. 55-19191). An anode voltage V.sub.A 
=14 volts and a cathode voltage V.sub.c =12 volts were used as 
electrolytic conditions, so that the quantity of electricity at positive 
electrodes was 350 coulomb/dm.sup.2. An anode surface oxide coating of 2.5 
g/m.sup.2 was formed on each of the supports in a 20% sulfuric acid, and 
then dried. 
Each of the substrate samples 1 to 5 thus prepared was coated with the same 
photosensitive composition as used in Example 1 so that the weight of 
coating after drying was be 2.0 g/m.sup.2 to thereby provide a 
photosensitive layer. 
Each of the photosensitive planographic printing plates thus prepared was 
exposed to a metal halide lamp of 3 kW at a distance of 1 m for 50 seconds 
through a transparent negative film in a vacuum printing frame, developed 
with a developing solution of the same type used in Example 1 above, and 
then gummed with an aqueous solution of gum arabic to thereby prepare a 
planographic printing plate. 
Using the planographic printing plates thus prepared, printing was 
performed in a general procedure. As a result, the data of Table 4 was 
obtained. 
TABLE 4 
______________________________________ 
Sample Evaluation Presence of stripe 
No. of Printing 
irregularities 
State of pits 
______________________________________ 
1 good absent uniform 
2 poor present nonuniform 
3 poor present nonuniform 
4 poor present nonuniform 
______________________________________ 
The same samples as subjected to the above-mentioned printing test with 
their surfaces grained before application of the photosensitive layer were 
observed with an electron microscope. It was found from the observation 
that Samples Nos. 2, 3 and 4, which were classified as poor results in the 
printing test had nonuniform pits formed in the graining process compared 
with Sample No. 1. 
Example 3 
By using such a continuous casting apparatus as shown in FIG. 1, an 
aluminum plate having a thickness of 7.3 mm was formed, subjected to cold 
rolling so that the plate thickness became 0.5 mm, then subjected to 
annealing in the annealing conditions shown in Table 5, and then subjected 
to finishing cold rolling so that the thickness became 0.24 mm to thereby 
prepare test materials. 
TABLE 5 
______________________________________ 
Sam- Plate Conditions 
Conditions 
ple thickness at 
of first of second 
No. Example annealing annealing annealing 
______________________________________ 
5 Example 3 t = 0.5 mm 
500.degree. C., 3 sec 
280.degree. C., 10 
hrs 
6 Comparative 
t = 0.5 mm 
500.degree. C., 3 sec 
None 
Example 4 
7 Comparative 
t = 0.5 mm 
280.degree. C., 10 hrs 
None 
Example 5 
8 Comparative 
t = 0.5 mm 
None None 
Example 6 
______________________________________ 
The thus-prepared aluminum plates were used as supports for planographic 
printing plates and subjected to surface graining under the same 
conditions as in the Example 2, and the substrates formed in the same 
manner as described above were subjected to appearance evaluation in order 
to judge the presence/absence of irregularities after treatment. Table 6 
shows the results of evaluation. 
______________________________________ 
Presence of 
irregularities on 
Sample No. 
Example treated surface 
______________________________________ 
5 Example 3 No irregularities 
6 Comparative Example 4 
Stripe irregularities 
7 Comparative Example 5 
No irregularities 
8 Comparative Example 6 
Stripe irregularities 
______________________________________ 
Further, in order to carry out streak severe evaluation testing, the same 
test materials as those of Table 5 were used and the materials were made 
to be in a state where streaking could easily occur. Streak appearance 
evaluation was carried out under such conditions. Table 7 shows the 
results of the evaluation. 
TABLE 7 
______________________________________ 
Presence of 
streaking on treated 
Sample No. 
Example surface 
______________________________________ 
5 Example 3 No streaks 
6 Comparative Example 4 
No streaks 
7 Comparative Example 5 
Streaks present 
8 Comparative Example 6 
Streaks present 
______________________________________ 
As seen in Tables 4, 6 and 7, the planographic printing plate using the 
support for planographic printing plate produced by the process according 
to the present invention can improve the yield of electrolytic graining 
because the variation in the quality of the aluminum support is reduced. 
Furthermore, the planographic printing plate produced according to the 
invention has excellent printing characteristics because o the support is 
well adapted for graining, and the planographic printing plate has no 
stripe irregularities and has an improved appearance. 
Further, there is attained an important effect that the aluminum support 
producing process can be rationalized to thereby attain a reduction in 
cost of raw materials. Particularly, the present invention greatly 
contributes to improvement in quality and reduction in cost of the support 
for a planographic printing plate.