Electrolytic treatment apparatus

An electrolytic treatment apparatus is provided in which one or more electrolyte discharge outlets and one or more electrolyte supply inlets are provided between main counter electrodes so that the concentration and temperature of the electrolytic treatment solution at the the inlets and at the outlets can be made close to one another. As a result, uniformity and fineness in grains can be maintained, electrolysis efficiency can be raised, and the production speed can be improved.

BACKGROUND OF THE INVENTION 
The present invention relates to an electrolytic treatment apparatus 
suitable for providing a rough surface on a metal web by using an AC 
current, and particularly relates to an electrolytic treatment apparatus 
for producing a printing-plate support constituted by a rough-surfaced 
aluminum plate to be used as a offset printing plate. 
Aluminum plates have been used as printing-plate supports, particularly, as 
planographic printing plate supports. Such aluminum plates have been 
diversified from an aluminum plate formed of substantially pure aluminum 
to an aluminum plate in which manganese is added to increase the strength 
of the aluminum plate corresponding to different user applications. 
In order to use an aluminum plate as a planographic printing plate support, 
it is necessary that the aluminum plate have a proper adhesion property to 
a photosensitive material and a proper water-retention property. 
To this end, it is necessary to make the surface of an aluminum plate rough 
so that the aluminum plate has a uniformly and finely grained surface. 
This surface-roughing treatment greatly affects the printing performance, 
such as anti-stain performance, of a plate material printing. Accordingly, 
the quality of the surface-roughing treatment has been an important factor 
in producing plate materials. 
As a method of performing surface-roughing on an aluminum printing-plate 
support, it is possible to use one of a mechanical graining method, an 
electrochemical graining method, or to use those graining methods in 
combination. 
As a mechanical graining method, there are, for example, a ball graining 
method, a wire graining method, a brush graining method, a liquid horning 
method, and the like. As an electrochemical graining method, on the other 
hand, an AC electrolytic etching method has been generally employed. In 
this case, an electric current of an ordinary sinusoidal waveform, or a 
special waveform, such as a square waveform, has been used. Further, as 
pre-treatment for the foregoing electrochemical graining, a chemical 
etching treatment or oil removing treatment with alkaline solution such as 
sodium hydroxide or sodium silicate may be performed. 
In the AC electrolytic etching method among the foregoing methods, however, 
there has been a problem in that counter electrodes of carbon, metal, or 
the like are very easily deteriorated. For example, in the case of using 
counter electrodes of carbon, deterioration of a binder is significant 
because oxidation and reduction are repeated every time the polarity 
changes, and therefore it has been very difficult to perform a stable 
operation for a long time. 
In order to solve the problems, Japanese Patent Examined Publication No. 
Sho. 61-48596 discloses an electrolytic treatment apparatus which is 
characterized in that a circuit for an auxiliary counter electrode is 
connected in parallel to a circuit connected to main counter electrodes, 
and a diode for controlling an anode current flowing in the main counter 
electrodes, or a mechanism functioning as such a diode, are provided in 
the circuit for the auxiliary counter electrode. The electrolytic 
treatment apparatus has such a configuration as shown in FIG. 2, in which 
a metal web 1, that is, a material to be treated, is supported on the 
circumference of a radial drum roller 2, and a clearance between the metal 
web 1 and each of the main counter electrodes 3a and 3b disposed in 
opposition to the metal web 1 is filled with an electrolytic treatment 
solution 5 containing metal ions in a manner so that the electrolytic 
treatment solution 5 is supplemented from an electrolyte supply inlet 4 
and discharged from an electrolyte discharge outlet 6 to thereby form an 
electrolyte path 15. An AC current is supplied through electrolyte path 15 
from an AC power source to the main counter electrodes 3a and 3b so as to 
perform electrochemical treatment. The counter electrodes opposed to the 
metal web 1 are constituted by the main counter electrodes 3a and 3b and 
the auxiliary counter electrode 8; a circuit for the auxiliary counter 
electrodes 8 and a circuit for making an anode current flow into the main 
counter electrodes are connected in parallel to a circuit connected to the 
main counter electrodes 3a and 3b, and a diode 9 for controlling the anode 
current flowing in the main counter electrodes or a mechanism functioning 
as such a diode is provided in the circuit for the auxiliary counter 
electrode 8 so that currents are made to flow in those circuits. 
In this case, the main counter electrodes 3a and 3b are connected to 
opposite sides of the AC power source 7 so as to have polarities which are 
different from each other. Further, each of the main counter electrodes 3a 
and 3b is constituted by a large number of small electrodes (3a.sub.1, 
3a.sub.2, 3a.sub.3, . . . , 3a.sub.n,), (3b.sub.1, 3b.sub.2, 3b.sub.3, . . 
. , 3b.sub.n,) (for example, n=10 to 24), each separated from adjacent 
ones through insulators 10 so as to raise the current efficiency. 
In the conventional electrolytic treatment apparatus, however, there has 
been a problem in that the electrolytic treatment solution 5 supplemented 
from the electrolyte supply inlet 4 passes through the narrow electrolyte 
path 15 between the metal web 1 and each of the electrodes 3a and 3b, and 
flows into the opposite side of the radial drum roller 2 supply inlet 4 so 
as to come out the path 15 to the electrolyte discharge outlet 6. This 
result is that the electrolytic treatment solution gradually fatigues 
because of electrolysis in the flow path and a component difference is 
caused between the electrolytic treatment solution at the electrolyte 
supply inlet 4 and that at the electrolyte discharge outlet 6. This makes 
it impossible to obtain satisfactory electrolysis efficiency as the whole 
with the electrolytic treatment apparatus. 
Further, a difference between the temperature at the electrolyte supply 
inlet 4 and that at the electrolyte discharge outlet 6 increases in the 
vicinity of the metal web so that it is impossible to obtain a desired 
grained surface. 
In the electrolyte path 15, the treatment solution at the metal web 1 side 
is not sufficiently mixed with the treatment solution at the side of the 
counter electrodes 3a and 3b so that the difference in degree of fatigue 
of the component of the treatment solution between at the metal web side 
and the counter electrodes side, as well as the temperature difference 
therebetween, are significant. As a result, unevenness is caused in 
graining, that is, the electrolytic quality is lowered and the 
electrolysis efficiency is reduced. 
In order to raise the electrolysis efficiency while maintaining uniform and 
fine grain, therefore, a method has been used in which the flow rate of 
the treatment solution supplied from the electrolyte supply inlet 4 is 
increased. In this method, however, the increase in supply of the 
treatment solution not only causes an increase in cost, but also brings 
about no sufficiently desirable grain even if the rate of flow of 
treatment solution is increased. 
The foregoing problems become significant when the length of electrolytic 
treatment is prolonged corresponding to a rise of the line speed, so that 
there has been a significant limit in increasing the line speed. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to solve the foregoing 
problems in the prior art and to thereby provide an electrolytic treatment 
apparatus in which graining is uniformly and finely performed, and which 
offers better electrolysis efficiency and is effective in increasing the 
line speed. 
That is, the above object of the present invention can be achieved by an 
electrolytic treatment apparatus for performing electrolytic treatment 
continuously on a metal web in an electrolytic treatment solution 
containing metal ions while supplying an AC current across the metal web 
and counter electrodes, characterized in that one or more electrolyte 
discharge outlets and one or more electrolyte supply inlets are provided 
between main counter electrodes. 
The provision of one or more electrolyte discharge outlets and one or more 
electrolyte supply inlets between the main counter electrodes according to 
the present invention includes, for example, the provision of one 
electrolyte discharge outlet and three electrolyte supply inlets, the 
provision of two electrolyte discharge outlets and three electrolyte 
supply inlets, and, of course the provision of electrolyte discharge 
outlets and electrolyte supply inlets which are equal in number to each 
other. 
By the provision of one or more electrolyte discharge outlets and one or 
more electrolyte supply inlets between the main counter electrodes 
according to the present invention, the flowing-in/out quantity of the 
electrolyte treatment solution in the electrolyte path increases. 
Accordingly, even if the original quality of electrolyte treatment 
solution is fixed, supplied, and discharged while being circulated, the 
surface of the metal web existing in the electrolyte path has many 
opportunities to contact fresh electrolyte treatment solution by mixing 
and agitating the electrolyte treatment solution during the circulation in 
comparison with the conventional apparatus. As a result, the grain is made 
uniform and fine, and the electrolysis efficiency is improved. Further, if 
fresh electrolyte treatment solution is added to the electrolyte treatment 
solution to be supplied, it is possible to significantly promote the 
electrolyte reaction. 
Moreover, by the provision of the electrolyte discharge outlets and 
electrolyte supply inlets, the length of the electrolyte path therebetween 
is shortened so that the resistance of the path against the flow of 
solution can be reduced, and the rate of flow of the treatment solution in 
the path can be made large in comparison with the conventional apparatus 
to thereby make it possible to further promote the electrolytic reaction. 
As a result, the grain formed by electrolytic surface-roughing can be made 
uniform and fine to raise the electrolysis efficiency of the electrolyte 
treatment apparatus to thereby make it possible to increase the production 
speed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the accompanying drawings, an embodiment of the present 
invention will be described hereunder. 
FIG. 1 shows an embodiment of the electrolytic treatment apparatus 
according to the present invention. Reference numeral 1 designates a metal 
web, and reference numeral 2 designates a radial drum roller for 
supporting the web 1. The metal web 1 is running while keeping a fixed 
clearance between the metal web 1 and each of main counter electrodes 3a 
and 3b and an auxiliary counter electrode 8. Usually, it is suitable to 
select the clearance to be about 3-50 mm. The charging rate of the main 
counter electrodes to the auxiliary counter electrode varies in accordance 
with required electrolytic etching conditions. Reference numeral 7 
designates an AC power source. Usually, an AC power source having a 
frequency of 0.1 -500 Hz is used as the AC power source 7. Although the 
frequency is changed in accordance with a required etching mode, 
deterioration of the main counter electrodes 3a and 3b is large if the 
frequency is detected to be not higher than 15 Hz, and is remarkably large 
particularly in case of carbon electrodes. As the waveform, although 
various waveforms can be used, it is also possible to use a special 
alternating waveform as described in Japanese Patent Examined Publications 
No. Sho. 56-19280 and Sho. 55-19191. Reference numeral 9 designates a 
diode for controlling a current flowing in the auxiliary counter electrode 
8. As the material of the auxiliary counter electrode 8, it is preferable 
to use platinum or ferrite which is durable against deterioration. 
According to the present invention, an electrolyte supply inlet 4b is 
provided at the boundary between the main counter electrodes 3a and 3b in 
addition to, for example, a conventional electrolyte supply inlet 4a. 
An electrolytic treatment solution 5 comes into the electrolyte supply 
inlets 4a and 4b, comes further into respective cavities 13 so as to be 
distributed uniformly over the whole in the direction of width of the 
radial drum roller 2, through corresponding distributors 12, and then is 
injected into an electrolyte path 15 through corresponding slits 14. 
Although description has been made as to the case where an electrolyte 
supply inlet is provided between the counter electrodes in FIG. 1, one or 
more electrolyte supply inlets may be provided between the counter 
electrodes, and the position and structure of the electrolyte supply inlet 
are not limited to this embodiment. 
According to the present invention, an electrolyte discharge outlet 6a is 
provided in front of the electrolyte supply inlet 4b corresponding to the 
electrolyte supply inlet 4a in addition, for example, to the conventional 
electrolyte discharge outlet 6. 
In the electrolyte discharge outlet 6a, the electrolytic treatment solution 
5 comes into a cavity 16 fully extended in the widthwise direction from 
the electrolyte path 15 so as to be discharged collectively through a 
discharge pipe 17. 
Although description has been made as to the case where the electrolyte 
discharge outlets correspond to the electrolyte supply inlets in FIG. 1, 
it is not necessary that the number of electrolyte supply inlets be made 
equal to that of electrolyte discharge outlets. The electrolytic treatment 
solution supplied through a large number of supply inlets may be 
collectively discharged through one discharge outlet or through a 
plurality of discharge outlets. The important point is that the 
flowing-in/out quantity of the electrolytic treatment solution is 
increased by providing one or more electrolyte discharge outlets and one 
or more electrolyte supply inlets. 
By the provision of one or more electrolyte discharge outlets and one or 
more electrolyte supply inlets, it is possible to increase the 
flowing-in/out quantity of the electrolyte treatment solution to thereby 
make it possible to realize uniformity in concentration and temperature of 
the electrolytic treatment solution owing to natural mixing and agitation 
of the electrolytic treatment solution, the uniformity in concentration 
and temperature of the electrolytic treatment solution being in contact 
with the metal web, the refreshment of the electrolytic treatment 
solution, and the temperature rising of the electrolytic treatment 
solution. As a result, it is possible to realize uniform and fine grains 
and to improve electrolysis efficiency to thereby increase the line speed. 
EXAMPLE-1 
By using such an apparatus as illustrated in FIG. 1, the electrolytic 
treatment solution was supplied at 3000 l/min in sum, that is, at 2500 
l/min through the electrolyte supply inlet 4a, and at 500 l/min through 
the electrolyte supply inlet 4b, while the electrolytic treatment solution 
was discharged at 800 l/min through the electrolyte discharge outlet 6a 
and at 2200 l/min through the electrolyte discharge outlet 6b. 
The conditions at this time were as follows: 
______________________________________ 
Main counter electrodes carbon 
Auxiliary counter electrode 
platinum 
Clearance between web and 
10 mm 
counter electrodes 
______________________________________ 
Conditions of the electrolytic treatment solution at the main electrodes: 
______________________________________ 
treatment solution nitric acid 
concentration 50 g/l 
temperature 60.degree. C. 
______________________________________ 
Conditions of the electrolytic treatment solution at the auxiliary 
electrode: 
______________________________________ 
treatment solution nitric acid 
concentration 50 g/l 
temperature 20.degree. C. 
Web width 1000 mm 
Treatment speed 15 m/min 
Frequency 100 Hz 
______________________________________ 
When graining was performed under the foregoing conditions, the outlet 
nitric acid concentration in the vicinity of the metal web was 48 g/l 
while the inlet nitric acid concentration of 50 g/l, and the outlet 
temperature in the vicinity of the metal web was 62.degree. C. while the 
inlet temperature of 60.degree. C., so that uniform and fine graining 
could be performed and the electrolysis efficiency could be raised. 
COMATIVE EXAMPLE-1 
By using the apparatus of FIG. 2, treatment was performed under the same 
conditions as that in the Example-1. The upper limit of the rate of supply 
of the electrolytic treatment solution was 2500 l/min, and the inlet 
nitric acid concentration of 50 g/l was reduced to 40 g/l at the outlet in 
the vicinity of a metal web because the electrolytic treatment solution 
could not be uniformly mixed. Further, the outlet temperature in the 
vicinity of the metal web was 68.degree. C. while the inlet temperature 
was 60.degree. C. As a result, the products became non-conforming ones 
because of uneven grains. 
As seen from the foregoing example, according to the present invention, one 
or more electrolyte discharge outlets and one or more electrode supply 
inlets are provided between the main counter electrodes so that the 
concentration and temperature of the electrolytic treatment solution at 
the inlets and at the outlets can be made close to each other. As a 
result, uniformity and fineness in grains can be maintained and 
electrolysis efficiency can be raised to thereby make it possible to 
improve the production speed. As a result, the present invention improves 
quality and reduces the cost of products.