Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
The present invention relates to a method of
electrolytic treatment on the surface of metal web with
..~ which the stability of graphite electrodes used in the
electrolytic treatment of a metal plate is remarkably
improved.
Examples of a method of applying an electrolytic
treatment to the surface of a metal member made of aluminum,
iron or the like are the plating method, the electrolytic
roughening method, the electrolytic etching method, the
anodic oxidation method, the electrolytic coloring method
and the electrolytic satin finishing method all wish have
been extensively employed in the art. DO sources, power
. . - mains ARC. sources, superposed-waveform current sources, and
lo thyristor-controlled special-waveform or square-wave ARC.
sources have been employed with these methods in order Jo
meet requirements of quality of the electrolytic treatment
or to improve the reaction efficiency. For instance,
. CA 1,093,009 discloses-a process in which
an ARC. is applied in the electrolytic treatment of an
aluminum plate with the voltage applied to the anode
electrode being higher than that applied to the cathode
electrode, whereby an aluminum
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1; substrate for lithographic printing whose surface is electroqra:Lned
satisfactorily is obtained. When using a regulated ARC.,
it is essential to employ electrodes which are
highly stable In general, platinum, tantalum, titanium,
iron, lead and graphite are employed as electrode materials.
Graphite electrodes are widely employed because they are
chemically relatively stable and are of low cost.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is an explanatory diagram schematically
showing an example of a conventional continuous electrolytic
treatment system;
Fig. 2 is a diagram showing current waveforms for
a description of the invention; and
Figs. 3, 4 and 5 are explanatory diagrams
schematically showing examples of continuous electrolytic
treatment systems for practicing an electrolytic treatment
method according to the invention.
Fig. 1 shows an example of a conventional
continuous electrolytic treatment system for metal webs
which utilizes graphite electrodes. In this system, a metal
web 1 is introduced into an electrolytic cell 4 while being
guided by a guide roll 2, and is conveyed horizontally
through the cell while being supported by a roll 3.
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l Finally, the web 1 is moved out of the cell passing around a
guide roll 5. The electrolytic cell 4 is divided by an
insulator 6 into two chambers in which graphite electrodes
are arranged on both sides of the metal web 1. A supply of
electrolytic solution 28 is stored in a tank 9. A pump 10
supplies the electrolytic solution 28 to electrolytic
solution supplying pipes 11 and 12 which debauch into the
electrolytic cell 4. The electrolytic solution thus
supplied covers the graphite electrodes 7 and 8 and the
metal web and then returns to the tank 9 through a
discharging pipe 13. A power source 14 connected to the
graphite electrodes 7 and 8 applies a voltage thereto. An
electrolytic treatment can be continuously applied to the
metal web 1 with this system.
The power source 14 may produce (1) direct
current, (2) symmetric alternate Kent waveform, I and (4) asymmetric
alternate current waveform, and (5) and I as~trlc scurvy
alternate current waveform as shown in Fig. 20 In general, in
such an ARC. waveform, the average value of the forward
I current In is not equal to the average value of the reverse
current If.
A graphite electrode is very stable when
used as a cathode electrode. however, when a graphite
electrode is used as an anode electrode J it is consumed in
the electrolytic solution, forming C02 by anode oxidation
and, at the same time, it decays due to erosion ox the
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l graphite inter layers, which occurs at a rat depending on
electrolytic conditions. When decay occurs, the current
distribution in the electrode changes so that the
electrolytic treatment becomes nonuniform. Therefore, the
occurrence of such a phenomenon should be avoided in a case
where the electrolytic treatment must be done with high
accuracy. Accordingly, it is necessary to replace the
electrodes periodically. This requirement is a drawback for
mass production, and is one of the factors which lowers
productivity.
An object of the invention is to provide an
electrolytic treatment method in which, based on the
properties of graphite, the electrodes are maintained
sufficiently stable even in an electrolytic treatment using
15~ an asymmetric waveform ARC
SUMMARY OF TIE INVENTION
The inventors have conducted intensive research
regarding ways to prevent the consumption of graphite
electrodes and found conditions exist under which graphite
. 20 electrodes employed in a system using asymmetric waveform
ARC. can be stabilized. Specifically, in the
electrolytic cell shown in Fig. 1, an asymmetric waveform
current yin If) as shown at (4) in Fig. 2 was used. The
forward terminal was connected to the electrode 7 and the
reverse terminal to the electrode 8. Under these
conditions, an electrolytic treatment was carried out by
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1 using a I Hal electrolytic bath with a current density of
50 Adam and a frequency of 60 Ho. In this case, the
graphite electrode 7 was consumed quickly, while when the
connection of the terminals was reversed, the electrode 8
was consumed but not the electrode 7. This means that, for
the use of an asymmetric waveform current, the graphite
electrode is consumed when Anode > Cathode and it is not
consumed when Anode Cathode where Anode is the current
i value in the periods in which the graphite electrode
electrochemically acts as an anode electrode and Cathode is
the current value in the periods in which the graphite
electrode electrochemically acts as a cathode electrode.
eased on this stabilization condition, the
inventors have developed a novel electrolytic treatment
method with which graphite electrodes can be maintained
stable with an asymmetric waveform current.
DESCRIPTION OF TIE PUFF RUED EMBODIMENTS
the invention will now be described in detail with
reference to preferred embodiments shown in Figs. 3, 4 and
5.
Fig. 3 is an explanatory diagram showing an
example of a continuous electrolytic treatment method for
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1 metal webs according to the invention. The parts (3)
through (6) of Fig. 2 show a variety of asymmetric waveforms
which may be employed with the invention.
First, a metal web 1 is passed through an
auxiliary electrolytic cell 15 by a guide roll 16~ and then
through an electrolytic cell 4 via pass rolls 17 and 18 and
a guide roll 2. In the electrolytic cell 4, the web 1 is
conveyed horizontally by a backing roll 3. Finally, the web
is moved out of the cell 4 by a roll 5.
-The auxiliary electrolytic cell has an auxiliary
electrode, namely, an insoluble anode electrode 20 which is
disposed confronting the metal web. The insoluble anode
electrode is made of platinum or lead. A pump 10 is used to
deliver the electrolytic solution 28 to an electrolytic
solution supplying pipe 19 which debauches into the
auxiliary electrolytic cell 15. The electrolytic solution
thus delivered covers the insoluble anode electrode 20 and
the metal web 1 in the cell 15/ and is then returned to the
tank 9 through a discharging pipe 21.
The electrolytic cell 4 is divided by an insulator
6 into two parts in which respective graphite electrodes 7
and 8 are disposed confronting the metal web 1. The pump 10
supplies the electrolytic solution from the tank g to
electrolytic solution supplying pips LO and 12 op^nlng unto
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1 the electrolytic cell 4. The electrolytic solution thus
supplied is returned through the discharging pipe 13 to the
tank 9. In general, the electrolytic solution circulating
system includes a heat exchanger and a filter so that the
temperature of the electrolytic solution is controlled
precisely and foreign matter is removed from the solution.
A power source 14 is provided to apply an
asymmetric alternate waveform current, for instance, having
a waveform as shown in parts (3) through (6) of Fig. 2, to
the electrolytic cell with the electrodes arranged as
described. The current waveform is such that In If and In
= If + a are maintained, where In is the forward current
value and If is the reverse current value. The positive
terminal of the power source 14 is connected to the graphite
electrode 7, and is further connected through a thruster or
diode 22 to the insoluble anode electrode 20 in the
auxiliary electrolytic cell I The negative terminal of
the power source is connected to the graphite electrode 8.
In the forward period (positive half cycle) of the
current flow, the current In is applied to both the graphite
electrode 7 and the insoluble anode electrode 20. The
current thus applied, which causes an anode reaction to
occur on the surfaces of these electrodes, flows through the
electrolytic solution to the metal web 1. At the same time
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1 a cathode reaction treatment occurs on the metal web
confronting the electrodes. The current Inn which flows in
the metal web due to electron conduction, is returned
through the electrolytic solution and the graphite electrode
8 to the power source 14. In this operation, the part of
the metal web 1 which confronts the electrode 8 is subjected
to an anode reaction treatment, while the surface of -the
electrode 8 is subjected to a cathode reaction treatment.
Assuming that the currents applied to the graphite
electrode 7 and the insoluble anode electrode 20 are
represented by In and I, respectively, then control is
carried out so as to satisfy the following condition:
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Such control may be achieved, if a thruster is employed, by
controlling its ON time, or in the case of a diode, by
inserting a variable resistor in its ` circuit.
Alternatively, control may be achieved by adjusting the
distance between the anode electrode 20 and the metal web 1,
or by adjusting the effective area of the anode electrode
20. Further, a separate electrolytic solution circulating
tank (not shown) or the auxiliary electrolytic cell 15 can
be provided so that the type of electrolytic solution and
parameters thereof including its temperature and density can
be varied.
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l In the reverse current period (negative half
cycle), the current If is supplied from the power source 14
to the graphite electrode 8, and is applied through the
electrolytic solution to the metal web l. In this
operation, an anode reaction treatment occurs on the surface
of the graphite electrode 8, while a cathode reaction
treatment occurs on the surface of the metal web l. The
current Inn which flows in the metal web by electron
conduction, is returned thrush the electrolytic solution
and the graphite electrode 7 Jo the power source 14. In
this operation, a cathode reaction treatment occurs on the
surface of the graphite electrode 7, while the part of the
metal web 1 confronting the graphite electrode 7 is
subjected to an anode reaction treatment. In the reverse
period, the current If does not flow to the anode electrode
20 due to the presence of the thruster or diode.
In the above-described electrolytic treatment
method according to the invention, the electrodes 7 and 8
are very stable, being free from oxidation
consumption. When the graphite electrode 7 acts as an anode
electrode, the current Anode there through is In and when
it acts as a cathode electrode, the current Cathode
there through is If. In this case, In = If n = In +
I, and > are established, and therefore In < In
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1 Accordingly, for the graphite electrode 7, Anode <
Cathode- Thus, the stabilization condition is satisfied.
On the other hand, when the graphite electrode 8 acts as an
anode electrode, the current Anode there through is Inn and
when it acts as a cathode electrode, the current Cathode
there through is In. That is, since If In is established,
the stabilization condition Anode < Cathode is maintained.
The auxiliary electrode 20 in the auxiliary electrolytic
cell 15 is always stable because it is an insoluble anode
electrode, and only an anode reaction occurs therewith.
In electrolytic treatment system shown in Figs. 4
and 5, in which figures those components which have been
described with reference to Fig. 3 are designated by the
same reference numerals, the insoluble anode electrode 20 is
positioned on one side of the metal web 1 opposite the side
on which the graphite electrodes 7 and 8 are disposed. In
this system, the electrodes are stable. However, an
electrolytic reaction also occurs on the rear side of the
metal web, thus forming a film thereon. This phenomenon is
undesirable. Furthermore, as a part of the current flows to
the rear surface, the reaction efficiency is lowered as
much. Thus, the employment of these systems may not be
economical for some applications, and accordingly, the
system shown in Fig. 3 is usually preferable.
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