JP3398601B2 - Method for producing aluminum electrode foil for electrolytic capacitor and etching apparatus used for the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an aluminum electrode foil for an electrolytic capacitor and an etching apparatus used for the same, and particularly to a method for producing an aluminum electrode foil for an electrolytic capacitor which can be suitably used for an electrolytic capacitor for low voltage. And an etching apparatus used therefor.

[0002]

2. Description of the Related Art Aluminum electrolytic capacitors are required to be smaller and smaller in size with the recent miniaturization of electronic devices. In order to downsize an aluminum electrolytic capacitor, it is necessary to increase the capacitance per unit area of the aluminum electrode foil used for it, and with such a configuration, resource saving and raw material cost Will be reduced.

Therefore, conventionally, in order to increase the capacitance per unit area of the aluminum electrode foil, the aluminum foil is immersed in an acidic aqueous solution and chemically or electrically etched to form a surface of the aluminum foil. A method of increasing the surface area by roughening the surface is used.

When such etching is performed, the surface area of the aluminum foil is generally increased and the electrostatic capacity is increased, but the mechanical strength of the aluminum foil itself becomes weaker as the etching proceeds. Therefore, it is necessary to increase the surface area while maintaining the strength of the foil by controlling the location and shape of the etch pit formed by adjusting the applied voltage and the like.

In particular, in the production of an electrode foil for an aluminum electrolytic capacitor for low voltage, a method of applying an AC voltage to perform etching has been conventionally used to form fine pits.

FIG. 5 shows a conventional method of manufacturing an electrode foil for a low voltage aluminum electrolytic capacitor. Etching tank 1
Contains an acidic aqueous solution 3 containing hydrochloric acid as a main component as an etching solution.

The strip-shaped aluminum foil 2 is conveyed in the direction of arrow A through the roller 4 and passes through the acidic aqueous solution 3. Electrode plates 5a to 5d for power supply are provided on the inlet side and the outlet side of the etching tank 1 through the aluminum foil 2, and when an AC voltage is applied, the space between the electrode plates 5a and 5b and the electrode plate 5c is provided. , 5d is subjected to etching treatment.

When the etching treatment is performed, a large number of cubic fine pits connected in a cluster form from the surface to the inside of the aluminum foil 2 are formed, and finally, as a whole, a sponge-like porous pit is formed. It becomes a structure.
At this time, the core is left at the center of the foil to ensure the mechanical strength. Ideally, the pits have a high density and are uniform, and the deviation of the pit diameter is small.

[0009]

In the conventional etching method described above, initially, hydrogen ions at the pit tip end are concentrated due to the formation of aluminum ion complex ions at the pit tip end, and aluminum is easily dissolved. Therefore, pits are formed in the depth direction in accordance with the etching loss, and the surface area increases.

However, as the etching progresses, the concentration of aluminum ions in the pits increases at a rate controlled by the diffusion from the inside of the foil toward the surface, and the reaction resistance increases conversely. It becomes difficult to form hepits.

Therefore, there is a problem that the vicinity of the surface is gradually excessively etched, the already formed porous structure is destroyed, and the capacity per etching loss decreases.

In order to solve this problem, a method of adjusting the applied voltage as the etching progresses has been taken, but the hydrogen ion concentration of the etching solution is not sufficiently controlled and is ideal. It was not set to a proper state.

As one of the methods for solving such a problem, there has been proposed a method of adding an additive to the acidic aqueous solution 3 to suppress excessive etching. As the additive, an acid other than hydrochloric acid which is contained in the acidic aqueous solution 3 in advance, such as sulfuric acid, is used, and a film is formed on the surface of the aluminum foil 2 by anions generated by dissociation of the acid added as the additive. It creates a state that is difficult to be etched and suppresses overetching.

However, since the acidic aqueous solution 3 contains hydrochloric acid in advance, when the hydrogen ion concentration of this acidic aqueous solution 3 is high, the acid added as an additive is less likely to dissociate and its effect is exhibited. There was a problem that it became difficult. Further, in an acidic aqueous solution having a low hydrogen ion concentration, although the effect of the additive is likely to appear, it is difficult to increase the etching rate, and there is a problem that it is impossible to increase the surface area and increase the capacitance. .

As described above, in the conventional etching method of the aluminum foil 2, the applied voltage or the like is controlled to adjust the pit formation position or the like, or the additive is added to the acidic aqueous solution 3 to adjust the etching state. But
No setting was made considering the relationship between the hydrogen ion concentration and the progress of etching in the depth direction, and the relationship between the hydrogen ion concentration and the passivation property of the additive.
Therefore, it was not possible to manufacture an aluminum electrode foil for an electrolytic capacitor that suppresses excessive etching near the surface of the aluminum foil 2 to prevent the destruction of the porous structure and has a high capacitance per unit area.

The present invention solves the above problems and provides a method of manufacturing an aluminum electrode foil for an electrolytic capacitor having a high electrostatic capacity per unit area, and an etching apparatus used for the method.

[0017]

The method for producing an aluminum electrode foil for an electrolytic capacitor according to the present invention is characterized by individually controlling the hydrogen ion concentration of an acidic aqueous solution used as an etching solution.

According to the present invention, it is possible to obtain an electrolytic capacitor aluminum foil which suppresses excessive etching and has a high capacitance per unit area. Further, the etching apparatus of the present invention is characterized in that the etching tank is provided with a control means for controlling the hydrogen ion concentration of the acidic aqueous solution.

According to this invention, an electrolytic capacitor aluminum foil having a high electrostatic capacity per unit area can be easily and stably produced.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing an aluminum electrode foil for an electrolytic capacitor according to claim 1 is such that the aluminum foil is poured into an etching bath containing an acidic aqueous solution, and a voltage is applied to the aluminum foil to perform etching. When manufacturing aluminum electrode foil for electrolytic capacitors by forming pits on the foil, a plurality of etching tanks are provided, and the aluminum foil sequentially passes through the plurality of etching tanks,
It is characterized in that each hydrogen ion concentration of the acidic aqueous solution contained in the etching tank is independently controlled in each etching tank to perform etching.

According to this structure, the gradient of the hydrogen ion concentration inside the pit can be controlled by independently controlling the hydrogen ion concentration of the acidic aqueous solution in each etching tank.
Pits can be formed at any position in the depth direction.

According to a second aspect of the present invention, in the method for producing an aluminum electrode foil for an electrolytic capacitor according to the first aspect, the hydrogen ion concentration of the etching bath through which the aluminum foil passes is set so that the hydrogen ion concentration of the etching bath in the preceding step is relative to the traveling direction of the aluminum foil. It is characterized in that the hydrogen ion concentration is controlled to be equal to or higher than the hydrogen ion concentration of the etching tank in the subsequent step.

According to this structure, it is possible to suppress excessive etching near the surface of the aluminum foil even if the amount of etching reduction is increased, and therefore it is possible to further increase the capacitance per unit area.

According to a third aspect of the present invention, in the method for producing an aluminum electrode foil for an electrolytic capacitor according to the first or second aspect, the hydrogen ion concentration is controlled by supplying and discharging an acidic aqueous solution independently in each etching tank. It is characterized by performing.

According to this structure, the hydrogen ion concentration of the acidic aqueous solution in each etching tank can be easily adjusted. The method for producing an aluminum electrode foil for an electrolytic capacitor according to claim 4 is the method according to claim 1 or 2, wherein the hydrogen ion concentration is controlled by supplying an acidic aqueous solution to an etching tank in the final step with respect to the traveling direction of the aluminum foil. Then, the etching bath of the front process is sequentially overflowed, and at the same time, an acidic aqueous solution having a higher hydrogen ion concentration than the acidic aqueous solution of the subsequent process is additionally supplied to the etching bath of the previous process.

According to this structure, the hydrogen ion concentration of the acidic aqueous solution in each tank can be easily adjusted, and the amount of the acidic aqueous solution used can be reduced, which is economical.

A method of manufacturing an aluminum electrode foil for an electrolytic capacitor according to claim 5 is characterized in that, in any one of claims 1 to 4, hydrochloric acid is used as the acidic aqueous solution to control the hydrogen ion concentration. .

According to this structure, since the hydrogen ion concentration can be controlled without impairing the etching property, it becomes easy to advance the pits in the depth direction of the foil. The method for producing an aluminum electrode foil for an electrolytic capacitor according to claim 6 is the method according to any one of claims 1 to 4, wherein the acidic aqueous solution contains hydrochloric acid as a main component, and sulfuric acid as an additive.
It is characterized in that the hydrogen ion concentration is controlled by using an acidic aqueous solution to which at least one acid selected from oxalic acid and phosphoric acid is added.

According to this structure, since the passivation property of the additive can be controlled by changing the hydrogen ion concentration of the etching solution, the effect of the additive suppressing excessive etching can be sufficiently obtained. Therefore, excessive etching near the surface of the aluminum foil can be suppressed, and the capacitance per unit area can be increased.

An aluminum electrode foil for an electrolytic capacitor according to a seventh aspect is characterized by being manufactured by the method according to any one of the first to sixth aspects. According to this structure, an aluminum electrode foil having a large surface area and a large electrostatic capacity can be obtained, so that it can be suitably used especially for an electrolytic capacitor for low voltage, and it is also effective for downsizing of the capacitor.

In the etching apparatus according to the present invention, an aluminum foil is poured into an etching bath containing an acidic aqueous solution, a voltage is applied to the aluminum foil to perform etching, and pits are formed on the aluminum foil for electrolytic capacitors. An etching apparatus for manufacturing an electrode foil, wherein a sensor for detecting hydrogen ion concentration is provided in the etching tank, and flow rate adjusting means for increasing or decreasing the amount of acidic aqueous solution supplied to the etching tank is provided, and the sensor is detected. A control device for controlling the hydrogen ion concentration in the etching tank by feedback to a controller for controlling the flow rate adjusting means based on the hydrogen ion concentration is provided.

According to this structure, the change in the hydrogen ion concentration of the acidic aqueous solution in the etching tank due to the etching can be detected by the sensor for detecting the hydrogen ion concentration, and the controller can immediately adjust the amount of the acidic aqueous solution additionally supplied to the etching tank. The hydrogen ion concentration of the acidic aqueous solution in the etching tank can be kept constant at any set value. Therefore, a foil having stable characteristics can be manufactured all the time.

According to a ninth aspect of the present invention, in the etching apparatus according to the eighth aspect, the controller controls the hydrogen ion concentration of the etching tank of the previous step to be higher than the hydrogen ion concentration of the etching tank of the subsequent step with respect to the traveling direction of the aluminum foil. It is characterized in that it is configured to control so as to be equal or higher.

According to this structure, even if the amount of etching reduction is increased, it is possible to suppress excessive etching near the surface of the aluminum foil, and it is possible to consistently produce a foil having an increased capacitance per unit area.

Each embodiment of the present invention will be described below. (Embodiment 1) FIGS. 1 and 2 show (Embodiment 1) of the present invention.

Although the structure is almost the same as that of the conventional example shown in FIG. 5, in this (Embodiment 1), a plurality of etching tanks 1 are provided and the hydrogen ion concentration of the acidic aqueous solution 3 contained in the etching tank 1 is They differ in that they are individually controlled.

Specifically, as shown in FIG. 1, a plurality of etching tanks 1a-1c are provided. Etching tank 1
An acidic aqueous solution 3 containing hydrochloric acid as a main component is placed as an etching solution in a to 1c.

The strip-shaped aluminum foil 2 is conveyed in the direction of arrow A through the roller 4 and sequentially passes through the acidic aqueous solution 3 contained in the etching tanks 1a to 1c. Electrodes 5a to 5 for power supply are provided on the inlet side and the outlet side of the respective etching tanks 1a to 1c via the aluminum foil 2 passing therethrough.
1 is provided, and when an AC voltage is applied, the aluminum foil 2 passing between the respective electrode plates is subjected to etching treatment.

By the way, as described above, the aluminum foil 2
Since the porous structure is easily destroyed due to excessive etching from the vicinity of the surface as the etching magnification increases, the etching tank 1 uses an acid other than hydrochloric acid, which is previously contained in the acidic aqueous solution, as an additive in the etching tank 1 in the direction of arrow A. The method of adding is effective.

Examples of the acid added as an additive include sulfuric acid, oxalic acid, phosphoric acid and the like, and at least one acid selected from these acids is added. When an acid other than hydrochloric acid is added as an additive to an acidic aqueous solution, its anions form a film on the surface of the aluminum foil to create a state in which it is difficult to etch, but dissociation of the acid added as an additive is generally The lower the hydrogen ion concentration, the greater the acid dissociation. That is, the effect of the additive strongly appears in the tank where the hydrogen ion concentration of the acidic aqueous solution is low, making it difficult to etch, and conversely, the tank where the hydrogen ion concentration is high becomes easy to etch.

Therefore, in this (Embodiment 1), the hydrogen ion concentration in each of the etching tanks 1a to 1c is controlled so that each hydrogen ion concentration of the acidic aqueous solution 3 contained in the etching tanks 1a to 1c can be independently controlled. Control means were provided.

That is, as shown in FIG. 2, each etching tank 1a-1c is provided with a sensor 7 for detecting the hydrogen ion concentration, and valves 8a, 8b as flow rate adjusting means for increasing / decreasing the amount of the acidic aqueous solution supplied. Was set up. In FIG. 2, the power supply boards 5a to 5l are omitted.

The etching baths 1a to 1c are controlled by the sensor 7.
When the hydrogen ion concentration of the acidic aqueous solution 3 is detected, it is fed back to the controller 9 that controls the valves 8a and 8b based on the detected hydrogen ion concentration. The controller sets the hydrogen ion concentration of the etching tanks 1a to 1c in the direction of arrow A so that the hydrogen ion concentration of the etching tank of the previous step is equal to or higher than the hydrogen ion concentration of the etching tank of the subsequent step. To control.

Since the hydrogen ion concentration of the acidic aqueous solution 3 in each of the etching tanks 1a to 1c decreases with the passage of the aluminum foil 2, an acidic aqueous solution having a concentration higher than that of the acidic aqueous solution having a reduced hydrogen ion concentration, or Add hydrochloric acid as a component from the arrow B side, and at the same time increase the volume increase with arrow C.
It is necessary to keep the hydrogen ion concentration constant while discharging in the direction. The flow rate adjustment at this time is performed by the valves 8a and 8b.

With such a structure, as the process progresses, acids added other than hydrochloric acid are easily dissociated, and a passivation film is easily formed, so that excessive etching near the surface of the aluminum foil 2 is suppressed. , The capacity per weight loss can be increased without destroying the porous structure.

If an AC voltage is applied during etching, minute pits can be formed on the surface of the aluminum foil 2 and the capacitance can be increased. It can be preferably used.

Since the aluminum foil for electrolytic capacitors manufactured as described above has a large surface area per weight loss and a large capacitance, it is particularly effective for downsizing of low voltage electrolytic capacitors.

A specific example of this (Embodiment 1) is shown below. Example 1 In the above (Embodiment 1), as the strip-shaped aluminum foil 2, a high-purity foil having a thickness of 100 μm and a purity of 99.9% or more was used. As the acidic aqueous solution 3, a chloride ion concentration of 2.75 N was used, and sulfuric acid was further added as an additive so that the sulfuric acid concentration became 0.1%.

As the etching tank 1 for the aluminum foil 2, first to third etching tanks 1 are provided, and each of the etching tanks 1 has the acidic aqueous solution 3 adjusted as described above.
Was added as an etching solution.

Then, the acidic aqueous solution 3 in each etching tank 1
The hydrogen ion concentration of the first etching tank is controlled to be 2.50 N from the condition where the hydrogen ion concentration is high to the condition where the hydrogen ion concentration is low as the etching progresses from the pre-process to the post-process. The hydrogen ion concentration of the second solution etching tank was 2.25N, and the hydrogen ion concentration of the third etching tank was 2.00N.

Using the etching tank 1 having the above-mentioned structure, the aluminum foil 2 is removed from the first etching tank to the third etching tank.
While continuously flowing into the etching tank of No. 2, an alternating voltage was applied to carry out the etching treatment. That is, the aluminum foil 2 traveling in the direction of arrow A was subjected to the etching treatment in three steps.

The aluminum foil 2 that had been subjected to the etching treatment was finally formed to complete an electrode foil having a withstand voltage of 22V.
Table 1 shows the capacitance of the obtained aluminum electrode foil for electrolytic capacitors.

A micrograph of the surface and cross section of the aluminum electrode foil for electrolytic capacitors is shown in FIG. In addition,
In FIGS. 3A and 3B, the white part is the aluminum foil that is the base material, and the black part is the etched pit part.

[0054]

[Table 1]

Example 2 The hydrogen ion concentration of the acidic aqueous solution 3 was controlled so as to be equal in the first etching tank and the third etching tank.
The aluminum foil 2 was subjected to etching treatment in the same manner as in Example 1 except for the above.

The electrostatic capacity of the obtained aluminum electrode foil for electrolytic capacitors is shown in Table 1.

Comparative Example 1 Unlike the above Examples 1 to 3, the aluminum foil 2 was etched without controlling the hydrogen ion concentration of the acidic aqueous solution 3.

The acidic aqueous solution 3 and sulfuric acid as an additive are the same as in Example 1.2 above, but the acidic aqueous solution 3
The same acidic aqueous solution sequentially overflows from the third etching tank 1 to the first etching tank 1.

Therefore, the third side on the side where the acidic aqueous solution is supplied
Since the hydrogen ion concentration of the liquid is the highest and the hydrogen ion concentration decreases toward the first liquid,
Contrary to ~ 3, the hydrogen ion concentration of the acidic aqueous solution is configured to increase as the aluminum foil 2 advances in the direction of arrow A, which is the traveling direction.

The aluminum foil 2 was etched in the same manner as in Example 1 except for the above. The capacitance of the obtained aluminum electrode foil for electrolytic capacitors is shown in Table 1.
6 and a micrograph of the surface and cross section thereof is shown in FIG. In FIGS. 6A and 6B, the white portion is the aluminum foil that is the base material, and the black portion is the etched pit portion.

As shown in Table 1, in Examples 1 and 2, the hydrogen ion concentrations in the first to third etching baths were controlled so that the passivation properties were equal or gradually increased as the etching progressed. Because I tried to be strong,
As compared with Comparative Example 1 in which the hydrogen ion concentration was not controlled, an aluminum electrode foil for electrolytic capacitors having a large electrostatic capacity per unit area was obtained.

Further, comparing FIG. 3 (a) with FIG. 6 (a), the surface of the aluminum electrode foil 2 obtained in Example 1 is the same as that of the aluminum electrode foil 2 obtained in Comparative Example 1. Compared with this, there are less lumpy black spots. That is, excessive etching near the surface is suppressed, and many fine and uniform pits are formed.

Further, comparing FIG. 3B with FIG. 6B, the cross section of the aluminum electrode foil 2 obtained in Example 1 is the same as the cross section of the aluminum electrode foil 2 obtained in Comparative Example 1. In comparison, cubic pits are formed that are connected not only near the surface but also inside as clusters.

Therefore, as described above, in Example 1, an aluminum electrode foil 2 having a larger electrostatic capacity per unit area than that of Comparative Example 1 was obtained, which is preferably used as an aluminum electrode foil for a low voltage electrolytic capacitor. In addition, it was effective in reducing the size of the capacitor.

Although sulfuric acid was used as the additive in the above (Example), the present invention is not limited to this, and similar effects can be obtained by using oxalic acid or phosphoric acid instead of sulfuric acid. can get. Further, the additive may be used not only alone but also as a mixture of two or more kinds of acids.

Even if the acidic aqueous solution is used without adding any additive and only hydrochloric acid is used, a practical electrode foil can be obtained depending on the etching conditions. (Embodiment 2) FIG. 4 shows (Embodiment 2) of the present invention.

The structure is almost the same as that of the etching apparatus in the above (Embodiment 1), but the above (Embodiment 1)
Then, the hydrogen ion concentration was controlled by individually supplying and discharging the acidic aqueous solution 3 in each of the etching tanks 1a to 1c, but in this (Embodiment 2),
The difference is that the acidic aqueous solution 3 is sequentially overflowed from the etching bath of the final process to the etching bath of the front process to control the hydrogen ion concentration.

More specifically, as shown in FIG. 4, a pipe 9 for overflowing the acidic aqueous solution 3 is provided and connected between the etching tanks 1a to 1c. Then, an acidic aqueous solution is supplied to the side of the etching tank 1c to etch the etching tank 1c.
Overflow from b to the etching bath 1a is made through the pipe 9 in sequence.

At the same time, each etching tank 1a
1 to 1c, each valve 8a is the same as the above (Embodiment 1).
An acidic aqueous solution having a hydrogen ion concentration higher than that of the acidic aqueous solution in the later step is additionally supplied while adjusting the flow rate.

Although not shown in FIG. 4, the hydrogen ion concentration of each etching tank is adjusted in (Embodiment 2) of the present invention as in FIG. 2 showing (Embodiment 1) above. A control device such as the sensor 7 and the controller 9 is provided as a control unit for controlling the operation.

When the acidic aqueous solution is overflowed, the acidic aqueous solution 3 is supplied in the direction of arrow A, which is the opposite of the above, and the concentrated acidic aqueous solution or hydrochloric acid is added to the etching tank in which hydrogen ions are reduced as described above. At this time, hydrogen ions added in the direction of arrow A also flow, and the hydrogen ion concentrations in all the tanks are made uniform, which is not preferable.

[0072]

As described above, according to the method for producing an aluminum electrode foil for an electrolytic capacitor of the present invention, a plurality of etching baths are provided, and the aluminum foils are sequentially passed through the plurality of etching baths so that the acidity in the etching bath is increased. By controlling each hydrogen ion concentration of the aqueous solution independently in each etching tank to perform etching, the shape and density of the etch pits formed on the surface of the aluminum foil by etching can be controlled. It is possible to obtain an etch pit having a high uniformity and a small deviation in pit diameter.
Therefore, an aluminum electrode foil for an electrolytic capacitor having a large capacitance per unit area can be obtained.

At this time, the hydrogen ion concentration in the etching tank through which the aluminum foil passes is set so that the hydrogen ion concentration in the etching tank in the preceding process is higher than that in the etching tank in the following process with respect to the traveling direction of the aluminum foil. By controlling so as to be equal or higher, an aluminum electrode foil for an electrolytic capacitor having a larger electrostatic capacity per unit area can be obtained.

The control of the hydrogen ion concentration is performed by controlling the hydrogen ion concentration of the acidic aqueous solution to be supplied,
The hydrogen ion concentration in each tank can be easily adjusted. Further, by individually controlling the hydrogen ion concentration in each etching tank as described above, when at least one acid of sulfuric acid, oxalic acid, and phosphoric acid is added, the anion of the acid is an aluminum foil. Since a film is formed on the surface of
Excessive etching near the surface of the aluminum foil due to the progress of etching can be prevented, the surface area can be increased and the capacitance can be increased without destroying the porous structure.

The aluminum electrode foil for electrolytic capacitors manufactured as described above eliminates excessive etching and prevents destruction of the porous structure, so that the surface area can be increased without impairing the strength of the aluminum foil. . Such an aluminum foil for electrolytic capacitors can be suitably used especially for low voltage electrolytic capacitors.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an etching apparatus in (Embodiment 1)

FIG. 2 is an enlarged view of a main part of the etching apparatus according to (Embodiment 1).

FIG. 3 is a micrograph showing a state of a plane and a cross section of an aluminum foil etched in Example 1.

FIG. 4 is a diagram showing a configuration of an etching apparatus in (Embodiment 2).

FIG. 5 is a block diagram of a conventional etching apparatus

FIG. 6 is a micrograph showing a state of a plane and a cross section of an aluminum foil etched in Comparative Example 1.

[Explanation of symbols]

1 etching tank 2 Aluminum foil 3 acidic aqueous solution 7 sensors 8 valves 9 Controller

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuyuki Nakamura 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Koichi Kojima 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. (56) Reference JP-A-11-283874 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01G 13/00 371 H01G 9/04 304

Claims (9)

(57) [Claims] 1. When manufacturing an aluminum electrode foil for an electrolytic capacitor by flowing an aluminum foil into an etching tank containing an acidic aqueous solution, applying a voltage to the aluminum foil to perform etching, and forming pits on the aluminum foil. , A plurality of etching tanks are provided, the aluminum foil sequentially passes through the plurality of etching tanks, and each hydrogen ion concentration of the acidic aqueous solution in the etching tanks is independently controlled in each etching tank to perform etching. Manufacturing method of aluminum electrode foil for electrolytic capacitors. 2. The hydrogen ion concentration of the etching tank through which the aluminum foil passes is equal to the hydrogen ion concentration of the etching tank of the subsequent step in the traveling direction of the aluminum foil as compared with the hydrogen ion concentration of the etching tank of the subsequent step. The method for producing an aluminum electrode foil for an electrolytic capacitor according to claim 1, wherein the aluminum electrode foil is controlled to be higher or higher. 3. The method for producing an aluminum electrode foil for an electrolytic capacitor according to claim 1, wherein the hydrogen ion concentration is controlled by independently supplying and discharging the acidic aqueous solution in each etching tank. 4. The control of the hydrogen ion concentration is performed by supplying an acidic aqueous solution to the etching bath of the final step in the traveling direction of the aluminum foil and causing the acidic bath to sequentially overflow into the etching bath of the front step, and at the same time to the etching bath of the previous step. The method for producing an aluminum electrode foil for an electrolytic capacitor according to claim 1 or 2, wherein an acidic aqueous solution having a hydrogen ion concentration higher than that of the acidic aqueous solution in the subsequent step is additionally supplied. 5. The method for producing an aluminum electrode foil for an electrolytic capacitor according to claim 1, wherein the hydrogen ion concentration is controlled by using hydrochloric acid as the acidic aqueous solution. 6. An acidic aqueous solution containing hydrochloric acid as a main component,
5. The electrolytic capacitor according to claim 1, wherein the hydrogen ion concentration is controlled by using an acidic aqueous solution containing at least one acid selected from sulfuric acid, oxalic acid and phosphoric acid as an additive. For manufacturing aluminum electrode foil for automobiles. 7. An aluminum electrode foil for an electrolytic capacitor, which is produced by the method according to any one of claims 1 to 6. 8. An etching apparatus for producing an aluminum electrode foil for an electrolytic capacitor, wherein an aluminum foil is flown into an etching tank containing an acidic aqueous solution, a voltage is applied to the aluminum foil to perform etching, and pits are formed on the aluminum foil. A sensor for detecting the hydrogen ion concentration is provided in the etching tank, and a flow rate adjusting means for increasing or decreasing the amount of the acidic aqueous solution supplied to the etching tank is provided, and the hydrogen ion concentration is detected based on the hydrogen ion concentration detected by the sensor. An etching apparatus provided with a control device that feeds back to a controller that controls a flow rate adjusting means to arbitrarily control the hydrogen ion concentration in an etching tank. 9. The control device is controlled so that the hydrogen ion concentration in the etching tank in the previous step is equal to or higher than the hydrogen ion concentration in the etching tank in the subsequent step in the traveling direction of the aluminum foil. 9. The etching apparatus according to claim 8, which is configured.