JPH0760782B2 - Method for manufacturing electrode foil for aluminum electrolytic capacitor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing an electrode foil for an aluminum electrolytic capacitor used in various electronic devices.

Conventional example configuration and its problems Conventional aluminum electrolytic capacitors of this type are usually wound with an aluminum foil and an insulating paper whose effective surface area is expanded by performing electrolytic etching in an electrolytic solution containing chlorine ions,
It was constructed by impregnating the driving electrolyte.

The effect of increasing the surface area of the electrode foil by electrolytic etching is a number of factors, such as etching current waveform, current density, type of etching solution, concentration, temperature, and type and concentration of additives, as well as pretreatment, intermediate treatment, and posttreatment. It is affected by the type of aluminum foil.

Studies on the current waveform have been conducted for some time, and as methods of using a rectangular wave current, British Patent No. 1169234, JP-A-57-132322 and the like are known.

These methods, in an aqueous solution containing chloride ions,
This is a method in which a rectangular wave current is passed and electrolytic etching is performed.

However, these methods have a drawback in that the surface expansion rate is limited, and there is a limitation in downsizing and cost reduction of the aluminum electrolytic capacitor.

An object of the present invention is to eliminate the above-mentioned conventional drawbacks, and to provide a method for manufacturing an electrode foil for an aluminum electrolytic capacitor, which can be miniaturized by using an aluminum foil which can obtain a higher surface expansion ratio than the conventional one. It is intended.

Structure of the invention In order to achieve the above object, a method for producing an electrode foil for an aluminum electrolytic capacitor of the present invention, the concentration is 1 ~ 4.5mol /
Aqueous solution containing chlorine ions, which has the effect of forming an oxide film on the aluminum surface, has a concentration of 0.1
~ 1mol / sulfate ion or oxalate ion is added, in this aqueous solution, between the aluminum foil and the counter electrode,
The aluminum foil is electrolytically etched at the same time as forming an oxide film on the surface of the aluminum foil by applying a rectangular wave current such that the potential with respect to the counter electrode of the aluminum foil is repeatedly positive or negative, and the rectangular wave current is the aluminum foil. The positive current density flowing from the counter electrode to the counter electrode is 0.5 to ^{2 A} / cm ² , and the flowing time is ² to 15 ms, while the negative current density flowing from the counter electrode to the aluminum foil is 0.1 to 0.5 A / cm ² , and the flowing time is Is a rectangular wave current of 2 to 15 ms.

With this manufacturing method, the amount of oxide film on the surface can be increased as compared with the conventional method, and a higher surface expansion ratio than that of the conventional method can be obtained.

The reason is as described below.

The electrolytic etching with a rectangular wave current is repeated when a positive current flows from the aluminum foil to the counter electrode to cause melting and a negative current flows from the counter electrode to the aluminum foil to form an oxide film on the surface. This is because, when a positive current flows, chlorine ions in the electrolytic solution attack aluminum and dissolve it. When a negative current flows, an electrochemical reaction occurs in which electrons are transferred from the aluminum foil to the electrolytic solution at the interface between the aluminum foil and the electrolytic solution, so that H ⁺ ions near the interface are reduced and escape to the outside as hydrogen gas.

As a result, the hydrogen ion concentration at the aluminum foil interface decreases, the PH of the electrolytic solution increases, and an aluminum oxide film is formed on the surface.

The oxide film on the surface has an effect of preventing the corrosion hole from chipping off or being dissolved and disappeared in the middle when etching progresses and the corrosion hole becomes deep and thin.

However, according to the conventional method, the reaction in which a negative current flows and an oxide film is formed is limited to the electrochemical reaction at the interface between the H ⁺ ion in the electrolytic solution and the aluminum foil, and is formed on the surface after etching. The amount of oxide film is about 0.1 mg / cm ² . As a result, it was not possible to sufficiently stop the dissolution and lack of corrosion holes, and it was not possible to obtain the target high surface expansion ratio.

According to the production method of the present invention, when a negative current flows to form an oxide film, the amount of the oxide film on the surface is reduced by the conventional method due to the effect of the sulfate ion or oxalate ion of the additive having the action of forming the oxide film. More, reaching 0.3-0.6 mg / cm ² .

As a result, dissolution and loss of corrosion holes are prevented, and a high surface expansion ratio can be obtained.

Description of Embodiments Next, specific embodiments will be described with reference to the drawings.

[Example 1] Fig. 1 shows the results of studies on the chlorine ion concentration. However, a saline solution was used as the chlorine ions. As is clear from FIG. 1, it is understood that a high surface expansion ratio is obtained in the range of chlorine ion concentration of 1 to 4.5 mol /.

[Example 2] Fig. 2 and Fig. 3 show the results of studies on the relationship between the additive concentration, the amount of oxide film on the surface, and the surface expansion ratio. It is clear that the effect is high in the additive concentration range of 0.1 to 1.0 mol /, and when the additive concentration exceeds 1 mol /, on the contrary, the surface expansion ratio decreases when the amount of oxide film on the surface exceeds a certain amount. On the contrary, it is considered that the activity of the surface is reduced and the frequency of occurrence of corrosion holes is reduced.

[Embodiment 3] The examination results of the current density are shown in FIG. 4 and FIG.
However, salt was used as the chlorine ion, and Glauber's salt was used as the additive.

As is clear from FIGS. 4 and 5, the positive current density is 0.5
It can be seen that a high surface expansion ratio is obtained in the range of up to 2.0 A / cm ² and negative current density of 0.1 to 0.5 A / cm ² .

[Embodiment 4] FIG. 6 shows the results of study on positive current time and negative current time.
It is shown in FIG. As is clear from FIGS. 6 and 7, it is understood that a high surface expansion ratio is obtained in the range of the positive current time of 2 to 15 ms and the negative current time of 2 to 15 ms.

[Embodiment 5] The results of the examination of the transient time between the positive current and the negative current are shown in Section 8.
Shown in the figure. As is clear from FIG. 8, the surface expansion ratio decreases as the transition time becomes longer, but it can be seen that a high surface expansion ratio is obtained at 2 ms or less. It is considered that the proportion of etching at an inappropriate current density relatively increases as the transition time increases.

EFFECTS OF THE INVENTION As described above, according to the method for producing an electrode foil for an aluminum electrolytic capacitor of the present invention, an aqueous solution containing chlorine ions having a concentration of 1 to 4.5 mol / has the action of forming an oxide film on the aluminum surface. Together with the concentration of 0.1-1 mol /
Sulfate ion or oxalate ion is added, and in this aqueous solution, a rectangular wave current is repeatedly applied between the aluminum foil and the counter electrode so that the potential with respect to the counter electrode of the aluminum foil becomes positive or negative. Since the aluminum foil is electrolytically etched at the same time that the oxide film is formed on the surface of the foil, the amount of the oxide film formed on the surface of the aluminum foil after etching can be increased as compared with the conventional method. Since it is possible to sufficiently prevent the dissolution and loss of the corrosion holes, it is possible to obtain a surface expansion ratio higher than before. In addition, the rectangular wave current applied to the aluminum foil has a positive current density of 0.5 to ^{2 A} / cm ² flowing from the aluminum foil to the counter electrode and a flowing time of 2 seconds.
-15 ms, the negative current density flowing from the counter electrode to the aluminum foil is 0.1-0.5 A / cm ² , and the flowing time is 2-15 ms. By using such an aluminum foil as the anode foil, the aluminum electrolytic capacitor can be downsized and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing the relationship between the chlorine ion concentration in the electrolytic solution and the surface expansion ratio, FIG. 2 is a characteristic diagram showing the relationship between the additive concentration and the surface expansion ratio, and FIG. 3 is the additive concentration. FIG. 4 is a characteristic diagram showing the relationship between the surface coating amount, FIG. 4 is a characteristic diagram showing the relationship between the positive current density and the surface expansion ratio, and FIG. 5 is a characteristic diagram showing the relationship between the negative current density and the surface expansion ratio. 6 is a characteristic diagram showing the relationship between the positive current time and the surface expansion ratio, FIG. 7 is a characteristic diagram showing the relationship between the negative current time and the surface expansion ratio, and FIG. 8 is a graph showing the relationship between the positive current and the negative current. It is a characteristic view which shows the relationship between transient current time and surface expansion ratio.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kenji Toyama, 1006 Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Nobuyoshi Kanzaki, 1006, Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. 56) References JP-A-58-223311 (JP, A)

Claims (2)

[Claims] 1. An aqueous solution containing chloride ions having a concentration of 1 to 4.5 mol /, which has a function of forming an oxide film on the aluminum surface and is added with a sulfate ion or an oxalate ion having a concentration of 0.1 to 1 mol /. , In this aqueous solution,
Between the aluminum foil and the counter electrode, a rectangular wave current that repeatedly causes the potential of the counter electrode of the aluminum foil to become positive or negative is applied to form an oxide film on the surface of the aluminum foil and at the same time electrolytically etch the aluminum foil. The square wave current has a positive current density of 0.5 to ^{2 A} / cm ² flowing from the aluminum foil to the counter electrode and a flowing time of 2 to 1
5 ms, while the negative current density flowing from the counter electrode to the aluminum foil is 0.1 to 0.5 A / cm ² , and the flowing time is ² to 15 m.
A method of manufacturing an electrode foil for an aluminum electrolytic capacitor, characterized in that a rectangular wave current of s is used. 2. The aluminum electrolytic capacitor according to claim 1, wherein the rectangular wave current has a transition time of 2 ms or less at which it changes from a positive current to a negative current or from a negative current to a positive current. Method for manufacturing electrode foil.