JPH0787166B2 - Method for manufacturing electrode foil for aluminum electrolytic capacitor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing an electrode foil for an aluminum electrolytic capacitor.

2. Description of the Related Art Aluminum electrolytic capacitors are generally constructed by winding an aluminum electrode foil together with insulating paper and impregnating it with an electrolytic solution. Electrode foil for aluminum electrolytic capacitors is roughened by performing electrochemical or chemical etching treatment on the surface in a solution containing chlorine ions, and by increasing the capacitance per unit area,
We have realized downsizing and weight reduction of aluminum electrolytic capacitors. A certain amount of electricity in this etching process (usually
The capacitance increases linearly with the increase in the aluminum dissolution amount up to 50 coulombs / cm ² ), but when the amount of electricity exceeds that amount, the increase in the capacitance occurs despite the increase in the aluminum dissolution amount. Not only is it slowed down, but it may be reduced on the contrary when excessive etching treatment is performed.
This is because the etching depth increases in proportion to the amount of electricity up to a certain amount of electricity, but above a certain amount of electricity, corrosion holes progress to the inside as the etching process progresses, and at the same time near the surface. This is because the uneven surface that is effective for expanding the formed area is destroyed and the etching depth does not change so much. This tendency is more remarkable in the AC etching in which a fine uneven surface is obtained than in the DC etching treatment.

Problems to be Solved by the Invention Various methods have been developed in order to eliminate such adverse effects, and are roughly classified into: 1. Pretreatment conditions for etching, 2. Etching solution composition, 3 It consists of the one related to the etching current waveform and the one related to the intermediate processing of etching. Regarding the etching current waveform, for example, a pulse waveform is proposed, and according to this method, the electrostatic capacitance linearly increases in proportion to the amount of electricity, resulting in a large electrostatic capacitance. However, this method has a problem that it is difficult to apply a large-current pulse waveform on a mass production scale. Further, regarding other pretreatment conditions, etching solution composition, and intermediate treatment conditions, although some effects are recognized, satisfactory results have not yet been obtained.

The present invention solves such a conventional problem, in which the electrostatic capacity is increased in proportion to the amount of electricity, and as a result, a higher electrostatic capacity than the conventional one can be obtained and a mass-produced capacity for an aluminum electrolytic capacitor. A method for manufacturing an electrode foil is provided.

Means for Solving the Problems In order to achieve this object, the method for producing an electrode foil for an aluminum electrolytic capacitor of the present invention has a function of removing a natural oxide film on the surface of an aluminum foil and forms a protective film on the surface. It is constituted by immersing in an aqueous solution having the above action, and then performing an etching treatment for gradually raising the initial current density.

Action The aluminum foil targeted by the present invention is high-purity aluminum of 50 to 150 μm obtained by ordinary rolling. As the treatment liquid capable of removing the natural oxide film on the surface of the aluminum foil and forming the protective film, one of aqueous solutions of phosphoric acid, sulfuric acid and chromic acid is selected.

In general, various acids and alkalis are used as an aqueous solution used for pre-etching treatment, and these all play the role of degreasing the aluminum foil surface or removing the natural oxide film. Is carried out for the purpose of uniformly dividing the surface of the aluminum foil.

In the present invention, an aqueous solution of an acid capable of forming a protective film on the surface of the aluminum foil is used among them. By this process, the impurities on the surface of the aluminum foil act as active sites, while the adjacent surface of the aluminum foil with high aluminum purity acts as an inactive site with a protective film formed.

In the subsequent electrolytic etching process, by giving the feature that the current density is gradually raised,
Corrosion holes are generated from active sites dispersed on the surface of the aluminum foil, and corrosion does not proceed from the surface on which the protective film is formed. If a current density having a steep rise as usual is used in the electrolytic etching process, corrosion holes will be generated from the entire surface of the aluminum foil regardless of the protective film. In order to selectively generate corrosion holes, the current density needs to reach the steady current density over 3 seconds. If the current density rises in a time shorter than 3 seconds, corrosion holes will be generated from the entire surface of the aluminum foil.

After the corrosion holes are selectively generated in this way, by performing a known electrolytic etching method, the capacitance linearly increases in proportion to the amount of electricity, resulting in a large capacitance. To be This is because the protective film is formed on the surface of the aluminum foil in advance, so that even if the etching progresses, the uneven surface near the surface is not destroyed and the corrosion hole progresses inside.

The effect of using this method is particularly great in AC etching. In other words, conventional AC etching has the advantages of higher productivity and comparatively higher bending strength than etching using DC or other special waveforms, but on the other hand, the capacitance saturates when the amount of etching electricity increases. It had the drawback of showing a tendency. On the other hand, the present invention provides a method in which the electrostatic capacity increases in proportion to the amount of etching electricity while maintaining the advantages of AC etching.

Example Hereinafter, one example of the present invention will be described.

The conventional etching method was performed under the following conditions.

[Etching solution] 8% HCl + 2% AlCl ₃ [Etching conditions] 35 ° C sine wave 60Hz Current density 0.3A / cm ² Next, in the method of the present invention, the etching solution and etching conditions are the same as the conventional ones, and a pretreatment is added. Let The conditions of the present invention are summarized below.

[Pretreatment] Phosphoric acid 2 WT% aqueous solution 80 ° C [Etching liquid] 8% HCl + 2% AlCl ₃ [Etching conditions] 35 ° C Sine wave 60Hz Current density 0.3A / cm ² The current at the initial stage of etching is started for 7 seconds.

The first one shows the relationship between the electrostatic capacity after forming the electrode foil obtained in this way at 70 V and the amount of etching electricity.
It is a figure. As shown in FIG. 1, it can be seen that the capacitance increases linearly as compared with the conventional AC etching, and as a result, the capacitance is increased by 10 to 30% in the range of normal etching electric quantity. .

Fig. 2 shows the relationship between the rise time of the current and the capacitance after 70V formation under these conditions. As shown in FIG. 2, a high capacitance can be obtained by setting the rising time of the current at the initial stage of etching to 3 seconds or more.

EFFECTS OF THE INVENTION As described above, by using the present invention, it is possible to industrially easily manufacture an electrode foil having a capacitance of 10 to 30% higher than that of the conventional method, and to reduce the size of the aluminum electrolytic capacitor. It has a great effect in promoting weight reduction and weight reduction.

[Brief description of drawings]

Fig. 1 shows the amount of etching electricity and the conventional method and the method of the present invention
FIG. 2 is a characteristic diagram showing the relationship of the electrostatic capacity after V formation, and FIG. 2 is a characteristic diagram showing the relationship between the rise time of the current and the electrostatic capacity after formation of 70V in the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ryoichi Shimatani 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Nobuyoshi Kanzaki 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] 1. An aluminum foil is immersed in an aqueous solution which has a function of removing a natural oxide film on the surface and a function of forming a protective film on the surface of the aluminum foil, and then an etching treatment for gradually raising the initial current density. A method of manufacturing an electrode foil for an aluminum electrolytic capacitor, comprising: 2. The method for producing an electrode foil for an aluminum electrolytic capacitor according to claim 1, wherein the time required for the initial rise of the current density during etching is 3 seconds or more.