JPH0754791B2 - Aluminum electrolytic capacitor manufacturing method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an aluminum electrolytic capacitor used in various electronic devices.

Conventional technology Conventionally, this type of aluminum electrolytic capacitor has been electrolytically etched to form an insulating film by chemical conversion treatment on the surface of the electrode foil whose effective surface area has been expanded. To form a capacitor element.

As a method of forming an insulating film, a method of forming an insulating film by performing pre-chemical conversion in a phosphoric acid, sulfuric acid or oxalic acid bath and then chemical conversion in a boric acid bath is known.

The composite oxide film produced in this way has excellent heat resistance, so if it is used as a chemical conversion film for electrolytic capacitors, the leakage current at high temperature of the electrolytic capacitor will be extremely small, and the life of the electrolytic capacitor will be improved. Is known to do.

This type of electrode foil is widely used, for example, as an electrode foil for a welding machine capacitor, which has a high operating temperature.

By the way, the film formation by pre-chemical conversion is performed by chemical conversion in an oxalic acid, sulfuric acid or phosphoric acid bath, and the electrolytic waveform used for pre-chemical conversion has conventionally been DC or AC.

Problems to be Solved by the Invention Such a conventional method has the following problems.

When forming a film by pre-chemical formation, there is no temporal change in the current when the current waveform used for chemical formation is a direct current as shown in FIG. 4 (A), so the reaction rate of chemical formation is constant over time. is there. As a result, thermal energy due to the reaction is accumulated inside the film, so that the temperature inside the film rises. However, since the reaction is always continued and there is no interruption of the reaction,
Dissipation of reaction heat is not sufficient. Therefore, due to the cracking and strain of the film due to heat, the stress in the film becomes uneven,
Defects occurred and there was a limit to reducing the leakage current.

When an alternating current as shown in FIG. 4 (B) is used as the current waveform, the formation proceeds only when the aluminum foil has a positive potential with respect to the counter electrode, so that the aluminum foil has a negative potential with respect to the counter electrode. When the potential is reached, the reaction is stopped and the reaction heat energy accumulated in the film is radiated. As a result, the rate of occurrence of coating defects due to heat can be reduced, but only half of the supplied electric energy can be used for chemical conversion, resulting in poor conversion efficiency.

The present invention solves such a problem, and an object thereof is to reduce the occurrence rate of film defects without lowering the chemical conversion efficiency.

Means for Solving the Problems In order to solve the above problems, the present invention uses a six-phase half-wave rectification waveform as a current waveform in a phosphoric acid, sulfuric acid, or oxalic acid bath to pre-form an aluminum foil. Done, then
The electrode foil is formed by forming a composite oxide film formed on a surface of an aluminum foil by chemical conversion in a boric acid bath to grow an insulating film.

Action The action of the technical means according to the present invention is as follows.

When a direct current or an alternating current is used as the pre-formation current waveform, there are the above problems, but when the six-phase half-wave rectification waveform of the present invention is used, the electrochemical reaction proceeds as follows.

That is, in the current waveform of the present invention in which the absolute value of the current fluctuates temporally and is temporarily interrupted, when the current is interrupted, the chemical reaction is also interrupted, and the thermal energy accumulated on the surface is radiated. Since this process is repeated, the surface of the film does not reach a certain temperature or higher, so that the film does not crack or distort due to the heat generated when a direct current is applied. As a result, the occurrence rate of film defects can be reduced and the leakage current of the oxide film can be reduced.

Further, since the electric current always flows from the aluminum foil toward the opposite electrode, all the power source energy is consumed for the chemical conversion, whereby the chemical conversion efficiency is good.

Embodiments Embodiments of the present invention will be described below with reference to the drawings. First,
In FIG. 1, reference numeral 1 denotes a bottomed cylindrical case made of metal such as aluminum, and the driving electrolyte is stored in the case 1 together with the capacitor element 2. The capacitor element 2 has an anode foil 3 made of an aluminum electrode foil having a surface area enlarged to form an anodized film.
And a cathode foil 4 facing the anode foil 3 and a separator 5 interposed between the anode foil 3 and the cathode foil 4, and the anode foil 3 and the cathode foil 4 are separated from each other. ,
Lead wires 6 are drawn out.

The opening 7 of the case 1 is sealed with a sealing body 7 having the lead wire 6 penetrating therethrough.

Further, as shown in the enlarged cross-sectional view of the main part of the anode foil 3 described above, the surface of the aluminum foil 8 whose surface area has been enlarged is subjected to pre-chemical formation in a phosphoric acid, sulfuric acid or oxalic acid bath. After that, the composite oxide film 9 is formed by chemical conversion in a boric acid bath.

However, the pre-chemical formation uses a six-phase half-wave rectified waveform as shown in FIG. 3 as the current waveform.

Table 1 shows the leakage current value of the composite oxide film when an oxalic acid solution was used as the pre-chemical conversion liquid, and the ratio of the energy consumed for chemical conversion to the supplied energy (chemical conversion efficiency).

In the above examples, the case of using the oxalic acid solution was described, but even if sulfuric acid or phosphoric acid is used as the pre-chemical conversion solution, the same result can be obtained.

However, the leakage current value is the leakage current value per unit area when 400 V _F formation is performed.

As is clear from Table 1 above, the use of the present invention makes it possible to efficiently form an oxide film having few defects and a small current.

EFFECTS OF THE INVENTION As described above, according to the present invention, it is possible to reduce the leakage current of the aluminum electrode foil and improve the formation efficiency, which improves the quality of the aluminum electrolytic capacitor and reduces the cost. This has the effect of achieving

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing an embodiment of the aluminum electrolytic capacitor of the present invention, FIG. 2 is a sectional view of an anode foil used in the same, FIG. 3 is a schematic view of a current waveform used in the present invention, and FIG. Figures (A) and (B) are schematic diagrams of current waveforms used when manufacturing a conventional aluminum electrolytic capacitor. 1 ... Case, 2 ... Capacitor element, 3 ... Anode foil,
4 ... Cathode foil, 5 ... Separator, 6 ... Lead wire, 7
...... Sealing body, 8 ...... Aluminum foil, 9 ...... Composite oxide film.

Claims (1)

[Claims] 1. A phosphoric acid, sulfuric acid or oxalic acid bath was used for pre-chemical conversion using a six-phase half-wave rectification waveform as a current waveform, and then chemical conversion was carried out in a boric acid bath to grow an insulating film. A method for manufacturing an aluminum electrolytic capacitor in which a composite oxide film is formed on the surface of an aluminum foil to form an electrode foil, and a capacitor element formed by winding the electrode foil together with a separator is enclosed in a case together with an electrolytic solution. .