JPH0620028B2 - Method for forming electrode foil for aluminum electrolytic capacitors - Google Patents

Description

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

Structure of conventional example and its problems Conventionally, this type of aluminum electrolytic capacitor has a dielectric film formed by chemical conversion treatment on the surface of the electrode foil whose effective surface area has been expanded by electrolytic etching in an electrolytic solution containing chlorine ions. Then, it was wound together with the insulating paper and impregnated with the driving electrolytic solution.

Hydrochloric acid or salt is industrially used as an electrolytic solution for electrolytic etching. As the current waveform, alternating current, direct current, and pulse current have been industrially put to practical use.

Various chemical conversion methods for forming a dielectric film have been studied, and an aqueous solution of ammonium adipate has been widely adopted as a low-voltage chemical conversion solution of 100 WV or less. The reason is that the pH of the ammonium adipate aqueous solution is almost neutral, so that a large amount of white precipitates of aluminum hydroxide will be generated when the aluminum foil is formed with this forming solution, which results in the same forming. This is because the electrostatic capacity at voltage becomes larger than that of other chemical conversion liquids.

On the other hand, JP-A-57-132322 proposes ammonium pentaborate as a chemical conversion liquid as a method for forming an etched foil that is electrolytically etched using a pulsed current. Also, Japanese Patent Publication No. Sho 55-36280 proposes boric acid.

However, with these conventional chemical conversion methods, sufficient capacitance cannot be obtained, and the capacitance per unit area of the electrode foil of the aluminum electrolytic capacitor is limited.

As a result, there is a drawback that there is a limit to downsizing and cost reduction of the aluminum electrolytic capacitor.

OBJECT OF THE INVENTION The present invention eliminates such conventional drawbacks, and provides an etched foil electrolytically etched using a pulse current,
The purpose of the present invention is to obtain a high electrostatic capacity by chemical formation in an aqueous solution of ammonium adipate, to realize the downsizing and cost reduction of an aluminum electrolytic capacitor.

In order to achieve this object, the present invention is to perform electrolytic etching by applying a pulse current with an aluminum foil as an anode between an aluminum foil and a counter electrode in an aqueous solution containing chloride ions, and then adipic acid. By forming in an ammonium aqueous solution, an electrode foil having a high electrostatic capacity per unit area is obtained.

With this configuration, the object of the present invention is achieved, as will be described in detail below.

That is, when chemical conversion is carried out in the conventional examples of ammonium pentaborate and boric acid, the dielectric constant of the dielectric oxide film produced is 8
10 to 10 and 14 Å / to withstand unit external voltage
It is known that a V thickness is required.

However, the oxide film formed in the aqueous solution of ammonium adipate has a thickness of 10 to 11 withstanding a unit external voltage.
Å / V is known to be good. As a result, even if the formation is performed at the same formation voltage, the obtained oxide film is thin and a high capacitance can be obtained. Furthermore, when the etched foil that has been etched using a pulsed current is formed by an ammonium adipate conversion solution, the thickness that can withstand a unit external voltage may be 6 to 8Å / V. As a result, the resulting oxide film is even thinner. Therefore, a high capacitance can be obtained.

The electrochemical description of this development is as follows. When chemical conversion is carried out in an aqueous solution of ammonium adipate, a large amount of white precipitates of aluminum hydroxide are generated from the aluminum foil during chemical conversion. White precipitation hardly occurs with the boric acid-based chemical conversion liquid.

This indicates that the pH of the interface between the aluminum foil and the chemical conversion liquid hardly decreases in the chemical conversion liquid of ammonium adipate, and the pH is neutral. This is because the white precipitate of aluminum hydroxide occurs when the liquid is near neutral. On the other hand, in the boric acid-based chemical conversion liquid, the pH at the interface is lowered, so that aluminum hydroxide is not generated so much.

As a result, since the reaction interface is kept neutral in the ammonium adipate conversion solution, a dense barrier film containing no porous component is produced, and the withstand voltage per unit thickness is increased. In the boric acid-based chemical conversion liquid, the PH at the interface is slightly lowered, so that a barrier film containing a porous component is generated and the withstand voltage is lowered. In the pulse-etched foil, the hydrated film attached to the surface prevents a decrease in PH, so that a higher withstand voltage effect can be obtained compared to other foils.

Description of Examples Next, specific examples will be described.

Capacitance per unit area was investigated by performing chemical conversion in an aqueous solution of ammonium adipate using an etched foil that was electrolytically etched using a pulsed current. The results are shown in the figure.

The experimental conditions are a concentration of 2 to 13% and a temperature of 60 to 90 ° C.
Is.

[Brief description of drawings]

The figure shows the relationship between the concentration and temperature of an aqueous solution of ammonium adipate and the capacitance.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor 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-51-142442 (JP, A) JP-A-56-129317 (JP, A)

Claims (1)

[Claims] 1. Electrolytic etching is performed by applying a pulse current with an aluminum foil as an anode between an aluminum foil and a counter electrode in an aqueous solution containing chlorine ions, and then performing chemical conversion in an ammonium adipate aqueous solution. And method for forming electrode foil for aluminum electrolytic capacitors.