JPS61121419A - Chemical synthesis of electrode foil for aluminum electrolytic capacitor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for forming an electrode foil for an aluminum electrolytic capacitor.

Conventional structure and problems Conventionally, this type of aluminum electrolytic capacitor has been electrolytically etched in an electrolytic solution containing chlorine ions to increase the effective surface area, and a dielectric film is formed on the surface of the electrode foil through chemical conversion treatment. However, it was constructed by winding it together with insulating paper and impregnating it with a driving electrolyte.

Hydrochloric acid or common salt is industrially used as the electrolytic solution for electrolytic etching. As current waveforms, alternating current, direct current, and pulsed current are commercially available.

Various chemical conversion methods for forming dielectric films have been studied, and ammonium adipate aqueous solution is widely used as a chemical conversion liquid for low pressures of 100 WV or less. The reason for this is that ammonium adipate and rum aqueous solution hardly attack aluminum and rarely elute aluminum in the chemical solution, so the capacitance at the same forming voltage is lower than that of other chemical solutions. It's because it's big.

On the other hand, as a method for chemically converting an etched foil that has been electrolytically etched using a pulsed current, ammonium pentaborate is proposed as a chemical forming solution in Japanese Patent Laid-Open No. 132322/1983. Moreover, boric acid is proposed in Japanese Patent Publication No. 66-36'280.

However, with these conventional chemical formation methods, sufficient capacitance cannot be obtained, and the capacitance per unit area of the electrode foil of aluminum electrolytic capacitors tends to be limited to 15°C.

As a result, there is a drawback that there is a limit to miniaturization and cost reduction of aluminum electrolytic capacitors.

OBJECTS OF THE INVENTION The present invention eliminates these conventional drawbacks and provides an etched foil that is electrolytically etched using pulsed current.
The purpose is to obtain high capacitance by chemical conversion in an ammonium adipate aqueous solution, and to realize downsizing and cost reduction of aluminum electrolytic capacitors.

Structure of the Invention In order to achieve this object, the present invention performs electrolytic etching by applying a pulse current in an aqueous solution containing chloride ions, and then performs chemical conversion in an ammonium adipate aqueous solution, thereby achieving a high static etching rate per unit area. It is designed to obtain capacitance.

This configuration achieves the objectives of the present invention, as detailed below.

That is, when complete chemical conversion is carried out in conventional ammonium pentaborate or boric acid, the dielectric constant of the dielectric oxide film produced is 8 to 10, and in order to withstand a unit external voltage, the dielectric constant is 14 people/V. It is known that an oxide film that is required to have a thickness of The oxide film is small and high capacitance can be obtained.However, etched foil etched using pulsed current has a large effect, and when ammonium adipate is formed, the thickness that can withstand unit voltage is e~ 8 people/
V is sufficient. Therefore, even higher capacitance can be obtained.

The electrochemical explanation of this development is as follows.

When chemical conversion is carried out in an aqueous ammonium adipate solution, many white precipitates of aluminum hydroxide are generated from the aluminum foil during the chemical conversion. Boric acid-based chemical solutions hardly produce white precipitates.

This shows that in the case of ammonium adipate chemical solution, the pH at the interface between the aluminum foil and the chemical solution hardly decreases and is neutral. This is because white precipitates of aluminum hydroxide occur when the liquid is near neutral. On the other hand, with a boric acid-based chemical solution, PR at the interface decreases, so aluminum hydroxide is not produced as much.

As a result, since the reaction interface is kept neutral in the ammonium adipate chemical solution, a dense barrier film containing no porous components is formed, resulting in the production of 1lIIt per unit thickness.
[Pressure increases. In boric acid-based chemical liquids, P)! at the interface!
As a result, a rear film containing porous components is formed, resulting in a lower withstand voltage. Pulse-etched foil has a hydration film attached to its surface that prevents a drop in pH, making it more effective than other foils.

Description of examples Next, specific examples will be described.

Etched foil electrolytically etched using pulsed current was chemically formed in an aqueous ammonium adipate solution, and the capacitance per unit area was investigated. The results are shown in the figure.

The experimental conditions were a concentration of 2 to 13% and a temperature of 60'C to 90°C.
It is ℃.

[Brief explanation of drawings]

The figure is a diagram showing the relationship between the concentration/temperature of an ammonium adipate aqueous solution and the capacitance.

Claims (1)

[Claims] An aluminum electrolytic capacitor characterized in that electrolytic etching is performed by applying a pulse current between an aluminum foil and a counter electrode in an aqueous solution containing chlorine ions using the aluminum foil as an anode, and then chemical conversion is performed in an aqueous ammonium adipate solution. Method of chemically forming electrode foil for use.