JPH0338728B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing an aluminum electrolytic capacitor with improved electrode foil. In response to the miniaturization of sets in the electronic equipment field in recent years,
The miniaturization of electronic components and the development of their high-density packaging technology are remarkable, and as a result, there is an extremely high demand for the development of new materials and application technologies.

Aluminum electrolytic capacitors used as passive elements are no exception, and for this purpose research has long been conducted on chemical or electrochemical etching methods for the surface of high-purity aluminum foil, and recently, alloys made of aluminum and different metals have been studied. Applications of foil have also been devised.

It is well known that aluminum foil, which has an expanded surface area in this way, is used as an electrode material after being etched and then anodized to form a dielectric film made of Al ₂ O ₃ on its surface. be. The quality of etching technology is an important factor in determining the shape and dimensions of a product, and it goes without saying that the amount of aluminum foil used is a major factor in determining product cost. For this reason, many studies have been conducted in the past and various methods have been proposed.

On the other hand, in order to make effective use of the etched surface with such an expanded surface area, various studies have been conducted regarding anodizing methods, but all of these methods have been used to obtain pure γ-Al ₂ O ₃ as a dielectric film. It was a great effort.

Therefore, its relative dielectric constant is about 7 to 10, which is by no means a high value compared to other metal oxides, and therefore, if the external dimensions are restricted, it is necessary to rely on etching to improve the surface magnification. As a result, the resulting etched foil had extremely complicated and deep etched holes, and had the major drawback of reduced physical strength.

The present invention was made in order to improve the above-mentioned drawbacks, and the pores of the anodic oxide film made of porous Al ₂ O ₃ are sealed with an oxide having a dielectric constant higher than that of Al ₂ O ₃ . By using the resulting composite oxide film as a dielectric, the present invention attempts to provide a method for manufacturing an aluminum electrolytic capacitor that is small and has a large capacitance that could not be obtained using conventional methods.

Hereinafter, a detailed explanation will be given based on one embodiment of the present invention.

High-purity aluminum foil whose surface area has been expanded by electrolytic etching is soaked in an aqueous solution of 55-66% oxalic acid.
C. for 5 to 10 minutes at a current density of 2 to 3 A/dm ² to form a porous film with a thickness of 0.4 to 0.5 μm. Next, the aluminum foil was immersed in a 4% TiO ₂ alcoholate benzene solution at room temperature, and then pulled up at a speed of 30 to 35 cm/min to adsorb the TiO ₂ alcoholate solution into the pores of the porous film.
Thereafter, the pores were filled with amorphous TiO ₂ using a coating film pyrolysis method in which heat treatment was performed in an atmosphere of 400±20°C.

According to the pulling method, the alcoholate was adsorbed relatively easily in the pores of the porous film due to its strong adsorption power, but the film surface had poor wettability, so almost no TiO ₂ oxide layer was formed.

The anodic oxide film obtained in this way is Al ₂ O ₃
By forming a composite oxide with Al _{2 O 2} and TiO 2 , it is possible to obtain the same results as when the dielectric constant of Al ₂ O ₃ is apparently improved, and the capacitance per unit area is 50% lower than in the normal case. ~70% improvement.

Conventionally, this type of porous coating has a low electrical withstand voltage and cannot be put to practical use as it is, so a secondary anodization treatment is performed in an aqueous solution of ammonium borate, ammonium carbonate, or phosphoric acid. What fills the pores is Al ₂ O ₃ .

The anodic oxide film obtained in this way has excellent physical properties such as high heat resistance, so
It has been found to be highly effective in special applications, such as circuits where large ripple currents are continuously applied or where alternating current is applied intermittently.

Therefore, the anode foil of conventional aluminum electrolytic capacitors used for this purpose is generally etched at a low magnification or plain foil without etching, which reduces the capacitance required for circuit design. In order to achieve this, a larger electrode area is inevitably required than that of a normal aluminum electrolytic capacitor, and as a result, the wound capacitor element also becomes larger, and the size and cost are not necessarily satisfactory. According to the present invention, it is possible to manufacture a small electrolytic capacitor with excellent characteristics, which is of great industrial and practical value.

Claims (1)

[Claims] ₁ Electrode foil for aluminum electrolytic capacitors having a porous anodic oxide film anodized in an aqueous solution of phosphoric acid, oxalic acid, _sulfuric acid, _etc.
After immersing or coating metal oxides such as _BaTiO2 , which have a dielectric constant higher than aluminum oxide, or composite oxides alone or in an alcoholate solution containing a mixture thereof, aluminum is processed using a coating pyrolysis method. A method for manufacturing an aluminum electrolytic capacitor, comprising using an electrode foil in which the pores of a porous oxide film are filled with the oxide to form a composite dielectric film.