JPH079870B2 - Method for manufacturing aluminum electrode for electrolytic capacitor - Google Patents

Description

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

2. Description of the Related Art Metals that produce a very thin dielectric film electrochemically are used for the electrodes of electrolytic capacitors, and currently aluminum and tantalum are industrialized as electrode materials.

Among them, the relative permittivity of Al ₂ O ₃ which is the dielectric of the aluminum electrode is about 7 to 10, and is not larger than the relative permittivity of the valve metal because of other factors.

For example, Ta ₂ O ₅ has a relative permittivity ε = 25.2, and TiO ₂ has ε = 6.
It is 6.1. For this reason, the aluminum foil used for the aluminum electrolytic capacitor is subjected to high-magnification etching treatment to increase the electrostatic capacity, thereby increasing the surface area.

In this etching process, studies have been conducted on an electrochemical or chemical etching method in order to geometrically maximize the surface area in consideration of the foil thickness, that is, to achieve an ideal etching state. However, the etching technology has progressed considerably, and is currently twice the current surface expansion rate,
The doubling has become impossible by simply making the surface fine.

Problems to be Solved by the Invention Even if the miniaturization is succeeded, the etching shape cannot be utilized due to the so-called clogging phenomenon of the etching holes at a high voltage, and the capacitance is lowered.
Further, even when an electrolytic capacitor is produced, the interface contact with the electrolytic solution is reduced, which leads to various foil characteristics such as increased foil resistance, tan δ, and impedance characteristics.

On the other hand, it has been attempted to increase the capacitance by an anodizing method (chemical conversion method). This is a composite film of a boehmite film and an electrochemically generated film by boiling pure water, a composite film of a chemical conversion film of a boric acid solution and a chemical conversion film of a phosphoric acid solution, and a special thin film is formed in the chemical conversion pretreatment, Various studies have been conducted such as a composite film of a thin film and an electrochemical film. However, a method of significantly increasing the capacitance has not been found.

Thus 99.99% or 99 is currently used.
The improvement using 9% high-purity aluminum foil faces considerable difficulty in increasing the capacitance significantly. Even if it is attempted to increase the electrostatic capacity, the leakage current increases and the breakdown voltage decreases, and good results cannot be obtained.

Means for Solving the Problems The present invention intends to provide a method of manufacturing an aluminum electrode for an electrolytic capacitor, which can reasonably obtain a large electrostatic capacitance based on such a background.

The gist of the present invention is to spray barium titanate or barium lanthanate having a high dielectric constant onto an aluminum surface,
It is a thin film of 0.1 μm or less, and if it remains as it is, voids, cracks, etc. remain in barium titanate and barium lanthanate, and there are unfinished parts for thermal spraying. In order to obtain an electrode for an electrolytic capacitor having a high CV by anodizing aluminum to have an electric field strength.

That is, a dielectric film in which barium titanate or barium lanthanate is mixed in an aluminum oxide thin film is produced, and the capacitance is significantly increased by barium titanate or barium lanthanate, and the dielectric strength (electric field strength) is increased.
Is intended to be supported by aluminum oxide.

Also, barium titanate, etc. are used in ceramic capacitors and have a very high relative dielectric constant, but because of the large thickness as a dielectric in the production of products, As can be seen from the equation, since d is large, it is almost the same as that of the aluminum electrolytic capacitor subjected to the etching treatment. This is due to the dielectric breakdown voltage and the thickening due to factors such as voids and cracks during dielectric preparation. The present invention can make up for these drawbacks of both aluminum and ceramic.

However, in the present invention, barium titanate or barium lanthanate and aluminum oxide must be mixed together, and if both of them are arranged in series by separators, there is no effect and a large decrease in capacitance. Invite.

As a result of various studies to solve this problem, the present inventor has determined that the deposition thickness of barium titanate and barium lanthanate deposited on the surface by thermal spraying is 0.1 μm or less, and that oxidation of a proper sparse density is achieved in a short time. It was found that forming a film significantly increases the capacitance.

In the case of thermal spraying on aluminum, as the thermal sprayed thickness d ', d' = 14Å × V (V is a voltage to be anodized later) was good.

Action The electrode foil created in this way is a capacitor with a sprayed metal oxide film and aluminum oxide film that are equivalently connected in parallel, resulting in an extremely high capacitance product and a good dielectric film withstand voltage. The size of the electrolytic capacitor can be greatly reduced. Further, since the thermal spraying was smoothly performed even on the aluminum foil having a considerably uneven surface on the etched surface, the size was remarkably reduced.

Example Electrolytic etching was performed on an aluminum foil having a purity of 99.99% and a thickness of 70 μm using an etching solution mainly containing hydrochloric acid.
An etching foil having a surface area of about 30 times was prepared. Next, sample A having barium titanate sprayed on the front and back so as to have a thickness of about 0.1 μm, and sample b having barium lanthanate sprayed thereon.
Were created respectively. The above samples A and B and sample C not subjected to thermal spraying were subjected to 80 V anodic oxidation with an ammonium phosphate solution having a pH of 6.5, and the film characteristics were measured. The capacitance was measured at 120Hz in a 5% ammonium borate solution, and the film breakdown voltage was measured by voltage-time characteristics when energized at 0.1mA / cm ² in the above chemical conversion solution. did. The leak current was applied 50 V with the above-mentioned measurement solution and the value was read after 2 minutes. The results are shown in the table.

EFFECTS OF THE INVENTION As shown in the table, the electrode produced by the method of the present invention has a large increase in capacitance, and can be made into a small size when it is used as a product. In addition, the characteristics of other electrical products are almost comparable to those of conventional products, and are of great industrial and practical value.

Claims (3)

[Claims] 1. Electrolysis characterized by spraying barium titanate or barium lanthanate, or both on the surface of aluminum metal, followed by anodizing to form a composite mixed dielectric film with a valve metal. Manufacturing method of aluminum electrode for capacitor. 2. The method according to claim 1, wherein after the aluminum metal is etched, one or both of barium titanate and barium lanthanate is sprayed on the surface of the metal to carry out anodizing treatment. A method for manufacturing an aluminum electrode for an electrolytic capacitor according to the first aspect. 3. The method for producing an aluminum electrode for an electrolytic capacitor according to claim 1 or 2, wherein the thickness of the barium titanate or barium lanthanate sprayed is 0.1 μm or less. .