JPS63304613A - Manufacture of aluminum electrode for electrolytic capacitor - Google Patents

Abstract

PURPOSE:To improve the electrostatic capacity of electrolytic capacitors and make them small-sized by generating a dielectric film wherein barium titanate or barium lanthanate is contained in an aluminum oxide thin film, thereby providing breakdown strength to be obtained by the aluminum oxide. CONSTITUTION:With the deposition thickness of the barium titanate or barium lanthanate to be sprayed and deposited onto the surface being limited to 0.1mum or less, an oxide film of an appropriate density is formed within a short time. When sprayed to aluminum, d'=14Angstrom XV (V is for the later anodization) is preferable as the thickness d' to be sprayed. The electrode foil produced in this way becomes an article of a very high electrostatic capacity since the capacitors by the oxide film of the sprayed metal and the aluminum oxide film are eqivalently connected in parallel, and the breakdown strength of the dielectric film is also good, so that electrolytic capacitors can substantially be made small. In addition, the spray coating is smoothly performed also on an aluminum foil having considerable irregularities on the etched surface thereof, electrolytic capacitors can remarkably be made small.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing aluminum electrodes for electrolytic capacitors.

BACKGROUND OF THE INVENTION The electrodes of electrolytic capacitors use metals in which very thin dielectric films are electrochemically produced, and aluminum and tantalum are currently being industrialized as electrode materials.

Among these, the dielectric constant of Aβ203, which is the dielectric material of the aluminum electrode, is about 7 to 10, which is by no means larger than the dielectric constant of other valve metals.

For example, Taz 05 has a dielectric constant ε-25.2,
The ε-66,1 of TiO2. For this reason, aluminum foil used in aluminum electrolytic capacitors is subjected to high-magnification etching treatment to increase the surface area in order to increase the capacitance.

In this etching process, research is being carried out on electrochemical or chemical etching methods in order to achieve the ideal etching condition, that is, in consideration of the thickness of the foil, the surface area can be maximized geometrically. However, etching technology has progressed considerably, and at present the current surface magnification rate can be doubled or tripled.
It is becoming impossible to double the size simply by making the surface finer.

Problems to be Solved by the Invention Even if it were possible to achieve finer etching, the etching/notching shape cannot be utilized due to the so-called clogging phenomenon of the etching holes when the voltage is high, resulting in a decrease in capacitance. Furthermore, when an electrolytic capacitor is produced, the interfacial contact with the electrolyte decreases, leading to a decrease in various mechanical properties such as an increase in foil resistance, an increase in tan δ, and a decrease in impedance characteristics.

On the other hand, attempts have also been made to increase the capacitance using an anodizing method (chemical conversion method). This is achieved by creating a composite film of a boehmite film and an electrochemically generated film by boiling in pure water, a composite film of a chemical conversion film using a boric acid solution and a chemical conversion film using a phosphoric acid solution, and a special thin film created by a pre-chemical treatment. Various studies are being conducted, including composite films of thin films and electrochemical films. However, no method has been found to significantly increase capacitance.

As described above, improvements using 99.99% or 99.9% high-purity aluminum foil currently in use face considerable difficulties in significantly increasing capacitance. Even if the capacitance is increased by force, the leakage current increases and the withstand voltage decreases, and good results cannot be obtained.

Means for Solving the Problems Based on this background, the present invention aims to provide a method for manufacturing aluminum electrodes for electrolytic capacitors, which allows reasonably large capacitance to be obtained.

The gist of the present invention is to thermally spray barium titanate or barium lanthanate with a high dielectric constant onto the aluminum surface,
A thin film of 0.1 μm or less is formed, and if left as is, voids and cracks may remain in the barium titanate and barium lanthanate, and there may be unfinished areas of thermal spraying. The purpose is to anodize the aluminum inside to provide an electrolytic capacitor electrode with high electric field strength and high CV.

In other words, a dielectric film is created in which barium titanate or barium lanthanate is mixed in an aluminum oxide thin film, and the capacitance is greatly increased by barium titanate or barium lanthanate, and the withstand voltage (electric field strength) is increased.
is intended to be made of aluminum oxide.

In addition, barium titanate is used in ceramic capacitors, and although it has a very high dielectric constant, it is thick as a dielectric material in product manufacturing, so d is thick as can be seen from C = ε・□. Because of its high quality, there is no big difference from etching-treated aluminum electrolytic capacitors. This thickness is due to factors such as dielectric breakdown voltage and voids and cranks during dielectric preparation.The present invention can compensate 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 are arranged in series with a separator, not only will it not be effective, but the capacitance will be reduced. This results in a significant decrease.

As a result of various studies in order to solve this problem, the inventor of the present invention determined that the thickness of barium titanate and barium lanthanate deposited on the surface by thermal spraying was set to 0.1 μm or less, and an appropriate density could be achieved in a short period of time. We found that forming an oxide film significantly increases capacitance.

In the case of thermal spraying on aluminum, it was found that the sprayed thickness d' was d'-14V (V is the voltage at which the aluminum is later anodized).

Function The electrode foil created in this way has a capacitor made of a thermally sprayed metal oxide film and an aluminum oxide film, which are equivalently connected in parallel, resulting in an extremely high capacitance product, and the dielectric film has a good withstand voltage. , it is possible to significantly reduce the size of electrolytic capacitors. Furthermore, thermal spraying can be carried out smoothly even on etched aluminum foil, which has considerable irregularities on the surface, making it possible to significantly reduce the size.

Example An aluminum foil having a purity of 99.99% and a thickness of 70 μm was electrolytically etched using an etching solution mainly containing hydrochloric acid to produce an etched foil having a surface area approximately 30 times larger. Next, Sample A was prepared by thermally spraying barium titanate on the front and back surfaces to a thickness of approximately 0.1 μm, and Sample A was thermally sprayed with barium lanthanate. Samples A and B and sample C which was not subjected to thermal spraying were subjected to 80VII polar oxidation using an ammonium phosphate solution having a pH of 6.5, and the film properties were measured.

The capacitance is 12 in 5% ammonium borate solution.
Measured with 011z, film withstand pressure is 0.1mA in the above chemical solution
The voltage one-hour characteristic when current was applied at /cJ was measured, and the voltage rise stop point was defined as the film breakdown voltage. In addition, the leakage current was measured by applying 50V to the test liquid and reading the value after 2 minutes. The results are shown in the table.

As shown in the Effects of the Invention table, the electrodes produced by the method of the present invention have a significant increase in capacitance, and when manufactured into products, they can be significantly miniaturized.

In addition, other electrical product characteristics are almost comparable to conventional products, and have great industrial and practical value.

Claims (3)

[Claims] (1) For electrolytic capacitors characterized by spraying barium titanate or barium lanthanate, or both, onto the surface of aluminum metal and then anodizing it to form a composite mixed dielectric film with valve metal. Method for manufacturing aluminum electrodes. (2) After etching the aluminum metal,
The method for manufacturing an aluminum electrode for an electrolytic capacitor according to claim 1, characterized in that one or both of barium titanate and barium lanthanate is thermally sprayed onto the surface of the metal and anodization treatment is performed. (3) The method for manufacturing an aluminum electrode for an electrolytic capacitor according to claim 1 or 2, wherein the thickness of the thermally sprayed barium titanate or barium lanthanate is 0.1 μm or less.