JPS6279610A - Anode for electrolytic condenser - 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 Industrial Application] The present invention relates to improvements in anode bodies for electrolytic capacitors, and particularly to a structure of anode bodies that is advantageous for downsizing capacitors.

[Prior Art] In order to reduce the size of a capacitor, it is necessary to increase the capacitance per geometric unit area of the anodic oxide film of the anode body. As methods for this, it is well known to increase the effective unit area and to use a material with a high dielectric constant.

As a first method, for example, in the case of an aluminum electrolytic capacitor, the aluminum plain foil is roughened by etching to increase the effective area. FIG. 2 schematically shows an aluminum anode body. When a plain foil is etched, the surface 1 becomes uneven and the effective area increases. Therefore, when anodized, the effective area of the oxide film 2 increases, and the capacitance per geometric unit area increases. If the degree of roughness is expressed as the ratio of effective area to projected plane area, it will be 50 to 80 times.

A second method is to use a material with a high dielectric constant, such as titanium, niobium, or tantalum, as the anodic oxide film.

[Problem that the invention seeks to solve]

If cost is not a consideration, use the second method to use titanium or niobium whose oxide has a high dielectric constant.

You can use Kuntal. Comparing the dielectric constant per unit area, TiOx: 2.66 to 8.8511 F/cIIt
.

Nb2O5: 3.63μF/cnl.

Ta2O: 2.48 uF/cffl,
Al2O2 of commonly used aluminum: 1.18
Very large compared to μF/cffl.

On the other hand, the first method of roughening the surface is that in the case of aluminum, the degree of roughening is 50 to 80 times as described above, but in the case of titanium and niobium, the degree of roughening is 2 to 5 times, and in the case of tantalum, it is 10 to 2 times.
It is 0 times.

In this way, methods for increasing capacitance per unit area are limited depending on the material used. That is, even if the first method and the second method were to be combined, each method would be suitable for each material, and there would be a limit to the increase in capacitance. Furthermore, the second method is generally limited by the fact that metals whose oxides exhibit a high dielectric constant are expensive.

An object of the present invention is to eliminate the above-mentioned drawbacks and to obtain substantially the same effect as using both the first method and the second method at a cost advantage. It is about providing.

[Means for solving problems]

In the anode body according to the present invention, on the roughened surface of the conductor foil,
A thin metal film having a valve action and a high dielectric constant as an anodic oxide film is formed, and the metal thin film is anodized to form an anodized film of an electrolytic capacitor. In particular, the conductor foil is aluminum foil, and the valve metal is titanium, niobium, etc.
It is suitable if it is a type of tantalum lining.

[Effect]

Since a high dielectric constant anodic oxide film is formed on the roughened conductor foil surface, the effective area increases and the high dielectric constant increases the capacitance per geometric unit area compared to that of a single material. becomes significantly larger.

〔Example〕

Hereinafter, as an embodiment of the present invention, an example in which aluminum is used as the metal to be roughened and titanium is used as the material for forming the anodic oxide film will be described in detail.

99. A 99% pure aluminum foil was etched to make the surface approximately 20 times rougher, and then platinum was etched on the anode and cathode in a 10% (wt%) aqueous solution of potassium oxalate titanate dihydrate. Using roughened aluminum foil, the liquid temperature was 40°.
Electrolysis is carried out at a C1 current density of 5 mA/cnl. This causes titanium to be electrodeposited on the surface of the aluminum foil of the cathode. After thoroughly washing the foil thus formed, it is chemically converted at 80° C. in a mixed solution of 4% boric acid and 1% ammonium borate (both weight %) to form a titanium anodic oxide film. FIG. 2 schematically shows the cross section of the anode body formed in this way, where 10 is an aluminum foil, 11 is an aluminum foil, and 11 is an aluminum foil.
is a titanium oxide film.

Aluminum is used as the conductor foil to roughen the surface, and the degree of roughening is approximately 20 times. The degree of surface roughness is 50 to 80 times that of aluminum, but if the degree of roughness is increased too much, and the thickness of the titanium electrodeposition is large, the formation of the titanium film will not faithfully follow the unevenness of the aluminum surface. , the effective area will not increase as much. Therefore, the degree of roughness of the aluminum may be appropriately selected depending on the required thickness of the titanium film. Note that the conductor foil to be roughened does not necessarily have to be a metal with valve action, but aluminum is currently most suitable due to its ease of surface roughening and past experience with capacitors.

〔Effect of the invention〕

As explained above in detail, the anode body of an electrolytic capacitor has a composite film structure, and the anodization of a valve metal whose anodic oxide film has a high dielectric constant, such as titanium/niobium tanker, is carried out on a roughened conductor foil. Forming a film increases the capacitance per geometric unit area, making it possible to downsize the capacitor.

Although the titanium, niobium, tanker, etc. are extremely expensive metals, they can be formed by electrodeposition on the surface of the conductor foil to a required thickness, which is advantageous in terms of cost. By using inexpensive aluminum as the roughened conductor foil, miniaturization can be achieved at low cost.

[Brief explanation of drawings]

FIGS. 1 and 2 are diagrams schematically showing cross sections near the surface of an anode body according to an embodiment of the present invention and a conventional example, respectively. 1.10--Aluminum foil, 2-Aluminum oxide film, 11-Titanium oxide film. Patent applicant Nippon Tsushin Kogyo Co., Ltd. Agent Patent attorney Akihiko Sato Figure 1 Fang 2 Figure 7 Luminium foil

Claims (2)

[Claims] (1) A thin metal film with valve action and a high dielectric constant of the anodic oxide film is formed on the roughened surface of the conductor foil, and the metal thin film is anodized to form the anodized film of the electrolytic capacitor. An anode body for an electrolytic capacitor characterized by: (2) The anode body according to claim 1, wherein the conductor foil is an aluminum foil, and the valve metal is one of titanium, niobium, and tantalum.