JPS6215813A - Anode material for 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 This invention relates to anode materials for aluminum electrolytic capacitors.

In this specification, the term aluminum is used to include its alloys.

Conventional Technology and Invention Challenges Recently, as electronic products have become smaller and more sophisticated, there has been a strong demand for electrolytic capacitors used in these products to be smaller and more efficient. There is a strong need to increase this.

By the way, the capacitance of the electrode material in an aluminum electrolytic capacitor is expressed as: C=ε・A/l C: Capacitance ε: Dielectric constant A: Surface area t: Dielectric film thickness. 1) is generally limited by the voltage used, so capacitance! The increase in 1i(C) must be considered mainly due to the increase in the dielectric constant (ε) and the expansion of the surface area.

Conventionally, as an anode material for aluminum electrolytic capacitors, the surface of a high-purity aluminum foil base material is etched to enlarge the surface area, and then anodized in a neutral aqueous solution such as ammonium borate solution to improve the surface area of the base material. However, the expansion of the base material surface film by etching has reached its limit, and it is difficult to expect a significant increase in capacitance from that surface. It has reached this point.

From this, based on the above formula, it is possible to form a dielectric film with an extremely high dielectric constant, such as BaTiO3 (relative permittivity ε: 500 to 6000), but this method may be considered in terms of withstand voltage, leakage current, etc. cannot be put into practical use.

On the other hand, on the aluminum foil base material, the oxide is Ag30
It has also been proposed to increase capacitance by forming an oxide film made of a metal with a dielectric constant higher than 3 and anodizing it, but this is insufficient in terms of expanding the surface area. However, it did not fully satisfy the recent demand for an increase in capacitance.

This invention is based on the above-mentioned conventional technology.
By further increasing the area expansion ratio and improving the dielectric constant, the capacitance is even higher than that of conventional products, resulting in smaller capacitors and higher performance. The purpose of the present invention is to provide an anode material for aluminum capacitors that can be used as an anode material for aluminum capacitors.

Means for Solving the Problems For the above-mentioned purpose, the present invention roughens the surface of an aluminum foil base material to have a large number of fine bores (concavities), and applies the effects of the particularly fine irregularities to the base material surface. By making the conductive metal film appear on the surface of the formed conductive metal film, the surface area can be sufficiently expanded, and the film can be formed so that the oxide film of the film and the electrolyte can produce an electrical valve action. composed of metal, that is, valve metal fine particles,
In addition, by forming respective oxide films on the valve metal fine particle film on the uneven surface and the surface in the bore where the base material aluminum is normally exposed by chemical conversion treatment, both oxide films are combined. By configuring the anode material to contribute to an increase in capacitance, it is possible to provide an anode material for an aluminum electrolytic capacitor that exhibits a capacitance much superior to conventional products.

That is, the structure of the present invention is such that a metal made of valve metal fine particles is applied to at least the uneven surface of an aluminum foil base material which has fine unevenness and has been roughened to have a large number of bores in the uneven surface. The object of the present invention is to provide an anode material for an electrolytic capacitor, characterized in that a film is formed thereon, and an oxide film is formed on the surface of the metal film and on the inner surface of the bore by the metal on each surface.

In this invention, the valve metal that constitutes the metal film is the membrane formed by oxidizing it as described above and the electrolyte that produces an electrical valve action, and the combination of the membrane and the electrolyte causes rectification. metals that exhibit properties, most commonly Tr, Ta, /l
, Nb, and others having similar properties include Mq, Zr, Zn, s;
Alloy with B and 3n added to sr, tu'', ``r;, T1
Examples include an alloy in which Pb and sb are added to li, and an alloy in which Or and V are added to li.

The structure of the present invention will be explained in more detail as follows with reference to the accompanying drawings.

The purpose of roughening the surface of aluminum @ base material (1) to form fine irregularities (3) is to use the irregularity effect to form a metal film (2) made of fine particles of valve metal formed on the base material, as described above.
) to help improve the area expansion ratio of the film. Further, the reason why a large number of bores (4) are formed in the base material (1) is to further expand the surface area of the base material and to improve the wettability of the electrolyte. The roughening of the surface of the base material and the formation of the bore (4) are achieved by etching.

can be achieved at times. For such etching, in addition to chemical or electrochemical wet etching methods, it is also possible to employ dry etching methods such as sandblasting, hairline processing, or plasma etching.

The cross-sectional shape of the bore (4) is of course irregular;
Typical cross-sectional shapes include, for example, a cylindrical shape with an approximately constant inner diameter regardless of depth, a pot shape with a narrow inner diameter at the opening, or a bowl shape with an inner diameter that widens from the bottom to the opening. . The dimensions of the bore (4) are not particularly limited, but the maximum depth is 25 JM or less, and the maximum inner diameter is 10 mm.
It is desirable to set it to 0p or less. If the maximum depth exceeds 25p or the maximum inner diameter exceeds 100p, a drawback arises in that it becomes difficult for the base material (1) to maintain the required mechanical strength as an electrode material.

In addition, in order to increase the area expansion ratio of the base material (1), it is preferable that the bores (4) have relatively small diameters distributed as densely as possible, and therefore, at least 100 bores/holes should be formed.
It is desirable that the density be distributed at a density equal to or higher than that of crA. Although the inner surface of the bore (4) does not necessarily have to be roughened, it is preferable that the inner surface also be formed into a roughened surface with fine irregularities in order to increase the capacitance. In this specification, the fine irregularities due to surface roughening refer to microscopic irregularities that do not include not only the bore portion of the surface of the base material but also the undulation components of the same surface.

A conductive metal film (
The material of 2) is one in which the valve metal is used,
Among them, it is common to use metals such as Ti1TaSAΩ and Nb, and in particular, the use of T: gives favorable results in terms of capacitance, Nagano whitening of capacitors, and high reliability. can. From this valve metal fine particles
As shown in the drawing, the metal coating (2) may be formed to cover the entire surface portion of the base material (1) excluding at least the bore (4), that is, the entire finely uneven surface (3). Although it is necessary, it is of course preferable to form a coating on the inner surface of the bore (4) at the same time, since the capacitance can be further increased. The average particle diameter of the valve metal fine particles constituting such a coating should be in the range of 0.01 to 1.0 from the viewpoint of improving the area expansion ratio. That is, if it is less than 0.01, the film is smoothed and contributes little to the enlargement effect, and conversely, if it is less than 1.0. This is because even if the thickness exceeds OJJm, the effect of expanding the surface area will be poor and the capacitance will be small.

The thickness of the coating should also be in the range of 0.05 to 5.0 tones. This is because if it is less than 0.05 JM, the effect of surface expansion due to roughening of the film cannot be expected, and conversely if it is less than 5.0 JM. c.
This is because, even if the value exceeds i, the effect is not commensurate with the increase in the amount of valve metal material used, the increase in cost, and the deterioration in workability.

As a method for forming such a fine particle metal coating (2) on the surface of the base material (1), a vacuum evaporation method, an inert gas evaporation method, a sputtering method, an ion blating method, etc. can be used.

Incidentally, such a process for forming a titanium film by vapor deposition can be performed semi-continuously while winding up a coiled base material.

The oxide films (5) and (6) formed on the outermost surface of the anode material are made by coating the surface of the base material (1) on which the metal film (2) made of fine particles of valve metal is formed with boric acid or ammonium borate. This is done by anodizing using a neutral solution such as ammonium tartrate, and the metal film (2)
It is simultaneously formed both on the surface and on the surface of the base aluminum inside the bore (4) which does not have a metal coating, as oxides of the metals constituting the respective surfaces. Such oxide films (5) and (6) need to be formed at least 1oA as a dielectric of the anode material, but
In particular, as a low-pressure anode foil, it is necessary and sufficient to form the anode foil with a thickness of 3000 Å or less, and it is practically useless to make it thicker than that.

Effects of the Invention As described above, the anode material for an aluminum electrolytic capacitor according to the present invention uses an aluminum base material that has fine irregularities and is roughened to have a large number of bores in the irregular surface, Furthermore, since at least the surface of the base material excluding the bore is coated with a metal film made of fine valve metal particles, this film, together with the surface area expansion effect, is superior to conventional products. It is possible to significantly increase the effective surface area compared to the conventional method, which in turn greatly contributes to increasing capacitance. In addition, since both the oxide films formed on the film surface made of the valve metal fine particles and the inner surface of the bore of the aluminum foil base material contribute to the electrostatic capacitance, the oxide film can be reduced depending on the selection of the valve metal. It is possible to make the dielectric constant of the material high and to have a large capacitance per unit area. Of course, this capacitance is much higher than that of conventional anode materials in which the surface of an aluminum foil base material is roughened simply by etching and anodized to form an aluminum oxide film.
Therefore, it is possible to further reduce the size and improve the performance of the electrolytic capacitor.

In addition, the use of a base material with numerous bores on the surface improves the wetting properties of the electrolyte on the anode surface, which in turn improves the durability and retention of initial performance of the capacitor. sell.

EXAMPLES Next, examples of the present invention will be shown in comparison with comparative examples.

Example 1 Thickness 0.1! An aluminum foil with a purity of 99.99% was immersed in a 2.5 wt% hydrochloric acid solution at a temperature of 60°C, and subjected to AC electrolytic etching at a current density of 2 OA/crrt for 300 seconds. After this etching, the surface of the aluminum cylindrical base material has fine irregularities of 0.5 JM or less on the entire surface, a depth of about 20p, and an inner diameter of 3.
A large number of etched bores of about 0P were formed, and the surface magnification was about 50 times. Next, on the surface of the etching foil base material, 5 x 10'To
Evaporate titanium in argon gas at rr to a maximum thickness of 1
．． A titanium vapor-deposited film of 0 was formed. Then, this base material was anodized by applying a direct current of 10 V in a 1 mwt% ammonium borate solution at a liquid temperature of 30°C, so that the surface of the titanium vapor-deposited film and the aluminum in the bore where titanium was not vapor-deposited were coated. Each oxide film was formed on the exposed surface of the film base material.

Comparative Example 1 As a comparative example with Example 1, an etching foil base material similar to that of Example 1 was used, and anodization treatment was performed in exactly the same manner as in Example 1, except that a titanium vapor-deposited film was not formed.

Example 2 An aluminum foil having a thickness of 0.1 m and having a purity of 99.99% was immersed in a 3 wt % aqueous hydrochloric acid solution at a temperature of 60° C. to undergo chemical etching. After this etching, the foil base material had fine irregularities formed on its surface with an average surface roughness of 0.5 p or less, and a large number of etching pores with a depth of about 10 p and an inner diameter of about 20 ttm. Moreover, the surface magnification ratio of the base material was about 30 times. Next, tantalum was evaporated on the surface of the etching foil base material at a vacuum level of 2×10 −5 Torr to form a tantalum vapor-deposited film having a maximum thickness of 0.8P. Then, this base material was heated to 5°C at a liquid temperature of 35℃
Anodization is carried out by applying a DC voltage of 20 V in a wt% ammonium tartrate solution to form each oxide film on both surfaces of the tantalum vapor-deposited film surface and the exposed surface of the aluminum base material on the inner surface of the bore where tantalum is not vapor-deposited. did.

Comparative Example 2 As a comparative example with Example 2, the same etched aluminum foil was used and the same anodization treatment as in Example 2 was performed without forming a tantalum vapor deposition film.

Example 3 An aluminum foil with a purity of 99.99% was immersed in a 3wt% hydrochloric acid aqueous solution with a liquid temperature of 60°C.
Direct current electrolytic etching was performed for 300 seconds at a current density of A150Cd. The surface of this base material was finely roughened and had a large number of etched bores, and the surface area expansion rate was about 40 times. Next, 1 was applied to the surface of this base material.
Aluminum was evaporated in argon gas at a vacuum level of X 10-3 Torr to form an aluminum vapor-deposited film with a maximum film thickness of 0.5 JM. Next, this base material was heated to 30'
Apply a DC voltage of 50 V in an aqueous boric acid solution of C to perform anodization treatment to form oxide films on both surfaces of the aluminum vapor-deposited film and the exposed surface of the base aluminum in the bore that does not have the aluminum vapor-deposited film. did.

Comparative Example 3 In comparison with Example 3, the same etched aluminum base material was used and the same anodization treatment as in Example 1 was performed without forming an aluminum vapor deposition film.

The capacitance of each sample of the anode material for electrolytic capacitors obtained in Examples 1 to 3 and Comparative Examples 1 to 3 was measured in an aluminum borate aqueous solution at a liquid temperature of 30°C. The results are shown in section 6 of the table below.

[Below, remainder white]

As is clear from the results in the table above, the anode material for electrolytic capacitors according to the present invention is comparable to conventional products in which the surface of the aluminum foil base material is simply roughened by etching and then subjected to anodization treatment to form an oxide film. By comparison, it was confirmed that the capacitance was significantly superior.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of the surface portion of the anode material for an electrolytic capacitor according to the present invention. (1)...Base material, (2)...Metal coating, (3)...
・Minute irregularities, (4)...Bore, (5)(6)...
Oxide film. that's all

Claims (3)

[Claims] (1) A metal film made of fine valve metal particles is formed on at least the uneven surface of an aluminum foil base material that has been roughened to have fine unevenness and a large number of bores in the uneven surface. An anode material for an electrolytic capacitor, characterized in that an oxide film is formed on the metal film surface and on the inner surface of the bore by the metal on each surface. (2) The metal film made of fine valve metal particles has an average particle size of 0.
．． Thickness 0.05~ consisting of fine particles of 01~1.0μm
The anode material for an electrolytic capacitor according to claim 1, which is a 5.0 μm film. (3) The anode material for an electrolytic capacitor according to claim 1 or 2, wherein the oxide film has a thickness of 10 to 3000 Å.