JPS59200411A - Tantalum electrolytic condenser anode element - 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 The present invention relates to an anode body element for a tantalum electrolytic capacitor.

As is well known, tantalum electrolytic capacitors are manufactured as follows.

First, tantalum powder is press-molded into a desired shape and size, and then sintered at a temperature of 1500° C. or higher in a vacuum atmosphere to obtain an element with three anodes. These three anodes are connected to the anode (7. By anodization, a tantalum oxide film is generated on the surface of the particles constituting the anode body element. Next, when the capacitor is a solid electrolytic capacitor, on the tantalum oxide film, A manganese dioxide layer, a graphite layer, and a solder layer, which will become the cathode, are formed in sequence, and finally the capacitor is covered with a resin, etc. If the capacitor is a wet electrolytic capacitor, the anode body element l on which a tantalum oxide film has been formed is The capacitor is completed by placing it in a metal container containing an electrolytic solution such as sulfuric acid.

On the other hand, with the progress of the electronic industry in recent years, there has been a demand for particularly small and inexpensive electronic components, and efforts are being made to reduce the size of the anode element, which accounts for most of the size of electrolytic capacitors. . For example, there is a method of using tantalum powder with a fine particle size, or a method of sintering a molded body at the lowest possible temperature. However, using fine powder particles in this way narrows the pores in the anode element, so especially when the cathode layer is solid, the manganese dioxide layer, which is the cathode material, will form inside the anode element. However, this increases dielectric loss, which is an important characteristic of capacitor characteristics, and increases leakage current. Also,
Sintering at a low temperature weakens the bonds between particles and further reduces the effect of removing elements other than tantalum metal contained in the powder, resulting in an increase in leakage current and a decrease in withstand voltage.

An object of the present invention is to provide a new anode element different from the conventional method, which improves the above-mentioned drawbacks, and also to provide a small and inexpensive electrolytic capacitor.

That is, according to the present invention, the wall thickness of the tube is 0.3 μm.
By using the tantalum metal tubes having a substantially cylindrical shape as described above, and collecting and bundling them together to obtain the desired capacitor, the surface area per unit weight and the surface area per unit volume can be increased compared to conventional methods. Furthermore, an anode element for a tantalum electrolytic capacitor in which the cathode layer can be easily formed up to the inside of the element can be obtained.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

First, the anode body element 1 of the present invention will be explained. As the central axis, organic chemicals or inorganic chemicals other than hydrofluoric acid, or elongated substances of the desired diameter that evaporate at temperatures of several hundred degrees, such as synthetic fibers such as polyethylene, or low melting point metals such as aluminum, are coated with vacuum evaporation or ion spraying. By means such as the proboscis method! l) 0
．． A tantalum film of 3 μm or more is deposited. Next, the central shaft is removed using a chemical or heat treatment capable of removing the central shaft, and the tube body of the tankle is manufactured. This tantalum tube can be used alone as an anode element, but in order to obtain an anode element for a large capacity capacitor, the tubes are further bundled and at the same time twisted wires are added to provide the mechanical strength of the bundled tubes. The tube bodies may be twisted together using a machine or the like, or the tube bodies may be melted together in a high-temperature, high-vacuum atmosphere.

Note that when the anode body element 1 obtained in this manner is made into a capacitor, a tip portion where no oxide film 2 is formed can be provided and used as an anode lead.

Next, regarding the surface area per unit weight of the present invention,
□Explain. Single anode body element 1 of the present invention shown in FIG.
When the element is immersed in a chemical solution to a distance t and a υ oxide film is formed by a commonly used mechanical oxidation method, an oxide film 2 is formed on the outer, inner and bottom surfaces of the element, as shown in FIG.
is formed. The area Sp of the surface on which this oxide film 2 is formed,
The ratio of the weight Wp of the tantalum metal in the area where the oxide film is formed, that is, the area per unit weight Sp/Wp, is given by the density of the tantalum metal being ρTa%, the thickness of the tube wall being t(=(a-b)/2 )
Then, the following equation (1) is obtained.

Sp/Wp=(2 to 10t)/lt・ρTa...
・(1) Here, the units are C, G, and S, and the same applies to the formulas described below. The thickness t of the wall of the tube needs to be greater than the thickness at which the oxide film 2 can be formed, and therefore varies depending on the anodizing voltage during anodization. In the present invention, as a practical forming voltage, the maximum forming voltage is 250 V,
The wall thickness of the tube was at least 0.3 μm. That is, as is well known, the oxide film 2 produced by anodic oxidation has a thickness of 1/3 on the inside of the tantalum metal and 2/3 on the outside of the tantalum metal.
3 and a thickness of 17λ per chemical formation voltage of 1μ. Therefore, at the maximum anodizing voltage of 250V, an oxide film 2 with a thickness of approximately 1400^ is formed on the inside of the tantalum metal.

In addition, this tantalum metal requires a conductive metal part as an anode, and the thickness of the metal part is about the same as the thickness of the oxide film 2, and the thickness of the wall of the tube is about 300 OA (= 0.3 μm).
). This thickness is very small compared to the distance t (>1 mm) formed in a normal capacitor. Therefore, the above equation (1) is approximated as follows.

8p/Wp=2/l・ρT8 ・・・・・・・・・
(2) On the other hand, as is well known, the surface area of a conventional sintered body of tantalum powder as the anode element l is calculated by correcting the surface area obtained from the average particle diameter of the powder by the reduction in surface area due to sintering. You can ask for it. That is, if the ratio of the effective surface area after sintering to the surface area determined by the average particle diameter is K (hereinafter referred to as a correction coefficient) and the average particle diameter is D, then the surface area S5 of the anode body element l and the weight of the tantalum metal are The ratio of Ws, that is, the area per unit weight 8 s/W5, is the following (3)
It is expressed by the formula.

Ss/ Ws = 6 ・K/ D−ρTa ++
・・＋＋・++ (3) Here, K must be a value of 1 or less,
In the inventor's experience, it is O15 to 0.9.

From equations (2) and (3), the area ratio (Sp/Wp)/(as/W
s) is given by the following equation (4).

(Sp/Wp) / (Ss/Ws) = D/3k
t...(4) In this equation (4), the previously mentioned t
value (-” 0.3 ttm), maximum value of K (= 0
．． 9 μm), the area per unit weight of each anode body element l of the present invention and the conventional anode body element l becomes the same as shown by the solid line A in FIG. 3 showing the relationship between the area ratio per unit weight and the particle diameter D. is found to be 0.81 μm.

This means that the average particle diameter is 0 when the tantalum particles are the same.
．． Anode body element 1 made of a sintered body of powder exceeding 81 μm
This means that the anode body element l manufactured according to the present invention can have a larger surface area than when using . for example,
Compared to powders currently in practical use with an average particle diameter of about 3 μm, the present invention makes it possible to obtain a surface area 3.7 times larger. In the case of obtaining a capacitor of the same capacity, it becomes possible to manufacture it by reducing the weight of tantalum to 1/3.7.

Next, with respect to the surface area per unit volume of the present invention, the volume occupied by the metal of the conventional anode body element 1 made of a powder sintered body is:
Although it varies depending on the particle size and sintering conditions, the apparent volume is 35 to 65% of the volume (volume determined by external dimensions).
Well, on average it's 50%. The value of jin is approximated by the ratio of the volume of the cube to the volume of the sphere when the particle is assumed to be a sphere and the particle is placed in a cube whose side is the particle diameter. Therefore, this can be evaluated as an element having one volume of an anode element.

In the case of the present invention, evaluation can also be made by placing the particles in a cube with the particle diameter as one side, with the outer diameter being the same as the particle diameter, and with the top and bottom surfaces facing each other and in contact with the surface of the cube.

In this way, the surface area per unit volume Sp/Vp of the anode body element J of the present invention and the surface area per unit volume S8/V of the anode body element 1 of the conventional means.

The ratio (8p/Vp)/(8s/Vs) is obtained from the following equation (5) through a simple formula.

(8p/■p)/(Ss/Vs) =2-(2t2/D
2) =・(5) In this equation (5), the value of t mentioned earlier (=
According to the dotted line B in FIG. 3, which shows the relationship between the surface area ratio per unit weight and the particle diameter, the area per unit volume of each anode body element l of the present invention and the conventional one is the same. When D is calculated, it is 0.42 μm. This is because, in a single anode element, when the anode body element 1 is used with a powder sintered body having an average particle diameter exceeding 0.42 μm, the anode body element 1 manufactured by the means of the present invention is This means that the surface area can be increased. For example, when compared with powders currently in practical use having an average particle diameter of about 3 μm, the present invention makes it possible to obtain about twice the surface area. In the case of obtaining a capacitor of the same capacity, the volume can be reduced to about 1/2.

The above is an explanation of a single element of an anode body. However, in an actual anode body element l, which is a single element, in the conventional means, -C is significantly reduced in surface area due to sintering, and its correction coefficient is Since it is expressed in the denominator of the entire equation (5), the effect of the present invention is greater than the above explanation.

Next, the ease of forming manganese dioxide, which is a cathode material, will be explained.

As is well known, manganese dioxide is produced by adhering or impregnating a manganese nitrate solution to an anodized anode core, and then thermally decomposing the solution. The internal pores of the anode body element 1 made of a conventional powder sintered body become finer and have a more complicated structure as the particle size of the powder becomes finer.

On the other hand, in the anode body element 1 according to the present invention, the holes have a simple and substantially linear structure. Therefore, it can be easily inferred that in the anode body element of the present invention, capillary phenomenon also works, and the manganese nitrate solution penetrates into the anode body element more easily than in the conventional anode body element.

As described above, since the anode element of the present invention (i) can have a larger surface area per unit volume and weight than the conventional anode element, it is possible to manufacture a small and inexpensive anode element. (ii) Therefore, it is possible to provide a small, inexpensive electrolytic capacitor with excellent electrical characteristics.

Although the present invention has been described using a concentric cylindrical tantalum metal as an example of a single anode body element, it is of course possible to use a polygonal cross-sectional shape as long as the minimum wall thickness of the tube is 0.3 μm. It is.

The present invention also relates to an anode element, and it is effective whether the cathode material of the electrolytic capacitor is solid or liquid.
Needless to say, the present invention can also be applied to anode elements made of valve metals other than tantalum.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a single anode element according to the present invention. Figure 2 shows
A cross-sectional view of a single anode element of the present invention on which a tantalum oxide film is formed, Figure 3, and a relationship diagram between the area ratio of the present invention and the conventional anode element and the average particle diameter constituting the conventional anode element. It is. l... Anode body element alone, 2... Oxide film, A... Ratio of the area of the anode body of the present invention to the area of the conventional anode body per unit weight, B... ... Ratio of the area of the anode body of the present invention to the area of the conventional anode body per unit volume.

Claims (1)

[Claims] 1. An anode body element for a tantalum electrolytic capacitor, characterized in that a positive body is made of 1211 cylindrical tantalum metal having a wall thickness of 0.3 μm or more.