JPS6048089B2 - Manufacturing method of electrolytic capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing an electrolytic capacitor, and more particularly to a method of manufacturing an anode body of an electrolytic capacitor that is small in size, large in capacity, and highly reliable.

In general, the anode body of a sintered electrolytic capacitor is made by press-molding powder of a so-called valve metal such as tantalum, aluminum, or niobium into a certain shape, and then sintering it in a high-temperature vacuum. The resulting porous body is used.

After the surface of the anode body is electrochemically oxidized to form a dielectric film, a cathode layer is further provided on the outside thereof to form an electrolytic capacitor. Conventionally, this type of anode sintered body 1
As shown in FIGS. 1a, b, and c, the external shape is cylindrical, prismatic, disk-like, etc., and an anode lead wire 2 made of a valve metal is provided at the center thereof.

In other words, the anode lead wire 2 is placed in the valve metal powder in advance.
This anode lead wire 2 is fixed inside the anode molded body by embedding and pressure molding. Thereafter, this anode molded body is sintered in a vacuum to form an anode sintered body 1. When electrochemically oxidizing the anode body 1 thus obtained, a current is supplied to the anode body 1 from the anode body lead wire 2.

For this reason, the anode lead wire 2 and the anode body 1 must be electrically connected reliably, and the current density inside the anode body 1 increases as it approaches the anode lead wire 2.
As shown in FIG. 3, it is required that the connection between the powders becomes stronger as the center approaches the center. On the other hand, in order to obtain the structure of conventional electrolytic capacitor elements, particularly those having a cylindrical shape and a prismatic shape, a molding method using a mold by applying pressure from two directions, upper and lower, is generally used. Therefore, the pressure applied to the inside of the anode molded body acts through the powder.
As shown in FIG. 2, the finished anode body has a powder density lower toward the inside. In other words, contrary to the state of connection between the powders inside the anode body 1 required when electrochemically oxidizing the anode body (anodic oxidation), the connection between the powders becomes worse the closer to the anode body lead-out line. You can say it's getting weaker. This has a large impact on powder interaction during pressurization, and attempts have been made to improve the fluidity of the powder and reduce this reverse density gradient, but the reverse density gradient is
This is an essential problem with applying pressure from five directions (two-sided press), and no significant effects have been achieved. Therefore, the anode sintered body 1 of this type of conventional electrolytic capacitor has a small effective contact area in contact between the anode lead wire 2 and the powder, and in contact between the powders in the vicinity of the anode lead wire 2. Due to variations in conductivity, it was not possible to distribute current evenly to each part of the anode body 1, which adversely affected the quality characteristics of the dielectric oxide film.

Furthermore, since a decrease in the powder density inside the anode body 1 also decreases the mechanical strength of the connection, thermal stress and mechanical stress during the manufacturing process after forming the dielectric film may cause the powder to bond with each other. The connection may become unstable, or the slight movement of the powder may cause destruction or damage to the dielectric film near the connection point.

The problem caused by such a reverse density gradient becomes more significant as the external dimensions of the anode body sintered body 1 become larger, that is, as the product becomes a larger capacity product and a higher rated voltage product.

This is a natural result considering that as the external dimensions increase, the difference between the powder density on the surface and the powder density at the center of the interior increases. Furthermore, if the pressing pressure is increased to adjust the powder density at the center of the interior to an appropriate value, the peripheral portion of the anode body 1, which has a density distribution as shown in Figure 2, becomes over-densed and no longer has the characteristics of a porous body. .

In other words, even if the electrolyte does not sufficiently penetrate into the anode body during anodic oxidation, or an oxide film that serves as a dielectric is formed, the manganese nitrate solution is not used when forming the cathode layer covering it. The essential problem of insufficient penetration occurs, making it impossible to obtain a large-capacity electrolytic capacitor. On the other hand, if the powder density distribution inside the anode body 1 could be uniformly uniform, the electrostatic charge could be reduced by uniformly forming the powder density near the center of the interior of the conventional capacitor anode body 1. It is possible to significantly increase capacity and stabilize quality.

An object of the present invention is to provide a two-electrolytic capacitor that overcomes these conventional drawbacks.

According to the present invention, in the manufacturing method of an electrolytic capacitor in which an anode body is formed by pressure molding a valve metal powder, a protrusion higher than the peripheral part is formed in the center of at least one of the facing pressurized surfaces of the anode body molded product. An electrolytic capacitor characterized by comprising a first stage molding step of forming 4, and a second stage molding step of pressurizing the protrusion to make its height lower than the height of the first stage molded product. A manufacturing method is obtained.

The invention will now be explained in detail with reference to the drawings.

FIGS. 4 to 7 are cross-sectional views showing embodiments of the present invention. In the first forming step of pressure forming, a part of the anode lead wire 2 is preliminarily applied to the cylindrical and flat anode body 2 which is pressurized from the upper and lower surfaces as shown in FIGS. 4a and 5a, for example. The distance between the pressurizing surfaces near the central part in which the mold is buried is longer than the distance between the pressurizing surfaces in the peripheral part. Next, the long distance between the pressurized surfaces obtained in this way is shortened by pressure forming in the second forming step as shown in FIG. 4 b and FIG. Close the distance between pressurized surfaces. In this case, of course, the first
The pressing force in the second molding stage is greater than the pressing force in the molding stage.

Therefore, it is necessary to mold the molded product in the first molding stage with a lower pressure so that the density of the metal powder is lower than the metal powder density of the target anode body 1. The anode body 1 thus obtained has almost no external dimensions compared to the conventional anode body 1, since the protrusion 1a that was present in the first molding stage almost disappears after the second molding stage. It has become indistinguishable.

Moreover, the metal powder density distribution inside the anode body 1 is significantly improved compared to the conventional anode body 1, and the second aspect of the present invention
The anode body 1 obtained by the stepwise molding method has a large capacitance and becomes a high-quality, highly stable electrolytic capacitor. Figures 6A, b, and c compare the metal powder relative density distribution in the internal cross-section B-B'' direction of the anode body (Figure 6a) for the conventional anode body and the embodiment of the present invention. .

As is clear from the distribution of the embodiment of the present invention shown in FIG. 6c, in contrast to the distribution of the conventional anode body 1 shown in FIG. 6b,
The internal density of the anode body is clearly uniform. that's all,
The present invention has an extremely large improvement effect on productivity, such as reduction in materials due to increased capacity and improvement in manufacturing yield due to high quality and high stability.

[Brief explanation of the drawing]

1a-c are perspective views of a conventional electrolytic capacitor anode body. FIG. 2 is a cross-sectional view showing the metal powder distribution of a conventional electrolytic capacitor anode body. FIG. 3 is a cross-sectional view showing the ideal metal powder distribution of an anode body required for manufacturing characteristics of electrolytic capacitors. 4A, b and 5A, b are cross-sectional views showing embodiments of the present invention, in which FIG. 4 a1, FIG. The second stage molded product is shown. FIGS. 6a-c are comparison diagrams of metal powder density distributions of a conventional electrolytic capacitor (FIG. 6b) and an embodiment of the present invention (FIG. 6c). 1
. . . Anode body (sintered anode), 2 . . . Anode lead wire, 1a . . . Projection.

Claims (1)

[Claims] 1. In a method for manufacturing an electrolytic capacitor in which an anode body is formed by pressure molding a valve metal powder, a protrusion higher than the peripheral part is formed in the center of at least one of the facing pressurized surfaces of the anode body molded product. A method for manufacturing an electrolytic capacitor, comprising a first-stage molding step and a second-stage molding step in which the protrusion is pressurized to make its height lower than the height of the first-stage molded product.