JPH11224833A - Manufacture of porous anode of solid electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a solid electrolytic capacitor in electrostatic capacitance change rate and electric resistance characteristics and to prevent a leakage current from degrading, by a method wherein a mixture of camphor and bulk sublimating cyclododecane is used as a binder which is mixed into valve action metal powder when valve action metal powder is granulated. SOLUTION: Binder is mixed into valve action metal powder, a mixture is granulated, the granulated powder where an anode lead wire is implanted is molded under pressure into a molded body, and the molded body is sintered in a vacuum at a high temperature into a porous anode of a solid electrolytic capacitor. At this point, a mixture of camphor and bulk sublimating cyclododecane is used as a binder which is mixed into valve action metal powder. Through this manufacturing method, binder of bulk sublimating cyclododecane is present in the granulated powder, so that granulated powder can be molded keeping high in density or many gaps are left between granulated particles, gaps are loss crushed, and moreover gaps between granulated particles serve as pores in a porous anode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a porous anode for a solid electrolytic capacitor.

[0002]

2. Description of the Related Art In general, a solid electrolytic capacitor is formed by mixing and granulating a powder made of a valve metal such as tantalum using camphor or an acrylic resin, and then pressurizing a state in which an anode lead wire made of a valve metal is implanted. A molded body is formed by molding, and the molded body is sintered in a high temperature and high vacuum to form a porous anode body. Thereafter, a dielectric oxide film layer and a semiconductor layer are formed on the surface of the porous anode body. , A carbon layer and a silver paint layer are sequentially formed to form a capacitor element.

In addition, the above-mentioned semiconductor layer is obtained by impregnating a porous anode body on which a dielectric oxide film layer is formed with a solid electrolyte mother liquor,
It is formed by a method such as thermal decomposition and polymerization.Since the state of formation of this semiconductor layer depends on the impregnation property of the solid electrolyte mother liquor into the porous anode body, the surface state of the porous anode body, especially the pore state of the surface, Strong influence. That is, the larger the surface pore diameter, the better the state of formation of the semiconductor layer. It is known that the state of formation of this semiconductor layer strongly affects the rate of change in capacitance and electric resistance characteristics of the solid electrolytic capacitor, and that if the state of formation is poor, these characteristics are significantly deteriorated.

In recent years, as the size and capacity of solid electrolytic capacitors have been increased, the CV of the valve metal powder used has been increased (however, CV is an index indicating the electrical characteristics of the valve metal powder, and the formation of a dielectric oxide film is not required). The product of the voltage V (V) and the capacitance C (μF) per unit weight of the valve metal powder developed at that time)
However, the higher CV of the valve action metal powder is realized by increasing the particle surface area due to the finer powder particles constituting the valve action metal. Of the surface pores of the solid electrolytic capacitor, and the surface of the molded product during the molding process are crushed, and this impairs the impregnation of the solid electrolyte mother liquor. Was causing.

[0005] In order to prevent the impregnation of the solid electrolyte mother liquor from deteriorating, the camphor used as a binder and the valve action metal powder are mixed and granulated before forming the valve action metal powder. It has been practiced to increase the pore size or mix the binder in advance and then mix the bulk acrylic binder again, or to secure the pore diameter of the sintered body by setting the density of the compact to be low.

[0006]

However, in the above-mentioned conventional manufacturing method, the miniaturization of the valve action metal powder particles causes deterioration of the moldability, the reduction of the surface pore diameter of the porous anode body, and the compact at the time of molding. Causing surface blindness,
Impregnation of the chemical solution during anodic oxidation, impregnation of the porous anode body with the solid electrolyte mother liquor during formation of the semiconductor solid electrolyte layer becomes difficult, and as a result, the capacitance change rate of the solid electrolytic capacitor,
This caused deterioration of the electric resistance characteristics. Therefore, as shown in the above prior art, as a means for securing pores of the sintered body to prevent impairment of the impregnation of the solid electrolyte mother liquor, it is possible to set the density of the compact to be low, or to use a valve metal powder. When mixing and granulating with a binder, a method of increasing the binder mixing ratio or adding a non-sublimable binder such as an acrylic resin whose particle size is easily adjusted in a granular form is performed. There is a disadvantage in that the strength of the electrode element is reduced, which causes a reduction in the leakage current characteristics and reliability of the solid electrolytic capacitor. In addition, the use of a non-sublimable binder such as an acrylic binder has a problem that the binder is not easily removed during vacuum sintering, and the leakage current characteristics of the solid electrolytic capacitor are deteriorated due to the influence of the remaining carbon. Was.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems. A porous electrolytic capacitor for a solid electrolytic capacitor capable of obtaining a solid electrolytic capacitor having an extremely excellent capacitance change rate and electric resistance characteristics and having no deterioration in leakage current. It is an object of the present invention to provide a method for manufacturing a high quality anode body.

[0008]

In order to solve the above-mentioned problems, a method for producing a porous anode body for a solid electrolytic capacitor according to the present invention is characterized in that camphor is used as a binder to be mixed in granulation of valve metal powder before molding. A mixture of massive sublimable cyclododecane is used. According to this manufacturing method, a large pore diameter can be secured on the surface of the sintered body. Thus, a solid electrolytic capacitor having extremely excellent capacitor capacitance and electric resistance characteristics can be obtained.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The invention according to claim 1 of the present invention is characterized in that valve action metal powder is mixed with a binder and granulated,
A molded body is formed by pressure molding with the anode lead wire made of a valve action metal implanted, and the molded body is sintered at high temperature and high vacuum to produce a porous anode body for a solid electrolytic capacitor. At this time, as a binder to be mixed with the valve action metal powder, a mixture of camphor and massive sublimable cyclododecane is used, and according to this production method,
Due to the presence of the aggregated sublimable cyclododecane binder in the granulated powder during molding, a large amount of gaps between the granulated particles remain even when the molding is performed at a high density, and there is little blindness. The pores become pores of the porous anode body after sintering, so that a porous anode body having a large surface pore diameter of the sintered body can be obtained. As a result, impregnation with a chemical solution during anodic oxidation, semiconductor solid electrolyte It has an effect that the porous anode body can be easily impregnated with the solid electrolyte mother liquor at the time of forming the layer, and the capacitor capacitance and electric resistance characteristics can be improved.

[0010] According to a second aspect of the present invention, in the first aspect of the invention, the valve action metal has tantalum as a main component, and has the same operation as that of the first aspect of the invention. .

Next, specific embodiments of the present invention will be described together with comparative examples. (Embodiment) Hereinafter, an embodiment of the present invention will be described.
A description will be given of a tantalum solid electrolytic capacitor as an example.

First, tantalum powder (50000 CV) and bulk sublimable cyclododecane having an average diameter of 0.1 mm were mixed and kneaded in an acetone solution in which camphor was dissolved, and then dried at room temperature to perform granulation. . Subsequently, the granulated powder 150
mg with the anode lead made of tantalum wire implanted,
A compact is formed by pressure molding into a column having a compact density of 6.0 and a diameter of 3.0 × 4.0 mm to form a compact. The compact is further sintered at a sintering temperature of 1400 ° C. and a vacuum degree of 10 ⁻³ Pa. By sintering in the inside for 20 minutes, a porous anode body was prepared.

Comparative Example 1 As Comparative Example 1, tantalum powder (50000 CV) was put in an acetone solution in which camphor was dissolved, mixed, kneaded, and dried at normal temperature to perform granulation. Subsequently, 150 mg of this granulated powder was implanted with an anode lead made of tantalum wire, and the compact density was 6.0, φ
A compact was formed by pressure molding into a 3.0 × 4.0 mm cylindrical shape.
The sintering was performed for 20 minutes in a vacuum having a degree of vacuum of 10 ⁻³ Pa to produce a porous anode body.

Comparative Example 2 As Comparative Example 2, tantalum powder (50000 CV) was put into an acetone solution in which camphor was dissolved and mixed, and then a 0.1 mm particle size isobutyl methacrylate polymer was mixed and kneaded. Thereafter, the mixture was dried at normal temperature and granulated. Subsequently, a compact is formed by pressing 150 mg of the granulated powder into a cylindrical shape having a compact density of 6.0 and a diameter of 3.0 × 4.0 mm with an anode lead made of tantalum wire implanted. The molded body was sintered in a vacuum at a sintering temperature of 1400 ° C. and a degree of vacuum of 10 ⁻³ Pa for 20 minutes to produce a porous anode body.

[0015]

[Table 1]

Table 1 shows the maximum pore diameter on the surface of each porous anode body obtained in the embodiment of the present invention and Comparative Examples 1 and 2, and 0.5 wt% of each porous anode body. After anodic oxidation was performed at 50 V for 2 hours in a phosphoric acid aqueous solution to form a dielectric oxide film, the porous anode body having the dielectric oxide film formed thereon was immersed in a 0.2 wt% aqueous phosphoric acid solution.
It shows the result of measuring the leakage current after charging for 2 minutes by applying a voltage of V.

As is clear from Table 1, the maximum pore diameter on the surface of the porous anode body was 1.0 μm or less in Comparative Example 1, but was 1.5 μm or more in the present embodiment. It is shown that the use of the binder of the present invention increases the maximum pore diameter. In addition, since the binder used in the present invention is sublimable, an increase in leakage current as seen in the acrylic binder of Comparative Example 2, which has the same effect, is not observed.

Next, the porous anode body obtained in the embodiment of the present invention and Comparative Example 1 was subjected to chemical conversion at 20 V in a phosphoric acid solution to form a dielectric film, which was then impregnated with manganese nitrate and heated. A manganese dioxide semiconductor layer, a carbon layer, and a silver electrode layer are sequentially formed by decomposition to create a capacitor element.Then, a cathode lead and an anode lead for external lead-out are pulled out, and then a resin sheath is applied to make a tantalum solid electrolytic capacitor. did.

A high-temperature load test was performed on these tantalum solid electrolytic capacitors by applying 85 ° C. and 6 V. The test results are shown in FIG. 1 for the tan δ characteristic, and FIG. 2 for the capacitance change rate.

As is clear from FIGS. 1 and 2, the tantalum solid electrolytic capacitor using the porous anode body manufactured by the manufacturing method according to the embodiment of the present invention has a smaller interparticle gap than the comparative example. Since the pore size is large, the pore diameter on the surface of the porous anode body is increased.
It was confirmed that the an δ characteristic and the rate of change in capacitance were significantly better than those of the comparative example.

In the above-described embodiment of the present invention, a case where a tantalum metal powder as a valve metal is formed and sintered as a porous anode body constituting a capacitor element has been described. Even if the porous anode body is formed using other valve action metals such as titanium, the same effects as those of the present invention can be obtained.

[0022]

As described above, the method for producing a porous anode body for a solid electrolytic capacitor according to the present invention is characterized in that camphor and a lump having an average diameter of 0.1 mm are used as a binder to be mixed in the granulation of valve metal powder before molding. A mixture of sublimable cyclododecane is used. According to this manufacturing method, a large pore diameter can be secured on the surface of the sintered body, so that the solid electrolyte forming mother liquor is easily impregnated into the inside of the porous anode body. The solid electrolyte capacitor has a good formation state of the solid electrolyte of the semiconductor layer, can improve the rate of change in capacitance and electric resistance characteristics, and has very good leakage current characteristics compared to conventional products. A solid electrolytic capacitor having characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram comparing tan δ characteristics in a high-temperature load test of a tantalum solid electrolytic capacitor using a porous anode body obtained in one embodiment of the present invention and Comparative Example 1.

FIG. 2 is a characteristic diagram comparing a capacitance change rate in a high-temperature load test of a tantalum solid electrolytic capacitor using the porous anode obtained in one embodiment of the present invention and Comparative Example 1.

Claims (2)

[Claims] 1. A valve metal powder is mixed with a binder and granulated, and then molded under pressure with an anode lead wire made of a valve metal implanted to form a compact. When producing a porous anode body for a solid electrolytic capacitor by sintering in a high vacuum, as a binder to be mixed with the valve action metal powder, for a solid electrolytic capacitor using a mixture of camphor and massive sublimable cyclododecane A method for producing a porous anode body. 2. The method for producing a porous anode body for a solid electrolytic capacitor according to claim 1, wherein the valve action metal powder is mainly composed of tantalum.