JP2000040642A - Manufacture of solid electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a solid electrolytic capacitor excellent in high frequency characteristics by forming a conductive polymer film on a sintered body of valve action metal which has an anodic oxidation film on the surface. SOLUTION: After an anodic oxidation film is formed on the surface of a valve action metal sintered body, it is dipped in mixed solution which is composed of heterocyclic compound monomer and oxidizing agent and/or dopant, and maintained at 30-60 deg.C. By chemical oxidative polymerization, a solid electrolytic capacitor wherein a conductive polymer film as solid electrolyte is formed on the valve action metal sintered body is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a solid electrolytic capacitor having a high-frequency characteristic using a conductive polymer film as a solid electrolyte.

[0002]

2. Description of the Related Art In recent years, with the digitization of electrical equipment, there has been a demand for a capacitor having a small size, a large capacity, and a low impedance in a high frequency region and having excellent high frequency characteristics. Until now, capacitors used in the high-frequency range include plastic film capacitors, mica capacitors, and multilayer ceramic capacitors.However, film capacitors and mica capacitors are difficult to increase in capacity due to their large size. Multilayer ceramic capacitors have the disadvantage that the smaller the size and the larger the capacity, the worse the temperature characteristics.

On the other hand, as a large-capacity capacitor, an aluminum dry electrolytic capacitor or an aluminum or tantalum solid electrolytic capacitor is known. Aluminum dry-type electrolytic capacitors can be obtained at low cost and have a large capacity.However, since the electrolytic solution is used, a decrease in capacity or an increase in loss occurs due to leakage of the electrolytic solution, evaporation, etc. There are drawbacks such as poor low temperature characteristics.

The use of solid manganese dioxide as an electrolyte can overcome capacity degradation of aluminum or tantalum solid electrolytic capacitors. However, in order to increase the amount of manganese dioxide deposited, immersion in an aqueous solution of manganese nitrate and thermal decomposition are usually performed. It must be repeated several times to several tens of times. For this reason, it has been pointed out that the oxide film as a dielectric is damaged during the thermal decomposition and the leakage current increases.

[0005] From the above, a capacitor using a 7,7,8,8-tetracyanoquinodimethane complex salt (hereinafter, referred to as TCNQ) as an organic solid electrolyte instead of manganese dioxide has been proposed. Kaikai 58-17609
No. 2), the TCNQ complex has high conductivity, but has poor thermal stability, so that it may be decomposed into an insulator during the capacitor manufacturing process, resulting in a problem in thermal characteristics.

In addition, a method for producing a capacitor using a polymer of a heterocyclic compound such as pyrrole, thiophene or furan as a solid electrolyte has been proposed (Japanese Patent Laid-Open No. Sho 60-2).
No. 44017). This method attempts to form a polymer of a heterocyclic compound as a conductive polymer film on an anodized film by electrolytic oxidation polymerization. However, since the anodized film layer is insulated, it is difficult for current to flow. It is very difficult to form a sufficient heterocyclic compound polymer film on the anodic oxide film layer.

[0007]

In order to form a polymer film of a heterocyclic compound on an anodic oxide film, in addition to the electrolytic oxidation polymerization described above, a method using chemical oxidation polymerization has been studied. After immersing the valve-acting metal on which the anodic oxide film has been formed in the solution of the heterocyclic compound monomer, immediately perform chemical oxidative polymerization in an oxidant solution at a lower temperature than the solution of this monomer, or use the monomer, oxidant, dopant Is immersed in a mixed solution maintained at a room temperature or lower at a temperature equal to or lower than the above, and the chemical oxidative polymerization is performed while suppressing the formation rate of the high molecular polymer. However, this chemical oxidative polymerization has been carried out as a preceding step in order to eliminate the difficulty of forming a conductive polymer film by electrolytic oxidative polymerization on the anodic oxide film described above. Therefore, even if a conductive polymer film made of a heterocyclic compound monomer is applied only by such chemical oxidative polymerization and an appropriate capacity as a capacitor is to be obtained, the monomer viscosity is high under such a low temperature condition, but the anode viscosity is high. It has been pointed out that it is very difficult to penetrate into the oxide film, so that the steps of permeation and drying have to be repeated several tens of times, which is extremely troublesome.

According to the present invention, it is possible to form a polymer film of a heterocyclic compound on an anodized film, which can obtain a proper capacity as a capacitor only by chemical oxidation polymerization without the above-mentioned trouble. It is an object of the present invention to provide a method for manufacturing a solid electrolytic capacitor.

[0009]

In order to achieve the above-mentioned object, according to the first aspect of the present invention, a valve-acting metal sintered body having an anodic oxide film formed on a surface thereof comprises a heterocyclic compound monomer. Solid electrolyte obtained by forming a conductive polymer film as a solid electrolyte on the anodic oxide film of the sintered body by chemical oxidative polymerization by impregnating with a mixed solution of 30 to 60 ° C. It is characterized by obtaining a capacitor.

A second aspect of the present invention is characterized in that, in the first aspect, at least one monomer selected from pyrrole, thiophene, furan and derivatives thereof is used as the heterocyclic compound monomer. is there.

In short, the present invention relates to forming a conductive polymer film made of a heterocyclic compound monomer as a solid electrolyte on a anodic oxide film on the surface of a metal anode body having a valve action by chemical oxidative polymerization. Impregnation treatment in a mixed solution of
After conducting at a high temperature of 0 to 60 ° C., a conductive polymer film is formed by performing a polymerization reaction when drying at room temperature. To obtain a solid electrolytic capacitor having a high capacitance appearance ratio and excellent high-frequency characteristics. You can do it.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, as a valve action metal used as an anode of a solid electrolytic capacitor, any metal having a valve action such as aluminum, tantalum, niobium, titanium and an alloy using these as a substrate can be used. Good.

The dielectric oxide film formed on the surface of the valve metal may be an oxide layer of the valve metal itself provided on the surface portion of the valve metal, or may be provided on the surface of the valve metal. May be a layer of another dielectric oxide,
In particular, the layer is preferably a layer made of an oxide of the valve metal itself.

In the present invention, as the heterocyclic compound monomer used for obtaining the conductive polymer film by chemical oxidation polymerization, one of pyrrole, thiophene, furan and derivatives thereof can be used. In addition, as an oxidizing agent or a dopant used together with the heterocyclic compound monomer in the chemical oxidative polymerization, one substance itself becomes a dopant of the heterocyclic polymer formed by the oxidative polymerization,
Examples of the substance imparting conductivity include iron p-toluenesulfonate. In addition, for example, FeCl ₃ , AsF ₅ , PF ₅ , and BF which are conventionally known as oxidizing agents
_{3, SbF 5, KMnO 4,} (Na 2) S 2 O 8, (N
H ₄ ) ₂ S ₂ O ₈ or the like may be used. Furthermore, in order to enhance the conductivity of the formed heterocyclic polymer, it is also preferable to use a well-known dopant other than the oxidizing agent.

According to the present invention, a mixed solution of a heterocyclic compound monomer, an oxidizing agent and a dopant is heated to a high temperature of 30 to 60 ° C.,
The sintered body is impregnated in the mixed solution under the high temperature. This lowers the viscosity and surface tension of the mixed solution, allowing the solution to penetrate into the pores inside the oxide film on the surface of the sintered body, and also penetrate into such an interior together with the monomer attached to the oxide film. The polymerization of the monomer occurs, and a dense conductive polymer film can be obtained. Capacitors can be extracted from those portions, and a capacitor having a high capacitance appearance rate and excellent high-frequency characteristics can be obtained.
Therefore, even when a conductive polymer film having a desired thickness is obtained, the number of times the sintered body is impregnated into the mixed solution can be reduced, which contributes to simplification of the capacitor manufacturing operation.

[0016]

The present invention will be described below in detail with reference to examples. An aluminum sintered body was used as a metal sintered body having a valve action, and was subjected to electrolytic oxidation to form an anodic oxide film on its surface. Separately, a 2.0 mol / l ethanol solution of a pyrrole monomer and an oxidizing agent, 0.6 mol / l as a dopant
Butanol solution of paratoluenesulfonic acid iron salt (manufactured by Bayer AG, Germany) was prepared. Then, the two solutions were mixed and diluted with ethanol to prepare a mixed solution.

Next, the mixed solution prepared above was heated to 60 ° C., and the solution maintained at that temperature was impregnated with an aluminum sintered body having an anodized film on the surface for 15 minutes. Thereafter, the mixture was taken out of the mixed solution and left at room temperature for 15 minutes to remove the solvent and to carry out the polymerization reaction of the impregnated pyrrole monomer.
After cleaning for 5 minutes, the resultant was dried at 60 ° C. for 5 minutes to form a conductive polymer film made of polypyrrole as a cathode layer on the anodized film of the aluminum sintered body.
After repeating the above steps several times, a carbon paste and a silver paste were sequentially adhered onto the obtained conductive polymer film to produce a solid electrolytic capacitor.

In the above embodiment, since iron para-toluenesulfonate having a dopant as an oxidizing agent was used, the monomer was oxidized by iron ions, and simultaneously with the reaction, toluenesulfonic acid ions were introduced to act as dopants. And a dense conductive polymer film.

For comparison, the same mixed solution as in the above example was used. However, in order to perform the impregnation at room temperature and to obtain the same thickness as the conductive polymer film obtained in the above example, The process was repeated 20 times or more, and thereafter, a carbon paste and a silver paste were sequentially deposited on the conductive polymer film in the same manner as in the above-described example, to produce a solid electrolytic capacitor.

The capacitance at 120 Hz of the capacitor according to the example thus obtained was 95.5 μF (capacitance appearance rate was 97.4%). On the other hand, the capacitance at 120 Hz of the capacitor obtained in the comparative example is 2
0.2 μF (capacitance appearance rate is 20.6%), which is due to a mixed solution of a heterocyclic compound, an oxidizing agent and a dopant in the process of forming a conductive polymer film, which is the greatest feature of the method of the present invention. It clearly shows how great the effect of performing the impregnating treatment at a high temperature of 30 to 60 ° C. is.

[0021]

As described above, according to the present invention, a valve-acting metal sintered body having an anodic oxide film formed on its surface is heated to a temperature of 30 to 60 ° C. comprising a heterocyclic compound monomer and an oxidizing agent and / or a dopant. After impregnating the held mixed solution, chemical oxidative polymerization is performed during drying at room temperature.By maintaining the temperature of the mixed solution during the impregnation within the above range, the viscosity and surface tension of the mixed solution are reduced, and firing is performed. The solution can penetrate into the pores inside the oxide film on the surface of the condensate, and together with the monomer adhering to the oxide film, polymerization of the penetrated monomer occurs inside such a region, resulting in a dense conductive polymer film Thus, a solid electrolytic capacitor having a high capacitance appearance rate and excellent high-frequency characteristics can be obtained.

Claims (2)

[Claims] 1. A valve metal sintered body having an anodic oxide film formed on its surface is impregnated with a mixed solution of a heterocyclic compound monomer and an oxidizing agent and / or a dopant at 30 to 60 ° C., and then subjected to chemical oxidative polymerization. Forming a conductive polymer film as a solid electrolyte on the anodized film of the sintered body. 2. Pyrole as a heterocyclic compound monomer,
2. The method according to claim 1, wherein at least one monomer selected from thiophene, furan, and derivatives thereof is used.