JPH11238648A - Solid electrolytic capacitor and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively utilize ethylene-dioxythiophene(EDT) charged as a raw material. SOLUTION: In this manufacturing method, a metallic pellet having a dielectric oxide film is dipped into an EDT solution of prescribed concentration for a prescribed time for having EDT stick to the surface of the dielectric oxide film, the pellet is dipped into an oxidizer solution of prescribed concentration for a prescribed period to cause oxidizer to stick to EDT and then the pellet is cleaned by water, hot water, an organic solvent, etc., and dried. These processes from the dipping of the pellet into the EDT solution up to the dry of the pellet are repeated a prescribed number of times. Then carbon and silver paste are applied, a cathode terminal is drawn out by a silver bonding agent, and resin is externally applied to execute aging.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolytic capacitor having a solid electrolyte layer formed by chemically oxidizing and polymerizing ethylenedioxythiophene (hereinafter, referred to as EDT). And a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, a solid electrolytic capacitor using a conductive polymer as a solid electrolyte of an electrolytic capacitor to reduce impedance in a high frequency region has been developed. Such a solid electrolytic capacitor is made of a film-forming metal such as aluminum or tantalum having an anodized film,
It has a structure with a solid electrolyte attached. Conventionally, manganese dioxide formed mainly by thermal decomposition of manganese nitrate has been used as a solid electrolyte of this type of solid electrolytic capacitor. However, the high heat required during the thermal decomposition of manganese nitrate and the oxidizing action of the generated NOx gas damage the metal oxide films such as aluminum and tantalum, which are dielectric materials. , The leakage current increases, and the dielectric properties deteriorate.

Therefore, a conductive polymer compound having high conductivity and good adhesion to a dielectric film has been attracting attention as a solid electrolyte for an electrolytic capacitor (Japanese Patent Publication No. 7-2).
2077, JP-A-2-15611, etc.). Note that polythiophene is known as a typical example of the conductive polymer compound. As the polythiophene, a polymer of a thiophene compound such as thiophene, 3-methylthiophene, or 3,4 ethylenedioxythiophene, or a copolymer or a mixture thereof is used.

Here, a conventional method for manufacturing a solid electrolytic capacitor using polythiophene as a conductive polymer compound will be described. That is, after a film-forming metal pellet such as aluminum or tantalum is immersed in a mixed solution of EDT and an oxidizing agent, the metal pellet is pulled up from the mixed solution and polymerized in the air. After that, the solvent was quantitatively removed at room temperature, and carbon and silver paste were applied.
The cathode is pulled out with a silver adhesive, resin-encased and aged.

[0005] As described above, in the conventional method for manufacturing a solid electrolytic capacitor, the metal pellets are pulled up from the mixed solution and polymerized by evaporating the solvent of the mixed solution in air to increase the concentration of the oxidizing agent in the mixed solution. By doing so, the polymerization reaction proceeds. The mixed solution of EDT and oxidizing agent is usually prepared as follows. For example, 10 wt% of EDT as a monomer, 36 wt% of ferric p-toluenesulfonate as an oxidizing agent, and 54 wt% of butyl alcohol as a solvent are mixed.

[0006]

However, the conventional method for manufacturing a solid electrolytic capacitor as described above has the following problems. That is, since a mixed solution of EDT and an oxidizing agent is used when forming the solid electrolyte layer, the EDT in the mixed solution is also polymerized by the oxidizing action of the oxidizing agent in the mixed solution to form polyethylenedioxythiophene. (Hereinafter, referred to as PEDT), the PEDT had to be discarded, EDT in the mixed solution could not be effectively used, and the material efficiency was extremely poor.

Further, the process of forming the solid electrolyte layer is influenced by the life of the mixed solution, for example, the oxidizing action of the oxidizing agent is weakened by denaturation of the mixed solution of EDT and the oxidizing agent. Further, in preparing a mixed solution of EDT and an oxidizing agent, since there are certain restrictions on the concentrations, mixing ratios, and the like of the two, the concentration of EDT cannot be set arbitrarily, and a solid electrolyte layer having a desired thickness is formed. For this purpose, there has been a problem that the number of polymerizations must be increased.

The present invention has been proposed to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide a solid electrolytic capacitor which makes effective use of EDT which is charged as a raw material. . Another object of the present invention is to provide a method of manufacturing a solid electrolytic capacitor that can effectively use EDT supplied as a raw material.

[0009]

In order to solve the above problems, the solid electrolytic capacitor of the present invention is manufactured by the following method. That is, a metal pellet having a dielectric oxide film is immersed in an EDT solution having a predetermined concentration for a predetermined time to adhere EDT on the dielectric oxide film, and then the metal pellet is immersed in an oxidant solution having a predetermined concentration. After immersing for a predetermined time, the oxidizing agent is attached to the EDT, and then washed with water, hot water, an organic solvent or the like, and dried. Then, the steps from immersion to drying in the EDT solution are repeated a predetermined number of times. After that, carbon and silver pastes are applied, the cathode terminal is pulled out with a silver adhesive, and a resin exterior is used to perform aging.

In this case, when the solvent of the oxidizing agent solution is an organic solvent, the polymerization may be carried out in air or in a solution depending on the type of the solvent. For example, if the oxidizing agent is p-
When ferric toluenesulfonic acid (FePTS) is used and γ-butyrolactone is used as a solvent, the polymerization is performed in a liquid because the polymerization rate is high. On the other hand, when the solvent is a monohydric alcohol, the polymerization is performed in air because the polymerization rate is low. The reason why the polymerization is performed in the air when the polymerization rate is low is that the solvent evaporates in the air and the concentration of the oxidizing agent increases.

On the other hand, when the solvent of the oxidizing agent solution is water, EDT is not well compatible with water, so the oxidizing agent does not adhere to the EDT simply by dipping in the oxidizing agent aqueous solution. However, when polymerization is carried out in an aqueous solution of an oxidizing agent, the polymerization proceeds favorably, and a solid electrolyte layer of PEDT is formed. Therefore,
When the solvent of the oxidizing agent solution is water, it is desirable to carry out the polymerization in the oxidizing agent aqueous solution.

The number of times the metal pellets are alternately immersed in the EDT solution and the oxidizing agent solution is 1 to 20, preferably 3 times.
10 to 10 times, immersion time in the oxidizing agent solution is 5 minutes to 5 hours,
Preferably, it is 15 minutes to 3 hours.

Here, among the oxidizing agents used in the present invention, aqueous solutions include peroxodisulfuric acid and Na
Salt, K salt, NH ₄ salt, cerium (IV) nitrate, cerium nitrate
(IV) ammonium, iron (III) sulfate, iron (III) nitrate, iron (III) chloride and the like. In addition, as an organic solvent system,
Ferric salts of organic sulfonic acids such as iron (III) dodecylbenzenesulfonate, iron (III) p-toluenesulfonate
And the like. Here, examples of the organic solvent include γ-butyrolactone and monohydric alcohols such as butanol and propanol. The concentration of the oxidizing agent solution was 5 to 50 wt%, and the temperature of the oxidizing agent solution was -15 to 6%.
0 ° C. is preferred.

As a solvent for EDT, a monohydric alcohol (methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, etc.) is used. The EDT solution may have any concentration.

Next, as a metal having a valve action used for the anode, a metal having a valve action such as aluminum, tantalum, niobium, titanium or an alloy using these metals as a substrate can be used. The shape of the anode is not particularly limited, such as a porous sintered body of such a metal, a plate (including a ribbon, a foil, and the like) surface-treated by etching or the like, a wire, and the like. Further, as a method of forming a dielectric oxide film on the surface of the metal pellet, a conventionally known method can be used. For example, when a sintered body of tantalum powder is used, it can be anodized in a phosphoric acid aqueous solution to form an oxide film on the sintered body.

(Effect) According to the method for manufacturing a solid electrolytic capacitor of the present invention as described above, the metal pellet is
Since the polymerization is carried out by immersing in a solution and then immersing in an oxidizing agent solution and alternately repeating immersing in both solutions a predetermined number of times, as in the case of using a conventional mixed solution of EDT and oxidizing agent, It is possible to prevent the progress of the polymerization of EDT therein. Therefore, the ED
T can be used, and the raw material efficiency of EDT is 1
00%.

In addition, since the EDT solution and the oxidizing agent solution are prepared separately without using the conventional mixed solution of EDT and the oxidizing agent, the concentration and amount of the oxidizing agent solution are independent of each other.
It is possible to use an EDT solution of any concentration.
Furthermore, there is no need to consider the life of the mixed solution of EDT and the oxidizing agent, and the process of forming the solid electrolyte layer can be performed with high accuracy and high reliability.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for manufacturing a solid electrolytic capacitor according to the present invention and the initial characteristics of the solid electrolytic capacitor obtained by the method will be described below. A conventional solid electrolytic capacitor using manganese dioxide for the solid electrolyte layer was used as a comparative example, and its initial characteristics were compared and examined.

[1. Examples of Reagents Used] Monomer: Ethylenedioxythiophene (EDT) Solvent of Monomer Solution: Monohydric alcohol (for example, methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol,
Isobutyl alcohol, sec-butyl alcohol, t
ert-butyl alcohol, etc.) Oxidizing agent: An aqueous solution or an organic solvent may be used. For example, ammonium peroxodisulfate, sodium peroxodisulfate, iron (III) sulfate, iron (III) nitrate, iron (III) chloride, cerium (IV) nitrate, cerium (IV) ammonium nitrate, cerium (IV) sulfate, cerium sulfate (IV) ammonium, iron (III) dodecylbenzenesulfonate, iron (III) p-toluenesulfonate

[2. Application conditions] Oxidant solution concentration: 5 to 50 wt% Oxidant solution temperature: -15 to 60 ° C

[3. Manufacturing Method] As shown in the flowchart of FIG. 1, tantalum pellets (for A size, powder C)
V = 30 k, 41 FV, 6 μF) at room temperature for 2 minutes, 5
Immerse in 0% EDT in isopropyl alcohol solution.
Next, the tantalum pellets are immersed in an oxidizing agent aqueous solution (water: ammonium peroxodisulfate = 2: 1 <wt>), and left at room temperature for 3 hours to polymerize. Then, it is washed with water for 10 minutes and dried at 100 ° C. for 20 minutes. This operation was repeated six times, and after applying carbon and silver paste, the cathode terminal was pulled out with a silver adhesive, and then sealed with a resin.
Aging was performed at 5 ° C. and 16 V for 1 hour.

[4. Comparative Example] A solid electrolytic capacitor using manganese dioxide for the solid electrolyte layer was used as a comparative example. The manganese dioxide solid electrolyte layer was formed as follows. That is, instead of repeating the operation of immersing in the EDT solution and drying in the manufacturing method of the present invention shown in FIG. To form This operation of immersion and thermal decomposition is repeated a total of five times.

[5. Comparative results] Table 1 shows the initial characteristics of the solid electrolytic capacitor obtained by the manufacturing method of the present invention and the initial characteristics of the comparative example.

[0024]

[Table 1]

As is apparent from Table 1, the solid electrolytic capacitor according to the present invention has an ESR (equivalent series resistance) of about 比 べ as compared with the comparative example, and excellent characteristics of PEDT are obtained. .

[0026]

As described above, according to the present invention,
It is possible to provide a solid electrolytic capacitor that makes effective use of EDT supplied as a raw material. Further, it is possible to provide a method for manufacturing a solid electrolytic capacitor that can effectively use EDT supplied as a raw material.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a method for manufacturing a solid electrolytic capacitor of the present invention.

Claims (8)

[Claims] 1. A method of manufacturing a solid electrolytic capacitor in which a solid electrolyte layer is formed on the surface of a metal pellet on which a dielectric oxide film is formed by chemically oxidatively polymerizing a monomer that forms a conductive polymer compound and an oxidizing agent solution. 3. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the metal pellets are alternately immersed in each of the monomer and the oxidizing agent solution. 2. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the number of times of immersion alternately in each of the monomer and the oxidizing agent solution is 1 to 20 times. 3. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the time of immersion in the oxidizing agent solution is 5 minutes to 5 hours. 4. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein said monomer is ethylenedioxythiophene (EDT). 5. A solid electrolytic capacitor in which a solid electrolyte layer is formed on the surface of a metal pellet on which a dielectric oxide film is formed by chemically oxidatively polymerizing a monomer forming an electroconductive polymer compound and an oxidizing agent solution. A solid electrolytic capacitor, wherein the solid electrolyte layer is formed by alternately immersing and polymerizing the metal pellet in each of the monomer and the oxidant solution a predetermined number of times. 6. The solid electrolytic capacitor according to claim 5, wherein the number of times of alternate immersion in each of the monomer and the oxidant solution is 1 to 20 times. 7. The solid electrolytic capacitor according to claim 5, wherein the immersion time in the oxidant solution is 5 minutes to 5 hours. 8. The solid electrolytic capacitor according to claim 5, wherein the monomer is ethylenedioxythiophene (EDT).