JPH10321473A - Solid electrolytic capacitor and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliable solid electrolytic capacitor having a large capacitance and an excellent impedance characteristic, by using conductive high polymers for its solid electrolyte. SOLUTION: In a solid electrolytic capacitor in which a dielectric oxide film 1a is formed on the surface of a capacitor element 1 composed of a metal 1b serving as a valve which becomes an anode and a conductive high polymer layer is formed on the surface of the film 1a, the conductive high polymer layer is composed of a first conductive high polymer layer 2 which is formed by heating a solution in which polyaniline or its derivative is dissolved, and a second conductive high polymer layer 3 formed by electrolyzing and polymerizing polyaniline or its derivative. In a method for manufacturing the capacitor, the layer 2 is formed by heating a solution prepared by dissolving polymeric- aniline in a solvent containing water.

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 using a conductive polymer compound as a solid electrolyte and a method for producing the same. The present invention also provides a solid electrolytic capacitor having a large capacitance, excellent frequency characteristics, and excellent reliability even in a capacitor element comprising:

[0002]

2. Description of the Related Art Conventionally, various solid electrolytic capacitors have been proposed in which a conductive polymer is used as a solid electrolyte of an electrolytic capacitor to reduce impedance in a high frequency range. FIG. 3 is a sectional view of an example of a conventional solid electrolytic capacitor. A dielectric film 1a is formed by anodic oxidation on the surface of a capacitor element 1 made of a valve metal 1b serving as an anode, a conductive polymer layer 2 serving as a solid electrolyte is formed thereon, and a carbon layer 4 is provided thereon. A silver layer 5 is formed, and is further covered with an epoxy resin 8. An anode lead 6 is connected to the anode side of the capacitor element 1, and a cathode lead 7 is connected to the silver layer 5.

[0003] Polyacetylene, polypyrrole, polyaniline, polythiophene, polyparaphenylene, and the like are known as conductive polymers used for the solid electrolyte of the above-mentioned solid electrolytic capacitor. Among them, polypyrrole, polythiophene, and polyaniline are particularly conductive polymers. And it is often used because of its excellent thermal stability.

For example, Japanese Patent Application Laid-Open No. 4-48710 discloses that a conductive polymer layer is first formed on a dielectric oxide film by chemical polymerization of polypyrrole, and then a conductive polymer layer of polypyrrole is newly formed by electrolytic polymerization. Although a solid electrolytic capacitor using a two-layer conductive polymer layer as a solid electrolyte is disclosed, it is difficult to form a uniform layer of a polypyrrole layer by chemical polymerization, and it is difficult to form a uniform layer such as a concave portion of a sintered body or an etching pit. It is hard to be formed in a very fine part, resulting in undesired results such as a reduction in product capacity and an increase in impedance.

Further, a method of applying a solution of polyaniline which has been polymerized in advance on the surface of a dielectric film and drying it,
A solid electrolytic capacitor in which a polyaniline thin film is formed and used as a solid electrolyte has been proposed (JP-A-3-35516).
No.). However, this method has the disadvantage that the viscosity of the polyaniline solution is high and does not penetrate into the recesses of the tantalum sintered body composed of finely divided powder particles or the recesses of the oxide film on the aluminum foil. was there.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a capacitor which can maintain a large capacitance even in a capacitor element made of fine powder particles and has excellent impedance characteristics in a high frequency range. And

Further, when a conductive polymer layer is formed on the surface of a capacitor element such as an aluminum foil or a tantalum sintered body, in the conventional method, an increase in leakage current of the capacitor and a decrease in reliability due to a stress at the time of resin sheathing. Because it occurs, a conductive polymer layer of uniform thickness is formed on the capacitor element surface,
It is also intended to improve mechanical strength.

[0008]

According to the present invention, a dielectric oxide film 1a is formed on the surface of a capacitor element 1 made of a valve metal 1b serving as an anode, and a conductive polymer layer is formed on the surface of the dielectric oxide film 1a. In the formed solid electrolytic capacitor,
A first conductive polymer layer 2 formed by heating a solution of polyaniline or a derivative thereof, and a second conductive polymer layer formed by electrolytic polymerization of polyaniline or a derivative thereof 3 is a solid electrolytic capacitor.

In the above solid electrolytic capacitor,
The first conductive polymer layer 2 is a method for manufacturing a solid electrolytic capacitor, wherein the first conductive polymer layer 2 is formed by heating in a solution in which a polymeric aniline is dissolved in a solvent containing water.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention solves the above-mentioned problems by using a two-layer conductive polymer compound as a solid electrolyte. The first conductive polymer is converted into a solvent containing water. Dissolve, easily penetrate into the pores of the dielectric film of the capacitor element by the permeation of water, and dissolve aniline or its derivative in a solvent containing water with high conductivity polyaniline or its derivative. It is formed by heating. A mechanically strong polyaniline or its derivative layer is formed thereon by electrolytic polymerization as a second conductive polymer layer.

In the solid electrolytic capacitor of the present invention, tantalum, aluminum, niobium, titanium, zirconium, magnesium and the like can be used as the valve metal. Further, these valve action metals can be used in the form of a rolled foil, a fine powder sintered material, or the like. The valve metal is anodized in an electrolytic solution to form a dielectric oxide film. The electrolyte and solvent used are not particularly limited, and known materials can be used. In addition, a constant voltage method or a constant current method can be applied as a method of anodic oxidation, and the voltage, the method of increasing the current, the holding time after the voltage becomes constant, the temperature, and the like are not limited, and if necessary Can be set.

Further, in the solid electrolytic capacitor of the present invention, a valve metal provided with a dielectric for improving characteristics such as a capacitance value and an impedance value of the capacitor is heat-treated at a predetermined temperature and a predetermined atmosphere. Various surface treatments can also be applied to the working metal.

The polyaniline or the derivative thereof forming the first conductive polymer layer inside the pores of the solid electrolytic capacitor of the present invention is obtained by polymerizing the polymer after or during the polymerization.
After dissolving in a solvent containing water, introducing into a porous body of a film-forming metal, and then heating and drying to form a conductive polymer, the capacitor element is washed with a solvent in which water or an oxidizing agent is easily soluble. Then, an oxidizing agent that does not contribute to conductivity is removed.

The polyaniline or its derivative forming the second conductive polymer layer on the surface of the capacitor element is formed by electrolytic polymerization.

After forming a conductive polymer as an electrolyte,
Drying is performed as necessary, and a graphite layer and a silver paint layer are formed thereon, and an extraction electrode is provided by a known method, and assembled into a capacitor. In the present invention, the graphite layer and the silver paint layer are not particularly limited, and conventionally known layers can be used.

[0016]

FIG. 1 is a flow chart for explaining a manufacturing process according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing the basic structure of the solid electrolytic capacitor of the present invention, in which a valve action metal 1b serving as an anode is formed of a sintered body of fine tantalum powder, and a dielectric film 1a is formed by anodic oxidation. . A first layer 2 of a conductive polymer to be a solid electrolyte is formed inside the pores of the tantalum pellet 1, a second layer 3 of a conductive polymer is formed thereon, and a carbon layer 4 is further formed thereon. Silver layers 5 are sequentially formed. Then, the anode lead 6 is connected to the tantalum pellet, the cathode lead 7 is connected to the silver layer 5,
These are covered with an exterior epoxy resin 8.

[Example] Diameter 1.1 mm, height 1.2 m
m, powder CV value per gram (product of capacity and formation voltage)
Was anodized at 20 V in a 0.05 wt% aqueous solution of phosphoric acid, washed and dried, and then water-soluble polyaniline (PAS manufactured by Nitto Chemical Co., Ltd.) was used. The process of immersion and drying at 100 ° C. for 10 minutes was repeated six times to form polyanilinesulfonic acid. Thereafter, on the formed polyaniline sulfonic acid layer, aniline 0.1 mol / l, sulfuric acid 0.1 m
A current of 1 mA was passed for 5 hours with an aqueous solution containing ol / l to form a polyaniline layer by electrolytic polymerization. Next, after washing with pure water and ethanol, drying was performed at 100 ° C. for 5 minutes. A graphite layer and a silver paint layer were sequentially formed on the generated conductive polyaniline layer. While the anode lead was welded to the obtained capacitor element, the cathode lead was joined with a conductive adhesive, and then covered with a resin by transfer molding to complete the capacitor, and the electrical characteristics were measured.

Comparative Example After the same sintered element as in Example 1 was anodized in the same manner as in Example 1, polymerized soluble polyaniline and N-methylpyrrolidone were added in a weight ratio of 5: 9.
After immersion in a polyaniline solution containing 5
Drying was performed at 5 ° C. for 5 minutes to form a polyaniline layer in a undoped state. Next, the resultant was impregnated with an aqueous sulfuric acid solution, and the polyaniline layer was doped, washed with acid and ethanol, and dried at 100 ° C. for 5 minutes to form polyaniline as a conductive polymer layer. Hereinafter, leads were led out in the same manner as in the example to complete the capacitor.

The capacitance ratio (C / C., The capacity in the electrolyte solution is C) before and after the solder heat resistance test (immersion at 260 ° C. for 10 seconds) of the capacitors in the above Examples and Comparative Examples, and the leakage current value ( LC, 1 minute after applying 6.3 V) and impedance (Z) at 100 kHz are shown in Table 1 below.

[0020]

[Table 1]

As shown in Table 1, all of the examples of the present invention exhibited excellent capacity ratio and impedance characteristics, and showed good results with little increase in leakage current even after the heat resistance test.

[0022]

As described above, according to the present invention, polyaniline or a dielectric thereof formed by heating a polymer aniline solution of a first conductive polymer compound, and a second conductive polymer compound. A solid electrolytic capacitor having a two-layered solid electrolyte in combination with polyaniline or a derivative thereof formed by electrolytic polymerization of a solid electrolytic capacitor can maintain a large capacity, has excellent impedance characteristics, and has excellent reliability. Can be provided.

[Brief description of the drawings]

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

FIG. 2 is a sectional view showing a basic structure of the solid electrolytic capacitor of the present invention.

FIG. 3 is a sectional view of a conventional solid electrolytic capacitor.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 capacitor element 1 a dielectric oxide film 1 b valve metal 2 conductive polymer (first layer) 3 conductive polymer (second layer) 4 carbon layer 5 silver layer 6 anode lead 7 cathode lead 8 epoxy resin

Claims (2)

[Claims] 1. A dielectric oxide film (1a) on a surface of a capacitor element (1) made of a valve metal (1b) serving as an anode.
And a conductive polymer layer formed on the surface of the dielectric oxide film (1a), wherein the conductive polymer layer is a solution of polyaniline or a derivative thereof in the form of a solution of polymer aniline or a derivative thereof. Characterized by comprising a first conductive polymer layer (2) formed by heating a polymer and a second conductive polymer layer (3) formed by electrolytic polymerization of polyaniline or a derivative thereof. Electrolytic capacitor. 2. The solid electrolytic capacitor according to claim 1, wherein the first conductive polymer layer (2) is formed by dissolving a polymer aniline or a derivative thereof in a solvent containing water. A method for manufacturing a solid electrolytic capacitor, characterized by being formed by heating.