JPH08288184A - Manufacture of aluminum solid electrolytic capacitor - Google Patents

Abstract

PURPOSE: To obtain a solid electrolytic capacitor in the lamination structure of aluminum/alumina/conductive macromolecule with a simple method. CONSTITUTION: Alumina and conductive macromolecule are simultaneously formed and laminated by performing electrolytic operation of aluminum in an aqueous solution where a conductive macromolecular monomer and a surface active agent are dissolved.

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 an aluminum solid electrolytic capacitor using a conductive polymer as a solid electrolyte.

[0002]

2. Description of the Related Art Conventionally, an aluminum electrolytic capacitor has an electrolytic solution prepared by dissolving a solute of a monoammonium salt of an organic polyvalent carboxylic acid such as phthalic acid or maleic acid in a solvent such as γ-butyrolactone, dimethylformamide or tetrahydrofuran. Are used (JP-A-1114030, JP-A-62-145715, USP4377692,
Special publication 87/5149).

Recently, aluminum solid electrolytic capacitors using a conductive polymer as a solid electrolyte have been commercialized. Since the conductive polymer such as polypyrrole as the solid electrolyte has a high electric conductivity of about 100 to 1000 times that of the electrolytic solution, the aluminum solid electrolytic capacitor has a low impedance even in a high frequency region, and further has a large capacitance or tangent. It has excellent electrical characteristics such as low temperature dependence of loss.

As a method of manufacturing an aluminum solid electrolytic capacitor using a conductive polymer as a solid electrolyte, aluminum is anodized in an electrolytic solution such as an aqueous solution of ammonium adipate to form alumina, which is a dielectric, and then, There is a method of forming a conductive polymer on alumina by electrolytic polymerization in an electrolytic solution containing a conductive polymer monomer such as pyrrole. However, in the case of such a two-step manufacturing method, since the alumina formed in the first step has a large insulating property, the formation of the conductive polymer by electrolytic polymerization in the next step is often inconvenient. For example, it is necessary to carry out electrolytic polymerization at a low temperature of -25 to -45 ° C. (JP-A-62-189714)

As a method for manufacturing a solid electrolytic capacitor at room temperature to high temperature, Japanese Patent Laid-Open No. 63-158829 discloses that a dielectric oxide film is formed on a film forming metal of aluminum or tantalum, and the dielectric oxide film is oxidized. A conductive polymer film chemically-oxidized using an agent is formed, and a conductive polymer film of polypyrrole obtained by electrolytic polymerization is further laminated on the conductive polymer film to form a double conductive film. Solid electrolytic capacitor using a conductive polymer film as a solid electrolyte,
JP-A-63-173313 discloses a dielectric oxide film formed on a film forming metal, a thin film of a metal or a metal compound having conductivity formed on the dielectric oxide film, and the metal or the conductive film. We propose a solid electrolytic capacitor formed by forming a conductive polymer film obtained by electrolytic polymerization as a solid electrolyte on a thin film of a metal compound having properties.

However, in these methods, in addition to increasing the number of manufacturing steps, when conducting chemical polymerization, the electric conductivity of the conductive polymer formed is lower than that of the conductive polymer formed by electrolytic polymerization. It has the drawback. Further, there is a document that alumina and a conductive polymer are simultaneously formed by electrolyzing aluminum in a liquid electrolyte containing a conductive polymer monomer (P. Hulser and
F. Beck, J. et al. Appl. Electro. Che
m. , 20, 596-605 (1990)). However, as described in the document, alumina formed by this method has a porous structure, and it is difficult to apply it to an aluminum solid electrolytic capacitor.

In addition to the above problems, the anode aluminum foil normally used for aluminum electrolytic capacitors is etched for the purpose of increasing the electrostatic capacity by increasing the surface area, so that the inside of the etching pit is electrically conductive when electrolysis is performed. A structure filled with a functional polymer must be formed. Because
This is because if there are voids inside the etching pit, it is not possible to obtain the same capacity appearance rate as that of a capacitor using a driving electrolyte solution.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a simpler method for producing an aluminum solid electrolytic capacitor using a conductive polymer as a solid electrolyte.

[0009]

The first aspect of the present invention is to simultaneously form and laminate alumina and a conductive polymer by electrolyzing aluminum in an aqueous solution in which a conductive polymer monomer and a surfactant are dissolved. A method for manufacturing an aluminum solid electrolytic capacitor characterized by the above.

The second aspect of the present invention is to form a conductive polymer laminated on alumina by electrolyzing aluminum having alumina formed on its surface in an aqueous solution in which a conductive polymer monomer and a surfactant are dissolved. The present invention provides a method for manufacturing an aluminum solid electrolytic capacitor characterized by the above.

[0011]

[Function] When a surfactant is present in an aqueous solution, a lipophilic conductive polymer monomer forms a micellar structure surrounded by the surfactant, which facilitates transfer (supply) to the site of electrolytic polymerization. That is, the formation of aluminum alumina by electrolysis and the polymerization of the conductive polymer monomer can be performed at the same time, and a laminate in which the conductive polymer is laminated on the surface of alumina can be easily obtained. When an aluminum etching foil whose surface area is increased by etching is used, the conductive polymer is simultaneously laminated and formed so as to fill the inside of the etching pit by the same action.

(Summary of the Invention) The aluminum used as a raw material for forming aluminum / alumina film / conductive polymer film of an aluminum capacitor element is not particularly limited as long as it is an aluminum foil which can be used for aluminum electrolytic capacitor applications. It is preferable that the surface area is increased by etching for the purpose of improving the electrostatic capacity. Further, the aluminum may be aluminum having aluminum oxide (alumina) formed on its surface in advance by chemical conversion treatment.

Conductive Polymer Monomer As the monomer for forming a conductive polymer by electrolysis used in the present invention, heterocyclic compounds such as pyrrole, N-methylpyrrole, thiophene, furan, indole and carbazoles, aniline and azo. Aromatic amino compounds such as phenylenes, o-phenylenediamine, o-aminophenol, azulene, pyrene, acene, acetylene,
Examples include monomers such as aromatic hydrocarbon compounds such as cyanoacetylene and phenylacetylene, and phenylene compounds such as benzene, phenol and thiophenol. The concentration of these aqueous solutions is suitably in the range of 0.01 to 1 mol / liter.

Surfactant As the surfactant used in the present invention, an anionic surfactant or a zwitterionic surfactant is used. As the anionic surfactant, alkyl sulfonic acids such as decyl sulfonic acid and dodecyl sulfonic acid; carbon number of alkyl group attached to benzene ring such as octylbenzene sulfonic acid, dodecyl benzene sulfonic acid and tridecyl benzene sulfonic acid 8 to 23 alkylbenzene sulfonic acids; alkylnaphthalene sulfonic acids, sulfuric acid monoesters such as dodecyl sulfate, tetradecyl sulfate, hexadecyl sulfate, decanoic acid, dodecanoic acid, perfluorohexanoic acid, perfluorooctanoic acid, 2-sulfonatotetradecanoic acid, etc. The salts of carboxylic acids of are used.

As the cation forming a salt, alkali metal ions such as sodium ion, lithium ion and potassium ion, quaternary ammonium ion such as tetramethylammonium ion, triethylmethylammonium ion, tetraethylammonium ion and tetrabutylammonium ion. , Quaternary phosphonium ions such as tetramethylphosphonium ion, triethylmethylphosphonium ion, tetraethylphosphonium ion and tetrabutylphosphonium ion. As the zwitterionic surfactant, dodecyldimethylammoniopropanecarboxylate, 3- (dimethyldodecylammonio) propane-1-sulfonate, 3-
(Dodecylmethylammonio) propane-1-sulfonate, N-dodecyl-N, N-dimethylglycine, C-
Examples include dodecyl-N, N-dimethylglycine.

These surfactants may be used alone or in admixture of two or more. The molar concentration of these aqueous solutions is suitably 0.01 to 1 mol / liter. The molar concentration of the surfactant relative to the conductive polymer monomer is preferably in the range of 1: 0.2 to 1: 5, and more preferably 1: 1.

Electrolysis In the electrolysis, aluminum or aluminum having alumina formed on the surface is used as an anode, and a metal such as platinum, stainless steel, or aluminum is used as a counter electrode, which is subjected to an electric current in an aqueous solution containing a conductive polymer monomer and a surfactant. Aluminum / alumina / conductive polymer is formed by performing constant current electrolysis at a density of 0.1 to 100 mA / cm ² for 10 to 120 minutes.

Aluminum Solid Electrolytic Capacitor The anode and cathode leads are attached to the capacitor element composed of the above aluminum / alumina film / conductive polymer film, and resin encapsulation and case encapsulation are performed to produce an aluminum solid electrolytic capacitor.

[0019]

【Example】

Example 1 A 1 cm × 1 cm aluminum foil was used as an anode, a platinum plate was used as a cathode, and a 0.1 mol / 1 sodium dodecylbenzenesulfonate aqueous solution containing 0.1 mol / 1 pyrrole was used as an electrolytic solution, with a current density of 1 mA / cm ^2. Constant current electrolysis was carried out for 20 minutes. The voltage increased to 35 V, and a black polypyrrole film was formed on the entire surface.

Colloidal graphite and silver paste were sequentially applied to the obtained aluminum / alumina / polypyrrole element, dried, and a cathode lead was attached, followed by epoxy resin encapsulation to produce an aluminum solid electrolytic capacitor. When the electrical characteristics of this capacitor were measured, the capacitance was 0.1 μF / cm ² , the tangent loss was 1.2%, the leakage current was 2.
It was 0 μA.

EXAMPLE 2 A 1 cm × 1 cm etched aluminum foil for an aluminum electrolytic capacitor was used as an anode, a platinum plate was used as a cathode, and 0.1 mol containing 0.1 mol / 1 of pyrrole was used as an electrolytic solution.
Using an aqueous solution of sodium dodecylbenzenesulfonate of 1/1, constant current electrolysis was performed for 15 minutes at an apparent current density of 10 mA / cm ² . The voltage increased to 12 V, and a black polypyrrole film was formed on the entire surface. When the cross section was observed with an electron microscope, it was found that polypyrrole was filled up to the inside of the etching pit. An aluminum solid electrolytic capacitor was produced in the same manner as in Example 1 except that this was used as a capacitor element. When the electrical characteristics of this capacitor were measured, the capacitance was 12 μF / c.
It was m ² , the tangent loss was 1.2%, and the leakage current was 2.0 μA.

Example 3 Alumina was formed on the surface by chemical conversion treatment as an anode 1
cm x 1 cm aluminum foil, platinum plate as the cathode,
0.1 containing 0.1 mol / 1 of pyrrole as electrolyte
A constant current electrolysis was performed at a current density of 1 mA / cm ² using a mol / 1 sodium dodecylbenzenesulfonate aqueous solution.
I went for 0 minutes. The voltage increased to 35 V, and a black polypyrrole film was formed on the entire surface. An aluminum solid electrolytic capacitor was produced in the same manner as in Example 1 except that this was used as a capacitor element. When the electrical characteristics of this capacitor were measured, the capacitance was 0.1 μF / cm ² , the tangent loss was 1.2%, and the leakage current was 2.0 μA.

Comparative Example 1 Electrolysis was carried out under the same conditions as in Example 1 except that sodium p-toluenesulfonate having a function as an electrolyte was used in place of sodium dodecylbenzenesulfonate as a surfactant. Although a polypyrrole film was formed, the voltage increased only by a few volts, and aluminum was dissolved while gas was being generated. Therefore, an aluminum solid electrolytic capacitor element could not be manufactured.

Comparative Example 2 Comparative Example 1 except that the electrolyte was replaced with ammonium adipate
Electrolysis was performed under the same conditions as in. The voltage increased and an alumina film was formed, but a polypyrrole film was not formed. Therefore, an aluminum solid electrolytic capacitor could not be manufactured.

[0025]

By electrolyzing aluminum in an aqueous solution of a conductive polymer monomer and a surfactant, it is possible to obtain a solid electrolytic capacitor element in which alumina and a conductive polymer are laminated simultaneously.

Claims (3)

[Claims] 1. A method for producing an aluminum solid electrolytic capacitor, wherein aluminum and a conductive polymer are simultaneously formed and laminated by electrolyzing aluminum in an aqueous solution in which a conductive polymer monomer and a surfactant are dissolved. Method. 2. A conductive polymer laminated on alumina is formed by electrolyzing aluminum having alumina formed on its surface in an aqueous solution in which a conductive polymer monomer and a surfactant are dissolved. Aluminum solid electrolytic capacitor manufacturing method. 3. The conductive polymer monomer is added in an aqueous solution of 0.
3. Aluminum according to claim 1 and claim 2, characterized in that it is used in a molar concentration of from 0 to 1 mol / l and the surfactant is used in a molar concentration of from 0.01 to 1 mol / l in an aqueous solution. Manufacturing method of solid electrolytic capacitor.