JPH0645195A - Manufacture of solid-state electrolytic capacitor - Google Patents

Abstract

PURPOSE:To manufacture a solid-state electrolytic capacitor excellent in characteristics by a method wherein a dedoped polyaniline film is formed on a dielectric oxide film and then brought into contact with a dope solution to turn into a conductive polyaniline film. CONSTITUTION:A roughened aluminum etched foil is cut off, a lead is fixed to the cut foil by caulking, and the foil is subjected to a chemical conversion treatment for the formation of a dielectric oxide film. This element is dipped into dedoped polyaniline solution, then dried up, and then dipped into naphthalene sulfonic acid butanol solution and dried up, and this process is repeated ten times to form a conductive polyaniline film. A dedoped polyaniline solution is prepared using polyaniline polymerized by chemical oxidation at a reaction temperature of 25C or below. By this setup, a polyaniline film can be formed without causing damage to a dielectric oxide film or an aluminum foil by dissolving, and an excellent capacitor can be 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 producing a solid electrolytic capacitor using a conductive polyaniline film as a solid electrolyte.

[0002]

2. Description of the Related Art There has been proposed a solid electrolytic capacitor having a structure in which a dielectric oxide film is formed on the surface of a valve metal and a conductive polymer film is formed on the dielectric oxide film to form a solid electrolyte. In Japanese Unexamined Patent Publication No. 63-173313, a conductive polymer film is formed as a precoat layer on a dielectric oxide film by chemical oxidation polymerization, and a conductive polymer film is formed on the conductive polymer film by electrolytic polymerization. A capacitor having a structure in which a solid electrolyte is used is disclosed. Also, JP-A-63-15
8829 has a structure in which a thin film of a conductive metal compound such as manganese dioxide is formed as a precoat layer on a dielectric oxide film, and a conductive polymer film is formed on the thin film by electrolytic polymerization to form a solid electrolyte. Capacitors have been proposed. These capacitors are superior in frequency characteristics, electrical characteristics and heat resistance to conventional capacitors. However, in order to form a conductive polymer by the electrolytic polymerization method, a complicated device or process is required such as a special electrolytic tank or a jig for feeding power.

Polyaniline is one of the conductive polymers. Since polyaniline uses inexpensive aniline as a raw material, it is very economically advantageous. But,
In general, in order to synthesize conductive polyaniline, it is necessary to react in the presence of a high concentration of a protonic acid such as sulfuric acid, while aluminum commonly used for capacitors is
Since it is extremely weak against acid, even if an attempt is made to directly form such a conductive polyaniline film on an aluminum foil, the dielectric oxide film and aluminum are dissolved and the capacitor cannot be formed. There wasn't.

Further, as a method for easily forming a conductive polymer film, there is a chemical oxidative polymerization method using an oxidizing agent, but polyaniline by the chemical oxidative polymerization generally has a low electric conductivity and a small packing density. Even when applied to the solid electrolyte of a capacitor, excellent capacitor characteristics could not be obtained.

[0005]

An object of the present invention is to form a dielectric oxide film on the surface of a valve metal and to form a conductive polyaniline film on the dielectric oxide film to obtain a solid electrolyte. A method for manufacturing a solid electrolytic capacitor, which comprises forming a conductive polyaniline film without dissolving a dielectric oxide film and aluminum and providing a solid electrolytic capacitor having excellent characteristics.

[0006]

As a result of intensive studies, the present inventors have completed a method of manufacturing a solid electrolytic capacitor which can solve the above problems.

That is, in a method for producing a solid electrolytic capacitor in which a conductive polyaniline film is formed as a solid electrolyte on the surface of a valve metal having a dielectric oxide film formed thereon, a polyaniline solution dedoped on the dielectric oxide film is used. A method for producing a solid electrolytic capacitor, comprising forming a dedoped polyaniline film by using the polyaniline film, and then contacting it with a doping solution to form a conductive polyaniline film. Hereinafter, the method for manufacturing the present solid electrolytic capacitor will be described in detail.

Aluminum, tantalum or titanium is used as the valve action metal, and is used in the form of a flat single plate or a laminated plate, a wound body, a sintered body or the like. Next, the case where aluminum is used as the valve metal in the present invention will be described.

After etching the surface of the aluminum foil, the anode lead is connected through a lead tab, and electrolytic oxidation is performed in an aqueous solution of ammonium adipate to form a dielectric oxide film on the surface to obtain a device. A dedoped polyaniline film is formed on the dielectric oxide film by a method such as immersing the device in a dedoped polyaniline solution or coating and then drying. Next, the element having the dedoped polyaniline film formed thereon is brought into contact with the doping solution to be made conductive. By repeating this operation several times, a conductive polyaniline film is formed.

The dedoped polyaniline solution used in the present invention is prepared by dedoping the conductive polyaniline produced by chemical oxidative polymerization and dissolving it in an organic solvent. In order to chemically oxidatively polymerize aniline, aniline salt may be oxidatively polymerized with an oxidizing agent in a solution in the presence of a protic acid. The aniline salt used is usually aniline hydrochloric acid,
Examples thereof include salts of sulfuric acid, perchloric acid, and hydrofluoric acid. Further, as the oxidizing agent, persulfates such as ammonium persulfate and potassium persulfate, peroxides such as hydrogen peroxide and sodium peroxide, high atoms such as potassium permanganate, potassium dichromate and ferric chloride. Any oxidizing agent capable of oxidizing aniline such as a valent metal compound can be used.
Further, hydrochloric acid, sulfuric acid, perchloric acid, borofluoric acid, hexafluorophosphoric acid or the like is used as the protonic acid.

The polyaniline obtained by the chemical oxidative polymerization is dedoped when it is brought into contact with aqueous ammonia to become dedoped polyaniline. When this is dissolved in N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) or a mixed solvent of NMP and another organic solvent, a dedoped polyaniline solution is obtained.

[0012] It is preferable to control the reaction temperature at 25 ° C or lower when chemically oxidizing the aniline. A capacitor prepared by preparing a dedoped polyaniline solution from the polyaniline obtained under these conditions and forming a conductive polyaniline film on a dielectric oxide film and using it as a solid electrolyte provides excellent characteristics. It is more preferably 10 ° C or lower.
On the other hand, if chemical oxidative polymerization is performed without controlling the reaction temperature,
It becomes higher than 25 ℃ due to heat of reaction. A capacitor using polyaniline obtained under the condition that the reaction temperature becomes too high has a poor performance as a capacitor.

The doping solution is a solution of a protic acid dissolved in an organic solvent. The organic solvent used in the present invention is not particularly limited, and examples thereof include ketones, esters, alcohols, aromatic hydrocarbons, nitriles, cellosolves, and nitrogen-containing compounds. As the protic acid, inorganic acids such as hydrochloric acid, sulfuric acid, perchloric acid, borofluoric acid, hexafluorophosphoric acid, benzenesulfonic acid, p-toluenesulfonic acid, naphthalenesulfonic acid,
Organic sulfonic acids such as styrene sulfonic acid and its polymers, phthalic acid, oxalic acid, maleic acid, pyruvic acid,
Examples thereof include malonic acid, salicylic acid, citric acid, fumaric acid, acrylic acid and its polymers, and boron complex acids such as bissalicylateboronic acid, with organic sulfonic acids being preferred. Further, the concentration is 0.5 mol / l or less, and the contact time is several minutes to several tens of minutes, so that the dielectric oxide film is not damaged. For contact with the doping solution, methods such as dipping, coating and spraying are used. The drying temperature after contact is from room temperature to 200 ° C.

By the above method, a conductive polyaniline film is formed on a valve metal having a dielectric oxide film formed on its surface, and then a conductive coating film is formed on the surface of the element with a carbon paste and a conductive paste. Then, the cathode lead is taken out from a part thereof, and the capacitor can be obtained by a method such as sealing with a resin mold or an outer case.

According to the method of manufacturing a solid electrolytic capacitor of the present invention, a dedoped polyaniline film is formed on a dielectric oxide film using a dedoped polyaniline solution, and then the conductive polyaniline film is contacted with the doping solution to form a conductive polyaniline film. Since it is formed, the polyaniline film can be formed without melting and damaging the dielectric oxide film and the aluminum foil. Further, the capacitor thus manufactured has excellent characteristics such as a small equivalent series resistance. Furthermore, since the polyaniline film can be formed on the dielectric oxide film by a simple method such as dipping, the process is simplified, and the aniline monomer is not wasted, thus reducing the manufacturing cost.

[0016]

EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples. Example 1 4.7 g of aniline in a 300 ml glass reactor cooled to 5 ° C.
And ammonium persulfate in an aqueous solution containing 9.8 g of concentrated sulfuric acid 11.
An aqueous solution containing 4 g was dropped to carry out chemical oxidative polymerization. The formed precipitate was filtered to obtain polyaniline. This powder 4
g was mixed with 50 ml of ammonia water, and the mixture was stirred and filtered to obtain dedoped polyaniline. This dedoped polyaniline is made of NMP50wt%, butanol
0.3 wt of polyaniline dissolved in 50 wt% solvent and dedoped
% Solution was obtained. A roughened aluminum etched foil having a thickness of 50 μm and a width of 5 mm was obtained. After cutting the foil into 10 mm, the leads were attached by crimping, and chemical conversion treatment was carried out in an aqueous solution of ammonium adipate at 15 V to form a dielectric oxide film. This device was dipped in the previously prepared undoped polyaniline solution for 5 minutes and dried at 70 ° C., then dipped in a butanol solution of 0.3 mol / l naphthalenesulfonic acid for 5 minutes and dried at 100 ° C. The operation was repeated 10 times to form a conductive polyaniline film. This element is dipped in colloidal carbon, and a silver paste is applied to form a conductive coating film. A counter electrode is taken out from a part of the element and molded with an epoxy resin to obtain a rated voltage of 6.3 V and a rated capacitance. twenty two
A μF capacitor was completed. The initial characteristics of the obtained capacitor are shown in Table 1.

Example 2 Polyaniline dedoped by dissolving the dedoped polyaniline obtained in the same manner as in Example 1 except that the chemical polymerization temperature was 15 ° C. in a solvent of NMP 60 wt% and ethanol 40 wt%.
A 0.3 wt% solution was obtained. A roughened aluminum etched foil having a thickness of 50 μm and a width of 5 mm was obtained. After cutting the foil into 10 mm,
The lead was attached by crimping, and chemical conversion treatment was performed in an aqueous solution of ammonium adipate at 15 V to form a dielectric oxide film. This device was immersed in the previously prepared solution for 10 minutes and then dried at 70 ° C.
soak in ol / l ethanol solution for 5 minutes and dry at 100 ℃,
A doping reaction was performed. This operation was repeated 8 times to form a conductive polyaniline film. This element is dipped in colloidal carbon, and a silver paste is applied to form a conductive coating film. A counter electrode is taken out from a part of the element and molded with an epoxy resin to obtain a rated voltage of 6.3 V and a rated capacitance. A 22μF capacitor was completed. The initial characteristics of the obtained capacitor are shown in Table 1.

Example 3 Except that the chemical oxidative polymerization temperature of polyaniline was 28 ° C.
A capacitor was completed in the same manner as in Example 1. The initial characteristics of the obtained capacitor are shown in Table 1.

Example 4 0.3 wt% of polyaniline dedoped as in Example 1
% Solution was obtained. A roughened aluminum etched foil having a thickness of 50 μm and a width of 5 mm was obtained. After cutting the foil into 10 mm, the leads were attached by crimping, and chemical conversion treatment was carried out in an aqueous solution of ammonium adipate at 15 V to form a dielectric oxide film. The dedoped polyaniline solution prepared above was applied to the surface of this device using a # 16 bar coater.
It was dried at 80 ° C. Thereafter, an ethanol solution of isopropylnaphthalenesulfonic acid 0.2 mol / l was applied and dried at 100 ° C. This operation was repeated 10 times to form a conductive polyaniline film. Immersing this element in colloidal carbon,
Further, a silver paste was applied to form a conductive coating film, a counter electrode was taken out from a part thereof, and then molded with an epoxy resin to complete a capacitor having a rated voltage of 6.3 V and a rated capacitance of 22 μF. The initial characteristics of the obtained capacitor are shown in Table 1.

Comparative Example 1 A roughened aluminum etched foil having a thickness of 50 μm and a width of 5 mm was obtained. After cutting the foil into 10 mm, the leads were attached by crimping, and chemical conversion treatment was carried out in an aqueous solution of ammonium adipate at 15 V to form a dielectric oxide film. This element was immersed in an acetone solution containing 20 wt% of aniline monomer for 1 minute, and further ammonium persulfate 0.3 mol / l and sulfuric acid 4 m
It was immersed in an ol / l aqueous solution for 5 minutes to carry out chemical oxidative polymerization. This operation was repeated 5 times to form a polyaniline film by chemical oxidative polymerization. This element is dipped in colloidal carbon, and a silver paste is applied to form a conductive coating film. A counter electrode is taken out from a part of the element and molded with an epoxy resin to obtain a rated voltage of 6.3 V and a rated capacitance. A 22μF capacitor was completed. Twenty capacitors were produced by the method, but 19 capacitors could not be formed in a short-circuited state. Table 1 shows the initial characteristics of the remaining one capacitor.

[0021]

[Table 1] The capacitance (C) and the dielectric loss (tan δ) represent the measured value at 120 Hz, the equivalent series resistance (ESR) represents the measured value at 100 kHz, and the leakage current (LC) represents the measured value at a rated voltage of 1 minute. When the chemical oxidative polymerization temperature of polyaniline is 28 ° C. (Example 3), the ESR is slightly higher than when it is 5 ° C. (Example 1) or 15 ° C. (Example 2). In Comparative Example 1, 4 mol / l
When contacted with sulfuric acid, the dielectric oxide film was damaged and almost all were in a short state, and the remaining one had a large LC, and the conductivity and packing density of polyaniline were small, so ES
R and tan δ are large.

[0022]

According to the method of manufacturing a solid electrolytic capacitor of the present invention, a dedoped polyaniline film is formed on a dielectric oxide film by using a dedoped polyaniline solution, and then the conductive polyaniline is brought into contact with a doping solution. Since the film is formed, the polyaniline film can be formed without melting and damaging the dielectric oxide film and the aluminum foil, and the capacitor characteristics are excellent. Further, since the polyaniline film can be formed on the dielectric oxide film by a simple method such as dipping, the process is simplified, the aniline monomer is not wasted, and the manufacturing cost is reduced.

Claims (2)

[Claims] 1. A method for producing a solid electrolytic capacitor in which a conductive polyaniline film is formed as a solid electrolyte on the surface of a valve metal having a dielectric oxide film formed thereon, wherein a polyaniline solution dedoped on the dielectric oxide film is used. A method for producing a solid electrolytic capacitor, comprising forming a dedoped polyaniline film by using the polyaniline film, and then forming a conductive polyaniline film by contacting with a doping solution. 2. The dedoped polyaniline solution is at 25 ° C.
The method for producing a solid electrolytic capacitor according to claim 1, which is prepared using polyaniline chemically oxidized and polymerized at the following reaction temperatures.