JP2570600B2 - Method for manufacturing solid electrolytic capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a solid electrolytic capacitor using a conductive polymer as an electrolyte, and more particularly to a solid electrolytic capacitor using polyaniline, polypyrrole or a derivative thereof as an electrolyte and having a high capacitance appearance rate and excellent high-frequency characteristics. The present invention relates to a method for manufacturing an electrolytic capacitor.

[0002]

2. Description of the Related Art A solid electrolytic capacitor comprises a first electrode (anode) formed of a film-forming metal such as tantalum or aluminum, a surface oxide film formed of a dielectric, and a solid electrolyte formed thereon formed of a first electrode (anode). It has a structure that is a part of the second electrode (cathode). Since the solid electrolyte plays a role of electrically connecting the entire surface of the dielectric inside the porous body and the electrode leads, a substance having high conductivity is preferable from this viewpoint. On the other hand, the solid electrolyte is also required to have a function of repairing an electrical short circuit caused by a defect in the dielectric film. As a result, metals having high conductivity but without a dielectric repair function cannot be used as a solid electrolyte, and manganese dioxide or the like that transfers to an insulator by heat or the like due to short-circuit current has been used.
Manganese dioxide as a solid electrolyte is formed by thermal decomposition of manganese nitrate at a high temperature of 200 to 300 ° C. Since thermal decomposition at such a high temperature is repeated several times, the surface oxide film serving as a dielectric material is damaged, which lowers the withstand voltage of the electrolytic capacitor and causes an increase in leakage current. Further, the conductivity of manganese dioxide is about 0.1 S / cm, which is not always sufficient as a solid electrolyte of an electrolytic capacitor. Therefore, recently, the development of an electrolytic capacitor using a conductive polymer such as polyaniline or polypyrrole which has a high conductivity and can be easily formed at room temperature as a solid electrolyte has been vigorously advanced.

The method of forming a conductive polymer can be roughly classified into two methods, namely, an electrolytic polymerization method and a chemical polymerization method. A conductive polymer cannot be formed on an oxide film by an electrolytic polymerization method using a valve metal as an anode through an insulating oxide film. Therefore, a method has been proposed in which a conductive prepolymer layer is formed on the surface of an oxide film in advance, and then the conductive polymer is formed by electrolytic polymerization using the precoat layer as an electrode. By this method, an electrolytic capacitor using polypyrrole as a solid electrolyte has been developed and a part of it has been put to practical use (Japanese Patent Publication No. 04-74853). The latter is a method of forming a conductive polymer directly on an oxide film by oxidative polymerization of a monomer. The present inventors have proposed an electrolytic capacitor using chemically polymerized polyaniline as a solid electrolyte (Japanese Patent Application No. 04-206227).

[0004]

As described above, a conductive polymer obtained by chemical polymerization can be easily formed under mild conditions and has a high conductivity. Therefore, a high-performance capacitor using this as a solid electrolyte is expected. . However, the conductive polymer formed by the oxidative polymerization of the monomer becomes particulate and precipitates on the dielectric surface of the capacitor, so that the adhesion to the dielectric is inferior and the capacity appearance rate is not sufficiently obtained.

An object of the present invention is to solve the above-mentioned problems and to provide a method for manufacturing an electrolytic capacitor having a low equivalent series resistance in a high-frequency region and a high capacitance appearance ratio by sufficiently utilizing the high conductivity of a conductive polymer. It is to provide.

[0006]

Means for Solving the Problems The present inventors have made intensive studies to solve the above problems. As a result, it was found that the capacity appearance ratio was effectively improved by treating the dielectric oxide film with a polyhydric alcohol solution containing an electrolyte before forming the conductive polymer by a chemical polymerization method. Reached.

[0007] That is, the present invention provides a method using an oxidizing agent.
Of conductive polymer by chemical polymerization method to polymerize polymer
Then, in a method for manufacturing a solid electrolytic capacitor using this as a solid electrolyte, a polyhydric alcohol solution containing an electrolyte is applied on the surface oxide film of the film-forming metal before forming the conductive polymer, and then dried. A method for manufacturing a solid electrolytic capacitor characterized by the following.

The conductive polymer of the present invention is a conjugated polymer formed by oxidative polymerization of a monomer and having an electron-donating or electron-accepting compound (dopant) added (doped). For example, polyaniline, polypyrrole, polythiophene, polyparaphenylene, polyacetylene, and the like. Among them, polyaniline and polypyrrole having high conductivity and excellent reliability are preferable.

The polyhydric alcohol of the present invention is an organic compound having two or more hydroxy groups in the same molecule. For example, ethylene glycol , propylene glycol, die
Tylene glycol , hexylene glycol, phenylene
Glycol , glycerin, 3-methylpentane-1,
3, 5-triol, hexitol and the like can be mentioned.

The electrolyte contained in the polyhydric alcohol of the present invention is various acids, bases, salts, or a mixture thereof. For example, boric acid, inorganic acids such as phosphoric acid, formic acid, acetic acid, butyric acid, oleic acid, aromatic carboxylic acids, organic acids such as aromatic sulfonic acids, ethylamine , diethylamine,
A compound having an amine group such as triethylamine, naphthylamine, and benzylamine; and
A salt with a compound having the same is used. Further, when the solid electrolyte is polyaniline, it is preferable to use a protonic acid or a salt thereof serving as a dopant of polyaniline. preferable.

The method of applying the polyhydric alcohol containing the electrolyte of the present invention is not particularly limited, and a method of dipping tantalum pellets or aluminum foil in a polyhydric alcohol electrolyte solution,
It can be performed by a method of exposing to the vapor of the solution. The drying means can be used without any particular limitation such as room temperature drying, vacuum drying, and heat drying. However, among these, heat drying is most preferable.

In the present invention, the film-forming metal includes tantalum, aluminum, niobium, titanium, zirconium, magnesium, silicon, etc.
It can be used in the form of an etched product of a rolled foil.

The method for forming the conductive polymer during the production of the capacitor of the present invention is not particularly limited. That is, after introducing the oxidizing agent as it is, or after dissolving it in a suitable solvent to form a porous forming body of a film-forming metal having a surface oxide film formed thereon, the monomer of the conductive polymer as it is, or its solution, or vaporized it It is performed by a method of contacting with a gas, a method of first introducing a monomer of a conductive polymer into a porous formed body of a film-forming metal, and then contacting it with an oxidizing agent. After completion of the polymerization, necessary operations such as washing and drying are performed, and a lead electrode is provided by a usual method and assembled into a capacitor. In addition,
Repeat the operation of polymerization, washing and drying, and then
It is also possible to set up a lead electrode and build it up into a capacitor
Wear.

[0014]

FIG. 1 shows an example of the overall structure of a method for manufacturing a solid electrolytic capacitor according to the present invention. When the film-forming metal is an aluminum foil, the aluminum foil is etched to form many pores on the surface. When the film-forming metal is tantalum powder, the tantalum powder is pressed into a sintered body. Then, a chemical conversion is performed on the film-forming metal to form an oxide film serving as a dielectric. After the surface of the dielectric oxide film is treated with a polyhydric alcohol electrolyte solution, a conductive polymer serving as a solid electrolyte is formed. Thereafter, a carbon paste and a silver paste are applied and baked, and lead wires are connected and sealed to obtain a product.

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples. (Example 1) Powder CV value (product of capacity and formation voltage) of 1.5 mm in diameter, 2 mm in height, and gram per 30,000 /
g of cylindrical sintered tantalum powder
Anodized at 60 V in a t% nitric acid aqueous solution, washed and dried. Thereafter, the tantalum pellets were immersed in an ethylene glycol solution containing 20 wt% ammonium paratoluenesulfonate for 30 seconds, and then heat-treated at 120 ° C. for 20 minutes.

On the other hand, a water / ethanol (volume ratio of 1: 1) solution in which aniline and paratoluenesulfonic acid are equimolar and the aniline concentration is 5 wt%, and the molar ratio between ammonium dichromate and paratoluenesulfonic acid is 1 : 0 ° C at 3
The oxidizing agent aqueous solution of 20 wt% which was held in was prepared.
Subsequently, at room temperature, the tantalum pellets subjected to the above treatment in an aniline solution were immersed for 30 seconds and taken out. Twenty minutes later, the tantalum pellet impregnated with aniline was immersed in an oxidizing agent solution for 30 seconds. When the pellets were kept in the air for further 30 minutes for polymerization, black polyaniline could be formed on the dielectric surface. Thereafter, the resultant was washed with a 0.5 M solution of paratoluenesulfonic acid in water / ethanol (1: 1) at room temperature and dried.

After filling the above tantalum pellets with the mixed solution of aniline and paratoluenesulfonic acid, contacting with the oxidizing agent solution, polymerization, washing and drying five times, carbon paste and silver paste are applied and baked. Was. Thereafter, the cathode lead was pulled out and sealed with epoxy resin to complete the capacitor. (Example 2) In Example 1, the tantalum pellets were treated with a glycerin solution containing ammonium paratoluenesulfonate instead of the ethylene glycol solution containing ammonium paratoluenesulfonate. Otherwise, a capacitor was completed in the same manner as in Example 1. (Example 3) In Example 1, the tantalum pellets were treated with an ethylene glycol solution containing paratoluenesulfonic acid instead of the ethylene glycol solution containing ammonium paratoluenesulfonate. Otherwise, a capacitor was completed in the same manner as in Example 1. (Comparative Example 1) In Example 1, the tantalum pellets were treated with an ethanol solution containing ammonium paratoluenesulfonate instead of the ethylene glycol solution containing ammonium paratoluenesulfonate. Otherwise, a capacitor was completed in the same manner as in Example 1. (Comparative Example 2) In Example 1, the tantalum pellets were treated with a benzyl alcohol solution containing ammonium paratoluenesulfonate instead of the ethylene glycol solution containing ammonium paratoluenesulfonate. Otherwise, a capacitor was completed in the same manner as in Example 1. Comparative Example 3 In Example 1, the treatment of the tantalum pellets with the polyhydric alcohol solution containing the electrolyte was not performed. other than that,
A capacitor was completed in the same manner as in Example 1. Example 4 Using the tantalum pellets on which the oxide film of Example 1 was formed, the tantalum pellets were immersed in an ethylene glycol solution containing 20 wt% ammonium paratoluenesulfonate for 30 seconds in the same manner as in Example 1, and then at 120 ° C. For 20 minutes.

On the other hand, a 35% methanol solution of ferric dodecylbenzenesulfonate , which is an oxidizing agent, is kept at -50.degree. C. while stirring, and the amount is 3 times the number of moles of ferric dodecylbenzenesulfonate in the solution. Was added dropwise to prepare a mixed solution of ferric dodecylbenzenesulfonate and pyrrole. Subsequently, the tantalum pellet was immersed in a mixed solution of ferric dodecylbenzenesulfonate and pyrrole for 30 seconds. Then, further in air at room temperature
When pyrrole was polymerized by holding for 0 minutes, black polypyrrole was formed on the dielectric surface. Then, it was washed with methanol and dried.

Filling, polymerization, washing and drying of the above mixed solution of ferric dodecylbenzenesulfonate and pyrrole are performed in 3 steps.
After repetition, silver paste was applied and the cathode lead was pulled out and sealed with epoxy resin to complete the capacitor. (Comparative Example 4) In Example 4, the treatment of the tantalum pellets with the polyhydric alcohol containing the electrolyte was not performed. Otherwise, a capacitor was completed in the same manner as in Example 4. (Example 5) A 300 μm-thick 1 × 0.5 cm ² aluminum layer whose surface area was enlarged almost 50 times by etching was added to a 0.1 mm thick aluminum layer.
Anodized at 75 V in a 1% aqueous ammonium phosphate solution, washed and dried. Subsequently, the aluminum foil was treated with an ethylene glycol solution containing 20 wt% ammonium paratoluenesulfonate in the same manner as in Example 1,
Heat treatment was performed at 00 ° C. for 50 minutes. Thereafter, the polymerization, washing, and drying of aniline were repeated in the same manner as in Example 1,
The lead was pulled out to complete the capacitor. (Comparative Example 5) In Example 5, the tantalum pellets were not treated with a polyhydric alcohol containing an electrolyte. Otherwise, a capacitor was completed in the same manner as in Example 5.

In Examples 1 to 5 and Comparative Examples 1 to 5,
Table 1 shows the capacity appearance ratio (C / Co, and the capacity in the electrolyte solution of Co) of the obtained electrolytic capacitor. As can be seen from Table 1, the electrolytic capacitor manufactured by the method of the present invention had a high capacitance appearance rate and excellent characteristics at high frequencies.

[0021]

[Table 1]

[0022]

As described above, the present invention forms a conductive polymer by a chemical polymerization method after treating the surface of a dielectric oxide film with a higher alcohol solution containing an electrolyte. ADVANTAGE OF THE INVENTION According to this invention, the high conductivity of a conductive polymer is fully utilized, and the electrolytic capacitor excellent in the appearance rate of capacity | capacitance and the characteristic in high frequency is obtained, and the effect is large.

[Brief description of the drawings]

FIG. 1 shows an example of an overall configuration of a method for manufacturing a solid electrolytic capacitor of the present invention.

Claims (1)

(57) [Claims] 1. A chemistry for polymerizing a monomer using an oxidizing agent.
In a method for producing a solid electrolytic capacitor , which forms a conductive polymer by a polymerization method and uses this as a solid electrolyte, a polyhydric alcohol containing an electrolyte before forming the conductive polymer
A method for producing a solid electrolytic capacitor, comprising applying a solution onto a surface oxide film of a film-forming metal and then drying the solution.