JPH0794367A - Manufacture of solid electrolytic capacitor - Google Patents

Abstract

PURPOSE:To obtain a solid electrolytic capacitor which can be lessened in thickness of covering resin by a method wherein the capacitor is lessened in induction loss, leakage current, less deteriorated with time, and furthermore can be set free from a leakage current by repairing through a comparatively simple method. CONSTITUTION:A solid electrolytic capacitor is manufactured through such a manner that a solid electrolyte 3 is formed on a dielectric oxide film 1 provided onto the surface of a valve metal through the intermediary of a conductive precoating layer 2 through an electrolytic polymerization method. Solid electrolyte is composition composed of hetero-aromatic compound, polymer of aniline or aniline derivative, and high molecular electrolyte possessed of sulfuric ester groups, a dielectric oxide film covered with solid electrolyte is subjected to a formation treatment by the use of a solution which contains an interfacial active agent for the formation of a solid electrolytic capacitor.

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 highly reliable solid electrolytic capacitor using a conductive polymer as a solid electrolyte.

[0002]

2. Description of the Related Art In a conventional electrolytic capacitor, for example, an aluminum electrolytic capacitor, an aluminum oxide layer which is a dielectric is provided on a porous aluminum foil having a large specific surface area that has been subjected to etching treatment, and a liquid electrolyte is formed on an electrolytic paper between the cathode foil and the cathode foil. Although it has a structure in which the electrolytic solution is impregnated with the electrolytic solution, it has a drawback that the resistance is remarkably increased in the high frequency region and the impedance is increased because it functions by the ion conduction of the electrolytic solution.

In recent years, attempts have been made to replace this electrolytic layer with a solid electrolyte. Such a solid electrolytic capacitor has a structure in which a solid electrolyte is attached to an anodized film of a film-forming metal such as aluminum or tantalum. For example, a heterocyclic compound such as pyrrole is used as an oxidizing agent (for example, FeCl ₃ Etc.) or a solution containing an electrolyte as a suitable dopant is polymerized (electrolytically polymerized) by an electrochemical method to be deposited on the dielectric layer, which is used as a solid electrolyte. The polypyrrole formed by these methods has a high electric conductivity, and a solid electrolytic capacitor using the polypyrrole has excellent high frequency characteristics.

[0004]

However, in the conventional solid electrolytic capacitor of polypyrrole using a dopant, the dopant is desorbed due to heat or the presence of water molecules,
Since the electrical resistance increases, it tends to change over time, and in order to prevent this, there is a problem in that the exterior resin must be made extremely thick and various additives must be added.
Further, the conventional solid electrolytic capacitor of polypyrrole using the dopant, if the dielectric oxide film is damaged during the formation of the solid electrolyte, the polypyrrole is chemically unstable, so there is no simple method for repairing it. Leak current,
There is a problem in that reliability is poor in terms of withstand voltage.

The present invention solves these problems of the prior art and provides a method of manufacturing a solid electrolytic capacitor having excellent heat resistance and humidity resistance, a small leakage current, and a small size, and high reliability. To aim.

[0006]

The inventors of the present invention have made extensive studies for this reason, and as a result, a solid electrolyte containing a polymer such as a heteroaromatic compound or aniline and a polymer electrolyte having a sulfate ester group as a dopant. In a solid electrolytic capacitor (Japanese Patent Application No. 4-153032) using the above, it was found that the above object can be achieved by subjecting a dielectric oxide film to chemical conversion treatment under specific conditions, and the present invention was completed.

That is, the present invention provides a method for producing a solid electrolytic capacitor in which a solid electrolyte is formed by an electrolytic polymerization method on a dielectric oxide film formed on a valve metal surface via a conductive precoat layer. Is a composition comprising a polymer of a heteroaromatic compound, aniline or an aniline derivative, and a polymer electrolyte having a sulfate ester group, and a dielectric oxide film covered with the solid electrolyte is treated with a solution containing a surfactant. A method for producing a solid electrolytic capacitor, which comprises performing chemical conversion treatment using the method.

The present invention will be specifically described below. FIG. 1 is a vertical cross-sectional explanatory view of the solid electrolytic capacitor of the present invention.
A porous dielectric oxide film 1 is provided by electrolytic oxidation on the surface of an anode 6 made of a valve metal such as aluminum, tantalum, niobium, or titanium, and a conductive polymer is chemically polymerized on the dielectric oxide film by chemical polymerization. The precoat layer 2 is formed. Using this precoat layer as an electrode, a solid electrolyte 3 composed of a composite of the above-mentioned conductive polymer and polymer electrolyte is formed by electrolytic polymerization, and a part of this solid electrolyte is placed in the pores of the dielectric oxide film 1. It is included. Further, after the carbon paste 4 and the silver paste 5 are formed, they are sealed with the resin 10. Also, 7 is an anode lead wire, 9 is a cathode lead wire,
8 shows a masking layer.

A metal foil of aluminum, tantalum, niobium, titanium or the like or a sintered body of these metal powders is used for the anode of the solid electrolytic capacitor of the present invention. The surface of the metal foil is etched to form pores. The metal foil or the sintered body is electrolytically oxidized in a solution of boric acid, adipic acid, phosphoric acid or an ammonium salt thereof, and an oxide thin film of a dielectric is formed on the metal foil or the sintered body. The composite of the conductive polymer and the polymer electrolyte according to the present invention adheres to this dielectric layer and a part thereof penetrates into the pores.

A known technique is used as a method for producing a precoat layer which becomes an electrode for electrolytic polymerization. For example, a metal foil or a sintered body on which a dielectric oxide film is formed is impregnated with an oxidant solution, and this is used. Is immersed in a vapor or a liquid of the above-mentioned conductive polymer monomer. Examples of the oxidizing agent include ammonium persulfate, ferric chloride, hydrogen peroxide, etc., but are not limited thereto. The amount of the oxidizing agent used is not particularly limited, but is usually 1 to 50 parts by weight, preferably 5 to 30 parts by weight, relative to 100 parts by weight of the solvent. The solvent for polymerization can be selected from water, methyl alcohol, ethyl alcohol, ethylene glycol, dimethylformamide, propylene carbonate and the like. The polymerization conditions are as follows: the above anode at a temperature of 0 to 70 ° C.
Immersion in the monomer for 30 minutes is preferred.

Examples of the conductive polymer used in the solid electrolyte in the present invention include heteroaromatic compound polymers such as polypyrrole, polythiophene and polyfuran, and polymers of aniline and aniline derivatives such as polyaniline. Is excellent in electrical conductivity and thermal stability. Next, as the polymer electrolyte complexed with the conductive polymer of the present invention by electrolytic polymerization, a polymer obtained by partially esterifying the alcoholic hydroxyl groups of a polymer having alcoholic hydroxyl groups in the molecule is used. The molar ratio of free alcohol groups to sulfate ester groups is 50: 1 to 1:50, preferably 10: 1 to 1: 1.
It is 10. The sulfate ester group is at the terminal in the polymer skeleton,

[0012]

[Chemical 1]

As a side chain, --CH ₂ --O--S
O ₃ ^- as, in a central position

[0014]

[Chemical 2]

Or

[Chemical 3]

Exists as The sulfate group is preferably 0.1 to 0. per structural unit of the conductive polymer monomer.
It can have 5, most preferably 0.2-0.4. Since conventional dopants have a relatively small molecular size, when left in a high-temperature atmosphere, the self-vibration of the dopant becomes large, and the movement causes the bond with the conductive polymer to be broken or to bond to the polymer fibril surface. The existing dopant is released to the outside of the polymer, which lowers the electric conductivity of the conductive polymer. In addition, the presence of water molecules causes the dopant to be dissolved, and the electrical conductivity is reduced as in the above case. However, since the polymer electrolyte used in the present invention has a large molecular weight and a large molecular size, it is considered that the above-mentioned desorption is unlikely to occur.

Although there are various methods for producing a composite of a conductive polymer and a polymer electrolyte, usually, a conductive polymer is electrochemically synthesized by a known method in the presence of the above-mentioned polymer electrolyte. Obtained by At this time, the polymer electrolyte is preferably dissolved in the polymerization solution, but it does not matter even if it is in an emulsified state.

The solid electrolyte used in the present invention is, as described above, a heteroaromatic compound in the presence of a polymer having a sulfate ester group in an aqueous solution, an aqueous-organic solution or an organic solution by a method known per se. It is produced by electrochemically polymerizing a monomer such as aniline or an aniline derivative. Electrochemical polymerization can be carried out at constant potential or constant current. Current density is 0.5mA / cm ²
The above is preferably 1 to 5 mA / cm ² . The electrochemical polymerization preferably uses a buffer at the same time. Examples of the buffer include alkyl ammonium phosphate having 1 to 3, preferably 2 or 3 alkyl groups having 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms. Specific examples of preferable buffering agents include trimethylammonium phosphate, triethylammonium phosphate and tri-ammonium phosphate.
n-propyl ammonium phosphate, and tri-n
-Butyl ammonium phosphate. Further, a protonated cation exchanger is also preferable.

In a conventional solid electrolytic capacitor using a conductive polymer, when a defective portion of a dielectric oxide film is repaired after the formation of the conductive polymer, an exchange reaction of a dopant occurs in a general chemical conversion treatment, resulting in polypyrrole. May be undoped or doped with a material not intended for it. However, the polyelectrolyte used in the present invention is not dedoped because the sulfuric acid group binding to the conductive polymer is fixed to the main chain of the polyelectrolyte. Therefore, the conductive polymer doped with the polymer electrolyte used in the present invention can be subjected to usual chemical conversion treatment for repairing the dielectric oxide film.

However, despite the above reasons, it was difficult for the conductive polymer using the polymer electrolyte of the present invention to restore the dielectric oxide film by the usual chemical conversion treatment. This is because the solid electrolyte layer using the polymer electrolyte prevents water molecules in the chemical conversion liquid from entering the dielectric oxide film under normal conditions. However, good results can be obtained by performing chemical conversion treatment after pretreatment with a chemical conversion liquid containing a surfactant or a solution containing a surfactant.

As a method for repairing the dielectric oxide film, a known chemical conversion solution such as a solution of boric acid, adipic acid, phosphoric acid or an ammonium salt thereof, to which a surfactant has been added, or immersion in a solution containing a surfactant. After that, a chemical conversion treatment is performed with the above-mentioned chemical conversion liquid by a known method. The conditions may be such that the chemical conversion liquid is maintained at a temperature of 0 to 80 ° C. and a predetermined voltage is applied, but it is preferable that the voltage is not less than the rated voltage and not more than the initial conversion voltage. The surfactant used in the present invention is not particularly limited, but either an ionic surfactant or a nonionic surfactant can be used, and a nonionic surfactant is particularly preferable. For example, polyoxyethylene alkylphenyl ether, polyoxyethylene alkyl ether, fatty acid alkylolamide, sorbitan fatty acid ester and the like can be mentioned.

[0022]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto.

Example 1 Using a 100 μm thick aluminum foil having a surface etched as an anode, a dielectric oxide film was electrochemically formed on the aluminum foil in a solution of ammonium adipate. Next, 80g of ferric chloride on this dielectric oxide film
Apply a solution of the solution in 1,000 ml of deionized water,
This was immersed in a pyrrole monomer solution and left standing for 30 minutes. It was thoroughly washed with deionized water and dried to form a conductive precoat layer. Next, the repeating structural unit is

[0024]

[Chemical 4]

A phenoxy resin obtained by the reaction of bisphenol A and epichlorohydrin having a ratio of m to n of 3: 1 (polymerization degree of about 100, the above formula is shown schematically, and is a sulfate ester group). Is actually added at random) 14 g of tributylammonium salt,
Pyrrole 10 ml, deionized water 2 ml, propylene carbonate 20
In a solution dissolved in 0 ml, an aluminum foil on which a conductive precoat layer was formed as an anode and a stainless steel net as a cathode were subjected to constant current electrolysis at a current density of 3.8 mA / cm ² for 5 minutes to obtain foil. A uniform thin film of polypyrrole was formed as a solid electrolyte on the surface of. This was washed with dimethylformamide and ethanol in this order, and then dried at room temperature.

The aluminum foil having this polypyrrole thin film was subjected to chemical conversion treatment in the same manner as in the above chemical conversion method in a solution prepared by dissolving 200 g of ammonium adipate and 1 g of polyoxyethylene alkylphenyl ether in 1,000 ml of deionized water. Then, a carbon paste, a silver paste, and an electrode were sequentially formed and sealed with an exterior resin to obtain a solid electrolytic capacitor. The characteristic values of the obtained capacitor are shown in Table 1, the high temperature load test results at 105 ° C. and 100 kHz are shown in FIG. 2, and the humidity resistance test results at 40 ° C. and 90% RH are shown in FIG.

Example 2 The same as Example 1 except that 8.3 g of a polymer electrolyte in which the ratio of m to n of the sulfate ester adduct of the phenoxy resin used in Example 1 was changed to 1: 1 was used. A solid electrolytic capacitor was prepared by the operation, and its characteristic values are shown in Table 1.

Comparative Example 1 A solid electrolytic capacitor was prepared in the same manner as in Example 1 except that the sulfuric acid ester adduct of Example 1 was changed to sodium p-toluenesulfonate. The characteristic values of the obtained capacitor are shown in Table 1, and the results of the high temperature load test and the humidity resistance test under the same conditions as in Example 1 are shown in FIGS. 2 and 3, respectively.

Comparative Example 2 Example 1 except that the surfactant polyoxyethylene alkylphenyl ether of Example 1 was not used.
A solid electrolytic capacitor was prepared in the same manner as in, and the characteristic values thereof are shown in Table 1.

[0030]

[Table 1]

[0031]

As is apparent from Tables 1, 2 and 3, the solid electrolytic capacitor according to the present invention has smaller dielectric loss and leakage current than the conventional solid electrolytic capacitor using a low molecular weight dopant. It is a solid electrolytic capacitor with little deterioration over time. As a result, the resin sheath can be made thin, and the leakage current can be repaired by a relatively simple method.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional explanatory view of a specific example of a solid electrolytic capacitor of the present invention.

FIG. 2 is a graph showing the high temperature load test results of the solid electrolytic capacitors implemented in Example 1 and Comparative Example 1.

FIG. 3 is a graph showing the results of humidity resistance test of the solid electrolytic capacitors implemented in Example 1 and Comparative Example 1.

[Explanation of symbols]

 1 Dielectric Oxide Film 2 Precoat Layer 3 Solid Electrolyte 4 Carbon Paste 5 Silver Paste 6 Anode 7 Anode Lead Wire 8 Masking Layer 9 Cathode Lead Wire 10 Sealing Resin

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Satoshi Okumura Satoshi Okumura 2-2-7 Muroya, Nishi-ku, Kobe-shi, Hyogo Kamei Co., Ltd. Kobe Techno Center (72) Susumu Kobayashi 2-7-2 Muroya, Nishi-ku, Kobe-shi, Hyogo Shinei Kobe Co., Ltd. Techno Center

Claims (1)

[Claims] 1. A method for producing a solid electrolytic capacitor in which a solid electrolyte is formed by an electrolytic polymerization method on a dielectric oxide film formed on a valve metal surface via a conductive precoat layer, wherein the solid electrolyte is a heteroaromatic group. A composition comprising a compound, a polymer of aniline or an aniline derivative, and a polymer electrolyte having a sulfate ester group, wherein a dielectric oxide film covered with the solid electrolyte is subjected to a chemical conversion treatment using a solution containing a surfactant. A method of manufacturing a solid electrolytic capacitor, comprising: