JP2898443B2 - 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 for manufacturing a solid electrolytic capacitor using a conductive polymer 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. As a method of forming a conductive polymer film, there are a method by electrolytic polymerization and a method by chemical oxidative polymerization using an oxidizing agent, but the method of forming an electrolytic polymerized film directly on an insulating dielectric oxide film is not. On the other hand, a conductive polymer film formed by chemical oxidative polymerization is generally inferior in heat resistance and low in packing density, so that it does not provide a capacitor having excellent characteristics even when applied to a solid electrolyte of the capacitor.

In order to apply a conductive polymer film formed by electrolytic polymerization as a solid electrolyte, a conductive polymer film formed by chemical oxidation polymerization is formed on a dielectric oxide film as a precoat layer.
Further, there has been proposed a solid electrolytic capacitor having a structure in which a conductive polymer film is formed on the conductive polymer film by electrolytic polymerization to form a solid electrolyte (JP-A-63-173313). In addition, a thin film of a conductive metal compound such as manganese dioxide is formed as a precoat layer on the dielectric oxide film,
Further, there has been proposed a solid electrolytic capacitor having a structure in which a conductive polymer film is formed on the thin film by electrolytic polymerization to form a solid electrolyte (JP-A-63-158829). These capacitors have excellent frequency characteristics, electrical characteristics, and heat resistance as compared with conventional capacitors.

[0004] These solid electrolytic capacitors generally use polypyrrole as a conductive polymer, and polypyrrole is excellent in terms of stability and conductivity. However, in forming a precoat layer on a dielectric oxide film, a capacitor using a chemical oxidation polymerization method has excellent characteristics, but a conductive polymer that does not adhere to the dielectric oxide film during chemical oxidation polymerization. However, this is economically wasted because it is discarded, and improvement has been desired.
On the other hand, the method of forming a thin film of a conductive metal compound such as manganese dioxide requires complicated steps such as heating at a high temperature, and the dielectric oxide film is easily damaged.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to form a dielectric oxide film on a valve metal surface and form a conductive polymer film on the dielectric oxide film to form a solid electrolyte. It is an object of the present invention to provide a method of manufacturing a solid electrolytic capacitor having a structure which makes the process extremely simple and inexpensive.

[0006]

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

That is, after a undoped polyaniline layer is formed on a valve metal having a dielectric oxide film formed on the surface, electrolytic polymerization is performed in an electrolytic solution containing a conductive polymer monomer and a supporting electrolyte. This is a method for manufacturing a solid electrolytic capacitor. Hereinafter, the method for manufacturing the solid electrolytic capacitor will be described in detail.

As the valve metal, aluminum, tantalum or titanium is used, and is used in the form of a flat plate or a laminated plate, a roll, a sintered body or the like. 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, an anode lead is connected through a lead tab, and electrolytic oxidation is performed in an aqueous solution of ammonium adipate or the like to form a dielectric oxide film on the surface to obtain an element. By immersing the device in a undoped polyaniline solution or applying a undoped polyaniline solution to the device and drying it, a undoped polyaniline layer is formed on the valve metal having the dielectric oxide film formed thereon.

The undoped polyaniline solution used in the present invention is a solution in which polyaniline produced by electrolytic polymerization or chemical oxidative polymerization is undoped and dissolved in an organic solvent. In order to carry out chemical oxidative polymerization of aniline, an aniline salt may be oxidatively polymerized with an oxidizing agent in a solution in the presence of a protonic acid. Examples of the aniline salt to be used include salts of aniline such as hydrochloric acid, sulfuric acid, perchloric acid and borofluoric acid. As the oxidizing agent, ammonium persulfate, persulfate such as potassium persulfate, or hydrogen peroxide, peroxide such as sodium peroxide, or potassium permanganate, potassium dichromate, ferric chloride and the like Any oxidizing agent that can oxidize aniline, such as a high-valent metal compound, can be used. Further, hydrochloric acid, sulfuric acid, perchloric acid, borofluoric acid, hexafluorophosphoric acid and the like are used as the protonic acid. Polyaniline by the chemical oxidative polymerization is undoped when brought into contact with aqueous ammonia,
Dedoped polyaniline, NMP or NMP
Is dissolved in a mixed solvent of the above and another organic solvent to obtain a undoped polyaniline solution.

According to the above method, a undoped polyaniline layer is formed on a valve metal having a dielectric oxide film formed on its surface, and then a conductor is brought into contact with the undoped polyaniline layer from the outside to form an anode. When the electrolytic polymerization was performed, a conductive polymer film was formed on the undoped polyaniline layer by uniform electrolytic polymerization. It was thought that the undoped polyaniline was inherently electrically insulating and could not form a conductive polymer film by electrolytic polymerization. However, according to the present production method, electrolytic polymerization was possible. Although the reason is not clear, when a conductor is brought into contact with the undoped polyaniline layer from the outside and an electric potential is applied as an anode, a doping reaction to the undoped polyaniline occurs to make it conductive, and the conductive polyaniline becomes conductive on this conductive polyaniline. It is presumed that electrolytic polymerization of the polymer occurs in a concerted manner.

The electrolytic polymerization is carried out using a supporting electrolyte of 0.01 mol / l to 2 mol.
The reaction is performed in an electrolytic solution containing l / l and 0.01 mol / l to 5 mol / l of a conductive polymer monomer. It is more effective to add a small amount of an organic acid or an inorganic acid to keep the acid concentration of the solution at 10 ^-6 to 10 ^-1 mol / l. As the conductive polymer monomer, pyrrole, thiophene, and furan are used, and pyrrole is particularly preferably used in view of the stability of the conductive polymer.

The supporting electrolyte used in the electropolymerization of the present invention has an anion of hexafluoroline, hexafluoroarsenic,
Halide anions such as tetrafluoroboron and perchlorate anions; or halogen anions such as iodine, bromine and chlorine; or methanesulfonic acid, benzenesulfonic acid, alkylbenzenesulfonic acid, naphthalenesulfonic acid, alkylnaphthalenesulfonic acid, and diamines thereof. Or a sulfonate anion such as a trisulfone group-substituted product,
Alternatively, the cation is a proton or an alkali metal cation such as lithium, potassium, or sodium, or a quaternary ammonium cation such as ammonium or tetraalkylammonium. The compound is HCl
O ₄ , LiPF ₆ , LiAsF ₆ , LiBF ₄ , KI, NaPF
₆ , NaClO ₄ , sodium toluenesulfonate, tetrabutylammonium toluenesulfonate, 2-naphthalenesulfonic acid, sodium 1,7-naphthalenedisulfonic acid, tetraethylammonium alkylnaphthalenesulfonate, tetramethylammonium bissulfylate, and the like. Can be

Thereafter, a conductive film is formed on the element surface with a carbon paste and a conductive paste, a cathode lead is taken out from a part thereof, and a capacitor is obtained by a method such as sealing with a resin mold or an outer case. Can be.

According to the method for manufacturing a solid electrolytic capacitor of the present invention, after a polyaniline layer is formed by undoping by a simple method such as immersion in a valve metal having a dielectric oxide film formed thereon, electrolytic polymerization is carried out. Not only is it wasted but also the doping step is not required, which greatly simplifies the process and reduces manufacturing costs.

[0016]

The present invention will be described below in detail with reference to examples. In the examples, capacitance (C) and dielectric loss (tan δ)
Is the measured value at 120Hz, the equivalent series resistance (ESR) is 100k
Represents measured values in Hz. Example 1 An aqueous solution containing 11.4 g of ammonium persulfate was dropped into an aqueous solution containing 4.7 g of aniline and 9.8 g of concentrated sulfuric acid, and the resulting precipitate was filtered to obtain polyaniline. 4 g of this powder was mixed with 50 ml of aqueous ammonia and stirred and separated to obtain undoped polyaniline. The undoped polyaniline is dissolved in an NMP solvent, and the undoped polyaniline is dissolved.
A 0.4 wt% NMP solution was obtained. A roughened aluminum etch foil having a thickness of 70 μm and a width of 5 mm was obtained. After cutting the foil to 10 mm, a lead was attached by crimping, and a chemical conversion treatment was performed at 20 V in an aqueous solution of ammonium adipate to form a dielectric oxide film. The device was immersed in the previously prepared NMP solution for 5 minutes and dried, and this operation was repeated three times to form a undoped polyaniline layer. Further, this element was added to an aqueous solution prepared by adding 0.2 mol / l of a pyrrole monomer and 0.2 mol / l of sodium 1,7-naphthalenedisulfonic acid as a supporting electrolyte and 2-naphthalenesulfonic acid to adjust the acid concentration to 10 ^-5 mol / l. A stainless steel wire is contacted from outside with the immersed and undoped polyaniline layer to form an anode, and a constant current electrolytic polymerization (0.5 mA / cm ² , 90 minutes) between the anode and the external electrode
Was performed to form a polypyrrole film by electrolytic polymerization. This element was immersed in colloidal carbon, and then a silver paste was applied to form a conductive coating.
A capacitor with a rated capacitance of 10 μF was completed. Table 1 shows the initial characteristics of the obtained capacitors.

Example 2 By performing the same operation as in Example 1, undoped polyaniline was obtained. This undoped polyaniline is NMP50wt
%, Butanol dissolved in a solvent of 50 wt% to obtain a solution of 0.3 wt% of polyaniline which was dedoped. The tantalum sintered body element to which the anode lead was attached was anodized at 60 V to form a dielectric oxide film. The device was immersed in the previously prepared solution for 10 minutes and dried, and this operation was repeated twice to form a undoped polyaniline layer on the dielectric oxide film. Further, this device was prepared by using 0.2 mol / l of a pyrrole monomer and tetraethylammonium paratoluenesulfonate as a supporting electrolyte.
It is immersed in acetonitrile containing 2 mol / l and acetic acid 0.03 mol / l, and a platinum wire is brought into contact with the undoped polyaniline layer to form an anode, and a constant current electrolytic polymerization (1.0 mA / cm ² , 30 min.) ) To form a polypyrrole film by electrolytic polymerization. This element is immersed in colloidal carbon, a silver paste is further applied to form a conductive coating film, a counter electrode is taken out from a part thereof, and then molded with an epoxy resin to obtain a rated voltage of 16 V and a rated capacitance of 1.5 μF. Completed the capacitor. Table 1 shows the initial characteristics of the obtained capacitors.

Example 3 Dedoped polyaniline was obtained in the same manner as in Example 1. This undoped polyaniline is NMP50wt
%, Butanol dissolved in a solvent of 50 wt% to obtain a solution of 0.3 wt% of polyaniline which was dedoped. A roughened aluminum etch foil having a thickness of 70 μm and a width of 5 mm was obtained. After cutting the foil to 10 mm, a lead was attached by crimping, and a chemical conversion treatment was performed at 20 V in an aqueous solution of ammonium adipate to form a dielectric oxide film. The solution prepared above was applied to the surface of this element with a # 12 bar coater and dried. This operation was repeated four times to form a undoped polyaniline layer. Further, this element was added to an aqueous solution prepared by adding 0.2 mol / l of a pyrrole monomer and 0.2 mol / l of sodium 1,7-naphthalenedisulfonic acid as a supporting electrolyte and 2-naphthalenesulfonic acid to adjust the acid concentration to 10 ^-5 mol / l. A stainless steel wire is brought into contact with the immersed and undoped polyaniline layer from outside to form an anode, and a constant current electrolytic polymerization (0.5 mA / cm ² , 90 minutes) is performed between the electrode and the external electrode to form a polypyrrole film by electrolytic polymerization. did. This element was immersed in colloidal carbon, and a silver paste was further applied to form a conductive coating film. A counter electrode was taken out from a part of the element, and then molded with epoxy resin to obtain a rated voltage of 10 V and a rated capacitance of 10 μF. The capacitor was completed. Table 1 shows the initial characteristics of the obtained capacitors.

[0019]

[Table 1] As shown in Table 1, the results of Example 1 and Example 2 sufficiently satisfy the general characteristic values of a solid electrolytic capacitor using polypyrrole as a solid electrolyte.

[0020]

According to the method for manufacturing a solid electrolytic capacitor of the present invention, a valve metal having a dielectric oxide film formed thereon is undoped by a simple method such as immersion to form a polyaniline layer, which is then subjected to electrolytic polymerization. Not only is the monomer not wasted, but the doping step is not required, greatly simplifying the process and reducing manufacturing costs. In general, to synthesize conductive polyaniline, it is necessary to react in the presence of a high concentration of protonic acid such as sulfuric acid, but in the present invention, since a strong acid is not used in the treatment after the formation of the dielectric oxide film, A conductive polymer film can be formed without damaging the dielectric oxide film.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-80522 (JP, A) JP-A-64-74712 (JP, A) JP-A-3-71618 (JP, A) JP-A-2- 58821 (JP, A) JP-A-3-139816 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01G 9/028

Claims (2)

(57) [Claims] 1. A method for forming a dedoped polyaniline layer on a valve metal having a dielectric oxide film formed on a surface thereof,
A method for producing a solid electrolytic capacitor, characterized by performing electrolytic polymerization in an electrolytic solution containing a conductive polymer monomer and a supporting electrolyte. 2. The method according to claim 1, wherein the conductive polymer monomer is pyrrole.