JP4960425B2 - Manufacturing method of aqueous conductive polymer suspension, conductive organic material, electrolytic capacitor and manufacturing method thereof - Google Patents

Description

  Embodiments according to the present invention relate to a conductive polymer suspension aqueous solution and a manufacturing method thereof, a conductive polymer material obtained from the suspension aqueous solution, an electrolytic capacitor using the same, and a manufacturing method thereof.

  Conductive polymer materials are used for electrodes for capacitors, electrodes for dye-sensitized solar cells, electrodes for electroluminescence displays, and the like. As such a conductive polymer material, a polymer material obtained by increasing the molecular weight of pyrrole, thiophene, 3,4-ethylenedioxythiophene, aniline, etc. is known, and related techniques are disclosed in Patent Documents 1 to 3. Has been.

  Patent Document 1 relates to a solution (dispersion) of polythiophene, a production method thereof, and the use of a salt for antistatic treatment of a plastic molded body. Specifically, polythiophene dispersions consisting of 3,4-dialkoxythiophene structural units in the presence of polyanions are described. It is described that this polythiophene dispersion is produced by oxidative polymerization of 3,4-dialkoxythiophene at a temperature of 0 to 100 ° C. in the presence of a polyacid.

  Patent Document 2 discloses an aqueous dispersion of a complex of poly (3,4-dialkoxythiophene) and a polyanion, a method for producing the same, a coating composition containing the aqueous dispersion, and the composition applied. The present invention relates to a coated substrate having a transparent conductive film. Specifically, poly (3,4-dialkoxythiophene produced by polymerizing 3,4-dialkoxythiophene in an aqueous solvent using peroxodisulfuric acid as an oxidizing agent in the presence of a polyanion. ) And polyanions in aqueous dispersions are described.

  Patent Document 3 relates to a water-based antistatic coating composition. Specifically, (a) a conductive polymer comprising a polythiophene in the form of a cation composed of repeating structural units of 3,4-dialkoxythiophene and a polyanion, and (b) an amide bond or a hydroxyl group in the molecule. A water-based antistatic coating composition containing a water-soluble compound that is liquid at room temperature and (c) an aqueous dispersion of a self-emulsifying polyester resin is described. In this water-based antistatic coating composition, the (b) water-soluble compound is contained in the range of 40 to 6000 parts by weight with respect to 100 parts by weight of the (a) conductive polymer, and (c) A water dispersion of a self-emulsifying polyester resin is formed from an aromatic carboxylic acid and a diol, and 5 to 5 mol% of 5-sulfoisophthalic acid is contained in the aromatic dicarboxylic acid, and the (c) The self-emulsifying type polyester resin aqueous dispersion is contained in the range of 20 to 5000 parts by weight as a solid content with respect to 100 parts by weight of the conductive polymer (a).

JP 07-090060 A JP 2004-059666 A JP 2002-060736 A

  However, in the method of oxidative chemical polymerization of 3,4-dialkoxythiophene in the presence of a polyanion acting as a dopant, it is difficult to control the doping rate, and it does not contribute to the undoped polyanion, that is, conductivity. Excessive polyanions will be present. Therefore, the methods described in Patent Documents 1 and 2 are hardly sufficient as a method for producing a polymer material having high conductivity.

In addition, the surface resistivity of antistatic materials is generally classified as 10 ⁵ to 10 ¹⁴ Ω / □, and if the conductivity is too high (less than 10 ⁵ Ω / □), it may cause severe electrostatic discharge. Therefore, it is considered that the charged object does not have conductivity enough to dissipate the static electricity quickly. Even when the conductivity is sufficient as an antistatic material, for example, when used as an electrode of a capacitor, it is difficult to sufficiently satisfy the requirement for low ESR from the viewpoint of conductivity. In addition, since conductive polymer materials containing excessive polyanions have very poor water resistance, capacitors using such conductive organic materials as electrolytes are reliable, especially in high humidity atmospheres. There is a disadvantage that the characteristics are inferior.

  In the method of Patent Document 3, the self-emulsification type polyester resin aqueous dispersion improves the adhesion to the substrate and the water resistance of the coating film. However, since an insulating resin is added, the conductivity of the film is increased. There is a problem that decreases. In addition, even if the electrical conductivity is sufficient as an antistatic material, when this water-based antistatic coating composition is used, for example, as an electrode of a capacitor, the electrical conductivity is low, and the capacitor is required to have low ESR. It is difficult to satisfy. Further, the self-emulsifying type resin has a problem that it is easily segregated in the composition for antistatic coating as compared with a completely dissolving type resin.

  An object of an embodiment according to the present invention is to solve the above-described problem, and is a conductive polymer suspension for providing an organic material having excellent adhesion and water resistance to a base material and high conductivity. An object of the present invention is to provide a turbid aqueous solution and a method for producing the same, and to provide an electrolytic capacitor and a method for producing the same that have low ESR and reliability, particularly excellent characteristics in a high humidity atmosphere.

Embodiments according to the present invention
A first step of obtaining a mixture containing a conductive polymer by chemically oxidatively polymerizing a monomer which gives a conductive polymer in a solvent containing an organic acid or a salt thereof as a dopant using an oxidizing agent;
A second step of recovering the conductive polymer from the mixture;
A third step of allowing an oxidizing agent to act on the conductive polymer in an aqueous solvent containing a polyacid;
It is a method for producing an aqueous conductive polymer suspension characterized by having a fourth step of mixing at least one water-soluble polyhydric alcohol and ortho-phthalic acid .

Embodiments of the present invention, drying the conductive polymer suspension solution obtained by the above method, the solvent all SANYO removing the water-soluble polyhydric alcohol and ortho - phthalate condensation polymerization reaction It is a conductive organic material characterized by containing a resin that can be produced .

An embodiment according to the present invention is an electrolytic capacitor having an aqueous conductive polymer suspension obtained by the above method or an electrolyte layer containing the above conductive organic material.

Embodiments according to the present invention
Forming a dielectric layer on the surface of the anode conductor made of a valve metal;
And a step of applying or impregnating a conductive polymer suspension obtained by the above method on the dielectric layer to form an electrolyte layer.

Embodiments according to the present invention
Forming a dielectric layer on the surface of the anode conductor made of a valve metal;
Forming a first conductive polymer compound layer on the dielectric layer by chemical oxidative polymerization or electrolytic polymerization of a monomer that gives the first conductive polymer compound;
Said first conductive polymer compound layer, having a step of applying or impregnating the conductive polymer suspension aqueous solution obtained by the above method, forming a second conductive polymer compound layer This is a method for manufacturing an electrolytic capacitor.

  According to the embodiment of the present invention, an aqueous conductive polymer suspension for providing an organic material having excellent adhesion to a substrate and water resistance and having high conductivity can be obtained. Further, according to the embodiment of the present invention, an electrolytic capacitor having low ESR and reliability, particularly excellent characteristics in a high humidity atmosphere can be obtained.

2 is an X-ray diffraction chart of conductive polymer films obtained in Example 1 and Comparative Example 2. FIG. It is typical sectional drawing which shows the structure of the solid electrolytic capacitor which concerns on this embodiment.

  Hereinafter, the conductive polymer suspension aqueous solution and the manufacturing method thereof, the conductive polymer material obtained from the suspension aqueous solution, the electrolytic capacitor using the same, and the manufacturing method thereof will be described in detail.

<Aqueous conductive polymer suspension>
The aqueous conductive polymer suspension according to the present embodiment is an aqueous solution having a conductive polymer, at least one water-soluble polyhydric alcohol, and two or more functional groups capable of polycondensation with the water-soluble polyhydric alcohol. And at least one kind of organic material. In this conductive polymer suspension, the water-soluble polyhydric alcohol and the water-soluble organic substance are completely dissolved in water, and both can be subjected to a condensation polymerization reaction during the drying process. In the conductive organic material obtained by drying, a water-insoluble resin is present without uneven distribution, and by the effect, the conductive organic material is excellent in adhesion to the substrate and water resistance.

  Examples of the conductive polymer contained in the aqueous conductive polymer suspension include polypyrrole, polythiophene, polyaniline, and derivatives thereof. Among these, poly (3,4-ethylenedioxythiophene) having a structural unit represented by the following formula (1) or a derivative thereof is preferable. The conductive polymer may be a homopolymer, a copolymer, one type, or two or more types.

  The content of the conductive polymer in the aqueous conductive polymer suspension is preferably 0.1 to 30 parts by weight, and 0.5 to 20 parts by weight with respect to 100 parts by weight of water as the solvent. Is more preferable.

  The water-soluble polyhydric alcohol contained in the aqueous conductive polymer suspension is an alcohol having two or more OH groups. The term “water-soluble” as used herein means that the compound is completely dissolved in a solution containing water as a main solvent. One type of water-soluble polyhydric alcohol may be used, or two or more types may be used.

  Examples of water-soluble polyhydric alcohols include ethylene glycol, butylene glycol, propylene glycol, 3-methyl-1,3-butanediol, hexylene glycol, diethylene glycol, dipropylene glycol, glycerin, diglycerin, inositol, xylose, glucose, mannitol. Trehalose, erythritol, xylitol, sorbitol, pentaerythritol, polyethylene glycol, polypropylene glycol, polyvinyl alcohol and the like are preferable, but erythritol or pentaerythritol is more preferable. Erythritol or pentaerythritol interacts with the undoped polyacid anion (resistive component) in the vicinity of the conductive polymer particles in the conductive polymer suspension solution. In addition to lowering the resistance and increasing the density of the conductive polymer, higher conductivity can be achieved.

  The water-soluble polyhydric alcohol is preferably trivalent or higher. A resin obtained by polycondensation of a water-soluble polyhydric alcohol having a valence of 3 or more and a water-soluble organic substance having two or more functional groups capable of polycondensation has a cross-linked structure. Low water absorption and excellent water resistance. From this viewpoint, erythritol or pentaerythritol is more preferable.

  Since erythritol has higher crystallinity than, for example, sorbitol or maltose, it has low hygroscopicity and is easy to handle. In addition, erythritol is known as a food additive used as a sweetener, is excellent in safety and stability, and has a solubility in water several times higher than that of, for example, ethylene glycol or glycerin. There is an advantage that the degree of freedom in designing the addition amount is high.

  Pentaerythritol has a characteristic that it gradually sublimes when heated, and dehydrates and polymerizes when heated above its melting point. This has the advantage that the physical properties of the organic material change and the density and strength are improved. Such a reaction is caused by the chemical structure, and is unlikely to occur in a chemical structure such as erythritol or sorbitol.

  The content of the water-soluble polyhydric alcohol in the aqueous conductive polymer suspension is 100% by weight or more (preferably 200 parts by weight or more) with respect to 100 parts by weight of the conductive polymer. The upper limit of the content of the water-soluble polyhydric alcohol is not particularly limited as long as it is an amount that can be dissolved in water as a solvent, but is preferably 3000 parts by weight or less.

  The water-soluble organic substance contained in the aqueous conductive polymer suspension has two or more functional groups capable of polycondensation with the water-soluble polyhydric alcohol. As this functional group, an epoxy group, a hydroxyl group, and a carboxyl group are preferable, and a carboxyl group is particularly preferable from the viewpoint of stability in an aqueous conductive polymer suspension and reactivity with a water-soluble polyhydric alcohol. The term “water-soluble” as used herein means that the compound is completely dissolved in a solution containing water as a main solvent. One type of water-soluble organic substance may be used, or two or more types may be used.

  Examples of water-soluble organic substances having two or more epoxy groups include sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, diglycerol polyglycidyl ether, glycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, and polypropylene glycol diglycidyl ether. It is done. The “polyglycidyl ether” means that H in at least two OH groups is substituted with a glycidyl group, and the upper limit of the number of substituted glycidyl groups is the OH group of the compound before substitution. Is the number of A water-soluble organic substance having two or more water-soluble polyhydric alcohols and epoxy groups becomes a polyether resin by a condensation polymerization reaction.

  Water-soluble organic substances having two or more carboxyl groups include oxalic acid, acetylenedicarboxylic acid, malonic acid, succinic acid, fumaric acid, malic acid, oxaloacetic acid, glutaric acid, oxoglutaric acid, adipic acid, citric acid, oxalosuccinic acid Ortho-phthalic acid, hemimellitic acid, trimesic acid, merophanic acid, benzenepentacarboxylic acid, melittic acid and the like. Ortho-phthalic acid is preferred from the viewpoint of stability in aqueous solution and reactivity with water-soluble polyhydric alcohol. A water-soluble polyhydric alcohol and a water-soluble organic substance having two or more carboxyl groups are subjected to condensation polymerization to become a polyester resin.

  The content of the water-soluble organic substance in the conductive polymer suspension aqueous solution is preferably 1 to 200 parts by weight with respect to 100 parts by weight of the conductive polymer, and contains 50 to 100 parts by weight of the water-soluble organic substance. Is more preferable.

  The aqueous conductive polymer suspension preferably further contains a polyacid. Examples of the polyacid include polycarboxylic acids such as polyacrylic acid, polymethacrylic acid, and polymaleic acid; polysulfonic acids such as polyvinyl sulfonic acid and polystyrene sulfonic acid; and copolymers having these structural units. Among these, polystyrene sulfonic acid having a structural unit represented by the following (2) is preferable. One or more polyacids may be used.

  The weight average molecular weight of the polyacid is preferably 2,000 to 500,000, and more preferably 10,000 to 200,000.

  The content of the polyacid in the aqueous conductive polymer suspension is preferably 20 to 3,000 parts by weight and more preferably 30 to 1,000 parts by weight with respect to 100 parts by weight of the conductive polymer. preferable.

<Method for producing conductive polymer suspension aqueous solution>
The method for producing a conductive polymer suspension aqueous solution according to the present embodiment includes the following steps.

[First step]
In the present embodiment, first, a monomer containing a conductive polymer is chemically oxidatively polymerized using an oxidizing agent in a solvent containing an organic acid or a salt thereof as a dopant to obtain a mixture containing the conductive polymer. . In the first step, a conductive polymer having a high degree of polymerization and a high degree of crystallization can be obtained.

  Examples of the dopant include alkyl sulfonic acid, benzene sulfonic acid, naphthalene sulfonic acid, anthraquinone sulfonic acid, camphor sulfonic acid and derivatives thereof, and salts thereof such as iron (III). These sulfonic acids may be monosulfonic acid, disulfonic acid or trisulfonic acid. Examples of alkylsulfonic acid derivatives include 2-acrylamido-2-methylpropanesulfonic acid. Examples of benzenesulfonic acid derivatives include phenolsulfonic acid, styrenesulfonic acid, toluenesulfonic acid, and dodecylbenzenesulfonic acid. Examples of naphthalene sulfonic acid derivatives include 1-naphthalene sulfonic acid, 2-naphthalene sulfonic acid, 1,3-naphthalene disulfonic acid, 1,3,6-naphthalene trisulfonic acid, and 6-ethyl-1-naphthalene sulfonic acid. It is done. Examples of the derivatives of anthraquinone sulfonic acid include anthraquinone-1-sulfonic acid, anthraquinone-2-sulfonic acid, anthraquinone-2,6-disulfonic acid, and 2-methylanthraquinone-6-sulfonic acid. Among these, 1-naphthalenesulfonic acid, 2-naphthalenesulfonic acid, 1,3,6-naphthalenetrisulfonic acid, anthraquinone disulfonic acid, p-toluenesulfonic acid, camphorsulfonic acid or iron (III) salts thereof are preferable. Camphorsulfonic acid is more preferable because it has a great influence on the high crystallization of the polymer. Camphorsulfonic acid may be an optically active substance. 1 type may be sufficient as a dopant and 2 or more types may be sufficient as it.

  The amount of the dopant used is not particularly limited because it can be removed in the second step even if it is excessive, but 1 to 100 parts by weight is preferable with respect to 1 part by weight of the monomer, and 1 to 50 parts by weight. Is more preferable.

  The solvent may be water, an organic solvent, or a water-miscible organic solvent, preferably a solvent having good compatibility with the monomer, and particularly preferably a solvent having good compatibility with the dopant and the oxidizing agent. Examples of the organic solvent include alcohol solvents such as methanol, ethanol and propanol; and low polar solvents such as acetonitrile and acetone. 1 type may be sufficient as an organic solvent, and 2 or more types may be sufficient as it. Of these, ethanol or a mixed solvent of ethanol and water is preferable.

  The monomer that provides the conductive polymer may be selected according to the target conductive polymer. The monomer may be one type or two or more types.

  Polypyrrole and its derivatives are obtained by polymerizing the corresponding pyrrole or a derivative of pyrrole. As derivatives of pyrrole, 3-alkyl pyrrole such as 3-hexyl pyrrole, 3,4-dialkyl pyrrole such as 3,4-dihexyl pyrrole, 3-alkoxy pyrrole such as 3-methoxy pyrrole, 3,4-dimethoxy pyrrole, etc. 3,4-dimethoxypyrrole.

  Polythiophene and derivatives thereof are obtained by polymerizing the corresponding thiophene or a derivative of thiophene. Examples of thiophene derivatives include 3,4-ethylenedioxythiophene and derivatives thereof, 3-alkylthiophenes such as 3-hexylthiophene, and 3-alkoxythiophenes such as 3-methoxythiophene. Examples of 3,4-ethylenedioxythiophene derivatives include 3,4- (1-alkyl) ethylenedioxythiophene such as 3,4- (1-hexyl) ethylenedioxythiophene.

  Polyaniline and derivatives thereof are obtained by polymerizing a corresponding aniline or a derivative of aniline. Examples of aniline derivatives include 2-alkylanilines such as 2-methylaniline and 2-alkoxyanilines such as 2-methoxyaniline.

  Among these, poly (3,4-ethylenedioxythiophene) represented by the following formula (3) or a derivative thereof is preferable.

  The concentration of the monomer in the solvent is preferably 0.1 to 50% by weight, and more preferably 0.5 to 30% by weight.

  The oxidizing agent is not particularly limited, and iron (III) chloride hexahydrate, anhydrous iron (III) chloride, iron (III) nitrate nonahydrate, anhydrous ferric nitrate, iron (III) sulfate n water Japanese (n = 3-12), iron (III) sulfate dodecahydrate, iron (III) perchlorate n hydrate (n = 1,6), iron (III) tetrafluoroborate, etc. Iron (III) salts of inorganic acids of copper; copper (II) salts of inorganic acids such as copper (II) chloride, copper (II) sulfate, copper (II) tetrafluoroborate; nitrosonium tetrafluoroborate; ammonium persulfate Persulfates such as sodium persulfate and potassium persulfate; periodates such as potassium periodate; hydrogen peroxide, ozone, potassium hexacyanoferrate (III), tetraammonium cerium sulfate (IV) dihydrate , Bromine, iodine; p-toluenesulfo Iron (III) salts of organic acids, iron (III), or the like can be used. Among these, inorganic acid or organic acid iron salt (III) or persulfate is preferable, ammonium persulfate or iron p-toluenesulfonate (III) is more preferable, and p has the property of serving as a dopant. -More preferred is iron (III) toluenesulfonate. 1 type may be sufficient as an oxidizing agent, and 2 or more types may be sufficient as it.

  The amount of the oxidizing agent used is not particularly limited because it can be removed in the second step even if it is excessive, but in order to obtain a high conductivity polymer by reacting in a milder oxidizing atmosphere, 0.5-100 weight part is preferable with respect to 1 weight part of monomers, and 1-50 weight part is more preferable.

  The reaction temperature of chemical oxidative polymerization is not particularly limited, but is generally around the reflux temperature of the solvent used, preferably 0 to 100 ° C, more preferably 10 to 50 ° C. If the reaction temperature is not appropriate, the conductivity may be impaired. The reaction time of chemical oxidative polymerization is about 5 to 100 hours, although it depends on the type and amount of oxidant, reaction temperature, stirring conditions and the like.

  The first step is preferably performed in the presence of a substance having a surface active action. As the substance having a surface active action, an anionic surfactant, a cationic surfactant, and an amphoteric surfactant can be used, and dodecylbenzenesulfonic acid, polyethylene glycol, and the like are preferable.

[Second step]
In this embodiment, the conductive polymer is recovered from the mixture obtained in the first step. Specifically, by separating and washing the conductive polymer from the reaction liquid containing the conductive polymer obtained by chemical oxidative polymerization, dopants, unreacted monomers, residual metal ions and anions derived from the oxidizing agent Remove. By the second step, sufficient purification treatment is possible, and a highly pure conductive polymer can be obtained.

  Examples of the method for separating the conductive polymer from the reaction solution include a filtration method and a centrifugal separation method.

  The washing solvent is preferably performed using a solvent capable of dissolving the monomer and / or the oxidizing agent without dissolving the conductive polymer. Examples of the cleaning solvent include water and alcohol solvents such as methanol, ethanol, and propanol. The cleaning solvent may be one type or two or more types. The degree of washing can be confirmed by performing pH measurement and colorimetric observation of the washing solvent after washing.

  Furthermore, since the metal component derived from the oxidizing agent can be removed to a higher degree, it is preferable to wash the conductive polymer and / or heat-treat the conductive polymer. The temperature of the heat treatment is not particularly limited as long as it is equal to or lower than the decomposition temperature of the conductive polymer, but it is preferably performed at less than 300 ° C. In addition, performing an ion exchange treatment using an ion exchange resin is also effective as a method for removing metal ions and anions derived from an oxidizing agent.

  Impurities contained in the conductive polymer can be quantified by ICP emission analysis or ion chromatography.

[Third step]
In this embodiment, an oxidizing agent is allowed to act on the conductive polymer recovered in the second step in an aqueous solvent containing a polyacid. In the third step, a conductive polymer suspension aqueous solution having good dispersibility of the conductive polymer is obtained by allowing the polyacid and the oxidant as the dispersant to act on the conductive polymer. As a dispersion mechanism, at least the doping action of polyanions derived from polyacids can be considered.

  As the polyacid, the above-mentioned polyacid can be used. Of these, polystyrene sulfonic acid is preferable. The weight average molecular weight of the polyacid is preferably 2,000 to 500,000, and more preferably 10,000 to 200,000.

  The amount of polyacid used is preferably 20 to 3,000 parts by weight and more preferably 30 to 1,000 parts by weight with respect to 100 parts by weight of the conductive polymer obtained in the second step. preferable.

  As the oxidizing agent, the same oxidizing agent used in the first step can be used, and among them, ammonium persulfate or hydrogen peroxide is preferable.

  10-500 weight part is preferable with respect to 100 weight part of conductive polymers obtained at the 2nd process, and, as for the usage-amount of an oxidizing agent, 50-300 weight part is more preferable.

  As the aqueous solvent, water is preferable, but there is no problem even if a water-soluble organic solvent is added.

  Although the reaction temperature in a 3rd process is not specifically limited, 0-100 degreeC is preferable and 10-50 degreeC is more preferable. The reaction time is not particularly limited, but is about 5 to 100 hours. Moreover, it is preferable to perform the ion exchange process mentioned above after a 3rd process.

[Fourth step]
In this embodiment, at least one water-soluble polyhydric alcohol and at least one water-soluble organic substance having two or more functional groups capable of polycondensation with the water-soluble polyhydric alcohol are mixed during or after the third step. To do. The water-soluble polyhydric alcohol and water-soluble organic substance mixed in the fourth step undergo a condensation polymerization reaction in the drying process, so that a water-insoluble resin exists in the conductive organic material without uneven distribution, and the effect Thus, a conductive organic material having excellent adhesion to the substrate and water resistance is obtained.

  As the water-soluble polyhydric alcohol, those described above can be used. In particular, the conductivity is improved by mixing erythritol or pentaerythritol as the water-soluble polyhydric alcohol. That is, erythritol or pentaerythritol interacts with the undoped dopant anion (resistance component) introduced in the third step, present in the vicinity of the conductive polymer particles in the conductive polymer suspension aqueous solution, While lowering the resistance between the conductive polymer particles and increasing the density of the conductive polymer, it is possible to further increase the conductivity.

  Furthermore, by using a water-soluble polyhydric alcohol having a valence of 3 or more as the water-soluble polyhydric alcohol, a resin having a cross-linked structure can be obtained by a condensation polymerization reaction with a water-soluble organic substance. From this viewpoint, erythritol or pentaerythritol is preferable.

  By mixing the water-soluble polyhydric alcohol with 100 parts by weight or more (preferably 200 parts by weight or more) with respect to 100 parts by weight of the conductive polymer, a high effect can be obtained. The upper limit of the content of the water-soluble polyhydric alcohol is not particularly limited as long as it is an amount that can be dissolved in water as a solvent, but is preferably 3000 parts by weight or less.

  As the water-soluble organic material, those described above can be used, but a water-soluble organic material having two or more carboxyl groups is preferable. In particular, by mixing ortho-phthalic acid as a water-soluble organic substance, a resin can be formed without segregation in a conductive organic material by condensation polymerization with a water-soluble polyhydric alcohol in the drying process. A conductive organic material having excellent properties can be obtained.

  The mixing amount of the water-soluble organic substance is preferably 1 to 200 parts by weight, and more preferably 50 to 100 parts by weight with respect to 100 parts by weight of the conductive polymer.

<Conductive organic material>
The conductive organic material according to this embodiment is obtained by drying the aqueous conductive polymer suspension and removing the solvent. The conductive organic material has excellent adhesion and water resistance to the base material and high conductivity. is there. The drying temperature for removing the solvent is not particularly limited as long as it is equal to or lower than the decomposition temperature of the conductive polymer, but is preferably 300 ° C. or lower.

  Before drying the conductive polymer suspension aqueous solution, the water-soluble polyhydric alcohol contained in the conductive polymer suspension aqueous solution and the water-soluble organic substance contained in the conductive polymer suspension aqueous solution are mixed at 70 to 100 ° C. The condensation polymerization reaction may be performed at a temperature of In the conductive organic material obtained by drying, the water-insoluble resin obtained by the polycondensation reaction is present evenly, and the effect is excellent in adhesion to the substrate and water resistance. It becomes an organic material.

<Electrolytic capacitor and manufacturing method thereof>
The electrolytic capacitor according to the present embodiment has an electrolyte layer containing the above-mentioned aqueous conductive polymer suspension or conductive organic material. The electrolyte layer is preferably solid. In the electrolytic capacitor according to the present embodiment, since the material forming the electrolyte has high conductivity, the electrolytic capacitor has a low ESR. In addition, polymer materials with a high degree of crystallinity also have a high oxygen barrier property, and due to the effects of the crosslinked resin, they have excellent adhesion to substrates and water resistance, so the reliability of electrolytic capacitors is also high. It is expected to improve sufficiently.

  FIG. 2 is a schematic cross-sectional view showing the structure of the solid electrolytic capacitor according to this embodiment. This electric field capacitor has a structure in which a dielectric layer 2, a solid electrolyte layer 3, and a cathode conductor 4 are formed in this order on an anode conductor 1.

  The anode conductor 1 is formed of a valve metal plate, foil, or wire; a sintered body made of fine particles of the valve metal; a porous metal that has been subjected to surface expansion treatment by etching. Examples of the valve action metal include tantalum, aluminum, titanium, niobium, zirconium, and alloys thereof. Among these, at least one valve action metal selected from aluminum, tantalum and niobium is preferable.

  The dielectric layer 2 is a layer that can be formed by electrolytic oxidation of the surface of the anode conductor 1, and is also formed in pores such as a sintered body and a porous body. The thickness of the dielectric layer 2 can be adjusted as appropriate by the voltage of electrolytic oxidation.

  The solid electrolyte layer 3 contains the above-described aqueous conductive polymer suspension or conductive organic material. The solid polymer electrolyte layer 3 may have a single layer structure or a multilayer structure. In the solid electrolytic capacitor shown in FIG. 2, the solid polymer electrolyte layer 3 is composed of a first conductive polymer compound layer 3A and a second conductive polymer compound layer 3B. The first conductive polymer contained in the first conductive polymer compound layer 3A and the second conductive polymer contained in the second conductive polymer compound layer 3B are the same type of polymer. Preferably there is.

  The solid electrolyte layer 3 further comprises a conductive polymer obtained by polymerizing pyrrole, thiophene, aniline or a derivative thereof; an oxide derivative such as manganese dioxide or ruthenium oxide; TCNQ (7,7,8,8-tetracyano) An organic semiconductor such as quinodimethane complex salt) may be contained.

  Examples of a method for forming the solid electrolyte layer 3 include a method of applying or impregnating the conductive polymer suspension onto the dielectric layer 2 and removing the solvent from the conductive polymer suspension. In addition, the solid electrolyte layer 3 in the solid electrolytic capacitor shown in FIG. 2 is formed on the dielectric layer by chemical oxidative polymerization or electrolytic polymerization of a monomer that gives the first conductive polymer compound. The layer 3A is formed, and the first conductive polymer compound layer 3A is coated or impregnated with the above-described conductive polymer suspension to form a second conductive polymer compound layer. can do.

  As a monomer that gives the first conductive polymer compound, at least one selected from pyrrole, thiophene, aniline, and derivatives thereof can be used. The dopant used when the monomer is chemically oxidatively polymerized or electrolytically polymerized to obtain the first conductive polymer compound includes benzenesulfonic acid, naphthalenesulfonic acid, phenolsulfonic acid, styrenesulfonic acid, and derivatives thereof. Acid compounds are preferred. The molecular weight of the dopant can be appropriately selected from low molecular weight compounds to high molecular weight compounds. As the solvent, only water or a mixed solvent containing water and an organic solvent soluble in water may be used.

  The method of application or impregnation is not particularly limited, but it is preferably left for several minutes to several tens of minutes after application or impregnation in order to sufficiently fill the inside of the porous pores with the conductive polymer suspension. . Repeated immersion, reduced pressure method or pressurized method is preferred.

  Removal of the solvent from the conductive polymer suspension can be performed by drying the conductive polymer. The drying temperature is not particularly limited as long as the solvent can be removed, but the upper limit temperature is preferably less than 300 ° C. from the viewpoint of preventing element deterioration due to heat. The drying time must be appropriately optimized depending on the drying temperature, but is not particularly limited as long as the conductivity is not impaired.

  Before drying the conductive polymer suspension aqueous solution, the water-soluble polyhydric alcohol contained in the conductive polymer suspension aqueous solution and the water-soluble organic substance contained in the conductive polymer suspension aqueous solution are mixed at 70 to 100 ° C. The condensation polymerization reaction may be performed at a temperature of In the solid electrolyte layer 3 obtained by drying, the water-insoluble resin obtained by the polycondensation reaction is present without uneven distribution. Due to the effect, the adhesion to the dielectric layer 2 and water resistance are excellent. The solid polymer electrolyte layer 3 is obtained.

  The cathode conductor 4 is not particularly limited as long as it is a conductor. For example, the cathode conductor 4 can have a two-layer structure including a carbon layer 5 such as graphite and a silver conductive resin 6.

  Hereinafter, the present embodiment will be described more specifically based on examples, but the present embodiment is not limited to only these examples.

[Example 1]
(First step)
As a solvent, 3,4-ethylenedioxythiophene (1 g) as a monomer, camphorsulfonic acid (1 g) as a dopant, and iron (III) p-toluenesulfonate (9 g) functioning as an oxidizing agent and a dopant. In ethanol (30 ml). The resulting solution was stirred at room temperature for 24 hours to oxidize the monomer. At this time, the mixture changed from yellow to dark blue.

(Second step)
The mixed liquid obtained in the first step was filtered with a vacuum filtration device to recover the powder. The obtained powder was washed with pure water to remove excess oxidizing agent / dopant. Washing with pure water was repeated until the pH of the filtrate was 6-7. After the pH of the filtrate reached 6-7, it was further washed with ethanol to remove the monomer, the oxidizing agent and the oxidizing agent after reaction (iron (II) -toluenesulfonate). Washing with ethanol was performed until the color of the filtrate became colorless and transparent.

(Third process)
After the powder (0.5 g) washed in the second step was dispersed in water (50 ml), a 20% by weight aqueous solution of polystyrene sulfonic acid (weight average molecular weight: 50,000) as a polyacid (3. 3 g) was added. To this mixture, ammonium persulfate (1.5 g) as an oxidizing agent was further added, and the mixture was stirred at room temperature for 24 hours.

(Fourth process)
Add erythritol (5 g) and ortho-phthalic acid (0.3 g) to the mixture obtained in the third step and stir at room temperature for 24 hours to completely dissolve erythritol and ortho-phthalic acid. It was. The resulting aqueous polythiophene suspension was dark blue.

(Evaluation of aqueous polythiophene suspension)
100 μl of the obtained polythiophene suspension was dropped onto a glass substrate and subjected to a polycondensation reaction between erythritol and ortho-phthalic acid in a 90 ° C. thermostat, and the temperature of the thermostat was further set to 125 ° C. The conductive polymer film was formed by evaporating the solvent and drying.

  The resulting conductive polymer film was measured for surface resistance (Ω / □) and film thickness by the four probe method, and the conductivity (S / cm) was calculated. Moreover, the obtained conductive polymer film was immersed in water for 10 minutes, and water resistance was evaluated by observing the change of the conductive polymer film. In addition, “○” indicates that there is no change in the conductive polymer film, “△” indicates that the conductive polymer is partially swollen, and “×” indicates that the entire conductive polymer is swollen. did. The results are shown in Table 1.

  Further, the crystallinity of the conductive polymer film was evaluated by an X-ray diffraction method. In the measurement, 2θ was scanned from 5 ° C to 40 ° C. The measurement result of X-ray diffraction is shown in FIG.

[Example 2]
In the third step, an aqueous polythiophene suspension was produced in the same manner as in Example 1 except that polystyrene sulfonic acid having a weight average molecular weight of 14,000 was used as the polyacid. And except having used the obtained polythiophene suspension aqueous solution, it carried out similarly to Example 1, and formed the conductive polymer film, and evaluated the electrical conductivity and water resistance. The results are shown in Table 1.

Example 3
In the second step, an aqueous polythiophene suspension was produced in the same manner as in Example 1 except that washing with pure water and washing with ethanol were followed by washing with boiling hot pure water. And except having used the obtained polythiophene suspension aqueous solution, it carried out similarly to Example 1, and formed the conductive polymer film, and evaluated the electrical conductivity and water resistance. The results are shown in Table 1.

Example 4
In the second step, an aqueous polythiophene suspension was produced in the same manner as in Example 1, except that washing with pure water and washing with ethanol were followed by heat drying in a thermostatic bath at 125 ° C. And except having used the obtained polythiophene suspension aqueous solution, it carried out similarly to Example 1, and formed the conductive polymer film, and evaluated the electrical conductivity and water resistance. The results are shown in Table 1.

Example 5
(First step)
The monomer 3,4-ethylenedioxythiophene (1 g) was dispersed in 100 ml of water as a solvent using a dopant and dodecylbenzenesulfonic acid (2.3 g) functioning as a surfactant. The obtained dispersion was stirred at room temperature for 1 hour to thoroughly disperse the monomer, and then ammonium persulfate (2.4 g) as an oxidizing agent was added. The obtained dispersion was stirred at room temperature for 100 hours to oxidize the monomer. At this time, the solution changed from yellow to dark blue.

(Second step)
The liquid mixture obtained in the first step was centrifuged (5,000 rpm) to collect the powder. The obtained powder was washed by a decantation method using pure water with a centrifuge to remove excess oxidant / dopant. Washing with pure water was repeated until the pH of the supernatant was 6-7.

  After the third step, an aqueous polythiophene suspension was produced in the same manner as in Example 1. And except having used the obtained polythiophene suspension aqueous solution, it carried out similarly to Example 1, and formed the conductive polymer film, and evaluated the electrical conductivity and water resistance. The results are shown in Table 1.

Example 6
(First step)
The monomer 3,4-ethylenedioxythiophene (1 g) and the dopant camphorsulfonic acid (1 g) are dispersed in 100 ml of water as a solvent using polyethylene glycol (2 g) functioning as a surfactant. It was. Polyethylene glycol having a weight average molecular weight of 4,000 was used. The obtained dispersion was stirred at room temperature for 1 hour to thoroughly disperse the monomer, and then ammonium persulfate (2.4 g) as an oxidizing agent was added. The obtained dispersion was stirred at room temperature for 100 hours to oxidize the monomer. At this time, the solution changed from yellow to dark blue.

  After the second step, an aqueous polythiophene suspension was produced in the same manner as in Example 4. And except having used the obtained polythiophene suspension aqueous solution, it carried out similarly to Example 1, and formed the conductive polymer film, and evaluated the electrical conductivity and water resistance. The results are shown in Table 1.

Example 7
In the fourth step, an aqueous polythiophene suspension was produced in the same manner as in Example 1 except that pentaerythritol (5 g) was used as the water-soluble polyhydric alcohol. And except having used the obtained polythiophene suspension aqueous solution, it carried out similarly to Example 1, and formed the conductive polymer film, and evaluated the electrical conductivity and water resistance. The results are shown in Table 1.

Example 8
In the fourth step, an aqueous polythiophene suspension was produced in the same manner as in Example 1 except that ethylene glycol (5 g), which is a divalent alcohol, was used as the water-soluble polyhydric alcohol. And except having used the obtained polythiophene suspension aqueous solution, it carried out similarly to Example 1, and formed the conductive polymer film, and evaluated the electrical conductivity and water resistance. The results are shown in Table 1.

Example 9
In the same manner as in Example 1, an aqueous polythiophene suspension was produced. 100 microliters of obtained polythiophene suspension aqueous solution was dripped on a glass substrate, and the conductive polymer film was formed by volatilizing a solvent completely in a 125 degreeC thermostat, and drying. And it carried out similarly to Example 1, and evaluated the electrical conductivity and water resistance of the obtained conductive polymer film. The results are shown in Table 1.

[Comparative Example 1]
An aqueous polythiophene suspension was produced by the method described in Example 1 of Patent Document 1. Specifically, polystyrene sulfonic acid (2 g) having a weight average molecular weight of 4,000, 3,4-ethylenedioxythiophene (0.5 g) and iron (III) sulfate (0.05 g) are dissolved in water (20 ml). And air was introduced over 24 hours to produce an aqueous polythiophene suspension. And except having used the obtained polythiophene suspension aqueous solution, it carried out similarly to Example 1, and formed the conductive polymer film, and evaluated the electrical conductivity and water resistance. The results are shown in Table 1.

[Comparative Example 2]
A polythiophene suspension was prepared in the same manner as in Comparative Example 1 except that polystyrene sulfonic acid having a weight average molecular weight of 50,000 was used. And except having used the obtained polythiophene suspension aqueous solution, it carried out similarly to Example 1, and formed the conductive polymer film, and evaluated the electrical conductivity and water resistance. The results are shown in Table 1. Further, in the same manner as in Example 1, the crystallinity of the conductive polymer film was evaluated by the X-ray diffraction method. The measurement result of X-ray diffraction is shown in FIG.

[Comparative Example 3]
By adding the self-emulsifying polyester dispersion (0.3 g) to the polythiophene suspension aqueous solution (20 g) obtained in Comparative Example 2, and stirring for 24 hours at room temperature to dissolve the self-emulsifying polyester dispersion. An aqueous polythiophene suspension was prepared. And except having used the obtained polythiophene suspension aqueous solution, it carried out similarly to Example 1, and formed the conductive polymer film, and evaluated the electrical conductivity and water resistance. The results are shown in Table 1.

Example 10
Porous aluminum was used as an anode conductor made of a valve metal, and an oxide film serving as a dielectric layer was formed on the surface of the aluminum by anodic oxidation. The anode part and the cathode part were separated by an insulating resin. Next, the cathode part of the anode conductor on which the dielectric layer was formed was dipped in the aqueous polythiophene suspension produced in Example 1 and pulled up, and then subjected to a condensation polymerization reaction in a 90 ° C. constant temperature bath, and further the temperature of the constant temperature bath Was dried and solidified at 125 ° C. to form a solid electrolyte layer. And a graphite layer and a silver content resin layer were formed in order on the solid electrolyte layer, and the solid electrolytic capacitor was manufactured.

The ESR (equivalent series resistance) of the obtained solid electrolytic capacitor was measured at a frequency of 100 kHz using an LCR meter. The value of ESR normalized the total cathode area to a unit area (1 cm ² ). The results are shown in Table 2.

Example 11
Porous aluminum was used as an anode conductor made of a valve metal, and an oxide film serving as a dielectric layer was formed on the surface of the aluminum by anodic oxidation. The anode part and the cathode part were separated by an insulating resin. Next, the cathode part of the anode conductor on which the dielectric layer was formed was mixed with a monomer solution obtained by dissolving pyrrole (10 g) in pure water (200 ml), p-toluenesulfonic acid (20 g) as a dopant, and excess as an oxidizing agent. A first conductive polymer compound layer was formed by repeating immersion and pulling up 10 times sequentially with an oxidizing agent solution in which ammonium sulfate (10 g) was dissolved in pure water (200 ml), and performing chemical oxidative polymerization. .

  On the first conductive polymer compound layer, the polythiophene suspension aqueous solution produced in Example 1 is dropped, and the polycondensation reaction is performed in a 90 ° C. constant temperature bath. -Solidified to form a second conductive polymer compound layer. Then, a solid electrolytic capacitor was manufactured by sequentially forming a graphite layer and a silver-containing resin layer on the solid electrolyte layer composed of the first conductive polymer compound layer and the second conductive polymer compound layer. .

  The ESR (equivalent series resistance) of the obtained solid electrolytic capacitor was measured by the same method as in Example 10. The results are shown in Table 2.

Example 12
A solid electrolytic capacitor was manufactured in the same manner as in Example 10 except that porous tantalum was used as the anode conductor made of a valve metal. The ESR (equivalent series resistance) of the obtained solid electrolytic capacitor was measured by the same method as in Example 10. The results are shown in Table 2.

[Comparative Example 4]
A solid electrolytic capacitor was produced in the same manner as in Example 10 except that the polythiophene suspension aqueous solution produced in Comparative Example 2 was used instead of the polythiophene suspension aqueous solution produced in Example 1. The ESR (equivalent series resistance) of the obtained solid electrolytic capacitor was measured by the same method as in Example 10. The results are shown in Table 2.

[Comparative Example 5]
A solid electrolytic capacitor was produced in the same manner as in Example 10 except that the polythiophene suspension aqueous solution produced in Comparative Example 3 was used instead of the polythiophene suspension aqueous solution produced in Example 1. The ESR (equivalent series resistance) of the obtained solid electrolytic capacitor was measured by the same method as in Example 10. The results are shown in Table 2.

  As shown in Table 1, the conductive polymer films obtained in Examples 1 to 9 have a water resistance equal to or higher than that of the conductive polymer films obtained in Comparative Examples 1 to 3, And it was high electrical conductivity. That is, the effects of increasing water resistance and increasing conductivity according to the present embodiment are clear.

  The effect of increasing the water resistance is that the aqueous conductive polymer suspension contains a water-soluble polyhydric alcohol and a water-soluble organic substance having two or more functional groups capable of polycondensation with the water-soluble polyhydric alcohol. This is because a water-insoluble resin is formed without segregation in the conductive organic material obtained by drying the aqueous conductive polymer suspension.

  The conductive polymer films obtained in Examples 1 to 7 were superior in water resistance as compared to the conductive polymer film obtained in Example 8. This is because, as in Examples 1 to 3, a resin having a crosslinked structure obtained by polycondensation reaction of erythritol or pentaerythritol, which is a trivalent or higher water-soluble polyhydric alcohol, and a water-soluble organic substance is the same as that of Example 8. This is because the water absorption is low and the water resistance is excellent as compared with a linear resin obtained by condensation polymerization reaction of ethylene glycol, which is a divalent water-soluble polyhydric alcohol, and a water-soluble organic substance. .

  The conductive polymer films obtained in Examples 1 to 7 were excellent in water resistance as compared with the conductive polymer film obtained in Example 9. In Examples 1 to 7, before drying a conductive polymer suspension and obtaining a conductive organic material, a polycondensation reaction between erythritol and ortho-phthalic acid was performed in a constant temperature bath at 90 ° C. This is because the water-insoluble resin can be sufficiently formed in the conductive organic material and the water resistance is improved.

  In particular, by going through the first to third steps, (1) a dopant that increases the crystallinity can be selected because of a wide range of dopant options, and (2) a solvent that is highly compatible with the monomer. Since the configuration can be selected, the degree of polymerization can be increased, and (3) since the washing is easy, high purity can be achieved, and as a result, high conductivity can be achieved.

  Further, in the second step, it becomes possible to increase the solubility of unnecessary components by hot water washing and / or to remove volatile components by heat treatment, and to further increase the purity. As a result, the conductivity is further increased. improves.

  Furthermore, in the fourth step, conductivity is improved by adding erythritol or pentaerythritol. This is because erythritol or pentaerythritol interacts with the undoped dopant anion (resistance component) introduced in the third step, which is present in the vicinity of the conductive polymer particles in the aqueous conductive polymer suspension. This is because the resistance between the conductive polymer particles is lowered and the density of the conductive polymer is increased.

  As shown in Table 2, the solid electrolytic capacitors obtained in Examples 10 to 12 had lower resistance (ESR) than the solid electrolytic capacitors obtained in Comparative Examples 4 to 5. In Examples 10 to 12, since the conductivity of the conductive organic material used is high, the resistance of the solid electrolyte can be reduced, and the resistance (ESR) can be reduced.

1 Anode conductor 2 Dielectric layer 3 Solid electrolyte layer 3A First conductive polymer compound layer 3B Second conductive polymer compound layer 4 Cathode conductor 5 Graphite layer 6 Silver conductive resin layer

Claims (19)

A first step of obtaining a mixture containing a conductive polymer by chemically oxidatively polymerizing a monomer which gives a conductive polymer in a solvent containing an organic acid or a salt thereof as a dopant using an oxidizing agent;
A second step of recovering the conductive polymer from the mixture;
A third step of allowing an oxidizing agent to act on the conductive polymer in an aqueous solvent containing a polyacid;
A method for producing an aqueous conductive polymer suspension, comprising a fourth step of mixing at least one water-soluble polyhydric alcohol and ortho-phthalic acid . The method for producing an aqueous conductive polymer suspension according to claim 1 , wherein the monomer that gives the conductive polymer is selected from pyrrole, thiophene, aniline, and derivatives thereof. The dopant is, benzenesulfonic acid, naphthalenesulfonic acid, camphorsulfonic acid and its derivatives, and suspended conductive polymer according to claim 1 or 2, characterized in that at least one selected from the salts thereof A method for producing a turbid aqueous solution. The method for producing a conductive polymer suspension aqueous solution according to any one of claims 1 to 3 , wherein the first step is performed in the presence of a substance having a surfactant activity. In the second step, the conductive polymer, the conductive polymer according to any one of claims 1 to 4, characterized in that washing the monomer and / or the oxidizing agent in a dissolvable solvent A method for producing an aqueous suspension. 6. The method for producing an aqueous conductive polymer suspension solution according to claim 5 , wherein in the second step, the conductive polymer is further subjected to hot water washing and / or heat treatment. The method for producing a conductive polymer suspension aqueous solution according to any one of claims 1 to 6 , wherein polystyrene sulfonic acid is used as the polyacid in the third step. The weight average molecular weight of the said polystyrene sulfonic acid is 2,000-500,000, The manufacturing method of the conductive polymer suspension aqueous solution of Claim 7 characterized by the above-mentioned. The method for producing an aqueous conductive polymer suspension solution according to any one of claims 1 to 8 , wherein the water-soluble polyhydric alcohol is trivalent or higher. The method for producing a conductive polymer suspension aqueous solution according to claim 9 , wherein the water-soluble polyhydric alcohol is at least one selected from erythritol and pentaerythritol. Drying the conductive polymer suspension solution obtained by the method according to any one of claims 1 to 10, the solvent all SANYO removing the water-soluble polyhydric alcohol and ortho - phthalate polycondensation reaction A conductive organic material containing a resin made by the process. A polycondensation reaction of the water-soluble polyhydric alcohol contained in the aqueous conductive polymer suspension and ortho-phthalic acid contained in the aqueous conductive polymer suspension at a temperature of 70 to 100 ° C. The conductive organic material according to claim 11 , wherein: An electrolytic capacitor comprising an aqueous conductive polymer suspension obtained by the method according to any one of claims 1 to 10 , or an electrolyte layer containing the conductive organic material according to claim 11 or 12 . 14. The method according to claim 13 , further comprising: an anode conductor made of a valve action metal; and a dielectric layer formed on a surface of the anode conductor, wherein the electrolyte layer is formed on the dielectric layer. The electrolytic capacitor as described. 15. The electrolytic capacitor according to claim 14 , wherein the valve metal is at least one selected from aluminum, tantalum, and niobium. Forming a dielectric layer on the surface of the anode conductor made of a valve metal;
11. An electrolysis method comprising: applying or impregnating a conductive polymer suspension obtained by the method according to any one of claims 1 to 10 on the dielectric layer to form an electrolyte layer. Capacitor manufacturing method. Forming a dielectric layer on the surface of the anode conductor made of a valve metal;
Forming a first conductive polymer compound layer on the dielectric layer by chemical oxidative polymerization or electrolytic polymerization of a monomer that gives the first conductive polymer compound;
Said first conductive polymer compound layer, claims 1 to 10 a conductive polymer suspension aqueous solution obtained by the method according to any one of the applied or impregnated, the second conductive polymer compound And a step of forming a layer. The method for producing an electrolytic capacitor according to claim 17 , wherein the first conductive polymer compound includes at least one polymer selected from pyrrole, thiophene, aniline, and derivatives thereof. The method for manufacturing an electrolytic capacitor according to any one of claims 16 to 18 , wherein the valve metal is at least one selected from aluminum, tantalum, and niobium.

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