Manufacturing method of electrolytic capacitor

Abstract

To provide a method for manufacturing an electrolytic capacitor with small leakage current and excellent heat resistance and moisture resistance.SOLUTION: A method for manufacturing an electrolytic capacitor includes a step of applying a voltage by using, as an anode, a capacitor element immersed in a conductive polymer dispersion liquid containing a conductive polymer that is a polymer of thiophene or a derivative thereof and contains a polymer anion as a dopant, thereby forming a solid electrolyte layer on the capacitor element. It is preferable that the conductive polymer dispersion preferably has an electrical conductivity of 0.01 to 40 mS / cm and a pH of 1.0 to 7.0.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing an electrolytic capacitor having a small leakage current and excellent heat resistance and moisture resistance. [Background technology]

[0002] Due to their high conductivity, conductive polymers are used as electrolytes (solid electrolytes) in, for example, aluminum electrolytic capacitors, tantalum electrolytic capacitors, niobium electrolytic capacitors, and the like.

[0003] As the conductive polymer for this application, for example, those obtained by chemical oxidative polymerization or electrolytic oxidative polymerization of pyrrole or its derivatives, thiophene or its derivatives, etc. are used.

[0004] When using a conductive polymer as the solid electrolyte of an electrolytic capacitor, a commonly used method is to apply a dispersion of powdered conductive polymer obtained by chemical oxidation polymerization or electrolytic oxidation polymerization in a solvent to the surface of a capacitor element by coating or the like, and then dry it to form a layer of solid electrolyte (conductive polymer).

[0005] However, when a dispersion of a conductive polymer is directly applied to the surface of a capacitor element, the dispersion is likely to be repelled, and the conductive polymer cannot adhere well, for example, to the edges of the capacitor element, resulting in an uneven thickness of the solid electrolyte layer made of the conductive polymer, and particularly at the edges of the capacitor element, the solid electrolyte layer tends to become thin or there are likely to be areas where the solid electrolyte is absent. Electrolytic capacitors using capacitor elements with such a solid electrolyte layer have the problem of being prone to short-circuit defects (large leakage current).

[0006] On the other hand, Patent Document 1 proposes a technique for electrolytically oxidatively polymerizing thiophene or its derivatives in an electrolytic polymerization solution containing a sulfonated polyester having a specific degree of sulfonation and using a water-soluble organic solvent and water as solvents. This technique allows a conductive polymer to be synthesized on the capacitor element to form a solid electrolyte layer, thereby avoiding the above-mentioned problems.

[0007] Also, a technique for solving the above-mentioned problems by applying a pretreatment agent to the surface of the capacitor element prior to applying a dispersion of a conductive polymer is known. For example, Patent Document 2 proposes a technique for applying a solution or dispersion containing a crosslinking agent such as a polymeric amine to the surface of the capacitor body (capacitor element) prior to applying a solution or dispersion containing an electrically conductive material (conductive polymer) that will become a solid electrolyte. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2020-4758 [Patent Document 2] Special Publication No. 2012-517113 Summary of the Invention [Problem to be solved by the invention]

[0009] However, the inventors' investigations have revealed that it is difficult to produce electrolytic capacitors with excellent heat resistance and moisture resistance using the technique described in Patent Document 2, in which a pretreatment agent such as a solution containing a crosslinking agent is applied to the surface of a capacitor element prior to coating with a conductive polymer dispersion. When a pretreatment agent is applied to the surface of a capacitor element, components of the pretreatment agent tend to remain on the element, and it is presumed that these residual components cause the above-mentioned problems.

[0010] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for manufacturing an electrolytic capacitor that has a small leakage current and excellent heat resistance and moisture resistance. [Means for solving the problem]

[0011] The method for producing an electrolytic capacitor of the present invention is characterized by comprising the steps of applying a voltage to a capacitor element as an anode, the capacitor element being immersed in a conductive polymer dispersion containing a conductive polymer that is a polymer of thiophene or a derivative thereof and that contains a polymeric anion as a dopant, to form a solid electrolyte layer on the capacitor element. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a method for manufacturing an electrolytic capacitor that has a small leakage current and excellent heat resistance and moisture resistance. DETAILED DESCRIPTION OF THE INVENTION

[0013] In the method for manufacturing an electrolytic capacitor of the present invention, a solid electrolyte layer is formed on a capacitor element by using a conductive polymer dispersion containing a conductive polymer that is a polymer of thiophene or its derivatives and that contains a polymeric anion as a dopant, and applying a voltage to a capacitor element immersed in the conductive polymer dispersion as an anode. As a result, the conductive polymer in the conductive polymer dispersion adheres to the capacitor element even to its edges with high uniformity to form a layer (solid electrolyte layer), and the application of current (voltage) promotes a reaction between the conductive polymers, making the layer structure denser.

[0014] An electrolytic capacitor manufactured using a capacitor element having such a solid electrolyte layer reduces the occurrence of short-circuit defects and reduces leakage current, is not affected by residues that are present when a pretreatment agent containing a crosslinking agent is used, and has excellent heat resistance and moisture resistance because the solid electrolyte layer has a dense structure.

[0015] In the method of the present invention, a conductive polymer dispersion liquid which is a polymer of thiophene or its derivatives and contains a polymeric anion as a dopant is used to form a solid electrolyte layer of an electrolytic capacitor.

[0016] Examples of thiophene derivatives for forming a polymer of thiophene or a derivative thereof include 3,4-ethylenedioxythiophene (EDOT), 3-alkylthiophene, 3-alkoxythiophene, 3-alkyl-4-alkoxythiophene, 3,4-alkylthiophene, 3,4-alkoxythiophene, and alkylated ethylenedioxythiophene (alkylated EDOT) obtained by modifying the above-mentioned 3,4-ethylenedioxythiophene with an alkyl group. The number of carbon atoms in the alkyl group or alkoxy group is preferably 1 or more, and is preferably 16 or less, more preferably 10 or less, and even more preferably 4 or less.

[0017] To explain in detail about alkylated EDOT, which is the above-mentioned EDOT modified with an alkyl group, EDOT and alkylated EDOT correspond to compounds represented by the following general formula (1).

[0018] [ka]

[0019] In general formula (1), R 1 is hydrogen or an alkyl group having 1 to 10 carbon atoms.

[0020] In addition, R in the general formula (1) 1The compound where R is hydrogen is EDOT, and its IUPAC name is "2,3-Dihydro-thieno[3,4-b][1,4]dioxine." However, this compound is more often referred to by its general name, "3,4-ethylenedioxythiophene," than by its IUPAC name. Therefore, in this specification, this "2,3-Dihydro-thieno[3,4-b][1,4]dioxine" is referred to as "3,4-ethylenedioxythiophene (EDOT)." Furthermore, R in the above general formula (1) 1 When R is an alkyl group, the alkyl group preferably has 1 to 10 carbon atoms, and more preferably has 1 to 4 carbon atoms. That is, the alkyl group is particularly preferably a methyl group, an ethyl group, a propyl group, or a butyl group. Specific examples of these include R in general formula (1). 1 The compound where R is a methyl group is designated by the IUPAC name "2-Methyl-2,3-dihydro-thieno[3,4-b][1,4]dioxine", but in this specification, this will be abbreviated and referred to as "methylated ethylenedioxythiophene (methylated EDOT)". 1 The compound with an ethyl group has the IUPAC name "2-Ethyl-2,3-dihydro-thieno[3,4-b][1,4]dioxine," but in this specification it is abbreviated to "ethylated ethylenedioxythiophene (ethylated EDOT)."

[0021] R in general formula (1) 1The compound where R is a propyl group is expressed in IUPAC name as "2-propyl-2,3-dihydro-thieno[3,4-b][1,4]dioxine", but in this specification, this is abbreviated to "propylated ethylenedioxythiophene (propylated EDOT)". 1 The IUPAC name for compounds with a butyl group is "2-butyl-2,3-dihydro-thieno[3,4-b][1,4]dioxine," but this specification abbreviates it to "butylated ethylenedioxythiophene (butylated EDOT)." Furthermore, this specification abbreviates "2-alkyl-2,3-dihydro-thieno[3,4-b][1,4]dioxine" to "alkylated ethylenedioxythiophene (alkylated EDOT)." Among these alkylated EDOTs, methylated EDOT, ethylated EDOT, propylated EDOT, and butylated EDOT are preferred.

[0022] It is preferable to use a mixture of EDOT (i.e., 2,3-dihydro-thieno[3,4-b][1,4]dioxin) and alkylated EDOT (i.e., 2-alkyl-2,3-dihydro-thieno[3,4-b][1,4]dioxin), with the mixing ratio being preferably 0.05:1 to 1:0.1, more preferably 0.1:1 to 1:0.1, even more preferably 0.2:1 to 1:0.2, and particularly preferably 0.3:1 to 1:0.3, in terms of molar ratio.

[0023] In the conductive polymer dispersion, a polymeric anion capable of functioning as a dopant for the conductive polymer is used as a dopant for the conductive polymer, and this polymeric anion also has the function of increasing the dispersibility of the conductive polymer in the dispersion.

[0024] Examples of polymeric anions include polystyrene sulfonic acid; copolymers (A) of styrene sulfonic acid and at least one non-sulfonic acid monomer selected from the group consisting of hydroxyalkyl methacrylate, glycidyl methacrylate, hydroxyalkyl acrylate, glycidyl acrylate, and unsaturated hydrocarbon-containing alkoxysilane compounds or hydrolysates thereof; sulfonated polyesters; and the like.

[0025] The polystyrene sulfonic acid preferably has a number average molecular weight of 10,000 to 1,000,000 as estimated using a high performance liquid chromatography (HPLC) system with a gel permeation chromatography (GPC) column and dextran as a standard.

[0026] Examples of hydroxyalkyl methacrylates that serve as monomers for the copolymer (A) include hydroxymethyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, hydroxyhexyl methacrylate, hydroxystearyl methacrylate, etc. Among these, hydroxyalkyl methacrylates having an alkyl group of 1 to 4 carbon atoms, such as hydroxymethyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, and hydroxybutyl methacrylate, are preferred in terms of their properties as a dopant when copolymerized with styrenesulfonic acid.

[0027] Examples of the hydroxyalkyl acrylate that serves as a monomer for the copolymer (A) include hydroxyalkyl acrylates having an alkyl group with 1 to 4 carbon atoms, such as hydroxymethyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, and hydroxybutyl acrylate. These hydroxyalkyl methacrylates having an alkyl group with 1 to 4 carbon atoms are preferred in terms of their properties as a dopant when copolymerized with styrenesulfonic acid.

[0028] Examples of the unsaturated hydrocarbon-containing alkoxysilane compound or hydrolysate thereof that can be used as a monomer for the copolymer (A) include unsaturated hydrocarbon-containing alkoxysilane compounds and hydrolysates thereof, such as 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyldimethylmethoxysilane, 3-methacryloxypropyldimethylethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-acryloxymethyldimethoxysilane, 3-acryloxymethyldiethoxysilane, 3-acryloxytriethoxysilane, p-styryltrimethoxysilane, p-styryltriethoxysilane, p-styrylmethyldimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinylmethyldimethoxysilane, and vinyldimethylmethoxysilane. For example, when the unsaturated hydrocarbon-containing alkoxysilane compound is the above-mentioned 3-methacryloxypropyltrimethoxysilane, the hydrolyzate of this unsaturated hydrocarbon-containing alkoxysilane compound is 3-methacryloxytrihydroxysilane, which is a structure in which the methoxy group is hydrolyzed to a hydroxyl group, or a compound in which silanes condense to form an oligomer, and the methoxy group not used in the reaction is converted to a hydroxyl group.The unsaturated hydrocarbon-containing alkoxysilane compound is preferably 3-methacryloxypropyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, p-styryltrimethoxysilane, vinyltrimethoxysilane, etc., in terms of its properties as a dopant when copolymerized with styrenesulfonic acid.

[0029] Furthermore, compounds containing a glycidyl group, such as glycidyl methacrylate and glycidyl acrylate, become structures containing a hydroxyl group upon ring-opening of the glycidyl group, and therefore, these compounds having a glycidyl group are also preferred in terms of their properties as dopants when copolymerized with styrenesulfonic acid.

[0030] The ratio of styrene sulfonic acid to at least one non-sulfonic acid monomer selected from the group consisting of hydroxyalkyl methacrylate, glycidyl methacrylate, hydroxyalkyl acrylate, glycidyl acrylate, and unsaturated hydrocarbon-containing alkoxysilane compounds or hydrolysates thereof in the copolymer (A) is preferably 1:0.01 to 0.1:1 by mass.

[0031] The copolymer (A) preferably has a number average molecular weight of 5,000 to 500,000, determined by the same method as for polystyrene sulfonic acid, from the viewpoint of water solubility and properties as a dopant.

[0032] Sulfonated polyesters that can be used as polymer anions are those that are obtained by condensation polymerization of dicarboxybenzenesulfonic acid diesters, such as sulfoisophthalic acid esters and sulfoterephthalic acid esters, with alkylene glycols in the presence of a catalyst, such as antimony oxide or zinc oxide. The sulfonated polyesters preferably have a number-average molecular weight of 5,000 to 500,000, as measured by GPC using a column packed with polyvinyl alcohol (Asahipak GF-7M HQ, manufactured by Showa Denko K.K.) and a 0.1 M aqueous sodium nitrate solution as the solvent.

[0033] The conductive polymer dispersion can be obtained, for example, by oxidatively polymerizing thiophene or a derivative thereof in an aqueous liquid (water or a mixture of water and a water-miscible solvent) containing the polymer anion as a dopant, to synthesize a conductive polymer (a polymer of thiophene or a derivative thereof) doped with the polymer anion.

[0034] Examples of the water-miscible solvent constituting the aqueous liquid used for synthesizing the conductive polymer include methanol, ethanol, propanol, acetone, acetonitrile, etc. The proportion of the water-miscible solvent in the total amount of solvent in the polymerization solution is preferably 50 mass % or less.

[0035] In the polymerization solution (a solution containing thiophene or a derivative thereof, the polymeric anion, and a solvent) for oxidative polymerization, the concentration of thiophene or a derivative thereof is preferably 0.5 to 5.0 mass %. The concentration of the polymeric anion in the polymerization solution is preferably 0.5 to 5.0 mass %.

[0036] The polymerization liquid may contain a cationic surfactant, a nonionic surfactant, an anionic surfactant, or the like, as required.

[0037] The oxidative polymerization for synthesizing the conductive polymer can be either chemical oxidative polymerization or electrolytic oxidative polymerization.

[0038] As an oxidizing agent for carrying out chemical oxidative polymerization, for example, a persulfate is used, and examples of the persulfate that can be used include ammonium persulfate, sodium persulfate, potassium persulfate, calcium persulfate, and barium persulfate.

[0039] The amount of persulfate used may be adjusted so that, for example, the amount of persulfate is preferably 0.4 mol or more, more preferably 0.5 mol or more, and preferably 4.0 mol or less, more preferably 3.5 mol or less, per 1 mol of the polymeric anion as the dopant.

[0040] In the chemical oxidative polymerization, the polymerization conditions are not particularly limited, but the temperature during the chemical oxidative polymerization is preferably 5°C to 95°C, more preferably 10°C to 30°C, and the polymerization time is preferably 1 hour to 72 hours, more preferably 8 hours to 24 hours.

[0041] The electrolytic oxidation polymerization can be carried out at a constant current or a constant voltage. For example, when the electrolytic oxidation polymerization is carried out at a constant current, the current value is 0.05 mA / cm. 2 ~10mA / cm 2 is preferred, and 0.2 mA / cm 2 ~4mA / cm 2When electrolytic oxidation polymerization is carried out at a constant voltage, the voltage is preferably 0.5 V to 10 V, and more preferably 1.5 V to 5 V. The temperature during electrolytic oxidation polymerization is preferably 5°C to 95°C, and particularly preferably 10°C to 30°C. The polymerization time is preferably 1 hour to 72 hours, and more preferably 8 hours to 24 hours. In addition, ferrous sulfate or ferric sulfate may be added as a catalyst during electrolytic oxidation polymerization.

[0042] The conductive polymer obtained as described above (the conductive polymer doped with the polymeric anion) is dispersed in water or an aqueous solution immediately after polymerization and contains persulfate as an oxidizing agent, iron sulfate used as a catalyst, and its decomposition products. Therefore, it is preferable to disperse the impurities in the aqueous dispersion of the conductive polymer using a dispersing machine such as an ultrasonic homogenizer, high-pressure homogenizer, or planetary ball mill, and then remove the metal components with a cation exchange resin. The particle size of the conductive polymer measured by dynamic light scattering is preferably 100 μm or less, more preferably 10 μm or less, and preferably 0.01 μm or more, and more preferably 0.1 μm or more. Subsequent removal of the oxidizing agent and catalyst decomposition products by ethanol precipitation, ultrafiltration, anion exchange resin, or the like is preferable.

[0043] Furthermore, water or the above-mentioned water-miscible solvent can be further added to the obtained conductive polymer dispersion, for example, to adjust the content of the conductive polymer so as to satisfy the preferred amount described below.

[0044] The conductive polymer dispersion may further contain a component (adhesion improver) that improves the adhesion between the solid electrolyte layer and the capacitor element, such as polyvinyl alcohol, polyurethane, polyester, acrylic resin, polyamide, polyimide, epoxy resin, polyacrylonitrile resin, polymethacrylonitrile resin, polystyrene resin, novolac resin, sulfonated polyester, sulfonated polyvinyl, sulfonated polyvinyl, sulfonated polyallyl, sulfonated polystyrene, or a silane coupling agent.

[0045] In the method of the present invention, a capacitor element is immersed in the conductive polymer dispersion thus obtained, and a voltage is applied using the capacitor element as an anode to form a solid electrolyte layer on the capacitor element.

[0046] Electrolytic capacitors manufactured by the method of the present invention include aluminum electrolytic capacitors, tantalum electrolytic capacitors, niobium electrolytic capacitors, etc. These electrolytic capacitors use a capacitor element having an anode made of a porous body of a valve metal such as aluminum, tantalum, or niobium, and a dielectric layer made of an oxide film of the valve metal.

[0047] Therefore, when electrolytic polymerization is performed by the method of the present invention, the above-mentioned capacitor element is used as the anode, and a solid electrolyte layer (a layer of conductive polymer) is formed on the surface of the dielectric layer. However, as described above, these capacitor elements have a dielectric layer made of an oxide film on the surface, but because this dielectric layer has poor conductivity, it is necessary to form a conductive precoat layer on the dielectric layer of the capacitor element to enable the application of voltage to this surface.

[0048] Although there are no particular limitations on the precoat layer, it is preferable to synthesize a polymer of thiophene or its derivatives by chemical oxidative polymerization to form the precoat layer. For example, the precoat layer can be formed by applying a dispersion (dispersion in an alcohol such as ethanol as a solvent) containing an oxidant-cum-dopant, such as a known organic ferric sulfonate, to the surface of the capacitor element by coating or the like, drying the dispersion, and then immersing the resulting solution in thiophene or its derivative (as exemplified above for synthesizing conductive polymers related to the conductive polymer dispersion), followed by chemical oxidative polymerization at 20 to 50°C for 30 to 240 minutes. This method allows a precoat layer with a thickness of approximately several microns to be formed on the surface of the dielectric layer of the capacitor element.

[0049] The capacitor element on which the precoat layer has been formed is then immersed in a conductive polymer dispersion liquid, and a voltage is applied to the capacitor element as the anode. The voltage application can be performed at a constant current or a constant voltage. For example, when the voltage is applied at a constant current, the current value is set to 0.05 mA / cm. 2 ~10mA / cm 2 is preferred, and 0.2 mA / cm 2 ~4mA / cm 2 When the voltage is applied at a constant voltage, the voltage is preferably 0.5 V to 10 V, more preferably 1.5 V to 5 V. The temperature during voltage application is preferably 5° C. to 95° C., particularly preferably 10° C. to 30° C. The time for applying the voltage is preferably 10 to 600 minutes, more preferably 60 to 300 minutes.

[0050] In the conductive polymer dispersion liquid used for forming the solid electrolyte layer, the content of the conductive polymer containing the polymer anion as a dopant is preferably 0.5 to 5 mass %. Furthermore, the conductive polymer dispersion liquid may contain a cationic surfactant, a nonionic surfactant, an anionic surfactant, or the like, as necessary.

[0051] The conductive polymer dispersion used to form the solid electrolyte layer preferably has an electrical conductivity of 0.01 mS / cm or more, more preferably 0.1 mS / cm or more, and preferably 40 mS / cm or less, more preferably 20 mS / cm or less. By using a conductive polymer dispersion with an electrical conductivity within the above range, it is possible to form an electrolytic capacitor with better characteristics. The electrical conductivity of the conductive polymer dispersion can be adjusted by adjusting the ratio of thiophene or its derivative to the polymer anion used in synthesizing the conductive polymer, or by adjusting the concentrations of these in the polymerization solution.

[0052] The electrical conductivity of the conductive polymer dispersion liquid referred to in this specification is a value measured using a conductivity meter (F-55) manufactured by Horiba, Ltd., but it may also be measured using an equivalent conductivity meter (the values ​​described in the examples below are values ​​measured using the above F-55).

[0053] Furthermore, the pH of the conductive polymer dispersion used to form the solid electrolyte layer is preferably 1.0 or higher, more preferably 1.5 or higher, and preferably 7.0 or lower, more preferably 5.0 or lower. By using a conductive polymer dispersion having an electrical conductivity within the above range, it is possible to form an electrolytic capacitor with better characteristics. The pH of the conductive polymer dispersion can be adjusted by adding a known acid or alkali as needed.

[0054] In addition, it is preferable to add thiophene or a derivative thereof to the conductive polymer dispersion liquid used to form the solid electrolyte layer, which improves the characteristics of the electrolytic capacitor, possibly because the solid electrolyte layer thus formed has a denser structure. The amount of thiophene or a derivative thereof added to the conductive polymer dispersion liquid is preferably 0.05% by mass or more, and preferably 1.0% by mass or less.

[0055] Furthermore, it is preferable to add the above-mentioned polymer anion to the conductive polymer dispersion used to form the solid electrolyte layer, which improves the conductivity of the conductive polymer that constitutes the solid electrolyte layer and thereby improves the characteristics of the electrolytic capacitor. The amount of the above-mentioned polymer anion added to the conductive polymer dispersion is preferably 0.1 mass % or more and 2.0 mass % or less.

[0056] The thickness of the solid electrolyte layer formed on the capacitor element is preferably 10 to 25 μm.

[0057] The capacitor element with the solid electrolyte layer formed is washed and then dried. Carbon paste and silver paste are then applied to the dried capacitor element, which is then dried and packaged to produce a laminated or flat electrolytic capacitor (aluminum electrolytic capacitor, tantalum electrolytic capacitor, niobium electrolytic capacitor, etc.).

[0058] Alternatively, an electrolytic capacitor may be constructed by impregnating the solid electrolyte layer of the capacitor element with a conductive auxiliary liquid containing a high-boiling organic solvent having a boiling point of 150°C or higher or a high-boiling organic solvent having a boiling point of 150°C or higher and an aromatic compound having at least one hydroxyl group or carboxyl group.

[0059] Examples of high-boiling organic solvents having a boiling point of 150°C or higher that can be used in the conductive auxiliary liquid include γ-butyrolactone (boiling point: 203°C), butanediol (boiling point: 230°C), dimethyl sulfoxide (boiling point: 189°C), sulfolane (boiling point: 285°C), N-methylpyrrolidone (boiling point: 202°C), dimethyl sulfolane (boiling point: 233°C), ethylene glycol (boiling point: 198°C), diethylene glycol (boiling point: 244°C), triethyl phosphate (boiling point: 215°C), tributyl phosphate (289°C), triethylhexyl phosphate [215°C (4 mmHg)], and polyethylene glycol.

[0060] Furthermore, as the above-mentioned hydroxyl group (which refers to a hydroxyl group bonded to a constituent carbon of an aromatic ring, and does not mean an -OH moiety in a carboxyl group, etc.) or aromatic compound having at least one carboxyl group, any of benzene-based compounds, naphthalene-based compounds, and anthracene-based compounds can be used, and specific examples thereof include hydroxybenzenecarboxylic acid, nitrophenol, dinitrophenol, trinitrophenol, aminonitrophenol, hydroxyanisole, hydroxydinitrobenzene, dihydroxydinitrobenzene, alkylhydroxyanisole, hydroxynitroanisole, hydroxynitrobenzenecarboxylic acid (i.e., hydroxynitrobenzoic acid), dihydroxynitrobenzenecarboxylic acid (i.e., dihydroxynitrobenzoic acid), phenol, dihydroxybenzene, trihydrobenzoic acid, ... hydroxybenzene, dihydroxybenzenecarboxylic acid, trihydroxybenzenecarboxylic acid, hydroxybenzenedicarboxylic acid, dihydroxybenzenedicarboxylic acid, hydroxytoluenecarboxylic acid, nitronaphthol, aminonaphthol, dinitronaphthol, hydroxynaphthalenecarboxylic acid, dihydroxynaphthalenecarboxylic acid, trihydroxynaphthalenecarboxylic acid, hydroxynaphthalene dicarboxylic acid, dihydroxynaphthalene dicarboxylic acid, hydroxyanthracene, dihydroxyanthracene, trihydroxyanthracene, tetrahydroxyanthracene, hydroxyanthracenecarboxylic acid, hydroxyanthracenedicarboxylic acid, dihydroxyanthracenedicarboxylic acid, tetrahydroxyanthracenedione, benzenecarboxylic acid, benzenedicarboxylic acid, naphthalenecarboxylic acid, and naphthalene dicarboxylic acid.

[0061] In addition, the high-boiling organic solvent or conductive auxiliary liquid having a boiling point of 150°C or higher may contain at least one binder selected from the group consisting of epoxy compounds or hydrolysates thereof, silane compounds or hydrolysates thereof, and polyalcohols.

[0062] The electrolytic capacitor produced by the method of the present invention has a small leakage current and excellent heat resistance and moisture resistance, and therefore can be suitably used in applications requiring such properties (e.g., automotive applications), and can also be used in the same applications in which electrolytic capacitors have traditionally been used. [Example]

[0063] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples.

[0064] [Preparation of Conductive Polymer Dispersion] Preparation Example 1 600 g of a 4% by weight aqueous solution of polystyrene sulfonic acid (manufactured by Teika Corporation, number average molecular weight: 100,000) was placed in a 1 L stainless steel vessel, and 0.3 g of ferrous sulfate heptahydrate was added and dissolved therein as a catalyst. 4 mL of EDOT was slowly added dropwise to the vessel. The reaction solution in the vessel was stirred with a stainless steel stirring blade, and an anode was attached to the vessel and a cathode was attached to the base of the stirring blade. A current of 1 mA / cm was applied. 2 A conducting polymer doped with polystyrene sulfonic acid was synthesized by electrolytic oxidation polymerization at a constant current of 0.05V for 18 hours.

[0065] The reaction solution after electrolytic oxidation polymerization was diluted 6-fold with water and then dispersed for 30 minutes using an ultrasonic homogenizer (US-T300 (trade name), manufactured by Nippon Seiki Co., Ltd.). 100 g of a cation exchange resin (Amberlite 120B (trade name), manufactured by Organo Corporation) was then added to the reaction solution, which was stirred for 1 hour using a stirrer. The mixture was then filtered through No. 131 filter paper manufactured by Toyo Roshi Co., Ltd. This treatment with the cation exchange resin and filtration were repeated three times to remove all cationic components, such as iron ions, from the solution.

[0066] The treated liquid was passed through a filter with a pore size of 1 μm, and the effluent was treated with an ultrafiltration device (Vivaflow 200 (trade name), manufactured by Sartorius, molecular weight cutoff 50,000) to remove free low-molecular-weight components from the liquid. The treated liquid was diluted with water to adjust the concentration of the conductive polymer doped with polystyrene sulfonic acid to 1% by mass, thereby obtaining conductive polymer dispersion (1).

[0067] Preparation Example 2 A conductive polymer dispersion (2) was prepared in the same manner as in Preparation Example 1, except that the concentration of the aqueous solution of polystyrene sulfonic acid was changed to 2.5% by mass.

[0068] Preparation Example 3 A conductive polymer dispersion (3) was prepared in the same manner as in Preparation Example 1, except that the concentration of the aqueous solution of polystyrene sulfonic acid was changed to 5% by mass.

[0069] Preparation Example 4 A conductive polymer dispersion (4) was prepared in the same manner as in Preparation Example 1, except that the concentration of the aqueous solution of polystyrene sulfonic acid was changed to 2.5% by mass and the final concentration of the conductive polymer doped with polystyrene sulfonic acid was adjusted to 0.5% by mass.

[0070] Preparation Example 5 A conductive polymer dispersion (5) was prepared in the same manner as in Preparation Example 1, except that the concentration of the aqueous solution of polystyrene sulfonic acid was changed to 5% by mass and the final concentration of the conductive polymer doped with polystyrene sulfonic acid was adjusted to 2.5% by mass.

[0071] Preparation Example 6 A conductive polymer dispersion (6) was prepared in the same manner as in Preparation Example 1, except that when adjusting the final concentration of the conductive polymer doped with polystyrene sulfonic acid, ammonia water was added to adjust the pH to 4.

[0072] Preparation Example 7 A conductive polymer dispersion (7) was prepared in the same manner as in Preparation Example 1, except that when adjusting the final concentration of the conductive polymer doped with polystyrene sulfonic acid, ammonia water was added to adjust the pH to 6.

[0073] Preparation Example 8 A conductive polymer dispersion (8) was prepared in the same manner as in Preparation Example 1, except that when adjusting the final concentration of the conductive polymer doped with polystyrene sulfonic acid, ammonia water was added to adjust the pH to 8.

[0074] Preparation Example 9 A conductive polymer dispersion (9) was prepared in the same manner as in Preparation Example 1, except that a copolymer (number average molecular weight: 90,000) obtained by copolymerizing styrene sulfonic acid and hydroxyethyl methacrylate in a mass ratio of 8:2 was used instead of polystyrene sulfonic acid.

[0075] Preparation Example 10 A conductive polymer dispersion (10) was prepared in the same manner as in Preparation Example 1, except that a sulfonated polyester (manufactured by GOO Chemical Industry Co., Ltd., PLASCOAT Z-561 (trade name), number average molecular weight: 27,000) was used instead of polystyrene sulfonic acid.

[0076] Preparation Example 11 A conductive polymer dispersion (11) was prepared in the same manner as in Preparation Example 1, except that instead of the aqueous solution of polystyrene sulfonic acid, an aqueous solution containing the same polystyrene sulfonic acid as used in Preparation Example 1 and the same sulfonated polyester as used in Preparation Example 10, at concentrations of 3 mass % and 1 mass %, respectively, was used.

[0077] Preparation Example 12 A conductive polymer dispersion (12) was prepared in the same manner as in Preparation Example 1, except that a 7:3 (mass ratio) mixture of EDOT and butylated EDOT was used instead of EDOT.

[0078] Preparation Example 13 A conductive polymer dispersion (13) was prepared in the same manner as in Preparation Example 1, except that when adjusting the final concentration of the conductive polymer doped with polystyrene sulfonic acid, polystyrene sulfonic acid (the same as that used in Preparation Example 1) was added in an amount to give a concentration of 0.5 mass %.

[0079] Preparation Example 14 A conductive polymer dispersion (14) was prepared in the same manner as in Preparation Example 1, except that, when adjusting the final concentration of the conductive polymer doped with polystyrene sulfonic acid, an acetonitrile solution of EDOT (concentration: 20% by mass) was added in an amount such that the EDOT concentration was 0.5% by mass.

[0080] Preparation Example 15 A conductive polymer dispersion (15) was prepared in the same manner as in Preparation Example 1, except that when adjusting the final concentration of the conductive polymer doped with polystyrene sulfonic acid, polystyrene sulfonic acid (the same as that used in Preparation Example 1) was added in an amount to give a concentration of 0.25% by mass, and an acetonitrile solution of EDOT (concentration: 10% by mass) was added in an amount to give an EDOT concentration of 0.25% by mass.

[0081] Preparation Example 16 A conductive polymer dispersion (16) was prepared in the same manner as in Preparation Example 1, except that when adjusting the final concentration of the conductive polymer doped with polystyrene sulfonic acid, an amount of sulfonated polyester (the same as that used in Preparation Example 10) was added to give a concentration of 0.5 mass %.

[0082] Preparation Example 17 A conductive polymer dispersion (17) was prepared in the same manner as in Preparation Example 10, except that when adjusting the final concentration of the conductive polymer doped with sulfonated polyester, an acetonitrile solution of EDOT (concentration: 10% by mass) was added in an amount such that the EDOT concentration was 0.1% by mass.

[0083] Preparation Example 18 A conductive polymer dispersion (18) was prepared in the same manner as in Preparation Example 10, except that when adjusting the final concentration of the conductive polymer doped with sulfonated polyester, an amount of sulfonated polyester (the same as that used in Preparation Example 10) was added so that the concentration would be 0.25% by mass, and an acetonitrile solution of EDOT (concentration: 10% by mass) was added so that the concentration of EDOT would be 0.25% by mass.

[0084] Preparation Example 19 A conductive polymer dispersion (19) was prepared in the same manner as in Preparation Example 1, except that when adjusting the final concentration of the conductive polymer doped with polystyrene sulfonic acid, dimethyl sulfoxide was added in an amount to give a concentration of 10 mass %.

[0085] Preparation Example 20 A conductive polymer dispersion (20) was prepared in the same manner as in Preparation Example 1, except that when adjusting the final concentration of the conductive polymer doped with polystyrene sulfonic acid, polyoxyethylene alkyl ether (nonionic surfactant) was added in an amount to give a concentration of 0.03 mass %.

[0086] Preparation Example 21 A conductive polymer dispersion (21) was prepared in the same manner as in Preparation Example 1, except that 3-glycidoxypropyltrimethoxysilane (adhesion improver) was added in an amount to give a concentration of 0.5 mass % when adjusting the final concentration of the conductive polymer doped with polystyrene sulfonic acid.

[0087] The compositions, electrical conductivities, and pHs of the conductive polymer dispersions prepared in Preparation Examples 1 to 21 are shown in Table 1. The abbreviations used in Table 1 are as follows. EDOT / Bu-EDOT: A mixture of EDOT and butylated EDOT PSS: Polystyrene sulfonate P(SS-HME): Copolymer of styrene sulfonic acid and hydroxyethyl methacrylate SPE: Sulfonated polyester DMSO: dimethyl sulfoxide POEAE: Polyoxyethylene alkyl ether

[0088] [Table 1]

[0089] [Fabrication of electrolytic capacitors] Example 1 A rectangular tantalum sintered body (one tip of a lead wire is embedded in the tantalum sintered body, and the other tip protrudes from one surface of the tantalum sintered body) was immersed in a 2% by mass aqueous solution of phosphoric acid, and a voltage of 10 V was applied, thereby forming a dielectric layer (dielectric oxide film) on the surface of the tantalum sintered body.

[0090] A precoat layer was then formed on the dielectric layer of the tantalum sintered compact to enable electrolytic polymerization, producing a capacitor element. The tantalum sintered compact was immersed in a 30% by mass ethanol solution of ferric toluenesulfonate, removed, and dried at 105°C for 30 minutes. After drying, the tantalum sintered compact was immersed in EDOT and subjected to chemical oxidative polymerization for 1 hour in an atmosphere at 25°C and 60% relative humidity. A precoat layer composed of EDOT polymer was formed on the dielectric layer of the tantalum sintered compact. The tantalum sintered compact was then washed with water for 1 hour and dried at 105°C.

[0091] Next, the capacitor element and a SUS304 plate were immersed in the conductive polymer dispersion (1) obtained in Preparation Example 1, and the capacitor element was used as the anode and the SUS304 plate as the cathode at a liquid temperature of 20 to 30°C and a current of 1 mA / cm 2 A constant current voltage was applied so that a solid electrolyte layer (a layer of conductive polymer) was formed on the precoat layer of the capacitor element. The solid electrolyte layer of the capacitor element was then covered with carbon paste and silver paste, and then packaged with an exterior material to obtain a tantalum electrolytic capacitor.

[0092] Examples 2 to 21 Tantalum electrolytic capacitors were produced in the same manner as in Example 1, except that the conductive polymer dispersion was changed to any one of the conductive polymer dispersions (2) to (21) obtained in Preparation Examples 2 to 21.

[0093] Example 22 A tantalum electrolytic capacitor was fabricated in the same manner as in Example 1, except that the solid electrolyte layer was formed on the precoat layer of the capacitor element by applying a constant voltage of 3 V.

[0094] Comparative Example 1 200 g of a 5% by mass aqueous solution of paratoluenesulfonic acid was stirred at room temperature while measuring the pH, and ethylenediamine was added until the pH reached 1.5. The mixture was then filtered through a 0.4 μm glass filter to remove insoluble matter, yielding a pretreatment agent.

[0095] A capacitor element having a precoat layer formed in the same manner as in Example 1 was immersed in the pretreatment agent, pulled out, and then dried at 120°C for 10 minutes. This capacitor element was immersed in the conductive polymer dispersion (1) obtained in Preparation Example 1, pulled out, and then dried at 120°C for 10 minutes to form a solid electrolyte layer (conductive polymer layer) on the precoat layer. A tantalum electrolytic capacitor was then fabricated in the same manner as in Example 1, except that the capacitor element having the solid electrolyte layer thus obtained was used.

[0096] For the tantalum electrolytic capacitors of the examples and comparative examples, the leakage current and ESR (equivalent series resistance) were measured as initial characteristics by the following methods, and durability evaluation was also carried out by the following methods.

[0097] Leakage current: A rated voltage of 25 V was applied to 10 tantalum electrolytic capacitors of each of the example and comparative example at 25°C for 60 seconds, and then the leakage current was measured using a digital oscilloscope, and the average value of the 10 measured values ​​was calculated for each of the example and comparative example.

[0098] ESR: The ESR of 10 tantalum electrolytic capacitors of each of the Examples and Comparative Examples was measured at 100 kHz under conditions of 25°C using an LCR meter (4284A) manufactured by Hewlett Packard, and the average value of the 10 measured values ​​was calculated for each of the Examples and Comparative Examples by rounding off to one decimal place.

[0099] Durability rating: (Heat resistance evaluation) Ten tantalum electrolytic capacitors from each of the Examples and Comparative Examples were stored in an environment of 150°C for 500 hours, and then the ESR was measured using the same method as in the initial characteristic evaluation. For each of the Examples and Comparative Examples, the average value of the 10 measured values ​​was calculated by rounding to the first decimal place, and this was divided by the average ESR value in the initial characteristic evaluation to determine the rate of change (times).

[0100] (Moisture resistance evaluation) Ten tantalum electrolytic capacitors each from the Examples and Comparative Examples (different electrolytic capacitors from those used in the heat resistance evaluation) were stored for 500 hours in an environment of 85°C and a relative humidity of 85%, and then the ESR was measured in the same manner as in the initial characteristic evaluation. For each of the Examples and Comparative Examples, the average value of the 10 measured values ​​was calculated by rounding to the first decimal place, and this was divided by the average ESR value in the initial characteristic evaluation to determine the rate of change (times).

[0101] The evaluation results above, along with the thickness of the edge of the solid electrolyte layer formed on the capacitor element used to fabricate each tantalum electrolytic capacitor, are shown in Table 2. The thickness of the edge of the solid electrolyte layer was measured using an optical microscope to measure the thickness of the solid electrolyte layer on the corner between the upper surface (the surface from which the lead wires protrude) and the side surface of five capacitor elements for each of the examples and comparative examples, and the thickness was calculated as the average value for each of the five measurements, rounded to one decimal place.

[0102] The descriptions in the voltage application column in Table 2 are as follows: A: Voltage is applied (Condition: Constant current) B: Voltage applied (Condition: Constant voltage) None: No voltage applied

[0103] [Table 2]

[0104] As shown in Table 2, the tantalum electrolytic capacitors of Examples 1 to 22 had small leakage current during initial characteristic evaluation, suppressed changes in ESR under high temperature and high humidity environments, and had excellent heat resistance and moisture resistance.

[0105] On the other hand, the tantalum electrolytic capacitor of Comparative Example 1 was constructed using a capacitor element having a solid electrolyte layer formed using a conductive polymer dispersion after applying a pretreatment agent containing a salt of paratoluenesulfonic acid and ethylenediamine, which corresponds to a crosslinking agent, as in Patent Document 1. However, the leakage current during initial characteristic evaluation was small, and although a certain effect of using the pretreatment agent was recognized, it was larger than that of the electrolytic capacitors of the Examples. Furthermore, the electrolytic capacitor of Comparative Example 1 showed a large rate of change in ESR under high temperature and high humidity environments.

Claims

1. forming a conductive precoat layer on the surface of a capacitor element having a porous valve metal body and a dielectric layer made of an oxide film of the valve metal; and applying a voltage at a constant current of 0.05 to 10 mA / cm 2 or at a constant voltage of 0.5 to 10 V for 10 to 600 minutes to the capacitor element, the capacitor element being immersed in a conductive polymer dispersion containing a conductive polymer that is a polymer of thiophene or a derivative thereof and that contains a polymeric anion as a dopant, to the anode, thereby forming a solid electrolyte layer on the capacitor element.

2. 2. The method for producing an electrolytic capacitor according to claim 1, wherein the conductive polymer dispersion has an electrical conductivity of 0.01 to 40 mS / cm.

3. 3. The method for producing an electrolytic capacitor according to claim 1, wherein the conductive polymer dispersion has a pH of 1.0 to 7.

0.

4. 4. The method for producing an electrolytic capacitor according to claim 1, wherein the conductive polymer dispersion contains thiophene or a derivative thereof.

5. 4. The method for producing an electrolytic capacitor according to claim 1, wherein the conductive polymer dispersion contains a polymer anion capable of functioning as a dopant for the conductive polymer.

6. The method for producing an electrolytic capacitor according to any one of claims 1 to 5, wherein the polymer anion is polystyrene sulfonic acid, or a copolymer of styrene sulfonic acid and at least one non-sulfonic acid monomer selected from the group consisting of hydroxyalkyl methacrylate, glycidyl methacrylate, hydroxyalkyl acrylate, glycidyl acrylate, and an unsaturated hydrocarbon-containing alkoxysilane compound or a hydrolyzate thereof, or a sulfonated polyester.

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