Manufacturing method for solid electrolytic capacitors

Abstract

The present invention provides a solid electrolytic capacitor which has excellent withstand voltage characteristics and high capacitance by performing a process for having a zwitter ion compound held on an anode metal with use of a pretreatment agent that contains the zwitter ion compound, the anode metal having been provided with a dielectric oxide coating film, and subsequently forming a solid electrolyte, which is formed of a conductive polymer, on the anode metal.

Description

[Technical Field]

[0001] This invention relates to a method for manufacturing solid electrolytic capacitors. [Background technology]

[0002] Conductive polymers such as polyaniline, polypyrrole, and polythiophene are used as electrolytes for solid electrolytic capacitors due to their excellent stability and conductivity.

[0003] These conductive polymers are generally insoluble or sparingly soluble in solvents and are infusible, making them difficult to mold and process.

[0004] Solid electrolytic capacitors are known to be constructed by forming a solid electrolyte layer containing a conductive polymer that functions as a cathode on an anode metal having a dielectric oxide film.

[0005] A known method for forming a solid electrolyte layer is chemical oxidation polymerization. For example, a solid electrolyte layer made of a conductive polymer can be formed on an anode metal on which a dielectric oxide film has been formed by applying and contacting a solution containing a monomer compound and an oxidizing agent, thereby causing polymerization.

[0006] However, this chemical oxidation polymerization method had a problem in that the dielectric oxide film was damaged by the oxidizing agent used during chemical oxidation polymerization, which reduced the voltage withstand capability of the solid electrolytic capacitor.

[0007] Patent Document 1 discloses a method for obtaining a capacitor with high dielectric strength by pre-adding boric acid and a divalent glycol that does not contain trivalent or higher glycols to a solid electrolyte-forming composition, thereby generating a boric acid ester having dielectric oxide film repair ability in the solid electrolyte when it is dried and solidified. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2017-004986 [Overview of the project] [Problems that the invention aims to solve]

[0009] Our investigations have revealed that the solid electrolytic capacitor described in Patent Document 1, which generates borate ester in a solid electrolyte, has insufficient voltage resistance and capacitance. Therefore, the present invention provides a method for manufacturing a solid electrolytic capacitor that has excellent voltage resistance characteristics and high capacitance. [Means for solving the problem]

[0010] The present inventors have found that by performing a pretreatment using a pretreatment agent containing a zwitterionic compound to retain the zwitterionic compound on an anode metal on which a dielectric oxide film has been formed, and then forming a solid electrolyte made of a conductive polymer on the anode metal, it is possible to provide a solid electrolytic capacitor that exhibits excellent voltage resistance and high capacitance.

[0011] In other words, the present invention is as follows.

[0012] [1] A method for manufacturing a solid electrolytic capacitor, comprising at least the steps of (a) holding a zwitterionic compound on an anode metal on which a dielectric oxide film has been formed using a pretreatment agent containing a zwitterionic compound, and (b) forming a solid electrolyte layer.

[0013] [2] The method for producing a solid electrolytic capacitor according to [1], characterized in that the pretreatment agent is diluted with 0.1 to 10,000 parts by weight of a solvent per 1 part by weight of a zwitterionic compound.

[0014] [3] The method for manufacturing a solid electrolytic capacitor according to [1] or [2], wherein the zwitterionic compound has one or more anion sites selected from the group consisting of a sulfonic acid anion, a carboxylic acid anion, a phosphoric acid anion, and an anion represented by the following formula (1).

[0015]

Chemical formula

[0016] [4] The method for manufacturing a solid electrolytic capacitor according to any one of [1] to [3], wherein the zwitterionic compound has one or more cation sites selected from the group consisting of an ammonium ion, an imidazolium ion, a pyrazolium ion, a pyridinium ion, and a piperidinium ion.

[0017] [5] The method for manufacturing a solid electrolytic capacitor according to any one of [1] to [3], characterized in that the zwitterionic compound is one or more compounds selected from the group consisting of compounds represented by the following general formulas (2) to (6).

[0018]

Chemical formula

[0019] (In formulas (2) to (6), R1 to R 20 are each independently an organic group or a hydrogen atom which may have one or both of a primary amino group and a secondary amino group, and adjacent Rs may be linked to form an alkylene group having 2 to 碳数6のアルキレン基を形成しても良く、X1~X5はスルホン酸アニオン、カルボン酸アニオン、リン酸アニオン、又は式(1)で表されるアニオンのいずれかを含有する炭素数0~15の基を表す)

[0020] It should be noted that there seems to be an incomplete or incorrect expression in the original text where "R1 to R " and "碳数6のアルキレン基を形成しても良く" are not properly formatted. The translation is done as accurately as possible based on the existing text.[6] A method for manufacturing a solid electrolytic capacitor according to any one of [1] to [5], characterized in that the molecular weight of the zwitterionic compound is 50 to 500.

[0021] [7] The zwitterionic compound is 1-methyl-3-(3-sulfonatopropyl)-1H-imidazole-3-ium, 1-methyl-3-(4-sulfonatobutyl)-1H-imidazole-3-ium, 1-ethyl-3-(3-sulfonatopropyl)-1H-imidazole-3-ium, 1-ethyl-3-(4-sulfonatobutyl)-1H-imidazole-3-ium, 1-butyl-3-(3-sulfonatopropyl)-1H-imidazole-3-ium, 1-butyl-3-(4-sulfonatobutyl)-1H-imidazole-3-ium, 1-hexyl-3-(3-sulfonato A method for producing a solid electrolytic capacitor according to either [1] or [2], wherein the compound is one or more compounds selected from the group consisting of propyl)-1H-imidazole-3-ium, 1-hexyl-3-(4-sulfonatobutyl)-1H-imidazole-3-ium, trimethylglycine, 2-(methacryloyloxy)ethyl-2-(trimethylammonio)ethyl phosphate, 1-(3-sulfonatopropyl)pyridine-1-ium, 1-methyl-2-(3-sulfonatopropyl)-1H-pyrazole-2-ium, and 1-methyl-1-(3-sulfonatopropyl)piperidine-1-ium.

[0022] [8] A method for manufacturing a solid electrolytic capacitor according to any one of [1] to [7], characterized in that the pretreatment agent comprises colloidal silica and a silicone-based surfactant.

[0023] [9] A method for manufacturing a solid electrolytic capacitor according to any one of [1] to [8], characterized in that the anode metal is aluminum or tantalum.

[0024]

[10] A pretreatment agent for solid electrolytic capacitors according to any one of [1] to [8], comprising a zwitterionic compound.

[0025]

[11] A solid electrolytic capacitor containing a zwitterionic compound. [Effects of the Invention]

[0026] According to the present invention, it is possible to provide a method for manufacturing a solid electrolytic capacitor with significantly improved breakdown voltage and high capacitance. In other words, the present invention provides a method for manufacturing a solid electrolytic capacitor that achieves both excellent voltage withstand characteristics and high capacitance. [Modes for carrying out the invention]

[0027] The present invention will be described below.

[0028] The solid electrolytic capacitor manufactured according to the present invention is a solid electrolytic capacitor in which a solid electrolyte is formed on an anode metal on which a dielectric oxide film is formed.

[0029] [Anode metal with a dielectric oxide film formed on it] Examples of anode metals include aluminum, tantalum, niobium, and titanium. The anode metal can be used in the form of a sintered body formed by sintering fine particles, or in the form of a foil or plate roughened by etching or other processes. Among these anode metals, foil-shaped aluminum that has been roughened by etching or the like is extremely suitable because it readily exhibits the effects of the present invention.

[0030] A dielectric oxide film can be formed on the surface of the anode metal by subjecting it to a known chemical conversion treatment. For example, an anodic oxidation treatment can be performed in an aqueous solution of diammonium adipate or the like to form a dielectric oxide film on the anode metal.

[0031] [Zwitterionic compounds] A zwitterionic compound is a compound that has both a cationic and anionic moiety within the same molecule, with each moiety being covalently bonded to one of the atoms in the molecule. An example of a zwitterionic compound is X + -AY - These are represented as such, and within the same molecule, there is a cation site (X +) and an anion site (Y - ) It has. A is a cation site (X + ) and an anion site (Y - ) is a linking group that covalently links them. The linking group A is usually a single bond or an organic group having 1 to 20 carbon atoms.

[0032] Since the cation site and the anion site of the zwitterionic compound are present in the same molecule by a covalent bond, it is difficult for ions to diffuse due to the electric field near the electrode. Therefore, it is presumed that the withstand voltage characteristics, capacitance, and equivalent series resistance of the solid electrolytic capacitor are improved.

[0033] The zwitterionic compound that can be used in the present invention is not particularly limited, and a known zwitterionic compound can be used. Examples of the anion site in the zwitterionic compound include, for example, halogen ions, sulfonic acid anions, carboxylic acid anions, phosphoric acid anions, phosphate ester anions, phosphonic acid anions, carbonate ester anions, sulfate ester anions, hydroxy anions, and anions represented by the following formula. Among them, from the viewpoint of exhibiting excellent withstand voltage characteristics, high capacitance, tan δ, low leakage current characteristics of the solid electrolytic capacitor and having good heat and humidity resistance, the zwitterionic compound is a sulfonic acid anion (SO3 - ), a carboxylic acid anion (COO - ), a phosphoric acid anion (PO3 - ), and it is preferable to have one or more anion sites selected from the group consisting of anions represented by the following formula (1).

[0034] In JPEG0007905343000003.jpg3676 formula (1), Z represents an alkyl group having 1 to 15 carbon atoms, a halogenated alkyl group having 1 to 15 carbon atoms, an aryl group having 6 to 15 carbon atoms, a halogenated aryl group having 6 to 15 carbon atoms, or a halogen, and * represents a bond. Among them, Z is preferably an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, or a halogen. The leftmost sulfur atom on the paper surface in formula (1) forms a covalent bond with any atom in the zwitterionic compound.

[0035] Among the anionic moieties exemplified above, the sulfonate anion is preferred as the anionic moiety of the zwitterionic compound. When the zwitterionic compound contains a sulfonate anion, the voltage withstand characteristics, capacitance, leakage current characteristics, tanδ, equivalent series resistance, and moisture and heat resistance characteristics of the solid electrolytic capacitor tend to be good.

[0036] Examples of cationic sites in zwitterionic compounds include imidazolium ions, ammonium ions, pyridinium ions, sulfonium ions, piperidinium ions, and pyrazolium ions, which may have substituents. In particular, from the viewpoint of improving the high voltage resistance, capacitance, tanδ, leakage current characteristics, and moisture and heat resistance characteristics of solid electrolytic capacitors, it is preferable that the zwitterionic compound has one or more cationic sites selected from the group consisting of imidazolium ions, pyridinium ions, and pyrazolium ions.

[0037] The zwitterionic compound of the present invention preferably contains at least one of the compounds represented by the following formulas (2) to (6). By using these zwitterionic compounds, the voltage withstand characteristics, capacitance, leakage current characteristics, tanδ, equivalent series resistance, and moisture and heat resistance characteristics of the solid electrolytic capacitor are more easily improved. [ka]

[0038] In equations (2) to (6) above, R1 to R 20 Each of these is a hydrogen atom, a C1-C18 alkyl group, a C1-C18 alkoxy group, or a hydroxyl group, which may be the same or different. Adjacent R groups may be linked together to form a C2-C6 alkylene group. In equations (2) to (6) above, R1 to R 20 These are preferably hydrogen atoms, C1-C5 alkyl groups, C1-C5 alkoxy groups, or hydroxyl groups, which may be the same or different, and adjacent R groups may be linked together to form C2-C6 alkylene groups. X1 to X5 are preferably groups having 0 to 15 carbon atoms that contain one of the following: a sulfonate anion, a carboxylic acid anion, a phosphate anion, or an anion represented by formula (1). In particular, in formulas (2) to (6) above, X1 to X5 are more preferably organic groups having 1 to 10 carbon atoms that contain a sulfonate anion, and even more preferably sulfonathalkyl groups having 1 to 5 carbon atoms (-(CH2)n-SO3-; n is an integer from 1 to 5).

[0039] The zwitterionic compounds used in the present invention are 1-methyl-3-(3-sulfonatopropyl)-1H-imidazole-3-ium, 1-methyl-3-(4-sulfonatobutyl)-1H-imidazole-3-ium, 1-ethyl-3-(3-sulfonatopropyl)-1H-imidazole-3-ium, 1-ethyl-3-(4-sulfonatobutyl)-1H-imidazole-3-ium, and 1-butyl-3-(3-sulfonatopropyl)-1H- Imidazole-3-ium, 1-butyl-3-(4-sulfonatobutyl)-1H-imidazole-3-ium, 1-hexyl-3-(3-sulfonatopropyl)-1H-imidazole-3-ium, 1-hexyl-3-(4-sulfonatobutyl)-1H-imidazole-3-ium, trimethylglycine, 2-(methacryloyloxy)ethyl-2-(trimethylammonio)ethyl phosphate, 1-(3-sulfonatopropyl)pyridyl n-1-i Examples include 1-methyl-2-(3-sulfonatopropyl)-1H-pyrazole-2-ium and 1-methyl-1-(3-sulfonatopropyl)piperidine-1-ium.

[0040] [Solvent of pretreatment agent] The pretreatment agent of the present invention may use water or an organic solvent as a solvent.

[0041] Suitable organic solvents include alcohols, ketones, esters, ethers, cellosolves, aromatic hydrocarbons, aliphatic hydrocarbons, sulfones, and the like.

[0042] Examples of alcohols include methanol, ethanol, 1-propanol, isopropyl alcohol, n-butanol, s-butanol, t-butanol, n-amyl alcohol, s-amyl alcohol, t-amyl alcohol, allyl alcohol, isoamyl alcohol, isobutyl alcohol, 2-ethylbutanol, 2-octanol, n-octanol, cyclohexanol, tetrahydrofurfuryl alcohol, furfuryl alcohol, n-hexanol, n-heptanol, 2-heptanol, 3-heptanol, benzyl alcohol, methylcyclohexanol, ethylene glycol, ethylene glycol monomethyl ether, glycerin, diethylene glycol, and propylene glycol.

[0043] Examples of ketones include acetone, methyl ethyl ketone, diethyl ketone, cyclohexanone, methyl isobutyl ketone, and methyl-n-propyl ketone.

[0044] Examples of esters include ethyl acetoacetate, ethyl benzoate, methyl benzoate, isobutyl formate, ethyl formate, propyl formate, methyl formate, isobutyl acetate, ethyl acetate, propyl acetate, methyl acetate, methyl salicylate, diethyl oxalate, diethyl tartrate, dibutyl tartrate, ethyl phthalate, methyl phthalate, butyl phthalate, γ-butyrolactone, ethyl malonate, and methyl malonate.

[0045] Examples of cellosolves include methyl cellosolve and ethyl cellosolve.

[0046] Examples of aromatic hydrocarbons include benzene, toluene, and xylene.

[0047] Examples of aliphatic hydrocarbons include hexane and cyclohexane.

[0048] Examples of sulfones include sulfolane, dimethyl sulfone, ethyl methyl sulfone, ethyl isopropyl sulfone, and 3-methylsulfolane.

[0049] The aforementioned solvents can be used alone or in combination.

[0050] Among the aforementioned solvents, it is particularly preferable that at least one is selected from the group consisting of water, methanol, ethanol, butanol, isopropyl alcohol, ethylene glycol, polyethylene glycol, gamma butyrolactone, and sulfolane.

[0051] [A pretreatment agent obtained by diluting a zwitterionic compound with a solvent to a predetermined concentration.] The pretreatment agent, diluted to a predetermined concentration with a solvent, is preferably diluted in an amount of 0.1 to 10,000 parts by weight of solvent per 1 part by weight of zwitterionic compound, more preferably 0.5 to 5,000 parts by weight of solvent per 1 part by weight of zwitterionic compound, and particularly preferably 1.0 to 1,000 parts by weight of solvent per 1 part by weight of zwitterionic compound. By using this range, the zwitterionic compound can be efficiently retained on the anode metal, and in particular, solid electrolytic capacitors with high withstand voltage and low leakage current characteristics can be manufactured.

[0052] [Process for retaining zwitterionic compounds] The process for retaining the zwitterionic compound described above is described below. The zwitterionic compound can be retained by contacting the pretreatment agent, which is the zwitterionic compound diluted to a predetermined concentration in a solvent, with the anode metal having an anode metal dielectric oxide film, and then drying it to remove the solvent. Any method of contact is acceptable, but preferably, the anode metal having the dielectric oxide film is immersed in the pretreatment agent.

[0053] In other words, it is preferable to have a step of immersing the anode metal having a dielectric oxide film in a pretreatment agent in which the above-mentioned zwitterionic compound is diluted to a predetermined concentration in a solvent, then removing it and drying it to deposit the zwitterionic compound onto the anode metal having a dielectric oxide film.

[0054] The process of immersing the anode metal having a dielectric oxide film in the above pretreatment agent, removing it, and drying it may be repeated multiple times.

[0055] Drying can be done by natural drying at room temperature or by heating, but it is preferable to dry by heating to 80°C or higher.

[0056] As a more specific example of the process, one can cite a step in which an anode metal having a dielectric oxide film is immersed in a pretreatment agent for 30 seconds, and then dried at 155°C for 30 minutes.

[0057] As a process for retaining the zwitterionic compound described above, methods include depositing the zwitterionic compound onto an anode metal having a dielectric oxide film, or contacting the anode metal having a dielectric oxide film with a molten zwitterionic compound and then cooling it.

[0058] [Solid electrolyte] The conductive polymer used in the step of forming the solid electrolyte layer is preferably a dopant-doped polymer. The monomer compound used to produce the polymer is not particularly limited, and for example, pyrroles, thiophenes, anilines, etc. can be used, but a thiophene compound represented by the following general formula (7) is more preferred because it has excellent conductivity.

[0059] [ka]

[0060] In the above general formula (7), R 21 X represents a hydrogen atom or a linear or branched alkyl group having 1 to 6 carbon atoms, and X represents an oxygen atom or a sulfur atom, which may be the same or different.

[0061] Examples of thiophene compounds represented by the above general formula (7) include 3,4-ethylenedioxythiophene, methyl-3,4-ethylenedioxythiophene, ethyl-3,4-ethylenedioxythiophene, propyl-3,4-ethylenedioxythiophene, 3,4-propylenedioxythiophene, methyl-3,4-propylenedioxythiophene, ethyl-3,4-propylenedioxythiophene, propyl-3,4-propylenedioxythiophene, 3,4-ethylenedithiathiophene, methyl-3,4-ethylenedithiathiophene, ethyl-3,4-ethylenedithiathiophene, propyl-3,4-ethylenedithiathiophene, 3,4-propylenedithiathiophene, methyl-3,4-propylenedithiathiophene, ethyl-3,4-propylenedithiathiophene, and propyl-3,4-propylenedithiathiophene.

[0062] Among these, 3,4-ethylenedioxythiophene, methyl-3,4-ethylenedioxythiophene, and ethyl-3,4-ethylenedioxythiophene are particularly preferred due to their excellent electrical properties in solid electrolytic capacitors.

[0063] The conductive polymer that can be used in the present invention can be obtained by chemical oxidative polymerization of a monomer compound such as a thiophene compound represented by the above general formula (7) in the presence of the above dopant. For chemical oxidative polymerization, a known oxidizing agent such as the one described in Japanese Patent Application Publication No. 2010-31160 can be used.

[0064] The dopant should have a functional group capable of chemical oxidative doping of the polymer, and preferably include sulfate ester groups, phosphate ester groups, phosphate groups, carboxyl groups, and sulfo groups. Among these, sulfate ester groups, carboxyl groups, and sulfo groups are more preferred in terms of doping effect, and sulfo groups are particularly preferred.

[0065] Examples of dopants include halogen ions such as iodine, bromine, and chlorine; halide ions such as hexafluoroline, hexafluoroarsenide, hexafluoroantimony, tetrafluoroboron, and perchloric acid; alkyl-substituted organic sulfonate ions such as methanesulfonic acid and dodecylsulfonic acid; cyclic sulfonate ions such as camphorsulfonic acid; alkyl-substituted or unsubstituted benzene mono or disulfonic acid ions such as benzenesulfonic acid, p-toluenesulfonic acid, dodecylbenzenesulfonic acid, and benzenedisulfonic acid; 2-naphthalenesulfonic acid; and 1,7-naphthalenedisulfonic acid. Examples include alkyl-substituted or unsubstituted ions of naphthalene sulfonic acid in which 1 to 4 sulfonic acid groups such as nic acid are substituted, anthracene sulfonic acid ions, anthraquinone sulfonic acid ions, alkyl-substituted or unsubstituted biphenyl sulfonic acid ions such as alkyl biphenyl sulfonic acid and biphenyl disulfonic acid, polymer sulfonic acid ions such as polystyrene sulfonic acid and naphthalene sulfonic acid formalin condensate, or heteropoly acid ions such as molybd phosphoric acid, tungstonic acid, and tungstomolybdonic acid, methoxybenzene sulfonic acid, ethoxybenzene sulfonic acid, and xylene sulfonic acid. Among these, at least one selected from polystyrene sulfonic acid, benzene sulfonic acid, p-toluenesulfonic acid, methoxybenzene sulfonic acid, ethoxybenzene sulfonic acid, and xylene sulfonic acid is more preferred, with p-toluenesulfonic acid being particularly preferred.

[0066] [Process for forming a solid electrolyte layer] The process for forming the solid electrolyte layer is described below. A capacitor element is fabricated by bringing a mixed solution containing the above-mentioned monomer compound, dopant, and oxidizing agent into contact with an anode metal holding the zwitterionic compound, and then polymerizing it, thereby forming a conductive polymer on the anode metal holding the zwitterionic compound. Any method of contact is acceptable, but preferably, the contact is made by immersing the metal in the mixed solution containing the above-mentioned monomer compound, dopant, and oxidizing agent.

[0067] In other words, it is preferable to have a step of immersing the anode metal holding the zwitterionic compound in a solution containing the above-mentioned monomer compound and dopant, then removing it and heating it to chemically oxidize and polymerize it on the anode metal having a dielectric oxide film to form a conductive polymer.

[0068] The process of immersing the anode metal having a dielectric oxide film in a mixed solution containing the above-mentioned monomer compound, dopant, and oxidizing agent, removing it, and drying it may be repeated multiple times.

[0069] The process for forming a solid electrolyte can include a chemical polymerization method in which monomer compounds and an oxidizing agent solution containing a dopant are alternately brought into contact, an electropolymerization method, or a method in which a conductive polymer dispersion is brought into contact with the anode metal.

[0070] Drying can be carried out by natural drying at room temperature or by heating, but if the conductive polymer dispersion contains a high-boiling point organic solvent, it is preferable to dry it by heating to 150°C or higher.

[0071] [Solid electrolytic capacitors] Depending on the type and shape of the anode metal used, solid electrolytic capacitors can be of the chip type or wound type.

[0072] The pretreatment agent of the present invention may further contain colloidal silica and / or a silicone-based activator. By using a pretreatment agent containing colloidal silica and / or a silicone-based activator for pretreatment of the anode metal, the voltage withstand characteristics of the solid electrolytic capacitor can be improved.

[0073] <Colloidal Silica> Colloidal silica is a colloid of SiO2 or its hydrate, with a particle size of 1 to 300 nm and no fixed structure. It can be obtained by dialysis after reacting a silicate with dilute hydrochloric acid. Gelation proceeds more easily as the particle size decreases, but it becomes more difficult as the particle size increases. The particle size of the colloidal silica used in this invention is preferably 10 to 50 nm, and more preferably 10 to 30 nm. By using colloidal silica of this particle size, it is less likely to become gel-like, and a stable dispersed state can be maintained even when using a pretreatment agent.

[0074] Colloidal silica is practically insoluble in water or organic solvents and can generally be used as a colloidal solution dispersed in a suitable dispersion solvent, added to a pretreatment agent.

[0075] The colloidal silica used in this invention may be sodium-stabilized colloidal silica, acidic colloidal silica, or ammonia-stabilized colloidal silica. Sodium-stabilized colloidal silica has ONa groups on its surface. Acidic colloidal silica has OH groups on its surface after removing Na, and ammonia-stabilized colloidal silica is colloidal silica that has been stabilized by adding ammonia after removing Na to create OH groups. Among these, acidic colloidal silica or ammonia-stabilized colloidal silica with a low sodium ion content are preferred.

[0076] The colloidal silica content in the pretreatment agent is 0.01 to 20% by mass, more preferably 0.03 to 15% by mass, and particularly preferably 0.05 to 10% by mass. Within this range, pretreatment of the anode metal using the pretreatment agent improves the dielectric strength characteristics of the electrolytic capacitor.

[0077] The average particle size of the colloidal silica can be any of the above, preferably 1 to 100 nm, more preferably 10 to 50 nm, and particularly preferably 10 to 30 nm. By setting the average particle size to the above, a pretreatment agent with excellent dispersibility in the solvent can be obtained.

[0078] The shape of colloidal silica may be spherical, linear, or cyclic, in which colloidal silica aggregates in a ring and is dispersed in the solvent.

[0079] <Silicone-based surfactants> Silicone-based surfactants include compounds that have a siloxane bond (Si-O-Si) as their main structure, as well as a Si-C bond. Specifically, examples include dimethyl silicone, methylphenyl silicone, chlorophenyl silicone, alkyl-modified silicone, fluorine-modified silicone, amino-modified silicone, alcohol-modified silicone, phenol-modified silicone, carboxy-modified silicone, epoxy-modified silicone, fatty acid ester-modified silicone, and polyether-modified silicone.

[0080] The molecular weight of the silicone-based surfactant is preferably between 100 and 100,000. By using a silicone-based surfactant with a molecular weight in this range, it is possible to prevent the charge balance of colloidal silica from being disrupted, thus preventing gelation of the pretreatment agent over a long period of time. As a result, the anode metal is sufficiently pretreated with the pretreatment agent, and a solid electrolytic capacitor with higher voltage resistance characteristics can be obtained.

[0081] Alkyl-modified silicones are modified silicones having alkyl groups with 6 or more carbon atoms or 2-phenylpropyl groups, etc. Alcohol-modified silicones are modified silicones having alcoholic hydroxyl groups. Epoxy-modified silicones are modified silicones having glycidyl groups or alicyclic epoxy groups, etc. Amino-modified silicones are modified silicones having amino groups such as aminopropyl groups or N-(2-aminoethyl)aminopropyl groups. Fatty acid ester silicones are modified silicones having fatty acid ester groups. Polyether-modified silicones are modified silicones having polyoxyalkylene groups (e.g., polyoxyethylene groups, polyoxypropylene groups, polyoxyethyleneoxypropylene groups, etc.).

[0082] Silicone-based surfactants can be used alone or in combination of two or more types. Among these, polyether-modified silicones are particularly preferred because they prevent the gelation of the pretreatment agent.

[0083] Examples of polyether-modified silicones include pendant-type polymers, ABA-type polymers, (AB)n-type polymers, and branched-type polymers, but among these, pendant-type polymers or ABA-type polymers are preferred.

[0084] The pendant type is typically a compound represented by general formula (A), and the ABA type is typically a compound represented by general formula (B).

[0085] [ka]

[0086] R in the compounds represented by the above general formulas (A) and (B) A or R B represents an alkyl group having 1 to 20 carbon atoms, and Y or Z represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. m is an integer from 0 to 1000, and n or P is an integer from 1 to 1000. a, b, c, and d are each independently integers from 0 to 100. [Examples]

[0087] (Example 1) A capacitor element was prepared by preparing an aluminum anode foil measuring 7 x 100 mm as the anode metal, winding it together with a cathode foil placed opposite it via separator paper, and attaching leads to both the anode and cathode foils. The aluminum anode foil was pre-treated with a chemical conversion process to form a dielectric oxide film.

[0088] (Manufacturing of pretreatment agents) Five parts by weight of 1-methyl-3-(3-sulfonatopropyl)-1H-imidazole-3-ium, a zwitterionic compound, was diluted with five parts by weight of ethylene glycol and ninety parts by weight of water to obtain a pretreatment agent.

[0089] (Preparation of a mixed solution containing conductive polymer monomers, dopants, and oxidizing agents) Four parts of 2-ethyl-2,3-dihydrothieno[3,4-b]-1,4-dioxin (2-ethyl-EDOT) and ten parts of a 50% ferric p-toluenesulfonate / ethanol solution were mixed to obtain a mixed solution containing conductive polymer monomers, dopants, and an oxidizing agent.

[0090] (Steps for retaining zwitterionic compounds) Next, the capacitor element was immersed in the pretreatment agent for 30 seconds, then slowly removed, and air-dried at 155°C for 30 minutes.

[0091] (Process for forming a solid electrolyte layer) Next, the capacitor element was immersed for 30 seconds in a mixed solution containing the conductive polymer monomer, dopant, and oxidizing agent obtained above, dried at 85°C for 30 minutes, and then heat-treated at 230°C for 3 minutes to form a solid electrolyte layer, thereby manufacturing a capacitor element, which was then subjected to evaluation.

[0092] (Example 2) A solid electrolytic capacitor was manufactured in the same manner as in Example 1, except that 1-methyl-3-(4-sulfonatobutyl)-1H-imidazole-3-ium was used as the zwitterionic compound. (Example 3) A solid electrolytic capacitor was manufactured in the same manner as in Example 1, except that 1-butyl-3-(4-sulfonatobutyl)-1H-imidazole-3-ium was used as the zwitterionic compound. (Example 4) A solid electrolytic capacitor was manufactured in the same manner as in Example 1, except that 1-methyl-2-(3-sulfonatopropyl)-1H-pyrazole-2-ium was used as the zwitterionic compound. (Example 5) A solid electrolytic capacitor was manufactured in the same manner as in Example 1, except that 1-(3-sulfonatopropyl)pyridine-1-ium was used as the zwitterionic compound. (Example 6) A solid electrolytic capacitor was manufactured in the same manner as in Example 1, except that 1-methyl-1-(3-sulfonatopropyl)piperidine-1-ium was used as the zwitterionic compound. (Example 7) A solid electrolytic capacitor was manufactured in the same manner as in Example 1, except that 5 parts by mass of polyether-modified silicone (Momentive, "Silwet L-7657", molecular weight 5000) and 5 parts by mass of colloidal silica (Nissan Chemical Industries, Snowtex N-40, aqueous dispersion, solid content 40%, average particle size 20-30 nm, pH 9.0-10) were added in the preparation of the pretreatment agent.

[0093] (Comparative Example 1) A solid electrolytic capacitor was manufactured in the same manner as in Example 1, except that the step of retaining the zwitterionic compound described in Example 1 was omitted. (Comparative Example 2) Solid electrolytic capacitors were manufactured using a polymerization solution containing a borate ester compound in a mixed solution containing a conductive polymer monomer, a dopant, and an oxidizing agent. Specifically, 4 parts of 2-ethyl-2,3-dihydrothieno[3,4-b]-1,4-dioxin (2-ethyl-EDOT), 10 parts of 50% ferric p-toluenesulfonate / ethanol solution, and 1.4 parts of tributyl borate (manufactured by Tokyo Chemical Industry Co., Ltd.) were mixed to obtain a mixed solution containing a conductive polymer monomer, a dopant, an oxidizing agent, and a borate ester compound. Solid electrolytic capacitors were manufactured in the same manner as in Example 1, except that the step of retaining the zwitterionic compound described in Example 1 was omitted and the mixed solution was used.

[0094] <Evaluation of Solid Electrolytic Capacitors> For the solid electrolytic capacitors obtained from Examples 1-7 and Comparative Examples 1-2, the capacitance (μF) and tanδ at 120 Hz were measured using an Agilent Technologies, Inc. Precision LCR meter E4980A, and the equivalent series resistance (ESR) at 100 kHz was measured. In addition, using an Advantest Corporation DC voltage / current source / monitor R6243, a DC voltage was applied to both electrodes of the solid electrolytic capacitor, and the voltage was boosted at a rate of 0.2 V / sec. The current value after 60 seconds was measured and defined as the leakage current value. The voltage when the current reached 0.5 A was measured and defined as the withstand voltage. The measurement results are shown in Table 1.

[0095] [Table 1]

[0096] As described above, in the examples, we were able to obtain a solid electrolytic capacitor that achieves both excellent voltage resistance and high capacitance. [Industrial applicability]

[0097] Because the solid electrolytic capacitor of the present invention has excellent voltage resistance and capacitance, it can be applied to high-frequency digital devices and the like.

Claims

1. A method for manufacturing a solid electrolytic capacitor, comprising at least the steps of (a) holding a zwitterionic compound on an anode metal on which a dielectric oxide film has been formed using a pretreatment agent containing a zwitterionic compound, colloidal silica, and a silicone-based surfactant, and (b) subsequently forming a solid electrolyte layer.

2. The method for producing a solid electrolytic capacitor according to claim 1, characterized in that the pretreatment agent is diluted with 0.1 to 10,000 parts by weight of solvent per 1 part by weight of zwitterionic compound.

3. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the zwitterionic compound has one or more anionic moieties selected from the group consisting of sulfonate anions, carboxylate anions, phosphate anions, and anions represented by the following formula (1). 【Chemistry 1】 (In formula (1), Z represents an alkyl group having 1 to 15 carbon atoms, an alkyl halide having 1 to 15 carbon atoms, an aryl group having 6 to 15 carbon atoms, an aryl halide having 6 to 15 carbon atoms, or a halogen, and * represents a bond.)

4. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the zwitterionic compound has one or more cationic moieties selected from the group consisting of ammonium ions, imidazolium ions, pyrazolium ions, pyridinium ions, and piperidinium ions.

5. The method for manufacturing a solid electrolytic capacitor according to claim 1, characterized in that the zwitterionic compound is one or more compounds selected from the group consisting of compounds represented by the following general formulas (2) to (6). 【Chemistry 2-6】 (In formulas (2) to (6), R １ ~R ２０ Each of these is an organic group or hydrogen atom that may independently have one or both of a primary amino group and a secondary amino group, and adjacent Rs may be linked together to form an alkylene group having 2 to 6 carbon atoms, X １ ~X ５ (This represents a group having 0 to 15 carbon atoms that contains one of the following: a sulfonate anion, a carboxylate anion, a phosphate anion, or an anion represented by formula (1)).

6. The method for manufacturing a solid electrolytic capacitor according to claim 1, characterized in that the molecular weight of the zwitterionic compound is 50 to 500.

7. The aforementioned zwitterionic compounds are 1-methyl-3-(3-sulfonatopropyl)-1H-imidazole-3-ium, 1-methyl-3-(4-sulfonatobutyl)-1H-imidazole-3-ium, 1-ethyl-3-(3-sulfonatopropyl)-1H-imidazole-3-ium, 1-ethyl-3-(4-sulfonatobutyl)-1H-imidazole-3-ium, 1-butyl-3-(3-sulfonatopropyl)-1H-imidazole-3-ium, 1-butyl-3-(4-sulfonatobutyl)-1H-imidazole-3-ium, and 1-hexyl-3-(3-sulfonatopropyl). A method for producing a solid electrolytic capacitor according to claim 1, wherein the compound is one or more compounds selected from the group consisting of honatopropyl)-1H-imidazole-3-ium, 1-hexyl-3-(4-sulfonatobutyl)-1H-imidazole-3-ium, trimethylglycine, 2-(methacryloyloxy)ethyl-2-(trimethylammonio)ethyl phosphate, 1-(3-sulfonatopropyl)pyridine-1-ium, 1-methyl-2-(3-sulfonatopropyl)-1H-pyrazole-2-ium, and 1-methyl-1-(3-sulfonatopropyl)piperidine-1-ium.

8. The method for manufacturing a solid electrolytic capacitor according to claim 1, characterized in that the anode metal is aluminum or tantalum.

9. A pretreatment agent for manufacturing a solid electrolytic capacitor according to any one of claims 1 to 8, comprising a zwitterionic compound, colloidal silica, and a silicone-based surfactant.

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