Capacitor solutions and electrolytic capacitors

Abstract

To improve the performance (capacitance and ESR) of electrolytic capacitors. [Solution] The capacitor solution contains conductive composite particles formed from a conjugated conductive polymer and polyanions, but does not contain conductive composite particles with a particle size of 1000 nm or more, and the proportion of conductive composite particles with a particle size of 300 nm or more in the volume particle size distribution is 3.0% or less. A polythiophene-based conductive polymer can be used as the conjugated conductive polymer, and polystyrene sulfonic acid can be used as the polyanion.

Description

Technical Field

[0001] The present invention relates to a capacitor solution used for forming an electrolyte of an electrolytic capacitor and an electrolytic capacitor having an electrolyte layer formed from this capacitor solution.

Background Art

[0002] Manufacturing electrolytic capacitors with high capacitance and low equivalent series resistance (ESR) has been studied by various methods in the past. As one of these means, encapsulating a material having a conductive polymer in the capacitor has been advanced in recent years. As these capacitors, aluminum capacitors, aluminum hybrid capacitors, etc. have been attracting attention in the market. Since these capacitors have high voltage and high temperature resistance, they are the trend in the future.

[0003] For example, Patent Document 1 discloses a method for manufacturing an electrolytic capacitor in which particles of a conductive polymer in a dispersion have an average particle diameter of 70 to 500 nm. Further, Patent Document 2 discloses a method for manufacturing an electrolytic capacitor in which the weight ratio of particles of a conductive polymer having a particle diameter of less than 700 nm in a dispersion of an outer layer of a conductive polymer is at least 5% by mass of the solid content of the dispersion.

[0004] Patent Document 3 discloses a method for manufacturing an electrolyte capacitor (capacitor) in which particles of a conductive polymer in a dispersion liquid have an average diameter of 1 to 100 nm. Patent Document 4 discloses a method for forming a solid electrolytic capacitor in which a conductive polymer layer includes first particles containing a conductive polymer and a polyanion and second particles containing a conductive polymer and a polyanion, the first particles having an average particle diameter of at least 1 micron to 10 microns or less, and the second particles having an average particle diameter of at least 1 nm to 600 nm or less.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2006-295184 [Patent Document 2] Japanese Patent Publication No. 2007-027767 [Patent Document 3] Japanese Patent Publication No. 2015-046633 [Patent Document 4] Special Publication No. 2020-537350 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, the methods described in the aforementioned Patent Documents 1 to 4 still have room for improvement in obtaining excellent capacitance and low ESR. As a result of diligent research, the inventors of the present invention have found that the particle size distribution of conductive composite particles formed from conjugated conductive polymers and polyanions affects the performance (ESR and capacitance) of solid electrolytic capacitors, and have completed the present invention. Herein, while Patent Documents 1 to 4 describe defining the particle size of conductive polymers, they do not focus on the particle size distribution of conductive polymers. [Means for solving the problem]

[0007] The capacitor solution according to the first invention of this application contains conductive composite particles formed from a conjugated conductive polymer and polyanions. Here, conductive composite particles with a particle size of 1000 nm or more are not included, and the proportion of conductive composite particles with a particle size of 300 nm or more in the volume particle size distribution is 3.0% or less.

[0008] The capacitor solution may contain at least one of a surfactant and a polyol compound. A polythiophene-based conductive polymer can be used as the conjugated conductive polymer. Polystyrene sulfonic acid can be used as the polyanion.

[0009] The electrolytic capacitor according to the second invention of this application has an electrolyte layer formed from the capacitor solution according to the first invention of this application. [Effects of the Invention]

[0010] By using the capacitor solution of the present invention, the performance (capacitance and ESR) of electrolytic capacitors can be improved. [Modes for carrying out the invention]

[0011] <Conductive composite particles> Conductive composite particles are particles formed from a conjugated conductive polymer and polyanions. Conductive composite particles are formed by doping the conjugated conductive polymer with polyanions. The polyanion has some anionic groups that dope the conjugated conductive polymer and excess anionic groups that do not participate in doping the conjugated conductive polymer. Since the excess anionic groups are hydrophilic groups, the conductive composite particles are water-dispersible. In this invention, the conductive composite particles in the capacitor solution do not contain conductive composite particles with a particle size of 1000 nm or more, and the proportion of conductive composite particles with a particle size of 300 nm or more in the volume particle size distribution is 3.0% or less. Here, the volume particle size distribution of the conductive composite particles is measured by dynamic light scattering (JIS Z8828 (2019)).

[0012] <Conjugated conductive polymers> The conjugated conductive polymer that forms the conductive composite particles can be any organic polymer whose main chain is composed of a conjugated system. Examples include polythiophene-based conductive polymers, polypyrrole-based conductive polymers, polyaniline-based conductive polymers, polyacetylene-based conductive polymers, polyphenylene-based conductive polymers, polyphenylene-vinylene-based conductive polymers, polyacene-based conductive polymers, polythiophene-vinylene-based conductive polymers, and copolymers thereof. From the viewpoint of stability in air, polythiophene-based conductive polymers, polypyrrole-based conductive polymers, and polyaniline-based conductive polymers are preferred, and from the viewpoint of transparency, polythiophene-based conductive polymers are particularly preferred.

[0013] Examples of polythiophene-based conductive polymers include polythiophene, poly(3-methylthiophene), poly(3-ethylthiophene), poly(3-propylthiophene), poly(3-butylthiophene), poly(3-hexylthiophene), poly(3-heptylthiophene), poly(3-octylthiophene), poly(3-decylthiophene), poly(3-dodecylthiophene), poly(3-octadecylthiophene), poly(3-bromothiophene), poly(3-chlorothiophene), and poly(3- Iodothiophene, poly(3-cyanothiophene), poly(3-phenylthiophene), poly(3,4-dimethylthiophene), poly(3,4-dibutylthiophene), poly(3-hydroxythiophene), poly(3-methoxythiophene), poly(3-ethoxythiophene), poly(3-butoxythiophene), poly(3-hexyloxythiophene), poly(3-heptyloxythiophene), poly(3-octyloxythiophene), poly(3-decyloxythiophene), poly(3-dodecylthiophene) Poly(3,4-Octadecyloxythiophene), Poly(3,4-Dihydroxythiophene), Poly(3,4-Dimethoxythiophene), Poly(3,4-Diethoxythiophene), Poly(3,4-Dipropoxythiophene), Poly(3,4-Dibutoxythiophene), Poly(3,4-Dihexyloxythiophene), Poly(3,4-Diheptyloxythiophene), Poly(3,4-Dioctyloxythiophene), Poly(3,4-Didecyloxythiophene), Poly(3,4- Examples include poly(3,4-ethylenedioxythiophene), poly(3,4-propylenedioxythiophene), poly(3,4-butylenedioxythiophene), poly(3-methyl-4-methoxythiophene), poly(3-methyl-4-ethoxythiophene), poly(3-carboxythiophene), poly(3-methyl-4-carboxythiophene), poly(3-methyl-4-carboxyethylthiophene), and poly(3-methyl-4-carboxybutylthiophene).

[0014] Examples of polypyrrole-based conductive polymers include polypyrrole, poly(N-methylpyrrole), poly(3-methylpyrrole), poly(3-ethylpyrrole), poly(3-n-propylpyrrole), poly(3-butylpyrrole), poly(3-octylpyrrole), poly(3-decylpyrrole), poly(3-dodecylpyrrole), poly(3,4-dimethylpyrrole), poly(3,4-dibutylpyrrole), poly(3-carboxypyrrole), poly(3-methyl-4-carboxypyrrole), poly(3-methyl-4-carboxyethylpyrrole), poly(3-methyl-4-carboxybutylpyrrole), poly(3-hydroxypyrrole), poly(3-methoxypyrrole), poly(3-ethoxypyrrole), poly(3-butoxypyrrole), poly(3-hexyloxypyrrole), and poly(3-methyl-4-hexyloxypyrrole).

[0015] Examples of polyaniline-based conductive polymers include polyaniline, poly(2-methylaniline), poly(3-isobutylaniline), poly(2-aniline sulfonic acid), and poly(3-aniline sulfonic acid). Among the conjugated conductive polymers mentioned above, poly(3,4-ethylenedioxythiophene), a polythiophene-based conductive polymer, is preferably used because of its excellent conductivity and heat resistance. On the other hand, the conjugated conductive polymer contained in the conductive composite particles may be one type from the above types used alone, or two or more types may be used in combination.

[0016] <Polyanion> Polyanions that form conductive composite particles are polymers having two or more monomer units, each containing anionic groups. The anionic groups of the polyanion function as dopants for conjugated conductive polymers, improving the conductivity of the conductive composite particles. Examples of anionic groups in polyanions include sulfo groups and carboxyl groups. Specific examples of polyanions include polystyrene sulfonic acid, polyvinyl sulfonic acid, polyallyl sulfonic acid, polyacrylic acid esters having sulfo groups, polymethacrylic acid esters having sulfo groups (for example, polymers having sulfo groups such as poly(4-sulfobutyl methacrylate), polysulfoethyl methacrylate, polymethacryloyloxybenzene sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), and polyisoprene sulfonic acid), and polymers having carboxyl groups such as polyvinyl carboxylic acid, polystyrene carboxylic acid, polyallyl carboxylic acid, polyacrylic acid, polymethacrylic acid, poly(2-acrylamido-2-methylpropanecarboxylic acid), and polyisoprene carboxylic acid. Here, in terms of improving conductivity, it is preferable to use polymers having sulfo groups, and it is more preferable to use polystyrene sulfonic acid.

[0017] The polyanion may be a homopolymer formed by the polymerization of a single monomer, or a copolymer formed by the polymerization of two or more monomers. Furthermore, one type of polyanion may be used alone, or two or more types may be used in combination. The weight-average molecular weight of the polyanion is preferably 20,000 to 1,000,000, and more preferably 40,000 to 300,000. The weight-average molecular weight is determined by measuring using gel filtration chromatography and obtaining the average molecular weight on a weight basis in terms of pullulan. The polyanion content in the conductive composite particles is preferably, for example, 0.5% to 50% by mass, more preferably 1% to 30% by mass, and even more preferably 1% to 20% by mass, per 1% by mass of the conjugated conductive polymer.

[0018] <Method for manufacturing conductive composite particles> In a reaction vessel containing a reaction solution including a monomer that forms a conjugated conductive polymer, a polyanion, and an aqueous dispersion medium, a conjugated conductive polymer can be formed by subjecting the monomer to a polymerization reaction. Here, when the polyanion dopes into the conjugated conductive polymer, conductive composite particles dispersed in the aqueous dispersion medium can be obtained. For example, the two-step polymerization method described in JP-A-2021-172742 is also useful. If the produced conductive composite particles have the above-described predetermined particle size distribution (a particle size distribution that does not include conductive composite particles having a particle size of 1000 nm or more and in which the abundance ratio of conductive composite particles having a particle size of 300 nm or more is 3.0% or less), these conductive composite particles can be used.

[0019] When producing conductive composite particles, by containing a surfactant, it becomes easier to obtain conductive composite particles having a predetermined particle size distribution. If the produced conductive composite particles deviate from the predetermined particle size distribution, the particle size of the conductive composite particles may be adjusted. For example, the particle size of the conductive composite particles can be adjusted by redispersion or filtration. On the other hand, the conductive composite particles may aggregate over time, and the particle size distribution may change due to aggregation. When the conductive composite particles are aggregated, the conductive composite particles can be redispersed by applying an external force to the aggregate. As this means, for example, ultrasonic waves can be applied to the aggregate or a homogenizer can be used. Furthermore, it is also useful to delay the variation in particle size by refrigerated heat preservation, and it is preferable to store the conductive composite particles at a temperature of 1°C or higher and 15°C or lower.

[0020] <Solution for capacitor> The capacitor solution contains conductive composite particles and a dispersion medium. The content of the conductive composite particles (i.e., conjugated conductive polymer and polyanion) with respect to the total mass of the capacitor solution is preferably 0.1% by mass or more and 5.0% by mass or less, more preferably 0.5% by mass or more and 2.5% by mass or less, and even more preferably 0.8% by mass or more and 2.0% by mass or less. If the content of the conductive composite particles is within the above-mentioned range, the ESR of the electrolytic capacitor having an electrolyte layer formed from the capacitor solution can be reduced.

[0021] <Dispersion medium> As the dispersion medium of the capacitor solution, water can be used. The dispersion medium may also be other than water and is not particularly limited as long as it does not significantly impair the dispersibility of the conductive composite particles. As the dispersion medium other than water, a water-soluble organic solvent can be used. The water-soluble organic solvent is an organic solvent having a solubility of 1 g or more in 100 g of water at 20°C, and examples thereof include alcohol solvents, ketone solvents, and ester solvents. The water-soluble organic solvent may be used alone or in combination of two or more.

[0022] The water content with respect to the total mass of the dispersion medium excluding the non-volatile components of the capacitor solution is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 100% by mass. When the water content is not less than the above-mentioned lower limit value, the dispersibility of the conductive composite particles contained in the capacitor solution is improved, and the ESR of the electrolytic capacitor having an electrolyte layer formed from the capacitor solution can be reduced.

[0023] <Basic compound> The capacitor solution may contain one or more basic compounds. The basic compound functions as a Brønsted base, accepting protons from the excess anionic groups of the polyanion. To perform this function, the amount of basic compound that dissolves in water is preferably 0.001 g or more per 100 g of water at 20°C. There is no particular upper limit to the amount that dissolves, but even if it is as low as 0.1 g, the function as a Brønsted base can be obtained. As the basic compound, you can use organic or inorganic basic compounds containing nitrogen, hydroxides of alkali metals or group 2 metals, various carbonates and bicarbonates, etc. For example, alkali metal hydroxides, quaternary ammonium hydroxides or their salts, ammonia, and amines can be used.

[0024] Examples of alkali metal hydroxides include potassium hydroxide and sodium hydroxide. Examples of carbonates or bicarbonates include ammonium bicarbonate, ammonium carbonate, potassium bicarbonate, potassium carbonate, sodium bicarbonate, and sodium carbonate. Examples of quaternary ammonium hydroxides or their salts include tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrabutylammonium hydroxide. Examples of amines include aliphatic tertiary amines and nitrogen-containing aromatic compounds. Examples of aliphatic tertiary amines include triethanolamine, trimethylamine, triethylamine, tripropylamine, tributylamine, trihexylamine, trioctylamine, triphenylamine, trynzylamine, trinaphthylamine, N,N-dimethylamine, and N,N-diethylamine. Examples of nitrogen-containing aromatic compounds (aromatic compounds in which at least one nitrogen atom forms a ring structure) include pyrrole, indole, imidazole, 2-methylimidazole, 2-propylimidazole, N-methylimidazole, and N-propylimidazole. The content of basic compounds in the capacitor solution is preferably such that the pH of the capacitor solution (at 25°C) is between 2.0 and 8.0, more preferably between 2.0 and 5.0, and even more preferably between 2.0 and 3.9. By keeping the pH of the capacitor solution within the above range, the ESR of the electrolytic capacitor can be reduced.

[0025] <Polyol compounds> Capacitor solutions may contain one or more polyol compounds. Unlike conjugated conductive polymers, polyanions, and basic compounds, polyol compounds are compounds having two or more hydroxyl groups. The inclusion of polyol compounds can reduce the ESR of electrolytic capacitors. Examples of polyol compounds include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,4-butanediol, glycerin, pentaerythritol, trimethylolpropane, and trimethylolethane. One type of polyol compound may be used alone, or two or more types may be used in combination. Particularly useful additives are one or more selected from the group consisting of polyoxyalkylene polyglyceryl ethers and polyglycerin fatty acid esters.

[0026] The polyglycerin used in the present invention, which constitutes the polyoxyalkylene polyglyceryl ether and polyglycerin fatty acid ester, is preferably polyglycerin with an average degree of polymerization of 2 to 20, calculated from the hydroxyl value, and more preferably polyglycerin with an average degree of polymerization of 2 to 10. Specific examples include diglycerin, triglycerin, tetraglycerin, hexaglycerin, and decaglycerin. Commercially available products include diglycerin S, R-PG, R-PG3, polyglycerin #310, polyglycerin #500, and polyglycerin #750 (all manufactured by Sakamoto Pharmaceutical Co., Ltd.). Furthermore, using polyglycerin with an average degree of polymerization of 2 to 20 increases both the heat resistance and breakdown voltage of the electrolytic capacitor.

[0027] Examples of polyoxyalkylene polyglyceryl ethers used in the present invention include polyoxyethylene polyglyceryl ether, polyoxypropylene polyglyceryl ether, and polyoxyethylene polyoxypropylene polyglyceryl ether. Of these, polyoxyethylene polyoxypropylene polyglyceryl ether may be block-added or randomly added. In the case of block addition, the order of addition of ethylene oxide (EO) and propylene oxide (PO) is arbitrary, for example, EO / PO, PO / EO, EO / PO / EO, etc. Furthermore, the alkylene oxide is preferably EO or EO / PO, and more preferably EO.

[0028] The polyoxyalkylene polyglyceryl ether content used in this invention is preferably 0.01% to 30% by mass, more preferably 0.5% to 20% by mass, and most preferably 1.0% to 10% by mass, based on 100% by mass of the dispersion medium in the capacitor solution. When the polyoxyalkylene polyglyceryl ether content is 0.01% to 30% by mass, the effect of improving wettability to the capacitor element material is enhanced, and the capacitance increases. Furthermore, this range is preferred because it provides excellent improvements in the heat resistance and breakdown voltage of the resulting electrolytic capacitor.

[0029] The polyoxyalkylene polyglyceryl ethers and polyglycerin fatty acid esters used in the present invention are described in Japanese Patent Application Publication No. 2018-125410. The content of the polyoxyalkylene polyglyceryl ethers and polyglycerin fatty acid esters in the dispersion is preferably, for example, 1% to 100% by mass, more preferably 2% to 30% by mass, and even more preferably 3% to 25% by mass, based on 100% by mass of the total of the conjugated conductive polymer and polyanion (i.e., 100% by mass of conductive composite particles). This makes it possible to reduce the ESR of the electrolytic capacitor.

[0030] The content of the polyol compound relative to the total mass of the capacitor solution is preferably 1% to 30% by mass, more preferably 3% to 25% by mass, and even more preferably 5% to 22% by mass. This improves the coating properties of the dispersion and reduces the ESR of the solid electrolytic capacitor.

[0031] <Surfactants> The capacitor solution may contain a surfactant. Examples of surfactants include nonionic, anionic, and cationic surfactants, but nonionic surfactants are preferred in terms of storage stability. Polymer-based surfactants such as polyvinyl alcohol and polyvinylpyrrolidone may also be added. One type of surfactant may be used alone, or two or more types may be used in combination.

[0032] <Optional additives> The capacitor solution may contain any additives, and the amount of additives can be appropriately determined depending on the type of additive. The amount of additives relative to 100% by mass of the total conjugated conductive polymer and polyanion (i.e., 1% by mass of conductive composite particles) can be, for example, 0.011% by mass or more and 10% by mass or less.

[0033] Examples of additives include water-soluble resins, latex, solid dispersion resins, inorganic conductive agents, defoamers, coupling agents, antioxidants, and UV absorbers. Examples of inorganic conductive agents include metal ions and conductive carbon. Metal ions can be generated by dissolving metal salts in water. Examples of defoamers include silicone resins, polydimethylsiloxane, and silicone oil. Examples of coupling agents include silane coupling agents having vinyl groups, amino groups, epoxy groups, etc. Examples of antioxidants include phenolic antioxidants, amine antioxidants, phosphorus antioxidants, sulfur antioxidants, and sugars. Examples of UV absorbers include benzotriazole UV absorbers, benzophenone UV absorbers, salicylate UV absorbers, cyanoacrylate UV absorbers, oxanilide UV absorbers, hindered amine UV absorbers, and benzoate UV absorbers.

[0034] (Method of impregnation with additives) The method of impregnating the capacitor element with the additive is not particularly limited, as long as it is a method that allows the capacitor element to properly hold the additive. For example, one method is to first mix a predetermined amount of additive solution with the dispersion medium of the capacitor solution and then impregnate the capacitor element in the electrolyte layer formation procedure described later; another method is to impregnate the capacitor element with the dispersion medium of the capacitor solution and then immerse the capacitor element in the additive solution; yet another method is to drop a predetermined amount of additive solution onto the capacitor element; and yet another method is to drop a predetermined amount of additive solution onto the outer casing of the electrolytic capacitor and then insert the capacitor element into it. Furthermore, in these methods, a depressurization step or a pressurization step may be performed as needed.

[0035] <Manufacturing method for electrolytic capacitors> A known manufacturing method can be used to manufacture an electrolytic capacitor. For example, this manufacturing method includes a step of forming a dielectric layer by oxidizing the surface of an anode made of a porous valve metal (dielectric formation step), a step of forming a cathode at a position opposite the dielectric layer (cathode formation step), and a step of impregnating a winding body in which the anode and cathode are wound with a capacitor solution to form a solid electrolyte layer on at least a part of the surface of the dielectric layer (film formation step). In the dielectric formation step, the method of forming the dielectric layer is not particularly limited, and examples include an anodic oxidation of the surface of the anode in an electrolyte solution for chemical conversion treatment such as an aqueous solution of ammonium adipate, an aqueous solution of ammonium borate, or an aqueous solution of ammonium phosphate. In the cathode formation step, the method of forming the cathode is not particularly limited, and examples include a method of forming the cathode using a conductive paste such as carbon paste or silver paste, or a method of arranging a metal foil such as aluminum foil at a position opposite the dielectric layer.

[0036] In the film formation process, a solid electrolyte layer is formed by applying a capacitor solution to at least a portion of the surface of the dielectric layer and drying it. Here, it is preferable to immerse the winding body in the dispersion under reduced pressure. This allows the capacitor solution to penetrate into the porous structure of the dielectric layer. After immersion, the winding body is removed from the capacitor solution and the drying process is carried out. Examples of drying methods include room temperature drying, hot air drying, and far-infrared drying. Among these, hot air drying is preferred. The drying temperature is preferably 100°C to 180°C, and more preferably 120°C to 150°C. The drying time is preferably 0.2 hours to 1 hour. After the drying process, the electrolytic capacitor can be assembled by a known method.

[0037] <Structure of an electrolytic capacitor> An electrolytic capacitor comprises an anode made of a porous valve metal, a dielectric layer made of an oxide of the valve metal, an electrolyte layer formed on the surface of the dielectric layer, and a cathode located on the outermost side. The cathode is positioned between the dielectric layer and the electrolyte layer and is located on the opposite side from the anode. Examples of valve metals that make up the anode include aluminum, tantalum, niobium, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. Of these, aluminum, tantalum, and niobium are preferred. Specific examples of anodes include aluminum foil that has been etched to increase its surface area and then oxidized, or sintered tantalum particles or niobium particles whose surfaces have been oxidized to form pellets. Materials treated in this way become porous bodies with irregularities formed on their surface.

[0038] The dielectric layer is a layer formed by oxidation of the anode surface, for example, by anodizing the surface of a metal anode in an electrolyte solution such as an aqueous solution of ammonium adipate. Similar to the anode, the dielectric layer also has irregularities. As the cathode, a conductive layer formed from a conductive paste or a metal layer made of a conductive material such as aluminum foil can be used. The electrolyte layer is formed on the surface of the dielectric layer. The electrolyte layer covers at least a part of the surface of the dielectric layer, and may cover the entire surface of the dielectric layer. The thickness of the electrolyte layer may be constant or not, for example, it can be between 1 μm and 100 μm.

[0039] <Electrolyte> The electrolytic capacitor of the present invention may have an electrolyte solution that impregnates the electrolyte layer. Examples of solvents constituting the electrolyte solution include alcohol-based solvents such as ethylene glycol, diethylene glycol, propylene glycol, 1,4-butanediol, and glycerin; lactone-based solvents such as γ-butyrolactone, γ-valerolactone, and δ-valerolactone; sulfur-based solvents such as sulfolane, dimethyl sulfoxide, and dimethyl sulfone; amide-based solvents such as N-methylformamide, N,N-dimethylformamide, N-methylacetamide, and N-methylpyrrolidinone; nitrile-based solvents such as acetonitrile and 3-methoxypropionitrile; and water.

[0040] The electrolytes constituting the electrolyte solution include, for example, adipic acid, glutaric acid, succinic acid, benzoic acid, isophthalic acid, phthalic acid, terephthalic acid, maleic acid, toluic acid, enanthic acid, malonic acid, formic acid, decanedicarboxylic acids such as 1,6-decanedicarboxylic acid and 5,6-decanedicarboxylic acid, octanedicarboxylic acids such as 1,7-octanedicarboxylic acid, organic acids such as azelaic acid and sebacic acid; or boric acid, polyhydric alcohol complex compounds of boric acid obtained from boric acid and polyhydric alcohols; and inorganic acids such as phosphoric acid, carbonic acid, and silicic acid as anionic components, with primary amines (methylamine, ethylamine, propylamine, Examples include electrolytes with cationic components such as butylamine, ethylenediamine, secondary amines (dimethylamine, diethylamine, dipropylamine, methylethylamine, diphenylamine, etc.), tertiary amines (trimethylamine, triethylamine, tripropylamine, triphenylamine, 1,8-diazabicyclo(5,4,0)-undecene-7, etc.), and tetraalkylammonium (tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, methyltriethylammonium, dimethyldiethylammonium, etc.).

[0041] Electrolytic capacitors are not limited to the configuration described above, and a separator may be provided between the dielectric layer and the cathode. Examples of separators include sheets (including nonwoven fabrics) made of cellulose, polyvinyl alcohol, polyester, polyethylene, polystyrene, polypropylene, polyimide, polyamide, polyvinylidene fluoride, etc., and glass fiber nonwoven fabrics. The density of the separator is, for example, 0.1 g / cm³. 3 More than 1.0g / cm 3 The following is possible: If a separator is provided, the separator can be impregnated with carbon paste or silver paste to form the cathode. [Examples]

[0042] (Example 1) 3 g of ferrous sulfate hydrate was added to 754 g of pure water at 20°C and stirred well. Then, 140 g of an 18% by mass aqueous solution of poly(4-styrenesulfonic acid) (molecular weight approximately 70,000) was added and stirred to prepare a mixture. The oxygen concentration of this mixture was 8.4 mg / L (0.263 mM / L). 2.5 g of 3,4-ethylenedioxythiophene (EDOT) (0.0189 M / L) was added dropwise to this mixture, and then 30 g of a 14.5% by mass aqueous solution of sodium persulfate was added. Pure water was then added to make a total volume of 1000 ml to prepare a mixed solution. Here, the molar ratio of 3,4-ethylenedioxythiophene to oxygen in the reaction medium ([EDOT] / [O2]) was 72.

[0043] The mixed solution was stirred at 20°C to carry out the first stage of oxidative polymerization. After 60 minutes, 5 g of 3,4-ethylenedioxythiophene (EDOT) and 65 g of 14.5% by mass sodium persulfate were added to this polymerization solution, and the mixture was stirred for 9 hours to carry out the second stage of polymerization, obtaining a reaction solution with a solid content (conductive composite particles, PEDOT / PSS particles) concentration of approximately 3.27% by mass. Next, the reaction solution was diluted with pure water to obtain a diluted solution with a solid content concentration of 2.5% by mass. Then, 12% by mass each of cation exchange resin and anion exchange resin were added, and the mixture was stirred for another 12 hours before being filtered through a nylon mesh (a combination of 100 mesh and 200 mesh). The filtrate was diluted to a solid content concentration of 2.0% by mass, and the mixture was subjected to five dispersion treatments at 200 MPa using a high-pressure homogenizer to obtain a conductive composite solution containing PEDOT / PSS particles (conductive composite particles), which is Example 1. The pH of the conductive composite solution was 1.9. The PEDOT / PSS particles exhibited excellent conductivity, with a conductivity of 550 S / cm.

[0044] (Example 2) In Example 1, the conductive composite solution of Example 2 was obtained in exactly the same manner as in Example 1, except that the dispersion treatment was performed seven times.

[0045] (Example 3) In Example 1, the conductive composite solution of Example 3 was obtained in exactly the same manner as in Example 1, except that the pressure of the high-pressure homogenizer was set to 240 MPa.

[0046] (Comparative Example 1) Comparative Example 1, a conductive composite solution, was obtained in exactly the same manner as in Example 1, except that the pressure of the high-pressure homogenizer was set to 150 MPa.

[0047] (Comparative Example 2) Comparative Example 2, a conductive composite solution, was obtained in exactly the same manner as in Example 1, except that the pressure of the high-pressure homogenizer was set to 180 MPa.

[0048] (Preparation of capacitor solution) Capacitor solutions were prepared using the conductive composite solutions of Examples 1, 2, and 3 and Comparative Examples 1 and 2. Specifically, 1.2% by mass of conductive composite particles, 2% by mass of triethylene glycol (polyol compound), 10% by mass of diglycerin (polyol compound), 6% by mass of triglycerin (polyol compound), 2% by mass of adipic acid (electrolyte), 0.3% by mass of poly(N-vinylacetamide) (electrolyte), and 0.5% by mass of N-2-aminopropyltrimethoxysilane (additive) were mixed, and the pH was further adjusted with aqueous ammonia to between 3.1 and 3.3 to obtain each capacitor solution.

[0049] The particle size distribution of conductive composite particles contained in the capacitor solution was measured using dynamic light scattering (JIS Z8828(2019)). The results are shown in Table 1 below.

[0050] Next, the capacitor element was impregnated with a capacitor solution. The impregnation process involved immersing the capacitor element in the capacitor solution at 25°C and subjecting it to a vacuum of 50 mmHg for 1 minute. Following this, it was heated and dried at 150°C for 30 minutes. This series of impregnation and drying processes constituted one cycle, and this process was repeated twice to produce an electrolytic capacitor. The capacitor element used was cylindrical, with a rated voltage of 30V, a rated capacitance of 220 μF, and dimensions of φ8 mm × 10 mm.

[0051] (Evaluation of electrolytic capacitor performance) Capacitance and equivalent series resistance (ESR) were measured for electrolytic capacitors prepared using the capacitor solutions of Examples 1-3 and Comparative Examples 1 and 2, respectively.

[0052] (Measurement of capacitance) Capacitance was measured using an LCR meter (ZM2376: manufactured by NF Circuit Design Block Co., Ltd.) at 20°C, voltage 0.5V, DC bias 1.0V, and frequency 120Hz. Capacitance was evaluated according to the following criteria. ○:110μF or more △: Less than 110μF ~ 95μF ×: Less than 95μF

[0053] (ESR measurement) The equivalent series resistance (ESR) was measured using an LCR meter (ZM2376: manufactured by NF Circuit Design Block Co., Ltd.) at 20°C, effective voltage of 0.5V, DC bias of 1.0V, and frequency of 100kHz. The ESR was evaluated according to the following criteria. ○: Less than 12mΩ △: 12~20mΩ ×:20mΩ or more

[0054] (Evaluation results) The evaluation results for capacitance and ESR mentioned above are shown in Table 1 below.

[0055] [Table 1]

[0056] As in Comparative Examples 1 and 2, when a capacitor solution containing conductive composite particles with a particle size of 1000 nm or more was used, both capacitance and ESR were negative (×). On the other hand, as in Examples 1, 2, and 3, by not containing conductive composite particles with a particle size of 1000 nm or more and by reducing the proportion of conductive composite particles with a particle size of 300 nm or more to 3.0% or less, capacitance and ESR were reduced to a moderate (△) or moderate (〇), clearly demonstrating that the capacitor solutions of Examples 1 to 3 have superior properties.

Claims

1. It contains conductive composite particles formed from a conjugated conductive polymer and polyanions, A capacitor solution characterized in that it does not contain conductive composite particles having a particle size of 1000 nm or more, and in the volume particle size distribution, the proportion of conductive composite particles having a particle size of 300 nm or more is 3.0% or less.

2. The capacitor solution according to claim 1, characterized by comprising at least one of a surfactant and a polyol compound.

3. The capacitor solution according to claim 1, characterized in that the conjugated conductive polymer is a polythiophene-based conductive polymer.

4. The capacitor solution according to claim 1, characterized in that the polyanion is polystyrene sulfonic acid.

5. An electrolytic capacitor characterized by having an electrolyte layer formed from a capacitor solution according to any one of claims 1 to 4.

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