Capacitor manufacturing method

Abstract

To provide a capacitor with reduced equivalent series resistance and a manufacturing method thereof.SOLUTION: A capacitor (10) includes an anode (11) made of a porous body of a valve metal, a dielectric layer (12) made of an oxide of the valve metal, a cathode (13) made of a conductive material provided on the opposite side of the dielectric layer to the anode, and a solid electrolyte layer (14) formed between the dielectric layer and the cathode, and the solid electrolyte layer contains a conductive composite containing a π-conjugated conductive polymer and a polyanion, the solid electrolyte layer is formed of a cured product of a coating composition containing a conductive polymer dispersion having an absorbance at 600 nm within a predetermined range, and the conductive polymer dispersion is composed of the conductive composite and water.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a capacitor provided with a solid electrolyte layer containing a π-conjugated conductive polymer and a method for manufacturing the same.

Background Art

[0002] There is known a capacitor in which a solid electrolyte layer containing a conductive composite containing a π-conjugated conductive polymer and a polyanion is disposed between a dielectric layer and a cathode (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The solid electrolyte layer of the capacitor of Patent Document 1 contains a sulfide represented by a specific chemical formula in addition to the conductive composite, so that the equivalent series resistance (ESR) is reduced and the heat resistance is also improved. On the other hand, there may be a demand for a capacitor in which the equivalent series resistance is reduced regardless of the above sulfide. The present invention provides a capacitor with reduced equivalent series resistance and a method for manufacturing the same.

Means for Solving the Problems

[0005] [1] A capacitor comprising an anode made of a porous body of valve metal, a dielectric layer made of an oxide of the valve metal, a cathode made of a conductive material provided on the dielectric layer opposite to the anode, and a solid electrolyte layer formed between the dielectric layer and the cathode, wherein the solid electrolyte layer contains a conductive composite comprising a π-conjugated conductive polymer and a polyanion, the solid electrolyte layer is formed of a cured product of a paint composition, the paint composition contains a conductive polymer dispersion made of the conductive composite and water, and the absorbance of the conductive polymer dispersion at 600 nm is 0.59 or more and 1.20 or less when the conductive composite is contained in an amount of 0.033% by mass. [2] The capacitor according to [1], wherein the paint composition further contains a basic compound. [3] The capacitor according to [2], wherein the basic compound is a nitrogen-containing aromatic compound. [4] The capacitor according to [2], wherein the basic compound is imidazole. [5] The capacitor according to any one of [1] to [4], wherein the coating composition further contains a polyol compound having two or more hydroxyl groups. [6] The capacitor according to [5], wherein the polyol compound is diethylene glycol. [7] The capacitor according to any one of [1] to [6], wherein the π-conjugated conductive polymer is poly(3,4-ethylenedioxythiophene). [8] The capacitor according to any one of [1] to [7], wherein the polyanion is polystyrene sulfonic acid. [9] A method for manufacturing a capacitor, comprising the step of applying the paint composition described in any one of [1] to [8] to the surface of a dielectric layer formed on the surface of an anode made of a porous valve metal, and drying it to form a solid electrolyte layer.

[10] The method for manufacturing a capacitor according to [9], wherein the content of the conductive composite relative to the total mass of the paint composition is 0.5% by mass or more and 1.6% by mass or less. [Effects of the Invention]

[0006] The capacitor of the present invention has reduced equivalent series resistance because the solid electrolyte layer is a cured product of a specific paint composition. According to the manufacturing method of the capacitor of the present invention, the above-mentioned capacitor can be easily manufactured.

[0007] This invention is believed to contribute to SDG Goal 12, "Responsible Consumption and Production."

[0008] In this specification and the claims, the lower and upper limits of the numerical ranges indicated by "~" are to be included within those numerical ranges. [Brief explanation of the drawing]

[0009] [Figure 1] This is a cross-sectional view showing one embodiment of the capacitor of the present invention. [Modes for carrying out the invention]

[0010] Capacitor A first aspect of the present invention is a capacitor. An example of its embodiment will be described. The capacitor 10 shown in Figure 1 comprises an anode 11 made of a porous body of valve metal, a dielectric layer 12 made of an oxide of valve metal, a solid electrolyte layer 14 formed on the surface of the dielectric layer 12, and a cathode 13 provided on the outermost side. The cathode 13 is provided on the opposite side from the anode 11, with the dielectric layer 12 and the solid electrolyte layer 14 in between.

[0011] Examples of valve metals that constitute the anode 11 include aluminum, tantalum, niobium, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. Of these, aluminum, tantalum, and niobium are preferred. Specific examples of anode 11 include aluminum foil that has been etched to increase its surface area and then oxidized, or sintered tantalum or niobium particles whose surface has been oxidized and formed into pellets. Materials processed in this way become porous bodies with irregularities formed on their surface.

[0012] In this embodiment, the dielectric layer 12 is a layer formed by oxidation of the surface of the anode 11. For example, it is formed by anodizing the surface of the metal anode 11 in an electrolyte such as an aqueous solution of ammonium adipate. Similar to the anode 11, the dielectric layer 12 also has irregularities formed on it.

[0013] In this embodiment, the cathode 13 can be a conductive layer formed from a conductive paste or a metal layer made of a conductive material such as aluminum foil.

[0014] In this embodiment, the solid electrolyte layer 14 is formed on the surface of the dielectric layer 12. The solid electrolyte layer 14 covers at least a portion of the surface of the dielectric layer 12, and may cover the entire surface of the dielectric layer 12. The thickness of the solid electrolyte layer 14 may be constant or not; for example, a thickness of 1 μm or more and 100 μm or less is possible.

[0015] <Conductive composite> The conductive composite contained in the solid electrolyte layer will now be described. The conductive composite in this embodiment contains a π-conjugated conductive polymer and a polyanion. The polyanion in the conductive composite dops the π-conjugated conductive polymer to form a conductive composite. In polyanions, only some anionic groups are doped into the π-conjugated conductive polymer, leaving excess anionic groups that do not participate in doping. Since these excess anionic groups are hydrophilic, the conductive composite is water-dispersible.

[0016] (π-conjugated conductive polymers) As the π-conjugated conductive polymer, any organic polymer whose main chain is composed of a π-conjugated system may be used. Examples thereof include polypyrrole-based conductive polymers, polythiophene-based conductive polymers, polyacetylene-based conductive polymers, polyphenylene-based conductive polymers, polyphenylene vinylene-based conductive polymers, polyaniline-based conductive polymers, polyacene-based conductive polymers, polythiophene vinylene-based conductive polymers, and copolymers thereof. From the viewpoint of stability in air, polypyrrole-based conductive polymers, polythiophenes, and polyaniline-based conductive polymers are preferable, and from the viewpoint of transparency, polythiophene-based conductive polymers are more preferable.

[0017] 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-iodine). 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-Dodecyl Poly(3-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-di Examples include dodecyloxythiophene, 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). 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). Examples of polyaniline-based conductive polymers include polyaniline, poly(2-methylaniline), poly(3-isobutylaniline), poly(2-anilinesulfonic acid), and poly(3-anilinesulfonic acid). Among these π-conjugated conductive polymers, poly(3,4-ethylenedioxythiophene) is particularly preferred because of its excellent conductivity, transparency, and heat resistance. The π-conjugated conductive polymer contained in the conductive composite may be one type or two or more types.

[0018] (Polyanion) A polyanion is a polymer having two or more monomer units with anionic groups in the molecule. The anionic group of this polyanion functions as a dopant for the π-conjugated conductive polymer and improves the conductivity of the π-conjugated conductive polymer. The anionic group of the polyanion is preferably a sulfo group or a carboxy group. Specific examples of such 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, poly(4-sulfobutyl methacrylate, polysulfoethyl methacrylate, polymethacryloyloxybenzene sulfonic acid), poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, and other polymers having sulfo groups, as well as 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. Polyanions may be homopolymers formed by the polymerization of a single monomer, or copolymers formed by the polymerization of two or more monomers. Among these polyanions, polymers having sulfo groups are preferred because they can achieve higher conductivity, and polystyrene sulfonic acid is even more preferred. The aforementioned polyanions may be used individually or in combination of two or more types. The mass-average molecular weight of the polyanion is preferably between 20,000 and 1,000,000, and more preferably between 100,000 and 500,000. The mass-average molecular weight is the average molecular weight on a mass basis, determined by measuring it using gel filtration chromatography and converting it to pullulan equivalent.

[0019] The polyanion content in the conductive composite is preferably in the range of 1 to 1000 parts by mass, more preferably 10 to 700 parts by mass, and even more preferably 100 to 500 parts by mass, per 100 parts by mass of the π-conjugated conductive polymer. If the polyanion content is above the lower limit, the doping effect on the π-conjugated conductive polymer tends to be stronger, resulting in higher conductivity. On the other hand, if the polyanion content is below the upper limit, the π-conjugated conductive polymer can be sufficiently contained, thus ensuring sufficient conductivity.

[0020] The content of the conductive composite relative to the total mass of the solid electrolyte layer is preferably 1% to 99% by mass, more preferably 50% to 98% by mass, and even more preferably 70% to 97% by mass. This range is preferable because it makes it easier to lower the equivalent series resistance of the capacitor.

[0021] <Basic compounds> The solid electrolyte layer in this embodiment may further contain a basic compound different from the conductive composite and the polyanion. The inclusion of a basic compound can further reduce the ESR of the capacitor.

[0022] The basic compound functions as a Brønsted base, accepting protons from the excess anionic group of the polyanion. To perform this function, the solubility of the basic compound used in this invention in water is preferably 0.001 g or more per 100 g of water at 20°C. The upper limit of the solubility is not particularly limited, but even a solubility of about 0.1 g is sufficient to perform the above function.

[0023] Examples of basic compounds that can be used include nitrogen-containing organic or inorganic basic compounds, alkali metal or group 2 metal hydroxides, and various carbonates and bicarbonates. Specific examples of alkali metal hydroxides include potassium hydroxide and sodium hydroxide. Specific examples of carbonates or bicarbonates include ammonium bicarbonate, ammonium carbonate, potassium bicarbonate, potassium carbonate, sodium bicarbonate, and sodium carbonate. Specific examples of quaternary ammonium hydroxides or their salts include tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrabutylammonium hydroxide.

[0024] 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, and trinaphthylamine.

[0025] 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, N-propylimidazole, N-butylimidazole, 1-(2-hydroxyethyl)imidazole, 2-ethyl-4-methylimidazole, 1,2-dimethylimidazole, 1-benzyl-2-methylimidazole, 1-cyanoethyl-2-methylimidazole, and 1-cyanoethyl-2-ethyl-4-methylimidazole. Examples of derivatives include dazole, 2-phenyl-4,5-dihydroxymethylimidazole, 1-acetylimidazole, 2-aminobenzimidazole, 2-amino-1-methylbenzimidazole, 2-hydroxybenzimidazole, 2-(2-pyridyl)benzimidazole, pyridine, pyrimidine, pyrazine, and their alkyl-substituted derivatives (e.g., derivatives with C1-C4 alkyl groups such as methyl, ethyl, propyl, and butyl), halogen-substituted derivatives (e.g., derivatives with halogen groups such as fluoro, chloro, and brom), and nitrile-substituted derivatives. Among these, nitrogen-containing aromatic compounds are preferred, and imidazole is more preferred.

[0026] The solid electrolyte layer may contain one basic compound or two or more basic compounds. The content ratio of the basic compound in the solid electrolyte layer is preferably, for example, 1 to 1000 parts by mass, more preferably 5 to 100 parts by mass, and even more preferably 10 to 50 parts by mass, per 100 parts by mass of the conductive composite. Within the above preferred range, the ESR of the capacitor can be further reduced.

[0027] <Polyol compounds> The solid electrolyte layer of this embodiment may further contain one or more compounds having two or more hydroxyl groups (hereinafter sometimes referred to as polyol compounds) that are different from the conductive composite, the polyanion, and the basic compound. By including polyol compounds, the ESR of the capacitor can be further reduced.

[0028] Examples of polyol compounds include one or more selected from ethylene glycol, diethylene glycol, propylene glycol, 1,4-butanediol, glycerin, pentaerythritol, trimethylolpropane, and trimethylolethane.

[0029] The total content of polyol compounds in the solid electrolyte layer is preferably, for example, 100 parts by mass or more and 10,000 parts by mass or less, more preferably 200 parts by mass or more and 2,000 parts by mass or less, and even more preferably 300 parts by mass or more and 1,000 parts by mass or less, relative to 100 parts by mass of the total of π-conjugated conductive polymers and polyanions contained in the solid electrolyte layer (i.e., 100 parts by mass of conductive composite). Within the above range, the ESR of the capacitor tends to decrease more easily, which is preferable. The solid electrolyte layer may contain one type of polyol compound or two or more types.

[0030] [Electrolyte] The capacitor in this embodiment may have an electrolyte that impregnates a solid electrolyte layer. Examples of solvents that constitute the electrolyte 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. 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.).

[0031] The capacitor in this embodiment is not limited to the above configuration, and a separator may be provided between the dielectric layer and the cathode. An example of a capacitor with a separator between the dielectric layer and the cathode is a wound capacitor. 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 are listed: When a separator is provided, a method can be applied in which carbon paste or silver paste is impregnated into the separator to form the cathode.

[0032] <Paint composition> The solid electrolyte layer of the capacitor in this embodiment is formed by a cured product of a paint composition. The paint composition includes a conductive polymer dispersion consisting of the conductive composite and water. The paint composition may also contain any components other than the conductive composite and the dispersion medium.

[0033] [Conductive polymer dispersion] The conductive polymer dispersion contained in the coating composition exhibits an absorbance of 0.59 to 1.20 at 25°C in its absorption spectrum at 600 nm when it contains 0.033% by mass (i.e., 0.0325% to 0.0334% by mass) of the conductive composite (i.e., π-conjugated conductive polymer and polyanion). Here, the absorbance of the conductive polymer dispersion at 600 nm is the value measured when the conductive polymer dispersion is measured alone before it is incorporated into the paint composition. When the absorbance at 600 nm is within the above range, it is possible to form a solid electrolyte layer with reduced contact resistance while maintaining the same capacitance compared to when the absorbance at 600 nm is outside the above range. Furthermore, since the absorbance at 600 nm is thought to reflect the length of the π-conjugated system in the π-conjugated conductive polymer structure, it is considered that π-conjugated conductive polymers contained in conductive polymer dispersions with different absorbances at 600 nm have different molecular structures.

[0034] The absorbance values ​​mentioned above were measured at 25°C in accordance with JIS K0115:2020. For example, they can be measured using a UV-Vis spectrophotometer (Shimadzu Corporation, UV-1900i).

[0035] The content ratio of the conductive polymer dispersion to the total mass of the coating composition is preferably 80% by mass or more and 100% by mass or less, more preferably 85% by mass or more and 99% by mass or less, and even more preferably 90% by mass or more and 98% by mass or less. Within the above preferred range, the ESR of the capacitor having a solid electrolyte layer formed from the paint composition can be further reduced.

[0036] The water content in the conductive polymer dispersion of the paint composition is preferably 95.0% by mass or more and 99.9% by mass or less, more preferably 97.5% by mass or more and 99.5% by mass or less, and even more preferably 98.0% by mass or more and 99.0% by mass or less, based on the total mass of the conductive polymer dispersion. Within the above preferred range, the ESR of the capacitor having a solid electrolyte layer formed from the paint composition can be further reduced.

[0037] The content of the conductive composite (i.e., π-conjugated conductive polymer and polyanion) in the conductive polymer dispersion of the paint composition 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 1.0% by mass or more and 2.0% by mass or less, based on the total mass of the conductive polymer dispersion. Within the above preferred range, the ESR of the capacitor having a solid electrolyte layer formed from the paint composition can be further reduced.

[0038] The content of the conductive composite (i.e., π-conjugated conductive polymer and polyanion) in the paint composition 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 1.0% by mass or more and 2.0% by mass or less, based on the total mass of the paint composition. Within the above preferred range, the ESR of the capacitor having a solid electrolyte layer formed from the paint composition can be further reduced.

[0039] The conductive polymer dispersion may contain optional components other than the conductive composite and water, but it is preferable that it does not contain optional components. On the other hand, the paint composition may contain optional components other than the conductive polymer dispersion.

[0040] (dispersion medium) The paint composition may contain a dispersion medium other than water. Such a dispersion medium is not particularly limited, as long as it does not significantly impair the dispersibility of the conductive composite in the paint composition. Since the conductive composite has excess anionic groups derived from polyanions and exhibits high dispersibility in water, a water-soluble organic solvent is preferred as the dispersion medium other than water. Here, a water-soluble organic solvent is an organic solvent whose solubility in 100g of water at 20°C is 1g or more, and examples include alcohol-based solvents, ketone-based solvents, and ester-based solvents. The dispersion medium may consist of one or more water-soluble organic solvents.

[0041] The water content relative to the total mass of the dispersion medium excluding the non-volatile components of the aforementioned paint composition is preferably 50% by mass or more, preferably 60% by mass or more, more preferably 80% by mass or more, and may be 100% by mass.

[0042] (Basic compounds) The paint composition may also contain the basic compound mentioned above. The amount of the basic compound in the paint composition is preferably, for example, 1 to 1000 parts by mass, more preferably 5 to 100 parts by mass, and even more preferably 10 to 50 parts by mass, based on 100 parts by mass of the total of the π-conjugated conductive polymer and polyanion (i.e., 100 parts by mass of the conductive composite). Within the above preferred range, the ESR of the capacitor can be further reduced.

[0043] The amount of basic compound contained in the aforementioned coating composition is preferably such that the pH of the conductive polymer dispersion (at 25°C) is 2.0 to 8.0, more preferably 2.0 to 5.0, and even more preferably 2.0 to 3.0. Within the above preferred range, the ESR of the capacitor can be further reduced.

[0044] (Polyol compounds) The aforementioned paint composition may contain the aforementioned polyol compound. The amount of the polyol compound contained in the paint composition is preferably, for example, 100 parts by mass or more and 10,000 parts by mass or less, more preferably 200 parts by mass or more and 2,000 parts by mass or less, and even more preferably 300 parts by mass or more and 1,000 parts by mass or less, based on 100 parts by mass of the total of the π-conjugated conductive polymer and polyanion (i.e., 100 parts by mass of the conductive composite). Within the above preferred range, the ESR of the capacitor can be further reduced.

[0045] The content of the polyol compound relative to the total mass of the coating composition is preferably 1% to 15% by mass, more preferably 3% to 12% by mass, and even more preferably 5% to 9% by mass. Within this preferred range, the coating properties of the coating composition are improved, and the ESR of the capacitor can be further reduced.

[0046] (Optional additives) The aforementioned paint composition may contain any additives, the proportion of which can be appropriately determined depending on the type of additive, but can be, for example, 1 to 1000 parts by mass per 100 parts by mass of the total of the π-conjugated conductive polymer and polyanion (i.e., 100 parts by mass of the conductive composite). Here, the optional additives are compounds other than the conductive composite, the basic compound, the polyol compound, and the dispersion medium.

[0047] Optional additives include, for example, surfactants, inorganic conductive agents, defoamers, coupling agents, antioxidants, and UV absorbers. 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. Examples of inorganic conductive agents include metal ions and conductive carbon. Metal ions can be generated by dissolving metal salts in water. Examples of defoaming agents include silicone resins, polydimethylsiloxanes, and silicone oils. 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-based UV absorbers, benzophenone-based UV absorbers, salicylate-based UV absorbers, cyanoacrylate-based UV absorbers, oxanilide-based UV absorbers, hindered amine-based UV absorbers, and benzoate-based UV absorbers.

[0048] <Method for producing conductive polymer dispersion> The conductive polymer dispersion is preferably manufactured by the following method: a manufacturing method (polymerization step) which includes polymerizing monomers that form a π-conjugated conductive polymer in a reaction solution containing a polyanion and a dispersion medium to obtain a conductive polymer dispersion containing a conductive composite containing the π-conjugated conductive polymer and the polyanion, and the dispersion medium.

[0049] The synthesis of the conductive composite in the reaction solution can be carried out in the same manner as the synthesis of conventional conductive composites.

[0050] The dispersion medium contained in the reaction solution is preferably water. The presence of water in the dispersion medium allows the polymerization reaction of the monomer to proceed stably, resulting in the obtained conductive composite being stably dispersed in the dispersion medium.

[0051] The monomers can be polymerized by chemical oxidation. Chemical oxidation polymerization can be carried out using known catalysts and oxidizing agents. Examples of catalysts include transition metal compounds such as ferric chloride, ferric sulfate, ferric nitrate, and cupric chloride. Examples of oxidizing agents include persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate.

[0052] The catalyst content relative to the total mass of the reaction solution during the polymerization reaction is preferably 0.01% by mass or more and 0.50% by mass or less, and more preferably 0.01% by mass or more and 0.30% by mass or less. When the catalyst is within the above range, chemical oxidation polymerization is performed well, and it becomes easy to adjust the absorbance at 600 nm of the conductive polymer dispersion (conductive composite concentration 0.033% by mass, 25°C) to the predetermined range. Furthermore, when the catalyst concentration is lowered, the absorbance at 600 nm of the conductive polymer dispersion tends to decrease.

[0053] The content of the oxidizing agent relative to the total mass of the reaction solution during the polymerization reaction is preferably 0.10% by mass or more and 1.00% by mass or less, more preferably 0.30% by mass or more and 0.80% by mass or less, and even more preferably 0.50% by mass or more and 0.70% by mass or less. When the concentration of the oxidizing agent is low, the absorbance at 600 nm of the conductive polymer dispersion (conductive composite concentration 0.033% by mass, 25°C) tends to decrease, and conversely, when the concentration of the oxidizing agent is high, the absorbance at 600 nm of the conductive polymer dispersion tends to increase.

[0054] The content of the monomer relative to the total mass of the reaction solution immediately before the start of the polymerization reaction is preferably, for example, 0.01% by mass or more and 2.0% by mass or less, more preferably 0.1% by mass or more and 1.0% by mass or less, and even more preferably 0.3% by mass or more and 0.5% by mass or less. The content of the polyanion relative to the total mass of the reaction solution immediately before the start of the polymerization reaction is preferably, for example, 0.1% by mass or more and 3.0% by mass or less, more preferably 0.5% by mass or more and 2.0% by mass or less, and even more preferably 1.0% by mass or more and 1.5% by mass or less. By setting the concentration of the conductive composite to the preferred content described above, a conductive polymer dispersion can be easily obtained.

[0055] In a conductive composite formed by a polymerization reaction, from the viewpoint of achieving the above-mentioned preferred ratio of the π-conjugated conductive polymer and the polyanion, the ratio of the monomer and the polyanion contained in the reaction solution immediately before the start of the polymerization reaction is preferably in the range of 1 to 1000 parts by mass, more preferably 10 to 700 parts by mass, and even more preferably 100 to 500 parts by mass, per 100 parts by mass of the monomer.

[0056] The mass-average molecular weight of the polyanion used in the polymerization reaction is preferably between 20,000 and 1,000,000, and more preferably between 100,000 and 500,000. The mass-average molecular weight is the average molecular weight on a mass basis, determined by measuring it using gel filtration chromatography and converting it to pullulan equivalent.

[0057] A π-conjugated conductive polymer can be synthesized by chemical oxidative polymerization of the monomers, thereby obtaining the desired conductive polymer dispersion.

[0058] <Effects and Effects> In the capacitor manufacturing method of this embodiment, a conductive polymer dispersion and a paint composition containing a conductive composite in a state suitable for reducing ESR can be obtained, using the absorbance of the conductive polymer dispersion at 600 nm as an indicator. The absorbance of the conductive polymer dispersion at 600 nm can be set to a predetermined range by adjusting the concentrations of the oxidizing agent and catalyst within the above-mentioned preferred range.

[0059] It is preferable to remove the catalyst and oxidizing agent added to the reaction solution from the conductive polymer dispersion after the chemical oxidative polymerization of the monomer. Methods for removal include, for example, contacting a conductive polymer dispersion with an ion exchange resin to adsorb the catalyst and oxidizing agent onto the ion exchange resin, and removing them along with the displacement of the dispersion medium by ultrafiltration of the conductive polymer dispersion. Of these, the method using an ion exchange resin is preferred because it is simple. It is preferable to use a combination of a cation exchange resin and an anion exchange resin.

[0060] The aforementioned paint composition can be obtained by further adding a basic compound, a polyol compound, or any other additive to the conductive polymer dispersion obtained above.

[0061] Capacitor manufacturing method A second aspect of the present invention is a method for manufacturing a capacitor, comprising the step of applying the paint composition described in the first aspect to the surface of a dielectric layer formed on the surface of an anode made of a porous valve metal, and drying it to form a solid electrolyte layer. The manufacturing method of the first aspect can be easily manufactured by this aspect.

[0062] The manufacturing method in this embodiment preferably includes the steps of: oxidizing the surface of an anode made of a porous valve metal to form a dielectric layer (dielectric formation step); arranging a cathode at a position opposite the dielectric layer (cathode formation step); and forming a solid electrolyte layer on at least a part of the surface of the dielectric layer (film formation step). Each step will be described below with reference to Figure 1.

[0063] [Dielectric Formation Process] In this process, the surface of the anode 11, which is made of a porous valve metal, is oxidized to form a dielectric layer 12. The method for forming the dielectric layer 12 is not particularly limited, and examples include anodic oxidation of the surface of the anode 11 in an electrolyte solution for chemical treatment, such as an aqueous solution of ammonium adipate, an aqueous solution of ammonium borate, or an aqueous solution of ammonium phosphate.

[0064] [Cathode formation process] In this process, a cathode 13 is placed opposite the dielectric layer 12. The method of arranging the cathode 13 is not particularly limited, and examples include forming the cathode 13 using a conductive paste such as carbon paste or silver paste, or arranging a metal foil such as aluminum foil opposite the dielectric layer 12.

[0065] [Film forming process] This process involves applying the aforementioned paint composition to at least a portion of the surface of the dielectric layer 12 and drying it to form a solid electrolyte layer 14.

[0066] For example, the coating method for the paint composition can include dip coating, comma coating, reverse coating, lip coating, and microgravure coating. Of these, the method of immersing the anode 11 in the paint composition under reduced pressure is preferred. With the dip method, the paint composition can be sufficiently applied to the interior of the porous structure on the surface of the dielectric layer 12. After immersion, it is removed and the drying process is carried out.

[0067] Drying methods include, for example, room temperature drying, hot air drying, and far-infrared drying. Among these, hot air drying is preferred. The drying temperature is preferably 100 to 180°C, and more preferably 120 to 150°C. The drying time is preferably 0.2 to 1 hour. After drying, the capacitor can be assembled using conventional methods. [Examples]

[0068] (Manufacturing Example 1) Production of Polystyrene Sulfonic Acid 1 206 g of sodium styrene sulfonate was dissolved in 1000 ml of deionized water, and while stirring at 80°C, 1.14 g of ammonium persulfate oxidizing agent solution, which had been previously dissolved in 10 ml of water, was added dropwise for 20 minutes, and this solution was stirred for 12 hours. To the obtained sodium polystyrene sulfonate-containing solution, 1000 ml of sulfuric acid diluted to 10% by mass was added, and approximately 1000 ml of the solvent from the resulting polystyrene sulfonate-containing solution was removed by ultrafiltration. Next, 2000 ml of deionized water was added to the remaining solution, and approximately 2000 ml of solvent was removed by ultrafiltration to wash the polystyrene sulfonate with water. This washing procedure was repeated three times. The water in the resulting solution was removed under reduced pressure to obtain colorless, solid polystyrene sulfonic acid. Next, 10 g of the obtained polystyrene sulfonic acid was dissolved in 90 g of deionized water to obtain a 10% by mass aqueous solution of polystyrene sulfonic acid.

[0069] Using gel permeation chromatography (GPC), the weight-average molecular weight (Mw) of the polystyrene sulfonic acid (PSS) obtained above was measured using pullulan of known weight-average molecular weight as a standard substance, and the result showed a weight-average molecular weight of 180,000. Weight-average molecular weight was measured using a Prominence high-performance liquid chromatograph manufactured by Shimadzu Corporation. A 0.1% NaNO3 aqueous solution was used as the solvent, a Shodex OHpack SB-806M HQ column was used, and a RID-20A detector was used. The solvent temperature was set to 40°C, the flow rate to 0.6 ml / min, and the PSS concentration in the sample was adjusted to 0.1% by mass. 100 μl of the sample, filtered through a 0.2 μm pore size membrane filter, was injected, and the analysis was performed using Lab Solutions software (Shimadzu Corporation).

[0070] (Manufacturing Example 2) Production of Polystyrene Sulfonic Acid 2 206 g of sodium styrene sulfonate was dissolved in 1000 ml of deionized water, and while stirring at 80°C, 0.38 g of ammonium persulfate oxidizing agent solution, which had been previously dissolved in 10 ml of water, was added dropwise for 20 minutes, and this solution was stirred for 12 hours. To the obtained sodium polystyrene sulfonate-containing solution, 1000 ml of sulfuric acid diluted to 10% by mass was added, and approximately 1000 ml of the solvent from the resulting polystyrene sulfonate-containing solution was removed by ultrafiltration. Next, 2000 ml of deionized water was added to the remaining solution, and approximately 2000 ml of solvent was removed by ultrafiltration to wash the polystyrene sulfonate with water. This washing procedure was repeated three times. The water in the resulting solution was removed under reduced pressure to obtain colorless, solid polystyrene sulfonic acid. Next, 10 g of the obtained polystyrene sulfonic acid was dissolved in 90 g of deionized water to obtain a 10% by mass aqueous solution of polystyrene sulfonic acid. The weight-average molecular weight of the polystyrene sulfonic acid (PSS) obtained above, measured using GPC as in Production Example 1, was 540,000.

[0071] (Manufacturing Example 3) Creation of capacitor elements After connecting anode lead terminals to etched aluminum foil (anodic foil), a voltage of 40V was applied in a 10% by mass aqueous solution of ammonium adipate to perform a chemical conversion (oxidation treatment) to form dielectric layers on both sides of the aluminum foil and obtain the anode foil. Next, opposing aluminum cathode foils, each with cathode lead terminals welded to both sides of an anode foil, were laminated with a cellulose separator in between, and this was wound into a cylindrical shape to obtain a capacitor element.

[0072] (Example 1) 3.0 g of 3,4-ethylenedioxythiophene (EDOT), 90 g of the polystyrene sulfonic acid aqueous solution (10% solids by mass) from Production Example 1, and 325 g of deionized water were mixed at 20°C. The resulting mixed solution was kept at 20°C, and 1.8g of ferric sulfate was added while stirring. Next, a solution of 4.4 g of sodium persulfate dissolved in 295.6 g of deionized water was slowly added, and the resulting reaction mixture was stirred for 8 hours to allow the reaction to proceed. The above reaction yielded a conductive polymer dispersion containing a conductive composite (PEDOT-PSS) comprising poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid, which are π-conjugated conductive polymers, and water as a dispersion medium. 39 g of Duolite C255LFH (manufactured by Sumika Chemtex, cation exchange resin) and 39 g of Duolite A368MS (manufactured by Sumika Chemtex, anion exchange resin) were added to this conductive polymer dispersion, and the dispersion was filtered to remove the ion exchange resins, obtaining 710 g of conductive polymer dispersion A from which the oxidizing agent and catalyst had been removed, and the non-volatile components (solid content) were measured.

[0073] Next, a portion of the obtained conductive polymer dispersion A was separated, water was added to adjust the non-volatile component concentration to 0.033% by mass, and conductive polymer dispersion B was obtained. The absorbance of conductive polymer dispersion B at 600 nm was measured at 25°C under the following conditions in accordance with JIS K0115:2020, and the values ​​are shown in Table 1.

[0074] • Measuring instrument: UV-Vis spectrophotometer (Shimadzu Corporation, UV-1900i) • Analysis: "LabSolution UV-Vis Color Measurement Software" • Cell: Quartz cell ·Optical path length: 10mm ·Measurement wavelength range: 380-780nm ·Viewing angle: 10° ·Light source: D65 standard light source

[0075] Meanwhile, water was removed from conductive polymer dispersion A under reduced pressure using an evaporator to obtain 1.6% by mass of non-volatile components. To the obtained conductive polymer dispersion (100 g), imidazole (0.3 g) was added to adjust the pH to 2.5, and diethylene glycol (8 g) was added to obtain conductive polymer dispersion C (paint composition).

[0076] Next, the capacitor element obtained in Manufacturing Example 3 was immersed in the above-mentioned paint composition under reduced pressure, and then dried in a hot air dryer at 125°C for 30 minutes to form a solid electrolyte layer containing a conductive composite on the surface of the dielectric layer. Finally, the capacitor element with the solid electrolyte layer described above was loaded into an aluminum case, sealed with a rubber seal, and the capacitor was fabricated.

[0077] (Example 2) Conductive polymer dispersions A to C were obtained in the same manner as in Example 1, except that the "solution of 4.4 g of sodium persulfate dissolved in 295.6 g of deionized water" was changed to "a solution of 2.2 g of sodium persulfate dissolved in 297.8 g of deionized water," and conductive films and capacitors were fabricated. The measured values ​​for each are listed in Table 1.

[0078] (Example 3) Conductive polymer dispersions A to C were obtained in the same manner as in Example 1, except that "1.8g of ferric sulfate" was changed to "1.2g of ferric sulfate," and conductive films and capacitors were fabricated. The measured values ​​for each are listed in Table 1.

[0079] (Example 4) Conductive polymer dispersions A to C were obtained in the same manner as in Example 1, except that "1.8g of ferric sulfate" was changed to "1.2g of ferric sulfate," and "a solution of 4.4g of sodium persulfate dissolved in 295.6g of deionized water" was changed to "a solution of 2.2g of sodium persulfate dissolved in 297.8g of deionized water." Conductive films and capacitors were then fabricated. The measured values ​​are listed in Table 1.

[0080] (Example 5) Conductive polymer dispersions A to C were obtained in the same manner as in Example 1, except that "1.8g of ferric sulfate" was changed to "0.6g of ferric sulfate," and "a solution of 4.4g of sodium persulfate dissolved in 295.6g of deionized water" was changed to "a solution of 6.6g of sodium persulfate dissolved in 293.4g of deionized water." Conductive films and capacitors were then fabricated. The measured values ​​are listed in Table 1.

[0081] (Example 6) Conductive polymer dispersions A to C were obtained in the same manner as in Example 1, except that "1.8g of ferric sulfate" was changed to "0.6g of ferric sulfate," and conductive films and capacitors were fabricated. The measured values ​​for each are listed in Table 1.

[0082] (Example 7) Conductive polymer dispersions A to C were obtained in the same manner as in Example 1, except that "1.8g of ferric sulfate" was changed to "0.3g of ferric sulfate," and conductive films and capacitors were fabricated. The measured values ​​for each are listed in Table 1.

[0083] (Example 8) Conductive polymer dispersions A to C were obtained in the same manner as in Example 1, except that "1.8g of ferric sulfate" was changed to "0.15g of ferric sulfate," and conductive films and capacitors were fabricated. The measured values ​​for each are listed in Table 1.

[0084] (Comparative Example 1) Conductive polymer dispersions A to C were obtained in the same manner as in Example 1, except that the "solution of 4.4 g of sodium persulfate dissolved in 295.6 g of deionized water" was changed to "a solution of 6.6 g of sodium persulfate dissolved in 293.4 g of deionized water," and conductive films and capacitors were fabricated. The measured values ​​for each are listed in Table 1.

[0085] (Comparative Example 2) Conductive polymer dispersions A to C were obtained in the same manner as in Example 1, except that "1.8g of ferric sulfate" was changed to "1.2g of ferric sulfate," and "a solution of 4.4g of sodium persulfate dissolved in 295.6g of deionized water" was changed to "a solution of 6.6g of sodium persulfate dissolved in 293.4g of deionized water." Conductive films and capacitors were then fabricated. The measured values ​​are listed in Table 1.

[0086] (Comparative Example 3) Conductive polymer dispersions A to C were obtained in the same manner as in Example 1, except that "1.8g of ferric sulfate" was changed to "0.6g of ferric sulfate," and "a solution of 4.4g of sodium persulfate dissolved in 295.6g of deionized water" was changed to "a solution of 2.2g of sodium persulfate dissolved in 297.8g of deionized water." Conductive films and capacitors were then fabricated. The measured values ​​are listed in Table 1.

[0087] (Comparative Example 4) Conductive polymer dispersions A to C were obtained in the same manner as in Example 1, except that "1.8g of ferric sulfate" was changed to "0.3g of ferric sulfate," and "a solution of 4.4g of sodium persulfate dissolved in 295.6g of deionized water" was changed to "a solution of 6.6g of sodium persulfate dissolved in 293.4g of deionized water." Conductive films and capacitors were then fabricated. The measured values ​​are listed in Table 1.

[0088] (Comparative Example 5) Conductive polymer dispersions A to C were obtained in the same manner as in Example 1, except that "1.8g of ferric sulfate" was changed to "0.3g of ferric sulfate," and "a solution of 4.4g of sodium persulfate dissolved in 295.6g of deionized water" was changed to "a solution of 2.2g of sodium persulfate dissolved in 297.8g of deionized water." Conductive films and capacitors were then fabricated. The measured values ​​for each are listed in Table 1.

[0089] (Comparative Example 6) Conductive polymer dispersions A to C were obtained in the same manner as in Example 1, except that "1.8g of ferric sulfate" was changed to "0.15g of ferric sulfate," and "a solution of 4.4g of sodium persulfate dissolved in 295.6g of deionized water" was changed to "a solution of 6.6g of sodium persulfate dissolved in 293.4g of deionized water." Conductive films and capacitors were then fabricated. The measured values ​​are listed in Table 1.

[0090] (Comparative Example 7) Conductive polymer dispersions A to C were obtained in the same manner as in Example 1, except that "1.8g of ferric sulfate" was changed to "0.15g of ferric sulfate," and "a solution of 4.4g of sodium persulfate dissolved in 295.6g of deionized water" was changed to "a solution of 2.2g of sodium persulfate dissolved in 297.8g of deionized water." Conductive films and capacitors were then fabricated. The measured values ​​are listed in Table 1.

[0091] (Example 9) Conductive polymer dispersions A to C were obtained in the same manner as in Example 1, except that "polystyrene sulfonic acid aqueous solution (10% solid content by mass) of Production Example 1" was replaced with "polystyrene sulfonic acid aqueous solution (10% solid content by mass) of Production Example 2," and conductive films and capacitors were fabricated. The measured values ​​for each are listed in Table 1.

[0092] (Example 10) Conductive polymer dispersions A to C were obtained in the same manner as in Example 1, except that "90 g of the polystyrene sulfonic acid aqueous solution (10% solid content by mass) from Production Example 1 and 325 g of deionized water" was replaced with "150 g of the polystyrene sulfonic acid aqueous solution (10% solid content by mass) from Production Example 1 and 265 g of deionized water," and conductive films and capacitors were fabricated. The measured values ​​for each are listed in Table 1.

[0093] [Measuring pH] The pH was measured at 25°C using a commercially available pH meter and a standard method.

[0094] <Rating> [Capacitance and equivalent series resistance] For each example capacitor, the capacitance (in μF) at 120 Hz and the equivalent series resistance (ESR) (in Ω) at 100 kHz were measured using an LCR meter ZM2376 (manufactured by NF Circuit Design Block Co., Ltd.). The measurement results are shown in Table 1.

[0095] [Table 1]

[0096] It was confirmed that the equivalent series resistance of the capacitor according to the present invention, which has a solid electrolyte layer formed by a cured product of a specific conductive polymer dispersion (paint composition), is significantly reduced. [Explanation of Symbols]

[0097] 10 Capacitors 11 Anode 12 Dielectric layer 13 Cathode 14 Solid electrolyte layer

Claims

1. A method for manufacturing a capacitor, comprising the step of applying a paint composition to the surface of a dielectric layer formed on the surface of an anode made of a porous valve metal, and drying it to form a solid electrolyte layer. The aforementioned paint composition comprises a conductive polymer dispersion in which a conductive composite containing a π-conjugated conductive polymer and a polyanion is dispersed in water. A method for manufacturing a capacitor, comprising the step of confirming, before applying the coating composition, that the absorbance at 600 nm of the conductive polymer dispersion is 0.59 or more and 1.20 or less when the concentration of the conductive composite is adjusted to 0.033% by mass.

2. The method for manufacturing a capacitor according to claim 1, wherein the content of the conductive composite relative to the total mass of the paint composition is 0.5% by mass or more and 1.6% by mass or less.

3. The method for manufacturing a capacitor according to claim 1, wherein the paint composition further contains a basic compound.

4. The method for manufacturing a capacitor according to claim 3, wherein the basic compound is a nitrogen-containing aromatic compound.

5. The method for manufacturing a capacitor according to claim 3, wherein the basic compound is imidazole.

6. The method for producing a capacitor according to claim 1, wherein the paint composition further contains a polyol compound having two or more hydroxyl groups.

7. The method for manufacturing a capacitor according to claim 6, wherein the polyol compound is diethylene glycol.

8. The method for manufacturing a capacitor according to claim 1, wherein the π-conjugated conductive polymer is poly(3,4-ethylenedioxythiophene).

9. The method for manufacturing a capacitor according to claim 8, wherein the polyanion is polystyrene sulfonic acid.

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