Method of manufacturing capacitor

Abstract

To provide a method of manufacturing a capacitor which is improved in a performance relating to equivalent series resistance.SOLUTION: A method of manufacturing a capacitor comprising a positive electrode consisting of a porous body of a valve metal, a dielectric layer which is formed on a surface of the positive electrode, a negative electrode made of a conductive substance which is provided on an opposite side of the positive electrode and a solid electrolyte layer which covers at least a part of a surface of the dielectric layer includes: a step (A) of dispersing a conductive composite containing π-conjugated conductive polymers and polyanions in a dispersant and obtaining a conductive polymer dispersed fluid; a step (B) of adding an additive to the conductive polymer dispersed fluid and obtaining a conductive polymer processed fluid on which dispersion processing is performed; and a step (C) of applying the conductive polymer processed fluid to the surface of the dielectric layer, drying the surface and forming the solid electrolyte layer. A time from a point of time in which the dispersion processing of the step (B) is completed to applying the conductive polymer processed fluid to the surface of the dielectric layer in the step (C) is 60 hours or longer.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a capacitor having a solid electrolyte layer containing a π-conjugated conductive polymer and a polyanion. [Background technology]

[0002] A π-conjugated conductive polymer whose main chain is composed of a π-conjugated system forms a conductive complex by doping with a polyanion having an anionic group, and becomes dispersible in water. A method for manufacturing a capacitor has been disclosed (for example, Patent Document 1), in which a paint made from a conductive polymer dispersion containing a conductive complex is applied to a dielectric layer provided on the surface of an anode made of a valve metal, dried to form a solid electrolyte layer, and then a cathode is placed opposite this. According to this disclosure, the performance of the capacitor is improved by adding a specific unsaturated aliphatic alcohol compound to the paint. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-071400 Summary of the Invention [Problem to be solved by the invention]

[0004] The present inventors have focused on the possibility that the state of the paint used to form the solid electrolyte layer may change over time, and as a result of extensive investigation, have found that applying the paint after allowing a certain amount of time to pass after preparation results in a high-performance capacitor with reduced equivalent series resistance (ESR) compared to applying the paint immediately after preparation, and have thus completed the present invention.

[0005] The present invention provides a method for manufacturing a capacitor with excellent performance in terms of equivalent series resistance. [Means for solving the problem]

[0006] [1] A method for manufacturing a capacitor including an anode made of a porous valve metal, a dielectric layer formed on the surface of the anode, a cathode made of a conductive material provided on the side opposite the anode, and a solid electrolyte layer covering at least a portion of the surface of the dielectric layer, the method comprising: step (A) of dispersing a conductive complex containing a π-conjugated conductive polymer and a polyanion in a dispersion medium to obtain a conductive polymer dispersion; step (B) of adding, to the conductive polymer dispersion, one or more additives selected from the group consisting of a nitrogen-containing compound different from the conductive complex, a polyol compound having two or more hydroxy groups, a surfactant, an antifoaming agent, a coupling agent, an antioxidant, and an ultraviolet absorber, to obtain a dispersed conductive polymer treatment liquid; and step (C) of applying the conductive polymer treatment liquid to the surface of the dielectric layer and drying it to form the solid electrolyte layer, wherein the time from the completion of the dispersion treatment in step (B) to the application of the conductive polymer treatment liquid to the surface of the dielectric layer in step (C) is 60 hours or more. [2] The method for producing a capacitor according to [1], wherein a nitrogen-containing compound is added as the additive. [3] The method for producing a capacitor according to [1] or [2], wherein a polyol compound having two or more hydroxy groups is added as the additive. [4] The method for producing a capacitor according to any one of [1] to [3], wherein the π-conjugated conductive polymer is a polythiophene-based conductive polymer. [5] The method for producing a capacitor according to any one of [1] to [4], wherein the polyanion is polystyrene sulfonic acid. [6] The method for producing a capacitor according to any one of [1] to [5], wherein the dispersion medium is water. [7] The method for producing a capacitor according to any one of [1] to [6], wherein in step (B), the dispersion treatment is carried out using a high-pressure homogenizer. [8] The method for producing a capacitor according to any one of [1] to [7], wherein the amount of the additive contained in the conductive polymer treatment liquid is 5 parts by mass or more and 40 parts by mass or less per 100 parts by mass of the conductive composite. [9] The method for producing a capacitor according to any one of [1] to [7], wherein the amount of the additive contained in the conductive polymer treatment solution is 50 parts by mass or more and 1000 parts by mass or less per 100 parts by mass of the conductive composite. [Effects of the Invention]

[0007] According to the present invention, it is possible to manufacture a high-performance capacitor with low ESR and a capacitor with excellent heat resistance.

[0008] This invention is believed to contribute to SDG Goal 12, "Responsible Consumption and Production."

[0009] In this specification and claims, the lower and upper limits of numerical ranges indicated with "to" are included in the numerical range. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view illustrating one embodiment of a capacitor. DETAILED DESCRIPTION OF THE INVENTION

[0011] <Capacitor manufacturing method> A first aspect of the present invention is a method for manufacturing a capacitor including an anode made of a porous valve metal, a dielectric layer formed on a surface of the anode, a cathode made of a conductive material provided on the opposite side of the anode, and a solid electrolyte layer covering at least a portion of the surface of the dielectric layer, the method including at least the following steps (A) to (C):

[0012] [Process (A)] Step (A) is a step of dispersing a conductive complex containing a π-conjugated conductive polymer and a polyanion in a dispersion medium to obtain a conductive polymer dispersion.

[0013] <Conductive composite> The conductive composite contains a π-conjugated conductive polymer and a polyanion. The polyanion in the conductive composite dopes the π-conjugated conductive polymer to form a conductive composite having conductivity. In polyanions, only some of the anionic groups are doped into the π-conjugated conductive polymer, leaving excess anionic groups that are not involved in the doping. Because the excess anionic groups are hydrophilic groups, conductive composites that are not modified with these excess anionic groups are dispersible in water. In this specification, unless otherwise specified, there is no distinction between dispersion and dissolution, and there is no distinction between dispersion medium and solvent.

[0014] (π-conjugated conductive polymer) The π-conjugated conductive polymer may be an organic polymer whose main chain is composed of a π-conjugated system, and 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 preferred, and from the viewpoints of transparency and conductivity, polythiophene-based conductive polymers are more preferred.

[0015] 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). thiophene), 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-dodecyloxythiophene) oxythiophene), 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 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, polythiophene-based conductive polymers are preferred because of their excellent conductivity, transparency, and heat resistance, and poly(3,4-ethylenedioxythiophene) is particularly preferred. The conductive composite may contain one type of π-conjugated conductive polymer, or two or more types of polymers.

[0016] (polyanion) A polyanion is a polymer having two or more monomer units with an anionic group in the molecule. The anionic group of this polyanion functions as a dopant for a π-conjugated conductive polymer, improving 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 polymers having sulfo groups, such as 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, polymethacryloyloxybenzenesulfonic acid), poly(2-acrylamido-2-methylpropanesulfonic acid), and polyisoprene sulfonic acid; and polymers having carboxy 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. The polyanion may be a homopolymer formed by polymerizing a single monomer, or a copolymer formed by polymerizing two or more types of monomers. Among these polyanions, polymers having sulfo groups are preferred, and polystyrene sulfonic acid is more preferred, since they can further increase the conductivity. The polyanions may be used alone or in combination of two or more. The mass average molecular weight of the polyanion is preferably from 20,000 to 1,000,000, more preferably from 100,000 to 500,000. The mass average molecular weight is measured using gel filtration chromatography and is the average molecular weight based on mass calculated as pullulan.

[0017] The content of polyanion in the conductive composite is preferably 1 part by mass or more and 1,000 parts by mass or less, more preferably 10 parts by mass or more and 700 parts by mass or less, and even more preferably 100 parts by mass or more and 500 parts by mass or less, per 100 parts by mass of the π-conjugated conductive polymer. When the content of polyanion is equal to or greater than the lower limit, the doping effect on the π-conjugated conductive polymer tends to be stronger, resulting in higher conductivity. On the other hand, when the content of polyanion is equal to or less than the upper limit, the relative proportion of the π-conjugated conductive polymer, which is the main component of conductivity, increases, resulting in higher conductivity.

[0018] (dispersion medium) The dispersion medium contained in the conductive polymer dispersion is preferably an aqueous dispersion medium containing water because the conductive composite is hydrophilic. Alternatively, a dispersion medium other than water may be contained. The dispersion medium other than water is not particularly limited as long as it does not impair the dispersibility of the conductive composite. Since the conductive composite has excess anionic groups derived from the polyanion and has high dispersibility in water, the dispersion medium other than water is preferably a water-soluble organic solvent. Here, the water-soluble organic solvent is an organic solvent that dissolves in an amount of 1 g or more in 100 g of water at 20°C, and examples thereof include alcohol-based solvents, ketone-based solvents, and ester-based solvents. The water-soluble organic solvent contained as the dispersion medium may be one type or two or more types.

[0019] The water content relative to the total mass of the dispersion medium excluding the solid content (non-volatile components) of the conductive polymer dispersion is preferably 70 mass% or more, more preferably 80 mass% or more, even more preferably 90 mass% or more, and may be 100 mass%. When water is contained in an amount equal to or greater than the above lower limit, the dispersibility of the conductive composite contained in the conductive polymer dispersion is improved.

[0020] The concentration of the conductive complex (π-conjugated conductive polymer and polyanion) contained in the conductive polymer dispersion to be subjected to the subsequent step (B) is preferably 0.1 mass % or more and 4.0 mass % or less, more preferably 0.5 mass % or more and 3.0 mass % or less, and even more preferably 1.0 mass % or more and 2.0 mass % or less, relative to the total mass of the conductive polymer dispersion. When the content is within the above suitable range, the dispersibility of the conductive composite in the conductive polymer treatment liquid obtained in step (B) can be further improved.

[0021] The conductive polymer dispersion may be obtained by chemically oxidatively polymerizing a monomer that forms a π-conjugated conductive polymer in an aqueous solution of a polyanion by a known method, or a commercially available one may be used. A preferred embodiment of chemically oxidative polymerization will be described below.

[0022] (Method for preparing conductive polymer dispersion) A reaction solution containing the monomer, the polyanion, and an aqueous dispersion medium is prepared, and the monomer is polymerized to form a π-conjugated conductive polymer. In the reaction solution, the π-conjugated conductive polymer is spontaneously doped with the polyanion, forming a conductive complex consisting of the π-conjugated conductive polymer and the polyanion.

[0023] Since the aqueous dispersion medium contained in the reaction liquid contains water, the polymerization reaction of the monomers proceeds stably, and the resulting conductive composite is obtained in a state where it is stably dispersed in the aqueous dispersion medium. The aqueous dispersion medium may contain a dispersion medium other than water. The dispersion medium other than water is not required to inhibit polymerization, and a water-soluble organic solvent is preferred. The content of water relative to the total mass of the aqueous dispersion medium is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, and may be 100% by mass.

[0024] It is preferable to add a known catalyst and oxidizing agent to the reaction solution to promote chemical oxidation of the monomer. Examples of the catalyst include transition metal compounds such as ferric chloride, ferric sulfate, ferric nitrate, and cupric chloride. Examples of the oxidizing agent include persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate.

[0025] The amount of the catalyst to be added relative to the total mass of the reaction liquid (including the catalyst) is, for example, 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.

[0026] The amount of the oxidizing agent relative to the total mass of the reaction liquid (including the oxidizing agent) is, for example, preferably 0.10 mass % or more and 1.20 mass % or less, more preferably 0.50 mass % or more and 1.10 mass % or less, and even more preferably 0.70 mass % or more and 1.00 mass % or less.

[0027] The amount of the monomer relative to the total mass of the reaction liquid is, for example, preferably 0.01% by mass to 2.0% by mass, more preferably 0.1% by mass to 1.0% by mass, and even more preferably 0.3% by mass to 0.5% by mass. The amount of the polyanion relative to the total mass of the reaction solution is, for example, preferably 0.1% by mass to 3.0% by mass, more preferably 0.5% by mass to 2.0% by mass, and even more preferably 1.0% by mass to 1.5% by mass. By setting the content within the above preferred range, a conductive polymer dispersion liquid having the conductive complex concentration in the preferred content described above can be easily obtained.

[0028] From the viewpoint of ensuring that the content ratio of the π-conjugated conductive polymer and the polyanion in the conductive composite formed by the polymerization reaction is the preferred ratio described above, the content ratio of the monomer and the polyanion to be mixed in the reaction solution is preferably in the range of 1 part by mass to 1,000 parts by mass, more preferably 10 parts by mass to 700 parts by mass, and even more preferably 100 parts by mass to 500 parts by mass, per 100 parts by mass of the monomer.

[0029] The reaction temperature in the reaction solution can be, for example, 20 to 30°C. At the reaction temperature, the polymerization reaction is usually completed in about 4 to 12 hours. The completion of the polymerization reaction can be determined by measuring the amount of unreacted monomer in the reaction solution by gas chromatography or the like.

[0030] The catalyst and oxidizing agent added to the reaction liquid are preferably removed from the conductive polymer dispersion after the chemical oxidative polymerization of the monomer. Examples of removal methods include a method of bringing the conductive polymer dispersion into contact with an ion exchange resin to adsorb the catalyst and oxidant onto the ion exchange resin, and a method of ultrafiltrating the conductive polymer dispersion to replace the dispersion medium and remove the catalyst and oxidant. Of these, the method using an ion exchange resin is preferred because it is simple. It is preferable to use a cation exchange resin and an anion exchange resin in combination as the ion exchange resin.

[0031] [Process (B)] Step (B) is a step of adding an additive to the conductive polymer dispersion liquid obtained in step (A) to obtain a dispersed conductive polymer treatment liquid.

[0032] Examples of additives include nitrogen-containing compounds, polyol compounds having two or more hydroxy groups, surfactants, antifoaming agents, coupling agents, antioxidants, and ultraviolet absorbers.

[0033] (nitrogen-containing compounds) The nitrogen-containing compound may be an organic or inorganic compound containing nitrogen, such as ammonium or its salt, ammonia, or an amine. Specific examples include ammonium hydrogen carbonate, ammonium carbonate, tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrabutylammonium hydroxide.

[0034] Examples of the amine include aliphatic tertiary amines and nitrogen-containing aromatic compounds. Examples of the aliphatic tertiary amine include triethanolamine, trimethylamine, triethylamine, tripropylamine, tributylamine, trihexylamine, trioctylamine, triphenylamine, tribenzylamine, and trinaphthylamine.

[0035] 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 suitable hydroxybenzoates include benzotriazole, 2-phenyl-4,5-dihydroxymethylimidazole, 1-acetylimidazole, 2-aminobenzimidazole, 2-amino-1-methylbenzimidazole, 2-hydroxybenzimidazole, 2-(2-pyridyl)benzimidazole, pyridine, pyrimidine, pyrazine, and derivatives thereof such as alkyl-substituted products thereof (e.g., products substituted with an alkyl group having 1 to 4 carbon atoms, such as methyl, ethyl, propyl, or butyl), halogen-substituted products thereof (e.g., products substituted with a halogen group, such as fluoro, chloro, or bromine), and nitrile-substituted products. Of these, nitrogen-containing aromatic compounds are preferred, and imidazole is more preferred.

[0036] The amount of the nitrogen-containing compound added to the conductive polymer treatment solution is, for example, preferably 1 part by mass to 100 parts by mass, more preferably 5 parts by mass to 60 parts by mass, and even more preferably 10 parts by mass to 30 parts by mass, relative to 100 parts by mass of the conductive complex (total of the π-conjugated conductive polymer and the polyanion). Within the above preferred range, the ESR of the capacitor can be further reduced.

[0037] (Polyol compound) The polyol compound is a compound having two or more hydroxy groups, which is different from the π-conjugated conductive polymer, the polyanion, and the nitrogen-containing compound. By including the polyol compound, the ESR of the capacitor can be further reduced.

[0038] Examples of the polyol compound include one or more selected from ethylene glycol, diethylene glycol, propylene glycol, 1,4-butanediol, glycerin, pentaerythritol, trimethylolpropane, and trimethylolethane.

[0039] The content of the polyol compound added to the conductive polymer treatment liquid is, for example, preferably 100 parts by mass or more and 1,000 parts by mass or less, more preferably 150 parts by mass or more and 600 parts by mass or less, and even more preferably 200 parts by mass or more and 400 parts by mass or less, relative to 100 parts by mass of the conductive complex (total of the π-conjugated conductive polymer and the polyanion). Within the above preferred range, the ESR of the capacitor can be further reduced.

[0040] The content of the polyol compound relative to the total mass of the conductive polymer treatment liquid is preferably from 1 to 15% by mass, more preferably from 3 to 10% by mass, and even more preferably from 4 to 6% by mass. Within these preferred ranges, the coatability of the conductive polymer treatment liquid obtained in this step is improved, and the ESR of the capacitor can be further reduced.

[0041] The surfactant may be a nonionic, anionic, or cationic surfactant, with nonionic surfactants being preferred from the standpoint of storage stability. Polymer surfactants such as polyvinyl alcohol and polyvinylpyrrolidone may also be added. Examples of inorganic conductive agents include metal ions, conductive carbon, etc. Metal ions can be generated by dissolving a metal salt in water. Examples of the antifoaming agent include silicone resin, polydimethylsiloxane, and silicone oil. Examples of the coupling agent include silane coupling agents having a vinyl group, an amino group, an epoxy group, or the like. Examples of the antioxidant include phenol-based antioxidants, amine-based antioxidants, phosphorus-based antioxidants, sulfur-based antioxidants, and sugars. Examples of the ultraviolet absorber include benzotriazole-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, salicylate-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorbers, oxanilide-based ultraviolet absorbers, hindered amine-based ultraviolet absorbers, and benzoate-based ultraviolet absorbers.

[0042] The conductive polymer treatment liquid is obtained by dispersing a mixture obtained by blending the additives into a conductive polymer dispersion. The mixture is obtained by mixing the materials in a conventional manner. A specific method for dispersing the mixture is preferably a high-dispersion treatment, which will be described below.

[0043] (Highly distributed processing) The high dispersion treatment is a treatment in which a shear force is applied to the mixed liquid, preferably while applying pressure, to improve the dispersibility of the conductive composite in the aqueous dispersion medium. In the high dispersion treatment, it is preferable to use a dispersing machine, such as a homogenizer, a high-pressure homogenizer, or a bead mill, with a high-pressure homogenizer being preferred. The high-pressure homogenizer is, for example, a device equipped with a high-pressure generating section that pressurizes the mixed liquid to be highly dispersed, and a counter-collision section, an orifice section, or a slit section that performs dispersion. A high-pressure pump such as a plunger pump is preferably used as the high-pressure generating section. The high pressure pump may be of any type, such as a single-type, double-type, or triple-type. Specific examples of high-pressure homogenizers include Nanomizer (trade name) manufactured by Yoshida Kikai Kogyo Co., Ltd., Microfluidizer (trade name) manufactured by Microfluidic Co., Ltd., and Ultimizer (trade name) manufactured by Sugino Machine Co., Ltd. The time for the high dispersion treatment is preferably, for example, about 10 minutes to 1 hour.

[0044] The conductive polymer treatment liquid obtained as described above contains the target conductive complex and additives. When replacing the dispersion medium with a desired one, adjusting the concentration of the conductive complex, or adding other additives, it is preferable to perform these operations at the stage of the conductive polymer dispersion liquid before the dispersion treatment. After the dispersion treatment is completed, the conductive polymer treatment liquid is preferably left to stand at room temperature (10 to 30°C) and allowed to mature.

[0045] In the manufacturing method of this embodiment, the time (aging period) from the point at which the dispersion treatment is completed in step (B) to the point at which the conductive polymer treatment liquid is applied to the surface of the dielectric layer in the next step (C) is preferably 60 hours or more, more preferably 100 hours or more, and even more preferably 140 hours or more.

[0046] Although the detailed mechanism is unclear, it is thought that because the conductive complexes in the primary particles contained in the conductive polymer treatment solution immediately after dispersion treatment are separated from each other, the intermolecular distance between the conductive polymer molecules is relatively large even in the solid electrolyte layer that is coated and dried at this point, making it difficult to form dense conductive paths. On the other hand, in the conductive polymer treatment solution that has undergone an aging period, the aggregation state becomes stable due to the intermolecular interactions between the conductive polymers, making it easier to form denser conductive paths, and thus achieving a decrease in equivalent series resistance (see Examples).

[0047] [Process (C)] Step (C) is a step of applying the conductive polymer treatment liquid that has been aged in step (B) to the surface of the dielectric layer and drying it to form a solid electrolyte layer. This step provides a laminate for a capacitor (hereinafter sometimes referred to as a "solid electrolytic capacitor") in which a solid electrolyte layer is laminated on at least a portion of the surface of the dielectric layer formed on the surface of the anode. The capacitor laminate obtained in this step and a cathode facing the anode of this capacitor laminate are placed in a case to produce a capacitor. At this time, an electrolyte may be placed in the case. An example of a method for producing a capacitor will be described below.

[0048] The method for manufacturing a capacitor according to this embodiment preferably includes the following steps. The method preferably includes the steps of: oxidizing the surface of an anode made of a porous valve metal to form a dielectric layer (dielectric forming step), disposing a cathode in a position opposite to the dielectric layer (cathode forming step), and forming a solid electrolyte layer on at least a part of the surface of the dielectric layer (film forming step). Each step will be described below with reference to FIG.

[0049] [Dielectric formation process] In this step, the surface of anode 11 made of a porous valve metal is oxidized to form dielectric layer 12. The method for forming dielectric layer 12 is not particularly limited, and examples thereof include a method of anodizing the surface of anode 11 in a chemical conversion treatment electrolyte such as an aqueous solution of ammonium adipate, an aqueous solution of ammonium borate, or an aqueous solution of ammonium phosphate.

[0050] [Cathode formation process] In this step, the cathode 13 is disposed at a position facing the dielectric layer 12. The method for disposing the cathode 13 is not particularly limited, and examples thereof include a method of forming the cathode 13 using a conductive paste such as a carbon paste or a silver paste, and a method of disposing a metal foil such as an aluminum foil facing the dielectric layer 12.

[0051] [Film forming process] In this step, the conductive polymer treatment liquid is applied to at least a portion of the surface of the dielectric layer 12 and then dried to form the solid electrolyte layer 14.

[0052] The conductive polymer treatment solution can be applied by, for example, immersion (dip coating), comma coating, reverse coating, lip coating, microgravure coating, etc. Among these, the method of immersing the anode 11 in the conductive polymer treatment solution under reduced pressure is preferred. The immersion method allows the conductive polymer treatment solution to be sufficiently applied even to the interior of the porous structure on the surface of the dielectric layer 12. After immersion, the anode is removed and then subjected to the subsequent drying process.

[0053] Drying methods include, for example, room temperature drying, hot air drying, far infrared drying, etc. Among these, hot air drying is preferred. The drying temperature is, for example, preferably 100 to 180° C., more preferably 120 to 150° C. The drying time is, for example, preferably 0.2 to 1 hour. After the drying process, the capacitor can be assembled in the usual manner.

[0054] The composition of the components contained in the solid electrolyte layer 14 reflects the composition of the applied conductive polymer treatment liquid.

[0055] <Capacitor> The capacitor comprises an anode made of a porous body of a 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 the anode, and a solid electrolyte layer formed between the dielectric layer and the cathode, and the solid electrolyte layer contains a cured product of the conductive polymer treatment liquid of the first aspect.

[0056] An example of an embodiment of a capacitor will be described with reference to Fig. 1. Capacitor 10 shown in Fig. 1 includes an anode 11 made of a porous valve metal, a dielectric layer 12 made of an oxide of the valve metal, a solid electrolyte layer 14 formed on the surface of dielectric layer 12, and a cathode 13 provided on the outermost side. Cathode 13 is provided on the opposite side of anode 11, with dielectric layer 12 and solid electrolyte layer 14 sandwiched therebetween.

[0057] Examples of valve metals that can be used to form 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 the anode 11 include an aluminum foil that has been etched to increase its surface area and then oxidized, and a tantalum or niobium particle sintered body whose surface has been oxidized and then pelletized. Such a processed body becomes a porous body with irregularities formed on the surface.

[0058] The dielectric layer 12 in this embodiment is a layer formed by oxidizing the surface of the anode 11, for example, by anodizing the surface of the metallic anode 11 in an electrolyte such as an aqueous solution of ammonium adipate. Similar to the anode 11, the dielectric layer 12 also has projections and recesses.

[0059] The cathode 13 in this embodiment may be a conductive layer formed from a conductive paste or a metal layer made of a conductive material such as aluminum foil.

[0060] The solid electrolyte layer 14 in this embodiment 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 or may not be constant, and may be, for example, 1 μm or more and 100 μm or less.

[0061] [Electrolyte] The capacitor may have an electrolyte solution impregnating the solid electrolyte layer. Examples of the solvent that constitutes the electrolytic 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. Examples of the electrolyte constituting the electrolytic solution include organic acids such as 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, azelaic acid, and sebacic acid; or boric acid, polyhydric alcohol complex compounds of boric acid obtained from boric acid and polyhydric alcohols; inorganic acids such as phosphoric acid, carbonic acid, and silicic acid; and primary amines (methylamine, ethylamine, propylamine, butylamine, ethylenediamine, etc.), secondary amines (dimethylamine, diethylamine, dipropylamine, methylethylamine, diphenylamine, etc.), tertiary amines (trimethylamine, triethylamine, tripropylamine, triphenylamine, 1,8-diazabicyclo(5,4,0)-undecene-7, etc.), tetraalkylammonium (tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, methyltriethylammonium, dimethyldiethylammonium, etc.), etc. as a cationic component;

[0062] The capacitor 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 having a separator provided between the dielectric layer and the cathode is a wound capacitor. Examples of the separator include sheets (including nonwoven fabrics) made of cellulose, polyvinyl alcohol, polyester, polyethylene, polystyrene, polypropylene, polyimide, polyamide, polyvinylidene fluoride, etc., and nonwoven fabrics of glass fibers. The density of the separator is, for example, 0.1 g / cm 3 More than 1.0g / cm 3 The following are included: When a separator is provided, a method of forming a cathode by impregnating the separator with carbon paste or silver paste can also be applied.

[0063] <Method for manufacturing conductive laminate> In the manufacturing method of the first aspect of the present invention, a laminate for a capacitor is manufactured. However, by changing the target to which the conductive polymer treatment solution is applied in step (C) to the surface of a general substrate instead of the surface of the dielectric layer, a conductive laminate can also be manufactured.

[0064] Examples of a method for applying (coating) the conductive polymer treatment liquid to any surface of a substrate include a method using a coater such as a gravure coater, roll coater, curtain flow coater, spin coater, bar coater, reverse coater, kiss coater, fountain coater, rod coater, air doctor coater, knife coater, blade coater, cast coater, or screen coater; a method using a sprayer such as an air spray, airless spray, or rotor dampening; and an immersion method such as dipping.

[0065] The amount of the conductive polymer treatment liquid to be applied to the substrate is not particularly limited, but for example, it is 0.01 to 10.0 g / m as a non-volatile component. 2 The range is preferred.

[0066] The conductive layer can be formed by drying the coating film made of the conductive polymer treatment liquid applied onto the substrate to remove at least a portion of the dispersion medium and then curing the coating film. Methods for drying the coating film include heat drying, vacuum drying, etc. Heat drying can be performed using, for example, hot air heating or infrared heating. When heat drying is applied, the heating temperature is appropriately set depending on the dispersion medium used, but is usually within the range of 50°C to 200°C. Here, the heating temperature is the temperature set in the drying device. A suitable drying time within the above heating temperature range is preferably 0.5 minutes to 30 minutes, more preferably 1 minute to 15 minutes.

[0067] <Conductive laminate> The conductive laminate obtained by the above-described manufacturing method comprises a substrate and a conductive layer formed on at least a portion of the surface of the substrate, and this conductive layer contains a cured product of the conductive polymer treatment liquid.

[0068] [Conductive layer] The conductive layer may be formed over the entire surface of the substrate or over only a portion of the surface. In a conductive film, it is preferable that a conductive layer of substantially uniform thickness is formed over substantially the entire surface of one or the other of the film substrate. When a conductive layer is formed over only a portion of the surface of the substrate, the conductive layer may be, for example, a fine conductive pattern such as a circuit or electrode, or may be simply a roughly divided area where a conductive layer is provided and an area where a conductive layer is not provided exist on the same surface.

[0069] The average thickness of the conductive layer is, for example, preferably 10 nm or more and 100 μm or less, more preferably 20 nm or more and 50 μm or less, and even more preferably 30 nm or more and 30 μm or less. When the average thickness of the conductive layer is equal to or greater than the lower limit, high conductivity can be exhibited, and when the average thickness is equal to or less than the upper limit, the adhesiveness of the conductive layer to the substrate is further improved.

[0070] [Base material] The substrate may be made of an insulating material or a conductive material. The shape of the substrate is not particularly limited, and examples thereof include a shape mainly having a flat surface, such as a film or a substrate. Examples of insulating materials include glass, synthetic resin, and ceramics. Examples of conductive materials include metals, conductive metal oxides, and carbon.

[0071] (Film substrate) When a film substrate is used as the substrate, the conductive laminate becomes a conductive film. Examples of the film substrate include plastic films made of synthetic resins, such as ethylene-methyl methacrylate copolymer resin, ethylene-vinyl acetate copolymer resin, polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyvinyl alcohol, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyacrylate, polycarbonate, polyvinylidene fluoride, polyarylate, styrene-based elastomers, polyester-based elastomers, polyethersulfone, polyetherimide, polyetheretherketone, polyphenylene sulfide, polyimide, cellulose triacetate, and cellulose acetate propionate. From the viewpoint of improving the adhesion between the film substrate and the conductive layer, the synthetic resin for the film substrate is preferably a polyester resin, and among these, polyethylene terephthalate is preferred.

[0072] The synthetic resin for the film substrate may be amorphous or crystalline. The film substrate may be unstretched or stretched. The film substrate may be subjected to a surface treatment such as corona discharge treatment, plasma treatment, or flame treatment in order to further improve the adhesion of the conductive layer.

[0073] The average thickness of the film substrate is preferably 5 μm or more and 500 μm or less, and more preferably 20 μm or more and 200 μm or less. When the average thickness of the film substrate is equal to or more than the lower limit, the film is less likely to break, and when the average thickness is equal to or less than the upper limit, the film can have sufficient flexibility. The average thickness of the film substrate is determined by measuring the thickness at 10 randomly selected locations and averaging the measured values.

[0074] (glass substrate) Examples of the glass substrate include an alkali-free glass substrate, a soda-lime glass substrate, a borosilicate glass substrate, and a quartz glass substrate. If the substrate contains an alkali component, the conductivity of the conductive layer tends to decrease. Therefore, among the glass substrates, an alkali-free glass is preferred. Here, alkali-free glass refers to a glass composition having an alkali component content of 0.1% by mass or less relative to the total mass of the glass composition.

[0075] The average thickness of the glass substrate is preferably 100 μm or more and 3000 μm or less, and more preferably 100 μm or more and 1000 μm or less. When the average thickness of the glass substrate is equal to or more than the lower limit, the glass substrate is less likely to break, and when the average thickness is equal to or less than the upper limit, the conductive laminate can be made thinner. The average thickness of the glass substrate is determined by measuring the thickness at 10 randomly selected locations and averaging the measured values. [Example]

[0076] (Production Example 1) Production of polystyrene sulfonic acid 206 g of sodium styrenesulfonate was dissolved in 1000 ml of ion-exchanged water, and while stirring at 80°C, 1.14 g of an oxidizing agent solution of ammonium persulfate, which had been dissolved in 10 ml of water in advance, was added dropwise over 20 minutes, and the solution was stirred for 12 hours. To the resulting sodium polystyrene sulfonate solution, 1000 ml of sulfuric acid diluted to 10% by mass was added, and approximately 1000 ml of the solvent from the resulting polystyrene sulfonic acid solution was removed by ultrafiltration. Next, 2000 ml of ion-exchanged water was added to the remaining solution, and approximately 2000 ml of the solvent was removed by ultrafiltration, and the polystyrene sulfonic acid was washed with water. This water washing procedure was repeated three times. Water in the resulting solution was removed under reduced pressure to obtain colorless solid polystyrene sulfonic acid (PSS).

[0077] (Production Example 2) Production of PEDOT-PSS aqueous dispersion 14.2 g of 3,4-ethylenedioxythiophene and a solution prepared by dissolving 36.7 g of polystyrene sulfonic acid in 2000 ml of ion-exchanged water were mixed at 20°C. The resulting mixed solution was kept at 20°C and, while stirring, an oxidation catalyst solution of 29.64 g of ammonium persulfate and 8.0 g of ferric sulfate dissolved in 200 ml of ion-exchanged water was slowly added, followed by stirring for 3 hours to allow the reaction to proceed. To the resulting reaction solution, 2000 ml of ion-exchanged water was added, and about 2000 ml of the solvent was removed by ultrafiltration. This procedure was repeated three times. Then, 200 ml of sulfuric acid diluted to 10% by mass and 2000 ml of ion-exchanged water were added to the obtained solution, and about 2000 ml of the solvent was removed by ultrafiltration. 2000 ml of ion-exchanged water was added to the remaining liquid, and about 2000 ml of the solution was removed by ultrafiltration. This procedure was repeated three times. 2000 ml of ion-exchanged water was added to the resulting solution, and approximately 2000 ml of solvent was removed by ultrafiltration. This procedure was repeated five times to obtain a 1.2% by weight polystyrene sulfonate-doped poly(3,4-ethylenedioxythiophene) solution (PEDOT-PSS aqueous dispersion). Further ultrafiltration yielded a 1.6% by weight PEDOT-PSS aqueous dispersion (conductive polymer dispersion).

[0078] (Production Example 3) To 100 g of the conductive polymer dispersion obtained in Production Example 2, 0.3 g of imidazole (18.8 parts by mass relative to 100 parts by mass of the conductive composite) and 5 g of diethylene glycol (312.5 parts by mass relative to 100 parts by mass of the conductive composite) were added, and the mixture was treated at 160 MPa using a high-pressure dispersion treatment machine (high-pressure homogenizer) to obtain a conductive polymer treatment liquid.

[0079] (Manufacturing Example 4) Preparation of capacitor element After connecting an anode lead terminal to the etched aluminum foil (anode foil), a voltage of 40 V was applied in a 10% by mass aqueous solution of ammonium adipate to perform chemical conversion (oxidation treatment), forming a dielectric layer on both sides of the aluminum foil to obtain an anode foil. Next, opposing aluminum cathode foils with cathode lead terminals welded thereto were laminated on both sides of the anode foil with a cellulose separator interposed therebetween, and the resultant was rolled up into a cylindrical shape to obtain a capacitor element.

[0080] (Production Example 5) Driving Electrolyte A driving electrolyte solution was obtained by mixing 55 parts by mass of γ-butyrolactone, 35 parts by mass of sulfolane, and 10 parts by mass of diammonium adipate.

[0081] Example 1 The capacitor element obtained in Production Example 4 was immersed under reduced pressure in the conductive polymer treatment solution obtained in Production Example 3, and then dried once for 30 minutes in a hot air dryer at 125°C to form a solid electrolyte layer containing a conductive composite on the surface of the dielectric layer, thereby obtaining a solid electrolytic capacitor. Next, the solid electrolytic capacitor with the solid electrolyte layer formed thereon and the driving electrolyte solution obtained in Production Example 5 were loaded into an aluminum case, and the case was sealed with a rubber seal. A voltage of 50 V was applied in an atmosphere at 120°C to obtain a capacitor. Here, the time (aging period) from when the conductive polymer treatment solution was obtained in Production Example 3 until the capacitor element was started to be immersed was set to 60 hours.

[0082] Example 2 A capacitor was obtained in the same manner as in Example 1, except that the time (aging period) from when the conductive polymer treatment solution obtained in Production Example 3 was obtained until the capacitor element was immersed in the solution was changed to one week.

[0083] Example 3 A capacitor was obtained in the same manner as in Example 1, except that the time (aging period) from when the conductive polymer treatment solution obtained in Production Example 3 was obtained until the start of immersion in the capacitor element was changed to one month.

[0084] (Comparative Example 1) A capacitor was obtained in the same manner as in Example 1, except that the time (aging period) from when the conductive polymer treatment solution obtained in Production Example 3 was obtained until the capacitor element was immersed in the solution was changed to less than 1 hour.

[0085] <Evaluation> [Capacitance / Equivalent Series Resistance] The capacitance at 120 Hz and the equivalent series resistance at 100 kHz of the solid electrolytic capacitor and capacitor fabricated in each example were measured using an LCR meter ZM2376 (NF Corporation). The equivalent series resistance of the solid electrolytic capacitor was defined as ESR(s), and the equivalent series resistance of the capacitor was defined as ESR(0). The measurement results are shown in Tables 1 and 2.

[0086] [Heat resistance test] The capacitor obtained above was placed in a hot air dryer at 145°C, and after 1000 hours, it was removed and cooled at room temperature for 30 minutes. After cooling, the capacitance (Cap.) at 120 Hz and the equivalent series resistance (ESR) at 100 kHz of the capacitor were measured using an LCR meter ZM2376 (manufactured by NF Corporation). The measurement results are shown in Table 2.

[0087] [Table 1]

[0088] [Table 2]

[0089] The capacitors manufactured in the examples according to the present invention had low ESR and high performance. These results clearly show that by forming the solid electrolyte layer after a predetermined time has elapsed since the preparation of the conductive polymer treatment solution, a capacitor with excellent conductivity and reduced ESR can be obtained. [Explanation of symbols]

[0090] 10 Capacitors 11 Anode 12 Dielectric layer 13 Cathode 14 Solid electrolyte layer

Claims

1. A method for manufacturing a capacitor comprising: an anode made of a porous valve metal body; a dielectric layer formed on a surface of the anode; a cathode made of a conductive material and provided on an opposite side of the anode; and a solid electrolyte layer covering at least a portion of a surface of the dielectric layer, a step (A) of dispersing a conductive complex containing a π-conjugated conductive polymer and a polyanion in a dispersion medium to obtain a conductive polymer dispersion; a step (B) of adding, as an additive, one or more additives selected from the group consisting of a nitrogen-containing compound different from the conductive composite, a polyol compound having two or more hydroxy groups, a surfactant, an antifoaming agent, a coupling agent, an antioxidant, and an ultraviolet absorber to the conductive polymer dispersion, thereby obtaining a dispersed conductive polymer treatment liquid; and (C) a step of applying the conductive polymer treatment solution to the surface of the dielectric layer and drying the solution to form the solid electrolyte layer, the time from the completion of the dispersion treatment in the step (B) to the application of the conductive polymer treatment liquid to the surface of the dielectric layer in the step (C) is 60 hours or more; A method for manufacturing a capacitor.

2. The method for producing a capacitor according to claim 1 , wherein a nitrogen-containing compound is added as the additive.

3. The method for producing a capacitor according to claim 1 , wherein a polyol compound having two or more hydroxy groups is added as the additive.

4. The method for producing a capacitor according to claim 1 , wherein the π-conjugated conductive polymer is a polythiophene-based conductive polymer.

5. The method for producing a capacitor according to claim 4 , wherein the polyanion is polystyrene sulfonic acid.

6. The method for producing a capacitor according to claim 1 , wherein the dispersion medium is water.

7. The method for producing a capacitor according to claim 1 , wherein in the step (B), the dispersion treatment is performed using a high-pressure homogenizer.

8. 3. The method for producing a capacitor according to claim 2, wherein the amount of the additive contained in the conductive polymer treatment solution is 5 parts by mass or more and 40 parts by mass or less with respect to 100 parts by mass of the conductive composite.

9. 4. The method for producing a capacitor according to claim 3, wherein the amount of the additive contained in the conductive polymer treatment solution is 50 parts by mass or more and 1000 parts by mass or less with respect to 100 parts by mass of the conductive composite.

Images