Method for manufacturing capacitor

Abstract

To provide a method for manufacturing a capacitor having excellent performance with respect to equivalent series resistance.SOLUTION: There is provided a method for manufacturing a capacitor, the method including the steps of: obtaining a conductive polymer dispersion liquid including a conductive composite containing a π-conjugated conductive polymer, a polyanion, and an acetylene-based surfactant, and an aqueous dispersion medium, by polymerizing a monomer forming the π-conjugated conductive polymer in a reaction solution containing the polyanion, the acetylene-based surfactant, and the aqueous dispersion medium; and forming a solid electrolyte layer by applying the conductive polymer dispersion liquid onto a surface of a dielectric layer formed on a surface of an anode composed of a porous body of a valve metal, and drying the surface.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a capacitor using a conductive polymer dispersion 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 producing a capacitor has been disclosed (e.g., Patent Document 1), in which a coating material made from a conductive polymer dispersion liquid containing a conductive complex is applied to a dielectric layer provided on the surface of an anode made of a valve metal, the coating material is dried to form a solid electrolyte layer, and a cathode is then placed opposite the solid electrolyte layer. According to this disclosure, the capacitor performance is improved by including a linear unsaturated aliphatic alcohol in 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] Conductive polymer dispersions used in capacitor manufacturing must have low viscosity so that they can penetrate the porous structure of the dielectric layer. Furthermore, capacitors with solid electrolyte layers made from cured conductive polymer dispersions must have good capacitance and low equivalent series resistance (ESR). Furthermore, because capacitors may be exposed to high-temperature environments depending on their application, it is also necessary to suppress the increase in ESR due to heating.

[0005] The present invention provides a method for manufacturing a capacitor with excellent ESR performance. [Means for solving the problem]

[0006] [1] A method for manufacturing a capacitor, comprising: a step of polymerizing a monomer that forms a π-conjugated conductive polymer in a reaction solution containing a polyanion, an acetylene-based surfactant, and an aqueous dispersion medium, to obtain a conductive polymer dispersion containing a conductive complex containing the π-conjugated conductive polymer, the polyanion, and the acetylene-based surfactant, and the aqueous dispersion medium; and a step of applying the conductive polymer dispersion to a surface of a dielectric layer formed on a surface of an anode made of a porous valve metal, and drying the applied conductive polymer dispersion to form a solid electrolyte layer. [2] The method for producing a capacitor according to [1], wherein the acetylene surfactant has one or more hydroxyl groups in the molecule. [3] The method for producing a capacitor according to [1] or [2], wherein the acetylene surfactant is an ethoxylated product in which one or more of the hydroxyl groups have reacted with ethylene oxide. [4] The method for producing a capacitor according to any one of [1] to [3], wherein the acetylene surfactant is a compound represented by the formula (2) or (3) described below. [5] The method for manufacturing a capacitor according to any one of [1] to [4], wherein the content of the acetylene-based surfactant relative to the total mass of the π-conjugated conductive polymer, the polyanion, and the acetylene-based surfactant contained in the conductive polymer dispersion liquid applied to the dielectric layer is 3% by mass or more and 30% by mass or less. [6] The method for manufacturing a capacitor according to any one of [1] to [5], wherein the content of the π-conjugated conductive polymer is 20% by mass or more and 30% by mass or less, and the content of the polyanion is 50% by mass or more and 70% by mass or less, relative to the total mass of the π-conjugated conductive polymer, the polyanion, and the acetylene surfactant contained in the conductive polymer dispersion applied to the dielectric layer. [7] The π-conjugated conductive polymer is poly(3,4-ethylenedioxythiophene), or the polyanion is polystyrene sulfonic acid, or The method for producing a capacitor according to any one of [1] to [6], wherein the π-conjugated conductive polymer is poly(3,4-ethylenedioxythiophene) and the polyanion is polystyrenesulfonic acid. [8] The method for producing a capacitor according to any one of [1] to [7], wherein the conductive polymer dispersion applied to the dielectric layer has a pH at 25°C of 2.0 to 4.0. [9] The method for producing a capacitor according to any one of [1] to [8], wherein the conductive polymer dispersion liquid applied to the dielectric layer contains imidazole.

[10] The method for producing a capacitor according to any one of [1] to [9], wherein the conductive polymer dispersion liquid applied to the dielectric layer contains diethylene glycol. [Effects of the Invention]

[0007] According to the present invention, it is possible to manufacture a capacitor that has a good capacitance, a low initial ESR, and a suppressed increase in ESR after heat treatment.

[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> The method for producing a capacitor according to the first aspect of the present invention includes step 1 of obtaining a conductive polymer dispersion liquid, and step 2 of forming a solid electrolyte layer to be provided in the capacitor.

[0012] [Process 1] In this step, a monomer that forms a π-conjugated conductive polymer is polymerized in a reaction solution containing a polyanion, an acetylene-based surfactant, and an aqueous dispersion medium, thereby obtaining a conductive polymer dispersion that contains the π-conjugated conductive polymer, a conductive complex containing the polyanion and the acetylene-based surfactant, and the aqueous dispersion medium.

[0013] <Preparation of polyanions> The polyanion used in the polymerization step of the monomer can be prepared by a conventional method, for example, by adding a polymerization initiator to a reaction solution containing a polymerizable anionic monomer and water to obtain an aqueous solution containing a polyanion formed by polymerizing the polymerizable anionic monomer.

[0014] Polymerizable anionic monomers are organic compounds that form polyanions upon polymerization and contain at least one anionic group per molecule. The anionic group is a functional group that can be ionized in water and may form a salt with a cation such as sodium or potassium. The polymerizable anionic monomer used in this step is preferably one or more selected from known monomers capable of forming polyanions, which will be described in detail later. Among them, styrenesulfonic acid or a salt thereof is most preferred, as it can form polystyrenesulfonic acid, which is particularly excellent as a dopant for π-conjugated conductive polymers. It should be noted that acetylene surfactants do not fall under the category of polymerizable anionic monomers.

[0015] The amount of the polymerizable anionic monomer to be mixed relative to the total mass of the reaction solution for synthesizing the polyanion is, for example, preferably 1.0 to 25.0 mass %, more preferably 10.0 to 20.0 mass %, and even more preferably 12.0 to 18.0 mass %.

[0016] Examples of the polymerization initiator include persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate. The amount of the polymerization initiator to be added relative to the total mass of the reaction liquid is, for example, 0.01 to 0.50% by mass.

[0017] The weight-average molecular weight Mw of the polyanion formed can be adjusted by adjusting the amount of polymerization initiator in the reaction solution. Generally, a high concentration of the polymerization initiator tends to decrease Mw, while a low concentration of the polymerization initiator tends to increase Mw. The weight average molecular weight Mw of the polyanion used in this step is, for example, preferably from 10,000 to 800,000, more preferably from 50,000 to 500,000, and even more preferably from 100,000 to 300,000. When the weight average molecular weight Mw of the polyanion is within the above range, a capacitor with better ESR performance can be easily produced. The weight average molecular weight Mw of the polyanion is measured using gel filtration chromatography and is the average molecular weight on a mass basis calculated in terms of pullulan with known Mw.

[0018] The completion of the polymerization reaction of the polyanion in the reaction solution is determined when all of the polymerization initiator added to the reaction solution has been consumed. For example, when the reaction is carried out at 70 to 95°C with stirring, the reaction may be completed in about 4 to 12 hours.

[0019] When the anion groups of the polyanion obtained above form salts with counter cations, it is preferable to remove the cations by contacting the polyanion with a cation exchange resin.

[0020] <Preparation of polymerization reaction solution> A conductive composite in which the formed π-conjugated conductive polymer is doped with the polyanion is obtained by polymerizing the monomer in a reaction solution containing a polyanion, an acetylene-based surfactant, a monomer that forms a π-conjugated conductive polymer, and an aqueous dispersion medium. At this time, at least a portion of the acetylene-based surfactant in the reaction solution is contained in the conductive composite. The type of intermolecular interaction between the acetylene surfactant and the conductive composite is not particularly limited, but is thought to be mainly a hydrophobic interaction.

[0021] (Polyanion formulation) The amount of polyanion to be blended relative to the total mass of the reaction solution is preferably 0.1% by mass to 2.5% 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. Within this range, a conductive composite suitable for producing a capacitor with excellent ESR performance is likely to be obtained.

[0022] The amount of polyanion blended in the reaction solution relative to the total mass of the π-conjugated conductive polymer monomer, polyanion, and acetylene surfactant is preferably 50% by mass or more and 80% by mass or less, more preferably 55% by mass or more and 75% by mass or less, and even more preferably 60% by mass or more and 70% by mass or less. Within this range, a conductive composite suitable for producing a capacitor with excellent ESR performance is likely to be obtained.

[0023] The ratio of the π-conjugated conductive polymer monomer to the polyanion blended in the reaction solution is, for example, preferably 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 π-conjugated conductive polymer monomer. If the blending ratio of the 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, if the blending ratio of the polyanion is equal to or less than the upper limit, the content of the π-conjugated conductive polymer is sufficient, ensuring sufficient conductivity.

[0024] (Contains acetylene surfactant) An acetylene surfactant is an organic compound having one carbon-carbon triple bond in the molecule. To enhance its function as a surfactant, it preferably has one or more branched alkyl groups in the molecule. To enhance its function as a surfactant, it preferably has one or more hydroxyl groups in the molecule. Furthermore, it is preferable that the surfactant be an ethoxylated product (EO adduct) in which ethylene oxide reacts with the hydroxyl group, as this reduces the viscosity of the conductive polymer dispersion and makes it easier to obtain a capacitor with excellent ESR performance.

[0025] The acetylene surfactant is preferably a compound represented by formula (2) or formula (3).

[0026] [ka]

[0027] In formula (2), R 3 , R 4 , R 5 , R 6 each independently represents an alkyl group having 1 to 5 carbon atoms. R 3 and R 6 are each independently preferably a branched alkyl group, and more preferably have a branched chain in which a methyl group or an ethyl group is bonded to the second alkylene group from the end. R 4 and R 5 are each independently preferably a linear alkyl group, more preferably a methyl group or an ethyl group. In formula (2), l and m are each independently an integer of 0 to 25, and l+m is 0 to 40. When it is 0, it is a hydroxyl group, and when it is other than 0, it is an ethoxylated product formed by the reaction of a hydroxyl group with ethylene oxide. l and m are not particularly limited and may, for example, each independently be any of 1 to 20, 3 to 15, or 5 to 10. l+m is not particularly limited and may, for example, be any of 1 to 30, 3 to 20, or 5 to 10.

[0028] In formula (3), R 7 , R 8 each independently represents an alkyl group having 1 to 5 carbon atoms. R 7 is preferably a branched alkyl group, and more preferably has a branched chain in which a methyl group or an ethyl group is bonded to the second alkylene group from the end. R 8 is preferably a linear alkyl group, more preferably a methyl group or an ethyl group. In formula (3), n is an integer of 0 to 25. When it is 0, it is a hydroxyl group, and when it is other than 0, it is an ethoxylated product formed by the reaction of a hydroxyl group with ethylene oxide. n is not particularly limited and may be, for example, any of 1 to 20, 3 to 15, and 5 to 10.

[0029] Specific examples of the acetylene surfactant include 2,4,7,9-tetramethyl-5-decyne-4,7-diol and its ethoxylated derivatives, 3,5-dimethyl-1-hexyn-3-ol and its ethoxylated derivatives, and 3,6-dimethyl-4-octyne-3,6-diol and its ethoxylated derivatives. Commercially available products of these acetylene surfactants can be used.

[0030] The type of acetylene surfactant to be added to the reaction liquid may be one type or two or more types. The amount of the acetylene surfactant blended relative to the total mass of the reaction solution is preferably 0.01% by mass to 1.00% by mass, more preferably 0.05% by mass to 0.80% by mass, and even more preferably 0.10% by mass to 0.50% by mass. Within this range, a conductive composite suitable for producing a capacitor with excellent ESR performance is likely to be obtained.

[0031] The content of the acetylene surfactant relative to the total mass of the π-conjugated conductive polymer, the polyanion, and the acetylene surfactant blended in the reaction solution is preferably 3.0 to 30.0 mass%, more preferably 10.0 to 30.0 mass%, even more preferably 15.0 to 30.0 mass%, and most preferably 18.0 to 30.0 mass%. Within this range, a conductive composite suitable for producing a capacitor with excellent ESR performance is likely to be obtained.

[0032] (Polymerization of π-conjugated conductive polymers) The monomer of the π-conjugated conductive polymer can be polymerized by adding any radical polymerization initiator and catalyst to a reaction solution. The polymerization can be carried out by a known method except that the π-conjugated conductive polymer is formed in the presence of a polyanion and an acetylene surfactant.

[0033] The polymerizable monomer for forming the π-conjugated conductive polymer is preferably one or more selected from known monomers capable of forming π-conjugated conductive polymers, which will be described in detail later. Among them, 3,4-ethylenedioxythiophene is most preferred, as it can form PEDOT, which has excellent conductivity and heat resistance.

[0034] The amount of the monomer relative to the total mass of the reaction solution is preferably 0.10% by mass to 1.50% by mass, more preferably 0.20% by mass to 1.00% by mass, and even more preferably 0.30% by mass to 0.70% by mass. Within this range, a conductive composite suitable for producing a capacitor with excellent ESR performance is likely to be obtained.

[0035] The amount of the monomer blended in the reaction solution relative to the total mass of the π-conjugated conductive polymer monomer, polyanion, and acetylene surfactant is preferably 10.0 mass% to 45.0 mass%, more preferably 20.0 mass% to 35.0 mass%, and even more preferably 25.0 mass% to 30.0 mass%. Within this range, a conductive composite suitable for producing a capacitor with excellent ESR performance is likely to be obtained.

[0036] Examples of the radical polymerization initiator include persulfates such as ammonium persulfate, sodium persulfate, potassium persulfate, etc. It is preferable to add a catalyst such as a transition metal compound such as ferric chloride, ferric sulfate, ferric nitrate, or cupric chloride to the reaction liquid together with the radical polymerization initiator.

[0037] The amount of the radical polymerization initiator to be added relative to the total mass of the reaction solution during the polymerization reaction is, for example, 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.

[0038] (aqueous dispersion medium) The dispersion medium constituting the reaction solution is preferably an aqueous dispersion medium containing water because the conductive composite is hydrophilic. The aqueous dispersion medium may contain a dispersion medium other than water. The dispersion medium other than water is not particularly limited as long as it does not significantly 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. Examples of the water-soluble organic solvent include those described below.

[0039] The water content relative to the total mass of the dispersion medium excluding the solids (non-volatile components) incorporated into the reaction liquid is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 100% by mass. When the water content is equal to or greater than the lower limit, the dispersibility of the conductive composite formed by the polymerization reaction is increased, improving the coatability. Furthermore, the ESR performance of a capacitor having a solid electrolyte layer formed from the conductive polymer dispersion can be further improved.

[0040] <Polymerization reaction> The temperature of the polymerization reaction in the reaction solution can be, for example, 20 to 30°C. At this 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 using gas chromatography or the like. After the polymerization reaction, the reaction solution containing the conductive complex is obtained as a conductive polymer dispersion.

[0041] It is preferable to remove residues of the catalyst and radical polymerization initiator added to the reaction liquid from the conductive polymer dispersion after the polymerization reaction. 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 radical polymerization initiator onto the ion exchange resin, and a method of ultrafiltrating the conductive polymer dispersion to replace the dispersion medium and remove the catalyst and radical polymerization initiator. Of these, the method using an ion exchange resin is preferred because it is simple. The ion exchange resin preferably uses a cation exchange resin and an anion exchange resin in combination.

[0042] The obtained conductive polymer dispersion may be subjected to a dispersion treatment by a conventional method such as using a high-pressure homogenizer.

[0043] An acetylene surfactant, a polyol compound, a nitrogen-containing aromatic compound, any additives, etc. may be further added to the conductive polymer dispersion liquid obtained above.

[0044] <Conductive polymer dispersion> The conductive polymer dispersion obtained in step 1 contains a conductive complex containing a π-conjugated conductive polymer, a polyanion, and an acetylene-based surfactant, and an aqueous dispersion medium.

[0045] (Conductive composite) The polyanion in the conductive composite of this embodiment dopes the π-conjugated conductive polymer, contributing to improved conductivity. In the polyanion, only a portion of the anionic groups dopes the π-conjugated conductive polymer, leaving excess anionic groups that are not involved in the doping. Because the excess anionic groups are hydrophilic groups, the conductive composite has water dispersibility. When the number of all anionic groups in the polyanion is taken as 100 mol %, the excess anionic groups are preferably 30 mol % or more and 90 mol % or less, and more preferably 45 mol % or more and 75 mol % or less.

[0046] (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 viewpoint of transparency, polythiophene-based conductive polymers are more preferred.

[0047] 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, poly(3,4-ethylenedioxythiophene) is particularly preferred because of its excellent conductivity, transparency, and heat resistance. The conductive composite may contain one type of π-conjugated conductive polymer, or two or more types of polymers.

[0048] (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.

[0049] The content of the polyanion contained in the conductive complex in the conductive polymer dispersion applied to the dielectric layer in step 2 is, for example, 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, relative to 100 parts by mass of the π-conjugated conductive polymer. If the content of the 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, if the content of the polyanion is equal to or less than the upper limit, the content of the π-conjugated conductive polymer is sufficient, ensuring sufficient conductivity and allowing the production of a capacitor with higher ESR performance.

[0050] The total content of the π-conjugated conductive polymer and polyanion relative to the total mass of the conductive polymer dispersion applied to the dielectric layer in step 2 is preferably 0.1% by mass to 5.0% by mass, more preferably 0.5% by mass to 2.5% by mass, and even more preferably 0.8% by mass to 2.0% by mass. Within these preferred ranges, the dispersibility of the conductive composite is improved, improving coatability. Furthermore, the ESR performance of a capacitor having a solid electrolyte layer formed from the conductive polymer dispersion can be further improved.

[0051] It is preferable that the content of the π-conjugated conductive polymer is 20% by mass or more and 30% by mass or less, and the content of the polyanion is 50% by mass or more and 70% by mass or less, relative to the total mass of the π-conjugated conductive polymer, polyanion, and acetylene surfactant contained in the conductive polymer dispersion applied to the dielectric layer in step 2. Within these ranges, the ESR performance of the capacitor can be further improved.

[0052] The content of the acetylene surfactant is preferably 3.0% by mass or more and 30.0% by mass or less, more preferably 6.0% by mass or more and 25.0% by mass or less, and even more preferably 9.0% by mass or more and 20.0% by mass or less, relative to the total mass of the π-conjugated conductive polymer, polyanion, and acetylene surfactant contained in the conductive polymer dispersion liquid applied to the dielectric layer in step 2. Within the above range, the ESR performance of the capacitor can be further improved.

[0053] The content of the acetylene surfactant relative to the total mass of the conductive polymer dispersion applied to the dielectric layer in step 2 is preferably 0.01% by mass to 1.00% by mass, more preferably 0.05% by mass to 0.80% by mass, and even more preferably 0.10% by mass to 0.50% by mass. Within this range, the ESR performance of the capacitor can be further improved.

[0054] (aqueous dispersion medium) The dispersion medium contained in the conductive polymer dispersion is an aqueous dispersion medium containing water because the conductive composite is hydrophilic. The aqueous dispersion medium may contain one or more water-soluble organic solvents as long as the dispersion of the conductive composite is not hindered.

[0055] Examples of alcohol-based solvents include methanol, ethanol, 1-propanol, 2-propanol (isopropanol), 2-methyl-2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, allyl alcohol, ethylene glycol, propylene glycol, propylene glycol monomethyl ether, and ethylene glycol monomethyl ether. Examples of the ether solvent include diethyl ether, dimethyl ether, propylene glycol dialkyl ether, and diethylene glycol diethyl ether. Examples of ketone solvents include diethyl ketone, methyl propyl ketone, methyl butyl ketone, methyl isopropyl ketone, methyl isobutyl ketone, methyl amyl ketone, diisopropyl ketone, methyl ethyl ketone, acetone, and diacetone alcohol. Examples of nitrogen atom-containing solvents include N-methylpyrrolidone, dimethylacetamide, and dimethylformamide. As the water-soluble organic solvent, an alcohol-based solvent or a ketone-based solvent is preferred, and an alcohol-based solvent is more preferred, since this improves the wettability of the conductive polymer dispersion liquid with respect to the substrate.

[0056] The water content relative to the total mass of the dispersion medium excluding the solid content (non-volatile components) of the conductive polymer dispersion applied to the dielectric layer in step 2 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 the water content is equal to or greater than the lower limit, the dispersibility of the conductive complex contained in the conductive polymer dispersion is increased, improving coatability. In addition, the ESR performance of a capacitor having a solid electrolyte layer formed from the conductive polymer dispersion can be further improved.

[0057] The viscosity at 25°C of the conductive polymer dispersion obtained in step 1, when the concentration of the conductive complex relative to the total mass of the conductive polymer dispersion is adjusted to 1.6 mass%, is preferably 30 mPa s or less, more preferably 25 mPa s or less, even more preferably 20 mPa s or less, particularly preferably 15 mPa s or less, and most preferably 13 mPa s or less. There is no particular restriction on the lower limit of the viscosity, and a guideline is 1 mPa s or more. When measuring the viscosity, the dispersion medium contained in the conductive polymer dispersion is preferably ion-exchanged water alone. Furthermore, the conductive polymer dispersion for which the viscosity is measured contains an acetylene-based surfactant, but preferably does not contain any other additives. The viscosity is measured at 25°C using a tuning fork vibration viscometer in accordance with JIS Z8803:2011 (viscosity measurement method using a vibration viscometer).

[0058] (Polyol compound) The conductive polymer dispersion applied to the dielectric layer in step 2 may contain one or more polyol compounds. Here, the polyol compound refers to a compound having two or more hydroxy groups and different from the π-conjugated conductive polymer, the polyanion, and the acetylene surfactant. By including a polyol compound, the ESR of a capacitor having a solid electrolyte layer formed from the conductive polymer dispersion can be further reduced.

[0059] Examples of the polyol compound include one or more selected from ethylene glycol, diethylene glycol, propylene glycol, 1,4-butanediol, glycerin, pentaerythritol, trimethylolpropane, trimethylolethane, and polyethylene glycol.

[0060] The content of the polyol compound in the conductive polymer dispersion is, for example, preferably 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 the π-conjugated conductive polymer, polyanion, and acetylene surfactant. Within the above preferred range, the coatability of the conductive polymer dispersion is improved, and the ESR performance of the capacitor can be further improved.

[0061] The content of the polyol compound relative to the total mass of the conductive polymer dispersion is preferably from 1 to 20% by mass, more preferably from 1 to 15% by mass, and even more preferably from 1 to 10% by mass. Within this preferred range, the ESR performance of the capacitor can be further improved while suppressing an increase in the viscosity of the conductive polymer dispersion.

[0062] (Nitrogen-containing aromatic compounds) The conductive polymer dispersion applied to the dielectric layer in step 2 may contain one or more nitrogen-containing aromatic compounds. Here, the nitrogen-containing aromatic compound refers to an aromatic compound in which at least one nitrogen atom forms a ring structure. By including a nitrogen-containing aromatic compound, the ESR of a capacitor having a solid electrolyte layer formed from the conductive polymer dispersion can be further reduced.

[0063] Examples of nitrogen-containing aromatic compounds 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, 1-cyanoethyl-2-ethyl-4-methylimidazole, 2-phenyl-4, Examples of such derivatives include 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 derivatives (e.g., those substituted with an alkyl group having 1 to 4 carbon atoms, such as methyl, ethyl, propyl, or butyl), halogen-substituted derivatives (e.g., those substituted with a halogen group, such as fluoro, chloro, or bromine), and nitrile-substituted derivatives. Of these, imidazole is more preferred.

[0064] The content of the nitrogen-containing aromatic compound in the conductive polymer dispersion is, for example, preferably 1 part by mass to 100 parts by mass, more preferably 10 parts by mass to 50 parts by mass, and even more preferably 15 parts by mass to 30 parts by mass, relative to 100 parts by mass of the total of the π-conjugated conductive polymer and polyanion. Within the above preferred range, the ESR performance of the capacitor can be further improved.

[0065] The content of the nitrogen-containing aromatic compound relative to the total mass of the conductive polymer dispersion is preferably 0.01% by mass or more and 1.0% by mass or less, more preferably 0.10% by mass or more and 0.60% by mass or less, and even more preferably 0.15% by mass or more and 0.40% by mass or less. Within these preferred ranges, the ESR of the capacitor can be further reduced.

[0066] (Optional additives) The conductive polymer dispersion applied to the dielectric layer in step 2 may contain any additive other than those described above, provided that the gist of the present invention is not impaired. The content ratio is determined appropriately depending on the type of additive, but can be, for example, 1 to 1,000 parts by mass per 100 parts by mass of the total of the π-conjugated conductive polymer and polyanion. Here, the optional additive is a compound other than the acetylene surfactant, the polyol compound, and the dispersion medium.

[0067] Examples of optional additives include other surfactants, inorganic conductive agents, antifoaming agents, coupling agents, antioxidants, and ultraviolet absorbers. Other surfactants include nonionic, anionic, and cationic surfactants, 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.

[0068] [Process 2] In this step, a solid electrolyte layer to be provided in the capacitor is formed. The conductive polymer dispersion obtained in step 1 can be applied to the surface of the dielectric layer formed on the surface of the anode made of a porous valve metal, and then dried to form a solid electrolyte layer.

[0069] A method for manufacturing a capacitor 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), arranging 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.

[0070] [Dielectric formation process] 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.

[0071] [Cathode formation process] 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 in which the cathode 13 is formed using a conductive paste such as a carbon paste or a silver paste, and a method in which a metal foil such as an aluminum foil is disposed opposite the dielectric layer 12.

[0072] [Film forming process] The conductive polymer dispersion liquid described above 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 .

[0073] Examples of methods that can be used to apply the conductive polymer dispersion include immersion (dip coating), comma coating, reverse coating, lip coating, and microgravure coating. Of these, a method in which the anode 11 is immersed in the conductive polymer dispersion under reduced pressure is preferred. The immersion method allows the conductive polymer dispersion to be applied thoroughly, 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 next drying process.

[0074] 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.

[0075] <Capacitor> A preferred example of a capacitor produced by the present invention 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, wherein the solid electrolyte layer contains a cured product of the conductive polymer dispersion obtained in step 1.

[0076] 1, which is an example of an embodiment of a capacitor, 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 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 of the anode 11, with the dielectric layer 12 and the solid electrolyte layer 14 sandwiched therebetween.

[0077] 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.

[0078] Dielectric layer 12 is a layer formed by oxidizing the surface of anode 11, for example, by anodizing the surface of metal anode 11 in an electrolyte such as an aqueous solution of ammonium adipate. Similar to anode 11, dielectric layer 12 also has irregularities formed thereon.

[0079] The cathode 13 may be a conductive layer formed from a conductive paste or a metal layer made of a conductive material such as aluminum foil.

[0080] 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 or may not be constant, and may be, for example, 1 μm or more and 100 μm or less.

[0081] [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;

[0082] 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 in which a separator is 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. [Example]

[0083] (Production Example 1) Production of polystyrene sulfonic acid 1 206 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 obtained solution was removed under reduced pressure to obtain colorless solid polystyrene sulfonic acid (PSS). 10 g of this polystyrene sulfonic acid was dissolved in 90 g of ion-exchanged water to obtain a 10 mass % aqueous polystyrene sulfonic acid solution.

[0084] The weight-average molecular weight (Mw) of the polystyrene sulfonic acid aqueous solution obtained above was measured by gel permeation chromatography (GPC) using pullulan of known weight-average molecular weight as the standard substance, and the weight-average molecular weight was found to be 200,000.

[0085] The weight-average molecular weight was measured using a Prominence high-performance liquid chromatograph manufactured by Shimadzu Corporation, using 0.1% aqueous NaNO3 solution as the solvent, a Shodex OHpack SB-806M HQ column, and a RID-20A detector. The solvent temperature was set to 40°C, the flow rate was set to 0.6 ml / min, the PSS concentration in the sample was set to 0.1% by mass, and 100 μl of the sample filtered through a membrane filter with a pore size of 0.2 μm was injected, and the measurement was performed using the Lab Solutions analysis software (Shimadzu Corporation).

[0086] (Production Example 2) Production of polystyrene sulfonic acid 2 206 g of sodium styrenesulfonate was dissolved in 1000 ml of ion-exchanged water, and while stirring at 80°C, 0.38 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. Next, 10 g of the obtained polystyrene sulfonic acid was dissolved in 90 g of ion-exchanged water to obtain a 10 mass % aqueous polystyrene sulfonic acid solution. The weight average molecular weight of the polystyrene sulfonic acid (PSS) obtained above, measured by GPC in the same manner as in Production Example 1, was 540,000.

[0087] (Manufacturing Example 3) 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.

[0088] Example 1: Preparation of conductive polymer dispersion 5.7 g of 3,4-ethylenedioxythiophene (EDOT), 130.7 g of the polystyrene sulfonic acid (10% by mass aqueous solution) of Production Example 1, 1.4 g of an ethoxylated acetylene surfactant 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 4), and 786.2 g of ion-exchanged water were mixed at 25°C. The resulting mixed solution was kept at 25°C and 19.2 g of a 6% aqueous solution of ferric sulfate was added while stirring. Next, 56.8 g of an 11% aqueous solution of sodium persulfate was added, and the resulting reaction solution was stirred for 8 hours to react. By the above reaction, a conductive polymer dispersion liquid was obtained containing poly(3,4-ethylenedioxythiophene), which is a π-conjugated conductive polymer, a conductive composite (PEDOT-PSS) containing polystyrene sulfonic acid, the acetylene-based surfactant, and water, which is a dispersion medium.

[0089] When the obtained conductive polymer dispersion was analyzed by GPC, the amount of unpolymerized EDOT was below the detection limit.

[0090] To this conductive polymer dispersion, 132 g of Duolite C255LFH (a cation exchange resin manufactured by Sumika Chemtex Corporation) and 132 g of Duolite A368MS (an anion exchange resin manufactured by Sumika Chemtex Corporation) were added, and the mixture was filtered to remove the ion exchange resin, yielding 850 g of a conductive polymer dispersion from which the oxidizing agent and the catalyst had been removed, and the solid content (non-volatile components) was measured. Next, water was removed from the resulting conductive polymer dispersion under reduced pressure using an evaporator to reduce the solid content to 1.6% by mass, consisting of 28.2 parts by mass of PEDOT, 64.9 parts by mass of PSS, and 6.9 parts by mass of the acetylene surfactant. To 100 g of the obtained conductive polymer dispersion, imidazole was added to adjust the pH to 2.5, and 8 g of diethylene glycol was added.

[0091] The capacitor element obtained in Production Example 3 was immersed in the above conductive polymer dispersion under reduced pressure, and then dried 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. Next, the capacitor element having the solid electrolyte layer formed thereon was loaded into an aluminum case and sealed with a sealing rubber to prepare a capacitor.

[0092] Example 2 A capacitor was produced in the same manner as in Example 1, except that the amount of ethoxylated 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 4) was 2.8 g and the amount of water was 784.8 g. The solid content of the conductive polymer dispersion liquid prepared in this example was broken down as follows: 26.4 parts by mass of PEDOT, 60.6 parts by mass of PSS, and 13.0 parts by mass of the acetylene surfactant.

[0093] Example 3 A capacitor was produced in the same manner as in Example 1, except that the amount of ethoxylated 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 4) was 4.2 g and the amount of water was 783.4 g. The solid content of the conductive polymer dispersion liquid prepared in this example was broken down as follows: 24.8 parts by mass of PEDOT, 57.0 parts by mass of PSS, and 18.2 parts by mass of the acetylene surfactant.

[0094] Example 4 A capacitor was prepared in the same manner as in Example 1, except that the ethoxylated 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 4) in Example 1 was replaced with the ethoxylated 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 2).

[0095] Example 5 A capacitor was prepared in the same manner as in Example 1, except that the ethoxylated 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 4) in Example 1 was replaced with an ethoxylated 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 10).

[0096] Example 6 A capacitor was prepared in the same manner as in Example 1, except that the ethoxylated 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 4) in Example 1 was replaced with an ethoxylated 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 22).

[0097] Example 7 A capacitor was produced in the same manner as in Example 1, except that the ethoxylated product of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 4) was replaced with 3,5-dimethyl-1-hexyn-3-ol.

[0098] Example 8 A capacitor was produced in the same manner as in Example 1, except that the ethoxylated product of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 4) was replaced with 3,6-dimethyl-4-octyne-3,6-diol.

[0099] Example 9 A capacitor was fabricated in the same manner as in Example 1, except that the polystyrene sulfonic acid (10 mass % aqueous solution) in Production Example 1 was changed from 130.7 g to 91.3 g, and the water was changed to 813.0 g. The solid content of the conductive polymer dispersion liquid prepared in this example was broken down as follows: 35.1 parts by mass of PEDOT, 56.3 parts by mass of PSS, and 8.6 parts by mass of the acetylene surfactant.

[0100] Example 10 A capacitor was fabricated in the same manner as in Example 1, except that 130.7 g of polystyrene sulfonic acid (10% by mass aqueous solution, Mw: 200,000) of Production Example 1 was replaced with 130.7 g of polystyrene sulfonic acid (10% by mass aqueous solution, Mw: 540,000) of Production Example 2.

[0101] (Comparative Example 1) A capacitor was produced in the same manner as in Example 1, except that the ethoxylated 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 4) was not added.

[0102] (Comparative Example 2) A capacitor was produced in the same manner as in Example 9, except that the ethoxylated 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 4) was not added.

[0103] (Comparative Example 3) A capacitor was produced in the same manner as in Example 10, except that the ethoxylated 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 4) was not added.

[0104] Comparative Example 4 The same study as in Example 1 was carried out except that polystyrene sulfonic acid was not added, but particles precipitated and a conductive polymer dispersion liquid could not be obtained, so the study was discontinued.

[0105] (Comparative Example 5) 5.7 g of 3,4-ethylenedioxythiophene (EDOT), 130.7 g of polystyrene sulfonic acid (10% by mass aqueous solution) of Production Example 1, and 786.2 g of ion-exchanged water were mixed at 25°C. The resulting mixed solution was kept at 25°C and 19.2 g of a 6% aqueous solution of ferric sulfate was added while stirring. Next, 56.8 g of an 11% aqueous solution of sodium persulfate was added, and the resulting reaction solution was stirred for 8 hours to react. Through the above reaction, a conductive polymer dispersion was obtained containing poly(3,4-ethylenedioxythiophene), a π-conjugated conductive polymer, a conductive complex (PEDOT-PSS) containing polystyrene sulfonic acid, and water as a dispersion medium. When the obtained conductive polymer dispersion was analyzed by GPC, the amount of unpolymerized EDOT was below the detection limit. To this conductive polymer dispersion, 132 g of Duolite C255LFH (a cation exchange resin manufactured by Sumika Chemtex Corporation) and 132 g of Duolite A368MS (an anion exchange resin manufactured by Sumika Chemtex Corporation) were added, and 1.4 g of an ethoxylated acetylene surfactant 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 4) was added. The mixture was filtered to remove the ion exchange resin, yielding 850 g of a conductive polymer dispersion from which the oxidant and catalyst had been removed, and the solid content (non-volatile components) was measured. Next, water was distilled off under reduced pressure from the obtained conductive polymer dispersion using an evaporator to make the solid content 1.6 mass %. The breakdown of this solid content was the same as in Example 1. Imidazole was added to the obtained conductive polymer dispersion to adjust the pH to 2.5, and 8 g of diethylene glycol was added thereto.

[0106] (Comparative Example 6) A capacitor was prepared in the same manner as in Comparative Example 5, except that the ethoxylated 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 4) in Comparative Example 5 was replaced with the ethoxylated 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 2).

[0107] (Comparative Example 7) A capacitor was prepared in the same manner as in Comparative Example 5, except that the ethoxylated 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 4) in Comparative Example 5 was replaced with the ethoxylated 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 10).

[0108] (Comparative Example 8) A capacitor was prepared in the same manner as in Comparative Example 5, except that the ethoxylated 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 4) in Comparative Example 5 was replaced with the ethoxylated 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 22).

[0109] (Comparative Example 9) A capacitor was produced in the same manner as in Comparative Example 5, except that the ethoxylated product of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 4) was replaced with 3,5-dimethyl-1-hexyn-3-ol.

[0110] (Comparative Example 10) A capacitor was prepared in the same manner as in Comparative Example 5, except that the ethoxylated product of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 4) was replaced with 3,6-dimethyl-4-octyne-3,6-diol.

[0111] [pH measurement] The pH was measured at 25°C by a conventional method using a commercially available pH meter.

[0112] [Viscosity measurement method] A conductive polymer dispersion liquid prepared to a solids content of 1.6% by mass was obtained as described in Example 1, and this was dispersed using a high-pressure homogenizer. The viscosity of the sample was measured at 25°C using a tuning-fork vibration viscometer (model number: SV-10, manufactured by A&D Corporation) in accordance with JIS Z8803:2011 (Viscosity measurement method using a vibration viscometer). 1 Pa·s (pascal second) was converted to 1000 cP (centipoise).

[0113] <Evaluation> [Capacitance / Equivalent Series Resistance] For each capacitor, the capacitance (unit: μF) at 120 Hz and the equivalent series resistance (ESR) (unit: mΩ) at 100 kHz were measured using an LCR meter ZM2376 (NF Corporation). After measuring the initial ESR, the capacitor was subjected to a heat treatment in which it was left in a thermostatic chamber at 145°C for 300 hours, and then the ESR was measured again. The measurement results are shown in Tables 1 and 2.

[0114] [Table 1]

[0115] [Table 2]

[0116] From the above, in the examples of the present invention, the presence of an acetylene surfactant during the formation of a PEDOT-PSS composite by EDOT polymerization sufficiently reduced the viscosity of the conductive polymer dispersion, resulting in a reduction in the initial ESR of the capacitor and suppressing the increase in ESR after heat treatment. Furthermore, Example 1, which used an ethoxylated acetylene surfactant, had a better ESR rating than Examples 7 and 8, which used non-ethoxylated surfactants.

[0117] Furthermore, Example 1, in which the PEDOT-PSS complex was formed in the presence of an acetylene-based surfactant, had a lower viscosity of the conductive polymer dispersion and a better ESR evaluation than Comparative Examples 5 to 10, in which the acetylene-based surfactant was added after the PEDOT-PSS complex was formed. [Explanation of symbols]

[0118] 10 Capacitors 11 Anode 12 Dielectric layer 13 Cathode 14 Solid electrolyte layer

Claims

1. A monomer that forms a π-conjugated conductive polymer is polymerized in a reaction solution containing a polyanion, an acetylene-based surfactant, and an aqueous dispersion medium, obtaining a conductive polymer dispersion liquid containing a conductive complex containing the π-conjugated conductive polymer, the polyanion, and the acetylene-based surfactant, and the aqueous dispersion medium; a step of applying the conductive polymer dispersion onto a surface of a dielectric layer formed on a surface of an anode made of a porous valve metal body, and drying the applied conductive polymer dispersion to form a solid electrolyte layer; A method for manufacturing a capacitor comprising the steps of:

2. 2. The method for producing a capacitor according to claim 1, wherein the acetylene surfactant has one or more hydroxyl groups in the molecule.

3. The method for manufacturing a capacitor according to claim 2 , wherein the acetylene surfactant is an ethoxylated product in which one or more of the hydroxyl groups have reacted with ethylene oxide.

4. 2. The method for manufacturing a capacitor according to claim 1, wherein the acetylene-based surfactant is a compound represented by formula (2) or formula (3). 【Chemical 1】 [In formula (2), R ３ , R ４ , R ５ , R ６ each independently represents an alkyl group having 1 to 5 carbon atoms, l and m each independently represents an integer of 0 to 25, and l+m is 0 to 40. ７ , R ８ each independently represents an alkyl group having 1 to 5 carbon atoms, and n is an integer of 0 to 25.

5. 5. The method for manufacturing a capacitor according to claim 4, wherein a content of the acetylene-based surfactant relative to a total mass of the π-conjugated conductive polymer, the polyanion, and the acetylene-based surfactant contained in the conductive polymer dispersion applied to the dielectric layer is 3 mass% or more and 30 mass% or less.

6. 6. The method for manufacturing a capacitor according to claim 5, wherein a content of the π-conjugated conductive polymer is 20% by mass or more and 30% by mass or less, and a content of the polyanion is 50% by mass or more and 70% by mass or less, relative to a total mass of the π-conjugated conductive polymer, the polyanion, and the acetylene surfactant contained in the conductive polymer dispersion applied to the dielectric layer.

7. The π-conjugated conductive polymer is poly(3,4-ethylenedioxythiophene), or the polyanion is polystyrene sulfonic acid, or 7. The method for producing a capacitor according to claim 6, wherein the π-conjugated conductive polymer is poly(3,4-ethylenedioxythiophene) and the polyanion is polystyrene sulfonic acid.

8. 8. The method for producing a capacitor according to claim 7, wherein the pH of the conductive polymer dispersion applied to the dielectric layer at 25° C. is 2.0 to 4.

0.

9. The method for producing a capacitor according to claim 8 , wherein the conductive polymer dispersion liquid applied to the dielectric layer contains imidazole.

10. The method for manufacturing a capacitor according to claim 9 , wherein the conductive polymer dispersion liquid applied to the dielectric layer contains diethylene glycol.

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