Method for producing conductive polymer dispersion and method for producing capacitor

Abstract

To provide a method for producing a conductive polymer dispersion suitable for production of a capacitor excellent in performance regarding equivalent series resistance.SOLUTION: A polymerization step of polymerizing a monomer for forming a π - conjugated conductive polymer in a reaction liquid containing a polyanion and water to form a conductive composite containing the π - conjugated conductive polymer and the polyanion, thereby obtaining a conductive polymer dispersion liquid containing the conductive composite and the water, wherein in the polymerization step, the monomer is polymerized so that a total concentration of the π - conjugated conductive polymer and the polyanion with respect to a total mass of the reaction liquid is 1.90 mass% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a conductive polymer dispersion containing a π-conjugated conductive polymer and a polyanion, and a method for producing a capacitor. [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 producing a capacitor having excellent performance in terms of equivalent series resistance, and a method for producing a conductive polymer dispersion suitable for producing the capacitor. [Means for solving the problem]

[0006] [1] A method for producing a conductive polymer dispersion, comprising a polymerization step of polymerizing a monomer that forms a π-conjugated conductive polymer in a reaction solution containing a polyanion and water to form a conductive complex containing the π-conjugated conductive polymer and the polyanion, and obtaining a conductive polymer dispersion containing the conductive complex and the water, wherein in the polymerization step, the monomer is polymerized so that the total concentration of the π-conjugated conductive polymer and the polyanion relative to the total mass of the reaction solution is 1.90 mass% or less. [2] The method for producing a conductive polymer dispersion according to [1], further comprising a metal catalyst removal step of blending a metal catalyst into the reaction liquid in the polymerization step and removing the metal catalyst contained in the conductive polymer dispersion obtained in the polymerization step. [3] The method for producing a conductive polymer dispersion according to [2], wherein a total concentration of the π-conjugated conductive polymer and the polyanion relative to the total mass of the conductive polymer dispersion obtained in the metal catalyst removal step is 1.24 mass% or less. [4] The method for producing a conductive polymer dispersion according to [2] or [3], further comprising a concentration step of removing a portion of the water contained in the conductive polymer dispersion that has been subjected to the metal catalyst removal step, thereby increasing the content concentration of the conductive composite. [5] The method for producing a conductive polymer dispersion according to [4], wherein a total concentration of the π-conjugated conductive polymer and the polyanion relative to the total mass of the conductive polymer dispersion obtained in the concentration step is 1.6 mass% or more. [6] The method for producing a conductive polymer dispersion according to any one of [1] to [5], wherein the π-conjugated conductive polymer is poly(3,4-ethylenedioxythiophene), or the polyanion is polystyrenesulfonic acid. [7] A method for producing a capacitor, comprising the steps of optionally adding an additive to the conductive polymer dispersion obtained by the production method according to any one of [1] to [6], 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. [8] The method for producing a capacitor according to [7], wherein the additive is at least one selected from the group consisting of a basic compound and a polyol compound containing two or more hydroxyl groups. [9] The method for producing a capacitor according to [8], wherein imidazole is added as the basic compound to the conductive polymer dispersion, and the pH of the conductive polymer dispersion at 25°C is adjusted to 3.0 or less.

[10] The method for producing a capacitor according to [9], wherein diethylene glycol is added as the polyol compound to the conductive polymer dispersion. [Effects of the Invention]

[0007] According to the method for manufacturing a capacitor of the present invention, it is possible to manufacture a capacitor that has a good capacitance, a low initial ESR, and in which the increase in ESR after heat treatment is suppressed. According to the method for producing a conductive polymer dispersion liquid of the present invention, a conductive polymer dispersion liquid having low viscosity and excellent dispersibility can be produced.

[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] <Method for producing conductive polymer dispersion> A first aspect of the present invention is a method for producing a conductive polymer dispersion, comprising a polymerization step of polymerizing a monomer that forms a π-conjugated conductive polymer in a reaction solution containing a polyanion and water to form a conductive composite containing the π-conjugated conductive polymer and the polyanion, and obtaining a conductive polymer dispersion containing the conductive composite and the water.

[0012] In the polymerization step of this embodiment, it is preferable to polymerize the monomers so that the total concentration of the π-conjugated conductive polymer and the polyanion relative to the total mass of the reaction solution is 1.90 mass% or less. By adjusting the total concentration as described above, the dispersibility of the complex of the π-conjugated conductive polymer and the polyanion formed in the polymerization reaction can be increased, and a low-viscosity conductive polymer dispersion can be obtained. As shown in the comparative examples described below, when the total concentration is high, the viscosity of the resulting conductive polymer dispersion increases.

[0013] From the viewpoint of reducing the viscosity of the resulting conductive polymer dispersion, the total concentration is preferably 1.80% by mass or less, more preferably 1.50% by mass or less, and even more preferably 1.20% by mass or less. On the other hand, from the viewpoint of improving the production efficiency of the conductive composite, an excessively low total concentration is undesirable. From the above viewpoints, the lower limit of the total concentration is preferably 0.30% by mass or more, more preferably 0.50% by mass or more, even more preferably 0.75% by mass or more, and particularly preferably 0.90% by mass or more.

[0014] [Polymerization process] In the polymerization step, a monomer that forms a π-conjugated conductive polymer is polymerized in a reaction solution containing a polyanion and water, thereby obtaining a conductive polymer dispersion that contains a conductive complex that includes the π-conjugated conductive polymer and the polyanion, and water.

[0015] <Preparation of polyanions> The polyanion 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.

[0016] 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.

[0017] 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 %.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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 or by solvent substitution.

[0022] <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 the polyanion, a monomer that forms the π-conjugated conductive polymer, and water.

[0023] (Polyanion formulation) The amount of polyanion blended relative to the total mass of the reaction solution is preferably 0.1% by mass to 1.5% by mass, more preferably 0.5% by mass to 1.4% by mass, and even more preferably 1.0% by mass to 1.3% by mass. Within this range, a conductive composite suitable for producing a capacitor with excellent ESR performance is easily obtained.

[0024] The ratio of the π-conjugated conductive polymer monomer to the polyanion blended in the reaction solution is, for example, preferably 100 to 1,000 parts by mass of the polyanion per 100 parts by mass of the π-conjugated conductive polymer monomer, more preferably 150 to 700 parts by mass, and even more preferably 200 to 500 parts by mass. 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.

[0025] (Polymerization of π-conjugated conductive polymers) Monomers of π-conjugated conductive polymers can be polymerized by adding any radical polymerization initiator and metal catalyst to a reaction solution in the presence of a polyanion. The π-conjugated conductive polymer formed by polymerization spontaneously forms a conductive complex with the polyanion. As described above, in the reaction solution in which this polymerization reaction is carried out, the total concentration of the π-conjugated conductive polymer and polyanion is adjusted to 1.90 mass% or less relative to the total mass of the reaction solution.

[0026] Specifically, since the total concentration of the monomer and the polyanion is the theoretical maximum value of the total concentration of the π-conjugated conductive polymer and the polyanion formed after polymerization of the monomer, by setting the total concentration of the monomer and the polyanion to be mixed in the reaction solution to 1.90 mass% or less, the total concentration of the π-conjugated conductive polymer and the polyanion formed in the reaction solution can be set to 1.90 mass% or less.

[0027] The total concentration of the π-conjugated conductive polymer monomer and polyanion relative to the total mass of the reaction solution is preferably 0.50% by mass or more and 1.90% by mass or less, more preferably 0.60% by mass or more and 1.80% by mass or less, even more preferably 0.75% by mass or more and 1.50% by mass or less, and particularly preferably 0.90% by mass or more and 1.20% by mass or less. Within the above range, a conductive composite suitable for producing a capacitor with excellent ESR performance is likely to be obtained.

[0028] The amount of the monomer relative to the total mass of the reaction solution is preferably 0.10% by mass or more and 1.20% by mass or less, more preferably 0.20% by mass or more and 0.90% by mass or less, and even more preferably 0.30% by mass or more and 0.60% by mass or less. Within this range, a conductive composite suitable for producing a capacitor with excellent ESR performance is likely to be obtained.

[0029] Examples of the radical polymerization initiator include persulfates such as ammonium persulfate, sodium persulfate, potassium persulfate, etc. It is preferable to add a metal 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.

[0030] 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 0.20% by mass or more and 0.80% by mass or less, and even more preferably 0.30% by mass or more and 0.70% by mass or less.

[0031] 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.

[0032] (aqueous dispersion medium) The dispersion medium constituting the reaction solution is preferably an aqueous dispersion medium containing water, since the conductive composite is hydrophilic. The aqueous dispersion medium may consist of water alone, or 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.

[0033] 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.

[0034] The water content relative to the total mass of the dispersion medium excluding the solids (non-volatile components) blended in 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.

[0035] <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.

[0036] [Metal catalyst removal process] It is preferable to remove residues of the metal 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.

[0037] The metal catalyst removal step may result in a partial loss of the π-conjugated conductive polymer and polyanion. For example, this loss may be due to adsorption to an ion exchange resin, adsorption to an ultrafiltration membrane, permeation through the ultrafiltration membrane, or adsorption to other processing equipment. In this case, the total concentration of the π-conjugated conductive polymer and the polyanion relative to the total mass of the conductive polymer dispersion treated in the metal catalyst removal step is preferably 1.24 mass% or less. Here, the total concentration can be measured as the concentration of the solids (non-volatile components) after removing the dispersion medium (volatile components) from the conductive polymer dispersion. By adjusting the total concentration as described above, it is possible to improve the dispersibility of the complex of the π-conjugated conductive polymer and the polyanion in the conductive polymer dispersion that has been subjected to the metal catalyst removal step, and to obtain a conductive polymer dispersion having a low viscosity. As will be shown in the comparative examples described later, when the total concentration is high, the viscosity of the resulting conductive polymer dispersion increases.

[0038] [Concentration process] A concentration treatment may be performed to remove a portion of the water contained in the conductive polymer dispersion that has undergone the metal catalyst removal step and increase the total concentration of the π-conjugated conductive polymer and the polyanion. In this case, while the total concentration is adjusted to 1.90% by mass or less in the polymerization step, the total concentration may be greater than 1.90% by mass in the concentration step. The total concentration after concentration may be, for example, 1.60% by mass or more, 1.80% by mass or more, or 2.00% by mass or more. To improve the dispersibility of the conductive composite, the upper limit is preferably 5.00% by mass or less, more preferably 4.00% by mass or less, and even more preferably 3.00% by mass or less. Here, the total concentration can be measured as the concentration of the solids (non-volatile components) obtained by removing the dispersion medium (volatile components) from the conductive polymer dispersion.

[0039] In this embodiment, the reason why a conductive polymer dispersion with low viscosity and excellent dispersibility can be obtained even when the concentration in the concentration step exceeds the total concentration at the time of the polymerization step is thought to be as follows. That is, when the total concentration at the time of the polymerization step is high, an aggregate structure in which molecular chains of the conductive composite containing a π-conjugated conductive polymer and a polyanion are physically entangled with each other is likely to occur, whereas when the total concentration at the time of polymerization is low, the aggregate structure is unlikely to occur, and a stable conductive composite is formed. After a stable conductive composite is formed in the polymerization step, even if the total concentration is high in the concentration step, entanglement that occurs during polymerization is unlikely to occur, and concentration can be performed in a stable state.

[0040] The conductive polymer dispersion thus obtained may be dispersed by a conventional method using a high shear force such as a high-pressure homogenizer.

[0041] Any additives such as a basic compound and a polyol compound, which will be described later, may be further added to the conductive polymer dispersion liquid obtained above.

[0042] <Conductive polymer dispersion> The conductive polymer dispersion obtained by the production method of the first embodiment contains a conductive complex containing a π-conjugated conductive polymer and a polyanion, and an aqueous dispersion medium.

[0043] (Conductive composite) The polyanions in the conductive composite dope into the π-conjugated conductive polymer, contributing to improved conductivity. In the polyanion, 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, 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.

[0044] (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.

[0045] 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.

[0046] (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.

[0047] The content of the polyanion in the conductive composite is, for example, preferably in the range of 100 to 1,000 parts by mass, more preferably 150 to 700 parts by mass, and even more preferably 200 to 500 parts by mass, relative to 100 parts by mass of the π-conjugated conductive polymer. When 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, when 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 enabling the production of a capacitor with higher ESR performance.

[0048] The total content of the π-conjugated conductive polymer and the polyanion relative to the total mass of the conductive polymer dispersion can be set appropriately depending on the intended use, and when used in the production of a capacitor, which will be described later, it is preferably 1.60 mass % or more and 5.00 mass % or less, more preferably 1.80 mass % or more and 4.00 mass % or less, and even more preferably 2.00 mass % or more and 3.00 mass % or less. When the content is within the above preferred range, the dispersibility of the conductive composite is improved, improving the coatability, and the ESR performance of a capacitor having a solid electrolyte layer formed from the conductive polymer dispersion can be further improved.

[0049] (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.

[0050] 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.

[0051] 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 the water content is equal to or greater than the lower limit, the dispersibility of the conductive composite 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.

[0052] The viscosity of the conductive polymer dispersion at 25°C is preferably 40 mPa s or less, more preferably 35 mPa s or less, even more preferably 30 mPa s or less, and particularly preferably 25 mPa s or less, when the concentration of the conductive complex relative to the total mass of the conductive polymer dispersion is adjusted to 1.6 mass % or more and 2.0 mass % or less. There is no particular restriction on the lower limit of the viscosity, and a guideline is 5 mPa s or more. When measuring the viscosity, the dispersion medium contained in the conductive polymer dispersion preferably contains only ion-exchanged water, i.e., it is preferable that the dispersion medium does not contain additives such as basic compounds and polyols. 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).

[0053] (basic compounds) The addition of a basic compound neutralizes some of the acid groups that the polyanion may have, thereby bringing the acidity of the pH of the conductive polymer dispersion closer to neutral. From the viewpoint of reducing erosion of the object to which the conductive polymer dispersion is applied, it is preferable that the pH of the conductive polymer dispersion be on the neutral side rather than a strongly acidic pH of about 1.0.

[0054] The content of the basic compound contained in the conductive polymer dispersion is preferably such that the pH of the conductive polymer dispersion (25°C) is 2.0 to 7.0, more preferably 2.0 to 5.0, and even more preferably 2.0 to 3.0. Within the above preferred range, the ESR of the capacitor can be further reduced.

[0055] The basic compound functions as a Bronsted base that accepts protons from excess anion groups of the polyanion. To fulfill this function, the amount of the basic compound dissolved in water is preferably 0.001 g or more per 100 g of water at 20° C. There is no particular upper limit to the amount dissolved, but even an amount of about 0.1 g can fulfill the above function.

[0056] Examples of the basic compound that can be used include organic or inorganic basic compounds containing nitrogen, hydroxides of alkali metals or Group 2 metals, various carbonates and hydrogen carbonates, etc. Examples include hydroxides of alkali metals, quaternary ammonium hydroxides or salts thereof, ammonia, and amines. Specific examples of alkali metal hydroxides include potassium hydroxide and sodium hydroxide. Specific examples of carbonates or hydrogen carbonates include ammonium hydrogen carbonate, ammonium carbonate, potassium hydrogen carbonate, potassium carbonate, sodium hydrogen carbonate, sodium carbonate, and the like. Specific examples of quaternary ammonium hydroxides or salts thereof include tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrabutylammonium hydroxide.

[0057] 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.

[0058] 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.

[0059] (Polyol compound) The conductive polymer dispersion 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 and the polyanion. By including the polyol compound, the ESR of a capacitor having a solid electrolyte layer formed from the conductive polymer dispersion can be further reduced.

[0060] 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.

[0061] 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 and polyanion. 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.

[0062] 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.

[0063] (Other additives) The conductive polymer dispersion may contain any additive other than those described above, provided that the gist of the present invention is not impaired. The content ratio of the additive 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 other additive is a compound other than the basic compound, the polyol compound, and the dispersion medium.

[0064] Examples of other additives include surfactants, inorganic conductive agents, antifoaming agents, coupling agents, antioxidants, and ultraviolet absorbers. 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.

[0065] <Capacitor manufacturing method> A second aspect of the present invention is a method for producing a capacitor, comprising the steps of optionally adding an additive to the conductive polymer dispersion obtained by the production method of the first aspect, applying the conductive polymer dispersion to a surface of a dielectric layer formed on the surface of an anode made of a porous valve metal, and drying the applied conductive polymer dispersion to form a solid electrolyte layer.

[0066] This embodiment preferably includes the steps of: oxidizing the surface of an anode made of a porous valve metal to form a dielectric layer (dielectric forming step); disposing a cathode in a position opposite the dielectric layer (cathode forming step); and forming a solid electrolyte layer on at least a portion of the surface of the dielectric layer (film forming step). Each step will be described below with reference to FIG.

[0067] [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.

[0068] [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.

[0069] [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 .

[0070] 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.

[0071] 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.

[0072] <Capacitor> A preferred example of a capacitor produced in the second embodiment 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 the first embodiment.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] [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;

[0079] 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]

[0080] (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 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.

[0081] 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.

[0082] 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).

[0083] (Manufacturing Example 2) 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.

[0084] Example 1: Preparation of conductive polymer dispersion 3.1 g of 3,4-ethylenedioxythiophene (EDOT), 79.9 g of polystyrene sulfonic acid (10% by mass aqueous solution) of Production Example 1, and 875.1 g of ion-exchanged water were mixed at 25°C. The resulting mixed solution was kept at 25°C and 10.6 g of a 6% aqueous solution of ferric sulfate was added while stirring. Next, 31.2 g of an 11% aqueous solution of sodium persulfate was added, and the resulting reaction solution (total mass: 1000 g) was stirred for 8 hours to allow the reaction to occur. By the above reaction, a conductive polymer dispersion liquid containing a conductive composite (PEDOT-PSS) containing poly(3,4-ethylenedioxythiophene) and polystyrenesulfonic acid, which are π-conjugated conductive polymers, and water, which is a dispersion medium, was obtained.

[0085] The resulting conductive polymer dispersion was analyzed by GPC, and the amount of unpolymerized EDOT was below the detection limit. Therefore, the total concentration of the π-conjugated conductive polymer and polyanion in the polymerization reaction solution was 1.11% by mass, which was the same as the combined concentration of EDOT and PSS.

[0086] To this conductive polymer dispersion, 72.6 g of Duolite C255LFH (a cation exchange resin manufactured by Sumika Chemtex Co., Ltd.) and 72.6 g of Duolite A368S (an anion exchange resin manufactured by Sumika Chemtex Co., Ltd.) 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 catalyst had been removed, and the solids content (non-volatile components) was measured. The solids content of the resulting conductive polymer dispersion was 0.74 mass%. Next, water was removed from the obtained conductive polymer dispersion using an ultrafilter to adjust the solid content to 1.6% by mass. Imidazole was added to 100 g of the obtained conductive polymer dispersion using a high-pressure homogenizer, the pH was adjusted to 2.5, and 8 g of diethylene glycol was added, and the resulting dispersion was used to fabricate a capacitor.

[0087] Example 2: Preparation of conductive polymer dispersion 4.0 g of 3,4-ethylenedioxythiophene (EDOT), 101.7 g of polystyrene sulfonic acid (10% by mass aqueous solution) of Production Example 1, and 841.1 g of ion-exchanged water were mixed at 25°C. The resulting mixed solution was kept at 25°C and 13.4 g of a 6% aqueous solution of ferric sulfate was added while stirring. Next, 39.8 g of an 11% aqueous solution of sodium persulfate was added, and the resulting reaction solution (total mass: 1000 g) was stirred for 8 hours to allow the reaction to occur. By the above reaction, a conductive polymer dispersion liquid containing a conductive composite (PEDOT-PSS) containing poly(3,4-ethylenedioxythiophene) and polystyrenesulfonic acid, which are π-conjugated conductive polymers, and water, which is a dispersion medium, was obtained.

[0088] The resulting conductive polymer dispersion was analyzed by GPC, and the amount of unpolymerized EDOT was below the detection limit. Therefore, the total concentration of the π-conjugated conductive polymer and polyanion in the polymerization reaction solution was 1.41% by mass, which was the same as the blend concentration of EDOT and PSS.

[0089] To this conductive polymer dispersion, 92.4 g of Duolite C255LFH (a cation exchange resin manufactured by Sumika Chemtex Co., Ltd.) and 92.4 g of Duolite A368S (an anion exchange resin manufactured by Sumika Chemtex Co., Ltd.) 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 catalyst had been removed, and the solids content (non-volatile components) was measured. The solids content of the resulting conductive polymer dispersion was 0.96 mass%. Next, water was removed from the obtained conductive polymer dispersion using an ultrafilter to reduce the solid content to 1.6% by mass. Imidazole was added to 100 g of the conductive polymer dispersion obtained by dispersion using a high-pressure homogenizer to adjust the pH to 2.5, and 8 g of diethylene glycol was added, and the resulting mixture was used to fabricate a capacitor.

[0090] Example 3: Preparation of conductive polymer dispersion 4.8 g of 3,4-ethylenedioxythiophene (EDOT), 123.5 g of polystyrene sulfonic acid (10% by mass aqueous solution) of Production Example 1, and 807.1 g of ion-exchanged water were mixed at 25°C. The resulting mixed solution was kept at 25°C and 16.3 g of a 6% aqueous solution of ferric sulfate was added while stirring. Next, 48.3 g of an 11% aqueous solution of sodium persulfate was added, and the resulting reaction solution (total mass: 1000 g) was stirred for 8 hours to allow the reaction to occur. By the above reaction, a conductive polymer dispersion liquid containing a conductive composite (PEDOT-PSS) containing poly(3,4-ethylenedioxythiophene) and polystyrenesulfonic acid, which are π-conjugated conductive polymers, and water, which is a dispersion medium, was obtained.

[0091] The resulting conductive polymer dispersion was analyzed by GPC, and the amount of unpolymerized EDOT was below the detection limit. Therefore, the total concentration of the π-conjugated conductive polymer and polyanion in the polymerization reaction solution was 1.71% by mass, which was the same as the blend concentration of EDOT and PSS.

[0092] To this conductive polymer dispersion, 111.2 g of Duolite C255LFH (a cation exchange resin manufactured by Sumika Chemtex Co., Ltd.) and 111.2 g of Duolite A368S (anion exchange resin manufactured by Sumika Chemtex Co., Ltd.) were added, and the ion exchange resin was removed by filtration to obtain 850 g of a conductive polymer dispersion from which the oxidizing agent and catalyst had been removed, and the solid content (non-volatile components) was measured. The solid content of the resulting conductive polymer dispersion was 1.24 mass%. Next, water was removed from the obtained conductive polymer dispersion using an ultrafilter to reduce the solid content to 1.6% by mass. Imidazole was added to 100 g of the conductive polymer dispersion obtained by dispersion using a high-pressure homogenizer to adjust the pH to 2.5, and 8 g of diethylene glycol was added, and the resulting mixture was used to fabricate a capacitor.

[0093] Example 4 A conductive polymer dispersion was obtained by adding imidazole and diethylene glycol in the same manner as in Example 1, except that the conductive polymer dispersion having a solid content of 0.74% by mass obtained after treatment with an ion exchange resin in Example 1 was concentrated to 2.0% by mass using an ultrafilter.

[0094] Example 5 A conductive polymer dispersion was obtained by adding imidazole and diethylene glycol in the same manner as in Example 1, except that the conductive polymer dispersion having a solid content of 0.96% by mass obtained after treatment with an ion exchange resin in Example 2 was concentrated to 2.0% by mass using an ultrafilter.

[0095] Example 6 A conductive polymer dispersion was obtained by adding imidazole and diethylene glycol in the same manner as in Example 1, except that the conductive polymer dispersion having a solids content of 1.24% by mass obtained after treatment with an ion exchange resin in Example 3 was concentrated to 2.0% by mass using an ultrafilter.

[0096] Example 7 A conductive polymer dispersion was obtained by adding imidazole and diethylene glycol in the same manner as in Example 1, except that the conductive polymer dispersion having a solid content of 0.74% by mass obtained after treatment with an ion exchange resin in Example 1 was concentrated to 1.6% by mass using an evaporator.

[0097] Example 8 A conductive polymer dispersion was obtained by adding imidazole and diethylene glycol in the same manner as in Example 1, except that the conductive polymer dispersion having a solid content of 0.74% by mass obtained after treatment with an ion exchange resin in Example 1 was concentrated to 2.0% by mass using an evaporator.

[0098] (Comparative Example 1) Preparation of Conductive Polymer Dispersion 5.7 g of 3,4-ethylenedioxythiophene (EDOT), 145.3 g of polystyrene sulfonic acid (10% by mass aqueous solution) of Production Example 1, and 773.0 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, 48.3 g of an 11% aqueous solution of sodium persulfate was added, and the resulting reaction solution (total mass: 992 g) was stirred for 8 hours to react. By the above reaction, a conductive polymer dispersion liquid containing a conductive composite (PEDOT-PSS) containing poly(3,4-ethylenedioxythiophene) and polystyrenesulfonic acid, which are π-conjugated conductive polymers, and water, which is a dispersion medium, was obtained.

[0099] The resulting conductive polymer dispersion was analyzed by GPC, and the amount of unpolymerized EDOT was below the detection limit. Therefore, the total concentration of the π-conjugated conductive polymer and polyanion in the polymerization reaction solution was 2.04 mass%, which was the same as the blend concentration of EDOT and PSS.

[0100] To this conductive polymer dispersion, 132.0 g of Duolite C255LFH (a cation exchange resin manufactured by Sumika Chemtex Co., Ltd.) and 132.0 g of Duolite A368S (anion exchange resin manufactured by Sumika Chemtex Co., Ltd.) 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 catalyst had been removed, and the solids content (non-volatile components) was measured. The solids content of the resulting conductive polymer dispersion was 1.37 mass%. Next, water was distilled off from the obtained conductive polymer dispersion using an ultrafilter to adjust the solid content to 1.6% by mass. Imidazole was added to 100 g of the conductive polymer dispersion obtained by dispersion using a high-pressure homogenizer to adjust the pH to 2.5, and 8 g of diethylene glycol was added, and the resulting mixture was used to fabricate a capacitor.

[0101] (Comparative Example 2) A conductive polymer dispersion was obtained by adding imidazole and diethylene glycol in the same manner as in Comparative Example 1, except that the conductive polymer dispersion having a solid content of 1.37% by mass obtained after treatment with an ion exchange resin in Comparative Example 1 was concentrated to 2.0% by mass using an ultrafilter.

[0102] (Comparative Example 3) A conductive polymer dispersion was obtained by adding imidazole and diethylene glycol in the same manner as in Comparative Example 1, except that the conductive polymer dispersion having a solids content of 1.37% by mass obtained after treatment with an ion exchange resin in Comparative Example 1 was concentrated to 1.6% by mass using an evaporator.

[0103] Comparative Example 4 A conductive polymer dispersion was obtained by adding imidazole and diethylene glycol in the same manner as in Comparative Example 1, except that the conductive polymer dispersion having a solids content of 1.37% by mass obtained after treatment with an ion exchange resin in Comparative Example 1 was concentrated to 2.0% by mass using an evaporator.

[0104] (Comparative Example 5) 6.7 g of 3,4-ethylenedioxythiophene (EDOT), 170.0 g of the polystyrene sulfonic acid (10% by mass aqueous solution) of Production Example 1, and 744.3 g of ion-exchanged water were mixed at 25°C. The resulting mixed solution was kept at 25°C and 22.5 g of a 6% aqueous solution of ferric sulfate was added while stirring. Next, 56.5 g of an 11% aqueous solution of sodium persulfate was added, and the resulting reaction solution (total mass: 1000 g) was stirred for 8 hours to react. By the above reaction, a conductive polymer dispersion liquid containing a conductive composite (PEDOT-PSS) containing poly(3,4-ethylenedioxythiophene) and polystyrenesulfonic acid, which are π-conjugated conductive polymers, and water, which is a dispersion medium, was obtained.

[0105] The resulting conductive polymer dispersion was analyzed by GPC, and the amount of unpolymerized EDOT was below the detection limit. Therefore, the total concentration of the π-conjugated conductive polymer and polyanion in the polymerization reaction solution was 2.37% by mass, which was the same as the blend concentration of EDOT and PSS.

[0106] To this conductive polymer dispersion, 154.4 g of Duolite C255LFH (a cation exchange resin manufactured by Sumika Chemtex Co., Ltd.) and 154.4 g of Duolite A368S (anion exchange resin manufactured by Sumika Chemtex Co., Ltd.) were added, and the ion exchange resin was removed by filtration to obtain 850 g of a conductive polymer dispersion from which the oxidizing agent and catalyst had been removed, and the solid content (non-volatile components) was measured. The solid content of the resulting conductive polymer dispersion was 1.60 mass%. Next, imidazole was added to 100 g of the conductive polymer dispersion obtained by dispersing using a high-pressure homogenizer to adjust the pH to 2.5, and 8 g of diethylene glycol was added, and the mixture was used to fabricate a capacitor.

[0107] (Comparative Example 6) 8.4 g of 3,4-ethylenedioxythiophene (EDOT), 212.9 g of polystyrene sulfonic acid (10% by mass aqueous solution) of Production Example 1, and 679.8 g of ion-exchanged water were mixed at 25°C. The resulting mixed solution was kept at 25°C and 28.1 g of a 6% aqueous solution of ferric sulfate was added while stirring. Next, 70.8 g of an 11% aqueous solution of sodium persulfate was added, and the resulting reaction solution (total mass: 1000 g) was stirred for 8 hours to allow the reaction to occur. By the above reaction, a conductive polymer dispersion liquid containing a conductive composite (PEDOT-PSS) containing poly(3,4-ethylenedioxythiophene) and polystyrenesulfonic acid, which are π-conjugated conductive polymers, and water, which is a dispersion medium, was obtained.

[0108] The resulting conductive polymer dispersion was analyzed by GPC, and the amount of unpolymerized EDOT was below the detection limit. Therefore, the total concentration of the π-conjugated conductive polymer and polyanion in the polymerization reaction solution was 2.97% by mass, which was the same as the blend concentration of EDOT and PSS.

[0109] To this conductive polymer dispersion, 193.4 g of Duolite C255LFH (a cation exchange resin manufactured by Sumika Chemtex Co., Ltd.) and 193.4 g of Duolite A368S (anion exchange resin manufactured by Sumika Chemtex Co., Ltd.) 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 catalyst had been removed, and the solid content (non-volatile components) was measured. The solid content of the resulting conductive polymer dispersion was 2.0 mass %. Next, imidazole was added to 100 g of the conductive polymer dispersion obtained by dispersing using a high-pressure homogenizer to adjust the pH to 2.5, and 8 g of diethylene glycol was added, and the mixture was used to fabricate a capacitor.

[0110] <Capacitor fabrication> The capacitor element obtained in Production Example 2 was immersed under reduced pressure in the conductive polymer dispersion prepared in each of the above examples, 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.

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

[0112] [Viscosity measurement method] In each example, the conductive polymer dispersion immediately before the addition of imidazole and diethylene glycol was dispersed in a high-pressure homogenizer to prepare a sample, which was then 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 the ESR was then measured again.

[0114] [Table 1]

[0115] [Table 2]

[0116] As described above, in the examples of the present invention, the EDOT polymerization reaction was carried out, and the concentration of PEDOT-PSS formed in the reaction solution was set to a maximum of 1.90 mass% or less, so the dispersibility of the resulting conductive polymer dispersion was excellent. Furthermore, compared to the comparative conductive polymer dispersion containing PEDOT-PSS at the same concentration, the viscosity was lower, and as a result, both the initial ESR and the ESR after heat treatment were excellent, and a high-performance capacitor could be produced. [Explanation of symbols]

[0117] 10 Capacitors 11 Anode 12 Dielectric layer 13 Cathode 14 Solid electrolyte layer

Claims

1. A method for producing a conductive polymer dispersion, comprising a polymerization step of polymerizing a monomer that forms a π-conjugated conductive polymer in a reaction solution containing a polyanion and water to form a conductive complex containing the π-conjugated conductive polymer and the polyanion, and obtaining a conductive polymer dispersion containing the conductive complex and the water, the polymerization step is performed by polymerizing the monomers so that a total concentration of the π-conjugated conductive polymer and the polyanion relative to the total mass of the reaction solution is 1.90 mass% or less.

2. In the polymerization step, a metal catalyst is added to the reaction solution, a metal catalyst removal step of removing the metal catalyst contained in the conductive polymer dispersion obtained in the polymerization step; A method for producing the conductive polymer dispersion according to claim 1 .

3. a total concentration of the π-conjugated conductive polymer and the polyanion relative to the total mass of the conductive polymer dispersion obtained in the metal catalyst removal step is 1.24 mass% or less; A method for producing the conductive polymer dispersion according to claim 2 .

4. The method further comprises a concentration step of removing a part of the water contained in the conductive polymer dispersion that has been subjected to the metal catalyst removal step, thereby increasing the content concentration of the conductive complex. A method for producing the conductive polymer dispersion according to claim 3 .

5. a total concentration of the π-conjugated conductive polymer and the polyanion relative to the total mass of the conductive polymer dispersion obtained in the concentration step is 1.6 mass% or more; A method for producing the conductive polymer dispersion according to claim 4 .

6. 6. The method for producing a conductive polymer dispersion according to claim 5, wherein the π-conjugated conductive polymer is poly(3,4-ethylenedioxythiophene), or the polyanion is polystyrenesulfonic acid.

7. Additives are optionally added to the conductive polymer dispersion obtained by the manufacturing method according to any one of claims 1 to 6, and then a conductive polymer dispersion liquid applied to a surface of a dielectric layer formed on a surface of an anode made of a porous valve metal body, and then dried to form a solid electrolyte layer.

8. The method for producing a capacitor according to claim 7 , wherein the additive is at least one selected from the group consisting of a basic compound and a polyol compound containing two or more hydroxyl groups.

9. 9. The method for producing a capacitor according to claim 8, wherein imidazole is added as the basic compound to the conductive polymer dispersion, and the pH of the conductive polymer dispersion at 25°C is adjusted to 3.0 or less.

10. The method for producing a capacitor according to claim 9 , wherein diethylene glycol is added as the polyol compound to the conductive polymer dispersion.

Images