Method for manufacturing conductive polymer dispersion liquid, and method for manufacturing solid electrolytic capacitor

Abstract

The present disclosure relates to a method for manufacturing a conductive polymer dispersion liquid containing a conjugated conductive polymer-containing liquid and a conductivity enhancing agent, the method including: a step for purifying the conjugated conductive polymer-containing liquid which contains a polyanion and then performing dispersion to obtain a first dispersion liquid; and a step for adding the conductivity enhancing agent to the first dispersion liquid, wherein at least either ion exchange or ultrafiltration is performed in the purification.

Description

Method for producing conductive polymer dispersion and method for producing solid electrolytic capacitor

[0001] The present disclosure relates to a method for producing a dispersion containing a conjugated conductive polymer, and a method for producing a solid electrolytic capacitor using the same.

[0002] A solid electrolytic capacitor typically has a structure in which a valve metal, such as aluminum, tantalum, or niobium, is used as an anode foil and a cathode foil, with a solid electrolyte sandwiched between them. To increase the capacitance, the surface area of ​​the valve metal in the anode foil is increased by etching or other processes, and a dielectric oxide film is formed on the surface. The solid electrolyte is typically a conjugated conductive polymer, such as polypyrrole, polyaniline, or polythiophene.

[0003] Solid electrolytic capacitors are used in electronic devices because they can reduce equivalent series resistance (ESR) in the high frequency range. In addition, with the recent increase in the number of cars equipped with electrical equipment, development of solid electrolytic capacitors for automotive use is progressing.

[0004] A known method for forming a solid electrolyte using a conductive polymer is, for example, to permeate an aqueous dispersion of the conductive polymer into a dielectric oxide film of an anode body and then dry it. When forming a solid electrolyte using this method, the ESR of the solid electrolytic capacitor can be reduced by adding a water-soluble compound such as ethylene glycol to the aqueous dispersion of the conductive polymer as an additive for improving conductivity (see, for example, Patent Document 1).

[0005] Furthermore, Patent Document 2 discloses that in the production of a dispersion liquid containing a conductive polymer, a solid electrolytic capacitor having a lower ESR can be obtained by adding an additive (electrical conductivity improver) that improves conductivity and then carrying out a dispersion treatment.

[0006] JP 2013-55308 A International Publication No. 2023 / 119762

[0007] In recent years, capacitors for in-vehicle devices have become increasingly high-output, and even when a dispersion of a conductive polymer is produced by the method described in Patent Document 2, the reduction in ESR is not necessarily sufficient. Therefore, in order to achieve higher output through electronic control, there is a demand for improving the performance of capacitors by further reducing the ESR.

[0008] The present disclosure has been made in view of the above circumstances, and aims to provide a method for producing a conductive polymer dispersion capable of reducing the ESR of a solid electrolytic capacitor, and a method for producing a solid electrolytic capacitor.

[0009] The present disclosure is based on the discovery of production conditions in the production of a conductive polymer dispersion that can reduce the ESR of a solid electrolytic capacitor produced using the conductive polymer dispersion.

[0010] The present disclosure provides the following means. [1] A method for producing a conductive polymer dispersion containing a conjugated conductive polymer-containing liquid and an electrical conductivity enhancer, comprising the steps of purifying a conjugated conductive polymer-containing liquid containing a polyanion and then dispersing the purified liquid to obtain a first dispersion, and adding an electrical conductivity enhancer to the first dispersion, wherein the purification step involves at least one of ion exchange and ultrafiltration. [2] A method for producing the conductive polymer dispersion of [1], wherein the electrical conductivity enhancer is added and then further dispersed. [3] A method for producing the conductive polymer dispersion of [1] or [2], wherein the electrical conductivity enhancer is at least one selected from the group consisting of tetrahydrofuran, γ-butyrolactone, N-methylformamide, N-methylpyrrolidone, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, diglycerin, dimethyl sulfoxide, and sorbitol. [4] The method for producing a conductive polymer dispersion according to any one of [1] to [3], wherein the amount of the electrical conductivity improver added is 1 to 50 parts by mass per part by mass of the solid content in the first dispersion. [5] The method for producing a conductive polymer dispersion according to any one of [1] to [4], wherein a monomer that becomes a structural unit of the conjugated conductive polymer contains at least one compound selected from the group consisting of pyrroles, anilines, and thiophenes. [6] The method for producing a conductive polymer dispersion according to [5], wherein the thiophene compound is represented by the following formula (1): (In formula (1), R １ and R ２ are each independently a hydrogen atom, a hydroxyl group, an alkyl group having 1 to 18 carbon atoms which may have a substituent, an alkoxy group having 1 to 18 carbon atoms which may have a substituent, an alkylthio group having 1 to 18 carbon atoms which may have a substituent, or R １ and R ２and an optionally substituted alicyclic ring having 3 to 10 carbon atoms, an optionally substituted aromatic ring having 6 to 10 carbon atoms, an optionally substituted oxygen-atom-containing heterocyclic ring having 2 to 10 carbon atoms, an optionally substituted sulfur-atom-containing heterocyclic ring having 2 to 10 carbon atoms, or an optionally substituted sulfur-atom and oxygen-atom-containing heterocyclic ring having 2 to 10 carbon atoms, which are formed by bonding together. [7] The method for producing a conductive polymer dispersion according to any of [1] to [6], wherein the polyanion is a polymer having two or more groups selected from the group consisting of sulfonic acid groups and sulfonate salts.

[0011] [8] A method for producing a solid electrolytic capacitor, comprising the steps of: depositing the conductive polymer dispersion produced by the method for producing any one of [1] to [7] on a porous anode body that is a valve metal having a dielectric coating on its surface; and then removing the dispersion medium from the conductive polymer dispersion deposited on the porous anode body to form a solid electrolyte layer.

[0012] According to the present disclosure, it is possible to provide a method for producing a conductive polymer dispersion capable of reducing the ESR of a solid electrolytic capacitor, and a method for producing a solid electrolytic capacitor.

[0013] The definitions and meanings of terms and notations used in this specification are as follows. Regarding a compound group, "optionally substituted" means that the group may be substituted or unsubstituted (unsubstituted). The term "class" attached to a compound name refers to a group of compounds containing the compound structure, including those compounds having a substituent. For example, "polypyrroles" refers to a group of compounds containing a polypyrrole structure. "(Meth)acrylic acid" is a general term for acrylic acid and methacrylic acid. Similarly, "(meth)acrylate" is a general term for acrylate and methacrylate, and "(meth)acryloyl" is a general term for acryloyl and methacryloyl. Unless otherwise specified, "ethylenically unsaturated bond" refers to an ethylenically unsaturated bond having radical polymerizability. Furthermore, "ethylenically unsaturated monomer" refers to a compound having an ethylenically unsaturated bond and is a compound from which a structural unit of a polymer is derived. "Polymer component" refers to a conjugated conductive polymer and a polyanion. When the conductive polymer dispersion contains a polymer (Z) described below, "polymer (Z)" is also included. The solid content is determined based on the actual measurement of the evaporation residue in the solid content concentration measurement method described in the Examples. The notation "X to Y" (X and Y are numerical values) means a numerical range with X as the lower limit and Y as the upper limit. In a numerical range (e.g., a range of content, etc.), the lower limit and upper limit values ​​described in stages may be independently combined. The lower limit and upper limit values ​​of the numerical range may be replaced with numerical values ​​described in the Examples.

[0014] [Method for Producing Conductive Polymer Dispersion] The method for producing a conductive polymer dispersion according to the present disclosure is a method for producing a conductive polymer dispersion containing a conjugated conductive polymer-containing liquid and an electrical conductivity enhancer, and includes the steps of: (1) purifying a conjugated conductive polymer-containing liquid containing a polyanion and then dispersing the purified liquid to obtain a first dispersion; and (2) adding an electrical conductivity enhancer to the first dispersion. The purification step is at least one of ion exchange and ultrafiltration. In the production of the conductive polymer dispersion, by performing a dispersion step after the purification step before adding the electrical conductivity enhancer, the ESR of a solid electrolytic capacitor produced using the conductive polymer dispersion can be reduced.

[0015] [Step (1)] In step (1), a liquid containing a conjugated conductive polymer containing a polyanion is purified and then dispersed to obtain a first dispersion.

[0016] (Conjugated conductive polymer-containing liquid) The conjugated conductive polymer-containing liquid before purification treatment contains a polyanion. There are no particular limitations on the method for producing the conjugated conductive polymer-containing liquid (hereinafter also simply referred to as "polymer-containing liquid") containing a polyanion. When producing the polymer-containing liquid by synthesis from a monomer, for example, it can be obtained by polymerizing a monomer that becomes a structural unit of the conjugated conductive polymer in a liquid containing a polyanion.

[0017] From the viewpoint of dispersion stability of the conjugated conductive polymer and the polyanion, the polymer-containing liquid may contain a polymer (Z) which does not fall into the category of either a conjugated conductive polymer or a polyanion, and may also contain other additives.

[0018] <Conjugated conductive polymer> The conjugated conductive polymer is not particularly limited as long as it is an organic polymer compound having a π-conjugated system in the main chain. The conjugated conductive polymer may be used alone or in combination of two or more types. In addition, it may be a homopolymer of a monomer described below that becomes a structural unit of the conjugated conductive polymer, or a copolymer of two or more types of monomers.

[0019] The content of the conjugated conductive polymer in the polymer-containing liquid is preferably 5 to 70 mass %, more preferably 10 to 60 mass %, and even more preferably 15 to 50 mass %, relative to 100 mass % of the polymer component, from the viewpoints of the dispersion stability of the conductive polymer dispersion and the effect of reducing the ESR of a solid electrolytic capacitor produced using the conductive polymer dispersion.

[0020] Examples of conjugated conductive polymers include polypyrroles, polythiophenes, polyisothianaphthenes, polyacetylenes, polyphenylenes, polyphenylene vinylenes, polyanilines, polyacenes, polythiophene vinylenes, and copolymers thereof. Among these, polypyrroles, polythiophenes, and polyanilines are preferred from the viewpoints of ease of handling and availability, and polythiophenes are more preferred. Furthermore, from the viewpoint of high conductivity, the conjugated conductive polymer preferably has a substituent such as an alkyl group, a carboxy group, a sulfo group, an alkoxy group, a hydroxyl group, or a cyano group.

[0021] Examples of polypyrroles 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), poly(3-methyl-4-hexyloxypyrrole), and poly(3-methyl-4-hexyloxypyrrole).

[0022] Examples of polythiophenes include polythiophene, poly(3-methylthiophene), poly(3-hexylthiophene), poly(3-heptylthiophene), poly(3-octylthiophene), poly(3-decylthiophene), poly(3-dodecylthiophene), poly(3-octadecylthiophene), poly(3-bromothiophene), poly(3-chlorothiophene), poly(3-iodothiophene), poly(3-cyanothiophene), poly(3-phenylthiophene), and 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), 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-didodecyloxythiophene), poly(3,4-ethylenedioxythiophene), thiophene), 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), poly(3-methyl-4-carboxybutylthiophene), poly(3,4-ethyleneoxythiathiophene), and the like.

[0023] Examples of polyanilines include polyaniline, poly(2-methylaniline), poly(3-isobutylaniline), poly(2-anilinesulfonic acid), and poly(3-anilinesulfonic acid).

[0024] Among these compounds, the conjugated conductive polymer is preferably polypyrrole, polythiophene, poly(N-methylpyrrole), poly(3-methylthiophene), poly(3-methoxythiophene), or poly(3,4-ethylenedioxythiophene) from the viewpoint of high conductivity, and more preferably poly(3,4-ethylenedioxythiophene) from the viewpoint of good heat resistance.

[0025] The monomer for obtaining a conjugated conductive polymer, i.e., the monomer that serves as a structural unit of the conjugated conductive polymer, preferably contains at least one compound selected from the group consisting of pyrroles, anilines, and thiophenes. The compound may have a substituent X. Examples of the substituent X include an alkyl group having 1 to 18 carbon atoms, an aryl group having 6 to 10 carbon atoms, a heteroaryl group having 5 to 10 carbon atoms, an alkoxy group having 1 to 18 carbon atoms, an alkylthio group having 1 to 18 carbon atoms, a carboxy group, a hydroxyl group, a halogen atom, and a cyano group. Two or more of these substituents X may be bonded to each other by condensation or the like to form a ring. These alkyl groups, aryl groups, heteroaryl groups, alkoxy groups, and alkylthio groups may also have a further substituent Y, such as a carboxy group, a hydroxyl group, a halogen atom, or a cyano group.

[0026] Examples of monomers that can be structural units of conjugated conductive polymers include pyrroles such as pyrrole, N-methylpyrrole, 3-methylpyrrole, 3-ethylpyrrole, 3-n-propylpyrrole, 3-butylpyrrole, 3-octylpyrrole, 3-decylpyrrole, 3-dodecylpyrrole, 3,4-dimethylpyrrole, 3,4-dibutylpyrrole, 3-carboxylpyrrole, 3-methyl-4-carboxylpyrrole, 3-methyl-4-carboxyethylpyrrole, 3-methyl-4-carboxybutylpyrrole, 3-hydroxypyrrole, 3-methoxypyrrole, 3-ethoxypyrrole, 3-butoxypyrrole, 3-hexyloxypyrrole, 3-methyl-4-hexyloxypyrrole, and 3-methyl-4-hexyloxypyrrole;Thiophene, 3-methylthiophene, 3-ethylthiophene, 3-propylthiophene, 3-butylthiophene, 3-hexylthiophene, 3-heptylthiophene, 3-octylthiophene, 3-decylthiophene, 3-dodecylthiophene, 3-octadecylthiophene, 3-bromothiophene, 3-chlorothiophene, 3-iodothiophene, 3-cyanothiophene, 3-phenylthiophene, 3,4-dimethylthiophene, 3,4-dibutylthiophene, 3-hydroxythiophene, 3-methoxythiophene, 3-ethoxythiophene, 3-butoxythiophene, 3-hexyloxythiophene, 3-heptyloxythiophene, 3-octyloxythiophene, 3-decyloxythiophene, 3-dodecyloxythiophene, 3-octadecyloxythiophene, 3,4-dihydroxythiophene, 3,4-dimethoxythiophene, 3,4-diethoxythiophene Examples of suitable thiophenes include thiophene, 3,4-dipropoxythiophene, 3,4-dibutoxythiophene, 3,4-dihexyloxythiophene, 3,4-diheptyloxythiophene, 3,4-dioctyloxythiophene, 3,4-didecyloxythiophene, 3,4-didodecyloxythiophene, 3,4-ethylenedioxythiophene, 3,4-propylenedioxythiophene, 3,4-butylenedioxythiophene, 3-methyl-4-methoxythiophene, 3-methyl-4-ethoxythiophene, 3-carboxythiophene, 3-methyl-4-carboxythiophene, 3-methyl-4-carboxyethylthiophene, 3-methyl-4-carboxybutylthiophene, and 3,4-ethyleneoxythiathiophene; and anilines such as aniline, 2-methylaniline, 3-isobutylaniline, 2-anilinesulfonic acid, and 3-anilinesulfonic acid. These may be used alone or in combination of two or more.

[0027] Among these compounds, the monomer that becomes the structural unit of the conjugated conductive polymer preferably contains a thiophene compound represented by the following formula (1), from the viewpoint of obtaining a conjugated conductive polymer with high conductivity. The compound represented by formula (1) may be used alone or in combination of two or more.

[0028]

[0029] In formula (1), R １ and R ２ are each independently a hydrogen atom, a hydroxyl group, an optionally substituted alkyl group having 1 to 18 carbon atoms, an optionally substituted alkoxy group having 1 to 18 carbon atoms, or an optionally substituted alkylthio group having 1 to 18 carbon atoms; or R １ and R ２ and are bonded to each other to form an optionally substituted alicyclic ring having 3 to 10 carbon atoms, an optionally substituted aromatic ring having 6 to 10 carbon atoms, an optionally substituted oxygen atom-containing heterocyclic ring having 2 to 10 carbon atoms, an optionally substituted sulfur atom-containing heterocyclic ring having 2 to 10 carbon atoms, or an optionally substituted sulfur atom- and oxygen atom-containing heterocyclic ring having 2 to 10 carbon atoms.

[0030] Examples of the substituent include a carboxy group, a hydroxyl group, a halogen atom, and a cyano group. The oxygen-atom-containing heterocycle preferably contains 1 to 3 oxygen atoms constituting the ring, and examples thereof include an oxirane ring, an oxetane ring, a furan ring, a hydrofuran ring, a pyran ring, a pyrone ring, a dioxane ring, and a trioxane ring. The sulfur-atom-containing heterocycle preferably contains 1 to 3 nitrogen atoms constituting the ring, and examples thereof include a thiirane ring, a thietane ring, a thiophene ring, a thiane ring, a thiopyran ring, a thiopyrylium ring, a benzothiopyran ring, a dithiane ring, a dithiolane ring, and a trithiane ring. The sulfur-atom- and oxygen-atom-containing heterocycle preferably contains 1 to 3 sulfur and oxygen atoms constituting the ring in total, and examples thereof include an oxathiolane ring and an oxathiane ring.

[0031] The content of the compound represented by formula (1) in the monomer that becomes a structural unit of the conjugated conductive polymer is preferably 90 to 100 mass %, more preferably 95 to 100 mass %, and even more preferably 100 mass %, from the viewpoints of uniformity and good conductivity of the conjugated conductive polymer.

[0032] The monomer that becomes the structural unit of the conjugated conductive polymer more preferably contains a compound represented by the following formula (2) among the compounds represented by formula (1), and further preferably contains 3,4-ethylenedioxythiophene:

[0033]

[0034] In formula (2), R ３ and R ４ are each independently a hydrogen atom, an optionally substituted alkyl group having 1 to 4 carbon atoms, or R ３ and R ４ and are bonded to each other to form an optionally substituted oxygen atom-containing heterocycle having 3 to 6 carbon atoms.

[0035] R ３ and R ４ is R ３ and R ４ and are bonded to each other, and are preferably oxygen atom-containing heterocycles having 3 to 6 carbon atoms, which may be substituted. The oxygen atom-containing heterocycle preferably has 1 to 3 oxygen atoms constituting the ring, and examples thereof include a dioxane ring and a trioxane ring, with a dioxane ring being preferred. The oxygen atom-containing heterocycle is preferably unsubstituted. The substituent to be substituted here is the same as the above-mentioned substituent Y, and examples thereof include a carboxy group, a hydroxyl group, a halogen atom, and a cyano group.

[0036] <Polyanion> A polyanion is a polymer having two or more anionic groups, and functions as a dopant for a conjugated conductive polymer.

[0037] From the viewpoints of the dispersion stability of the conductive polymer dispersion and the effect of reducing the ESR of a solid electrolytic capacitor produced using the conductive polymer dispersion, the content of the polyanion in the polymer-containing liquid is preferably 30 to 95% by mass, more preferably 40 to 90% by mass, and even more preferably 50 to 85% by mass, relative to 100% by mass of the polymer component. The content of the polyanion in the polymer-containing liquid is preferably 45 to 1,900 parts by mass, more preferably 70 to 900 parts by mass, and even more preferably 100 to 500 parts by mass, relative to 100 parts by mass of the conjugated conductive polymer.

[0038] Examples of anionic groups include sulfonic acid groups, sulfonates, phosphoric acid groups, phosphoric acid salts, mono-substituted phosphoric acid ester groups, carboxylic acids, carboxylates, and mono-substituted sulfate ester groups. Among these, strongly acidic groups are preferred, with sulfonic acid groups, sulfonic acid, phosphoric acid groups, and phosphoric acid being more preferred, and sulfonic acid groups and sulfonates being even more preferred. That is, the polyanion is preferably a polymer having two or more of any one selected from the group consisting of sulfonic acid groups and sulfonates. Examples of salts include salts of sodium, potassium, magnesium, calcium, and ammonium.

[0039] The anionic group may be bonded to the main chain or side chain of the polymer constituting the polyanion. When the anionic group is bonded to the side chain, it is preferable that the anionic group be bonded to the end of the side chain from the viewpoint of obtaining a high doping effect on the conjugated conductive polymer. The anionic group may be bonded directly to the main chain or via another structure. The anionic group is preferably bonded via a benzene ring, and in this case, it is more preferable that the anionic group be bonded at the para position relative to the main chain.

[0040] The polyanion may have a substituent other than the anionic group. The substituent may be bonded to the main chain or to a side chain of the polymer constituting the polyanion. When a substituent is bonded to a side chain, it is preferable that the substituent is bonded to the end of the side chain in order to exhibit the properties of the substituent. Examples of the substituent to be used here include an alkyl group, a hydroxyl group, an alkoxy group, a cyano group, a phenyl group, a hydroxyphenyl group, an ester group, an alkenyl group, an imide group, an amide group, an amino group, an oxycarbonyl group, a carbonyl group, and a halogen atom. Among these, an alkyl group, a hydroxyl group, a cyano group, a hydroxyphenyl group, and an oxycarbonyl group are preferred, and an alkyl group, a hydroxyl group, and a cyano group are more preferred.

[0041] The main chain structure of the polymer constituting the polyanion is not particularly limited, and examples thereof include polyalkylene, polyimide, polyamide, polyester, etc. Among these, polyalkylene is preferred from the viewpoint of ease of synthesis or availability. The polyalkylene in the main chain structure is a polymer containing a structural unit derived from an ethylenically unsaturated monomer and may contain a carbon-carbon double bond. Examples of such main chain structures include polyethylene, polypropylene, polybutene, polypentene, polyhexene, polyvinyl alcohol, polyvinylphenol, poly(3,3,3-trifluoropropylene), polyacrylonitrile, poly(meth)acrylate, polystyrene, polybutadiene, polyisoprene, etc.

[0042] As the polyanion, a compound having two or more anionic groups selected from the group consisting of sulfonic acid groups and sulfonate salts is preferred, as described above, in order to improve the dispersibility in the dispersion medium of the monomer that becomes the structural unit of the conjugated conductive polymer. ２ Examples of polyanions having a hydroxyl group (OH) include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyethyl acrylate sulfonic acid, polybutyl acrylate sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, and copolymers of these structural units. Among these, from the viewpoints of stability in the conductive polymer dispersion and the effect of reducing the ESR of a solid electrolytic capacitor produced using the conductive polymer dispersion, polystyrene sulfonic acid, polyisoprene sulfonic acid, polyethyl acrylate sulfonic acid, and polybutyl acrylate sulfonic acid are preferred, with polystyrene sulfonic acid being more preferred.

[0043] Furthermore, the polyanion contained in the conductive polymer dispersion and the polyanion added in the production process may have the same structure, or may have a different structure, such as one in which different cations are bound. For example, from the viewpoint of water solubility, sodium polystyrene sulfonate may be added as the polyanion, and then converted to polystyrene sulfonic acid by ion exchange or the like. The polyanion can be produced, for example, by the production method described in JP-A-2005-76016, or a commercially available product can also be used.

[0044] From the viewpoints of solubility in the dispersion medium and doping effect on the conjugated conductive polymer, the polyanion preferably has a weight-average molecular weight of 1,000 to 1,000,000, more preferably 5,000 to 500,000, and even more preferably 50,000 to 300,000. The weight-average molecular weight referred to here is a standard polystyrene-equivalent molecular weight measured by gel permeation chromatography. Specifically, it is measured by the method described in the Examples.

[0045] <Polymer (Z)> The polymer (Z) is a polymer other than a conjugated conductive polymer and a polyanion. The polymer (Z) may form a complex with a polyanion, or may form a complex in which a polyanion is coordinated outside the domain of the polymer (Z). The polymer (Z) is preferably insoluble in the dispersion medium of the polymer-containing liquid, and its presence in the form of particles in the conductive polymer dispersion can contribute to suppressing dedoping of the polyanion from the conjugated conductive polymer and suppressing dedoping and oxidative degradation of the polymer components.

[0046] The content of the polymer (Z) in the polymer-containing liquid is preferably 0 to 50 mass%, more preferably 0 to 40 mass%, and even more preferably 0 to 25 mass%, relative to 100 mass% of the polymer component, from the viewpoints of the dispersion stability of the conductive polymer dispersion and the effect of reducing the ESR of a solid electrolytic capacitor produced using the conductive polymer dispersion.

[0047] The polymer (Z) is not particularly limited, but for example, a polymer containing a structural unit derived from an ethylenically unsaturated monomer is preferred, and a polymer consisting of a structural unit derived from an ethylenically unsaturated monomer is more preferred. The polymer (Z) is preferably a nonionic polymer, and more preferably a hydrocarbon. The polymer (Z) may include either a homopolymer or a copolymer, or both. The polymer (Z) may be used alone or in combination of two or more types. The polymer (Z) may also have a crosslinked structure.

[0048] Examples of ethylenically unsaturated monomers from which the structural units of polymer (Z) are derived include (meth)acrylates having a linear, branched, or cyclic alkyl group; aromatic vinyl compounds such as styrene and α-methylstyrene; heterocyclic vinyl compounds such as vinylpyrrolidone; hydroxyalkyl (meth)acrylates; dialkylaminoalkyl (meth)acrylates such as 2-ethylhexyl (meth)acrylate; vinyl esters such as vinyl acetate and vinyl alkanoate; monoolefins such as ethylene, propylene, butylene, and isobutylene; conjugated diolefins such as butadiene, isoprene, and chloroprene; α,β-unsaturated mono- or dicarboxylic acids such as (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, and fumaric acid; vinyl cyanide compounds such as acrylonitrile; and carbonyl group-containing vinyl compounds such as acrolein and diacetone acrylamide. The ethylenically unsaturated monomers may be used alone or in combination of two or more.

[0049] The polymer (Z) may have a crosslinked structure. Examples of the crosslinked structure include a structure derived from a compound having a plurality of independent ethylenically unsaturated bonds. Here, "a plurality of independent ethylenically unsaturated bonds" refers to a plurality of ethylenically unsaturated bonds that do not form a conjugated diene. The crosslinked structure may be formed, for example, by a polymer having a first reactive functional group and a crosslinking agent having a plurality of second reactive functional groups that react with the first reactive functional group, or by reacting a polymer having both a first reactive functional group and a second reactive functional group intramolecularly or intermolecularly. By forming a crosslinked copolymer, the water resistance, moisture resistance, heat resistance, etc. of a solid electrolyte using the same are likely to be improved.

[0050] When a crosslinking agent is not used, the content of structural units forming a crosslinked structure in 100% by mass of polymer (Z) is preferably 50% by mass or less, more preferably 30% by mass or less, and even more preferably 15% by mass or less. When a crosslinking agent is used, the total content of structural units forming a crosslinked structure and components derived from the crosslinking agent in 100% by mass of polymer (Z) is preferably 50% by mass or less, more preferably 30% by mass or less, and even more preferably 15% by mass or less.

[0051] Examples of compounds that form crosslinked structures include epoxy group-containing α,β-ethylenically unsaturated compounds such as glycidyl (meth)acrylate; hydrolyzable alkoxysilyl group-containing α,β-ethylenically unsaturated compounds such as vinyltriethoxysilane and γ-methacryloxypropyltrimethoxysilane; and polyfunctional vinyl compounds such as ethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, allyl (meth)acrylate, divinylbenzene, and diallyl phthalate. Furthermore, crosslinkable monomers such as carbonyl group-containing α,β-ethylenically unsaturated compounds (those containing ketone groups) may be crosslinked in combination with polyhydrazine compounds (particularly those having two or more hydrazide groups such as oxalic acid dihydrazide, succinic acid dihydrazide, adipic acid dihydrazide, and polyacrylic acid hydrazide).

[0052] The polymer (Z) is preferably obtained as a dispersion containing the polymer (Z) in a state of being dispersed in a dispersion medium, and more preferably obtained in the state of an emulsion.

[0053] From the viewpoint of dispersion stability and suppression of sedimentation, the particles contained in the dispersion liquid containing the polymer (Z) have a cumulative volume 50% particle diameter (d ５０ ) is preferably 0.01 to 10 μm, more preferably 0.05 to 1 μm, even more preferably 0.1 to 0.8 μm, and even more preferably 0.3 to 0.6 μm. ５０ is determined by the method described in the Examples below.

[0054] The polymer (Z) can be produced by a radical polymerization reaction in a normal pressure or pressure-resistant reactor, and the production method may be any of a batch method, a semi-continuous method, and a continuous method.

[0055] The polymer (Z) may have a polyanion on its surface, and is preferably produced by emulsion polymerization, in which a raw material solution containing an ethylenically unsaturated monomer is continuously or intermittently added to a polyanion-containing solution and polymerized. Emulsion polymerization efficiently produces composite particles in which the polyanion is coordinated to the polymer (Z), forming a polyanion domain outside the polymer (Z) domain. In such composite particles, the polyanion is thought to act as a protective colloid. The polyanion used here contributes to the dispersion stability of the polymer (Z)-containing dispersion. The polyanion in the polymer (Z)-containing dispersion and the polyanion contained in the first dispersion may be the same or different (e.g., different cations may be bound).

[0056] The amount of the ethylenically unsaturated monomer used in the synthesis of the polymer (Z) is preferably 10 to 100 parts by mass, more preferably 20 to 90 parts by mass, and even more preferably 30 to 80 parts by mass, per 100 parts by mass of the polyanion, from the viewpoints of suppressing thickening of the dispersion containing the polymer (Z) and improving dispersion stability.

[0057] The dispersion medium used in the synthesis of polymer (Z) is preferably an aqueous medium, more preferably water or a mixed solvent of water and a water-soluble solvent. The proportion of the water-soluble solvent in the mixed solvent is preferably 30 mass% or less from the viewpoint of dispersion stability of particles during the polymerization reaction. The dispersion medium used in the synthesis of polymer (Z) may be the same component as the dispersion medium contained in the conductive polymer dispersion, or may be a different component. Examples of water-soluble solvents include alcohols such as methanol, ethanol, and isopropanol; ketones such as acetone; glycols such as ethylene glycol and propylene glycol; and ethers such as ethylene glycol monomethyl ether and ethylene glycol monobutyl ether.

[0058] The content of the dispersion medium in the dispersion liquid containing polymer (Z) is preferably 30 to 99% by mass, more preferably 50 to 95% by mass, and even more preferably 70 to 90% by mass, from the viewpoint of the dispersion stability of the dispersion liquid containing polymer (Z).

[0059] From the viewpoint of good dispersion stability, additives such as emulsifiers and aliphatic amines may be added to the dispersion containing polymer (Z) as needed. The type and amount of additives are appropriately adjusted depending on the content and composition of the ethylenically unsaturated monomer and polyanion. The emulsifier and aliphatic amine contained in the dispersion containing polymer (Z) may be one type alone or two or more types.

[0060] Examples of the emulsifier include anionic surfactants such as alkyl sulfates, alkyl benzene sulfonates, alkyl sulfosuccinates, alkyl diphenyl ether disulfonates, polyoxyalkylene alkyl sulfates, and polyoxyalkylene alkyl phosphates; and nonionic surfactants such as polyoxyalkylene alkyl ethers, polyoxyalkylene alkylphenol ethers, polyoxyalkylene fatty acid esters, and polyoxyalkylene sorbitan fatty acid esters.

[0061] Examples of aliphatic amines include primary amines such as octylamine, laurylamine, myristylamine, stearylamine, and oleylamine; secondary amines such as dioctylamine, dilaurylamine, distearylamine, and dioleylamine; and tertiary amines such as N,N-dimethyllaurylamine, N,N-dimethylmyristylamine, N,N-dimethylpalmitylamine, N,N-dimethylstearylamine, N,N-dimethylbehenylamine, N,N-dimethyloleylamine, N-methyldidecylamine, and N-methyldioleylamine.

[0062] Furthermore, from the viewpoint of dispersion stability of the dispersion containing polymer (Z), a water-soluble polymer such as polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, or polyvinylpyrrolidone may be contained within a range that does not impair the properties of the conductive polymer dispersion of the present disclosure.

[0063] Examples of polymerization initiators for the radical polymerization reaction to obtain polymer (Z) include inorganic peroxides such as hydrogen peroxide, persulfuric acid, ammonium persulfate, potassium persulfate, and sodium persulfate; organic peroxides such as benzoyl peroxide and tert-butyl hydroperoxide; and azo compounds such as 2,2'-azobisisobutyronitrile and 4,4'-azobis(4-cyanovaleric acid). These polymerization initiators may be combined with sodium sulfoxylate formaldehyde, ascorbic acids, sulfites, tartaric acid or its salts, iron(II) sulfate, or the like to carry out redox polymerization. Chain transfer agents such as alcohols and mercaptans may also be used as needed. The reaction temperature in the radical polymerization reaction is preferably 10 to 100°C, more preferably 30 to 90°C. The reaction time is not particularly limited and can be adjusted appropriately depending on the amount of raw materials, the type of polymerization initiator, the reaction temperature, and other factors.

[0064] From the viewpoint of the quality stability of the dispersion containing polymer (Z), it is preferable to desalt the reaction product obtained by the radical polymerization reaction. The desalting method is not particularly limited, and examples thereof include dialysis, centrifugation washing, and ion exchange using an ion exchange resin.

[0065] <Dispersion medium> The dispersion medium used in producing the polymer-containing liquid is not particularly limited, but is preferably one that can more efficiently obtain the conductive polymer dispersion and maintain high dispersion stability. In addition, the dispersion medium is preferably one that can dissolve or disperse the electrical conductivity enhancer, more preferably one that can dissolve it, and even more preferably one that can dissolve all of the electrical conductivity enhancer contained in the conductive polymer dispersion.

[0066] Examples of the dispersion medium include water; amides such as N-vinylpyrrolidone, hexamethylphosphortriamide, N-vinylformamide, and N-vinylacetamide; phenols such as cresol, phenol, and xylenol; diols such as 1,3-butylene glycol, 1,4-butylene glycol, isoprene glycol, butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, and neopentyl glycol; carbonates such as ethylene carbonate and propylene carbonate; ethers such as dioxane, diethyl ether, propylene glycol dialkyl ether, polyethylene glycol dialkyl ether, and polypropylene glycol dialkyl ether; heterocyclic compounds such as 3-methyl-2-oxazolidinone; and nitriles such as acetonitrile, glutarodinitrile, methoxyacetonitrile, propionitrile, and benzonitrile. The dispersion medium may be used alone or in combination of two or more. Among these, from the viewpoint of good dispersion stability of the conductive polymer dispersion and ease of production, it is preferable that the dispersion medium contains 1 to 99 mass %, more preferably 50 to 99 mass %, and even more preferably water alone. The same applies to the dispersion medium in the conductive polymer dispersion.

[0067] <Polymerization Reaction> When a polymer-containing liquid is produced by polymerizing a monomer that becomes a structural unit of a conjugated conductive polymer in a liquid containing a polyanion, the content of components other than the dispersion medium in the polymerization raw material liquid is preferably 0.1 to 99% by mass, more preferably 1 to 90% by mass, and even more preferably 2 to 70% by mass, from the viewpoint of appropriate viscosity and reactivity during the polymerization reaction.

[0068] From the viewpoints of the dispersion stability of the conductive polymer dispersion and the effect of reducing the ESR of a solid electrolytic capacitor produced using the conductive polymer dispersion, the total content of polyanions in the polymerization raw material liquid is preferably an amount such that the number of anionic groups is 0.25 to 30 mol, more preferably 0.5 to 25 mol, and even more preferably 0.8 to 20 mol per mol of the monomer that becomes the structural unit of the conjugated conductive polymer.

[0069] In order to prevent the polymerization reaction from proceeding unevenly, the polymerization raw material liquid preferably contains a monomer that is a structural unit of the conjugated conductive polymer dissolved, emulsified, or dispersed in the polymerization raw material liquid. The polymerization raw material liquid can be prepared, for example, by stirring with a stirrer such as a homomixer or a homogenizer, or by ultrasonic irradiation.

[0070] The polymerization reaction is preferably carried out in the presence of an oxidizing agent. Examples of the oxidizing agent include peroxodisulfuric acid salts such as peroxodisulfuric acid, ammonium peroxodisulfate, sodium peroxodisulfate, and potassium peroxodisulfate; metal halide compounds such as boron trifluoride; transition metal compounds such as iron(III) chloride, iron(III) sulfate, and copper(II) chloride; metal oxides such as silver oxide and cesium oxide; peroxides such as hydrogen peroxide and ozone; organic peroxides such as benzoyl peroxide; and oxygen. Among these, peroxodisulfuric acid, peroxodisulfates, and transition metal compounds are preferred, and peroxodisulfates and transition metal compounds are more preferred. The oxidizing agent may be used alone or in combination of two or more.

[0071] From the viewpoint of appropriately promoting the polymerization reaction, the amount of the oxidizing agent used is preferably 50 to 1500 parts by mass, more preferably 70 to 1000 parts by mass, and even more preferably 100 to 500 parts by mass relative to 100 parts by mass of the monomer that becomes the structural unit of the conjugated conductive polymer.

[0072] The temperature in the polymerization reaction is preferably 5 to 80° C., more preferably 10 to 60° C., and even more preferably 15 to 40° C., from the viewpoint of achieving an appropriate reaction rate and suppressing an increase in the viscosity of the reaction solution. The temperature may be changed as appropriate depending on the progress of the reaction.

[0073] The polymerization reaction is preferably carried out with stirring from the viewpoint of homogenizing the reaction system and suppressing aggregation of particles in the reaction solution. The stirring method is not particularly limited, and examples thereof include a method of circulating and stirring the reaction solution using a high-shear mixer or the like.

[0074] From the viewpoint of uniform and efficient purification, the polymer-containing liquid is preferably obtained by dispersing the product liquid obtained by the polymerization reaction. Examples of the dispersion treatment device include a homogenizer, a ball mill, a high-shear mixer, and an ultrasonic disperser. For example, a dispersing device having a shear rate of 5000 s －１ It is preferable to use means that apply a strong shear force of at least 100 Hz, such as stirring, a pressure homogenizer, or ultrasonic irradiation at a frequency of about 15 to 100 Hz. The dispersion treatment may be performed by flow or batch processing, and may be performed once or multiple times. When a pressure homogenizer is used, the pressure is preferably 1 to 200 MPa, more preferably 2 to 150 MPa, and even more preferably 5 to 100 MPa, from the viewpoint of improving the efficiency of the dispersion treatment and suppressing the rise in liquid temperature. When a pressure homogenizer is used, the dispersion treatment time is preferably 15 to 240 minutes, more preferably 20 to 210 minutes, and even more preferably 30 to 180 minutes, from the viewpoint of improving the efficiency of the dispersion treatment. If the dispersion treatment involves an increase in liquid temperature, a cooler may be used. The cooler is not particularly limited as long as it can control the increase in liquid temperature. Examples include a plate-type heat exchanger, a spiral-type heat exchanger, a tubular heat exchanger, a throw-in heat exchanger, and a jacketed tank. Among these, plate-type heat exchangers and spiral-type heat exchangers are preferred from the viewpoints of heat exchange efficiency and device size.

[0075] The obtained polymer-containing liquid preferably has a solids concentration of 0.2 to 15% by mass, more preferably 0.5 to 10% by mass, and even more preferably 1 to 8% by mass, from the viewpoint of good miscibility with the electrical conductivity improver added later. The polymer-containing liquid may be diluted as appropriate. Dilution may be performed before, during, or after the dispersion treatment. From the viewpoint of improving the efficiency of the dispersion treatment and suppressing re-aggregation of particles in the liquid, it is preferable to dilute the polymer-containing liquid during the dispersion treatment and repeat the dispersion treatment multiple times. The dispersion medium used for dilution is preferably the same as the dispersion medium used in preparing the polymerization raw material liquid, from the viewpoint of avoiding a significant change in the dispersibility of the polymer-containing liquid, and water or an aqueous medium is more preferable.

[0076] (Purification Treatment) The polymer-containing liquid is subjected to a purification treatment in order to suppress aggregation of particles in the conductive polymer dispersion, to suppress corrosion of metals and the like that come into contact with the conductive polymer dispersion, and to suppress dedoping of polyanions from the conjugated conductive polymer.

[0077] The purification process involves at least one of ion exchange and ultrafiltration. Ion exchange removes unnecessary ions from the polymer-containing solution. Ultrafiltration removes fine particles from the polymer-containing solution. Other purification processes, such as dialysis and centrifugation washing, may also be performed.

[0078] In ion exchange, for example, an ion exchange resin is used to desalt the polymer-containing liquid. The polymer-containing liquid after ion exchange may be strongly acidic with a pH of less than 3.0. In this case, the pH is adjusted to preferably 3.0 to 8.0, more preferably 4.0 to 7.5, and even more preferably 4.5 to 7.0, by adding an alkaline compound. The amount of alkaline compound added is adjusted appropriately depending on the desired pH. The alkaline compound is not particularly limited, and organic or inorganic alkaline compounds can be used. The alkaline compounds may be used alone or in combination of two or more.

[0079] Examples of organic alkaline compounds include aromatic amines, aliphatic amines, heterocyclic amines, and alkali metal alkoxides. Examples of aromatic amines include nitrogen-containing heteroaryls such as pyridines, imidazoles, pyrimidines, pyrazines, and triazines. Among these, pyridines, imidazoles, and pyrimidines are preferred from the viewpoint of solubility and the like. Examples of aliphatic amines include ethylamine, n-octylamine, diethylamine, diisobutylamine, methylethylamine, trimethylamine, triethylamine, allylamine, 2-ethylaminoethanol, 2,2'-iminodiethanol, and N-ethylethylenediamine. Examples of heterocyclic amines include azetidines, pyrrolidines, piperidines, piperazines, morpholines, and thiomorpholines. Among these, morpholines are preferred from the viewpoint of versatility.

[0080] Specific examples of morpholines include morpholine, 4-methylmorpholine, 4-ethylmorpholine, 4-n-propylmorpholine, 4-isopropylmorpholine, 4-n-butylmorpholine, 4-isobutylmorpholine, 4-pentylmorpholine, 4-hexylmorpholine, (R)-3-methylmorpholine, (S)-3-methylmorpholine, cis-2,6-dimethylmorpholine, 4-(1-cyclohexenyl)morpholine, 1-morpholino-1-cyclopentene, 4-phenylmorpholine, 4-(p-tolyl)morpholine, 4-(2-aminoethyl)morpholine, 4-(3-aminopropyl)morpholine, 2-morpholinoaniline, and 4-morpholinoaniline. , 4-(2-morpholinoethoxy)aniline, 4-(4-pyridyl)morpholine, 4-aminomorpholine, 4-(2-hydroxypropyl)morpholine, 4-(2-hydroxyethyl)morpholine, 4-(3-hydroxypropyl)morpholine, 2-hydroxy-3-morpholinopropanesulfonic acid, 2-morpholinoethanesulfonic acid, 3-morpholinopropanesulfonic acid, 4-acetylmorpholine, 4-acetoacetylmorpholine, 4-acryloylmorpholine, 4-allylmorpholine, phenylmorpholine, ethyl 3-(morpholino)propionate, 4-formylmorpholine, 4-(4-formylphenyl)morpholine, and salts thereof. Among these, from the viewpoints of availability and ease of handling, morpholine, 4-ethylmorpholine, 4-n-butylmorpholine, 4-isobutylmorpholine, 4-phenylmorpholine, 4-(2-hydroxypropyl)morpholine, 4-(2-hydroxyethyl)morpholine, and 4-(3-hydroxypropyl)morpholine are preferred, morpholine, 4-ethylmorpholine, and 4-(2-hydroxyethyl)morpholine are more preferred, and morpholine is even more preferred.

[0081] Examples of alkali metal alkoxides include sodium alkoxides such as sodium methoxide and sodium ethoxide; potassium alkoxides; and calcium alkoxides.

[0082] Examples of inorganic alkaline compounds include ammonia, sodium hydroxide, potassium hydroxide, calcium hydroxide, and ammonia.

[0083] (Dispersion treatment) After the polymer-containing liquid is purified, it is dispersed to obtain a first dispersion. It is presumed that by dispersing after the purification treatment, aggregation of polymer particles is more effectively suppressed and the dispersion stability of the polymer-containing liquid is improved. The dispersion treatment can be carried out using the same equipment, method, and conditions as the dispersion treatment described above before the purification treatment.

[0084] The first dispersion may be diluted as appropriate in the same manner as in the dispersion treatment before the purification treatment. The solids concentration of the first dispersion is preferably 0.2 to 15 mass %, more preferably 0.5 to 10 mass %, and even more preferably 1 to 8 mass %, from the viewpoint of good miscibility with the electrical conductivity improver to be added later.

[0085] [Step (2)] In step (2), an electrical conductivity improver is added to the first dispersion. By adding the electrical conductivity improver after step (1), the ESR of the solid electrolytic capacitor produced using the conductive polymer dispersion can be effectively reduced.

[0086] In order to obtain a more homogeneous conductive polymer dispersion, it is preferable to further carry out a dispersion treatment after adding the electrical conductivity improver. It is believed that the more homogeneous the dispersion state of the conductive polymer dispersion, the more easily an appropriate conductive path is formed in a solid electrolyte formed using the conductive polymer dispersion, and the performance of the solid electrolyte is improved.

[0087] The dispersion treatment in step (2) can be carried out using the same apparatus, method and conditions as those for the dispersion treatment in step (1).

[0088] The conductive polymer dispersion obtained in step (2) preferably has a solids concentration of 0.2 to 15 mass%, more preferably 0.5 to 10 mass%, and even more preferably 1 to 8 mass%, from the viewpoint of production efficiency of the solid electrolyte of the solid electrolytic capacitor. The conductive polymer dispersion may be diluted appropriately in the same manner as the dispersion treatment in step (1). Dilution may be performed before, during, or after the dispersion treatment. From the viewpoint of improving the efficiency of the dispersion treatment, dilution before the dispersion treatment is preferred. The dispersion medium used for dilution is preferably the same as the dispersion medium used in preparing the polymerization raw material liquid, from the viewpoint of avoiding a significant change in the dispersibility of the first dispersion, and water or an aqueous medium is more preferred.

[0089] The content of the conjugated conductive polymer in the conductive polymer dispersion is preferably 5 to 70 mass %, more preferably 10 to 60 mass %, and even more preferably 15 to 50 mass %, relative to 100 mass % of the polymer component, from the viewpoints of the dispersion stability of the conductive polymer dispersion and the effect of reducing the ESR of a solid electrolytic capacitor produced using the conductive polymer dispersion.

[0090] The content of the polyanion in the conductive polymer dispersion is preferably 30 to 95% by mass, more preferably 40 to 90% by mass, and even more preferably 50 to 85% by mass, relative to 100% by mass of the polymer component, from the viewpoints of stability in the conductive polymer dispersion and the effect of reducing the ESR of a solid electrolytic capacitor produced using the conductive polymer dispersion. The content of the polyanion is preferably 45 to 1900 parts by mass, more preferably 70 to 900 parts by mass, and even more preferably 100 to 500 parts by mass, relative to 100 parts by mass of the conjugated conductive polymer.

[0091] The content of the polymer (Z) in the conductive polymer dispersion is preferably 0 to 50 mass%, more preferably 0 to 40 mass%, and even more preferably 0 to 25 mass%, relative to 100 mass% of the polymer component, from the viewpoints of the dispersion stability of the conductive polymer dispersion and the effect of reducing the ESR of a solid electrolytic capacitor produced using the conductive polymer dispersion.

[0092] The content of the dispersion medium in the conductive polymer dispersion is preferably 30 to 98 mass %, more preferably 45 to 97 mass %, and even more preferably 60 to 94 mass %, from the viewpoint of appropriate viscosity and dispersion stability of the conductive polymer dispersion.

[0093] (Electrical Conductivity Enhancer) The electrical conductivity enhancer is added for the purpose of improving the electrical conductivity of the solid electrolyte layer formed from the conductive polymer dispersion. It is thought that the electrical conductivity is improved by making the polymer arrangement of the conjugated conductive polymer more likely to form a good conductive path when the electrical conductivity enhancer volatilizes together with the dispersion medium during the formation of the solid electrolyte layer using the conductive polymer dispersion.

[0094] Examples of the electrical conductivity improver include ethers such as tetrahydrofuran; lactones such as γ-butyrolactone and γ-valerolactone; amides or lactams such as caprolactam, N-methylcaprolactam, N,N-dimethylacetamide, N-methylacetamide, N,N-dimethylformamide, N-methylformamide, N-methylformanilide, N-methylpyrrolidone, N-octylpyrrolidone, and pyrrolidone; sulfones or sulfoxides such as tetramethylene sulfone and dimethyl sulfoxide; sugars and derivatives thereof such as sucrose, glucose, fructose, and lactose; sugar alcohols such as sorbitol and mannitol; imides such as succinimide and maleimide; furans such as 2-furancarboxylic acid and 3-furancarboxylic acid; and polyhydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, and diglycerin. Among these, ethers, lactones, amides or lactams, sugar alcohols, and polyhydric alcohols are preferred, and polyhydric alcohols are more preferred. Specific examples of the compound include, from the viewpoint of improving electrical conductivity, tetrahydrofuran, γ-butyrolactone, N-methylformamide, N-methylpyrrolidone, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, diglycerin, dimethyl sulfoxide, and sorbitol, more preferably ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, and diglycerin, and even more preferably triethylene glycol, glycerin, and diglycerin. The electrical conductivity improver may be used alone or in combination of two or more.

[0095] The content of the electrical conductivity improver in the conductive polymer dispersion is preferably 1 to 50 parts by mass, more preferably 2 to 40 parts by mass, and even more preferably 3 to 30 parts by mass per part by mass of the solid content of the first dispersion. By having this content of 1 part by mass or more, the ESR of the solid electrolytic capacitor can be effectively reduced. Furthermore, if the content is 50 parts by mass or less, good dispersion stability of the conductive polymer dispersion is easily maintained. Furthermore, from the viewpoint of the stability of the conductive polymer dispersion and effectively reducing the ESR of the solid electrolytic capacitor, the content of the electrical conductivity improver in the conductive polymer dispersion is preferably 0.5 to 50% by mass, more preferably 3 to 40% by mass, and even more preferably 5 to 25% by mass.

[0096] (Other Additives) From the viewpoint of imparting properties suitable for solid electrolytic capacitors, the conductive polymer dispersion of the present disclosure may contain other additives that do not fall under any of the categories of conjugated conductive polymers, polyanions, polymers (Z), electrical conductivity improvers, and alkaline compounds. The types and amounts of the other additives are not particularly limited. The other additives may be added in step (1). Examples of the other additives include water-soluble polymer compounds, water-dispersible compounds, surfactants, antifoaming agents, coupling agents, and antioxidants. The other additives may be used alone or in combination of two or more.

[0097] The water-soluble polymer compound and the water-dispersible compound can adjust the viscosity of the conductive polymer dispersion and improve the coating performance. When at least one of the water-soluble polymer compound and the water-dispersible compound is added, the total content of the water-soluble polymer compound and the water-dispersible compound is preferably 1 to 50 parts by mass, more preferably 2 to 40 parts by mass, and even more preferably 3 to 30 parts by mass per part by mass of the polymer component contained in the conductive polymer dispersion.

[0098] Examples of water-soluble polymer compounds include polyoxyalkylenes, water-soluble polyurethanes, water-soluble polyesters, water-soluble polyamides, water-soluble polyimides, water-soluble polyacrylics, water-soluble polyacrylamides, polyvinyl alcohols, and polyacrylic acids. Among these, polyoxyalkylenes are preferred. Examples of polyoxyalkylenes include oligopolyethylene glycol, triethylene glycol monochlorhydrin, diethylene glycol monochlorhydrin, oligoethylene glycol monochlorhydrin, triethylene glycol monobromohydrin, diethylene glycol monobromohydrin, oligoethylene glycol monobromohydrin, glycidyl ethers, polyethylene glycol glycidyl ethers, polyethylene oxide, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, dipropylene glycol, tripropylene glycol, polypropylene glycol, polypropylene dioxide, polyoxyethylene alkyl ethers, polyoxyethylene glycerin fatty acid esters, and polyoxyethylene fatty acid amides.

[0099] The water-dispersible compound is preferably one that disperses in water without precipitating, for example, by substituting a portion of a less hydrophilic compound with a more hydrophilic functional group. Examples of the water-dispersible compound include polyester, polyurethane, acrylic resin, silicone resin, and compounds obtained by modifying these by introducing a functional group or the like. Other examples include block copolymers and graft copolymers of acrylic resin with polyester or polyurethane.

[0100] Examples of surfactants include anionic surfactants such as carboxylates, sulfonates, sulfates, and phosphates; cationic surfactants such as amine salts and quaternary ammonium salts; amphoteric surfactants such as carboxybetaine, aminocarboxylates, and imidazolium betaine; and nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene glycerin fatty acid esters, ethylene glycol fatty acid esters, and polyoxyethylene fatty acid amides. Examples of antifoaming agents include silicone resins, polydimethylsiloxanes, and silicone oils. Examples of antioxidants include phenolic antioxidants, amine antioxidants, phosphorus antioxidants, sulfur-based antioxidants, and vitamins.

[0101] [Method for manufacturing a solid electrolytic capacitor] The method for manufacturing a solid electrolytic capacitor of the present disclosure includes the steps of: depositing the conductive polymer dispersion obtained by the above-described method for manufacturing a solid electrolytic capacitor of the present disclosure onto a porous anode body that is a valve metal having a dielectric coating on its surface; and then removing the dispersion medium from the conductive polymer dispersion deposited on the porous anode body to form a solid electrolyte layer. By forming a solid electrolyte layer using the conductive polymer dispersion obtained by the method for manufacturing a solid electrolytic capacitor of the present disclosure through the above-described steps, a solid electrolytic capacitor with a low ESR can be suitably manufactured.

[0102] Examples of valve metals include aluminum, beryllium, bismuth, magnesium, germanium, hafnium, niobium, antimony, silicon, tin, tantalum, titanium, vanadium, tungsten, and zirconium, as well as alloys or compounds containing at least one of these metals. Among these, aluminum, niobium, and tantalum are preferred from the viewpoint of versatility.

[0103] A porous anode body can be produced by forming a dielectric coating on the surface of a porous valve metal. The porous valve metal can be obtained, for example, by sintering a valve metal powder with a high specific surface area or by etching a valve metal foil. The dielectric coating can be formed as a dielectric oxide coating on the surface of the porous valve metal, for example, by anodizing the porous valve metal in a phosphate solution. The formation voltage in the anodization is set depending on the thickness of the dielectric oxide coating and the withstand voltage of the capacitor, and is preferably 1 to 800 V, more preferably 1 to 500 V, and even more preferably 1 to 300 V.

[0104] The conductive polymer dispersion can be applied to the porous anode body by, for example, coating, spraying, immersion, etc. Among these methods, the method of immersing the porous anode body in the conductive polymer dispersion is preferred because it allows the conductive polymer dispersion to penetrate evenly and uniformly into the porous anode body and adhere to it. Furthermore, impregnation may be performed under reduced pressure in order to allow the conductive polymer dispersion to fully penetrate into the pores and other details of the porous anode body.

[0105] When the conductive polymer dispersion is attached to the porous anode body by immersing it therein, the conductive polymer dispersion is usually impregnated into the porous anode body at a temperature of about 10 to 35° C. for about 10 seconds to 10 minutes, although the temperature varies depending on the type and viscosity of the dispersion medium of the conductive polymer dispersion.

[0106] From the viewpoint of removal efficiency, the dispersion medium is preferably removed by heating and drying the porous anode body to which the conductive polymer dispersion is attached. The heating conditions are appropriately set taking into consideration the boiling point and volatility of the dispersion medium, and oxidative degradation of the polymer component, etc., and the heat treatment is typically performed at room temperature to 300°C, preferably 40 to 250°C, and more preferably 50 to 200°C, for 5 seconds to several hours. Examples of heating devices that can be used include a hot plate, oven, and hot air dryer. From the viewpoint of drying efficiency, drying may be performed under reduced pressure. Note that the removal of the dispersion medium here does not necessarily mean achieving a state in which the dispersion medium is completely removed; some dispersion medium may remain within a range that does not interfere with the production of the solid electrolytic capacitor.

[0107] From the viewpoint of achieving a uniform thickness of the solid electrolyte layer, the above steps may be repeated. The solid electrolyte layer formed in the above steps may be impregnated with an arbitrary electrolytic solution. Examples of the electrolytic solution to be impregnated into the solid electrolyte layer include polar organic solvents that may contain salts.

[0108] As the polar organic solvent for the electrolytic solution, a protic solvent can be used, and examples thereof include monohydric alcohols such as ethanol, propanol, butanol, pentanol, hexanol, cyclobutanol, cyclopentanol, cyclohexanol, and benzyl alcohol; polyhydric alcohols such as ethylene glycol, diethylene glycol, propylene glycol, glycerin, methyl cellosolve, ethyl cellosolve, methoxypropylene glycol, dimethoxypropanol, and alkylene oxide adducts of polyethylene glycol and polyoxyethylene glycerin; and oxyalcohol compounds. In addition, an aprotic solvent can also be used as the polar organic solvent, and examples thereof include sulfones such as dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, sulfolane, 3-methyl sulfolane, and 2,4-dimethyl sulfolane; amides such as N-methylformamide, N,N-dimethylformamide, N-ethylformamide, N,N-diethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylacetamide, N,N-diethylacetamide, and hexamethylphosphoric amide; lactones and cyclic amides such as γ-butyrolactone, γ-valerolactone, δ-valerolactone, N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butylene carbonate, and isobutylene carbonate; nitriles such as acetonitrile, 3-methoxypropionitrile, and glutaronitrile; and oxides such as dimethyl sulfoxide.

[0109] Examples of salts include ammonium salts; quaternary ammonium salts such as tetramethylammonium salt, triethylmethylammonium salt, and tetraethylammonium salt; amidinium salts such as ethyldimethylimidazolinium salt and tetramethylimidazolinium salt; primary amine salts such as methylamine salt, ethylamine salt, and propylamine salt; secondary amine salts such as dimethylamine salt, diethylamine salt, ethylmethylamine salt, and dibutylamine salt; tertiary amine salts such as trimethylamine salt, triethylamine salt, tributylamine salt, ethyldimethylamine salt, and ethyldiisopropylamine salt; sodium salts; and potassium salts.

[0110] Examples of acids that can form salts include carboxylic acids such as oxalic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, maleic acid, adipic acid, benzoic acid, toluic acid, enanthic acid, malonic acid, 1,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, azelaic acid, resorcylic acid, phloroglucinic acid, gallic acid, gentisic acid, protocatechuic acid, pyrocatechuic acid, trimellitic acid, and pyromellitic acid; and organic acids such as sulfonic acids. Further examples include boric acid, phosphoric acid, phosphorous acid, hypophosphorous acid, carbonic acid, and silicic acid. Further examples include boron complexes such as borodisalicylic acid, borodisalic acid, borodiglycolic acid, borodimalonic acid, borodisuccinic acid, borodiadipic acid, borodiazelaic acid, borodibenzoic acid, borodimaleic acid, borodilactic acid, borodimalic acid, boroditartaric acid, borodicitric acid, borodiphthalic acid, borodi(2-hydroxy)isobutyric acid, borodiresorcylic acid, borodimethylsalicylic acid, borodinaphthoic acid, borodimandelic acid, and borodi(3-hydroxy)propionic acid.

[0111] The electrolytic solution may contain an additive. Examples of the additive include complex compounds of boric acid and polysaccharides such as mannitol and sorbitol; complex compounds of boric acid and polyhydric alcohols; boric acid esters; nitro compounds such as o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, p-nitrophenol, and p-nitrobenzyl alcohol; and phosphate esters. These may be used alone or in combination of two or more.

[0112] Hereinafter, embodiments of the present disclosure will be specifically described based on examples. The present disclosure is not limited to the following examples, and various modifications are possible within the scope of the present disclosure.

[0113] [Measurement Methods] The methods for measuring various physical properties in the Examples and Comparative Examples are as follows. [Weight Average Molecular Weight] The weight average molecular weight (Mw) of sodium polystyrene sulfonate was determined as the molecular weight in terms of standard polystyrene measured by gel permeation chromatography under the following measurement conditions. <Measurement Conditions> Measurement apparatus: "Shodex GPC 101", manufactured by Resonac Co., Ltd. Column used: "OHpak SB-806M HQ", manufactured by Resonac Co., Ltd. Column temperature: 40°C Eluent: Water Elution rate: 1 mL / min Standard sample: Polystyrene

[0114] [Cumulative volume 50% particle diameter (d ５０ ) )] Cumulative volume 50% particle diameter of particles (d ５０ The particle size distribution was measured using a particle size distribution analyzer (Microtrac UPA type, manufactured by Nikkiso Co., Ltd.) and calculated using the accompanying software (Microtrac II) under the following conditions: <Setting conditions> Particles: transparent, spherical, refractive index 1.59, density 1.00 g / cm ３ Solvent: refractive index 1.333, viscosity 0.797 mPa·s (30°C), 1.002 mPa·s (20°C)

[0115] [Solid content concentration] The solid content concentration was calculated by weighing 10 g of the sample liquid and heating it for 30 minutes using an infrared moisture meter (FD-720, manufactured by Kett Electric Laboratory) at a temperature 10°C higher than the boiling point of the dispersion medium with the highest boiling point among the dispersion mediums contained (110°C when the dispersion medium is water), and then estimating the evaporation residue (excluding morpholine) as the solid content.

[0116] [pH] The pH was measured using a pH meter ("HM-30G", manufactured by DKK-TOA Corporation; 25°C).

[0117] [Production of Conductive Polymer Dispersion] [Synthesis of Polymer (Z)-Containing Liquid] 86 g of styrene, 49 g of 2-ethylhexyl acrylate, 15 g of divinylbenzene, and 500 g of a 22% by weight aqueous solution of sodium polystyrene sulfonate (SPS: "Polinas PS-5," manufactured by Tosoh Finechem Corporation; Mw 120,000; the same applies hereinafter) (110 g of SPS) were mixed with stirring to prepare polymerization raw material liquid (a). Furthermore, 1,000 g of a 22% by weight aqueous solution of SPS was heated to 80°C with stirring, and 2 g of potassium persulfate was added thereto to prepare polymerization raw material liquid (b). Polymerization raw material liquid (a) was added dropwise to polymerization raw material liquid (b) over 2 hours, followed by dropwise addition of 40 g of a 2.5% by weight aqueous solution of potassium persulfate over 2.5 hours. The mixture was allowed to react at 80°C for 2 hours and then cooled to room temperature (25°C). To the reaction product, 1500 mL of a cation exchange resin ("Amberlite IR120B-H" manufactured by Organo Corporation; the same applies hereinafter) and 1500 mL of an anion exchange resin ("Amberlite IRA410-OH" manufactured by Organo Corporation; the same applies hereinafter) were added, and the mixture was stirred for 12 hours. The ion exchange resin was then filtered off. Pure water was added to obtain a polymer (Z)-containing solution (solid concentration 15.0% by mass, d of contained particles) containing polyanion (SPS). ５０ 0.46 μm).

[0118] Example 1 (Production process of conjugated conductive polymer-containing liquid) In a 1 L polyethylene container, 34.0 g of polymer (Z)-containing liquid, 31.5 g of a 12% by mass aqueous solution of SPS, and 150.2 g of pure water were mixed by stirring at 32°C. 2.8 g of 3,4-ethylenedioxythiophene (EDOT) was added thereto, and the mixture was stirred in a homomixer (Robomix, manufactured by Primix Corporation) for 4000 min. －１ The resulting monomer solution (218.5 g) was emulsified and mixed in a high-shear mixer (Milder MDN303V, manufactured by Pacific Machinery Works, Ltd.; 5000 min). －１ The reaction solution was stirred while circulating with a stirring blade and a high-shear mixer, and 5.9 g of sodium peroxodisulfate and 6.9 g of a 1 mass % aqueous solution of iron (III) sulfate hexahydrate were added, and the polymerization reaction was carried out for 24 hours to obtain a product solution (1) containing a conjugated conductive polymer (PEDOT) (solid concentration 7.6 mass %, 270 parts by mass of SPS per 100 parts by mass of the conjugated conductive polymer).

[0119] The product liquid (1) was diluted with pure water to 1500 mL (solid content concentration 4.7% by mass) and then subjected to a dispersion treatment for 45 minutes using a pressure homogenizer ("TwinPanda 600", manufactured by Niro Soavi; 400 bar (40 MPa); the same applies hereinafter). Further, pure water was added for dilution, and 1500 mL (solid content concentration 3.9% by mass) was subjected to a dispersion treatment for 135 minutes using a pressure homogenizer to obtain a conjugated conductive polymer-containing liquid (1).

[0120] (Step (1)) The conjugated conductive polymer-containing liquid (1) was purified by ion exchange for 3 hours using 125.6 mL of a cation exchange resin and 109.9 mL of an anion exchange resin. To the obtained liquid (pH 1.9, solid content concentration 1.65 mass%), 10.0 g of morpholine and pure water were added to adjust the pH (pH 4.7, solid content concentration 1.6 mass%), and then the liquid was subjected to a dispersion treatment for 60 minutes using a pressure homogenizer to obtain a first dispersion (1).

[0121] (Step (2)) To the first dispersion (1), 6.3 parts by mass of triethylene glycol and 18.7 parts by mass of diglycerin (total 25.0 parts by mass) were added as an electrical conductivity improver relative to 1 part by mass of the solid content in the first dispersion (1), and the mixture was subjected to a dispersion treatment for 60 minutes using a pressure homogenizer, thereby obtaining a conductive polymer dispersion (solid content concentration 1.1% by mass, pH 4.9).

[0122] Comparative Example 1 A conductive polymer dispersion was produced through the same steps as in Example 1, except that the dispersion treatment after the purification treatment in step (1) was not carried out.

[0123] Example 2 (Manufacturing Process for Conjugated Conductive Polymer-Containing Liquid) In a 1 L polyethylene container, 23.8 g of polymer (Z)-containing liquid, 22.1 g of a 12% by weight aqueous solution of SPS, and 170.6 g of pure water were stirred and mixed at 32°C. 2.1 g of EDOT was added to this mixture, and the mixture was emulsified and mixed using a homomixer for 30 minutes to prepare monomer liquid (2). 218.5 g of the resulting monomer liquid (2) was placed in a stainless steel container connected to a high-shear mixer and a circulation pump, stirred while circulating using a stirring blade and high-shear mixer, and 4.1 g of sodium peroxodisulfate and 4.8 g of a 1% by weight aqueous solution of iron (III) sulfate hexahydrate were added. The polymerization reaction was carried out for 24 hours to obtain a PEDOT-containing product liquid (2) (257 parts by weight of SPS per 100 parts by weight of the conjugated conductive polymer). The product liquid (2) was diluted and dispersed in the same manner as the product liquid (1) in Example 1 to obtain a conjugated conductive polymer-containing liquid (2).

[0124] (Step (1)) In the same manner as in step (1) of Example 1, a first dispersion (2) was obtained from the conjugated conductive polymer-containing liquid (2).

[0125] (Step (2)) To the first dispersion (2), 6.3 parts by mass of triethylene glycol and 12.5 parts by mass of diglycerin (total 18.8 parts by mass) were added as electrical conductivity improvers relative to 1 part by mass of the solid content in the first dispersion (2), and the mixture was subjected to a dispersion treatment for 60 minutes using a pressure homogenizer, thereby obtaining a conductive polymer dispersion (solid content concentration 1.2% by mass, pH 4.9).

[0126] Comparative Example 2 A conductive polymer dispersion was produced through the same steps as in Example 2, except that the dispersion treatment after the purification treatment in step (1) was not carried out.

[0127] Example 3 (Manufacturing Process for Conjugated Conductive Polymer-Containing Liquid) In a 1 L polyethylene container, 23.8 g of polymer (Z)-containing liquid, 22.1 g of a 12% by weight aqueous solution of SPS, and 170.5 g of pure water were stirred and mixed at 32 ° C. 2.2 g of EDOT was added to the mixture, and the mixture was emulsified and mixed using a homomixer for 30 minutes to prepare a monomer solution (3). 218.5 g of the resulting monomer solution (3) was placed in a stainless steel container connected to a high-shear mixer and a circulation pump, and stirred while circulating using a stirring blade and high-shear mixer. 4.1 g of sodium peroxodisulfate and 4.8 g of a 1% by weight aqueous solution of iron (III) sulfate hexahydrate were added, and the polymerization reaction was carried out for 24 hours to obtain a PEDOT-containing product solution (3) (245 parts by weight of SPS per 100 parts by weight of the conjugated conductive polymer). The product liquid (3) was diluted and dispersed in the same manner as the product liquid (1) in Example 1 to obtain a conjugated conductive polymer-containing liquid (3).

[0128] (Step (1)) In the same manner as in step (1) of Example 1, a first dispersion (3) was obtained from the conjugated conductive polymer-containing liquid (3).

[0129] (Step (2)) To the first dispersion (3), 6.3 parts by mass of triethylene glycol and 12.5 parts by mass of diglycerin (total 18.8 parts by mass) were added as an electrical conductivity improver relative to 1 part by mass of the solid content in the first dispersion (3), and an electrical conductivity improver addition step was carried out in the same manner as in Example 1, thereby obtaining a conductive polymer dispersion (solid content concentration 1.2% by mass, pH 4.9).

[0130] Comparative Example 3 A conductive polymer dispersion was produced through the same steps as in Example 2, except that the dispersion treatment after the purification treatment in step (1) in Example 3 was not carried out.

[0131] Example 4 A conductive polymer dispersion (solid content concentration 1.3 mass%, pH 4.9) was obtained in the same manner as in Example 3, except that the electrical conductivity enhancer added in Example 3 was 3.1 parts by mass of triethylene glycol and 9.4 parts by mass of diglycerin (total 12.5 parts by mass) per 1 part by mass of the solid content in the first dispersion (3).

[0132] Comparative Example 4 A conductive polymer dispersion was produced in the same manner as in Example 4, except that the dispersion treatment after the purification treatment in step (1) was not carried out.

[0133] [Production of Solid Electrolytic Capacitor] Using each of the conductive polymer dispersions produced in the above Examples and Comparative Examples, solid electrolytic capacitors were produced as follows: A porous anode body of an aluminum electrolytic capacitor element (withstand voltage 35 V, design capacity 400 μF) was impregnated with the conductive polymer dispersion under reduced pressure at 20 kPa and 25° C. for 5 minutes, and then dried in a hot air dryer ("ST-110", manufactured by Espec Corporation) at 150° C. for 30 minutes to obtain a solid electrolytic capacitor sample in which a solid electrolyte layer was formed on the surface of the dielectric coating of the porous anode body.

[0134] The equivalent series resistance (ESR) [mΩ] of each solid electrolytic capacitor sample was measured at 100 kHz and 120 Hz using a precision LCR meter ("E4980A", manufactured by Agilent Technologies, Inc.). The measurement results are shown in Table 1.

[0135]

[0136] As can be seen from the results shown in Table 1, it was confirmed that the conductive polymer dispersions (Examples 1 to 4) produced by adding an electrical conductivity improver after the dispersion treatment following the purification treatment in step (1) were capable of reducing the ESR of solid electrolytic capacitors.

Claims

1. A method for producing a conductive polymer dispersion containing a conjugated conductive polymer-containing liquid and an electrical conductivity enhancer, comprising: a step of purifying a conjugated conductive polymer-containing liquid containing a polyanion, followed by a dispersion step to obtain a first dispersion; and a step of adding an electrical conductivity enhancer to the first dispersion, wherein the purification step involves at least one of ion exchange and ultrafiltration.

2. The method for producing a conductive polymer dispersion according to claim 1, wherein after the addition of the electrical conductivity improver, a dispersion treatment is further carried out.

3. The method for producing a conductive polymer dispersion according to claim 1, wherein the electrical conductivity enhancer is at least one selected from the group consisting of tetrahydrofuran, γ-butyrolactone, N-methylformamide, N-methylpyrrolidone, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, diglycerin, dimethyl sulfoxide, and sorbitol.

4. The method for producing a conductive polymer dispersion according to claim 1, wherein the amount of the electrical conductivity improver added is 1 to 50 parts by mass per 1 part by mass of the solid content in the first dispersion.

5. The method for producing a conductive polymer dispersion according to claim 1, wherein the monomer that becomes a structural unit of the conjugated conductive polymer contains at least one compound selected from the group consisting of pyrroles, anilines, and thiophenes.

6. The method for producing a conductive polymer dispersion according to claim 5, wherein the thiophene compound is represented by the following formula (1): (In formula (1), R １ and R ２ are each independently a hydrogen atom, a hydroxyl group, an alkyl group having 1 to 18 carbon atoms which may have a substituent, an alkoxy group having 1 to 18 carbon atoms which may have a substituent, an alkylthio group having 1 to 18 carbon atoms which may have a substituent, or R １ and R ２ and are bonded to each other to form an alicyclic ring having 3 to 10 carbon atoms which may have a substituent, an aromatic ring having 6 to 10 carbon atoms which may have a substituent, an oxygen-atom-containing heterocyclic ring having 2 to 10 carbon atoms which may have a substituent, a sulfur-atom-containing heterocyclic ring having 2 to 10 carbon atoms which may have a substituent, or a sulfur- and oxygen-atom-containing heterocyclic ring having 2 to 10 carbon atoms which may have a substituent.

7. The method for producing a conductive polymer dispersion according to claim 1, wherein the polyanion is a polymer having two or more groups selected from the group consisting of sulfonic acid groups and sulfonate salts.

8. A method for producing a solid electrolytic capacitor, comprising the steps of: depositing the conductive polymer dispersion produced by the method of any one of claims 1 to 7 on a porous anode body that is a valve metal having a dielectric coating on its surface; and then removing the dispersion medium from the conductive polymer dispersion deposited on the porous anode body to form a solid electrolyte layer.

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