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

Abstract

A method for producing a conductive polymer dispersion, the method comprising a step for adding an electric conductivity improving agent to a dispersion that contains a conjugated conductive polymer and a polyanion and dispersing the same, wherein the step is performed at a liquid temperature of 30°C or higher.

Description

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

[0001] The present invention 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 and other devices because they can reduce equivalent series resistance (ESR) in the high-frequency range. Furthermore, with the recent trend toward more electronically equipped vehicles, development of solid electrolytic capacitors for automotive use is progressing. In particular, capacitors for vehicle electronic control devices are required to have a lower ESR in order to accommodate the increased output power provided by electronic control.

[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] However, in capacitors for in-vehicle devices, which have become increasingly high-output in recent years, even when a dispersion of a conductive polymer is produced by the method described in Patent Document 2, it cannot be said that the reduction in ESR is necessarily sufficient.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is 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 invention 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 invention provides the following means: [1] A method for producing a conductive polymer dispersion, comprising a step of adding an electrical conductivity enhancer to a dispersion containing a conjugated conductive polymer and a polyanion and performing a re-dispersion treatment, the step being carried out at a liquid temperature of 30°C or higher. [2] A method for producing a conductive polymer dispersion according to [1], wherein the liquid temperature is 40 to 80°C. [3] A method for producing a conductive polymer dispersion according to [1] or [2], wherein the amount of the electrical conductivity enhancer added is 1 to 50 parts by mass per part by mass of the solid content in the dispersion. [4] A method for producing a conductive polymer dispersion according to any of [1] to [3], wherein the electrical conductivity enhancer is one or more selected from tetrahydrofuran, γ-butyrolactone, N-methylformamide, N-methylpyrrolidone, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, diglycerin, dimethyl sulfoxide, and sorbitol. [5] The method for producing a conductive polymer dispersion according to any one of [1] to [4], wherein a monomer serving as a structural unit of the conjugated conductive polymer contains one or more compounds 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 ２are 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 a carbon atom-containing heterocycle which may have a substituent, 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-containing heterocyclic ring having 2 to 10 carbon atoms which may have a substituent, a sulfur-containing heterocyclic ring having 2 to 10 carbon atoms which may have a substituent, or a sulfur- and oxygen-containing heterocyclic ring having 2 to 10 carbon atoms which may have a substituent, formed by bonding together. (7) The method for producing the conductive polymer dispersion according to any one of [1] to [6], wherein the polyanion is a polymer having two or more groups formed of sulfonic acid or a salt thereof. (8) A method for producing a solid electrolytic capacitor, comprising the steps of: depositing the conductive polymer dispersion obtained by the method for producing any one of [1] to [7] on a porous anode body made of a valve metal having a dielectric coating on its surface; and removing the dispersion medium from the conductive polymer dispersion deposited on the porous anode body to form a solid electrolyte layer.

[0011] According to the present invention, 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.

[0012] 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 combined independently. The lower limit and upper limit values ​​of the numerical range may be replaced with numerical values ​​described in the Examples.

[0013] [Method for producing conductive polymer dispersion] A method for producing a conductive polymer dispersion according to an embodiment of the present invention (hereinafter referred to as "this embodiment") includes a step of adding an electrical conductivity improver to a dispersion (1) containing a conjugated conductive polymer and a polyanion and performing a re-dispersion treatment, and this step is carried out at a liquid temperature of 30° C. or higher. In the production of the conductive polymer dispersion, by setting the liquid temperature during dispersion in the step of adding the electrical conductivity improver and performing the re-dispersion treatment to a predetermined temperature, it is possible to reduce the ESR of a solid electrolytic capacitor produced using the conductive polymer dispersion.

[0014] (Dispersion (1)) The method for producing the dispersion (1) containing a conjugated conductive polymer and a polyanion is not particularly limited. When the dispersion (1) is produced by synthesis from a monomer, it can be obtained, for example, by polymerizing a monomer that becomes a structural unit of the conjugated conductive polymer in a liquid containing a polyanion.

[0015] From the viewpoint of dispersion stability of the conjugated conductive polymer and the polyanion, the dispersion liquid (1) may contain a polymer (Z) which does not fall into the category of either a conjugated conductive polymer or a polyanion, and may contain other additives.

[0016] <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. Furthermore, it may be a homopolymer of a monomer described below, which is a constituent unit of the conjugated conductive polymer, or a copolymer of two or more types of monomers.

[0017] The content of the conjugated conductive polymer in the dispersion (1) 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.

[0018] 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.

[0019] 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).

[0020] 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.

[0021] Examples of polyanilines include polyaniline, poly(2-methylaniline), poly(3-isobutylaniline), poly(2-anilinesulfonic acid), and poly(3-anilinesulfonic acid).

[0022] 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 excellent heat resistance.

[0023] 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 one or more compounds 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.

[0024] Examples of monomers that can be used as 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.

[0025] Among these compounds, the monomer serving as a constituent 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 having high conductivity. The compound represented by formula (1) may be used alone or in combination of two or more.

[0026]

[0027] 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.

[0028] 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.

[0029] The content of the compound represented by formula (1) in the monomer that serves as a constituent 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.

[0030] The monomer serving as a constituent unit of the conjugated conductive polymer preferably contains a compound represented by the following formula (2) among the compounds represented by formula (1), and more preferably contains 3,4-ethylenedioxythiophene:

[0031]

[0032] 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.

[0033] 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.

[0034] <Polyanion> A polyanion is a polymer having two or more anionic groups, and functions as a dopant for a conjugated conductive polymer.

[0035] The content of the polyanion in dispersion (1) 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 parts by 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. The content of the polyanion in dispersion (1) 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.

[0036] Examples of anionic groups include groups consisting of sulfonic acid or its salts, groups consisting of phosphoric acid or its salts, mono-substituted phosphate ester groups, groups consisting of carboxylic acid or its salts, and mono-substituted sulfate ester groups. Among these, strongly acidic groups are preferred, groups consisting of sulfonic acid or its salts, groups consisting of phosphoric acid or its salts are more preferred, and groups consisting of sulfonic acid or its salts are even more preferred. That is, as polyanions, polymers having two or more groups consisting of sulfonic acid or its salts are preferred. Examples of salts include salts of sodium, potassium, magnesium, calcium, ammonium, etc.

[0037] 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.

[0038] 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 the substituent is bonded to the 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.

[0039] The main chain structure of the polymer constituting the polyanion is not particularly limited, but from the viewpoints of synthesis and availability, for example, polyalkylene such as polyethylene is preferred.

[0040] As the polyanion, a compound having a group consisting of sulfonic acid or a salt thereof as an anionic group is preferred, as described above, in order to improve the dispersibility in the dispersion medium of the monomer that is the structural unit of the conjugated conductive polymer. A group consisting of sulfonic acid, i.e., a sulfo group (-SO ２Examples 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-methylpropane sulfonic acid), polyisoprene sulfonic acid, and copolymers thereof. 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.

[0041] Furthermore, the polyanion contained in the conductive polymer dispersion and the polyanion added in the production stage may have the same structure, or may have a different structure, such as one in which different cations are bound. For example, in the production stage, sodium polystyrene sulfonate is preferably used as the polyanion from the viewpoint of water solubility, etc., but it may be converted to polystyrene sulfonic acid in a production process such as ion exchange. The polyanion can be produced by the production method described in, for example, JP 2005-76016 A, or a commercially available product can also be used.

[0042] From the viewpoints of solubility in the dispersion medium and doping effect on the conjugated conductive polymer, the weight-average molecular weight of the polyanion is preferably 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.

[0043] <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 dispersion liquid (1), 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.

[0044] The content of the polymer (Z) in the dispersion (1) 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.

[0045] 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 consists of 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.

[0046] 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.

[0047] 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 with each other. 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.

[0048] 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.

[0049] 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 a ketone group) 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).

[0050] 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.

[0051] From the viewpoints of dispersion stability and suppression of sedimentation, the particles contained in the dispersion liquid containing the polymer (Z) have a 50% volume cumulative 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.

[0052] 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.

[0053] 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 a polyanion is coordinated to the polymer (Z), and a polyanion domain is formed outside the domain of the polymer (Z). 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 dispersion containing the polymer (Z). The polyanion in the dispersion containing the polymer (Z) and the polyanion contained in the dispersion (1) may be the same or different (e.g., different cations may be bonded).

[0054] 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.

[0055] 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.

[0056] 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).

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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 this embodiment.

[0061] 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 a salt thereof, or iron(II) sulfate 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.

[0062] 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 in advance. The desalting method is not particularly limited, and examples thereof include dialysis, centrifugation washing, and ion exchange using an ion exchange resin.

[0063] <Dispersion medium> The dispersion medium used in producing the dispersion liquid (1) is not particularly limited, but is preferably one that can more efficiently maintain high dispersion stability of the conductive polymer dispersion. In addition, the dispersion medium is preferably one that can dissolve or disperse the electrical conductivity enhancer, more preferably one that can dissolve the electrical conductivity enhancer, and even more preferably one that can dissolve all of the electrical conductivity enhancer contained in the conductive polymer dispersion.

[0064] 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; carbonate compounds 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.

[0065] <Polymerization Reaction> When the dispersion liquid (1) 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, in terms of appropriate viscosity and reactivity during the polymerization reaction.

[0066] 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 serves as a constituent unit of the conjugated conductive polymer.

[0067] From the viewpoint of suppressing uneven progress of the polymerization reaction, it is preferable that the polymerization raw material liquid contains a monomer that is a constituent 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.

[0068] 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.

[0069] 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 a constituent unit of the conjugated conductive polymer.

[0070] 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.

[0071] 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.

[0072] <First Dispersion Treatment> The obtained reaction product (intermediate product liquid) is subjected to a first dispersion treatment to obtain a dispersion liquid (1). The first dispersion treatment is carried out for the purpose of breaking down aggregated particles of the polymer in the intermediate product liquid into primary particles. Examples of dispersion treatment devices include a homogenizer, a ball mill, a high-shear mixer, and an ultrasonic dispersion device. For example, a dispersion liquid (1) can be obtained by dispersing the polymer in a shear rate of 5000 s －１ It is preferable to use means that apply a strong shear force such as stirring, a high-pressure homogenizer, ultrasonic irradiation at a frequency of about 15 to 100 Hz, etc. The dispersion treatment may be carried out by a flow method or a batch method, and may be carried out once or multiple times.

[0073] When a high-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 an increase in liquid temperature. The liquid temperature may be room temperature (room temperature environment), and heating is not required. The total treatment time in the dispersion treatment using a high-pressure homogenizer is preferably 15 to 900 minutes, more preferably 30 to 600 minutes, and even more preferably 60 to 300 minutes, from the viewpoint of improving the efficiency of the dispersion treatment.

[0074] If the dispersion treatment involves an increase in the liquid temperature, a cooler may be used. The cooler is not particularly limited as long as it can control the increase in the liquid temperature. Examples of the cooler include a plate-type heat exchanger, a spiral-type heat exchanger, a tubular-type heat exchanger, a immersion-type heat exchanger, and a jacket tank. Among these, plate-type heat exchangers and spiral-type heat exchangers are preferred from the viewpoints of heat exchange efficiency and equipment size.

[0075] The dispersion (1) obtained by the first dispersion treatment has a solids concentration of preferably 0.2 to 15% by mass, more preferably 0.5 to 10% by mass, and more preferably 1 to 8% by mass, from the viewpoint of effectively performing the subsequent re-dispersion treatment. The dispersion (1) may be diluted as appropriate. The dilution may be performed before, during, or after the dispersion treatment. From the viewpoint of improving the efficiency of the dispersion treatment and suppressing reagglomeration of particles in the liquid, it is preferable to dilute the dispersion 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 dispersion, and is more preferably water or an aqueous medium.

[0076] From the viewpoint of maintaining dispersibility, it is preferable that the dispersion liquid (1) be desalted after the first dispersion treatment. The desalting method is not particularly limited, and examples thereof include dialysis, centrifugation washing, and ion exchange.

[0077] (Re-dispersion treatment (second dispersion treatment) step) In the re-dispersion treatment step, an electrical conductivity improver is added to the dispersion liquid (1) and a re-dispersion treatment (second dispersion treatment) is performed. The second dispersion treatment is a dispersion treatment performed again after adding an electrical conductivity improver to the dispersion liquid (1) obtained by performing the first dispersion treatment.

[0078] By using the conductive polymer dispersion obtained by the second dispersion treatment, a solid electrolytic capacitor with a lower ESR can be obtained. It is believed that performing the dispersion treatment at a predetermined temperature in the presence of an electrical conductivity improver optimizes the polymer arrangement within the particles in the dispersion (1), making it easier to form appropriate conductive paths when the solid electrolyte is formed, thereby improving the performance of the solid electrolyte. Furthermore, even if the intermediate product solution is subjected to the second dispersion treatment without performing the first dispersion treatment (without obtaining the dispersion (1)), it is difficult to sufficiently break down the aggregated particles in the intermediate product solution into primary particles in the presence of the electrical conductivity improver, and a uniformly dispersed dispersion cannot be obtained.

[0079] The dispersion treatment device and method used in the second dispersion treatment may be the same as those in the first dispersion treatment. When a high-pressure homogenizer is used, the pressure may be the same as those in the first dispersion treatment.

[0080] The liquid temperature in the second dispersion treatment is set to 30° C. or higher in order to obtain a conductive polymer dispersion that can produce a solid electrolytic capacitor with a lower ESR. From the viewpoints of good dispersibility of particles in the dispersion (1) and production costs, the liquid temperature is preferably 30 to 90° C., more preferably 40 to 80° C., and even more preferably 40 to 60° C.

[0081] In the second dispersion treatment, when a high-pressure homogenizer is used, the total treatment time is preferably 30 to 480 minutes, more preferably 60 to 300 minutes, and even more preferably 90 to 240 minutes, from the viewpoints of the dispersion stability of the conductive polymer dispersion and the effect of reducing the ESR of the solid electrolytic capacitor produced using the conductive polymer dispersion.

[0082] The conductive polymer dispersion obtained through the second dispersion treatment preferably has a solids concentration of 0.2 to 15 mass%, more preferably 0.5 to 10 mass%, and 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 as appropriate. 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 dispersion, and water or an aqueous medium is more preferred.

[0083] 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.

[0084] 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 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.

[0085] 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.

[0086] 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.

[0087] <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.

[0088] 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 particularly preferred. Specific compounds, from the viewpoint of improving electrical conductivity, include preferably 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 ethylene glycol, diethylene glycol, and triethylene glycol. The electrical conductivity improver may be used alone or in combination of two or more.

[0089] From the viewpoint of stabilizing the 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 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 dispersion (1). 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.

[0090] <Alkaline Compound> The conductive polymer dispersion of this embodiment may contain an alkaline compound from the viewpoints of pH adjustment and corrosion inhibition of metals and the like that come into contact with the conductive polymer dispersion. The alkaline compound is preferably added to the dispersion (1) in the re-dispersion treatment step. The amount of alkaline compound added is an amount that makes the pH of the dispersion (1) preferably 3 to 13, more preferably 3 to 8, and even more preferably 4 to 7, from the viewpoints of corrosion inhibition of metals and the like that come into contact with the conductive polymer dispersion and inhibition of undoping of polyanions from the conjugated conductive polymer.

[0091] 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.

[0092] 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.

[0093] 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, and one or more selected from morpholine, 4-ethylmorpholine, and 4-(2-hydroxyethyl)morpholine are more preferred, with morpholine being more preferred.

[0094] Examples of alkali metal alkoxides include sodium alkoxides such as sodium methoxide and sodium ethoxide; potassium alkoxides; and calcium alkoxides.

[0095] Examples of inorganic alkaline compounds include ammonia, sodium hydroxide, potassium hydroxide, calcium hydroxide, and ammonia.

[0096] <Other Additives> From the viewpoint of imparting properties suitable for solid electrolytic capacitors, the conductive polymer dispersion of this embodiment 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 the process of obtaining dispersion (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 dispersed 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 antioxidants, and vitamins.

[0101] [Method for manufacturing a solid electrolytic capacitor] The method for manufacturing a solid electrolytic capacitor of this embodiment includes the steps of depositing the conductive polymer dispersion obtained by the manufacturing method of this embodiment described above onto a porous anode body made of a valve metal having a dielectric coating on its surface, and then removing the dispersion medium from the 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 manufacturing method of this embodiment through the above 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, zirconium, and alloys or compounds containing at least one of these metals. Among these, aluminum, niobium, and tantalum are preferred from the viewpoint of versatility.

[0103] The 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; and 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] The present embodiment will be described in detail below based on examples. The present invention is not limited to the following examples, and various modifications are possible within the scope of the present invention.

[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 a standard polystyrene-equivalent molecular weight measured by gel permeation chromatography under the following measurement conditions. <Measurement Conditions> Measurement device: "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] (50% volume cumulative particle diameter (d ５０ )) 50% volume cumulative particle diameter (d ５０ ) 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 setting 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 a dispersion sample 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] (Example 1) <Step of Synthesizing Polymer (Z) Dispersion> 86 g of styrene, 49 g of 2-ethylhexyl acrylate, 15 g of divinylbenzene, and 500 g of a 22 mass% aqueous solution of sodium polystyrene sulfonate ("Polinas PS-5", manufactured by Tosoh Finechem Corporation; Mw 120,000; the same applies hereinafter) (110 g of PSS) as a polyanion were mixed with stirring to prepare a polymerization raw material solution (a). Furthermore, 1,000 g of a 22 mass% aqueous solution of sodium polystyrene sulfonate (220 g of PSS) was heated to 80°C with stirring, and 2 g of potassium persulfate was added thereto to prepare a polymerization raw material solution (b). To the polymerization raw material liquid (b), the polymerization raw material liquid (a) was added dropwise over 2 hours, and then 40 g of a 2.5 mass % aqueous solution of potassium persulfate was added dropwise over 2.5 hours. The mixture was allowed to react at 80°C for 2 hours, and then cooled to room temperature (25°C). 1500 mL of a cation exchange resin ("Amberlite IR120B-H" manufactured by Organo Corporation; the same applies hereinafter) and 1500 mL of anion exchange resin ("Amberlite IRA410-OH" manufactured by Organo Corporation; the same applies hereinafter) were added to the reaction product, and the mixture was stirred for 12 hours. The ion exchange resin was then filtered off. Pure water was added to obtain a dispersion containing a polyanion and polymer (Z). The d of particles contained in this polymer (Z) dispersion (solids concentration 15.0 mass %) was ５０ was 0.46 μm.

[0118] <Step for Producing Intermediate Solution> In a 1 L polyethylene container, 34.0 g of the polymer (Z) dispersion obtained above, 31.5 g of a 12 mass % aqueous solution of sodium polystyrene sulfonate (3.78 g of sodium polystyrene sulfonate), and 223.2 g of pure water were mixed with stirring at 32° C. To this was added 2.80 g of 3,4-ethylenedioxythiophene, and the mixture was emulsified and mixed for 30 minutes in a homomixer ("ROBOMIX," manufactured by PRIMIX Corporation; 4000 rpm; the same applies hereinafter) to prepare a raw material solution (total amount of sodium polystyrene sulfonate: 1.9 moles of sodium sulfonate groups per mole of 3,4-ethylenedioxythiophene). 291.5 g of the obtained raw material solution was placed in a stainless steel vessel connected to a high-shear mixer ("Milder MDN303V", manufactured by Pacific Machinery Works, Ltd.; 5000 rpm, 32 ° C.) and a circulation pump, and the mixture was stirred while circulating with the stirring blade and high-shear mixer. 5.89 g of sodium peroxodisulfate and 6.88 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 produce an intermediate product solution (solids concentration 5.80 mass %) containing a conjugated conductive polymer. The above raw material solution preparation and polymerization reaction procedures were repeated, and a total of 1223.3 g of an intermediate product solution containing a conjugated conductive polymer was obtained.

[0119] <Dispersion and desalting process> 1223.3 g of the intermediate product liquid was diluted with pure water to 1500 mL (solid content concentration 4.73% by mass), and then subjected to a dispersion treatment for 45 minutes using a high-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 3.99% by mass) was subjected to a dispersion treatment for 135 minutes using a high-pressure homogenizer. After that, 125.6 mL of cation exchange resin and 109.9 mL of anion exchange resin were used for 3 hours for ion exchange and desalting to obtain a dispersion (1) (pH 1.9, solid content concentration 1.65% by mass).

[0120] <Preparation of Conductive Polymer Dispersion> 7.5 g of morpholine and 22.5 g of pure water were added to 1,000 g of dispersion (1), and the pH was adjusted to 4.7 (solid content concentration 1.60 mass%). Then, 205 g of triethylene glycol (12.5 parts by mass per part by mass of solid content) was added, and the mixture was subjected to a re-dispersion treatment at 40 to 50°C for 180 minutes using a high-pressure homogenizer, thereby obtaining a conductive polymer dispersion (triethylene glycol content 16.7 mass%).

[0121] Examples 2 to 4, Comparative Examples 1 and 2 Each conductive polymer dispersion was produced in the same manner as in Example 1, except that the re-dispersion treatment in Example 1 was carried out at the temperature and for the time shown in Table 1.

[0122] Comparative Example 3 A conductive polymer dispersion was produced in the same manner as in Example 1, except that after adding triethylene glycol to the dispersion (1), the dispersion was not subjected to re-dispersion treatment using a high-pressure homogenizer.

[0123] [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 in 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 in which a solid electrolyte layer was formed on the surface of the dielectric oxide film of the porous anode body.

[0124] The equivalent series resistance (ESR) [mΩ] of each solid electrolytic capacitor sample at 100 kHz was measured using a precision LCR meter (E4980A, manufactured by Agilent Technologies, Inc.). The measurement results are shown in Table 1.

[0125]

[0126] As can be seen from the results shown in Table 1, it was confirmed that the conductive polymer dispersions (Examples 1 to 4) obtained by adding an electrical conductivity improver and then carrying out a re-dispersion treatment at 30°C or higher could reduce the ESR of the solid electrolytic capacitor.

Claims

1. A method for producing a conductive polymer dispersion, comprising the step of adding an electrical conductivity enhancer to a dispersion containing a conjugated conductive polymer and a polyanion and subjecting it to a re-dispersion treatment, the step being carried out at a liquid temperature of 30°C or higher.

2. The method for producing a conductive polymer dispersion according to claim 1, wherein the liquid temperature is 40 to 80°C.

3. 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 part by mass of the solid content in the dispersion.

4. 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.

5. The method for producing a conductive polymer dispersion according to claim 1, wherein the monomer that constitutes the structural unit of the conjugated conductive polymer contains one or more compounds selected from 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 consisting of sulfonic acid or a salt thereof.

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

Images