Method for producing a conductive polymer dispersion and method for producing a capacitor

Abstract

The present invention provides a method for producing a conductive polymer dispersion suitable for the manufacture of capacitors, and a method for producing capacitors. [Solution] A method for producing a conductive polymer dispersion, comprising adding a surfactant to a conductive complex containing a conductive complex containing a π-conjugated conductive polymer and a polyanion, and water to obtain a mixed solution, and then performing a purification treatment to remove the surfactant from the mixed solution to obtain a conductive polymer dispersion from which the surfactant has been removed. Examples of the surfactant include one or more selected from the group consisting of dodecylbenzenesulfonic acid or its salt, polyoxyethylene alkyl ether-sulfate ester or its salt, alkylnaphthalenesulfonic acid or its salt, polyoxyalkylene alkenyl ether, and benzenedodecyldimethylammonium or its salt.

Description

Technical Field

[0001] The present invention relates to a method for producing a conductive polymer dispersion containing a π-conjugated conductive polymer and a method for producing a capacitor.

Background Art

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

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, for the above-mentioned conductive polymer dispersion used in the production of a capacitor and the paint containing the same, it is required to penetrate into the porous structure of the dielectric layer, and preferably the filling amount of the conductive polymer in the porous structure is increased. In order to increase this filling amount, it is conceivable to increase the concentration of the conductive polymer contained in the conductive polymer dispersion. However, when the concentration is high, the viscosity increases, the penetration into the porous structure deteriorates, and there is a problem that the performance of the capacitor cannot be sufficiently enhanced.

[0005] The present invention provides a method for producing a conductive polymer dispersion suitable for the manufacture of a capacitor, and a method for producing a capacitor. [Means for solving the problem]

[0006] [1] A method for producing a conductive polymer dispersion, comprising adding a surfactant to a conductive composite containing a π-conjugated conductive polymer and a polyanion and water to obtain a mixed solution, and then performing a purification treatment to remove the surfactant from the mixed solution to obtain a conductive polymer dispersion from which the surfactant has been removed. [2] A method for producing a conductive polymer dispersion according to [1], wherein the mixture is subjected to a dispersion treatment under pressure and then the purification treatment is performed. [3] The method for producing a conductive polymer dispersion according to [2], wherein the mixed liquid is stirred at atmospheric pressure for 30 minutes or more before the dispersion treatment. [4] A method for producing a conductive polymer dispersion according to any one of [1] to [3], wherein the purification process is a process of bringing the mixture into contact with an ion exchange resin. [5] A method for producing a conductive polymer dispersion according to any one of [1] to [4], wherein the step of first polymerizing monomers that form the π-conjugated conductive polymer in a reaction solution containing the polyanion and an aqueous dispersion medium is performed to obtain the conductive composite-containing solution. [6] A method for producing a conductive polymer dispersion according to any one of [1] to [5], wherein the π-conjugated conductive polymer is poly(3,4-ethylenedioxythiophene). [7] A method for producing a conductive polymer dispersion according to any one of [1] to [6], wherein the polyanion is polystyrene sulfonic acid. [8] A method for producing a conductive polymer dispersion according to any one of [1] to [7], wherein the surfactant is one or more selected from the group consisting of dodecylbenzenesulfonic acid or a salt thereof, polyoxyethylene alkyl ether sulfate ester or a salt thereof, alkylnaphthalenesulfonic acid or a salt thereof, polyoxyalkylene alkenyl ether, and benzenedodecyldimethylammonium or a salt thereof. [9] A method for producing a conductive polymer dispersion according to any one of [1] to [8], wherein the surfactant is dodecylbenzenesulfonic acid or a salt thereof. A method for manufacturing a capacitor, comprising the steps of: obtaining a conductive polymer dispersion by a manufacturing method described in any one of the items [1] to [9]; and applying the conductive polymer dispersion to the surface of a dielectric layer formed on the surface of an anode made of a porous valve metal, and drying it to form a solid electrolyte layer. [Effects of the Invention]

[0007] According to the manufacturing method of the present invention, it is possible to provide a capacitor equipped with a solid electrolyte layer having a low equivalent series resistance (ESR), and a conductive polymer dispersion suitable for manufacturing the capacitor. The conductive polymer dispersion produced by the present invention can easily penetrate the porous structure of the dielectric layer used in the manufacture of a capacitor, enabling the production of a high-performance capacitor.

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

[0009] In this specification and the claims, the lower and upper limits of the numerical ranges indicated by "~" are to be included within those numerical ranges. [Brief explanation of the drawing]

[0010] [Figure 1] This is a cross-sectional view showing one embodiment of the capacitor of the present invention. [Modes for carrying out the invention]

[0011] ≪Method for producing conductive polymer dispersions≫ A first aspect of the present invention is a method for producing a conductive polymer dispersion, comprising the steps of: obtaining a mixed solution by adding a surfactant to a conductive composite containing a π-conjugated conductive polymer and a polyanion, and a conductive composite containing water (mixed solution preparation step); and obtaining a conductive polymer dispersion from which the surfactant has been removed by performing a purification treatment to remove the surfactant from the mixed solution (purification step).

[0012] [Mixed liquid preparation process] <Conductive composite> The conductive composite used in this process contains a π-conjugated conductive polymer and polyanions. The polyanions in the conductive composite dope the π-conjugated conductive polymer to form a conductive composite. In the polyanions, only some of the anionic groups dope the π-conjugated conductive polymer, leaving excess anionic groups that do not participate in doping. Since the excess anionic groups are hydrophilic, the conductive composite is water-dispersible.

[0013] (π-conjugated conductive polymers) Any organic polymer whose main chain is composed of a π-conjugated system can be used as the π-conjugated conductive polymer. Examples include polypyrrole-based conductive polymers, polythiophene-based conductive polymers, polyacetylene-based conductive polymers, polyphenylene-based conductive polymers, polyphenylene-vinylene-based conductive polymers, polyaniline-based conductive polymers, polyacene-based conductive polymers, polythiophene-vinylene-based conductive polymers, and copolymers thereof. From the viewpoint of stability in air, polypyrrole-based conductive polymers, polythiophenes, and polyaniline-based conductive polymers are preferred, and from the viewpoint of transparency, polythiophene-based conductive polymers are more preferred.

[0014] Examples of polythiophene-based conductive polymers include polythiophene, poly(3-methylthiophene), poly(3-ethylthiophene), poly(3-propylthiophene), poly(3-butylthiophene), poly(3-hexylthiophene), poly(3-heptylthiophene), poly(3-octylthiophene), poly(3-decylthiophene), poly(3-dodecylthiophene), poly(3-octadecylthiophene), poly(3-bromothiophene), poly(3-chlorothiophene), and poly(3-iodine). Poly(3-Cyanothiophene), Poly(3-Phenylthiophene), Poly(3,4-Dimethylthiophene), Poly(3,4-Dibutylthiophene), Poly(3-Hydroxythiophene), Poly(3-Methoxythiophene), Poly(3-Ethoxythiophene), Poly(3-Butoxythiophene), Poly(3-Hexyloxythiophene), Poly(3-Heptyloxythiophene), Poly(3-Octyloxythiophene), Poly(3-Decyloxythiophene), Poly(3-Dodecyl Poly(3-octadecyloxythiophene), poly(3,4-dihydroxythiophene), poly(3,4-dimethoxythiophene), poly(3,4-diethoxythiophene), poly(3,4-dipropoxythiophene), poly(3,4-dibutoxythiophene), poly(3,4-dihexyloxythiophene), poly(3,4-diheptyloxythiophene), poly(3,4-dioctyloxythiophene), poly(3,4-didecyloxythiophene), poly(3,4-di Examples include dodecyloxythiophene, poly(3,4-ethylenedioxythiophene), poly(3,4-propylenedioxythiophene), poly(3,4-butylenedioxythiophene), poly(3-methyl-4-methoxythiophene), poly(3-methyl-4-ethoxythiophene), poly(3-carboxythiophene), poly(3-methyl-4-carboxythiophene), poly(3-methyl-4-carboxyethylthiophene), and poly(3-methyl-4-carboxybutylthiophene). Examples of polypyrrole-based conductive polymers include polypyrrole, poly(N-methylpyrrole), poly(3-methylpyrrole), poly(3-ethylpyrrole), poly(3-n-propylpyrrole), poly(3-butylpyrrole), poly(3-octylpyrrole), poly(3-decylpyrrole), poly(3-dodecylpyrrole), poly(3,4-dimethylpyrrole), poly(3,4-dibutylpyrrole), poly(3-carboxypyrrole), poly(3-methyl-4-carboxypyrrole), poly(3-methyl-4-carboxyethylpyrrole), poly(3-methyl-4-carboxybutylpyrrole), poly(3-hydroxypyrrole), poly(3-methoxypyrrole), poly(3-ethoxypyrrole), poly(3-butoxypyrrole), poly(3-hexyloxypyrrole), and poly(3-methyl-4-hexyloxypyrrole). Examples of polyaniline-based conductive polymers include polyaniline, poly(2-methylaniline), poly(3-isobutylaniline), poly(2-anilinesulfonic acid), and poly(3-anilinesulfonic acid). Among these π-conjugated conductive polymers, poly(3,4-ethylenedioxythiophene) is particularly preferred because of its excellent conductivity, transparency, and heat resistance. The π-conjugated conductive polymer contained in the conductive composite may be one type or two or more types.

[0015] (Polyanion) A polyanion is a polymer having two or more monomer units having anionic groups in the molecule. The anionic groups of this polyanion function as dopants for the π-conjugated conductive polymer and improve the conductivity of the π-conjugated conductive polymer. The anionic group of the polyanion is preferably a sulfo group or a carboxy group. Specific examples of such polyanions include polystyrene sulfonic acid, polyvinyl sulfonic acid, polyallyl sulfonic acid, polyacrylic acid esters having a sulfo group, polymethacrylic acid esters having a sulfo group (e.g., poly(4-sulfobutyl methacrylate), polysulfoethyl methacrylate, polymethacryloyloxybenzene sulfonic acid), polymers having a sulfo group such as poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, etc., and polymers having a carboxy group such as polyvinyl carboxylic acid, polystyrene carboxylic acid, polyallyl carboxylic acid, polyacrylic acid, polymethacrylic acid, poly(2-acrylamido-2-methylpropane carboxylic acid), polyisoprene carboxylic acid, etc. The polyanion may be a homopolymer in which a single monomer is polymerized, or a copolymer in which two or more monomers are polymerized. Among these polyanions, polymers having a sulfo group are preferred, and polystyrene sulfonic acid is more preferred because the conductivity can be made higher.

[0016] The weight-average molecular weight Mw of the polyanion is not particularly limited, and for example, it is preferably from 10,000 to 1,400,000, more preferably from 50,000 to 800,000, and even more preferably from 100,000 to 600,000. When the weight-average molecular weight Mw of the polyanion is within the above range, the viscosity of the conductive polymer dispersion becomes appropriately low, and a capacitor with a sufficiently low ESR can be easily manufactured. The weight-average molecular weight Mw of the polyanion is the average molecular weight based on mass measured using gel permeation chromatography and determined in terms of pullulan.

[0017] The polyanion content in the conductive composite-containing liquid of this process is preferably in the range of 1 to 1000 parts by mass, more preferably 10 to 700 parts by mass, and even more preferably 100 to 500 parts by mass, per 100 parts by mass of the π-conjugated conductive polymer. If the polyanion content is above the lower limit, the doping effect on the π-conjugated conductive polymer tends to be stronger, resulting in higher conductivity. On the other hand, if the polyanion content is below the upper limit, the π-conjugated conductive polymer can be sufficiently contained, thus ensuring sufficient conductivity.

[0018] The content of the π-conjugated conductive polymer relative to the total mass of the conductive composite-containing liquid in this process is preferably 0.1% by mass or more and 1.0% by mass or less, more preferably 0.2% by mass or more and 0.8% by mass or less, and even more preferably 0.3% by mass or more and 0.6% by mass or less. Within the above preferred range, the improvement in dispersibility by the surfactant is further promoted.

[0019] In this embodiment, the total content of the π-conjugated conductive polymer and polyanion relative to the total mass of the conductive composite-containing liquid is preferably 0.1% by mass or more and 2.5% by mass or less, more preferably 0.5% by mass or more and 2.2% by mass or less, and even more preferably 0.9% by mass or more and 2.0% by mass or less. Within the above preferred range, the improvement in dispersibility by the surfactant is further promoted.

[0020] <Dispersion medium> The dispersion medium contained in the conductive composite-containing liquid is preferably an aqueous dispersion medium containing water, given that the conductive composite is hydrophilic. However, it may also contain a dispersion medium other than water. The dispersion medium other than water is not particularly limited, as long as it does not significantly impair the dispersibility of the conductive composite. The conductive composite has excess anionic groups derived from polyanions and exhibits high dispersibility in water; therefore, a water-soluble organic solvent is preferred as the dispersion medium other than water. Here, the water-soluble organic solvent is an organic solvent whose solubility in 100g of water at 20°C is 1g or more, and examples include alcohol-based solvents, ketone-based solvents, and ester-based solvents. The dispersion medium may consist of one or more water-soluble organic solvents.

[0021] The water content relative to the total mass of the dispersion medium, excluding the solid content (non-volatile components) of the conductive polymer dispersion, is preferably 30% by mass or more, more preferably 60% by mass or more, even more preferably 90% by mass or more, and may also be 100% by mass. Including water at or above the lower limit of the above values ​​increases the dispersibility of the conductive composite contained in the conductive composite-containing liquid, further promoting the improvement of dispersibility by the surfactant.

[0022] <Surfactants> The surfactant used in this process may be anionic, nonionic, or cationic, but from the viewpoint of enhancing interaction with the π-conjugated conductive polymer, anionic or nonionic surfactants are preferred, and anionic surfactants are more preferred. The anionic functional groups of anionic surfactants may or may not form salts with cations such as sodium ions or potassium ions.

[0023] (Anionic surfactant) Anionic surfactants are low-molecular-weight substances that have hydrophilic anionic groups and hydrophobic atomic groups in their molecules. The number of anionic groups in the molecule may be one or two or more, but one is preferred from the viewpoint of easily exhibiting surfactant function. The molecular weight of the anionic surfactant is preferably 100 to 2000, and more preferably 200 to 1000. It is preferable that the anionic surfactant can form micelles in water.

[0024] From the viewpoint of reducing the viscosity of the mixture obtained in this process and improving the dispersibility of the conductive composite, it is preferable that the anionic surfactant has a sulfo group and an alkyl group having 6 or more carbon atoms.

[0025] Specific preferred anionic surfactants include, for example, one or more selected from the group consisting of alkylbenzenesulfonic acids having 6 or more carbon atoms, such as hexanesulfonic acid, octanesulfonic acid, and dodecylbenzenesulfonic acid, dioctyl sulfosuccinate, alkylnaphthalenesulfonic acid, and polyoxyalkyl sulfates having an alkyl group of 6 or more carbon atoms, polyoxyethylene alkyl ether sulfate esters, and salts thereof. The number of carbon atoms in the alkyl group of the molecule exemplified here is preferably 6 to 30, more preferably 6 to 20, and even more preferably 6 to 18, from the viewpoint of fully exhibiting its function as a surfactant. The carbon number may be linear or branched.

[0026] Specific examples of preferred nonionic surfactants include polyoxyalkylene alkenyl ethers and polyoxyalkylene alkyl ethers.

[0027] Specific examples of preferred cationic surfactants include, for example, various quaternary ammonium salts.

[0028] The surfactant used in this process is preferably one or more selected from the group consisting of dodecylbenzenesulfonic acid or its salts, polyoxyethylene alkyl ether sulfate ester or its salts, alkylnaphthalenesulfonic acid or its salts, polyoxyalkylene alkenyl ethers, and benzenedodecyldimethylammonium or its salts. These surfactants enhance the dispersibility of the conductive complex and are easy to remove in the subsequent purification step.

[0029] The surfactant used in this process may be one type or two or more types. In the mixed solution obtained by adding a surfactant to the conductive composite dispersion, the total content of the surfactant is preferably, for example, 0.1 parts by mass or more and 20 parts by mass or less, more preferably 1 part by mass or more and 15 parts by mass or less, and even more preferably 5 parts by mass or more and 10 parts by mass or less, per 100 parts by mass of the conductive composite (total of π-conjugated conductive polymer and polyanion). If the value is above the lower limit mentioned above, the dispersibility of the conductive composite can be further improved. If the value is below the above upper limit, the removal of surfactants in the subsequent purification process becomes easier, and the ESR of the capacitor formed using the obtained conductive polymer dispersion can be further reduced.

[0030] In the mixed solution obtained by adding a surfactant to the conductive composite dispersion, the concentration of the surfactant relative to the total mass of the mixed solution is preferably, for example, 0.01% by mass or more and 0.40% by mass or less, more preferably 0.05% by mass or more and 0.30% by mass or less, and even more preferably 0.10% by mass or more and 0.20% by mass or less. If the value is above the lower limit mentioned above, the dispersibility of the conductive composite can be further improved. If the value is below the above upper limit, the removal of surfactants in the subsequent purification process becomes easier, and the ESR of the capacitor formed using the resulting conductive polymer dispersion can be further reduced.

[0031] It is preferable to disperse the mixture obtained by adding a surfactant to the conductive composite dispersion under pressure before subjecting it to a subsequent purification step. In this case, using a high-pressure homogenizer makes it easy to perform the dispersion under pressure. The strong shear force of the high-pressure homogenizer reduces the diameter of the conductive composite particles, further improving the dispersibility of the conductive composite. Furthermore, before dispersing the mixture obtained by adding a surfactant to the conductive composite dispersion under pressure, it is preferable to stir the mixture at atmospheric pressure for 30 minutes or more. Allowing time for gentle stirring allows the conductive composite and the surfactant to chemically interact, thereby further improving the dispersibility of the conductive composite. The stirring time at atmospheric pressure is preferably about 60 minutes, and about 120 minutes is sufficient.

[0032] <Preparation of conductive composite-containing solution; preliminary steps> The manufacturing method according to this embodiment may include a preliminary step of obtaining a conductive composite-containing liquid to be used in the mixing step. In the preliminary step, the conductive composite-containing liquid can be obtained by polymerizing monomers that form the π-conjugated conductive polymer in a reaction solution containing the polyanion and an aqueous dispersion medium.

[0033] By polymerizing the monomer in the reaction solution, a π-conjugated conductive polymer is formed, and polyanions are spontaneously doped into the π-conjugated conductive polymer, forming a conductive composite consisting of the π-conjugated conductive polymer and polyanions. The synthesis of the conductive composite in the reaction solution can be carried out in the same manner as the synthesis of conventional conductive composites.

[0034] It is preferable to add a known catalyst and oxidizing agent to the reaction solution to promote the chemical oxidation of the monomer. Examples of catalysts include transition metal compounds such as ferric chloride, ferric sulfate, ferric nitrate, and cupric chloride. Examples of oxidizing agents include persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate.

[0035] The catalyst content relative to the total mass of the reaction solution (including the catalyst) is preferably, for example, 0.01% by mass or more and 0.50% by mass or less, and more preferably 0.01% by mass or more and 0.30% by mass or less.

[0036] The content of the oxidizing agent relative to the total mass of the reaction solution (including the oxidizing agent) is preferably, for example, 0.10% by mass or more and 2.00% by mass or less, more preferably 0.30% by mass or more and 1.50% by mass or less, and even more preferably 0.60% by mass or more and 1.25% by mass or less.

[0037] The monomer content relative to the total mass of the reaction solution is preferably, for example, 0.01% by mass or more and 2.0% by mass or less, more preferably 0.1% by mass or more and 1.0% by mass or less, and even more preferably 0.3% by mass or more and 0.8% by mass or less. The content of the polyanion relative to the total mass of the reaction solution is preferably, for example, 0.1% by mass or more and 3.0% by mass or less, more preferably 0.5% by mass or more and 2.0% by mass or less, and even more preferably 1.0% by mass or more and 1.5% by mass or less. By setting the concentration of the conductive composite to the preferred range described above, a conductive composite-containing solution with the aforementioned preferred content can be easily obtained.

[0038] The reaction temperature in the reaction solution can be, for example, 20-30°C. At this reaction temperature, the polymerization reaction is usually completed in about 4-12 hours. The completion of the polymerization reaction can be confirmed by gas chromatography or other measurement when the amount of unreacted monomer in the reaction solution has almost completely disappeared.

[0039] It is preferable to remove the catalyst and oxidizing agent added to the reaction solution from the conductive composite-containing solution after the chemical oxidative polymerization of the monomer. Methods for removing catalysts and oxidizing agents include, for example, contacting a conductive polymer dispersion with an ion exchange resin to adsorb the substances to be removed onto the ion exchange resin, and removing them along with the displacement of the dispersion medium by ultrafiltration of the conductive polymer dispersion. Of these, the method using an ion exchange resin is preferred because it is simple. It is preferable to use a combination of a cation exchange resin and an anion exchange resin as the ion exchange resin.

[0040] [Refining process] In this process, methods for performing a purification treatment to remove the surfactant from the mixture include, for example, contacting a conductive polymer dispersion with an ion exchange resin to adsorb the substance to be removed onto the ion exchange resin, and removing the surfactant along with the replacement of the dispersion medium by ultrafiltration of the conductive polymer dispersion. For the removal of anionic or cationic surfactants, the use of ion exchange resins is preferred because it is simple. It is preferable to use a combination of cation exchange resins and anion exchange resins. Ultrafiltration is preferred for removing nonionic surfactants. In some cases, at least a portion of the nonionic surfactant can be removed using ion exchange resin. While the detailed mechanism is unclear, it is thought that adsorption occurs due to physicochemical interactions between the ion exchange resin and the nonionic surfactant. Whether or not at least a portion of the surfactant has been removed from the mixture can be simply determined, for example, by whether or not the amount of non-volatile components contained in the mixture has decreased before and after the purification treatment.

[0041] Ideally, the conductive polymer dispersion obtained through the purification process should be free of surfactants, but residual surfactants may remain that cannot be completely removed. Anionic surfactants may also dopine π-conjugated conductive polymers. If a large amount of free surfactant remains, the conductivity of the conductive layer and solid electrolyte layer formed as the cured product of the conductive polymer dispersion may decrease, so it is preferable to have as little residual surfactant as possible.

[0042] The conductive polymer dispersion obtained above contains a conductive composite with enhanced dispersibility. The conductive polymer dispersion obtained in the purification step may be used as is in the production of the capacitor described later, or the dispersion medium may be replaced with a desired one, the concentration of the conductive composite may be adjusted, or polyol compounds, optional additives, etc., may be added before use in the production of the capacitor.

[0043] (Polyol compounds) The conductive polymer dispersion may contain one or more polyol compounds. Here, the polyol compound refers to a compound having two or more hydroxyl groups, which is different from the π-conjugated conductive polymer, the polyanion, and the surfactant. By including a polyol compound, the conductivity of the conductive layer formed from the conductive polymer dispersion can be increased, and the ESR of the capacitor having the conductive layer (solid electrolyte layer) formed from the conductive polymer dispersion can be further reduced.

[0044] Examples of polyol compounds include one or more selected from ethylene glycol, diethylene glycol, propylene glycol, 1,4-butanediol, glycerin, pentaerythritol, trimethylolpropane, and trimethylolethane.

[0045] The content of the polyol compound in the conductive polymer dispersion is preferably, for example, 100 parts by mass or more and 10,000 parts by mass or less, more preferably 200 parts by mass or more and 2,000 parts by mass or less, and even more preferably 300 parts by mass or more and 1,000 parts by mass or less, based on 100 parts by mass of the total of the π-conjugated conductive polymer and polyanion. Within the above preferred range, the conductivity of the conductive layer can be increased, and the ESR of the capacitor can be further reduced.

[0046] The content of the polyol compound relative to the total mass of the conductive polymer dispersion is preferably 0.1 to 15.0% by mass, more preferably 1.0 to 12.0% by mass, and even more preferably 5.0 to 10.0% by mass. Within these preferred ranges, the coating properties of the conductive polymer dispersion are improved, the conductivity of the conductive layer is enhanced, and the ESR of the capacitor can be further reduced.

[0047] (Optional additives) The conductive polymer dispersion may contain any additive other than the conductive composite, as long as it does not impair the spirit of the present invention. The proportion of the additive can be appropriately determined depending on the type of additive, but for example, it can be 1 to 1000 parts by mass per 100 parts by mass of the total of the π-conjugated conductive polymer and polyanion. Here, the optional additive is a compound other than the polyol compound and the dispersion medium.

[0048] Optional additives include, for example, polyethylene glycol, inorganic conductive agents, defoaming agents, coupling agents, antioxidants, and ultraviolet absorbers. As polyethylene glycol, a low molecular weight type with a molecular weight of 200 to 1000 is preferred. Hydrophilic polymers such as polyvinyl alcohol and polyvinylpyrrolidone may also be added. Examples of inorganic conductive agents include metal ions and conductive carbon. Metal ions can be generated by dissolving metal salts in water. Examples of defoaming agents include silicone resins, polydimethylsiloxanes, and silicone oils. Examples of coupling agents include silane coupling agents having vinyl groups, amino groups, epoxy groups, etc. Examples of antioxidants include phenolic antioxidants, amine antioxidants, phosphorus antioxidants, sulfur antioxidants, and sugars. Examples of UV absorbers include benzotriazole-based UV absorbers, benzophenone-based UV absorbers, salicylate-based UV absorbers, cyanoacrylate-based UV absorbers, oxanilide-based UV absorbers, hindered amine-based UV absorbers, and benzoate-based UV absorbers.

[0049] The viscosity of the conductive polymer dispersion obtained by the manufacturing method of this embodiment at 25°C is preferably 10.0 cP or more and 26.0 cP or less, more preferably 12.0 cP or more and 24.0 cP or less, and even more preferably 14.0 cP or more and 22.0 cP or less. If the value is above the lower limit mentioned above, it becomes easier to apply and adhere to a substrate such as a dielectric layer, and a thick solid electrolyte layer can be easily formed. When the value is below the upper limit mentioned above, it becomes easier for the material to penetrate the fine porous structure of the dielectric layer, allowing for the easy formation of a high-performance solid electrolyte layer. The viscosity measurements described above were taken at 25°C using a tuning fork vibrating viscometer, in accordance with JIS Z8803:2011 (Viscosity measurement method using vibrating viscometer).

[0050] Capacitor manufacturing method A second aspect of the present invention is a method for manufacturing a capacitor, comprising the steps of obtaining a conductive polymer dispersion by the manufacturing method of the first aspect, and applying the conductive polymer dispersion to the surface of a dielectric layer formed on the surface of an anode made of a porous valve metal, and drying it to form a solid electrolyte layer.

[0051] The method for manufacturing a capacitor according to this embodiment preferably includes the steps of: oxidizing the surface of an anode made of a porous valve metal to form a dielectric layer (dielectric formation step); arranging a cathode at a position opposite the dielectric layer (cathode formation step); and forming a solid electrolyte layer on at least a part of the surface of the dielectric layer (film formation step). Each step will be described below with reference to Figure 1.

[0052] [Dielectric Formation Process] In this process, the surface of the anode 11, which is made of a porous valve metal, is oxidized to form a dielectric layer 12. The method for forming the dielectric layer 12 is not particularly limited, and examples include anodic oxidation of the surface of the anode 11 in an electrolyte solution for chemical treatment, such as an aqueous solution of ammonium adipate, an aqueous solution of ammonium borate, or an aqueous solution of ammonium phosphate.

[0053] [Cathode formation process] In this process, a cathode 13 is placed opposite the dielectric layer 12. The method of arranging the cathode 13 is not particularly limited, and examples include forming the cathode 13 using a conductive paste such as carbon paste or silver paste, or arranging a metal foil such as aluminum foil opposite the dielectric layer 12.

[0054] [Film forming process] In this process, the aforementioned conductive polymer dispersion is applied to at least a portion of the surface of the dielectric layer 12 and dried to form a solid electrolyte layer 14.

[0055] Methods for applying the conductive polymer dispersion include, for example, dip coating, comma coating, reverse coating, lip coating, and microgravure coating. Of these, the method of immersing the anode 11 in the conductive polymer dispersion under reduced pressure is preferred. With the dip method, the conductive polymer dispersion can be sufficiently applied to the interior of the porous structure on the surface of the dielectric layer 12. After immersion, it is removed and the drying process is carried out.

[0056] Drying methods include, for example, room temperature drying, hot air drying, and far-infrared drying. Among these, hot air drying is preferred. The drying temperature is preferably 100 to 180°C, and more preferably 120 to 150°C. The drying time is preferably 0.2 to 1 hour. After drying, the capacitor can be assembled using conventional methods.

[0057] Capacitor One example of a capacitor embodiment is a capacitor comprising an anode made of a porous valve metal, a dielectric layer made of an oxide of the valve metal, a cathode made of a conductive material provided on the side of the dielectric layer opposite to the anode, and a solid electrolyte layer formed between the dielectric layer and the cathode, wherein the solid electrolyte layer contains a cured product of a conductive polymer dispersion obtained by the manufacturing method of the first embodiment. The capacitor of this embodiment can be manufactured by the second embodiment.

[0058] An example of a capacitor embodiment will be described with reference to Figure 1. The capacitor 10 shown in Figure 1 comprises an anode 11 made of a porous valve metal, a dielectric layer 12 made of an oxide of the valve metal, a solid electrolyte layer 14 formed on the surface of the dielectric layer 12, and a cathode 13 provided on the outermost side. The cathode 13 is provided on the opposite side from the anode 11, with the dielectric layer 12 and the solid electrolyte layer 14 in between.

[0059] Examples of valve metals that constitute the anode 11 include aluminum, tantalum, niobium, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. Of these, aluminum, tantalum, and niobium are preferred. Specific examples of anode 11 include aluminum foil that has been etched to increase its surface area and then oxidized, or sintered tantalum or niobium particles whose surface has been oxidized and formed into pellets. Materials processed in this way become porous bodies with irregularities formed on their surface.

[0060] In this embodiment, the dielectric layer 12 is a layer formed by oxidation of the surface of the anode 11. For example, it is formed by anodizing the surface of the metal anode 11 in an electrolyte such as an aqueous solution of ammonium adipate. Similar to the anode 11, the dielectric layer 12 also has irregularities formed on it.

[0061] In this embodiment, the cathode 13 can be a conductive layer formed from a conductive paste or a metal layer made of a conductive material such as aluminum foil.

[0062] In this embodiment, the solid electrolyte layer 14 is formed on the surface of the dielectric layer 12. The solid electrolyte layer 14 covers at least a portion of the surface of the dielectric layer 12, and may cover the entire surface of the dielectric layer 12. The thickness of the solid electrolyte layer 14 may be constant or not; for example, a thickness of 1 μm or more and 100 μm or less is possible.

[0063] [Electrolyte] The capacitor may have an electrolyte that impregnates a solid electrolyte layer. Examples of solvents that constitute the electrolyte include alcohol-based solvents such as ethylene glycol, diethylene glycol, propylene glycol, 1,4-butanediol, and glycerin; lactone-based solvents such as γ-butyrolactone, γ-valerolactone, and δ-valerolactone; sulfur-based solvents such as sulfolane, dimethyl sulfoxide, and dimethyl sulfone; amide-based solvents such as N-methylformamide, N,N-dimethylformamide, N-methylacetamide, and N-methylpyrrolidinone; nitrile-based solvents such as acetonitrile and 3-methoxypropionitrile; and water. The electrolytes constituting the electrolyte solution include, for example, adipic acid, glutaric acid, succinic acid, benzoic acid, isophthalic acid, phthalic acid, terephthalic acid, maleic acid, toluic acid, enanthic acid, malonic acid, formic acid, decanedicarboxylic acids such as 1,6-decanedicarboxylic acid and 5,6-decanedicarboxylic acid, octanedicarboxylic acids such as 1,7-octanedicarboxylic acid, organic acids such as azelaic acid and sebacic acid; or boric acid, polyhydric alcohol complex compounds of boric acid obtained from boric acid and polyhydric alcohols; and inorganic acids such as phosphoric acid, carbonic acid, and silicic acid as anionic components, with primary amines (methylamine, ethylamine, propylamine, Examples include electrolytes with cationic components such as butylamine, ethylenediamine, secondary amines (dimethylamine, diethylamine, dipropylamine, methylethylamine, diphenylamine, etc.), tertiary amines (trimethylamine, triethylamine, tripropylamine, triphenylamine, 1,8-diazabicyclo(5,4,0)-undecene-7, etc.), and tetraalkylammonium (tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, methyltriethylammonium, dimethyldiethylammonium, etc.).

[0064] The capacitor is not limited to the configuration described above; a separator may be provided between the dielectric layer and the cathode. An example of a capacitor with a separator between the dielectric layer and the cathode is a wound-type capacitor. Examples of separators include sheets (including nonwoven fabrics) made of cellulose, polyvinyl alcohol, polyester, polyethylene, polystyrene, polypropylene, polyimide, polyamide, polyvinylidene fluoride, etc., and glass fiber nonwoven fabrics. The density of the separator is, for example, 0.1 g / cm³. 3 More than 1.0g / cm 3 The following are listed: When a separator is provided, a method can be applied in which carbon paste or silver paste is impregnated into the separator to form the cathode. [Examples]

[0065] (Manufacturing Example 1) Production of polystyrene sulfonic acid; Mw120000 220 g of sodium styrene sulfonate was dissolved in 1640 ml of deionized water, and 17.08 g of sodium peroxodisulfate, which had been previously dissolved in 110 ml of water, was added dropwise over 2 hours while stirring at 80°C, and the solution was stirred for 4 hours. A cation exchange resin was added to the resulting sodium polystyrene sulfonate-containing solution to remove sodium ions. The solid content of the resulting polystyrene sulfonic acid (PSS) aqueous solution 1 was 10% by mass. For PSS aqueous solution 1, the weight-average molecular weight was measured using pullulan manufactured by Showa Denko K.K. as a standard substance, with a GPC (gel permeation chromatography) column and a differential refractive index detector in an HPLC (high-performance liquid chromatography) system. Analysis of the GPC chart, where the vertical axis represents the signal intensity of the differential refractive index and the horizontal axis represents the retention time, revealed that the peak for polystyrene sulfonic acid showed a weight-average molecular weight (Mw) of 120,000.

[0066] (Manufacturing Example 2) Production of PEDOT-PSS aqueous dispersion 57.1 g of 3,4-ethylenedioxythiophene, 1354 g of the polystyrene sulfonic acid aqueous solution obtained in Production Example 1, and 7829.73 g of deionized water were mixed together. The mixture was kept at 26°C and, while stirring, an oxidation catalyst solution of 11.5 g of ferric sulfate dissolved in 180.3 g of deionized water was added. Then, 62.5 g of sodium peroxodisulfate dissolved in 505.5 g of deionized water was gradually added dropwise in a constant amount over 2 hours, and the mixture was stirred for a further 4 hours to allow the reaction to proceed. A cation exchange resin (Duolite C255LFH, manufactured by Sumika Chemtex Co., Ltd.) and an anion exchange resin (Duolite A368S, manufactured by Sumika Chemtex Co., Ltd.) were added to the resulting reaction solution to remove the polymerization initiator and iron. This yielded a blue PEDOT-PSS aqueous dispersion (conductive composite-containing solution) with a PEDOT:PSS ratio of 1:2.5 (mass ratio). The concentration of the non-volatile component PEDOT-PSS was 1.9% by mass.

[0067] [Example 1] 500 g of the PEDOT-PSS aqueous dispersion prepared in Production Example 2 was mixed with 0.78 g of dodecylbenzenesulfonic acid (DBSA), stirred for 1 hour, and then dispersed using a high-pressure homogenizer. To the resulting solution, 33 g each of the same cation exchange resin and anion exchange resin as in Production Example 2 were added, stirred for 1 hour, and then a conductive polymer dispersion was obtained by removing the surfactant DBSA.

[0068] [Example 2] A conductive polymer dispersion was obtained in the same manner as in Example 1, except that the surfactant in Example 1 was changed to a polyoxyethylene alkyl ether sulfate sodium salt (Persoft EF, manufactured by NOF Corporation, with 12 or 14 carbon atoms in the alkyl chain). "Persoft" is a registered trademark.

[0069] [Example 3] A conductive polymer dispersion was obtained in the same manner as in Example 1, except that the surfactant in Example 1 was changed to sodium alkylnaphthalene sulfonate (Perex NBL, manufactured by Kao Corporation). Note that "Perex" is a registered trademark.

[0070] [Example 4] A conductive polymer dispersion was obtained in the same manner as in Example 1, except that the surfactant in Example 1 was changed to polyoxyalkylene alkenyl ether (Latemul PD-420, manufactured by Kao Corporation). "Ramtel" is a registered trademark.

[0071] [Example 5] A conductive polymer dispersion was obtained in the same manner as in Example 1, except that the surfactant in Example 1 was changed to benzenedodecyldimethylammonium.

[0072] [Comparative Example 1] 500g of the PEDOT-PSS aqueous dispersion prepared in Production Example 2 was dispersed using a high-pressure homogenizer to obtain a conductive polymer dispersion.

[0073] [Comparative Example 2] 500 g of the PEDOT-PSS aqueous dispersion prepared in Production Example 2 was mixed with 0.78 g of DBSA, stirred for 1 hour, and then dispersed using a high-pressure homogenizer to obtain a conductive polymer dispersion. No surfactant removal treatment was performed.

[0074] [Comparative Example 3] A conductive polymer dispersion was obtained in the same manner as in Comparative Example 2, except that the surfactant in Comparative Example 2 was changed to Persoft EF.

[0075] [Comparative Example 4] A conductive polymer dispersion was obtained in the same manner as in Comparative Example 2, except that the surfactant in Comparative Example 2 was changed to Perex NBL.

[0076] [Comparative Example 5] A conductive polymer dispersion was obtained in the same manner as in Comparative Example 2, except that the surfactant was changed to Latemul PD-420.

[0077] [Comparative Example 6] A conductive polymer dispersion was obtained in the same manner as in Comparative Example 2, except that the surfactant in Comparative Example 2 was changed to benzenedodecyldimethylammonium.

[0078] <Capacitor Performance Evaluation> (Preparation of paint composition) The concentration of PEDOT-PSS, the non-volatile component of the conductive polymer dispersion obtained in each example, was adjusted to 1.6% by mass by adding deionized water or ultrafiltration. 85.27 g of this conductive polymer dispersion was mixed with 9.0 g of diethylene glycol, 5.5 g of PEG600, and 0.23 g of imidazole to prepare a coating composition for forming a solid electrolyte layer.

[0079] (Capacitor fabrication) After connecting anode lead terminals to etched aluminum foil (anodic foil), a voltage of 50V was applied in a 10% by mass aqueous solution of ammonium adipate to perform a chemical conversion (oxidation treatment), thereby forming dielectric layers on both sides of the aluminum foil and obtaining the anode foil. Next, opposing aluminum cathode foils, each with cathode lead terminals welded to both sides of an anode foil, were laminated with a cellulose separator in between, and this was wound into a cylindrical shape to obtain a capacitor element. Next, the capacitor element was immersed in the paint composition under reduced pressure, and then dried twice in a hot air dryer at 120°C for 20 minutes, thereby forming a solid electrolyte layer containing a conductive composite on the surface of the dielectric layer, resulting in a capacitor element. Finally, the capacitor components were loaded into an aluminum case, sealed with rubber seal, and the capacitor was fabricated.

[0080] [Measurement of capacitance and equivalent series resistance] For capacitors fabricated using the paint compositions of each example, the equivalent series resistance (ESR) (unit: mΩ) at 100 kHz was measured using an LCR meter 2345 (manufactured by NF Circuit Design Block Co., Ltd.). The ESR measurement results are shown in Table 1.

[0081] [Viscosity measurement] The paint compositions obtained in each example were used as samples, and their viscosity was measured at 25°C using a tuning fork vibrating viscometer (model: SV-10, manufactured by A&D Corporation) in accordance with JIS Z8803:2011 (Method for measuring viscosity using a vibrating viscometer). The viscosity measurement results are shown in Table 1.

[0082] [Table 1]

[0083] Comparing the experimental examples of Examples 1-5 and Comparative Examples 2-6, which all used the same surfactant, it is clear that the examples in which the surfactant was added to the PEDOT-PSS aqueous dispersion, dispersed, and then removed, yielded capacitors with lower ESR and superior performance compared to the comparative examples in which the surfactant was not removed. [Explanation of symbols]

[0084] 10 Capacitors 11 Anode 12 Dielectric layer 13 Cathode 14 Solid electrolyte layer

Claims

1. After obtaining a mixed solution by adding a surfactant to a conductive composite containing a π-conjugated conductive polymer and a polyanion, and a conductive composite containing water, A method for producing a conductive polymer dispersion, comprising a purification process to remove the surfactant from the mixture to obtain a conductive polymer dispersion from which the surfactant has been removed.

2. A method for producing a conductive polymer dispersion according to claim 1, wherein the mixture is subjected to a dispersion treatment under pressure and then the purification treatment is performed.

3. A method for producing a conductive polymer dispersion according to claim 2, wherein the mixed liquid is stirred at atmospheric pressure for 30 minutes or more before the dispersion treatment.

4. The method for producing a conductive polymer dispersion according to claim 3, wherein the purification process is a process of contacting the mixed solution with an ion exchange resin.

5. A method for producing a conductive polymer dispersion according to claim 4, wherein a step is performed in advance to obtain the conductive composite-containing liquid by polymerizing monomers that form the π-conjugated conductive polymer in a reaction solution containing the polyanion and an aqueous dispersion medium.

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

7. The method for producing a conductive polymer dispersion according to claim 6, wherein the polyanion is polystyrene sulfonic acid.

8. The method for producing a conductive polymer dispersion according to claim 7, wherein the surfactant is one or more selected from the group consisting of dodecylbenzenesulfonic acid or a salt thereof, polyoxyethylene alkyl ether-sulfate ester or a salt thereof, alkylnaphthalenesulfonic acid or a salt thereof, polyoxyalkylene alkenyl ether, and benzenedodecyldimethylammonium or a salt thereof.

9. The method for producing a conductive polymer dispersion according to claim 8, wherein the surfactant is dodecylbenzenesulfonic acid or a salt thereof.

10. A method for manufacturing a capacitor, comprising the steps of: obtaining a conductive polymer dispersion by a manufacturing method described in any one of claims 1 to 9; and applying the conductive polymer dispersion to the surface of a dielectric layer formed on the surface of an anode made of a porous valve metal, and drying it to form a solid electrolyte layer.

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