Electrolytic solution for polymerizing pyrrole and method for producing solid electrolytic capacitor using the same

Abstract

To provide an electrolytic solution for polymerizing pyrrole giving polypyrrole having high conductivity, and to provide a method for producing a solid electrolytic capacitor having high electrostatic capacity, low ESR and excellent durability by using the electrolytic solution.SOLUTION: An electrolytic solution for pyrrole polymerization is an electrolytic solution for pyrrole polymerization in which pyrrole and a supporting electrolyte are dissolved in a solvent, the electrolytic solution containing a supporting electrolyte composed of a copolymer containing a repeating unit represented by general formula (1) (R represents an alkylene group, and A represents an aromatic group having a substituent other than a sulfonic acid group) and a repeating unit represented by a predetermined general formula, and SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an electrolyte solution for pyrrole polymerization capable of forming a highly conductive polypyrrole layer, and a method for producing a solid electrolytic capacitor using the same and having a solid electrolyte layer made of polypyrrole formed thereon. [Background technology]

[0002] In recent years, as electronic devices have become more sophisticated, the capacitors used in them are required to be small in size, have large capacitance, be highly durable, exhibit low impedance in the high frequency range, and have excellent equivalent series resistance (hereinafter abbreviated as "ESR") and dielectric loss (hereinafter abbreviated as "tanδ") characteristics.

[0003] To meet these demands, solid electrolytic capacitors have been developed that use a conductive polymer as a solid electrolyte layer, unlike conventional liquid electrolyte capacitors that use a liquid electrolyte as the true cathode.

[0004] The above-mentioned solid electrolytic capacitors are generally known to be manufactured by forming a dielectric oxide film on the surface of a valve action metal foil whose surface area has been increased by etching, or a sintered body whose surface area has been increased by sintering valve action metal particles, through a chemical conversion treatment, and then forming a solid electrolyte layer made of a conductive polymer on the dielectric oxide film, followed by forming a conductive layer made of carbon and silver paste, and then connecting the resultant to external terminals such as a lead frame, and then applying an exterior package using transfer molding or the like to produce a commercial product.

[0005] The ESR of solid electrolytic capacitors is primarily determined by the combined resistance of the specific resistance of each component that makes up the capacitor and the contact resistance that occurs between the components, and there is a need to reduce the ESR by improving these factors.

[0006] Patent Document 1 discloses a method for producing a solid electrolytic capacitor, characterized in that when forming an electrolytic polymerized layer of ethylenedioxythiophene or alkylated ethylenedioxythiophene as a solid electrolyte layer, a sulfonated polyester having a sulfonation degree of 3 to 9% is used as a dopant anion.

[0007] However, electrolytic polymerization of poly-3,4-ethylenedioxythiophene has the drawback of being difficult to produce a uniform polymerized film and prone to the formation of protruding burrs on the surface, resulting in problems with the withstand voltage and leakage current (LC) characteristics of the resulting solid electrolytic capacitor. Furthermore, when a sulfonated polyester with a low degree of sulfonation, such as that disclosed in Patent Document 1, is used as a dopant anion in the polymerization of pyrrole, the resulting polypyrrole layer has insufficient electrical conductivity, making it difficult to improve the capacitance and ESR of the solid electrolytic capacitor.

[0008] Patent Document 2 proposes a method for producing a solid electrolytic capacitor having a pyrrole electrolytic polymerization step, in which an electrolyte solution for pyrrole polymerization is used, which contains an aromatic sulfonic acid compound such as anthraquinone 2-sulfonates, naphthalenesulfonates, or benzenesulfonates as a supporting electrolyte. However, the durability of the resulting solid electrolytic capacitor is insufficient, and improvements have been desired. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 2020-004758 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-236339 Summary of the Invention [Problem to be solved by the invention]

[0010] An object of the present invention is to provide an electrolyte solution for pyrrole polymerization that gives highly conductive polypyrrole, and a method for producing a solid electrolytic capacitor that uses the electrolyte solution for pyrrole polymerization and has high capacitance, low ESR, and excellent durability. [Means for solving the problem]

[0011] As a result of extensive research, the present inventors have discovered and completed an electrolyte solution for pyrrole polymerization, which uses a sulfonated polyester having a specific degree of sulfonation as a first supporting electrolyte and further contains a specific aromatic sulfonic acid compound as a second supporting electrolyte, and a solid electrolytic capacitor produced using the same, which can solve the above-mentioned problems.

[0012] The present invention will be described in detail below.

[0013] The first invention provides an electrolyte solution for pyrrole polymerization, which is obtained by dissolving pyrrole and a supporting electrolyte in a solvent, comprising: a supporting electrolyte (D1) made of a copolymer containing a repeating unit represented by the following general formula (1) and a repeating unit represented by the following general formula (2); An electrolyte solution for pyrrole polymerization containing a supporting electrolyte (D2) made of an aromatic sulfonic acid compound having two or more electron-withdrawing groups, either sulfonic acid groups or carboxy groups, substituted per molecule, The electrolyte solution for pyrrole polymerization is characterized in that the repeating unit represented by general formula (2) in the supporting electrolyte (D1) is 10 mol % or more and 70 mol % or less.

[0014] [ka] (In formula (1), R represents an alkylene group, A represents an aromatic ring which may have a substituent other than a sulfonic acid group, and n represents 1 or 2.)

[0015] [ka] (In formula (2), R represents an alkylene group, B represents an aromatic ring, and n represents 1 or 2.)

[0016] A second invention is the electrolyte solution for pyrrole polymerization according to the first invention, characterized in that the weight ratio of the supporting electrolyte (D1) to the supporting electrolyte (D2) is 5:95 to 80:20.

[0017] A third invention is the electrolyte solution for pyrrole polymerization according to the first or second invention, wherein the solvent contains water.

[0018] A fourth invention is the electrolyte solution for pyrrole polymerization according to any one of the first to third inventions, wherein the aromatic sulfonic acid compound having two or more electron-withdrawing groups, either sulfonic acid groups or carboxy groups, substituted per molecule is at least one selected from the group consisting of naphthalene-1,3,6-trisulfonic acid, naphthalene-1,5-disulfonic acid, naphthalene-2,6-disulfonic acid, naphthalene-2,7-disulfonic acid, 4-sulfoisophthalic acid, 5-sulfoisophthalic acid, dimethyl 5-sulfoisophthalate, and 5-sulfosalicylic acid.

[0019] A fifth invention is the electrolyte solution for pyrrole polymerization according to any one of the first to fourth inventions, further comprising one or more additives selected from the group consisting of compounds represented by the following general formulas (4) to (6) and aliphatic cyclic amine compounds:

[0020] [ka] (In the formulas (4) to (6), R may be the same or different and represent a hydrogen atom, a linear or branched alkyl group having 1 to 6 carbon atoms, or a phenyl group.)

[0021] A sixth invention is a method for producing a solid electrolytic capacitor, comprising at least a step of forming a polypyrrole layer by electrolytic polymerization on a valve metal having a dielectric oxide film formed thereon in the electrolyte solution for pyrrole polymerization according to any one of the first to fifth inventions.

[0022] A seventh invention is a method for producing a solid electrolytic capacitor, comprising the steps of: forming a preliminary conductive layer on a valve metal having a dielectric oxide film formed thereon; and forming a polypyrrole layer on the preliminary conductive layer by electrolytic polymerization in the electrolyte solution for pyrrole polymerization according to any one of the first to fifth inventions. [Effects of the Invention]

[0023] According to the present invention, it is possible to provide an electrolyte solution for pyrrole polymerization that has excellent electrical conductivity and that provides a polypyrrole layer suitable for the solid electrolyte of a solid electrolytic capacitor, and also to provide a method for producing a solid electrolytic capacitor that exhibits significantly better capacitance and ESR characteristics than conventional solid electrolytic capacitors and has excellent moist heat resistance. DETAILED DESCRIPTION OF THE INVENTION

[0024] First, the electrolyte solution for pyrrole polymerization of the present invention will be described.

[0025] The base of the electrolyte solution for pyrrole polymerization of the present invention is a solution of pyrrole and a supporting electrolyte dissolved in a solvent. The supporting electrolyte is capable of releasing a dopant. The pyrrole monomer is a conductive polymer monomer.

[0026] The pyrrole polymerization electrolyte solution of the present invention is a pyrrole polymerization electrolyte solution obtained by dissolving pyrrole and a supporting electrolyte in a solvent, and further contains a supporting electrolyte (D1) containing a compound containing a repeating unit represented by the following general formula (1) and a repeating unit represented by the following general formula (2), and a supporting electrolyte (D2) containing an aromatic sulfonic acid compound having two or more electron-withdrawing groups, either sulfonic acid groups or carboxy groups, substituted per molecule:

[0027] Examples of the solvent for the pyrrole polymerization electrolyte include water, a single solvent of a water-soluble organic solvent such as methanol, ethanol, or isopropanol, and a mixed solvent of water and a water-soluble organic solvent. A solvent containing water and a water-soluble organic solvent preferably contains the water-soluble organic solvent at a ratio of 30% by mass or less. Among these solvents, a solvent containing water is preferred, and a solvent containing water as the single solvent is more preferred.

[0028] Among the repeating units constituting the supporting electrolyte (D1) contained in the electrolyte solution for pyrrole polymerization of the present invention, the repeating unit represented by general formula (1) will be described.

[0029] [ka] (In formula (1), R represents an alkylene group, A represents an aromatic ring which may have a substituent other than a sulfonic acid group, and n represents 1 or 2.)

[0030] The alkylene group for R in formula (1) is not particularly limited, but is preferably an alkylene group having 1 to 6 carbon atoms, and more preferably an alkylene group having 1 to 4 carbon atoms.

[0031] The aromatic ring of A in formula (1) is not particularly limited, but examples thereof include aromatic rings such as a benzene ring, a naphthalene ring, and an anthracene ring, with a benzene ring and a naphthalene ring being particularly preferred.

[0032] Furthermore, the substituent other than a sulfonic acid group that A may have is not particularly limited, but is, for example, an alkyl group having 1 to 4 carbon atoms. Note that "A may have a substituent other than a sulfonic acid group" means that A may have a substituent other than a sulfonic acid group.

[0033] When the supporting electrolyte (D1) has a repeating structure represented by the above general formula (1), it has good compatibility with pyrrole, which has the effect of improving the mechanical properties of the resulting polypyrrole.

[0034] Among the repeating units constituting the supporting electrolyte (D1) contained in the electrolyte solution for pyrrole polymerization of the present invention, the repeating unit represented by general formula (2) will be described.

[0035] [ka] (In formula (2), R represents an alkylene group, B represents an aromatic ring, and n represents 1 or 2.)

[0036] The alkylene group for R in formula (2) is not particularly limited, but is preferably an alkylene group having 1 to 6 carbon atoms, and more preferably an alkylene group having 1 to 4 carbon atoms.

[0037] The aromatic ring of B in formula (2) is not particularly limited, but examples thereof include aromatic rings such as a benzene ring, a naphthalene ring, and an anthracene ring, with a benzene ring being particularly preferred.

[0038] The repeating unit of the supporting electrolyte (D1) represented by the general formula (2) has good miscibility and compatibility with pyrrole, similar to the repeating unit of the general formula (1), thereby improving the mechanical properties of polypyrrole. In addition, the sulfonic acid group functions as a dopant anion for polypyrrole, improving the electrical conductivity.

[0039] A copolymer having repeating units represented by the above general formulas (1) and (2) can be obtained, for example, by transesterifying a polycarboxylic acid component (a component corresponding to A and the carboxylic acid residue in the above general formulas (1) and (2)) with a glycol component (a component corresponding to RO in the above general formulas (1) and (2)). The ratio of the components of the above general formulas (1) and (2) can be adjusted, for example, by changing the amounts of the polycarboxylic acid component and the glycol component used in the transesterification reaction.

[0040] In the copolymer having repeating units represented by the general formulas (1) and (2), the repeating unit represented by the general formula (2) is preferably contained in an amount of 10 to 70 mol %, more preferably 15 to 65 mol %, because the resulting polypyrrole has particularly excellent conductivity and durability. If the molar percentage of repeating units having sulfonic acid groups of general formula (2) in this copolymer is taken as the sulfonation rate, the sulfonation rate is preferably at least 10% or more, more preferably 15% to 65%, and even more preferably 20 to 60%. If the sulfonation rate is less than 10%, sufficient conductivity may not be obtained.

[0041] Particularly preferred copolymers having repeating units represented by the above general formulas (1) and (2) are copolymers having repeating units represented by the following general formulas (1a) and / or (1b) and (2a):

[0042] [ka] (In the above formula, n represents 1 or 2.)

[0043] [ka] (In the above formula, n represents 1 or 2.)

[0044] [ka] (In the above formula, n represents 1 or 2.)

[0045] In these copolymers, the repeating unit represented by general formula (2a) preferably accounts for at least 10 mol %, more preferably 15 to 65 mol %, and particularly preferably 20 to 60 mol %. That is, if the molar percentage of the repeating unit having a sulfonic acid group (2a) is taken as the sulfonation rate, the sulfonation rate is preferably at least 10% or more, more preferably 15 to 65%, particularly preferably 20 to 60%, and most preferably 35 to 45%. If the sulfonation rate is less than 10%, the resulting polypyrrole may not exhibit sufficient conductivity. Plascoat Z-4000-100 manufactured by GOO Chemical Industry Co., Ltd. is a commercially available copolymer having the above repeating unit and a sulfonation rate of 40%, and is preferably used in the present invention.

[0046] Specifically, the copolymer having repeating units represented by the above general formulas (1a) and / or (1b) and (2a) can be produced by using 20 to 60 mol% of dimethyl 2,6-naphthalenedicarboxylate, 0 to 40 mol% of dimethyl terephthalate, and 40 mol% of dimethyl sodium 5-sulfoisophthalate as polycarboxylic acid components, and 70 to 100 mol% of ethylene glycol and 0 to 30 mol% of diethylene glycol as glycol components, mixing the polycarboxylic acid component and the glycol component in a molar ratio of 1:2 and charging the mixture into a transesterification reactor, adding potassium titanium oxalate as a catalyst in an amount of 0.01 mass% of the total components, and heating the mixture to 250°C under a nitrogen atmosphere to promote transesterification reaction and distill off the by-product methanol. Next, the temperature inside the reactor is raised to 255-260°C, and the pressure is reduced to 1 mmHg (1.3 hPa), allowing the polycondensation reaction to proceed appropriately while the by-product diol is recovered, thereby obtaining a copolymer (polyester resin) with a sulfonation rate of 40%.

[0047] The supporting electrolyte (D2) is as follows: An aromatic sulfonic acid compound is used in which one molecule is substituted with two or more electron-withdrawing groups, either sulfonic acid groups or carboxy groups. Here, "one molecule is substituted with two or more electron-withdrawing groups, either sulfonic acid groups or carboxy groups" refers to a compound in which, in addition to the sulfonic acid group possessed by the aromatic sulfonic acid compound, one or more other sulfonic acid groups or carboxy groups are further possessed, and two or more electron-withdrawing groups are substituted per molecule. In other words, the aromatic sulfonic acid compound has at least one sulfonic acid group. Examples of aromatic sulfonic acid compounds having two or more electron-withdrawing groups, either sulfonic acid groups or carboxy groups, substituted per molecule include at least one selected from the group consisting of naphthalene-1,3,6-trisulfonic acid, naphthalene-1,5-disulfonic acid, naphthalene-2,6-disulfonic acid, naphthalene-2,7-disulfonic acid, 4-sulfoisophthalic acid, 5-sulfoisophthalic acid, dimethyl 5-sulfoisophthalate, and 5-sulfosalicylic acid. One or more of the above compounds can be used.

[0048] The pyrrole polymerization electrolyte solution of the present invention contains pyrrole as a monomer, a supporting electrolyte, a solvent, etc., and the pyrrole polymerization electrolyte solution preferably contains pyrrole at a concentration of 0.01 to 5 mol / L. In addition, in the pyrrole polymerization electrolyte solution of the present invention, the supporting electrolyte is preferably contained in a total of 0.1 to 500 mmol / L, more preferably 1 to 20 mmol / L, of the supporting electrolytes (D1) and (D2).

[0049] The mass ratio of the supporting electrolyte (D1) to the supporting electrolyte (D2) in the electrolytic solution for pyrrole polymerization is preferably 5:95 to 80:20, and more preferably 10:90 to 75:25.

[0050] In addition to the above-mentioned essential components, the pyrrole polymerization electrolyte solution of the present invention preferably contains additives, since this will result in significantly superior durability. The additives used in the present invention are preferably those having the properties of either an antioxidant or a surfactant. More preferred examples of such additives are compounds represented by the following general formulas (4) to (6) and aliphatic cyclic amine compounds. These additives may be used alone or in combination of two or more.

[0051] [ka]

[0052] In the above general formulas (4) to (6), R may be the same or different and represents a hydrogen atom, a linear or branched alkyl group having 1 to 6 carbon atoms, or a phenyl group.

[0053] Specific examples of the compound represented by the general formula (4) include nitrophenols such as 4-nitrophenol, 2-methyl-4-nitrophenol, 3-methyl-4-nitrophenol, 2-ethyl-4-nitrophenol, 3-ethyl-4-nitrophenol, 2-hexyl-4-nitrophenol, and 3-hexyl-4-nitrophenol. Specific examples of the compound represented by the general formula (5) include nitronaphthols such as 4-nitro-1-naphthol. Specific examples of the compound represented by the general formula (6) include nitroanthraquinones such as 1-hydroxy-4-nitroanthraquinone.

[0054] The compounds represented by the general formulas (4) to (6) may be used singly or in combination of two or more. From the viewpoint of the wet heat durability of the resulting polypyrrole, the compound represented by the general formulas (4) to (6) is preferably 4-nitrophenol (PNP).

[0055] The content of the compounds represented by general formulas (4) to (6) in the pyrrole polymerization electrolyte solution of the present invention is not particularly limited, but is preferably 0.1 to 2% by mass. If the content is less than 0.1% by mass, the desired effect may not be obtained, while if it exceeds 2% by mass, the electrical conductivity of the resulting conductive polymer may deteriorate, which may adversely affect the properties of the resulting solid electrolytic capacitor.

[0056] The aliphatic cyclic amine compound used in the present invention preferably has a saturated aliphatic cyclic amine structure. Examples of the saturated aliphatic cyclic amine structure include saturated aliphatic cyclic amines having 2 to 10 carbon atoms, such as a pyrrolidine ring, a piperidine ring, or a morpholine ring. These saturated aliphatic cyclic amine structures may be used in any combination.

[0057] Furthermore, the cyclic amine structure of the aliphatic cyclic amine compound may have a substituent within a range that does not impair the effects of the present invention. Examples of the substituent include a hydrocarbon group and a halogen atom. Examples of the cyclic amine structure substituted with a substituent include a dimethylpyrrolidine ring.

[0058] Among these aliphatic cyclic amine compounds, at least one aliphatic cyclic amine compound represented by the following general formula (7) is preferred in terms of the electrical conductivity and durability of the resulting polypyrrole.

[0059] [ka]

[0060] In the above general formula (7), n is a repeating unit and represents an integer of 1 to 4. Among the aliphatic cyclic amine compounds represented by this general formula (7), pyrrolidine, where n is 3, is preferred.

[0061] The content of the aliphatic cyclic amine compound in the pyrrole polymerization electrolyte solution of the present invention is not particularly limited, but is preferably 0.001 to 0.06% by mass. If the content is less than 0.001% by mass, the effect may not be obtained, while if it exceeds 0.06% by mass, the electrical conductivity of the resulting conductive polymer may deteriorate, which may adversely affect the properties of the resulting solid electrolytic capacitor.

[0062] By carrying out electrolytic polymerization using an electrolyte solution for pyrrole polymerization containing the additives as described above, polypyrrole with extremely excellent durability can be obtained.

[0063] A method for producing a solid electrolytic capacitor using the pyrrole polymerization electrolyte of the present invention will now be described. To produce a solid electrolytic capacitor using the pyrrole polymerization electrolyte of the present invention, a polypyrrole layer may be formed using the pyrrole polymerization electrolyte of the present invention in a conventional method for producing a solid electrolytic capacitor. Specifically, the method may include a step of electrolytically polymerizing a polypyrrole layer in the pyrrole polymerization electrolyte of the present invention on a valve metal on which a dielectric oxide film has been formed.

[0064] The (anode) valve metal may be one selected from the group consisting of aluminum, tantalum, niobium, and titanium, and these are used in the form of a sintered body or foil.

[0065] The method for forming the dielectric oxide film on the valve metal is not particularly limited, but for example, a known chemical conversion treatment may be carried out.

[0066] The method for forming a polypyrrole layer by electropolymerization in the pyrrole polymerization electrolyte of the present invention on a valve metal having a dielectric oxide film formed thereon is not particularly limited, but it can be a method of polymerizing polypyrrole by electrolysis (anodic oxidation) in the pyrrole polymerization electrolyte of the present invention. That is, a polypyrrole layer can be formed on the valve metal by electrolysis between the valve metal, optionally provided with a preliminary conductive layer, and a counter electrode (cathode). The current density and electrolysis time during anodization are not particularly limited and can be appropriately set depending on the type and size of the capacitor element used. For example, a current of 0.001 to 50 mA can be applied for 1 to 1,000 minutes, or a current of 0.01 to 30 mA can be applied for 5 to 600 minutes, per capacitor element having a polypyrrole layer formed on the valve metal. After electropolymerization, a chemical conversion treatment can be performed, if necessary, to repair the dielectric oxide film.

[0067] Next, an anode lead terminal is connected to the valve metal, and a cathode lead terminal is connected to the cathode layer to form electrodes, and the entire element is sealed in an insulating resin such as epoxy resin, or in an exterior case made of ceramic or metal, to obtain a solid electrolytic capacitor. The cathode layer is formed by applying a conductive paste such as carbon paste or silver paste to the polypyrrole layer and drying it.

[0068] The method preferably includes the steps of forming a preliminary conductive layer on the valve metal having the dielectric oxide film formed thereon, and forming a polypyrrole layer on the preliminary conductive layer by electrolytic polymerization in the pyrrole polymerization electrolyte. The provision of such a preliminary conductive layer improves the electrical properties (capacitance, tan δ, ESR) of the resulting solid electrolytic capacitor.

[0069] Examples of methods for forming a preliminary conductive layer include known methods such as (1) a method for forming a conductive polymer layer by chemical polymerization, (2) a method for forming a conductive polymer layer by applying and drying a conductive polymer solution / conductive polymer dispersion, and (3) a method for forming a manganese dioxide layer. These methods for forming a preliminary conductive layer may be repeated.

[0070] The conductive polymer layer formed by chemical polymerization as the preliminary conductive layer in (1) will now be described. Examples of the conductive polymer monomer include pyrrole, aniline, ethylenedioxythiophene, and derivatives thereof. As a method of chemical polymerization, there is a method in which a solution containing the conductive polymer monomer is brought into contact with an oxidizing agent on a valve metal on which a dielectric oxide film has been formed, to carry out oxidative polymerization. Examples of the oxidizing agent include inorganic oxidizing agents such as hydrogen peroxide, persulfates, and perborates; inorganic ferric salts such as ferric chloride and ferric sulfate; and organic ferric sulfonates such as ferric paratoluenesulfonate. Preferably, a solution of any of these oxidizing agents adjusted to an appropriate concentration can be used as the oxidizing agent. A preliminary conductive layer can be formed by bringing the solution containing the conductive polymer monomer as described above into contact with the oxidizing agent-containing solution on the valve metal.

[0071] A specific example of the conductive polymer solution in (2) is a solution in which 0.1 to 10 mass % of polyaniline is dissolved in N-methylpyrrolidone (NMP). Such a solution can be applied to a valve metal on which a dielectric oxide film has been formed, and then heated and dried at 50°C to 160°C to form a preliminary conductive layer. Furthermore, the conductive polymer dispersion liquid in (2) specifically includes a solution in which polymer fine particles of polypyrrole or polyethylenedioxythiophene are dispersed and mixed in water or an organic solvent such as alcohol, methyl ethyl ketone, toluene, or a mixture thereof. If necessary, the dispersion solution may contain an organic sulfonic acid anion or an organic polymeric sulfonic acid anion that serves as a dopant. Such a solution can be applied to a valve metal on which a dielectric oxide film has been formed, and then heated and dried at 50°C to 160°C to form a preliminary conductive layer.

[0072] The manganese dioxide layer in (3) can be obtained by a method of impregnating manganese nitrate and then thermally decomposing it to form a manganese dioxide layer, or by a method of applying an aqueous permanganate solution, heating it, and reducing it to form a manganese dioxide layer.

[0073] Next, the method for forming a polypyrrole layer on the preliminary conductive layer by electrolytic polymerization in the electrolyte solution for pyrrole polymerization may be the same as the method for forming a polypyrrole layer on a valve metal on which a dielectric oxide film has been formed by electrolytic polymerization in the electrolyte solution for pyrrole polymerization.

[0074] A polypyrrole layer is formed on the preliminary conductive layer by electrolytic polymerization using the electrolyte solution for pyrrole polymerization of the present invention, and then a conductive paste such as carbon paste or silver paste is applied to the polypyrrole layer and dried to form a cathode layer. Thereafter, as described above, an anode lead terminal is connected to the valve metal, and a cathode lead terminal is connected to the cathode layer to form an electrode, forming an element. The entire element is sealed with an insulating resin such as epoxy resin, or with an exterior case made of ceramic or metal, to obtain a solid electrolytic capacitor.

[0075] The method for producing a solid electrolytic capacitor of the present invention can be applied to either a chip type or a wound type production method depending on the type and shape of the (anode) valve metal used.

[0076] By using the electrolyte solution for pyrrole polymerization of the present invention, polypyrrole having excellent conductivity and maintaining a stable structure even when a specific voltage is applied can be obtained. Furthermore, by using the polypyrrole as a solid electrolyte, a solid electrolytic capacitor having significantly better durability, capacitance, and ESR characteristics than conventional capacitors can be obtained. [Example]

[0077] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0078] (Comparative Example 1) Tantalum metal powder was pressed and molded into a sintered anode body, which was used as the valve metal. This was then subjected to a chemical conversion treatment at a constant voltage of approximately 8 V for approximately 9 hours in an electrolyte of 0.2 mass% aqueous phosphoric acid solution, to form a dielectric oxide film on the valve metal.

[0079] Next, the chemically treated anode body was immersed in a monomer solution of pyrrole:EtOH=2:1, and then removed. After that, it was immersed in an oxidant solution of 15 mass% hydrogen peroxide, 35 mass% water, 45 mass% EtOH, and 5 mass% paratoluenesulfonic acid, and then removed and subjected to chemical oxidative polymerization.

[0080] Furthermore, the polypyrrole layer formation operation by chemical oxidative polymerization was carried out once again to form a preliminary conductive layer.

[0081] Next, the anode body on which a polypyrrole layer (preliminary conductive layer) was formed by chemical oxidative polymerization was again subjected to chemical conversion treatment in an electrolyte of 0.2 mass % aqueous phosphoric acid solution at a constant voltage of 8 V for approximately 5 minutes to repair the dielectric oxide film.

[0082] Next, a current of 0.15 mA was passed for 100 minutes in an electropolymerization solution of 5 (g) of a solution prepared by dissolving PLASCOAT Z221 (manufactured by GOO Chemical Industry Co., Ltd., sulfonation rate 5%), a polyester resin compound having sulfonic acid groups, in water at a concentration of 20 mass %, + 1.2 (g) of pyrrole + 93.8 (g) of HO, to form a cathode layer made of a polypyrrole film.

[0083] After the electrolytic polymerization was completed, carbon paste and silver paste were applied in that order onto the cathode layer and dried to complete a total of 20 capacitor elements.

[0084] The average equivalent series resistance (ESR) value of these 20 capacitor elements at 100 kHz at room temperature of 20°C was taken as the ESR value, and the average electrostatic capacitance (μF) at 120 Hz at room temperature of 20°C was taken as the capacitance value.The ESR value after leaving at 125°C for 300 hours was divided by the measurement value at the time of initial characteristic evaluation to obtain the heat resistance change rate (times).In addition, the ESR value after leaving at 85°C and 85% RH for 500 hours was divided by the measurement value at the time of initial characteristic evaluation to obtain the humidity resistance change rate (times).

[0085] (Comparative Example 2) Twenty capacitor elements were obtained in the same manner as in Comparative Example 1, except that the polypyrrole manufacturing method was changed to the following method. Specifically, electropolymerization was performed using a mixed solution of 5 (g) of a solution in which a 40% sulfonated polyester resin compound, Plascoat Z4000-100, was dissolved in water at a concentration of 20 mass % + 1.2 (g) of pyrrole + 93.8 (g) of HO as the electropolymerization solution, forming a polypyrrole layer. The characteristics of the capacitor elements were evaluated in the same manner as in Comparative Example 1.

[0086] (Comparative Example 3) Twenty capacitor elements were obtained in the same manner as in Comparative Example 1, except that the polypyrrole manufacturing method was changed to the following method. Specifically, electropolymerization was performed using a mixed solution of 1 (g) of PLASCOAT Z221 (manufactured by GOO Chemical Industry Co., Ltd., sulfonation rate 5%), a polyester resin compound having sulfonic acid groups, dissolved in water at a concentration of 20 mass%, + 0.8 (g) of 5-monosodium sulfoisophthalate + 1.2 (g) of pyrrole + 97.0 (g) of HO to form a polypyrrole layer. The characteristics of the capacitor elements were evaluated in the same manner as in Comparative Example 1.

[0087] Comparative Example 4 Twenty capacitor elements were obtained in the same manner as in Comparative Example 1, except that the polypyrrole manufacturing method was changed to the following method. Specifically, electropolymerization was performed using a mixed solution of 5 (g) of PLASCOAT Z221 (manufactured by GOO Chemical Industry Co., Ltd., sulfonation rate 5%), a polyester resin compound having sulfonic acid groups, dissolved in water at a concentration of 20 mass %, + 1 (g) of monosodium 5-sulfoisophthalate + 1.2 (g) of pyrrole + 92.8 (g) of HO to form a polypyrrole layer. The characteristics of the capacitor elements were evaluated in the same manner as in Comparative Example 1.

[0088] (Comparative Example 5) Twenty capacitor elements were obtained in the same manner as in Comparative Example 1, except that the polypyrrole manufacturing method was changed to the following method. Specifically, electropolymerization was performed using a mixed solution of 5 (g) of a solution in which a polyester resin compound with a sulfonation rate of 80% (only the sulfonation rate of the above-mentioned PLASCOAT was changed) dissolved in water at a concentration of 20% by mass, + 1 (g) of monosodium 5-sulfoisophthalate, + 1.2 (g) of pyrrole, + 92.8 (g) of HO, to form a polypyrrole layer. The characteristics of the capacitor elements were evaluated in the same manner as in Comparative Example 1.

[0089] (Comparative Example 6) Twenty capacitor elements were obtained in the same manner as in Comparative Example 1, except that the polypyrrole manufacturing method was changed to the following method. That is, electrolytic polymerization was performed using a mixed solution of 5 (g) of a solution in which sodium polystyrene sulfonate was dissolved in water at a concentration of 20 mass%, + 1 (g) of monosodium 5-sulfoisophthalate, + 1.2 (g) of pyrrole, + 92.8 (g) of HO as the electrolytic polymerization solution, to form a polypyrrole layer. The characteristics of the capacitor elements were evaluated in the same manner as in Comparative Example 1.

[0090] (Comparative Example 7) Twenty capacitor elements were obtained in the same manner as in Comparative Example 1, except that the polypyrrole manufacturing method was changed to the following method. That is, electrolytic polymerization was performed using a mixed solution of 1 (g) of monosodium 5-sulfoisophthalate + 1.2 (g) of pyrrole + 97.8 (g) of HO as the electrolytic polymerization solution, and a polypyrrole layer was formed. The characteristics of the capacitor elements were evaluated in the same manner as in Comparative Example 1.

[0091] (Comparative Example 8) Twenty capacitor elements were obtained in the same manner as in Comparative Example 1, except that the polypyrrole manufacturing method was changed to the following method. That is, electrolytic polymerization was performed using a mixed solution of 1 (g) of 5-sodium sulfosalicylate dihydrate + 1.2 (g) of pyrrole + 97.8 (g) of HO as the electrolytic polymerization solution, and a polypyrrole layer was formed. The characteristics of the capacitor elements were evaluated in the same manner as in Comparative Example 1.

[0092] Comparative Example 9 Twenty capacitor elements were obtained in the same manner as in Comparative Example 1, except that the polypyrrole manufacturing method was changed to the following method. That is, electrolytic polymerization was performed using a mixed solution of 1 (g) of disodium 2,7-naphthalenedisulfonate + 1.2 (g) of pyrrole + 97.8 (g) of HO as the electrolytic polymerization solution, and a polypyrrole layer was formed. The characteristics of the capacitor elements were evaluated in the same manner as in Comparative Example 1.

[0093] (Comparative Example 10) Twenty capacitor elements were obtained in the same manner as in Comparative Example 1, except that the polypyrrole manufacturing method was changed to the following method. That is, electrolytic polymerization was performed using a mixed solution of naphthalene-1,3,6-trisulfonic acid trisodium salt hydrate: 1 (g) + pyrrole: 1.2 (g) + HO: 97.8 (g) as the electrolytic polymerization solution, and a polypyrrole layer was formed. The characteristics of the capacitor elements were evaluated in the same manner as in Comparative Example 1.

[0094] (Comparative Example 11) Twenty capacitor elements were obtained in the same manner as in Comparative Example 1, except that the polypyrrole manufacturing method was changed to the following method. Specifically, a polypyrrole layer was formed by electropolymerization using a mixed solution of 5 (g) of a solution in which a 40% sulfonated polyester resin compound, Plascoat Z4000-100, was dissolved in water at a concentration of 20% by mass, 2.5 (g) of a solution in which an alkylnaphthalenesulfonate sodium salt was dissolved in water at a concentration of 40% by mass, 1.2 (g) of pyrrole, and 91.3 (g) of H2O. The characteristics of the capacitor elements were evaluated in the same manner as in Comparative Example 1.

[0095] Example 1 Twenty capacitor elements were obtained in the same manner as in Comparative Example 1, except that the polypyrrole manufacturing method was changed to the following method. Specifically, electropolymerization was performed using a mixed solution of 0.15 (g) of a solution of 40% sulfonated polyester resin compound Plascoat Z4000-100 dissolved in water at a concentration of 20 mass % + 1 (g) of 5-monosodium sulfoisophthalate + 1.2 (g) of pyrrole + 97.65 (g) of HO to form a polypyrrole layer. The characteristics of the capacitor elements were evaluated in the same manner as in Comparative Example 1.

[0096] Example 2 Twenty capacitor elements were obtained in the same manner as in Comparative Example 1, except that the polypyrrole manufacturing method was changed to the following method. Specifically, electropolymerization was performed using a mixed solution of 4.5 (g) of a solution of 40% sulfonated polyester resin compound Plascoat Z4000-100 dissolved in water at a concentration of 20 mass % + 0.1 (g) of 5-monosodium sulfoisophthalate + 1.2 (g) of pyrrole + 94.2 (g) of HO to form a polypyrrole layer. The characteristics of the capacitor elements were evaluated in the same manner as in Comparative Example 1.

[0097] Example 3 Twenty capacitor elements were obtained in the same manner as in Comparative Example 1, except that the polypyrrole manufacturing method was changed to the following method. Specifically, electropolymerization was performed using a mixed solution of 1 (g) of a 20% by mass solution of 40% sulfonated polyester resin compound Plascoat Z4000-100 dissolved in water, 0.8 (g) of 5-monosodium sulfoisophthalate, 1.2 (g) of pyrrole, and 97.0 (g) of H2O to form a polypyrrole layer. The characteristics of the capacitor elements were evaluated in the same manner as in Comparative Example 1.

[0098] Example 4 Twenty capacitor elements were obtained in the same manner as in Comparative Example 1, except that the polypyrrole manufacturing method was changed to the following method. Specifically, electropolymerization was performed using a mixed solution of 2.5 (g) of a solution of 40% sulfonated polyester resin compound Plascoat Z4000-100 dissolved in water at a concentration of 20 mass % + 0.5 (g) of monosodium 5-sulfoisophthalate + 1.2 (g) of pyrrole + 95.8 (g) of HO to form a polypyrrole layer. The characteristics of the capacitor elements were evaluated in the same manner as in Comparative Example 1.

[0099] Example 5 Twenty capacitor elements were obtained in the same manner as in Comparative Example 1, except that the polypyrrole manufacturing method was changed to the following method. Specifically, electropolymerization was performed using a mixed solution of 3.5 (g) of a solution of 40% sulfonated polyester resin compound Plascoat Z4000-100 dissolved in water at a concentration of 20 mass % + 0.3 (g) of 5-monosodium sulfoisophthalate + 1.2 (g) of pyrrole + 95.0 (g) of HO to form a polypyrrole layer. The characteristics of the capacitor elements were evaluated in the same manner as in Comparative Example 1.

[0100] Example 6 Twenty capacitor elements were obtained in the same manner as in Comparative Example 1, except that the polypyrrole manufacturing method was changed to the following method. Specifically, a polypyrrole layer was formed by electropolymerization using a mixed solution of 2.5 (g) of a solution in which a polyester resin compound with a sulfonation rate of 20% (only the sulfonation rate of the above-mentioned PLASCOAT was changed) was dissolved in water at a concentration of 20 mass%, 0.5 (g) of monosodium 5-sulfoisophthalate, 1.2 (g) of pyrrole, and 95.8 (g) of HO. The characteristics of the capacitor elements were evaluated in the same manner as in Comparative Example 1.

[0101] Example 7 Twenty capacitor elements were obtained in the same manner as in Comparative Example 1, except that the polypyrrole manufacturing method was changed to the following method. Specifically, a polypyrrole layer was formed by electropolymerization using a mixed solution of 2.5 (g) of a solution in which a polyester resin compound with a sulfonation rate of 60% (only the sulfonation rate of the above-mentioned PLASCOAT was changed) dissolved in water at a concentration of 20 mass%, 0.5 (g) of monosodium 5-sulfoisophthalate, 1.2 (g) of pyrrole, and 95.8 (g) of HO as the electropolymerization solution. The characteristics of the capacitor elements were evaluated in the same manner as in Comparative Example 1.

[0102] Example 8 Twenty capacitor elements were obtained in the same manner as in Comparative Example 1, except that the polypyrrole manufacturing method was changed to the following method. Specifically, electropolymerization was performed using a mixed solution of 2.5 (g) of a solution of 40% sulfonated polyester resin compound Plascoat Z4000-100 dissolved in water at a concentration of 20 mass % + 0.5 (g) of 5-sodium sulfosalicylate dihydrate + 1.2 (g) of pyrrole + 95.8 (g) of HO to form a polypyrrole layer. The characteristics of the capacitor elements were evaluated in the same manner as in Comparative Example 1.

[0103] Example 9 Twenty capacitor elements were obtained in the same manner as in Comparative Example 1, except that the polypyrrole manufacturing method was changed to the following method. Specifically, electropolymerization was performed using a mixed solution of 2.5 (g) of a solution of 40% sulfonated polyester resin compound Plascoat Z4000-100 dissolved in water at a concentration of 20 mass % + 0.5 (g) of disodium 2,7-naphthalenedisulfonate + 1.2 (g) of pyrrole + 95.8 (g) of H2O as the electropolymerization solution to form a polypyrrole layer. The characteristics of the capacitor elements were evaluated in the same manner as in Comparative Example 1.

[0104] Example 10 Twenty capacitor elements were obtained in the same manner as in Comparative Example 1, except that the polypyrrole manufacturing method was changed to the following method. Specifically, electropolymerization was performed using a mixed solution of 2.5 (g) of a solution of 40% sulfonated polyester resin compound Plascoat Z4000-100 dissolved in water at a concentration of 20 mass%, 0.5 (g) of naphthalene-1,3,6-trisulfonic acid trisodium salt hydrate, 1.2 (g) of pyrrole, and 95.8 (g) of HO to form a polypyrrole layer. The characteristics of the capacitor elements were evaluated in the same manner as in Comparative Example 1.

[0105] Example 11 Twenty capacitor elements were obtained in the same manner as in Comparative Example 1, except that the polypyrrole manufacturing method was changed to the following method. Specifically, electropolymerization was performed using a mixed solution of 2.5 (g) of a solution of 40% sulfonated polyester resin compound Plascoat Z4000-100 dissolved in water at a concentration of 20 mass % + 0.5 (g) of 5-monosodium sulfoisophthalate + 1.2 (g) of pyrrole + 0.5 (g) of PNP (paranitrophenol) + 95.3 (g) of HO to form a polypyrrole layer. The characteristics of the capacitor elements were evaluated in the same manner as in Comparative Example 1.

[0106] Example 12 Twenty capacitor elements were obtained in the same manner as in Comparative Example 1, except that the polypyrrole manufacturing method was changed to the following method. Specifically, electropolymerization was performed using a mixed solution of 2.5 (g) of a solution of 40% sulfonated polyester resin compound Plascoat Z4000-100 dissolved in water at a concentration of 20 mass % + 0.5 (g) of 5-monosodium sulfoisophthalate + 1.2 (g) of pyrrole + 0.01 g of PD (pyrrolidine) + 95.79 (g) of H2O to form a polypyrrole layer. The characteristics of the capacitor elements were evaluated in the same manner as in Comparative Example 1.

[0107] Table 1 shows the measurement results of the capacitor elements of Comparative Examples 1 to 11 and Examples 1 to 12.

[0108] [Table 1]

[0109] The abbreviations in the table are as follows: SIP: Monosodium 5-sulfoisophthalate PSS: Polystyrene sodium sulfonate SSA: 5-sodium sulfosalicylate dihydrate NDS: 2,7-naphthalenedisulfonic acid disodium salt NTS: Naphthalene-1,3,6-trisulfonic acid trisodium salt hydrate ANS: Sodium alkylnaphthalene sulfonate PNP: paranitrophenol PD: pyrrolidine

[0110] Comparing Comparative Examples 1 to 11 with Examples 1 and 2, it was found that Examples 1 and 2 maintained high capacity and low ESR while improving durability.

[0111] It was found that by setting the mass ratio of (D1):(D2) to 5:95 to 80:20 in Examples 3 to 10, the capacitance characteristics, ESR characteristics, and durability were further improved.

[0112] Furthermore, Examples 11 and 12, in which additives were added, had better ESR characteristics and durability.

[0113] [Evaluation of polymerization burrs on conductive polymer films obtained by electropolymerization]

[0114] (Comparative Example 12) Tantalum metal powder was pressed and molded into a sintered anode body, which was used as the valve metal. This was then subjected to a chemical conversion treatment at a constant voltage of approximately 8 V for approximately 9 hours in an electrolyte of 0.2 mass% aqueous phosphoric acid solution, to form a dielectric oxide film on the valve metal.

[0115] Next, the chemically treated anode body was immersed in a monomer solution of pyrrole:EtOH=2:1, and then removed. After that, it was immersed in an oxidant solution of 15 mass% hydrogen peroxide, 35 mass% water, 45 mass% EtOH, and 5 mass% p-toluenesulfonic acid, and then removed and subjected to chemical oxidative polymerization.

[0116] Furthermore, the polypyrrole layer formation operation by chemical oxidative polymerization was carried out once again to form a preliminary conductive layer.

[0117] Next, the anode body on which a polypyrrole layer (preliminary conductive layer) was formed by chemical oxidative polymerization was again subjected to chemical conversion treatment in an electrolyte of 0.2 mass % aqueous phosphoric acid solution at a constant voltage of 8 V for approximately 5 minutes to repair the dielectric oxide film.

[0118] Next, a current of 0.15 mA was applied for 100 minutes to an electropolymerization solution containing 5 g of PLASCOAT Z221 (manufactured by GOO Chemical Industry Co., Ltd., sulfonation rate 5%), a polyester resin compound having sulfonic acid groups, dissolved in water at a concentration of 20% by mass, + 1.2 g of 3,4-ethylenedioxythiophene + 46.9 g of HO + 46.9 g of ethanol, to form 20 cathode layers made of poly-3,4-ethylenedioxythiophene. The number of polymerization flashes on the resulting poly-3,4-ethylenedioxythiophene layers was visually confirmed.

[0119] (Comparative Example 13) Twenty cathode layers made of conductive polymer layers were obtained in the same manner as in Comparative Example 9, except that the manufacturing method of the polypyrrole layer was changed to the following method. That is, electrolytic polymerization was performed using a mixed solution of 2.5 (g) of a solution in which a polyester resin-based compound Plascoat Z4000-100 with a sulfonation rate of 40% was dissolved in water at a concentration of 20 mass%, + 0.5 (g) of monosodium 5-sulfoisophthalate + 1.2 (g) of 3,4-ethylenedioxythiophene + 47.9 (g) of HO + 47.9 (g) of ethanol as the electrolytic polymerization solution to form a cathode layer made of a poly-3,4-ethylenedioxythiophene layer, and the number of polymerization burrs generated in the obtained poly-3,4-ethylenedioxythiophene layer was visually confirmed.

[0120] Example 13 Twenty cathode layers each consisting of a polypyrrole layer were obtained in the same manner as in Comparative Example 9, except that the manufacturing method of the polypyrrole layer was changed to the following method. That is, electrolytic polymerization was performed using a mixed solution of 0.15 (g) of a solution in which a polyester resin-based compound Plascoat Z4000-100 with a sulfonation rate of 40% was dissolved in water at a concentration of 20 mass%, 1 (g) of 5-monosodium sulfoisophthalate, 1.2 (g) of pyrrole, and 97.65 (g) of HO as the electrolytic polymerization solution to form a cathode layer consisting of a polypyrrole layer, and the number of polymerization burrs generated in the obtained polypyrrole layer was visually confirmed.

[0121] Example 14 Twenty cathode layers each consisting of a polypyrrole layer were obtained in the same manner as in Comparative Example 9, except that the manufacturing method of the polypyrrole layer was changed to the following method. That is, electrolytic polymerization was performed using a mixed solution of 2.5 (g) of a solution in which a polyester resin-based compound Plascoat Z4000-100 with a sulfonation rate of 40% was dissolved in water at a concentration of 20 mass%, 0.5 (g) of monosodium 5-sulfoisophthalate, 1.2 (g) of pyrrole, and 95.8 (g) of HO as the electrolytic polymerization solution to form a cathode layer consisting of a polypyrrole layer, and the number of polymerization burrs generated in the obtained polypyrrole layer was visually confirmed.

[0122] The measurement results of the number of polymerization flashes generated in Comparative Examples 12 and 13 and Examples 13 and 14 are shown in Table 2.

[0123] [Table 2]

[0124] The abbreviations in the table are as follows: SIP: Monosodium 5-sulfoisophthalate EDOT: 3,4-ethylenedioxythiophene Py: Pyrrole

[0125] Comparing Comparative Examples 12 and 13 with Examples 13 and 14, it was found that Examples 13 and 14 were able to reduce the occurrence of burrs. [Industrial Applicability]

[0126] The polypyrrole obtained from the electrolyte solution for pyrrole polymerization of the present invention can be suitably used not only for solid electrolytic capacitors but also for organic EL displays, organic transistors, polymer batteries, solar cells, various sensor materials, electromagnetic wave shielding materials, antistatic materials, electrochromic materials, artificial muscles, and the like.

Claims

1. The electrolyte solution for pyrrole polymerization, which is obtained by dissolving pyrrole and a supporting electrolyte in a solvent, comprises: a supporting electrolyte (D1) made of a copolymer containing a repeating unit represented by the following general formula (1) and a repeating unit represented by the following general formula (2); a supporting electrolyte (D2) comprising an aromatic sulfonic acid compound having two or more electron-withdrawing groups, either sulfonic acid groups or carboxy groups, substituted per molecule; An electrolyte solution for pyrrole polymerization comprising: An electrolyte solution for pyrrole polymerization, characterized in that in the supporting electrolyte (D1), the repeating unit represented by general formula (2) is 10 mol % or more and 70 mol % or less. 【Chemistry 1】 (In formula (1), R represents an alkylene group, A represents an aromatic ring which may have a substituent other than a sulfonic acid group, and n represents 1 or 2.) 【Chemistry 2】 (In formula (2), R represents an alkylene group, B represents an aromatic ring, and n represents 1 or 2.)

2. 2. The electrolytic solution for pyrrole polymerization according to claim 1, wherein the mass ratio of the supporting electrolyte (D1) to the supporting electrolyte (D2) is 5:95 to 80:

20.

3. 2. The electrolyte solution for pyrrole polymerization according to claim 1, wherein the solvent contains water.

4. 3. The electrolyte solution for pyrrole polymerization according to claim 1, wherein the aromatic sulfonic acid compound having two or more electron-withdrawing groups, either sulfonic acid groups or carboxy groups, substituted per molecule is at least one selected from the group consisting of naphthalene-1,3,6-trisulfonic acid, naphthalene-1,5-disulfonic acid, naphthalene-2,6-disulfonic acid, naphthalene-2,7-disulfonic acid, 4-sulfoisophthalic acid, 5-sulfoisophthalic acid, dimethyl 5-sulfoisophthalate, and 5-sulfosalicylic acid.

5. The electrolyte solution for pyrrole polymerization according to any one of claims 1 to 3, further comprising one or more additives selected from the group consisting of compounds represented by the following general formulas (4) to (6) and aliphatic cyclic amine compounds: 【Transformation 3】 (In formulas (4) to (6), R may be the same or different and represent a hydrogen atom, a linear or branched alkyl group having 1 to 6 carbon atoms, or a phenyl group.)

6. 4. A method for producing a solid electrolytic capacitor, comprising the step of forming a polypyrrole layer by electrolytic polymerization on a valve metal having a dielectric oxide film formed thereon in the electrolyte solution for pyrrole polymerization according to claim 1.

7. 4. A method for manufacturing a solid electrolytic capacitor, comprising: a step of forming a preliminary conductive layer on a valve metal having a dielectric oxide film formed thereon; and a step of forming a polypyrrole layer on the preliminary conductive layer by electrolytic polymerization in the electrolyte solution for pyrrole polymerization according to claim 1.

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