JP7516891B2 - Conductive polymer aqueous solution and its uses - Google Patents

Description

The present invention aims to provide a novel conductive polymer film that can produce a low-resistance conductive polymer film, and to provide an electrolytic capacitor using the same that has a low ESR and a low leakage current. In particular, the present invention relates to an aqueous solution of a novel conductive composition that contains a specific self-doped conductive polymer with high conductivity and a specific sulfonic acid compound, and further to a conductive polymer film obtained by drying the aqueous solution and its uses.

In recent years, conductive polymer materials have been developed in which π-conjugated polymers, such as polyacetylene, polythiophene, polyaniline, and polypyrrole, are doped with electron-accepting compounds as dopants. Applications of these materials to, for example, antistatic agents, solid electrolytes for electrolytic capacitors, conductive paints, electrochromic elements, electrode materials, thermoelectric conversion materials, transparent conductive films, chemical sensors, actuators, and the like are being considered. In the field of electrolytic capacitors, there is a strong demand for electrolytic capacitors with high capacity and low ESR as electronic devices become faster and operate at higher frequencies. Polythiophene-based conductive polymer materials are practically useful as conductive polymer materials that meet this demand due to their chemical stability.

Known polythiophene-based conductive polymer materials include (i) a PEDOT/PSS aqueous dispersion solution obtained by polymerizing 3,4-ethylenedioxythiophene (EDOT) in an aqueous solution of polystyrene sulfonic acid (PSS) as a dopant, and (ii) so-called self-doped conductive polymers (e.g., sulfonated polyaniline, PEDOT-S, etc.) that have substituents (sulfo groups, sulfonate groups, etc.) that combine water solubility and doping properties directly or via a spacer in the polymer main chain (see, for example, Non-Patent Documents 1 and 2).

Electrolytic capacitors using PEDOT/PSS are known (Patent Document 1). However, since PEDOT/PSS exists on particles, it is known that it is not possible to cover every corner of the surface of the electrolytic capacitor dielectric that has been subjected to an expansion treatment, making it difficult to fully utilize the capacitance of the electrolytic capacitor. As a method for solving this problem, development is being carried out of self-doped conductive polymers that are water-soluble and have the potential to cover every corner of the electrolytic capacitor dielectric surface.

Journal of American Chemical Society, 112, 2801-2803 (1990) Advanced Materials, Vol. 23 (38) 4403-4408 (2011)

JP 2017-147466 A

In addition to the high capacity described above, a low ESR is also required as a desirable characteristic of an electrolytic capacitor, and there has been a demand for improvement in the low ESR characteristic of conventionally known self-doped conductive polymers. Therefore, the present invention aims to provide a conductive polymer composition for producing an electrolytic capacitor that has excellent low ESR characteristics while maintaining a high capacity.

As a result of extensive research into solving the above problems, the inventors discovered that a self-doped water-soluble conductive polymer to which a specific sulfonic acid compound has been added can provide an electrolytic capacitor with excellent low ESR characteristics while maintaining a high capacity, and thus completed the present invention.

That is, the present invention relates to a conductive polymer aqueous solution composition, a conductive polymer film, and an electrolytic capacitor using the same, as described below.
[1] A conductive polymer aqueous solution containing 0.01 to 10% by weight of a polythiophene (A) containing at least one structural unit selected from the group consisting of a structural unit represented by the following formula (1) and a structural unit represented by the following formula (2), and containing 0.001 to 20% by weight of a sulfonic acid compound (B) having 1 to 3 sulfo groups:

[In general formulas (1) and (2), ^R2 represents a hydrogen atom, a methyl group, an ethyl group, a linear or branched alkyl group having 3 to 6 carbon atoms, or a fluorine atom, m represents an integer of 1 to 10, and n represents 0 or 1.]
[2] The conductive polymer aqueous solution according to [1], wherein the sulfonic acid compound (B) having 1 to 3 sulfo groups is a sulfonic acid compound having 1 to 3 sulfo groups and a total of 1 to 20 carbon atoms.
[3] The conductive polymer aqueous solution according to [1], wherein the sulfonic acid compound (B) having 1 to 3 sulfo groups is one or a mixture of two or more selected from the group consisting of sulfosalicylic acid, sulfophthalic acid, sulfoisophthalic acid, sulfosuccinic acid, toluenesulfonic acid, aminobenzenesulfonic acid, dodecylbenzenesulfonic acid, naphthalenesulfonic acid, camphorsulfonic acid, aminomethanesulfonic acid, aminopropanesulfonic acid, and hydroxypropanesulfonic acid.
[4] The conductive polymer aqueous solution according to any one of [1] to [3], further comprising an ion (C) selected from the group consisting of an alkali metal ion, an ammonium ion, an organic ammonium ion, and a quaternary ammonium cation, and having a pH in the range of 1.5 to 10.0.
[5] A conductive polymer membrane comprising: a polythiophene (A) containing at least one structural unit selected from the group consisting of a structural unit represented by the following formula (1) and a structural unit represented by the following formula (2); and a sulfonic acid compound (B) having 1 to 3 sulfo groups:

[In general formulas (1) and (2), ^R2 represents a hydrogen atom, a methyl group, an ethyl group, a linear or branched alkyl group having 3 to 6 carbon atoms, or a fluorine atom, m represents an integer of 1 to 10, and n represents 0 or 1.]
[6] A method for producing a conductive polymer film according to [5], characterized in that an aqueous conductive polymer solution containing 0.01 to 10% by weight of polythiophene (A) containing at least one structural unit selected from the group consisting of a structural unit represented by the following formula (1) and a structural unit represented by the following formula (2), and containing 0.001 to 20% by weight of a sulfonic acid compound (B) having 1 to 3 sulfo groups, is applied and dried.

[In general formulas (1) and (2), ^R2 represents a hydrogen atom, a methyl group, an ethyl group, a linear or branched alkyl group having 3 to 6 carbon atoms, or a fluorine atom, m represents an integer of 1 to 10, and n represents 0 or 1.]
[7] An electrolytic capacitor comprising the conductive polymer film according to [5] above.

The present invention provides an electrolytic capacitor that has a low ESR and low leakage current while maintaining a high capacity.

The present invention is described in detail below.

The present invention is a conductive polymer aqueous solution containing 0.01 to 10% by weight of polythiophene (A) containing at least one structural unit selected from the group consisting of structural units represented by the following formula (1) and structural units represented by the following formula (2), and containing 0.001 to 20% by weight of a sulfonic acid compound (B) having 1 to 3 sulfo groups.

[In general formulas (1) and (2), ^R2 represents a hydrogen atom, a methyl group, an ethyl group, a linear or branched alkyl group having 3 to 6 carbon atoms, or a fluorine atom, m represents an integer of 1 to 10, and n represents 0 or 1.]
In the above general formulas (1) and (2), R ² represents a hydrogen atom, a methyl group, an ethyl group, a linear or branched alkyl group having 3 to 6 carbon atoms, or a fluorine atom.

Examples of linear or branched alkyl groups having 3 to 6 carbon atoms include, but are not limited to, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, cyclopentyl, n-hexyl, 2-ethylbutyl, and cyclohexyl.

From the viewpoint of film-forming properties, the above ^R2 is preferably a hydrogen atom, a methyl group, an ethyl group, or a fluorine atom.

In the above general formulas (1) and (2), m represents an integer of 1 to 10, and from the viewpoint of film-forming properties, it is preferably an integer of 1 to 6, more preferably an integer of 1 to 4, and even more preferably 3 or 4.

In the above general formulas (1) and (2), n represents 0 or 1, and it is preferable that n is 1 in terms of excellent electrical conductivity.

The structural unit represented by the above formula (2) represents the doped state of the structural unit represented by the above formula (1).

Dopants that cause an insulator-metal transition by doping can be divided into acceptors and donors. The former enter close to the polymer chain of a conductive polymer and take away π electrons from the conjugated system of the main chain. As a result, a positive charge (hole) is injected into the main chain, so it is also called a p-type dopant. Conversely, the latter donates electrons to the conjugated system of the main chain, and these electrons move through the conjugated system of the main chain, so it is also called an n-type dopant.

The dopant in the present invention is a sulfo group or a sulfonate group that is covalently bonded within the polymer molecule, and is a p-type dopant. Polymers that exhibit conductivity without the addition of an external dopant are called self-doped polymers.

The polythiophene (A) of the present invention can be produced by polymerizing a thiophene monomer represented by the following general formula (3) in water or an alcohol solvent in the presence of an oxidizing agent, and then optionally treating with an acid.

[In the general formula (3), M represents a hydrogen ion or a metal ion. ^R2 represents a hydrogen atom, a methyl group, an ethyl group, a linear or branched alkyl group having 3 to 6 carbon atoms, or a fluorine atom. m represents an integer of 1 to 10, and n represents 0 or 1.]
The metal ion represented by M in formula (3) is not particularly limited, but examples thereof include transition metal ions, precious metal ions, non-ferrous metal ions, alkali metal ions (e.g., Li ions, Na ions, and K ions), and alkaline earth metal ions.

When the polymer obtained after polymerization of the thiophene monomer represented by general formula (3) is a metal salt, M can be converted to a hydrogen ion by treating the obtained metal salt polymer with an acid.

The thiophene monomer represented by the above general formula (3) is not particularly limited, but specifically includes 6-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-yl)hexane-1-sulfonic acid, sodium 6-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-yl)hexane-1-sulfonate, lithium 6-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-yl)hexane-1-sulfonate, 8-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-yl)hexane-1-sulfonic acid, sodium 8-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-yl)octane-1-sulfonic acid, and potassium 8-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-yl)octane-1-sulfonic acid, 3-[(2,3-dihydrothieno[3,4-b][1,4]dioxin-2-yl)methoxy]-1-propane sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-propanesulfonate, potassium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-ethyl-1-propanesulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-ethyl-1-propanesulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-propyl-1-propanesulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-butyl-1-propanesulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-pentyl-1-propanesulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-hexyl-1-propanesulfonate thorium, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-isopropyl-1-propanesulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-isobutyl-1-propanesulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-isopentyl-1-propanesulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b] -[1,4]dioxin-2-yl)methoxy]-1-fluoro-1-propanesulfonic acid sodium salt, 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonic acid potassium salt, 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonic acid, 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonic acid a ammonium, 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonate triethylammonium, 4-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-butanesulfonate sodium, 4-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-butanesulfonate potassium, 4-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-butanesulfonate ) methoxy]-1-methyl-1-butanesulfonate sodium, 4-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl) methoxy]-1-methyl-1-butanesulfonate potassium, 4-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl) methoxy]-1-fluoro-1-butanesulfonate sodium, and 4-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl) methoxy]-1-fluoro-1-butanesulfonate potassium are examples.

In the present invention, the electrical conductivity of the polythiophene (A) is not particularly limited, but it is preferable that the electrical conductivity (electrical conductivity) in the film state is 10 S/cm or more.

In addition, the polythiophene (A) used in the present invention may be one synthesized based on publicly known information.

In the conductive polymer aqueous solution of the present invention, the content of polythiophene (A) containing at least one structural unit selected from the group consisting of the structural unit represented by the general formula (1) and the structural unit represented by the general formula (2) is 0.01 to 10% by weight, but in terms of excellent low ESR, it is preferably 0.05 to 8% by weight, and more preferably 0.1 to 7% by weight.

In terms of low ESR, the sulfonic acid compound (B) having 1 to 3 sulfo groups in the present invention is preferably a sulfonic acid compound having 1 to 3 sulfo groups and a total of 1 to 20 carbon atoms, more preferably a sulfonic acid compound having 1 or 2 sulfo groups and a total of 1 to 20 carbon atoms, and even more preferably a sulfonic acid compound having only one sulfo group and a total of 1 to 20 carbon atoms.

The above-mentioned sulfonic acid compounds are not particularly limited, but examples thereof include sulfosalicylic acid (5-sulfosalicylic acid, etc.), sulfophthalic acid (3-sulfophthalic acid, 4-sulfophthalic acid), sulfoisophthalic acid (5-sulfoisophthalic acid, etc.), sulfosuccinic acid, toluenesulfonic acid (o-toluenesulfonic acid, m-toluenesulfonic acid, p-toluenesulfonic acid, etc.), aminobenzenesulfonic acid (o-aminobenzenesulfonic acid, m-aminobenzenesulfonic acid, p-aminobenzenesulfonic acid), dodecylbenzenesulfonic acid, naphthalenesulfonic acid (1-naphthalenesulfonic acid, Examples of the sulfonic acid include any one or a mixture of several selected from the group consisting of aminonaphthalenesulfonic acid (4-amino-1-naphthalenesulfonic acid, 5-amino-1-naphthalenesulfonic acid, 6-amino-1-naphthalenesulfonic acid, 8-amino-1-naphthalenesulfonic acid, 8-amino-2-naphthalenesulfonic acid, etc.), camphorsulfonic acid, aminomethanesulfonic acid, aminopropanesulfonic acid (3-amino-1-propanesulfonic acid, etc.), and hydroxypropanesulfonic acid (3-hydroxypropanesulfonic acid, etc.).

Among these, in terms of low ESR, any one or a mixture of any one selected from the group consisting of sulfosalicylic acid, sulfophthalic acid, sulfoisophthalic acid, sulfosuccinic acid, p-toluenesulfonic acid, aminobenzenesulfonic acid, dodecylbenzenesulfonic acid, naphthalenesulfonic acid, camphorsulfonic acid, aminomethanesulfonic acid, 3-amino-1-propanesulfonic acid, and 3-hydroxypropanesulfonic acid is more preferred, and any one or a mixture of any one selected from the group consisting of 5-sulfosalicylic acid, 2-naphthalenesulfonic acid, p-aminobenzenesulfonic acid, p-toluenesulfonic acid, and aminomethanesulfonic acid is more preferred.

In the conductive polymer aqueous solution of the present invention, the content of the sulfonic acid compound (B) having 1 to 3 sulfo groups is 0.001 to 20% by weight, but in terms of excellent low ESR, it is preferably 0.01 to 15% by weight, and more preferably 0.1 to 10% by weight.

The conductive polymer aqueous solution of the present invention preferably further contains ions (C) selected from the group consisting of alkali metal ions, ammonium ions, organic ammonium ions, and quaternary ammonium cations, in that it has excellent low ESR.

The alkali metal ion is not particularly limited, but examples thereof include lithium ions, potassium ions, sodium ions, rubidium ions, and cesium ions. The alkali metal ions can be contained in the conductive polymer aqueous solution of the present invention by adding an alkali metal compound. The alkali metal compound is not particularly limited, but examples thereof include alkali metal salt compounds (e.g., lithium chloride, potassium chloride, sodium chloride, rubidium chloride, cesium chloride, lithium bromide, potassium bromide, sodium bromide, rubidium bromide, cesium bromide, etc.) or alkali metal hydroxides (e.g., lithium hydroxide, potassium hydroxide, sodium hydroxide, rubidium hydroxide, cesium hydroxide, etc.).

The organic ammonium ion is not particularly limited, but examples thereof include primary, secondary, or tertiary ammonium ions having a total carbon number of 1 to 30. More specifically, examples thereof include methylammonium, dimethylammonium, ethylammonium, triethylammonium, normal-propylammonium, isopropylammonium, normal-butylammonium, hexylammonium, 2-hydroxyethylammonium, N,N-dimethyl-N-(2-hydroxyethyl)ammonium, N-methyl-N-(2-hydroxyethyl)ammonium, di(2-hydroxyethyl)ammonium, N-methyl-N-(2-hydroxyethyl)ammonium, It can represent N,N-tyl-N,N-di(2-hydroxyethyl)ammonium, N,N,N-tri(2-hydroxyethyl)ammonium, 2,3-dihydroxypropylammonium, N-methyl-N-(2,3-dihydroxypropyl)ammonium, N,N-dimethyl-N-(2,3-dihydroxypropyl)ammonium, 1,4-butanediammonium, triisobutylammonium, triisopentylammonium, triisooctylammonium, imidazole cation, N-methylimidazole cation, 1,2-dimethylimidazole cation, pyridinium ion, picolinium ion, or lutidinium ion.

The organic ammonium ions can be contained in the conductive polymer aqueous solution of the present invention by adding an amine compound. By adding the amine compound, a part or all of the amine compound interacts with the sulfonic acid groups of the polythiophene (A) and exists in the conductive aqueous solution as the corresponding organic ammonium ions. The amine compound is not particularly limited, but examples thereof include primary, secondary, or tertiary amine compounds having a total carbon number of 1 to 30. More specifically, examples thereof include methylamine, dimethylamine, ethylamine, triethylamine, normal-propylamine, isopropylamine, normal-butylamine, hexylamine, aminoethanol, dimethylaminoethanol, methylaminoethanol, diethanolamine, N-methyldiethanolamine, triethanolamine, 3-amino-1,2-propanediol, 3-methylamino-1,2-propanediol, 3-dimethylamino-1,2-propanediol, 1,4-butanediamine, triisobutylamine, triisopentylamine, triisooctylamine, imidazole, N-methylimidazole, 1,2-dimethylimidazole, pyridine, picoline, and lutidine.

The quaternary ammonium ion is not particularly limited, but examples thereof include tetramethylammonium cation, tetraethylammonium cation, tetra-normal-propylammonium cation, tetra-normal-butylammonium cation, and tetra-normal-hexylammonium cation. The quaternary ammonium ion can be contained by adding a quaternary ammonium compound corresponding to the conductive polymer aqueous solution of the present invention. The quaternary ammonium compound is not particularly limited, but examples thereof include tetramethylammonium chloride, tetraethylammonium chloride, tetra-normal-propylammonium chloride, tetra-normal-butylammonium chloride, and tetra-normal-hexylammonium chloride.

In the conductive polymer aqueous solution of the present invention, the content of the above-mentioned ion (C) is characterized by being 0.001 to 20% by weight, but in terms of excellent low ESR, it is preferably 0.01 to 15% by weight, and more preferably 0.1 to 10% by weight.

The pH of the conductive polymer aqueous solution of the present invention is preferably in the range of 1.5 to 10.0, more preferably in the range of 2.0 to 8.0, and even more preferably in the range of 2.5 to 7.0, in terms of its excellent low ESR.

The conductive polymer aqueous solution of the present invention may contain a component (D) other than those described above.

The other components (D) than those mentioned above are not particularly limited, but examples thereof include binders, surfactants, solvents, etc.

The binder is not particularly limited, but examples thereof include polyvinyl alcohol, polyvinylpyrrolidone, cellulose, a water-soluble polyester resin compound, a water-soluble polyurethane resin compound, and a mixture of a polyhydric alcohol and an organic acid having two or more carboxyl groups.

Examples of the water-soluble polyester resin compound include polyethylene terephthalate and polytrimethylene terephthalate. The water-soluble polyester resin compound may be a self-emulsifying type or a reinforced emulsifying type, but from the viewpoint of water resistance and solvent resistance, a self-emulsifying water-soluble polyester resin compound is preferable.

Examples of the water-soluble polyester resin compound include those that are readily available commercially, such as Toyobo Co., Ltd. (trade name: Vylonal), Takamatsu Oil Co., Ltd. (trade name: PES Resin), GOO Chemical Co., Ltd. (trade name: Pluscoat), Toagosei Co., Ltd. (trade name: Aronmelt), Takamatsu Oil Co., Ltd. (trade name: PES Resin A), and DIC Corporation (trade name: Watersol).

The water-soluble polyester resin compounds can be used alone or in combination of two or more.

The water-soluble polyurethane resin compound is used mainly for industrial purposes as a urethane resin emulsion, and may be a self-emulsifying type or a reinforced emulsion type. From the viewpoint of water resistance and solvent resistance, however, a self-emulsifying water-soluble polyurethane resin compound is preferable. Examples of the self-emulsifying type include an anionic type, a cationic type, and a non-ionic type, but any of them may be used. In addition, the water-soluble polyurethane resin compound is not particularly limited, but examples thereof include a polyether type, a polyester type, and a polycarbonate type.

Examples of water-soluble polyurethane resin compounds that can be easily obtained commercially include those manufactured by Sanyo Chemical Industries, Ltd. under the trade names U-coat, Permalin, and Euplen, those manufactured by Kusumoto Chemical Industries, Ltd. under the trade name NeoRez, those manufactured by ADEKA Corporation under the trade name Adeka Bontiter, those manufactured by Meisei Chemical Industry Co., Ltd. under the trade name Pascall, and those manufactured by DIC Corporation under the trade name Hydran.

The water-soluble polyurethane resin compounds can be used alone or in combination of two or more.

The polyhydric alcohol is not particularly limited, but examples thereof include erythritol and pentaerythritol.

The organic acid having two or more carboxyl groups is not particularly limited, but examples include adipic acid and phthalic acid.

The surfactant is not particularly limited, but may be, for example, an anionic surfactant, a cationic surfactant, a nonionic surfactant, an amphoteric surfactant, a fluorine-based surfactant, or a silicone-based surfactant, and more preferably at least one selected from the group consisting of a nonionic surfactant and an amphoteric surfactant.

The anionic surfactant is not particularly limited, but examples thereof include sodium lauryl alcohol sulfate and sodium dodecylbenzenesulfonate.

The cationic surfactant is not particularly limited, but a commercially available product can be used, or a commonly known product can be separately manufactured and used. The nonionic surfactant is not particularly limited, but examples thereof include polyethylene glycol type surfactants, acetylene glycol type surfactants, polyhydric alcohol type surfactants, and polymer type nonionic surfactants.

The polyethylene glycol surfactant is not particularly limited, but examples thereof include higher alcohol ethylene oxide adducts, alkylphenol ethylene oxide adducts, fatty acid ethylene oxide adducts, polyhydric alcohol fatty acid ester ethylene oxide adducts, higher alkylamine ethylene oxide adducts, ethylene oxide adducts of oils and fats, and polypropylene glycol ethylene oxide adducts.

The acetylene glycol surfactant is not particularly limited, but examples include 2,4,7,9-tetramethyl-5-decyne-4,7-diol, Surfynol (manufactured by Air Products Co., Ltd.), and Olfin (manufactured by Nissin Chemical Industry Co., Ltd.).

The polyhydric alcohol surfactant is not particularly limited, but examples thereof include fatty acid esters of glycerol, fatty acid esters of pentaerythritol, fatty acid esters of sorbitol and sorbitan, fatty acid esters of sucrose, alkyl ethers of higher alcohols, fatty acid amides of alkanolamines, etc.

The amphoteric surfactant is not particularly limited, but examples thereof include betaine-type amphoteric surfactants. The betaine-type amphoteric surfactant is not particularly limited, but examples thereof include alkyl dimethyl betaine, lauryl dimethyl betaine, stearyl dimethyl betaine, lauryl dihydroxyethyl betaine, etc.

The fluorosurfactant is not particularly limited as long as it has a perfluoroalkyl group, but examples include PLASCOAT RY-2, perfluoroalkane, perfluoroalkyl carboxylic acid, perfluoroalkyl sulfonic acid, and perfluoroalkyl ethylene oxide adducts.

The silicone surfactant is not particularly limited, but examples thereof include polyether-modified polydimethylsiloxane, polyetherester-modified polydimethylsiloxane, hydroxyl group-containing polyether-modified polydimethylsiloxane, acrylic group-containing polyether-modified polydimethylsiloxane, acrylic group-containing polyester-modified polydimethylsiloxane, perfluoropolyether-modified polydimethylsiloxane, perfluoropolyester-modified polydimethylsiloxane, and silicone-modified acrylic compounds.

Furthermore, fluorosurfactants and silicone surfactants are effective as leveling agents to improve the flatness of the coating film.

The solvent is not particularly limited, but examples include methanol, ethanol, propanol, butanol, methoxyethanol, ethoxyethanol, butoxyethanol, and ethylene glycol.

In the conductive polymer aqueous solution of the present invention, the content of the aforementioned component (D) is characterized by being 0.001 to 20% by weight, but from the viewpoint of excellent operability, it is preferably 0.01 to 15% by weight, and more preferably 0.1 to 10% by weight.

The method for preparing the conductive polymer aqueous solution of the present invention is not particularly limited, but may be, for example, a method in which an aqueous solution or solid of the polythiophene (A) of the present invention is mixed with a sulfonic acid compound (B) having 1 to 3 sulfo groups, and water as necessary, and homogenized by stirring or the like. In this case, other additives (e.g., the above ions (C) and component (D), etc.) may be added as necessary and then mixed and adjusted, or a conductive polymer aqueous solution containing the polythiophene (A) and the sulfonic acid compound (B) may first be prepared, and then the other additives may be added and mixed to adjust.

Here, the temperature during mixing is not particularly limited, but may be, for example, room temperature or heated. Preferably, the temperature is 0°C or higher and 100°C or lower.

The atmosphere in which the mixture is mixed is not particularly limited, but may be air or an inert gas.

When mixing the conductive polymer aqueous solution of the present invention, in addition to the general mixing and dissolving operation using a stirrer tip or stirring blade, ultrasonic irradiation and homogenization treatment (for example, using a mechanical homogenizer, ultrasonic homogenizer, high-pressure homogenizer, etc.) may be performed. When homogenization treatment is performed, it is preferable to perform it at a low temperature to prevent thermal degradation of the polymer.

The concentration of the conductive polymer aqueous solution of the present invention may be adjusted by the blending ratio, or may be adjusted by concentrating after blending. The concentration method may be a method of distilling off the solvent under reduced pressure, or a method using an ultrafiltration membrane.

The concentration of polythiophene (A) in the aqueous conductive polymer solution of the present invention is not particularly limited as long as it is 0.001% by weight or more, but is preferably in the range of 0.01% by weight to 10% by weight. The aqueous conductive polymer solution of the present invention containing polythiophene (A) and sulfonic acid compound (B) is dried and dehydrated after application, so that a good uniform film can be obtained within the above concentration range.

The particle size of the solid content in the conductive polymer aqueous solution of the present invention is not particularly limited, but the smaller the particle size, the better the water solubility, which is also desirable from the viewpoint of conductivity and uniform film formation during film formation. For example, when the solid content concentration of the conductive polymer aqueous solution prepared at room temperature or under heating is 10% by weight or less, it is preferable that the particle size (D50) of the solid content is 0.02 μm or less.

The viscosity (20°C) of the conductive polymer aqueous solution of the present invention is preferably 200 mPa·s or less, more preferably 100 mPa·s or less, and even more preferably 50 mPa·s or less.

The conductive polymer film of the present invention can be formed using the conductive polymer aqueous solution of the present invention. The method for forming the conductive polymer film of the present invention is not particularly limited, but an example of the method is to apply the conductive polymer aqueous solution of the present invention to a substrate and dry it.

The drying atmosphere may be air, an inert gas, a vacuum, or a reduced pressure. From the viewpoint of preventing deterioration of the polymer film, an inert gas such as nitrogen or argon is preferable.

The above substrate is not particularly limited, but examples include glass, plastic, polyester, polyacrylate, polycarbonate, metal oxide, ceramic, or resist substrate.

The above coating method is not particularly limited, but examples include casting, dipping, bar coating, roll coating, gravure coating, flexographic printing, spray coating, spin coating, and inkjet printing.

The drying temperature for the coating is not particularly limited as long as a uniform conductive film is obtained, but it is preferably in the range of room temperature to 300°C, more preferably in the range of room temperature to 250°C, and even more preferably in the range of room temperature to 200°C.

The thickness of the coating film is not particularly limited, but is preferably in the range of 10 ⁻² to 10 ² μm. The surface resistance of the resulting coating film is not particularly limited, but is preferably in the range of 1 to 10 ⁹ Ω/.

The conductivity of the conductive polymer film obtained by the present invention is not particularly limited, but it is preferable that the conductivity (electrical conductivity) in the film state is 10 S/cm or more.

The conductive polymer film of the present invention can be used, for example, as an antistatic agent, a solid electrolyte for electrolytic capacitors, a conductive paint, an electrochromic element, an electrode material, a thermoelectric conversion material, a transparent conductive film, a chemical sensor, an actuator, etc. In particular, it is extremely useful as a solid electrolyte for electrolytic capacitors. When used in electrolytic capacitors, it is possible to provide an electrolytic capacitor that has excellent characteristics such as low ESR while maintaining a high capacity.

The present invention will be described in detail below with reference to examples. However, the present invention should not be construed as being limited in any way by these examples.

The analytical instruments and measurement methods used in this example are listed below.

[NMR Measurement]
Equipment: VARIAN, Gemini-200
[Method of producing conductive polymer film]
Specifically, 0.5 ml of an aqueous solution containing the composition of the present invention described below was applied to a 25 mm square alkali-free glass plate, heated on a hot plate in the atmosphere at 60° C. for 30 minutes, and further heated at 200° C. for 60 minutes to obtain a conductive polymer film.

[Measurement of Conductive Polymer Film Thickness]
Apparatus: DEKTAK XT manufactured by BRUKER.

The conductive polymer film produced by the above method was cut at intervals of 6.25 mm in the x direction and 6.25 mm in the y direction to expose the glass portion, and the film thickness was measured at nine measurement points in an atmosphere of 25°C and 50% RH.

[Measurement of surface resistivity of conductive polymer film]
Apparatus: Mitsubishi Chemical Loresta GP MCP-T600.
Using a surface resistance measuring instrument Loresta GP MCP-T600 and a measuring probe as an ASP, the surface resistance was measured at nine measurement points at intervals of 6.25 mm in the x direction and 6.25 mm in the y direction in an atmosphere of 25° C. and 50% RH.

[Conductivity measurement of conductive polymer film]
The electrical conductivity was calculated from the film thickness and surface resistivity of the conductive polymer film measured by the above-mentioned measuring method according to the following formula.

Electrical conductivity [S/cm] = 10 ⁴ / (Surface resistivity [Ω/□] x Film thickness [μm])
[Fabrication of Solid Electrolytic Capacitor]
An aluminum foil having a thickness of 100 μm was used, and the surface of the aluminum foil was subjected to an etching treatment. The aluminum foil was welded to a part of the etched aluminum foil having a thickness of 100 μm, and a lead wire was attached. The aluminum foil that was subjected to the etching treatment was immersed in an aqueous solution of ammonium dihydrogen phosphate with a concentration of 0.2 wt %, and a direct current voltage of 130 V was applied for 20 minutes to form a dielectric layer of aluminum oxide. Separately, an etched aluminum foil having a thickness of 50 μm and having a lead wire attached thereto was wound as a cathode, with a separator made of insulating paper interposed between the anode and the cathode. Next, the wound element was immersed in an aqueous conductive polymer solution, taken out, and then dried at 150° C. for 30 minutes to obtain a solid electrolytic capacitor.

[Characteristics measurement of solid electrolytic capacitors]
The characteristics of the solid electrolytic capacitor prepared by the above method were evaluated using the following device, including the initial capacitance [μF] at initial 120 Hz, the ESR [mΩ] at initial 100 kHz, and the leakage current [μA] after 2 minutes when 63 V was applied.

Equipment: Hioki E.E. Corporation LCR meter IM3536
Synthesis Example 1
According to Synthesis Examples 1 and 2 of the known literature (JP 2019-196443), an aqueous solution of poly(3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonic acid [polymer containing a structural unit represented by the following formula (4)] (hereinafter referred to as "PEDOT-MPS") (conductive polymer aqueous solution) was prepared. The amount of polymer contained in the aqueous solution was 0.74 wt%. In addition, iron ions and sodium ions were contained in amounts of 44 ppm and 12 ppm (relative to the polymer), respectively. The conductivity of this polymer was 342 S/cm.

Example 1.

(Preparation of Conductive Polymer Solution)
The conductive polymer aqueous solution obtained in Synthesis Example 1 was dehydrated under reduced pressure to prepare an aqueous solution containing 2.0% by weight of PEDOT-MPS. 0.5 g of 5-sulfosalicylic acid was added to 99.5 g of the aqueous solution containing 2.0% by weight of PEDOT-MPS, and the mixture was thoroughly stirred and mixed. Next, 0.5 g of methylethanolamine was added and the mixture was thoroughly stirred and mixed to obtain an aqueous conductive polymer solution with a pH of 3. A solid electrolytic capacitor was produced using the aqueous conductive polymer solution according to the method described above, and its characteristics were evaluated. The evaluation results are shown in Table 1.

Example 2
The capacitor characteristics were evaluated in the same manner as in Example 1, except that 0.5 g of 2-naphthalenesulfonic acid was used instead of 0.5 g of 5-sulfosalicylic acid in Example 1. In order to achieve a pH of 3, the amount of methylethanolamine added was set to 0.5 g. The evaluation results are shown in Table 1.

Example 3
The capacitor characteristics were evaluated in the same manner as in Example 1, except that 0.5 g of p-aminobenzenesulfonic acid was used instead of 0.5 g of 5-sulfosalicylic acid in Example 1. In order to achieve a pH of 3, the amount of methylethanolamine added was 0.4 g. The evaluation results are shown in Table 1.

Example 4
The capacitor characteristics were evaluated in the same manner as in Example 1, except that 0.5 g of p-toluenesulfonic acid was used instead of 0.5 g of 5-sulfosalicylic acid in Example 1. In order to achieve a pH of 3, the amount of methylethanolamine added was set to 0.5 g. The evaluation results are shown in Table 1.

Example 5
The capacitor characteristics were evaluated in the same manner as in Example 1, except that 0.5 g of aminomethanesulfonic acid was used instead of 0.5 g of 5-sulfosalicylic acid in Example 1. In order to achieve a pH of 3, the amount of methylethanolamine added was set to 0.4 g. The evaluation results are shown in Table 1.

Example 6
The capacitor characteristics were evaluated in the same manner as in Example 1, except that 0.5 g of 5-sulfosalicylic acid and 0.5 g of p-aminobenzenesulfonic acid were used instead of 0.5 g of 5-sulfosalicylic acid in Example 1. In order to achieve a pH of 3, the amount of methylethanolamine added was set to 0.6 g. The evaluation results are shown in Table 1.

Reference Example 1
The conductive polymer aqueous solution obtained in Synthesis Example 1 was dehydrated under reduced pressure to prepare an aqueous solution containing 2.0% by weight of PEDOT-MPS. 0.4 g of methylethanolamine was added to 99.5 g of the aqueous solution containing 2.0% by weight of PEDOT-MPS, and the mixture was thoroughly stirred to obtain an aqueous conductive polymer solution with a pH of 3. A solid electrolytic capacitor was produced using the aqueous conductive polymer solution according to the method described above, and its characteristics were evaluated. The evaluation results are shown in Table 1.

Comparative Example 1
0.5 g of 5-sulfosalicylic acid was added to 99.5 g of a dispersion of polystyrenesulfonic acid externally doped poly3,4-ethylenedioxythiophene (Clevios PH500 manufactured by Heraeus was used) and mixed thoroughly with stirring. Next, 0.3 g of methylethanolamine was added and mixed thoroughly with stirring to obtain a conductive polymer dispersion with a pH of 3. A solid electrolytic capacitor was produced using the conductive polymer dispersion according to the method described above, and its characteristics were evaluated. The evaluation results are shown in Table 1.

Comparative Example 2
The capacitor characteristics were evaluated in the same manner as in Comparative Example 1, except that 0.5 g of 2-naphthalenesulfonic acid was used instead of 0.5 g of 5-sulfosalicylic acid. The amount of methylethanolamine added was 0.3 g to achieve a pH of 3. The evaluation results are shown in Table 1.

Reference Example 2
The conductive polymer aqueous solution obtained in Synthesis Example 1 was dehydrated under reduced pressure to prepare an aqueous solution containing 2.0% by weight of PEDOT-MPS. 0.4 g of methylethanolamine was added to 99.5 g of the aqueous solution containing 2.0% by weight of PEDOT-MPS, and the mixture was thoroughly stirred to obtain an aqueous conductive polymer solution with a pH of 3. A solid electrolytic capacitor was produced using the aqueous conductive polymer solution according to the method described above. Next, the obtained solid electrolytic capacitor was immersed in a polyethylene glycol solution containing 0.5% by weight of 5-sulfosalicylic acid and having an average molecular weight of 300, and impregnated under reduced pressure. That is, a hybrid electrolytic capacitor of a solid electrolyte and an aqueous polymer solution was produced. The obtained hybrid electrolytic capacitor was subjected to a characteristic evaluation according to the method described above. The evaluation results are shown in Table 1.

From the results shown in Table 1, Examples 1 to 6 using the conductive polymer aqueous solution of the present invention have the effect of achieving low ESR while maintaining high capacity. This is presumed to be the result of the conductive polymer aqueous solution of the present invention filling the gap between the anode foil and the cathode foil. Furthermore, it was found that an electrolytic capacitor with low leakage current can be obtained when the conductive polymer aqueous solution of the present invention is used. This effect is presumed to be due to the conductive polymer aqueous solution of the present invention having a high ability to repair oxide film defects that occur in the process of making an electrolytic capacitor. When PEDOT/PSS was used as a substitute, gelation occurred when the solution was left at room temperature for several days after stirring, so a capacitor could not be made and could not be evaluated. Reference Example 2 was intended to investigate the capacitor characteristics when sulfonic acid was added to a water-soluble polymer solution instead of adding a sulfonic acid compound to a solid electrolyte. As a result, the leakage current decreased, but the ESR could not be reduced. This is thought to be due to the inability to fill the gap between the anode foil and the cathode foil.

As described above, by using the conductive polymer aqueous solution of the present invention, it is possible to provide an electrolytic capacitor that has excellent characteristics such as low ESR while maintaining a high capacity.

Claims (5)

A conductive polymer aqueous solution containing 0.01 to 10% by weight of polythiophene (A) containing at least one structural unit selected from the group consisting of a structural unit represented by the following formula (1) and a structural unit represented by the following formula (2), and containing 0.001 to 20% by weight of one or a mixture of two or more acids selected from the group consisting of sulfosalicylic acid, sulfophthalic acid, sulfoisophthalic acid, sulfosuccinic acid, toluenesulfonic acid, aminobenzenesulfonic acid, dodecylbenzenesulfonic acid, naphthalenesulfonic acid, camphorsulfonic acid, aminomethanesulfonic acid, aminopropanesulfonic acid, and hydroxypropanesulfonic acid:

[In general formulas (1) and (2), ^R2 represents a hydrogen atom, a methyl group, an ethyl group, a linear or branched alkyl group having 3 to 6 carbon atoms, or a fluorine atom, m represents an integer of 1 to 10, and n represents 0 or 1.] The conductive polymer aqueous solution according to claim 1 , further comprising an ion (C) selected from the group consisting of an alkali metal ion, an ammonium ion, an organic ammonium ion, and a quaternary ammonium cation, and having a pH in the range of 1.5 to 10.0. A conductive polymer membrane comprising: polythiophene (A) containing at least one structural unit selected from the group consisting of a structural unit represented by the following formula (1) and a structural unit represented by the following formula (2 ); and one or a mixture of two or more selected from the group consisting of sulfosalicylic acid, sulfophthalic acid, sulfoisophthalic acid, sulfosuccinic acid, toluenesulfonic acid, aminobenzenesulfonic acid, dodecylbenzenesulfonic acid, naphthalenesulfonic acid, camphorsulfonic acid, aminomethanesulfonic acid, aminopropanesulfonic acid, and hydroxypropanesulfonic acid.

[In general formulas (1) and (2), ^R2 represents a hydrogen atom, a methyl group, an ethyl group, a linear or branched alkyl group having 3 to 6 carbon atoms, or a fluorine atom, m represents an integer of 1 to 10, and n represents 0 or 1.] 4. A method for producing a conductive polymer film according to claim 3, comprising applying and drying an aqueous conductive polymer solution containing 0.01 to 10% by weight of polythiophene (A) containing at least one structural unit selected from the group consisting of a structural unit represented by the following formula (1) and a structural unit represented by the following formula (2), and containing 0.001 to 20% by weight of a mixture of one or more acids selected from the group consisting of sulfosalicylic acid, sulfophthalic acid, sulfoisophthalic acid, sulfosuccinic acid, toluenesulfonic acid, aminobenzenesulfonic acid, dodecylbenzenesulfonic acid, naphthalenesulfonic acid, camphorsulfonic acid, aminomethanesulfonic acid, aminopropanesulfonic acid, and hydroxypropanesulfonic acid :

[In general formulas (1) and (2), ^R2 represents a hydrogen atom, a methyl group, an ethyl group, a linear or branched alkyl group having 3 to 6 carbon atoms, or a fluorine atom, m represents an integer of 1 to 10, and n represents 0 or 1.] An electrolytic capacitor comprising the conductive polymer film according to claim 3 .