JP7083280B2 - How to manufacture electrolytic capacitors - Google Patents

Description

The present invention relates to a method for manufacturing an electrolytic capacitor having excellent heat resistance and moisture resistance.

Due to its high conductivity, the conductive polymer is used as an electrolyte (solid electrolyte) such as an aluminum electrolytic capacitor, a tantalum electrolytic capacitor, and a niobium electrolytic capacitor.

As the conductive polymer in this application, for example, one obtained by chemically oxidatively polymerizing or electrolytically oxidatively polymerizing pyrrole or a derivative thereof, thiophene or a derivative thereof, or the like is used.

When using a conductive polymer as a solid electrolyte for an electrolytic capacitor, for example, a dispersion liquid in which a powdered conductive polymer obtained by chemical oxidative polymerization or electrolytic oxidative polymerization is dispersed in a solvent is used as a capacitor element. A method of adhering to the surface of a solid electrolyte (conductive polymer) by coating or the like and drying to form a layer of a solid electrolyte (conductive polymer) is generally adopted (Patent Document 1 and the like).

International Publication No. 2009/1311024

By the way, recently, the application of electrolytic capacitors to equipment placed in a high temperature environment or a high humidity environment is expanding, and in response to this, electrolytic capacitors are required to have higher heat resistance and moisture resistance. ing.

However, as described above, in the electrolytic capacitor in which the solid electrolyte layer is formed by using the powdery conductive polymer dispersed in the dispersion liquid, there is room for improvement in terms of moisture resistance. Further, in the synthesis of the conductive polymer by chemical oxidation polymerization, not only as a dispersion liquid in which the conductive polymer is dispersed as described above, but also, for example, the conductive polymer may be formed in a layer on the surface of a capacitor element. Although it is possible, it is difficult to improve the moisture resistance of the electrolytic capacitor regardless of which of these methods is adopted.

On the other hand, for forming the solid electrolyte layer on the capacitor element, there is also a method of directly polymerizing the conductive polymer on the surface of the capacitor element, and in this case, the moisture resistance of the electrolytic capacitor may be improved. However, for example, when pyrrole or a derivative thereof is used as a monomer, the heat resistance of the electrolytic capacitor becomes insufficient, and when thiophene or a derivative thereof is used as a monomer, the electrolytic oxidation polymerization method polymerizes a conductive polymer. There is a problem that the degree does not increase and it is difficult to form a good layer.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for manufacturing an electrolytic capacitor having excellent heat resistance and moisture resistance.

The method for producing an electrolytic capacitor of the present invention is to perform electrolytic oxidation polymerization in a state where the capacitor element is immersed in an electrolytic polymerization solution containing a polymerizable monomer, a polymer anion, a water-soluble organic solvent having a specific dielectric constant of 10 to 50, and water. A step of forming a conductive polymer layer on at least a part of the surface of the condenser element is provided, thiophene or a derivative thereof is used as the polymerizable monomer, and the degree of sulfonate is 3 to 3 as the polymer anion. It is characterized in that 9% sulfonated polymer is used and the ratio of water to the water-soluble organic solvent is 40:60 to 90:10 in terms of mass ratio.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a method for manufacturing an electrolytic capacitor having excellent heat resistance and moisture resistance.

As described above, an electrolytic capacitor having a conductive polymer layer (solid electrolyte layer) formed by using a dispersion liquid in which a powdery conductive polymer obtained by chemically oxidatively polymerizing thiophene or a derivative thereof is dispersed. Is excellent in heat resistance, but inferior in moisture resistance. This is because the layer obtained by using a powdery conductive polymer has low moisture resistance due to its structure, and is an organic sulfonic acid that is usually used as an oxidizing agent during chemical oxidative polymerization of thiophene or a derivative thereof. This is because the iron component derived from the iron salt remains in the conductive polymer, which lowers the moisture resistance of the conductive polymer layer. Further, even when a conductive polymer layer containing a polymer of thiophene or a derivative thereof is directly formed on the surface of the capacitor element by chemical oxidation polymerization, it is conductive as in the above case due to the influence of the iron component derived from the oxidizing agent. Moisture resistance of the polymer layer is lowered.

On the other hand, if a method of synthesizing a conductive polymer by electrolytic oxidation polymerization and forming a layer on the surface of a capacitor element at the same time, a layer structure having excellent moisture resistance can be obtained and an iron salt as described above can be obtained. Since it is not necessary to use an oxidizing agent made of the above material, there is a possibility that an electrolytic capacitor having excellent moisture resistance can be manufactured. However, when electrolytic oxidative polymerization is carried out using thiophene or a derivative thereof, the degree of polymerization of the synthesized conductive polymer cannot be increased to such an extent that a layer can be formed satisfactorily.

Therefore, in the production method of the present invention, thiophene or a derivative thereof is electrolytically oxidatively polymerized in an electrolytic polymerization solution containing a sulfonated polyester having a specific degree of sulfonate and using a water-soluble organic solvent and water as a solvent. It was decided to. This makes it possible to simultaneously proceed with the formation of a polymer of thiophene or a derivative thereof and the formation of a conductive polymer layer (solid electrolyte layer) containing the polymer on the surface of the capacitor element, and is excellent in heat resistance and moisture resistance. It is possible to manufacture electrolytic capacitors.

In the method of the present invention, thiophene or a derivative thereof is used as the polymerizable monomer, and examples of the thiophene derivative include 3,4-ethylenedioxythiophene, 3-alkylthiophene, 3-alkoxythiophene, and 3-alkyl-. Examples thereof include 4-alkoxythiophene, 3,4-alkylthiophene, 3,4-alkoxythiophene, and alkylated ethylenedioxythiophene obtained by modifying the above 3,4-ethylenedioxythiophene with an alkyl group, and the alkyl group thereof. The number of carbon atoms of the alkoxy group is preferably 1 or more, preferably 16 or less, more preferably 10 or less, and further preferably 4 or less.

The alkylated ethylenedioxythiophene obtained by modifying the above 3,4-ethylenedioxythiophene with an alkyl group will be described in detail. The above-mentioned 3,4-ethylenedioxythiophene and the alkylated ethylenedioxythiophene have the following general formulas ( It corresponds to the compound represented by 1).

General formula (1):

In the general formula (1), R ¹ is hydrogen or an alkyl group having 1 to 10 carbon atoms.

The compound in which ^R1 is hydrogen in the general formula (1) is 3,4-ethylenedioxythiophene, and when this is represented by the IUPAC name, "2,3-dihydro-thieno [3,4-b] ] [1,4] dioxin (2,3-Dihydro-thieno [3,4-b] [1,4] dioxin) ", but this compound is more generic than it appears in the IUPAC name. Since it is often displayed as "3,4-ethylenedioxythiophene", in the present specification, this "2,3-dihydro-thieno [3,4-b] [1,4] dioxin" is referred to as "3". , 4-Ethylenedioxythiophene ”. When R ¹ in the general formula (1) is an alkyl group, the alkyl group preferably has 1 to 10 carbon atoms, and particularly preferably 1 to 4 carbon atoms. That is, as the alkyl group, a methyl group, an ethyl group, a propyl group, and a butyl group are particularly preferable, and when these are specifically exemplified, the compound in which R ¹ is a methyl group in the general formula (1) is represented by the IUPAC name. Then, "2-methyl-2,3-dihydro-thieno [3,4-b] [1,4] dioxin (2-Methyl-2,3-dihydro-thieno [3,4-b] [1,4] ] Dioxine) ”, but in the present specification, this is abbreviated as“ methylated ethylenedioxythiophene ”. The compound in which R ¹ is an ethyl group in the general formula (1) is represented by the IUPAC name as "2-ethyl-2,3-dihydro-thieno [3,4-b] [1,4] dioxin (2). -Ethyl-2,3-dihydro-thiono [3,4-b] [1,4] dioxin) ”, but in the present specification, this is abbreviated as“ ethylated ethylenedioxythiophene ”. ..

The compound in which R ¹ is a propyl group in the general formula (1) is represented by the IUPAC name as "2-propyl-2,3-dihydro-thieno [3,4-b] [1,4] dioxin (2). -Propyl-2,3-dihydro-thiono [3,4-b] [1,4] dioxin) ”, but in the present specification, this is abbreviated as“ propylated ethylenedioxythiophene ”. .. The compound in which R ¹ is a butyl group in the general formula (1) is represented by the IUPAC name as "2-butyl-2,3-dihydro-thieno [3,4-b] [1,4] dioxin. (2-Butyl-2,3-dihydro-thiono [3,4-b] [1,4] dioxin) ”, but in the present specification, this is abbreviated as“ butylated ethylenedioxythiophene ”. indicate. Further, "2-alkyl-2,3-dihydro-thieno [3,4-b] [1,4] dioxine" is abbreviated as "alkylated ethylenedioxythiophene" in the present specification. Among those alkylated ethylenedioxythiophenes, methylated ethylenedioxythiophene, ethylated ethylenedioxythiophene, propylated ethylenedioxythiophene, and butylated ethylenedioxythiophene are preferable.

Then, 3,4-ethylenedioxythiophene (ie, 2,3-dihydro-thieno [3,4-b] [1,4] dioxine) and alkylated ethylenedioxythiophene (ie, 2-alkyl-2, It is preferable to use it in combination with 3-dihydro-thieno [3,4-b] [1,4] dioxin), and the mixing ratio thereof is 0.05: 1 to 1: 0.1 in terms of molar ratio. It is preferably 0.1: 1 to 1: 0.1, more preferably 0.2: 1 to 1: 0.2, and even more preferably 0.3: 1 to 1: 0. 3 is particularly preferable.

In the method of the present invention, the electrolytic oxidative polymerization of thiophene or a derivative thereof is carried out in the coexistence of a sulfonated polyester having a sulfonate degree of 3% or more and 9% or less. The sulfonated polyester is a polymer anion, and is incorporated into the polymer of thiophene or a derivative thereof obtained by electrolytic oxidation polymerization and functions as a dopant.

In the conductive polymer obtained by polymerizing thiophene or a derivative thereof, low molecular weight sulfonic acid such as p-toluenesulfonic acid, polystyrene sulfonic acid (and its salt) and the like are used as dopants. Even if thiophene or a derivative thereof is electrolytically oxidatively polymerized in the coexistence of such a dopant material, it is not possible to increase the molecular weight of a layer having good properties to such an extent that it can be directly formed on the surface of a capacitor element, for example. ..

However, when thiophene or a derivative thereof is electrolytically oxidatively polymerized in the coexistence of a sulfonated polyester having a degree of sulfonate of 3% or more and 9% or less, the polymer is satisfactorily polymerized. The formation of the conductive polymer layer can be promoted. Therefore, according to the method of the present invention, it is possible to manufacture an electrolytic capacitor having excellent heat resistance and moisture resistance.

The degree of sulfonated sulfonated polyester as used herein is sulfonated by titrating an aqueous solution of sulfonated polyester with a standard solution of cationic surfactant under acidic conditions using methylene blue, which is a kind of Epton method, as an indicator and chloroform as a solvent. The content of sulfonic acid present in the aqueous polyester solution is calculated and expressed as the degree of sulfonate. Specifically, the finely weighed sulfonated polyester aqueous solution is diluted with water, chloroform and 30 ppm methylene blue solution are added, and titrated with a 2 mM concentration benzalkonium chloride solution (cationic surfactant standard solution) to form an aqueous layer. The point at which both layers of the chloroform layer and the chloroform layer exhibit the same blue color is defined as the end point. Then, the degree of sulfonate is calculated according to the following formula from the weight of the sulfonated polyester, the titration amount, and the molecular weight of the sulfonic acid (= 80).

In the above formula, A: the amount of the cationic surfactant standard solution having a concentration of 2 mM (ml), f: the factor of the cationic surfactant standard solution having a concentration of 2 mM, and C: the concentration (% by mass) of the sulfonated polyester aqueous solution. be.

Since the molecular weight of the sulfonated polyester used as the polymer anion is easy to synthesize and obtain, a column containing polyvinyl alcohol as a filler by gel permeation chromatography (GPC) (Asahipak GF-7M HQ manufactured by Showa Denko Co., Ltd.) ), And the weight average molecular weight measured by using a 0.1 M sodium nitrate aqueous solution as a solvent is preferably 5,000 or more, more preferably 10,000 or more, and 40,000. It is preferably less than or equal to, and more preferably 30,000 or less.

The sulfonated polyester having the above-mentioned degree of sulfonate is synthesized, for example, by using a monomer having a sulfonic acid group or a salt of a sulfonic acid group as a copolymerization component when polymerizing the polyester by a known method. Can be done.

More specifically, for example, when a dicarboxylic acid diester and a diol are used and a polyester is synthesized through an ester exchange reaction according to a conventional method, a dicarboxylic acid diester having a sulfonic acid group (or a salt thereof) is used in combination. , Sulfonated polyester can be synthesized.

There are also commercially available sulfonated polyesters [for example, sulfonated polyester manufactured by Takamatsu Oil & Fat Co., Ltd. (product name: pesresin), sulfonated polyester manufactured by Reciprocal Chemical Co., Ltd. (product name: Plus Coat)], such commercially available products. From the products, those having the above-mentioned degree of sulfonate may be selected and used.

In the method of the present invention, the electrolytic polymerization solution for performing electrolytic oxidative polymerization contains a water-soluble organic solvent and water as solvents. While the sulfonated polyester having the above-mentioned degree of sulfonate is water-soluble, the polymerizable monomer thiophene or a derivative thereof is difficult to dissolve in water. Therefore, a water-soluble organic solvent is used together with water so that thiophene or a derivative thereof can be well dissolved in the electrolytic polymerization solution.

As the water-soluble organic solvent, one having a relative permittivity of 10 or more, preferably 30 or more, is used because the solubility of thiophene or a derivative thereof is good. However, when a water-soluble organic solvent having an excessively high relative permittivity is used, a part of the conductive polymer formed in layers on the surface of the capacitor element by electrolytic oxidation polymerization may be dissolved in the electrolytic polymerization solution. Therefore, from the viewpoint of suppressing this, a water-soluble organic solvent having a relative permittivity of 50 or less is used.

Specific examples of the water-soluble organic solvent satisfying the above relative permittivity include acetonitrile (relative permittivity: 38), N-methylpyrrolidone (relative permittivity: 32), dimethylsulfoxide (relative permittivity: 47), and sulfolane (relative permittivity: 47). Relative permittivity: 44), ethylene glycol (relative permittivity: 38), propylene glycol (relative permittivity: 32), γ-butyrolactone (relative permittivity: 42), propylene glycol monomethyl ether (relative permittivity: 12), etc. Can be mentioned. As the solvent of the electrolytic polymerization solution, only one of these water-soluble organic solvents may be used, or two or more of them may be used in combination.

In the electrolytic polymerization solution, the ratio of water to the water-soluble organic solvent is preferably 40:60 to 90:10 and preferably 60:40 to 90:10 in terms of mass ratio. By using water and a water-soluble organic solvent in the above ratio, thiophene or a derivative thereof or a polymer anion can be better dissolved in the electrolytic polymerization solution, and the highly conductive layer formed on the surface of the capacitor element. It is possible to better suppress the elution of the molecule into the electrolytic polymer solution.

In the electrolytic polymerization solution, the concentration of thiophene or a derivative thereof is preferably 0.5 to 5.0% by mass. The concentration of the sulfonated polyester in the electrolytic polymerization solution is preferably 0.5 to 5.0% by mass.

The electrolytic polymerization solution may contain thiophene, which is a polymerizable monomer, or a derivative thereof, a sulfonated polyester which is a polymer anion satisfying the above-mentioned degree of sulfonate, and a water-soluble organic solvent and water, if necessary. It may also contain a cationic surfactant, a nonionic surfactant, an anionic surfactant and the like.

Electrolytic oxidative polymerization is carried out in a state where the capacitor element is used as an anode and immersed in the electrolytic polymerization solution.

The electrolytic capacitor manufactured by the method of the present invention includes an aluminum electrolytic capacitor, a tantalum electrolytic capacitor, a niobular electrolytic capacitor and the like. For these electrolytic capacitors, a capacitor element having an anode made of a porous body of a valve metal such as aluminum, tantalum, and niobium and a dielectric layer made of an oxide film of those valve metals is used.

Therefore, when performing electrolytic polymerization by the method of the present invention, the above-mentioned capacitor element may be used as an anode, and a conductive polymer layer may be formed on the surface of the dielectric layer thereof. However, as described above, these capacitor elements have a dielectric layer made of an oxide film on the surface, but since this dielectric layer is inferior in conductivity, electrolytic polymerization is possible on this surface. In addition, it is necessary to form a conductive precoat layer on the dielectric layer of the capacitor element.

The precoat layer is not particularly limited, but it is preferable to synthesize a polymer of thiophene or a derivative thereof by chemical oxidative polymerization to form the precoat layer. For the precoat layer, for example, a dispersion liquid containing an oxidizing agent and a dopant such as a known organic sulfonic acid ferrous salt (a dispersion liquid using an alcohol such as ethanol as a solvent) is adhered to the surface of the capacitor element by coating or the like. After drying, a method of immersing this in thiophene or a derivative thereof (previously exemplified as one that can be used as a polymerizable monomer in the method of the present invention) and chemically oxidatively polymerizing it at 20 to 50 ° C. for 30 to 240 minutes. Can be formed by. By such a method, a precoat layer having a thickness of about several μm can be formed on the surface of the dielectric layer of the capacitor element.

The electrolytic oxidative polymerization can be performed with a constant current or a constant voltage. For example, when the electrolytic oxidative polymerization is performed with a constant current, the current value is preferably 0.05 mA / cm ² to 10 mA / cm ² and 0.2 mA / cm. ² to 4 mA / cm ² is more preferable, and when electrolytic oxidative polymerization is performed at a constant voltage, the voltage is preferably 0.5 V to 10 V, more preferably 1.5 V to 5 V. The temperature at the time of electrolytic oxidation polymerization is preferably 5 ° C to 95 ° C, and particularly preferably 10 ° C to 30 ° C. The polymerization time is preferably 1 hour to 72 hours, more preferably 8 hours to 24 hours.

When performing electrolytic oxidation polymerization, in order to improve the formation of the conductive polymer layer on the surface of the capacitor element, the electrolytic polymer solution is not stirred or the conductive polymer does not peel off from the surface of the capacitor element. It is preferable to stir under such conditions, and it is more preferable not to stir the electrolytic polymer solution. The stirring conditions for performing electrolytic oxidation polymerization while stirring the electrolytic polymerization solution are not uniquely determined because they vary depending on the size and shape of the tank for performing electrolytic oxidation polymerization. For example, a preliminary experiment is conducted. After confirming the conditions under which the conductive polymer does not peel off from the capacitor element, the actual electrolytic oxidation polymerization may be carried out based on the knowledge.

A capacitor element having a conductive polymer layer formed on its surface by electrolytic oxidation polymerization is washed and then dried. Then, by applying carbon paste and silver paste to the dried capacitor element, drying it, and then exteriorizing it, a laminated or flat plate type electrolytic capacitor (aluminum electrolytic capacitor, tantalum electrolytic capacitor, niobium electrolytic capacitor, etc.) is manufactured. To.

Further, a high boiling point organic solvent having a boiling point of 150 ° C. or higher, a high boiling point organic solvent having a boiling point of 150 ° C. or higher, and an aromatic compound having at least one hydroxyl group or carboxyl group are formed on the conductive polymer layer of the condenser element. An electrolytic capacitor may be configured by impregnating the containing conductive auxiliary liquid.

Examples of the high boiling point organic solvent having a boiling point of 150 ° C. or higher that can be used in the conductive auxiliary liquid include γ-butyrolactone (boiling point: 203 ° C.), butanediol (boiling point: 230 ° C.), and dimethylsulfoxide (boiling point: 189 ° C.). ), Sulfolane (boiling point: 285 ° C.), N-methylpyrrolidone (boiling point: 202 ° C.), dimethylsulfolane (boiling point: 233 ° C.), ethylene glycol (boiling point: 198 ° C.), diethylene glycol (boiling point: 244 ° C.), triethyl phosphate. (Boiling point: 215 ° C.), tributyl phosphate (289 ° C.), triethylhexyl phosphate [215 ° C. (4 mmHg)], polyethylene glycol and the like can be mentioned.

Further, as the above-mentioned aromatic compound having at least one hydroxyl group (refers to a hydroxyl group bonded to the constituent carbon of the aromatic ring and does not mean an −OH moiety such as in a carboxyl group) or a carboxyl group. , Benzene-based, naphthalene-based, and anthracene-based ones can be used, and specific examples thereof include hydroxybenzenecarboxylic acid, nitrophenol, dinitrophenol, trinitrophenol, aminonitrophenol, and hydroxy. Anisol, hydroxydinitrobenzene, dihydroxydinitrobenzene, alkylhydroxyanisole, hydroxynitroanisole, hydroxynitrobenzenecarboxylic acid (ie, hydroxynitrobenzoic acid), dihydroxynitrobenzenecarboxylic acid (ie, dihydroxynitrobenzoic acid), phenol, dihydroxybenzene, tri Hydroxybenzene, dihydroxybenzenecarboxylic acid, trihydroxybenzenecarboxylic acid, hydroxybenzenedicarboxylic acid, dihydroxybenzenedicarboxylic acid, hydroxytoluenecarboxylic acid, nitronaphthol, aminonaphthol, dinitronaphthol, hydroxynaphthalenecarboxylic acid, dihydroxynaphthalenecarboxylic acid, trihydroxy Naphthalene carboxylic acid, hydroxynaphthalenedicarboxylic acid, dihydroxynaphthalenedicarboxylic acid, hydroxyanthracen, dihydroxyanthracene, trihydroxyanthracene, tetrahydroxyanthracene, hydroxyanthracene carboxylic acid, hydroxyanthracen dicarboxylic acid, dihydroxyanthracenedicarboxylic acid, tetrahydroxyanthracendione, benzenecarboxylic Acids, benzenedicarboxylic acids, naphthalenecarboxylic acids, naphthalenedicarboxylic acids and the like can be mentioned.

Further, at least one binder selected from the group consisting of an epoxy compound or a hydrolyzate thereof, a silane compound or a hydrolyzate thereof, and polyalcohol is added to a high boiling point organic solvent or a conductive auxiliary liquid having a boiling point of 150 ° C. or higher. It can also be contained.

Since the electrolytic capacitor manufactured by the method of the present invention is excellent in heat resistance and moisture resistance, it can be suitably used for applications requiring such characteristics (for example, in-vehicle applications), and electrolytic capacitors have been conventionally used. It can also be applied to the same applications as those used.

Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention.

[Synthesis of sulfonated polyester]
(Synthesis Example 1)
Dimethyl terephthalic acid: 116.5 g, dimethyl sodium 5-sulfoisophthalate: 29.6 g, ethylene glycol: 86.9 g, polyethylene glycol 400 (400 means molecular weight): 40.0 g, manganese acetate tetrahydrate A product: 0.2 g and tetrabutyl titanate: 0.1 g were placed in a 1 L flask, and a transesterification reaction was carried out at 200 ° C. After the transesterification reaction, 0.1 g of trimethyl phosphate was added to the flask, and the polycondensation reaction was carried out at 200 ° C. under a reduced pressure of 10 hPa for 1 hour to synthesize a sulfonated polyester. The obtained sulfonated polyester had a degree of sulfonate of 6% and a weight average molecular weight of 5000.

200 g of the sulfonated polyester was placed in 800 g of water and stirred to prepare a sulfonated polyester solution 1 having a concentration of 20% by mass.

(Synthesis Example 2)
1 L flask containing 116.5 g of dimethyl terephthalic acid, 29.6 g of dimethyl sodium 5-sulfoisophthalate, 86.9 g of ethylene glycol, 0.2 g of manganese acetate tetrahydrate, and 0.1 g of tetrabutyl titanate. The ester exchange reaction was carried out at 200 ° C. After the transesterification reaction, 0.1 g of trimethyl phosphate was added to the flask, and the polycondensation reaction was carried out at 200 ° C. under a reduced pressure of 10 hPa for 1 hour to synthesize a sulfonated polyester. The obtained sulfonated polyester had a degree of sulfonate of 6% and a weight average molecular weight of 15,000.

200 g of the sulfonated polyester was placed in 800 g of water and stirred to prepare a sulfonated polyester solution 2 having a concentration of 20% by mass.

(Synthesis Example 3)
Dimethyl terephthalic acid: 116.5 g, dimethyl sodium 5-sulfoisophthalate: 29.6 g, diethylene glycol: 148.6 g, manganese acetate tetrahydrate: 0.2 g, and tetrabutyl titanate: 0.1 g in a 1 L flask. The mixture was charged and a transesterification reaction was carried out at 200 ° C. After the transesterification reaction, 0.5 g of trimethyl phosphate was added to the flask, and the polycondensation reaction was carried out at 200 ° C. under a reduced pressure of 10 hPa for 1 hour to synthesize a sulfonated polyester. The obtained sulfonated polyester had a degree of sulfonate of 6% and a weight average molecular weight of 40,000.

200 g of the sulfonated polyester was placed in 800 g of water and stirred to prepare a sulfonated polyester solution 3 having a concentration of 20% by mass.

(Synthesis Example 4)
1 L flask containing 116.5 g of dimethyl terephthalic acid, 59.2 g of dimethyl sodium 5-sulfoisophthalate, 86.9 g of ethylene glycol, 0.2 g of manganese acetate tetrahydrate, and 0.1 g of tetrabutyl titanate. The ester exchange reaction was carried out at 200 ° C. After the transesterification reaction, 0.1 g of trimethyl phosphate was added to the flask, and the polycondensation reaction was carried out at 200 ° C. under a reduced pressure of 10 hPa for 1 hour to synthesize a sulfonated polyester. The obtained sulfonated polyester had a degree of sulfonate of 9% and a weight average molecular weight of 15,000.

200 g of the sulfonated polyester was placed in 800 g of water and stirred to prepare a sulfonated polyester solution 4 having a concentration of 20% by mass.

(Synthesis Example 5)
Dimethylterephthalic acid: 116.5 g, dimethylsodium 5-sulfoisophthalate: 88.9 g, diethylene glycol: 191.0 g, manganese acetate tetrahydrate: 0.2 g, and tetrabutyl titanate: 0.1 g in a 1 L flask. The mixture was charged and a transesterification reaction was carried out at 200 ° C. After the transesterification reaction, 0.1 g of trimethyl phosphate was added to the flask, and the polycondensation reaction was carried out at 200 ° C. under a reduced pressure of 10 hPa for 1 hour to synthesize a sulfonated polyester. The obtained sulfonated polyester had a degree of sulfonate of 10% and a weight average molecular weight of 40,000.

200 g of the sulfonated polyester was placed in 800 g of water and stirred to prepare a sulfonated polyester solution 5 having a concentration of 20% by mass.

(Synthesis Example 6)
Dimethyl terephthalic acid: 135.9 g, 5-Sodium 5-sulfoisophthalate: 14.8 g, Ethylene glycol: 86.9 g, Polyethylene glycol 300 (300 means molecular weight): 30 g, Manganese acetate tetrahydrate: 0.2 g and 0.1 g of tetrabutyl titanate were charged in a 1 L flask, and a transesterification reaction was carried out at 200 ° C. After the transesterification reaction, 0.1 g of trimethyl phosphate was added to the flask, and the polycondensation reaction was carried out at 200 ° C. under a reduced pressure of 10 hPa for 1 hour to synthesize a sulfonated polyester. The obtained sulfonated polyester had a degree of sulfonate of 2% and a weight average molecular weight of 5000.

200 g of the sulfonated polyester was placed in 800 g of water and stirred to prepare a sulfonated polyester solution 6 having a concentration of 20% by mass.

[Preparation of electrolytic polymer solution]
(Preparation Example 1)
1:25 g of the sulfonated polyester solution prepared in Synthesis Example 1, 765 g of water, 197 g of γ-butyrolactone (GBL), and 10 g of 3,4-ethylenedioxythiophene (EDOT) were combined and stirred to form two layers. The electrolytic polymerization solution 1 was prepared by visually confirming that it was not separated. The obtained electrolytic polymerization solution 1 had a sulfonated polyester concentration of 0.5% by mass and an EDOT concentration of 1.0% by mass, and the solvent ratio (mass ratio) was water: GBL = 80: 20. rice field.

(Preparation Example 2)
The electrolytic polymerization solution 2 was prepared in the same manner as in Preparation Example 1 except that the sulfonated polyester solution 2 prepared in Synthesis Example 2 was used instead of the sulfonated polyester solution 1.

(Preparation Example 3)
The electrolytic polymerization solution 3 was prepared in the same manner as in Preparation Example 1 except that the sulfonated polyester solution 3 prepared in Synthesis Example 3 was used instead of the sulfonated polyester solution 1.

(Preparation Example 4)
The electrolytic polymerization solution 4 was prepared in the same manner as in Preparation Example 1 except that the sulfonated polyester solution 4 prepared in Synthesis Example 4 was used instead of the sulfonated polyester solution 1.

(Preparation Example 5)
Instead of the sulfonated polyester solution 1, a solution prepared by dissolving "Plus Coat Z221 (trade name. Sulfonization degree: 5%, weight average molecular weight: 15000)" manufactured by Mutual Chemicals Co., Ltd. in water at a concentration of 20% by mass was used. The electrolytic polymerization solution 5 was prepared in the same manner as in Preparation Example 1 except that it was used.

(Preparation Example 6)
Instead of the sulfonated polyester solution 1, a solution prepared by dissolving "Plus Coat Z561 (trade name. Sulfonization degree: 3%, weight average molecular weight: 25000)" manufactured by Mutual Chemicals Co., Ltd. in water at a concentration of 25% by mass was used. The electrolytic polymerization solution 6 was prepared in the same manner as in Preparation Example 1 except that the amount used was 20 g.

(Preparation Example 7)
Instead of the sulfonated polyester solution 1, a solution prepared by dissolving "Plus Coat Z446 (trade name. Sulfonation degree: 4%, weight average molecular weight: 15000)" manufactured by Mutual Chemicals Co., Ltd. in water at a concentration of 25% by mass was used. The electrolytic polymer solution 7 was prepared in the same manner as in Preparation Example 1 except that the amount added was 20 g and acetonitrile was used instead of GBL.

(Preparation Example 8)
The electrolytic polymerization solution 8 was prepared in the same manner as in Preparation Example 7 except that dimethyl sulfoxide (DMSO) was used instead of acetonitrile.

(Preparation Example 9)
An electrolytic polymerization solution 9 was prepared in the same manner as in Preparation Example 7 except that N-methylpyrrolidone (NMP) was used instead of acetonitrile.

(Preparation Example 10)
The electrolytic polymerization solution 10 was prepared in the same manner as in Preparation Example 7 except that sulfolane was used instead of acetonitrile.

(Preparation Example 11)
The electrolytic polymerization solution 11 was prepared in the same manner as in Preparation Example 7 except that propylene glycol monomethyl ether (PGMME) was used instead of acetonitrile.

(Preparation Example 12)
The electrolytic polymerization solution 12 was prepared in the same manner as in Preparation Example 7 except that ethylene glycol (EG) was used instead of acetonitrile.

(Preparation Example 13)
The electrolytic polymerization solution 13 was prepared in the same manner as in Preparation Example 7 except that propylene glycol (PG) was used instead of acetonitrile.

(Preparation Example 14)
The electrolytic polymerization solution 14 was prepared in the same manner as in Preparation Example 6 except that the addition amounts of water and GBL were changed to 872 g and 99 g (mass ratio: water: GBL = 90: 10), respectively.

(Preparation Example 15)
The electrolytic polymerization solution 15 was prepared in the same manner as in Preparation Example 5 except that the addition amounts of water and GBL were changed to 379 g and 591 g (mass ratio: water: GBL = 40: 60), respectively.

(Preparation Example 16)
The electrolytic polymerization solution 16 was prepared in the same manner as in Preparation Example 7 except that ethylated ethylenedioxythiophene (ethylized EDOT) was used instead of EDOT and GBL was used instead of acetonitrile.

(Preparation Example 17)
The electrolytic polymerization solution 17 was prepared in the same manner as in Preparation Example 14 except that a mixture of ethylened EDOT and EDOT having a volume ratio of 1: 1 was used instead of EDOT.

(Preparation Example 18)
Pyrol: 10 g, 40% by mass concentration sodium butylnaphthalene sulfonate aqueous solution: 12.5 g, and water: 978 g were combined and stirred to prepare an electrolytic polymer solution 18.

(Preparation Example 19)
Instead of the sulfonated polyester solution 1, a solution prepared by dissolving 5 g of sodium toluenesulfonate in water at a concentration of 20% by mass was used, and the electrolytic polymerization solution was the same as in Preparation Example 1 except that the addition amount was 25 g. 19 was prepared.

(Preparation Example 20)
Preparation example except that a solution prepared by dissolving 5 g of sodium polystyrene sulfonate (degree of sulfonate: 43%) in water at a concentration of 20% by mass was used instead of the sulfonated polyester solution 1 and the addition amount was 25 g. The electrolytic polymerization solution 20 was prepared in the same manner as in 1.

(Preparation Example 21)
An attempt was made to prepare the electrolytic polymerization solution 21 containing only water as the solvent in the same manner as in Preparation Example 7 except that the amount of water added was changed to 965 g without using acetonitrile. 21 could not be prepared.

(Preparation Example 22)
An attempt was made to synthesize an electrolytic polymerization solution in the same manner as in Preparation Example 1 except that the sulfonated polyester solution 5 prepared in Synthesis Example 5 was used instead of the sulfonated polyester solution 1, but the electrolytic polymerization solution was not mixed and was not mixed. 22 could not be prepared.

(Preparation Example 23)
An attempt was made to synthesize an electrolytic polymerization solution in the same manner as in Preparation Example 1 except that the sulfonated polyester solution 5 prepared in Synthesis Example 6 was used instead of the sulfonated polyester solution 1, but the electrolytic polymerization solution was not mixed and was not mixed. 23 could not be prepared.

(Preparation Example 24)
An attempt was made to prepare the electrolytic polymerization solution 24 in the same manner as in Preparation Example 7 except that ethyl acetate (relative permittivity: 6) was used instead of acetonitrile, but since the electrolytic polymerization solution 24 was separated into two layers, the electrolytic polymerization solution 24 was prepared. could not.

(Preparation Example 25)
The electrolytic polymerization solution 25 was prepared in the same manner as in Preparation Example 7 except that formic acid (relative permittivity: 59) was used instead of acetonitrile.

(Preparation Example 26)
Preparation was attempted in the same manner as in Preparation Example 6 except that the addition amounts of water and GBL were changed to 921 g and 49 g (mass ratio: water: GBL = 95: 5), respectively, but electrolysis was performed because they were separated into two layers. The polymerization solution 26 could not be prepared.

(Preparation Example 27)
The electrolytic polymerization solution 27 was prepared in the same manner as in Preparation Example 6 except that the addition amounts of water and GBL were changed to 280 g and 688 g (mass ratio: water: GBL = 30: 70), respectively.

The compositions of the electrolytic polymerization solutions prepared in Preparation Examples 1 to 27 are shown in Tables 1 and 2. The "ratio" in the "solvent" column of Tables 1 and 2 means the ratio (mass ratio) of water to the water-soluble organic solvent.

[Manufacturing of electrolytic capacitors]
(Example 1)
A dielectric layer (dielectric oxide film) was formed on the surface of the tantalum sintered body by immersing the tantalum sintered body in a phosphoric acid aqueous solution having a concentration of 2% by mass and applying a voltage of 10 V.

Then, a precoat layer was formed on the dielectric layer of the tantalum sintered body to enable electrolytic polymerization, and a capacitor element was manufactured. The tantalum sintered body was immersed in a 30% by mass concentration of ferric toluenesulfonic acid ethanol solution, removed, and dried at 105 ° C. for 30 minutes. The dried tantalum sintered body is immersed in EDOT and chemically oxidatively polymerized for 1 hour in an atmosphere having a temperature of 25 ° C. and a relative humidity of 60%. A precoat layer composed of the polymer was formed, washed with water for 1 hour and then dried at 105 ° C.

Next, using the electrolytic polymer solution 1 obtained in Preparation Example 1, the capacitor element is used as an anode, the SUS304 plate is used as a cathode, and a constant current is applied so that the liquid temperature becomes 1 mA / cm ² at 20 to 30 ° C. Applying and electrolytic polymerization was carried out to form a conductive polymer layer having a thickness of 5 to 20 μm on the precoat layer of the capacitor element. Then, after covering the conductive polymer layer of the capacitor element with carbon paste and silver paste, the capacitor element was covered with an exterior material to obtain a tantalum electrolytic capacitor.

(Examples 2 to 17 and Comparative Example 1)
A tantalum electrolytic capacitor was produced in the same manner as in Example 1 except that any of the electrolytic polymerization liquids 2 to 18 was used instead of the electrolytic polymerization liquid 1.

(Comparative Examples 2 and 3)
An attempt was made to prepare a tantalum electrolytic capacitor in the same manner as in Example 1 except that the electrolytic polymerization solution 19 or 20 was used instead of the electrolytic polymerization solution 1, but the capacitor element was conductive on the dielectric layer (precoat layer). The sex polymer layer could not be formed well.

Comparative Example 4
The condenser element produced in the same manner as in Example 1 was immersed in a ferric ethanol solution of toluene sulfonate having a concentration of 30% by mass, taken out, and dried at 105 ° C. for 30 minutes. The dried tantalum sintered body is immersed in EDOT and chemically oxidatively polymerized for 2 hours in an atmosphere at a temperature of 25 ° C. and a relative humidity of 60% to form a conductive polymer layer on the dielectric layer in the capacitor element. did. Subsequently, the capacitor element was immersed in pure water, left for 30 minutes, pulled up, and dried at 105 ° C. for 60 minutes. The above steps from chemical oxidative polymerization to drying were repeated four times to obtain a capacitor element having a conductive polymer layer having a thickness of 10 μm on the dielectric layer.

Then, a tantalum electrolytic capacitor was produced in the same manner as in Example 1 except that the above-mentioned capacitor element was used.

Comparative Example 5
A 3% aqueous solution of polystyrene sulfonic acid (manufactured by Alpha Acer, molecular weight 75,000): 200 g was placed in a container having an internal volume of 1 L, 2 g of ammonium persulfate was added as an oxidizing agent, and the mixture was stirred and dissolved with a stirrer. Next, 0.4 g of a 40% aqueous solution of ferric sulfate was added, and 3 mL of 3,4-ethylenedioxythiophene was slowly added dropwise into the mixture while stirring, and 3,4-ethylenedioxy was added over 24 hours. Thiophene was polymerized. Then, after diluting 4-fold with water, dispersion treatment was performed for 30 minutes with an ultrasonic homogenizer [US-T300 (trade name) manufactured by Nippon Seiki Co., Ltd.]. Then, 100 g of the cation exchange resin Amberlite 120B (trade name) manufactured by Organo Corporation was added and stirred with a stirrer for 1 hour, and then the filter paper No. 1 manufactured by Toyo Filter Paper Co., Ltd. was added. Filtration was carried out with 131, and the treatment with this cation exchange resin and filtration were repeated three times to remove all the cation components in the liquid. The liquid after the above treatment is passed through a filter having a pore size of 1 μm, and the passing liquid is treated with an ultrafiltration device [Vivaflow 200 (trade name) manufactured by Sartorius, molecular weight fraction 50,000] to release small molecules in the liquid. The component was removed. The liquid after this treatment is diluted with water to adjust the concentration to 3%, and 4 g of dimethyl sulfoxide as a high boiling point solvent is added to 40 g of the 3% liquid and stirred to obtain a dispersion liquid of the conductive composition. Obtained.

The capacitor element produced in the same manner as in Example 1 is immersed in the conductive polymer dispersion for 15 minutes, pulled out, dried at 150 ° C. for 30 minutes, and has a thickness of 10 μm on the dielectric layer of the capacitor element. A conductive polymer layer was formed.

Then, a tantalum electrolytic capacitor was produced in the same manner as in Example 1 except that the above-mentioned capacitor element was used.

(Comparative Examples 6 and 7)
An attempt was made to prepare a tantalum electrolytic polymer in the same manner as in Example 1 except that the electrolytic polymerization solution 25 or 27 was used instead of the electrolytic polymerization solution 1, but the synthesized conductive polymer was eluted in the electrolytic polymerization solution. Therefore, the conductive polymer layer could not be formed well on the dielectric layer (on the precoat layer) of the capacitor element.

For the tantalum electrolytic capacitors of Examples 1 to 17 and Comparative Examples 1, 4 and 5, the capacitance and ESR were measured as initial characteristics by the following methods, respectively.

(Capacitance)
It was measured at 120 kHz under the condition of 25 ° C. using an LCR meter (4284A) manufactured by HEWLETT PACKARD.

(ESR)
It was measured at 100 kHz under the condition of 25 ° C. using an LCR meter (4284A) manufactured by HEWLETT PACKARD.

The above measurement was performed for 10 samples for each sample. These results are shown in Tables 3 and 4. Tables 3 and 4 show the average value of the 10 measured values rounded to the first decimal place for capacitance and ESR. In addition, in the column of "electrolytic polymerization solution (polymer formation method)" in Tables 3 and 4, electrolytic oxidation polymerization was performed using the electrolytic polymerization solution prepared in the above preparation example to form a conductive polymer layer. For those that have been formed, the number of the electrolytic polymerization solution is described, and for those in which the conductive polymer layer is formed by a method other than electrolytic oxidation polymerization, the method is described (also also in Tables 5 and 6 below). The same is true).

The initial characteristics of the tantalum electrolytic capacitors produced in Examples and Comparative Examples can be evaluated as non-defective products with a capacitance of 250 μF or more and an ESR of 50 mΩ or less. As shown in Tables 3 and 4, Examples 1 to 17 and Comparative Examples It can be said that the tantalum electrolytic capacitors 1 and 4 have good initial characteristics.

On the other hand, the tantalum electrolytic capacitor of Comparative Example 5 using a capacitor element having a conductive polymer layer formed by using a dispersion liquid of a conductive polymer obtained by chemical oxidation polymerization is inside the void of the capacitor element. Since it is difficult to fill the conductive polymer well, the capacitance is particularly low and the ESR is high.

[Evaluation of heat resistance of tantalum electrolytic capacitors]
After storing 10 tantalum electrolytic capacitors of Examples 1 to 17 and Comparative Examples 1, 4 and 5 at 105 ° C. for 500 hours, the ESR was measured by the same method as described above. These results are shown in Table 5. Table 5 shows the measured value of ESR at the time of heat resistance evaluation and the rate of change (times) obtained by dividing the measured value at the time of heat resistance evaluation by the measured value at the time of initial characteristic evaluation.

As shown in Table 5, the tantalum electrolytic capacitors of Examples 1 to 17 had good heat resistance because the increase in ESR after high temperature storage was suppressed.

On the other hand, the tantalum electrolytic capacitor of Comparative Example 1 using a capacitor element having a conductive polymer layer containing a pyrrole polymer had a significantly increased ESR after high-temperature storage and was inferior in heat resistance. ..

[Evaluation of moisture resistance of tantalum electrolytic capacitors]
Ten tantalum electrolytic capacitors of Examples 1 to 17 and Comparative Examples 1, 4 and 5 were stored for 100 hours in an environment of 60 ° C. and 90% relative humidity, and then the ESR was measured by the same method as described above. These results are shown in Table 6. In addition, Table 6 shows the measured value of ESR at the time of moisture resistance evaluation and the rate of change (times) obtained by dividing the measured value at the time of moisture resistance evaluation by the measured value at the time of initial characteristic evaluation.

As shown in Table 6, the tantalum electrolytic capacitors of Examples 1 to 17 had good moisture resistance because the increase in ESR after storage in a high humidity environment was suppressed.

On the other hand, the tantalum electrolytic capacitors of Comparative Examples 4 and 5 using the capacitor element having the conductive polymer layer containing the polymer obtained by the chemical oxidative polymerization of EDOT are ESR after storage in a high humidity environment. Was greatly increased, and the moisture resistance was inferior. As described above, since the iron component (iron ion) derived from the oxidizing agent remains in the layer of the conductive polymer obtained by the chemical oxidation polymerization even after repeated washing, the tantalum of Comparative Examples 4 and 5 remains. It is considered that the ESR of the electrolytic capacitor was increased by storage in a high humidity environment.

Claims (4)

By performing electrolytic oxidation polymerization in a state where the capacitor element is immersed in an electrolytic polymerization solution containing a polymerizable monomer, a polymer anion, a water-soluble organic solvent having a relative permittivity of 10 to 50, and water, at least one of the surfaces of the capacitor element. It has a step of forming a conductive polymer layer in the part,
Thiophene or a derivative thereof is used as the polymerizable monomer, and
As the polymer anion, a sulfonated polyester having a degree of sulfonate of 3 to 9% was used.
A method for manufacturing an electrolytic capacitor, wherein the ratio of water to the water-soluble organic solvent is 40:60 to 90:10 in terms of mass ratio. The method for producing an electrolytic capacitor according to claim 1, wherein ethylene dioxythiophene or alkylated ethylene dioxythiophene is used as the polymerizable monomer. The method for manufacturing an electrolytic capacitor according to claim 1 or 2, wherein the polymer anion has a weight average molecular weight of 5,000 to 40,000. Claimed to use at least one solvent selected from the group consisting of acetonitrile, N-methylpyrrolidone, dimethyl sulfoxide, sulfolane, ethylene glycol, propylene glycol, γ-butyrolactone, and propylene glycol monomethyl ether as the water-soluble organic solvent. Item 8. The method for manufacturing an electrolytic capacitor according to any one of Items 1 to 3.