Electrolytic capacitor

Abstract

The present invention relates to an electrolytic capacitor including a resin layer, and provides an electrolytic capacitor in which an increase in ESR over time is suppressed. The electrolytic capacitor includes: a capacitor element having an anode foil, a cathode foil, and an electrolytic solution; a case that houses the capacitor element; a sealing member that seals the case; and a resin layer disposed near the sealing member. The resin layer disposed near the sealing member contains an epoxy resin composition that does not have an ester bond.

Description

Technical Field

[0001] The present invention relates to an electrolytic capacitor including a resin layer. Background Art

[0002] An electrolytic capacitor using a valve metal such as tantalum or aluminum forms a dielectric surface by forming the valve metal as an anode-side facing electrode into a sintered body or an etched foil shape, etc., and obtains a small size and a large capacitance. Such an electrolytic capacitor fills the voids with an electrolyte in order to closely contact the dielectric oxide film of the anode with the facing electrode. That is, as an electrolytic capacitor, there are a liquid electrolytic capacitor having only an electrolytic solution, a hybrid electrolytic capacitor including an electrolytic solution and a solid electrolyte, and a bipolar electrolytic capacitor having dielectric films formed on both electrodes.

[0003] The electrolytic solution contains ethylene glycol or γ-butyrolactone as a solvent, and contains carboxylic acids such as 1,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, azelaic acid or salts thereof as solutes. The electrolytic solution directly contacts the dielectric film, acts as a true cathode, and has a dielectric film repair effect. However, the electrolytic solution evaporates and leaks to the outside of the electrolytic capacitor over time. Therefore, the electrolytic capacitor faces drying out, the electrostatic capacitance decreases over time, and the tangent of the loss angle (tanδ) increases over time, eventually reaching the end of its life.

[0004] Therefore, the capacitor element is housed in a bottomed outer package case, and the opening of the outer package case is sealed with a sealing member, thereby sealing the electrolytic solution impregnated in the capacitor element to suppress the evaporation and dispersion of the electrolytic solution, and thus achieving a long life. However, the sealing member uses an elastomer such as butyl rubber or ethylene propylene diene rubber (ethylenepropylene diene monomer, EPDM). Therefore, the electrolytic solution is not completely sealed in the case, but gradually volatilizes to the outside of the electrolytic capacitor through the sealing member. Therefore, as in Patent Document 1, in order to suppress the volatilization of the electrolytic solution caused by permeating through the sealing member, a method of covering the sealing member with a resin layer has been proposed.

[0005] Generally, a resin layer has excellent heat insulation. If the heat insulation of the electrolytic capacitor becomes high, the heat generated in the case is difficult to dissipate and is likely to accumulate heat. Therefore, as in Patent Document 2, it has been proposed to use ethylene glycol as a solvent for the electrolytic solution. The reason is that ethylene glycol has a thermal conductivity about twice as large as that of γ-butyrolactone or sulfolane. In Patent Document 2, it is implied that the higher the content ratio of ethylene glycol in the solvent, the more the thermal conductivity is improved, but in order to contain other types of solvents, ethylene glycol is preferably 90% by mass or less.

[0006] [Prior Art Documents]

[0007] [Patent Document]

[0008] Patent Document 1: Japanese Patent Laid-Open No. Sho 60-245106

[0009] Patent Document 2: WO2018 / 123525 Summary of the Invention

[0010] [Problems to be Solved by the Invention]

[0011] The resin layer contains a curable resin composition. As the curable resin composition, an epoxy resin composition containing an epoxy resin and an acid anhydride curing agent can be cited. The epoxy resin composition is a composition of an epoxy resin cured with an acid anhydride-based curing agent. The heat resistance of the epoxy resin composition containing an acid anhydride curing agent is improved, and the reaction temperature of the epoxy resin and the acid anhydride curing agent is 100°C or higher. Therefore, the temperature can be used as a trigger signal to promote the curing reaction. Thus, it is considered that the epoxy resin composition containing an epoxy resin and an acid anhydride curing agent is suitable for the resin layer.

[0012] The inventors of the present invention formed a resin layer on a part of an electrolytic capacitor using an epoxy resin cured with an acid anhydride curing agent. Then, the electrolytic capacitor was exposed to a temperature environment of 150°C. In this case, it was confirmed that the equivalent series resistance (ESR) of the electrolytic capacitor exposed to the temperature environment for 400 hours increased significantly.

[0013] The present invention is proposed to solve the above problems, and an object thereof is to relate to an electrolytic capacitor including a resin layer and to provide an electrolytic capacitor in which the time-dependent increase in ESR is suppressed.

[0014] [Technical Means for Solving the Problems]

[0015] The inventors of the present invention made diligent studies, and as a result, obtained the following insight: when using ethylene glycol as a solvent for the electrolyte in an epoxy resin composition (hereinafter, referred to as acid anhydride-cured epoxy resin) containing an epoxy resin and an acid anhydride curing agent, the time-dependent increase in ESR of the electrolytic capacitor is significant.

[0016] Furthermore, the inventors of the present invention made diligent studies based on the above insight, and as a result, found that the acid anhydride-cured epoxy resin reacts with water or ethylene glycol and decomposes, and then dissolves into the electrolyte. The presence of the acid anhydride-cured epoxy resin in the electrolyte is the cause of the increase in ESR of the electrolytic capacitor.

[0017] Here, the acid anhydride-cured epoxy resin contains an ester bond in its chemical structure. On the other hand, even when water is not deliberately added to the electrolytic capacitor, a small amount of water is mixed into the electrolytic capacitor during the manufacturing process. Ethylene glycol is a compound having a hydroxyl group, and a compound having a hydroxyl group has a structure to which water can easily access. In such a situation, when a compound having a hydroxyl group penetrates through the sealing member, water also penetrates together, and the water reacts with the ester bond of the acid anhydride-cured epoxy resin, and the acid anhydride-cured epoxy resin is hydrolyzed. In addition, an esterification reaction between the carbonyl group generated by hydrolysis and the compound having a hydroxyl group also occurs. Thus, it is considered that a part of the acid anhydride-cured epoxy resin component that reacts with water or a compound having a hydroxyl group penetrates through the sealing member and dissolves into the electrolytic solution.

[0018] The present invention is based on the above-mentioned findings. The electrolytic capacitor of the present invention is characterized by including: a capacitor element having an anode foil, a cathode foil, and an electrolytic solution; a case housing the capacitor element; a sealing member sealing the case; and a resin layer disposed near the sealing member, the resin layer including an epoxy resin composition not having an ester bond.

[0019] The epoxy resin composition may use a phenolic hardener or an amine hardener and an epoxy resin as raw materials. The epoxy resin composition may have a chemical structure including a phenolic hardener or an amine hardener and an epoxy resin.

[0020] The electrolytic solution may include at least one of a compound having a hydroxyl group, sulfolane, and γ-butyrolactone.

[0021] The compound having a hydroxyl group may be at least one of ethylene glycol, diethylene glycol, and polyethylene glycol.

[0022] The capacitor element may further have a solid electrolyte.

[0023] The cation component in the electrolytic solution may contain 76 mmol or less per 100 g of the electrolytic solution. Alternatively, the cation component in the electrolytic solution may contain 25 mmol or less per 100 g of the electrolytic solution.

[0024] [Effects of the Invention]

[0025] According to the present invention, the time-dependent increase in the ESR of the electrolytic capacitor including the resin layer can be suppressed. Description of the Drawings

[0026] Figure 1 is a perspective image taken from multiple directions of Comparative Example 1, Example 1, and Example 2. Detailed Description

[0027] Hereinafter, the electrolytic capacitor according to the embodiment of the present invention will be described. Furthermore, the present invention is not limited to the embodiments described below.

[0028] (Overall Structure)

[0029] An electrolytic capacitor is a passive component that stores and discharges electric charges through capacitance. The electrolytic capacitor includes a liquid electrolytic capacitor having only an electrolytic solution, and a hybrid electrolytic capacitor using a solid electrolyte such as a conductive polymer or gel and an electrolytic solution. In addition, the electrolytic capacitor includes an electrolytic capacitor in which a dielectric oxide film is specifically formed only on the anode side, and a bipolar electrolytic capacitor in which dielectric oxide films are formed on both electrodes. Furthermore, the electrolytic capacitor includes, in terms of appearance, an electrolytic capacitor with lead terminals led out, an electrolytic capacitor provided with a base and surface-mounted on a substrate, and an electrolytic capacitor integrally coated with resin together with other electronic circuit components. Hereinafter, these various combinations of electrolytic capacitors will be collectively referred to and simply called electrolytic capacitors.

[0030] The electrolytic capacitor has a capacitor element, a case, and a sealing member. The case houses the capacitor element. The sealing member is mounted on the opening of the case by a fastening process and seals the opening of the case. The capacitor element includes an anode foil, a cathode foil, a separator, and an electrolytic solution. The anode foil and the cathode foil face each other with the separator in between. A dielectric oxide film is formed on the surface of the anode foil. The cathode foil may also form a dielectric oxide film as needed. In addition to the electrolytic solution, a solid electrolyte may also be included. The solid electrolyte is present between the anode foil and the cathode foil with a separator in between and is in close contact with the dielectric oxide film. The electrolytic solution is filled in the void portion of the capacitor element. In addition, the electrolytic capacitor may also have a base as needed.

[0031] (Sealing Member)

[0032] The sealing member is mounted on the case by a fastening process. The case is made of aluminum, an aluminum alloy containing aluminum or manganese, or stainless steel, and is a cylindrical body with a bottom and an open end at the other end. In the fastening process, the opening of the case is bent inward and flattened so that the case is in close contact with the sealing member. The sealing member having an elastic force is a plate body including an elastomer, or a plate body formed by laminating a synthetic resin plate or a metal plate on the elastomer. The elastomer is in close contact with the case subjected to the fastening process through the elastic force and maintains the airtightness inside the case. However, with respect to the sealing member including an elastomer, the transmittance of the volatilized electrolytic solution is not zero. Examples of the elastomer include butyl rubber, ethylene propylene diene rubber (EPDM), silicone rubber, and butyl rubber.

[0033] (Resin Layer)

[0034] The electrolytic capacitor further includes a resin layer. The resin layer inhibits the evaporation of the electrolytic solution. That is, as long as it is a part near the sealing member where there is a risk of the electrolytic solution passing through, it can be provided at any part of the electrolytic capacitor. For example, the resin layer covers at least a part of the surface of the sealing member. The resin layer covers the sealing member by resin molding, thereby reducing the permeability of the electrolytic solution through the sealing member. That is, the so-called "nearby" can be in contact without a gap or can include a contact configuration. In addition, for example, in the case where the electrolytic capacitor is a chip type including a base, the resin layer is provided, for example, at the part where the base contacts the housing or around it and near the sealing member. The electrolytic solution passing through the sealing body is inhibited from evaporating by the resin layer. In other words, there is a risk that the resin layer reacts with water or ethylene glycol in the electrolytic solution passing through the sealing body and dissolves into the electrolytic solution through the sealing body.

[0035] The resin layer does not use an acid anhydride-cured epoxy resin and includes a phenolic-cured epoxy resin or an amine-cured epoxy resin. The resin layer may also include a compound other than the phenolic-cured epoxy resin or the amine-cured epoxy resin.

[0036] The phenolic-cured epoxy resin is an epoxy resin cured by a phenolic curing agent. Using the phenolic curing agent and the epoxy resin as raw materials, it is an epoxy resin composition that includes a phenolic curing agent and an epoxy resin in its chemical structure. The amine-cured epoxy resin is an epoxy resin cured by an amine-based curing agent. Using the amine-based curing agent and the epoxy resin as raw materials, it is an epoxy resin composition that includes an amine-based curing agent and an epoxy resin in its chemical structure. The acid anhydride-cured epoxy resin has an ester bond in its chemical structure. In contrast, these phenolic-cured epoxy resins and amine-cured epoxy resins do not have an ester bond in their chemical structures.

[0037] Specifically, the phenolic-cured epoxy resin is formed by the reaction and bonding of the phenolic hydroxyl group of the phenolic curing agent with the epoxy group. In addition, the amine-cured epoxy resin is formed by the reaction and bonding of the amino group of the amine-based curing agent with the epoxy group. The bond between these curing agents and the epoxy resin is an ether bond, and there is no risk of hydrolysis.

[0038] As can be seen from the reaction system described above, an epoxy resin composition containing a phenolic hardener and an epoxy resin in its chemical structure does not refer to an epoxy resin composition directly incorporated into the chemical structure in a state unchanged before the reaction. The statement that a phenolic hardener and an epoxy resin are included in the chemical structure means that substitutions of various groups occur for bonding and then they are incorporated into the chemical structure. Additionally, as can be seen from the reaction system described above, an epoxy resin composition containing an amine hardener and an epoxy resin in its chemical structure does not refer to an epoxy resin composition directly incorporated into the chemical structure in a state unchanged before the reaction. The statement that an amine hardener and an epoxy resin are included in the chemical structure means that substitutions of various groups occur for bonding and then they are incorporated into the chemical structure.

[0039] The epoxy resin contained in phenolic-hardened epoxy resin and amine-hardened epoxy resin is an epoxy oligomer having two or more reactive epoxy groups at its ends. The epoxy resin crosslinks between epoxy resin components through an addition reaction with an acid anhydride hardener and changes from a liquid to a solid resin. Typically, as the epoxy resin, bisphenol A diglycidyl ether, which is a condensate of bisphenol A and epichlorohydrin, can be cited. As the epoxy resin, other glycidyl-type epoxy resins and alicyclic epoxides such as 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate can be cited.

[0040] As the glycidyl-type epoxy resin, a bisphenol type obtained by glycidylating bisphenols can be cited. Examples of bisphenols include: bisphenol A, bisphenol F, bisphenol AD, bisphenol S, tetramethyl bisphenol A, tetramethyl bisphenol F, tetramethyl bisphenol AD, tetramethyl bisphenol S, tetrabromobisphenol A, tetrachlorobisphenol A, tetrafluorobisphenol A, etc.

[0041] Additionally, as the glycidyl-type epoxy resin, an epoxy resin obtained by glycidylating dihydric phenols can be cited. Examples of dihydric phenols include biphenol, dihydroxynaphthalene, 9,9-bis(4-hydroxyphenyl)fluorene, etc.

[0042] Additionally, as the glycidyl-type epoxy resin, an epoxy resin obtained by glycidylating trihydric phenols can be cited. Examples of trihydric phenols include: 1,1,1-tris(4-hydroxyphenyl)methane, 4,4-(1-(4-(1-(4-hydroxyphenyl)-1-methylethyl)phenyl)ethylidene)bisphenol, etc.

[0043] Additionally, as the glycidyl-type epoxy resin, an epoxy resin obtained by glycidylating tetrahydric phenols can be cited. Examples of tetrahydric phenols include 1,1,2,2-tetrakis(heright)-hydroxyphenyl)ethane, etc.

[0044] In addition, examples of glycidyl type epoxy resins include novolak type epoxy resins obtained by glycidylating novolaks. Examples of novolaks include phenol novolak, cresol novolak, bisphenol A novolak, brominated phenol novolak, brominated bisphenol A novolak, etc.

[0045] In addition, examples of glycidyl type epoxy resins include epoxy resins obtained by glycidylating polyhydric phenols, and aliphatic ether type epoxy resins obtained by glycidylating polyhydric alcohols such as glycerol or polyethylene glycol.

[0046] In addition, examples of glycidyl type epoxy resins include ether ester type epoxy resins obtained by glycidylating hydroxycarboxylic acids, ester type epoxy resins obtained by glycidylating polycarboxylic acids, glycidylates of amine compounds or amine type epoxy resins. Examples of hydroxycarboxylic acids include p-hydroxybenzoic acid, β-hydroxynaphthoic acid, etc. Examples of polycarboxylic acids include phthalic acid, terephthalic acid, etc. Examples of amine compounds include 4,4-diaminodiphenylmethane, m-aminophenol. Examples of amine type epoxy resins include triglycidyl isocyanurate, etc.

[0047] Examples of phenolic curing agents contained in phenolic cured epoxy resins include difunctional phenols and polyfunctional phenols, etc. Examples of difunctional phenols include hydroquinone, resorcinol, bisphenol F, biphenol, tetrabromobisphenol A, and naphthalene diol, etc. Examples of polyfunctional phenols include, for example, phenol novolak resin.

[0048] Examples of amine curing agents contained in amine cured epoxy resins include aliphatic polyamines, aromatic polyamines, and modified amines, etc. Examples of aliphatic polyamines include diethylenetriamine and triethylenetetramine, etc. Examples of aromatic polyamines include m-phenylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, etc. Examples of modified amines include amine adducts and ketimines, etc.

[0049] (Capacitor element)

[0050] (Electrolyte)

[0051] The electrolytic solution impregnated in the capacitor element is, for example, a solution of an ionic dissociative salt decomposed into an anion component and a cation component or a solvent that does not contain an ionic dissociative salt. As the solvent, for example, compounds having a hydroxyl group, cyclic lactones, and sulfone compounds can be cited. As the compound having a hydroxyl group, a protic organic polar solvent can be cited. As the protic organic polar solvent, the following can be cited: monohydric alcohols, polyhydric alcohols, and oxygen-containing alcohol compounds, etc. As the monohydric alcohols, the following can be cited: ethanol, propanol, butanol, pentanol, hexanol, cyclobutanol, cyclopentanol, cyclohexanol, benzyl alcohol, etc. As the polyhydric alcohols and oxygen-containing alcohol compounds, the following can be cited: ethylene glycol, diethylene glycol, propylene glycol, glycerin, methyl cellosolve, ethyl cellosolve, methoxypropylene glycol, dimethoxypropanol, alkylene oxide adducts of polyhydric alcohols such as polyethylene glycol or polyoxyethylene glycerin, etc. As the cyclic lactones, the following can be cited: γ-butyrolactone, γ-valerolactone, δ-valerolactone, etc. As the sulfone compounds, chain sulfones and cyclic sulfones can be cited. As the chain sulfones, for example, the following can be cited: dimethyl sulfone, diethyl sulfone, dipropyl sulfone, diphenyl sulfone. As the cyclic sulfones, for example, the following can be cited: sulfolane, 3-methyl sulfolane, 2,4-dimethyl sulfolane.

[0052] Here, the resin layer included in the sealing member is a phenolic cured epoxy resin or an amine cured epoxy resin. There is no ester bond in the phenolic cured epoxy resin and the amine cured epoxy resin. Therefore, even if the solvent of the electrolytic solution contains a compound having a hydroxyl group, the phenolic cured epoxy resin and the amine cured epoxy resin will not be decomposed by the compound having a hydroxyl group. Therefore, even if the solvent of the electrolytic solution contains a compound having a hydroxyl group, as long as the resin layer included in the sealing member is a phenolic cured epoxy resin or an amine cured epoxy resin, the resin component will not dissolve into the electrolytic solution, and the time-dependent increase in the ESR of the electrolytic capacitor is also suppressed.

[0053] Furthermore, in the case of using an electrolytic solution having ethylene glycol as a solvent and a solid electrolyte in combination, the conductivity of the conductive polymer is improved by the change in the higher-order structure of the conductive polymer and the reorientation of the crystal structure of the polymer chain. The cyclic lactones improve the ESR characteristics at low temperatures. Since the sulfone compound has a high boiling point, it suppresses the evaporation of the electrolytic solution and the high-temperature characteristics become good. As the solvent, ethylene glycol is particularly preferred.

[0054] From the viewpoint of suppressing the leakage of the electrolytic solution from the electrolytic capacitor through the resin layer, the solvent of the electrolytic solution is preferably ethylene glycol, and then preferably sulfolane. A mixed solvent of ethylene glycol and sulfolane can also be used in the electrolytic solution.

[0055] The organic acid that is an anionic component as the solute includes: oxalic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, maleic acid, adipic acid, benzoic acid, toluic acid, heptanoic acid, malonic acid, 1,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, azelaic acid, resorcylic acid, phloroglucinic acid, gallic acid, gentisic acid, protocatechuic acid, pyrocatechuic acid, trimellitic acid, pyromellitic acid and other carboxylic acids, or phenols, sulfonic acids. In addition, as the inorganic acid, there are: boric acid, phosphoric acid, phosphorous acid, hypophosphorous acid, carbonic acid, silicic acid and the like. As the composite compound of the organic acid and the inorganic acid, there are: diborono salicylic acid, diborono oxalic acid, diborono glycolic acid, diborono malonic acid, diborono succinic acid, diborono adipic acid, diborono azelaic acid, diborono benzoic acid, diborono maleic acid, diborono lactic acid, diborono malic acid, diborono tartaric acid, diborono citric acid, diborono phthalic acid, diborono (2-hydroxy) isobutyric acid, diborono resorcylic acid, diborono methyl salicylic acid, diborono naphthoic acid, diborono mandelic acid and diborono (3-hydroxy) propionic acid and the like.

[0056] In addition, as the salt of at least one of the organic acid, the inorganic acid and the composite compound of the organic acid and the inorganic acid, for example, there are ammonium salts, quaternary ammonium salts, amidinium salts, amine salts, sodium salts, potassium salts and the like. As the quaternary ammonium ion of the quaternary ammonium salt, there are tetramethylammonium, triethylmethylammonium, tetraethylammonium and the like. As the amidinium salt, there are ethyldimethylimidazolium, tetramethylimidazolium and the like. As the amine salt, there are salts of primary amines, secondary amines, and tertiary amines. As the primary amine, there are methylamine, ethylamine, propylamine and the like, as the secondary amine, there are dimethylamine, diethylamine, ethylmethylamine, dibutylamine and the like, as the tertiary amine, there are trimethylamine, triethylamine, tributylamine, ethyldimethylamine, ethyldiisopropylamine and the like.

[0057] The cation component in the solute is preferably added in an amount of 76 mmol or less per 100 g of the electrolyte, more preferably in an amount of 51 mmol or less per 100 g of the electrolyte, still more preferably in an amount of 34 mmol or less per 100 g of the electrolyte, particularly preferably in an amount of 25 mmol or less per 100 g of the electrolyte, and most preferably in an amount of 17 mmol or less per 100 g of the electrolyte. Furthermore, the ratio of the cation component to the anion component in the solute may be an equimolar amount, or the cation component may be in excess or the anion component may be in excess.

[0058] In a high-temperature environment such as the reflow step during the installation of an electrolytic capacitor, the cation component in the electrolyte tends to promote the dedoping reaction of the conductive polymer in the solid electrolyte. If the dedoping reaction is promoted by the cation component, the conductivity of the solid electrolyte decreases and the ESR of the electrolytic capacitor increases. On the other hand, when a resin layer is disposed near the sealing member, the resin layer hinders the evaporation of the cation component through the sealing member, thereby suppressing the reduction of the cation component in the electrolytic capacitor. Therefore, if a resin layer is disposed near the sealing member, many dedoping reactions due to the cation component occur, and the ESR of the electrolytic capacitor increases.

[0059] However, as long as the cation component of the solute in the electrolyte is in an amount of 76 mmol or less per 100 g of the electrolyte, the increase in ESR is suppressed compared to the case where it exceeds 76 mmol. Further, as long as the cation component of the solute in the electrolyte is in an amount of 51 mmol or less per 100 g of the electrolyte, for example, compared to the case where it is 76 mmol per 100 g of the electrolyte, the increase in ESR is dramatically suppressed. As long as the cation component of the solute in the electrolyte is in an amount of 25 mmol or less per 100 g of the electrolyte, for example, compared to the case where it is 51 mmol per 100 g of the electrolyte, the increase in ESR is further dramatically suppressed.

[0060] Furthermore, other additives can also be added to the liquid. Examples of the additives include complex compounds of boric acid and polysaccharides (such as mannitol and sorbitol), complex compounds of boric acid and polyols, borates, nitro compounds (such as o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, p-nitrophenol, and p-nitrobenzyl alcohol), and phosphates. These can be used alone or in combination of two or more.

[0061] (Electrode foil)

[0062] The anode foil and the cathode foil are long strip foils made of valve-acting metal. The valve-acting metals include aluminum, tantalum, niobium, niobium oxide, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. Regarding the purity, the anode foil is preferably 99.9% or more, and the cathode foil is preferably about 99% or more, and may contain impurities such as silicon, iron, copper, magnesium, and zinc.

[0063] The anode foil, which is a sintered body formed by sintering powders of valve action metal or an etched foil obtained by subjecting an extended foil to an etching treatment, has a surface with an enlarged area. The enlarged area structure includes tunnel-shaped pits, sponge-shaped pits, or voids between densely packed powders. Typically, the enlarged area structure is formed by applying direct current or alternating current direct etching or alternating current etching in an acidic aqueous solution containing halogen ions such as hydrochloric acid, or by vapor deposition or sintering of metal particles, etc. on the core. Regarding the cathode foil, an enlarged area structure can also be obtained by vapor deposition, sintering, or etching.

[0064] The dielectric oxide film is typically an oxide film formed on the surface layer of the anode foil. As long as the anode foil is made of aluminum, it is alumina formed by oxidizing the porous structure region. The dielectric oxide film is formed by a chemical conversion treatment in which voltage is applied in an aqueous solution of adipic acid, boric acid, phosphoric acid, etc. In addition, a thin dielectric oxide film (about 1V to 10V) can be formed on the surface layer of the cathode foil by chemical conversion treatment as needed. Furthermore, the dielectric oxide film can also be made using a layer formed by vapor deposition method and containing metal nitrides, metal carbides, metal carbonitrides, or having carbon on the surface.

[0065] (Separator)

[0066] Examples of the separator include cellulose such as kraft paper, manila hemp, esparto, hemp, rayon, and mixed papers thereof; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and derivatives thereof; polytetrafluoroethylene resins; polyvinylidene fluoride resins; vinylon resins; polyamide resins such as aliphatic polyamides, semi-aromatic polyamides, and wholly aromatic polyamides; polyimide resins; polyethylene resins; polypropylene resins; trimethylpentene resins; polyphenylene sulfide resins; acrylic resins; polyvinyl alcohol resins, etc. These resins can be used alone or in combination.

[0067] (Solid electrolyte)

[0068] In the case where a solid electrolyte is formed within a capacitor element, the solid electrolyte contains a conductive polymer. The conductive polymer is a conjugated polymer or a doped conjugated polymer. The conjugated polymer is obtained by chemically oxidative polymerization or electrolytic oxidative polymerization of a monomer having a π-conjugated double bond or a derivative thereof. By adding a small amount of an acceptor that easily accepts electrons or a donor that easily donates electrons to the conjugated polymer, conductivity is exhibited. When an acceptor or a donor is added to the conjugated polymer, in the case of the acceptor, π electrons are extracted from the conjugated polymer to generate negative charge carriers (holes); in the case of the donor, electrons are supplied to generate negative charge carriers, exhibiting conductivity.

[0069] As the conjugated polymer, a known conjugated polymer can be used without particular limitation. For example, polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, polybenzene, polyphenylene vinylene, polyacene, polythiophene vinylene, etc. can be mentioned. These conjugated polymers can be used alone, or two or more of them can be combined, and furthermore, they can also be copolymers of two or more monomers.

[0070] Among the conjugated polymers, a conjugated polymer formed by polymerizing thiophene or a derivative thereof is preferred, and a conjugated polymer formed by polymerizing 3,4-ethylenedioxythiophene (i.e., 2,3-dihydrothieno[3,4-b][1,4]dioxin), 3-alkylthiophene, 3-alkoxythiophene, 3-alkyl-4-alkoxythiophene, 3,4-alkylthiophene, 3,4-alkoxythiophene or a derivative thereof is preferred. As the thiophene derivative, a compound selected from thiophenes having substituents at the 3-position and 4-position is preferred, and the substituents at the 3-position and 4-position of the thiophene ring can form a ring together with the carbon at the 3-position and 4-position. The number of carbon atoms of the alkyl or alkoxy group is preferably 1 to 16, and in particular, a polymer of 3,4-ethylenedioxythiophene called EDOT (3,4-ethylene dioxythiophene), that is, poly(3,4-polyethylene dioxythiophene) called PEDOT (Poly(3,4-polyethylene dioxythiophene)) is particularly preferred. In addition, it can also be an alkylated ethylenedioxythiophene in which an alkyl group is added to 3,4-ethylenedioxythiophene. For example, methylated ethylenedioxythiophene (i.e., 2-methyl-2,3-dihydro-thieno[3,4-b][1,4]dioxin), ethylated ethylenedioxythiophene (i.e., 2-ethyl-2,3-dihydro-thieno[3,4-b][1,4]dioxin), etc. can be mentioned.

[0071] The dopant may be a known dopant without particular limitation. For example, inorganic acids such as boric acid, nitric acid, and phosphoric acid can be cited; organic acids such as acetic acid, oxalic acid, citric acid, ascorbic acid, tartaric acid, squaric acid, rhodizonic acid, croconic acid, salicylic acid, p-toluenesulfonic acid, 1,2-dihydroxy-3,5-benzenedisulfonic acid, methanesulfonic acid, trifluoromethanesulfonic acid, boronated disalicylate, bis(oxalato)borate, sulfonylimide acid, dodecylbenzenesulfonic acid, propylnaphthalenesulfonic acid, and butylnaphthalenesulfonic acid. In addition, as polyanions, polyvinylsulfonic acid, polystyrenesulfonic acid, polyallylsulfonic acid, polyacrylic acid sulfonic acid, polymethacrylic acid sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprenesulfonic acid, polyacrylic acid, polymethacrylic acid, and polymaleic acid can be cited.

[0072] These dopants can be used alone or in combination of two or more. In addition, these dopants can be polymers of individual monomers or copolymers of two or more monomers. In addition, high polymers or monomers can also be used as dopants.

[0073] [Examples]

[0074] Hereinafter, the electrolytic capacitor of the present invention will be further described in detail based on examples. Furthermore, the present invention is not limited to the following examples. Resin layers containing epoxy resin compositions are used to coat the sealing members to fabricate various electrolytic capacitors.

[0075] (Examples 1 to 4)

[0076] The electrolytic capacitors of Comparative Example 1 and Examples 1 to 4 are common in that they have an electrolyte using a combination of an electrolytic solution and a solid electrolyte. The differences between Examples 1 to 4 and Comparative Example 1 are the composition of the resin layer and the types of epoxy resin compositions. In addition, the differences between Examples 1 to 4 and Comparative Example 1 are that ethylene glycol or γ-butyrolactone is used as the solvent of the electrolytic solution. Ethylene glycol is an example of a compound having a hydroxyl group.

[0077] The common points of the electrolytic capacitors of Comparative Example 1 and Examples 1 to 3 will be described in detail. The anode foil is an aluminum foil, which is surface-expanded by an etching treatment and a dielectric oxide film is formed by a chemical conversion treatment. The cathode foil is a flat foil, that is, an aluminum foil without an etching treatment. The same anode foil and cathode foil are used for the all-solid electrolytic capacitor, and leads are connected to each of them, and the anode foil and the cathode foil are wound facing each other with a Manila-based separator interposed therebetween. The capacitor element is subjected to a repair chemical conversion by being immersed in an aqueous solution of ammonium dihydrogen phosphate at the same concentration for 10 minutes.

[0078] Next, a dispersion of polyethylenedioxythiophene doped with the same product, polystyrene sulfonic acid (PEDOT / PSS) as a conductive polymer, was prepared at the same concentration, the capacitor element was immersed, and then the capacitor element was lifted and dried at 150 °C for 30 minutes. The immersion and drying were repeated the same number of times. Thus, a solid electrolyte was formed on the capacitor element. Next, different electrolytes were prepared for each electrolytic capacitor, and the capacitor element with the solid electrolyte formed thereon was immersed in the electrolyte. The capacitor element was inserted into a bottomed cylindrical outer package case of the same metal type, the same size, and the same shape, and a sealing member was installed at the open end, and sealed by fastening with the same pressing force. Each electrolytic capacitor used a sealing member made of butadiene rubber.

[0079] Each electrolytic capacitor was housed in an aluminum container of the same size, and a resin layer was formed in such a manner that it was completely embedded with the same type of epoxy resin. However, the lead wire led out from the electrolytic capacitor was led out from the epoxy resin in advance so that the electrolytic capacitor could be energized. Thus, the outer surface of the sealing member of each electrolytic capacitor was completely covered with the epoxy resin composition.

[0080] The electrolytes and the epoxy resin compositions used in the resin layers prepared in the electrolytic capacitors of Comparative Example 1 and Examples 1 to 4 are shown in Table 1 below.

[0081] (Table 1)

[0082]

[0083] As shown in Table 1 above, the electrolytic capacitor of Comparative Example 1 formed a resin layer using an acid anhydride-cured epoxy resin. In contrast, the electrolytic capacitors of Examples 1 and 2 formed a resin layer using an amine-cured epoxy resin. In addition, the electrolytic capacitors of Examples 3 and 4 formed a resin layer using a phenol-cured epoxy resin. The acid anhydride-cured epoxy resin of Comparative Example 1 is an epoxy resin cured with an acid anhydride-based curing agent. The amine-cured epoxy resins of Examples 1 and 2 are epoxy resins cured with an amine-based curing agent. The phenol-cured epoxy resins of Examples 3 and 4 are epoxy resins cured with a phenol-based curing agent.

[0084] In Table 1 above, the composition ratio of the solvent represents the weight ratio relative to the total amount of the solvent. As shown in Table 1 above, in the electrolytic capacitor of Comparative Example 1, while using an acid anhydride-cured epoxy resin in the resin layer, the total amount of the solvent of the electrolytic solution was set to ethylene glycol. In the electrolytic capacitor of Example 1, the total amount of the solvent of the electrolytic solution was ethylene glycol, but an amine-cured epoxy resin was used in the resin layer. In the electrolytic capacitor of Example 2, the total amount of the solvent of the electrolytic solution was γ-butyrolactone, but an amine-cured epoxy resin was used in the resin layer. In the electrolytic capacitor of Example 3, the total amount of the solvent of the electrolytic solution was ethylene glycol, but a phenol-cured epoxy resin was used in the resin layer. In the electrolytic capacitor of Example 4, the total amount of the solvent of the electrolytic solution was γ-butyrolactone, but a phenol-cured epoxy resin was used in the resin layer.

[0085] Each electrolytic capacitor was filled with each epoxy resin composition shown in Table 1 above, and then while applying a constant voltage of 35 V to each electrolytic capacitor, it was placed in a temperature environment of 150 °C for 400 hours. The ESR before and after the thermal stress load was measured. The ESR was measured at 100 kHz. In addition, the inside of each electrolytic capacitor after the thermal stress load was photographed using an X-ray imaging device, and the internal state was observed through the fluoroscopic image.

[0086] The results of the ESR before and after the thermal stress load of each electrolytic capacitor and the internal state obtained from the fluoroscopic image are shown in Table 2 below.

[0087] (Table 2)

[0088]

[0089] As shown in Table 2, in Examples 1 to 4 relative to Comparative Example 1, the difference in ESR became significantly smaller. Relative to Comparative Example 1, the ESR of the group of Examples 1 to 4 was suppressed to a minimum of 1 / 56 and a maximum of about 1 / 74. As a result, it was confirmed that as long as the resin layer is formed of an amine-cured epoxy resin or a phenol-cured epoxy resin, the ESR after the load test is suppressed regardless of the solvent type.

[0090] In addition, as shown in Table 2, compared with Examples 2 and 4 using γ-butyrolactone as the solvent, the increase in ESR of Examples 1 and 3 using ethylene glycol as the solvent was further suppressed. When a solid electrolyte is used as the electrolyte and ethylene glycol is present in the solvent, the conductivity of the conductive polymer is increased by the change in the higher-order structure of the conductive polymer and the reorientation of the crystalline structure of the polymer chain, but γ-butyrolactone cannot achieve such an effect. Therefore, if the solvent is set to ethylene glycol and the resin layer is set to an amine-cured epoxy resin or a phenol-cured epoxy resin, it was confirmed that the ESR was further reduced.

[0091] Here, as shown in Table 2, cracks were generated in the resin layer of the acid anhydride-cured epoxy resin in which the electrolytic capacitor of Comparative Example 1 was filled, based on the fluoroscopic image obtained by the X-ray imaging device. In contrast, no cracks were found in the resin layer of the amine-cured epoxy resin or phenol-cured epoxy resin in which the electrolytic capacitors of Examples 1 to 4 were filled. The fluoroscopic images taken from multiple directions of Comparative Example 1, Example 1, and Example 2 are shown in Figure 1 . As Figure 1 shown, in Comparative Example 1, cracks were observable within the range surrounded by the dashed line. On the other hand, no cracks were present in each of the fluoroscopic images of Example 1 and Example 2. The range where cracks were observable was between the butadiene rubber sealing member and the resin layer of the acid anhydride-cured epoxy resin.

[0092] As a result, it can be understood that if the acid anhydride-cured epoxy resin having an ester bond is used in the resin layer and ethylene glycol, which is a compound having a hydroxyl group, is used as the solvent, the acid anhydride-cured epoxy resin decomposes by hydrolysis, the decomposition products react with the compound having a hydroxyl group, and these reaction products dissolve into the electrolyte, and the components from the resin layer in the electrolyte increase the ESR. Moreover, it was confirmed that by using an amine-cured epoxy resin or a phenol-cured epoxy resin having no ester bond in the resin layer, such hydrolysis reaction of the epoxy resin does not occur, the components from the resin layer do not dissolve into the electrolyte, and the increase in ESR is suppressed.

[0093] (Examples 5 to 12)

[0094] Next, electrolytic capacitors of Examples 5 to 12 were fabricated. In Examples 5 to 12, azelaic acid as an anionic component of the solute was added to the electrolyte, and ammonia as a cationic component of the solute was added to the electrolyte. In the electrolytic capacitors of Examples 5 to 12, the amount of the cationic component in the solute in the electrolyte was different. The electrolytic capacitors of Examples 5 to 12 were housed in an aluminum container of the same size as those of Examples 1 to 4 and were completely embedded using an amine-cured epoxy resin in the same manner as in Example 1. In addition, the electrolytic capacitors of Examples 5 to 12 were fabricated under the same manufacturing method and the same conditions as those of Examples 1 to 4.

[0095] The electrolytic capacitors of Examples 5 to 12 were filled with an amine-cured epoxy resin, and then while applying a constant voltage of 35 V to each electrolytic capacitor, they were placed in a temperature environment of 150 °C for 800 hours. The ESR before and after the thermal stress load was measured, and the change rate of the ESR after the thermal stress load was calculated. The ESR was measured at 100 kHz.

[0096] The compositions and addition amounts of the electrolytes of Examples 5 to 12, the ESR before thermal stress loading (initial ESR), the ESR after thermal stress loading (ESR after test), and the change rate of the ESR after thermal stress loading are shown in Table 3 below. Furthermore, the amount of the solvent in Table 3 represents the content relative to the whole solvent, and the amount of the solute in Table 3 is converted based on every 100 g of the electrolyte. The electrolytic capacitors of Examples 5 to 12 are wound type with a diameter of 6 mm and a total length of 6 mm, a rated voltage of 35 V, and a rated capacitance of 47 μF.

[0097] (Table 3)

[0098]

[0099] As shown in Table 3, for the electrolytic capacitor of Example 12 with 86 mmol of ammonia as the cation component, the change rate of the ESR of the electrolytic capacitor of Example 11 with 76 mmol of ammonia was suppressed to about 55%. Furthermore, for the electrolytic capacitor of Example 11 with 76 mmol of ammonia, the change rate of the ESR of the electrolytic capacitor of Example 10 with 51 mmol of ammonia was suppressed to about 24%. Furthermore, for the electrolytic capacitor of Example 10 with 51 mmol of ammonia, the change rate of the ESR of the electrolytic capacitor of Example 7 with 25 mmol of ammonia was suppressed to about 18%.

[0100] Thus, if the electrolytic capacitor has a resin layer, the cation component tends to promote the dedoping reaction and increase the ESR. However, it was confirmed that by adjusting the cation component to 76 mmol or less per 100 g of the electrolyte, the increase in the ESR can be suppressed, by adjusting the cation component to 51 mmol or less per 100 g of the electrolyte, the increase in the ESR can be further suppressed, and by adjusting the cation component to 25 mmol or less per 100 g of the electrolyte, the ESR after thermal stress loading can be greatly suppressed.

[0101] (Examples 13 to 16)

[0102] Electrolytic capacitors of Examples 13 to 16 were fabricated. The solvents of the electrolytes of Examples 13 to 16 are ethylene glycol, γ-butyrolactone, sulfolane, or a mixed solution of two of these, but the composition ratios are different. In the electrolytic capacitors of Examples 13 to 16, for the purpose of clarifying only the influence of the solvent of the electrolyte, no solute was added. In addition, regarding the electrolytic capacitors of Examples 13 to 16, they are housed in aluminum containers of the same size and completely embedded with resin, and are fabricated using the same manufacturing method and the same conditions as those of Examples 1 to 4. Furthermore, an amine-based cured epoxy resin is used in the resin layer.

[0103] After resin filling, each electrolytic capacitor was placed in a temperature environment of 150°C for 3,500 hours. The amount of electrolyte leakage after the thermal stress load was measured. The amount of electrolyte leakage was obtained by subtracting the weight of the electrolytic capacitor after the thermal stress load from the weight of the electrolytic capacitor before the thermal stress load. The composition and addition amount of the electrolyte in Examples 13 to 16, and the amount of electrolyte leakage after the thermal stress load are shown in Table 4 below. Furthermore, the electrolytic capacitors in each example were wound type with a diameter of 10 mm and a total length of 10 mm.

[0104] (Table 4)

[0105]

[0106] As shown in Table 4, compared with Example 13 in which γ-butyrolactone was used as the solvent of the electrolyte, in Example 14 in which sulfolane was used as the solvent of the electrolyte, the amount of electrolyte leakage was suppressed to less than half. Furthermore, compared with Example 14 in which sulfolane was used as the solvent of the electrolyte, in Example 16 in which ethylene glycol was used as the solvent of the electrolyte, the amount of electrolyte leakage was suppressed to 74%.

Claims

1. An electrolytic capacitor, characterized in that, Comprising: A capacitor element having an anode foil, a cathode foil, a solid electrolyte, and an electrolytic solution; A housing that houses the capacitor element; A sealing member that seals the housing; And A resin layer disposed near the sealing member, The resin layer contains an epoxy resin composition that uses a phenolic hardener or an amine hardener and epoxy resin as raw materials and does not have an ester bond, The cation component in the electrolytic solution contains 34 mmol or less per 100 g of the electrolytic solution.

2. The electrolytic capacitor according to claim 1, wherein The epoxy resin composition has a chemical structure containing a phenolic hardener or an amine hardener and epoxy resin.

3. The electrolytic capacitor according to claim 1 or 2, wherein The electrolytic solution contains at least one of a compound having a hydroxyl group, sulfolane, and γ-butyrolactone.

4. The electrolytic capacitor according to claim 3, wherein The compound having a hydroxyl group is at least one of ethylene glycol, diethylene glycol, and polyethylene glycol.

5. The electrolytic capacitor according to claim 1 or 2, wherein The cation component in the electrolytic solution contains 25 mmol or less per 100 g of the electrolytic solution.

6. The electrolytic capacitor according to claim 3, wherein The cation component in the electrolytic solution contains 25 mmol or less per 100 g of the electrolytic solution.

7. The electrolytic capacitor according to claim 4, wherein The cation component in the electrolytic solution contains 25 mmol or less per 100 g of the electrolytic solution.

Images