electrolytic capacitor

Abstract

The present invention relates to an electrolytic capacitor comprising a resin layer, and provides an electrolytic capacitor in which the chronological increase of ESR is inhibited. This electrolytic capacitor comprises a capacitor element that has an anode foil, a cathode foil, and an electrolyte, a case that accommodates the capacitor element, a sealing member that seals the case, and a resin layer that is disposed proximally to the sealing member. The resin layer disposed proximally to the sealing member includes an epoxy resin composition that does not have an ester bond.

Description

[Technical Field]

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

[0002] Electrolytic capacitors using valve metals such as tantalum or aluminum can achieve a small size and large capacitance by enlarging the surface area of ​​the dielectric by forming the valve metal as a sintered body or etched foil as the anode-side counter electrode. This type of electrolytic capacitor is constructed by filling the gaps with electrolyte to ensure close contact between the anode's dielectric oxide film and the counter electrode. Specifically, electrolytic capacitors include liquid electrolytic capacitors containing only an electrolyte, hybrid electrolytic capacitors containing both an electrolyte and a solid electrolyte, and bipolar electrolytic capacitors with a dielectric film formed on both electrodes.

[0003] The electrolyte uses ethylene glycol or gamma-butyrolactone as a solvent and contains a carboxylic acid or its salt, such as 1,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, or azelaic acid, as a solute. This electrolyte directly contacts the dielectric film, acting as a true cathode and repairing the dielectric film. However, over time, the electrolyte evaporates and escapes from the electrolytic capacitor. As a result, the electrolytic capacitor dries out, its capacitance decreases over time, its dissipation factor (tanδ) increases over time, and it eventually reaches the end of its life.

[0004] Therefore, the capacitor element is housed in a bottomed outer case, and the opening of the outer case is sealed with a sealing material to seal in the electrolyte impregnated in the capacitor element, suppress evaporation of the electrolyte, and extend the capacitor's lifespan. However, elastomers such as butyl rubber and ethylene propylene diene rubber (EPDM) are used for the sealing material. Therefore, the electrolyte is not completely contained within the case, but rather permeates the sealing material and gradually volatilizes to the outside of the electrolytic capacitor. Therefore, as in Patent Document 1, a proposal has been made to cover the sealing material with a resin layer to suppress evaporation of the electrolyte due to permeation through the sealing material.

[0005] Resin layers generally have excellent thermal insulation properties. As the thermal insulation properties of electrolytic capacitors increase, it becomes more difficult to dissipate heat generated within the case, making it easier for heat to accumulate. Therefore, Patent Document 2 proposes the use of ethylene glycol as a solvent for the electrolyte. This is because ethylene glycol has a thermal conductivity approximately twice as high as that of γ-butyrolactone or sulfolane. Patent Document 2 suggests that the higher the proportion of ethylene glycol in the solvent, the higher the thermal conductivity. However, it also suggests that the ethylene glycol content should be 90% by mass or less in order to allow for the inclusion of other types of solvents. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 60-245106 [Patent Document 2] WO2018 / 123525 Summary of the Invention [Problem to be solved by the invention]

[0007] The resin layer contains a curable resin composition. Examples of the curable resin composition include an epoxy resin composition containing an epoxy resin and an acid anhydride curing agent. The epoxy resin composition is a composition of epoxy resin cured with an acid anhydride curing agent. Epoxy resin compositions containing an acid anhydride curing agent have improved heat resistance, and because the reaction temperature between the epoxy resin and the acid anhydride curing agent is 100°C or higher, the curing reaction can be accelerated using temperature as a trigger. Therefore, epoxy resin compositions containing an epoxy resin and an acid anhydride curing agent are considered to be suitable for the resin layer.

[0008] The inventors formed a resin layer on a part of an electrolytic capacitor using an epoxy resin cured with an acid anhydride curing agent. Then, they exposed this electrolytic capacitor to a temperature environment of 150°C. They confirmed that the ESR of the electrolytic capacitor exposed to this temperature environment for 400 hours increased significantly.

[0009] The present invention has been proposed to solve the above-mentioned problems, and its purpose is to provide an electrolytic capacitor having a resin layer in which the increase in ESR over time is suppressed. [Means for solving the problem]

[0010] As a result of extensive research, the present inventors have found that the increase in ESR over time of an electrolytic capacitor is significant when the capacitor is provided with an epoxy resin composition containing an epoxy resin and an acid anhydride curing agent (hereinafter referred to as acid anhydride-cured epoxy resin) and when ethylene glycol is used as a solvent for the electrolyte.

[0011] As a result of extensive research based on this knowledge, the inventors have discovered that acid anhydride-cured epoxy resin reacts with water and ethylene glycol, decomposes, and dissolves into the electrolyte, and that the presence of acid anhydride-cured epoxy resin in the electrolyte is the cause of the increase in ESR of electrolytic capacitors.

[0012] Here, the acid anhydride-cured epoxy resin contains an ester bond in its chemical structure. Even when water is not intentionally added to electrolytic capacitors, a small amount of water may be mixed into the electrolytic capacitor during the manufacturing process. Ethylene glycol is a compound containing a hydroxyl group, and compounds containing a hydroxyl group have a structure that makes them easily accessible to water. Under these circumstances, when the compound containing a hydroxyl group permeates the sealing material, water also permeates. The ester bond in the acid anhydride-cured epoxy resin reacts with water, resulting in hydrolysis of the acid anhydride-cured epoxy resin. Furthermore, an esterification reaction occurs between the carbonyl group generated by hydrolysis and the compound containing a hydroxyl group. It is believed that, in this way, some of the acid anhydride-cured epoxy resin components that reacted with water or the compound containing a hydroxyl group permeated the sealing material and leached into the electrolyte.

[0013] The present invention was made based on this finding, and provides an electrolytic capacitor comprising: a capacitor element having an anode foil, a cathode foil, and an electrolyte; a case that houses the capacitor element; a sealing member that seals the case; and a resin layer that is disposed in the vicinity of the sealing member, wherein the resin layer contains an epoxy resin composition that does not have an ester bond.

[0014] The epoxy resin composition may be made from a phenolic or amine-based curing agent and an epoxy resin as raw materials, or may have a chemical structure containing the phenolic or amine-based curing agent and the epoxy resin.

[0015] The electrolytic solution may contain at least one of a compound having a hydroxy group, sulfolane, and γ-butyrolactone.

[0016] The compound having a hydroxy group may be at least one of ethylene glycol, diethylene glycol, and polyethylene glycol.

[0017] The capacitor element may further include a solid electrolyte.

[0018] The electrolyte solution may contain 76 mmol or less of cationic components per 100 g of the electrolyte solution, or 25 mmol or less of cationic components per 100 g of the electrolyte solution. [Effects of the Invention]

[0019] According to the present invention, it is possible to suppress an increase in ESR over time in an electrolytic capacitor provided with a resin layer. [Brief explanation of the drawings]

[0020] [Figure 1] 10 shows fluoroscopic images taken from a plurality of directions in Comparative Example 1, Example 1, and Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, electrolytic capacitors according to embodiments of the present invention will be described, but the present invention is not limited to the embodiments described below.

[0022] (Overall composition) Electrolytic capacitors are passive devices that store and discharge electric charge through capacitance. These include liquid electrolytic capacitors, which contain only an electrolyte solution, and hybrid electrolytic capacitors, which combine an electrolyte solution with a solid electrolyte such as a conductive polymer or gel. These also include electrolytic capacitors with a dielectric oxide film intentionally formed only on the anode side and bipolar electrolytic capacitors, which have a dielectric oxide film formed on both electrodes. Furthermore, these electrolytic capacitors include electrolytic capacitors with lead terminals, electrolytic capacitors that are surface-mounted on a board with a base, and electrolytic capacitors that are completely coated with resin along with other electronic circuit components. Hereinafter, these various combinations of electrolytic capacitors will be collectively referred to as "electrolytic capacitors."

[0023] An electrolytic capacitor has a capacitor element, a case, and a sealing member. The case houses the capacitor element. The sealing member is attached to the opening of the case by crimping, sealing the opening. The capacitor element includes an anode foil, a cathode foil, a separator, and an electrolyte. The anode foil and the cathode foil face each other via the separator. A dielectric oxide film is formed on the surface of the anode foil. A dielectric oxide film is also formed on the cathode foil, if necessary. In addition to the electrolyte, a solid electrolyte may be contained. The solid electrolyte is interposed between the anode foil and the cathode foil and is in close contact with the dielectric oxide film. The electrolyte is filled in the gaps in the capacitor element. The electrolytic capacitor may also have a base, if necessary.

[0024] (Sealing member) The sealing member is attached to the case by crimping. The case is made of aluminum, an aluminum alloy containing aluminum or manganese, or stainless steel, and is, for example, a cylindrical body with a bottom and an open end. During crimping, the opening of the case is bent inward and crushed, thereby tightly sealing the case to the sealing member. The elastic sealing member is a plate made of an elastomer, or a plate made by laminating a synthetic resin plate or a metal plate to an elastomer. The elastomer adheres to the crimped case by its elasticity, maintaining the airtightness of the case. However, sealing members containing elastomers have a non-zero permeability to volatilized electrolyte. Examples of such elastomers include butyl rubber, ethylene propylene diene rubber (EPDM), silicone rubber, and butyl rubber.

[0025] (resin layer) The electrolytic capacitor further includes a resin layer. The resin layer suppresses evaporation of the electrolyte. That is, the resin layer may be provided anywhere in the electrolytic capacitor near the sealing member through which the electrolyte may pass. For example, the resin layer covers at least a portion of the surface of the sealing member. This resin layer is molded to cover the sealing member and reduce the permeability of the electrolyte through the sealing member. That is, "nearby" does not necessarily mean being spaced apart, and also includes a contact arrangement. Furthermore, for example, if the electrolytic capacitor is a chip type with a base, the resin layer is provided near the sealing member, for example, at or around the contact point between the base and the case. The resin layer suppresses evaporation of the electrolyte that has passed through the sealing member. In other words, this resin layer may also react with water or ethylene glycol in the electrolyte that has passed through the sealing member and dissolve into the electrolyte through the sealing member.

[0026] This resin layer does not use an acid anhydride cured epoxy resin, but is made of a phenolic cured epoxy resin or an amine cured epoxy resin, and may contain a compound other than the phenolic cured epoxy resin or the amine cured epoxy resin.

[0027] Phenolic-cured epoxy resins are epoxy resins cured with a phenolic curing agent, and are epoxy resin compositions made from a phenolic curing agent and an epoxy resin and containing the phenolic curing agent and the epoxy resin in their chemical structure. Amine-cured epoxy resins are epoxy resins cured with an amine-curing agent, and are epoxy resin compositions made from an amine-curing agent and an epoxy resin and containing the amine-curing agent and the epoxy resin in their chemical structure. While acid anhydride-cured epoxy resins have ester bonds in their chemical structure, the acid anhydride-cured epoxy resins of these phenolic-cured epoxy resins and amine-cured epoxy resins do not have ester bonds in their chemical structure.

[0028] Specifically, phenol-based cured epoxy resins are produced by the reaction of phenolic hydroxyl groups in phenol-based curing agents with epoxy groups, while amine-based cured epoxy resins are produced by the reaction of amino groups in amine-based curing agents with epoxy groups, forming bonds. The bond between these curing agents and epoxy resins is an ether bond, which is not susceptible to hydrolysis.

[0029] As can be seen from this reaction system, an epoxy resin composition containing a phenolic curing agent and an epoxy resin in its chemical structure does not mean an epoxy resin composition in which they are incorporated into the chemical structure in the same state as before the reaction. Including a phenolic curing agent and an epoxy resin in its chemical structure means that they are incorporated into the chemical structure after substitution of each group for bonding. Furthermore, as can be seen from this reaction system, an epoxy resin composition containing an amine curing agent and an epoxy resin in its chemical structure does not mean an epoxy resin composition in which they are incorporated into the chemical structure in the same state as before the reaction. Including an amine curing agent and an epoxy resin in its chemical structure means that they are incorporated into the chemical structure after substitution of each group for bonding.

[0030] The epoxy resins contained in phenol-cured epoxy resins and amine-cured epoxy resins are epoxy oligomers with two or more reactive epoxy groups at the terminals. These epoxy resins undergo an addition reaction with an acid anhydride curing agent, crosslinking the epoxy resin components and converting them from a liquid to a solid resin. Typical examples of epoxy resins include bisphenol A diglycidyl ether, a condensation product of bisphenol A and epichlorohydrin. Other examples of epoxy resins include other glycidyl-type epoxy resins and alicyclic epoxides such as 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate.

[0031] Glycidyl epoxy resins include bisphenol types obtained by glycidylating bisphenols, such as bisphenol A, bisphenol F, bisphenol AD, bisphenol S, tetramethylbisphenol A, tetramethylbisphenol F, tetramethylbisphenol AD, tetramethylbisphenol S, tetrabromobisphenol A, tetrachlorobisphenol A, and tetrafluorobisphenol A.

[0032] Glycidyl epoxy resins include epoxy resins obtained by glycidylating dihydric phenols, such as biphenol, dihydroxynaphthalene, and 9,9-bis(4-hydroxyphenyl)fluorene.

[0033] Glycidyl epoxy resins include epoxy resins obtained by glycidylating trisphenols. Triphenols include 1,1,1-tris(4-hydroxyphenyl)methane and 4,4-(1-(4-(1-(4-hydroxyphenyl)-1-methylethyl)phenyl)ethylidene)bisphenol.

[0034] Glycidyl epoxy resins include epoxy resins obtained by glycidylating tetrakisphenols, such as 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane.

[0035] The glycidyl epoxy resins include novolac epoxy resins obtained by glycidylating novolacs, such as phenol novolac, cresol novolac, bisphenol A novolac, brominated phenol novolac, and brominated bisphenol A novolac.

[0036] 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 glycerin and polyethylene glycol.

[0037] Examples of glycidyl epoxy resins include ether ester epoxy resins obtained by glycidylating hydroxycarboxylic acids, ester epoxy resins obtained by glycidylating polycarboxylic acids, glycidyl compounds of amine compounds, and amine epoxy resins. Examples of hydroxycarboxylic acids include p-oxybenzoic acid and β-oxynaphthoic acid. Examples of polycarboxylic acids include phthalic acid and terephthalic acid. Examples of amine compounds include 4,4-diaminodiphenylmethane and m-aminophenol. Examples of amine epoxy resins include triglycidyl isocyanurate.

[0038] The phenolic curing agent contained in the phenolic cured epoxy resin may be a bifunctional phenol or a polyfunctional phenol. Examples of the bifunctional phenol include hydroquinone, resorcinol, bisphenol F, biphenol, tetrabromobisphenol A, and naphthalenediol. Examples of the polyfunctional phenol include phenol novolac resin.

[0039] Examples of amine-based curing agents contained in amine-based cured epoxy resins include aliphatic polyamines, aromatic polyamines, and modified amines. Examples of aliphatic polyamines include diethylenetriamine and triethylenetetramine. Examples of aromatic polyamines include metaphenylenediamine, diaminodiphenylmethane, and diaminodiphenylsulfone. Examples of modified amines include amine adducts and ketimines.

[0040] (Capacitor element) (electrolyte) The electrolyte to be impregnated into the capacitor element may be, for example, a solution of an ionically dissociable salt that dissociates into an anion component and a cation component, or a solvent that does not contain an ionically dissociable salt. Examples of the solvent include compounds having a hydroxyl group, cyclic lactones, and sulfone compounds. Examples of the compound having a hydroxyl group include protic organic polar solvents. Examples of the protic organic solvent include monohydric alcohols, polyhydric alcohols, and oxyalcohol compounds. Examples of the monohydric alcohols include ethanol, propanol, butanol, pentanol, hexanol, cyclobutanol, cyclopentanol, cyclohexanol, and benzyl alcohol. Examples of the polyhydric alcohols and oxyalcohol compounds include ethylene glycol, diethylene glycol, propylene glycol, glycerin, methyl cellosolve, ethyl cellosolve, methoxypropylene glycol, dimethoxypropanol, and alkylene oxide adducts of polyhydric alcohols such as polyethylene glycol and polyoxyethylene glycerin. Examples of cyclic lactones include γ-butyrolactone, γ-valerolactone, and δ-valerolactone. Examples of sulfone compounds include chain sulfones and cyclic sulfones. Examples of chain sulfones include dimethyl sulfone, diethyl sulfone, dipropyl sulfone, and diphenyl sulfone. Examples of cyclic sulfones include sulfolane, 3-methyl sulfolane, and 2,4-dimethyl sulfolane.

[0041] Here, the resin layer of the sealing member is a phenolic cured epoxy resin or an amine cured epoxy resin. Phenolic cured epoxy resins and amine cured epoxy resins do not have ester bonds. Therefore, even if the solvent of the electrolytic solution contains a compound having a hydroxy group, the phenolic cured epoxy resin and the amine cured epoxy resin are not decomposed by the compound having a hydroxy group. Therefore, even if the solvent of the electrolytic solution contains a compound having a hydroxy group, if the resin layer of the sealing member is a phenolic cured epoxy resin or an amine cured epoxy resin, the resin component will not leach into the electrolytic solution, and an increase in the ESR of the electrolytic capacitor over time will be suppressed.

[0042] Furthermore, when an electrolyte solution using ethylene glycol as a solvent is used in combination with a solid electrolyte, the electrical conductivity of the conductive polymer is improved by changing the higher-order structure of the conductive polymer and reorienting the crystalline structure of the polymer chain. Cyclic lactones improve ESR characteristics at low temperatures. Sulfone compounds have a high boiling point, which suppresses evaporation of the electrolyte solution and improves high-temperature characteristics. Ethylene glycol is particularly preferred as a solvent.

[0043] From the viewpoint of preventing the electrolyte from leaking out of the electrolytic capacitor through the resin layer, the solvent for the electrolyte is preferably ethylene glycol, and secondly, sulfolane. A mixed solvent of ethylene glycol and sulfolane may also be used for the electrolyte.

[0044] Examples of organic acids that serve as anionic solutes include carboxylic acids such as 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, enanthic 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, and pyromellitic acid, as well as phenols and sulfonic acids. Examples of inorganic acids include boric acid, phosphoric acid, phosphorous acid, hypophosphorous acid, carbonic acid, and silicic acid. Examples of composite compounds of organic acids and inorganic acids include borodisalicylic acid, borodioxalic acid, borodiglycolic acid, borodimalonic acid, borodisuccinic acid, borodiadipic acid, borodiazelaic acid, borodibenzoic acid, borodimaleic acid, borodilactic acid, borodimalic acid, boroditartaric acid, borodicitric acid, borodiphthalic acid, borodi(2-hydroxy)isobutyric acid, borodiresorcylic acid, borodimethylsalicylic acid, borodinaphthoic acid, borodimandelic acid, and borodi(3-hydroxy)propionic acid.

[0045] Furthermore, examples of at least one salt of an organic acid, an inorganic acid, or a composite compound of an organic acid and an inorganic acid include ammonium salts, quaternary ammonium salts, quaternized amidinium salts, amine salts, sodium salts, and potassium salts. Examples of quaternary ammonium ions of quaternary ammonium salts include tetramethylammonium, triethylmethylammonium, and tetraethylammonium. Examples of quaternized amidinium salts include ethyldimethylimidazolinium and tetramethylimidazolinium. Examples of amine salts include salts of primary amines, secondary amines, and tertiary amines. Examples of primary amines include methylamine, ethylamine, and propylamine. Examples of secondary amines include dimethylamine, diethylamine, ethylmethylamine, and dibutylamine. Examples of tertiary amines include trimethylamine, triethylamine, tributylamine, ethyldimethylamine, and ethyldiisopropylamine.

[0046] The cationic component of the solute is preferably added in an amount of 76 mmol or less per 100 g of electrolyte, more preferably 51 mmol or less per 100 g of electrolyte, even more preferably 34 mmol or less per 100 g of electrolyte, particularly preferably 25 mmol or less per 100 g of electrolyte, and most preferably 17 mmol or less per 100 g of electrolyte. The ratio of the cationic component to the anionic component of the solute may be equimolar, or there may be an excess of the cationic component or the anionic component.

[0047] Cationic components easily accelerate the dedoping reaction of conductive polymers in the solid electrolyte under high-heat environments, such as during the reflow process when mounting electrolytic capacitors. When the dedoping reaction is accelerated by cationic components, the electrical conductivity of the solid electrolyte decreases, and the ESR of the electrolytic capacitor increases. On the other hand, when a resin layer is placed near the sealing material, the resin layer prevents the cationic components from evaporating through the sealing material, suppressing the decrease in cationic components in the electrolytic capacitor. Therefore, when a resin layer is placed near the sealing material, dedoping reactions caused by cationic components occur frequently, and the ESR of the electrolytic capacitor increases.

[0048] However, if the amount of the cationic solute in the electrolyte is 76 mmol or less per 100 g of electrolyte, the increase in ESR is suppressed compared to when the amount exceeds 76 mmol. Furthermore, if the amount of the cationic solute in the electrolyte is 51 mmol or less per 100 g of electrolyte, the increase in ESR is dramatically suppressed compared to when the amount is, for example, 76 mmol per 100 g of electrolyte. If the amount of the cationic solute in the electrolyte is 25 mmol or less per 100 g of electrolyte, the increase in ESR is even more dramatically suppressed compared to when the amount is, for example, 51 mmol per 100 g of electrolyte.

[0049] Furthermore, other additives can be added to the liquid. Examples of additives include complex compounds of boric acid and polysaccharides (mannitol, sorbitol, etc.), complex compounds of boric acid and polyhydric alcohols, boric acid esters, nitro compounds (o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, p-nitrophenol, p-nitrobenzyl alcohol, etc.), and phosphate esters. These may be used alone or in combination of two or more.

[0050] (electrode foil) The anode foil and cathode foil are long foils made of valve metals such as aluminum, tantalum, niobium, niobium oxide, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. The purity of the anode foil is preferably 99.9% or higher, and that of the cathode foil is preferably about 99% or higher, but impurities such as silicon, iron, copper, magnesium, and zinc may be included.

[0051] The anode foil has an enlarged surface, either as a sintered body made by sintering valve metal powder or as an etched foil made by etching a drawn foil. The enlarged surface structure is formed by tunnel-like pits, spongy pits, or voids between densely packed powder particles. The enlarged surface structure is typically formed by direct current etching or alternating current etching, in which direct current or alternating current is applied in an acidic aqueous solution containing halogen ions, such as hydrochloric acid, or by vapor deposition or sintering metal particles or the like into the core. The cathode foil may also have an enlarged surface structure by vapor deposition, sintering, or etching.

[0052] The dielectric oxide film is typically an oxide film formed on the surface of the anode foil. If the anode foil is made of aluminum, it is aluminum oxide formed by oxidizing the porous structure region. This dielectric oxide film is formed by chemical conversion treatment in which a voltage is applied in an aqueous solution of adipic acid, boric acid, phosphoric acid, or the like. Alternatively, a thin dielectric oxide film (approximately 1 to 10 V) may be formed on the surface of the cathode foil by chemical conversion treatment, as needed. Furthermore, the dielectric oxide film may be formed by using a layer made of a metal nitride, metal carbide, or metal carbonitride formed by vapor deposition, or by using a material containing carbon on the surface.

[0053] (separator) Examples of materials for the separator include cellulose papers such as kraft, Manila hemp, esparto, hemp, and rayon, and mixtures thereof; polyester-based resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and derivatives thereof; polytetrafluoroethylene-based resins, polyvinylidene fluoride-based resins, vinylon-based resins; polyamide-based resins such as aliphatic polyamides, semi-aromatic polyamides, and wholly aromatic polyamides; polyimide-based resins, polyethylene resins, polypropylene resins, trimethylpentene resins, polyphenylene sulfide resins, acrylic resins, and polyvinyl alcohol resins. These resins can be used alone or in combination.

[0054] (solid electrolyte) When a solid electrolyte is formed within a capacitor element, it includes a conductive polymer. Conductive polymers are conjugated polymers or doped conjugated polymers. Conjugated polymers are obtained by chemical oxidative polymerization or electrolytic oxidative polymerization of monomers or their derivatives that have π-conjugated double bonds. Conductivity is exhibited by adding a small amount of an acceptor that easily accepts electrons or a donor that easily donates electrons to a conjugated polymer. When an acceptor or donor is added to a conjugated polymer, the acceptor extracts π electrons from the conjugated polymer, creating negatively charged atoms (positive holes), while the donor supplies electrons, creating negatively charged carriers, thereby exhibiting conductivity.

[0055] As the conjugated polymer, any known polymer can be used without any particular limitation. Examples include polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, polythiophene vinylene, etc. These conjugated polymers may be used alone or in combination of two or more types, or may even be a copolymer of two or more types of monomers.

[0056] Among the above conjugated polymers, conjugated polymers obtained by polymerizing thiophene or its derivatives are preferred, and conjugated polymers obtained 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 derivatives thereof are preferred. Thiophene derivatives are preferably compounds selected from thiophenes having substituents at the 3rd and 4th positions, and the substituents at the 3rd and 4th positions of the thiophene ring may form a ring together with the carbon atoms at the 3rd and 4th positions. Alkyl or alkoxy groups having 1 to 16 carbon atoms are suitable, and a polymer of 3,4-ethylenedioxythiophene known as EDOT, i.e., poly(3,4-ethylenedioxythiophene) known as PEDOT, is particularly preferred. Alternatively, alkylated ethylenedioxythiophenes in which an alkyl group is added to 3,4-ethylenedioxythiophene may be used, such as methylated ethylenedioxythiophene (i.e., 2-methyl-2,3-dihydro-thieno[3,4-b][1,4]dioxine) and ethylated ethylenedioxythiophene (i.e., 2-ethyl-2,3-dihydro-thieno[3,4-b][1,4]dioxine).

[0057] Known dopants can be used without any particular limitation. Examples of dopants include inorganic acids such as boric acid, nitric acid, and phosphoric acid, and organic acids such as acetic acid, oxalic acid, citric acid, ascot 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, borodisalicylic acid, bisoxalateborate acid, sulfonylimide acid, dodecylbenzenesulfonic acid, propylnaphthalenesulfonic acid, and butylnaphthalenesulfonic acid. Examples of polyanions include polyvinylsulfonic acid, polystyrenesulfonic acid, polyallylsulfonic acid, polyacrylicsulfonic acid, polymethacrylic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprenesulfonic acid, polyacrylic acid, polymethacrylic acid, and polymaleic acid.

[0058] These dopants may be used alone or in combination of two or more. Furthermore, these dopants may be polymers of a single monomer or copolymers of two or more monomers. Furthermore, the dopants may be polymers or monomers. [Example]

[0059] The electrolytic capacitor of the present invention will be described in more detail below based on examples. However, the present invention is not limited to the following examples. Various electrolytic capacitors were produced by coating a sealing member with a resin layer containing an epoxy resin composition.

[0060] (Examples 1 to 4) The electrolytic capacitors of Comparative Example 1 and Examples 1 to 4 have in common the fact that they contain an electrolyte that combines a liquid electrolyte and a solid electrolyte. Examples 1 to 4 differ from Comparative Example 1 in the composition of the resin layer, that is, the type of epoxy resin composition. Examples 1 to 4 also differ from Comparative Example 1 in that ethylene glycol or γ-butyrolactone is used as the solvent for the electrolyte. Ethylene glycol is an example of a compound having a hydroxy group.

[0061] The commonalities between the electrolytic capacitors of Comparative Example 1 and Examples 1 to 3 are detailed below. The anode foil was an aluminum foil, which was enlarged by etching and then subjected to a chemical conversion treatment to form a dielectric oxide film. The cathode foil was a plain foil, i.e., an unetched aluminum foil. The same anode and cathode foils were used in all electrolytic capacitors, and lead wires were connected to each. The anode and cathode foils were wound facing each other with a manila separator interposed between them. The capacitor elements were repaired by immersing them in an ammonium dihydrogen phosphate aqueous solution of the same concentration for 10 minutes.

[0062] Next, a dispersion of the same conductive polymer, polyethylenedioxythiophene doped with polystyrene sulfonic acid (PEDOT / PSS), was prepared at the same concentration. The capacitor elements were immersed in the dispersion, removed, and dried at 150°C for 30 minutes. The immersion and drying process was repeated the same number of times. This formed a solid electrolyte in the capacitor elements. Next, a different electrolyte solution was prepared for each electrolytic capacitor, and the capacitor elements with the solid electrolyte formed were immersed in the electrolyte solution. This capacitor element was inserted into a bottomed cylindrical outer case of the same metal type, dimensions, and shape. A sealing material was attached to the open end and the capacitors were sealed by crimping with the same pressure. A sealing material made of butadiene rubber was used for each electrolytic capacitor.

[0063] Each electrolytic capacitor was housed in an aluminum container of the same dimensions, and a resin layer was formed so that it was completely embedded in the same type of epoxy resin. However, the lead wires leading from the electrolytic capacitor were pulled out of the epoxy resin so that electricity could be passed through the electrolytic capacitor. As a result, the outer surface of the sealing member of each electrolytic capacitor was completely covered with the epoxy resin composition.

[0064] The electrolyte solutions prepared in the electrolytic capacitors of Comparative Example 1 and Examples 1 to 4 and the epoxy resin compositions used in the resin layers are as shown in Table 1 below. (Table 1) TIFF0007768123000001.tif46165

[0065] As shown in Table 1 above, the electrolytic capacitor of Comparative Example 1 has a resin layer formed using an acid anhydride-cured epoxy resin. In contrast, the electrolytic capacitors of Examples 1 and 2 have a resin layer formed using an amine-cured epoxy resin. Furthermore, the electrolytic capacitors of Examples 3 and 4 have a resin layer formed 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-curing agent. The amine-cured epoxy resin of Examples 1 and 2 is an epoxy resin cured with an amine-curing agent. The phenol-cured epoxy resin of Examples 3 and 4 is an epoxy resin cured with a phenol-curing agent.

[0066] In Table 1 above, the composition ratio of the solvent indicates the weight ratio relative to the total amount of solvent. As shown in Table 1 above, the electrolytic capacitor of Comparative Example 1 uses an acid anhydride-cured epoxy resin in the resin layer, while the total amount of solvent in the electrolyte is ethylene glycol. The electrolytic capacitor of Example 1 uses ethylene glycol in the total amount of solvent in the electrolyte, but uses an amine-based cured epoxy resin in the resin layer. The electrolytic capacitor of Example 2 uses gamma-butyrolactone in the total amount of solvent in the electrolyte, but uses an amine-based cured epoxy resin in the resin layer. The electrolytic capacitor of Example 3 uses ethylene glycol in the total amount of solvent in the electrolyte, but uses a phenol-based cured epoxy resin in the resin layer. The electrolytic capacitor of Example 4 uses gamma-butyrolactone in the total amount of solvent in the electrolyte, but uses a phenol-based cured epoxy resin in the resin layer.

[0067] Each electrolytic capacitor was filled with the epoxy resin composition shown in Table 1 above, and then left at 150°C for 400 hours while a constant voltage of 35 V was applied to each electrolytic capacitor. The ESR was measured before and after this thermal stress. The ESR was measured at 100 kHz. In addition, the inside of each electrolytic capacitor after the thermal stress was photographed with an X-ray device, and the internal condition was observed using a fluoroscopic image.

[0068] The ESR and internal condition of each electrolytic capacitor before and after thermal stress loading, as well as the results of fluoroscopic images, are shown in Table 2 below. (Table 2) TIFF0007768123000002.tif30161

[0069] As shown in Table 2, the ESR of Examples 1 to 4 is significantly smaller than that of Comparative Example 1. The ESR of Examples 1 to 4 was suppressed to at least 1 / 56 and at most approximately 1 / 74 of that of Comparative Example 1. As a result, it was confirmed that the ESR after the load test is suppressed as long as the resin layer is formed from an amine-based cured epoxy resin or a phenol-based cured epoxy resin, regardless of the solvent type.

[0070] Furthermore, as shown in Table 2, in Examples 1 and 3, in which ethylene glycol was used as the solvent, the increase in ESR was more suppressed than in Examples 2 and 4, in which γ-butyrolactone was used as the solvent. When ethylene glycol is used as the solvent in combination with a solid electrolyte, the higher-order structure of the conductive polymer changes and the crystalline structure of the polymer chains is reoriented, thereby improving the electrical conductivity of the conductive polymer; however, this effect cannot be obtained with γ-butyrolactone. Therefore, it was confirmed that the ESR could be further reduced by using ethylene glycol as the solvent and an amine-based cured epoxy resin or a phenol-based cured epoxy resin for the resin layer.

[0071] Here, as shown in Table 2, fluoroscopic images taken with an X-ray device revealed that cracks had occurred in the resin layer of acid anhydride-cured epoxy resin in which the electrolytic capacitor of Comparative Example 1 was embedded. In contrast, no cracks were found in the resin layers of amine-cured epoxy resin or phenol-cured epoxy resin in which the electrolytic capacitors of Examples 1 to 4 were embedded. Fluoroscopic images taken from multiple directions of Comparative Example 1, Example 1, and Example 2 are shown in Figure 1. As shown in Figure 1, cracks are visible in the area surrounded by the dotted line in Comparative Example 1. On the other hand, no cracks are found in the fluoroscopic images of Examples 1 and 2. The area in which cracks were visible was between the butadiene rubber sealing member and the resin layer of acid anhydride-cured epoxy resin.

[0072] As a result, it can be understood that when an acid anhydride-cured epoxy resin having an ester bond is used for the resin layer and ethylene glycol, a compound having a hydroxy group, is used as the solvent, the acid anhydride-cured epoxy resin decomposes due to hydrolysis, the decomposition products react with the compound having a hydroxy group, these reaction products dissolve into the electrolyte, and the components derived from the resin layer in the electrolyte increase the ESR.Furthermore, it was confirmed that when an amine-based cured epoxy resin or a phenol-based cured epoxy resin without an ester bond is used for the resin layer, such hydrolysis reaction of the epoxy resin does not occur, components derived from the resin layer do not dissolve into the electrolyte, and the increase in ESR is suppressed.

[0073] Examples 5 to 12 Next, electrolytic capacitors of Examples 5 to 12 were fabricated. In Examples 5 to 12, azelaic acid was added to the electrolyte as the anionic solute component, and ammonia was added to the electrolyte as the cationic solute component. The electrolytic capacitors of Examples 5 to 12 differed in the amount of cationic solute component in the electrolyte. The electrolytic capacitors of Examples 5 to 12 were housed in aluminum containers of the same dimensions as Examples 1 to 4 and completely embedded in the same amine-based cured epoxy resin as Example 1. Additionally, the electrolytic capacitors of Examples 5 to 12 were fabricated using the same manufacturing method and under the same conditions as Examples 1 to 4.

[0074] The electrolytic capacitors of Examples 5 to 12 were filled with an amine-based curing epoxy resin, and then left in a temperature environment of 150°C for 800 hours while applying a constant voltage of 35V to each electrolytic capacitor. The ESR was measured before and after this thermal stress load, and the rate of change in ESR after the thermal stress load was calculated. The ESR was measured at 100 kHz.

[0075] The compositions and amounts of the electrolytes of Examples 5 to 12, as well as the ESR before thermal stress (initial ESR), the ESR after thermal stress (post-test ESR), and the rate of change in ESR after thermal stress are shown in Table 3 below. The amount of solvent in Table 3 indicates the content relative to the total solvent, and the amount of solute in Table 3 is converted per 100 g of electrolyte. The electrolytic capacitors of Examples 5 to 12 were wound types with a diameter of 6 mm and a total length of 6 mm, with a rated voltage of 35 V and a rated capacitance of 47 μF. (Table 3) TIFF0007768123000003.tif76166

[0076] As shown in Table 3, the electrolytic capacitor of Example 11, which contained 76 mmol of ammonia as a cationic component, had an ESR change rate suppressed to about 55% compared to the electrolytic capacitor of Example 12, which contained 86 mmol of ammonia. Furthermore, the electrolytic capacitor of Example 10, which contained 51 mmol of ammonia, had an ESR change rate suppressed to about 24% compared to the electrolytic capacitor of Example 11, which contained 76 mmol of ammonia. Furthermore, the electrolytic capacitor of Example 7, which contained 25 mmol of ammonia, had an ESR change rate suppressed to about 18% compared to the electrolytic capacitor of Example 10, which contained 51 mmol of ammonia.

[0077] Thus, when an electrolytic capacitor has a resin layer, the cationic components tend to promote the undoping reaction and increase the ESR. However, it was confirmed that the increase in ESR can be suppressed by adjusting the cationic components to 76 mmol or less per 100 g of electrolyte, that the increase in ESR can be further suppressed by adjusting the cationic components to 51 mmol or less per 100 g of electrolyte, and that the ESR after thermal stress can be significantly suppressed by adjusting the cationic components to 25 mmol or less per 100 g of electrolyte.

[0078] (Examples 13 to 16) Electrolytic capacitors of Examples 13 to 16 were fabricated. The solvent of the electrolyte in Examples 13 to 16 was ethylene glycol, γ-butyrolactone, sulfolane, or a mixture of two of these, but the composition ratios were different. In the electrolytic capacitors of Examples 13 to 16, no solute was added to clarify the influence of the electrolyte solvent alone. Other than this, the electrolytic capacitors of Examples 13 to 16 were fabricated using the same manufacturing method and under the same conditions as Examples 1 to 4, including being housed in an aluminum container of the same dimensions and completely embedded in resin. An amine-based cured epoxy resin was used for the resin layer.

[0079] After being filled with resin, each electrolytic capacitor was left in a 150°C temperature environment for 3,500 hours. The amount of electrolyte lost after this thermal stress was measured. The amount of electrolyte lost was determined by subtracting the weight of the electrolytic capacitor after thermal stress from the weight of the electrolytic capacitor before thermal stress. The composition and amount of electrolyte added of Examples 13 to 16, as well as the amount of electrolyte lost after thermal stress, are shown in Table 4 below. The electrolytic capacitors in each example were wound capacitors with a diameter of 10 mm and a total length of 10 mm. (Table 4) TIFF0007768123000004.tif46161

[0080] As shown in Table 4, Example 14, in which sulfolane was used as the solvent for the electrolyte, reduced the amount of electrolyte loss by more than half compared to Example 13, in which γ-butyrolactone was used as the solvent for the electrolyte. Furthermore, Example 16, in which ethylene glycol was used as the solvent for the electrolyte, reduced the amount of electrolyte loss by 74% compared to Example 14, in which sulfolane was used as the solvent for the electrolyte.

Claims

1. a capacitor element having an anode foil, a cathode foil, a solid electrolyte, and an electrolytic solution; a case that houses the capacitor element; a sealing member that seals the case; a resin layer disposed in the vicinity of the sealing member; Equipped with the resin layer contains an epoxy resin composition that does not have an ester bond and is made from a phenol-based curing agent or an amine-based curing agent and an epoxy resin as raw materials, The electrolyte solution contains 34 mmol or less of cationic components per 100 g of the electrolyte solution. An electrolytic capacitor characterized by:

2. The epoxy resin composition has a chemical structure containing a phenol-based curing agent or an amine-based curing agent and an epoxy resin; 2. The electrolytic capacitor according to claim 1,

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

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

5. The electrolyte solution contains 25 mmol or less of cationic components per 100 g of the electrolyte solution; 2. The electrolytic capacitor according to claim 1,

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