Electrolytic capacitor

Abstract

An electrolytic capacitor according to the present disclosure includes: a container that has an opening; a capacitor element that is housed in the container and contains a conductive polymer; and a sealing body that seals the opening and contains an elastic polymer. The capacitor element contains an antioxidant component immobilized within a solidified resin component.

Description

electrolytic capacitor

[0001] The present disclosure relates to electrolytic capacitors.

[0002] Electrolytic capacitors with capacitor elements containing conductive polymers are considered promising as capacitors with small size, large capacity, and low ESR (equivalent series resistance). An electrolytic capacitor includes, for example, a container with an opening, a capacitor element housed in the container, and a sealing body that seals the opening. Elastic polymers such as rubber may be used for the sealing body. Conductive polymers are also called solid electrolytes.

[0003] In Patent Documents 1 and 2, a sealing plate using a rubber-backed phenolic insulating plate is used for an electrolytic capacitor.

[0004] Patent Document 3 discloses an additive for electrolytic capacitors used in electrolytic capacitors having a solid electrolyte layer, which contains a polymer (A) having a hydrophilic group, the concentration of the hydrophilic group in the polymer (A) being 18 mmol / g or less based on the weight of the polymer (A), and the solubility parameter of the polymer (A) being 12 (cal / cm ３ ) １／２ The additive for electrolytic capacitors described above has been proposed.

[0005] JP 2008-227265 A JP 2009-59780 A International Publication No. 2019 / 027019

[0006] Even if additives such as antioxidants are added to the sealant, deterioration of the sealant may not be sufficiently suppressed. When the sealant deteriorates, the contents evaporate and moisture and air enter the electrolytic capacitor. When moisture and air enter the electrolytic capacitor, the deterioration of the conductive polymer also progresses, causing fluctuations in ESR (equivalent series resistance) and reducing reliability.

[0007] A first aspect of the present disclosure relates to an electrolytic capacitor including: a container having an opening; a capacitor element housed in the container and including a conductive polymer; and a sealing body sealing the opening and including an elastic polymer, wherein the capacitor element includes an antioxidant component fixed in a solidified resin component.

[0008] According to the present disclosure, a highly reliable electrolytic capacitor can be provided.

[0009] FIG. 1 is a cross-sectional schematic view of an electrolytic capacitor according to an embodiment of the present disclosure.

[0010] The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0011] When an antioxidant is incorporated into the sealing body of an electrolytic capacitor, initial degradation of the sealing body is inhibited to some extent. However, the antioxidant gradually volatilizes from the portion of the sealing body exposed to the outside air, which tends to accelerate degradation of the sealing body. As degradation of the sealing body progresses, the elasticity of the sealing body is impaired and cracks occur. When the sealing effect of the sealing body is impaired, the contents volatilize and air and moisture enter the electrolytic capacitor. The action of air and moisture can cause dopants to be desorbed from the conductive polymer (sometimes called de-doping) or the conjugated polymer that constitutes the conductive polymer to deteriorate. As a result, the conductivity of the conductive polymer gradually decreases, the ESR fluctuates, and the reliability of the electrolytic capacitor decreases.

[0012] Technique (1): The electrolytic capacitor of the present disclosure includes a container having an opening, a capacitor element that is housed in the container and includes a conductive polymer, and a sealing body that seals the opening and includes an elastic polymer. The capacitor element includes an antioxidant component fixed in a solidified resin component.

[0013] According to the present disclosure, a capacitor element contains an antioxidant component fixed in a solidified resin component contained in the capacitor element. Therefore, the antioxidant component gradually volatilizes and acts on the sealing body and the conductive polymer. Because the antioxidant component's effect is sustained, degradation of the sealing body and the conductive polymer can be suppressed for a long period of time. As a result, fluctuations in ESR can be suppressed in the electrolytic capacitor, resulting in high reliability. The conductive polymer includes at least a conjugated polymer and a dopant.

[0014] The solidified resin component is a resin component of a capacitor element that has been solidified by polymerization, curing, drying and solidifying a resin solution, or cooling and solidifying a molten resin. The resin component includes, for example, a conductive polymer. Furthermore, if the capacitor element includes a resin layer, the solidified resin component also includes such a resin layer. The resin layer also includes a resin layer (e.g., a resin coating layer) that contacts a cathode portion containing a conductive polymer.

[0015] The term "an antioxidant component being fixed in a solidified resin component" refers to the antioxidant component being at least physically fixed in the solidified resin component, at least in the initial stage of the electrolytic capacitor. This state includes cases in which the antioxidant component interacts with, is complexed with, or is chemically bonded to the solidified resin component. The antioxidant component may be contained in, for example, the resin component (including a resin precursor) before solidification and fixed in the resin component upon solidification of the resin component. Alternatively, the antioxidant component may be dispersed in the matrix of the solidified resin component.

[0016] In this specification, the term "antioxidant component" refers to a component that has the effect of inactivating radicals generated by the involvement of oxygen. Antioxidant components include components generally called antioxidants, as well as components called antidegradants, antiaging agents, radical chain inhibitors, peroxide decomposers, chain initiation inhibitors, light stabilizers, heat stabilizers (or heat stabilizers), metal deactivators, ultraviolet absorbers, weathering stabilizers, etc.

[0017] Technique (2): In the technique (1), the antioxidant component may include an antioxidant having a melting point of 130°C or less. Such antioxidants are prone to volatilization. Even when such antioxidants are used, the present disclosure fixes them to the solidified resin component, allowing the antioxidant effect to be maintained for a long period of time.

[0018] Technique (3): In the technique (1) or (2), the antioxidant component may include a first antioxidant and a second antioxidant different from the first antioxidant. Using multiple different antioxidants further facilitates suppressing the deterioration of the conductive polymer and the sealing member. For example, it is possible to achieve both a high antioxidant effect for the conductive polymer and a high antioxidant effect for the sealing member.

[0019] Technique (4): In any one of the techniques (1) to (3), the capacitor element may include an anode body having a dielectric layer on at least a portion of its surface, a cathode portion covering at least a portion of the dielectric layer, and a resin coating layer covering at least a portion of the cathode portion. The cathode portion may include the conductive polymer in contact with at least a portion of the dielectric layer. The solidified resin component may be at least one of the resin coating layer and the conductive polymer. By fixing the antioxidant component to the resin coating layer or the conductive polymer, the antioxidant component gradually volatilizes and becomes more likely to act on the conductive polymer and the sealing member. Therefore, the effect of suppressing deterioration of the conductive polymer and the sealing member is more likely to be sustained, and fluctuations in ESR can be more effectively suppressed.

[0020] Technique (5): In the technique (4), the resin coating layer may include a first layer in contact with at least a portion of the cathode portion and a second layer covering at least a portion of the first layer. For example, if the first layer contains an antioxidant component, the antioxidant component is present near the conductive polymer, which makes it easier to further suppress deterioration of the conductive polymer. If the second layer contains an antioxidant component, it makes it easier to exert an antioxidant effect on the sealing member while ensuring a certain degree of antioxidant effect on the conductive polymer.

[0021] Technique (6): In the technique (5), the first layer may contain a first antioxidant, and the second layer may contain a second antioxidant different from the first antioxidant. The first antioxidant tends to suppress deterioration of the conductive polymer, and the second antioxidant tends to suppress deterioration of the sealing member.

[0022] Technique (7): In any one of the techniques (3) to (6), the molecular weight of the first antioxidant may be 700 or less. The molecular weight of the second antioxidant may be greater than 700. A first antioxidant with a relatively small molecular weight is likely to suppress deterioration of the conductive polymer. A second antioxidant with a relatively large molecular weight volatilizes slowly, thereby suppressing deterioration of the sealing body for a longer period of time, thereby ensuring high sealing performance for a long period of time. Therefore, fluctuations in ESR can be further suppressed.

[0023] The molecular weight of each antioxidant is usually the sum of atomic weights determined from the molecular structure. When the antioxidant has a molecular weight distribution, the above molecular weight means the weight average molecular weight (Mw).

[0024] In this specification, the weight average molecular weight (Mw) is a value calculated as polystyrene as measured by gel permeation chromatography (GPC). GPC is usually performed using a polystyrene gel column and water / methanol (volume ratio 8 / 2) as the mobile phase.

[0025] Technique (8): In any one of the techniques (3) to (7), the melting point of the first antioxidant may be 55°C or lower. The melting point of the second antioxidant may be higher than 55°C. When the melting point of the first antioxidant is low, such as 55°C or lower, it is prone to volatilization. In the present disclosure, the first antioxidant component is fixed to the solidified resin component, and therefore, even when a first antioxidant with such a low melting point is used, volatilization of the first antioxidant can proceed relatively slowly. Therefore, the effect of the first antioxidant is likely to be sustained, deterioration of the conductive polymer and the sealing body can be suppressed for a long period of time, and fluctuations in ESR can be suppressed.

[0026] Technique (9): In any one of the techniques (3) to (8), the capacitor element may include a wound body in which an anode foil as the anode body and a cathode foil are wound with a separator interposed therebetween, and the resin coating layer covering the surface of the wound body. The conductive polymer may be interposed between the anode foil and the cathode foil. The cathode portion may include the cathode foil and the conductive polymer. The resin coating layer may be in contact with at least the conductive polymer. If the resin coating layer contains an antioxidant component, the volatilized antioxidant component can act on both the conductive polymer and the sealing member. Therefore, the antioxidant component is gradually supplied to the conductive polymer and the sealing member, thereby suppressing fluctuations in ESR over a long period of time.

[0027] The electrolytic capacitor of the present disclosure will be described in more detail below, including the above techniques (1) to (9), with reference to the drawings as necessary. At least one of the above techniques (1) to (9) may be combined with at least one of the elements described below, provided that no technical contradiction exists. Note that the drawings are schematic illustrations of some embodiments, and the dimensional ratios (e.g., thickness) of each component in the drawings may differ from the actual ratios.

[0028] [Electrolytic Capacitor] An electrolytic capacitor includes a capacitor element containing a conductive polymer. The capacitor element is housed in a container having an opening, and the opening is sealed with a sealing member containing an elastic polymer.

[0029] (Capacitor Element) The capacitor element includes, for example, at least an anode body having a dielectric layer on at least a portion of its surface and a cathode portion covering at least a portion of the dielectric layer. The cathode portion includes a conductive polymer in contact with a portion of the dielectric layer. The conductive polymer may form a conductive polymer layer (in other words, a solid electrolyte layer). The cathode portion may include a cathode body such as a cathode foil. A separator may be interposed between the anode body and the cathode body. The conductive polymer may be impregnated into the separator. The capacitor element may include a resin layer (e.g., a resin coating layer) covering at least a portion of the cathode portion. In the present disclosure, the capacitor element includes an antioxidant component fixed in a solidified resin component. The antioxidant component gradually volatilizes, thereby maintaining the effect of suppressing deterioration of the conductive polymer and the sealing member, thereby suppressing fluctuations in ESR.

[0030] (Antioxidant Component) The antioxidant component is fixed to a solidified resin component contained in the capacitor element. The solidified resin component is preferably at least one of a resin coating layer and a conductive polymer. The antioxidant component may contain one type of antioxidant or two or more types of antioxidants.

[0031] In the present disclosure, the antioxidant component volatilized from the solidified resin component acts on the conductive polymer and the sealing member, so the antioxidant component preferably includes an antioxidant with a relatively low melting point or boiling point. However, when such an antioxidant is incorporated into the sealing member or the electrolyte solution, it volatilizes in the early stages, and the effect of suppressing deterioration of the sealing member or the conductive polymer is not sustained. This results in an increase in ESR, making it difficult to achieve the effect of suppressing ESR fluctuations over a long period of time. In the present disclosure, the antioxidant component is fixed in the solidified resin component, so even when an antioxidant with a relatively low melting point or boiling point is used, the antioxidant can be gradually volatilized, and the effect of suppressing deterioration of the conductive polymer and the sealing member can be sustained over a long period of time. Therefore, ESR fluctuations can be suppressed over a long period of time.

[0032] The electrolytic capacitor of the present disclosure may also be a so-called hybrid electrolytic capacitor that contains a liquid component such as an electrolyte solution. However, if an antioxidant with a relatively low melting point or boiling point is used, the antioxidant quickly dissolves in the liquid component, making it difficult to supply the antioxidant to the conductive polymer or sealing member over a long period of time. Therefore, the electrolytic capacitor of the present disclosure is preferably a solid electrolytic capacitor that does not use, or substantially does not use, such a liquid component. For example, the liquid component contained in the electrolytic capacitor is preferably less than 3 mass % of the mass of the solid electrolyte (conductive polymer), and more preferably 1 mass % or less.

[0033] The melting point of the antioxidant as described above may be 130°C or lower, 125°C or lower, or 120°C or lower. The antioxidant component may contain an antioxidant with a melting point exceeding 130°C. However, it is preferable that the mass ratio of antioxidants with a melting point of 130°C or lower is high relative to the entire antioxidant component (specifically, the total amount of antioxidants). The mass ratio of antioxidants with a melting point of 130°C or lower (or 125°C or lower, or 120°C or lower) relative to the entire antioxidant component is preferably greater than 50% by mass, more preferably 75% by mass or higher, and even more preferably 90% by mass or higher. The upper limit of the mass ratio of such antioxidants is 100% by mass. The melting points of all antioxidants contained in the antioxidant component may be 130°C or lower (or 125°C or lower, or 120°C or lower). Furthermore, it is preferable that the boiling point of the antioxidant is lower than 320°C. All of the antioxidants contained in the antioxidant component may have a boiling point of less than 320°C.

[0034] The antioxidant component may include a first antioxidant and a second antioxidant different from the first antioxidant. The first antioxidant and the second antioxidant may differ in at least one property selected from the group consisting of type (e.g., chemical structure, molecular weight), melting point, and boiling point.

[0035] The molecular weight of the first antioxidant may be 700 or less, or may be 650 or less. A first antioxidant having such a molecular weight is more likely to volatilize than an antioxidant with a larger molecular weight, and therefore more likely to act on the conductive polymer present in the vicinity of the solidified resin component, thereby further suppressing deterioration of the conductive polymer. The molecular weight of the first antioxidant may be 200 or more.

[0036] The molecular weight of the second antioxidant may be the same as or greater than the molecular weight of the first antioxidant. In the latter case, the second antioxidant volatilizes more gradually than the first antioxidant, which makes it easier to prolong the effect of inhibiting the deterioration of the conductive polymer and the sealing member. Because the first antioxidant inhibits the deterioration of the conductive polymer, the second antioxidant that is not consumed to inhibit the deterioration of the conductive polymer is more likely to act on the sealing member. This further inhibits the deterioration of the sealing member. The molecular weight of the second antioxidant may be 700 or more, may exceed 700, may be 850 or more, or may be 1000 or more. The molecular weight of the second antioxidant may be 2000 or less, or may be 1500 or less.

[0037] The molecular weight of the secondary antioxidant may be 700 or more and 2000 or less (or 1500 or less), more than 700 and 2000 or less (or 1500 or less), 850 or more and 2000 or less (or 1500 or less), or 1000 or more and 2000 or less (or 1500 or less).

[0038] The difference in molecular weight between the first antioxidant and the second antioxidant is equal to or greater than 0, and may be greater than 0, equal to or greater than 300, or equal to or greater than 400. The difference in molecular weight may be equal to or less than 1500, or may be equal to or less than 1000. When there is such a difference in molecular weight, the effect of using the first antioxidant and the second antioxidant in combination is more easily exhibited.

[0039] The difference in molecular weight between the first antioxidant and the second antioxidant may be 0 or more and 1500 or less (or 1000 or less), more than 0 and 1500 or less (or 1000 or less), 300 or more and 1500 or less (or 1000 or less), or 400 or more and 1500 or less (or 1000 or less).

[0040] The melting point of the first antioxidant may be the same as or lower than the melting point of the second antioxidant. The melting point of the first antioxidant may be 55°C or lower. The melting point of the first antioxidant may be 20°C or higher. A first antioxidant having such a melting point is more likely to volatilize than an antioxidant with a higher melting point, and therefore more likely to act on the conductive polymer present in the vicinity of the solidified resin component, thereby further suppressing deterioration of the conductive polymer. The first antioxidant may have the above-mentioned Mw.

[0041] The melting point of the second antioxidant may be 55°C or higher, or may be higher than 55°C, 75°C or higher, or 100°C or higher. The melting point of the second antioxidant may be 250°C or lower, 160°C or lower, or 125°C or lower. A second antioxidant having such a melting point volatilizes more gradually than the first antioxidant, and therefore the effect of suppressing the deterioration of the conductive polymer and the sealing member tends to last longer. Because the first antioxidant suppresses the deterioration of the conductive polymer, the second antioxidant that is not consumed to suppress the deterioration of the conductive polymer is more likely to act on the sealing member. This further suppresses the deterioration of the sealing member.

[0042] The melting point of the second antioxidant may be 55°C or higher and 250°C or lower (or 160°C or lower), ...75°C or higher and 250°C or lower (or 160°C or lower), 100°C or higher and 250°C or lower (or 160°C or lower), 55°C or higher (or 75°C or higher) and 125°C or lower, or 100°C or higher and 125°C or lower.

[0043] The difference between the melting points of the first antioxidant and the second antioxidant may be 0° C. or higher, or may be greater than 0° C., 10° C. or higher, 30° C. or higher, or 50° C. or higher. When the difference in melting points is within this range, the effect of using the first antioxidant and the second antioxidant in combination is more easily exhibited. The difference in melting points may be 100° C. or lower.

[0044] The antioxidant component includes, for example, at least one selected from the group consisting of a hydroxy group, a nitrogen atom, an oxygen atom, a sulfur atom, and a phosphorus atom. The antioxidant component includes, for example, at least one selected from the group consisting of a phenol-based antioxidant, a quinone-based antioxidant, an amine-based antioxidant, a phosphorus-based antioxidant, and a sulfur-based antioxidant. Among these antioxidants, antioxidants having a hindered group are preferred, and antioxidants having an aromatic ring with a hindered group are more preferred. The hindered group is usually bonded to the aromatic ring via a tertiary or quaternary carbon atom (particularly a quaternary carbon atom).

[0045] Examples of hindered groups include hindered alkyl groups. Examples of hindered alkyl groups include an isopropyl group, a sec-butyl group, a tert-butyl group, and a tert-pentyl group (tert-amyl group). Among these, a sec-butyl group, a tert-butyl group, and a tert-pentyl group are preferred. The antioxidant may have one or two or more of these hindered groups. Furthermore, each aromatic ring (such as a benzene ring) contained in the antioxidant may have one or two or more of the above-mentioned hindered groups. When the antioxidant or the aromatic ring has two or more hindered groups, at least two of the hindered groups may be the same, or all of the hindered groups may be different.

[0046] Examples of phenolic antioxidants include monophenolic antioxidants, polyphenolic antioxidants, and antioxidants having a hindered group (also referred to as hindered phenolic antioxidants) among these antioxidants. Examples of monophenolic antioxidants include 2,6-tert-butyl-4-methylphenol, butylhydroxyanisole, sesamol, and α-tocopherol. Examples of polyphenolic antioxidants include catechol, hydroquinone, resorcinol, urushiol, and pyrogallol. Examples of hindered phenol antioxidants include 4,4',4''-(1-methylpropanyl-3-ylidene)tris(6-tert-butyl-m-cresol), 6,6'-di-tert-butyl-4,4'-butylidene-di-m-cresol, octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 3,9-bis{2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecane.

[0047] The quinone antioxidant is preferably a quinone antioxidant having a hindered group, such as 2,5-di-tert-butylhydroquinone or 3,6-dihydroxybenzonorbornane.

[0048] Examples of the amine antioxidant include tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl)butane-1,2,3,4-tetracarboxylate, tetrakis(2,2,6,6-tetramethyl-4-piperidyl)butane-1,2,3,4-tetracarboxylate, and 6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline.

[0049] Examples of phosphorus-based antioxidants include tri-p-tolyl phosphite, trihexyl phosphite, tris(nonylphenyl) phosphite, etc. Examples of phosphorus-based antioxidants having a hindered group include 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, 2,2'-methylenebis(4,6-di-tert-butylphenyl) 2-ethylhexyl phosphite, tris(2,4-di-tert-butylphenyl) phosphite, etc.

[0050] Examples of sulfur-based antioxidants include 2,2-bis{[3-(dodecylthio)-1-oxopropoxy]methyl}propane-1,3-diyl bis[3-(dodecylthio)propionate] and di(tridecyl) 3,3'-thiodipropionate.

[0051] The first antioxidant and the second antioxidant may both be phenol-based antioxidants. From the viewpoint of further suppressing deterioration of the sealing member, it is preferable that at least the second antioxidant is a hindered phenol-based antioxidant.

[0052] The mass ratio of the antioxidant component to the conductive polymer (=antioxidant component / conductive polymer) is preferably 5.0 or more and 35 or less, and may be 8.0 or more and 25 or less. The mass ratio of the first antioxidant to the conductive polymer (first antioxidant / conductive polymer) is preferably 5.0 or more and 35 or less, and may be 8.5 or more and 25 or less. When the mass ratio of the antioxidant component or the first antioxidant to the conductive polymer is within such a range, deterioration of the conductive polymer is more easily suppressed, and fluctuations in ESR can be further suppressed.

[0053] When an antioxidant component (or a first antioxidant) is immobilized on a conductive polymer, the content of the antioxidant component (or the first antioxidant) in the conductive polymer is preferably 0.5% by mass or more and 25% by mass or less, and may be 1.0% by mass or more and 15% by mass or less. When the content of the antioxidant component or the first antioxidant is in such a range, high conductivity of the conductive polymer can be ensured, deterioration of the conductive polymer can be further easily suppressed, and fluctuations in ESR can be further suppressed.

[0054] The mass ratio of the antioxidant component to the elastic polymer contained in the sealing member (=antioxidant component / elastic polymer) is preferably 0.2 to 10, and may be 0.5 to 7.0. The mass ratio of the second antioxidant to the elastic polymer (second antioxidant / elastic polymer) is preferably 0.2 to 20, and may be 0.5 to 10. When the mass ratio of the antioxidant component or the second antioxidant to the elastic polymer is within such a range, deterioration of the elastic polymer is more easily suppressed, and fluctuations in ESR can be further suppressed.

[0055] When the resin coating layer contains an antioxidant component, the content of the antioxidant component in the resin coating layer is preferably 0.5% by mass to 40% by mass, and may be 1.0% by mass to 20% by mass. When the content of the antioxidant component is in this range, the initial ESR can be kept low, deterioration of the conductive polymer and the sealing member can be further easily suppressed, and fluctuations in ESR can be further suppressed.

[0056] When the resin coating layer includes a first layer and a second layer, for example, the first layer may include one of the first antioxidant and the second antioxidant, and the second layer may include the other. The first layer in contact with the cathode part (particularly the conductive polymer) may include the first antioxidant, and the outer second layer may include the second antioxidant. However, this is not limited to these cases, and the first layer and the second layer may include the same antioxidant.

[0057] The content of the first antioxidant in the first layer is preferably 0.5% by mass or more and 30% by mass or less, and may be 1.0% by mass or more and 15% by mass or less. When the content of the first antioxidant is in this range, deterioration of the conductive polymer can be further suppressed, and fluctuations in ESR can be further suppressed. The content of the second antioxidant in the second layer is preferably 0.5% by mass or more and 40% by mass or less, and may be 1.0% by mass or more and 20% by mass or less. When the content of the second antioxidant is in this range, deterioration of the sealing member can be further suppressed, and fluctuations in ESR can be further suppressed.

[0058] The antioxidant components, the mass, mass ratio, and content of each antioxidant are values ​​for an initial electrolytic capacitor. In this specification, the initial electrolytic capacitor refers to an electrolytic capacitor after aging or break-in charge / discharge, or an unused electrolytic capacitor if it is a commercially available product.

[0059] The analysis of the antioxidant present in the solidified resin component is carried out, for example, by the following procedure. First, the electrolytic capacitor is disassembled, the capacitor element is removed, and the surface is polished to expose the surface of the solidified resin component (conductive polymer, resin coating layer, etc.). All of the exposed resin component is scraped off and dried under reduced pressure. A predetermined amount is taken from the dried sample, and the sample is used to perform H １ - Analysis of antioxidants can be carried out by NMR.

[0060] (Anode Body) The anode body can contain a valve metal, an alloy containing a valve metal, a compound containing a valve metal, etc. These materials can be used alone or in combination of two or more. Preferred valve metals include aluminum, tantalum, niobium, and titanium.

[0061] The anode body may be in the form of a foil (also referred to as an anode foil) or a plate. The anode body may have a porous portion at least in the surface layer. An anode body having a porous portion in the surface layer can be obtained, for example, by roughening the surface of a substrate (such as a foil-shaped or plate-shaped substrate) containing a valve metal by etching or the like. The anode body may also be a compact of particles containing a valve metal or a sintered body thereof. The compact or sintered body has a porous structure as a whole.

[0062] (Dielectric Layer) The dielectric layer is formed by anodizing the valve metal on the surface of the anode body by chemical conversion treatment or the like. The dielectric layer may be formed so as to cover at least a portion of the anode body. The dielectric layer is usually formed on the surface of the anode body. Since the dielectric layer is formed on the porous surface of the anode body, it is formed along the inner wall surfaces of holes and depressions (pits) on the surface of the anode body.

[0063] The dielectric layer contains an oxide of the valve metal. For example, when tantalum is used as the valve metal, the dielectric layer contains Ta. ２ O ５ When aluminum is used as the valve metal, the dielectric layer contains Al ２ O ３ The dielectric layer is not limited to this, and may be any layer that functions as a dielectric. When the surface of the anode body is porous, the dielectric layer is formed along the surface of the anode body (including the inner wall surfaces of the pores).

[0064] (Conductive Polymer) The conductive polymer includes, for example, a conjugated polymer and a dopant. The conductive polymer is in contact with at least a portion of the dielectric layer. The conductive polymer may be attached so as to cover at least a portion of the surface of the dielectric layer. The conductive polymer attached to the surface of the dielectric layer may form a layer (sometimes referred to as a solid electrolyte layer). The conductive polymer forms at least a portion of the cathode part of the electrolytic capacitor. The conductive polymer may include an antioxidant component. Furthermore, the conductive polymer may further include an additive, if necessary.

[0065] (Conjugated Polymers) Examples of conjugated polymers include known conjugated polymers used in electrolytic capacitors, such as π-conjugated polymers. Examples of conjugated polymers include polymers with a basic skeleton of polypyrrole, polythiophene, polyaniline, polyfuran, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, and polythiophene vinylene. The above polymers may contain at least one monomer unit constituting the basic skeleton. The above polymers also include homopolymers, copolymers of two or more monomers, and derivatives thereof (e.g., substituted products having substituents). For example, polythiophenes include poly(3,4-ethylenedioxythiophene).

[0066] The conductive polymer may contain one type of conjugated polymer or a combination of two or more types of conjugated polymers.

[0067] The weight average molecular weight (Mw) of the conjugated polymer is, for example, 1,000 to 1,000,000, but is not limited to this range.

[0068] (Dopant) Examples of dopants include relatively low molecular weight anions and polymer anions. Examples of anions include sulfate ions, nitrate ions, phosphate ions, borate ions, organic sulfonate ions, and carboxylate ions. Compounds that generate these anions are used as dopants. Examples of dopants that generate sulfonate ions include paratoluenesulfonic acid and naphthalenesulfonic acid.

[0069] Examples of polymer anions include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallylsulfonic acid, polyacrylic sulfonic acid, polymethacrylic sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, polyester sulfonic acid (such as aromatic polyester sulfonic acid), phenolsulfonic acid novolac resin, and polyacrylic acid. The polymer anion may be a polymer of a single monomer or a copolymer of two or more monomers. These polymers may be substituted with a substituent. Among these, polymer anions having styrene sulfonic acid or a substituted product thereof as a monomer unit, such as polystyrene sulfonic acid, or polymer anions having a repeating structure of such monomer units are preferred.

[0070] However, these dopants are merely examples and are not limited to these. The dopants may be used alone or in combination of two or more.

[0071] The conductive polymer may be formed, for example, by chemically polymerizing or electrolytically polymerizing a precursor of a conjugated polymer on a dielectric layer in the presence of a dopant. An oxidizing agent may be used for the polymerization. When the conductive polymer contains an antioxidant component, a conductive polymer (solid electrolyte) may be formed by contacting a dispersion (or solution) containing the conductive polymer and the antioxidant component with a dielectric layer. Examples of precursors of conjugated polymers include raw material monomers of the conjugated polymer, and oligomers and prepolymers in which multiple molecular chains of the raw material monomers are linked together. One type of precursor may be used, or two or more types may be used in combination.

[0072] The amount of the dopant contained in the conductive polymer may be 10 parts by mass or more and 1,000 parts by mass or less, 20 parts by mass or more and 500 parts by mass or less, or 50 parts by mass or more and 200 parts by mass or less, relative to 100 parts by mass of the conjugated polymer.

[0073] The concentration of the antioxidant component in a solution (or liquid dispersion) containing a conjugated polymer, a dopant, and an antioxidant component for forming a conductive polymer (solid electrolyte) is preferably 1% by mass or more and 30% by mass or less, more preferably 3% by mass or more and 20% by mass or less, and may be 5% by mass or more and 15% by mass or less. When the concentration of the antioxidant component is in this range, the active antioxidant is likely to remain in the conductive polymer, and the effect of the antioxidant component is likely to be maintained for a long period of time.

[0074] The analysis of the conductive polymer contained in the electrolytic capacitor is similar to that of the antioxidant component, and １ - This can be done by NMR.

[0075] (Cathode Body) As with the anode body, a metal foil (cathode foil) may also be used for the cathode body. The type of metal is not particularly limited, but it is preferable to use a valve metal such as aluminum, tantalum, or niobium, or an alloy containing a valve metal. If necessary, the surface of the metal foil may be roughened. The surface of the metal foil may be provided with a chemical conversion coating, or may be provided with a coating of a metal (dissimilar metal) or a non-metal different from the metal constituting the metal foil. Examples of dissimilar metals and non-metals include metals such as titanium and non-metals such as carbon.

[0076] The cathode element may optionally include a conductive polymer that constitutes at least a portion of the anode element having a dielectric layer on its surface, and a cathode extraction layer covering the conductive polymer. The cathode extraction layer may include, for example, one or more conductive particle-containing layers, or may include a metal foil (cathode foil). The conductive particle-containing layer may include, for example, conductive particles (metal particles, conductive carbon particles, etc.) and a binder resin. The binder resin may be a thermoplastic resin or composition, or a curable resin composition. For example, the cathode extraction layer may be formed by a layer containing conductive carbon particles and a metal particle-containing layer covering this layer. The metal particles contained in the metal particle-containing layer may be, for example, silver, copper, or an alloy thereof. The cathode extraction layer may be a metal foil coated with particles (non-metallic particles such as carbon particles, metal particles, etc.).

[0077] The cathode part includes a conductive polymer and a cathode part. The solidified resin component containing the antioxidant component is preferably a conductive polymer or is disposed so as to be in contact with at least the cathode part (particularly, at least the conductive polymer), as in the resin coating layer. In these cases, the antioxidant component is more easily accessible to the conductive polymer and is continuously supplied to the conductive polymer, thereby further suppressing deterioration of the conductive polymer and further suppressing fluctuations in ESR. The antioxidant component may be fixed to the conductive polymer, or to at least a portion of the resin coating layer, or to both. For example, an antioxidant effective in preventing oxidation of the conductive polymer may be fixed in the conductive polymer or closer to the conductive polymer. Alternatively, the antioxidant may be effectively fixed to the elastic polymer of the sealing body in a portion of the resin coating layer that is not in contact with the conductive polymer.

[0078] (Separator) When a metal foil is used for the cathode body, a separator may be disposed between the metal foil (cathode foil) and the anode body (anode foil, etc.). The separator is not particularly limited, and may be, for example, a nonwoven fabric containing fibers of cellulose, polyethylene terephthalate, vinylon, or polyamide (e.g., aliphatic polyamide, aromatic polyamide such as aramid).

[0079] (Other) The electrolytic capacitor of the present disclosure uses a sealing member containing an elastic polymer. Such an electrolytic capacitor may be a chip type or a laminate type, but a wound type is preferable. The electrolytic capacitor may have at least one capacitor element, or may have multiple capacitor elements. For example, the electrolytic capacitor may have two or more wound capacitor elements, or may have a laminate of two or more capacitor elements. The configuration or number of capacitor elements may be selected depending on the type or application of the electrolytic capacitor.

[0080] A capacitor element including a resin coating layer is formed by covering at least a portion of the surface of a precursor of the capacitor element, such as a wound body or laminate including an anode body and a cathode part, with the resin coating layer. More specifically, the wound body may have a structure in which an anode foil and a cathode foil are wound with a separator interposed therebetween. In this case, a conductive polymer is interposed between the anode foil and the cathode foil. The conductive polymer may be impregnated into the separator. The conductive polymer is usually in contact with at least a portion of the dielectric layer. The conductive polymer is also usually in contact with at least a portion of the cathode foil. The resin coating layer is formed to cover (or be in contact with) at least a portion of the cathode part (particularly the conductive polymer). The resin coating layer is formed, for example, to cover the entire periphery of the wound body or laminate, except for a portion of the lead used for connection to an external terminal.

[0081] The resin coating layer may be a single layer or may have two or more layers. The resin coating layer may include, for example, a first layer and a second layer covering at least a portion of the first layer. The first layer does not necessarily need to be in contact with the cathode portion, but it is preferable that it be in contact with at least a portion of the cathode portion (especially the conductive polymer). When the first layer contains an antioxidant component, the antioxidant component is continuously supplied to the conductive polymer from the vicinity of the conductive polymer, thereby further suppressing deterioration of the conductive polymer. When the second layer contains an antioxidant component, the antioxidant component gradually volatilizes from the second layer, thereby continuously suppressing deterioration of the conductive polymer and the elastic polymer of the sealing body. Therefore, fluctuations in ESR can be suppressed for an even longer period of time.

[0082] The first layer may contain a first antioxidant, and the second layer may contain a second antioxidant. The first antioxidant and the second antioxidant may be the same, but if they are different, the antioxidant effect is more easily exerted. For example, an antioxidant effective in inhibiting the oxidation of conductive polymers may be used as the first antioxidant, and an antioxidant effective in inhibiting the oxidation of elastic polymers may be used as the second antioxidant. Alternatively, an antioxidant that volatilizes at a relatively early stage may be used as the first antioxidant, and an antioxidant that volatilizes more slowly than the first antioxidant may be used as the second antioxidant. In such cases, the first antioxidant may have a smaller molecular weight, melting point, or boiling point than the second antioxidant. The molecular weight, melting point, etc. of each antioxidant can be determined by referring to the description of each antioxidant, and can be selected from the ranges described for each antioxidant.

[0083] The resin coating layer is formed by coating or immersing at least a portion of the surface of the capacitor element precursor with a fluid resin or resin composition and then solidifying it. The fluid resin or resin composition may be a molten resin (or resin composition), a resin (or resin composition) dissolved in a solvent, or a curable resin (or curable resin material). The resin coating layer (or each layer forming the resin coating layer) is formed by cooling, drying, or curing (or polymerization) a coating of the resin or resin composition formed to cover the capacitor element precursor. The resin may be a thermoplastic resin, but a curable resin material is easier to handle. For example, the first layer is formed by immersing the wound body in a first curable resin material containing a first antioxidant, removing the wound body, and curing the coating of the first curable resin material under heat. The wound body on which the first layer has been formed is then immersed in a second curable resin material containing a second antioxidant, removed, and the coating of the second curable resin material is cured under heat to form the second layer. In this case, too, the antioxidants contained in each layer may be the same or different. That is, when the first layer contains a first antioxidant and the second layer contains a second antioxidant, the first antioxidant and the second antioxidant may be the same or different.

[0084] Because the resin coating layer is insulating, a large thickness increases the volume it occupies in the container, resulting in a small capacitance. Therefore, a relatively small thickness of the resin coating layer is preferable. The thickness of the resin coating layer is preferably 0.1 μm or more and 1.0 mm or less, and may be 1 μm or more and 100 μm or less. The thickness of the resin coating layer is the average value obtained by measuring the thickness at multiple locations (e.g., five locations) in a cross-sectional image of the capacitor element where the thickness of the resin coating layer can be observed.

[0085] Examples of curable resin materials include resin compositions containing a curable resin (e.g., a thermosetting resin), a component involved in the curing of the curable resin, and, if necessary, at least one selected from the group consisting of additives and liquid media. Depending on the type of curable resin, components involved in the curing of the curable resin include, for example, a polymerization initiator, a curing agent, a curing accelerator, a crosslinking agent, and a curing catalyst. These components may be used alone or in combination.

[0086] Preferred curable resins include epoxy resins, polyamideimide resins, polyimide resins, and phenolic resins. The curable resin material may contain one type of curable resin or a combination of two or more types. Epoxy resins may be used from the viewpoints of ease of handling and low cost. Examples of epoxy resins include aliphatic epoxy resins and epoxy resins having a ring structure. Examples of epoxy resins having a ring structure include cyclic epoxy compounds, alicyclic glycidyl ethers, alicyclic glycidyl ester compounds, and aromatic epoxy compounds (such as bisphenol-type epoxy resins). When an epoxy resin having a ring structure is used, higher strength is likely to be obtained.

[0087] When the first layer and the second layer are formed, the compositions of the curable resin materials in each layer may be different or the same except for the antioxidant.

[0088] The concentration of the antioxidant component contained in the liquid mixture for forming a resin coating layer of a curable resin material or the like may be 1% by mass or more and 30% by mass or less, 2% by mass or more and 25% by mass or less, 3% by mass or more and 20% by mass or less, or 5% by mass or more and 15% by mass or less. When the antioxidant concentration is within such a range, a resin coating layer in which an appropriate amount of the antioxidant component is fixed is easily obtained, and the antioxidant gradually volatilizes, making it easier to exert its effects over a longer period of time. From the viewpoint of further suppressing fluctuations in ESR, the concentration of the antioxidant contained in the liquid mixture (such as a curable resin material) may be 10% by mass or more and 25% by mass or less, or 10% by mass or more and 15% by mass or less. In particular, when the molecular weight of the antioxidant is small (e.g., 700 or less) or the melting point is low (e.g., 55°C or less), a concentration of the antioxidant of 10% by mass or more is likely to provide a greater effect. On the other hand, when the molecular weight of the antioxidant is large (for example, greater than 700) or the melting point is high (for example, greater than 55°C), a high effect is likely to be obtained even if the concentration of the antioxidant is relatively low.

[0089] (Container) The container may be made of a metal such as aluminum, stainless steel, copper, iron, brass, or an alloy thereof. The shape of the container is not particularly limited as long as it has an opening, the opening can be sealed with a sealing body containing an elastic polymer, and the container can accommodate a capacitor element.

[0090] (Sealing Body) The sealing body is not particularly limited as long as it contains an elastic polymer and seals the opening of the container. In the present disclosure, the antioxidant component is fixed to the solidified resin component in the electrolytic capacitor, and the antioxidant component gradually volatilizes and is supplied to the sealing body. This suppresses deterioration of the sealing body over a long period of time, maintaining high sealing performance and preventing the intrusion of air and moisture. Therefore, the high performance of the electrolytic capacitor is maintained and fluctuations in ESR are suppressed. The sealing body may further contain a crosslinking agent, additive, etc. that crosslinks the elastic polymer.

[0091] The elastic polymer used may be an insulating elastic polymer. Examples of the elastic polymer include butyl rubber, isoprene rubber, silicone rubber, fluororubber, ethylene propylene rubber, and chlorosulfonated polyethylene rubber (e.g., Hypalon rubber). The sealing body may contain one type of elastic polymer or a combination of two or more types.

[0092] The proportion of the elastic polymer in the sealing body may be 10% by mass or more, or may be 20% by mass or more. If the proportion of the elastic polymer is within this range, the sealing body is prone to deterioration. Even in such cases, the antioxidant component that gradually volatilizes within the electrolytic capacitor can suppress deterioration of the elastic polymer. Therefore, high sealing performance can be maintained over a long period of time, thereby suppressing fluctuations in ESR. The proportion of the elastic polymer in the sealing body may be 50% by mass or less. Note that, if the elastic polymer is crosslinked with a crosslinking agent, the proportion of the elastic polymer is the proportion of the elastic polymer including the crosslinking agent.

[0093] The additive may include, for example, at least one selected from the group consisting of a reinforcing agent (carbon such as carbon black), an antioxidant, an antiaging agent, a crosslinking agent, a crosslinking accelerator, a dispersing aid, a modifier, a vulcanizing agent, a vulcanization aid, and a processing aid.

[0094] From the viewpoint of further suppressing deterioration of the elastic polymer contained in the sealing member, the mass ratio of the antioxidant component immobilized in the electrolytic capacitor to the elastic polymer (=antioxidant component / elastic polymer) is, for example, from 0.001 to 1, or alternatively from 0.005 to 0.5, or from 0.01 to 0.3 (or from 0.2 to 0.2), or from 0.01 to 0.1. The mass ratio of the total amount of the first antioxidant and the second antioxidant to the elastic polymer may be within the above-mentioned range, and the mass ratio of the second antioxidant to the elastic polymer may also be within the above-mentioned range.

[0095] The qualitative and quantitative analysis of the elastic polymer contained in the sealing body can be performed, for example, by the following procedure. First, the sealing body is dried under reduced pressure for 1 hour, and the mass of the sealing body is measured. Next, the sealing body is cut out to prepare a sample, and the mass is measured. The sample is then dried under reduced pressure for 1 hour, and the mass of the sample is measured. １The components (e.g., elastic polymer) contained in the sealing body are identified using at least one of NMR and infrared absorption spectroscopy. The sample can also be quantitatively analyzed using thermogravimetric analysis (TG or TGA). The mass ratio is calculated from the mass of the elastic polymer and the mass of the antioxidant (or each antioxidant).

[0096] The electrolytic capacitor of the present disclosure will be described in more detail below based on embodiments. However, the electrolytic capacitor of the present disclosure is not limited to the following embodiments. Features of the following embodiments may be combined with the conceptual description above.

[0097] FIG. 1 is a schematic cross-sectional view of the electrolytic capacitor according to this embodiment.

[0098] Electrolytic capacitor 100 includes, for example, capacitor element 10, bottomed case 101 that houses capacitor element 10, sealing body 102 that closes the opening of bottomed case 101, seat plate 103 that covers sealing body 102, lead wires 104A and 104B that extend from sealing body 102 and pass through seat plate 103, and lead tabs 105A and 105B that connect the lead wires to electrodes of capacitor element 10. The vicinity of the open end of bottomed case 101 is drawn inward, and the open end is curled so as to be crimped to sealing body 102.

[0099] Capacitor element 10 is, for example, a wound body as shown in FIG. 1 . The wound body includes anode body 11 connected to lead tab 105A, cathode body 12 connected to lead tab 105B, and separator 13. A conductive polymer (solid electrolyte) (not shown) is interposed between anode body 11 and cathode body 12. More specifically, separator 13 interposed between anode body 11 and cathode body 12 is impregnated with a conductive polymer, and the conductive polymer is in contact with anode body 11 and cathode body 12. The conductive polymer and cathode body 12 form a cathode section. The outermost electrode of the wound body or separator 13 may be fixed with a stop tape (not shown).

[0100] The capacitor element 10 includes a resin coating layer 14 that covers the surface of the wound body. For example, at least one of the conductive polymer and the resin coating layer 14 may contain an antioxidant component. In the example of FIG. 1 , the resin coating layer 14 includes a first layer 14a that covers the surface of the wound body and a second layer 14b that covers the surface of the first layer 14a. For example, the first layer 14a may contain a first antioxidant, and the second layer 14b may contain a second antioxidant. The resin coating layer 14 is also formed on both end surfaces of the winding shaft of the wound body. The resin coating layer 14 (more specifically, the first layer 14a) is preferably in contact with the conductive polymer that constitutes the cathode portion.

[0101] EXAMPLES The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0102] <<Preparation of Electrolytic Capacitors E1 to E8>> Wound electrolytic capacitors (diameter 6.3 mm x height 6.0 mm) with a rated voltage of 25 V and a rated capacitance of 47 μF were prepared. A specific method for producing the electrolytic capacitors will be described below.

[0103] (Preparation of anode body) An aluminum foil with a thickness of 100 μm was subjected to an etching treatment to roughen the surface of the aluminum foil. Then, a dielectric layer was formed on the surface of the aluminum foil by chemical conversion treatment. The chemical conversion treatment was performed by immersing the aluminum foil in an ammonium adipate solution and applying a voltage thereto. Then, the aluminum foil was cut to prepare an anode body (anode foil).

[0104] (Preparation of Cathode Body) An aluminum foil having a thickness of 50 μm was subjected to an etching treatment to roughen the surface of the aluminum foil, and then the aluminum foil was cut to prepare a cathode body (cathode foil).

[0105] (Preparation of Wound Body) An anode lead tab and a cathode lead tab were connected to the anode foil and the cathode foil, respectively, and the anode foil and the cathode foil were wound around the lead tabs, with a separator interposed therebetween. An anode lead wire and a cathode lead wire were connected to the ends of each lead tab protruding from the wound body, respectively. The prepared wound body was again subjected to a chemical conversion treatment, and a dielectric layer was formed on the cut end of the anode body. Next, the ends of the outer surface of the wound body were fixed with a winding tape to prepare the wound body.

[0106] (Formation of Conductive Polymer) A liquid dispersion containing a conductive polymer was prepared according to the following procedure. 3,4-ethylenedioxythiophene (EDOT) and the dopant polystyrene sulfonic acid (PSS, weight-average molecular weight 100,000) were dissolved in ion-exchanged water to prepare a mixed solution. While stirring the mixed solution, iron (III) sulfate (oxidant) dissolved in ion-exchanged water was added to carry out a polymerization reaction. After the reaction, the resulting reaction solution was dialyzed to remove unreacted monomers and excess oxidant, yielding a liquid dispersion containing polyethylenedioxythiophene doped with approximately 5% by mass of PSS (PEDOT / PSS).

[0107] The wound body was immersed in a liquid dispersion contained in a specified container in a reduced pressure atmosphere (40 kPa) for 5 minutes, and then removed from the liquid mixture. The wound body impregnated with the liquid mixture was then dried in a drying oven at 150°C for 20 minutes, thereby coating at least a portion of the dielectric layer with the conductive polymer. In this way, a wound body was formed in which the conductive polymer was interposed between the anode foil and the cathode foil.

[0108] (Preparation of treatment solution for resin coating layer) A first antioxidant was blended into a curable resin material containing a bisphenol-type epoxy resin at the concentration (mass %) shown in Table 1. The wound body to which the conductive polymer had been applied was immersed in the obtained curable resin material, removed, and cured at 120°C to form a first layer. The first layer was formed on the entire surface of the wound body, including the base of the lead tab. In this manner, a capacitor element having a resin coating layer was formed.

[0109] A second antioxidant was blended into a curable resin material containing a bisphenol-type epoxy resin at the concentration (mass %) shown in Table 1. The wound body on which the first layer had been formed was immersed in the resulting curable resin material, and a second layer was formed so as to cover the entire surface of the first layer. In this way, a resin coating layer comprising the first and second layers was formed on the surface of the wound body. The first layer was in contact with both end faces of the winding shaft of the wound body. The thickness of the resin coating layer was determined using the procedure described above and was found to be 39 μm.

[0110] The antioxidants shown in Table 1 are as follows: Antioxidant A: octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (molecular weight 531, melting point 51°C to 54°C) Antioxidant B: pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (molecular weight 1178, melting point 110°C to 130°C) Antioxidant C: 4,4',4''-(1-methylpropanyl-3-ylidene)tris(6-tert-butyl-m-cresol) (molecular weight 545, melting point 183°C to 185°C) Antioxidant D: 2,2'-methylenebis(4,6-di-tert-butylphenyl) 2-ethylhexyl phosphite (molecular weight 583, melting point 146°C to 152°C)

[0111] (Assembly of Electrolytic Capacitor (Solid Electrolytic Capacitor)) The capacitor element was housed in a bottomed case, and the opening of the case was sealed with a sealing member. In this way, an electrolytic capacitor as shown in Fig. 1 was completed. Thereafter, an aging treatment was performed at 130°C for 2 hours while applying the rated voltage to the electrolytic capacitor.

[0112] The sealant was a disk-shaped elastic material containing butyl rubber obtained by kneading a butyl polymer, a peroxide-based cross-linking agent, and additives and molding them in a mold. The additives used were a reinforcing material (carbon black), a cross-linking accelerator, a dispersing aid (stearic acid), and a modifier (silane coupling agent). The amount of each component was adjusted so that the content of the elastic polymer, butyl rubber, in the sealant was 30% by mass.

[0113] [Evaluation: Measurement of ESR and Capacitance] Using a four-terminal LCR meter, the initial capacitance (mΩ) at a frequency of 120 Hz and the initial ESR (mF) at 100 kHz of each electrolytic capacitor were measured in an environment of 20° C. Then, the average values ​​(initial capacitance: c0, initial ESR: r0) of the 20 solid electrolytic capacitors were calculated.

[0114] The electrolytic capacitors were then subjected to two 3-minute reflow treatments, with a peak temperature of 250°C. An accelerated test was then performed by placing the electrolytic capacitors in a constant temperature bath at 165°C and applying a rated voltage of 25V for 750 hours. The ESR was then measured at 200 hours, 575 hours, and 750 hours in a 20°C environment using the same procedure as for the initial capacitance and ESR, and the average value (ESR after accelerated test: r1 to r3) of 20 solid electrolytic capacitors was calculated. The ratio of the average ESR (r1 to r3) at each elapsed time in the accelerated test to the average initial ESR (r0) was calculated.

[0115] <Electrolytic Capacitors E9 and E10> For these electrolytic capacitors, the antioxidant components shown in Table 1 were blended into the conductive polymer without forming a resin coating layer. The conductive polymer was prepared as follows: A mixture of p-toluenesulfonic acid (a dopant) and the antioxidant components was mixed with a solution of EDOT monomer and iron (III) sulfate (oxidant) dissolved in ion-exchanged water under stirring. The wound body was quickly immersed in the resulting liquid mixture and subjected to a polymerization reaction (in situ polymerization) at 150°C for 2 hours. After the reaction, the wound body was removed, washed with water, and dried to form a capacitor element. The blending amount of the antioxidant components in the liquid mixture was adjusted so that the concentration of the antioxidant components was the value shown in Table 1. Electrolytic capacitors E9 and E10 were assembled and evaluated in the same manner as electrolytic capacitor E1, except for the following points.

[0116] <Electrolytic Capacitor C1> In electrolytic capacitor C1, a resin coating layer was not formed and no antioxidant component was used. Except for these, electrolytic capacitor C1 was assembled in the same manner as electrolytic capacitor E1 and evaluated.

[0117] <Electrolytic Capacitor C2> A sealing member prepared by further using antioxidant A as an additive was used. Except for this, electrolytic capacitor C2 was assembled in the same manner as electrolytic capacitor C1, and was then evaluated.

[0118] The evaluation results are shown in Table 1. In the table, E1 to E10 are examples, and C1 and C2 are comparative examples.

[0119]

[0120] As shown in Table 1, C1, which does not use an antioxidant, and C2, which contains an antioxidant in the sealing material, exhibit relatively high initial characteristics, and fluctuations in ESR are suppressed to a certain extent in the accelerated test up to about 200 hours. However, when the accelerated test is extended to 575 hours or 750 hours, the ESR increases significantly, and a large leakage current occurs, causing a short circuit.

[0121] In the example in which the antioxidant component is fixed to the solidified resin component, the fluctuation of ESR after the accelerated test is suppressed compared to the comparative example. Furthermore, the example exhibits initial characteristics comparable to those of C1, which uses a sealing body containing an antioxidant.

[0122] In E9, in which one type of antioxidant is immobilized on a conductive polymer, the ESR is kept low at 575 hours of accelerated testing, but a short circuit occurs at 750 hours. On the other hand, in E10, in which two different types of antioxidants are immobilized on a conductive polymer, the ESR is kept low even after the accelerated testing compared to E9. These two types of antioxidants have different molecular weights and melting points. Based on these results, when immobilizing antioxidant components on a conductive polymer, it is advantageous to use two or more types of antioxidants from the perspective of suppressing fluctuations in ESR.

[0123] E1 to E3 show that fluctuations in ESR during accelerated testing can be suppressed even when the same antioxidant is used in both the first and second resin coating layers. When using an antioxidant with a relatively low molecular weight or melting point, it is preferable to set the concentration of the antioxidant in the curable resin material for forming the first or second layer (or both) to 10% by mass or higher, in order to maintain a low ESR for a longer period of time (comparison of E1 with E2 and E3).

[0124] It can be seen that E4, E7, and E8, compared to E1, can suppress ESR fluctuations even when the same antioxidant, which has a relatively high molecular weight and melting point, is used in the first and second layers. E4, E7, and E8 can suppress ESR fluctuations even after 750 hours of accelerated testing, compared to E1, with the use of a small amount of antioxidant. The ESR fluctuation suppression effect of E4 is particularly remarkable. It can be seen that, from the perspective of further suppressing ESR fluctuations, it is more preferable to use an antioxidant with a melting point of 130°C or less.

[0125] In E5, a first antioxidant with a low molecular weight (or low melting point) is immobilized in the first layer, and a second antioxidant with a relatively high molecular weight (or high melting point) is immobilized in the second layer. In E5, the ESR after 750 hours of accelerated testing is lower than both E1 and E4. In E6, the relationship between the molecular weights (or melting points) of the antioxidants immobilized in the first and second layers is the opposite of that in E5. Although E6 also has the effect of suppressing ESR fluctuations, from the perspective of suppressing ESR fluctuations over a longer period of time, it is preferable to immobilize a first antioxidant with a low molecular weight (or low melting point) in the first layer and a second antioxidant with a relatively high molecular weight (or high melting point) in the second layer, as in E5.

[0126] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.

[0127] The electrolytic capacitor of the present disclosure can be used, for example, as a solid electrolytic capacitor. The electrolytic capacitor is particularly suited to applications requiring high reliability over a long period of time. However, the applications of the electrolytic capacitor are not limited to these.

[0128] 100: Electrolytic capacitor 101: Bottomed case 102: Sealing body 103: Base plate 104A, 104B: Lead wires 105A, 105B: Lead tabs 10: Capacitor element 11: Anode body 12: Cathode body 13: Separator 14: Resin coating layer 14a: First layer 14b: Second layer

Claims

1. An electrolytic capacitor comprising: a container having an opening; a capacitor element housed in the container and including a conductive polymer; and a sealing body sealing the opening and including an elastic polymer, wherein the capacitor element includes an antioxidant component fixed in a solidified resin component.

2. The electrolytic capacitor according to claim 1, wherein the antioxidant component includes an antioxidant having a melting point of 130°C or less.

3. The electrolytic capacitor of claim 1, wherein the antioxidant component includes a first antioxidant and a second antioxidant different from the first antioxidant.

4. The electrolytic capacitor according to claim 1, wherein the capacitor element comprises an anode body having a dielectric layer on at least a portion of its surface, a cathode portion covering at least a portion of the dielectric layer, and a resin coating layer covering at least a portion of the cathode portion, wherein the cathode portion includes the conductive polymer in contact with at least a portion of the dielectric layer, and the solidified resin component is at least one of the resin coating layer and the conductive polymer.

5. The electrolytic capacitor according to claim 4, wherein the resin coating layer includes a first layer in contact with at least a portion of the cathode portion, and a second layer covering at least a portion of the first layer.

6. The electrolytic capacitor of claim 5, wherein the first layer includes a first antioxidant, and the second layer includes a second antioxidant different from the first antioxidant.

7. The electrolytic capacitor according to claim 3 or 6, wherein the molecular weight of the first antioxidant is 700 or less, and the molecular weight of the second antioxidant is greater than 700.

8. The electrolytic capacitor according to claim 3 or 6, wherein the melting point of the first antioxidant is 55°C or lower, and the melting point of the second antioxidant is higher than 55°C.

9. The electrolytic capacitor according to claim 4, wherein the capacitor element includes a wound body in which an anode foil as the anode body and a cathode foil are wound with a separator interposed therebetween, and the resin coating layer covers the surface of the wound body, the conductive polymer is interposed between the anode foil and the cathode foil, the cathode portion includes the cathode foil and the conductive polymer, and the resin coating layer is in contact with at least the conductive polymer.

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