Electrolytic capacitors

Abstract

An electrolytic capacitor 1 comprises: a body case 2 that is provided with an opening section; a capacitor element 10 that is accommodated inside the body case 2; and a sealing body 5 that seals the opening section in the body case 2. The capacitor element 10 is such that a positive electrode foil 11, which has an oxide film 16, and negative electrode foil 12, which faces the positive electrode foil 11 across a separator 13, are wound on a surface thereof, and has an electrolyte layer 19, which includes a solid electrolyte 17 containing a conductive polymer and a liquid electrolyte 18 covering at least a portion of the solid electrolyte 17, between the positive electrode foil 11 and the negative electrode foil 12. The liquid electrolyte 18 contains at least an unsaturated fatty acid salt. The unsaturated fatty acid salt alone or a mixture that is the unsaturated fatty acid salt with an unsaturated fatty acid added thereto accounts for 50 wt% or greater of the liquid electrolyte 17.

Description

【Technical Field】 【0001】 The present invention relates to an electrolytic capacitor having a solid electrolyte and a liquid electrolyte. 【Background Art】 【0002】 Conventional electrolytic capacitors are disclosed in Patent Document 1. This electrolytic capacitor has a capacitor element in which an anode foil with an oxide film formed thereon and a counter cathode foil are wound through a separator. The capacitor element is housed in an exterior case, and the exterior case is sealed by a sealing body. Lead terminals are connected to the anode foil and the cathode foil respectively, and the lead terminals penetrate the sealing body and are drawn out outside the exterior case. The capacitor element has a solid electrolyte layer made of a conductive polymer inside and is impregnated with an electrolytic solution. 【0003】 In addition, the solute of the electrolytic solution contains at least one selected from the group consisting of aliphatic hydroxy acids and their salts in an amount of 3 to 30 wt%. Thereby, the equivalent series resistance (hereinafter, ESR) of the electrolytic capacitor is lowered in a high-temperature environment. In addition, the oxidation of the conductive polymer can be suppressed by the oxidation deterioration prevention action of the aliphatic hydroxy acid itself. 【Prior Art Documents】 【Patent Documents】 【0004】 【Patent Document 1】 Japanese Patent Application Laid-Open No. 2018-198248 (pages 3 to 9, FIG. 1) 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0005】 However, with conventional electrolytic capacitors, during prolonged use (especially at high temperatures), the solvent from the gasified electrolyte evaporates from the gap between the lead terminals or the outer casing and the sealing body. This reduces the amount of electrolyte in the capacitor element, exposing the conductive polymer to the air inside the outer casing. The conductive polymer is oxidized by oxygen in the air at high temperatures, losing its conductivity and resulting in low electrical conductivity. This leads to an increase in the ESR of the electrolytic capacitor, which prevents it from having a long lifespan. 【0006】 The present invention aims to extend the lifespan of electrolytic capacitors. [Means for solving the problem] 【0007】 To achieve the above objective, the present invention provides an electrolytic capacitor comprising a main body case having an opening, a capacitor element housed within the main body case, and a sealing body that seals the opening of the main body case, The capacitor element comprises an anode foil having an oxide film on its surface and a cathode foil facing the anode foil via a separator, and has an electrolyte layer between the anode foil and the cathode foil, which comprises a solid electrolyte containing a conductive polymer and a liquid electrolyte covering at least a portion of the solid electrolyte. The liquid electrolyte is characterized in that it contains at least an unsaturated fatty acid salt, and the unsaturated fatty acid salt alone or a mixture of the unsaturated fatty acid salt and an unsaturated fatty acid accounts for 50% by weight or more of the liquid electrolyte. 【0008】 Furthermore, in the electrolytic capacitor having the above configuration, the present invention is characterized in that the unsaturated fatty acid salt is liquid at temperatures of 20°C or higher. 【0009】 Furthermore, the present invention is characterized in that, in an electrolytic capacitor having the above configuration, the liquid electrolyte includes the above mixture, and the unsaturated fatty acid is at least one of palmitoleic acid, oleic acid, linoleic acid, eicosadienoic acid, linolenic acid, pinolenic acid, ricinoleic acid, meadic acid, dihomo-γ-linolenic acid, eicosatrienoic acid, stearidonic acid, arachidonic acid, eicosatetraenoic acid, docosatetraenoic acid, boseopentaenoic acid, eicosapentaenoic acid, osbondic acid, sardine acid, tetracosapentaenoic acid, herringic acid, docosahexaenoic acid, 12-vinyl-8-octadecenedionic acid, or 7,12-dimethyl-7,11-octadecadiene-1,18-dicarboxylic acid. 【0010】 Furthermore, the present invention is characterized in that, in the electrolytic capacitor having the above configuration, at least one of trimethylamine, N,N-dimethylbenzylamine, pyridine, N,N-dimethylaniline, aniline, 2-mercaptobenzimidazole, 1-naphthylamine, morpholine, 1,10-phenanthroline, 2,2'-bipyridyl, acetanilide, acetamide, or derivatives thereof is used as the base of the unsaturated fatty acid salt. 【0011】 Furthermore, the present invention is characterized in that, in the electrolytic capacitor having the above configuration, the liquid electrolyte contains a lipid-soluble antioxidant. 【0012】 Furthermore, the present invention is characterized in that, in the electrolytic capacitor having the above configuration, the lipid-soluble antioxidant is present in an amount of 30% by weight or less of the liquid electrolyte. [Effects of the Invention] 【0013】 According to the present invention, an unsaturated fatty acid salt alone or a mixture of an unsaturated fatty acid salt and an unsaturated fatty acid constitutes 50% by weight or more of the liquid electrolyte. Therefore, evaporation of the liquid electrolyte can be prevented over a long period of time, and oxidative degradation of the conductive polymer can be suppressed. Consequently, the increase in ESR of the electrolytic capacitor can be suppressed, thereby extending the lifespan of the electrolytic capacitor. [Brief explanation of the drawing] 【0014】 [Figure 1] A longitudinal cross-sectional view showing an electrolytic capacitor according to an embodiment of the present invention. [Figure 2] A perspective view showing the capacitor element of an electrolytic capacitor according to an embodiment of the present invention. [Figure 3] Enlarged cross-sectional view showing a portion of the capacitor element of an electrolytic capacitor according to an embodiment of the present invention. [Figure 4] Figure showing the change in ESR over time for embodiments and comparative examples of the present invention. [Figure 5] Figure 4 shows an enlarged view of the ESR range from 10 to 1000 mΩ. [Modes for carrying out the invention] 【0015】 Embodiments of the present invention will be described below with reference to the drawings. Figure 1 is a longitudinal cross-sectional view showing an electrolytic capacitor 1 of one embodiment. The electrolytic capacitor 1 comprises a main body case 2, a capacitor element 10, and a sealing body 5. 【0016】 The main body case 2 is formed from a metal such as aluminum or resin in a bottomed cylindrical shape with a circular cross-section, with one end in the axial direction closed by a closing surface 2a and the other end having an opening 2b. From the viewpoint of processability and sealing performance, it is preferable to form the main body case 2 from aluminum. 【0017】 The sealing body 5 is formed in a disc shape from a molded elastic insulating material such as butyl rubber or ethylene propylene rubber, and has a pair of through holes 5a. The lead terminals 7 and 8 of the capacitor element 10 are inserted through the pair of through holes 5a by press fitting. As a result, the lead terminals 7 and 8 are pulled out to the outside of the sealing body and connected to a circuit board (not shown) by solder or the like. 【0018】 A capacitor element 10 is housed inside a main body case 2, and a sealing body 5 is arranged at an opening 2b. With the sealing body 5 arranged at the opening 2b of the main body case 2, the main body case 2 is subjected to a drawing process that presses the outer peripheral surface. As a result, a drawing processed portion 2c that protrudes toward the inner surface side is formed on the main body case 2. The outer peripheral surface of the sealing body 5 is compressed in the inner circumferential direction by the drawing processed portion 2c and adheres to the inner circumferential surface of the main body case 2. Further, due to the compression of the sealing body 5, the inner surface of the through hole 5a adheres to the lead terminals 7 and 8. Thereby, the opening 2b of the main body case 2 is sealed by the sealing body 5. 【0019】 An end portion on the opening 2b side of the main body case 2 is formed with a bent portion 2d that is curved and bent toward the sealing body 5 side. The bent portion 2d and the drawing processed portion 2c prevent the sealing body 5 from coming out of the main body case 2. 【0020】 In addition, in order to enhance the mountability to a circuit board, a well-known seat plate may be provided. The lead terminals 7 and 8 penetrate through the seat plate and are bent in the radial direction, and this bent portion can be used as a soldering portion to the circuit board. 【0021】 Figure 2 shows a perspective view of the capacitor element 10. The capacitor element 10 has an anode foil 11, a cathode foil 12, and a separator 13 formed in a long strip shape. A pair of electrode foils composed of the anode foil 11 and the cathode foil 12 facing each other through the separator 13 are wound in a substantially cylindrical shape to form the capacitor element 10. The end of the anode foil 11 or the separator 13 is fixed by an adhesive tape 14. 【0022】 The width of the separator 13 in the short side direction (axial direction) is formed larger than the width of the anode foil 11 and the cathode foil 12 in the short side direction. Thereby, the separator 13 protrudes toward the closing surface 2a side and the opening 2b side with respect to the anode foil 11 and the cathode foil 12, and a short circuit between the anode foil 11 and the cathode foil 12 is prevented. 【0023】 The anode foil 11 is formed from a valve metal such as aluminum, tantalum, niobium, or titanium, and its surface is roughened by etching. An oxide film 16 (see Figure 3) is formed on the anode foil 11 by applying a voltage in a chemical conversion solution. 【0024】 The cathode foil 12 is made of a metal such as aluminum, and its surface is roughened by etching. A conductive coating layer of carbon, titanium, or the like may be formed on the surface of the anode foil 11. Alternatively, a naturally occurring oxide film or a chemically converted oxide film may be formed on the surface of the cathode foil 12 by applying a voltage in a chemical conversion solution. 【0025】 The separator 13 can be made from paper made from natural cellulose fibers, or from nonwoven fabrics of chemical fibers such as rayon, polyethylene terephthalate, or polyamide. The separator 13 is porous and can hold electrolytes in the voids between the internal fibers. The thickness of the separator 13 is preferably greater than the size of protrusions such as burrs on the anode foil 11 and cathode foil 12, and is formed to a thickness of, for example, 20 μm to 60 μm. 【0026】 Figure 3 is an enlarged cross-sectional view showing the anode foil 11 of the capacitor element 10. An electrolyte layer 19 containing a solid electrolyte 17 and a liquid electrolyte 18 is provided between the anode foil 11 and the cathode foil 12. The liquid electrolyte 18 covers at least a portion of the solid electrolyte 17. The electrolyte layer 19 is arranged on the surface of the oxide film 16 of the anode foil 11, on the surface of the cathode foil 12, and on the fiber surface of the separator 13. The solid electrolyte 17 of the electrolyte layer 19 held by the separator 13 is formed in a layer on the surface of the fibers, and the liquid electrolyte 18 is held in the gaps between the fibers or in the gaps within the fibers. 【0027】 The solid electrolyte 17 is a conductive polymer doped with a dopant. The conductive polymer can be polypyrrole, polythiophene, polyaniline, or derivatives thereof. The dopant can be p-toluenesulfonic acid, polystyrenesulfonic acid, etc. The conductive polymer can be formed by polymerization within the capacitor element 10. Alternatively, the conductive polymer may be retained within the capacitor element 10 by impregnating the capacitor element 10 with a dispersion of the pre-polymerized conductive polymer in water and then drying it. 【0028】 It is preferable to use polyethylenedioxythiophene (hereinafter referred to as PEDOT) as a derivative of polythiophene and polystyrene sulfonic acid (hereinafter referred to as PSS) as a dopant. This allows the solid electrolyte 17 to be formed from a conductive polymer dispersion with excellent conductivity and stability. 【0029】 Furthermore, by providing a sulfonic acid group within the molecule as a derivative of polythiophene, it can be used as a self-doped conductive polymer soluble in solvents such as water. Similar to conductive polymer dispersions, the self-doped conductive polymer can be retained within the capacitor element 10 by impregnating it with the capacitor element 10 and then drying it. Such a self-doped conductive polymer does not redissolve in the liquid electrolyte 18 containing the unsaturated fatty acid salt described later. Additionally, since the self-doped conductive polymer's moisture absorption is suppressed by the liquid electrolyte 18, the moisture resistance of the electrolytic capacitor 1 can be improved. 【0030】 The liquid electrolyte 18 contains at least an unsaturated fatty acid salt and covers at least a portion of the solid electrolyte 17. The unsaturated fatty acid salt is formed by neutralizing at least a portion of the unsaturated fatty acid contained in the capacitor element 10 with a base. As a result, the liquid electrolyte 18 contains either the unsaturated fatty acid salt alone or a mixture of the unsaturated fatty acid salt and an unsaturated fatty acid. In this case, the liquid electrolyte 18 contains 50% by mass or more of the unsaturated fatty acid salt alone or a mixture of the unsaturated fatty acid salt and an unsaturated fatty acid. 【0031】 Unsaturated fatty acid salts react more readily with oxygen than conductive polymers and absorb surrounding oxygen, thus reducing the oxygen level around the conductive polymer covered by the liquid electrolyte 18. Furthermore, unsaturated fatty acid salts evaporate significantly less than solvents typically used in electrolytes. Therefore, oxidative degradation of the solid electrolyte 17, which consists of the conductive polymer covered by the liquid electrolyte 18, can be suppressed over a long period. 【0032】 Furthermore, unsaturated fatty acid salts have less penetration into the sealing body 5 than unsaturated fatty acids, allowing them to remain in the capacitor element 10 for a longer period of time. In addition, the inclusion of unsaturated fatty acid salts in the liquid electrolyte 18 improves the compatibility between unneutralized unsaturated fatty acids and the other components of the liquid electrolyte 18 described later. 【0033】 Furthermore, if the liquid electrolyte 18 contains solvent components, the evaporation of solvent components can be suppressed by including 50% by weight or more of a single unsaturated fatty acid salt or a mixture of an unsaturated fatty acid salt and an unsaturated fatty acid. In addition, even if solvent components evaporate, the state in which the surface of the conductive polymer is covered with unsaturated fatty acids can be maintained, resulting in a long-life electrolytic capacitor 1. Moreover, if the liquid electrolyte 18 contains 80% by weight or more of a single unsaturated fatty acid salt or a mixture of an unsaturated fatty acid salt and an unsaturated fatty acid, an even longer-life electrolytic capacitor 1 can be obtained. 【0034】 Unsaturated fatty acids are aliphatic compounds that contain at least one carboxyl group and one double bond between two carbon atoms in their molecule. Examples include palmitoleic acid, oleic acid, erucic acid, linoleic acid, eicosadienoic acid, docosadienoic acid, linolenic acid, pinolenic acid, ricinoleic acid, meadic acid, dihomo-γ-linolenic acid, eicosatrienoic acid, stearidonic acid, arachidonic acid, eicosatetraenoic acid, docosatetraenoic acid, boseopentaenoic acid, eicosapentaenoic acid, osbondic acid, sardine acid, tetracosapentaenoic acid, herringic acid, docosahexaenoic acid, 12-vinyl-8-octadecenedionic acid, 7,12-dimethyl-7,11-octadecadiene-1,18-dicarboxylic acid, and the like. Many of these unsaturated fatty acids have boiling points exceeding 250°C at atmospheric pressure, and their evaporation is very low, which can help extend the lifespan of the electrolytic capacitor 1. 【0035】 Among unsaturated fatty acids, compounds containing multiple double bonds between two carbon atoms within the molecule can react with more oxygen, thus stabilizing ESR characteristics over a longer period. Therefore, they are preferable because they significantly extend the lifespan of the electrolytic capacitor 1. 【0036】 In particular, unsaturated fatty acids that contain many double bonds within the molecule, or unsaturated fatty acids that have a branched structure with side chains attached to the main chain of the molecule, often exist as liquids from room temperature (20°C) up to their respective boiling or decomposition points. Their salts, the unsaturated fatty acid salts, are also preferable because they tend to become liquid at room temperature (20°C) or higher. 【0037】 Examples of such unsaturated fatty acids include palmitoleic acid, oleic acid, linoleic acid, eicosadienoic acid, linolenic acid, pinolenic acid, ricinoleic acid, meadic acid, dihomo-γ-linolenic acid, eicosatrienoic acid, stearidonic acid, arachidonic acid, eicosatetraenoic acid, docosatetraenoic acid, boseopentaenoic acid, eicosapentaenoic acid, osbondic acid, sardine acid, tetracosapentaenoic acid, herringic acid, docosahexaenoic acid, 12-vinyl-8-octadecenedionic acid, and 7,12-dimethyl-7,11-octadecadiene-1,18-dicarboxylic acid. 【0038】 Furthermore, compounds having a 1,4-pentadiene structure within the molecule are more preferable because the hydrogen atom of the methylene group sandwiched between two double bonds is easily abstracted, making them more reactive with oxygen. Examples of such compounds include linoleic acid, eicosadienoic acid, docosadienoic acid, linolenic acid, pinolenic acid, meadic acid, dihomo-γ-linolenic acid, eicosatrienoic acid, stearidonic acid, arachidonic acid, eicosatetraenoic acid, adrenaline, boseopentaenoic acid, eicosapentaenoic acid, osbondic acid, sardine acid, tetracosapentaenoic acid, herringic acid, docosahexaenoic acid, and the like. 【0039】 The base used in unsaturated fatty acid salts is a weakly basic organic amine because unsaturated fatty acids are weakly acidic. Unsaturated fatty acid salts neutralized with unsaturated fatty acids and a weak base have low evaporative properties like ionic liquids and possess the ability to repair oxide films 16. Furthermore, because a base weaker in basicity than those used in general ionic liquids is used, dedoping of conductive polymers can be suppressed. As a result, the properties can be maintained over a long period of time, and the electrolyte 18 can be used with high voltage resistance and low evaporative properties. To suppress dedoping of conductive polymers, the base is preferably pKb 4 or higher, and more preferably pKb 8 or higher. 【0040】 Furthermore, lipid-soluble organic amines that are highly compatible with unsaturated fatty acids are preferred because they readily form salts with unsaturated fatty acids. Specifically, trimethylamine, N,N-dimethylbenzylamine, pyridine, N,N-dimethylaniline, aniline, 2-mercaptobenzimidazole, 1-naphthylamine, morpholine, 1,10-phenanthroline, 2,2'-bipyridyl, acetanilide, acetamide, caffeine, or derivatives thereof can be used. 【0041】 Furthermore, since unsaturated fatty acids are weakly acidic, it is preferable that the amount of base relative to the unsaturated fatty acids be small, and even more preferable that it be half or less. 【0042】 Unsaturated fatty acid salts tend to exist in a highly polar state as unsaturated fatty acid ions compared to unsaturated fatty acids. Therefore, by using trace amounts of moisture within the capacitor element 10, defects in the oxide film 16 of the anode foil 11 can be repaired, reducing leakage current over a long period of time. As a result, the degradation of the characteristics of the electrolytic capacitor 1 can be reduced, resulting in an electrolytic capacitor 1 with a long lifespan. 【0043】 The liquid electrolyte 18 may contain, as additives, a solvent for adjusting viscosity, an electrolyte to facilitate the repair of defects in the oxide film 16, a gas absorbent to absorb hydrogen gas generated by the repair action, an antioxidant to suppress oxidative degradation of the conductive polymer, a voltage-resistant agent that acts on the surface of the oxide film 16 to improve its voltage resistance, a solubilizer to make the unsaturated fatty acid salt and the additive compatible, and the like. 【0044】 Adding a solvent to the liquid electrolyte 18 can lower its viscosity and improve its impregnation properties. Using a high-boiling-point polar solvent enhances the repairability of the oxide film 16, improving its dielectric strength and reducing leakage current. Furthermore, the solvent penetrates the conductive polymer layer and improves its electrical conductivity, thereby reducing the ESR of the electrolytic capacitor 1. Suitable solvents include high-boiling-point polar solvents such as γ-butyrolactone, sulfolane, ethylene glycol, and diethylene glycol. 【0045】 Furthermore, the solvent does not need to be completely miscible with the unsaturated fatty acid salt alone or with the mixture of the unsaturated fatty acid salt and the unsaturated fatty acid. The solvent can be used by having the unsaturated fatty acid salt alone or with the mixture of the unsaturated fatty acid salt and the unsaturated fatty acid cover at least a portion of the solid electrolyte 17. 【0046】 Furthermore, it is more preferable that the liquid electrolyte 18 contains an electrolyte solution in which the solute has dissolved in the solvent and undergone ion dissociation. This further enhances the repairability of the oxide film 16 and further reduces the leakage current of the electrolytic capacitor 1. 【0047】 As the antioxidant added to the liquid electrolyte 18, a water-soluble antioxidant and / or a lipid-soluble antioxidant can be used. 【0048】 Water-soluble antioxidants dissolve readily in high-boiling-point polar solvents and are thought to directly suppress the oxidation of conductive polymers. However, if the amount of water-soluble antioxidant added is increased too much, it can easily affect properties such as voltage resistance and durability. For this reason, the amount of water-soluble antioxidant is preferably 3% by weight or less of the liquid electrolyte 18, and more preferably 2% by weight or less. 【0049】 To elicit the antioxidant effect of a water-soluble antioxidant, it is preferable that the water-soluble antioxidant be present in an amount of 0.1% by weight or more of the liquid electrolyte 18. Examples of water-soluble antioxidants include catechol, hydroquinone, resorcinol, pyrogallol, protocatechuic acid, and gallic acid. 【0050】 The lipid-soluble antioxidant contained in the liquid electrolyte 18 readily dissolves in unsaturated fatty acid salts alone or in mixtures of unsaturated fatty acid salts and unsaturated fatty acids. The lipid-soluble antioxidant can accept free radicals generated when unsaturated fatty acid salts or unsaturated fatty acids react with oxygen or undergo thermal cleavage, thereby suppressing or eliminating the activity of free radicals. 【0051】 Therefore, oxidative degradation of unsaturated fatty acids and conductive polymers due to free radicals can be suppressed. As a result, the antioxidant effect of the conductive polymer can be dramatically improved through the combined action of oxygen gas absorption and oxidation suppression around the conductive polymer. Consequently, the degradation of the characteristics of the electrolytic capacitor 1 can be reduced over a long period of time. 【0052】 Furthermore, even if the amount of lipid-soluble antioxidant is increased, it does not impede the repairability of defects in the oxide film 16 of the anode foil 11. Therefore, the degree of freedom in designing the composition of the liquid electrolyte 18 can be increased. Compared to water-soluble antioxidants, lipid-soluble antioxidants have less impact on changes in properties such as voltage resistance and durability, and the amount added to the liquid electrolyte 18 can be 30% by weight or less. To obtain the oxidation-inhibiting effect of the lipid-soluble antioxidant, it is preferable to include 1% by weight or more of the liquid electrolyte 18. 【0053】 Furthermore, some of the lipid-soluble antioxidant can penetrate the sealing body 5, thereby suppressing its deterioration. Lipid-soluble antioxidants have high compatibility with unsaturated fatty acid salts. Therefore, the balance between the lipid-soluble antioxidant in the liquid electrolyte 18 and the lipid-soluble antioxidant penetrating the sealing body 5 can be adjusted by controlling the amount of unsaturated fatty acid salt in the liquid electrolyte 18. 【0054】 Furthermore, since the liquid electrolyte 18 contains 50% by weight or more of an unsaturated fatty acid salt or a mixture of an unsaturated fatty acid salt and an unsaturated fatty acid, an excessive amount of lipid-soluble antioxidant is supplied to the sealing body 5. This suppresses the deterioration of the sealing body 5 over a long period of time, thereby extending the lifespan of the electrolytic capacitor 1. It is also believed that some of the unsaturated fatty acids in the liquid electrolyte 18 penetrate the sealing body 5, contributing to the suppression of its deterioration. 【0055】 Examples of lipid-soluble antioxidants include retinol, β-carotene, α-carotene, β-cryptoxanthin, astaxanthin, tocopherol (α-tocopherol, β-tocopherol, γ-tocopherol, δ-tocopherol), tocotrienol (α-tocotrienol, β-tocotrienol, γ-tocotrienol, δ-tocotrienol), etc. Tocopherol is particularly preferred in terms of inhibiting the deterioration of the sealing body 5 due to its excellent permeability and antioxidant effect. 【0056】 According to this embodiment, the unsaturated fatty acid salt alone or a mixture of the unsaturated fatty acid salt and an unsaturated fatty acid accounts for 50% by weight or more of the liquid electrolyte 18. Therefore, evaporation of the liquid electrolyte 18 can be prevented over a long period of time, and oxidative degradation of the solid electrolyte 17, which is made of a conductive polymer, can be suppressed. Consequently, the increase in the ESR of the electrolytic capacitor 1 can be suppressed, thereby extending the lifespan of the electrolytic capacitor 1. 【0057】 Furthermore, since the unsaturated fatty acid salts contained in the liquid electrolyte 18 are liquid at temperatures above 20°C, the liquid electrolyte 18 can be easily realized. 【0058】 Furthermore, at least one of the following is used as the unsaturated fatty acid contained in the liquid electrolyte 18: palmitoleic acid, oleic acid, linoleic acid, eicosadienoic acid, linolenic acid, pinolenic acid, ricinoleic acid, meadic acid, dihomo-γ-linolenic acid, eicosatrienoic acid, stearidonic acid, arachidonic acid, eicosatetraenoic acid, docosatetraenoic acid, bosopentaenoic acid, eicosapentaenoic acid, osbondic acid, sardine acid, tetracosapentaenoic acid, herringic acid, docosahexaenoic acid, 12-vinyl-8-octadecenedionic acid, or 7,12-dimethyl-7,11-octadecadiene-1,18-dicarboxylic acid. This makes it possible to easily obtain liquid unsaturated fatty acid salts at temperatures above 20°C. 【0059】 Furthermore, as the base of the unsaturated fatty acid salt contained in the liquid electrolyte 18, at least one of trimethylamine, N,N-dimethylbenzylamine, pyridine, N,N-dimethylaniline, aniline, 2-mercaptobenzimidazole, 1-naphthylamine, morpholine, 1,10-phenanthroline, 2,2'-bipyridyl, acetanilide, acetamide, or derivatives thereof is used. This makes it easy to realize a liquid electrolyte 18 with low evaporability and suppression of dedoping of conductive polymers. 【0060】 Furthermore, if the liquid electrolyte 18 contains a lipid-soluble antioxidant, oxidative degradation of unsaturated fatty acids and conductive polymers due to free radicals can be suppressed. Therefore, the degradation of the characteristics of the electrolytic capacitor 1 can be reduced over a longer period. 【0061】 Furthermore, if the liquid electrolyte 18 contains 30% by weight or less of a lipid-soluble antioxidant, the oxidative degradation of unsaturated fatty acids and conductive polymers can be suppressed more reliably. 【0062】 The following describes examples of electrolytic capacitors 1 formed to evaluate the electrolytic capacitor 1 of this embodiment. The compositions of the liquid electrolyte 18 in Examples 1 to 13 and Comparative Examples 1 and 2 are shown in Table 1. 【0063】 [Table 1] [Examples] 【0064】 In Example 1, lead terminals 7 and 8 were first connected to the anode foil 11 and cathode foil 12, which had an oxide film 16 formed on their surfaces. Next, the two electrode foils were wound together via a separator 13 to form a capacitor element 10 with an element shape of φ6.3 mm × L7.7 mm. Then, the capacitor element 10 was immersed in an aqueous solution of ammonium adipate for 30 minutes and a voltage was applied to perform a repair chemical reaction. 【0065】 Next, the capacitor element 10 was immersed in a conductive polymer compound dispersion in which a composite of PEDOT and PSS was dispersed in water. After that, the capacitor element 10 was removed and dried at approximately 125°C to form a layer of solid electrolyte 17 made of conductive polymer. 【0066】 Next, a solution of 76% by weight of oleic acid and 24% by weight of 1,10-phenanthroline was impregnated into the capacitor element 10. Oleic acid is an unsaturated fatty acid, and 1,10-phenanthroline is a weak base. This formed a liquid electrolyte 18 containing an unsaturated fatty acid salt. The boiling point of oleic acid is 203-205°C (5 mmHg). 【0067】 Then, the capacitor element 10 was inserted into the bottomed cylindrical main case 2, the sealing body 5 was attached, and it was sealed by crimping. After that, aging was performed by applying voltage to form the electrolytic capacitor 1. The rated voltage of this electrolytic capacitor 1 is 25WV and the rated capacitance is 100μF. [Examples] 【0068】 In Example 2, the electrolytic capacitor 1 was impregnated with a solution containing 74% by weight of oleic acid and 26% by weight of caffeine during the formation of the liquid electrolyte 18. Oleic acid is an unsaturated fatty acid, and caffeine is a weak base. Otherwise, it is the same as in Example 1. [Examples] 【0069】 In Example 3, the electrolytic capacitor 1 was impregnated with a solution of 76% by weight of linoleic acid and 24% by weight of 1,10-phenanthroline during the formation of the liquid electrolyte 18. Linoleic acid is an unsaturated fatty acid, and 1,10-phenanthroline is a weak base. The boiling point of linoleic acid is 229-230°C (16 mmHg). Otherwise, it is the same as in Example 1. [Examples] 【0070】 In Example 4, the electrolytic capacitor 1 was impregnated with a solution containing 74% by weight of linoleic acid and 26% by weight of caffeine during the formation of the liquid electrolyte 18. Linoleic acid is an unsaturated fatty acid, and caffeine is a weak base. Otherwise, it is the same as in Example 1. [Examples] 【0071】 In Example 5, the electrolytic capacitor 1 was impregnated with a solution containing 77% by weight of arachidonic acid and 23% by weight of 1,10-phenanthroline during the formation of the liquid electrolyte 18. Arachidonic acid is an unsaturated fatty acid, and 1,10-phenanthroline is a weak base. The boiling point of arachidonic acid is 169-171°C (0.15 mmHg). Otherwise, it is the same as in Example 1. [Examples] 【0072】 In Example 6, the electrolytic capacitor 1 was impregnated with a solution containing 75% by weight of arachidonic acid and 25% by weight of caffeine during the formation of the liquid electrolyte 18. Arachidonic acid is an unsaturated fatty acid, and caffeine is a weak base. Otherwise, it is the same as in Example 1. [Examples] 【0073】 In Example 7, the electrolytic capacitor 1 was impregnated with a solution containing 42.7% by weight of linoleic acid, 14.5% by weight of 1,10-phenanthroline, and 42.7% by weight of diethylene glycol during the formation of the liquid electrolyte 18. Linoleic acid is an unsaturated fatty acid, 1,10-phenanthroline is a weak base, and ethylene glycol is a high-boiling point polar solvent. The dimensions of the electrolytic capacitor 1 are φ6.3mm × L7.7mm, the rated voltage is 35V, and the rated capacitance is 47μF. Otherwise, it is the same as in Example 1. [Examples] 【0074】 In Example 8, the electrolytic capacitor 1 was impregnated with a solution containing 43.1% by weight of linoleic acid, 13.8% by weight of caffeine, and 43.1% by weight of diethylene glycol during the formation of the liquid electrolyte 18. Linoleic acid is an unsaturated fatty acid, caffeine is a weak base, and ethylene glycol is a high-boiling point polar solvent. Otherwise, it is the same as in Example 7. [Examples] 【0075】 In Example 9, the electrolytic capacitor 1 was impregnated with a solution containing 50% by weight of oleic acid, 18% by weight of γ-butyrolactone, 27% by weight of sulfolane, 4% by weight of borodisalicylic acid, and 1% by weight of trimethylamine during the formation of the liquid electrolyte 18. Oleic acid is an unsaturated fatty acid, trimethylamine is a weak base and solute of the electrolyte, γ-butyrolactone and sulfolane are solvents of the electrolyte, and borodisalicylic acid is a solute of the electrolyte. Otherwise, it is the same as in Example 1. 【0076】 Furthermore, since the electrolyte and unsaturated fatty acids were not completely miscible, the electrolytic capacitor 1 was created by first impregnating the capacitor element 10 with the electrolyte and then further impregnating it with unsaturated fatty acids. [Examples] 【0077】 In Example 10, the electrolytic capacitor 1 was impregnated with a solution containing 50% by weight of linoleic acid, 18% by weight of γ-butyrolactone, 27% by weight of sulfolane, 4% by weight of borogisalicylic acid, and 1% by weight of trimethylamine during the formation of the liquid electrolyte 18. Linoleic acid is an unsaturated fatty acid, trimethylamine is a weak base and solute of the electrolyte, γ-butyrolactone and sulfolane are solvents of the electrolyte, and borogisalicylic acid is a solute of the electrolyte. Otherwise, it is the same as in Example 9. [Examples] 【0078】 In Example 11, the electrolytic capacitor 1 was impregnated with a solution containing 25% by weight of oleic acid, 25% by weight of linoleic acid, 18% by weight of γ-butyrolactone, 27% by weight of sulfolane, 4% by weight of borogisalicylic acid, and 1% by weight of trimethylamine during the formation of the liquid electrolyte 18. Oleic acid and linoleic acid are unsaturated fatty acids, trimethylamine is a weak base and solute of the electrolyte, γ-butyrolactone and sulfolane are solvents of the electrolyte, and borogisalicylic acid is a solute of the electrolyte. Otherwise, it is the same as in Example 9. [Examples] 【0079】 In Example 12, the electrolytic capacitor 1 was impregnated with a solution containing 50% by weight of oleic acid, 29% by weight of γ-butyrolactone, 12% by weight of sulfolane, 4% by weight of borodisalicylic acid, 1% by weight of trimethylamine, and 4% by weight of D-α-tocopherol during the formation of the liquid electrolyte 18. Oleic acid is an unsaturated fatty acid, trimethylamine is a weak base and solute of the electrolyte, γ-butyrolactone and sulfolane are solvents of the electrolyte, borodisalicylic acid is a solute of the electrolyte, and D-α-tocopherol is a lipid-soluble antioxidant. The boiling point of D-α-tocopherol is 220°C (0.1 mmHg). Otherwise, it is the same as in Example 9. [Examples] 【0080】 In Example 13, when forming the liquid electrolyte 18, the electrolytic capacitor 1 was impregnated with a solution containing 50% by weight of linoleic acid, 29% by weight of γ-butyrolactone, 12% by weight of sulfolane, 4% by weight of borogisalicylic acid, 1% by weight of trimethylamine, and 4% by weight of D-α-tocopherol. 【0081】 Linoleic acid is an unsaturated fatty acid, trimethylamine is a weak base and solute of the electrolyte, γ-butyrolactone and sulfolane are solvents of the electrolyte, borodisalicylic acid is a solute of the electrolyte, and D-α-tocopherol is a lipid-soluble antioxidant. Otherwise, it is the same as in Example 9. 【0082】 [Comparative Example 1] In addition, comparative examples were prepared for comparison. In Comparative Example 1, when forming the liquid electrolyte 18, the capacitor element 10 was impregnated with a mixture of 76% by weight of isostearic acid and 24% by weight of 1,10-phenanthroline. 1,10-phenanthroline is a weak base, while isostearic acid is a saturated fatty acid. The boiling point of isostearic acid is 183°C (5 mmHg). Otherwise, it is the same as Example 1. 【0083】 [Comparative Example 2] In Comparative Example 2, when forming the liquid electrolyte 18, the capacitor element 10 was impregnated with an electrolyte solution containing 36% by weight of γ-butyrolactone, 54% by weight of sulfolane, 8% by weight of borogisalicylic acid, and 2% by weight of trimethylamine. γ-butyrolactone and sulfolane were the solvents of the electrolyte, and borogisalicylic acid and trimethylamine were the solutes. Otherwise, it was the same as Example 1. 【0084】 Table 2, Figure 4, and Figure 5 show the changes in ESR when each of the above examples and comparative examples was subjected to a 10,000-hour durability test at 150°C with the rated voltage applied. In Figures 4 and 5, the vertical axis represents ESR (unit: mΩ), and the horizontal axis represents time (unit: Hrs). Note that Figure 5 shows an enlarged view of Figure 4 for the ESR range of 10 to 1000 mΩ for easier understanding. 【0085】 [Table 2] 【0086】 According to Table 2, Figures 4 and 5, Examples 1 to 13, which contain 50% by weight or more of an unsaturated fatty acid salt or a mixture of an unsaturated fatty acid salt and an unsaturated fatty acid in the liquid electrolyte 18, maintain low ESR in durability tests. This allows the ESR characteristics to be maintained stably for a long period of time even in high-temperature environments of 150°C. 【0087】 Furthermore, the ESR properties can be maintained stably for a long period of time even when a high-boiling-point polar solvent is added (Examples 7 and 8) or when an electrolyte is included (Examples 9 to 13). 【0088】 Furthermore, it was confirmed that the liquid electrolyte 18 remained inside the capacitor element 10 of each electrolytic capacitor 1 in Examples 1 to 13 after the durability test. Therefore, the liquid electrolyte 18 covers the conductive polymer solid electrolyte 17, suppressing the degradation of the conductive polymer and resulting in a long-life electrolytic capacitor 1. 【0089】 In contrast, Comparative Examples 1 and 2, which do not contain unsaturated fatty acids, showed significant deterioration in ESR characteristics after 3000 to 4000 hours in a high-temperature environment of 150°C. [Industrial applicability] 【0090】 This invention can be used in automobiles, electronic devices, and the like, which incorporate electrolytic capacitors into their circuits. [Explanation of symbols] 【0091】 1 Electrolytic capacitor 2. Main unit case 2a Occlusion surface 2b opening 2c Deep drawing section 2d bend part 5 Sealing body 5a through hole 6 Separators 7, 8 Lead terminals 10 Capacitor element 11 Anode foil 12 Cathode foil 13 Separator 14 Adhesive tape 16 Oxide film 17 Solid electrolyte 18 Liquid electrolyte 19 Electrolyte layer

Claims

[Claim 1] An electrolytic capacitor comprising a main body case having an opening, a capacitor element housed within the main body case, and a sealing body that seals the opening of the main body case, The capacitor element comprises an anode foil having an oxide film on its surface and a cathode foil facing the anode foil via a separator, and has an electrolyte layer between the anode foil and the cathode foil, which comprises a solid electrolyte containing a conductive polymer and a liquid electrolyte covering at least a portion of the solid electrolyte. The electrolytic capacitor is characterized in that the liquid electrolyte contains at least an unsaturated fatty acid salt, and the unsaturated fatty acid salt alone or a mixture of the unsaturated fatty acid salt and an unsaturated fatty acid accounts for 50% by weight or more of the liquid electrolyte. [Claim 2] The electrolytic capacitor according to claim 1, characterized in that the unsaturated fatty acid salt is liquid at 20°C or higher. [Claim 3] The electrolytic capacitor according to claim 2, wherein the liquid electrolyte comprises the mixture, and the unsaturated fatty acid used is at least one of palmitoleic acid, oleic acid, linoleic acid, eicosadienoic acid, linolenic acid, pinolenic acid, ricinoleic acid, meadic acid, dihomo-γ-linolenic acid, eicosatrienoic acid, stearidonic acid, arachidonic acid, eicosatetraenoic acid, docosatetraenoic acid, bosopentaenoic acid, eicosapentaenoic acid, osbondic acid, sardine acid, tetracosapentaenoic acid, herringic acid, docosahexaenoic acid, 12-vinyl-8-octadecenedionic acid, or 7,12-dimethyl-7,11-octadecadiene-1,18-dicarboxylic acid. [Claim 4] The electrolytic capacitor according to claim 2, characterized in that at least one of trimethylamine, N,N-dimethylbenzylamine, pyridine, N,N-dimethylaniline, aniline, 2-mercaptobenzimidazole, 1-naphthylamine, morpholine, 1,10-phenanthroline, 2,2'-bipyridyl, acetanilide, acetamide, or derivatives thereof is used as the base of the unsaturated fatty acid salt. [Claim 5] The electrolytic capacitor according to any one of claims 1 to 4, characterized in that the liquid electrolyte contains a lipid-soluble antioxidant. [Claim 6] The electrolytic capacitor according to claim 5, characterized in that the lipid-soluble antioxidant is contained in the liquid electrolyte in an amount of 30% by weight or less.

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