Electrolytic solution for electrolytic capacitor, electrolytic capacitor, and method for manufacturing electrolytic capacitor

Abstract

To provide an electrolytic solution for an electrolytic capacitor capable of suppressing an increase in leakage current under a high temperature environment, an electrolytic capacitor using the electrolytic solution for the electrolytic capacitor, and a method of manufacturing the electrolytic capacitor.SOLUTION: The electrolytic solution for an electrolytic capacitor contains inorganic oxide colloid particles, acid components which are phosphoric acids, hypophosphorous acids, or both of them, and a glycol compound, and the acid components are contained by 1. 7mmol or more and 5. 2mmol or less with respect to the electrolytic solution for an electrolytic capacitor. The electrolytic capacitor includes an anode body in which a dielectric film is formed on the surface of a foil using a valve action metal as a base material, and a cathode body, and the electrolytic solution for the electrolytic capacitor is interposed between the anode body and the cathode body. The electrolytic solution for an electrolytic capacitor is prepared in advance in an electrolytic solution preparation step, and an element composed of an anode body and a cathode body is impregnated with the electrolytic solution in an impregnation step.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electrolyte for an electrolytic capacitor, an electrolytic capacitor, and a method for manufacturing an electrolytic capacitor. [Background technology]

[0002] Electrolytic capacitors have valve metals such as tantalum or aluminum as anode and cathode bodies. The anode body is enlarged by shaping the valve metal into a sintered body or etched foil, and a dielectric film is formed on the enlarged surface. An electrolytic capacitor electrolyte is interposed between the anode and cathode bodies. The electrolytic capacitor electrolyte is in close contact with the uneven surface of the anode body and functions as a true cathode.

[0003] The electrolyte for electrolytic capacitors is interposed between the dielectric film of the anode body and the cathode body. Therefore, the electrical conductivity and temperature characteristics of the electrolyte for electrolytic capacitors have a significant effect on the electrical characteristics of the electrolytic capacitor, such as impedance, dielectric loss (tanδ), and equivalent series resistance (ESR). In addition, the electrolyte for electrolytic capacitors has chemical conversion properties that repair deteriorated or damaged parts of the dielectric film formed on the anode body, which affects the leakage current (LC) and life characteristics of the electrolytic capacitor.

[0004] Therefore, an electrolyte solution for electrolytic capacitors with at least high electrical conductivity is suitable for electrolytic capacitors, but increasing the electrical conductivity of the electrolyte solution for electrolytic capacitors tends to lower the spark voltage, which may impair the withstand voltage characteristics of the electrolytic capacitor.From the viewpoint of safety, it is desirable for the electrolyte solution to have a high withstand voltage so as not to cause a short circuit or fire, even under harsh conditions such as when an abnormal voltage exceeding the rated voltage is applied to the electrolytic capacitor.

[0005] Attempts have been made to add alkylene oxide adducts of tri- to octahydric polyhydric alcohols to electrolytes for electrolytic capacitors in order to improve voltage resistance while maintaining high electrical conductivity (see, for example, Patent Document 1). However, these alkylene oxide adducts are water-soluble polymers. When a water-soluble polymer is used as a voltage resistance improver, the capacitance of the electrolytic capacitor deteriorates when the electrolytic capacitor is used in a low-temperature environment, such as at -40°C.

[0006] Therefore, attempts have been made to add various inorganic oxide colloidal particles instead of water-soluble polymers (see Patent Document 2). The inorganic oxide colloidal particles are typically silica colloidal particles, but other particles such as zirconia, titania, aluminosilicate, and aluminosilicate-coated silica have also been proposed. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2016 / 143535 [Patent Document 2] Japanese Patent Application Publication No. 1-232713 Summary of the Invention [Problem to be solved by the invention]

[0008] Electrolytic capacitors may contain moisture. In addition to being intentionally contained in the electrolyte for electrolytic capacitors, moisture may also be mixed in during the manufacturing process of electrolytic capacitors. The valve metal of the anode body deteriorates due to hydration reactions. Deterioration of the valve metal of the anode body can cause, for example, an increase in leakage current of the electrolytic capacitor.

[0009] The valve metal of the anode body is usually covered with a dielectric film. However, inorganic oxide colloidal particles dissolve the dielectric film in a high-temperature environment, such as 105°C. When the dielectric film of the anode body dissolves, the valve metal is exposed and is inevitably subject to deterioration due to hydration reactions.

[0010] In other words, when an electrolytic solution for an electrolytic capacitor containing inorganic oxide colloidal particles is used, the low-temperature characteristics are good, but the high-temperature characteristics require improvement. The present invention has been proposed to solve the above-mentioned problems, and its object is to provide an electrolytic solution for an electrolytic capacitor that can suppress an increase in leakage current in a high-temperature environment, an electrolytic capacitor using this electrolytic solution for an electrolytic capacitor, and a method for manufacturing an electrolytic capacitor. [Means for solving the problem]

[0011] In order to achieve the above object, the electrolyte for electrolytic capacitors according to this embodiment comprises inorganic oxide colloidal particles, an acid component which is phosphoric acid, hypophosphorous acid, or both, and a solvent containing a glycol compound, and the acid component is contained in an amount of 1.7 mmol or more and 5.2 mmol or less relative to the electrolyte for electrolytic capacitors.

[0012] Azelaic acid, 1,6-decanedicarboxylic acid, or both of these may be further included as the chain dicarboxylic acid.

[0013] The glycol compound contains diethylene glycol, and the diethylene glycol is contained in an amount of 14 wt % or more relative to the total amount of the solvent.

[0014] The chain dicarboxylic acid may include at least the 1,6-decanedicarboxylic acid, and the 1,6-decanedicarboxylic acid may be contained in an amount of 25 mol % or more based on the total amount of the chain dicarboxylic acids.

[0015] In order to achieve the above object, the electrolytic capacitor according to the present embodiment includes an anode body having a valve metal foil as a base material and a dielectric coating formed on the surface thereof, a cathode body, and an electrolytic solution interposed between the anode body and the cathode body, the electrolytic solution including inorganic oxide colloidal particles, an acid component which is phosphoric acid, hypophosphorous acid, or both, and a solvent containing a glycol compound, and the acid component is contained in an amount of 1.7 mmol or more and 5.2 mmol or less relative to the electrolytic solution.

[0016] The electrolyte may further contain azelaic acid, 1,6-decanedicarboxylic acid, or both of them as a chain dicarboxylic acid.

[0017] The glycol compound contains diethylene glycol, and the diethylene glycol is contained in an amount of 14 wt % or more relative to the total amount of the solvent.

[0018] The chain dicarboxylic acid may include at least the 1,6-decanedicarboxylic acid, and the 1,6-decanedicarboxylic acid may be contained in an amount of 25 mol % or more based on the total amount of the chain dicarboxylic acids.

[0019] Furthermore, in order to achieve the above object, the method for manufacturing an electrolytic capacitor according to the present embodiment includes an anode-forming step of forming an anode body having a foil based on a valve metal and a dielectric film formed on the surface thereof, a cathode-forming step of forming a cathode body, an electrolyte-solution preparing step of preparing an electrolyte solution to be interposed between the anode body and the cathode body, an element-forming step of forming an element in which the anode body and the cathode body face each other, and an electrolyte-solution impregnation step of impregnating the element with the electrolyte, wherein the electrolyte solution includes inorganic oxide colloidal particles, an acid component which is phosphoric acid, hypophosphorous acid, or both, and a solvent containing a glycol compound, and the acid component is contained in an amount of 1.7 mmol or more and 5.2 mmol or less relative to the electrolyte solution. [Effects of the Invention]

[0020] According to the present invention, an increase in leakage current in a high-temperature environment can be suppressed. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a graph showing the relationship between the amount of each acid component added and leakage current. [Figure 2] 2 is a graph showing the relationship between the amount of each acid component added and the withstand voltage. [Figure 3]1 is a graph showing the relationship between the withstand voltage and the total amount of electricity of the spike current during the aging process relative to the content of diethylene glycol in the solvent. [Figure 4] 1 is a graph showing the relationship between the withstand voltage and the total amount of electricity of the spike current during the aging process relative to the content of 1,6-decanedicarboxylic acid in the chain dicarboxylic acid. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, an electrolytic solution for an electrolytic capacitor and an electrolytic capacitor according to an embodiment of the present invention will be described, but the present invention is not limited to the embodiment described below.

[0023] (Overall configuration of electrolytic capacitor) An electrolytic capacitor is a passive element that obtains capacitance through the dielectric polarization of a dielectric film and stores and discharges electric charge. An electrolytic capacitor includes an anode body and a cathode body, each having a dielectric film formed on its surface. The anode body and the cathode body are arranged opposite each other. An electrolytic capacitor electrolyte is filled between the dielectric film of the anode body and the cathode body. The electrolytic capacitor electrolyte is in close contact with the dielectric film to form a true cathode. The anode body and the cathode body are arranged opposite each other with a separator interposed between them. The separator prevents shorting between the anode body and the cathode body and also retains the electrolytic capacitor electrolyte.

[0024] An example of a method for manufacturing this electrolytic capacitor is outlined as follows. First, in an element formation process, the anode body and cathode body formed in the anode formation process and the cathode formation process are stacked with a separator interposed between them to form a capacitor element. Next, in an electrolyte impregnation process, the capacitor element is impregnated with the electrolytic capacitor electrolyte prepared in the electrolyte preparation process. Then, in a packaging process, the capacitor element is packaged by sealing the open end of the case containing the capacitor element with a sealing member, and in an aging process, a voltage is applied to repair defects that have occurred in the dielectric film.

[0025] (Electrolyte for electrolytic capacitors) The electrolyte for electrolytic capacitors is a mixed solution in which a solute is dissolved in a solvent and an additive is added to the solvent, and the additive is at least inorganic oxide colloid particles.

[0026] Examples of inorganic oxide colloidal particles include silica, alumina, titania, zirconia, antimony oxide, aluminosilicate, silica zirconia, titania zirconia, silica coated with aluminosilicate, silica coated with silica zirconia, etc., or mixtures thereof. Among these inorganic oxide colloidal particles, silica, aluminosilicate, or silica coated with aluminosilicate is particularly preferred from the viewpoints of ease of silylation treatment, stability of colloidal particles, and improvement in withstand voltage.

[0027] However, the inorganic oxide colloidal particles are preferably 1 wt% or more and 17 wt% or less relative to the electrolyte for electrolytic capacitors. If it is 1 wt% or more, the inorganic oxide colloidal particles have a better effect of improving the withstand voltage. On the other hand, if it is 17 wt% or less, the specific resistance of the electrolyte for electrolytic capacitors decreases. Furthermore, the average particle diameter of the inorganic oxide colloidal particles is preferably 5 nm or more and 50 nm or less. If it is 5 nm or more, the rate of change in withstand voltage after heat resistance testing is small. If it is 50 nm or less, the initial withstand voltage is high.

[0028] Here, exposure of the dielectric film of the anode body to inorganic oxide colloid particles affects the dissolution of the dielectric film. Although this is speculation and not limited to this mechanism, it is believed that the dissolution of the dielectric film of the anode body is due to the following reason: Hydroxyl groups on the surface of inorganic oxide colloid particles attract moisture in the electrolyte for electrolytic capacitors. Therefore, when inorganic oxide colloid particles are present near the dielectric film of the anode body, moisture attracted by the hydroxyl groups on the surface of the inorganic oxide colloid particles easily approaches the dielectric film of the anode body, dissolving the dielectric film and passing through the dielectric film to reach the valve metal, causing hydration degradation of the valve metal.

[0029] Therefore, the electrolyte for electrolytic capacitors contains phosphoric acid, hypophosphorous acid, or both as the acid component of the solute. The amount of phosphoric acid or hypophosphorous acid contained in the electrolyte for electrolytic capacitors is in the range of 1.7 mmol to 5.2 mmol per 100 g of the electrolyte for electrolytic capacitors. When both phosphoric acid and hypophosphorous acid are contained in the electrolyte for electrolytic capacitors, the total amount of phosphoric acid and hypophosphorous acid contained in the electrolyte for electrolytic capacitors is in the range of 1.7 mmol to 5.2 mmol per 100 g of the electrolyte for electrolytic capacitors.

[0030] Hereinafter, phosphoric acid, hypophosphorous acid, or both of them will be referred to as the specific acid component. The specific acid component forms a coating film that covers the dielectric film of the anode body. This coating film acts as a barrier, making it difficult for the hydroxyl groups of the inorganic oxide colloidal particles and the moisture attracted to these hydroxyl groups to approach the dielectric film. Therefore, dissolution of the dielectric film is suppressed.

[0031] However, the acid component itself generally dissolves the dielectric film, creating a path for moisture to reach the valve metal. However, phosphoric acid and hypophosphorous acid have little effect on dissolving the dielectric film. Therefore, when phosphoric acid and hypophosphorous acid are contained in the electrolyte for electrolytic capacitors, the inorganic oxide colloid particles increase the withstand voltage of the electrolytic capacitor and suppress an increase in leakage current of the electrolytic capacitor even when exposed to high-temperature environments.

[0032] When an acid component other than phosphoric acid or hypophosphorous acid is mixed, a chain dicarboxylic acid having a total of 9 to 22 carbon atoms is mixed. Although the specific acid component also has the effect of dissolving the dielectric film, albeit to a small extent, the chain dicarboxylic acid having a total of 9 to 22 carbon atoms has a high film-forming ability for the dielectric film, which can offset the dissolving effect of the specific acid component. As the chain dicarboxylic acid having a total of 9 to 22 carbon atoms, azelaic acid, 1,6-decanedicarboxylic acid, or both are preferred. Azelaic acid and 1,6-decanedicarboxylic acid also improve the withstand voltage of electrolytic capacitors.

[0033] Furthermore, if the content of the specific acid component in the electrolyte solution for electrolytic capacitors exceeds 5.2 mmol, the effect of improving the withstand voltage provided by the inorganic oxide colloidal particles is adversely affected, resulting in a decrease in the withstand voltage of the electrolytic capacitor. Therefore, when increasing the amount of the acid component as a solute in the electrolyte solution for electrolytic capacitors, it is preferable to set the upper limit of the specific acid component to 5.2 mmol or less, and make up the remainder with azelaic acid, 1,6-decanedicarboxylic acid, or both.

[0034] Particularly preferred is 1,6-decanedicarboxylic acid. By combining phosphoric acid, hypophosphorous acid, or both with diethylene glycol, the risk of short circuits that may occur during aging of electrolytic capacitors is reduced, and the yield of electrolytic capacitors is improved.

[0035] Although this is speculation and not intended to be limiting, it is a fact that the greater the total electrical charge of the spike current during the aging process of an electrolytic capacitor, the greater the possibility of a short circuit occurring during the aging process. On the other hand, when an electrolyte solution for an electrolytic capacitor is prepared by combining phosphoric acid, hypophosphorous acid, or both with 1,6-decanedicarboxylic acid, the total electrical charge of the spike current during the aging process becomes smaller.

[0036] However, when reducing the total amount of electricity in the spike current during the aging process, 1,6-decanedicarboxylic acid is contained in a proportion of 25 mol% or more relative to the total amount of chain dicarboxylic acids. If the amount of 1,6-decanedicarboxylic acid deviates from this range, the total amount of electricity in the spike current during the aging process cannot be reduced to a level sufficient to suppress the incidence of short circuits in the electrolytic capacitor.

[0037] The inorganic oxide colloidal particles may have their particle surfaces modified with an organic substance. The inorganic oxide colloidal particles having their surfaces modified with an organic substance suppress gelation of the electrolyte and aggregation of the colloidal particles, thereby maintaining the withstand voltage of the electrolytic capacitor.

[0038] The organic substance is substituted with the surface hydroxyl groups of the inorganic oxide colloidal particles to suppress the aggregation of the inorganic oxide colloidal particles, and examples thereof include silylating agents, silane coupling agents, titanate-based coupling agents, aluminum-based coupling agents, alcohols, latex, and various other polymer compounds. The silylating agent or silane coupling agent is represented by the following general formula (Chemical Formula 1): [ka] [In the formula, X1 is an alkyl group, alkenyl group, aryl group, or aralkyl group having 1 to 20 carbon atoms, and is a hydrocarbon group (-R) in which some of the hydrogen atoms may be substituted with a carboxyl group, ester group, amide group, cyano group, ketone group, formyl group, ether group, hydroxyl group, amino group, mercapto group, sulfide group, sulfoxide group, sulfone group, isocyanate group, ureido group, or epoxy group. X2 to X4 are an acetoxy group, an alkoxy group or alkyl group having 1 to 5 carbon atoms, and at least two of X2 to X4 are alkoxy groups.]

[0039] Specific examples of X1 include alkyl groups such as a methyl group, ethyl group, propyl group, butyl group, decyl group, and octadecyl group; alkenyl groups such as a vinyl group and allyl group; aryl groups such as a phenyl group, naphthyl group, and styryl group; aralkyl groups such as a benzyl group and phenethyl group; oxyhydrocarbon groups such as a methoxy group, ethoxy group, propoxy group, butoxy group, vinyloxy group, phenoxy group, and benzyloxy group; and a hydroxyl group. Examples of substituents include acrylic groups such as 3-methacryloxypropyl and 3-acryloxypropyl; epoxy groups such as 3-glycidoxypropyl and 2-(3,4-epoxycyclohexyl)ethyl; amino groups such as 3-aminopropyl, N-phenyl-3-aminopropyl, and N-2-(aminoethyl)-3-aminopropyl; mercapto groups such as 3-mercaptopropyl; isocyanate groups such as 3-isocyanatopropyl; and ureido groups such as 3-ureidopropyl. Specific examples of X2 to X4 include alkoxy groups such as methoxy, ethoxy, propoxy, and butoxy; alkyl groups such as methyl, ethyl, propyl, butyl, decyl, and octadecyl; and acetoxy, where at least two of X2 to X4 are alkoxy groups.

[0040] Among these combinations, methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, decyltrimethoxysilane, decyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 2-(3,4-epoxycyclohexyl)ethyl Preferred are aryltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, 3-ureidopropyltrialkoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, N-phenyl-3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-isocyanatepropyltriethoxysilane, and p-styryltrimethoxysilane.

[0041] Specific examples of titanate coupling agents include isopropyl triisostearoyl titanate, isopropyl tridodecylbenzenesulfonyl titanate, isopropyl tris(dioctylpyrophosphate)titanate, tetraisopropyl bis(dioctylphosphite)titanate, tetraoctyl bis(ditridecylphosphite)titanate, tetra(2,2-diallyloxymethyl-1-butyl)bis(ditridecyl)phosphite titanate, bis(dioctylpyrophosphate)oxyacetate titanate, isopropyl trioctanoyl titanate, isopropyl dimethacryloyl isostearoyl titanate, isopropyl tri(dioctylphosphate)titanate, isopropyl tricumylphenyl titanate, and isopropyl tri(N-aminoethylaminoethyl)titanate.

[0042] Specific examples of aluminum-based coupling agents include aluminum ethyl acetoacetate diisopropylate, aluminum tris(ethyl acetoacetate), aluminum tris(acetylacetonate), aluminum bis(ethyl acetoacetate) monoacetylacetonate, etc. Specific examples of alcohols include methanol, ethanol, n-propanol, iso-propanol, n-butanol, amyl alcohol, 4-methyl-2-pentanol, n-heptanol, n-octanol, 2-ethylhexanol, nonanol, decanol, tridecanol, 2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol, 3-methoxybutanol, 3-methyl-3-methoxybutanol, polyvinyl alcohol, etc.

[0043] The organic substances used for surface modification, such as silylating agents, silane coupling agents, titanate coupling agents, aluminum coupling agents, alcohols, and various polymer compounds, can be used alone or in combination.

[0044] Examples of the base component of the solute contained in the electrolyte for electrolytic capacitors include ammonium, quaternary ammonium, quaternized amidinium, amine, sodium, and potassium. Examples of quaternary ammonium include tetramethylammonium, triethylmethylammonium, and tetraethylammonium. Examples of quaternized amidinium include ethyldimethylimidazolinium and tetramethylimidazolinium. Examples of amines include primary amines, secondary amines, and tertiary amines. Examples of primary amines include methylamine, ethylamine, and propylamine. Examples of secondary amines include dimethylamine, diethylamine, ethylmethylamine, and dibutylamine. Examples of tertiary amines include trimethylamine, triethylamine, tributylamine, ethyldimethylamine, and ethyldiisopropylamine.

[0045] The solute may be added to the electrolyte solution for electrolytic capacitors in the form of an ion-dissociable salt, or the specific acid component and base component may be added separately to the electrolyte solution for electrolytic capacitors.

[0046] The solvent for the electrolyte for electrolytic capacitors may be a protic organic polar solvent, an aprotic organic polar solvent, or water. Typical examples of protic organic polar solvents include monohydric alcohols, polyhydric alcohols, and oxyalcohol compounds. Typical examples of aprotic organic polar solvents include sulfones, amides, lactones, cyclic amides, and nitriles.

[0047] Examples of monohydric alcohols include ethanol, propanol, butanol, pentanol, hexanol, cyclobutanol, cyclopentanol, cyclohexanol, benzyl alcohol, etc. Examples of polyhydric alcohols and oxyalcohol compounds include ethylene glycol, propylene glycol, diethylene glycol, glycerin, methyl cellosolve, ethyl cellosolve, methoxypropylene glycol, dimethoxypropanol, etc.

[0048] Examples of sulfones include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, sulfolane, 3-methyl sulfolane, and 2,4-dimethyl sulfolane. Examples of amides include N-methylformamide, N,N-dimethylformamide, N-ethylformamide, N,N-diethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylacetamide, N,N-diethylacetamide, and hexamethylphosphoric amide. Examples of lactones and cyclic amides include γ-butyrolactone, γ-valerolactone, δ-valerolactone, N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butylene carbonate, and isobutylene carbonate. Examples of nitriles include acetonitrile, 3-methoxypropionitrile, and glutaronitrile.

[0049] Glycol compounds are preferred as solvents for electrolytes for electrolytic capacitors. Glycol compounds are compounds in which hydrogen atoms bonded to two or more carbon atoms in an aliphatic hydrocarbon or cyclic aliphatic hydrocarbon are replaced with hydroxyl groups. Glycol compounds have a high boiling point of 150°C or higher. These glycol compounds improve the chemical conversion properties of dielectric films and reduce the ESR and improve the withstand voltage of electrolytic capacitors. Examples of glycol compounds include ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, and polyoxyethylene glycol. The electrolyte may contain one type of glycol compound solvent or two or more types of glycol compound solvents. Furthermore, glycol compounds may be used alone as solvents, or may be combined with other glycol compounds.

[0050] It is particularly preferred to add diethylene glycol as a glycol compound to the electrolyte for electrolytic capacitors. By combining phosphoric acid, hypophosphorous acid, or both with diethylene glycol, the total amount of electricity in the spike current during the aging process is reduced. This reduces the risk of short circuits that may occur during aging of electrolytic capacitors and improves the yield of electrolytic capacitors.

[0051] However, to reduce the total amount of electricity in the spike current during the aging process, diethylene glycol should be included in an amount of 14 wt% or more relative to the total amount of solvent in the electrolyte for electrolytic capacitors. If the amount of diethylene glycol falls outside this range, the total amount of electricity in the spike current during the aging process cannot be reduced to a level sufficient to suppress the incidence of short circuits in electrolytic capacitors.

[0052] More preferably, the diethylene glycol content is 18.7 wt % or more of the total amount of solvent in the electrolyte for electrolytic capacitors, which further reduces the total amount of electricity in the spike current during the aging process.

[0053] Examples of additives include complex compounds of boric acid and polysaccharides (e.g., mannitol, sorbitol), complex compounds of boric acid and polyhydric alcohols, boric acid esters, and nitro compounds. These may be used alone or in combination. Nitro compounds act as gas absorbents and suppress the generation of hydrogen gas in electrolytic capacitors. Examples of nitro compounds include o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, p-nitrophenol, o-nitrobenzyl alcohol, m-nitrobenzyl alcohol, p-nitrobenzyl alcohol, o-nitroacetophenone, m-nitroacetophenone, and p-nitroacetophenone. Examples of pressure resistance improvers include polyethylene glycol, polypropylene glycol, and polyoxyethylene glycerin. These pressure resistance improvers may be added to the extent that they do not deteriorate the characteristics at low temperatures such as -40°C.

[0054] (electrode body) The electrolyte for electrolytic capacitors is interposed between the dielectric film of the anode body and the cathode body, adhering closely to the dielectric film to form the true cathode. The anode body and cathode body are foils made of valve metals, such as aluminum, tantalum, niobium, niobium oxide, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. The purity of the anode body is preferably 99.9% or higher, and that of the cathode is preferably 99% or higher, although impurities such as silicon, iron, copper, magnesium, and zinc may be present.

[0055] The anode and cathode bodies have their surfaces enlarged as formed foils made from valve metal powder, sintered foils made by sintering formed foils, etched foils made from rolled foils that have been etched, or sintered or vapor-deposited foils made by forming valve metal powder on the surface of rolled foil and then sintering or vapor-depositing the powder. That is, the surface-enlarged layer is made up of tunnel-like pits, spongy pits, or voids between densely packed powder particles.

[0056] The tunnel-shaped etching pits are holes dug in the foil thickness direction. These tunnel-shaped etching pits are typically formed in the anode formation process and cathode formation process by passing a direct current in an acidic aqueous solution containing halogen ions, such as hydrochloric acid. The tunnel-shaped etching pits are further expanded by passing a direct current in an acidic aqueous solution, such as nitric acid. The spongy etching pits turn the surface-expanding layer into a sponge-like layer with fine, interconnected voids. These spongy etching pits are formed by passing an alternating current in an acidic aqueous solution containing halogen ions, such as hydrochloric acid.

[0057] The sintered foil is produced in the anode and cathode forming steps by obtaining a powder of a valve action metal of the same or different type as the foil body by a milling method, atomization method, melt spinning method, rotating disk method, rotating electrode method, etc., forming a paste with a binder or solvent, applying it to the foil body, drying it, and heating and sintering it in a vacuum or reducing atmosphere, etc. The atomization method may be any of water atomization, gas atomization, and water gas atomization. The evaporated foil is produced in the anode and cathode forming steps by, for example, resistance heating evaporation or electron beam evaporation. This evaporated foil is produced by heating and evaporating a valve action metal of the same or different type as the foil body by resistance heat or electron beam energy, and depositing the vapor of valve action metal particles on the surface of the foil body to form a film.

[0058] The dielectric film is typically an oxide film formed on the surface layer of the anode body. If the anode body is made of aluminum, it is an aluminum oxide layer formed by oxidizing the porous structure portion. An oxide film is also formed on the foil surface of the cathode body. The oxide film on the cathode body may be formed intentionally or naturally. This dielectric film and oxide film are formed by chemical conversion treatment in which a voltage is applied in a solution free of halogen ions, such as an acid such as ammonium borate, ammonium phosphate, or ammonium adipate, or an aqueous solution of such an acid. The oxide film intentionally formed on the foil surface of the cathode body is preferably thin, approximately 1 to 10 Vfs. A natural oxide film is formed by the cathode foil reacting with oxygen in the air.

[0059] (separator) Examples of materials for the separator include cellulose papers such as kraft, Manila hemp, esparto, hemp, and rayon, and mixtures thereof; polyester-based resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and derivatives thereof; polytetrafluoroethylene-based resins, polyvinylidene fluoride-based resins, vinylon-based resins; polyamide-based resins such as aliphatic polyamides, semi-aromatic polyamides, and wholly aromatic polyamides; polyimide-based resins, polyethylene resins, polypropylene resins, trimethylpentene resins, polyphenylene sulfide resins, acrylic resins, and polyvinyl alcohol resins. These resins can be used alone or in combination.

[0060] (Manufacturing method) An example of a manufacturing method for an electrolytic capacitor is as follows: First, in the anode formation process, a surface-expanding layer is formed on one or both sides of the anode foil, and a dielectric film is formed on the surface-expanding layer by chemical conversion treatment. In the cathode formation process, a surface-expanding layer is also formed on one or both sides of the cathode foil as needed, and an oxide film is formed on the surface, or a natural oxide film is left.

[0061] The anode body and the cathode body are connected to respective external terminals. The external terminals are electrically and mechanically connected to the anode body and the cathode body by stitch connection, cold welding, ultrasonic welding, laser welding, etc. The external terminals are conductors that protrude from the capacitor element and electrically connect the electrolytic capacitor to the mounting substrate.

[0062] Electrolytic capacitors include wound and stacked types. In wound electrolytic capacitors, the anode body, cathode body, and separator are long, and wound capacitor elements are wound bodies. In wound electrolytic capacitors, the anode body and cathode body are stacked with the separator interposed in the element formation process. The separator is stacked so that one end protrudes beyond one end of the anode body and cathode body. A core is created by starting to wind the protruding separator first so that the core of the wound body is aligned with the short sides of the anode body and cathode body. Then, the anode body and cathode body are wound by rolling up the long sides of the anode body and cathode body using the core as a winding axis. The wound body is then formed into a cylindrical shape by spirally winding the stack of the anode body, cathode body, and separator multiple times.

[0063] In a stacked electrolytic capacitor, the anode body, cathode body, and separator have a flat plate shape. In a stacked electrolytic capacitor, flat plate-shaped anode bodies and cathode bodies are stacked with separators interposed therebetween in an element formation process.

[0064] After the element formation step, a repair chemical conversion step may be provided to repair bare metal portions of the valve metal exposed when the anode body and the cathode body are cut to a desired width, or defects formed in the dielectric film of the anode body and the oxide film of the cathode body due to physical stress. In the repair chemical conversion step, the wound body or the laminate is immersed in a chemical conversion solution and a voltage is applied.

[0065] The chemical conversion solution used may be a phosphoric acid-based chemical conversion solution such as ammonium dihydrogen phosphate, a boric acid-based chemical conversion solution such as ammonium borate, or an adipic acid-based chemical conversion solution such as ammonium adipate. The voltage application method during repair chemical conversion may be appropriately selected from a method of applying a constant voltage from the start of repair chemical conversion, or a method of increasing the applied voltage stepwise at regular intervals.

[0066] In the impregnation step, the wound or laminated capacitor element is immersed in the electrolytic solution for electrolytic capacitors prepared in advance in the electrolytic solution preparation step, and the electrolytic solution for electrolytic capacitors is impregnated into the voids. A depressurization treatment or a pressurization treatment may be performed as necessary to impregnate the electrolytic solution for electrolytic capacitors into smaller voids. The impregnation step with the electrolytic solution for electrolytic capacitors may be repeated multiple times. For example, the pressure inside the wound or laminate may be reduced, and the electrolytic solution for electrolytic capacitors may be injected into the capacitor element while pressurizing the electrolytic solution for electrolytic capacitors.

[0067] The capacitor element produced after the impregnation process is packaged in an exterior packaging. The exterior packaging includes a case with one end closed and the other open, and a sealing body. The capacitor element is housed in the case, and the opening of the case is sealed with the sealing body. The opening of the case is bent inward by a crimping process, which closes the case, causing the sealing body to adhere tightly. After the capacitor element is sealed, an aging process is performed to complete the production of the electrolytic capacitor.

[0068] The exterior may be a laminate film, or may be a resin such as a heat-resistant resin or an insulating resin, which may be molded around the capacitor element or formed into a thin film by a method such as dip coating or printing. [Example]

[0069] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0070] Example 1 An electrolytic solution for electrolytic capacitors of Example 1 was prepared. The composition of the electrolytic solution for electrolytic capacitors of Example 1 was as follows: The composition of the electrolytic solution for electrolytic capacitors was 8.5 wt% water, 70.63 wt% ethylene glycol, 8.0 wt% azelaic acid, 0.17 wt% phosphoric acid, 7.5 wt% inorganic oxide colloidal particles, 2.0 wt% paranitrobenzyl alcohol, and 3.2 wt% dimethylamine, based on the weight of the electrolytic solution for electrolytic capacitors. Silica whose surface was modified with 3-glycidoxypropyltrimethoxysilane was used as the inorganic oxide colloidal particles.

[0071] Example 1 is an electrolyte for an electrolytic capacitor containing inorganic oxide colloidal particles and containing 1.7 mmol of phosphoric acid added to 100 g of the electrolyte.

[0072] Example 2 An electrolytic solution for electrolytic capacitors of Example 2 was prepared. The composition of the electrolytic solution for electrolytic capacitors of Example 2 was the same as that of Example 1, except that the amount of phosphoric acid was different from that of Example 1 and the difference in phosphoric acid was adjusted with ethylene glycol. The electrolytic solution for electrolytic capacitors of Example 2 contained 0.34 wt% of phosphoric acid based on the weight of the electrolytic solution for electrolytic capacitors. The content of ethylene glycol based on the weight of the electrolytic solution for electrolytic capacitors was 70.46 wt%.

[0073] Example 2 is an electrolyte for an electrolytic capacitor containing inorganic oxide colloid particles and containing 3.5 mmol of phosphoric acid added to 100 g of the electrolyte.

[0074] Example 3 An electrolytic solution for electrolytic capacitors of Example 3 was prepared. The composition of the electrolytic solution for electrolytic capacitors of Example 3 was the same as that of Example 1, except that the amount of phosphoric acid was different from that of Example 1 and the difference in phosphoric acid was adjusted with ethylene glycol. The electrolytic solution for electrolytic capacitors of Example 3 contained 0.51 wt% of phosphoric acid based on the weight of the electrolytic solution for electrolytic capacitors. The content of ethylene glycol based on the weight of the electrolytic solution for electrolytic capacitors was 70.29 wt%.

[0075] Example 3 is an electrolyte for an electrolytic capacitor containing inorganic oxide colloidal particles and containing 5.2 mmol of phosphoric acid added to 100 g of the electrolyte.

[0076] Example 4 An electrolytic solution for electrolytic capacitors of Example 4 was prepared. The electrolytic solution for electrolytic capacitors of Example 4 contained hypophosphorous acid instead of phosphoric acid. That is, the composition of the electrolytic solution for electrolytic capacitors was 8.5 wt% water, 70.69 wt% ethylene glycol, 8.0 wt% azelaic acid, 0.11 wt% hypophosphorous acid, 7.5 wt% inorganic oxide colloid particles, 2.0 wt% paranitrobenzyl alcohol, and 3.2 wt% dimethylamine, based on the weight of the electrolytic solution for electrolytic capacitors.

[0077] Example 4 is an electrolyte for an electrolytic capacitor containing inorganic oxide colloid particles and containing 1.7 mmol of hypophosphorous acid added to 100 g of the electrolyte.

[0078] Example 5 An electrolytic solution for electrolytic capacitors of Example 5 was prepared. The composition of the electrolytic solution for electrolytic capacitors of Example 5 was the same as that of Example 4, except that the amount of hypophosphorous acid was different from that of Example 4 and the difference in hypophosphorous acid was adjusted with ethylene glycol. The electrolytic solution for electrolytic capacitors of Example 5 contained 0.23 wt% hypophosphorous acid based on the weight of the electrolytic solution for electrolytic capacitors. The content of ethylene glycol based on the weight of the electrolytic solution for electrolytic capacitors was 70.57 wt%.

[0079] Example 5 is an electrolyte for an electrolytic capacitor containing inorganic oxide colloid particles and containing 3.5 mmol of hypophosphorous acid added to 100 g of the electrolyte.

[0080] Example 6 An electrolytic solution for electrolytic capacitors of Example 6 was prepared. The composition of the electrolytic solution for electrolytic capacitors of Example 6 was the same as that of Example 4, except that the amount of hypophosphorous acid was different from that of Example 4 and the difference in hypophosphorous acid was adjusted with ethylene glycol. The electrolytic solution for electrolytic capacitors of Example 6 contained 0.34 wt% hypophosphorous acid based on the weight of the electrolytic solution for electrolytic capacitors. The content of ethylene glycol based on the weight of the electrolytic solution for electrolytic capacitors was 70.46 wt%.

[0081] Example 5 is an electrolyte for an electrolytic capacitor containing inorganic oxide colloid particles and containing 5.2 mmol of hypophosphorous acid added to 100 g of the electrolyte.

[0082] (Comparative Example 1) An electrolytic solution for electrolytic capacitors of Comparative Example 1 was prepared in comparison with Examples 1 to 6. The electrolytic solution for electrolytic capacitors of Comparative Example 1 did not contain phosphoric acid or hypophosphorous acid. Specifically, the composition of the electrolytic solution for electrolytic capacitors of Comparative Example 1 was 8.5 wt% water, 70.8 wt% ethylene glycol, 8.0 wt% azelaic acid, 7.5 wt% inorganic oxide colloidal particles, 2.0 wt% paranitrobenzyl alcohol, and 3.2 wt% dimethylamine, based on the weight of the electrolytic solution for electrolytic capacitors. Silica whose surface was modified with 3-glycidoxypropyltrimethoxysilane was used as the inorganic oxide colloidal particles.

[0083] Comparative Example 1 is an electrolyte solution for electrolytic capacitors that contains inorganic oxide colloidal particles but does not contain phosphoric acid or hypophosphorous acid.

[0084] (Comparative Examples 2 and 3) Furthermore, electrolyte solutions for electrolytic capacitors of Comparative Examples 2 and 3 were prepared in comparison with Examples 1 to 3. The compositions of the electrolyte solutions for electrolytic capacitors of Comparative Examples 2 and 3 were the same as those of the electrolyte solutions for electrolytic capacitors of Examples 1 to 3, except that the amount of phosphoric acid was different from that of Examples 1 to 3 and the difference in phosphoric acid was adjusted with ethylene glycol.

[0085] The electrolyte for electrolytic capacitors of Comparative Example 2 contains 0.68 wt% of phosphoric acid based on the weight of the electrolyte for electrolytic capacitors. The electrolyte for electrolytic capacitors contains 70.12 wt% of ethylene glycol based on the weight of the electrolyte for electrolytic capacitors. The electrolyte for electrolytic capacitors of Comparative Example 3 contains 0.85 wt% of phosphoric acid based on the weight of the electrolyte for electrolytic capacitors. The electrolyte for electrolytic capacitors contains 69.95 wt% of ethylene glycol based on the weight of the electrolyte for electrolytic capacitors.

[0086] Thus, Comparative Example 2 is an electrolyte solution for electrolytic capacitors containing inorganic oxide colloidal particles and in which 6.9 mmol of phosphoric acid is added per 100 g of the electrolyte solution, and Comparative Example 3 is an electrolyte solution for electrolytic capacitors containing inorganic oxide colloidal particles and in which 8.7 mmol of phosphoric acid is added per 100 g of the electrolyte solution.

[0087] (Comparative Examples 4 and 5) Furthermore, electrolytic capacitor electrolytes of Comparative Examples 4 and 5 were prepared in comparison with Examples 4 to 6. The compositions of the electrolytic capacitor electrolytes of Comparative Examples 4 and 5 were the same as those of Examples 4 to 6, except that the amount of hypophosphorous acid was different from that of Examples 4 to 6 and the difference in hypophosphorous acid was adjusted with ethylene glycol. The electrolytic capacitor electrolyte of Comparative Example 4 contained 0.45 wt% hypophosphorous acid based on the weight of the electrolytic capacitor electrolyte. The ethylene glycol content was 70.35 wt% based on the weight of the electrolytic capacitor electrolyte. The electrolytic capacitor electrolyte of Comparative Example 5 contained 0.57 wt% hypophosphorous acid based on the weight of the electrolytic capacitor electrolyte. The ethylene glycol content was 70.23 wt% based on the weight of the electrolytic capacitor electrolyte.

[0088] Thus, Comparative Example 4 is an electrolyte solution for electrolytic capacitors containing inorganic oxide colloid particles and to which 6.9 mmol of hypophosphorous acid is added per 100 g of the electrolyte solution, and Comparative Example 5 is an electrolyte solution for electrolytic capacitors containing inorganic oxide colloid particles and to which 8.7 mmol of hypophosphorous acid is added per 100 g of the electrolyte solution.

[0089] (Comparative Examples 6 to 14) Electrolyte solutions for electrolytic capacitors of Comparative Examples 6 to 14 were prepared. In the electrolytic solutions for electrolytic capacitors of Comparative Examples 6 to 14, phosphorous acid, an ester of phosphoric acid and ethylene glycol, or dibutyl phosphate was added instead of phosphoric acid and hypophosphorous acid. The composition ratios of water, azelaic acid, inorganic oxide colloidal particles, paranitrobenzyl alcohol, and dimethylamine were the same as in Examples 1 to 6. The inorganic oxide colloidal particles were the same type as in Examples 1 to 6, and silica whose surface was modified with 3-glycidoxypropyltrimethoxysilane was used.

[0090] The electrolyte solutions for electrolytic capacitors of Comparative Examples 6 to 8 contain phosphorous acid. The composition ratio of phosphorous acid relative to the weight of the electrolyte solution for electrolytic capacitors is 0.14 wt% in Comparative Example 6, 0.29 wt% in Comparative Example 7, and 0.43 wt% in Comparative Example 8. The composition ratio of ethylene glycol relative to the weight of the electrolyte solution for electrolytic capacitors is 70.66 wt% in Comparative Example 6, 70.51 wt% in Comparative Example 7, and 70.37 wt% in Comparative Example 8.

[0091] The electrolyte solutions for electrolytic capacitors of Comparative Examples 9 to 11 contain an ester of phosphoric acid and ethylene glycol. The composition ratio of the phosphoric acid and ethylene glycol ester relative to the weight of the electrolyte solution for electrolytic capacitors is 0.37 wt% in Comparative Example 9, 0.76 wt% in Comparative Example 10, and 1.13 wt% in Comparative Example 11. The composition ratio of ethylene glycol relative to the weight of the electrolyte solution for electrolytic capacitors is 70.43 wt% in Comparative Example 9, 70.04 wt% in Comparative Example 10, and 69.67 wt% in Comparative Example 11.

[0092] The electrolyte solutions for electrolytic capacitors of Comparative Examples 12 to 14 contain dibutyl phosphate. The composition ratio of dibutyl phosphate relative to the weight of the electrolyte solution for electrolytic capacitors is 0.35 wt% in Comparative Example 12, 0.74 wt% in Comparative Example 13, and 1.1 wt% in Comparative Example 14. The composition ratio of ethylene glycol relative to the weight of the electrolyte solution for electrolytic capacitors is 70.45 wt% in Comparative Example 12, 70.06 wt% in Comparative Example 13, and 69.70 wt% in Comparative Example 14.

[0093] Comparative Example 6 is an electrolyte solution for electrolytic capacitors containing inorganic oxide colloidal particles and to which 1.7 mmol of phosphorous acid is added per 100 g of the electrolyte solution. Comparative Example 7 is an electrolyte solution for electrolytic capacitors containing inorganic oxide colloidal particles and to which 3.5 mmol of phosphorous acid is added per 100 g of the electrolyte solution. Comparative Example 8 is an electrolyte solution for electrolytic capacitors containing inorganic oxide colloidal particles and to which 5.2 mmol of phosphorous acid is added per 100 g of the electrolyte solution.

[0094] Comparative Example 9 is an electrolyte solution for electrolytic capacitors containing inorganic oxide colloidal particles and to which 1.7 mmol of phosphoric acid and ethylene glycol ester is added per 100 g of electrolyte solution. Comparative Example 10 is an electrolyte solution for electrolytic capacitors containing inorganic oxide colloidal particles and to which 3.5 mmol of phosphoric acid and ethylene glycol ester is added per 100 g of electrolyte solution. Comparative Example 11 is an electrolyte solution for electrolytic capacitors containing inorganic oxide colloidal particles and to which 5.2 mmol of phosphoric acid and ethylene glycol ester is added per 100 g of electrolyte solution.

[0095] Comparative Example 12 is an electrolyte solution for electrolytic capacitors containing inorganic oxide colloidal particles and to which 1.7 mmol of dibutyl phosphate ester is added per 100 g of the electrolyte solution. Comparative Example 13 is an electrolyte solution for electrolytic capacitors containing inorganic oxide colloidal particles and to which 3.5 mmol of dibutyl phosphate ester is added per 100 g of the electrolyte solution. Comparative Example 14 is an electrolyte solution for electrolytic capacitors containing inorganic oxide colloidal particles and to which 5.2 mmol of dibutyl phosphate ester is added per 100 g of the electrolyte solution.

[0096] (Reference example 1) An electrolyte solution for electrolytic capacitors of Reference Example 1 was prepared. The electrolyte solution for electrolytic capacitors of Reference Example 1 did not contain inorganic oxide colloidal particles, but instead contained polyoxyethylene glycerin, a water-soluble polymer. In addition, only azelaic acid was added as the acid component of the solute, and phosphoric acid, hypophosphorous acid, etc. were not added.

[0097] That is, the composition of the electrolyte solution for electrolytic capacitors in Reference Example 1 was 8.5 wt% water, 64.5 wt% ethylene glycol, 6.0 wt% azelaic acid, 17.0 wt% polyoxyethylene glycerin, 2.0 wt% paranitrobenzyl alcohol, and 2.0 wt% dimethylamine, based on the weight of the electrolyte solution for electrolytic capacitors. The polyoxyethylene glycerin used had an ethylene oxide group attached to the end of glycerin and a molecular weight of 3,000.

[0098] Reference Example 1 is an electrolyte solution for an electrolytic capacitor that contains a water-soluble polymer and does not contain inorganic oxide colloidal particles.

[0099] (LC and withstand voltage test) Electrolytic capacitors impregnated with the electrolytic solutions for electrolytic capacitors of Examples 1 to 6, Comparative Examples 1 to 14, and Reference Example 1 were fabricated, and the leakage current and withstand voltage of these electrolytic capacitors were measured.

[0100] In the fabrication of the electrolytic capacitor, a pair of electrodes was fabricated using aluminum foil in the anode and cathode formation processes. Both aluminum foils were subjected to an AC etching process to enlarge the surface area, forming a surface-enlarging layer. In the AC etching process, an AC current was passed through the aluminum foil in an aqueous solution containing hydrochloric acid, forming spongy etching pits in both aluminum foils.

[0101] The aluminum foil used as the anode was subjected to chemical conversion treatment to form a dielectric film on the surface of the foil. In the chemical conversion treatment process, the aluminum foil with the surface expansion layer formed thereon was subjected to chemical conversion treatment, and a dielectric film was formed on the surface of the aluminum foil at a chemical conversion voltage of 650 V.

[0102] Lead wires were attached to each of the anode body and cathode body by stitch connection. Next, the element was formed by winding the anode body and cathode body facing each other with a kraft fiber separator interposed therebetween.

[0103] The wound body was then impregnated with the electrolyte for electrolytic capacitors in the electrolyte impregnation process. The wound body was immersed in the electrolyte for electrolytic capacitors at room temperature, the pressure of the wound body was reduced to 0.002 MPa, and the electrolyte for electrolytic capacitors was pressurized to 0.2 MPa, and the electrolyte for electrolytic capacitors was impregnated into the wound body every 60 minutes. The electrolyte impregnation process was performed a total of two times.

[0104] The capacitor element, consisting of the anode body, cathode body, separator, and electrolytic capacitor electrolyte, was housed in an aluminum outer case with one end closed and the other open, and a seal was press-fitted into the opening of the outer case and crimped to seal it in place. The electrolytic capacitor measured 18 mm in diameter and 30 mm in height. The electrolytic capacitor was then subjected to an aging process in which a voltage of 475 V was applied for two hours at a temperature of 85°C.

[0105] The withstand voltage of these electrolytic capacitors was measured. The ambient temperature during the withstand voltage measurement was 25°C, and 2 mA was applied from a constant current power supply to increase the voltage. The voltage rise curve was examined, and the voltage (V) at which scintillation was observed was taken as the withstand voltage. A power supply (Texio Technology Co., Ltd., M-6186) and a recording device (YOKOGAWA, DX2030) were used to measure the withstand voltage.

[0106] These electrolytic capacitors were also left in a temperature environment of 105°C for 1000 hours, and the leakage current was measured. The leakage current was measured using a digital oscilloscope when a voltage of 450V was applied for 5 minutes at 20°C.

[0107] The measurement results of the withstand voltage and leakage current for Comparative Example 1, in which no specific acid component was added, Examples 1 to 3 and Comparative Examples 2 and 3, in which phosphoric acid was added, and Reference Example 1, in which no inorganic oxide colloidal particles were added, are shown in Table 1 below. (Table 1) TIFF2026009801000003.tif41161

[0108] The measurement results of the withstand voltage and leakage current for Comparative Example 1, in which no specific acid component was added, Examples 4 to 6 and Comparative Examples 4 and 5, in which hypophosphorous acid was added, and Reference Example 1, in which no inorganic oxide colloidal particles were added, are shown in Table 2 below. (Table 2) TIFF2026009801000004.tif41166

[0109] The results of measuring the leakage current for Comparative Example 1, in which no specific acid component was added, Comparative Examples 6 to 8, in which phosphorous acid was added, Comparative Examples 9 to 11, in which an ester of phosphoric acid and ethylene glycol was added, and Comparative Examples 12 to 14, in which a dibutyl phosphate ester was added, are shown in Table 3 below. (Table 3) TIFF2026009801000005.tif111162

[0110] Furthermore, as shown in FIG. 1, the relationship between the amount of acid component added and leakage current is summarized in graphs for each type of acid component based on Tables 1 to 3. The graph plotted with circles represents the series in which phosphoric acid was added. The graph plotted with x marks represents the series in which hypophosphorous acid was added. The graph plotted with triangles represents the series in which phosphorous acid was added. The graph plotted with squares represents the series in which phosphoric acid and ethylene glycol ester was added. The graph plotted with diamonds represents the series in which dibutyl phosphate ester was added.

[0111] Furthermore, as shown in Figure 2, the relationship between the amount of acid component added and the withstand voltage was plotted for each type of acid component based on Tables 1 and 2. The graph plotted with circles represents the series in which phosphoric acid was added. The graph plotted with x marks represents the series in which hypophosphorous acid was added.

[0112] As shown in Figures 1 and 2 and Tables 1 to 3, Examples 1 to 6, in which phosphoric acid and hypophosphorous acid were added, showed lower leakage currents than Comparative Example 1, in which phosphoric acid and hypophosphorous acid were not added. Comparative Examples 6 to 8, in which phosphorous acid was added, showed slightly worse leakage currents compared to Comparative Example 1. Comparative Examples 9 to 14, in which phosphoric acid and ethylene glycol ester or dibutyl phosphate ester were added, showed significantly worse leakage currents than Comparative Example 1.

[0113] This confirms that even if inorganic oxide colloidal particles are added to the electrolyte solution for electrolytic capacitors, the addition of phosphoric acid or hypophosphorous acid together can suppress an increase in leakage current of electrolytic capacitors exposed to high-temperature environments. Moreover, it can be confirmed that Examples 3 and 6, in which 5.2 mmol of the specific acid component was added, had lower leakage current than Reference Example 1, in which inorganic oxide colloidal particles were not added.

[0114] However, in Comparative Examples 2 to 5, which are electrolytic capacitor electrolytes to which 6.9 mmol or 8.7 mmol of phosphoric acid or hypophosphorous acid was added, the withstand voltage of the electrolytic capacitor decreased despite the inclusion of inorganic oxide colloidal particles. Therefore, it was confirmed that an electrolytic capacitor electrolyte containing an acid component, which is phosphoric acid, hypophosphorous acid, or both, and containing 1.7 mmol or more and 5.2 mmol or less of this acid component relative to the electrolytic capacitor electrolyte can eliminate the disadvantage of inorganic oxide colloidal particles, namely, an increase in leakage current, without affecting the withstand voltage, which is an advantage of inorganic oxide colloidal particles.

[0115] (Examples 7-11) Electrolyte solutions for electrolytic capacitors were prepared in Examples 7 to 11 and Comparative Example 15. The electrolytic solutions for electrolytic capacitors in Examples 7 to 11 had the same composition as Example 1, with some exceptions. The electrolytic solution for electrolytic capacitors in Comparative Example 15 had the same composition as Example 1 except that phosphoric acid was omitted. The solvent for the electrolytic solutions for electrolytic capacitors in Examples 7 to 11 and Comparative Example 15 was a mixed solvent of ethylene glycol and diethylene glycol.

[0116] The electrolyte for electrolytic capacitors of Comparative Example 15 contained 15.4 wt% of diethylene glycol relative to the total amount of the electrolyte for electrolytic capacitors. The remaining solvent was ethylene glycol, which accounted for 58.5 wt% of the total amount of the electrolyte for electrolytic capacitors. When the diethylene glycol content was converted to the content relative to the solvent, the diethylene glycol content of Comparative Example 15 was 18.7 wt% relative to the total amount of the solvent.

[0117] The electrolyte for electrolytic capacitors in Example 7 contained 5 wt% diethylene glycol relative to the total amount of the electrolyte for electrolytic capacitors. The remaining solvent was ethylene glycol, which accounted for 68.73 wt% of the total amount of the electrolyte for electrolytic capacitors. When the diethylene glycol content was converted to the solvent content, the diethylene glycol content in Example 7 was 6.1 wt% of the total amount of the solvent.

[0118] The electrolyte for electrolytic capacitors in Example 8 contained 11.6 wt% of diethylene glycol relative to the total amount of the electrolyte for electrolytic capacitors. The remaining solvent was ethylene glycol, which accounted for 62.13 wt% of the total amount of the electrolyte for electrolytic capacitors. When the diethylene glycol content was converted to the solvent content, the diethylene glycol content in Example 8 was 14.1 wt% of the total amount of the solvent.

[0119] The electrolyte for electrolytic capacitors in Example 9 contained 15.4 wt% of diethylene glycol relative to the total amount of the electrolyte for electrolytic capacitors. The remaining solvent was ethylene glycol, which accounted for 58.33 wt% of the total amount of the electrolyte for electrolytic capacitors. When the diethylene glycol content was converted to the solvent content, the diethylene glycol content in Example 9 was 18.7 wt% of the total amount of the solvent.

[0120] The electrolyte for electrolytic capacitors in Example 10 contained 30 wt% diethylene glycol relative to the total amount of the electrolyte for electrolytic capacitors. The remaining solvent was ethylene glycol, which accounted for 43.73 wt% of the total amount of the electrolyte for electrolytic capacitors. When the diethylene glycol content was converted to the solvent content, the diethylene glycol content in Example 10 was 36.5 wt% of the total amount of the solvent.

[0121] The electrolyte for electrolytic capacitors in Example 11 contained 50.53 wt% of diethylene glycol relative to the total amount of the electrolyte for electrolytic capacitors. The remaining solvent was ethylene glycol, which accounted for 23.20 wt% of the total amount of the electrolyte for electrolytic capacitors. When the diethylene glycol content was converted to the solvent content, the diethylene glycol content in Example 11 was 61.4 wt% of the total amount of the solvent.

[0122] In addition, the electrolyte solutions for electrolytic capacitors in Examples 7 to 11 and Comparative Example 15 contained 8.5 wt% water, 4.4 wt% azelaic acid, 2.0 wt% 1,6-decanedicarboxylic acid, 0.17 wt% phosphoric acid, 6 wt% inorganic oxide colloidal particles, 2.0 wt% paranitrobenzyl alcohol, and 3.2 wt% diethylamine based on the weight of the electrolyte solution for electrolytic capacitors.

[0123] Electrolytic capacitors impregnated with the electrolytic solutions for electrolytic capacitors of Examples 7 to 11 and Comparative Example 15 were fabricated. The configuration of the electrolytic capacitors, and the manufacturing method and manufacturing conditions for the electrolytic capacitors were the same as those of Example 1 and Comparative Example 1, with some exceptions. Specifically, the chemical conversion voltage applied to the anode body during chemical conversion treatment was 771 V. The cathode body was subjected to chemical conversion treatment at 3 V to form an oxide film. Kraft fiber was used for the separator. The electrolytic capacitors had a diameter of 10 mm and a height of 25 mm. For the individual capacitors used to evaluate the withstand voltage, the chemical conversion voltage applied to the anode body during chemical conversion treatment was 946 V.

[0124] (Various tests) In the aging process, a voltage of 500V was first applied to the electrolytic capacitor at room temperature for one hour, and then a voltage of 475V was applied for two hours at a temperature of 85°C. The leakage current was measured over time during this aging process. The leakage current was measured every 200msec. A five-point moving average of the leakage current was calculated to create a base chart. Leakage currents that differed from the base chart by 0.02mA or more were then extracted as spike currents, and the total amount of electricity was calculated by integrating all spike currents.

[0125] The withstand voltage and leakage current of these electrolytic capacitors were measured after the aging process. The withstand voltage and leakage current were measured using the same method and conditions as in Example 1.

[0126] (Test results) The measurement results of the withstand voltage, leakage current, and total amount of electricity of the electrolytic capacitors of Examples 7 to 11 and Comparative Example 15 are shown in Table 4 below.

[0127] (Table 4) TIFF2026009801000006.tif108161

[0128] Furthermore, based on Table 4 above, the relationship between the withstand voltage and the total amount of electricity of the spike current during the aging process versus the diethylene glycol content in the solvent is shown in the graph of Figure 3. In the graph of Figure 3, the circle plots represent the total amount of electricity of the spike current during the aging process, and the triangle plots represent the withstand voltage. In the graph of Figure 3, the solid plots represent Examples, and the open plots represent Comparative Examples.

[0129] 3, Examples 7 to 11, which contain phosphoric acid, have leakage currents that are less than half that of Comparative Example 15, which does not contain phosphoric acid, and thus effectively suppress deterioration of the anode body due to moisture attracted by the inorganic oxide colloidal particles. Furthermore, Examples 7 to 11, which contain phosphoric acid and diethylene glycol in combination, also have improved withstand voltages compared to Comparative Example 15.

[0130] Furthermore, the total electrical charge of the spike current during the aging process was low for Examples 8 to 11, in which the diethylene glycol content relative to the total amount of solvent was 14.1 wt% or more. In particular, the total electrical charge of the spike current during the aging process was significantly low for Examples 9 to 11, in which the diethylene glycol content relative to the total amount of solvent was 18.7 wt% or more.

[0131] This confirmed that by combining phosphoric acid and diethylene glycol and preparing an electrolyte solution for electrolytic capacitors with a diethylene glycol content of 14 wt% or more relative to the total amount of solvent, the risk of short-circuiting in electrolytic capacitors can be further reduced.

[0132] (Examples 12 to 16) Electrolyte solutions for electrolytic capacitors were prepared in Examples 12 to 16. With some exceptions, the electrolyte solutions for electrolytic capacitors in Examples 12 to 16 had the same compositions as the electrolyte solutions for electrolytic capacitors in Examples 7 to 11. The electrolyte solutions for electrolytic capacitors in Examples 12 to 16 contained 1,6-decanedicarboxylic acid in addition to azelaic acid as an acid component.

[0133] Specifically, Example 12 contains 7.36 wt % of 1,6-decanedicarboxylic acid relative to the total amount of the electrolyte for electrolytic capacitors, and does not contain azelaic acid. When converted to a content in mol % relative to the total amount of chain dicarboxylic acids, which is the sum of azelaic acid and 1,6-decanedicarboxylic acid, the content of 1,6-decanedicarboxylic acid in Example 12 is 100 mol % relative to the total amount of chain dicarboxylic acids.

[0134] Example 13 contained 5.52 wt% of 1,6-decanedicarboxylic acid and 1.50 wt% of azelaic acid relative to the total amount of the electrolyte for electrolytic capacitors. When converted to a content in mol% relative to the total amount of chain dicarboxylic acids, the content of 1,6-decanedicarboxylic acid in Example 13 was 75 mol% relative to the total amount of chain dicarboxylic acids.

[0135] Example 14 contained 3.68 wt% of 1,6-decanedicarboxylic acid and 3.00 wt% of azelaic acid relative to the total amount of the electrolyte for electrolytic capacitors. When converted to a content in mol% relative to the total amount of chain dicarboxylic acids, the content of 1,6-decanedicarboxylic acid in Example 14 was 50 mol% relative to the total amount of chain dicarboxylic acids.

[0136] Example 15 contained 1.84 wt% of 1,6-decanedicarboxylic acid and 4.50 wt% of azelaic acid relative to the total amount of the electrolyte for electrolytic capacitors. When converted to a content in mol% relative to the total amount of chain dicarboxylic acids, the content of 1,6-decanedicarboxylic acid in Example 15 was 25 mol% relative to the total amount of chain dicarboxylic acids.

[0137] Example 16 contained 6.00 wt% of azelaic acid relative to the total amount of the electrolyte for electrolytic capacitors, and did not contain 1,6-decanedicarboxylic acid. When converted to a content in mol% relative to the total amount of chain dicarboxylic acids, the content of 1,6-decanedicarboxylic acid in Example 16 relative to the total amount of chain dicarboxylic acids was 0 mol%.

[0138] In addition, the electrolyte solutions for electrolytic capacitors in Examples 12 to 16 contained 8.5 wt% water, 15.4 wt% diethylene glycol, 0.17 wt% phosphoric acid, 6 wt% inorganic oxide colloidal particles, 2.0 wt% paranitrobenzyl alcohol, 3.2 wt% diethylamine, and the remaining ethylene glycol, based on the weight of the electrolyte solution for electrolytic capacitors.

[0139] (Various tests) The withstand voltage, leakage current, and total amount of electricity of the spike current during the aging process of these electrolytic capacitors were measured. The withstand voltage and leakage current were measured after the aging process. The method and conditions for measuring the withstand voltage and the leakage current were the same as in Example 1, and the method and conditions for measuring the total amount of electricity of the spike current during the aging process were the same as in Examples 7 to 11 and Comparative Example 15.

[0140] (Test results) The measurement results of the withstand voltage, leakage current, and total electrical quantity of spike current during the aging process of the electrolytic capacitors of Examples 12 to 16 are shown in Table 5 below.

[0141] (Table 5) TIFF2026009801000007.tif135163

[0142] Furthermore, based on Table 5 above, the relationship between the withstand voltage and the total amount of electricity in the spike current during the aging process versus the amount of 1,6-decanedicarboxylic acid in the chain dicarboxylic acid is shown in the graph in Figure 4. In the graph in Figure 4, the circle plots the total amount of electricity in the spike current during the aging process, and the triangle plots the withstand voltage.

[0143] First, as shown in Table 5 above and FIG. 4, regardless of the content of 1,6-decanedicarboxylic acid, Examples 12 to 16 exhibited good withstand voltage and small leakage current, effectively suppressing deterioration of the anode body due to moisture attracted by the inorganic oxide colloidal particles.

[0144] Next, as shown in Table 5 above and Figure 4, even in Example 16, where 1,6-decanedicarboxylic acid was not added, the total amount of electricity in the spike current during the aging process was small. However, it can be confirmed that the total amount of electricity in the spike current during the aging process was even smaller in the electrolytic capacitors of Examples 12 to 15 than in Example 16.

[0145] It was confirmed that by preparing an electrolyte solution for an electrolytic capacitor by further adding 25 mol% or more of 1,6-decanedicarboxylic acid to the total amount of the electrolyte solution for an electrolytic capacitor, the risk of short-circuiting in the electrolytic capacitor can be further reduced while effectively suppressing deterioration of the anode body due to moisture attracted by the inorganic oxide colloidal particles.

Claims

1. Inorganic oxide colloidal particles; an acid component that is phosphoric acid, hypophosphorous acid, or both; a solvent containing a glycol compound; Including, the acid component is contained in an amount of 1.7 mmol or more and 5.2 mmol or less relative to the electrolyte solution for an electrolytic capacitor; An electrolyte for electrolytic capacitors, characterized by:

2. further containing azelaic acid, 1,6-decanedicarboxylic acid, or both of them as a chain dicarboxylic acid; 2. The electrolytic solution for electrolytic capacitors according to claim 1,

3. The glycol compound contains diethylene glycol, the diethylene glycol is contained in an amount of 14 wt % or more based on the total amount of the solvent; 2. The electrolytic solution for electrolytic capacitors according to claim 1,

4. The chain dicarboxylic acid contains at least 1,6-decanedicarboxylic acid, the 1,6-decanedicarboxylic acid is contained in an amount of 25 mol % or more based on the total amount of the chain dicarboxylic acids; 3. The electrolyte for an electrolytic capacitor according to claim 2, wherein

5. an anode body having a dielectric coating formed on the surface of a foil made of a valve metal as a base material; a cathode body; an electrolyte interposed between the anode body and the cathode body; Equipped with The electrolyte solution is Inorganic oxide colloidal particles; an acid component that is phosphoric acid, hypophosphorous acid, or both; a solvent containing a glycol compound; Including, the acid component is contained in the electrolyte solution in an amount of 1.7 mmol or more and 5.2 mmol or less; An electrolytic capacitor characterized by:

6. the electrolyte solution further contains azelaic acid, 1,6-decanedicarboxylic acid, or both of them as a chain dicarboxylic acid; 6. The electrolytic capacitor according to claim 5,

7. The glycol compound contains diethylene glycol, the diethylene glycol is contained in an amount of 14 wt % or more based on the total amount of the solvent; 6. The electrolytic capacitor according to claim 5,

8. The chain dicarboxylic acid contains at least 1,6-decanedicarboxylic acid, the 1,6-decanedicarboxylic acid is contained in an amount of 25 mol % or more based on the total amount of the chain dicarboxylic acids; 7. The electrolytic capacitor according to claim 6,

9. an anode forming step of forming an anode body having a dielectric coating formed on the surface of a foil based on a valve metal; a cathode forming step of forming a cathode body; an electrolyte solution preparation step of preparing an electrolyte solution to be interposed between the anode body and the cathode body; an element forming step of forming an element in which the anode body and the cathode body face each other; an electrolyte impregnation step of impregnating the element with the electrolyte; Including, The electrolyte solution is Inorganic oxide colloidal particles; an acid component that is phosphoric acid, hypophosphorous acid, or both; a solvent containing a glycol compound; Including, the acid component is contained in the electrolyte solution in an amount of 1.7 mmol or more and 5.2 mmol or less; A method for manufacturing an electrolytic capacitor, comprising:

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