Electrolyte for electrolytic capacitor and electrolytic capacitor

Abstract

An electrolyte for an electrolytic capacitor that can suppress expansion of a shell container even during reflow soldering is provided. An electrolyte for an electrolytic capacitor, characterized in that it has a capacitor element and an electrolyte impregnated in the capacitor element in a shell container, the capacitor element having an anode foil, a cathode foil and a solid electrolyte layer having a dielectric oxide film layer on the surface, the electrolyte containing an organic carboxylic acid having a hydroxyl group, a boron compound and a solvent, the content of the boron compound being 0.6 mol or more relative to 1 mol of the organic carboxylic acid having a hydroxyl group, the solvent containing a protic organic solvent, and the electrolyte being able to suppress a pressure rise in the shell container even when the electrolytic capacitor is exposed to a high temperature of 250°C or more.

Description

Technical Field

[0001] The present invention relates to an electrolyte solution for an electrolytic capacitor capable of suppressing expansion of an outer case container even when exposed to a high temperature atmosphere in a reflow process or the like, and an electrolytic capacitor using the electrolyte solution. Background Art

[0002] In recent years, there has been an increasing demand for higher reliability in audio-visual (AV) equipment, automotive electrical equipment, etc., and the electrolytic capacitors used therein are also required to have improved performance such as small size, large capacity, and equivalent series resistance (hereinafter also referred to as ESR) in the high frequency region.

[0003] In particular, as electronic devices become more high-frequency, electrolytic capacitors are also required to have large-capacity electrolytic capacitors with excellent ESR characteristics in the high-frequency region. Recently, in order to reduce the ESR in this high-frequency region, solid electrolytic capacitors having a conductive polymer or other solid electrolyte with higher conductivity than the conventional driving electrolyte as an electrolyte and an electrolyte have been studied and commercialized.

[0004] Specifically, Patent Documents 1 and 2 disclose solid electrolytic capacitors using solid electrolytes composed of conductive polymers such as polypyrrole, polythiophene, and polyaniline. In the solid electrolytic capacitors here, a composite compound of organic acids such as phthalic acid, maleic acid, adipic acid, and salicylic acid and inorganic acids such as boric acid, phosphoric acid, and fluoroboric acid, typically ammonium salts or amine salts of borodisalicylic acid, borodiglycolic acid, and borodioxalic acid, etc., is used as a solute, and various organic solvents such as γ-butyrolactone, γ-valerolactone, and ethylene glycol are used as solvents. The solid electrolytic capacitor has a large capacity and a small leakage current, and therefore has attracted much attention as an electrolytic capacitor with high characteristics.

[0005] In addition, Patent Document 3 discloses an electrolytic capacitor using an electrolyte solution, wherein the electrolyte solution contains an amine salt of a boron complex of a dicarboxylic acid or a hydroxycarboxylic acid as an electrolyte, contains γ-butyrolactone or the like as an aprotic organic solvent, and contains an aromatic carboxylic acid having a sulfonic acid group or its salt and a protic organic solvent such as ethylene glycol as an additive.

[0006] On the other hand, these electrolytic capacitors require heat resistance when using electronic devices assembled with them, and further heat resistance is required when mounting them on a substrate. Specifically, a reflow soldering process is used for surface mounting of electrolytic capacitors, but in recent years, lead-free is required, especially for environmental protection, and high heat resistance of more than 250°C is required in the reflow soldering process.

[0007] In such a high-temperature reflow process, the following phenomenon is observed: the pressure in the outer container increases due to the generation of gas by the electrolyte in the electrolytic capacitor, causing the outer container to expand, for example, the height dimension of the electrolytic capacitor increases. In this case, in addition to the occurrence of malfunctions when the electrolytic capacitor mounted on the substrate is mounted in the device, the characteristics of the electrolytic capacitor itself are sometimes reduced, and its reliability may also be impaired (see Patent Documents 4 and 5).

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Publication No. 2015-165550

[0011] Patent Document 2: Japanese Patent No. 5052746

[0012] Patent Document 3: Japanese Patent No. 4863626

[0013] Patent Document 4: Japanese Patent Application Publication No. 2004-186523

[0014] Patent Document 5: Japanese Patent No. 2007-59611 Summary of the invention

[0015] Problem that the invention aims to solve

[0016] An object of the present invention is to provide an electrolyte for an electrolytic capacitor having excellent heat resistance and containing a protic organic solvent such as a polyol as the electrolyte, which can suppress dimensional changes caused by expansion of an outer shell container even when exposed to a high temperature of 250°C or more such as in a reflow soldering process, and an electrolytic capacitor using the electrolyte.

[0017] Solutions for solving problems

[0018] The present inventors have conducted various studies to achieve the above-mentioned object and have obtained the following findings.

[0019] It is clear that in conventional electrolytic capacitors, especially those disclosed in Patent Documents 1 and 2 that use boranodisalicylic acid, a composite compound of an organic carboxylic acid having a hydroxyl group and boric acid, as a solute, and especially those that use protic organic solvents such as polyols such as ethylene glycol and propylene glycol that can obtain excellent ESR characteristics as a solvent, insufficient heat resistance at high temperatures such as in a reflow soldering process can be observed.

[0020] On the other hand, the relationship between the content of boric acid in the electrolyte of the electrolytic capacitor relative to 1 mol of the organic carboxylic acid and the above-mentioned heat resistance was investigated, and the content of boric acid in the electrolyte of the electrolytic capacitor disclosed in Patent Documents 1, 2, and 3 is at most 0.5 to 0.55 mol relative to 1 mol of the organic carboxylic acid. According to the research of the present inventors, when the content of boric acid relative to 1 mol of the organic carboxylic acid is small, the above-mentioned phenomenon of insufficient heat resistance occurs.

[0021] It was further discovered that the above-mentioned problem of heat resistance can be solved by using an electrolyte solution in an electrolytic capacitor that contains an organic carboxylic acid having a hydroxyl group and a boron compound as a solute in a protic organic solvent such as a polyol, and the content of the boron compound relative to 1 mol of the organic carboxylic acid having a hydroxyl group is increased to 0.6 mol or more, more preferably 0.7 mol or more, and particularly preferably 0.9 mol or more.

[0022] On the other hand, regarding the solvent, in the case of an electrolytic capacitor using an electrolyte whose solvent is mainly an aprotic organic solvent such as γ-butyrolactone, no heat resistance problems such as expansion of the outer shell container are observed. In addition, in the case of an electrolyte using an aprotic organic solvent as a solvent, as the content of boric acid relative to the organic carboxylic acid increases, for example, when the content of boric acid relative to 1 mole of organic carboxylic acid exceeds 0.5 moles, the solubility of boric acid, organic carboxylic acid or their composite compounds as solute components decreases. However, it has been clarified that in the case of a protic organic solvent, the solubility of these solute components can also be maintained, and the resistance of the resulting electrolyte can also be kept small.

[0023] The present invention is based on the above findings and has the following aspects.

[0024] (1) An electrolyte for an electrolytic capacitor, characterized in that it comprises a capacitor element and an electrolyte impregnated in the capacitor element in a housing container, wherein the capacitor element comprises an anode foil having a dielectric oxide film layer on its surface, a cathode foil, and a solid electrolyte layer,

[0025] The electrolyte comprises an organic carboxylic acid having a hydroxyl group, a boron compound and a solvent, wherein the content of the aforementioned boron compound is 0.6 mol or more relative to 1 mol of the aforementioned organic carboxylic acid having a hydroxyl group, and the aforementioned solvent contains a protic organic solvent. The electrolyte can also suppress the pressure increase in the outer shell container when the electrolytic capacitor is exposed to a high temperature of 250° C. or above.

[0026] (2) The electrolyte solution according to (1) above, wherein the boron compound is boric acid.

[0027] (3) The electrolyte solution according to (1) or (2), wherein the organic carboxylic acid having a hydroxyl group is an aromatic carboxylic acid having a hydroxyl group.

[0028] (4) The electrolyte according to any one of (1) to (3) above, further comprising ammonia or a primary amine, a secondary amine, a tertiary amine or a quaternary amine.

[0029] (5) The electrolyte solution according to any one of (1) to (4) above, wherein the protic organic solvent is ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, benzyl alcohol or glycerol.

[0030] (6) The electrolyte solution according to any one of (1) to (5), wherein the content of the boron compound is 0.7 to 2 mol per 1 mol of the organic carboxylic acid having a hydroxyl group.

[0031] (7) The electrolyte solution according to any one of (1) to (6) above, comprising 65% by mass or more of the protic organic solvent based on the electrolyte solution.

[0032] (8) The electrolyte solution according to any one of (1) to (7) above, wherein the water content is 1% by mass or less.

[0033] (9) The electrolyte according to any one of (1) to (8) above, wherein the pH thereof is 2 to 6.

[0034] (10) The electrolyte solution according to any one of (1) to (9) above, further comprising a nitro compound.

[0035] (11) The electrolyte solution according to any one of (1) to (10), wherein the organic carboxylic acid having a hydroxyl group forms a composite compound with the boron compound.

[0036] (12) The electrolyte solution according to any one of (1) to (11) above, wherein the solid electrolyte layer is a layer of polythiophene, polypyrrole, polyaniline or a derivative thereof.

[0037] (13) The electrolytic solution according to any one of (1) to (12), wherein the exposure of the electrolytic capacitor to a high temperature of 250° C. or higher is a reflow process of the electrolytic capacitor.

[0038] (14) An electrolytic capacitor using the electrolytic solution according to any one of (1) to (13).

[0039] (15) A reflow soldering method using the electrolytic capacitor of (14) above.

[0040] Effects of the Invention

[0041] According to the present invention, an electrolyte for an electrolytic capacitor can be obtained, which can suppress the pressure increase in the outer container and the expansion of the outer container even when an electrolytic capacitor using a protic organic solvent such as a polyol as an electrolyte is exposed to a high temperature of 250°C or more, or further 260°C or more in a reflow soldering process, and an electrolytic capacitor using the electrolyte.

[0042] In addition, the electrolytic capacitor obtained using the electrolyte of the present invention has its dimensional and characteristic changes caused by the expansion of the outer shell container suppressed in the high-temperature reflow process at 250°C or above. In addition, the characteristic changes are small in a high-temperature use environment, and it has high reliability.

[0043] The following is considered as a mechanism for suppressing the pressure rise in the outer container and improving the heat resistance in the electrolytic capacitor obtained by using the electrolyte of the present invention. By making the content of the boron compound contained in the electrolyte using a protic organic solvent as a solvent 0.6 mol or more relative to 1 mol of the organic carboxylic acid having a hydroxyl group, and further to this content or more, it is possible to suppress the generation of carbon dioxide and the like caused by the decomposition of the organic carboxylic acid having a hydroxyl group, its composite compound with the boron compound, or their salts. It can be considered that as the content of the boron compound increases to 0.7 mol or more relative to 1 mol of the organic carboxylic acid, and further increases to 0.9 mol or more, the generation of carbon dioxide and the like caused by the decomposition can be reliably prevented. DETAILED DESCRIPTION

[0044] In the following, embodiments of the present invention will be described. It should be noted that, when describing a numerical range in the present specification, if the unit of the lower limit value and the upper limit value is the same, the unit of the lower limit value may be omitted.

[0045] <Electrolytic capacitors>

[0046] The electrolyte solution of the present invention is used for a solid electrolytic capacitor having a capacitor element and an electrolyte solution impregnated in the capacitor element, wherein the capacitor element has an anode and a cathode having a dielectric oxide film layer on the surface, and a solid electrolyte. The solid electrolytic capacitor can be obtained by a known method.

[0047] The solid electrolyte used in the present invention is a conductive polymer doped with a doping component. As the conductive polymer, polypyrrole, polythiophene, polyaniline, or a derivative thereof can be used.

[0048] The solid electrolyte layer used in the present invention can be obtained by chemically oxidatively polymerizing or electrolytically oxidatively polymerizing the monomers of the conductive polymer in the presence of the above-mentioned doping component. Alternatively, it can be obtained by contacting a dispersion obtained by dispersing the conductive polymer formed into microparticles by chemically oxidatively polymerizing in a solvent such as water or a solution obtained by dissolving the conductive polymer with an anode or cathode. In addition, in the above-mentioned chemically oxidatively polymerizing or electrolytically oxidatively polymerizing, part or all of the monomers of the above-mentioned doping component and the conductive polymer can be replaced with monomers having functional groups capable of chemically oxidatively doping.

[0049] Specifically, the monomer of the conductive polymer includes 3,4-ethylenedioxythiophene, methyl-3,4-ethylenedioxythiophene, ethyl-3,4-ethylenedioxythiophene, propyl-3,4-ethylenedioxythiophene, 3,4-propylenedioxythiophene, methyl-3,4-propylenedioxythiophene, ethyl-3,4-propylenedioxythiophene, propyl-3,4-propylenedioxythiophene, 3,4-ethylenedioxyfuran, methyl-3,4-ethylenedioxyfuran, ethyl-3,4-ethylenedioxyfuran, propyl-3,4-propylenedioxythiophene, 3,4-ethylenedioxyfuran, -ethylenedioxyfuran, 3,4-propylenedioxyfuran, methyl-3,4-propylenedioxyfuran, ethyl-3,4-propylenedioxyfuran, propyl-3,4-propylenedioxyfuran, 3,4-ethylenedithiothiophene, methyl-3,4-ethylenedithiothiophene, ethyl-3,4-ethylenedithiothiophene, propyl-3,4-ethylenedithiothiophene, 3,4-propylenedithiothiophene, methyl-3,4-propylenedithiothiophene, ethyl-3,4-propylenedithiothiophene, propyl-3,4-ethylenedithiothiophene, 3,4-propylenedithiothiophene, methyl-3,4-propylenedithiothiophene, ethyl-3,4-propylenedithiothiophene, propyl-3,4-propylenedithiothiophene, etc.

[0050] Among the above, 3,4-ethylenedioxythiophene, methyl-3,4-ethylenedioxythiophene, or ethyl-3,4-ethylenedioxythiophene is particularly preferred because they are excellent in terms of low ESR of the electrolytic capacitor.

[0051] As the above-mentioned doping component, any functional group that can be chemically oxidatively doped in the polymer may be used, preferably a sulfate group, a phosphate group, a phosphoric acid group, a carboxyl group, a sulfonic acid group, etc. Among these, from the viewpoint of the doping effect, a sulfate group, a carboxyl group, a sulfonic acid group is more preferred, and a sulfonic acid group is particularly preferred.

[0052] As doping components, specifically, polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyacrylic acid ethyl sulfonic acid, polyacrylic acid butyl sulfonic acid, polyacrylic acid sulfonic acid, polymethacrylic acid sulfonic acid, poly (2-acrylamide-2-methylsulfonic acid), polyisoprene sulfonic acid, polyvinyl carboxylic acid, polystyrene carboxylic acid, polyallyl carboxylic acid, polyacrylic acid sulfonic acid, polymethacrylic acid carboxylic acid, poly (2-acrylamide-2-methylcarboxylic acid), polyisoprene carboxylic acid, p-toluene sulfonic acid, xylene sulfonic acid, methyl naphthalene sulfonic acid, butyl naphthalene sulfonic acid or their metal salts etc. can be listed. They can be a single polymer or a copolymer of two or more. Among these, polystyrene sulfonic acid is particularly preferred.

[0053] Examples of monomers having a functional group capable of chemical oxidation doping include 6-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-yl)hexane-1-sulfonic acid, sodium 6-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-yl)hexane-1-sulfonate, lithium 6-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-yl)hexane-1-sulfonate, and 6-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-yl)hexane-1-sulfonate. 8-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-yl)octane-1-sulfonic acid, 8-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-yl)octane-1-sulfonic acid sodium, 8-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-yl)octane-1-sulfonic acid potassium, 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl- Sodium 1-propanesulfonate, Sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-ethyl-1-propanesulfonate, Sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-propyl-1-propanesulfonate, Sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonate, Sodium 3-[(2,3-dihydrothieno[3,4-b]-[1 ,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonic acid potassium, 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonic acid, 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonic acid ammonium, 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonic acid triethylammonium, etc.

[0054] As the above-mentioned dispersion medium, water or an organic solvent can be used. As the organic solvent, alcohols, ketones, esters, ethers, cellosolves, aromatic hydrocarbons, aliphatic hydrocarbons, etc. can be used.

[0055] The conductive polymer dispersion or solution of the present invention may contain a high boiling point organic solvent. Among the high boiling point organic solvents, a high boiling point organic solvent having a boiling point of 150° C. or more is particularly preferred. Specific examples of the high boiling point organic solvent include N-methyl-2-pyrrolidone, dimethyl sulfoxide, γ-butyrolactone, cyclopentane, dimethyl sulfone, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, and the like. Among these, ethylene glycol or γ-butyrolactone is more preferred from the viewpoint of being able to form a solid electrolyte layer containing a conductive polymer having a uniform surface.

[0056] The content of the organic solvent in the conductive polymer dispersion or solution is preferably 1 to 20% by mass, particularly preferably 5 to 15% by mass. When the content of the organic solvent is less than 1% by mass, the effect of forming a solid electrolyte layer containing a conductive polymer with a uniform surface is slightly poor, and when it exceeds 20% by mass, there is a problem that the drying process takes time.

[0057] In order to adjust the film forming property and film strength, the conductive polymer dispersion or solution may contain a binder resin, a surfactant, or an alkaline compound. The conductive polymer dispersion is obtained by dispersing the conductive polymer in a dispersion medium, or a part of the conductive polymer may be dissolved in the dispersion medium.

[0058] As the anode and cathode used in the electrolytic capacitor, valve metals are preferred, and specifically, one selected from the group consisting of aluminum, tantalum, niobium and titanium can be cited, among which aluminum is preferred. Valve metals are usually used in the form of sintered bodies or foils. Electrolytic capacitors can be made into chip types or wound types depending on the shapes of the anode and cathode used.

[0059] In the electrolytic capacitor of the present invention, the solid electrolyte can be formed by immersing the capacitor element in a dispersion or solution of the conductive polymer to bring it into contact with the conductive polymer and then drying the solvent, or by immersing the capacitor element in a monomer solution of the conductive polymer and then using chemical polymerization or electrolytic polymerization.

[0060] <Electrolyte>

[0061] The electrolytic solution in the present invention contains an electrolyte and an organic solvent, and the electrolyte contains an organic carboxylic acid having a hydroxyl group and a boron compound.

[0062] The organic carboxylic acid having a hydroxyl group is preferably one having preferably 1 to 4, more preferably 1 or 2, particularly preferably 1 ring structure and preferably 1 to 4, more preferably 1 or 2, particularly preferably 1 hydroxyl group.

[0063] Preferred specific examples of the organic carboxylic acid having a hydroxyl group include glycolic acid, lactic acid, 3-hydroxypropionic acid, mandelic acid, salicylic acid, 3-methylsalicylic acid, 4-methylsalicylic acid, 5-methylsalicylic acid, 6-methylsalicylic acid, 3-nitrosalicylic acid, 4-nitrosalicylic acid, 5-nitrosalicylic acid, 3,5-dinitrosalicylic acid, 3-sulfosalicylic acid, 4-sulfosalicylic acid, 5-sulfosalicylic acid, 4-hydroxysalicylic acid, 5-hydroxysalicylic acid, 3-methoxysalicylic acid, 4-methoxysalicylic acid, 5-methoxysalicylic acid, methylenedisalicylic acid, 1-hydroxy-2-naphthoic acid, 2-hydroxy-1-naphthoic acid, 3-hydroxy-2-naphthoic acid, 3-hydroxy-7-methyl-2-naphthoic acid, and 4,4′-methylenebis(3-hydroxy-2-naphthoic acid). Among the above, aromatic carboxylic acids are preferred, and salicylic acid is particularly preferred.

[0064] Examples of the boron compound contained in the electrolyte of the present invention include boric acid and boric acid esters (trimethyl borate, triethyl borate, tripropyl borate, tributyl borate, triphenyl borate, etc.), etc. Boric acid is particularly preferred because of its excellent properties.

[0065] In the electrolyte of the present invention, the content ratio of the boron compound relative to the organic carboxylic acid having a hydroxyl group is important, and the boron compound is contained at least 0.6 mol, preferably at least 0.65 mol, more preferably at least 0.7 mol, and further preferably at least 0.9 mol, relative to 1 mol of the organic carboxylic acid having a hydroxyl group. When the boron compound is contained in a manner in which the content ratio is within the above range, the effect of sufficiently suppressing the expansion of the outer shell container can be obtained when exposed to a high temperature of 250°C or more.

[0066] On the other hand, when the content ratio of the boron compound is large, in order to cause deterioration of the ESR characteristics of the capacitor under high temperature conditions such as above 100°C, the content ratio of the boron compound is preferably 5 mol or less, more preferably 3.5 mol or less, further preferably 2.0 mol or less, and particularly preferably 1.5 mol or less relative to 1 mol of the organic carboxylic acid having a hydroxyl group.

[0067] The boron compound contained in the electrolyte of the present invention may exist separately from the organic carboxylic acid having a hydroxyl group in the electrolyte, or part or all of both may exist as a composite compound of the organic carboxylic acid having a hydroxyl group and the boron compound.

[0068] The electrolyte of the present invention preferably contains ammonia, primary amine, secondary amine, tertiary amine, quaternary amine, or amidine compound in addition to the organic carboxylic acid having a hydroxyl group and the boron compound. The primary amine, secondary amine, tertiary amine, or quaternary amine is preferably a tertiary amine.

[0069] Examples of the tertiary amine include trialkylamines (trimethylamine, dimethylethylamine, methyldiethylamine, triethylamine, dimethyl-n-propylamine, dimethylisopropylamine, methylethyl-n-propylamine, methylethylisopropylamine, diethyl-n-propylamine, diethylisopropylamine, tri-n-propylamine, triisopropylamine, tri-n-butylamine, tri-tert-butylamine, etc.), and phenyl-containing amines (dimethylphenylamine, methylethylphenylamine, diethylphenylamine, etc.).

[0070] Among them, the tertiary amine is preferably a trialkylamine, and more preferably contains one or more selected from the group consisting of trimethylamine, dimethylethylamine, methyldiethylamine, and triethylamine.

[0071] When the electrolyte of the present invention contains ammonia, primary amine, secondary amine, tertiary amine, quaternary amine, or amidine compound, the structure of some or all of them between the organic carboxylic acid and / or boron compound or the complex compound having a hydroxyl group is not necessarily clear, and it can be considered that they form a certain complex compound.

[0072] The organic solvent used in the electrolyte of the present invention is a protic organic solvent, and the solvent can be used alone or in combination. In the present invention, a protic organic solvent must be used. When a non-protic organic solvent such as γ-butyrolactone is used as a solvent, the expansion of the outer shell container is small during reflow soldering regardless of the amount of the boron compound added in the present invention, which violates the purpose of the present invention. In addition, the electrolyte of the present invention is characterized in that the boron compound is contained in a manner that the content ratio relative to 1 mole of an organic carboxylic acid having a hydroxyl group is 0.6 moles or more. When γ-butyrolactone or the like is used as an aprotic organic solvent, as shown in Comparative Example 6, when the content ratio of boric acid relative to 1 mole of salicylic acid as an organic carboxylic acid having a hydroxyl group is 1 mole, salicylic acid and / or boric acid as a solute will not be fully dissolved.

[0073] The content of the protic organic solvent in the electrolyte solution of the present invention is preferably 65% ​​by mass or more, more preferably 70% by mass or more, particularly preferably 80% by mass or more, and most preferably 85% by mass or more.

[0074] Examples of the protic organic solvent include monohydric alcohols (methanol, ethanol, propanol, butanol, pentanol, hexanol, cyclohexanol, benzyl alcohol, etc.), polyhydric alcohols and alkoxy alcohol compounds (ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, glycerol, methyl cellosolve, ethyl cellosolve, methoxypropylene glycol, dimethoxypropylene glycol, etc.), polyalkylene glycols (polyethylene glycol, polypropylene glycol, etc.), etc. Among them, solvents having a boiling point of preferably 150° C. or higher are suitable, and examples thereof include monohydric alcohols (hexanol, cyclohexanol, benzyl alcohol, etc.), polyhydric alcohols and alkoxy alcohol compounds (ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, glycerol, methyl cellosolve, ethyl cellosolve, methoxypropylene glycol, dimethoxypropylene glycol, etc.), polyalkylene glycols (polyethylene glycol, polypropylene glycol, etc.), etc.

[0075] Among the above, the organic solvent used in the electrolyte is preferably at least one selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, benzyl alcohol and glycerol, because the capacitance of the capacitor is high. Ethylene glycol, diethylene glycol or polyethylene glycol is particularly preferred.

[0076] The electrolyte of the present invention may contain an aprotic solvent. However, as observed in the comparative examples described later, when using γ-butyrolactone as an aprotic solvent, the solute of the electrolyte of the present invention, i.e., the organic carboxylic acid and / or boron compound having a hydroxyl group, has a low solubility relative to γ-butyrolactone and prevents the expansion of the outer shell container during reflow soldering, and its contribution is small. Therefore, even if the aprotic solvent in the electrolyte of the present invention is contained, it is preferably less than 80% by mass of the total solvent, preferably less than 40% by mass, more preferably less than 20% by mass, and particularly preferably less than 10% by mass.

[0077] Examples of the aprotic solvent include γ-butyrolactone, γ-valerolactone, amides (N-methylformamide, N,N-dimethylformamide, N-ethylformamide, N,N-diethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylacetamide, N,N-diethylacetamide, hexamethylphosphoramide, etc.), sulfolane (sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, etc.), chain sulfones (dimethyl sulfone, ethyl methyl sulfone, ethyl isopropyl sulfone), cyclic amides. series (N-methyl-2-pyrrolidone, etc.), carbonates (ethylene carbonate, propylene carbonate, isobutylene carbonate, etc.), nitrile series (acetonitrile, etc.), sulfoxide series (dimethyl sulfoxide, etc.), 2-imidazolidinone series [1,3-dialkyl-2-imidazolidinone (1,3-dimethyl-2-imidazolidinone, 1,3-diethyl-2-imidazolidinone, 1,3-di(n-propyl)-2-imidazolidinone, etc.), 1,3,4-trialkyl-2-imidazolidinone (1,3,4-trimethyl-2-imidazolidinone, etc.)], etc.

[0078] The content of the organic carboxylic acid having a hydroxyl group in the electrolyte of the present invention is preferably 0.1 to 40% by mass, more preferably 1 to 20% by mass, and particularly preferably 3 to 10% by mass. When the content is less than 0.1% by mass, it is difficult to obtain sufficient electrical properties, while when it exceeds 40% by mass, the maintenance rate of low ESR in a high temperature environment decreases.

[0079] In addition, the content of the boron compound is 0.6 mol or more, preferably 0.65 mol or more, more preferably 0.7 to 2.0 mol, and particularly preferably 0.9 to 1.5 mol relative to 1 mol of the organic carboxylic acid having a hydroxyl group. If the content is less than 0.6 mol relative to 1 mol of the organic carboxylic acid, it is difficult to obtain a sufficient effect of suppressing expansion during reflow soldering.

[0080] The electrolyte of the present invention is prepared by adding an organic carboxylic acid having a hydroxyl group, a boron compound, and preferably further adding ammonia or a primary amine, a secondary amine, a tertiary amine, or a quaternary amine to the organic solvent simultaneously or intermittently in such a manner that the above contents are achieved. When adding them, the mixture can be stirred as required and heated as required. The stirring and heating can be carried out under appropriate conditions, for example, the heating can be carried out at 35 to 120°C.

[0081] The electrolyte of the present invention can be manufactured by reacting an organic carboxylic acid having a hydroxyl group with a boron compound in advance and adding the reactants to the above-mentioned organic solvent. Furthermore, it can also be manufactured by reacting an organic carboxylic acid having a hydroxyl group with a boron compound and ammonia or a primary amine, a secondary amine, a tertiary amine, or a quaternary amine in advance and adding the reactants to the above-mentioned organic solvent.

[0082] In the electrolyte of the present invention, when the amount of water contained therein is preferably less than 1% by mass, excellent properties can be obtained in terms of being able to suppress the rise in internal pressure when heat of 250° C. or more is applied, for example, in the case of a reflow soldering process. The amount of water contained is more preferably less than 1% by mass, and particularly preferably less than 0.5% by mass. The amount of water contained can be adjusted by removing the water contained in the electrolyte raw materials such as the organic solvent used and the prepared electrolyte. The removal of water contained can be carried out by, for example, heating the electrolyte, decompressing and distilling, treating with a dehydrating agent, or a combination thereof.

[0083] Furthermore, it was found that the electrolyte solution of the present invention preferably has a pH of 2 to 6, which can provide excellent characteristics in terms of maintaining low ESR. The reason for this is not clear, but the pH is more preferably 2.5 to 5.5, and particularly preferably 3 to 5.

[0084] In the electrolyte of the present invention, substances other than the above may be added for the purpose of improving the life performance, resistance performance and other characteristics of the electrolytic capacitor. The added substances are not particularly limited. For example, the following substances may be listed.

[0085] Examples include phosphorus compounds (phosphate esters, etc.), polysaccharides (mannitol, sorbitol, etc.), complexes of boric acid and polysaccharides (mannitol, sorbitol, etc.), complexes of boric acid and polyols (ethylene glycol, glycerol, etc.), and nitro compounds (o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, p-nitrophenol, p-nitrobenzyl alcohol, etc.).

[0086] Furthermore, an antioxidant may be added to the electrolyte solution. Examples of the antioxidant include phenol compounds (catechol, hydroquinone, pyrogallol, etc.), amine compounds, azo compounds, silane compounds, quinone compounds, and carboxylic acid compounds.

[0087] <Heat resistance of solid electrolytic capacitors>

[0088] The solid electrolytic capacitor of the present invention is manufactured according to a known method by immersing a capacitor element having a solid electrolyte layer in the electrolyte of the present invention so that the gap in the capacitor element is filled with the electrolyte of the present invention, inserting the capacitor element into an outer shell container, and installing a sealing material at the open end to perform a fastening process.

[0089] As the material of the outer shell container used in the manufacture of the solid electrolytic capacitor of the present invention, aluminum, aluminum alloy, other metals, etc. can be preferably widely used. The wall thickness of the outer shell container is preferably 0.2 to 0.7 mm, more preferably 0.2 to 0.4 mm. In addition, as the sealing material of the outer shell container, butyl rubber, butadiene rubber, styrene butadiene rubber, EPM, EPDM or a mixture thereof can be preferably widely used.

[0090] The solid electrolytic capacitor of the present invention obtained in this way has excellent heat resistance, and can suppress dimensional changes and characteristic changes caused by the expansion of the outer shell container in the high-temperature lead-free reflow process of 250°C or more, and further 260°C or more, so that dimensional changes can be suppressed during surface mounting. In addition, in recent years, in the use environment reaching high temperatures such as in vehicle applications, the characteristic changes are small and the reliability is high.

[0091] Furthermore, the solid electrolytic capacitor of the present invention has excellent characteristics such as low ESR characteristics and high capacitance characteristics in a high frequency region, and has the above-mentioned high heat resistance, so these characteristics are not degraded by heat.

[0092] Example

[0093] Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples, and various modifications can be made within the scope of the present invention.

[0094] (Preparation of Conductive Polymer Dispersion)

[0095] 12.2 g of a 20% aqueous solution of polystyrene sulfonic acid (weight average molecular weight: 50,000) as a doping component was mixed with 187.5 g of water and stirred for 10 minutes. Then, 2.04 g of 3,4-ethylenedioxythiophene as a monomer was added and stirred for another 15 minutes to prepare a monomer solution. The obtained monomer solution exhibited a light yellow color.

[0096] The amount of polystyrene sulfonic acid contained in the above monomer solution is 119 parts by mass relative to 100 parts by mass of 3,4-ethylenedioxythiophene contained in the monomer solution. While stirring the monomer solution, 0.012 g of iron (III) sulfate and 4.46 g of ammonium persulfate as oxidants are added dropwise, and stirred at room temperature for 15 hours to perform chemical oxidative polymerization. At this time, the monomer solution changes from light yellow to dark blue. Next, 50.1 g of amphoteric ion exchange resin (ORGANO, trade name: MB-1, ion exchange form: -H, -OH) is added to the resulting reaction solution and stirred for 2 hours. As a result, the pH of the reaction solution changes from 1.15 to 1.83. In this way, a conductive polymer dispersion containing 1.3% by mass of poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid is prepared.

[0097] (Fabrication of capacitor elements)

[0098] An aluminum anode foil and an aluminum cathode foil are wound with a separator (thickness 0.05 mm) formed of cellulose fibers between them to produce a capacitor element. The aluminum anode foil is obtained by etching the surface and then performing chemical conversion treatment to form an oxide coating layer, and a lead terminal is installed. The aluminum cathode foil is obtained by etching the surface and performing lead terminals.

[0099] (Example 1)

[0100] The capacitor element obtained above is immersed in the conductive polymer dispersion liquid, the capacitor element is pulled out, and then the solvent is evaporated to form a solid electrolyte layer containing a conductive polymer.

[0101] Next, the components of salicylic acid, boric acid, dimethylethylamine, and ethylene glycol recorded in Table 1 were stirred and mixed at 90-95°C to produce an electrolyte, which was then impregnated into the capacitor element. Next, the capacitor element was inserted into a bottomed cylindrical metal aluminum shell (shell raw material thickness: 0.3 mm), and a sealing rubber was installed at the open end to perform a crimping process to seal it. Thereafter, an aging treatment was performed at 105°C to produce an aluminum electrolytic capacitor.

[0102] The rated voltage of the electrolytic capacitor is 35 V, and the outer dimensions of the sealed electrolytic capacitor are a cylinder with a diameter of 10 mm and a height of 10 mm.

[0103] (Examples 2 to 10, Comparative Examples 1 to 5)

[0104] Electrolytic capacitors of Examples 2 to 10 and Comparative Examples 1 to 5 were prepared in the same manner as in Example 1 except that an electrolyte solution obtained by mixing the components in the amounts shown in Table 1 at 90 to 95° C. was used.

[0105] (Comparative Example 6)

[0106] The components in the amounts shown in Table 1 were mixed and dissolved at 90 to 95° C. while being stirred. However, a white solid was precipitated when cooled to 25° C., and thus an electrolytic solution could not be prepared.

[0107] It should be noted that the water content (mass %) and pH of the electrolyte used in the electrolytic capacitors of Examples 1 to 10 and Comparative Examples 1 to 5 are shown in Table 1. The water content was measured by Karl Fischer coulometric titration using a trace moisture measuring device CA-200 (manufactured by Mitsubishi Chemical Analytical Science Co., Ltd.). The pH was measured using a pH meter HM-30R manufactured by DKK Toa Co., Ltd.

[0108] (Capacitor heating test)

[0109] The electrolytic capacitors prepared above were heated in a desktop reflow oven (manufactured by SHINAPEX; STR-2000) so that the peak temperature reached 260°C. During the heating in the desktop reflow oven, the temperature was first heated to 180°C at an average temperature increase rate of 2.1°C / second, and maintained at this temperature for 60 seconds, then increased to 260°C at an average temperature increase rate of 2.1°C / second, maintained at this temperature for 1 second, and then returned to room temperature at an average temperature decrease rate of 4.2°C / second.

[0110] The elongation ΔL (mm) of the height dimension of the cylindrical electrolytic capacitor was calculated by the following formula through the heating test and is shown in Table 1. In the following formula, the "height dimension" is the distance between the center portions of both bottom surfaces of the cylindrical capacitor and is measured using a vernier caliper.

[0111] ΔL = (height dimension after reflow test) - (height dimension before reflow test)

[0112] [Table 1]

[0113]

[0114] As shown in Table 1, the electrolytic capacitors of Examples 1 to 10 obtained using an electrolyte solution containing 0.6 mol or more of boric acid relative to 1 mol of an organic carboxylic acid having a hydroxyl group have a smaller ΔL (mm) than the electrolytic capacitors of Comparative Examples 1 to 5, and the expansion of the outer shell container is suppressed even at a high temperature of 260°C.

[0115] Industrial Applicability

[0116] The present invention can be widely used as an electrolyte in electrolytic capacitors commonly used in power supplies for various consumer devices such as audio-visual equipment, mobile phones, and notebook computers, in-vehicle electrical equipment, and industrial equipment.

[0117] It should be noted that the entire contents of the specification, claims, drawings, and abstract of Japanese Patent Application No. 2019-207008 filed on November 15, 2019 are cited herein and introduced as the disclosed contents of the present specification.

Claims

1. An electrolyte for an electrolytic capacitor, characterized in that: The invention comprises a capacitor element and an electrolyte solution impregnated in the capacitor element in a housing container, wherein the capacitor element comprises an anode foil having a dielectric oxide film layer on the surface, a cathode foil and a solid electrolyte layer. The electrolyte comprises an organic carboxylic acid having a hydroxyl group, a boron compound and a solvent, wherein the boron compound is boric acid or a boric acid ester, the organic carboxylic acid having a hydroxyl group is an aromatic carboxylic acid having a hydroxyl group, the content of the boron compound is 0.6 mol or more relative to 1 mol of the organic carboxylic acid having a hydroxyl group, the solvent contains a protic organic solvent, and the electrolyte can also suppress the pressure increase in the outer shell container when the electrolytic capacitor is exposed to a high temperature of 250° C. or above.

2. The electrolyte according to claim 1, further comprising ammonia or a primary amine, a secondary amine, a tertiary amine, or a quaternary amine.

3. The electrolyte according to claim 1 or 2, wherein The protic organic solvent is at least one selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, benzyl alcohol and glycerol.

4. The electrolyte according to claim 1 or 2, wherein The content of the boron compound is 0.7 to 2 mol relative to 1 mol of the organic carboxylic acid having a hydroxyl group. 5 . The electrolyte solution according to claim 1 , comprising 65 mass % or more of the protic organic solvent based on the electrolyte solution.

6. The electrolyte solution according to claim 1 or 2, which has a water content of 1 mass % or less.

7. The electrolyte according to claim 1 or 2, which has a pH of 2 to 6. The electrolyte according to claim 1 or 2, further comprising a nitro compound.

9. The electrolyte according to claim 1 or 2, wherein The organic carboxylic acid having a hydroxyl group forms a composite compound with the boron compound.

10. The electrolyte according to claim 1 or 2, wherein The solid electrolyte layer is a layer of polythiophene, polypyrrole, polyaniline or a derivative thereof.

11. The electrolyte according to claim 1 or 2, wherein Exposing the electrolytic capacitor to a high temperature of 250° C. or higher is a reflow process of the electrolytic capacitor. 12 . An electrolytic capacitor using the electrolytic solution according to claim 1 .

13. A reflow soldering method using the electrolytic capacitor according to claim 12.

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