Electrolytic capacitors

Abstract

This suppresses the increase in ESR of electrolytic capacitors and also suppresses the increase in leakage current. [Solution] The disclosed electrolytic capacitor comprises a capacitor element and a liquid component. The capacitor element comprises an anode having a dielectric layer on its surface and a conductive polymer compound covering at least a portion of the dielectric layer. The liquid component comprises an acid component, a base component, and a solvent. The solvent comprises an organic compound having a hydroxyl group, and the acid component comprises an organic carboxylic acid compound. The base component comprises at least one selected from the group consisting of primary amine compounds and secondary amine compounds.

Description

Technical Field

[0001] The present invention relates to an electrolytic capacitor including a conductive polymer compound and a liquid component.

Background Art

[0002] An electrolytic capacitor includes a capacitor element and a liquid component (electrolyte). The capacitor element includes an anode body having a dielectric layer on its surface and a conductive polymer compound covering at least a part of the dielectric layer. The liquid component includes an acid component, a base component, and a solvent. Various studies have been conducted on the liquid component.

[0003] In Patent Document 1, it is proposed to use ethylene glycol or the like as a solvent, ammonia as a base component, and azelaic acid or the like as an acid component for the electrolyte. In Patent Document 2, it is proposed to use a tertiary amine such as triethylamine or a quaternary ammonium such as 1,2-dimethylimidazolinium as the base component of the electrolyte and to include an antioxidant such as phenol in the electrolyte.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In liquid components, when organic compounds containing hydroxyl groups and organic carboxylic acid compounds containing carboxyl groups coexist, the amount of organic carboxylic acid compounds in the liquid component may decrease due to esterification reactions. In such cases, the pH of the liquid component may increase, leading to dedoping of the conductive polymer dopant and an increase in the ESR of the electrolytic capacitor. Furthermore, the decrease in organic carboxylic acid compounds may impair the film repair function of the liquid component, potentially increasing the leakage current of the electrolytic capacitor.

[0006] Using ammonia, tertiary amines, or quaternary ammonium as the base component of the liquid component, or including antioxidants such as phenol in the liquid component, can increase the leakage current of electrolytic capacitors. [Means for solving the problem]

[0007] One aspect of the present invention relates to an electrolytic capacitor. The electrolytic capacitor comprises a capacitor element and a liquid component, the capacitor element comprising an anode having a dielectric layer on its surface and a conductive polymer compound covering at least a portion of the dielectric layer, the liquid component comprising an acid component, a base component and a solvent, the solvent comprising an organic compound having a hydroxyl group, the acid component comprising an organic carboxylic acid compound, and the base component comprising at least one selected from the group consisting of primary amine compounds and secondary amine compounds.

[0008] Another aspect of the present invention relates to another electrolytic capacitor. This other electrolytic capacitor comprises a capacitor element and a liquid component, the capacitor element comprising an anode having a dielectric layer on its surface and a conductive polymer compound covering at least a portion of the dielectric layer, the liquid component comprising an acid component, a base component, a solvent, and an antioxidant, the base component comprising at least one selected from the group consisting of primary amine compounds and secondary amine compounds. [Effects of the Invention]

[0009] According to the present invention, it is possible to suppress the increase in ESR and the increase in leakage current of an electrolytic capacitor. Novel features of the present invention are described in the appended claims, but the present invention, both in terms of structure and content, and in conjunction with other objects and features of the present invention, will be better understood by the following detailed description in conjunction with the drawings. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic cross-sectional view of an electrolytic capacitor according to one embodiment of the present invention. [Figure 2] This is a schematic diagram illustrating the configuration of the capacitor element according to the same embodiment. [Modes for carrying out the invention]

[0011] An electrolytic capacitor according to one embodiment of the present invention comprises a capacitor element and a liquid component. The capacitor element comprises an anode having a dielectric layer on its surface and a conductive polymer compound covering at least a portion of the dielectric layer. The liquid component comprises an acid component, a base component, and a solvent. The solvent comprises an organic compound having a hydroxyl group. The acid component comprises an organic carboxylic acid compound. The base component comprises at least one selected from the group consisting of primary amine compounds and secondary amine compounds (hereinafter also referred to as primary amine compounds, etc.).

[0012] In the liquid component, when organic compounds containing hydroxyl groups and organic carboxylic acid compounds containing carboxyl groups coexist, the amount of organic carboxylic acid compounds in the liquid component may decrease due to esterification reactions. In such cases, the pH of the liquid component may increase, the dopants of the conductive polymer may be dedoped, and the ESR of the electrolytic capacitor may rise. The decrease in organic carboxylic acid compounds may also impair the film repair function of the liquid component (the function of repairing defects in the dielectric layer), which may increase the leakage current of the electrolytic capacitor.

[0013] In contrast, the present invention has found that by including at least one of a primary amine compound and a secondary amine compound (hereinafter also referred to as a primary amine compound, etc.) as a basic component in the liquid component, the increase in ESR is suppressed and the increase in leakage current is suppressed.

[0014] When the liquid component contains a primary amine compound, the amount of undissociated organic carboxylic acid compounds in the liquid component is reduced compared to when the liquid component contains at least one of a tertiary amine and ammonia, and the esterification reaction described above is suppressed. Therefore, the reduction of organic carboxylic acid compounds due to the esterification reaction is suppressed, and even when used for a long time, the increase in ESR due to dedoping of the conductive polymer dopant is suppressed, the film repair function of the liquid component is sufficiently maintained, and the increase in leakage current is suppressed.

[0015] When the liquid component contains a primary amine compound, the pH of the liquid component is maintained at a lower level compared to when the liquid component contains a quaternary ammonium compound. This suppresses the dedoping of dopants from the conductive polymer compound and inhibits the increase in ESR.

[0016] When the liquid component contains primary amine compounds, etc., the stability of the liquid component (e.g., thermal stability) is adequately ensured compared to when the liquid component contains ammonia, tertiary amines, and / or quaternary ammonium compounds. As a result, fluctuations in the amount of acidic and basic components dissociated in the liquid component are suppressed, the film repair function of the liquid component is stably maintained, and the increase in leakage current is suppressed.

[0017] Furthermore, in medium-to-high voltage type electrolytic capacitors (for example, those with a rated voltage of 160V or higher) where the dielectric layer is covered with a conductive polymer compound, leakage current tends to increase particularly easily. Therefore, the effect of suppressing the increase in leakage current by including a primary amine compound or the like in the liquid component of the present invention is significantly obtained.

[0018] The liquid component may contain an antioxidant. When the liquid component contains a primary amine compound or the like, the leakage current is smaller compared to the case where the liquid component contains ammonia, a tertiary amine, and / or a quaternary ammonium, and an increase in the leakage current due to the liquid component containing an antioxidant is suppressed.

[0019] Moreover, an electrolytic capacitor according to another embodiment of the present invention includes a capacitor element and a liquid component. The capacitor element includes an anode body having a dielectric layer on its surface and a conductive polymer compound covering at least a part of the dielectric layer. The liquid component includes an acid component, a base component, a solvent, and an antioxidant. The base component includes at least one selected from the group consisting of a primary amine compound and a secondary amine compound (hereinafter also referred to as a primary amine compound or the like). The antioxidant is used for the purpose of suppressing deterioration due to oxidation of the conductive polymer compound.

[0020] When the liquid component contains an antioxidant, the film repair function of the liquid component may be reduced due to the influence of the antioxidant, and the leakage current of the electrolytic capacitor may increase.

[0021] When the liquid component contains a primary amine compound or the like, the leakage current is smaller compared to the case where the liquid component contains ammonia, a tertiary amine, and / or a quaternary ammonium, and an increase in the leakage current due to the liquid component containing an antioxidant is suppressed. Even when an antioxidant is used, in a medium-high voltage type (for example, a rated voltage of 160 V or more) electrolytic capacitor, the effect of suppressing an increase in the leakage current by including a primary amine compound or the like in the liquid component is remarkably obtained.

[0022] Moreover, when the liquid component contains a primary amine compound or the like, the pH of the liquid component is maintained low compared to the case where the liquid component contains a quaternary ammonium, the dedoping of the dopant from the conductive polymer compound is suppressed, and an increase in the ESR is suppressed.

[0023] As described above, when the liquid component contains at least one of a primary amine compound and a secondary amine compound as a basic component, the increase in ESR is suppressed, and the increase in leakage current is suppressed.

[0024] The organic compound having a hydroxyl group preferably includes a glycerin compound. Organic carboxylic acid compounds interact more readily with the hydroxyl group of a glycerin compound than phenolic antioxidants that have a hydroxyl group bonded to an aromatic ring. When the solvent contains a glycerin compound, the influence of the organic carboxylic acid compound on the phenolic antioxidant is reduced, and the phenolic antioxidant's function of suppressing the oxidative degradation of conductive polymer compounds is more efficiently exerted.

[0025] Furthermore, glycerin compounds have a high boiling point, which suppresses their permeation to the outside from the sealing portion of the electrolytic capacitor. The amount of glycerin compounds fluctuates less, the stability of the liquid component containing primary amine compounds is further enhanced, the amount of dissociated acid and base components is stably maintained, the stability of the film repair function of the liquid component is further improved, and the increase in leakage current is further suppressed.

[0026] The liquid components will be described in detail below.

[0027] (Liquid component) The liquid component is in direct contact with the dielectric layer or via a conductive polymer compound. The liquid component only needs to be present between the dielectric layer of the anode and the cathode, together with the conductive polymer compound. The liquid component enhances the contact between the dielectric layer and the conductive polymer compound and also has a film repair function. Gas chromatography-mass spectrometry (GC / MS) or similar methods are used for the analysis of the liquid component.

[0028] Preferred examples of liquid components include components that are liquid at room temperature (25°C) (non-solidified components). Preferred examples of solvents for such liquid components include solvents that are liquid at room temperature (25°C). However, the liquid component may be a component that is liquid at a specific temperature during use of the electrolytic capacitor. Preferred examples of solvents for such liquid components include solvents that are liquid at a specific temperature during use of the electrolytic capacitor.

[0029] (Basic components) The basic component contains at least one of a primary amine compound and a secondary amine compound. Preferably, the total proportion of primary and secondary amine compounds in the basic component is the largest, and the entire basic component may consist of at least one of a primary and secondary amine compound. The basic component may also contain small amounts of other components other than primary and secondary amine compounds. The total proportion of ammonia, tertiary amines, and quaternary ammonium in the basic component is, for example, 2% by mass or less.

[0030] The primary amine compound preferably contains at least one selected from the group consisting of aliphatic primary amine compounds and aromatic primary amine compounds. The secondary amine compound preferably contains at least one selected from the group consisting of aliphatic secondary amine compounds, aromatic secondary amine compounds and heterocyclic secondary amine compounds. The primary amine compound and the secondary amine compound may each be used individually or in combination of two or more.

[0031] In aliphatic primary amine compounds, two hydrogen atoms and one aliphatic group are bonded to the nitrogen atom. In aliphatic secondary amine compounds, one hydrogen atom and two aliphatic groups are bonded to the nitrogen atom. The two aliphatic groups in aliphatic secondary amine compounds may be the same or different. Heterocyclic secondary amine compounds are heterocyclic compounds (heterocyclic compounds) that contain a nitrogen atom as a heteroatom, with one hydrogen atom bonded to the nitrogen atom in the ring. The heteroatom may also contain an atom other than a nitrogen atom (e.g., an oxygen atom). The number of members in the heterocycle is, for example, 3 or more and 6 or less. It is preferable that the heterocycle does not contain unsaturated bonds.

[0032] Aliphatic groups include linear or cyclic (excluding aromatic rings) hydrocarbon groups. From the viewpoint of reducing the effects of steric hindrance, aliphatic groups may be linear hydrocarbon groups. Hydrocarbon groups may be saturated hydrocarbon groups or unsaturated hydrocarbon groups. Aliphatic groups may contain ether bonds. Some of the hydrogen atoms bonded to the carbon atoms of the hydrocarbon group may be substituted with substituents other than hydrogen atoms. Examples of substituents include hydroxyl groups, nitro groups, and phenyl groups. Hydrocarbon groups include alkyl groups, cycloalkyl groups, and alkenyl groups, for example. From the viewpoint of ensuring electron-donating properties and reducing the effects of steric hindrance, the number of carbon atoms in a hydrocarbon group (e.g., alkyl groups) may be, for example, 1 or more and 6 or less, 1 or more and 4 or less, or 3 or more and 6 or less.

[0033] Aliphatic primary amine compounds include, for example, alkylamines, cycloalkylamines, polyamines, etheramines, and their derivatives. Alkylamines include methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, isobutylamine, t-butylamine, and their derivatives. Cycloalkylamines include cyclohexylamine, amantadine, and their derivatives. Polyamines include ethylenediamine, hexamethylenediamine, spermidine, spermine, and their derivatives. Among these, from the viewpoint of being readily available and relatively inexpensive, it is preferable that the aliphatic primary amine compounds include ethylamine, isopropylamine, t-butylamine, ethylenediamine, and hexamethylenediamine.

[0034] Aliphatic secondary amine compounds include, for example, dialkylamines and their derivatives. The two alkyl groups may be the same or different from each other. One of the two alkyl groups may be a cycloalkyl group and may contain an ether linkage. Dialkylamines include dimethylamine, diethylamine, N-methylethylamine, N-methylpropylamine, N-methylisopropylamine, N-ethylpropylamine, N-ethylisopropylamine, dipropylamine, diisopropylamine, dibutylamine, N-ethylisobutylamine, di-tert-butylamine, and their derivatives. Among these, from the viewpoint of being readily available and relatively inexpensive, it is preferable that the aliphatic secondary amine compounds include diethylamine, diisopropylamine, and dibutylamine.

[0035] In primary aromatic amine compounds, two hydrogen atoms and one aromatic group are bonded to the nitrogen atom. In secondary aromatic amine compounds, one hydrogen atom and two aromatic groups, or one aromatic group and one aliphatic group, are bonded to the nitrogen atom. In secondary aromatic amine compounds, the two aromatic groups may be the same or different. The aliphatic group may include the aliphatic groups listed in the above-mentioned aliphatic amine compounds.

[0036] Aromatic groups include at least one aromatic ring, such as aryl groups and aralkyl groups. Aryl groups include phenyl groups, 2-methylphenyl groups, 3-methylphenyl groups, 4-methylphenyl groups, 1-naphthyl groups, 2-naphthyl groups, and xylyl groups. Aalkyl groups include benzyl groups and 2-phenylethyl groups. Some of the hydrogen atoms bonded to the carbon atoms of the aromatic group may be substituted with substituents other than hydrogen atoms. Examples of substituents include hydroxyl groups, nitro groups, and phenyl groups.

[0037] Aromatic primary amine compounds include, for example, arylamines, aralkylamines, and their derivatives. Arylamines include aniline, 2-methylaniline, 3-methylaniline, 4-methylaniline, 1-naphthylamine, 2-naphthylamine, and their derivatives. Aalkylamines include benzylamine, phenylethylamine, and their derivatives. Among these, benzylamine and phenylethylamine are preferred from the viewpoint of being readily available and relatively inexpensive.

[0038] Aromatic secondary amine compounds include, for example, diarylamines, alkylarylamines, and their derivatives. Diarylamines include diphenylamine, N-phenyl-1-naphthylamine, N-phenyl-2-naphthylamine, and their derivatives. Alkylarylamines include N-methylaniline, N-ethylaniline, N-methyl-1-naphthylamine, N-methyl-2-naphthylamine, and their derivatives. Among these, diphenylamine is preferred from the viewpoint of being readily available and relatively inexpensive.

[0039] Furthermore, heterocyclic secondary amine compounds include aziridine, azetidine, pyrrolidine, piperidine, piperazine, morpholine, and their derivatives. Among these, from the viewpoint of being readily available and relatively inexpensive, it is preferable that heterocyclic secondary amine compounds include pyrrolidine, piperidine, morpholine, and their derivatives.

[0040] (acid component) The acidic component contributes to the film repair function. The acidic component may include at least an organic carboxylic acid compound. Preferably, the organic carboxylic acid compound accounts for the largest proportion of the acidic component, and the entire acidic component may be an organic carboxylic acid compound. The acidic component may also contain small amounts of other components besides organic carboxylic acid compounds. Examples of other components besides organic carboxylic acid compounds include inorganic acids such as phosphoric acid, boric acid, and sulfuric acid.

[0041] The organic carboxylic acid compound may include at least one selected from the group consisting of aromatic carboxylic acid compounds and aliphatic carboxylic acid compounds.

[0042] Aliphatic carboxylic acid compounds include saturated aliphatic carboxylic acids and unsaturated aliphatic carboxylic acids. Saturated aliphatic carboxylic acids include, for example, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebatic acid, 1,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, stearic acid, behenic acid, etc. Unsaturated aliphatic carboxylic acids include, for example, acrylic acid, methacrylic acid, maleic acid, fumaric acid, oleic acid, etc. Aliphatic carboxylic acid compounds may be used individually or in combination of two or more.

[0043] Aromatic carboxylic acid compounds include, for example, phthalic acid (ortho isomer), isophthalic acid (meta isomer), terephthalic acid (para isomer), benzoic acid, salicylic acid, trimellitic acid, pyromellitic acid, etc. Aromatic carboxylic acid compounds may be used individually or in combination of two or more.

[0044] In particular, from the viewpoint of improving film repair function and thermal stability, it is preferable that the organic carboxylic acid compound includes at least one selected from the group consisting of benzoic acid, adipic acid, azelaic acid, sebatic acid, 1,6-decanedicarboxylic acid, and 1,7-octanedicarboxylic acid. These organic carboxylic acid compounds are suitably used in medium-to-high voltage electrolytic capacitors (for example, those with a rated voltage of 160V or higher).

[0045] The liquid component preferably contains more acidic components than basic components. The acidic components lower the pH of the electrolyte from the beginning, suppressing the dedoping of dopants from the conductive polymer. By containing more acidic components than basic components, the dedoping of dopants from the conductive polymer (degradation of the solid electrolyte) can be suppressed. Furthermore, since the acidic components contribute to the film repair function of the liquid component, it is preferable to contain more acidic components than basic components.

[0046] From the viewpoint of suppressing dopant dedoping from conductive polymers (suppressing degradation of the solid electrolyte layer) and improving film repair function, the molar ratio of acid component to base component (acid component / base component) is, for example, 1.1 or more, preferably 1.5 or more, and more preferably 1.5 or more and 10 or less.

[0047] From the viewpoint of suppressing the dedoping of dopants from conductive polymers, the pH of the liquid component may be 6 or less, or it may be 1 or more and 5 or less.

[0048] The total content of acidic and basic components in the liquid component may be, for example, 5% by mass or more and 25% by mass or 7% by mass or more and 15% by mass or less, relative to the total liquid component. In the above range, the acidic and basic components are easily dissociated in the liquid component.

[0049] (solvent) The solvent may contain at least one organic compound having a hydroxyl group. The proportion of the organic compound having a hydroxyl group in the solvent may be, for example, 5% by volume or more, or 20% by volume or more, and the entire solvent may be an organic compound having a hydroxyl group. One organic compound having a hydroxyl group may be used alone, or two or more may be used in combination.

[0050] The organic compound having a hydroxyl group preferably includes a polyol compound. The polyol compound preferably includes at least one selected from the group consisting of glycerin compounds and glycol compounds (hereinafter also referred to as glycerin compounds, etc.). When the solvent includes glycerin compounds, etc., the conductive polymer compound swells easily, the orientation of the conductive polymer compound improves, the conductivity of the conductive polymer compound (layer) improves, and the ESR is easily reduced.

[0051] Glycerin compounds have relatively high boiling points, which suppresses permeation from the sealing portion of the electrolytic capacitor to the outside, thereby suppressing the decrease in film repair function due to solvent reduction and suppressing the increase in leakage current. Furthermore, organic carboxylic acid compounds interact more readily with hydroxyl groups in glycerin compounds than phenolic antioxidants that have hydroxyl groups bonded to aromatic rings. When the solvent contains glycerin compounds, the influence of organic carboxylic acid compounds on phenolic antioxidants is reduced, and the function of phenolic antioxidants in suppressing oxidative degradation of conductive polymer compounds is more efficiently exerted. Among these, glycerin compounds are more preferred from the viewpoint that they have a greater interaction with organic carboxylic acid compounds and that the above function of phenolic antioxidants is more efficiently exerted. The mass percentage of glycerin compounds in the solvent may be 20% by mass or more, or 25% by mass or more.

[0052] Glycerin compounds include glycerin, polyglycerin, and their derivatives. Examples of derivatives of glycerin or polyglycerin include esters in which at least some of the hydroxyl groups of glycerin or polyglycerin are esterified, and alkylene oxide adducts of glycerin or polyglycerin.

[0053] Polyglycerin contains a repeating structure of glycerin units. The number of repeating glycerin units in polyglycerin is, for example, 2 or more and 20 or less, may be 2 or more and 12 or less, may be 2 or more and 10 or less, or may be 2 or more and 6 or less. Examples of polyglycerin include diglycerin and triglycerin. The weight-average molecular weight of polyglycerin is preferably, for example, 200 or more and 3000 or less, and more preferably 300 or more and 800 or less.

[0054] Glycol compounds include alkylene glycols, etc. Examples of alkylene glycols include ethylene glycol, propylene glycol, butylene glycol, and hexylene glycol. Among these, ethylene glycol is preferred because it has low viscosity and readily dissolves acidic and basic components. Furthermore, ethylene glycol is preferred because it has high thermal conductivity and excellent heat dissipation properties, thus improving heat resistance.

[0055] The glycol compound may include a polyalkylene glycol compound. Examples of polyalkylene glycol compounds include polyalkylene glycol, copolymers containing two or more alkylene oxide units, and polyalkylene oxide adducts of polyhydric alcohols. Examples of alkylene oxide units include ethylene oxide (EO) units and propylene oxide (PO) units. Examples of polyhydric alcohols include glycerin. The weight-average molecular weight of the polyalkylene glycol compound is, for example, 100 or more and 3000 or less, and may be 100 or more and 2000 or less. The weight-average molecular weight of polyethylene glycol (PEG) is, for example, 100 or more and 600 or less, and may be 100 or more and 400 or less.

[0056] The solvent may contain components other than organic compounds having a hydroxyl group. Examples of such components include sulfone compounds, sulfoxide compounds, lactone compounds, and carbonate compounds.

[0057] Examples of sulfone compounds include dimethyl sulfone, diethyl sulfone, sulfolane, and 3-methylsulfolane. Examples of sulfoxide compounds include dimethyl sulfoxide and diethyl sulfoxide. Examples of lactone compounds include γ-butyrolactone and γ-valerolactone. Examples of carbonate compounds include dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, and fluoroethylene carbonate. Other components other than organic compounds having a hydroxyl group may be used individually or in combination of two or more.

[0058] From the viewpoint of the dissociability, ionic conductivity, and heat resistance of the salt formed by the acidic and basic components, other components other than organic compounds having a hydroxyl group are preferably γ-butyrolactone, sulfolane, and dimethyl sulfoxide.

[0059] (Antioxidant) The antioxidant may include at least one selected from the group consisting of phenolic antioxidants, amine antioxidants, phosphorus antioxidants, sulfur-based antioxidants, and aliphatic antioxidants. Among these, phenolic antioxidants are preferred from the viewpoint of reactivity with dissolved oxygen, etc.

[0060] The phenolic antioxidant preferably includes at least one selected from the group consisting of monophenolic antioxidants, bisphenolic antioxidants, and polyphenolic antioxidants. Among these, polyphenolic antioxidants are preferred. When a primary amine compound or the like is used instead of a polyphenolic antioxidant, the effect of suppressing the increase in leakage current is easily obtained.

[0061] The monophenol antioxidants preferably include 2,6-di-tert-butyl-4-methylphenol, butylhydroxyanisole, sesamol, tocopherol, tocotrienol, p-nitrophenol, etc. The monophenol antioxidants may also include mono, di, or tri(α-methylbenzyl)phenol, trolox, normelatonin, ferulic acid, etc.

[0062] The material may also contain a bisphenol-based antioxidant, preferably an anoxomer. Furthermore, it may contain other bisphenol-based antioxidants such as 2,2'-methylenebis(4-ethyl-6-tert-butylphenol), 2,2'-methylenebis(4-methyl-6-tert-butylphenol), 4,4'-butylidenebis(3-ethyl-6-tert-butylphenol), 4,4'-thiobis(3-ethyl-6-tert-butylphenol), or the butylation reaction product of p-cresol and dicyclopentadiene.

[0063] Polyphenol-based antioxidants preferably include gallic acid, propyl gallate, chlorogenic acid, catechin, epigallocatechin, epigallocatechin gallate, rosmarinic acid, genkwanin, luteolin, carnosic acid, carnosol, ursolic acid, pyrogallol, kebradic acid, hydroxytyrosol, dopamine, caffeic acid, adrenaline, noradrenaline, catechol, bouciol, hydroquinone, resorcinol, etc. Furthermore, polyphenol-based antioxidants preferably include hydroquinone and its dielectric. Hydroquinone derivatives include 2,5-di-tert-butylhydroquinone, 2,5-di-tert-amylhydroquinone, etc.

[0064] Furthermore, the polyphenol antioxidants may include protocatechuic acid, rutin, gnetin C, theaflavin, luteolin, resveratrol, pinosembrin, pinobanksin, 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 4,4',4”-(1-methylpropanyl-3-ylidene)tris(6-tert-butyl-m-cresol), etc.

[0065] Amine-based antioxidants include aromatic secondary amine antioxidants, benzotriazole antioxidants, benzimidazole antioxidants, amine-ketone antioxidants, and the like.

[0066] Aromatic secondary amine antioxidants include N-phenyl-1-naphthylamine, diphenylamine antioxidants, and phenylenediamine antioxidants. Diphenylamine antioxidants include alkylated diphenylamines such as p,p'-dioctyldiphenylamine, 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, and p-(p-toluenesulfonylamide)diphenylamine. Phenylenediamine antioxidants include N,N'-di-2-naphthyl-p-phenylenediamine, N-phenyl-N'-isopyropyr-p-phenylenediamine, N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine, and N-phenyl-N'-(3-methacryloyloxy-2-hydroxypropyl)-p-phenylenediamine.

[0067] Benzotriazole antioxidants include benzotriazole, etc. Benzimidazole antioxidants include benzimidazole, 2-mercapto-benzoimidazole, 2-mercaptomethyl-benzoimidazole, imidazole dipeptide, etc. Amine-ketone antioxidants include 2,2,4-trimethyl-1,2-dihydroquinoline polymer, 6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline, a reaction product of diphenylamine and acetone, acetylcysteine, melatonin, and the like.

[0068] Phosphorus-based antioxidants include phosphate ester antioxidants and phosphite ester antioxidants. Examples of esters include monoalkyl esters, dialkyl esters, and trialkyl esters. Examples of phosphite ester antioxidants include tris(nonylphenyl) phosphite.

[0069] Sulfur-based antioxidants include thioether-based antioxidants, isothiocyanates, sulfites, pyrosulfites, etc. Thioether-based antioxidants include phenothiazines, dibenzyl disulfide, diacetyl sulfide, dilauryl thiodipropionate, etc.

[0070] Aliphatic antioxidants include citric acid, L-ascorbic acid, erythorbic acid, ethylenediaminetetraacetic acid, and others.

[0071] The antioxidant may be used alone or in combination of two or more types. The amount of antioxidant in the liquid component is, for example, 1% by mass or more and 10% by mass or less of the total liquid component.

[0072] (Capacitor element) The capacitor element includes at least an anode having a dielectric layer on its surface and a conductive polymer compound covering at least a portion of the dielectric layer. The following provides a detailed explanation of capacitor elements.

[0073] (Anode) The anode body may include valve metals, alloys containing valve metals, and compounds containing valve metals. These materials can be used individually or in combination of two or more. As valve metals, aluminum, tantalum, niobium, and titanium are preferably used. An anode body with a porous surface can be obtained, for example, by roughening the surface of a substrate containing a valve metal (such as a foil or plate-shaped substrate) by etching. Alternatively, the anode body may be a molded body of particles containing a valve metal or a sintered body thereof. The sintered body has a porous structure.

[0074] (Dielectric layer) The dielectric layer is formed by anodizing the valve metal on the surface of the anode body through chemical conversion treatment or the like. The dielectric layer only needs to cover at least a portion of the anode body. The dielectric layer is usually formed on the surface of the anode body. Because the dielectric layer is formed on the porous surface of the anode body, it is formed along the inner walls of holes and depressions (pits) on the surface of the anode body.

[0075] The dielectric layer contains an oxide of the valve metal. For example, when tantalum is used as the valve metal, the dielectric layer contains Ta2O5, and when aluminum is used as the valve metal, the dielectric layer contains Al2O3. However, the dielectric layer is not limited to these; any material that functions as a dielectric is acceptable. If the surface of the anode is porous, the dielectric layer is formed along the surface of the anode (including the inner walls of the pores).

[0076] (Conductive polymer compound) Examples of conductive polymer compounds include π-conjugated polymer compounds. Examples of conductive polymer compounds include polypyrrole, polythiophene, polyfuran, and polyaniline. These may be used individually, in combination of two or more, or as copolymers of two or more monomers. The weight-average molecular weight of the conductive polymer compound is, for example, 1,000 to 1,000,000.

[0077] In this specification, polypyrrole, polythiophene, polyfuran, polyaniline, etc., refer to polymers that have polypyrrole, polythiophene, polyfuran, polyaniline, etc., as their basic skeletons. Therefore, polypyrrole, polythiophene, polyfuran, polyaniline, etc., may also include their respective derivatives. For example, polythiophene includes poly(3,4-ethylenedioxythiophene), etc.

[0078] Conductive polymer compounds can be doped with dopants. The dopants may be polyanions. Specific examples of polyanions include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyacrylic sulfonic acid, polymethacrylic sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, and polyacrylic acid. These may be used individually or in combination of two or more. Among these, polystyrene sulfonic acid is preferred.

[0079] At least a portion of the surface of the dielectric layer is covered with a conductive polymer layer (solid electrolyte layer). The conductive polymer layer may contain a dopant along with the conductive polymer compound. In an electrolytic capacitor, the conductive polymer layer, together with the cathode body, constitutes part of the cathode. The conductive polymer layer may further contain additives as needed.

[0080] The conductive polymer layer can be formed, for example, by chemical polymerization and / or electrolytic polymerization of raw material monomers on the dielectric layer. Alternatively, it can be formed by bringing a solution in which a conductive polymer compound is dissolved, or a dispersion in which a conductive polymer compound is dispersed, into contact with the dielectric layer. The conductive polymer layer only needs to be formed so as to cover at least a portion of the dielectric layer.

[0081] (Cathole body) In an electrolytic capacitor, a cathode may be positioned opposite the anode. A conductive polymer compound and a liquid component are interposed between the anode and the cathode. A metal foil may be used for the cathode. The type of metal is not particularly limited, but it is preferable to use a valve metal or an alloy containing a valve metal such as aluminum, tantalum, or niobium. The surface of the metal foil may be roughened as needed. A chemical conversion film may be provided on the surface of the metal foil, and a film of a different metal (dissimilar metal) or a nonmetal may be provided. Examples of dissimilar metals and nonmetals include metals such as titanium and nonmetals such as carbon.

[0082] (Separator) When a metal foil is used as the cathode, a separator may be placed between the metal foil and the anode. The separator is not particularly limited, and for example, nonwoven fabrics containing fibers of cellulose, polyethylene terephthalate, vinylon, or polyamide (e.g., aliphatic polyamides, aromatic polyamides such as aramids) may be used.

[0083] (others) An electrolytic capacitor only needs to have at least one capacitor element, but it may also have multiple capacitor elements. The number of capacitor elements included in an electrolytic capacitor should be determined according to its application.

[0084] (Exterior) Electrolytic capacitors typically include an enclosure that houses the capacitor element and the liquid component. The enclosure is not particularly limited, and known enclosures may be used. An example of an enclosure includes a bottomed case and a sealing member.

[0085] An example of an electrolytic capacitor of this embodiment will be described in detail below with reference to the drawings. The components of the example electrolytic capacitor described below can be the components described above. Furthermore, the components of the example electrolytic capacitor described below can be modified based on the above description. In addition, the matters described below may be applied to the above embodiment. Furthermore, in the example electrolytic capacitor described below, components that are not essential to the electrolytic capacitor of this embodiment may be omitted.

[0086] Here, Figure 1 is a schematic cross-sectional view of an example of an electrolytic capacitor according to this embodiment. Figure 2 is a schematic diagram showing a portion of the capacitor element related to the same electrolytic capacitor unfolded.

[0087] The electrolytic capacitor shown in Figure 1 comprises a capacitor element 10, a liquid component (not shown), a bottomed case 11 housing the capacitor element 10 and the liquid component, a sealing member 12 closing the opening of the bottomed case 11, a base plate 13 covering the sealing member 12, lead wires 14A and 14B extending from the sealing member 12 and passing through the base plate 13, and lead tabs 15A and 15B connecting the lead wires to the electrodes of the capacitor element 10. The open end of the bottomed case 11 is curled so as to be crimped to the sealing member 12.

[0088] The capacitor element 10 is manufactured from a wound body as shown in Figure 2. The wound body is a semi-finished product of the capacitor element 10, and it is characterized by the absence of a conductive polymer compound between the anode 21, which has a dielectric layer on its surface, and the cathode 22. The wound body is made by winding the anode 21, which is connected to a lead tab 15A, and the cathode 22, which is connected to a lead tab 15B, with a separator 23 in between. The outermost circumference of the wound body is fixed with a winding stopper tape 24. Note that Figure 2 shows a partially unfolded state of the wound body before the outermost circumference is fixed.

[0089] The anode body 21 comprises a metal foil with a roughened surface, and a dielectric layer is formed on the roughened surface. A capacitor element 10 is formed by attaching a conductive polymer compound to at least a portion of the surface of the dielectric layer.

[0090] The following describes an example of a manufacturing method for electrolytic capacitors. (Step of preparing an anode 21 and a cathode 22 having a dielectric layer) The anode 21 and cathode 22 are made from metal foil containing a valve metal. In the case of the anode 21, the surface of the metal foil is roughened by etching or the like, creating multiple irregularities on the surface of the metal foil. Next, a dielectric layer is formed on the roughened surface of the metal foil by chemical conversion treatment or the like. The surface of the cathode 22 may also be roughened as needed.

[0091] (Process for creating a wound body) The anode 21 and cathode 22 are wound together via a separator 23 to form a wound body. At this time, lead tabs 15A and 15B may be wound along with the winding, and the lead tabs 15A and 15B may be raised from the wound body as shown in Figure 2. A winding stopper tape 24 is placed on the outer surface of the cathode 22, which is located in the outermost layer of the wound body, to fix the end of the cathode 22. When a large sheet of metal foil cut into pieces is used as the anode 21, the wound body may be further treated with a chemical conversion process to form a dielectric layer on the cut surface of the anode 21.

[0092] (Process for forming the capacitor element 10) For example, a dispersion of a conductive polymer compound is impregnated into the dielectric layer to form a film of the conductive polymer compound that covers at least a portion of the dielectric layer. For example, the film of the conductive polymer compound may be formed by immersing the above-mentioned wound body in a dispersion of the conductive polymer compound. This results in a capacitor element 10 in which the conductive polymer compound is arranged between the anode 21 and the cathode 22. The step of applying the dispersion of the conductive polymer compound to the surface of the dielectric layer may be repeated two or more times. After that, the capacitor element 10 can be impregnated with the liquid component. This results in an electrolytic capacitor comprising the conductive polymer compound and the liquid component. By impregnating the capacitor element 10 with the liquid component, an electrolytic capacitor with excellent dielectric layer repair function can be obtained.

[0093] (Process of sealing capacitor elements) The capacitor element 10 is housed in the bottomed case 11 along with its liquid component such that the lead wires 14A and 14B are positioned on the opening side of the bottomed case 11. The material of the bottomed case 11 may be a metal such as aluminum, stainless steel, copper, iron, or brass, or an alloy containing these materials. Next, the opening of the bottomed case 11 is closed with a sealing member 12 through which the lead wires 14A and 14B pass, the open end is crimped to the sealing member 12 and curled, and a base plate 13 is placed on the curled portion to obtain an electrolytic capacitor as shown in Figure 1. After that, an aging process may be performed while applying the rated voltage.

[0094] Although the above embodiments described wound electrolytic capacitors, the scope of application of the present invention is not limited to those described above. It can also be applied to other electrolytic capacitors, such as chip-type electrolytic capacitors that use a sintered metal body as the anode, and multilayer electrolytic capacitors that use a metal plate as the anode.

[0095] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0096] Examples 1-2, Comparative Examples 1-3 In this example, a wound electrolytic capacitor (diameter 10.0 mm × length 20.0 mm) with a rated voltage of 250 W.V (Work Voltage) and a rated capacitance of 7 μF was fabricated. The specific manufacturing method of the electrolytic capacitor is described below.

[0097] (Preparation of the anode) A 100 μm thick aluminum foil was etched to roughen its surface. Subsequently, a dielectric layer was formed on the surface of the aluminum foil by a chemical conversion treatment. This treatment involved immersing the aluminum foil in an ammonium adipate solution and applying a voltage of 500 V. Afterward, the aluminum foil was cut to prepare the anode.

[0098] (Preparation of the cathode) A 50 μm thick aluminum foil was etched to roughen its surface. Then, the aluminum foil was cut to prepare the cathode.

[0099] (Preparation of coiled bodies) Anode lead tabs and cathode lead tabs were connected to the anode and cathode bodies, and the anode and cathode bodies were wound together with separators, incorporating the lead tabs. Anode lead wires and cathode lead wires were connected to the ends of each lead tab protruding from the wound body. The fabricated wound body was subjected to another chemical conversion treatment to form a dielectric layer on the cut ends of the anode bodies. Next, the ends of the outer surface of the wound body were secured with winding tape to create the wound body.

[0100] (Preparation of polymer dispersions) A mixed solution was prepared by dissolving 3,4-ethylenedioxythiophene and polystyrene sulfonic acid (PSS, weight-average molecular weight 100,000), a high molecular weight dopant, in deionized water. Iron(III) sulfate (oxidizing agent) dissolved in deionized water was added to the mixed solution while stirring, and a polymerization reaction was carried out. After the reaction, the resulting reaction solution was dialyzed to remove unreacted monomers and excess oxidizing agent, yielding a high molecular weight dispersion containing polyethylenedioxythiophene (PEDOT / PSS) doped with approximately 5% by mass of PSS.

[0101] (Formation of conductive polymer layer) A coiled body was immersed in a polymer dispersion contained in a designated container for 5 minutes in a reduced-pressure atmosphere (40 kPa), and then the coiled body was removed from the polymer dispersion. Next, the coiled body impregnated with the polymer dispersion was dried in a drying oven at 150°C for 20 minutes to form a conductive polymer layer that covers at least a portion of the dielectric layer. A capacitor element was thus formed.

[0102] (Preparation of liquid components) Liquid components a1-a2 and b1-b3 were prepared by adding the acid and base components shown in Table 1 to the solvent and mixing. The solvent used was a mixed solvent containing ethylene glycol (EG) and polyethylene glycol (PEG) (weight-average molecular weight MW: 300) in a mass ratio of 25:75. In Table 1, the primary amine of liquid component a1 is monoethylamine, the secondary amine of liquid component a2 is diethylamine, the tertiary amine of liquid component b1 is triethylamine, and the quaternary ammonium of liquid component b3 is tetraethylamine. The concentration of the acid component in the liquid components was 0.56 mol / kg. The concentration of the base component in the liquid components was 0.17 mol / kg. The molar ratio (acid component / base component) was 3.3.

[0103] (Assembly of electrolytic capacitors) The above-mentioned wound material, on which a conductive polymer layer was formed, was immersed in the liquid component in a reduced-pressure atmosphere (40 kPa) for 5 minutes. This resulted in obtaining a capacitor element impregnated with the liquid component. The obtained capacitor element was sealed to complete an electrolytic capacitor as shown in Figure 1. Subsequently, an aging treatment was performed at 125°C for 90 minutes while applying a voltage of 300 V.

[0104] In Table 1, A1 and A2 are the electrolytic capacitors of Examples 1 and 2, respectively, using liquid components a1 and a2. B1, B2, and B3 are the electrolytic capacitors of Comparative Examples 1 to 3, respectively, using liquid components b1, b2, and b3.

[0105] Examples 3-4, Comparative Examples 4-6 In the preparation of the liquid components, an antioxidant was added to the liquid components. Pyrogallol was used as the antioxidant. The antioxidant content in the liquid components was 3% by mass relative to the total liquid components. Liquid components a3-a4 and liquid components b4-b6 were obtained in the same manner as liquid components a1-a2 and liquid components b1-b3, respectively.

[0106] Except for using liquid components a3-a4 and b4-b6 instead of liquid component a1, electrolytic capacitors A3-A4 of Examples 3-4 and electrolytic capacitors B4-B6 of Comparative Examples 4-6 were obtained in the same manner as electrolytic capacitor A1 of Example 1.

[0107] Example 5 Liquid component a5 was obtained in the same manner as liquid component a4, except that a mixed solvent containing glycerin (GL) and polyethylene glycol (PEG) (weight-average molecular weight MW: 300) in a mass ratio of 25:75 was used as the solvent. Electrolytic capacitor A5 of Example 5 was obtained in the same manner as electrolytic capacitor A1 of Example 1, except that liquid component a5 was used instead of liquid component a1.

[0108] The following evaluations were performed using the electrolytic capacitors A1-A5 and B1-B6 obtained above.

[0109] [Evaluation 1: Measurement of leakage current] An electrolytic capacitor was subjected to its rated voltage at 20°C, and the leakage current (initial leakage current) was measured after 2 minutes. Next, the electrolytic capacitor was left at 145°C for 250 hours. Afterward, the leakage current was measured again after 250 hours using the same procedure as above.

[0110] [Evaluation 2: Measurement of ESR] The initial ESR (Z0) of the electrolytic capacitor at a frequency of 100 kHz was measured using a 4-terminal LCR meter in an environment of 20°C. Next, the electrolytic capacitor was held for 2000 hours while applying its rated voltage in an environment of 145°C. The ESR (Z1) of the electrolytic capacitor after holding at 145°C was measured using the same procedure as above. Using the initial ESR (Z0) and the ESR (Z1) after holding at 145°C, ΔESR (rate of change of ESR) was calculated using the following formula. ΔESR(%) = 100 × (Z1 - Z0) / Z0

[0111] The evaluation results are shown in Tables 1 and 2.

[0112] [Table 1]

[0113] [Table 2]

[0114] In electrolytic capacitors A1 to A5, the increase in leakage current after long-term storage was suppressed, and a small ΔESR was obtained. In A4 to A5, which used an antioxidant, an even smaller ΔESR was obtained. In electrolytic capacitor A5, which contained GL in the liquid component, the increase in leakage current and ESR was further suppressed. In electrolytic capacitors B1 to B6, the leakage current increased and the ΔESR increased after prolonged storage. [Industrial applicability]

[0115] The present invention can be used in electrolytic capacitors, and is particularly suitable for electrolytic capacitors that require low leakage current and low ESR. Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention. [Explanation of symbols]

[0116] 10: Capacitor element, 11: Bottomed case, 12: Sealing material, 13: Base plate, 14A, 14B: Lead wires, 15A, 15B: Lead tabs, 21: Anode, 22: Cathode, 23: Separator, 24: Winding tape

Claims

[Claim 1] It includes a capacitor element and a liquid component, The capacitor element comprises an anode having a dielectric layer on its surface, and a conductive polymer compound covering at least a portion of the dielectric layer. The aforementioned liquid component comprises an acid component, a basic component, and a solvent. The solvent comprises an organic compound having a hydroxyl group. The aforementioned acid component includes an organic carboxylic acid compound. The electrolytic capacitor wherein the base component includes at least one selected from the group consisting of primary amine compounds and secondary amine compounds.

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