Method for producing solid electrolytic capacitor

Abstract

The present invention provides a method for producing a solid electrolytic capacitor, the method at least including (a) a step of retaining a carbohydrate compound on an anode metal, on which is formed a dielectric oxide film, by a pretreatment agent containing a carbohydrate compound to which at least two or more monosaccharides are bound, followed by (b) a step of forming a solid electrolytic layer. This method makes it possible to produce a solid electrolytic capacitor with excellent leakage current characteristics and little adverse effect on other capacitor characteristics.

Description

Manufacturing method for solid electrolytic capacitors

[0001] The present invention relates to a method for manufacturing a solid electrolytic capacitor.

[0002] In general, a solid electrolytic capacitor has a solid electrolyte layer containing a conductive polymer that functions as a cathode formed on an anode metal having a dielectric oxide film.

[0003] In order to improve the performance of such solid electrolytic capacitors, various capacitors and manufacturing methods thereof have been reported. For example, a method for manufacturing a solid electrolytic capacitor (Patent Document 1) is known that includes at least the steps of: (a) using a pretreatment agent containing colloidal silica and a silicone surfactant to retain colloidal silica and a silicone surfactant on an anode metal on which a dielectric oxide film has been formed; and (b) subsequently forming a solid electrolyte layer.

[0004] Also known is a solid electrolytic capacitor that includes, as a solid electrolyte, a conductive composition containing a conductive polymer (A) that satisfies the following condition (i): condition (i): when a particle distribution is measured by dynamic light scattering using a conductive polymer solution containing 1% by mass of the conductive polymer with respect to the total mass of the conductive polymer solution, the volume average particle diameter of a minimum particle distribution including a peak showing the smallest particle diameter among one or more peaks obtained is less than 26 nm, and a water-soluble compound (B) that has three or more hydroxy groups and that satisfies the following condition (ii): condition (ii): the pH of a 1 mol / L aqueous solution is 9.0 or less (Patent Document 2).

[0005] Furthermore, a solid electrolytic capacitor is known that is characterized by sequentially including an anode body made of a valve metal provided with a porous layer for leading out an anode lead, a dielectric layer, an oxide film repair layer capable of forming an oxide film, a solid electrolyte layer, a graphite paste layer, and a silver paste layer (Patent Document 3).

[0006] Furthermore, a method for producing an electrolytic capacitor is known (Patent Document 4), which includes the steps of applying a dispersion a) containing particles b) of a conductive polymer containing polyaniline and / or polythiophene, a binder c) and a dispersant d) to a capacitor body including at least a porous electrode body made of an electrode material; a dielectric covering the surface of the electrode material; and a solid electrolyte containing at least a conductive material completely or partially covering the surface of the dielectric; and at least partially removing the dispersant d) and / or curing the binder c) to form a conductive polymer outer layer, wherein the proportion of the conductive polymer particles b) in the dispersion a) having a particle size of less than 700 nm is at least 5% by mass of the solid content of the dispersion.

[0007] The solid electrolytic capacitors described in the above Patent Documents 1 to 4 have insufficient leakage current characteristics, but the inventors have found through their studies that attempts to improve the leakage current characteristics have adverse effects on the equivalent series resistance and dielectric loss tangent.

[0008] JP 2023-22751 A International Publication No. 2014 / 061502 JP 2014-45115 A JP 2007-27767 A

[0009] Therefore, the present invention provides a solid electrolytic capacitor that has excellent leakage current characteristics and little adverse effect on other capacitor characteristics, and a method for manufacturing the same.

[0010] As a result of intensive research to solve the above problems, the inventors discovered that the above problems can be solved by retaining a specific carbohydrate compound on an anode metal on which a dielectric oxide film is formed, and thus completed the present invention.

[0011] That is, the present invention provides the following [1] to [9]. [1] A method for manufacturing a solid electrolytic capacitor, comprising at least the steps of: (a) using a pretreatment agent containing a carbohydrate compound having at least two or more monosaccharides bound thereto to retain the carbohydrate compound on an anode metal having a dielectric oxide film formed thereon, and then (b) forming a solid electrolyte layer. [2] A method for manufacturing a solid electrolytic capacitor according to [1], wherein the pretreatment agent contains an ionic electrolyte. [3] A method for manufacturing a solid electrolytic capacitor according to [1] or [2], wherein the solvent of the pretreatment agent contains one or more solvents selected from the group consisting of water, ethanol, methanol, and isopropyl alcohol. [4] A method for manufacturing a solid electrolytic capacitor according to any one of [1] to [3], wherein the concentration of the carbohydrate compound in the pretreatment agent is 0.001 to 25 mass %. [5] A method for manufacturing a solid electrolytic capacitor according to any one of [2] to [4], wherein the pretreatment agent contains 10 to 2,500 parts by mass of the carbohydrate compound per 100 parts by mass of the ionic electrolyte. [6] The method for manufacturing a solid electrolytic capacitor according to any one of [1] to [5], wherein the carbohydrate compound is a carbohydrate compound having a contact angle of 70 to 90° when a 0.5% by mass aqueous solution of the carbohydrate compound is dropped onto glass. [7] The method for manufacturing a solid electrolytic capacitor according to any one of [2] to [6], wherein the ionic electrolyte is an electrolyte having a nitrogen-containing cation having an unshared electron pair and an anion selected from a phosphate compound, a carboxylic acid compound, and a boric acid compound. [8] The method for manufacturing a solid electrolytic capacitor according to any one of [1] to [7], wherein the pretreatment agent includes a gelling agent. [9] The method for manufacturing a solid electrolytic capacitor according to any one of [1] to [8], wherein the step (b) of forming a solid electrolyte layer includes chemical oxidative polymerization.

[0012] According to the method for manufacturing a solid electrolytic capacitor of the present invention, a solid electrolytic capacitor that is excellent in leakage current characteristics and has little adverse effect on other capacitor characteristics can be manufactured.

[0013] The method for producing a solid electrolytic capacitor of the present invention (hereinafter referred to as the "method of the present invention") comprises at least the steps of (a) retaining a carbohydrate compound on an anode metal on which a dielectric oxide film has been formed using a pretreatment agent containing a carbohydrate compound having at least two or more monosaccharides bound thereto, and then (b) forming a solid electrolyte layer. Note that "retaining a carbohydrate compound" means that the carbohydrate compound is present on the anode metal on which a dielectric oxide film has been formed.

[0014] [Pretreatment Agent] Examples of the carbohydrate compound having at least two or more monosaccharides bonded thereto (hereinafter, sometimes simply referred to as "carbohydrate compound") contained in the pretreatment agent include pullulan, methylcellulose, xanthan gum, guar gum, maltodextrin, dextran, starch, sucrose and its derivatives, trehalose, β-cyclodextrin, carrageenan, etc. Furthermore, when a 0.5% aqueous solution of the carbohydrate compound is dropped onto glass, the contact angle is preferably 70° or more, and more preferably 70 to 90°. The contact angle can be measured with a contact angle meter. Examples of such carbohydrate compounds include pullulan, dextran, trehalose, starch, sucrose, carrageenan, methylcellulose, etc. These carbohydrate compounds can be used alone or in combination of two or more.

[0015] The content of the carbohydrate compound in the pretreatment agent is not particularly limited, but is, for example, 0.001 to 25% by mass (hereinafter simply referred to as "%"), preferably 0.1 to 10%.

[0016] The pretreatment agent further contains a solvent. The solvent is not particularly limited as long as it can dissolve the carbohydrate compound, and examples thereof include water, ethanol, methanol, isopropyl alcohol, etc. These solvents can be used alone or in combination of two or more.

[0017] The pretreatment agent preferably further contains an ionic electrolyte. The ionic electrolyte is not particularly limited as long as it is one that is typically used in electrolytic capacitors, but for example, an electrolyte having a nitrogen-containing cation with an unshared electron pair and an anion selected from a phosphate compound, a carboxylate compound, and a borate compound is preferred.

[0018] Examples of electrolytes having a nitrogen-containing cation with an unshared electron pair and an anion selected from phosphate compounds, carboxylate compounds, and borate compounds include compounds represented by the following general formulas (1) to (5) or ammonium salts. These electrolytes can be synthesized by well-known methods, or commercially available products can be used.

[0019]

[0020] In general formulas (1) to (5), the group R １ ~R ２５ are each independently a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, an alkoxy group having 1 to 18 carbon atoms, or a hydroxyl group, and may be the same or different; R １ ~R ２５ Adjacent groups among X may be linked to form an alkylene group having 2 to 6 carbon atoms. － is a carboxylate compound anion, a borate compound anion, or a phosphate compound anion.

[0021] Specific examples of the cation moiety of the compound represented by general formula (1) include ammonium cations; quaternary ammonium cations such as tetramethylammonium cation, tetraethylammonium cation, tetrapropylammonium cation, tetraisopropylammonium cation, tetrabutylammonium cation, trimethylethylammonium cation, triethylmethylammonium cation, dimethyldiethylammonium cation, dimethylethylmethoxyethylammonium cation, dimethylethylmethoxymethylammonium cation, dimethylethylethoxyethylammonium cation, trimethylpropylammonium cation, dimethylethylpropylammonium cation, triethylpropylammonium cation, spiro-(1,1')-bipyrrolidinium cation, piperidine-1-spiro-1'-pyrrolidinium cation, and spiro-(1,1')-bipiperidinium cation; trimethylamine cation, triethylamine cation, tripropylamine cation, triisopropylamine cation, tributylamine cation, and diethylmethylamine. cation, tertiary ammonium cations such as dimethylethylamine cation, diethylmethoxyamine cation, dimethylmethoxyamine cation, dimethylethoxyamine cation, diethylethoxyamine cation, methylethylmethoxyamine cation, N-methylpyrrolidine cation, N-ethylpyrrolidine cation, N-propylpyrrolidine cation, N-isopropylpyrrolidine cation, N-butylpyrrolidine cation, N-methylpiperidine cation, N-ethylpiperidine cation, N-propylpiperidine cation, N-isopropylpiperidine cation, and N-butylpiperidine cation; and secondary ammonium cations such as dimethylamine cation, diethylamine cation, diisopropylamine cation, dipropylamine cation, dibutylamine cation, methylethylamine cation, methylpropylamine cation, methylisopropylamine cation, methylbutylamine cation, ethylisopropylamine cation, ethylpropylamine cation, ethylbutylamine cation, isopropylbutylamine cation, and pyrrolidine cation.

[0022] Specific examples of the cation moiety of the compound represented by general formula (2) include tetramethylimidazolium cation, tetraethylimidazolium cation, tetrapropylimidazolium cation, tetraisopropylimidazolium cation, tetrabutylimidazolium cation, 1,3-dimethylimidazolium cation, 1,3-diethylimidazolium cation, 1,3-dipropylimidazolium cation, 1,3-diisopropylimidazolium cation, 1,3-dibutylimidazolium cation, and 1-methyl-3-ethylimidazolium cation. Examples thereof include 1-ethyl-3-methylimidazolium cation, 1-butyl-3-methylimidazolium cation, 1-butyl-3-ethylimidazolium cation, 1,2,3-trimethylimidazolium cation, 1,2,3-triethylimidazolium cation, 1,2,3-tripropylimidazolium cation, 1,2,3-triisopropylimidazolium cation, 1,2,3-tributylimidazolium cation, 1,3-dimethyl-2-ethylimidazolium cation, and 1,2-dimethyl-3-ethylimidazolium cation.

[0023] Specific examples of the cation moiety of the compound represented by general formula (3) include tetramethylimidazolinium cation, tetraethylimidazolinium cation, tetrapropylimidazolinium cation, tetraisopropylimidazolinium cation, tetrabutylimidazolinium cation, 1,3,4-trimethyl-2-ethylimidazolinium cation, 1,3-dimethyl-2,4-diethylimidazolinium cation, 1,2-dimethyl-3,4-diethylimidazolinium cation, 1- Methyl-2,3,4-triethylimidazolinium cation, 1,2,3-trimethylimidazolinium cation, 1,2,3-triethylimidazolinium cation, 1,2,3-tripropylimidazolinium cation, 1,2,3-triisopropylimidazolinium cation, 1,2,3-tributylimidazolinium cation, 1,3-dimethyl-2-ethylimidazolinium cation, 1-ethyl-2,3-dimethylimidazolinium cation, 4-cyano-1,2,3-trimethylimidazolinium cation, methylimidazolinium cation, 3-cyanomethyl-1,2-dimethylimidazolinium cation, 2-cyanomethyl-1,3-dimethylimidazolinium cation, 4-acetyl-1,2,3-trimethylimidazolinium cation, 3-acetylmethyl-1,2-dimethylimidazolinium cation, 4-methylcarboxymethyl-1,2,3-trimethylimidazolinium cation, 3-methylcarboxymethyl-1,2-dimethylimidazolinium cation, 4-methoxy-1, Examples include 2,3-trimethylimidazolinium cation, 3-methoxymethyl-1,2-dimethylimidazolinium cation, 4-formyl-1,2,3-trimethylimidazolinium cation, 3-formylmethyl-1,2-dimethylimidazolinium cation, 3-hydroxyethyl-1,2-dimethylimidazolinium cation, 4-hydroxymethyl-1,2,3-trimethylimidazolinium cation, and 2-hydroxyethyl-1,3-dimethylimidazolinium cation.

[0024] Specific examples of the cation moiety of the compound represented by general formula (4) include tetramethylpyrazolium cation, tetraethylpyrazolium cation, tetrapropylpyrazolium cation, tetraisopropylpyrazolium cation, tetrabutylpyrazolium cation, 1,2-dimethylpyrazolium cation, 1-methyl-2-ethylpyrazolium cation, 1,2-diethylpyrazolium cation, 1,2-dipropylpyrazolium cation, 1,2-dibutylpyrazolium cation, 1-methyl-2-propylpyrazolium cation, 1-methyl-2-butylpyrazolium cation, 1-methyl-2-hexylpyrazolium cation, 1-methyl-2-octylpyrazolium cation, 1-methyl-2-dodecylpyrazolium cation, 1,2,3-trimethyl ... Examples of the methylpyrazolium cation include methylpyrazolium cation, 1,2,3-triethylpyrazolium cation, 1,2,3-tripropylpyrazolium cation, 1,2,3-triisopropylpyrazolium cation, 1,2,3-tributylpyrazolium cation, 1-ethyl-2,3,5-trimethylpyrazolium cation, 1-ethyl-3-methoxy-2,5-dimethylpyrazolium cation, 3-phenyl-1,2,5-trimethylpyrazolium cation, 3-methoxy-5-phenyl-1-ethyl-2-ethylpyrazolium cation, 1,2-tetramethylene-3,5-dimethylpyrazolium cation, 1,2-tetramethylene-3-phenyl-5-methylpyrazolium cation, and 1,2-tetramethylene-3-methoxy-5-methylpyrazolium cation.

[0025] Specific examples of the cation moiety of the compound represented by general formula (5) include N-methylpyridinium cation, N-ethylpyridinium cation, N-propylpyridinium cation, N-isopropylpyridinium cation, N-butylpyridinium cation, N-hexylpyridinium cation, N-octylpyridinium cation, N-dodecylpyridinium cation, N-methyl-3-methylpyridinium cation, N-ethyl-3-methylpyridinium cation, N-propyl-3-methylpyridinium cation, N-butyl-3-methylpyridinium cation, N-butyl-4-methylpyridinium cation, and N-butyl-4-ethylpyridinium cation.

[0026] Anion X in combination with the above cation －is a carboxylic acid compound anion, a boric acid compound anion, or a phosphate compound anion. The carboxylic acid compound anion is an anion of an organic carboxylic acid such as an aromatic carboxylic acid or an aliphatic carboxylic acid, and the organic carboxylic acid may have a substituent.Specific examples thereof include aromatic carboxylic acid anions such as phthalate anion, salicylate anion, isophthalate anion, terephthalate anion, trimellitate anion, pyromellitate anion, benzoate anion, resorcylate anion, cinnamate anion, naphthoate anion, and mandelate anion; oxalate anion, malonate anion, succinate anion, glutarate anion, adipate anion, pimelate anion, suberate anion, azelaate anion, sebacate anion, undecanedioic acid anion, and dodecanedioic acid anion. Anions, tridecanedioic acid anion, tetradecanedioic acid anion, pentadecanedioic acid anion, hexadecanedioic acid anion, 3-tert-butyl adipate anion, methyl malonate anion, ethyl malonate anion, propyl malonate anion, butyl malonate anion, pentyl malonate anion, hexyl malonate anion, dimethyl malonate anion, diethyl malonate anion, methyl propyl malonate anion, methyl butyl malonate anion, ethyl propyl malonate anion, dipropyl malonate anion, methyl Succinate, ethylsuccinate, 2,2-dimethylsuccinate, 2,3-dimethylsuccinate, 2-methylglutarate, 3-methylglutarate, 3-methyl-3-ethylglutarate, 3,3-diethylglutarate, 3,3-dimethylglutarate, 3-methyladipic acid, 1,6-decanedicarboxylic acid, 5,6-decanedicarboxylic acid, formate, acetate, propionate, butyrate, isobutyrate, valerate Examples of such anions include saturated carboxylic acid anions such as caproate anion, enanthate anion, caprylate anion, pelargonate anion, laurate anion, myristate anion, stearate anion, behenate anion, undecanoate anion, itaconate anion, tartarate anion, glycolate anion, lactate anion, and pyruvate anion, and aliphatic carboxylic acid anions containing unsaturated carboxylic acids such as maleate anion, fumarate anion, acrylate anion, methacrylate anion, and oleate anion. These anions can be used alone or in combination of two or more.

[0027] Examples of the boric acid compound anion include borate anion, borodiazelaic acid anion, borodisalicylic acid anion, borodiglycolic acid anion, borodilactic acid anion, and borodisoxalic acid anion.

[0028] Examples of the phosphate compound anion include phosphate anion, dimethyl phosphate anion, diethyl phosphate anion, dipropyl phosphate anion, diisopropyl phosphate anion, dibutyl phosphate anion, dihexyl phosphate anion, methyl phosphate anion, ethyl phosphate anion, propyl phosphate anion, isopropyl phosphate anion, butyl phosphate anion, hexyl phosphate anion, 2-ethylhexyl phosphate anion, dioctyl phosphate anion, octyl phosphate anion, lauryl phosphate anion, butoxyethyl phosphate anion, isotridecyl phosphate anion, oleyl phosphate anion, tetracosyl phosphate anion, ethylene glycol phosphate anion, and 2-hydroxyethyl methacrylate phosphate anion.

[0029] Specific examples of ammonium salts include monoammonium phosphate, diammonium phosphate, ammonium oxalate, ammonium formate, ammonium benzoate, ammonium adipate, ammonium borate, ammonium polyphosphate, etc. Among these, monoammonium phosphate, diammonium phosphate, ammonium benzoate, ammonium adipate, and ammonium borate are preferably used.

[0030] The content of the ionic electrolyte in the pretreatment agent is not particularly limited, but for example, the pretreatment agent contains 10 to 2,500 parts by mass of the carbohydrate compound per 100 parts by mass of the ionic electrolyte, and preferably 10 to 1,000 parts by mass of the carbohydrate compound per 100 parts by mass of the ionic electrolyte.

[0031] The pretreatment agent preferably further contains a gelling agent.

[0032] [Gelling Agent] Examples of gelling agents that can be used include fine oxide particles such as fine silica particles and fine alumina particles, fine metal particles such as fine titanium particles, gelatin, polyvinyl alcohol, polystyrene sulfonic acid or its salts, polyethylene glycol, polyacrylic acid or its salts, polyacrylamide, polyvinylpyrrolidone, and hydrophilic polymers such as hydrophilic polyurethane. These gelling agents are preferably used because they form physical gels. Among these gelling agents, fine silica particles and polystyrene sulfonic acid are preferably used in consideration of quality stability, adhesiveness, conductivity, shape retention, and the like. Furthermore, the formation of a gel can be determined by the test tube inversion method described in Japanese Patent No. 6,508,480.

[0033] The hydrophilic polymers can be used alone or in combination of two or more.

[0034] As the fine particle silica of the gelling agent, colloidal silica is preferably used.

[0035] <Colloidal silica> Colloidal silica is SiO ２ Or a colloid of its hydrate, with a particle size of 1 to 300 nm and no fixed structure. It can be obtained by treating a silicate with dilute hydrochloric acid and then dialysis. The smaller the particle size, the more easily gelation occurs, while the larger the particle size, the less likely it is to gel. The particle size of the colloidal silica used in the present invention is preferably 10 to 50 nm, and more preferably 10 to 30 nm. By using colloidal silica with this particle size, it is less likely to gel when the pretreatment agent is prepared, and it can maintain a stably dispersed state even when the pretreatment agent is used.

[0036] Colloidal silica is practically insoluble in water or organic solvents, and can generally be used in the form of a colloidal solution dispersed in an appropriate dispersion solvent and added to the pretreatment agent.

[0037] The colloidal silica may be sodium-stable colloidal silica, acidic colloidal silica, or ammonia-stable colloidal silica. Sodium-stable colloidal silica has ONa groups on its surface. Acidic colloidal silica is colloidal silica whose surface has OH groups formed by removing Na, and ammonia-stable colloidal silica is colloidal silica that has been stabilized by removing Na to form OH groups and then incorporating ammonia. Among these, acidic colloidal silica or ammonia-stable colloidal silica with a low sodium ion content is preferred.

[0038] The average particle size of the colloidal silica may be any value, but is preferably 1 to 100 nm, more preferably 10 to 50 nm, and particularly preferably 10 to 30 nm. By adjusting the average particle size within the above range, a pretreatment agent with excellent dispersibility in a solvent can be obtained. This average particle size is a value measured by dynamic light scattering.

[0039] The shape of the colloidal silica may be any of a spherical type, a chain type, and a cyclic type in which colloidal silica particles are aggregated into rings and dispersed in a solvent.

[0040] Commercially available colloidal silica products include, for example, the Snowtex series manufactured by Nissan Chemical Co., Ltd., acidic sols "ST-OXS," "ST-OS," "ST-O," "ST-O40," "ST-OL," "ST-OYL," "ST-OUP," "ST-PS-MO," and "ST-N40," and NH4 ＋ Stable alkaline sol "ST-NXS", "ST-NS", "ST-N", "ST-N-40", Na ＋Examples of such sols include stable alkaline sols "ST-XS", "ST-S", "ST-30", "ST-50-T", "ST-30L", "ST-YL", "ST-ZL", "MP-1040", "MP-2040", "MP-4540M", "ST-UP", "ST-PS-S", "ST-PS-M", sols with improved stability in the neutral range "ST-CXS", "ST-C", "ST-CM", surface cationic acidic sols "ST-AK", "ST-AK-L", "ST-AK-YL", special silicate aqueous solutions "ST-K2", "LSS-35", "LSS-45", "LSS-75", etc. These can be used alone or in combination of two or more.

[0041] The content of colloidal silica in the pretreatment agent is not particularly limited, but is, for example, 0.01 to 20%, preferably 0.03 to 15%, and more preferably 0.05 to 10%.

[0042] The pretreatment agent may contain an appropriate amount of a water-soluble polymer other than the sugar compound as an additive, provided that the effect of the present invention is not impaired.

[0043] [Anode Metal Having Dielectric Oxide Film Formed Thereon] Examples of anode metals include aluminum, tantalum, niobium, and titanium. The anode metal may be in the form of a sintered body obtained by sintering fine particles, or in the form of a foil or plate that has been roughened by etching or the like. Among these anode metals, aluminum foil that has been roughened by etching or the like is particularly suitable because it is easy to achieve the effects of the present invention.

[0044] A dielectric oxide film can be formed on the surface of an anode metal by subjecting the anode metal to a known chemical conversion treatment. For example, a dielectric oxide film can be formed on the anode metal by anodizing in an aqueous solution of diammonium adipate or the like.

[0045] [(a) Step of retaining carbohydrate compounds on anode metal] The method for retaining carbohydrate compounds on anode metal having a dielectric oxide film formed thereon by the pretreatment agent is not particularly limited, but the carbohydrate compounds can be retained on the dielectric oxide film by contacting the pretreatment agent with the anode metal having a dielectric oxide film formed thereon and then drying the anode metal to partially remove the solvent, etc. Any contact method may be used, but a preferred method is to immerse the anode metal having a dielectric oxide film in the pretreatment agent.

[0046] The process of immersing the anode metal having the dielectric oxide film in the pretreatment agent, removing it from the pretreatment agent, and then drying it may be repeated several times.

[0047] The drying may be carried out by any method, from natural drying at room temperature to heat drying, but it is preferable to dry by heating at 80° C. or higher.

[0048] A more specific example of this process is a process in which an anode metal having a dielectric oxide film thereon is immersed in the pretreatment agent for 30 seconds, and then dried at 125° C. for 30 minutes.

[0049] After the step (a) is performed, the step (b) of forming a solid electrolyte layer is then performed.

[0050] [Solid Electrolyte] The conductive polymer used in the step of forming the solid electrolyte layer is preferably a polymer doped with a dopant. The monomer compound used to produce the polymer is not particularly limited, and examples thereof include pyrroles, thiophenes, and anilines. However, due to their excellent conductivity, thiophene compounds represented by the following general formula (6) are more preferred.

[0051] General formula (6)

[0052] In the above general formula (6), R ２６ represents a hydrogen atom or a linear or branched alkyl group having 1 to 6 carbon atoms, and each Y, which may be the same or different, represents an oxygen atom or a sulfur atom.

[0053] Specific examples of the thiophene compound represented by the general formula (6) include 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-ethylenedithiathiophene, methyl-3,4-ethylenedithiathiophene, ethyl-3,4-ethylenedithiathiophene, propyl-3,4-ethylenedithiathiophene, 3,4-propylenedithiathiophene, methyl-3,4-propylenedithiathiophene, ethyl-3,4-propylenedithiathiophene, and propyl-3,4-propylenedithiathiophene.

[0054] Among these, 3,4-ethylenedioxythiophene, methyl-3,4-ethylenedioxythiophene, and ethyl-3,4-ethylenedioxythiophene are particularly preferred because they have excellent electrical properties in solid electrolytic capacitors.

[0055] The conductive polymer can be obtained by chemically oxidatively polymerizing a monomer compound such as a thiophene compound represented by the general formula (6) in the presence of the dopant. The oxidizing agent for chemical oxidative polymerization can be a known oxidizing agent described in, for example, JP 2010-31160 A.

[0056] The dopant may have a functional group that can cause chemical oxidation doping of the polymer, and preferred examples thereof include a sulfate ester group, a phosphate ester group, a phosphate group, a carboxyl group, a sulfo group, etc. Among these, from the viewpoint of doping effect, the sulfate ester group, the carboxyl group, and the sulfo group are more preferred, and the sulfo group is particularly preferred.

[0057] Examples of the dopant include halogen ions such as iodine, bromine, and chlorine; halide ions such as hexafluorophosphorus, hexafluoroarsenic, hexafluoroantimony, tetrafluoroboron, and perchloric acid; alkyl-substituted organic sulfonate ions such as methanesulfonic acid and dodecylsulfonic acid; cyclic sulfonate ions such as camphorsulfonic acid ion; alkyl-substituted or unsubstituted benzene mono- or disulfonate ions such as benzenesulfonic acid, paratoluenesulfonic acid, dodecylbenzenesulfonic acid, and benzenedisulfonic acid; 2-naphthalenesulfonic acid; 1,7-naphthalenesulfonic acid; Examples of the cations include alkyl-substituted or unsubstituted ions of naphthalenesulfonic acids substituted with one to four sulfonic acid groups such as sulfonic acid, anthracenesulfonic acid ions, anthraquinonesulfonic acid ions, alkyl-substituted or unsubstituted biphenylsulfonic acid ions such as alkylbiphenylsulfonic acids and biphenyldisulfonic acids, polymeric sulfonic acid ions such as polystyrenesulfonic acid and naphthalenesulfonic acid-formaldehyde condensates, heteropolyacid ions such as molybdophosphoric acid, tungstophosphoric acid, and tungstomolybdophosphoric acid, methoxybenzenesulfonic acid, ethoxybenzenesulfonic acid, and xylenesulfonic acid. Among these, at least one selected from polystyrenesulfonic acid, benzenesulfonic acid, paratoluenesulfonic acid, methoxybenzenesulfonic acid, ethoxybenzenesulfonic acid, and xylenesulfonic acid is more preferred, with paratoluenesulfonic acid being particularly preferred.

[0058] [(b) Step of forming a solid electrolyte layer] The step of forming the solid electrolyte layer by chemical oxidative polymerization is described below. A mixed solution containing the above-mentioned monomer compound, dopant, and oxidant is brought into contact with an anode metal supporting a carbohydrate compound, followed by polymerization, to produce a capacitor element in which a solid electrolyte layer is formed on the anode metal supporting a carbohydrate compound. Any contact method may be used, but examples include a method of immersing the element in a mixed solution containing the above-mentioned monomer compound, dopant, and oxidant, and a method of alternately contacting the element with a monomer compound and an oxidant solution containing a dopant.

[0059] That is, a preferred example includes a step of immersing an anode metal carrying a carbohydrate compound in a solution containing the above-mentioned monomer compound and a dopant, lifting it out, and then heating it to cause chemical oxidation polymerization on the anode metal having a dielectric oxide film to form a solid electrolyte layer.

[0060] The anode metal carrying the carbohydrate compound may be immersed in a mixed solution containing the above-mentioned monomer compound, dopant and oxidizing agent, and then pulled out and dried. This process may be repeated several times.

[0061] The step of forming the solid electrolyte layer may be carried out by electrolytic polymerization or by contacting a conductive polymer dispersion with the anode metal.

[0062] Drying may be any method from natural drying at room temperature to heat drying, but when the conductive polymer dispersion contains a high-boiling organic solvent, it is preferable to dry by heating to 150° C. or higher.

[0063] The manufacturing method of the present invention involves at least step (a) followed by step (b). The solid electrolytic capacitor of the present invention can be assembled by a known method. After the above steps, the capacitor element is housed in an outer case made of metal or the like, sealed with epoxy resin, rubber, or the like, and aged by applying a voltage to obtain a solid electrolytic capacitor.

[0064] [Solid Electrolytic Capacitor] The solid electrolytic capacitor produced by the method of the present invention can be a chip type or a wound type depending on the type and shape of the anode metal used. This capacitor has excellent leakage current characteristics and is not adversely affected by other capacitor characteristics.

[0065] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0066] (Example 1) (1) Capacitor element An aluminum anode foil measuring 7 × 100 mm was prepared as the anode metal, and was wound with a cathode foil facing it via a separator paper. Leads were attached to the anode foil and cathode foil, respectively, to obtain a capacitor element. The aluminum anode foil had been subjected to a chemical conversion treatment in advance to form a dielectric oxide film.

[0067] (2) Pretreatment Agent A pretreatment agent was obtained by diluting 2 parts by mass of pullulan as a saccharide compound with 98 parts by mass of water.

[0068] (3) Conductive Polymer Polymerization Liquid 4 parts by mass of 2-ethyl-2,3-dihydrothieno[3,4-b]-1,4-dioxin (2-ethyl-EDOT) and 10 parts by mass of a 50% ferric paratoluenesulfonate / ethanol solution were mixed to obtain a conductive polymer polymerization liquid containing a conductive polymer monomer, a dopant, and an oxidizing agent.

[0069] <(a) Step of retaining the carbohydrate compound on the anode metal> The capacitor element obtained in (1) was immersed in the pretreatment agent obtained in (2) for 30 seconds, and the element was slowly pulled out and then dried with air at 125°C for 30 minutes to retain the carbohydrate compound on the anode metal on which the dielectric oxide film had been formed.

[0070] <(b) Step of forming a solid electrolyte layer on an anode metal> Next, the capacitor element subjected to step (a) was immersed for 30 seconds in a conductive polymer polymerization liquid containing the conductive polymer monomer obtained in (3), a dopant, and an oxidizing agent, and then dried at 85°C for 30 minutes. After that, a heat treatment was further performed at 230°C for 3 minutes to form a solid electrolyte layer, and the capacitor element was subjected to evaluation.

[0071] Example 2 A solid electrolytic capacitor was produced in the same manner as in Example 1, except that starch was used as the saccharide compound.

[0072] Example 3 A solid electrolytic capacitor was produced in the same manner as in Example 1, except that sucrose was used as the sugar compound.

[0073] Example 4 A solid electrolytic capacitor was manufactured in the same manner as in Example 1, except that a pretreatment agent was used that was prepared by diluting 2 parts by mass of pullulan as a saccharide compound and 1 part by mass of ammonium phosphate monobasic as an ionic electrolyte with 97 parts by mass of water.

[0074] Example 5 A solid electrolytic capacitor was manufactured in the same manner as in Example 1, except that a pretreatment agent was used that was prepared by diluting 2 parts by mass of dextran as a saccharide compound and 1 part by mass of ammonium phosphate monobasic as an ionic electrolyte with 97 parts by mass of water.

[0075] Example 6 A solid electrolytic capacitor was manufactured in the same manner as in Example 1, except that a pretreatment agent was used that was prepared by diluting 2 parts by mass of trehalose as the saccharide compound and 1 part by mass of ammonium phosphate monobasic as the ionic electrolyte with 97 parts by mass of water.

[0076] Example 7 A solid electrolytic capacitor was manufactured in the same manner as in Example 1, except that a pretreatment agent was used that was prepared by diluting 2 parts by mass of pullulan as a saccharide compound and 0.1 parts by mass of ammonium phosphate monobasic as an ionic electrolyte with 97.9 parts by mass of water.

[0077] Example 8 A solid electrolytic capacitor was manufactured in the same manner as in Example 1, except that a pretreatment agent was used that was prepared by diluting 0.5 parts by mass of pullulan as the saccharide compound and 1 part by mass of ammonium phosphate monobasic as the ionic electrolyte with 98.5 parts by mass of water.

[0078] Example 9 A solid electrolytic capacitor was manufactured in the same manner as in Example 1, except that a pretreatment agent was used that was prepared by diluting 2 parts by mass of pullulan as the saccharide compound, 1 part by mass of monoammonium phosphate as the ionic electrolyte, and 5 parts by mass of colloidal silica (manufactured by Nissan Chemical Industries, Ltd., Snowtex O, aqueous dispersion, solids content 20%, average particle size 10 to 15 nm, pH 2.0 to 4.0) with 92 parts by mass of water. Note that the pretreatment agent produced in Example 9 gelled because it contained colloidal silica as a gelling agent.

[0079] (Example 10) A solid electrolytic capacitor was manufactured in the same manner as in Example 1, except that a pretreatment agent was used that was prepared by diluting 0.5 parts by mass of carrageenan as a saccharide compound and 1 part by mass of ammonium phosphate monobasic as an ionic electrolyte with 98.5 parts by mass of water.

[0080] Example 11 A solid electrolytic capacitor was manufactured in the same manner as in Example 1, except that a pretreatment agent was used that was prepared by diluting 0.5 parts by mass of methyl cellulose as the saccharide compound and 1 part by mass of ammonium phosphate monobasic as the ionic electrolyte with 98.5 parts by mass of water.

[0081] Example 12 A solid electrolytic capacitor was manufactured in the same manner as in Example 1, except that a pretreatment agent was used that was prepared by diluting 2 parts by mass of pullulan as a saccharide compound and 1 part by mass of ammonium formate as an ionic electrolyte with 97 parts by mass of water.

[0082] Example 13 A solid electrolytic capacitor was manufactured in the same manner as in Example 1, except that a pretreatment agent was used that was prepared by diluting 2 parts by mass of pullulan as a saccharide compound and 1 part by mass of ammonium benzoate as an ionic electrolyte with 97 parts by mass of water.

[0083] Example 14 A solid electrolytic capacitor was manufactured in the same manner as in Example 1, except that a pretreatment agent was used that was prepared by diluting 2 parts by mass of pullulan as a saccharide compound and 1 part by mass of ammonium oxalate as an ionic electrolyte with 97 parts by mass of water.

[0084] Example 15 A solid electrolytic capacitor was manufactured in the same manner as in Example 1, except that a pretreatment agent was used that was prepared by diluting 2 parts by mass of pullulan as a saccharide compound and 1 part by mass of ammonium adipate as an ionic electrolyte with 97 parts by mass of water.

[0085] Example 16 A solid electrolytic capacitor was manufactured in the same manner as in Example 1, except that a pretreatment agent was used that was prepared by diluting 2 parts by mass of pullulan as a saccharide compound and 1 part by mass of ammonium borate as an ionic electrolyte with 97 parts by mass of water.

[0086] Comparative Example 1 A solid electrolytic capacitor was produced in the same manner as in Example 1, except that the step of supporting a saccharide compound on the anode metal described in Example 1 was not carried out.

[0087] Comparative Example 2 A solid electrolytic capacitor was manufactured in the same manner as in Example 1, except that a pretreatment agent was used that was prepared by diluting 2 parts by mass of glucose (monosaccharide) instead of the saccharide compound and 1 part by mass of ammonium phosphate monobasic as the ionic electrolyte with 97 parts by mass of water.

[0088] Comparative Example 3 A solid electrolytic capacitor was manufactured in the same manner as in Example 1, except that a pretreatment agent was used that was prepared by diluting 2 parts by mass of polyethylene glycol (average molecular weight 200) and 1 part by mass of monoammonium phosphate as an ionic electrolyte with 97 parts by mass of water.

[0089] Comparative Example 4 A solid electrolytic capacitor was manufactured in the same manner as in Example 1, except that a pretreatment agent was used that was prepared by diluting 2 parts by mass of polyvinyl alcohol (degree of polymerization: 500) and 1 part by mass of monoammonium phosphate as an ionic electrolyte with 97 parts by mass of water.

[0090] Comparative Example 5 A solution was obtained by diluting 2 parts by mass of pullulan as a saccharide compound and 1 part by mass of monoammonium phosphate as an ionic electrolyte with 97 parts by mass of water. A solid electrolytic capacitor was produced in the same manner as in Example 1, except that the step of retaining the saccharide compound on the anode metal described in Example 1 was not performed, and after forming a solid electrolyte layer, a capacitor element was immersed in the solution for 30 seconds, the element was slowly pulled out, and then air-dried at 125°C for 30 minutes.

[0091] Comparative Example 6 A solid electrolytic capacitor was manufactured in the same manner as in Example 1, except that the pretreatment agent used was a solution obtained by diluting 2.5 parts by mass of colloidal silica (Nissan Chemical Industries, Ltd., Snowtex N-40, aqueous dispersion, solids content 40%, average particle size 20 to 30 nm, pH 9.0 to 10), 0.01 parts by mass of polyether-modified silicone (pendant type: Momentive Corporation, "Silwet L-7657", molecular weight 5000), and 5 parts by mass of ethylene glycol with 92.5 parts by mass of water. Note that the pretreatment agent manufactured in Comparative Example 6 gelled because it contained colloidal silica, which is a gelling agent.

[0092] Comparative Example 7 A solid electrolytic capacitor was manufactured in the same manner as in Example 1, except that a pretreatment agent was used that was prepared by diluting 2 parts by mass of polyvinylidene fluoride and 1 part by mass of monoammonium phosphate as an ionic electrolyte with 97 parts by mass of water.

[0093] (Test Example 1) <Evaluation of Solid Electrolytic Capacitors> For the solid electrolytic capacitors obtained in Examples 1 to 16 and Comparative Examples 1 to 7, the capacitance (Cap) and dielectric dissipation factor (tanδ) at 120 Hz were measured using a Precision LCR Meter E4980A manufactured by Agilent Technologies, Inc., and the equivalent series resistance (ESR) at 100 kHz was measured. Furthermore, a DC voltage was applied to both electrodes of the solid electrolytic capacitor using a DC voltage / current source / monitor R6243 manufactured by Advantest Corporation, and the leakage current (LC) was measured 60 seconds after application. The measurement results are shown in Table 1.

[0094]

[0095] <Contact Angle Measurement> 0.5 parts by mass of each of the carbohydrate compounds (pullulan, starch, dextran, sucrose, trehalose, carrageenan, and methylcellulose) used in Examples 1 to 16 was diluted with 99.5 parts by mass of water to obtain a solution. The contact angle of each solution on a glass substrate was measured using an automatic contact angle meter DMo-602 manufactured by Kyowa Interface Science Co., Ltd. The measurement results are shown in Table 2.

[0096]

[0097] As shown in Table 1, the Examples provided solid electrolytic capacitors with reduced leakage current and less adverse effects on equivalent series resistance and the like compared to Comparative Example 1. Comparing Example 1 and Example 4, the inclusion of an ionic electrolyte in the pretreatment agent reduced leakage current more. Furthermore, as shown in Table 2, Examples 1 to 10, which used a saccharide compound with a contact angle of 90° or less, experienced less capacity loss than Example 11, which used a saccharide compound with a contact angle of more than 90°. This is thought to be because a smaller contact angle provides higher wettability, allowing the pretreatment agent to penetrate into the pits in the anode foil when the capacitor element was impregnated with the pretreatment agent, thereby acting more uniformly on the anode foil.

[0098] On the other hand, in Comparative Examples 2 to 7, although a reduction in leakage current was observed in some samples, the equivalent series resistance was deteriorated in all samples.

[0099] The manufacturing method of the present invention can be used to manufacture solid electrolytic capacitors.

Claims

1. A method for manufacturing a solid electrolytic capacitor comprising at least the steps of: (a) retaining a carbohydrate compound on an anode metal having a dielectric oxide film formed thereon by using a pretreatment agent containing a carbohydrate compound having at least two or more monosaccharides bonded thereto; and then (b) forming a solid electrolyte layer.

2. The method for producing a solid electrolytic capacitor according to claim 1, wherein the pretreatment agent contains an ionic electrolyte.

3. The method for producing a solid electrolytic capacitor according to claim 1, wherein the solvent of the pretreatment agent contains one or more solvents selected from the group consisting of water, ethanol, methanol and isopropyl alcohol.

4. The method for producing a solid electrolytic capacitor according to claim 1, wherein the concentration of the carbohydrate compound in the pretreatment agent is 0.001 to 25% by mass.

5. The method for producing a solid electrolytic capacitor according to claim 2, wherein the pretreatment agent contains 10 to 2,500 parts by mass of a carbohydrate compound per 100 parts by mass of the ionic electrolyte.

6. A method for manufacturing a solid electrolytic capacitor described in any one of claims 1 to 5, wherein the carbohydrate compound includes a carbohydrate compound having a contact angle of 70 to 90° when an aqueous solution of the carbohydrate compound at 0.5% by mass is dropped onto glass.

7. The method for producing a solid electrolytic capacitor according to any one of claims 2 to 5, wherein the ionic electrolyte is an electrolyte having a nitrogen-containing cation having an unshared electron pair and an anion selected from a phosphoric acid compound, a carboxylic acid compound, and a boric acid compound.

8. The method for producing a solid electrolytic capacitor according to any one of claims 1 to 5, wherein the pretreatment agent contains a gelling agent.

9. The method for producing a solid electrolytic capacitor according to any one of claims 1 to 5, wherein the step (b) of forming a solid electrolyte layer includes chemical oxidative polymerization.

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