Electrolyte solution for electrolytic capacitors, and electrolytic capacitor

Abstract

The present invention provides an electrolyte solution for electrolytic capacitors, which contains at least colloidal silica (A), a polyether-modified silicone-based surfactant (B), an electrolyte salt (C), and an organic solvent (D). The electrolyte solution is characterized in that: the colloidal silica (A) has an average particle diameter of 5-15 nm; and at least one phosphoric acid ester compound (E) represented by general formula (1) (in the formula (1), R1 represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a phenyl group, or a benzyl group, R2 represents an alkyl group having 1 to 10 carbon atoms, a phenyl group, or a benzyl group, and R1 and R2 may be the same as or different from each other) is contained as an additive, the total mass ratio of the phosphoric acid ester compounds (E) to the mass of the colloidal silica (A) taken as 1 being 0.01-2.0. The present invention also provides an electrolytic capacitor which comprises the electrolyte solution for electrolytic capacitors. The electrolyte solution for electrolytic capacitors has a high spark voltage and excellent conductivity, and is suppressed in gelation even after long-term use, thereby achieving excellent durability. The present invention also provides an electrolytic capacitor which uses such an electrolyte solution for electrolytic capacitors and has excellent withstand voltage characteristics.

Description

Electrolyte for electrolytic capacitor and electrolytic capacitor

[0001] The present invention relates to an electrolyte for electrolytic capacitors that has excellent electrical conductivity, spark voltage, and durability (heat resistance), and to an electrolytic capacitor using the same.

[0002] Conventionally, electrolytes for electrolytic capacitors have been prepared by dissolving an organic acid, an inorganic acid, or a salt thereof in an organic solvent as an electrolyte.

[0003] Since the conductivity of an electrolyte directly affects the dielectric loss, impedance characteristics, etc. of an electrolytic capacitor, there has been active development of electrolytes for electrolytic capacitors with high conductivity. Furthermore, with the recent increase in the operating voltage of automotive electrical power supplies and digital home appliances, there is a demand for electrolytes for electrolytic capacitors with even higher spark voltage and higher durability.

[0004] In order to improve the spark voltage while maintaining high electrical conductivity, additives to the electrolyte have been investigated, and for example, an electrolyte for electrolytic capacitors containing colloidal silica, which is an inorganic oxide colloid particle, is known. However, although the electrolyte containing colloidal silica has a high initial spark voltage, it can cause short circuit failures due to gelation of the electrolyte during use, and it has the problem of poor durability.

[0005] Patent Document 1 discloses a technology in which gelation of the electrolyte solution is suppressed by adding a silicone surfactant to an electrolyte solution containing colloidal silica, thereby improving durability while maintaining a high spark voltage. However, the electrolyte solution containing the colloidal silica and silicone surfactant does not provide the voltage resistance characteristics required in recent years. Attempts have been made to increase the spark voltage by further reducing the particle size of the colloidal silica to be added, but the use of colloidal silica with a small particle size has the problem of gelation progressing in a short period of time, making it difficult to achieve both improved spark voltage and improved durability.

[0006] International Publication No. 2014 / 208607

[0007] The present invention has been made in view of the above circumstances, and its object is to provide an electrolyte for an electrolytic capacitor that has a high spark voltage, excellent electrical conductivity, suppresses gelation even after long-term use, and is excellent in durability, and also to provide an electrolytic capacitor that uses such an electrolyte for an electrolytic capacitor and has excellent voltage resistance characteristics.

[0008] As a result of intensive research aimed at solving the above problems, the present inventors have found that the above problems can be solved by adding a predetermined amount of a phosphate ester compound to an electrolyte solution for electrolytic capacitors, the electrolyte solution containing at least colloidal silica, a polyether-modified silicone surfactant, an electrolyte salt, and an organic solvent, and have thus completed the present invention. That is, the present invention is as follows: [1] to

[10]

[0009] [1] An electrolyte solution for an electrolytic capacitor, comprising at least (A) colloidal silica, (B) a polyether-modified silicone surfactant, (C) an electrolyte salt, and (D) an organic solvent, wherein the average particle size of the (A) colloidal silica is 5 to 15 nm, and the electrolyte solution contains, as an additive, (E) a phosphate ester compound represented by the following general formula (1), and the mass ratio of the total of the (E) at least one phosphate ester compound to 1 of the (A) colloidal silica is 0.01 to 2.0: (In formula (1), R １ is a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a phenyl group, or a benzyl group, and R ２ represents an alkyl group having 1 to 10 carbon atoms, a phenyl group, or a benzyl group. １ and R ２may be the same or different.) [2] The electrolyte solution for electrolytic capacitors according to [1], wherein the (E) phosphate ester compound is at least one phosphate ester compound selected from the group consisting of monoethyl phosphate, monobutyl phosphate, monoisopropyl phosphate, diethyl phosphate, dibutyl phosphate, diisopropyl phosphate, and diphenyl phosphate. [3] The electrolyte solution for electrolytic capacitors according to [1] or [2], wherein the content of the (A) colloidal silica is 0.1% by mass to 20% by mass. [4] The electrolyte solution for electrolytic capacitors according to any one of [1] to [3], wherein the (B) polyether-modified silicone-based surfactant is a pendant-type polymer. [5] The electrolyte solution for electrolytic capacitors according to any one of [1] to [3], wherein the (B) polyether-modified silicone-based surfactant is an ABA-type polymer. [6] The electrolyte solution for electrolytic capacitors according to any one of [1] to [5], wherein the (C) electrolyte salt is any one of compounds represented by the following general formulas (2) to (6): (In formulas (2) to (6), the group R ３ ~R ２７ 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 ３ ~R ２７ Adjacent groups among X may be linked to form an alkylene group having 2 to 6 carbon atoms. - is a carboxylate anion or a boron compound anion.) [7] The electrolyte solution for electrolytic capacitors according to any one of [1] to [6], wherein the electrolyte solution contains 0.1 to 30% water. [8] The electrolyte solution for electrolytic capacitors according to any one of [1] to [7], further containing an antifoaming agent containing at least one selected from the group consisting of an acetylene compound and a polyglycol. [9] An electrolytic capacitor containing the electrolyte solution for electrolytic capacitors according to any one of [1] to [8].

[10] The electrolytic capacitor according to [9], which is for high voltage use.

[0010] According to the present invention, an electrolyte solution for electrolytic capacitors having a high spark voltage and excellent electrical conductivity and durability can be provided. Furthermore, by using the electrolyte solution of the present invention, an electrolytic capacitor having a high withstand voltage can be provided.

[0011] The electrolyte for electrolytic capacitors according to the present invention will be described below.

[0012] The essential components of the electrolyte for an electrolytic capacitor of the present invention include at least the following (A) to (E), that is, all of (A) to (E): (A) colloidal silica, (B) polyether-modified silicone surfactant, (C) electrolyte salt, (D) organic solvent, and (E) phosphate ester compound.

[0013] Hereinafter, (A) colloidal silica will be described. Colloidal silica is a type of silica containing SiO ２ It is a colloid of silicate or its hydrate, generally 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. In an electrolyte, the smaller the particle size, the more easily gelation occurs. The colloidal silica used in the present invention has an average particle size of 5 to 15 nm, and even when colloidal silica of this particle size is used, it is less likely to gel and can maintain a stably dispersed state in the electrolyte of an electrolytic capacitor.

[0014] Colloidal silica is practically insoluble in water or organic solvents, and is generally dispersed in a suitable dispersion solvent to form a colloidal solution, which is added to the electrolytic solution, and can be used in the dispersed state even when the electrolytic capacitor is in use.

[0015] The colloidal silica used in the present invention 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 are preferred.

[0016] The content of colloidal silica in the electrolyte for electrolytic capacitors is 0.1 to 20% by mass, more preferably 0.2 to 15% by mass, and particularly preferably 0.3 to 10% by mass. If the content is less than 0.1% by mass, the effect of improving the electrical properties of the electrolytic capacitor may be reduced, while if the content exceeds 20% by mass, the viscosity of the electrolyte may increase, making it difficult to handle.

[0017] The average particle size of colloidal silica is 5 to 15 nm. By using colloidal silica with this average particle size, an excellent electrolytic solution for electrolytic capacitors with high spark voltage can be obtained. In particular, the average particle size of colloidal silica used in electrolytic solutions for low- and medium-voltage electrolytic capacitors is preferably 10 to 15 nm, and the average particle size of colloidal silica used in electrolytic solutions for high-voltage electrolytic capacitors is preferably 5 to 10 nm. The average particle size can be calculated from the specific surface area measured by BET specific surface area measurement. As used herein, low- and medium-voltage electrolytic capacitors refer to capacitors with a rated voltage of 250 V or less, medium- and high-voltage electrolytic capacitors refer to capacitors with a rated voltage of more than 250 V but less than 450 V, and high-voltage electrolytic capacitors refer to capacitors with a rated voltage of 450 V or more.

[0018] 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.

[0019] The content of colloidal silica in the electrolyte of the present invention can be measured by ICP atomic emission spectroscopy. The particle size can be measured by observation with a transmission electron microscope, and the average particle size can be calculated by BET specific surface area measurement. In the case of nanoparticles, particle size can also be measured by dynamic light scattering.

[0020] These colloidal silicas can be synthesized by known methods or commercially available products.

[0021] The polyether-modified silicone surfactant (B) will be described below. The polyether-modified silicone surfactant has a siloxane bond (Si—O—Si) in its main skeleton, contains a compound also having a Si—C bond, and is further modified with a compound (polyether) having an ether bond (—O—).

[0022] The molecular weight of the polyether-modified silicone surfactant contained in the electrolyte solution of the present invention is preferably 100 to 100,000. The use of a polyether-modified silicone surfactant with a molecular weight within this range can prevent the charge balance of the colloidal silica from being disrupted, making gelation less likely to occur over a long period of time. This allows for the production of an electrolyte solution for electrolytic capacitors with high spark voltage and excellent heat resistance. This molecular weight is the weight-average molecular weight measured by gel permeation chromatography (GPC).

[0023] Examples of polyether-modified silicone surfactants include pendant polymers, ABA polymers, (AB) ｎ Among these, pendant type polymers are preferred for low- to medium-voltage electrolytic capacitors, and ABA type polymers are preferred for high-voltage electrolytic capacitors. These polyether-modified silicone surfactants may be used alone or in combination of two or more.

[0024] The pendant type is a compound represented by general formula (A), and the ABA type is a compound represented by general formula (B).

[0025]

[0026] R in the compound represented by the above general formula (A) or (B) Ａ or R Ｂ represents an alkyl group having 1 to 20 carbon atoms, and Y or Z represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. m represents an integer of 0 to 1000, and n or p represents an integer of 1 to 1000. a, b, c, and d each independently represent an integer of 0 to 100.

[0027] Y or Z is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and it is preferable that Y or Z is a hydrogen atom from the viewpoint of dispersibility.

[0028] The content of the polyether-modified silicone surfactant in the electrolytic solution of the present invention can be determined by liquid chromatography.

[0029] The content of the polyether-modified silicone surfactant in the electrolyte for electrolytic capacitors is preferably 0.01 to 20% by mass, more preferably 0.05 to 15% by mass, and particularly preferably 0.1 to 10% by mass. If the content is less than 0.01% by mass, the effect of preventing aggregation of colloidal silica may not be sufficient, and if the content is more than 20% by mass, the conductivity of the electrolyte may decrease.

[0030] These polyether-modified silicone surfactants can be synthesized by known methods or commercially available products.

[0031] The content ratio (mass ratio) of colloidal silica to polyether-modified silicone surfactant in the electrolyte for electrolytic capacitors may be any mass ratio, but it is preferable that the polyether-modified silicone surfactant is contained in an amount of 0.01 to 10 parts by weight, more preferably 0.05 to 5.0 parts by weight, and particularly preferably 0.1 to 2.0 parts by weight, per 1 part of colloidal silica. By keeping the content within this range, gelation of the electrolyte can be suppressed and better heat resistance can be obtained.

[0032] As described above, by including a polyether-modified silicone surfactant in the electrolyte solution for electrolytic capacitors, gelation caused by colloidal silica during heating, storage, and use can be prevented, and excellent electrical conductivity and spark voltage can be maintained for a long period of time.

[0033] The electrolyte salt (C) will be described below. The electrolyte salt used in the present invention may be any of those commonly used in electrolytic capacitors. Among these electrolyte salts, it is particularly preferable to use any of the compounds represented by the following general formulas (2) to (6).

[0034] In general formulas (2) to (6), R ３ ~R ２７ 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 ３ ~R ２７ Adjacent groups among X may be linked to form an alkylene group having 2 to 6 carbon atoms. － is a carboxylate anion or a boron compound anion.

[0035] Specific examples of the cation moiety of the compound represented by general formula (2) include quaternary ammonium cations such as ammonium cations, 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.

[0036] Among these, ammonium cation, tetraethylammonium cation, triethylmethylammonium cation, spiro-(1,1')-bipyrrolidinium cation, N-methylpyrrolidine cation, dimethylethylamine cation, diethylmethylamine cation, trimethylamine cation, triethylamine cation, diethylamine cation, and the like are preferably used because they have an excellent effect of improving spark voltage and / or electrical conductivity and an excellent effect of improving heat resistance.

[0037] Specific examples of the cation moiety of the compound represented by general formula (3) 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. , 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, 1,2-dimethyl-3-ethylimidazolium cation, etc. Among these, tetramethylimidazolium cation, tetraethylimidazolium cation, 1,3-dimethylimidazolium cation, 1,3-diethylimidazolium cation, 1-ethyl-3-methylimidazolium cation, etc. are preferably used because they exhibit high electrical conductivity and are excellent in improving heat resistance.

[0038] Specific examples of the cation moiety of the compound represented by general formula (4) 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.Among these, tetramethylimidazolinium cation, tetraethylimidazolinium cation, 1,2,3-trimethylimidazolinium cation, 1,2,3-triethylimidazolinium cation, and 1-ethyl-3-methylimidazolinium cation are preferably used because they exhibit high electrical conductivity and are excellent in improving heat resistance.

[0039] Specific examples of the cation moiety of the compound represented by general formula (5) 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. Among these, tetramethylpyrazolium cation, tetraethylpyrazolium cation, 1,2-dimethylpyrazolium cation, 1,2-diethylpyrazolium cation, 1-methyl-2-ethylpyrazolium cation, etc. are preferably used because they exhibit high electrical conductivity and are excellent in improving heat resistance.

[0040] Specific examples of the cation moiety of the compound represented by general formula (6) 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, N-butyl-4-ethylpyridinium cation, etc. Among these, N-methylpyridinium cation, N-ethylpyridinium cation, N-butylpyridinium cation, N-butyl-3-methylpyridinium cation, etc. are preferably used because they exhibit high electrical conductivity and are excellent in improving heat resistance.

[0041] Anion X in combination with the above cation －is a carboxylate anion or a boron compound anion. The carboxylate 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, undecanedioate anion, dodecanedioate anion, tridecanedioate anion, tetradecanedioate anion, pentadecanedioate anion, hexadecanedioate anion, 3-tert-butyladipate anion, methylmalonate anion, ethylmalonate anion, and propylmalonate anion. ion, butylmalonate anion, pentylmalonate anion, hexylmalonate anion, dimethylmalonate anion, diethylmalonate anion, methylpropylmalonate anion, methylbutylmalonate anion, ethylpropylmalonate anion, dipropylmalonate anion, methylsuccinate anion, ethylsuccinate anion, 2,2-dimethylsuccinate anion, 2,3-dimethylsuccinate anion, 2-methylglutaric acid anion, 3-methylglutaric acid anion, 3-methyl-3-ethylglutaric acid anion, 3,3-diethylglutaric acid anion, methylsuccinate anion, 2-methylglutaric acid anion, 3-methylglutaric acid anion, 3,3-dimethylglutaric acid anion, 3-methyladipic acid anion, 1,6-decanedicarboxylic acid anion, 5,Examples of the anions include saturated carboxylic acids such as 6-decanedicarboxylic acid anion, formate anion, acetate anion, propionate anion, butyrate anion, isobutyrate anion, valerate anion, caproate anion, enanthate anion, caprylate anion, pelargonate anion, laurate anion, myristate anion, stearate anion, behenate anion, undecanoate anion, borate anion, borodiglycolate anion, borodisalicylate anion, borodiazelaate anion, borodilactic acid anion, itaconate anion, tartrate anion, glycolate anion, lactate anion, and pyruvate anion, and aliphatic carboxylic acids containing unsaturated carboxylic acids such as maleate anion, fumarate anion, acrylate anion, methacrylate anion, and oleate anion. These may be used alone or in combination of two or more. Among these, from the viewpoints of improving spark voltage and being thermally stable, preferred examples include phthalate anion, maleate anion, salicylate anion, benzoate anion, adipate anion, sebacate anion, azelaate anion, 1,6-decanedicarboxylic acid anion, and 3-tert-butyladipate anion.

[0042] Examples of the boron compound anion include borate anion, borodiazelaate anion, borodisalicylate anion, borodiglycolate anion, borodilactic acid anion, borodisoxalate anion, etc. Among these, borate anion, borodisalicylate anion, borodiglycolate anion, etc. are preferably used because of their excellent spark voltage.

[0043] Among the above anions, when used in low- to medium-voltage electrolytic capacitors, phthalate anion, maleate anion, salicylate anion, benzoate anion, adipate anion, borodisalicylate anion, borodiglycolate anion, etc. are preferably used, as they provide high electrical conductivity and excellent heat resistance.On the other hand, when used in high-voltage electrolytic capacitors, sebacate anion, azelaate anion, 1,6-decanedicarboxylic acid anion, 3-tert-butyladipate anion, borate anion, borodisalicylate anion, borodiglycolate anion, etc. are preferably used, as they provide excellent effects in terms of spark voltage and heat resistance.

[0044] Among the compounds represented by the above general formulas (2) to (6), any of the compounds represented by the general formulas (2) to (4) is preferably used because it is stable for a long period of time, can provide a high spark voltage, and has excellent heat resistance. Specifically, examples of electrolyte salts used in electrolytes for low and medium voltage electrolytic capacitors include dimethylethylamine maleate, dimethylethylamine phthalate, tetraethylammonium maleate, tetraethylammonium phthalate, trimethylamine maleate, trimethylamine phthalate, triethylamine maleate, triethylamine phthalate, diethylamine maleate, diethylamine phthalate, spiro-(1,1')-bipyrrolidinium maleate, spiro-(1,1')-bipyrrolidinium phthalate, 1-ethyl-3-methylimidazolium maleate, 1-ethyl-3-methylimidazolium phthalate, 1-ethyl-3-methylimidazolium maleate, 1-ethyl-3-methylimidazolinium phthalate, tetramethylimidazolium phthalate, tetramethylimidazolinium phthalate, tetraethylimidazolium phthalate, and tetraethylimidazolinium phthalate. On the other hand, as the electrolyte salt used in the electrolyte solution for high-voltage electrolytic capacitors, dimethylamine sebacate, diethylamine sebacate, trimethylamine sebacate, triethylamine sebacate, ammonium sebacate, dimethylamine azelate, diethylamine azelate, trimethylamine azelate, triethylamine azelate, ammonium azelate, ammonium 1,6-decanedicarboxylate, dimethylamine 1,6-decanedicarboxylate, diethylamine 1,6-decanedicarboxylate, trimethylamine 1,6-decanedicarboxylate, triethylamine 1,6-decanedicarboxylate, N-methylpyrrolidine borodisalicylate, and the like are preferably used.

[0045] The content of the electrolyte salt in the electrolytic solution for electrolytic capacitors is preferably 1.0 to 60% by mass, more preferably 5.0 to 50% by mass, and particularly preferably 10 to 40% by mass. If the content is less than 1.0% by mass, the electrolytic solution may not have sufficient conductivity, while if it exceeds 60% by mass, the viscosity of the electrolytic solution may increase, which may increase the equivalent series resistance (ESR) of the electrolytic capacitor.

[0046] The content of the electrolyte salt in the electrolytic solution of the present invention can be determined by ion chromatography.

[0047] These electrolyte salts can be synthesized by known methods or commercially available products.

[0048] The organic solvent (D) will be described below. The organic solvent used in the electrolytic solution for electrolytic capacitors may be a protic polar solvent or an aprotic polar solvent, and may be used alone or in combination of two or more kinds.

[0049] Examples of protic polar solvents include monohydric alcohols (methanol, ethanol, propanol, butanol, pentanol, hexanol, cyclobutanol, cyclopentanol, cyclohexanol, and benzyl alcohol), polyhydric alcohols, and oxyalcohol compounds (ethylene glycol, propylene glycol, glycerin, methyl cellosolve, ethyl cellosolve, methoxypropylene glycol, and dimethoxypropanol).

[0050] Aprotic polar solvents include γ-butyrolactone, γ-valerolactone, amides (N-methylformamide, N,N-dimethylformamide, N-ethylformamide, N,N-diethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylacetamide, N,N-diethylacetamide, hexamethylphosphoric amide), sulfolane (sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane), chain sulfones (dimethylsulfone, ethylmethylsulfone), and the like. sulfone, ethyl isopropyl sulfone), cyclic amides (N-methyl-2-pyrrolidone), carbonates (ethylene carbonate, propylene carbonate, isobutylene carbonate), nitriles (acetonitrile), sulfoxides (dimethyl sulfoxide), 2-imidazolidinones (1,3-dimethyl-2-imidazolidinone, 1,3-diethyl-2-imidazolidinone, 1,3-di(n-propyl)-2-imidazolidinone, 1,3,4-trimethyl-2-imidazolidinone), and the like.

[0051] When used as an electrolyte for low- to medium-voltage electrolytic capacitors, a solvent containing γ-butyrolactone as the main solvent is preferably used, and when used for high-voltage electrolytic capacitors, a solvent containing ethylene glycol as the main solvent is preferably used.

[0052] The phosphoric acid ester compound (E) will be described below. The phosphoric acid ester compound in the present invention is a general term for phosphoric acid monoesters or phosphoric acid diesters, and does not include phosphorous acid, phosphorous acid compounds such as phosphorous acid monoesters and phosphorous acid diesters, phosphoric acid triesters, or phosphoric acid. The phosphoric acid ester compound is represented by the following general formula (1):

[0053] In formula (1), R １ is a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a phenyl group, or a benzyl group, and R ２ represents an alkyl group having 1 to 10 carbon atoms, a phenyl group, or a benzyl group. １ and R ２may be the same or different. In addition, in the case of an alkyl group, it may be either a straight chain or a branched chain, and specific examples of the alkyl group include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a s-butyl group, a tert-butyl group, a pentyl group, a hexyl group, a 2-ethylhexyl group, a heptyl group, an octyl group, a nonyl group, and a decyl group. １ and R ２ may be substituted with a substituent.

[0054] At least one type of phosphate ester compound represented by formula (1) can be used. Specific examples of phosphate ester compounds include phosphate monoesters such as monoethyl phosphate, monobutyl phosphate, and monoisopropyl phosphate, and phosphate diesters such as diethyl phosphate, dibutyl phosphate, diisopropyl phosphate, and diphenyl phosphate. Furthermore, the phosphate ester compound represented by formula (1) can also be a mixture of a phosphate monoester and a phosphate diester, using two or more of the above phosphate ester compounds. Examples of such a mixture of a phosphate monoester and a phosphate diester include monoethyl phosphate and diethyl phosphate, monobutyl phosphate and dibutyl phosphate, and monoisopropyl phosphate and diisopropyl phosphate. Among these phosphate ester compounds, a mixture of monoisopropyl phosphate and diisopropyl phosphate is preferred in terms of spark voltage and withstand voltage. The mixing ratio of the phosphoric acid monoester and phosphoric acid diester in the mixture of the phosphoric acid monoester and phosphoric acid diester is not particularly limited, but for example, it is preferable that the phosphoric acid diester is contained in a larger amount than the phosphoric acid monoester, and it is more preferable that the phosphoric acid diester is contained in an amount of more than 50 mass% in the mixture. By adding a phosphoric acid ester compound to the electrolyte for electrolytic capacitors, the repairability of the dielectric oxide film of the aluminum anode in the electrolytic capacitor when damaged is improved, and excellent electrical conductivity and spark voltage can be maintained for a long period of time. Furthermore, by using the phosphoric acid ester compound in combination with a polyether-modified silicone surfactant, gelation of the electrolyte can be synergistically suppressed.

[0055] The total content of the phosphate ester compounds in the electrolyte for electrolytic capacitors is preferably 0.001 to 20% by mass, and particularly preferably 0.01 to 10% by mass. If the content is less than 0.001% by mass, the electrolyte may be prone to gelation, and if it exceeds 20% by mass, the conductivity of the electrolyte may be reduced.

[0056] The content of the phosphate ester compound in the electrolyte solution of the present invention can be determined by gas chromatography.

[0057] These phosphate ester compounds can be synthesized by known methods or commercially available products.

[0058] The total content ratio (mass ratio) of colloidal silica and phosphate ester compound in the electrolyte for electrolytic capacitors is 1 part colloidal silica to 0.01 to 2.0 parts phosphate ester compound, more preferably 0.1 to 2.0, and particularly preferably 0.3 to 2.0.

[0059] <Antifoaming Agent> The electrolyte solution for electrolytic capacitors of the present invention preferably further contains an antifoaming agent containing at least one selected from the group consisting of acetylene compounds and polyglycols. Specific examples of defoaming agents containing an acetylene compound include Surfynol 104E, DF-75, MD-20, Olfine E1004, E1010, E1020, PD-001, PD-002W, PD-004, PD-005, EXP4001, EXP4200, EXP4123, EXP4300, WE-003, P-10PG, AF-103, and SK-14 manufactured by Nissin Chemical Industry Co., Ltd.; and examples of defoaming agents containing polyglycol include BYK-018, BYK-021, BYK-022, BYK-024, BYK-028, BYK-093, and BYK-1730 manufactured by BYK-Chemie; and SN Deformer 170 and 260 manufactured by San Nopco Ltd. The above-mentioned antifoaming agent can be used in both low- and medium-voltage electrolytic capacitors and high-voltage electrolytic capacitors, but is preferably used in high-voltage electrolytic capacitors, in which foaming is likely to occur during preparation of the electrolyte solution of the present invention.

[0060] The inclusion of an antifoaming agent in the electrolytic solution for electrolytic capacitors suppresses foaming of the electrolytic solution when a polyether-modified silicone surfactant is added, and when the electrolytic solution is impregnated into an electrolytic capacitor element, the electrolytic solution can be more uniformly impregnated into the separator and the inner part of the anode electrode of the element. As a result, when an electrolytic capacitor is manufactured, the colloidal silica and the phosphate ester compound can act more uniformly on the anode electrode, and an electrolytic capacitor with high withstand voltage can be provided.

[0061] The content ratio (mass ratio) of the polyether-modified silicone surfactant to the antifoaming agent in the electrolyte solution for electrolytic capacitors may be any mass ratio, but it is preferable to include 0.001 to 3.0 parts of antifoaming agent per 1 part of polyether-modified silicone surfactant, more preferably 0.005 to 1.5 parts, and particularly preferably 0.01 to 0.5 parts.

[0062] The content of the antifoaming agent in the electrolytic solution for electrolytic capacitors is preferably 0.001 to 10% by mass, and more preferably 0.01 to 5% by mass.

[0063] <Electrolytic Capacitor Electrolyte> When the electrolytic capacitor electrolyte of the present invention is used as an electrolyte for low- to medium-voltage electrolytic capacitors, the conductivity after a heat resistance test (135°C, 2000 hours) is preferably 3.1 mS / cm or more, more preferably 3.5 mS / cm or more, and even more preferably 3.7 mS / cm or more. The spark voltage after a heat resistance test (135°C, 2000 hours) is preferably 430 V or more, more preferably 480 V or more, even more preferably 500 V or more, and particularly preferably 530 V or more. When used in low- to medium-voltage electrolytic capacitors, the withstand voltage after a heat resistance test (135°C, 2000 hours) is preferably 430 V or more, more preferably 480 V or more, even more preferably 500 V or more, and particularly preferably 530 V or more. The conductivity, spark voltage, and withstand voltage can be determined, for example, by the measurement methods described in the Examples.

[0064] When used as an electrolyte for high-voltage electrolytic capacitors, the conductivity after a heat resistance test (135°C, 2000 hours) is preferably 2.5 mS / cm or more, more preferably 2.9 mS / cm or more, and even more preferably 3.1 mS / cm or more. The spark voltage after a heat resistance test (135°C, 2000 hours) is preferably 550 V or more, more preferably 600 V or more, even more preferably 630 V or more, and particularly preferably 655 V or more. When used in high-voltage electrolytic capacitors, the withstand voltage after a heat resistance test (135°C, 2000 hours) is preferably 550 V or more, more preferably 600 V or more, even more preferably 630 V or more, and particularly preferably 655 V or more. The conductivity, spark voltage, and withstand voltage can be determined, for example, by the measurement methods described in the Examples.

[0065] Typically, electrolytes containing colloidal silica have excellent initial spark voltage, but suffer from the drawback of progressive gelation with use, resulting in a decline in performance (conductivity, spark voltage). Therefore, electrolytic capacitors using conventional electrolytes for electrolytic capacitors, which contain only a silicone surfactant or only a phosphate ester compound in addition to electrolyte salt and colloidal silica, have insufficient withstand voltage or durability (heat resistance). The reason for the decline in spark voltage is that the inclusion of electrolyte salt disrupts the charge balance of the colloidal silica during use, causing the colloidal silica to aggregate and / or polymerize, resulting in gelation. Gelling tends to progress more easily, particularly when colloidal silica with a small particle size is used.

[0066] According to the present invention, by incorporating a specific ratio of the amount of colloidal silica to the amount of phosphate ester compound or the amount of polyether-modified silicone surfactant in the electrolyte for electrolytic capacitors, it is possible to prevent the charge balance of the colloidal silica from being disrupted, and aggregation is less likely to occur, thereby preventing gelation. As a result, it is possible to provide an electrolyte for electrolytic capacitors that has excellent initial spark voltage and excellent properties in terms of electrical conductivity and spark voltage even after long-term use.

[0067] The electrolyte solution for electrolytic capacitors of the present invention can be prepared as follows: (D) An acid, a base, etc. are added to an organic solvent so as to form an electrolyte salt of any one of the above formulas (1) to (5), thereby obtaining a solution of the electrolyte salt (C). Then, (A) an aqueous dispersion of colloidal silica, (B) a polyether-modified silicone surfactant, and (E) a phosphate ester compound are added and mixed, and the mixture is concentrated. After that, water is added as necessary to prepare the electrolyte solution for electrolytic capacitors. The order of addition of (B) a polyether-modified silicone surfactant and (E) a phosphate ester compound does not matter, but it is preferable to add them quickly so as not to reduce the dispersibility of the colloidal silica in the solution.

[0068] The amount of water contained in the electrolytic solution for electrolytic capacitors is not particularly limited, but is preferably 0.1 to 30% by mass, and more preferably 0.5 to 20% by mass. This range enhances the chemical conversion properties of the electrode foil (the ability to repair damaged dielectric oxide films on the electrode foil in electrolytic capacitors) and improves electrical conductivity. If the water content is too high, heat generated during use in an electrolytic capacitor can cause the water in the electrolyte to evaporate, increasing internal pressure and causing the outer container to break, or the electrolytic solution can decrease when gas is released through the pressure valve of the outer container, resulting in a decrease in the capacitance of the electrolytic capacitor. If the water content is too low, the chemical conversion properties of the electrode foil can decrease, resulting in a deterioration in voltage resistance, or insufficient ionization (ionization) of the electrolyte salt, resulting in a decrease in electrical conductivity. The water content in the electrolyte can be measured using a Karl Fischer method using a Karl Fischer moisture meter, for example.

[0069] <Electrolytic Capacitor> The electrolytic capacitor of the present invention contains the above-mentioned electrolytic solution for electrolytic capacitors. The electrolytic capacitor of the present invention will be described using an aluminum electrolytic capacitor as an example. The aluminum electrolytic capacitor uses a chemically formed foil, on the surface of which an oxide film is formed as a dielectric by anodizing treatment, as an anode electrode, a cathode electrode disposed opposite the anode electrode, and a separator interposed between the two electrodes, which holds an electrolytic solution.

[0070] Electrolytic capacitors using the above-described electrolytic solutions for electrolytic capacitors can be manufactured as follows. First, a capacitor element is formed by winding an anode foil and a cathode foil with a separator interposed therebetween. An anode tab and a cathode tab are connected to the anode foil and the cathode foil, respectively. These anode tab and cathode tab are made of high-purity aluminum and comprise a flat portion connected to the respective foils and a round bar portion continuous with the flat portion. The anode lead wire and the cathode lead wire are connected to the round bar portion, respectively. The respective foils and electrode tabs are connected by welding. The capacitor element thus constructed is then impregnated with the above-described electrolytic solutions for electrolytic capacitors. The electrolyte-impregnated capacitor element is then housed in a cylindrical aluminum outer case with a bottom. A butyl rubber sealer with through holes for leading out the lead wires is inserted into the open end of the outer case, and the end of the outer case is further crimped to seal the electrolytic capacitor, thereby obtaining an aluminum electrolytic capacitor.

[0071] The present invention will be described below based on examples. However, the present invention is not limited to these examples. In the examples, "parts" means "parts by mass" and "%" means "% by mass."

[0072] (Examples 1-7, 9-12, Comparative Examples 1-6) First, examples of the production of low- to medium-voltage electrolytic capacitors and the electrolyte solution therefor are described. 166 parts of phthalic acid and 870 parts of gamma-butyrolactone as a solvent were mixed and stirred, and 200 parts of 1,2,3,4-tetramethylimidazolium methylcarbonate salt was added dropwise to obtain a 1,2,3,4-tetramethylimidazolium phthalate solution. 40.0 parts of colloidal silica (Nissan Chemical Industries, Ltd., Snowtex O, aqueous dispersion, 20% solids, average particle size 10-15 nm, pH 2.0-4.0), a polyether-modified silicone surfactant and a phosphate ester compound (described below), and an antifoaming agent, if necessary, were added, mixed, and concentrated at 80°C to obtain an electrolyte solution for electrolytic capacitors.

[0073] Examples 8 and 13 An electrolyte solution for an electrolytic capacitor was obtained in the same manner as in the above-described Production Examples, except that a commercially available mixture of diisopropyl phosphate and monoisopropyl phosphate (manufactured by Nippon Chemical Industry Co., Ltd., PAP: diisopropyl phosphate: 55 to 80%, monoisopropyl phosphate: 20 to 45%, phosphoric acid: 3% or less) was used as the phosphate ester compound.

[0074] The average particle size of colloidal silica and the types and amounts of phosphate ester compound, polyether-modified silicone surfactant, and antifoaming agent used in each Example and Comparative Example are shown in Table 1. The values ​​in parentheses are the mass ratio of surfactant and phosphate ester compound when the mass of colloidal silica (solid content) is standardized as 1, and the mass ratio of antifoaming agent when the mass of surfactant is standardized as 1.

[0075] Details of the polyether-modified silicone surfactant and defoamer are as follows: "Pendant type": Polyether-modified silicone surfactant (pendant type): Momentive Corporation, "Silwet L-7657", molecular weight 5000 "ABA type": Polyether-modified silicone surfactant (ABA type): Momentive Corporation, "Silwet L-8500", molecular weight 2800 "BYK": Polyglycol-containing defoamer: BYK-Chemie Corporation, "BYK-024"

[0076]

[0077] <Manufacturing of Electrolytic Capacitors> First, a capacitor element was formed by winding an anode foil and a cathode foil with a separator interposed therebetween. An anode tab and a cathode tab were attached to the anode foil and cathode foil, respectively. These anode tabs and cathode tabs were made of high-purity aluminum and consisted of a flat portion connected to the respective foil and a round bar portion connected to the flat portion. The anode lead wire and cathode lead wire were connected to the round bar portion, respectively. The respective foils and electrode tabs were connected by welding. The capacitor element thus constructed was impregnated with the above-described electrolytic capacitor electrolyte. The impregnated capacitor element was then placed in a cylindrical aluminum outer case with a bottom. A butyl rubber sealer with through holes for leading out the lead wires was inserted into the open end of the outer case, and the end of the outer case was further crimped to seal the electrolytic capacitor, obtaining an aluminum electrolytic capacitor. The specifications of the aluminum electrolytic capacitor elements using the electrolytes of the above examples and comparative examples were a rated voltage of 250 V and a rated capacitance of 47 μF.

[0078] The electrolytic solutions for electrolytic capacitors and electrolytic capacitors using the electrolytic solutions were evaluated as follows.

[0079] (Method for Evaluating Electrical Conductivity) The initial electrical conductivity was evaluated by measuring the electrical conductivity (mS / cm) of the electrolytic solution for electrolytic capacitors at 30° C. using an SC meter SC72 manufactured by Yokogawa Electric Corporation. After the heat resistance test, the electrolytic solution was left at a temperature of 135° C. for 2000 hours, and then the electrical conductivity was measured in the same manner.

[0080] (Method for Evaluating Spark Voltage) The initial spark voltage was evaluated by applying 5 mA / cm2 at 25°C to the electrolyte for the electrolytic capacitor. ２ A constant current of 1000 V was applied to the electrolyte, and the voltage-time curve was recorded. The voltage at which scintillation was observed on the voltage rise curve was defined as the spark voltage (V). After the heat resistance test, the electrolyte was left at a temperature of 135° C. for 2000 hours, and then the spark voltage was measured in the same manner.

[0081] (Method for Evaluating Electrolytic Capacitors) For the initial withstand voltage of the electrolytic capacitors, a current of 5 mA / element and a voltage of 1000 V were applied to the prepared electrolytic capacitors at 105°C, and the value at which the first spike or scintillation was observed in the voltage-time rise curve was recorded as the withstand voltage. For the heat resistance test, the electrolytic capacitor electrolyte was stored at a temperature of 135°C for 2000 hours, and then the electrolytic capacitors were prepared and the withstand voltage was measured in the same manner. In addition, a high-temperature load test was conducted for 1000 hours at a temperature of 105°C, a voltage of 250 V, and a current of 1 mA / element, and the number of defective products that developed short circuits was counted.

[0082] (Method for evaluating gelation) The gelation was evaluated according to the test tube inversion method described in Japanese Patent No. 6508480. First, the electrolyte for the electrolytic capacitor was kept at 135°C for 2000 hours in a thermostatic chamber. The electrolyte was then gently removed from the thermostatic chamber and allowed to stand until it reached room temperature. The test sample was then slowly inverted 180°. If a gel was formed that did not deform or crumble, it was judged to have gelled.

[0083] The measurement results of the conductivity (mS / cm), spark voltage (V) of the electrolytic solution for electrolytic capacitors, and the state of the electrolytic solution after the heat resistance test are shown in Table 2. The evaluation results of the electrolytic capacitors are also shown.

[0084]

[0085] Using Comparative Example 1, which contains an extremely small amount of phosphate ester compound, as a reference, Examples 1 to 13 and Comparative Example 2, which contain sufficient amounts of phosphate ester compound in the electrolyte, maintain high spark voltage after the heat resistance test. Furthermore, Comparative Example 2, in which an excessive amount of phosphate ester compound is added, exhibits a significant decrease in conductivity. Even if an appropriate amount of phosphate ester compound is added, as in Comparative Example 3, if the colloidal silica particle size is large, no improvement in spark voltage and withstand voltage is observed. Even when a phosphite diester, a phosphate triester, or phosphoric acid other than phosphate ester compounds is used, as in Comparative Examples 4, 5, and 6, the spark voltage and withstand voltage are not maintained after the heat resistance test. Comparing the number of short-circuited elements, many short circuits occurred in Comparative Examples 1, 4, and 5, in which the electrolyte was in a gelled state after the heat resistance test. Furthermore, it can be seen that in Comparative Examples 1, 3, 4, and 5, in which short circuits occurred, both the spark voltage and withstand voltage after the heat resistance test did not reach the rated voltage of 250 V. Of the phosphate ester compounds described in the examples, a mixture of diisopropyl phosphate and monoisopropyl phosphate was particularly effective in terms of spark voltage and withstand voltage.

[0086] (Examples 14 to 20, 22 to 25, Comparative Examples 7 to 12) The following production and evaluation examples are directed to high-voltage electrolytic capacitors and the electrolytes therefor.

[0087] A manufacturing example of a high-voltage electrolytic capacitor and its electrolyte solution is described below. 94 parts of azelaic acid and 820 parts of ethylene glycol as a solvent were mixed and stirred, and 73 parts of diethylamine was added dropwise to obtain a diethylamine azelaic acid ethylene glycol solution. 100.0 parts of colloidal silica (Nissan Chemical Industries, Ltd., Snowtex NS, aqueous dispersion, 20% solids, average particle size 8-11 nm, pH 9.0-10.0), a polyether-modified silicone surfactant and a phosphate ester compound (described below), and an optional defoamer were added, mixed, and concentrated at 80°C to obtain an electrolyte solution for electrolytic capacitors.

[0088] Examples 21 and 26 An electrolyte solution for an electrolytic capacitor was obtained in the same manner as in the above-described Production Examples, except that a commercially available mixture of diisopropyl phosphate and monoisopropyl phosphate (manufactured by Nippon Chemical Industry Co., Ltd., PAP: diisopropyl phosphate: 55 to 80%, monoisopropyl phosphate: 20 to 45%, phosphoric acid: 3% or less) was used as the phosphate ester compound.

[0089] The average particle size of colloidal silica and the types and amounts of phosphate ester compounds, polyether-modified silicone surfactants, and antifoaming agents used in each example and comparative example are shown in Table 3. The notation format is the same as above.

[0090]

[0091] <Production of Electrolytic Capacitors> Aluminum electrolytic capacitor elements using the electrolytic solutions of the above Examples and Comparative Examples were produced in the same manner as the low- to medium-voltage electrolytic capacitors described above. The specifications of these aluminum electrolytic capacitors were a rated voltage of 450 V and a rated capacitance of 47 μF.

[0092] (Method of Evaluating Electrical Conductivity) The electrical conductivity was evaluated in the same manner as in the case of the low- and medium-voltage electrolytic capacitor described above.

[0093] (Method of Evaluating Sparkover Voltage) The sparkover voltage was evaluated in the same manner as in the case of the low- and medium-voltage electrolytic capacitor described above.

[0094] (Method for Evaluating Electrolytic Capacitors) For the initial withstand voltage of the electrolytic capacitors, a current of 5 mA / element and a voltage of 1000 V were applied to the prepared electrolytic capacitors at 105°C, and the value at which the first spike or scintillation was observed in the voltage-time rise curve was recorded as the withstand voltage. For the heat resistance test, the electrolytic capacitor electrolyte was stored at a temperature of 135°C for 2000 hours, and then the electrolytic capacitors were prepared and the withstand voltage was measured in the same manner. In addition, a high-temperature load test was conducted for 1000 hours at a temperature of 105°C, a voltage of 450 V, and a current of 1 mA / element, and the number of defective products that developed short circuits was counted.

[0095] (Method for Evaluating Gelation) Evaluation was carried out in the same manner as in the case of the low- and medium-voltage electrolytic capacitor described above.

[0096] The electrical conductivity (mS / cm), spark voltage (V) of the electrolytic solution for electrolytic capacitors, and the measurement results of the state of the electrolytic solution after the heat resistance test are shown in Table 4. The evaluation results of the electrolytic capacitors are also shown.

[0097]

[0098] As in the case of the low- and medium-voltage electrolytic capacitors described above, Comparative Example 7, which contains an extremely small amount of phosphate ester compound, is used as a reference. High spark voltages are maintained after the heat resistance test in Examples 14 to 26 and Comparative Example 8, which contain sufficient amounts of phosphate ester compound in the electrolyte. Furthermore, a significant decrease in conductivity is observed in Comparative Example 8, in which an excessive amount of phosphate ester compound is added. Even if an appropriate amount of phosphate ester compound is added, as in Comparative Example 9, improvements in spark voltage and withstand voltage are not observed if the colloidal silica particle size is large. Even when a phosphite diester, phosphate triester, or phosphoric acid other than phosphate ester compounds is used, as in Comparative Examples 10, 11, and 12, spark voltage and withstand voltage are not maintained after the heat resistance test. Comparing the number of short-circuited elements, many short circuits occurred in Comparative Examples 7, 10, and 11, in which the electrolyte was in a gelled state after the heat resistance test. Furthermore, in Comparative Examples 7, 9, 10, and 11, in which short circuits occurred, it can be seen that the spark voltage and withstand voltage after the heat resistance test both did not reach the rated voltage of 450 V. Of the phosphate ester compounds described in the examples, a mixture of diisopropyl phosphate and monoisopropyl phosphate was particularly effective in terms of spark voltage and withstand voltage.

[0099] By using the electrolyte of the present invention, it is possible to realize an aluminum electrolytic capacitor having high electrical conductivity, high spark voltage, and high withstand voltage. Therefore, as the withstand voltage of power supplies in the market continues to increase, the market value of the electrolyte of the present invention is very high. The electrolyte of the present invention is particularly useful for aluminum electrolytic capacitors used in power supplies for automotive electrical equipment and digital home appliances.

Claims

1. An electrolyte solution for electrolytic capacitors containing at least (A) colloidal silica, (B) a polyether-modified silicone surfactant, (C) an electrolyte salt, and (D) an organic solvent, wherein the average particle size of the (A) colloidal silica is 5 to 15 nm, and the electrolyte solution contains, as an additive, (E) at least one or more phosphate ester compounds represented by the following general formula (1), and the mass ratio of the total of the (E) phosphate ester compounds to 1 part of the (A) colloidal silica is 0.01 to 2.0: (In formula (1), R １ is a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a phenyl group, or a benzyl group, and R ２ represents an alkyl group having 1 to 10 carbon atoms, a phenyl group, or a benzyl group. １ and R ２ may be the same or different.) 2. The electrolyte for electrolytic capacitors according to claim 1, wherein the (E) phosphate ester compound is at least one phosphate ester compound selected from the group consisting of monoethyl phosphate, monobutyl phosphate, monoisopropyl phosphate, diethyl phosphate, dibutyl phosphate, diisopropyl phosphate, and diphenyl phosphate.

3. The electrolyte for electrolytic capacitors according to claim 1, wherein the content of said colloidal silica (A) is 0.1% by mass to 20% by mass.

4. The electrolyte for electrolytic capacitors according to any one of claims 1 to 3, wherein the polyether-modified silicone surfactant (B) is a pendant polymer.

5. The electrolyte for electrolytic capacitors according to any one of claims 1 to 3, wherein the polyether-modified silicone surfactant (B) is an ABA type polymer.

6. The electrolyte solution for electrolytic capacitors according to any one of claims 1 to 3, wherein the electrolyte salt (C) is any one of the compounds represented by the following general formulas (2) to (6): (In formulas (2) to (6), the group R ３ ~R ２７ 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 ３ ~R ２７ Adjacent groups among X may be linked to form an alkylene group having 2 to 6 carbon atoms. - is a carboxylate anion or a boron compound anion.

7. The electrolyte for electrolytic capacitors according to any one of claims 1 to 3, which contains 0.1 to 30% water.

8. The electrolyte for electrolytic capacitors according to any one of claims 1 to 3, further comprising an antifoaming agent containing at least one selected from the group consisting of acetylene compounds and polyglycols.

9. An electrolytic capacitor containing the electrolytic solution for electrolytic capacitors according to any one of claims 1 to 3.

10. The electrolytic capacitor according to claim 9, which is for high voltage use.

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