JP5936096B2 - Electrolytic solution for electrolytic capacitors - Google Patents

Description

  The present invention relates to an electrolytic solution for an electrolytic capacitor.

An aluminum electrolytic capacitor uses an oxide film formed on an anode made of high-purity aluminum foil as a dielectric, and must be able to be used stably in a wide temperature range from about −40 ° C. to over 100 ° C. It becomes. With the recent spread of digital home appliances and the electrification of automobiles, the demand for digital devices and in-vehicle devices is expanding, but when used under high voltage, problems such as short-circuits may occur, and spark generation voltage Improvement is demanded.
As a driving electrolyte used for an aluminum electrolytic capacitor, a polar solvent mainly composed of ethylene glycol or γ-butyrolactone, an inorganic acid such as boric acid, a dibasic acid such as adipic acid or maleic acid, and a salt thereof. Solvent driving electrolytes are known. However, electrolytes using these carboxylic acids as solutes have a problem of low electrical spark generation voltage although they are highly conductive.

  As a method for improving the spark generation voltage, a method using butyloctanedioic acid (for example, Patent Document 1), a method using 5,6-decanedicarboxylic acid (for example, Patent Document 2), and the like have been reported. Although an electrolyte using such a carboxylic acid having a long alkyl chain length is effective in improving the spark generation voltage, it is crystallized and precipitated at a low temperature because the solubility of the long chain carboxylic acid in a polar solvent is low. As a result, the spark generation voltage and electrical conductivity may be reduced.

  As another method for improving the spark generation voltage, a method of adding a polyalkylene glycol compound to the electrolytic solution is known. For example, a compound (for example, Patent Document 3) in which ethylene oxide and other alkylene oxides are randomly added to a lower alcohol has been reported. This compound has an effect of improving the spark generation voltage by enhancing the chemical conversion of the anode of the aluminum electrolytic capacitor. However, since this compound is a random copolymer, its surface activity is low, and the effect of suppressing the precipitation of crystals by improving the dispersibility of long-chain carboxylic acids at low temperatures is not observed. In addition, a compound in which ethylene oxide and propylene oxide are sequentially added to alcohol in a block form (for example, Patent Document 4) has been reported. Although such a compound has an effect in improving the spark generation voltage, an alkyl group-hydrophilic property It is a triblock type copolymer of group-lipophilic group, and since it does not have a block site of a hydrophilic group necessary for dissolution in a solvent at the end, it is difficult to orient in a solvent, and long chain carboxylic acid is dispersed at a low temperature. Thus, no effect of suppressing crystal precipitation was observed.

Japanese Patent Publication No. 60-13293 Japanese Patent Publication No. 63-15738 Japanese Patent Application Laid-Open No. 10-106882 JP-A-3-257810

  The problem to be solved by the present invention has a sufficient effect for improving the spark generation voltage, has a high degree of improvement in the spark generation voltage compared to the increase in specific resistance, and further precipitates carboxylic acid crystals at low temperatures. An object of the present invention is to provide an electrolytic solution for an electrolytic capacitor that can be suppressed.

As a result of earnest research, the present inventor has improved the spark generation voltage and added the butylene oxide-alkylene oxide block adduct of an alcohol having 1 to 4 carbon atoms to the electrolytic solution for electrolytic capacitors, even under low temperature conditions. The inventors have found that precipitation of carboxylic acid crystals can be avoided without separating the additive, and the present invention has been completed.
That is, the present invention is as follows.
[1] An electrolytic solution for electrolytic capacitors containing the following components (a), (b), and (c):
(A) Compound represented by formula (1) (b) Polar solvent (c) One or more electrolytes selected from the group consisting of organic acids, inorganic acids or salts thereof R—O— (BO) _a — ( EO) _b / (PO) _c- H (1)
(In the formula, R is a hydrocarbon group having 1 to 4 carbon atoms. BO is an oxybutylene group, EO is an oxyethylene group, PO is an oxypropylene group. A is an average addition of oxybutylene groups. The number of moles is 3 to 15. b is the average number of moles added of oxyethylene groups and is 4 to 45. c is the average number of moles added of oxypropylene groups and is 2 to 23. a / (A + b + c) is 0.15 to 0.4 and b / (b + c) is 0.65 to 0.9 (EO) _b / (PO) _c is a random addition of EO and PO. Represents.)
[2] The electrolyte is a dicarboxylic acid or an electrolyte containing a salt having a total carbon number of 10 to 14, [1] Symbol mounting electrolyte for the electrolytic capacitor.

  The compound represented by the formula (1) according to the present invention itself has an effect of improving the spark generation voltage of the electrolytic solution for electrolytic capacitors, and is useful as a withstand voltage improver that does not separate in a low temperature region. Further, since the degree of improvement of the spark generation voltage is higher than the degree of increase in the specific resistance, it is possible to suppress the precipitation of crystals in the low temperature region of a long-chain carboxylic acid known as a spark generation voltage improver, so that the withstand voltage improver The electrolytic solution of the present invention containing s is extremely useful in various applications such as a vehicle-mounted capacitor that requires stability in a wide temperature range.

(A) Compound represented by the formula (1) In the formula (1), R is a hydrocarbon group having 1 to 4 carbon atoms, which may be linear or branched, specifically a methyl group. , Ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, and tert-butyl group. R is preferably a methyl group or an ethyl group, and more preferably a methyl group. When the carbon number of R is larger than 4, the solubility of the compound represented by formula (1) in the solvent is lowered.
In Formula (1), a is the average added mole number of an oxybutylene group, and is 3-25, Preferably it is 3-20, More preferably, it is 3-15. When a is less than 3, the dispersibility of the carboxylic acid is lowered and carboxylic acid crystals are precipitated in the electrolytic solution at a low temperature, and when it is more than 25, the solubility of the compound represented by the formula (1) in the solvent is lowered.
In Formula (1), b is an average addition mole number of an oxyethylene group, and is 3-60, Preferably it is 4-50, More preferably, it is 4-45. If b is smaller than 3, the solubility of the compound represented by formula (1) in the solvent is lowered, and if it is larger than 60, crystals of the compound itself represented by formula (1) are likely to precipitate in the electrolyte at a low temperature.
In Formula (1), c is an average addition mole number of an oxypropylene group, and is 0-30, Preferably it is 1-25, More preferably, it is 2-23. When c is larger than 30, the solubility of the compound represented by formula (1) in the solvent is lowered.

In the formula (1), a / (a + b + c) is 0.1 to 0.5, preferably 0.1 to 0.4, and more preferably 0.15 to 0.4. If a / (a + b + c) is less than 0.1, the dispersibility of the carboxylic acid is lowered, and carboxylic acid crystals are precipitated in the electrolyte at a low temperature. If a / (a + b + c) is more than 0.5, the solvent of the compound represented by the formula (1) Solubility is reduced.
In the formula (1), b / (b + c) is 0.6 to 1, more preferably 0.6 to 0.95, and more preferably 0.65 to 0.9. When b / (b + c) is smaller than 0.6, the solubility of the compound represented by the formula (1) in the solvent decreases.
In the formula (1), (EO) _b / (PO) _c represents random addition of EO and PO. If it is a block-like addition, a triblock type structure of lipophilic group-hydrophilic group-lipophilic group may be formed, and the dispersibility of the carboxylic acid is lowered, so that crystals of carboxylic acid are precipitated in the electrolyte at low temperature. This is not preferable.
The molecular weight of the compound represented by the formula (1) is preferably 500 to 10,000, more preferably 800 to 4,000. If the molecular weight is less than 500, a sufficient effect for dispersing the acid cannot be obtained, and if the molecular weight is more than 10,000, the viscosity of the electrolytic solution tends to increase and foaming tends to increase.

The compound represented by the formula (1) is a diblock surfactant comprising a lipophilic oxybutylene group and a hydrophilic oxyethylene group, or a random copolymer of an oxyethylene group and an oxypropylene group. is there. When the compound represented by the formula (1) is blended with a polar solvent and an organic acid, an inorganic acid or a salt thereof and used as an electrolytic solution for an electrolytic capacitor, it is adsorbed to the lipophilic part of the acid by a polyoxybutylene chain. At the same time, the oxyethylene chain or the random copolymer chain of the oxyethylene group and the oxypropylene group is oriented toward the polar solvent to improve the dispersibility of the carboxylic acid in the electrolytic solution. Since the oxybutylene group has a branched ethyl group, the steric repulsion between the molecules is large and has a high dispersion effect. As a result, the capacitor can be stably used in a wide temperature range without lowering the conductivity and spark generation voltage even at low temperatures.
The compound represented by the formula (1) can be produced by a known method. For example, a butylene oxide-alkylene oxide block adduct of alcohol is obtained by addition-polymerizing butylene oxide and alkylene oxides having 2 and 3 carbon atoms in order to an alcohol having 1 to 4 carbon atoms in the presence of an alkali catalyst.

(B) Polar solvent The polar solvent used in the present invention includes monohydric alcohols such as ethanol and propanol, and dihydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol, 1,3-butanediol, and 1,4-butanediol. , Trivalent alcohols such as glycerin, ether solvents such as ethylene glycol monomethyl ether and diethylene glycol diethyl ether, lactone solvents such as γ-butyrolactone, amide solvents such as N-methylformamide, water, etc. Or two or more types may be mixed and used. As the latter example, a mixed solvent of ethylene glycol and water or γ-butyrolactone and water is preferable.

(C) One or more electrolytes selected from the group consisting of organic acids, inorganic acids or salts thereof Examples of inorganic acids used in the present invention include boric acid, and examples of organic acids include maleic acid, adipic acid, Aliphatic carboxylic acids such as azelaic acid, sebacic acid, 1,10-decanedicarboxylic acid, butyloctanedioic acid, 5,6-decanedicarboxylic acid, 1,11-undecanedicarboxylic acid, 1,12-dodecanedicarboxylic acid, benzoic acid Examples thereof include aromatic carboxylic acids such as acid, salicylic acid, phthalic acid, and trimellitic acid. These may be used alone or in combination of two or more, or may be used as a neutralized salt with a basic compound. The organic acid is preferably a dicarboxylic acid having a total carbon number of 10 to 14, and specifically, sebacic acid, 1,10-decanedicarboxylic acid, butyloctanedioic acid, 5,6-decanedicarboxylic acid, 1,11- Examples include undecanedicarboxylic acid and 1,12-dodecanedicarboxylic acid. Examples of basic compounds include tertiary amines such as ammonia, aqueous ammonia, triethylamine, and triethanolamine, polyalkylene polyamines such as ethylenediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine, and alkylene oxide adducts of polyalkylenepolyamine. Can be mentioned. Ammonia and aqueous ammonia are preferred.

In the electrolytic solution of the present invention, the amount of the compound represented by the formula (1) is 0.1 to 50% by mass. If the addition amount is less than 0.1% by mass, the effect of improving the spark generation voltage is insufficient, and if it is more than 50% by mass, the viscosity of the electrolytic solution tends to increase.
EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to this.

[Example 1]
<Synthesis Example 1>
32.0 g (1.0 mol) of methanol and 3.5 g of potassium hydroxide as a catalyst were charged into a 5 L autoclave, the air in the autoclave was replaced with nitrogen, and the catalyst was completely dissolved at 120 ° C. with stirring. I let you. Next, 360.5 g (5.0 mol) of butylene oxide was added dropwise from the dropping device and stirred for 4 hours. Thereafter, a mixture of 882.0 g (20.0 mol) of ethylene oxide and 232.4 g (4.0 mol) of propylene oxide was further added dropwise from a dropping device and stirred for 4 hours. Thereafter, the product was taken out from the autoclave, neutralized with hydrochloric acid to pH 6 to 7, and treated at 100 ° C. for 1 hour at a reduced pressure of −0.095 MPa (gauge pressure, 50 mmHg) in order to remove the contained water. Further, filtration was carried out to remove the salt produced after the treatment, and compound A in Table 1 was obtained.

<Preparation of electrolyte>
It mixed by the composition shown in Table 2, and it stirred until it became uniform at 60 degreeC, and obtained electrolyte solution.
<Appearance evaluation>
The following criteria evaluated the presence or absence of isolation | separation when the electrolyte solution 50g was put into the glass bottle, and left still for 1 hour with a 25 degreeC and -40 degreeC thermostat.
○: No separation or precipitation of crystals is uniform ×: Results of separation of compounds represented by formula (1) or precipitation of crystals of acids and compounds represented by formula (1) are shown in Table 2. Shown in

<Measurement of specific resistance>
The specific resistance at 30 ° C. of the electrolytic solution was measured with an electric conductivity meter (CM-60S manufactured by Toa Radio Industry Co., Ltd.). The results are shown in Table 2.
<Measurement of spark generation voltage>
700 g of the electrolytic solution was put into a 1 L capacity stainless steel container, aluminum foil having a purity of 99.99% or more cut to 60 mm × 10 mm was immersed, and a spark generation voltage of the electrolytic solution at 25 ° C. was measured by connecting a DC power source. The spark generation voltage improvement effect was calculated according to the following equation and evaluated according to the following criteria. The results are shown in Table 2.

[Spark Generation Voltage Improvement Level (V) = Spark Generation Voltage of Electrolyte Solution Added with Compound (a) −Spark Generation Voltage of Electrolyte Solution Not Added with Compound (a)]

○: Spark generation voltage improvement degree is 30 V or more ×: Spark generation voltage improvement degree is less than 30 V Further, the spark generation voltage improvement degree with respect to the specific resistance increase degree is calculated according to the following formula and evaluated according to the following criteria. The results are shown in Table 2.

[Spark generation voltage improvement degree / specific resistance increase degree = (spark generation voltage of electrolyte solution added with compound (a) −spark generation voltage of electrolyte solution not added with compound (a)) / ((a) Specific Resistance of Electrolyte Solution Added with Compound No.-Specific Resistance of Electrolyte Solution Not Added with Compound (a))]

○: Spark generation voltage improvement / specific resistance increase is 1.20 or more ×: Spark generation voltage improvement / specific resistance increase is less than 1.20

[Examples 2 to 9]
In the same manner as in Example 1, compounds B to G shown in Table 1 were synthesized, and an electrolytic solution having a blending composition shown in Table 2 was prepared, and the appearance and electrical characteristics were evaluated. The results are shown in Table 2.
[Comparative Examples 1 to 9]
The compounds H to N shown in Table 1 were synthesized by the same method as in Example 1, and the compounds O and P were synthesized by the following method to prepare an electrolytic solution having the composition shown in Table 2, with or without separation. In addition, the presence or absence of crystal precipitation was evaluated. Moreover, the specific resistance and the spark generation voltage were measured, the spark generation voltage improvement degree was calculated, and the spark generation voltage improvement degree was evaluated and the spark generation voltage improvement degree was evaluated with respect to the specific resistance increase degree. The results are shown in Table 2. In addition, in the evaluation of the appearance of the electrolytic solution, when it was not uniform at 25 ° C., the evaluation at −40 ° C. was not performed.

<Synthesis of Compound O>
46.1 g (1.0 mol) of ethanol and 5.0 g of potassium hydroxide as a catalyst were charged into a 5 L autoclave, the air in the autoclave was replaced with nitrogen, and the catalyst was completely dissolved at 120 ° C. with stirring. I let you. Next, a mixture of 970.2 g (22.0 mol) of ethylene oxide and 1009.4 g (14.0 mol) of butylene oxide was added dropwise from a dropping device, and the mixture was stirred for 4 hours. Thereafter, the product was taken out from the autoclave, neutralized with hydrochloric acid to pH 6 to 7, and treated at 100 ° C. for 1 hour at a reduced pressure of −0.095 MPa (gauge pressure, 50 mmHg) in order to remove the contained water. Further, filtration was carried out to remove the salt produced after the treatment, whereby Compound O was obtained. Compound O is an ethanol-EO22 mol / BO14 mol random adduct (molecular weight 2000).
<Synthesis of Compound P>
32.0 g (1.0 mol) of methanol and 6.0 g of potassium hydroxide as a catalyst were charged into a 5 L autoclave, the air in the autoclave was replaced with nitrogen, and the catalyst was completely dissolved at 120 ° C. with stirring. I let you. Next, 1764.0 g (40.0 mol) of ethylene oxide was dropped from the dropping device, and the mixture was stirred for 4 hours. Thereafter, 581.0 g (10.0 mol) of propylene oxide was further dropped from the dropping device, and the mixture was stirred for 4 hours. Thereafter, the product was taken out from the autoclave, neutralized with hydrochloric acid to pH 6 to 7, and treated at 100 ° C. for 1 hour at a reduced pressure of −0.095 MPa (gauge pressure, 50 mmHg) in order to remove the contained water. Further, filtration was carried out to remove the salt produced after the treatment, whereby Compound P was obtained. Compound P is methanol-EO 40 mol-PO 10 mol block adduct (molecular weight 2400).

  As is apparent from Table 2, the electrolyte solutions of Examples 1 to 9 were uniform without separation and without precipitation of crystals at low temperatures. Further, it has been clarified that the spark generation voltage improvement degree is high and the spark generation voltage improvement degree is high with respect to the specific resistance increase degree. When this electrolytic solution was used for an aluminum electrolytic capacitor, it was confirmed that it showed high conductivity and high spark voltage improvement effect.

On the other hand, since the electrolyte solution of Comparative Example 1 has a carbon number of R larger than the range of the present invention, the solubility of the compound represented by the formula (1) in the solvent is reduced and the electrolyte solution is separated. became.
In Comparative Example 2, since a / (a + b + c) was larger than the range of the present invention, the solubility of the compound represented by formula (1) in the solvent was lowered, and the electrolytic solution was separated.
In Comparative Example 3, since a was larger than the range of the present invention, the solubility of the compound represented by the formula (1) in the solvent was lowered, and the electrolytic solution was separated.
In Comparative Example 4, since a and a / (a + b + c) were smaller than the range of the present invention, acid dispersibility was lowered, and acid crystals were precipitated in the electrolytic solution at a low temperature. Moreover, the spark generation voltage improvement degree was not sufficient, and the spark generation voltage improvement degree with respect to the specific resistance increase degree was also insufficient.
In Comparative Example 5, since b is larger than the range of the present invention, the crystal of the compound represented by the formula (1) and the acid are precipitated in the electrolytic solution at a low temperature, and the spark generation voltage improvement degree with respect to the specific resistance increase degree is high. It was insufficient.
In Comparative Example 6, since a / (a + b + c) was larger than the range of the present invention, the solubility of the compound represented by the formula (1) in the solvent was lowered, and the electrolytic solution was separated.
In Comparative Example 7, since c is larger than the range of the present invention and b / (b + c) is smaller than the range of the present invention, the solubility of the compound represented by the formula (1) in the solvent is lowered, and the electrolytic solution is reduced. separated.
In Comparative Example 8, since the component (a) is different from the compound represented by the formula (1) of the present invention and EO and BO are random addition, the solubility of the compound represented by the formula (1) in the solvent is low. The electrolyte solution separated.
In Comparative Example 9, since the component (a) is different from the compound represented by the formula (1) of the present invention and does not contain BO, the dispersibility of the acid is lowered, and the crystal of the acid is present in the electrolyte at a low temperature. Precipitated. Moreover, the spark generation voltage improvement degree was not sufficient, and the spark generation voltage improvement degree with respect to the specific resistance increase degree was also insufficient.

Claims (2)

An electrolytic solution for an electrolytic capacitor containing the following components (a), (b), and (c):
(A) Compound represented by formula (1) (b) Polar solvent (c) One or more electrolytes selected from the group consisting of organic acids, inorganic acids or salts thereof R—O— (BO) _a — ( EO) _b / (PO) _c- H (1)
(In the formula, R is a hydrocarbon group having 1 to 4 carbon atoms. BO is an oxybutylene group, EO is an oxyethylene group, PO is an oxypropylene group. A is an average addition of oxybutylene groups. The number of moles is 3 to 15. b is the average number of moles added of oxyethylene groups and is 4 to 45. c is the average number of moles added of oxypropylene groups and is 2 to 23. a / (A + b + c) is 0.15 to 0.4 and b / (b + c) is 0.65 to 0.9 (EO) _b / (PO) _c is a random addition of EO and PO. Represents.) Electrolyte, an electrolyte containing a dicarboxylic acid or a salt thereof having a total carbon number of 10 to 14, the electrolytic solution for electrolytic capacitor according to claim 1 Symbol placement.