JPH10321478A - Electrolyte for electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolyte for intermediate and high voltages which has a high sparking voltage, high conductivity, and high-temperature stability. SOLUTION: An electrolyte for electrolytic capacitor is obtained by dissolving a 10-17C aliphatic saturated dicarboxylic acid compound expressed by the formula or its salt in a solvent composed mainly of an organic polar solvent. Since the compound expressed by the formula is used as the solute of the electrolyte, the sparking voltage of the electrolyte is improved. In addition, since the compound has an alkylic group as a side chain at a specific position, the compound has high solubility to the solvent and increases the concentration of the solute in the electrolyte. Therefore, the electrolyte can obtain high conductivity while maintaining the high sparking voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolytic solution for electrolytic capacitors, and more particularly to an electrolytic solution for medium and high pressures.

[0002]

2. Description of the Related Art An electrolytic solution for an electrolytic capacitor uses a valve metal having an insulating oxide film formed on the surface such as aluminum or tantalum for an anode electrode, and uses the oxide film layer as a dielectric material. An electrolyte for forming an electrolyte layer is brought into contact with the surface of the substrate, and a current collecting electrode usually called a cathode is arranged.

As described above, the electrolytic solution for an electrolytic capacitor directly contacts the dielectric layer and acts as a true cathode. That is, the electrolytic solution is interposed between the dielectric of the electrolytic capacitor and the collector cathode, and the resistance of the electrolytic solution is inserted in series with the electrolytic capacitor. Therefore, the characteristics of the electrolytic solution are a major factor affecting the characteristics of the electrolytic capacitor.

In the prior art of electrolytic capacitors, since a relatively high spark voltage can be obtained as an electrolytic solution for medium and high pressures, an electrolytic solution in which boric acid or ammonium borate is dissolved as a solute in a solvent composed of ethylene glycol is used. I was However, such an electrolytic solution has a low electric conductivity and a large amount of water is generated by esterification of ethylene glycol and boric acid.
If the temperature is 0 ° C. or higher, the internal pressure increases due to the evaporation of water, and there is a problem in that the internal pressure easily reacts with aluminum as an electrode.

In order to solve such a drawback, organic dicarboxylic acids such as sebacic acid and azelaic acid are sometimes used. However, since these compounds have low solubility, crystals are easily precipitated at low temperatures and low temperatures of capacitors. The disadvantage of deteriorating the characteristics could not be avoided. Furthermore, Tokiko Sho 60
As disclosed in JP-A-13-13296, an example using butyloctane diacid as a solute or JP-B-63-15538.
There is an example in which 5,6-decanedicarboxylic acid is used as a solute as shown in Japanese Patent Application Laid-Open Publication No. H11-209,878. Electrolyte solutions using these dibasic acids or salts thereof have high sparking voltage and conductivity, are very slow in esterification, and generate little water, so that high-temperature stability can be obtained.

[0006]

However, in recent years,
The operating speed of an inverter using a medium-to-high voltage electrolytic capacitor has been increased to a higher frequency, and furthermore, a highly reliable electrolytic solution having a high spark voltage and a high electrical conductivity, and being stable at a high temperature has been demanded.

The present invention focuses on the fact that the use of an aliphatic saturated dicarboxylic acid having a large number of molecules increases the spark voltage.
It has been found that if a specific aliphatic saturated dicarboxylic acid is used for the electrolyte, the spark voltage and the conductivity are high, and a stable electrolytic solution can be obtained at a high temperature.The spark voltage and the conductivity are high and the It is an object of the present invention to provide an electrolyte solution for medium and high pressure which is stable.

[0008]

In order to solve the above-mentioned problems, an electrolytic solution for an electrolytic capacitor of the present invention comprises a solvent mainly composed of an organic polar solvent represented by a general formula:

[0009]

Embedded image (Wherein, R is an alkyl group having 1 to 8 carbon atoms), and is characterized by dissolving an aliphatic saturated dicarboxylic acid compound having 10 to 17 carbon atoms represented by the following formula or a salt thereof. Further, the alkyl group of R in the aliphatic saturated dicarboxylic acid compound (formula 2) is an alkyl group having 3 or more carbon atoms.

[0010]

DETAILED DESCRIPTION OF THE INVENTION Examples of the aliphatic saturated dicarboxylic acid of the present invention include 1,1,3,4-tetramethyl-1,
4-butanedicarboxylic acid, 1,1,3-trimethyl-4
-Ethyl-1,4-butanedicarboxylic acid, 1,1,3
-Trimethyl-4-propyl-1,4-butanedicarboxylic acid, 1,1,3-trimethyl-4-butyl-1,4-
Butanedicarboxylic acid, 1,1,3-trimethyl-4-pentyl-1,4-butanedicarboxylic acid, 1,1,3-trimethyl-4-hexyl-1,4-butanedicarboxylic acid, 1,1,3- Trimethyl-4-heptyl-1,4-
Butanedicarboxylic acid and 1,1,3-trimethyl-4-octyl-1,4-butanedicarboxylic acid.

In general, when the total number of carbon atoms of the organic carboxylic acid used in the electrolytic solution of the electrolytic capacitor increases, the spark voltage increases for a certain concentration, but the electrical conductivity decreases accordingly. Furthermore, since the solubility is reduced, it is not possible to increase the concentration to increase the electric conductivity.

However, the aliphatic saturated dicarboxylic acid represented by the formula (2) of the present invention has an alkyl group as a side chain at the position represented by the formula (2). As a result, the solubility is improved, so that high conductivity can be obtained by increasing the concentration, and at that time, the spark voltage does not decrease. In addition, increasing the concentration also improves the chlorine resistance.

In the case of using a solvent having a hydroxyl group, such as ethylene glycol, in such an organic acid having a carboxyl group, the esterification reaction between the carboxyl group and the hydroxyl group usually proceeds during storage at a high temperature, and the conductivity is increased. Is reduced.

However, in the aliphatic saturated dicarboxylic acid represented by the chemical formula (2) of the present invention, two methyl groups are bonded to a carbon atom bonded to one carboxyl group, and in addition, the other Since the alkyl group R is bonded to the carbon atom bonded to the group, the reactivity between the carboxyl group and the hydroxyl group is reduced due to the steric hindrance of the methyl group and the alkyl group. As a result, even when a solvent having a hydroxyl group such as ethylene glycol is used, the esterification reaction between the carboxyl group and the hydroxyl group is less likely to occur, and a decrease in conductivity during high-temperature storage can be suppressed. Therefore, in an electrolytic capacitor using this electrolytic solution, an increase in tan δ after storage at a high temperature can be suppressed.

At this time, since a hydrogen atom is bonded to the carbon atom to which the alkyl group is bonded, the degree of dissociation of the carboxyl group is not reduced, and high conductivity can be maintained.
Here, when this hydrogen atom is an alkyl group, the electric conductivity decreases. In the case of trimethyladipic acid, in which the alkyl group is a hydrogen atom, the spark voltage is low,
Furthermore, the effect of suppressing an increase in tan δ after high-temperature storage is small. As described above, in the aliphatic saturated carboxylic acid represented by the chemical formula (2) of the present invention, the molecular structure as described above acts to reduce the conductivity during high-temperature storage while maintaining the high conductivity. It is presumed that the suppression of the above has been performed.

When the alkyl group of R is an alkyl group having 3 or more carbon atoms, the increase in tan δ after high-temperature storage can be further suppressed. This means that this alkyl group
This is probably because the esterification reaction between the carboxyl group and the hydroxyl group was suppressed while maintaining the degree of dissociation of the carboxyl group.

The total number of carbon atoms of the aliphatic saturated dicarboxylic acid of the present invention is 10 to 17. In the aliphatic saturated dicarboxylic acid of the present invention, if the total number of carbon atoms is less than 10, the spark voltage tends to decrease, and if the total number of carbon atoms exceeds 17, the conductivity does not increase so much even if the concentration is increased.

The aliphatic saturated dicarboxylic acid salt of the present invention includes ammonium salts, amine salts, quaternary ammonium salts and quaternary salts of cyclic amidine compounds of aliphatic saturated dicarboxylic acids. Examples of the amine constituting the amine salt include primary amines (methylamine, ethylamine, propylamine, butylamine, ethylenediamine, etc.), secondary amines (dimethylamine, diethylamine, dipropylamine, methylethylamine, diphenylamine, etc.), tertiary amines ( Trimethylamine, triethylamine, tripropylamine, triphenylamine, 1,8-diazabicyclo (5,4,0) -undecene-7). As the quaternary ammonium constituting the quaternary ammonium salt, tetraalkylammonium (tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, methyltriethylammonium, dimethyldiethylammonium, etc.), pyridium (1-methylpyridium) , 1-ethylpyridium, 1,3-diethylpyridium, etc.). In addition, examples of the cation constituting the quaternary salt of the cyclic amidine compound include cations obtained by quaternizing the following compounds. That is, the imidazole monocyclic compound (1
-Methylimidazole, 1,2-dimethylimidazole, 1,4-dimethyl-2-ethylimidazole, 1-
Imidazole homologs such as phenylimidazole, 1-methyl-2-oxymethylimidazole, 1-methyl-2
Oxyalkyl derivatives such as -oxyethylimidazole, 1-methyl-4 (5) -nitroimidazole,
Nitro and amino derivatives such as 2-dimethyl-4 (5) -nitroimidazole, benzimidazole (such as 1-methylbenzimidazole and 1-methyl-2-benzylbenzimidazole), and compounds having a 2-imidazoline ring (1- Methylimidazoline, 1,2-dimethylimidazoline, 1,2,4-trimethylimidazoline, 1,
4-dimethyl-2-ethylimidazoline, 1-methyl-
2-phenylimidazoline, etc.), compounds having a tetrahydropyrimidine ring (1-methyl-1,4,5,6-tetrahydropyrimidine, 1,2-dimethyl-1,4,4)
5,6-tetrahydropyrimidine, 1,8-diazabicyclo [5.4.0] undecene-7, 1,5-diazabicyclo [4.3.0] nonene, and the like. Of these, ammonium salts are preferred.

The organic polar solvent is generally a solvent mainly comprising glycols of a protic polar solvent, but an aprotic polar solvent can also be used. Protic organic polar solvents include monohydric alcohols (ethanol, propanol, butanol, pentanol,
Hexanol, cyclobutanol, cyclopentanol, cyclohexanol, benzyl alcohol, etc.), polyhydric alcohols and oxy alcohol compounds (ethylene glycol, propylene glycol, glycerin,
Methylcellosolve, ethyl cellosolve, methoxypropylene glycol, dimethoxypropanol, etc.). Examples of aprotic organic polar solvents include amides (N-methylformamide, N, N-dimethylformamide, N-ethylformamide, N, N-diethylformamide, N-methylacetamide, N, N-dimethylacetamide, -Ethylacetamide, N, N-
Diethylacetamide, hexamethylphosphoric amide, etc.), lactones, cyclic amides (γ-butyrolactone, N-methyl-2-pyrrolidone, ethylene carbonate, propylene-carbonate, isobutylene carbonate, isobutylene carbonate, etc.), nitriles (Acetonitrile and the like), oxides (dimethylsulfoxide and the like) and the like.

The content of the aliphatic saturated dicarboxylic acid represented by Chemical Formula 1 in the electrolytic capacitor of the present invention is usually 0.1 to 30% by weight, preferably 3 to 20% by weight based on the weight of the electrolytic solution. %. If it is less than 3%, the electric conductivity decreases, and if it exceeds 20%, the spark voltage decreases.

Further, by adding boric acid, mannitol, nonionic surfactant, colloidal silica and the like to the electrolytic solution for an electrolytic capacitor of the present invention, the effect can be improved.

Various additives can be added for the purpose of reducing leakage current and absorbing hydrogen gas. Examples of the additive include an aromatic nitro compound, phosphoric acid, phosphorous acid, polyphosphoric acid, an acidic phosphoric acid ester compound, an oxycarboxylic acid compound, and the like.

[0023]

Embodiments of the present invention will be described below.

(Table 1) and (Table 2) show the composition, spark voltage and conductivity of the electrolytic solution for the electrolytic capacitor of each embodiment of the present invention, and (Table 3) show the electrolytic solution for the electrolytic capacitor of the comparative example. 3 shows the composition of the liquid, the spark voltage and the conductivity.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

[Table 3]

As is clear from Tables 1 to 3,
In Examples 1 to 11, the spark voltage was maintained higher and the electric conductivity was higher than those in Comparative Examples 1 to 4.

In Tables 4 and 5, 20 aluminum electrolytic capacitors each using the electrolytic solution for electrolytic capacitors shown in Tables 1 to 3 were prepared, and these aluminum electrolytic capacitors were prepared. 3 shows the results of a life test performed on the sample. The rating of the aluminum electrolytic capacitor used here is 45 in the case of (Table 4).
0WV220μF, and in the case of (Table 5), 400W
V220 μF. The preservation treatment was performed at 105 ° C. for 1000 hours under the conditions of applying 450 V and 400 V, respectively.

[0030]

[Table 4]

[0031]

[Table 5]

As apparent from (Table 4) and (Table 5),
In the aluminum electrolytic capacitors using the electrolytic solutions of Examples 1 to 11 of the present invention, the initial tan δ, the change in capacitance after the preservation treatment, and the change in tan δ are all small.

In Examples 3 to 5 and 8 to 11 in which the alkyl group of R has 3 or more carbon atoms, R has 1 carbon atom.
The tan δ after the preservation treatment is more stable as compared with Examples 1, 2, and 6, and 7, which are 2.

As described above, the aluminum electrolytic capacitors using Examples 1 to 11 of the present invention are small in initial tan δ and have high life characteristics and high reliability.

[0035]

As described above, the electrolytic solution for an electrolytic capacitor of the present invention is represented by the formula (2) in a solvent mainly composed of an organic polar solvent, wherein R in the formula (2) has 1 to 8 carbon atoms. The compound is obtained by dissolving an aliphatic saturated dicarboxylic acid compound having a total of 10 to 17 carbon atoms or a salt thereof as a solute.

This aliphatic saturated dicarboxylic acid has an alkyl group as a side chain at the position shown in Chemical formula 2. As a result, the solubility is improved, so that high conductivity can be obtained by increasing the concentration, and at that time, the spark voltage does not decrease. Therefore, the spark voltage and the electric conductivity can be kept high.

Further, in the aliphatic saturated dicarboxylic acid represented by the chemical formula (2), two methyl groups are bonded to a carbon atom bonded to one carboxyl group, and in addition, another methyl group is bonded to the other carboxyl group. Since the alkyl group R is bonded to the bonded carbon atom, the reactivity between the carboxyl group and the hydroxyl group is reduced by the steric hindrance of the methyl group and the alkyl group. As a result, even when a solvent having a hydroxyl group such as ethylene glycol is used, the esterification reaction between the carboxyl group and the hydroxyl group is less likely to occur, and a decrease in conductivity during high-temperature storage can be suppressed. Therefore, in an electrolytic capacitor using this electrolytic solution, an increase in tan δ after storage at a high temperature can be suppressed, and stability at a high temperature can be obtained.

At this time, since a hydrogen atom is bonded to the carbon atom to which the alkyl group is bonded, the degree of dissociation of the carboxyl group is maintained, and high conductivity can be maintained.

When the alkyl group of R is an alkyl group having 3 or more carbon atoms, the esterification reaction between the carboxyl group and the hydroxyl group is further suppressed while maintaining the degree of dissociation of the carboxyl group, and tan δ after storage at high temperature. Can be suppressed.

Therefore, by using the electrolytic solution of the present invention, a high-reliability electrolytic capacitor having a low tan δ and a high reliability can be obtained.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor: Masao Takagi 10-day Nippon Adtech Co., Ltd., 4-1-1 Nishi-Shinjuku, Shinjuku-ku, Tokyo

Claims (2)

[Claims] (1) A solvent mainly composed of an organic polar solvent, a compound represented by the following general formula: (In the formula, R is an alkyl group having 1 to 8 carbon atoms.) An electrolytic solution for an electrolytic capacitor in which an aliphatic saturated dicarboxylic acid compound having a total of 10 to 17 carbon atoms or a salt thereof is dissolved. 2. The electrolytic solution for an electrolytic capacitor according to claim 1, wherein the R alkyl group of the aliphatic saturated dicarboxylic acid compound (Chem. 1) is an alkyl group having 3 or more carbon atoms.