JP4081617B2 - Electrolytic solution for electrolytic capacitors - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrolytic solution for electrolytic capacitors, and more particularly to an electrolytic solution for medium to high pressure.
[0002]
[Prior art]
The electrolytic solution for the electrolytic capacitor uses a valve metal having an insulating oxide film formed on the surface of aluminum or tantalum as an anode electrode, and the oxide film layer is a dielectric, and an electrolyte layer is formed on the surface of the oxide film layer. And an electrode for current collection, usually called a cathode, is arranged.
[0003]
The electrolytic solution for electrolytic capacitors directly contacts the dielectric layer as described above and acts as a true cathode. That is, the electrolytic solution is interposed between the dielectric of the electrolytic capacitor and the current collecting cathode, and the resistance component of the electrolytic solution is inserted in series with the electrolytic capacitor. Therefore, the characteristics of the electrolytic solution are a major factor that affects the characteristics of the electrolytic capacitor.
[0004]
In the prior art of electrolytic capacitors, an electrolytic solution in which boric acid or ammonium borate is dissolved as a solute in a solvent made of ethylene glycol has been used because a spark voltage is relatively high as an electrolytic solution for medium and high pressures. However, in such an electrolytic solution, electrical conductivity is low, and a large amount of water is produced by esterification of ethylene glycol and boric acid. The problem of being easy to react with the liquid also occurred, and it was not suitable for use at high temperatures.
[0005]
In order to solve these disadvantages, organic dicarboxylic acids such as sebacic acid and azelaic acid are sometimes used, but these have low solubility, so that crystals are likely to precipitate at low temperatures, which deteriorates the low temperature characteristics of capacitors. I couldn't escape the drawback of making it happen. Furthermore, as shown in JP-B-60-13296, examples using butyloctanedioic acid as a solute, and as shown in JP-B-63-15738, 5,6-decanedicarboxylic acid is used as a solute. There is an example used. Electrolytic solutions using these dibasic acids or their salts have high spark voltage and electrical conductivity, are very slow in esterification, and produce little water, so that stability at high temperatures can be obtained.
[0006]
[Problems to be solved by the invention]
However, in recent years, the operating speed of inverters using medium- and high-voltage electrolytic capacitors has been increased, and there has been a demand for a highly reliable electrolytic solution that has high spark voltage and electrical conductivity and is stable at high temperatures. It has been.
[0007]
The present invention pays attention to the fact that the use of aliphatic saturated dicarboxylic acid having a large molecular weight increases the spark voltage. If a specific aliphatic saturated dicarboxylic acid is used in the electrolyte, the spark voltage and conductivity are high and stable at high temperatures. It is an object of the present invention to provide an electrolyte for medium and high pressures that has a high spark voltage and electrical conductivity and is stable at high temperatures.
[0008]
[Means for Solving the Problems]
In order to solve the above problems, the electrolytic solution for an electrolytic capacitor of the present invention has a general formula:
[0009]
[Chemical 2]
Wherein R ₁ is an alkyl group having 2 to 4 carbon atoms or a hydrogen atom, R ₂ to R ₄ are alkyl groups having 1 to ₄ carbon atoms or a hydrogen atom, and at least two of R ₁ to R ₄ And an aliphatic saturated dicarboxylic acid compound having a total carbon number of 12 to 20 or a salt thereof represented by the following formula:
[001 0 ]
Further, the aliphatic saturated dicarboxylic acid (chemical formula 2) dissolved in the electrolytic solution is characterized in that the alkyl group of R ₁ to R _{4 is} an alkyl group having 3 to 4 carbon atoms.
[001 1 ]
Further, R _{1 of} the aliphatic saturated dicarboxylic acid (Chemical Formula 2) dissolved in the electrolytic solution is a hydrogen atom.
[001 2 ]
DETAILED DESCRIPTION OF THE INVENTION
Of the present invention, examples of aliphatic saturated dicarboxylic acids, 2,4─ diethyl ─7─ methyl ─1,7─ heptane dicarboxylic acid, 2,4─ diisopropyl ─7─ methyl ─1,7─ heptane dicarboxylic acid, 1-isobutyl-3-ethyl-7-methyl-1,7-heptanedicarboxylic acid, 2-isobutyl-3-propyl-7-methyl-1,7-heptanedicarboxylic acid, 1,4,7-trimethyl-1, 7-heptanedicarboxylic acid, 1-ethyl-2, 4-dibutyl-7-methyl-1,7-heptanedicarboxylic acid, and the like.
[001 3 ]
Generally, 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 conductivity decreases accordingly. Furthermore, since the solubility is also reduced, it is impossible to increase the conductivity by increasing the concentration.
[001 4 ]
However, the aliphatic saturated dicarboxylic acid represented by (Chemical Formula 2) of the present invention maintains high solubility even when the total number of carbon atoms is large. The reason is considered to be due to having an alkyl group as a side chain at the position shown in (Chemical Formula 2). And since solubility improves in this way, the density | concentration of the aliphatic saturated dicarboxylic acid shown by (Chemical Formula 2) can be raised, and it becomes possible to obtain high electroconductivity. Furthermore, even if the concentration is increased in this way, the spark voltage does not decrease. Further, it is possible to enhance the indicated chlorine resistance is also improved by increasing the concentration of aliphatic saturated dicarboxylic acids, at least two of of from R ₁ R ₄ is an alkyl group, further solubility (of 2) .
[001 5 ]
In the aliphatic saturated dicarboxylic acid represented by (Chemical Formula 2), when the alkyl group of R ₁ to R _{4 is} an alkyl group having 3 to 4 carbon atoms, the solubility can be further increased.
[001 6 ]
In addition, in such an organic acid having a carboxyl group, when a solvent having a hydroxyl group such as ethylene glycol is used, the esterification reaction by the carboxyl group and the hydroxyl group usually proceeds during high-temperature storage, resulting in a decrease in conductivity. There is a phenomenon.
[001 7 ]
However, in the aliphatic saturated dicarboxylic acid represented by (Chemical Formula 2) of the present invention, an alkyl group is bonded to at least one of the carbon atoms bonded to the carboxyl group. This steric hindrance of the alkyl group reduces the reactivity of the carboxyl group. As a result, even when a solvent having a hydroxyl group such as ethylene glycol is used, the esterification reaction by the carboxyl group and the hydroxyl group is difficult to occur, and the decrease in conductivity during high-temperature storage can be suppressed. As a result, in an electrolytic capacitor using this electrolytic solution, an increase in tan δ after high-temperature storage can be suppressed.
[00 18 ]
Further, when R ₁ is a hydrogen atom, the reactivity of the carboxyl group is not lowered and the degree of dissociation is not reduced, so that higher conductivity can be obtained.
[0019]
The total number of carbon atoms of the aliphatic saturated dicarboxylic acid of the present invention is 12 to 20, preferably 12 to 16. Even in the aliphatic saturated dicarboxylic acid of the present invention, if the total number of carbon atoms exceeds 20, high conductivity cannot be obtained even if the concentration is increased. Moreover, if the total number of carbon atoms is less than 12 , a high spark voltage cannot be obtained. Flame voltage, considering the balance of conductivity, the total number of carbon atoms is preferably from 12 to 16.
[00 20 ]
Examples of the aliphatic saturated dicarboxylate of the present invention include an ammonium salt, an amine salt, a quaternary ammonium salt, and a quaternary salt of a cyclic amidine compound. As amines constituting the amine salt, 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, etc.). The quaternary ammonium constituting the quaternary ammonium salt includes tetraalkylammonium (tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, methyltriethylammonium, dimethyldiethylammonium, etc.), pyridium (1-methylpyridium) 1-ethylpyridium, 1,3-diethylpyridium, etc.). Examples of the cation constituting the quaternary salt of the cyclic amidine compound include cations obtained by quaternizing the following compounds. That is, imidazole monocyclic compounds (1-methylimidazole, 1,2-dimethylimidazole, 1,4-dimethyl-2-ethylimidazole, imidazole homologues such as 1-phenylimidazole, 1-methyl-2-oxymethylimidazole, Oxyalkyl derivatives such as 1-methyl-2-oxyethylimidazole, nitro and amino derivatives such as 1-methyl-4 (5) -nitroimidazole, 1,2-dimethyl-4 (5) -nitroimidazole), benzimidazole (1-methylbenzimidazole, 1-methyl-2-benzylbenzimidazole, etc.), compounds having a 2-imidazoline ring (1-methylimidazoline, 1,2-dimethylimidazoline, 1,2,4-trimethylimidazoline, 1, 4-Dimethyl-2-ethylimidazoli , 1-methyl-2-phenylimidazoline, etc.), compounds having a tetrahydropyrimidine ring (1-methyl-1,4,5,6-tetrahydropyrimidine, 1,2-dimethyl-1,4,5,6-tetrahydropyrimidine) 1,8-diazabicyclo [5.4.0] undecene-7, 1,5-diazabicyclo [4.3.0] nonene, etc.). Of these, ammonium salts are preferred.
[002 1 ]
The organic polar solvent is generally a solvent mainly composed of glycols of protic polar solvents, but aprotic polar solvents 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 oxyalcohol compounds ( Ethylene glycol, propylene glycol, glycerin, methyl cellosolve, 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, N --Ethylacetamide, N, N-diethylacetamide, hexamethylphosphoricamide, etc.), lactones, cyclic amides (γ-butyrolactone, N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, isobutylene carbonate, Typical examples include isobutylene carbonate and the like, nitrile type (acetonitrile and the like), oxide type (dimethyl sulfoxide and the like), and the like.
[002 2 ]
The content of the aliphatic saturated dicarboxylic acid represented by (Chemical formula 1) in the electrolytic capacitor for electrolytic capacitors of the present invention is usually 0.1 to 30% by weight, preferably 3 to 20% based on the weight of the electrolytic solution. .
[002 3 ]
Further, by adding boric acid, mannitol, nonionic surfactant, colloidal silica or the like to the electrolytic solution for electrolytic capacitors of the present invention, the effect can be improved.
[002 4 ]
Various additives can be added for the purpose of reducing leakage current or absorbing hydrogen gas. Examples of the additive include aromatic nitro compounds, phosphoric acid, phosphorous acid, polyphosphoric acid, acidic phosphoric acid ester compounds, and the like.
[002 5 ]
【Example】
Examples of the present invention will be described below.
[002 6 ]
(Table 1) shows the composition, spark voltage and conductivity of the electrolytic capacitor electrolyte solution of each example of the present invention, and (Table 2) shows the composition of the electrolytic capacitor electrolyte solution, spark voltage, and It shows the conductivity.
[002 7 ]
[Table 1]
[00 28 ]
[Table 2]
[00 29 ]
(Table 1), as is clear from (Table 2), as compared with Example 1-3 Comparative Example 1-4, the spark voltage is kept high, and, what is obtained with high conductivity, R ₁ Since aliphatic saturated dicarboxylic acid in which two or more of R ₄ are alkyl groups is used, the concentration of the aliphatic saturated dicarboxylic acid can be increased. In the case of Example 2 in which an aliphatic saturated dicarboxylic acid whose alkyl group in the side chain is an isobutyl group having 4 carbon atoms is used, the concentration of the aliphatic saturated dicarboxylic acid can be increased. In Examples 1 and 3 in which R ₁ is a hydrogen atom, higher electrical conductivity is obtained in consideration of molecular weight and concentration.
[003 0 ]
(Table 3) shows the results of preparing 20 aluminum electrolytic capacitors each using the electrolytic solution for electrolytic capacitors shown in (Table 1) and (Table 2), and conducting a life test on these aluminum electrolytic capacitors. It is shown. The ratings of the aluminum electrolytic capacitors used here were 450 WV 180 μF, and the storage treatment was performed at 105 ° C. for 1000 hours under the condition where 450 V was applied.
[003 1 ]
[Table 3]
[003 2 ]
As apparent from Table 3, the aluminum electrolytic capacitors using the electrolytic solutions of Examples 1 to 3 of the present invention have small initial tan δ, capacitance change after storage treatment, and tan δ change. Thus, the aluminum electrolytic capacitors using Examples 1 to 3 of the present invention are highly reliable aluminum electrolytic capacitors having a small initial tan δ and excellent life characteristics.
[0033]
【The invention's effect】
As described above, the electrolytic solution for an electrolytic capacitor of the present invention is represented by (Chemical Formula 2) in a solvent mainly composed of an organic polar solvent, and R _{1 in} (Chemical Formula 2) is an alkyl group having 2 to 4 carbon atoms or An aliphatic group having a total carbon number of 12 to 20, which is a hydrogen atom, R ₂ to R ₄ are an alkyl group having 1 to ₄ carbon atoms or a hydrogen atom, and at least two of R ₁ to R ₄ are an alkyl group; A saturated dicarboxylic acid compound or a salt thereof is dissolved as a solute.
[003 4 ]
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 the spark voltage does not decrease at that time. Therefore, it is possible to improve the flame voltage and conductivity, since at least two of of from R ₁ R ₄ is an alkyl group, it is possible to further increase the solubility.
[003 5 ]
Also, the solubility can be increased when the alkyl group has 3 to 4 carbon atoms.
[003 6 ]
Furthermore, in the aliphatic saturated dicarboxylic acid shown in (Chemical Formula 2), an alkyl group is bonded to at least one of the carbon atoms bonded to the carboxyl group. This steric hindrance of the alkyl group reduces the reactivity of the carboxyl group. As a result, even when a solvent having a hydroxyl group such as ethylene glycol is used, the esterification reaction due to the carboxyl group and the hydroxyl group is less likely to occur, and a decrease in conductivity during high-temperature storage can be further suppressed. Stability can be obtained.
[00 37 ]
Further, when R ₁ is a hydrogen atom, the reactivity of the carboxyl group is not lowered and the degree of dissociation is not reduced, so that a higher electrical conductivity can be maintained.
[00 38 ]
Therefore, by using the electrolytic solution of the present invention, it is possible to obtain a highly reliable electrolytic capacitor for medium and high voltage with low tan δ.

Claims (3)

In a solvent mainly composed of an organic polar solvent, a general formula:
Wherein R ₁ is an alkyl group having 2 to 4 carbon atoms or a hydrogen atom, R ₂ to R ₄ are alkyl groups having 1 to ₄ carbon atoms or a hydrogen atom, and at least two of R ₁ to R ₄ One is an alkyl group.) An electrolytic solution for an electrolytic capacitor in which an aliphatic saturated dicarboxylic acid compound having 12 to 20 carbon atoms or a salt thereof is dissolved. The electrolytic solution for electrolytic capacitor according to claim 1, wherein the alkyl group of R ₁ to R ₄ of the aliphatic saturated dicarboxylic acid compound (Chemical Formula 1) is an alkyl group having 3 to 4 carbon atoms. The electrolytic solution for an electrolytic capacitor according to claim 1, wherein R _{1 of the} aliphatic saturated dicarboxylic acid compound (Chemical Formula 1) is a hydrogen atom.