JP4081615B2 - 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 a spark voltage is increased when an aliphatic saturated dicarboxylic acid having a large number of molecules is used. When a specific aliphatic saturated dicarboxylic acid is used in an electrolyte, the spark voltage and the conductivity are high, and at a high temperature. It has been found that a stable electrolytic solution can be obtained, and an object thereof is to provide a medium-high pressure electrolytic solution 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 to R ₈ are an alkyl group having 1 to 4 carbon atoms or a hydrogen atom, and at least two are alkyl groups) and an aliphatic saturated dicarboxylic acid compound having a total carbon number of 14 to 24 Alternatively, the salt is dissolved.
[0010]
Further, the alkyl group of R ₁ to R ₈ of the aliphatic saturated dicarboxylic acid (Chemical Formula 2) dissolved in the electrolytic solution is an alkyl group having 3 to 4 carbon atoms.
[0011]
In addition, R _{5 of} the aliphatic saturated dicarboxylic acid (Chemical Formula 2) dissolved in the electrolytic solution is an alkyl group.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Of the present invention, examples of aliphatic saturated dicarboxylic acids are 1,6-dimethyl ─1,6─ decanedicarboxylic acid, 2,8─ dimethyl ─1,6─ decanedicarboxylic acid, 2,7─ diethyl ─1, 6-decanedicarboxylic acid, 3,7-diethyl-1,6-decanedicarboxylic acid, 3,8-diethyl-1,6-decanedicarboxylic acid, 3,7-diisopropyl-1,6-decanedicarboxylic acid, 3, 7-dibutyl-1,6-decanedicarboxylic acid, 2-butyl-1,6-dimethyl-1,6-decanedicarboxylic acid, 2-butyl-7,9-diethyl-1,6-decanedicarboxylic acid, 2, 7-diisobutyl-1,6-dimethyl-1,6-decanedicarboxylic acid, 2,7-diisobutyl-3,6-diethyl-1,6-decanedicarboxylic acid, 2,4,6,8-tetramethyl-1 , 6-de Candicarboxylic acid, 2,4,7,9-tetramethyl-1,6-decanedicarboxylic acid, and the like.
[0013]
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.
[0014]
However, the aliphatic saturated dicarboxylic acid represented by (Chemical Formula 2) of the present invention has an alkyl group as a side chain at the position represented by (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. Further, chlorine resistance is also improved by increasing the concentration, since at least two of of from R ₁ R ₈ is an alkyl group, it is possible to further increase the solubility.
[001 5 ]
In the aliphatic saturated dicarboxylic acid represented by (Chemical Formula 2), when the alkyl group of R ₁ to R _{8 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, the aliphatic saturated dicarboxylic acid represented by (Chemical Formula 2) of the present invention has an alkyl group, particularly an alkyl group represented by (Chemical Formula 3), on the carbon atom 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.
[001 8 ]
Further, in (Chemical Formula 2), when R ₅ is an alkyl group attached to the other carbon atom bonded to the carboxyl group, this effect becomes remarkable.
[00 19 ]
[Chemical 3]
[0020]
The total number of carbon atoms of the aliphatic saturated dicarboxylic acid of the present invention is 14 to 24, preferably 14 to 16. Even in the aliphatic saturated dicarboxylic acid of the present invention, if the total number of carbon atoms exceeds 24, high conductivity cannot be obtained even if the concentration is increased. Moreover, if the total number of carbon atoms is less than 14 , a high spark voltage cannot be obtained. Considering the balance of spark voltage and conductivity, the total carbon number is preferably 14-16 .
[00 21 ]
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 2 ]
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 3 ]
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 4 ]
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 5 ]
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 6 ]
【Example】
Examples of the present invention will be described below.
[002 7 ]
(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 8 ]
[Table 1]
[00 29 ]
[Table 2]
[003 0 ]
As is clear from (Table 1) and (Table 2), in Examples 1 to 3 , the spark voltage is maintained higher than that in Comparative Examples 1 to 4, and a high conductivity is obtained. Further, since the aliphatic saturated dicarboxylic acid having two or more alkyl groups in the side chain is used , the concentration of this aliphatic saturated dicarboxylic acid can be increased as compared with Comparative Examples 5 and 6 .
[003 1 ]
(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 2 ]
[Table 3]
[003 3 ]
As apparent from (Table 3), the aluminum electrolytic capacitors using the electrolytic solutions of Examples 1 to 3 of the present invention are small in initial tan δ, capacitance change after storage treatment, and tan δ change, In particular, in Examples 1 and 3 using an aliphatic saturated dicarboxylic acid in which R ₅ is an alkyl group in (Chemical Formula 2), the tan δ change is even smaller. Thus, the aluminum electrolytic capacitors using Examples 1 to 5 of the present invention are highly reliable aluminum electrolytic capacitors having a small initial tan δ and excellent life characteristics.
[0034]
【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 to R _{8 in} (Chemical Formula 2) are those having 1 to 4 carbon atoms. An aliphatic saturated dicarboxylic acid compound having a total carbon number of 14 to 24 or a salt thereof, which is an alkyl group or a hydrogen atom and at least two are alkyl groups, is dissolved as a solute.
[003 5 ]
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, you are possible to maintain a high sparking voltage and electrical conductivity, since at least two of of from R ₁ R ₈ is an alkyl group, it is possible to further increase the solubility.
[003 6 ]
Moreover, also when an alkyl group is C3-C4, solubility can be improved.
[003 7 ]
Furthermore, since the aliphatic saturated dicarboxylic acid represented by (Chemical Formula 2) has an alkyl group, particularly an alkyl group represented by (Chemical Formula 3), on the carbon atom bonded to the carboxyl group, the carboxyl group is blocked by steric hindrance. This reduces the reactivity of the group, and 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 the decrease in conductivity is suppressed. Stability is obtained.
[00 38 ]
Moreover, in the aliphatic saturated dicarboxylic acid represented by (Chemical Formula 2), when R ₅ is an alkyl group, this effect is more remarkable.
[00 39 ]
Therefore, by using the electrolytic solution of the present invention, it is possible to obtain an electrolytic capacitor for medium and high voltage with low tan δ and high reliability.

Claims (3)

In a solvent mainly composed of an organic polar solvent, a general formula:
(Wherein R ₁ to R ₈ are an alkyl group having 1 to 4 carbon atoms or a hydrogen atom, and at least two are alkyl groups), and an aliphatic saturated dicarboxylic acid compound having a total carbon number of 14 to 24 Alternatively, an electrolytic solution for an electrolytic capacitor in which the salt is dissolved. The electrolytic solution for electrolytic capacitors according to claim 1, wherein the alkyl group of R ₁ to R ₈ 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 _{5 of the} aliphatic saturated dicarboxylic acid compound (Chemical Formula 1) is an alkyl group.