JP2000286155A - Electrolytic solution for electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve high-temperature service life characteristic of an electrolytic capacitor. SOLUTION: Since aurin tricarboxylic acid or a salt thereof is added to an electrolytic solution for an electrolytic capacitor, dissolution of aluminum into the electrolytic solution can be suppressed, whereby the high-temperature service life characteristic of the electrolytic capacitor using this electrolytic solution can be improved. Furthermore, since satisfactory high-temperature service life characteristic can be maintained even if its water content is increased, an electrolytic capacitor having low impedance characteristic can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art An electrolytic capacitor generally has the following configuration. That is, a high-purity aluminum foil formed in a belt shape is chemically or electrochemically etched to enlarge the surface, and the expanded aluminum foil is subjected to a chemical conversion treatment in a chemical conversion solution such as an ammonium borate aqueous solution. By doing so, a capacitor element is formed by winding, via a separator, an anode foil having an oxide film layer formed on the surface of an aluminum foil and a cathode foil having a high-purity aluminum foil expanded. The capacitor element is impregnated with a driving electrolyte, and is housed in a metal bottomed cylindrical outer case. Further, a sealing body made of elastic rubber is housed at the opening end of the outer case, and the opening end of the outer case is sealed by drawing to form an electrolytic capacitor.

Conventionally, the electrolytic solution impregnated in the capacitor element has a main solvent of ethylene glycol and a solute of an ammonium salt such as adipic acid or benzoic acid, or a main solvent of γ-butyrolactone. And those using a quaternized cyclic amidinium salt such as phthalic acid and maleic acid as a solute.

[0004]

In such an electrolytic capacitor, the capacitor element is impregnated with an electrolytic solution.
If the cathode foil is kept in contact with the electrolytic solution at a high temperature, aluminum hydroxide or aluminum oxide is formed on the surface, the capacitance is reduced, and the leakage current is increased. Further, there is a problem that the safety valve is opened due to the generation of hydrogen gas at this time. Therefore, the present invention
It is an object of the present invention to improve this problem and to improve the high-temperature life characteristics of an electrolytic capacitor.

[0005]

The present invention is characterized in that aurin tricarboxylic acid or a salt thereof is added to an electrolytic solution for an electrolytic capacitor.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION As a solute of an electrolytic solution used in the present invention, an ammonium salt such as adipic acid, formic acid or benzoic acid, a quaternary ammonium salt or an amine salt can be used. 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.)
Is mentioned. Examples of the amine constituting the amine salt include primary amines (methylamine, ethylamine, propylamine, butylamine, ethylenediamine, monoethanolamine, etc.), and secondary amines (dimethylamine, diethylamine, dipropylamine, ethylmethylamine,
Diphenylamine, diethanolamine, etc.) and tertiary amines (trimethylamine, triethylamine, tributylamine, 1,8-diazabicyclo (5,4,0) -undecene-7, triethanolamine, etc.).

Further, a salt containing a quaternized cyclic amidinium ion as a cation component can be used. Examples of the acid serving as the anion component of this salt include phthalic acid, isophthalic acid, terephthalic acid, maleic acid, benzoic acid, toluic acid, enanthic acid, and malonic acid.

The quaternized cyclic amidinium ion serving as the cation component is a cation obtained by quaternizing a cyclic compound having an N, N, N'-substituted amidine group.
Examples of the cyclic compound having an N′-substituted amidine group include the following compounds. Imidazole monocyclic compound (1-
Methylimidazole, 1-phenylimidazole, 1,
Imidazole homologs such as 2-dimethylimidazole, 1-ethyl-2-methylimidazole, 1,2-dimethylimidazole, 1-ethyl-2-methylimidazole, 1,2-dimethylimidazole and 1,2,4-trimethylimidazole Oxyalkyl derivatives such as 1-methyl-2-oxymethylimidazole, 1-methyl-2-oxyethylimidazole, nitro derivatives such as 1-methyl-4 (5) -nitroimidazole, 1,2-dimethyl-5 (4) amino derivatives such as -aminoimidazole), benzimidazole compounds (1-methylbenzimidazole, 1-methyl-2-benzimidazole, 1
-Methyl-5 (6) -nitrobenzimidazole, etc.),
Compounds having a 2-imidazoline ring (1-methylimidazoline, 1,2-dimethylimidazoline, 1,2,4-
Trimethylimidazoline, 1-methyl-2-phenylimidazoline, 1-ethyl-2-methyl-imidazoline,
1,4-dimethyl-2-ethylimidazoline, 1-methyl-2-ethoxymethylimidazoline, etc.), and compounds having a tetrahydropyrimidine ring (1-methyl-1,4,
5,6-tetrahydropyrimidine, 1,2-dimethyl-
1,4,5,6-tetrahydropyrimidine, 1,5-diazabicyclo [4,3,0] nonene-5 and the like.

[0009] As the solvent, a protic polar solvent, an aprotic polar solvent, water, and a mixture thereof can be used. Protic polar solvents include monohydric alcohols (methanol, ethanol, propanol, butanol, hexanol, cyclohexanol,
Cyclopentanol, benzyl alcohol, etc.), polyhydric alcohols and oxy alcohol compounds (ethylene glycol, propylene glycol, glycerin, methyl cellosolve, ethyl cellosolve, 1,3-butanediol, methoxypropylene glycol, etc.). As aprotic polar solvents, amides (N-methylformamide, N, N-dimethylformamide, N
-Ethylformamide, N, N-dimethylformamide, N-methylacetamide, hexamethylphosphoramide, etc.), lactones (γ-butyrolactone, δ-
Valerolactone), cyclic amides (N-methyl-2-
Pyrrolidone, etc.), carbonates (ethylene carbonate, propylene carbonate, etc.), nitriles (acetonitrile, etc.), oxides (dimethylsulfoxide, etc.), 2-imidazolidinone [1,3-dialkyl-
2-imidazolidinone (1,3-dimethyl-2-imidazolidinone, 1,3-diethyl-2-imidazolidinone, 1,3-di (n-propyl) -2-imidazolidinone, etc.), 1 , 3,4-trialkyl-2-imidazolidinone (eg, 1,3,4-trimethyl-2-imidazolidinone)] and the like.

An electrolytic solution of the present invention is constituted by adding aurin tricarboxylic acid or a salt thereof to these electrolytic solutions. The amount of addition is 0.05 to 10 wt%, preferably 0.1 to 2.0 wt%. Below this range,
If the effect is reduced, and if it exceeds this range, the solubility is reduced.

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 withstand voltage 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.

The electrolytic solution of the present invention has good high-temperature load life characteristics and high-temperature storage characteristics. The reason is presumed to be as follows.

Normally, in a high temperature life test, a state in which the cathode foil is in contact with the electrolytic solution at a high temperature continues, but in this state, the aluminum of the cathode foil dissolves in the electrolytic solution,
At this time, heat is generated, and hydrogen gas is generated. And
The aluminum reacts with the water in the electrolyte to form aluminum hydroxide or aluminum oxide (hereinafter, aluminum hydroxide, etc.) on the surface of the cathode foil. These will increase the thickness of the oxide film, which is a capacitance component on the surface of the cathode foil, and reduce the capacitance of the cathode foil,
The capacitance of the electrolytic capacitor, which is the combined capacitance of the capacitance of the anode foil and the capacitance of the cathode foil, decreases. Further, it is thought that this heat generation is caused by the hydrogen gas. However, the oxide film of the anode foil is damaged, and the leakage current in a high-temperature storage test increases. In addition, when the production of aluminum hydroxide and the like is severe, the aluminum becomes corrosive.

Further, since these aluminum oxides and the like are fragile, they are separated from the cathode foil, and the aluminum is again dissolved from the cathode foil into the electrolytic solution to form aluminum hydroxide and the like. In this case, heat is generated and hydrogen gas is generated. By repeating such a process, the pressure in the condenser may increase and the safety valve may be opened.

However, in the present invention, since aurin tricarboxylic acid or its salt is added to the electrolytic solution, aluminum dissolved in the electrolytic solution from the cathode foil forms a complex with aurin tricarboxylic acid or its salt.
Then, this complex is adsorbed on the foil surface and suppresses the dissolution of aluminum in the electrolytic solution, so that the formation of aluminum hydroxide and the like on the cathode foil is suppressed, and as a result, static electricity in a high-temperature life test of the electrolytic capacitor is suppressed. A decrease in electric capacity can be suppressed. Furthermore, since there is no heat generation and no generation of hydrogen gas, there is no damage to the oxide film of the anode foil, and an increase in leakage current when left at high temperatures is suppressed. In addition, since the formation of aluminum hydroxide and the like is suppressed, the safety valve does not open due to the generation of hydrogen gas.

Heretofore, as an electrolytic solution for electrolytic capacitors having low impedance characteristics, an electrolytic solution using γ-butyrolactone as a solvent and a quaternized cyclic amidinium salt as a solute has been generally used. , 80-1
00 Ωcm was the limit. Further, there is a demand for further lowering the impedance, and this can be met by using an electrolytic solution containing ethylene glycol and water as a solvent and ammonium adipate as a solute and having a high water content. However, by increasing the amount of water, the formation of aluminum hydroxide and the like on the surface of the cathode foil described above is promoted, the capacitance is reduced during the high-temperature life test, and the safety valve is frequently opened. Although it did not withstand use, this problem can be solved by the addition of the aurin tricarboxylic acid of the present invention or a salt thereof. That is, as described above, the dissolution of aluminum from the cathode foil in the electrolytic solution can be suppressed, the formation of aluminum hydroxide and the like is suppressed, and the decrease in capacitance in a high-temperature life test of the electrolytic capacitor is prevented. In addition, since there is no heat generation and no generation of hydrogen gas, the oxide film of the anode foil is not damaged, and the rise of leakage current when left at high temperature is suppressed. Also, there is no need to open the safety valve due to the generation of hydrogen gas.

In this case, the amount of water that satisfies the low impedance and high temperature life characteristics is 10 to 100 wt% in the solvent. Preferably, it is 30 to 100 wt%, more preferably 50 to 100 wt%. As described above, in the electrolytic solution of the present invention, water can be used as the main solvent, and thereby the impedance of the electrolytic capacitor can be reduced.

Further, in an electrolytic solution containing γ-butyrolactone as a main solvent, the water content is usually low, so that the characteristic deterioration due to the deterioration of the cathode foil in the high-temperature life test as described above is not remarkable. However, even in such an electrolytic solution, in a moisture resistance test, the moisture content increases due to moisture absorption,
The formation of aluminum hydroxide and the like on the surface of the above-mentioned cathode foil was promoted, a decrease in capacitance during a high-temperature life test, the opening of a safety valve, and the like occurred. It is considered that the addition of the salt suppresses the formation of aluminum hydroxide or the like on the surface of the cathode foil, and improves the moisture resistance. The same applies to an electrolytic solution containing ethylene glycol and water as main solvents.

Further, when the electrolytic capacitor is washed with a halogen-based cleaning agent, the halogen passes through the sealing rubber,
In some cases, the aluminum halide is formed into a corrosive state by being mixed with the electrolytic solution inside the capacitor and combined with aluminum ions dissolved in the electrolytic solution to form aluminum halide. However, in the present invention, as described above, since the dissolution of aluminum in the electrolytic solution can be suppressed, even if halogen is mixed in the electrolytic solution, the amount of aluminum ions bonded to the halogen is reduced, and the corrosion state is reduced. It is not considered to be.

[0021]

Next, embodiments of the present invention will be described in detail. The capacitor element is formed by winding an anode foil and a cathode foil via a separator. The anode electrode foil has a purity of 9
After a 9.9% aluminum foil was chemically or electrochemically etched in an acidic solution and subjected to surface expansion treatment, a chemical conversion treatment was performed in an aqueous solution of ammonium adipate to form an anodic oxide film layer on the surface. Use something. As the cathode foil, a foil obtained by etching an aluminum foil having a purity of 99.8% and expanding the surface was used.

In the capacitor element configured as described above,
An electrolytic solution for driving an electrolytic capacitor is impregnated. The capacitor element impregnated with this electrolytic solution is housed in a cylindrical outer case made of aluminum with a bottom, a butyl rubber sealing body is inserted into the open end of the outer case, and the end of the outer case is drawn. To seal the electrolytic capacitor.

The composition and characteristics of the electrolyte used here are shown in Table 1.

A high-temperature life test of the electrolytic capacitor constructed as described above was conducted. The rating of the electrolytic capacitor is 50W
V-150 μF. The test is a load test at 105 ° C. at a rated voltage for 2000 hours, and a test at 105 ° C. for 2000 hours. The results are shown in (Table 2) and (Table 3).

[0025]

[Table 1] (Note) EG: Ethylene glycol AAd: Ammonium adipate AATC: Ammonium aurin tricarboxylate (aluminon) The number in parentheses in the column of H ₂ O indicates the content of H ₂ O in the solvent.

[0026]

[Table 2] (Note) Cap: Capacitance (μF), tan δ: Tangent of dielectric loss, LC: Leakage current (μA), ΔCap: Capacitance change rate (%)

[0027]

[Table 3]

As is clear from Tables 1 to 3,
In Examples 1 to 7, the decrease in the capacitance after the life test and the increase in the leakage current are small as compared with the conventional example.
Further, in the comparative example having a water content of 15 wt%, the valve was opened during the test. However, in Examples 1 to 7 having a water content of 25 to 100 wt%, the initial tan δ and the leakage current were low, and the test was performed. There is no later valve opening and the characteristics are good. In particular, in Examples 3 to 7 having a water content of 55 to 100 wt%,
The specific resistance is as low as 18 to 42 Ωcm, which is unprecedented, and the tan δ of the electrolytic capacitor is also 0.020 to 0.0
26, which is a low value. As described above, the electrolytic solution of the present invention can provide an electrolytic capacitor having low impedance characteristics and good high-temperature life characteristics.

[0029]

According to the present invention, since an aurin tricarboxylic acid or a salt thereof is added to an electrolytic solution for an electrolytic capacitor, in an electrolytic capacitor using the same, dissolution of aluminum from a cathode foil at a high temperature is prevented. Restrained,
This suppresses the formation of aluminum hydroxide and the like in the cathode foil. Therefore, the high temperature life characteristics are improved. Furthermore, even if the water content is increased, good high-temperature life characteristics are maintained, so that an electrolytic capacitor having low impedance characteristics can be obtained. For the same reason, the moisture resistance is also improved. Furthermore, since the dissolution of aluminum from the cathode foil at a high temperature is suppressed, it is considered that even if halogen enters the inside of the capacitor, the generation of aluminum halide is suppressed and the halogen resistance is improved.

Claims (1)

[Claims] 1. An electrolytic solution for electrolytic capacitors to which aurin tricarboxylic acid or a salt thereof is added.