JP2002203753A - Electrolyte for electrolytic capacitor, and electrolytic capacitor using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolyte for an electrolytic capacitor which has a good shelf characteristic, and also to provide an electrolytic capacitor using the same. SOLUTION: The electrolyte for an electrolytic capacitor includes a phosphoric acid metallic complex, and the pH is kept at 7 or below. Accordingly, a quantity of phosphoric acid ions in the electrolyte can be kept at an appropriate one for a long time, and the deterioration of electrode foils after being on shelf can be suppressed. Consequently, an electrolyte for an electrolytic capacitor which has a good shelf characteristic, and an electrolytic capacitor using the same can be provided.

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 an electrolytic capacitor and an electrolytic capacitor using the same.

[0002]

2. Description of the Related Art An electrolytic capacitor generally has the following configuration. In other words, the 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 solution such as an ammonium borate aqueous solution. By doing so, a capacitor element is formed by winding 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 subjected to a surface-expansion treatment via a separator. 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.

[0003] As an electrolytic solution impregnated in the capacitor element of this electrolytic capacitor, a solution in which ethylene glycol is used as a main solvent and an ammonium salt such as adipic acid or benzoic acid is used as a solute, or γ- It is known to use butyrolactone as a main solvent and a quaternized cyclic amidinium salt such as phthalic acid and maleic acid as a solute.

[0004]

However, when such an electrolytic capacitor is left unattended, the capacitance is reduced, the leakage current characteristic is deteriorated, and the safety valve may be opened. Such a standing characteristic, which is a characteristic after a long period of time with or without a load, has a great influence on the reliability of the electrolytic capacitor.

Accordingly, an object of the present invention is to provide an electrolytic solution for an electrolytic capacitor having good standing characteristics and an electrolytic capacitor using the same.

[0006]

The electrolytic solution for an electrolytic capacitor of the present invention contains a metal phosphate complex, and has a pH maintained at 7 or less.

Further, the metal phosphate complex is an aluminum phosphate complex.

Further, in the electrolytic solution for an electrolytic capacitor, an amine salt is used as a solute.

An electrolytic capacitor according to the present invention is characterized in that the electrolytic solution for an electrolytic capacitor is used.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The electrolytic solution for an electrolytic capacitor of the present invention contains a metal phosphate complex and maintains the pH at 7 or less. In other words, the electrolytic capacitor is stored at room temperature for a certain period of time after manufacture, and then used after being mounted on an electronic device. The electrolytic capacitor of the present invention has a pH of 7 or less during the period of use immediately after the manufacture. Has been maintained.
The leaving characteristics of the electrolytic capacitor using the electrolytic solution for electrolytic capacitors are good. The electrolytic solution for an electrolytic capacitor of the present invention contains a metal phosphate complex, and by maintaining the pH at 7 or less, the phosphate ion concentration in the electrolytic solution can be maintained at an appropriate amount. The reaction between the aluminum electrode foil and the water in the electrolyte is suppressed,
The opening of the electrolytic capacitor due to the deterioration of the electrode foil and the generation of gas is prevented, and the leaving characteristics are improved. The appropriate amount of the phosphate ion concentration is 0.01 ppm or more when the storage temperature is 60 ° C. or more, and 0.1 ppm or more at 105 ° C.
At 5 ° C., it is 1 ppm or more.

In the above electrolytic solution for an electrolytic capacitor of the present invention, when the phosphate ion concentration in the electrolytic solution decreases,
The metal phosphate complex releases phosphate ions into the electrolyte,
The phosphate ion concentration in the electrolytic solution can be maintained at an appropriate amount. Thereby, the leaving characteristics of the electrolytic capacitor can be improved.

The above-mentioned metal phosphate complex can be obtained by dissolving a metal or a metal compound and a compound capable of forming phosphate ions in a solvent (hereinafter, a phosphate-forming compound) in a solvent. In this solution, phosphate ions and metal ions dissolved in the solvent form a complex. Then, this metal phosphate complex is added to the electrolytic solution to obtain the electrolytic solution for an electrolytic capacitor of the present invention. Further, the solvent used here may be a metal or a metal compound, a solvent capable of dissolving the phosphoric acid-forming compound in the solvent,
Among them, water, ethylene glycol, γ-butyrolactone and the like are preferable.

Further, by including a phosphoric acid-generating compound in the capacitor element, it reacts with the metal forming the electrode foil to form a phosphoric acid-generating compound metal complex, and the electrolytic solution for the electrolytic capacitor is formed. Can contain a metal phosphate complex, and thus the electrolytic solution for an electrolytic capacitor of the present invention can be prepared. As a method for incorporating the phosphoric acid-generating compound into the capacitor element, the phosphoric acid-generating compound may be added to an electrolytic solution for an electrolytic capacitor, or may be attached to an electrode foil or a separator forming the capacitor element.

As the metal, aluminum, iron, copper, nickel, manganese, zinc, calcium, magnesium,
Metals that form a complex with the chelating agent, such as barium, lead, titanium, niobium, and tantalum, can be used. Further, as the metal compound, oxides, hydroxides, chlorides,
In addition, compounds that generate metal ions in a solvent, such as metal salts such as sulfates and carbonates, can be used.

Examples of the phosphoric acid-generating compound include a phosphorus compound represented by the general formula (Chemical Formula 1), a salt thereof, a condensate thereof, or a salt of a condensate thereof.

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The following are examples of these phosphoric acid-generating compounds. Orthophosphoric acid, phosphorous acid,
Hypophosphorous acid, their salts, and ammonium salts, aluminum salts, sodium salts, calcium salts, and potassium salts. Orthophosphoric acid and its salts decompose in aqueous solution to produce phosphate ions. Phosphorous acid, hypophosphorous acid, and salts thereof are decomposed in an aqueous solution to generate phosphite ions and hypophosphite ions, and then oxidized to phosphate ions.

Phosphoric acid compounds such as ethyl phosphate, diethyl phosphate, butyl phosphate and dibutyl phosphate; and phosphonic compounds such as 1-hydroxyethylidene-1,1-diphosphonic acid, aminotrimethylene phosphonic acid and phenylphosphonic acid. Acid compounds and the like. In addition, phosphinic acid compounds such as methylphosphinic acid and butyl phosphinate are exemplified.

Further, the following condensed phosphoric acids or salts thereof can be mentioned. It is a linear condensed phosphoric acid such as pyrophosphoric acid, tripolyphosphoric acid, or tetrapolyphosphoric acid, or a cyclic condensed phosphoric acid such as metaphosphoric acid or hexametaphosphoric acid, or a combination of such chained or cyclic condensed phosphoric acids. . And, as salts of these condensed phosphoric acids, ammonium salts, aluminum salts, sodium salts, calcium salts, potassium salts and the like can be used.

These are also phosphoric acid-generating compounds that generate phosphate ions in an aqueous solution or generate phosphite ions and hypophosphite ions, and then oxidize to phosphate ions.

Of these, orthophosphoric acid or a salt thereof, a condensed phosphoric acid, or a phosphoric acid compound which easily generates a phosphate ion is preferred. Further, orthophosphoric acid which generates a lot of phosphate ions relatively quickly with respect to the amount added,
Linear condensed phosphoric acid such as pyrophosphoric acid and tripolyphosphoric acid,
Or a salt thereof is preferred. In addition, other than these compounds, the effect of the present invention can be obtained as long as the substance generates phosphate ions in an aqueous solution.

The solutes contained in the electrolytic solution include ammonium salts, amine salts, quaternary ammonium salts and cyclic amidine compounds which are usually used in electrolytic solutions for electrolytic capacitors and have an anionic component of a conjugate base of an acid. Grade salts. Primary amines (methylamine, ethylamine, propylamine,
Butylamine, ethylenediamine, etc.), secondary amines (dimethylamine, diethylamine, dipropylamine, methylethylamine, diphenylamine, etc.), tertiary amines (trimethylamine, dimethylethylamine, triethylamine, tripropylamine, triphenylamine,
1,8─diazabicyclo (5,4,0) ─undecene─
7 etc.). As the quaternary ammonium constituting the quaternary ammonium salt, tetraalkylammonium (tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, methyltriethylammonium, dimethyldiethylammonium, etc.), pyridium (1-methylpyridium) 1,1-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, imidazole monocyclic compounds (imidazole homologues such as 1-methylimidazole, 1,2-dimethylimidazole, 1,4-dimethyl-2-ethylimidazole, 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-5 (4) -aminoimidazole), benzimidazole (1-methylbenzimidazole, 1-methyl-2
-Benzylbenzimidazole, etc.) 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.), and 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-5 and the like.

Here, the electrolytic solution for an electrolytic capacitor of the present invention maintains the pH at 7 or less. However, the use of an amine salt is preferable because the pH can be maintained at 7 or less without increasing during standing. It is. It may be for the following reasons. Usually, during storage, the anion component in the electrolytic solution reacts with the metal constituting the electrode foil and decreases to increase the pH.
However, in the case of an amine salt, the amine, which is a cationic component, also evaporates from the electrolyte and decreases, so
Never rises. Among them, diethylamine, dimethylethylamine and triethylamine are preferred.

The anionic component includes adipic acid, glutaric acid, succinic acid, benzoic acid, isophthalic acid, phthalic acid, terephthalic acid, maleic acid, toluic acid, enanthic acid, malonic acid, formic acid, 1,6-decanedicarboxylic acid ,
Decanedicarboxylic acid such as 5,6-decanedicarboxylic acid,
Octanedicarboxylic acid such as 1,7-octanedicarboxylic acid, azelaic acid, organic acid such as sebacic acid, or
Examples thereof include boric acid, a polyhydric alcohol complex compound of boric acid obtained from boric acid and a polyhydric alcohol, and conjugate bases of inorganic acids such as phosphoric acid, carbonic acid, and silicic acid. Of these, preferred are decanedicarboxylic acid, octanedicarboxylic acid, azelaic acid, sebacic acid, adipic acid, glutaric acid, succinic acid, benzoic acid, isophthalic acid, organic carboxylic acids such as formic acid, or boric acid, boric acid. It is a polyhydric alcohol complex compound.

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 alcohol 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, etc.), 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.

Here, usually, when the solvent of the electrolytic solution for the electrolytic capacitor contains water, the deterioration of the electrode foil becomes remarkable,
Also in this case, in the present invention, the phosphate ion is 0.0
Since it is maintained at 1 ppm or more, the standing characteristics of the electrolytic capacitor of the present invention are good. Furthermore, even when a solvent containing water as a main component is used, the storage characteristics do not deteriorate,
By using such a solvent, the specific resistance of the electrolytic solution for the electrolytic capacitor can be reduced, and thereby the impedance of the electrolytic capacitor can be reduced. Here, the content of water in the solvent is 35 to 100 wt%, preferably 35 to 65 wt%. Above this range, the impedance characteristics are good, and below this range, the low-temperature characteristics are good. In addition, when a solvent containing water as a main component is used, there is no problem such as ignition when the capacitor fails due to nonstandard use such as high voltage use, and the environment resistance is good.

In order to stabilize the life characteristics of the electrolytic capacitor, nitrophenol, nitrobenzoic acid, nitroacetophenone, nitrobenzyl alcohol,
(Nitrophenoxy) ethanol, nitroanisole,
Aromatic nitro compounds such as nitrophenetol, nitrotoluene, dinitrobenzene and the like can be added.

Further, in order to improve the safety of the electrolytic capacitor, a nonionic surfactant, a polyhydric alcohol, ethylene oxide and / or
Alternatively, a polyoxyalkylene polyhydric alcohol ether compound or polyvinyl alcohol obtained by addition polymerization of propylene oxide can also be added.

Further, by adding boric acid, a polysaccharide (such as mannitol, sorbite, pentaerythritol), a complex compound of boric acid and a polysaccharide, and colloidal silica, to the electrolytic solution for an electrolytic capacitor of the present invention. The voltage can be improved.

For the purpose of reducing the leakage current, an oxycarboxylic acid compound or the like can be added.

The electrolytic capacitor containing the electrolytic solution of the present invention has a standing characteristic, that is, a long-term load,
Good characteristics after no-load test.

[0031]

The present invention will be described in detail below with reference to examples. The capacitor element is formed by winding an anode foil and a cathode foil via a separator. The anode electrode foil is obtained by chemically or electrochemically etching an aluminum foil having a purity of 99.9% in an acidic solution and expanding the surface thereof, and then performing a chemical conversion treatment in an aqueous solution of ammonium adipate. Use an oxide film layer. Purity 99.
9% of aluminum foil was etched and a foil subjected to a surface expansion treatment was used.

In the capacitor element configured as described above,
Impregnate the electrolytic solution for driving the aluminum electrolytic capacitor. 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 aluminum electrolytic capacitor. The electrolyte used here was prepared as follows.

Next, 0.2 part of aluminum hydroxide and 1 part of ammonium dihydrogen phosphate were added to 10 parts of water to complete the complex reaction between phosphoric acid and aluminum, thereby producing an aluminum phosphate complex. Next, the aqueous solution of the aluminum phosphate complex was added to the electrolyte solution shown in (Table 1) consisting of water, ethylene glycol, and triethylamine benzoate to prepare an electrolyte solution of the present invention. The composition is shown in parts. The specific resistance is shown in (Table 1). Further, as a comparative example, an electrolytic solution for an electrolytic capacitor was used in which 25 parts of water, 65 parts of ethylene glycol, and 10 parts of ammonium benzoate were used. The specific resistance was 106 Ωcm.

A high-temperature life test of the aluminum electrolytic capacitor constructed as described above was conducted. The rating of the aluminum electrolytic capacitor is 50 WV-820 μF. The test conditions were 10
5 ° C., no load, 3000 hours. Then, the capacitor after the test was disassembled, and the phosphate ion concentration and the pH of the electrolytic solution were measured. The lower limit of the measurement of the phosphate ion concentration is 0.1 ppm. The results are shown in (Table 2).

[0035]

[Table 1]

[0036]

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

As is clear from Table 2, the comparative example was open during the test, but in
Even at 000 hours, good characteristics are maintained. After the test, the pH of the electrolytic solution was maintained at 7 or less, and the phosphate ion concentration was also maintained at 0.1 ppm or more. This indicates that good standing characteristics were obtained.

[0038]

As described above, in the present invention, the electrolytic solution for an electrolytic capacitor contains a metal phosphate complex,
Since H is maintained at 7 or less, an appropriate amount of phosphate ions in the electrolytic solution can be maintained for a long time, and deterioration of the electrode foil after being left is suppressed, so that an electrolytic capacitor having good leaving characteristics can be obtained. An electrolytic solution for use and an electrolytic capacitor using the same can be provided.

Continuation of the front page (72) Inventor Hisatomi 1-167, Higashi-Ome, Ome-shi, Tokyo, Japan 1-167 Nippon Chemi-Con Corporation (72) Inventor Tatsuki Tsuji 1-167, Higashi-Ome, Ome-shi, Tokyo, 1 Nippon Chemi-Con Corporation

Claims (4)

[Claims] 1. An electrolytic solution for an electrolytic capacitor, comprising a metal phosphate complex and maintaining the pH at 7 or less. 2. The electrolytic solution for an electrolytic capacitor according to claim 1, wherein the metal phosphate complex is an aluminum phosphate complex. 3. The electrolytic solution for an electrolytic capacitor according to claim 1, wherein an amine salt is a solute. 4. An electrolytic capacitor using the electrolytic solution for an electrolytic capacitor according to claim 1.