JP2005039033A - Electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolytic capacitor in which the elctrolytic solution does not freeze nor separate out the electrolyte at low temperatures even though the amount of purified water is increased, a low specific resistance is realized, and no hydration reaction of an electrode foil is conducted at high temperatures. <P>SOLUTION: The time for measuring the increase of the breakdown voltage when testing a deterioration of an anode foil of the electrolytic capacitor in a boiled purified water after 60-minute immersed in the purified water of not less than 95°C is not more than 5 sec. The elctrolytic solution for driving comprises a mixed solvent of the purified water and 15.0 to 18.0 % ethylene glycol by weight disolved by adipic acid or its ammonium salt, formic acid or its ammonium salt, nitro compound, mannitol, orthophosphoric acid, citric acid or their ammonium salt. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrolytic capacitor that achieves low ESR (equivalent series resistance), improved low-temperature characteristics, and high reliability at high temperatures.

  The aluminum electrolytic capacitor was obtained by etching the surface of a high-purity aluminum foil, and winding the anode foil formed by anodizing aluminum oxide (dielectric film) and the etched cathode foil via a separator (electrolytic paper). A capacitor element is impregnated with a driving electrolyte (hereinafter referred to as electrolyte), stored in an aluminum case, and sealed with a sealing body.

A characteristic required for the aluminum electrolytic capacitor is low ESR. In order to realize low ESR, it is necessary to reduce the specific resistance of the electrolyte.
Therefore, in order to reduce the specific resistance, a method of increasing the amount of pure water in the electrolytic solution and reducing the amount of ethylene glycol has been proposed (see, for example, Patent Documents 1 and 2).
Japanese Patent No. 3366267 (page 1-10) Japanese Patent No. 3366268 (page 1-21)

In recent years, in order to reduce the ESR of electrolytic capacitors, it has been demanded that the specific resistance of the electrolytic solution be less than 20 Ω · cm.
However, when the amount of pure water in the electrolyte is increased, there is a problem that freezing or precipitation occurs under low temperature conditions, and the electrode foil causes a hydration reaction with pure water in the electrolyte under high temperature conditions. There was a problem.
In view of the above problems, an object of the present invention is to provide an electrolytic capacitor having a low specific resistance that does not cause freezing or precipitation under low temperature conditions and exhibiting stable electrical characteristics under high temperature conditions. There is.

  The present invention has been found as a result of various studies to solve the above-mentioned problems, and has been found to suppress freezing or precipitation under low temperature conditions while reducing the specific resistance of the electrolyte, and under high temperature conditions. The electrode foil is prevented from causing a hydration reaction with moisture in the electrolytic solution, and the characteristics of the electrolytic capacitor are stabilized.

That is, in an electrolytic capacitor in which a capacitor element impregnated with a driving electrolyte is stored in an aluminum case in a capacitor element in which an anode foil formed with a chemical conversion film and a cathode foil are wound through a separator,
The anode foil has a pure water boil deterioration test for measuring a rise time of a withstand voltage after immersion for 60 minutes in pure water at 95 ° C. or higher for 5 seconds or less,
The driving electrolyte includes a mixed solvent composed of pure water and 15.0 to 18.0% by weight of ethylene glycol, adipic acid or an ammonium salt thereof, formic acid or an ammonium salt thereof, a nitro compound, mannitol, An electrolytic capacitor obtained by dissolving orthophosphoric acid and citric acid or an ammonium salt thereof.

  The electrolytic capacitor is characterized in that the nitro compound is nitrobenzoic acid, dinitrobenzoic acid or an ammonium salt thereof, nitrophenol, nitroacetophenone, or nitroanisole.

  Furthermore, a specific resistance at 30 ° C. of the driving electrolyte is less than 20 Ω · cm.

  And the amount of dissolution of said adipic acid or its ammonium salt is 9.0-11.0 weight%, It is an electrolytic capacitor characterized by the above-mentioned.

  The electrolytic capacitor is characterized in that the amount of the formic acid or its ammonium salt is 10.0 to 12.0% by weight.

  Further, the electrolytic capacitor is characterized in that the amount of the nitro compound dissolved is 0.5 to 0.8% by weight.

  And it is an electrolytic capacitor characterized by the amount of dissolution of said mannit being 3.0 to 5.0 weight%.

  Further, the electrolytic capacitor is characterized in that the amount of the orthophosphoric acid dissolved is 0.3 to 0.5% by weight.

  Furthermore, the electrolytic capacitor is characterized in that the amount of the citric acid or its ammonium salt dissolved is 0.1 to 0.3% by weight.

  According to the present invention, even when the amount of pure water in the electrolytic solution is increased by using an electrode foil that hardly causes a hydration reaction with moisture in the electrolytic solution and the electrolytic solution, the frozen or electrolytic solution is obtained under low temperature conditions. It is possible to achieve a low specific resistance (less than 20 Ω · cm at 30 ° C) without causing precipitation, and at the same time as improving the low temperature characteristics of the electrolytic capacitor under the condition of applying high temperature voltage, high temperature reliability Can also be improved.

The anode foil used for the electrolytic capacitor according to the present invention has a pure water boil deterioration test for measuring the rise time of the withstand voltage after being immersed in pure water at 95 ° C. or higher for 60 minutes for 5 seconds or less. Specifically, the aluminum foil was etched, chemically washed with a phosphoric acid aqueous solution at 45 to 65 ° C., washed with water, immersed in a phosphoric acid aqueous solution having a lower concentration than the above phosphoric acid aqueous solution at room temperature, and then washed with water 320 to It can be obtained by chemical conversion of an etching foil heat-treated at 380 ° C. in an aqueous solution of ammonium adipate. In addition, when an etching foil immersed in pure water or weak alkaline aqueous solution at 40 to 60 ° C. and subjected to pseudo boehmite coating treatment without using chemical cleaning with phosphoric acid aqueous solution and phosphoric acid immersion treatment is used, an aqueous ammonium phosphate solution The former stage: ammonium adipate aqueous solution, the latter part: complex formation with ammonium phosphate aqueous solution, or the formation with ammonium adipate aqueous solution, the depolarization on the way is 3 minutes or more, and the repair process of the next process is 4 By performing the chemical conversion for at least 5 minutes, an anode foil having a pure water boil deterioration test of 5 seconds or less can be obtained.
An electrolytic solution is a mixture of pure water and ethylene glycol 15.0 to 18.0% by weight, adipic acid or its ammonium salt, formic acid or its ammonium salt, and paranitrobenzoic acid or its ammonium salt as a nitro compound. It is characterized by dissolving mannitol, orthophosphoric acid and citric acid or its ammonium salt.
In the mixed solvent, 9.0 to 11.0% by weight of adipic acid or an ammonium salt thereof and formic acid or an ammonium salt thereof 10.0 to so that the specific resistance at 30 ° C. of the electrolytic solution is less than 20 Ω · cm. 12.0% by weight, paranitrobenzoic acid or its salt 0.5-0.8% by weight, mannitol 3.0-5.0% by weight, orthophosphoric acid 0.3-0.5% by weight, Dissolve citric acid or its ammonium salt 0.1 to 0.3% by weight, and prepare an electrolyte solution.

  Hereinafter, the present invention will be specifically described based on examples.

〔Example〕
The electrolyte solutions of Examples 1 to 43 were prepared with the compositions shown in Tables 1 and 2, and the specific resistance of the electrolyte solution at 30 ° C. was measured. Moreover, the state in -25 degreeC was observed. The results are shown in Tables 1 and 2.

(Conventional example)
The specific resistance at 30 ° C. was measured in the same manner as in the examples for the electrolytic solution of the conventional example consisting of pure water, ethylene glycol, diammonium adipate or ammonium formate (phosphorous acid added), and ammonium paranitrobenzoate, and −25 ° C. The state in was observed. The results are shown in Table 2 (lower column).

Of the electrolytic solutions in Tables 1 and 2, Examples 1-27, 33-35, 37-40, 42, 43 were impregnated into a capacitor element formed by winding an anode foil subjected to the following treatment, and the diameter was 10 mm. Ten aluminum electrolytic capacitors each having a length of 12.5 mm, a rated voltage of 6.3 V, and a capacitance of 1000 μF were produced.
[Anode foil treatment]
Pure water boil degradation test Withstand voltage rise time: 3 seconds In the mixed solution of hydrochloric acid and sulfuric acid, the aluminum foil is etched by a known etching method in which AC electrolysis is performed, and the chlorine content on the foil surface is removed and water resistance is improved. Therefore, it was immersed in 60 ° C. and 20% by weight phosphoric acid for 1 minute, washed with water, then immersed in 0.1% by weight phosphoric acid at room temperature for 30 seconds, and then heat treated at 350 ° C. without washing with water.
After the above etching foil was converted to a withstand voltage of 11 V in an aqueous solution of ammonium adipate, a pure water boil deterioration test (over 60 minutes at 95 ° C.) was performed as follows, and the withstand voltage rise time was 3 seconds (n = 10 Average).
[Pure water boil deterioration test]
(1) After a test piece (size: 10 mm × 50 mm) is washed with pure water, it is put into a tank containing 500 ml of pure water at 95 ° C. or higher and left for 60 ± 1 minutes.
(2) A solution in which 150 g of ammonium adipate was dissolved in 1000 ml of pure water was prepared, the test piece was immersed, the measurement current of 1.0 ± 0.1 mA was passed at 85 ± 2 ° C., and the voltage rise curve Record.
(3) The time from when the measurement current starts to flow until the voltage reaches 90% of the withstand voltage (11 V) is recorded as the rise time.

  The rated voltage was applied to the above capacitor in a constant temperature bath at 105 ° C. for 2000 hours, and the capacitance change rate, tan δ, and leakage current with respect to the initial values were measured, and the results shown in Table 3 were obtained.

  In Table 3, when the electrical characteristics are compared, in Examples 8, 12, 13, 16, 20, 23, 24, 27, 35, 39, 42, and 43, the electrical characteristics after 2000 hours deteriorated and the valve expansion was reduced. It can be seen that in other examples, the electrical characteristics are stable and the valve expansion is small.

From the results in Tables 1 to 3, it was found that the following range is appropriate for the composition of the electrolytic solution.
When ethylene glycol was 13.0% by weight, freezing was observed at -25 ° C. Further, in the case of 20.0% by weight, the specific resistance becomes high, so that it is unsuitable for low specific resistance applications (Example 4). Accordingly, ethylene glycol is preferably in the range of 15.0 to 18.0% by weight.

  As shown in Table 1, when diammonium adipate was 8.0% by weight, freezing was observed at −25 ° C. (Example 5). As shown in Table 3, when diammonium adipate was 12.0% by weight, the electrical characteristics deteriorated after 2000 hours (Example 8). Accordingly, the diammonium adipate is preferably in the range of 9.0 to 11.0% by weight.

  As shown in Table 1, when ammonium formate was 9.0% by weight, freezing was observed at -25 ° C. As shown in Table 3, when ammonium formate was 13.0% by weight, the electrical characteristics deteriorated after 2000 hours (Example 12). Accordingly, the ammonium formate is preferably in the range of 10.0 to 12.0% by weight.

  As shown in Table 1, when ammonium paranitrobenzoate was 1.0% by weight, precipitation was observed at −25 ° C. (Example 15). As shown in Table 3, when ammonium paranitrobenzoate was 0.3% by weight, the electrical characteristics deteriorated after 2000 hours (Example 13). Therefore, ammonium paranitrobenzoate is preferably in the range of 0.5 to 0.8% by weight.

  As shown in Table 1, when mannit was 1.0% by weight, valve expansion was observed (Example 16). Further, when the mannit is 7.0% by weight, the specific resistance becomes high (Example 19), which is inappropriate. The mannit is preferably in the range of 3.0 to 5.0% by weight.

  As shown in Table 3, when orthophosphoric acid was 0.2% by weight, the electrical characteristics deteriorated after 2000 hours (Example 20). Also, in the case of 0.7% by weight, the electrical characteristics deteriorated after 2000 hours (Example 23). Accordingly, orthophosphoric acid is preferably in the range of 0.3 to 0.5% by weight.

  As shown in Table 3, when diammonium citrate was 0.05% by weight, electrical characteristics deteriorated after 2000 hours (Example 24). Also, in the case of 0.5% by weight, the electrical characteristics deteriorated after 2000 hours (Example 27). Accordingly, the diammonium citrate content is preferably in the range of 0.1 to 0.3% by weight.

Further, in the case of Table 2 where the lower limit of ethylene glycol was 15.0% by weight and the amounts of diammonium adipate and ammonium formate were changed, diammonium adipate was 9.0 to 11.0% by weight, and formic acid The amount of ammonium is suitably in the range of 10.0 to 12.0% by weight. If either falls below the lower limit, freezing occurs at −25 ° C., and if any exceeds the upper limit, the electrical characteristics deteriorate (Table 3).
Further, in the above examples, the specific resistance at 30 ° C. could be less than 12 Ω · cm, but considering the fluctuation when the amount of water was reduced and the dissolved mass was reduced, the upper limit value of the specific resistance is It was set to be less than 20 Ω · cm.

As a result, the electrolytic solutions of Examples 33, 34, 37, and 38 that were found to have excellent electrical characteristics were used with the following anode foil, and the withstand voltage rise time in the pure water boil deterioration test was 3 seconds. 5 seconds, 6 seconds, and 8 seconds. Similarly to the above, 10 electrolytic capacitors each having a rated voltage of 6.3 V and a capacitance of 1000 μF were produced, and the rated voltage was maintained in a constant temperature bath at 105 ° C. for 2000 hours. The change in capacitance, tan δ, and leakage current with respect to the initial values were measured, and the results shown in Table 4 were obtained.
[Anode foil of example]
Pure water boil deterioration test Withstand voltage rise time: 3 seconds, 5 seconds Etching aluminum foil in a mixed solution of hydrochloric acid and sulfuric acid using a known etching method in which AC electrolysis is performed, removing chlorine from the foil surface and water resistance In order to improve the properties, it was immersed in 2.0% by weight phosphoric acid at 60 ° C. for 1 minute, washed with water, then immersed in 0.1% by weight phosphoric acid at room temperature for 30 seconds, and then heat treated at 350 ° C. without washing with water.
The above-described etching foil was converted to a withstand voltage of 11 V in an aqueous solution of ammonium adipate, and then the pure water boil deterioration test was performed to confirm that the withstand voltage increase time was 5 seconds or less. Selected one.
[Anode foil of comparative example]
Pure water boil degradation test Withstand voltage rise time: 6 seconds, 8 seconds An etching foil similar to the above was prepared, and immersed in nitric acid at 60 ° C. and 2.5 wt% nitric acid to remove the chlorine content on the etching foil surface. And washed with water and heat-treated at 350 ° C.
The above-mentioned etching foil was converted to a withstand voltage of 11 V in an aqueous solution of ammonium adipate, and then the pure water boil deterioration test was conducted to confirm that the withstand voltage increase time was 6 seconds or more. 6 seconds, 8 seconds Selected one.

  From the comparison of Table 4, the anode foil of the example whose pure water boil deterioration test is 5 seconds or less (60 ° C. 2.0 wt% phosphoric acid immersion → water washing → normal temperature 0.1 wt% phosphoric acid immersion → no water washing → heat treatment ) Using the anode foil of the comparative example (60 ° C. 2.5 vol% nitric acid immersion → water washing → heat treatment), which has a pure water boil deterioration test of 6 seconds or more. It is understood that the hydration reaction is difficult to occur. Therefore, the anode foil is required to have a withstand voltage rise time of 5 seconds or less after the pure water boil deterioration test.

  Furthermore, when a high-capacity foil is required at a voltage exceeding a withstand voltage of 11 V, it can be dealt with by nitric acid chemical cleaning and pseudo-boehmite treatment. At this time, the chemical conversion is CC chemical conversion, CV chemical conversion (squeezing chemical conversion), Pure water boil by performing phosphoric acid depolarization (60 ° C., 2nd stage), restoration conversion (3rd stage), and phosphoric acid immersion in order, and phosphoric acid depolarization for 3 minutes or more and restoration formation for 4 minutes or more. An anode foil whose deterioration test is 5 seconds or less is obtained.

  In the above examples, paranitrobenzoic acid was used as the nitro compound, but dinitrobenzoic acid or its ammonium salt, or nitrophenol, nitroacetophenone, or nitroanisole was used in the same manner as above. An effect can be obtained.

Claims (9)

In an electrolytic capacitor in which a capacitor element in which a driving electrolyte is impregnated in a capacitor element obtained by winding an anode foil formed with a chemical conversion film and a cathode foil through a separator is stored in an aluminum case,
The anode foil has a pure water boil deterioration test for measuring a rise time of a withstand voltage after being immersed in pure water at 95 ° C. or higher for 60 minutes for 5 seconds or less,
The driving electrolyte includes a mixed solvent composed of pure water and 15.0 to 18.0% by weight of ethylene glycol, adipic acid or an ammonium salt thereof, formic acid or an ammonium salt thereof, a nitro compound, mannitol, An electrolytic capacitor obtained by dissolving orthophosphoric acid and citric acid or an ammonium salt thereof.
.   2. The electrolytic capacitor according to claim 1, wherein the nitro compound is nitrobenzoic acid, dinitrobenzoic acid or an ammonium salt thereof, or nitrophenol, nitroacetophenone, or nitroanisole.   The electrolytic capacitor according to claim 1, wherein a specific resistance at 30 ° C. of the driving electrolyte is less than 20 Ω · cm.   2. The electrolytic capacitor according to claim 1, wherein the amount of adipic acid or ammonium salt thereof dissolved is 9.0 to 11.0% by weight.   The electrolytic capacitor according to claim 1, wherein the amount of formic acid or its ammonium salt dissolved is 10.0 to 12.0% by weight.   2. The electrolytic capacitor according to claim 1, wherein the nitro compound is dissolved in an amount of 0.5 to 0.8% by weight.   2. The electrolytic capacitor according to claim 1, wherein the amount of mannitol dissolved is 3.0 to 5.0% by weight.   The electrolytic capacitor according to claim 1, wherein the amount of orthophosphoric acid dissolved is 0.3 to 0.5% by weight. The electrolytic capacitor according to claim 1, wherein the amount of citric acid or its ammonium salt dissolved is 0.1 to 0.3% by weight.