JPH09320903A - Driving electrolyte for electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent increase of tanδ and increase of a leakage current at the no load by using ethylene glycol as main solvent, dissolving organic acid or its salt and/or boric acid or its salt, and compounding a specific amount of very fine particle γ-alumina. SOLUTION: The following is used as the electrolyte of an aluminum electrolytic capacitor; ethylene glycol as used as the main solvent, organic acid or its salt and/or boric acid or its salt are dissolved, and very fine particle γ-alumina of 0.02-0.10wt.% is compounded. The very fine particle γ-alumina is positively charged in the driving electrolyte of the aluminum electrolytic capacitor, forms an electric double layer together with peripheral negative ions in the driving electrolyte, and is uniformly dispersed in the driving electrolyte by mutual repulsion. The very fine particle γ-alumina becomes seed crystal of formation film formation by aging, so that a formation film containing stable γ-alumina can be formed.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an electrolytic solution for driving an electrolytic capacitor.

[0002]

2. Description of the Related Art Conventionally, an electrolytic solution for driving an aluminum electrolytic capacitor for medium and high voltage (hereinafter, simply referred to as an electrolytic solution).
For this, an electrolytic solution in which an organic acid or a salt thereof and / or boric acid or a salt thereof are dissolved in a solvent mainly composed of ethylene glycol is used, and the electrolytic solution contains various additives.

The above-mentioned additives include a withstand voltage improver and a water resistance improver made of aluminum. In particular, in recent years, an additive applicable to long-life products at high temperatures has been required.

[0004]

In order to extend the life of the aluminum electrolytic capacitor for medium and high voltage, it is necessary to suppress the deterioration of the anode foil. One of the causes of deterioration of the anode foil is that the chemical conversion film formed during aging of the aluminum electrolytic capacitor is unstable. Until now, as measures against deterioration of the chemical conversion film due to this aging, polyvalent alcohols such as mannite and sorbit, and
It is known that the addition of a phosphoric acid compound to the electrolytic solution is effective, but even if the above electrolytic solution is used, only a chemically unstable chemical conversion film can be obtained, so In a long-term reliability test at
There is a problem in that the leakage current increases when there is no load.

[0005]

The present invention has been found as a result of various studies in order to solve the above problems. That is, the present invention uses ethylene glycol as a main solvent, dissolves an organic acid or a salt thereof, and / or boric acid or a salt thereof, and converts the ultrafine particle γ-alumina to 0.02 to 0.02.
0.10% by weight, and the above-mentioned ultrafine particles γ
-Alumina has an average particle diameter of 5 nm to 300 nm, which is an electrolytic solution for an aluminum electrolytic capacitor.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Ultrafine particle γ-alumina is positively charged in a driving electrolyte solution of an aluminum electrolytic capacitor, forms an electric double layer with surrounding anions in the driving electrolyte solution, and repels each other. In the driving electrolyte solution, it is uniformly dispersed. The structure of the electric double layer of the ultrafine particle γ-alumina is destroyed during aging, but the ultrafine particle γ-alumina on the surface of the anode foil of the aluminum electrolytic capacitor.
Alumina serves as a seed crystal for forming a chemical conversion film by aging, so that a stable chemical conversion film containing γ-alumina should be formed as compared with the chemically unstable aging conversion film that has been chemically unstable so far. You can

The chemical conversion film formed from ultrafine γ-alumina does not deteriorate even if a voltage is applied for a long time at high temperature or it is left unloaded, so that the aluminum electrolysis having stable characteristics for a long period of time is performed. A capacitor is obtained.

[0008]

EXAMPLES Specific examples of the present invention will be described below. The electrolytic solutions according to the present invention (sample symbols A-1 to A-3, B-1 to B-3, C-1 to C- as examples are shown in Tables 1 to 4).
3, D-1 to D-3), and a composition of a conventional electrolytic solution (sample symbols A-0, B-0, C-0, D-0) for comparison, specific resistance at 30 ° C., and 85. Withstand voltage at ° C.

[0009]

[Table 1]

[0010]

[Table 2]

[0011]

[Table 3]

[0012]

[Table 4]

As is clear from Tables 1 to 4, sample symbols A-1 to A-3, B-1 to B-3, C-1 according to the present invention.
To C-3 and D-1 to D-3 have the same specific resistance and withstand voltage as conventional electrolytic solutions (sample symbols A-0, B-0, C-0, D-0). .

Using the above electrolytic solution, a rating of 400 V-330
Made an aluminum electrolytic capacitor of μF, 105 ℃
The results of performing the rated voltage application test and the no-load test for 2000 hours are shown in Table 5 and Table 6, respectively.

[0015]

[Table 5]

[0016]

[Table 6]

As is clear from Table 5, sample symbols A-1 to A-3, B-1 to B-3, C-1 to C- according to the present invention.
In the 105 ° C rated voltage test, the electrolytic capacitors using the electrolytic solutions of Nos. 3, D-1 to D-3 are the same as those of the conventional electrolytic solutions (sample symbols A-0, B-0, C-0, D-0). Compared to ta
The increase in nδ is suppressed, and the change in capacitance is small and stable. In addition, in the 105 ° C. no-load test, as is clear from Table 6, in the example, the increase in leakage current is smaller than in the conventional example, and the change in capacitance and the change in tan δ are also small and stable. Here, the amount of the ultrafine γ-alumina compounded is effective when compounded in an amount of 0.02 to 0.10% by weight, and less than 0.02% by weight has no effect.
If it exceeds 5% by weight, it is insoluble in the solvent. Also,
The average particle size of the ultrafine γ-alumina is 5 nm to
When the thickness is 300 nm, the dispersibility is good, and when it is smaller than 5 nm, it becomes difficult to form a seed crystal for forming a chemical conversion film by aging, and when it is larger than 300 nm, the dispersibility in a solution becomes difficult.

[0018]

As described above, the electrolytic solution of the aluminum electrolytic capacitor according to the present invention is better than the conventional electrolytic solution.
It is possible to provide a highly reliable aluminum electrolytic capacitor under high temperature, which is of great industrial and practical value.

Claims (2)

[Claims] 1. An ethylene glycol as a main solvent, an organic acid or its salt, and / or boric acid or its salt are dissolved, and 0.02 to 0.10% by weight of ultrafine γ-alumina is added. An electrolytic solution for driving an electrolytic capacitor characterized by: 2. The ultrafine γ-alumina has an average particle size of 5 nm to 300 nm.
Electrolytic solution for driving the electrolytic capacitor of.