JPH0658868B2 - Electrolytic solution for driving electrolytic capacitors - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of an electrolytic solution for driving an electrolytic capacitor (hereinafter referred to as an electrolytic solution), and more particularly to an electrolytic solution capable of reducing leakage current of an electrolytic capacitor.

(Prior Art) Generally, in an aluminum electrolytic capacitor, an aluminum tab for drawing is joined to an anode foil having an anodic oxide film and a cathode foil having no anodic oxide film, and then the capacitor element is wound by interposing a separator therebetween. Is formed, and the capacitor element is impregnated with an electrolytic solution and hermetically sealed in a case.

This electrolytic capacitor is subjected to a voltage treatment called aging in order to reduce the leakage current.

Such electrolytic capacitors are used in various electronic devices such as communication devices and measuring devices.The performance of these electronic devices is largely related to the electrical characteristics of the electrolytic capacitors. Electrolytic capacitors with long life and high reliability are required.

However, when an aluminum electrolytic capacitor is left unloaded at a high temperature for a long time, the leakage current increases, and in some cases, the aluminum oxide film may be seriously damaged and the insulating property may deteriorate. It is considered that this is because the electrolytic solution enclosed in the case reacts with the oxide film to deteriorate the oxide film.

(Problems to be Solved by the Invention) As a method for preventing such deterioration of an oxide film, 10
Regarding a low voltage capacitor of 0 V or less, JP-A-54-1
Many methods have been proposed as shown in Japanese Patent No. 36651, Japanese Patent Laid-Open No. 62-145808 and the like. In these methods, various additives are added to the electrolytic solution, and some effects have been confirmed. For medium- and high-voltage capacitors of 100 V or more, JP-A-62-6615 and JP-A-63-7613 have been proposed as a method of adding an additive to an electrolytic solution, but the effect is still insufficient. Further, even if the water content in the electrolytic solution is reduced, the deterioration of the oxide film can be suppressed, but it is difficult to reduce the water content to a certain amount or less due to other characteristics such as chemical conversion and specific resistance.

The present invention has been made in view of the above problems, and an object thereof is to effectively suppress deterioration of the anode foil and reduce the leakage current of the electrolytic capacitor.

(Means for Solving the Problems) The present invention according to the above object is characterized in that urea phosphate or pyrophosphoric acid or a salt thereof is added to the electrolytic solution for an electrolytic capacitor.

The amount of urea phosphate or pyrophosphoric acid or a salt thereof added is preferably 0.05 to 3% by weight in the case of ethylene glycol-based electrolytic solution, and 0.05 to 5% by weight in the case of γ-butyrolactone-based electrolytic solution. Is preferred.

(Function) In the conventional electrolytic solution, phosphoric acid was added for the purpose of increasing the spark voltage, but when phosphoric acid was added, there was a problem that the deterioration of the leakage current of the electrolytic capacitor increased.

As a result of various studies on additives that maintain a high spark voltage and have little leakage current deterioration, the inventors have found that urea phosphate [C
It was found that O (NH ₂ ) ₂ · H ₃ PO ₄ ], pyrophosphoric acid [H ₄ P ₂ O ₇ ] and salts thereof are effective. Although the reason why these additives are effective in suppressing the deterioration of the leakage current is not clear, it is considered that they act on the aluminum oxide film of the anode foil to suppress the deterioration of the oxide film.

(Examples) Hereinafter, the present invention will be described in detail based on Examples.

Solvents for the electrolytic solution include alcohols such as ethylene glycol and diethylene glycol, glycol ethers such as ethylene glycol monomethyl ether, esters of ethylene glycol monomethyl acetate, N,
Polar organic solvents such as acid amides such as N'-dimethylformamide, nitriles such as acetonitrile, or cyclic esters such as γ-butyrolactone can be used, but those having ethylene glycol or γ-butyrolactone as a main solvent are particularly preferable. It is suitable.

As the solute, carboxylic acids such as succinic acid, adipic acid and azelaic acid or salts thereof, or aromatic carboxylic acids such as benzoic acid, salicylic acid and phthalic acid or salts thereof, or inorganic acids such as boric acid or salts thereof Dissolve at least one.

Table 1 shows the composition and the spark voltage of the electrolytic solution containing the additive according to the present invention and using ethylene glycol as the main solvent. Conventional Example 1 is a case where no additive is added, and the spark voltage is extremely low. In Conventional Example 2, phosphoric acid was added as an additive, and the spark voltage was considerably higher than that in Conventional Example 1. In Example 1, urea phosphate was added as an additive, and in Example 2, pyrophosphoric acid was added. In both Examples 1 and 2, a higher spark voltage than the conventional example could be achieved.

Table 2 shows the composition and spark voltage of those containing γ-butyrolactone as the main solvent. In Example 3, urea phosphate was added as an additive, and in Example 4, pyrophosphoric acid was added. In the past, phosphoric acid was added to increase the spark voltage,
It was possible to achieve a higher spark voltage in both Examples 3 and 4.

FIG. 1 shows a 250 WV 4.7 μF capacitor manufactured by impregnating the electrolytic solution of Conventional Example 2 and Examples 1 and 2.
It is a graph showing changes in leakage current in a 05 ° C. no-load standing test. It can be seen that in Conventional Example 2 in which phosphoric acid is added, the leakage current increases, whereas in all Examples, the leakage current increase is significantly suppressed.

FIG. 2 shows 1 of a 63 WV 100 μF capacitor manufactured by impregnating the electrolytic solution of Conventional Example 4 and Examples 3 and 4.
The change of the leak current in a 05 degreeC unloaded leaving test is shown.
It can be seen that even a γ-butyrolactone-based electrolytic solution has a remarkable effect of suppressing leakage current.

FIG. 3 is a graph showing the relationship between the amount of urea phosphate added and the spark voltage in an electrolytic solution containing ethylene glycol as a main solvent. As is clear from the figure, the effect of increasing the spark voltage is recognized when the addition amount is 0.05 to 3% by weight, but the effect is small when the addition amount is 0.05% or less or 3% or more.

FIG. 4 is a diagram showing the relationship between the amount of urea phosphate added to the γ-butyrolactone-based electrolyte and the spark voltage. In this case, a remarkable effect was observed when the addition amount was 0.05 to 5%.

Regarding the above relationship between the added amount and the spark voltage, it has been confirmed that similar effects can be obtained with pyrophosphoric acid and salts thereof.

(Effect of the Invention) As described above, according to the present invention, not only can the spark voltage of the electrolytic solution be remarkably increased to increase the working voltage of the capacitor, but also the change over time of the leakage current can be suppressed and the reliability is high. An electrolytic capacitor can be provided.

[Brief description of drawings]

Fig. 1 is a diagram showing the change over time in the leakage current in a 105 ° C no-load storage test of an electrolytic capacitor using an ethylene glycol-based electrolytic solution, and Fig. 2 is an electrolytic capacitor using a γ-butyrolactone-based electrolytic solution at 105 ° C The figure which shows the time-dependent change of the leak current in a load leaving test, FIG. 3 is a figure which shows the relationship between the addition amount of urea phosphate in an ethylene glycol electrolyte, and a spark voltage, and FIG. 4 is a gamma-butyrolactone electrolyte. It is a figure which shows the relationship between the addition amount of urea phosphate, and a spark voltage.

Claims (5)

[Claims] 1. An electrolytic solution for driving an electrolytic capacitor, wherein urea phosphate, pyrophosphoric acid or a salt thereof is added to the electrolytic solution for driving an electrolytic capacitor. 2. The electrolytic solution for driving an electrolytic capacitor according to claim 1, wherein the main solvent is ethylene glycol. 3. The electrolytic solution for driving an electrolytic capacitor according to claim 1, wherein the main solvent is γ-butyrolactone. 4. The electrolytic solution for driving an electrolytic capacitor according to claim 2, wherein urea phosphate or pyrophosphoric acid or a salt thereof is added in an amount of 0.05 to 3% by weight. 5. The electrolytic solution for driving an electrolytic capacitor according to claim 3, wherein urea phosphate, pyrophosphoric acid or a salt thereof is added in an amount of 0.05 to 5% by weight.