JPH0342695B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electrolytic solution for driving an electrolytic capacitor (hereinafter simply referred to as an electrolytic solution), and particularly to an electrolytic solution having excellent electrical conductivity.

(Prior art and its problems) In general, electrolytic capacitors include an anode foil, which is made by etching a high-purity aluminum foil to increase its surface area, and then anodizing the surface to make it a dielectric material, and an etched electrode facing the anode foil. The element is wound up with a separator paper interposed between it and the cathode foil, and is impregnated with an electrolyte.

In such electrolytic capacitors, the characteristics of the electrolytic solution are a major factor in determining the performance of the electrolytic capacitor.

In particular, with the miniaturization of electrolytic capacitors in recent years, anode foils or cathode foils with a high etching rate are being used, and the resistivity of the capacitor body is increasing. High conductivity with low resistivity (specific resistance) is always required.

By the way, conventional electrolyte solutions use ethylene glycol as the main solvent and water (1% to 30% by weight).
In many cases, ammonium carboxylate such as adipic acid or benzoic acid is dissolved as an electrolyte.

An electrolyte using ammonium carboxylate as an electrolyte has a specific resistance of 300 to 400 Ωcm, which is much lower than that using conventional boric acid as an electrolyte.

However, in those using this ammonium carboxylate, the limit was to lower the specific resistance to about 80 Ωcm.

In other words, the specific resistance of the electrolyte increases as the amount of solute increases.
It is possible to reduce this by increasing the amount of water added to other solvents such as ethylene glycol, but if the water concentration exceeds 30% by weight, the electrolyte will react with the electrode foil at high temperatures. This is to generate gas and increase the internal pressure of the electrolytic capacitor.

Therefore, in the past, the maximum amount of water was 30% by weight.
Although it was possible to reduce the specific resistance to about 80 Ωcm by adding a certain amount, it was impossible to expect a further reduction in the specific resistance, and furthermore, it was difficult to use it at high temperatures of 105° C. or higher.

(Object of the invention) The present invention has been made to solve the above problems, and its purpose is to reduce the concentration of water.
Even at a high concentration of 30% to 70% by weight, the increase in the internal pressure of the capacitor at high temperatures is suppressed, making it possible to use it at high temperatures and providing an electrolytic solution with low resistivity. be.

(Summary of the Invention) The present invention includes the following configuration to solve the above problems.

That is, the present invention provides ethylene glycol, ethylene glycol monomethyl ether, N.
An organic solvent such as N'dimethylformamide or γ-butyrolactone and water are used as a solvent, and an organic carboxylic acid or its salt such as adipic acid, benzoic acid, or salicylic acid is dissolved as a solute in this solvent, and gluconic acid is further added as an additive. and/or lactone of gluconic acid is added.

Gluconic acid and its lactone are compounds with the chemical formula shown below, and in an aqueous solution, each transforms into the other two, and exists as an equilibrium mixture of the three.

■■■ Tortoise Shell [0016] ■■■ Therefore, even if only D-gluconic acid is added, an equilibrium mixture of the above three components will be formed in an aqueous solution.

In the present invention, even if the above-mentioned additive such as gluconic acid is added, when the concentration of water is 30% by weight or less, the resistivity is not much different from that of the conventional one, but Stability has been significantly improved compared to conventional models.

In addition, what should be noted in the present invention is that by adding the above-mentioned gluconic acid etc. as an additive,
Even if the water concentration is 30% by weight or more, the reaction between the electrolytic solution and the electrode foil at high temperatures is suppressed, and almost no gas is generated. Therefore, the internal pressure of the capacitor does not increase even at high temperatures, making it possible to use it at high temperatures. Also, as expected, the resistivity decreases, and when the water concentration is 50% by weight, the resistivity is 20Ω.
cm, which is sufficiently low. Water concentration up to 70
Even at about % by weight, the reaction between the electrolytic solution and the electrode foil at high temperatures was suppressed.

The amount of gluconic acid and gluconic acid lactone added is
Even a trace amount of about 0.1 to 0.2% by weight was effective.

Although it is not certain that the reaction between the electrolytic solution and the electrode foil is suppressed by adding gluconic acid or the like, it is thought that the gluconic acid or the like makes the surface of the electrode foil inert.

As the solvent, a mixture of water and an organic solvent such as ethylene glycol, ethylene glycol monomethyl ether, NN/N' dimethylformamide, or γ-butyrolactane is used.

Further, as the solvent, an organic carboxylic acid such as adipic acid, benzoic acid, salicylic acid, sebacic acid, azelaic acid, or a salt thereof is used.

In addition to the gluconic acid and gluconic acid lactone mentioned above, the addition of ethylenediaminetetraacetic acid or its salt as an additive made it possible to further suppress the reaction between the electrolytic solution and the electrode foil at high temperatures.

(Example) Examples according to the present invention will be described below.

Table 1 shows the composition of a conventional example in which ethylene glycol is the main solvent, ammonium adipate and ammonium benzoate are dissolved as the main solutes, and ethylene glycol and water are the main solvents, ammonium adipate is the main solute, and ethylene diamine is used as the additive. An example of the present invention is shown in which tetraacetic acid and D-gluconic acid-δ lactone are dissolved.

The composition of the electrolyte is expressed in weight%, and the specific resistance depends on the temperature of the electrolyte.
It is at 30℃.

■■■ Turtle Shell [0010] ■■■ Table 2 also shows the results of a 1000-hour load test at 105° C. for electrolytic capacitors (10V 2200 μF) based on each composition in Table 1.

■■■ Tortoise Shell [0011] ■■■ As seen in Conventional Example 3 in Table 1, the specific resistance can be significantly lowered by increasing the concentration of water and ammonium adipate; As seen in No. 3, a lot of gas was generated during the load test, and the explosion-proof valve was activated in a short period of time.

However, as can be seen from the examples in Table 2, even if the specific resistance was lowered by increasing the concentration of water and ammonium adipate, the properties remained stable even after 1000 hours at 105°C by adding a small amount of the additive of the present invention. It shows.

Although excellent high-temperature load characteristics can be obtained even in the presence of a high concentration of water, the high-temperature load characteristics can be further improved by adding the additive of the present invention to a conventional electrolytic solution containing a low concentration of water. Needless to say.

(Effects of the Invention) As described above, the electrolytic solution according to the present invention has excellent stability at high temperatures, and in particular, even when the water concentration is 30% by weight or more, the electrolytic solution can be used at high temperatures of about 105°C. The reaction between the electrolyte and the electrode foil can be suppressed, and an electrolytic solution with high water concentration and low resistivity can be provided.

Further, by using the electrolyte of the present invention, an aluminum electrolytic capacitor with low loss and high reliability can be provided.

Although the present invention has been variously explained above with reference to preferred embodiments, the present invention is not limited to these embodiments, and it goes without saying that many modifications can be made without departing from the spirit of the invention. It is.

Claims (1)

[Scope of Claims] 1. An organic solvent such as ethylene glycol, ethylene glycol monomethyl ether, N/N' dimethylformamide, or γ-butyrolactone and water are used as a solvent, and an organic solvent such as adipic acid, benzoic acid, or salicylic acid is added to this solvent. An electrolytic solution for driving an electrolytic capacitor, comprising dissolving a carboxylic acid or a salt thereof as a solute, and further adding gluconic acid and/or lactone of gluconic acid as an additive. 2. The electrolytic solution for driving an electrolytic capacitor according to claim 1, further comprising ethylenediaminetetraacetic acid or a salt thereof as an additive. 3. The electrolytic solution for driving an electrolytic capacitor according to claim 1 or 2, wherein the concentration of water is 1% to 70% by weight. 4 Gluconic acid lactone is D-gluconic acid-
The electrolytic solution for driving an electrolytic capacitor according to claim 1, 2 or 3, which is γ-lactone or D-gluconic acid-δ-lactone.