JPH0748459B2 - Electrolytic solution for electrolytic capacitors - Google Patents

Description

The present invention relates to an electrolytic solution for an electrolytic capacitor.

(Prior Art) A conventional electrolytic solution in which boric acid or ammonium borate is dissolved in a polyhydric alcohol such as ethylene glycol is used for an aluminum electrolytic capacitor for medium and high voltage. This is because boric acid is a weak acid that is stable with respect to the aluminum oxide film, can improve the withstand voltage, and can obtain flame retardancy that cannot be obtained with an electrolytic solution containing an organic acid as a solute.
For this reason, it is often used for a high-voltage and large-capacity capacitor that is particularly required to have stability.

However, this conventional electrolytic solution generally has a large amount of water in the solution, which deteriorates the dielectric oxide film formed on the anode foil and increases the leakage current (hereinafter abbreviated as LC). Therefore, the amount of hydrogen gas generated is large at high temperatures. There is a problem that the internal pressure rises in a short period of time, causing the case to expand and the explosion-proof valve to operate. In order to solve this problem, a nitro compound is added as a hydrogen gas absorbent as shown in JP-B-49-14300 and JP-B-53-42110, or phosphoric acid is added to improve the water resistance of the dielectric oxide film. Have been added to.

(Problems to be Solved by the Invention) However, even if a nitro compound or phosphoric acid is added, at high temperature, each effect cannot be maintained for a long period of time, and after being left for a long time,
There are drawbacks that LC increases and tan δ changes with time.

Further, when the amount of nitro compound or the like added to the electrolytic solution increases, the leakage current increases, and when the amount is very small, the suppressing effect is low, and there is a drawback that manufacturing is difficult.

The object of the present invention is to improve the above-mentioned drawbacks by improving the LC characteristics and tan.
It is intended to provide an electrolytic solution for an electrolytic capacitor which can improve the δ characteristic and is easy to manufacture.

(Means for Solving the Problem) In order to achieve the above-mentioned object, the present invention is for an electrolytic capacitor that uses a solvent containing a polyhydric alcohol as a main component and at least one of boric acid or a salt thereof as a solute. In an electrolytic solution, at least one kind of polycondensate of phosphoric acid or polycondensate of phosphoric acid ester and at least one kind of mannitol, sorbitol, erythritol or inositol are dissolved. It provides a liquid.

(Function) Compared with phosphoric acid, polycondensation polymer of phosphoric acid or phosphoric acid ester reacts with aluminum ions to form a dense protective film on the electrode surface, which improves water resistance and suppresses gas generation. To be done. In particular, the ethylene glycol-boric acid-based electrolytic solution has a large water content, but when a condensation polymer such as phosphoric acid is added to this electrolytic solution, the dissolution of the aluminum electrode can be reduced, and therefore, the aluminum electrode and the electrolytic solution can be separated from each other. It is possible to suppress the local battery action that occurs in the above, the gas generation due to this action can be reduced, and the LC at the time of voltage application can be reduced.

In addition, even if a polycondensation polymer such as phosphoric acid is added in a relatively large amount, a decrease in spark voltage and an increase in LC can be suppressed.

Furthermore, since mannitol, sorbitol, etc. react with boric acid etc. to form a complex, they are stable at high temperatures and can improve LC characteristics and tan δ characteristics.

(Example) Hereinafter, the present invention will be described based on examples.

As the solvent, polyhydric alcohols such as ethylene glycol and diethylene glycol are used.

Boric acid or ammonium borate is used as the solute.

Then, at least one of a polycondensate of phosphoric acid or a polycondensate of phosphoric acid ester having the following structural formula is dissolved in a liquid containing the solvent and the solute. Addition amount is 0.01-10.0
If it is less than 0.01 wt%, the effect is low, and if it exceeds 10.0 wt%, the spark voltage tends to decrease.

Also, mannitol, sorbitol, erythritol,
Dissolve at least one of the inositols.

Next, a high temperature load test was performed using an aluminum electrolytic capacitor rated at 450 V and 330 μF in which a capacitor element was impregnated with the electrolytic solution of the above-mentioned example and the conventional example, and LC and tan δ were measured.

The composition of the electrolytic solution is as shown in Table 1. The high temperature load test conditions are a temperature of 110 ° C and an applied voltage of 400V.DC. The LC value is a value measured 5 minutes after the sample was left in an atmosphere at a temperature of 20 ° C. for 24 hours, a rated voltage was applied. The measurement results are shown in Table 2.

As is clear from Table 2, comparing the cases where only ammonium borate was used as the solute, Example 1 was observed after standing for 3000 hours.
-Example 10 and Example 12 were 85-130 microampere, and the conventional example 1-conventional example 6 were 130-365 microampere, and the former is a value lower than the latter overall. Also, regarding tan δ,
Examples 1 to 10 and 12 are 0.078 to 0.112, and Conventional Examples 1 to 6 are 0.101 to 0.173, and similarly, the former is suppressed to a lower value.

Examples using ammonium borate and boric acid as solutes
11 and the conventional example 7 also had LC and tan after being left for 3000 hours.
δ is lower in the former than in the latter, and 9/1
It is 1, 14/17.

(Effects of the Invention) As described above, according to the present invention, when mannitol, sorbitol, and the like are dissolved together with a condensation polymer of phosphoric acid or a phosphoric acid ester, the electrolytic capacitor is left at a high temperature. The deterioration of LC and tan δ can be suppressed, and the effect of suppressing gas generation is great, so that the life of the electrolytic capacitor can be improved and an electrolytic solution for an electrolytic capacitor that is easy to manufacture can be obtained.

Claims (1)

[Claims] 1. A polycondensed polymer of a phosphoric acid or a polyester of a phosphoric acid ester in an electrolytic solution for an electrolytic capacitor, comprising a solvent containing a polyhydric alcohol as a main component and at least one of boric acid or a salt thereof as a solute. At least one of the coalesces,
An electrolytic solution for an electrolytic capacitor, which dissolves at least one of mannitol, sorbitol, erythritol, and inositol.