JPS60136216A - Electrolyte for electrolytic condenser - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrolytic solution for an electrolytic capacitor.

A so-called dry electrolytic capacitor in which a capacitor element is impregnated with a liquid electrolyte, that is, an electrolytic solution, uses a metal such as aluminum with a valve action as an anode electrode 16, as shown in FIG. An uneven surface 2 is formed by processing such as etching to increase the surface area, and an oxide film layer 3 serving as a dielectric is formed on the surface by means such as anodic oxidation, and a separator paper 4 is placed on the upper surface.
Further, cathode electrodes 5 are successively stacked one on top of the other, and external leads 7 are connected to both the anode and cathode electrodes 1.5, respectively.

An electrolytic solution 6 is interposed between the oxide film layer 3 and the cathode electrode 5 and is held by a separator paper 4.

This electrolytic solution 6 is in contact with the uneven surface 2 of the oxide film layer 3, and serves as a true cathode. (The cathode electrode 5 serves as a current collector rather than a cathode.) Furthermore, this electrolytic solution 6 acts on the oxide film layer 3 to repair the defective and deteriorated parts of the oxide film layer 3. It has both functions.

As described above, the electrolyte is an extremely important component in an electrolytic capacitor, and the characteristics of the electrolyte greatly influence the characteristics of the electrolytic capacitor.

In order to reduce the loss or equal series resistance of the electrolytic capacitor, it is necessary to lower the specific resistance value of the electrolytic solution itself. Furthermore, the operating voltage of electrolytic capacitors ranges from a few volts to more than 450 volts, and as the voltage increases, the electrolyte must have sufficient withstand voltage (usually the electrolyte itself is exposed to the spark voltage that causes a spark). Ru.

Conventional electrolytes are made by dissolving adipic acid or its salts in a solvent mainly composed of ethylene glycol for low pressure applications.
Ethylene glycol-adipic acid based electrolytes are commonly used. This type of electrolyte has a specific resistance value of 300Ω.
The voltage can be lowered to cm or less, but the withstand voltage, that is, the spark voltage, can only reach about 250 cm, and in actual commercialization, the limit is a product with a rated voltage of 160 cm.

On the other hand, an ethylene glycol-boric acid electrolyte is known as an electrolyte for medium and high pressures, which is obtained by dissolving boric acid or a salt thereof in a solvent mainly composed of ethylene glycol. Although this type of electrolytic solution has a high spark voltage, it has a specific resistance value of 1/0 cm or more even in the normal operating temperature range, and has the disadvantage of large losses.

The present invention has been made to improve upon these conventional drawbacks, and aims to provide an electrolytic solution that has both low resistivity and high withstand voltage characteristics, and that enables an electrolytic capacitor with excellent characteristics in the medium and high voltage range to be obtained.

The electrolytic solution of the present invention is characterized by dissolving 3-methyladipic acid or its salt in a solvent mainly composed of ethylene glycol.The present invention will be described in detail below based on Examples.

First, a comparison will be shown between the 3-methyladipic acid used in the electrolytic solution of the present invention and the adipic acid conventionally used in the low-pressure electrolytic solution ζ.

FIG. 2 is a graph showing the relationship between the amount of 3-methyladipic acid and adipic acid dissolved in ethylene glycol and the specific resistance value. As is clear from this graph, both show almost the same curves of resistivity versus dissolved amount, but the dissolved amount of adipic acid is 20 g (weight%: 16.7') for 10.0 g of ethylene glycol.
), whereas 3-methyladipic acid can dissolve 45 g (31% by weight) or more, and even lower resistivity values are obtained in this region where the amount dissolved is large.

Next, let's look at the relationship between the amount of melting and the spark voltage.

Figure 3 is a graph showing this relationship, and like the previous one, this graph also shows 3-
This figure shows the relationship between the amount of dissolved methyladipic acid and the spark voltage. As can be seen from this graph, 3-methyladipic acid provides a much higher spark voltage value than adipic acid, although the reason is not clear, which is impossible with conventional ethylene glycol-adipic acid electrolytes. This indicates that it can be used in high pressure areas.

These results show that the electrolytic solution using 3-methyladipic acid of the present invention has a low resistivity value equivalent to that of the conventional ethylene glycol-adipic acid electrolytic solution, and can be used even in a high voltage range. .

Regarding the relationship between the solvent and the amount of solute dissolved, as mentioned above, the 3-methyladipic acid of this invention exhibits higher solubility than adipic acid, but as the amount of solute increases, the specific resistance value decreases. However, at the same time, the spark voltage also drops, and there is a risk that solutes will precipitate at low temperatures. On the other hand, if the amount dissolved is small, the specific resistance value cannot be reduced and corrosion resistance cannot be sufficiently obtained. For these reasons, the preferable solubility range for the electrolytic solution is 1 to 30% by weight of 3-methyladipic acid relative to ethylene glycol.

Next, an electrolytic solution of the present invention and an ethylene glycol-boric acid based electrolytic solution were produced as prototypes and their characteristics were compared.

The composition of the prototype electrolyte is as follows.

Examples of the present invention Ethylene glycol 87% by weight 3-methyladipic acid 9% by weight Ammonia water 4% by weight Specific resistance value 400Ωcm/30°C [Ethylene glycol 67% by weight Boric acid 16.5% by weight Ammonium pentaborate 16.5% by weight % Specific resistance value 1000 Ωcm/30°C As can be seen from this composition table, the specific resistance value at 30°C is 1000 Ωcm for conventional boric acid-based electrolytes, whereas the electrolyte of this invention has an extremely high 400 Ωcm. It shows a low value. Furthermore, Figure 4 is a graph showing the relationship between the specific resistance and temperature of both.As is clear from this graph, the electrolytic solution of this invention has a specific resistance value compared to the conventional one even at low temperatures. It can be seen that the characteristics at low temperatures are also excellent.

Next, an electrolytic capacitor is manufactured using both electrolytes,
We compared their characteristics.

The manufactured electrolytic capacitors had a rated voltage of 250 V and a capacitance of 470 μF, the electrolytes used were those of the above-mentioned example of the present invention and those of the conventional example, and all other components and assemblies were kept under the same conditions.

Then, the above capacitor was subjected to a 1000 hour load test under high temperature (85 degrees Celsius) with rated voltage (250V) applied.
Similarly, a no-load storage test was conducted at 85° C. for 1000 hours to determine changes in characteristics over time.

What was measured was the capacitance change rate (%) relative to the initial value.
, leakage current value (μA), tangent of loss angle (Tanδ),
Figure 5 shows the results of the load test, and Figure 6 shows the results of the no-load test. In both figures, (A) is the capacitance change rate, (
B) shows the change in leakage current and loss angle tangent. Note that the load test is the average value of 10 electrolytic capacitors for both the present invention example and the conventional example, and the no-load test is the average value of 5 electrolytic capacitors each.

In both figures, the lines connected by ○ represent the characteristics of the electrolytic capacitor of the present invention, and the lines connected by ◯ represent the characteristics of the conventional example.

Looking at the test results, it can be seen that in the load test, the rate of change in capacitance is smaller in the example of the present invention than in the example of the present invention. Next, although there is almost no difference in the leakage current between the two, the tangent of the loss angle has maintained a constant low value in the example of the present invention from the beginning, and this is due to the difference in the specific resistance value of the electrolyte itself. is clearly visible.

Next, looking at the no-load test, the capacitance change rate and loss angle tangent show the same trends as the load test, and the leakage current increases significantly over time in the conventional test, whereas the leakage current increases significantly over time. It is recognized that the material of the present invention shows little change and maintains stable characteristics even under high temperature and no-load conditions.

As described above, the electrolytic solution of the present invention can be used as an electrolytic solution for medium and high voltage electrolytic capacitors, which cannot be used with conventional ethylene glycol-adipic acid electrolytic solutions.

In addition, the ethylene glycol-boric acid electrolyte that has been conventionally used as an electrolyte for medium and high voltages has a high specific resistance, making it difficult to reduce the loss or equal series resistance value of electrolytic capacitors. Since the electrolytic solution has an extremely small specific resistance value, it is possible to reduce the loss of the electrolytic capacitor or the equal series resistance value. This makes it possible to use electrolytic capacitors in power supply circuits such as inverters that have high voltages and large ripple currents, which was previously difficult to do.

Furthermore, since the electrolytic solution of the present invention has a high solubility of 3-methyladipic acid as a solute in ethylene glycol, the electrolytic solution has improved corrosion resistance and can withstand cleaning with halogenated hydrocarbons. Furthermore, the high solubility means that there is little precipitation of solutes at low temperatures, and stable properties can be maintained even at low temperatures.

As described above, the electrolytic capacitor using the electrolyte of the present invention has excellent electrical characteristics and stable life characteristics.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the structure of an electrolytic capacitor, Figure 2 is a graph showing the relationship between the amount of dissolved adipic acid and 3-methyl adipic acid and the specific resistance, and Figure 3 is a graph showing the relationship between adipic acid and 3-methyl adipic acid.
- A graph showing the relationship between the dissolved amount of methyl adipic acid and the spark voltage. Figure 4 is a graph showing the relationship between the temperature and specific resistance of the electrolytic solution of this invention and the conventional example. Figures 5 and 6. is a graph showing the results of a life test of electrolytic capacitors using the electrolyte of the present invention and a conventional electrolyte, FIG. 5 shows the results of the load life test, and FIG. 6 shows the results of the no-load life test. In each figure, ('A) shows the rate of change in capacitance, and (B) shows the changes in leakage current and the tangent of the loss angle. 1. Anode electrode, 2. Uneven surface, 3. Oxide film layer, 4
...Separator paper, 5..Cathode electrode, 6..Electrolyte, 7.
・External lead. Patent applicant Nippon Chemi-Con Co., Ltd. Fig. 1 01510 20 30 4045 S551 "1i Mi 1hi (9) / EG1009 Fig. 3 > Sga JJ (9) / EG100g Fig. 4 Fig. 5 (A) 5th purchase B)

Claims (1)

[Scope of Claims] An electrolytic solution for an electrolytic capacitor, characterized in that 3-methyladipic acid or a salt thereof is dissolved in a solvent mainly containing +11 ethylene glycol. (2) The electrolytic solution for an electrolytic capacitor according to claim 1, wherein the amount of 3-methyladipic acid or its salt dissolved in ethylene glycol is in the range of 1 to 30% by weight. (3) The electrolytic solution for an electrolytic capacitor according to claim 1 or 2, wherein the salt of 3-methyladipic acid is an ammonium salt.