JPH027169B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to improvements in electrolytic solutions for electrolytic capacitors (hereinafter simply referred to as electrolytic solutions), and particularly relates to reducing the specific resistance and improving spark voltage characteristics of electrolytic solutions used in medium-high voltage electrolytic capacitors. Generally, the characteristics of dry electrolytic capacitors are determined by various factors. In particular, it has been found that the characteristics of the electrolytic solution housed in the outer case together with the capacitor element have a large effect on loss (tan δ) or equivalent series resistance (ESR). Conventional electrolytic capacitors, especially medium and high voltage electrolytic capacitors, use ethylene glycol as the main solvent.
An electrolytic solution containing boric acid or its ammonium salt as the main solute is used. However, this so-called ethylene glycol-boric acid electrolyte generally has a conductivity of about 1KΩcm, so it has a high specific resistance value, and therefore electrolytic capacitors using this electrolyte have a high loss and an equivalent series resistance. The value becomes high. In addition to the water contained in each chemical, this type of electrolytic solution generates a large amount of water due to the esterification reaction between ethylene glycol and boric acid. The moisture accelerates the deterioration of the dielectric oxide film formed on the surface of the anode electrode foil, making it difficult to maintain stable electrical characteristics for a long period of time as an electrolytic capacitor. Furthermore, water generated from the electrolytic solution sometimes vaporizes due to the heat generated inside the electrolytic capacitor, turning into a large amount of water vapor. In particular, at high temperatures of 100° C. or higher, the internal pressure caused by the water vapor could deform the outer case or cause the explosion-proof valve to operate. Furthermore, in a low temperature range, boric acid has low solubility, so crystals tend to precipitate. Therefore,
The limit of the low temperature range in which normal function as an electrolyte can be expected is -25°C, and in combination with the above-mentioned maximum operating temperature, electrolytic capacitors can only be obtained in a narrow operating temperature range of -25 to 100°C. In addition, so-called ethylene glycol-adipic acid electrolytes, in which ethylene glycol is the main solvent and adipic acid or its ammonium salt is the main solute, have a specific resistance value that is lower than that of ethylene glycol-boric acid electrolytes. Therefore, electrolytic capacitors using this electrolyte can reduce loss and equivalent series resistance, but the spark generation voltage is also extremely low, so it is difficult to withstand voltage, so it can only be used for low-voltage electrolytic capacitors. Can not. The purpose of this invention is to provide an electrolytic solution that overcomes the above-mentioned defects. Specifically, by using heptane, 4,4-dicarboxylic acid, or a salt thereof as a solute, it is possible to reduce the specific resistance value and generate a high spark. The purpose of this invention is to provide an electrolytic solution for medium-high voltage electrolytic capacitors that realizes voltage characteristics. The present invention is characterized in that it is an electrolytic solution in which heptane, 4,4-dicarboxylic acid, or a salt thereof is dissolved as a main solute in a solvent mainly composed of ethylene glycol. In general, linear dibasic acids such as sebacic acid and azelaic acid have low solubility in glycols, so it is difficult to obtain sufficient properties as an electrolytic solution. However, like heptane, 4,4-dicarboxylic acid,
Since dibasic acids having side chains have high solubility, it is easy to obtain electrolytes with excellent properties. Next, this invention will be specifically explained. An ethylene glycol-boric acid based electrolyte was used as a conventional example and compared with the electrolyte according to the present invention. The composition of each electrolytic solution is as follows. Conventional example ethylene glycol 67wt% Boric acid 16.5wt% Ammonium borate 16.5wt% Example ethylene glycol 84.3Wt% Heptane, 4,4-dicarboxylic acid 11.2Wt% Aqueous ammonia 4.5Wt% Specific resistance values of the above conventional example and example ( Rs), withstand voltage (Vs), and water content in the electrolyte are shown below. In the table, A indicates a conventional example, and B indicates an embodiment of the present invention.

[Table] As is clear from this comparison, the electrolytic solution of the example shows a lower specific resistance value than the electrolytic solution of the conventional example. This seems to be due to the fact that heptane and 4,4-dicarboxylic acid, which are solutes, have 9 carbon atoms as described above, and that they have a structure with side chains. Furthermore, although the specific resistance value is low as described above, the value of the spark generation voltage is conversely high.
Therefore, the withstand voltage is also high. It also has a low water content. That is, as in the conventional example, the esterification reaction between ethylene glycol and boric acid proceeds easily, and 3 moles of water are produced from 1 mole of boric acid. However, as in the example, when heptane and 4,4-dicarboxylic acid, which are dibasic organic acids, are dissolved in ethylene glycol, esterification of ethylene glycol and heptane and 4,4-dicarboxylic acid reaction, heptane,
The amidation reaction with 4,4-dicarboxylic acid and ammonia both has a slow reaction rate, and only 2 moles of water are produced from 1 mole of heptane and 4,4-dicarboxylic acid. Furthermore, since the electrolytic solution of the example has a lower molar concentration of solute than the electrolytic solution of the conventional example, the amount of water produced is also reduced from this point of view. Next, the relationship between the amount of solute, specific resistance value, and spark voltage is shown in FIGS. 1 and 2. FIG. 1 shows the relationship between the amount of solute and the specific resistance value, and FIG. 2 shows the relationship between the amount of solute and spark voltage. According to Figure 2,
When the amount of solute is 10 wt%, the specific resistance value can be reduced to 400 Ωcm or less. Furthermore, it is confirmed that the spark voltage is maintained at approximately 400V or higher even if the amount of solute increases. Next, electrolytic capacitors were manufactured using the electrolytic solution according to the conventional example and the electrolytic solution according to the example, and their electrical characteristics were compared. The sample electrolytic capacitors all have a rated voltage of 400V and a rated capacitance of 10μF.
The outer case used had a diameter of 16φ and a length of 30 mm. In the comparative test, we prepared 10 electrolytic capacitors each impregnated with the electrolytic solution of the conventional example and 10 electrolytic capacitors impregnated with the electrolytic solution of the above example, and measured the initial loss (tan δ) [120 Hz], leakage current (LC),
The average value of equivalent series resistance (ESR) [10KHz] was measured. The results are shown below. In the table, A indicates the conventional example and B indicates the embodiment. Initial characteristics

[Table] According to this result, in the initial characteristics, the example
Compared to the conventional example (A), the electrolytic capacitor (B) has
The loss at 120Hz was approximately 1/2, and the equivalent series resistance value at 10KHz was approximately 1/3. Next, a rated voltage (400V) was applied at a high temperature of 105°C, and the average values of loss and leakage current after 1000 hours were measured, as well as the incidence of appearance defects. The results are shown below. In the table, A indicates the conventional example and B indicates the embodiment. High temperature load characteristics

[Table] As is clear from the measurement results of the high temperature load characteristics, the electrolytic capacitor of Example (B) shows almost the same performance as the initial characteristics even after 1000 hours. Furthermore, there were no appearance defects. On the other hand, in the conventional electrolytic capacitor (A), the electrical characteristics deteriorate significantly, and appearance defects such as bulging of the outer case and operation of the explosion-proof valve occur very often. Furthermore, the temperature characteristics of the electrolytic capacitor according to the conventional example and the electrolytic capacitor according to the example were measured. In this measurement, ten 400V-10μF electrolytic capacitors were prepared as described above, and the average values of the initial characteristics of capacitance (CAP), loss (tanδ), and leakage current (LC) and the average value of temperature characteristics were calculated. It was measured. The average values at 20°C are shown below. In addition,
In the table, A indicates the conventional example and B indicates the embodiment.

[Table] Figure 3 also shows the measurement results of the temperature characteristics of capacitance change rate and loss (tan δ). In FIG. 3, a shows a conventional example, and b shows an embodiment. As is clear from FIG. 3, the electrolytic capacitor according to the example has a small rate of change in capacitance and has particularly good characteristics at low temperatures. In this example, the solute was dissolved in heptane and 4,4-dicarboxylic acid alone, but heptane and 4,4-dicarboxylic acid were dissolved in the form of salts such as ammonium salts and amine salts. Similar effects can be expected. As described above, this invention is characterized by an electrolytic solution in which heptane and 4,4-dicarboxylic acid are dissolved as main solutes in a solvent mainly composed of ethylene glycol, so that the specific resistance value is low and 105
Even at high temperatures exceeding .degree. C., it is possible to realize stable electrical characteristics with low loss and equivalent series resistance, and it is also possible to realize an electrolytic capacitor with low impedance. In particular, regarding the impedance-frequency characteristics of electrolytic capacitors, most of the impedance in the high frequency range of 10KHz to 30KHz near the resonance frequency of the impedance is controlled by the above-mentioned equivalent series resistance. By reducing the impedance of the electrolytic capacitor at high frequencies, it is possible to realize an electrolytic capacitor that exhibits excellent high-frequency characteristics. Furthermore, since the solubility of heptane and 4,4-dicarboxylic acid is high, there is little precipitation of crystals in the low temperature range, which has a favorable effect on the electrical properties. Also, ethylene glycol and heptane, 4,4
- Since the rate of esterification reaction with dicarboxylic acid is slow, the amount of water produced by this reaction is small. Therefore, the produced water does not turn into water vapor at high temperatures, increase the internal pressure of the outer case, and deform the outer appearance of the outer case. Furthermore, since the overall water content is small, deterioration of the dielectric oxide film formed on the anode foil of the electrolytic capacitor can be suppressed, and the life characteristics of the electrolytic capacitor can be improved. As explained above, this invention uses ethylene glycol as the main solvent and heptane, 4,4-dicarboxylic acid or its salt as the main solute, thereby realizing an electrolytic solution with a low specific resistance value and a high spark voltage. can do.

[Brief explanation of drawings]

Fig. 1 is a graph showing the relationship between the amount of heptane and 4,4-dicarboxylic acid, which are the solutes constituting this invention, and the spark voltage.
- A graph showing the relationship between the amount of dicarboxylic acid and specific resistance. FIG. 3 is a graph showing the results of a temperature characteristic measurement test. In the graph, a indicates the conventional example, and b indicates the embodiment of the present invention.

Claims (1)

[Claims] 1. An electrolytic solution for an electrolytic capacitor, characterized in that heptane, 4,4-dicarboxylic acid, or a salt thereof is dissolved as a solute in a solvent mainly composed of ethylene glycol.