JPS5832774B2 - Electrolyte for driving electrolytic capacitors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a driving electrolytic solution (hereinafter referred to as paste) that provides an electrolytic capacitor that exhibits stable characteristics over a wide temperature range.

There have been remarkable improvements in the performance of electrolytic capacitors in recent years, especially in the operating temperature range of 70 to -55℃.
Products have come to be manufactured and sold that fully cover a wide range of temperatures from low temperatures of 100 to 110 to +150'C.

However, in general, these are so-called low-voltage products with a voltage of 50 to 100 wv or less, and so-called medium-high voltage products with a working voltage higher than this are limited to a narrow temperature range of 25 to +85°C.

Therefore, for example, when low-voltage and medium-high-voltage devices are used simultaneously in the same equipment, the performance of the device is affected by the poor-performance medium-high-voltage products, and the high performance of the low-voltage products cannot be achieved. There is a strong demand for improved capacitor characteristics from various quarters.

The present invention aims to meet this demand, and improved experiments will be explained in detail below.

Currently, boric acid and its ammonium salt are the only solutes that are widely used as solutes for pastes for medium and high pressure applications, and other solutes such as sebacic acid, azelaic acid, and adipic acid are found in patents and other documents. However, none of these have yet been put into practical use.

In other words, even if one tries to make a paste for medium and high pressures using solutes other than boric acid based on patents and other literature, the chemical conversion property, that is, the ability to form an anodic oxide film on valve metals such as aluminum, is low, and the product is not satisfactory. It is impossible to make.

Therefore, if the resistivity of the paste is increased by a conventional method in order to improve the chemical formability, the temperature characteristics of the product will become extremely poor, and the actual situation is that the product must eventually rely on boric acid or its ammonium salt.

On the other hand, as a solvent, low viscosity used for low pressure paste,
There are many different solvents with low freezing points, such as N-N-dimethylformamide and ethylene glycol monomethyl ether.
Since none of these sufficiently dissolves boric acid or its ammonium salt used as a solute, ethylene glycol, which dissolves boric acid or its ammonium salt well, or a mixture thereof with water cannot be selected as the solvent system.

Therefore, various pastes were prepared using ethylene glycol and water as solvents, and boric acid and ammonium borate as solutes, and prototype products were manufactured.
ap) and the tangent of the loss angle (hereinafter referred to as tanδ), and C by a life test at 110°C.
ap.

Changes in tan δ and appearance were examined.

The experimental results regarding specific resistance are shown in the graph of Figure 1, and the temperature characteristics and problems with the life test results are shown in Table 1.

As will be seen from now on, with pastes in the region of good temperature characteristics, that is, in region (2) with relatively low specific resistance, the product was destroyed in the life test, and it was not possible to obtain a paste with good both in temperature characteristics and life test.

However, these results suggested that a paste with relatively low resistivity and a small amount of solute could produce a product with good properties.

Although it is possible to use paste in the area (1) to increase the strength of the capacitor against internal pressure and prevent it from breaking, this method is impractical as it costs 10 to 50 times more than the conventional method.

Although the electrical properties of the paste in the region (2) are good, the temperature properties are poor especially in this region because of the large amount of solute, and even if more solute is added, no significant improvement can be expected.

Therefore, based on the above suggestions, we investigated a method to lower the resistivity in the region I, and found that although it does not have the large chemical formability required for the main solute of medium and high voltage pastes, it has a high degree of ionization and a high electrical conductivity. It has been found that the addition of ammonium adipate, which can be given as a compound, is effective.

The graph of FIG. 2 shows the results of an experiment regarding changes in paste resistivity when ammonium adipate was added.

As can be seen from the graph in FIG. 2, as the amount of ammonium adipate added increases, the root resistivity value decreases.

If the amount of ammonium adipate added is 1.5 g in the same figure, that is, the weight ratio to the electrolyte is approximately 1.2 wt%, it is possible to achieve a specific resistance value of 700 Ω or less, but if the amount added is less than this, In this case, the effect of reducing specific resistance is almost negligible (there is not much difference from the conventional product and it is not suitable).

Therefore, it may be said that it is better to increase the amount of ammonium adipate added, but if one focuses only on reducing the specific resistance value, it can be said that the larger the amount added, the better.

However, as the amount added increases, as shown in FIG. 5, the withstand voltage (Vs) of the paste also decreases, making it impossible to use it as a high-voltage paste.

In the relationship between the rated voltage of the actual product and the withstand voltage of the paste itself, the withstand voltage of the paste must have a margin of about 20 to 30 factors relative to the rated voltage of the product. In order to achieve this, the paste's withstand voltage must be close to 400V.

In addition, when the rated voltage becomes 300V or less, it becomes possible to use other types of low resistivity pastes, so the upper limit of the amount added is naturally limited, and the amount added is approximately 6g, that is, the weight ratio to the electrolyte. It can be said that a range of up to 5 wt% is consistent with the purpose of the present invention.

When we measured the temperature characteristics of products using this paste and conducted a life test at 100℃, we found that the temperature characteristics were equal to or better than those in area (■), and at 110℃.
Even after 1000 hours of testing, the product had no abnormalities in appearance and its properties were very stable.

Next, a paste with the composition shown in Table 2 showing Examples was prepared, a prototype product was made using this, and the temperature characteristics were measured and
A life test at 10°C was conducted.

The experimental results are shown in FIGS. 3 and 4.

Regarding temperature characteristics, conventional electrolytic capacitors (A), (
While the Cap of B) decreases at 25°C to 60-7° of the Cap at 20°C, the present invention (4), (
When paste B) is used, the temperature at -25℃ is 85-90%.
The temperature was also significantly improved to about 70 to 80 at -40°C.

In addition, in the 110℃ life test, the conventional one (4),
While the properties of (B) are already markedly deteriorated after 1000 hours, when pastes of the present invention (4) and (B) are used, 2
It shows stable characteristics even after 1,000 hours, and even after t
The initial value of an δ is also 2/3 of that of conventional products (4) and (B).
and is getting smaller.

As detailed above, although the conventional boric acid-based paste has sufficient chemical formability for high-pressure applications, it has a high specific resistance and thus has performance problems. By adding a conductivity-improving solute that can lower the resistivity of the paste without lowering the resistivity, it is possible to obtain medium- to high-voltage electrolytic capacitors with the same characteristics as currently available wide-temperature-range, low-voltage electrolytic capacitors. Since there is no need to change the structure or other aspects of the product, it is possible to easily supply the product at the same cost, making it extremely useful industrially.

[Brief explanation of drawings]

Figure 1 is a graph showing the results of experiments regarding resistivity, Figure 2
The figure is a graph showing the change in resistivity of the paste when ammonium adipate is added, Figure 3 shows the measurement results of temperature characteristics according to Table 2, and Figure 4 shows the graph of the life test results according to Table 2. show. FIG. 5 is a graph showing the relationship between the amount of ammonium adipate added and the withstand voltage of the paste.

Claims (1)

[Claims] 1 Add 1.2wt% to 5w of ammonium adipate to a basic electrolytic solution using ethylene glycol as a solvent and boric acid and its ammonium salt as a solute, respectively.
An electrolytic solution for driving an electrolytic capacitor, which is added in a range of t%.