JPH0638382B2 - Electrolytic solution for electrolytic capacitors - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to improvement of an electrolytic solution for an electrolytic capacitor, and more specifically, addition of a solute that produces condensed water while maintaining and improving good characteristics of the electrolytic capacitor. The present invention relates to an improvement in an electrolytic solution for an electrolytic capacitor, the amount of which is reduced to improve withstand voltage properties and enable use at high temperatures.

[Conventional technology]

Electrolytic capacitors are small, large-capacity, inexpensive and have excellent characteristics such as smoothing of rectified output, and are one of the important components of various electric and electronic devices. Generally, aluminum whose surface is converted into an oxide film by electrolytic oxidation is used. The film is used as an anode, the oxide film is used as a dielectric, and an electrolytic solution is interposed between the film and the collector cathode. It is stable because the oxide film is constantly regenerated during use, but for example, if it is not used for a long period of time, regeneration will be insufficient and deteriorate. Since the electrolytic capacitor is used while undergoing a chemical reaction, its characteristics largely depend on the properties of the electrolytic solution. Maintaining a steady state of the chemical reaction that takes place between the aluminum electrode whose surface is an oxide film and the electrolytic solution, and maintaining a good state of the aluminum oxide film that is the dielectric are important for stabilizing performance. If the chemical steady state is disturbed by, for example, an excessive high voltage load, the aluminum oxide film will be destroyed and eventually the insulation will be broken, but even if it does not reach that level, it causes inconvenience other than the prescribed chemical reaction during use. When the chemical reaction progresses, particularly in the case of gas generation in a capacitor that does not have a valve for letting out gas, the appearance of the capacitor is significantly deteriorated, and there is a risk of explosion when the internal pressure rises extremely.

Since the capacitance of a capacitor is proportional to the dielectric constant of the dielectric, a dielectric having a high dielectric constant should be used to avoid physicochemical changes in the dielectric during use and maintain the dielectric constant high. The tangent of the loss angle, which is the difference between the phase of the charging current and the phase of the external electrolysis, that is, the dielectric loss tangent is used as a measure of the power consumption of the capacitor, and a small value indicates that the power consumption is low. The leakage current, which is the current that flows when a certain value is reached after the start of charging, is due to the steady movement of the charge carriers in the dielectric, and if the ions generated by dissociation of impurities in the dielectric are the main charge carriers. It is believed that the magnitude of the change in leakage current reflects the stability of the electrochemical state of the dielectric. Scintillation is a phenomenon in which the electrochemical state fluctuates as a result of a change in the physical properties of the dielectric material due to a high voltage load due to an increase in the load voltage of the capacitor and a temporal change in the dielectric constant. Can be used as a scintillation voltage (spark voltage) to measure the withstand voltage of the capacitor, and the higher the scintillation voltage, the greater the withstand voltage of the capacitor. The poor appearance of the electrolytic capacitor and the opening of the safety valve are mainly caused by the generation of gas due to the progress of inconvenient chemical reactions other than the specified chemical reactions.The chemical reactions depend on the temperature, and especially at high temperatures, there is a risk of explosion and explosion. This is one of the important indexes for evaluating the overall performance of capacitors because it may be accompanied.

In the conventional general electrolytic solution for electrolytic capacitors, it was necessary to add a large amount of boric acid in order to prepare an electrolytic solution that requires high voltage resistance. In this case, a protic solvent such as ethylene glycol must be used as a main solvent in the solvent of the electrolytic solution, and boric acid reacts with this type of solvent to generate a large amount of condensed water. It was difficult to use at high temperature because it caused internal pressure rise and valve opening failure when used at high temperature.The melting points of various solvents are shown here, but capacitors using a protic solvent such as ethylene glycol and glycerin have low temperatures ( At −40 to 55 ° C.), the electrostatic capacity is lost and it cannot be used. Therefore, in order to maintain the characteristics at low temperatures, it is necessary to use an aprotic solvent such as butyrolactone or dimethylformamide.

Melting point of protic solvent Ethylene glycol-12.6 ° C Glycerin-18.2 ° C Melting point of aprotic solvent Butyrolactone-44.0 ° C Dimethylformamide-60.4 ° C Dimethylacetamide-20.0 ° C Acetonitrile-43.8 ° C Also, In general, in an electrolytic capacitor, the increase of the dielectric loss tangent, that is, the increase of the power consumption is remarkable especially at the low temperature side. When the dielectric loss tangent is measured, at a constant frequency, even at about 100 ° C., for example, even at around 100 ° C., compared with the value at the normal temperature. Although it does not change so much, it increases geometrically as the temperature decreases on the low temperature side.
At 5 times, at about -50 ° C, the temperature is about 100 times at room temperature, and improvement in this respect has been desired.

Furthermore, when trying to use an aprotic electrolyte solution composed of an aprotic solvent in a wide temperature range of −55 to 130 ° C., in order to prevent the internal pressure of the capacitor from rising, the total dissolved mass of boric acid or the like that generates condensed water should be adjusted. Although it is necessary to reduce the amount, it is necessary to add a certain amount of boric acid in order to maintain a high withstand voltage, and if only an amount of boric acid that does not generate condensation water is added, the characteristics of the capacitor deteriorated significantly. . An electrolytic capacitor using a conventional electrolytic solution for electrolytic capacitors, which requires the addition of a certain amount of boric acid, has been difficult to use at a high temperature such as 130 ° C.

[Problems to be Solved by the Invention]

INDUSTRIAL APPLICABILITY The present invention improves the low temperature characteristics while maintaining good characteristics of the electrolytic solution for electrolytic capacitors, reduces the addition amount of solute necessary for imparting good characteristics, and progresses between solute and solvent during use. It is an object of the present invention to provide an electrolytic solution for an electrolytic capacitor, which suppresses the above-mentioned inconvenient chemical reaction, improves the withstand voltage property, can be used at high temperature, and gives good characteristics over a wide temperature range.

[Means for Solving the Problems]

According to the present invention, in an electrolytic solution for driving an aluminum electrolytic capacitor, an ethylene oxide-modified silicone oil, a methylstyrene-modified silicone oil, a fluorine-modified silicone oil, an amide-modified silicone oil, an alcohol-modified solvent is used in a solvent containing an aprotic solvent as a main solvent. There is provided an electrolytic solution for an electrolytic capacitor, characterized in that a modified silicone oil selected from the group consisting of silicone oil, amino-modified silicone oil, epoxy-modified silicone oil, carboxyl-modified silicone oil and olefill-modified silicone oil is added.

That is, the silicone oil added to the electrolytic solution for electrolytic capacitors of the present invention is a modified silicone oil having a siloxane-bonded main chain and side chains represented by the following formula: In the formula, R is a substituent having the following structure depending on the type of the modified silicone oil: When preparing the electrolytic solution for an electrolytic capacitor of the present invention, a desired effect can be obtained by dissolving a relatively small amount of the modified silicone oil. The concentration of the modified silicone oil to be dissolved is preferably 0.01% or more, more preferably 0.1% or more, 10% is sufficient, and it is not necessary to be higher than 50% at the highest. The optimum concentration varies somewhat depending on the type and amount of the solvent and other solutes used, but the value can be determined as a physical property value unique to each electrolyte solution.

The electrolytic solution for an electrolytic capacitor of the present invention is prepared by adding the modified silicone oil described above to a solvent having an aprotic solvent as a main solvent, and the aprotic solvent is γ-butyrolactone, dimethylformamide, dimethylacetamide,
If selected from the group consisting of acetonitrile, 3-methyl-2-oxazolidinone and dimethyl sulfoxide, a suitable electrolytic solution for electrolytic capacitors can be obtained.

[Action]

It is not clear what action the addition of the modified silicone oil disclosed in the present invention has on the aluminum oxide film dielectric in the electrolytic solution itself.

However, it is presumed that the modified silicone oil having the above-mentioned unique chemical structure has a unique action of suppressing the fluctuation of the electrochemical state when a high voltage is applied to the electrolytic capacitor. As an observable form, this effect is most largely reflected in the scintillation voltage or spark voltage lowering effect when the load voltage increases with time.

In the electrolytic solution for an electrolytic capacitor of the present invention containing the above-mentioned modified silicone oil, the amount of solute added necessary for imparting good characteristics to the electrolytic solution is reduced, and the main solvent is an aprotic solvent. It is possible to significantly reduce the amount of boric acid or the like that promotes the generation of condensed water, and to suppress the progress of an inconvenient chemical reaction between the solute and the solvent, especially during use, which is accompanied by gas generation. it can. This action is
As the observable form, for example, it is most reflected in the appearance defect or the presence or absence of valve opening when the electrolytic capacitor is used for a long time at a high temperature close to the boiling point of water.

The electrolytic solution for an electrolytic capacitor of the present invention uses an aprotic solvent having a freezing point significantly lower than that of a protic solvent, and further improves the low temperature characteristics by the synergistic action with the modified silicone oil described above, even at low temperatures. A stable operation can be performed. As an observable form, this action is most reflected in stabilization of the rate of change in capacitance and suppression of increase in dielectric loss tangent, especially on the low temperature side.

〔The invention's effect〕

The electrolytic capacitor prepared by using the electrolytic solution for electrolytic capacitors of the present invention can reduce the total dissolved mass of boric acid and the like while maintaining and improving the withstand voltage property by adding the organically modified silicone oil, and the temperature can reach 130 ° C. It was possible to use it at a very high temperature, and it was possible to use it up to -55 ° C without precipitation of solutes such as boric acid and solidification of the electrolytic solution at a low temperature.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples.
The invention is not limited to only these examples.

Example 1 An etched foil having an area of 55 x 4000 mm was anodized at 450 V in a boric acid solution. This was used as an anode foil and was wound with paper and a cathode foil to obtain a device. This element is rated at 250
V, 880 μF, size: 50 ^φ × 80 ^l . An electrolytic capacitor was prepared using this device and the electrolytic solution having the following composition (Example 1, Comparative Example 1a or Comparative Example 1b).

The specific resistances Rs of Example 1, Comparative Example 1a, and Comparative Example 1b are 900Ωcm, 1300Ωcm, and 800Ω, respectively.
It was cm.

The results of the high temperature test of the electrolytic capacitors using these electrolytic solutions are shown in Table 1, the scintillation curve is shown in FIG. 1, and the temperature characteristics are shown in FIG.

The electrolytic capacitor using the electrolytic solution of the present invention has almost no capacitance loss (Δcap) even if it is used at 130 ° C. for 1000 hours, and its dielectric loss tangent (tan δ) is slightly increased.
Although the leakage current (LC) also did not change significantly, the electrolytic capacitor using the conventional electrolytic solution was remarkably defective in appearance and was opened during the test.

The scintillation voltages (Vs) of Example 1, Comparative Example 1a and Comparative Example 1b are 520V, 500V and 3 respectively.
Comparative Example 1a having a high boric acid content has a higher Vs than Comparative Example 1b having a low boric acid content, and the electrolytic solution of Example 1 containing the silicone oil of the present invention has a low boric acid content. It showed a high Vs.

The electrolytic capacitor using the electrolytic solution of Comparative Example 1b having a small amount of boric acid exhibited a low temperature characteristic almost equivalent to that of Example 1 (capacitance change rate at low temperature and tangent of loss angle shown in FIG. 2). However, in Comparative Example 1a containing a large amount of boric acid, the low temperature characteristics were unavoidably deteriorated.

That is, when compared with the electrolytic capacitor of Example 1 using the electrolytic solution for electrolytic capacitors to which the modified silicone oil of the present invention is added, Comparative Example 1a has a relatively high Vs but a large amount of boric acid, so at low temperature characteristics and at 130 ° C. Comparative Example 1b, which is inferior in the life test and has a small amount of boric acid, has a low Vs of 130 ° C.
Inferior in life test in.

Examples 2 to 8 Electrolytic capacitors were prepared and tested in substantially the same manner as in Example 1 except that the electrolytic solution having the following composition was used. The composition of the electrolytic solution and the test results are shown below.

Composition of Electrolyte Solution (wt%) Example 2 Comparative Example 2 Dimethylformamide 86.6 90.3 Ammonium phthalate 8.2 8.3 Boric acid 1.2 1.4 Ethylene oxide modified 4.0-Silicone oil Test results Example 2 Comparative Example 2 Specific resistance (Ωcm) 180 170 Sparks Voltage (V) 150 80 Electrolyte composition (wt%) Example 3 Comparative Example 3 Dimethylacetamide 83.3 87.3 Phthalic acid 7.9 7.9 Boric acid 1.6 1.6 Triethylamine 3.2 3.2 Ethylene oxide modified 4.0-Silicone oil Test results Example 3 Comparative Example 3 Specific resistance (Ωcm) 258 245 Sparking voltage (V) 150 100 Composition of electrolyte (wt%) Example 4 Comparative Example 4 Acetonitrile 90.1 91.0 Tetrafluoroboric acid 9.0 9.0 Lutidine salt Ethylene oxide modified 0.9-Silicone oil Test result Example 4 Comparative Example 4 Specific resistance (Ωcm) 50 40 Spark voltage (V) 75
40 Composition of Electrolyte Solution (% by Weight) Example 5 Comparative Example 5 3-Methyl-2-83.0 87.0 Oxazolidinone Borodisalicylic Acid 13.0 13.0 Ammonium Ethylene Oxide Modified 4.0 Silicone Oil Test Results Example 5 Comparative Example 5 Specific Resistance (Ωcm) 215 140 Spark voltage (V) 203 80 Electrolyte composition (wt%) Example 6 Comparative Example 6 3-Methyl-2-85.1 87.0 Oxazolidinone Borodisalicylic acid 13.0 13.0 Ammonium α-methylstyrene modified 1.9-Silicone oil Test results conducted Example 6 Comparative Example 6 Specific resistance (Ωcm) 210 205 Spark voltage (V) 140 80 Composition of electrolyte (wt%) Example 7 Comparative Example 7 Acetonitrile 89.1 91.0 Tetrafluoroboron 9.0 9.0 Lutidine salt Fluorine modified 1.9-Silicone oil test Results Example 7 Comparative example 7 Specific resistance (Ωcm) 50 40 Sparking voltage (V) 75 40 Composition of electrolyte (wt%) Example 8 Tonitrile 91.0 Tetrafluoroboron 9.0 Lutidine salt Amide modified 1.9 Silicone oil test results Example 8 Specific resistance (Ωcm) 50 Spark voltage (V) 80 The above example is an example with an aprotic solvent, -55 Low m.p. for use at p. Must be used (aprotic). These solvents have low solubility of boric acid and low concentration limits. By adding silicone oil to these, it is possible to increase the working voltage without the need to add boric acid, or without increasing the amount, and there is a merit as an electrolytic solution. Although these cannot all be used at 130 ° C., the merit of increasing the breakdown voltage is not lost.

[Brief description of drawings]

FIG. 1 is a scintillation curve comparing an electrolytic capacitor using the electrolytic solution of the present invention with an electrolytic capacitor using a conventional electrolytic solution, and FIG. 2 is an electrolytic capacitor using the electrolytic solution of the present invention and electrolysis using a conventional electrolytic solution. It is a figure which shows the temperature characteristic (capacity change rate and the temperature dependence of the tangent (dielectric loss tangent) of a loss angle) which compared with a capacitor. FIG. 1 shows the measurement with a plain foil Vs (unetched and unformed), an electrode area of 1 cm ² , and a current density of 10 mA / cm ² . FIG. 2 shows initial values of 20 ° C., 120 Hz, W. V.
It was measured after setting for 3 minutes. In FIG. 2, x indicates that in Example 1, ◯ indicates that in Comparative Example 1a, and ● indicates that in Comparative Example 1b.
Shows the thing.

Claims (2)

[Claims] 1. An electrolytic solution for driving an aluminum electrolytic capacitor, wherein an ethylene oxide-modified silicone oil, a methylstyrene-modified silicone oil, a fluorine-modified silicone oil is used in a solvent containing an aprotic solvent as a main solvent.
For electrolytic capacitors, characterized in that a modified silicone oil selected from the group consisting of amide-modified silicone oil, alcohol-modified silicone oil, amino-modified silicone oil, epoxy-modified silicone oil, carboxyl-modified silicone oil and olefill-modified silicone oil is added. Electrolyte. 2. The aprotic solvent is γ-butyrolactone,
2. A compound selected from the group consisting of dimethylformamide, dimethylacetamide, acetonitrile, 3-methyl-2-oxazolidinone and dimethylsulfoxide.
The electrolytic solution for the electrolytic capacitor described.