JPH0426776B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to improvements in electrolytes for electrolytic capacitors. [Prior art] Electrolytic capacitors are small, large-capacity, inexpensive, and have excellent characteristics such as smoothing rectified output, and are one of the important components of various electrical and electronic devices. It is made by using an aluminum film that has been converted into an oxide film as an anode, the oxide film as a dielectric, and an electrolyte interposed between it and a current collecting cathode. During use, the oxide film is constantly regenerated, so it is stable, but if it is not used for a long time, for example, regeneration becomes insufficient and it deteriorates. Since electrolytic capacitors are used while undergoing chemical reactions, their characteristics greatly depend on the properties of the electrolyte. Maintaining the steady state of the chemical reaction that occurs between the aluminum electrode with an oxide film on its surface and the electrolyte, and maintaining the aluminum oxide film that serves as a dielectric well, is important for stabilizing performance. If the chemical steady state is accidentally disturbed, for example by an excessive high voltage load, the aluminum oxide film will be destroyed and the insulation will eventually break, but even if this does not happen, undesirable chemical reactions other than the prescribed chemical reactions may occur during use. As the reaction progresses, especially when accompanied by gas generation, the appearance of the capacitor will be markedly deteriorated.
If the internal pressure rises to an extreme level, there is a risk of explosion. Since the capacitance of a capacitor is proportional to the dielectric constant of the dielectric material, it is necessary to use a dielectric material with a high dielectric constant and maintain a high dielectric constant during use by avoiding physical and chemical changes in the dielectric material. The loss angle tangent, which is the difference between the phase of the charging current and the phase of the external electrolysis, or the dielectric loss tangent, is used as a measure of the power consumption of a capacitor, and a small value indicates that the power consumption is low. 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 charge carriers in the dielectric, and ions generated due to dissociation of impurities in the dielectric, etc. It is believed that 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 changes in the physical properties of the dielectric due to the high voltage load that occur as the load voltage of the capacitor increases, resulting in changes in the dielectric constant over time.Scintillation is a phenomenon that has been observed. The scintillation voltage can be used as a measure of the voltage resistance of a capacitor, and the higher the scintillation voltage, the greater the voltage resistance of the capacitor. The main cause of poor appearance of electrolytic capacitors is the generation of gas due to the progress of undesirable chemical reactions other than the specified chemical reactions.The rate of chemical reactions depends on the temperature, and especially at high temperatures, the reaction progresses rapidly and may pose a risk of explosion. Therefore, it is one of the important indicators for evaluating the overall performance of a capacitor. In conventional general electrolyte solutions for electrolytic capacitors, it has been necessary to add boric acid to the electrolyte solution in order to obtain high voltage resistance. In this case, a proton solvent such as ethylene glycol is used as the main solvent for the electrolyte, but since boric acid reacts with this type of solvent and generates condensed water, it is especially difficult to use at high temperatures where condensed water is easily gasified. was difficult. The melting points of each solvent are shown here, but capacitors using proton solvents such as ethylene glycol and glycerin lose capacitance at low temperatures (-40 to -55°C) and cannot be used, so their characteristics at low temperatures may vary. In order to maintain this, it becomes necessary to use solvents such as butyrolactone and dimethylformamide (DMF). Pronto ethylene glycol −12.6℃ Melting point Glycerin 18.2℃ Melting point Aprotic butyrolactone −44.0℃ Melting point Dimethylformamide −60.4℃ Melting point Dimethylacetamide −20.0℃ Melting point Acetonitrile −43.8℃ Melting point [Problems to be solved by the invention] The present invention The purpose of this invention is to increase the chemical stability of silicone oil, which has the function of improving voltage resistance, in an electrolytic solution for electrolytic capacitors, and to provide an aluminum electrolytic capacitor that can be used over a wide temperature range. [Means for Solving the Problems] According to the present invention, an electrolytic solution for an electrolytic capacitor, which is characterized in that modified silicone oil is added to a solvent having an aprotic solvent as a main solvent in an electrolytic solution for driving an aluminum electrolytic capacitor. liquid is provided. The electrolytic solution for electrolytic capacitors of the present invention is a modified silicone oil in which a carborane group is introduced into the main chain of siloxane bonds and some or all of the side chain residues are substituted with hydrophobic groups, and an aprotic solvent is used as the main solvent. It is characterized by being added to a solvent. Even if the modified silicone oil introduces something other than a carborane group into the main chain of siloxane bonds, it is possible to obtain a suitable electrolytic solution for electrolytic capacitors, as disclosed below along with preferred embodiments of the present invention for reference. is possible. In other words, if the modified silicone oil has organic and inorganic groups introduced into the main chain of siloxane bonds and some or all of the side chain residues are substituted with hydrophobic groups, a suitable electrolytic solution for electrolytic capacitors can be obtained. I can do it. The modified silicone oil has organic and inorganic groups selected from the group consisting of methylene groups, phenylene groups, borane groups, and carborane groups introduced into the siloxane bond main chain, and some or all of the side chain residues are methyl groups and A more suitable electrolytic solution for electrolytic capacitors can be obtained if the modified silicone oil is substituted with a hydrophobic group selected from the group consisting of phenyl groups. That is, the silicone oil of the present invention is not soluble in protic solvents such as water and ethylene glycol, but is soluble in aprotic solvents such as γ-butyrolactone and DMF (dimethylformamide), and structurally, for example, _R : _{- (} - _{CH 2} -) is a modified silicone oil in which the side chain residue is substituted with a methyl group (-CH ₃ ) and/or a phenyl group. Among these, carborane (−
C ₂ B ₁₀ H ₁₀ −) skeleton has high heat resistance and is most suitable for use at high temperatures. When preparing the electrolytic solution for an electrolytic capacitor of the present invention, the desired effect can be obtained by dissolving a relatively small amount of modified silicone oil. The concentration of modified silicone oil to be dissolved is preferably 0.1%
or more, more preferably 0.5% or more, and 1
% is sufficient, and there is no need to make it higher than 20% at most. Note that the optimum concentration differs somewhat depending on the type of solvent and other solutes used, but the value is a physical property value specific to each electrolytic solution. The electrolytic solution for electrolytic capacitors of the present invention is prepared by dissolving the above-mentioned modified silicone oil in a solvent whose main solvent is an aprotic solvent. 3
-Methyl-2-oxazolidinone and dimethyl sulfoxide, a suitable electrolytic solution for electrolytic capacitors can be obtained. [Function] The mechanism by which the addition of the modified silicone oil disclosed in the present invention acts on the aluminum oxide film dielectric in the electrolytic solution is not clear. However, it is presumed that an organic compound whose main chain is a repeating structure of siloxane bonds has a unique effect of suppressing fluctuations in the electrochemical state of the electrolytic capacitor when high voltage is applied. This effect is most significantly reflected in the scintillation voltage reduction effect when the load voltage increases over time in an observable form. Regarding the improvement of the high temperature characteristics or stability of the electrolytic codenser using the electrolytic solution of the present invention, it is estimated that the organic and inorganic groups introduced into the main chain and side chain of the modified silicone oil added to the electrolytic solution make a large contribution. Also, by adding silicone oil, the amount of boric acid can be reduced or the need for addition can be eliminated, thereby reducing the possibility of condensed water formation due to the progress of unfavorable chemical reactions during use and suppressing gas generation. I can do it. This effect is most reflected in the observable form, for example, in the presence or absence of appearance defects when an electrolytic capacitor is used for a long time at a high temperature of 100° C. or higher, the boiling point of water. [Effects of the Invention] An electrolytic capacitor produced using the electrolytic solution for electrolytic capacitors of the present invention has high voltage resistance not only at room temperature but also at high temperatures. Furthermore, no appearance defects occur even when used at high temperatures for long periods of time. [Example] The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited thereto. In addition, in all _the following examples, a _modified silicone oil having a carborane ( _-C2B10H10- ) skeleton with high heat resistance was used. Example 1 An anodic etched foil having an area of 20 x 300 mm was chemically converted in a boric acid solution at 385V. An element was prepared by winding the obtained anode foil, paper, and cathode foil. The rating of this element was 250V, 20μF, and the size was 16〓× ^31.5L . This element and an electrolytic solution with the following composition (Example 1)
Alternatively, an electrolytic capacitor was created using Comparative Example 1). Composition of electrolytic solution (wt%) Example 1 Comparative Example 1 Butyrolactone 79.2 79.7 Ethylene glycol 8.7 8.8 Ammonium benzoate 4.3 4.4 Boric acid 2.6 2.7 Mannite 4.3 4.4 Modified silicone oil 0.9 - (Chitsuso PS097) Note that Example 1 and Comparison Rs of the electrolyte in Example 1
(specific resistance) were 620Ωcm and 610Ωcm, respectively. Table 1 shows the results of high-temperature tests on electrolytic capacitors using these electrolytes, and FIG. 1 shows the scintillation curves. Even after being used for 1000 hours at 110°C, the electrolytic capacitor using the electrolyte of the present invention shows almost no loss in capacitance, only a slight increase in dielectric loss tangent (tanδ), and no large change in leakage current. On the other hand, electrolytic capacitors using conventional electrolytes had significant appearance defects and suffered a puncture during the test. Further, the electrolytic capacitor using the electrolytic solution of the present invention exhibited a higher scintillation voltage at both room temperature and high temperature than the conventional capacitor. Example 2 An anodic etched foil having an area of 20 x 1200 mm was chemically converted in a boric acid solution at 98V. An element was prepared by winding the obtained anode foil, paper, and cathode foil. The rating of this element was 63V, 1000μF, and the size was 18〓× ^40L . An electrolytic capacitor was created using this element and an electrolytic solution (Example 2 or Comparative Example 2) having the following composition. Composition of electrolytic solution (wt%) Example 2 Comparative Example 2 DMF 80.9 81.3 Ethylene glycol 8.9 9.0 Ammonium phthalate 8.2 8.3 Boric acid 1.2 1.4 Modified silicone oil 0.8 - (PS097 manufactured by Chitsuso) Electrolyte Rs.
(specific resistance) were 175Ωcm and 170Ωcm, respectively. Table 1 shows the results of high-temperature tests on electrolytic capacitors using these electrolytes, and FIG. 2 shows the scintillation curves. Even after being used for 1000 hours at 110°C, the electrolytic capacitor using the electrolyte of the present invention shows almost no loss in capacitance, only a slight increase in dielectric loss tangent (tanδ), and no large change in leakage current. On the other hand, electrolytic capacitors using conventional electrolytes had significant appearance defects and suffered a puncture during the test. Further, the electrolytic capacitor using the electrolytic solution of the present invention exhibited a higher scintillation voltage at both room temperature and high temperature than the conventional capacitor. Example 3 An electrolytic capacitor was prepared and tested in substantially the same manner as in Example 1 except that an electrolytic solution having the following composition was used. The results are shown in Table 2. Composition of electrolyte (wt%) Example 3 Comparative Example 3 Dimethylacetamide 78.0 78.6 Ethylene glycol 8.6 8.7 Phthalic acid 7.9 7.9 Boric acid 1.6 1.6 Triethylamine 3.1 3.2 Modified silicone oil 0.8 - (Chitsuso PS097) Example 4 The following composition An electrolytic capacitor was prepared and tested in substantially the same manner as in Example 1, except that the electrolytic solution was used. The results are shown in Table 2. Composition of electrolyte (wt%) Example 4 Comparative Example 4 Acetonitrile 90.1 91.0 Lutidine tetrafluoroborate 9.0 9.0 Modified silicone oil 0.9 - Example 5 Abbreviated as Example 1 except that an electrolyte having the following composition was used. An electrolytic capacitor was created in the same manner and tested. The results are shown in Table 2. Composition of electrolytic solution (wt%) Example 5 Comparative Example 5 3-Methyl-2-oxazolidinone 77.6 78.3 Ethylene glycol 8.6 8.7 Ammonium polydisalicylate 12.9 13.0 Modified silicone oil 0.9 - (PS097 manufactured by Chitsuso) As explained above, the present invention The electrolytic capacitor produced using the electrolytic solution for electrolytic capacitors had high voltage resistance not only at room temperature but also at high temperatures, and no appearance defects occurred even when used for long periods at high temperatures. [Table] *: I had a flat tire during the test.
【table】

[Brief explanation of drawings]

Figure 1 shows the scintillation curve of an electrolytic capacitor using the electrolytic solution of the present invention (Example 1) using γ-butyrolactone as the solvent, and Figure 2 shows the scintillation curve of an electrolytic capacitor using the electrolytic solution of the present invention (Example 1) using DMF as the solvent used. It is a scintillation curve of an electrolytic capacitor using Example 2).

Claims (1)

[Claims] 1 In an electrolytic solution for driving an aluminum electrolytic capacitor, a modified silicone oil in which a carborane group is introduced into the main chain of siloxane bonds and some or all of the side chain residues are substituted with hydrophobic groups is used as the main solvent in an aprotic solvent. An electrolytic solution for an electrolytic capacitor, characterized in that it is added to a solvent.