JP4520286B2 - Electrolytic solution for driving electrolytic capacitors - Google Patents

Description

  The present invention relates to an improvement in an electrolytic solution for driving an electrolytic capacitor (hereinafter referred to as an electrolytic solution), and particularly relates to an electrolytic solution that improves product reliability at high temperatures.

2. Description of the Related Art Conventionally, an electrolytic solution of a medium / high pressure aluminum electrolytic capacitor has a carboxylic acid or an ammonium salt thereof, boric acid or an ammonium salt thereof, and a polyhydric alcohol such as mannitol dissolved in a solvent such as ethylene glycol. In this electrolytic solution, carboxylic acid or boric acid and polyhydric alcohols form an ester compound, and the withstand voltage of the electrolytic solution is improved due to its structural characteristics (see, for example, Patent Documents 1 to 3). ).
Japanese Examined Patent Publication No. 7-48459 (page 1-4) Japanese Examined Patent Publication No. 7-48460 (page 1-3) Japanese Examined Patent Publication No. 7-63047 (page 1-4)

However, the ester compound generates amides due to heat generated in the electrolytic capacitor, atmospheric temperature, and the like. The amides cause a radical chain thermal oxidation reaction with oxygen remaining in the capacitor element or in the electrolytic solution and oxygen gas generated in the anode, and the product generated by the oxidation reaction of the amides causes a ratio of the electrolytic solution. There is a problem of increasing resistance.
In addition, carboxylic acid also has a problem that oxygen radicals act as initiators to cause a polycondensation reaction and increase the specific resistance of the electrolytic solution.

  As a method for solving the above problems, for example, it is conceivable to suppress radical chain thermal reaction with protocatechuic acid. However, if the electrolytic solution in which a large amount of protocatechuic acid is dissolved is allowed to stand at a high temperature and the change in the specific resistance is examined, the effect of suppressing the increase in specific resistance is not sufficient, and the increase in loss of the electrolytic capacitor in the reliability test is prevented. Is not effective.

  In view of the above problems, an object of the present invention is to provide an electrolytic solution for driving an electrolytic capacitor that can improve the reliability of the electrolytic capacitor.

  As a result of various studies to solve the above problems, the present inventor added an ethyl-2-ethoxyquinolinecarboxylic acid ester to the electrolytic solution, thereby oxidizing amides in the electrolytic solution, polycondensation reaction of carboxylic acid. It was found that it can be suppressed for a long time.

  The present invention has been made on the basis of such knowledge, and the electrolytic solution for driving an electrolytic capacitor according to the present invention includes at least a carboxylic acid or a salt thereof and a chemical formula shown below in a solvent mainly composed of ethylene glycol or the like. It is characterized by dissolving ethyl-2-ethoxyquinolinecarboxylic acid ester represented by

  In the present invention, the amount of the ethyl-2-ethoxyquinolinecarboxylate dissolved is preferably 0.10 to 5.00 wt%. If it exceeds 5.00 wt%, an increase in the initial specific resistance value of the electrolytic solution is observed, and if it is less than 0.10 wt%, the effect of suppressing the decrease in capacity and the increase in tan δ tends to decrease.

  Examples of carboxylic acids used in the present invention include formic acid, acetic acid, lauric acid, stearic acid, decanoic acid, benzoic acid, salicylic acid, maleic acid, phthalic acid, fumaric acid, succinic acid, glutaric acid, azelaic acid, sebacic acid 2-methyl azelaic acid, 1,6-decanedicarboxylic acid, 5,6-decanedicarboxylic acid, 7-vinylhexadecene-1,16-dicarboxylic acid and the like.

  In addition to ammonium salts, primary amine salts such as methylamine, ethylamine and t-butylamine, secondary amine salts such as dimethylamine, ethylmethylamine and diethylamine, trimethylamine, diethylmethylamine and ethyl Examples thereof include tertiary amine salts such as dimethylamine and triethylamine, quaternary ammonium salts such as tetramethylammonium, triethylmethylammonium and tetraethylammonium, and molten salts such as imidazolinium salts.

  As a co-solvent mixed with ethylene glycol, water, glycols such as propylene glycol, lactones such as γ-butyrolactone and N-methyl-2-pyrrolidone, N-methylformamide, N, N-dimethylformamide, N -Amides such as ethylformamide, N, N-diethylformamide, N-methylacetamide, N, N-dimethylacetamide, N-ethylacetamide, N, N-diethylacetamide, hexamethylphosphoricamide, ethylene carbonate, propylene carbonate Examples thereof include carbonic acids such as isobutylene carbonate, nitriles such as acetonitrile, oxides such as dimethyl sulfoxide, ethers, ketones, esters, sulfolane, and sulfolane derivatives. These solvents can be used by mixing not only one type but also two or more types.

  In addition to the carboxylic acid, its salt, and solvent, various additives can be added to the above electrolyte for the purpose of reducing leakage current, improving withstand voltage, and absorbing gas. Examples of additives include phosphoric acid compounds, boric acid compounds, polyhydric alcohols, polyvinyl alcohol, polyethylene glycol, polypropylene glycol, polyoxyethylene polyoxypropylene glycol random copolymers and block copolymers Examples include molecular compounds and nitro compounds.

  In the present invention, since ethyl-2-ethoxyquinolinecarboxylate is added to the electrolytic solution, it is possible to suppress a change in capacitance of the electrolytic capacitor at a high temperature and an increase in loss (tan δ). Reliability can be improved.

  The electrolytic solution of the electrolytic capacitor according to the present invention is obtained by dissolving at least carboxylic acid or a salt thereof and ethyl-2-ethoxyquinolinecarboxylic acid ester represented by the above chemical formula in a solvent mainly composed of ethylene glycol. As will be described later, the reliability of the electrolytic capacitor can be improved. Here, it is preferable that the dissolution amount of ethyl-2-ethoxyquinolinecarboxylic acid ester is 0.10 to 5.00 wt% with respect to the entire electrolytic solution.

The reason why the reliability is improved in the electrolytic solution of the electrolytic capacitor according to the present invention is considered as follows. First, ethyl-2-ethoxyquinolinecarboxylic acid ester is a compound having a carbonyl group, and this carbonyl group reacts preferentially with residual oxygen in the electrolytic capacitor to eliminate the radical nature of oxygen and oxidize amides. It is thought that the reaction and the polycondensation reaction of carboxylic acid are suppressed.
In addition, because of the above structure, the reactivity with the electrode foil is relatively low, and the oxidation reaction and polycondensation reaction can be suppressed over a long period. When the electrolytic capacitor is used or left in a high temperature atmosphere for a long time However, the initial characteristics of the product can be maintained for a long time. Furthermore, it also has an effect of suppressing the excessive adsorption of carboxylic acid to the anode foil.

  Hereinafter, the present invention will be described more specifically based on examples. First, as shown in Table 1, the compositions of various electrolytes were prepared, respectively, the electrolytes according to Examples, Comparative Examples, and Conventional Examples, and then the specific resistance of the electrolyte at 30 ° C. and the spark generation voltage at 85 ° C. (The withstand voltage of electrolyte solution) was measured. The results are shown in Table 1. In Table 1, the radical reaction inhibitor “A” represents ethyl-2-ethoxyquinolinecarboxylic acid ester.

Next, after preparing an electrolytic solution with the composition shown in Table 1, a capacitor element was impregnated with the electrolytic solution to obtain an aluminum electrolytic capacitor having a diameter of 10.0 mm, a length of 12.5 mm, a rated voltage of 350 V, and a capacitance of 10 μF. 20 pieces were prepared each.
Ten of these samples were applied with a rated voltage for 5000 hours in a constant temperature bath at 105 ° C., and then the capacitance and loss (tan δ) were measured. The results shown in Table 2 were obtained.
Then, after applying the rated voltage for 5000 hours in a constant temperature bath at 115 ° C. for the remaining 10 pieces, the capacitance and loss (tan δ) were measured, and the results shown in Table 3 were obtained.

As is clear from the results shown in Table 2, in the electrolytic capacitor according to the example in which ethyl-2-ethoxyquinolinecarboxylic acid ester was dissolved, the capacitance decreased and tan δ at a high temperature of 105 ° C. compared to the conventional example and the comparative example. The rise is suppressed.
Further, as is apparent from the results shown in Table 3, the electrolytic capacitor according to the example in which ethyl-2-ethoxyquinolinecarboxylic acid ester is dissolved has a capacity even at a high temperature of 115 ° C. as compared with the conventional example and the comparative example. Reduction and tan δ increase are suppressed.

Further, according to the results shown in Tables 1 to 3, the larger the amount of ethyl-2-ethoxyquinolinecarboxylate dissolved, the greater the effect of suppressing the capacity decrease and the tan δ increase. When the amount of ethoxyquinolinecarboxylic acid ester dissolved exceeds 5.0 wt% (see Example 6), an increase in the initial specific resistance value of the electrolytic solution is observed.
Moreover, if it is less than 0.1 wt% (refer Example 1), it exists in the tendency for the effect which suppresses capacity | capacitance reduction and a tan-delta rise to reduce.
Therefore, the dissolution amount of ethyl-2-ethoxyquinolinecarboxylic acid ester is preferably in the range of 0.1 to 5.0 wt% with respect to the entire electrolytic solution.

In addition, this invention is not limited to the said Example, The electrolyte solution which melt | dissolved various solutes illustrated previously individually or in multiple, the electrolyte solution which added the additive mentioned above, and the electrolyte solution which mixed the subsolvent are also used. There was an effect equivalent to the said Example.
Further, the present invention is not limited to the electrolytic solution of the medium / high pressure aluminum electrolytic capacitor but can be applied to the electrolytic solution of the low pressure aluminum electrolytic capacitor.

Claims (2)

An electrolytic solution for driving an electrolytic capacitor, wherein at least carboxylic acid or a salt thereof and ethyl-2-ethoxyquinolinecarboxylic acid ester represented by the following chemical formula are dissolved in a solvent containing ethylene glycol as a main component.

  2. The electrolytic solution for driving an electrolytic capacitor according to claim 1, wherein the amount of ethyl-2-ethoxyquinolinecarboxylate dissolved is 0.10 to 5.00 wt% with respect to the entire electrolytic solution.