JP4804063B2 - Electrolytic solution for electrolytic capacitors - Google Patents

Description

The present invention relates to an electrolytic solution for an electrolytic capacitor.

Electrolytic capacitors such as aluminum electrolytic capacitors are composed of an anode foil whose surface is etched to form an oxide film, and a cathode foil whose surface is etched to form no oxide film, or an oxide film is formed by low-pressure chemical conversion. The capacitor element wound through the separator is impregnated with an electrolytic solution, the capacitor element is housed in a case, a lid is attached and sealed, and a lead is attached from the anode and the cathode.

By the way, conventionally, the electrolytic solution impregnated in the capacitor element has used a component in which boric acid, a higher dibasic acid or the like is dissolved in a solvent mainly composed of a polyhydric alcohol such as ethylene glycol.

Electrolytic solutions containing boric acid as a solute can take a relatively high spark voltage, that is, a high working voltage, but not only have a high specific resistance, but also with crystal water, ethylene glycol, and boric acid in the molecule. A large amount of water is generated by the esterification reaction that takes place. For this reason, when the electrolytic capacitor is used at a high temperature exceeding 90 ° C., the water generated by the esterification reaction reacts with the oxide film of the anode foil, the leakage current increases, and a large amount of hydrogen gas is generated. The pressure in the case easily rises, and the explosion-proof mechanism provided in the lid and the case operates relatively early, resulting in a short life.

In addition, when an electrolytic solution in which azelaic acid, sebacic acid, 1,6-decanedicarboxylic acid, etc. are dissolved as a higher dibasic acid is used, not only the specific resistance is small and the impedance as a capacitor is difficult to increase. Since the esterification reaction with ethylene glycol is slow and does not generate a large amount of water, the reaction with the anodized film hardly occurs and it can be used at a higher temperature than when boric acid is dissolved. Long life can be achieved. However, an electrolytic capacitor using an electrolytic solution in which such a higher dibasic acid is dissolved has a spark generation voltage that is not so high, and its use voltage is limited to about 450 wV. In recent years, in order to improve the reliability of electrical equipment, an electrolytic capacitor incorporated in this equipment has been required to have a higher withstand voltage, and there has been a drawback that the withstand voltage is not sufficient.
In order to improve this withstand voltage in higher dibasic acids, the addition of poly 4,4-dimethyl-1,2-butanedicarboxylic acid or a salt thereof has been proposed (Japanese Patent Laid-Open No. 5-152167), and the operating voltage is about 560 wV. It is described that the voltage rises by 100V or more.
JP-A-5-152167

However, when this poly 4,4-dimethyl-1,2-butanedicarboxylic acid or its salt is used at high temperature, the esterification reaction proceeds with the polyhydric alcohol as the solvent, and the viscosity of the electrolyte solution As a result, the specific resistance of the electrolyte increases.
In particular, if this poly 4,4-dimethyl-1,2-butanedicarboxylic acid or its salt is first added in a large amount for high pressure use, the viscosity of the electrolyte solution will rapidly increase due to this esterification. The specific resistance of the electrolytic solution also increases rapidly.
The object of the present invention is to improve the above-mentioned drawbacks, facilitate the adjustment of the viscosity of the electrolytic solution, and maintain the high withstand voltage of the electrolytic capacitor while not increasing the specific resistance of the electrolytic solution more than necessary. It is an object of the present invention to provide an electrolytic solution for an electrolytic capacitor that maintains the temporal stability of capacitor characteristics such as characteristics and ripple characteristics.

In order to solve the above problems, polyhydric alcohols in the electrolytic solution for an electrolytic capacitor according to the main solvent, dissolving the carboxylic acid as a main solute, further the same material as port re polyhydric alcohols of the main Solvent it is to provide an electrolytic solution for an electrolytic capacitor, characterized in that dissolved esters of 4,4-dimethyl-1,2-butane dicarboxylic acid.
The ethylene glycol, diethylene glycol, propylene glycol or 1,4-butanediol in the electrolytic solution for an electrolytic capacitor whose main solvent, dissolving the carboxylic acid as a main solute, further same as polyhydric alcohols of the main Solvent it is to provide an electrolytic solution for an electrolytic capacitor, characterized in that dissolved esters of substance and Po Li 4,4-dimethyl-1,2-butane dicarboxylic acid.

When the copolymer used in the present invention is dissolved, an appropriate viscosity can be obtained from its molecular weight and molecular structure, which is a factor for improving the breakdown voltage of the device. Further, this copolymer has a lipophilic functional group such as —CH 3, —CH 2 — and the like in its molecule and a hydrophilic group of —COOH, and exhibits a surface activity action with this molecular structure. Due to this surface activation action, the contact between the electrolytic solution and the anodized film is improved, and the damaged portion of the oxide film is easily repaired by the electrolytic solution during aging treatment or use. From these results, the spark generation voltage is improved, the withstand voltage of the electrolytic capacitor is increased, and the reliability is improved.
First, poly 4,4-dimethyl-1,2-butanedicarboxylic acid and esters of ethylene glycol, diethylene glycol, propylene glycol and 1,4-butanediol are dissolved, so that poly 4,4-dimethyl-1,2- The esterification of butanedicarboxylic acid does not proceed and the electrolyte resistivity is less likely to increase compared to the case where only poly-4,4-dimethyl-1,2-butanedicarboxylic acid is dissolved.
Particularly in high pressure applications, it is effective when it is desired to increase the pressure resistance to some extent by increasing the viscosity, and when a slight increase in the viscosity leads to an increase in the specific resistance of the electrolytic solution.

Embodiments of the present invention will be described below.
As the solvent, ethylene glycol, diethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, hexylene glycol, glycerin, polyethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol dimethyl ether, In addition to polyhydric alcohols such as ethylene glycol diethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, β-butyrolactone, γ-butyrolactone, δ-valerolactone, γ-caprolactone, ε-caprolactone, γ-heptalactone, γ-nonalactone, δ-nonalactone, Lactones such as δ-decalactone and γ-undecalactone can also be used.
These solvents can be used alone or in combination.

  The main solutes include ammonium azelate, ammonium 2-methylazelate, ammonium 3-tert-octyladipate, ammonium trimethyladipate, ammonium sebacate, ammonium dodecanedioate, ammonium 1,6-decanedicarboxylate, 5, One or more types of carboxylic acids such as ammonium 6-decanedicarboxylate, ammonium 7-vinyl-hexadecene-1,16-dicarboxylate, and ammonium caprylate, as well as diethylamine and triethylamine are dissolved. The amount of these dissolved is preferably in the range of 1 to 30 wt%, particularly preferably in the range of 5 to 15 wt%. If the amount of dissolution is less than 1 wt%, tan δ, leakage current characteristics, etc. are likely to deteriorate. On the other hand, if the amount of dissolution is greater than 30 wt%, the solute approaches a saturated state and the low temperature characteristics of the electrolytic capacitor are deteriorated.

  Further, boric acid, ammonium borate, mannitol, and sorbitol are dissolved as secondary solutes.

Furthermore, the ester of the present invention is dissolved. The amount of the ester dissolved is preferably in the range of 0.1 to 30 wt%, particularly preferably in the range of 0.5 to 15 wt%. When the dissolution amount is less than 0.1 wt%, the effect of improving the withstand voltage characteristics of the capacitor is small. Further, when the dissolution amount is 0.5 to 15 wt%, good capacitor characteristics can be obtained. Further, the molecular weight of the dissolved ester is preferably in the range of 200 to 1,000,000, and particularly preferably in the range of 1,000 to 500,000. When the molecular weight is less than 200, the effect of improving the withstand voltage characteristics of the capacitor is small. On the other hand, if the molecular weight is larger than 500,000, it is difficult to dissolve in a solvent, so that the effect of improving the withstand voltage of the electrolytic capacitor is small. Therefore, good capacitor characteristics can be obtained when the molecular weight is 1,000 to 500,000.

In the preparation of the electrolytic solution of the present invention, the above-mentioned main solute and sub-solute are further dissolved in the above-mentioned solvent, the ester of the present invention is further heated to about 130 ° C., cooled to room temperature, and then ammonia gas is passed with stirring. Alternatively, the pH of the electrolytic solution is adjusted to around 6 to 7 by adding an amine.

First, an electrolytic solution shown in Table 1 was prepared and left in an atmosphere at 105 ° C. for 2000 hours. From Table 1, when the ester is added in the initial stage, the specific resistance and viscosity are higher than when poly-4,4-dimethyl-1,2-butanedicarboxylic acid is added, but the increase rate after standing at 105 ° C is small. I understand. Therefore, appropriate characteristics can be obtained by adjusting the concentration of the ester in the initial stage.

Next, examples of the present invention will be described.
First, an electrolytic solution having the composition shown in Tables 2 and 3 is prepared. Further, with respect to the electrolytic solutions shown in Tables 2 and 3, specific resistance at a liquid temperature of 30 ° C. and spark generation voltage at a liquid temperature of 85 ° C. were measured, and are shown in Tables 2 and 3 together.

When Examples 1 to 7 in which the esters of the present invention in Table 1 were dissolved were compared with Conventional Examples 1 to 7 in which the esters of the present invention in Table 2 were omitted, the specific resistance was almost the same and the spark generation voltage was from 440 to 480V. It turns out that it is improving significantly to 570-590V.

  Moreover, using the electrolytic solutions having the compositions shown in Tables 1 and 2, an aluminum electrolytic capacitor rated 500 wV 330 μF was prepared. The initial characteristics of the capacitor and the characteristics at 20 ° C. after the high temperature load test were measured. The anode used in this aluminum electrolytic capacitor was a foil formed at a voltage of 700V. The aging conditions at the time of trial production were 550 VDC and 3 h applied in an atmosphere at 85 ° C. and then 550 VDC and 2 h continuously applied in an atmosphere at 105 ° C. The number of samples was 40 each.

  At the time of this aging, the capacitors using the electrolytes of Conventional Examples 1 to 7 all shorted between the electrodes due to insufficient breakdown voltage. In addition, all the capacitors using the electrolyte solutions of Examples 1 to 7 were not abnormal.

Next, for the capacitors using the electrolyte solutions of Examples 1 to 7, the initial characteristics, the characteristics after the high temperature load test, and the like were measured, and the average values are shown in Table 3. The conditions for the high temperature load test were that the rated voltage (500V) was applied continuously for 3,000 hours in an atmosphere at 105 ° C., and the number of samples was 20 each. Further, the characteristics after the test were measured after each sample was left in an atmosphere at 20 ° C. for 24 hours.

表４から明らかな通り、実施例では３，０００ｈ後全数外観異常なく、容量変化率、ｔａｎδ、漏れ電流とも従来例と比べて安定した特性を示しており、発明の効果が大きいことがわかる。

As is apparent from Table 4, the examples show no abnormalities in appearance after 3,000 hours, and the capacitance change rate, tan δ, and leakage current show stable characteristics as compared with the conventional example, indicating that the effect of the invention is great.

Claims (2)

In polyhydric alcohols the main solvent to the electrolytic capacitor electrolytic solution, to dissolve the carboxylic acid as a main solute, further the main soluble polyhydric alcohols with the same material and the port Li 4,4-dimethyl-1,2 of medium - electrolyte for an electrolytic capacitor, characterized in that dissolving esters of butane dicarboxylic acid.
Ethylene glycol, diethylene glycol, propylene glycol or in the electrolytic solution for an electrolytic capacitor which 1,4-butanediol as a main solvent, by dissolving the carboxylic acid as a main solute, and further the same material as the polyhydric alcohols of the main Solvent electrolyte for an electrolytic capacitor, characterized in that dissolved esters of Po Li 4,4-dimethyl-1,2-butane dicarboxylic acid.