JP2011071238A - Electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolytic capacitor having low impedance characteristics, suppressed in the characteristic change of an electrostatic capacity or the like even after the lapse of 10,000 hours in a load test at a high temperature of 105°C, and having a long lifetime. <P>SOLUTION: A capacitor element is configured by winding an anode including an oxide film on a surface and composed of a valve metal and a cathode composed of the valve metal via a separator. The capacitor element is impregnated with an electrolyte, and housed in a sealed case, thus configuring the electrolytic capacitor. The electrolyte is obtained by dissolving a salt of an azelaic acid and secondary amine having a hydrophobic substitutional group to a solvent containing water and ethylene glycol, and the content of the salt is kept within a range of 14 to 22 mass% of the whole electrolyte. Since a large quantity of an azelaic acid salt having a large electrode deterioration-restraining effect is contained in the electrolyte and the secondary amine is further adsorbed on the surface of the anode and forms a hydrophobic layer, the hydration deterioration of an electrode is hardly caused, and the capacitor having excellent high-temperature lifetime characteristics is obtained. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electrolytic capacitor having low impedance characteristics and a long life.

  The electrolytic capacitor has a structure in which an anode made of a valve metal having an oxide film on its surface, a cathode made of a valve metal, and a separator holding an electrolytic solution disposed between the anode and the cathode are contained in a sealed case. The shape of a winding type, a lamination type, etc. is widely used. As an electrolytic solution used for an electrolytic capacitor, an electrolytic solution using ethylene glycol as a main solvent and a carboxylic acid such as adipic acid or benzoic acid or an ammonium salt thereof as an electrolyte is known, and has a low impedance to the electrolytic capacitor. In order to meet the demand for characteristics, studies have been made to increase the water content of the electrolytic solution.

  However, the water in the electrolyte and the carboxylic acid in the electrolyte are chemically active substances for the electrode. For example, in the case of an aluminum electrolytic capacitor, an aluminum oxide film on the electrode surface is dissolved by reaction with a carboxylic acid anion to form an aluminum carboxylic acid complex. Further, when water reaches aluminum through the aluminum oxide film of the electrode, the aluminum dissolves to produce a hydroxide, and hydrogen gas is generated simultaneously with this reaction. Therefore, when the water content of the electrolytic solution is increased, the electrode foil is deteriorated, the leakage current is increased, and there is a problem that the life of the capacitor is shortened. This problem of electrode deterioration is particularly serious in a medium-high voltage capacitor (180 WV class or higher) and more serious in the use of a capacitor in a high temperature region where the above reaction occurs rapidly.

  To solve this problem, the use of azelaic acid or an ammonium salt thereof that can suitably suppress hydration deterioration of the electrode has been proposed as an electrolyte in the electrolytic solution. An electrolytic solution containing azelaic acid or an ammonium salt thereof is particularly useful for an electrolytic capacitor for medium to high voltage because of its high spark voltage. However, since the solubility of azelaic acid or its ammonium salt in a solvent containing water and ethylene glycol is low, a sufficient electrode deterioration suppressing effect cannot be obtained, and the decrease in the specific resistance value of the electrolytic solution is not satisfactory. It was.

  On the other hand, Patent Document 1 (Japanese Patent Application Laid-Open No. 2004-128076) dissolves azelaic acid in a solvent containing water and ethylene glycol, and further adjusts the pH of the electrolyte to a specific range with ammonia. A method for increasing the amount of azelaic acid dissolved is disclosed. By adjusting the pH of the electrolyte with ammonia in the range of 6.5 to 7.5, the amount of azelaic acid dissolved can be increased to 8 to 12% by mass of the total electrolyte, and the specific resistance value is low. An electrolytic solution excellent in the electrode deterioration preventing effect is obtained.

JP 2004-128076 A

  By the way, in a recent application such as a plasma display panel, it can be used at a medium or high pressure of 220 WV or 250 WV, and has a low impedance and good ripple resistance, and further, 10,000 hours in a load test at a high temperature of 105 ° C. There has been a demand for an electrolytic capacitor having a long life characteristic with little change in characteristics such as capacitance even after the passage.

  Although the electrolytic solution of Patent Document 1 can be used for a medium- and high-voltage capacitor having low impedance and good ripple resistance characteristics, the high-temperature life characteristics are insufficient to satisfy the above-described requirements.

  Accordingly, an object of the present invention is a long-life electrolytic capacitor having low impedance characteristics and having little change in characteristics such as capacitance even after a lapse of 10,000 hours in a load test at a high temperature of 105 ° C. It is providing the electrolytic capacitor which can be used as a use.

  As a result of intensive studies, the inventors have provided an anode made of a valve metal having an oxide film on the surface, a cathode made of a valve metal, and a separator holding an electrolytic solution disposed between the cathode and the anode. In an electrolytic capacitor, when a salt of azelaic acid and a secondary amine having a hydrophobic substituent is used as an electrolyte, a large amount of this salt can be dissolved in a solvent containing water and ethylene glycol. Capacitors with good ripple resistance and resistance to electrode hydration degradation can be obtained. Furthermore, the secondary amine is chemically adsorbed on the surface of the anode oxide film, and a hydrophobic layer is formed on the surface of the oxide film. Therefore, it has been found that even when the water content of the electrolytic solution is increased, hydration deterioration of the anode is suppressed, and as a result, a capacitor having good high-temperature life characteristics can be obtained.

  Therefore, the electrolytic capacitor of the present invention is an electrolysis comprising an anode made of a valve metal having an oxide film on its surface, a cathode made of a valve metal, and a separator holding an electrolytic solution disposed between the cathode and the anode. It is a capacitor | condenser, Comprising: The said electrolyte solution contains the salt of the solvent containing water and ethylene glycol, and the secondary amine which has 14-22 mass% of azelaic acid and a hydrophobic substituent of the whole electrolyte solution. The surface of the anode has a hydrophobic layer formed by bonding the secondary amine.

  The electrolytic capacitor of the present invention is preferably an aluminum electrolytic capacitor. The electrolytic capacitor of the present invention is particularly suitable as a medium-high voltage capacitor because the spark voltage of the electrolytic solution is large and hydration deterioration of the electrode is suitably suppressed.

  Content of the salt of azelaic acid and the secondary amine which has a hydrophobic substituent in the electrolyte solution used for the electrolytic capacitor of this invention is the range of 14-22 mass% of the whole electrolyte solution. If the salt content is less than 14% by mass, the effect of suppressing the hydration deterioration of the electrode is not sufficient. If the salt content is more than 22% by mass, the spark voltage of the electrolytic solution decreases, and the electrolytic capacitor Leakage current increases.

  The water content of the electrolytic solution used in the electrolytic capacitor of the present invention is preferably 5 to 20% by mass of the entire electrolytic solution. When the water content is less than 5% by mass of the entire electrolyte solution, the impedance of the electrolytic capacitor increases, and when the water content is more than 20% by mass of the entire electrolyte solution, the life at high temperature is shortened. Further, the secondary amine preferably has an alkyl group as a hydrophobic substituent, and particularly dimethylamine and / or diethylamine is preferable because the specific resistance value of the electrolytic solution is effectively reduced. .

  The electrolytic capacitor of the present invention contains a large amount of azelaic acid salt having an effect of suppressing electrode deterioration and has a hydrophobic layer on the anode surface, so that it has low impedance characteristics and is applied at a high temperature of 105 ° C. by applying a medium-high pressure. Even when the load test is performed for 10,000 hours, the change in characteristics such as capacitance before and after the test is small and the life is extremely long.

  The electrolytic capacitor of the present invention is an electrolytic capacitor comprising an anode made of a valve metal having an oxide film on its surface, a cathode made of a valve metal, and a separator holding an electrolytic solution disposed between the cathode and the anode. As the electrolytic solution, a solution in which a salt of azelaic acid and a secondary amine having a hydrophobic substituent is dissolved in a solvent containing water and ethylene glycol is used. Hereinafter, an aluminum electrolytic capacitor will be described as an example, but the present invention is not limited to the aluminum electrolytic capacitor.

  An aluminum electrolytic capacitor has a configuration including an anode made of an aluminum foil having an aluminum oxide film on the surface, a cathode made of an aluminum foil, and a separator holding an electrolytic solution disposed between the anode and the cathode. ing.

  The high-purity aluminum foil constituting the anode and the cathode is subjected to chemical or electrochemical etching treatment in order to increase its surface area, and then subjected to chemical conversion treatment on the aluminum foil constituting the anode, An aluminum oxide film is formed on the surface. The chemical conversion treatment is performed using a chemical conversion solution such as an ammonium borate aqueous solution, an ammonium adipate aqueous solution, or an ammonium phosphate aqueous solution.

  A capacitor element is formed by interposing a separator such as manila hemp and kraft paper between the anode and the cathode thus obtained. The capacitor element is impregnated with the electrolyte solution shown below, and further accommodated in a sealed case. Thus, the aluminum electrolytic capacitor of the present invention is configured.

  The solvent in the electrolytic solution used for the electrolytic capacitor of the present invention contains water and ethylene glycol as essential components. A solvent in which water and ethylene glycol are mixed is preferable because it provides an electrolyte having high solubility of various solutes and excellent temperature characteristics. However, other organic solvents may be included as long as the effects of the present invention are not adversely affected. Usable organic solvents include protic polar solvents such as monohydric alcohols (methanol, ethanol, propanol, butanol, hexanol, cyclohexanol, cyclopentanol, benzyl alcohol, etc.), polyhydric alcohols, and oxyalcohol compounds (propylene). Glycol, glycerin, methyl cellosolve, ethyl cellosolve, 1,3-butanediol, methoxypropylene glycol, etc.) and aprotic solvents amides (N-methylformamide, N, N-dimethylformamide, N-ethylformamide, N N-diethylformamide, N-methylacetamide, hexamethylphosphoric amide, etc.), lactones, cyclic amides, carbonates (γ-butyrolactone, N-methyl-2-pyrrolidone, ethylene Boneto, propylene carbonate, etc.), nitriles (acetonitrile), oxides (dimethyl sulfoxide, etc.) and the like. These organic solvents may be contained independently and 2 or more types of organic solvents may be contained.

  The content of water in the electrolytic solution is preferably 5 to 20% by mass of the entire electrolytic solution. When the water content is less than 5% by mass of the entire electrolyte solution, the impedance of the electrolytic capacitor increases, and when the water content is more than 20% by mass of the entire electrolyte solution, the life at high temperature is shortened.

  In the electrolytic solution used in the electrolytic capacitor of the present invention, a salt of azelaic acid and a secondary amine having a hydrophobic substituent is dissolved as an essential component in a solvent containing water and ethylene glycol. In the use of ammonium azelaate shown in Patent Document 1, the maximum dissolution amount of ammonium azelate was only 12% by mass of the total electrolyte solution, but by using a salt of azelaic acid and a secondary amine, More azelaic acid salt having a high electrode deterioration suppressing effect can be dissolved in a solvent. Further, the salt of azelaic acid and secondary amine does not cause transpiration like an ammonium salt, so that the specific resistance of the electrolytic solution can be kept stable for a long time. Furthermore, since the salt of azelaic acid and secondary amine reduces the specific resistance value of the electrolyte more effectively than the salt of azelaic acid and tertiary amine, it has a low impedance characteristic. Useful for capacitors. By reducing the impedance of the electrolytic capacitor, the rise in the capacitor temperature due to the ripple heat generation and the deterioration of the electrolyte and the electrode accompanying this temperature rise are effectively suppressed.

  A separator composed of an aluminum foil having an aluminum oxide film on its surface and a cathode comprising an aluminum foil is prepared by dissolving a salt of azelaic acid and a secondary amine having a hydrophobic substituent in a solvent containing water and ethylene glycol. When impregnating the capacitor element disposed via the secondary amine, the secondary amine provides a non-conjugated electron pair of nitrogen atoms to the surface of the aluminum oxide film of the anode, and chemisorbs, so that the hydrophobic substituent is A hydrophobic layer facing the electrolyte side is formed on the surface of the aluminum oxide film. Therefore, even if the water content of the electrolytic solution is increased for the purpose of obtaining an electrolytic capacitor with low impedance and good ripple resistance, water molecules in the electrolytic solution are difficult to reach the anode surface, and hydration deterioration of the anode is caused. Effectively suppressed.

  Secondary amines having a hydrophobic substituent constituting a salt with azelaic acid include dialkylamines such as dimethylamine, N-methylethylamine, diethylamine, methyl n-propylamine, methylisopropylamine, ethyl n-propyl. Amine, ethylisopropylamine, di-n-propylamine, diisopropylamine, di-n-butylamine, N-ethylisobutylamine, di-t-butylamine; phenyl group-containing amines such as methylphenylamine, ethylphenylamine, diphenylamine; saturated cyclic Examples include amines such as aziridine, azetidine, pyrrolidine, and piperidine. These salts of secondary amines and azelaic acid may be used alone or in combination of two or more. It is preferable to use a dialkylamine salt. In particular, the use of a dimethylamine salt and / or a diethylamine salt is preferable because the specific resistance value of the electrolytic solution is effectively reduced.

  The content of the salt of azelaic acid and the secondary amine having a hydrophobic substituent in the electrolytic solution used in the electrolytic capacitor of the present invention is in the range of 14 to 22% by mass of the entire electrolytic solution. If the salt content is less than 14% by mass of the total electrolyte, the hydrophobic layer due to the secondary amine is not sufficiently formed on the surface of the aluminum oxide film of the anode, so that the effect of suppressing hydration deterioration of the anode is not sufficient. In addition, since the specific resistance value of the electrolytic solution becomes high, the temperature of the capacitor rises due to ripple heat generation during use of the electrolytic capacitor, and the electrode deterioration is promoted. If the salt content is more than 22% by mass of the total electrolyte, the spark voltage of the electrolyte will decrease, the leakage current of the electrolytic capacitor will increase, and the leakage current will increase significantly after the high-temperature load test, resulting in electrode deterioration. Progression is recognized.

  In the electrolytic solution used in the electrolytic capacitor of the present invention, a solute other than a salt of azelaic acid and a secondary amine having a hydrophobic substituent can be used as long as the effects of the present invention are not impaired. Solvents that can be used include inorganic acid electrolytes such as phosphoric acid, silicic acid, and carbonic acid, nonionic surfactants for improving the withstand voltage, colloidal silica, polyoxyethylene glycerin, boric acid, sugar alcohols such as mannitol, Prevents hydration degradation of aromatic nitro compounds such as p-nitrophenol, p-nitrobenzoic acid, paranitrotoluene, nitroxylene, nitrobenzene, nitroaniline, and electrode foil to absorb hydrogen that can be generated inside the electrolytic capacitor. And phosphoric acid ester compounds such as methyl phosphoric acid ester, dimethyl phosphoric acid ester, trimethyl phosphoric acid ester, ethyl phosphoric acid ester, diethyl phosphoric acid ester, and triethyl phosphoric acid ester.

  The present invention will be described below with reference to examples, but the present invention is not limited to the following examples.

1: Preparation of Electrolytic Solution Electrolytic solutions having different compositions shown in Table 1 below were prepared. Examples 1 to 6 are electrolytes in which 14 to 22% by mass of dimethylamine azelate or diethylamine azelate was dissolved in a solvent composed of water and ethylene glycol used in the electrolytic capacitor of the present invention. Comparative Example 1 is an example of an electrolytic solution in which less than 14% by mass of diethylamine azelate is dissolved in a solvent composed of water and ethylene glycol, and Comparative Example 2 is an example of water and ethylene. This is an example of an electrolytic solution in which diethylamine azelate more than 22% by mass of the entire electrolytic solution is dissolved in a solvent composed of glycol. In addition, the conventional example is an example of an electrolytic solution disclosed in Patent Document 1 in which 12% by mass of ammonium azelate of the entire electrolytic solution is dissolved in a solvent composed of water and ethylene glycol. The amount of ammonium azelate dissolved is the maximum amount dissolved in a solvent composed of water and ethylene glycol.

2: Characteristic evaluation of electrolyte solution About each obtained electrolyte solution, the spark voltage and the specific resistance value were measured. The obtained measurement results are shown in Table 1 together with the electrolyte composition.

  The electrolyte solutions of Examples 1 to 6 showed a spark voltage of 400 V or more sufficient for constituting a medium-high voltage capacitor, similarly to the electrolyte solution of the conventional example. The specific resistance value of the electrolytic solution using dimethylamine azelate of Example 6 as the electrolyte was substantially equal to the specific resistance value of the electrolytic solution of the conventional example. The specific resistance value of the electrolytic solution using diethylamine azelate of Examples 1 to 5 as the electrolyte was higher than the specific resistance value of the electrolytic solution of the conventional example, but the electrolytic capacitor having low impedance and good ripple resistance The specific resistance value was sufficient to constitute On the other hand, the electrolytic solution of Comparative Example 1 in which the content of diethylamine azelate is less than 14% by mass of the entire electrolytic solution is the same as the electrolytic solution of Example 4 in which the content of water is low, which leads to a lower specific resistance of the electrolytic solution Even when compared, a higher specific resistance value was exhibited. Moreover, the electrolyte solution of the comparative example 2 with more content of diethylamine azelate than 22 mass% of the whole electrolyte solution showed the low spark voltage compared with the electrolyte solution of Examples 1-6.

3: Preparation of electrolytic capacitor An aluminum foil was etched to increase the effective surface area, and an anode foil having a dielectric aluminum oxide film formed on the surface by anodization and a cathode foil obtained by etching the aluminum foil via a separator. To form a capacitor element, impregnating the capacitor element with the electrolytes of Examples 1 to 6, Comparative Examples 1 and 2, and the conventional example, and sealing the impregnated capacitor element in a metal case. Thus, an aluminum electrolytic capacitor having a rated voltage of 220 V and a rated capacitance of 200 μF was manufactured.

4: Characteristic evaluation of electrolytic capacitor For each of the obtained electrolytic capacitors, capacitance, dielectric loss (tan δ), leakage current, and impedance were measured. Next, each electrolytic capacitor was subjected to a high-temperature load test in which a rated voltage of 220 V was applied at 105 ° C. for 10,000 hours, and the capacitance, dielectric loss (tan δ), leakage current, and impedance were measured again after the test. The measurement results are shown in Table 2.

  The electrolytic capacitor using the electrolytic solution in which the content of diethylamine azelate in Comparative Example 1 is less than 14% by mass of the entire electrolytic solution has a large tan δ value compared to the values of the electrolytic capacitors in Examples 1 to 6, In addition, after the high temperature load test, although the capacitance was hardly changed, the leakage current and the impedance were increased. In particular, the increase rate of the leakage current reflecting the degree of electrode deterioration was a large value even when compared with the electrolytic capacitor of Example 5 using an electrolytic solution having a water content of about twice. This is because the hydrophobic layer due to diethylamine was not sufficiently formed on the aluminum oxide film of the anode, so that the hydration deterioration of the anode occurred during the high temperature load test, and the effect of suppressing electrode deterioration in the electrolyte was large. This is probably because the content of azelaic acid salt is small. In addition, as described above, since the specific resistance value of the electrolytic solution used in the electrolytic capacitor of Comparative Example 1 is high, it is considered that the temperature of the electrolytic capacitor is increased due to ripple heat generation, and electrode hydration deterioration is promoted.

  The leakage current of the electrolytic capacitor using the electrolytic solution in which the content of diethylamine azelate in Comparative Example 2 is more than 22% by mass of the entire electrolytic solution is compared with the electrolytic capacitors of Examples 1 to 6 even before the high temperature load test. Although large, the leakage current increased remarkably after the high temperature load test. Thus, too much diethylamine azelate was found to have an adverse effect.

  In the conventional electrolytic capacitor using the electrolyte containing ammonium azelate, the hydrophobic layer is not formed on the aluminum oxide film of the anode as in the case of using the electrolyte containing diethylamine azelate or dimethylamine azelate. Also, it seems that this is because the content of azelaic acid salt that has the effect of suppressing electrode deterioration is insufficient, but the leakage current significantly increased after the high temperature load test, the capacitance increased, and electrode deterioration was observed. It was. Moreover, although it is thought to be due to transpiration of the ammonium salt, the impedance was remarkably increased after the high temperature load test.

  On the other hand, the electrolytic capacitors of the present invention of Examples 1 to 6 had low impedance characteristics in the initial stage, and both the leakage current value and the tan δ value were small. The increase in leakage current after a 10000 hour load test at a high temperature of 105 ° C. was remarkably small as compared with the capacitors of Comparative Examples 1 and 2 and the conventional example, and electrode deterioration was suppressed. In addition, changes in capacitance, tan δ, and impedance before and after the load test were small, and it was confirmed that the electrolytic capacitor of the present invention has good high-temperature life characteristics.

  The electrolytic capacitor of the present invention is a long-life electrolytic capacitor having low impedance characteristics and little change in characteristics such as capacitance even after 10000 hours in a load test in which medium and high pressures are applied at a high temperature of 105 ° C. Therefore, the electrolytic capacitor of the present invention is extremely suitable for applications such as plasma display panels.

Claims (3)

An electrolytic capacitor comprising an anode made of a valve metal having an oxide film on the surface, a cathode made of a valve metal, and a separator holding an electrolytic solution disposed between the cathode and the anode,
The electrolyte contains a solvent containing water and ethylene glycol, and a salt of 14-22% by mass of azelaic acid and a secondary amine having a hydrophobic substituent, based on the whole electrolyte,
An electrolytic capacitor comprising a hydrophobic layer formed by bonding the secondary amine on the surface of the anode.   The electrolytic capacitor of Claim 1 whose content of water is 5-20 mass% of the whole electrolyte solution.   The electrolytic capacitor according to claim 1, wherein the secondary amine is at least one of dimethylamine and diethylamine.