JP2012084568A - Electrolytic solution for aluminum electrolytic capacitor and aluminum electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolytic solution which helps to obtain a low impedance and long life aluminum electrolytic capacitor.SOLUTION: The electrolytic solution for aluminum electrolytic capacitors of the present invention is an electrolytic solution prepared by dissolving, in a mixed solvent comprised of water and ethylene glycol, adipic acid as a carboxylic acid electrolyte, a basic compound capable of composing a salt with adipic acid, a phosphorus oxo acid ion formation compound capable of forming phosphorus oxo acid ions in an aqueous solution, and a chelator capable of forming a water soluble aluminum chelate complex by coordination to aluminum, characterized in that only a primary amine and/or a secondary amine having a hydrophobic substituent group is included as the basic compound and that the pH of the electrolytic solution is in the range from 5.6 to 7.0. This electrolytic solution helps to obtain a capacitor which has a low specific resistance and also a longer useful life than conventional capacitors.

Description

  The present invention relates to an electrolytic solution for an aluminum electrolytic capacitor that can provide an aluminum electrolytic capacitor having low impedance characteristics and a long lifetime. The present invention also relates to an aluminum electrolytic capacitor having a low impedance characteristic and a long life using the electrolytic solution.

  In an aluminum electrolytic capacitor, an anode made of an aluminum foil having an aluminum oxide film on its surface, a cathode made of an aluminum foil, and a separator holding an electrolytic solution disposed between the anode and the cathode are accommodated in a sealed case. A structure having a winding shape, a laminated shape, or the like is widely used.

  As a driving electrolyte for a small-sized, low-pressure aluminum electrolytic capacitor, an electrolytic solution containing 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, and γ-butyrolactone 2. Description of the Related Art Conventionally, an electrolytic solution using a quaternized cyclic amidinium salt of a carboxylic acid such as phthalic acid or maleic acid as an electrolyte is known as a main solvent.

  Such an aluminum electrolytic capacitor is required to have a low impedance characteristic with the recent miniaturization of electronic equipment. In addition, low impedance characteristics are required even when capacitors are used under high frequency conditions. In order to meet this requirement, it is desirable to use an electrolytic solution having a low specific resistance and high conductivity. Therefore, an electrolytic solution based on an electrolytic solution containing ethylene glycol as a main solvent and carboxylic acid and / or carboxylate as an electrolyte is used. Studies have been made to reduce the specific resistance by increasing the water content of the liquid.

  However, water in the electrolytic solution and carboxylic acid and / or carboxylate of the electrolyte are chemically active materials for the anode and cathode made of aluminum foil. The aluminum oxide film on the electrode surface is dissolved by the reaction with the 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. In particular, in a high-temperature life test at 105 ° C. or higher, if the water content of the solvent exceeds 15% by mass, a large amount of hydrogen gas is generated due to the rapid reaction described above, the pressure in the capacitor increases, and the safety valve opens. As a result, there was a problem that it could not be used.

  In order to prevent such deterioration of the electrode foil, a method of adding phosphoric acid to the electrolytic solution has been conventionally known. When an appropriate amount of phosphate ions is present in the electrolyte, dissolution of the anode and cathode aluminum, generation of aluminum hydroxide and the like are suppressed, and generation of hydrogen gas is also suppressed.

  However, even if phosphoric acid is added to the electrolytic solution, the phosphate ions are combined with aluminum ions dissolved in the electrolytic solution to form a compound insoluble in the electrolytic solution, and this insoluble compound adheres to the electrode foil, and phosphoric acid is added. Since ions disappear from the electrolytic solution, the effect of preventing deterioration of the electrode foil by phosphate ions was not sufficient. In addition, even if the amount of phosphoric acid added to the electrolytic solution is too large, the aluminum oxide film on the electrode surface dissolves due to the reaction with phosphate ions, resulting in an increase in the leakage current of the aluminum electrolytic capacitor. With respect to such a problem, the applicant pays attention to the fact that the capacitor characteristics are kept good while an appropriate amount of phosphate ion is present in the electrolyte solution. In Patent Document 1 (WO 00/55876 pamphlet), A compound that generates phosphate ions in an aqueous solution and a chelating agent that coordinates with aluminum to form a water-soluble aluminum chelate complex are added to the electrolyte solution containing the aluminum ion eluted from the electrode foil and the above chelating agent Discloses a method of forming a conjugate of a water-soluble aluminum chelate complex and a phosphate ion in an electrolytic solution by a reaction between the salt and a phosphate ion.

  The conjugate of the water-soluble aluminum chelate complex and phosphate ion is in the electrolyte solution in order to maintain chemical equilibrium with the phosphate ion in the electrolyte solution when dissolved in the electrolyte solution or attached to the electrode foil. It is possible to prolong the time in which a suitable amount is present, and to prevent deterioration of the anode and the cathode for a long time. And according to the Example of patent document 1, as an electrolytic solution for aluminum electrolytic capacitors, ammonium adipate useful for reducing the impedance of electrolytic capacitors is dissolved in a mixed solvent composed of water and ethylene glycol, and Using an electrolyte containing a water-soluble aluminum chelate complex and a phosphate ion conjugate, a capacitor showing a long life of 1000 hours or more in a high temperature no-load test, which is one of the most severe life tests, can be obtained. ing.

  As another method for preventing the deterioration of the electrode foil, a method of changing the basic compound constituting the salt with carboxylic acid from ammonia to an amine or a mixture of ammonia and an amine has been studied.

  Patent Document 2 (Japanese Patent Laid-Open No. 2002-207473) proposes an electrolytic solution for an electrolytic capacitor in which a secondary amine salt or a tertiary amine salt of carboxylic acid is dissolved in a solvent containing water and ethylene glycol. According to the examples and comparative examples of Patent Document 2, an aluminum electrolytic capacitor using an electrolytic solution in which ammonium benzoate is dissolved in a mixed solvent of water and ethylene glycol is subjected to a no-load test at 105 ° C. for 1000 hours. The safety valve has been opened before experience, but the aluminum electrolytic capacitor using an electrolytic solution in which triethylamine benzoate is dissolved instead of ammonium benzoate is the initial stage even after 1000 hours of no-load test at 105 ° C. It does not show a significant change from the characteristics.

  Patent Document 3 (Japanese Patent Application Laid-Open No. 2004-14666) discloses an electrolytic capacitor electrolytic solution in which water is a main solvent, an electrolyte acid component is a carboxylic acid and / or an inorganic acid, and a base component is ammonia. An electrolytic solution for an electrolytic capacitor having a pH of 6.0 to 8.5 at 30 ° C. by adding a basic compound other than ammonia is disclosed. According to Example 1 and Comparative Example 1 of Patent Document 3, an aluminum electrolytic capacitor using an electrolytic solution in which ammonium formate and ammonium adipate are dissolved in a mixed solvent composed of water and ethylene glycol is loaded at 105 ° C. The safety valve has been opened after 500 hours of testing, but an aluminum electrolytic capacitor using an electrolytic solution in which triethanolamine is dissolved in addition to ammonium formate and ammonium adipate is subjected to a load test at 105 ° C for 3000 hours. Experience has not shown a significant change from the initial characteristics. In addition to this, there are examples and comparative examples in which triethylamine, trishydroxymethylaminomethane, and diethanolamine are used as basic compounds constituting a salt with a carboxylic acid. However, no load test results, which are more severe life tests, are shown.

WO00 / 55876 pamphlet JP 2002-270473 A Japanese Patent Laid-Open No. 2004-14666

  According to the method disclosed in Patent Document 1 (Pamphlet of WO 00/55876), even if the water content of the electrolyte is increased, dissolution of aluminum in the electrode foil, generation of aluminum hydroxide and the like, and generation of hydrogen gas can be achieved. Since it can suppress, the impedance reduction and lifetime improvement of an aluminum electrolytic capacitor can be achieved. However, there is always a demand for further lower impedance and longer life for aluminum electrolytic capacitors. At present, in addition to having a low impedance characteristic, an extremely long life exceeding 8000 hours is required in a 105 ° C. no-load test, which is one of the most severe life tests for aluminum electrolytic capacitors.

  However, the electrolytic solution disclosed in Patent Document 1 in which ammonium adipate is dissolved in a mixed solvent composed of water and ethylene glycol and a combined body of a water-soluble aluminum chelate complex and a phosphate ion coexists is obtained. Although it sufficiently satisfies the demand for lower impedance, it did not fully meet the demand for longer life of the capacitor due to the electrode deterioration effect caused by a large amount of water and adipic acid anions.

  Therefore, in order to answer the demand for longer life, it is conceivable to change the basic compound constituting the salt with adipic acid from ammonia to amine. However, the change to amine may greatly increase the specific resistance of the electrolyte. This is shown in Example 3 while the specific resistance of the electrolyte solution consisting of 25 parts of water, 65 parts of ethylene glycol and 10 parts of ammonium benzoate shown in Comparative Example 1 of Patent Document 2 is 106 Ωcm. It is also understood from the fact that the specific resistance of an electrolytic solution consisting of 25 parts of water, 65 parts of ethylene glycol and 10 parts of triethylamine benzoate is 240 Ωcm, which is twice or more. For this reason, the use of amine as a basic compound has been avoided in the previous studies for obtaining a capacitor having a low impedance and a long life, and even if an amine is used, it is disclosed in Patent Document 3. In addition, ammonia and an amine were used in combination. Further, as will be described in detail below, it has been found by the inventors that the combined use of amine and ammonia cannot meet the current demand for long life of aluminum electrolytic capacitors.

  Accordingly, an object of the present invention is to provide an electrolytic solution for an aluminum electrolytic capacitor having a low specific resistance and capable of effectively suppressing the elution of aluminum from the electrode foil in order to meet the above-described demand for the aluminum electrolytic capacitor. It is. A further object of the present invention is to provide an aluminum electrolytic capacitor that has low impedance characteristics using such a suitable electrolyte and has a longer life than conventional capacitors.

  As a result of intensive studies, the inventors used only a primary amine and / or a secondary amine having a hydrophobic substituent as a basic compound capable of forming a salt with adipic acid, and electrolyzed with this amine. It has been discovered that adjusting the pH of the solution to a range of 5.6 to 7.0 can avoid a significant increase in the specific resistance of the electrolyte and can meet the current requirements for the lifetime of aluminum electrolytic capacitors. did.

  Accordingly, the electrolytic solution for an aluminum electrolytic capacitor of the present invention comprises a mixed solvent composed of water and ethylene glycol, an adipic acid as a carboxylic acid electrolyte, a basic compound capable of forming a salt of adipic acid, and an aqueous solution. An electrolyte solution in which a phosphorus oxo acid ion generating compound capable of generating a phosphorus oxo acid ion and a chelating agent capable of forming a water-soluble aluminum chelate complex by coordination with aluminum are dissolved, and the basic compound is Including only at least one compound selected from the group consisting of a primary amine and a secondary amine having a hydrophobic substituent, and the pH of the electrolyte is in the range of 5.6 to 7.0. Features.

  In the electrolytic solution of the present invention, the “phosphooxoacid ion” includes, in addition to phosphate ions, phosphite ions, hypophosphite ions, isomers of these phosphonate ions and phosphinate ions, In addition to a compound that generates a phosphorus oxoacid ion when this compound is dissolved in the above solvent, the phosphorus oxoacid ion generating compound includes a phosphorus oxoacid through oxidation at the anode after the electrolytic solution is introduced into the aluminum electrolytic capacitor. Also included are compounds that generate ions. In addition, since the electrolytic solution for an aluminum electrolytic capacitor of the present invention contains a large amount of water, a compound that generates a phosphoroxoate ion in an aqueous solution generates a phosphate salt in the electrolyte and is coordinated with aluminum to be water-soluble. A chelating agent that forms an aluminum chelate complex forms an aluminum chelate complex that dissolves in the electrolyte.

  The electrolytic solution of the present invention is capable of constituting a salt with adipic acid by dissolving the above-mentioned phosphoroxoacid ion, the above-mentioned chelating agent and adipic acid as a carboxylic acid electrolyte in a mixed solvent composed of water and ethylene glycol. As a basic compound, only a primary amine and / or secondary amine having a hydrophobic substituent is added, and the pH of the electrolyte solution is increased by the primary amine and / or secondary amine having the hydrophobic substituent. Can be obtained by adjusting to a range of 5.6 to 7.0, preferably 5.7 to 6.4. It is also possible to introduce at least part of the primary amine and / or secondary amine having a hydrophobic substituent into the electrolyte in the form of a salt with adipic acid. If the pH is less than 5.6 or greater than 7.0, the electrode foil may not be able to meet the demand for longer life due to the deterioration of the electrode foil. Adipic acid as a carboxylic acid electrolyte is also disclosed in Patent Document 1, but is suitable for reducing the impedance of a capacitor.

  In the electrolytic solution of the present invention, if an aluminum ion coexists in the electrolytic solution, a reaction between the aluminum ion, the chelating agent, and the phosphorus oxoacid ion generated from the phosphorus oxoacid ion-generating compound, A conjugate with a water-soluble aluminum chelate complex is formed in the electrolyte. An aluminum salt or the like may be added to the electrolytic solution in advance to contain aluminum ions, but the chelating agent and the phosphorus oxoacid ion-forming compound are contained but the aluminum ions are not contained. Even when the electrolytic solution is introduced into the aluminum electrolytic capacitor, aluminum ions are eluted from the electrode foil. Therefore, the electrolytic solution in the aluminum electrolytic capacitor contains a conjugate of a phosphoroxoacid ion and a water-soluble aluminum chelate complex. Become.

  In the electrolytic solution of the present invention, as a basic compound capable of forming a salt with adipic acid, ammonia is not used, an amine having a non-hydrophobic substituent such as a hydroxyl group is not used, and a tertiary amine is used. do not do. Primary amines and secondary amines having hydrophobic substituents have less action to increase the specific resistance of the electrolyte compared to tertiary amines, and aluminum from the anode and cathode of an aluminum electrolytic capacitor. Effectively suppresses elution.

  FIG. 1 shows the results of an accelerated test for investigating the influence of the type of basic compound. In this accelerated test, 6 parts of formic acid and 9 parts of adipic acid were dissolved in a mixed solvent consisting of 60 parts by weight of water and 18 parts by weight of ethylene glycol, and ammonia, ammonia and dimethylamine (DMA) as basic compounds were dissolved. A soaking solution having a pH adjusted to about 6 is prepared by adding a mixture of 3: 1 ratio, a mixture of ammonia and dimethylamine in a ratio of 1: 1, dimethylamine, or diethylamine (DEA), respectively, An electrode foil made of an aluminum foil having an aluminum oxide film was immersed in these immersion liquids, and the amount of aluminum ions dissolved from the electrodes was measured by ICP emission spectrometry. Since this was an accelerated test, a phosphorooxoate ion-forming compound and a chelating agent that had an effect of suppressing electrode deterioration were not included in the immersion liquid, and formic acid having an action of deteriorating the electrode foil was larger than that of adipic acid.

  From FIG. 1, when neutralized with dimethylamine or diethylamine, therefore, when dimethylamine or diethylamine is used as a basic compound constituting a salt with carboxylic acid, even if formic acid and adipic acid coexist, It can be seen that almost no aluminum ions are observed in the solution over a long period of time. On the other hand, when neutralized with ammonia, and therefore when ammonia is used as the basic compound that forms a salt with carboxylic acid, aluminum dissolves in the immersion liquid from the electrode foil even when used in combination with dimethylamine. Even when the amount of dimethylamine was adjusted, the results were almost the same as when ammonia alone was used as the basic compound. When neutralized with dimethylamine or diethylamine, aluminum ions are hardly observed. The reason is that dimethylamine or diethylamine is bonded to the surface of the aluminum oxide film of the electrode foil to form a hydrophobic layer. It seems to be for suppressing elution of selenium. When ammonia is contained, a portion where the hydrophobic layer is not formed is generated, and hydration proceeds from the portion. Therefore, as can be seen from FIG. 1, it is considered that the effect of the amine is almost lost.

  Separately, 5 parts of adipic acid is dissolved in a mixed solvent composed of 50 parts by weight of water and 45 parts by weight of ethylene glycol, and ammonia, methylamine, dimethylamine, trimethylamine or hydroxylamine is added as a basic compound, Prepare a dipping solution with a pH neutralized to about 6.4, dip an electrode foil made of an aluminum foil having an aluminum oxide film on its surface into these dipping solutions, keep the solution at 60 ° C. and dissolve from the electrode foil An accelerated test was performed in which the amount of aluminum ions measured was measured by ICP emission spectrometry. When 468 hours passed after the start of the experiment, elution of aluminum was observed only in the immersion liquid neutralized with hydroxylamine, and it was found that hydroxylamine having a non-hydrophobic substituent had a larger electrode deterioration effect than ammonia. It was. Also, an attempt is made to dissolve these basic compounds, adipic acid, phosphoric acid as a phosphorus oxoacid ion-forming compound, and diethylenetriaminepentaacetic acid as a chelating agent in a mixed solvent composed of water and ethylene glycol. However, insoluble matters remained only when hydroxylamine was used as the basic compound, and a liquid usable as an electrolytic solution for an aluminum electrolytic capacitor could not be obtained.

  From these findings, in order to meet the demand for lower impedance and longer life for aluminum electrolytic capacitors, primary amines having hydrophobic substituents as basic compounds capable of forming salts with adipic acid and / or It was judged essential to use only secondary amines. With the primary amine and / or secondary amine having the hydrophobic substituent, it is possible to avoid a significant increase in the specific resistance of the electrolytic solution, and to dissolve the aluminum in the anode and cathode of the aluminum electrolytic capacitor, Generation of hydroxide and the like and generation of hydrogen gas accompanying this can be suppressed. Further, by allowing a conjugate of a phosphorus oxoacid ion and a water-soluble aluminum chelate complex to coexist in the electrolytic solution, the phosphorous oxide ion in the electrolytic solution can be dissolved in the electrolytic solution or attached to the electrode foil. And the chemical equilibration, and the time required for the presence of an appropriate amount of the phosphorus oxoacid ion in the electrolyte solution can be prolonged, so that the phosphorus oxoacid ion also dissolves the aluminum and aluminum in the anode and cathode of the aluminum electrolytic capacitor. And the generation of hydrogen gas associated therewith can be suppressed. The combined effect of the amine having a hydrophobic substituent and the above conjugate surprisingly suppresses dissolution of aluminum in the anode and cathode, generation of hydroxide, and generation of hydrogen gas. As a result, it is possible to obtain an aluminum electrolytic capacitor having an extremely long life even when the water content of the electrolytic solution is increased and a large amount of adipic acid is used as the carboxylic acid electrolyte in order to reduce the specific resistance of the electrolytic solution. .

  In the electrolytic solution of the present invention, the electrolyte dissolved in the mixed solvent is selected from the group consisting of azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid, and tetradecanedioic acid in addition to adipic acid. It is also preferred to dissolve at least one long-chain dicarboxylic acid.

  These long-chain dicarboxylic acids not only act as electrolytes, but also suppress elution of aluminum from anodes and cathodes, as do primary and / or secondary amines with hydrophobic substituents. (See the PCT / JP2009 / 003262 international publication and the Japanese Patent Application No. 2010-084657 publication that are unpublished at the time of this application). This inhibitory action is considered to be brought about by these long-chain dicarboxylic acids adhering to the surfaces of the anode and cathode of the aluminum electrolytic capacitor to form a protective layer.

  In particular, azelaic acid is more soluble in the above mixed solvent and contributes to lowering the resistivity of the electrolyte compared to sebacic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid, and tetradecanedioic acid. Therefore, it is preferable. In addition, undecanedioic acid, dodecanedioic acid, and tridecanedioic acid are disadvantageous in terms of reducing the specific resistance of the electrolyte because they are less soluble in the above mixed solvent than azelaic acid. It is economically advantageous because it leads to a long life of the aluminum electrolytic capacitor by adding only about 1/10 in the electrolytic solution, and has an elution suppression effect superior to that of about 2 times molar amount of sebacic acid or tetradecanedioic acid. This is preferred for the sake of illustration.

  By the way, for a low-pressure aluminum electrolytic capacitor, an electrolytic solution having a specific resistance at 30 ° C. of 100 Ωcm or less is desirable, and for a capacitor of 50 WV or less, the specific resistance of the electrolytic solution at 30 ° C. is preferable. Is preferably 70 Ωcm or less, preferably 50 Ωcm or less.

  In order to obtain an electrolyte having a low specific resistance suitable for this low-voltage aluminum electrolytic capacitor, at least one compound selected from the group consisting of monomethylamine, monoethylamine and dimethylamine is used as the basic compound. It is preferred to use. These amines provide an electrolytic solution exhibiting a low specific resistance substantially equivalent to an electrolytic solution using ammonia as a basic compound.

  Moreover, in order to obtain the electrolyte solution with a low specific resistance suitable for the aluminum electrolytic capacitor for low voltage | pressure, content of the water in electrolyte solution is 35-70 mass% of the whole, Preferably it is 45-60 mass% Range. If the content of water with respect to the entire electrolyte is less than 35% by mass, the specific resistance of the electrolyte tends to increase because dissociation of adipic acid is not sufficient, and the viscosity of the electrolyte increases, making it difficult to handle. When the content of water with respect to the entire electrolytic solution exceeds 70% by mass, the life in the high temperature no-load test tends to be shortened even if other requirements in the electrolytic solution of the present invention are satisfied.

  Adipic acid can be added to the electrolytic solution up to a saturated dissolution amount at 50 ° C. Since the temperature of the electrolytic solution in the capacitor is 50 ° C. or higher under the normal use conditions of the aluminum electrolytic capacitor, adipic acid is completely dissolved in the electrolytic solution and acts as an electrolyte under the normal use conditions of the capacitor. If the amount of adipic acid is larger than the saturated dissolution amount at 50 ° C. in the electrolytic solution, precipitation of the adipic acid from the electrolytic solution at low temperatures becomes remarkable, which is not preferable. The amount of adipic acid saturated dissolved in an electrolytic solution at 50 ° C. varies somewhat depending on the type and amount of other components that coexist, but in the present invention, a mixed solvent composed of water and ethylene glycol is added to a mixed solvent other than adipic acid Prepare a solution in which the components are dissolved, add a desired amount of adipic acid to the solution while it is heated to 70 ° C, dissolve it, lower the temperature of the solution to 50 ° C, and leave it at 50 ° C for 1 hour. When no precipitate was observed later, the amount of adipic acid added was determined to be less than or equal to the saturated dissolution amount at 50 ° C. in the electrolytic solution.

  In order to obtain an electrolytic solution having a low specific resistance as the water content is small, a large amount of adipic acid is required, but in order to obtain an electrolytic solution having a low specific resistance that is suitable for an aluminum electrolytic capacitor for low pressure. The content of adipic acid is at least 8% by mass or more of the whole electrolyte solution, preferably in the range of 10 to 12% by mass. When the content of adipic acid with respect to the entire electrolytic solution is less than 8% by mass, the specific resistance of the electrolytic solution tends to increase due to a decrease in electrolytic mass.

  And water content is 35-70 mass% of the whole electrolyte solution, Preferably it is 45-60 mass%, Content of adipic acid is the amount of saturated dissolution in 50 degreeC from 8 mass% of the whole electrolyte solution. An electrolytic solution having a specific resistance at 30 ° C. of 100 Ωcm or less, preferably 70 Ωcm or less, particularly preferably 50 Ωcm or less, which is suitable for a low-pressure aluminum electrolytic capacitor when the content is in the range, preferably 10 to 12% by mass. The use of this electrolyte solution has a low impedance characteristic and an extremely long life, and in particular, a low-pressure aluminum electrolytic capacitor for a low-pressure aluminum electrolytic capacitor in which the safety valve does not open even after 8000 hours of no-load test at 105 ° C. Thus, an aluminum electrolytic capacitor can be obtained that can fully meet the demands for longer and longer life.

  In the present invention, the phosphorus oxoacid ion-generating compound includes phosphoric acid, phosphorous acid, hypophosphorous acid, phosphonic acid, phosphinic acid, and primary amines and / or secondary amines having hydrophobic substituents therewith. Salts with amines; esters of phosphoric acid and alkylphosphoric acid, esters and derivatives of phosphonic acid and diphosphonic acid, phosphinic acid esters, and primary and / or secondary amines with hydrophobic substituents A salt; and a salt of these condensates and salts of these condensates with primary amines and / or secondary amines having a hydrophobic substituent; Citric acid, tartaric acid, gluconic acid, malic acid, lactic acid, glycolic acid, α-hydroxybutyric acid, hydroxymalonic acid, α-methylmalic acid, dihydroxytartaric acid, γ Resorcylic acid, β-resorcylic acid, trihydroxybenzoic acid, hydroxyphthalic acid, dihydroxyphthalic acid, phenol tricarboxylic acid, aluminone, eriochrome cyanine R, sulfosalicylic acid, tannic acid, dicyandiamide, galactose, glucose, lignosulfonate, ethylenediamine Tetraacetic acid (EDTA), nitrilotriacetic acid (NTA), glycol etherdiaminetetraacetic acid (GEDTA), diethylenetriaminepentaacetic acid (DTPA), hydroxyethylethylenediaminetriacetic acid (HEDTA), triethylenetetraminehexaacetic acid (TTHA), and these It can be suitably selected from the group consisting of salts with primary amines and / or secondary amines having hydrophobic substituents.

  By introducing the electrolytic solution of the present invention into an aluminum electrolytic capacitor, an aluminum electrolytic capacitor having low impedance characteristics and a long life can be obtained. Therefore, the present invention also provides an aluminum electrolysis comprising an anode made of an aluminum foil having an aluminum oxide film on its surface, a cathode made of an aluminum foil, and a separator holding an electrolytic solution disposed between the anode and the cathode. The electrolytic solution of the present invention described above is used as an electrolytic solution. Therefore, hydrophobicity capable of forming a salt of adipic acid and adipic acid as a carboxylic acid electrolyte in the electrolytic solution of the capacitor. Provided is an aluminum electrolytic capacitor comprising a primary amine and / or a secondary amine having a substituent, and a conjugate of a phosphorus oxoacid ion and a water-soluble aluminum chelate complex.

  A phosphorus oxoacid ion-forming compound capable of generating a phosphorus oxoacid ion in an aqueous solution and a chelating agent capable of forming a water-soluble aluminum chelate complex by coordination with aluminum in a mixed solvent composed of water and ethylene glycol. Dissolve and dissolve adipic acid as a carboxylic acid electrolyte useful for lowering the resistivity of the electrolyte, and further, hydrophobic substitution with an electrode deterioration inhibiting effect as a basic compound that can form a salt with adipic acid According to the electrolytic solution for an aluminum electrolytic capacitor of the present invention, wherein a primary amine and / or a secondary amine having a group is used, and the pH is adjusted to a range of 5.6 to 7.0 by adding the amine to the solution. And a combination of phosphoroxoacid ion and water-soluble aluminum chelate complex formed in the electrolyte introduced into the aluminum electrolytic capacitor Due to the combined effect of this conjugate with a primary amine and / or secondary amine having a hydrophobic substituent, dissolution of aluminum on the anode and cathode of the aluminum electrolytic capacitor, generation of hydroxide, etc. The generation of the accompanying hydrogen gas is surprisingly suppressed. As a result, by using the electrolytic solution for an aluminum electrolytic capacitor of the present invention, an aluminum electrolytic capacitor having a low impedance characteristic and a longer life than a conventional capacitor can be obtained.

It is a figure which shows the result of having investigated the inhibitory effect of the basic compound with respect to melt | dissolution of the aluminum from electrode foil.

  Hereinafter, the present invention will be described in detail. The electrolytic solution for an aluminum electrolytic capacitor according to the present invention comprises a mixed solvent composed of water and ethylene glycol, a basic acid capable of forming a salt of adipic acid as a carboxylic acid electrolyte, and a salt of adipic acid, and phosphorous acid in an aqueous solution. An electrolyte solution in which an ion-forming compound capable of generating ions and a chelating agent capable of forming a water-soluble aluminum chelate complex by coordinating to aluminum is dissolved, and the above basic compound is hydrophobic It contains only a primary amine and / or a secondary amine having a substituent, and the pH of the electrolyte is in the range of 5.6 to 7.0.

  In the electrolytic solution of the present invention, a mixed solvent composed of water and ethylene glycol is used as a solvent. A mixed solvent of water and ethylene glycol gives an electrolytic solution having high solubility of various solutes and excellent temperature characteristics.

  The content of water in the electrolytic solution of the present invention is preferably 35 to 70% by mass, particularly preferably 45 to 60% by mass, based on the entire electrolytic solution. If the content of water with respect to the entire electrolyte is less than 35% by mass, the specific resistance of the electrolyte tends to increase because dissociation of adipic acid is not sufficient, and the viscosity of the electrolyte increases, making it difficult to handle. When the content of water with respect to the entire electrolytic solution exceeds 70% by mass, the lifetime in the high temperature no-load test tends to be shortened even if other requirements in the electrolytic solution of the present invention are satisfied. When the content of water in the electrolytic solution is 35 to 70% by mass, preferably 45 to 60% by mass, the use of this electrolytic solution has a low impedance characteristic and an extremely long life, particularly at high temperature and no load. Even in the test, a long-life aluminum electrolytic capacitor can be obtained. It is preferable that content of the said mixed solvent in electrolyte solution is 60-90 mass% of the whole electrolyte solution from a soluble viewpoint of adipic acid.

  The electrolytic solution of the present invention uses adipic acid as the carboxylic acid electrolyte. Adipic acid may be dissolved in the mixed solvent in the form of an acid, or dissolved in the mixed solvent in the form of a salt with a primary amine and / or a secondary amine having a hydrophobic substituent, which will be described in detail later. You may let them. Although adipic acid cannot be expected to suppress the electrode deterioration, it is suitable for reducing the impedance of the aluminum electrolytic capacitor.

  Adipic acid can be added to the electrolytic solution up to a saturated dissolution amount at 50 ° C. Since the temperature of the electrolytic solution in the capacitor is 50 ° C. or higher under the normal use conditions of the aluminum electrolytic capacitor, adipic acid is completely dissolved in the electrolytic solution and acts as an electrolyte under the normal use conditions of the capacitor. If the amount of adipic acid is larger than the saturated dissolution amount at 50 ° C. in the electrolytic solution, precipitation of the adipic acid from the electrolytic solution at low temperatures becomes remarkable, which is not preferable. When adipic acid is precipitated from the electrolytic solution in the aluminum electrolytic capacitor, the pH of the electrolytic solution increases, and dissolution of aluminum in the electrode foil may proceed. If the content of these compounds is equal to or less than the saturated dissolution amount at 50 ° C., even if adipic acid is precipitated at a low temperature, the pH of the electrolyte does not change so much that the dissolution of aluminum in the electrode foil proceeds.

  In order to obtain an electrolytic solution having a lower specific resistance as the water content is smaller, more adipic acid is required. However, in the electrolytic solution of the present invention, the content of adipic acid is at least 8% by mass of the entire electrolytic solution. The above is preferable, and the range of 10 to 12% by mass is particularly preferable. If adipic acid is less than 8 mass% with respect to the whole electrolyte solution, the specific resistance of the electrolyte solution tends to increase due to a decrease in electrolytic mass.

  In an electrolytic solution in which the water content is 35 to 70% by mass, preferably 45 to 60% by mass, based on the total electrolytic solution, the content of adipic acid is from 8% by mass to 50 ° C. In the range of 10 to 12% by mass, an electrolytic solution having a specific resistance at 30 ° C. of 100 Ωcm or less, preferably 70 Ωcm or less, particularly preferably 50 Ωcm or less suitable for an aluminum electrolytic capacitor for low pressure is used. By using this electrolytic solution, it is possible to obtain an aluminum electrolytic capacitor having a low impedance characteristic and having a very long life, in particular, a safety valve that does not open even after 8000 hours of 105 ° C. no-load test.

  In the electrolytic solution of the present invention, in addition to adipic acid, at least one selected from the group consisting of azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid, and tetradecanedioic acid that can act as an electrolyte It is preferable to dissolve the long-chain dicarboxylic acid. These long-chain dicarboxylic acids may be used alone or in combination of two or more, and can be dissolved in the above mixed solvent in the form of an acid. It can also be dissolved in the mixed solvent in the form of a salt with a primary amine and / or a secondary amine having a group. These long-chain dicarboxylic acids not only act as electrolytes, but also suppress elution of aluminum from anodes and cathodes, as do primary and / or secondary amines with hydrophobic substituents. I know you will. This inhibitory action is considered to be brought about by these long-chain dicarboxylic acids adhering to the surfaces of the anode and cathode of the aluminum electrolytic capacitor to form a protective layer.

  In particular, azelaic acid is more soluble in the above mixed solvent and contributes to lowering the resistivity of the electrolyte compared to sebacic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid, and tetradecanedioic acid. Therefore, it is preferable. Azelaic acid can be added to the electrolyte up to about ¼ mass of adipic acid. Although sebacic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid, and tetradecanedioic acid are less soluble in the above mixed solvent compared to azelaic acid, they are disadvantageous in terms of reducing the specific resistance of the electrolyte. , And can be added to the electrolytic solution up to a saturated dissolution amount at 50 ° C. In particular, undecanedioic acid, dodecanedioic acid, and tridecanedioic acid are economically advantageous because they lead to an aluminum electrolytic capacitor having a long life by adding only about 1/10 of the molar amount of azelaic acid to the electrolyte. , Which is preferable because it exhibits an elution suppression effect superior to that of about 2 times the molar amount of sebacic acid or tetradecandioic acid.

  In the electrolytic solution of the present invention, only a primary amine and / or secondary amine having a hydrophobic substituent is used as a basic compound capable of forming a salt with adipic acid, and the pH of the electrolytic solution is increased by this amine. In the range of 5.6 to 7.0, preferably 5.7 to 6.4. A primary amine and / or a secondary amine having a hydrophobic substituent may be used alone or in admixture of two or more, and dissolved in the above mixed solvent in the form of an amine. It is also possible to introduce at least part of the electrolyte into the electrolyte in the form of a salt with adipic acid and / or the above-mentioned long-chain dicarboxylic acid. If the pH is less than 5.6 or greater than 7.0, the electrode foil may not be able to meet the demand for longer life due to the deterioration of the electrode foil. On the other hand, if the pH is higher than 7.0, the initial leakage current increases, which is not preferable.

  In the present invention, as a basic compound capable of forming a salt with adipic acid, ammonia is not used and an amine having a non-hydrophobic substituent such as a hydroxylalkyl group (hydroxylamine, diethanolamine, trishydroxymethylaminomethane, etc.) And tertiary amines (trimethylamine, triethylamine, etc.) are not used. Primary amines and secondary amines having a hydrophobic substituent have less effect of increasing the specific resistance of the electrolyte compared to tertiary amines (see Examples 1 to 4 and Comparative Example 4). In order to obtain an electrolytic solution having a low specific resistance by using a tertiary amine having a large effect of increasing the specific resistance of the electrolytic solution, more water and adipic acid are required. However, this increased amount of water and adipic acid degrade the electrode foil. Therefore, in order to obtain an electrolytic solution having a low specific resistance, it is preferable to use a primary amine and / or a secondary amine. Moreover, as shown in FIG. 1, the primary amine and the secondary amine having a hydrophobic substituent effectively suppress the elution of aluminum from the electrode foil of the aluminum electrolytic capacitor.

  Examples of primary amines include alkylamines such as methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, isobutylamine, t-butylamine; arylamines such as aniline, xylylamine, 1-naphthylamine Can be mentioned. Examples of secondary amines include dialkylamines such as dimethylamine, diethylamine, N-methylethylamine, methyl n-propylamine, methylisopropylamine, ethyl n-propylamine, ethylisopropylamine, di-n-propylamine, Diisopropylamine, di-n-butylamine, N-ethylisobutylamine, di-t-butylamine; diarylamines such as diphenylamine, dixylylamine, N-phenylnaphthylamine; alkylarylamines such as N-methylphenylamine, N-ethylphenylamine , N-methylnaphthylamine; alicyclic amines such as aziridines, azetidines, pyrrolidines, piperidines;

  Especially, it is preferable to use at least 1 sort (s) of compounds selected from the group which consists of a monomethylamine, a monoethylamine, and a dimethylamine as a basic compound which can comprise a salt with adipic acid. These amines provide electrolytes that exhibit a lower specific resistance than primary amines and / or secondary amines having other hydrophobic substituents, and electrolytes that use ammonia as a basic compound; An electrolytic solution exhibiting substantially the same specific resistance is provided.

  The electrolytic solution for an aluminum electrolytic capacitor of the present invention further contains a phosphorus oxoacid ion generating compound capable of generating phosphorus oxoacid ions in an aqueous solution.

  Examples of the phosphorus oxoacid ion-generating compound include phosphoric acid, phosphorous acid, hypophosphorous acid, phosphonic acid, phosphinic acid, and salts thereof with a primary amine and / or a secondary amine having a hydrophobic substituent. Esters of phosphoric acid and alkyl phosphoric acid, esters and derivatives of phosphonic acid and diphosphonic acid, phosphinic acid esters, and salts of these with primary and / or secondary amines having hydrophobic substituents; and these These condensates and salts of these condensates with primary amines and / or secondary amines having a hydrophobic substituent can be used. The salt as the phosphorus oxoacid ion generating compound is also selected from a primary amine and / or secondary amine having a hydrophobic substituent, and the primary amine and / or secondary amine constituting the salt is selected. Can be those exemplified above.

  First, phosphoric acid, phosphorous acid, hypophosphorous acid, and salts thereof with a primary amine and / or a secondary amine having a hydrophobic substituent can be used as the phosphorus oxoacid ion generating compound. Phosphoric acid and its salts are decomposed in an aqueous solution to produce phosphate ions. In addition, phosphorous acid, hypophosphorous acid, and salts thereof generate phosphite ions, hypophosphite ions, phosphonate ions and phosphinate ions that are isomers thereof in an aqueous solution, and aluminum Phosphate ions are produced through oxidation at the anode of the electrolytic capacitor.

  Further, as a phosphorous acid ion-forming compound, phosphoric acid such as ethyl phosphate, diethyl phosphate, butyl phosphate, dibutyl phosphate, and esters of alkyl phosphoric acid; phosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid Phosphonic acids such as aminotrimethylenephosphonic acid and phenylphosphonic acid, esters and derivatives of diphosphonic acid, phosphonic acid and diphosphonic acid; phosphinic acids such as methylphosphinic acid; phosphinic acid esters such as butyl phosphinate; and hydrophobic A salt with a primary amine and / or a secondary amine having a functional substituent can be used. Among these, dibutyl phosphate, 1-hydroxyethylidene-1,1-diphosphonic acid, or salts thereof are preferable.

  In addition, as the phosphorus oxoacid ion-forming compound, condensed phosphoric acid that is a condensate of phosphoric acid and a salt thereof with a primary amine and / or a secondary amine having a hydrophobic substituent are used. Examples of the condensed phosphoric acid include linear condensed phosphoric acid such as pyrophosphoric acid, tripolyphosphoric acid and tetrapolyphosphoric acid, cyclic condensed phosphoric acid such as metaphosphoric acid and hexametaphosphoric acid, and such chain and cyclic condensed phosphoric acid. An acid bonded one can be used. Of these, pyrophosphoric acid, tripolyphosphoric acid, tetrapolyphosphoric acid and salts thereof are preferable, pyrophosphoric acid, tripolyphosphoric acid and salts thereof are more preferable, and tripolyphosphoric acid and its salts are most preferable. With salt.

  Furthermore, a condensate of the above-mentioned phosphooxoate ion-forming compound or a salt of this condensate with a primary amine and / or a secondary amine having a hydrophobic substituent can also be used.

  The above-mentioned compound for producing a phosphoroxate ion generates a phosphate ion in an aqueous solution, or generates a phosphite ion, a hypophosphite ion, phosphonate ions and phosphinate ions which are isomers thereof, and Phosphate ions are generated through oxidation at the anode of the aluminum electrolytic capacitor.

  Among these, phosphoric acid that easily generates phosphate ions and salts of phosphoric acid with a primary amine and / or secondary amine having a hydrophobic substituent, condensed phosphoric acid, and phosphoric acid derivatives such as phosphorus Acids and esters of alkyl phosphoric acids are preferred. Furthermore, linear condensed phosphoric acid such as phosphoric acid, pyrophosphoric acid, tripolyphosphoric acid, etc., which generate a large amount of phosphate ions relatively quickly with respect to the added amount, and a primary class having this condensed phosphoric acid and a hydrophobic substituent Also preferred are salts with amines and / or secondary amines. In addition to these phosphorus oxoacid ion-forming compounds, substances that generate phosphorus oxoacid ions in an aqueous solution, and in the case of a salt, a first compound having a hydrophobic substituent as a basic compound constituting the salt. If it is a substance containing only a secondary amine and / or a secondary amine, the effect of the present invention can be obtained.

  A single compound or two or more compounds may be used as the phosphorus oxoacid ion-forming compound. The amount of the phosphorus oxoacid ion-forming compound is 0.01 to 5.0% by mass, preferably 0.2 to 3.0% by mass, based on the entire electrolytic solution. Outside this range, the effect is reduced.

  The electrolytic solution for an aluminum electrolytic capacitor further contains a chelating agent capable of forming a water-soluble aluminum chelate complex by coordination with aluminum.

  Examples of the chelating agent include citric acid, tartaric acid, gluconic acid, malic acid, lactic acid, glycolic acid, α-hydroxybutyric acid, hydroxymalonic acid, α-methylmalic acid, α-hydroxycarboxylic acids such as dihydroxytartaric acid, γ- Resorcylic acid, β-resorcylic acid, trihydroxybenzoic acid, hydroxyphthalic acid, dihydroxyphthalic acid, phenol tricarboxylic acid, aluminone, eriochrome cyanine R and other aromatic hydroxycarboxylic acids, sulfosalicylic acid and other sulfocarboxylic acids, tannic acid, etc. Tannins, guanidines such as dicyandiamide, saccharides such as galactose and glucose, lignins such as lignosulfonate, and ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), glycol etherdiaminetetraacetic acid (GED) TA), aminopolycarboxylic acids such as diethylenetriaminepentaacetic acid (DTPA), hydroxyethylethylenediaminetriacetic acid (HEDTA), triethylenetetraminehexaacetic acid (TTHA), and primary amines having hydrophobic substituents therewith and / or Mention may be made of salts with secondary amines. As the chelating agent, a salt with a primary amine and / or secondary amine having a hydrophobic substituent is also selected, and the primary amine and / or secondary amine constituting the salt is as above. What was illustrated can be used.

  Among these, tannic acid, trihydroxybenzoic acid, citric acid, tartaric acid, gluconic acid, aurintricarboxylic acid, γ-resorcylic acid, DTPA, EDTA, GEDTA, HEDTA, which can easily form a chelate complex with aluminum, are preferable. , TTHA, and salts of these with a primary amine and / or secondary amine having a hydrophobic substituent, and more preferred are tannic acid, trihydroxybenzoic acid, citric acid, tartaric acid, and γ-resorcil. Acids and aurintricarboxylic acids, DTPA, GEDTA, HEDTA, TTHA, and salts of these with primary and / or secondary amines having a hydrophobic substituent.

  As these chelating agents, a single compound may be used, or two or more compounds may be used. And the addition amount of these chelating agents is 0.01-3.0 mass% of the whole electrolyte solution, Preferably it is 0.1-2.0 mass%. Outside this range, the effect is reduced.

  The chelating agent and the phosphorus oxoacid ion-forming compound to be added at the time of preparing the electrolytic solution are such that the chelating agent and the phosphorus oxoacid ion in the electrolytic solution are in a molar ratio of chelating agent: phosphoric acid ion = 1: 20-3: 1. Preferably, it is added so that it may become 1: 10-1: 1. When the chelating agent is less than this ratio, the leakage current characteristic of the aluminum electrolytic capacitor is degraded. Moreover, when there are more chelating agents than this ratio, although the reason is not certain, the high temperature life characteristic of an aluminum electrolytic capacitor will deteriorate.

  If aluminum ions coexist in the electrolytic solution, the conjugate of the phosphoroxoacid ion and the water-soluble aluminum chelate complex is electrolyzed by the reaction between the above-mentioned chelating agent and the phosphorusoxoacid ion generated from the compound capable of forming the phosphorusoxoacid ion and the aluminum ion. Formed in the liquid. By adding aluminum ions in advance to the electrolytic solution by adding an aluminum salt or the like, a combined body of a phosphoroxo acid ion and a water-soluble aluminum chelate complex is formed in the electrolytic solution, and this electrolytic solution is introduced into the aluminum electrolytic capacitor. be able to. However, even if an electrolytic solution containing a chelating agent and a compound capable of forming a phosphorus oxoacid ion but not containing aluminum ions is introduced into the aluminum electrolytic capacitor, the aluminum ions are eluted from the electrode foil. The electrolytic solution in the capacitor contains a conjugate of a phosphoroxoacid ion and a water-soluble aluminum chelate complex. And in the state which this conjugate | bonded body melt | dissolved in electrolyte solution, or the state adhered to electrode foil, a chemical equilibrium is maintained with the phosphorus oxo acid ion in electrolyte solution, and the phosphorus oxo acid ion in electrolyte solution is maintained in a suitable quantity. As a result, the phosphorus oxoacid ion in the electrolytic solution and the phosphorus oxoacid ion in the conjugate are detected over a long period of time after leaving the capacitor. Phosphooxo ion present in an appropriate amount in the electrolyte suppresses dissolution of aluminum on the anode and cathode, generation of aluminum hydroxide, etc., and suppresses generation of hydrogen, thereby improving the standing characteristics of the aluminum electrolytic capacitor. . In the electrolytic solution of the present invention, the combined effect of the conjugate and the primary amine and / or the secondary amine having a hydrophobic substituent further causes the conjugate and the hydrophobic substituent. Due to the combined effect of primary amines and / or secondary amines with long-chain dicarboxylic acids selected from azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid and tetradecanedioic acid, the anode and cathode The dissolution of aluminum, the formation of hydroxides and the generation of hydrogen gas are surprisingly suppressed.

  The electrolytic solution for an aluminum electrolytic capacitor of the present invention may contain other components in addition to the above-described components within a range that does not adversely affect the effects of the present invention.

  For example, the solvent of the electrolytic solution of the present invention is preferably composed only of water and ethylene glycol, but if it is a small amount that does not adversely affect the effects of the present invention, it is another organic solvent such as a protic polar solvent. 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 and the like), amides which are aprotic solvents (N-methylformamide, N, N-dimethylformamide, N-ethylformamide, N, N-diethylformamide, N-methylacetamide, hexamethylphosphoric acid) 1) lactones, cyclic amides, carbonates (γ-butyrolactone, N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, etc.), nitriles (acetonitrile), oxides (dimethyl sulfoxide, etc.) More than one species may be included.

  In addition, the carboxylic acid electrolyte of the electrolytic solution of the present invention is preferably composed of only adipic acid or a mixture of adipic acid and the above long-chain dicarboxylic acid, but these may be used in small amounts that do not adversely affect the effects of the present invention. Carboxylic acids other than these compounds, such as acetic acid, butanoic acid, succinic acid, pimelic acid, malonic acid, benzoic acid, isophthalic acid, phthalic acid, terephthalic acid, maleic acid, toluic acid, enanthic acid, 1,6-decanedicarboxylic acid 1 or more types of branched octane dicarboxylic acids, such as acid, branched decanedicarboxylic acid, such as 5, 6- decanedicarboxylic acid, and 1,7-octane dicarboxylic acid, may be contained.

  Further, as an electrolyte other than carboxylic acid, it may contain boric acid, a polyhydric alcohol complex compound of boric acid obtained from boric acid and polyhydric alcohol, an inorganic acid such as carbonic acid and silicic acid, and improve the withstand voltage. For the purpose, mannitol, nonionic surfactant, colloidal silica or the like may be added to the electrolytic solution.

  Furthermore, for the purpose of absorbing hydrogen generated rapidly particularly at high temperatures, p-nitrophenol, m-nitrophenol, o-nitrophenol, p-nitrobenzoic acid, m-nitrobenzoic acid, o-nitrobenzoic acid, Nitro compounds such as p-nitroanisole, m-nitroanisole and o-nitroanisole may be included.

  The electrolytic solution for an aluminum electrolytic capacitor of the present invention is a primary amine having a hydrophobic substituent capable of forming a salt of adipic acid and adipic acid as a carboxylic acid electrolyte in a mixed solvent composed of water and ethylene glycol. And / or a secondary amine, a phosphorus oxo acid ion generating compound capable of generating a phosphorus oxo acid ion in an aqueous solution, and a chelating agent capable of forming a water-soluble aluminum chelate complex by coordination with aluminum. Accordingly, it can be obtained by dissolving with a long chain dicarboxylic acid selected from azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid, and tetradecanedioic acid and / or other additives. The pH of the electrolytic solution is adjusted to 5.6 to 7.0, preferably 5. by adjusting the amount of primary component and / or secondary amine having an acid component such as adipic acid and a hydrophobic substituent. It is adjusted to a range of 7 to 6.4.

  The above-described electrolytic solution for an aluminum electrolytic capacitor of the present invention is suitably used in an aluminum electrolytic capacitor that includes an anode, a cathode, and a separator that holds the electrolytic solution disposed between the anode and the cathode.

  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 or kraft paper between the anode and the cathode thus obtained, and the capacitor element is impregnated with the electrolytic solution for an aluminum electrolytic capacitor of the present invention, and further a sealed case An aluminum electrolytic capacitor is configured by being housed inside.

  Examples of the present invention are shown below, but the present invention is not limited to the following examples.

Preparation of Aluminum Electrolytic Capacitor A strip-shaped aluminum foil having a purity of 99.9% was subjected to etching treatment and surface expansion treatment, and then the aluminum foil was treated with an ammonium adipate solution (concentration: 150 g / L, pH 4.7 to 7.0). Chemical conversion treatment was performed for 30 minutes under the condition of a conversion voltage of 13 V to form an aluminum oxide film on the surface.

  The above anode and a cathode that has been subjected to an etching treatment on a strip-shaped aluminum foil having a purity of 99.9% are wound through a separator of Manila hemp, and impregnated with electrolytes shown in Tables 1 to 5 below. And place it in an outer case made of cylindrical aluminum with a bottom, insert a sealing body made of butyl rubber into the opening end of the outer case, and further squeeze the end of the outer case to seal the electrolytic capacitor An aluminum electrolytic capacitor having a diameter of 10 mm, a height of 20 mm, a rating of 6.3 V, and 2200 μF was prepared. In addition, all the adipic acid and other solutes in the electrolytic solutions shown in Tables 1 to 5 were completely dissolved in the electrolytic solution at 50 ° C.

Characteristic Evaluation of Aluminum Electrolytic Capacitor With respect to the obtained aluminum electrolytic capacitor, initial capacitance and dielectric loss (tan δ) at 120 Hz, impedance, leakage current after 2 minutes, and dielectric loss after 8000 hours of 105 ° C. no-load test And evaluated. Moreover, about the capacitor | condenser which reached valve opening before 105 degreeC no-load test 8000 hours, the time which reached valve opening was recorded as a lifetime. The larger the rate of change of dielectric loss before and after the 105 ° C. no-load test, the shorter the life of the capacitor. It has also been found that when the rate of change in dielectric loss exceeds 200%, the valve opens sooner thereafter.

(1) Influence of the kind of a basic compound The aluminum electrolytic capacitor was created using the electrolyte solution from which the kind of basic compound which can comprise a salt with adipic acid differs, and the characteristic evaluation was performed. Table 1 below shows the composition of the electrolytic solution used for each aluminum electrolytic capacitor, the type of basic compound, the pH and specific resistance of the electrolytic solution at 30 ° C., the initial capacitance, impedance, and leakage current of the aluminum electrolytic capacitor. And dielectric loss (tan δ), dielectric loss after 8000 hours of 105 ° C. no-load test, change rate of dielectric loss before and after 8000 hours, and time when the capacitor is opened are collectively shown.

  In the electrolyte solution, a phosphoamine ion formed from dimethylamine as a secondary amine having a hydrophobic substituent, phosphoric acid, diethylenetriaminepentaacetic acid, and aluminum ions eluted from the electrode foil, and a water-soluble aluminum chelate complex (Hereinafter, a conjugate of a phosphorus oxoacid ion and a water-soluble aluminum chelate complex is simply referred to as a “conjugate”). The safety valve did not open and the change in dielectric loss was small. Further, in the capacitors of Examples 2 to 4 including both a primary amine or a secondary amine having a hydrophobic substituent in the electrolytic solution and a conjugate, a safety valve even after 8000 hours of 105 ° C. no-load test Did not open. However, the capacitor of Comparative Example 6 containing dimethylamine in the electrolytic solution but not containing the conjugate was opened after 2500 hours of 105 ° C. no-load test. From this, the combined effect of the primary amine or secondary amine having a hydrophobic substituent coexisting in the electrolyte and the conjugate resulted in a capacitor life exceeding 8000 hours at 105 ° C. no load test. I understand that. It is well known that the no-load test is more severe than the load test as the capacitor life test, but the capacitor of the present invention exhibits a very long life exceeding 8000 hours even in the 105 ° C. load test. .

  Comparing Examples 1 to 4, the electrolytic solution in Example 2 containing diethylamine had higher specific resistance than the electrolytic solutions in Examples 1, 3, and 4 containing dimethylamine, monomethylamine, and monoethylamine. The electrolytic solutions in Examples 1, 3, and 4 show a low specific resistance substantially equal to the electrolytic solution in Comparative Examples 1 and 2 in which ammonia and dimethylamine are used in combination, and a capacitor using these electrolytic solutions has a temperature of 105 ° C. The change in dielectric loss before and after 8000 hours of no-load test was small and the life was long. Therefore, it can be seen that it is advantageous to use monomethylamine, monoethylamine or dimethylamine as a basic compound in order to meet the demand for lowering the impedance and extending the life of the capacitor.

  Comparative Examples 1 to 3 are examples in which ammonia or a mixture of ammonia and dimethylamine was used as a basic compound capable of constituting a salt with adipic acid. The capacitor of Comparative Example 3 containing only ammonia as the basic compound in the electrolytic solution was opened after 7000 hours of 105 ° C. no-load test. In the capacitors of Comparative Examples 1 and 2 in which ammonia and dimethylamine coexist in the electrolyte, the rate of change in dielectric loss exceeded 200% after 8000 hours of 105 ° C. no-load test, and it was close to valve opening. It was. This shows that it is advantageous not to use ammonia as a basic compound.

  Comparative Example 4 is an example in which triethylamine, which is a tertiary amine, is used as a basic compound that can form a salt with adipic acid. The electrolyte solution in Comparative Example 4 has a higher specific resistance than the electrolyte solutions in Examples 1 to 4, and the use of a tertiary amine is disadvantageous in order to respond to the demand for lower impedance for the capacitor. I know that there is.

  Comparative Example 5 is an example in which hydroxylamine was used as a basic compound capable of constituting a salt with adipic acid. Insoluble matter was generated in the process of preparing the electrolytic solution, and a usable electrolytic solution could not be obtained.

  As can be understood from these Examples and Comparative Examples, the impedance of the capacitor can be reduced by coexisting a primary amine and / or a secondary amine having a hydrophobic substituent in the electrolyte and a conjugate. And it became possible to answer the request for longer life.

(2) Influence of pH Using dimethylamine as a basic compound that can form a salt with adipic acid, using an electrolytic solution whose pH is changed according to the amount added, an aluminum electrolytic capacitor is created and evaluated. It was. Table 2 below shows the composition of the electrolytic solution used for each aluminum electrolytic capacitor, the type of basic compound (dimethylamine), the pH and specific resistance of the electrolytic solution at 30 ° C., the initial capacitance of the aluminum electrolytic capacitor, The impedance, leakage current and dielectric loss (tan δ), dielectric loss after 8000 hours of 105 ° C. no-load test, and change rate of dielectric loss before and after 8000 hours are collectively shown.

  From a comparison between Comparative Examples 7 and 8 and Examples 5 to 7, it can be seen that the life of the capacitor is shortened if the pH is too low or too high. Further, the capacitor of Comparative Example 8 showed a large leakage current in the initial stage. Considering these results and the test results of Examples 16 and 17 shown below, it was found that the pH range should be adjusted to the range of 5.6 to 7.0.

  In particular, the electrolytic solutions in Examples 5 to 7 showed a specific resistance of 50 Ωcm or less, and capacitors using these electrolytic solutions showed an extremely long life exceeding 8000 hours even in a 105 ° C. no-load test. Therefore, these capacitors fully responded to current demands.

(3) Effect of water content Using dimethylamine as a basic compound that can form a salt with adipic acid, using an electrolytic solution with a changed water content, an aluminum electrolytic capacitor was created and evaluated. It was. Table 3 below shows the composition of the electrolytic solution used for each aluminum electrolytic capacitor, the type of basic compound (dimethylamine), the pH and specific resistance of the electrolytic solution at 30 ° C., the initial capacitance of the aluminum electrolytic capacitor, The impedance, leakage current and dielectric loss (tan δ), dielectric loss after 8000 hours of 105 ° C. no-load test, and change rate of dielectric loss before and after 8000 hours are collectively shown.

  As can be seen from Table 3, the specific resistance significantly decreased as the water content in the electrolyte increased. All the capacitors of Examples 8 to 15 showed a very long life exceeding 8000 hours in the 105 ° C. no-load test, and no valve opening was observed even in the capacitor whose water was increased to 75%. Therefore, it can be seen that the combined effect of dimethylamine and the conjugate provides an extremely long lifetime. In order to satisfy the requirement for a specific resistance of 70 Ωcm or less and a long life for a 50 WV class capacitor, it is preferable to adjust the water content to 35 to 70 mass%.

(4) Effect of adipic acid content Using dimethylamine as a basic compound that can form a salt with adipic acid, using an electrolytic solution with adipic acid content changed, an aluminum electrolytic capacitor was created and evaluated. Went. Table 4 below shows the composition of the electrolytic solution used for each aluminum electrolytic capacitor, the type of basic compound (dimethylamine), the pH and specific resistance of the electrolytic solution at 30 ° C., the initial capacitance of the aluminum electrolytic capacitor, The impedance, leakage current and dielectric loss (tan δ), dielectric loss after 8000 hours of 105 ° C. no-load test, and change rate of dielectric loss before and after 8000 hours are collectively shown.

  As can be seen from Table 4, it can be seen that when adipic acid is present in an amount of 8% by mass or more of the entire electrolytic solution, an electrolytic solution having a specific resistance of 100 Ωcm or less required for a 100 WV class capacitor can be obtained. Moreover, all the capacitors of Examples 16 to 18 exhibited extremely long lifetimes exceeding 8000 hours in the 105 ° C. no-load test.

(5) Influence of azelaic acid combined use Dimethylamine was used as a basic compound capable of forming a salt with adipic acid, and the combined effect of adipic acid and azelaic acid was investigated. Table 5 below shows the composition of the electrolytic solution used for each aluminum electrolytic capacitor, the type of basic compound (dimethylamine), the pH and specific resistance of the electrolytic solution at 30 ° C., the initial capacitance of the aluminum electrolytic capacitor, The impedance, leakage current and dielectric loss (tan δ), dielectric loss after 8000 hours of 105 ° C. no-load test, and change rate of dielectric loss before and after 8000 hours are collectively shown. Example 22 is an example when no azelaic acid is used in combination, and Example 19-21 is an example when azelaic acid is used in combination.

  As the content of azelaic acid increased, the specific resistance of the electrolyte decreased, and at the same time, the change in dielectric loss around 8000 hours at 105 ° C. no-load test was reduced. In particular, the capacitors of Examples 19 and 20 using the electrolytic solution to which 1% by mass or 3% by mass of azelaic acid was added showed almost no change in dielectric loss even after 8000 hours of 105 ° C. no-load test. I was not able to admit. This shows that a capacitor having a remarkably long life and low impedance can be obtained by the combined effect of dimethylamine, a conjugate, and azelaic acid.

  According to the present invention, it is possible to provide an aluminum electrolytic capacitor having low impedance characteristics and a long lifetime, and an electrolytic solution for an aluminum electrolytic capacitor capable of providing such an aluminum electrolytic capacitor.

Claims (10)

In a mixed solvent consisting of water and ethylene glycol,
Adipic acid as a carboxylic acid electrolyte;
A basic compound capable of forming a salt with adipic acid;
A phosphorus oxoacid ion-forming compound capable of generating a phosphorus oxoacid ion in an aqueous solution;
An electrolytic solution for an aluminum electrolytic capacitor in which a chelating agent capable of forming a water-soluble aluminum chelate complex by coordination with aluminum is dissolved,
The basic compound includes only at least one compound selected from the group consisting of a primary amine and a secondary amine having a hydrophobic substituent,
An electrolytic solution for an aluminum electrolytic capacitor, wherein the pH of the electrolytic solution is in the range of 5.6 to 7.0.   The at least one long-chain dicarboxylic acid selected from the group consisting of azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid, and tetradecanedioic acid is further dissolved. Electrolytic solution for aluminum electrolytic capacitors.   The electrolytic solution for an aluminum electrolytic capacitor according to claim 1 or 2, wherein the basic compound is at least one compound selected from the group consisting of monomethylamine, monoethylamine, and dimethylamine.   The electrolytic solution for an aluminum electrolytic capacitor according to any one of claims 1 to 3, wherein the water content is in the range of 35 to 70 mass% of the entire electrolytic solution.   The aluminum electrolysis according to any one of claims 1 to 4, wherein the content of adipic acid is at least 8% by mass or more of the entire electrolytic solution and at most a saturated dissolution amount at 50 ° C in the electrolytic solution. Electrolytic solution for capacitors.   The phosphorus oxoacid ion generating compound is phosphoric acid, phosphorous acid, hypophosphorous acid, phosphonic acid, phosphinic acid, and a salt thereof with a primary amine and / or a secondary amine having a hydrophobic substituent. Esters of phosphoric acid and alkyl phosphoric acid, esters and derivatives of phosphonic acid and diphosphonic acid, phosphinic acid esters, and salts of these with primary and / or secondary amines having hydrophobic substituents; and these And at least one compound selected from the group consisting of these condensates and salts of primary amines and / or secondary amines having a hydrophobic substituent. The electrolyte solution for aluminum electrolytic capacitors of any one of these.   The chelating agent is citric acid, tartaric acid, gluconic acid, malic acid, lactic acid, glycolic acid, α-hydroxybutyric acid, hydroxymalonic acid, α-methylmalic acid, dihydroxytartaric acid, γ-resorcylic acid, β-resorcylic acid, Trihydroxybenzoic acid, hydroxyphthalic acid, dihydroxyphthalic acid, phenol tricarboxylic acid, aluminone, eriochrome cyanine R, sulfosalicylic acid, tannic acid, dicyandiamide, galactose, glucose, lignosulfonate, ethylenediaminetetraacetic acid (EDTA), nitrilotri Acetic acid (NTA), glycol ether diamine tetraacetic acid (GEDTA), diethylenetriaminepentaacetic acid (DTPA), hydroxyethylethylenediaminetriacetic acid (HEDTA), triethylenetetramine hexaacetic acid (TTHA), and The compound according to any one of claims 1 to 6, which is at least one compound selected from the group consisting of a salt with a primary amine and / or a secondary amine having a hydrophobic substituent. Electrolytic solution for aluminum electrolytic capacitors. The electrolyte contains aluminum ions;
By the reaction of the aluminum ion, the chelating agent, and the phosphorus oxo acid ion generated from the phosphorus oxo acid ion generating compound, a conjugate of the phosphorus oxo acid ion and the water-soluble aluminum chelate complex is formed in the electrolyte. The electrolytic solution for an aluminum electrolytic capacitor according to any one of claims 1 to 7. The electrolytic solution is an electrolytic solution introduced into an aluminum electrolytic capacitor,
The electrolytic solution for an aluminum electrolytic capacitor according to claim 8, wherein the aluminum ions are ions eluted from an anode and a cathode of the aluminum electrolytic capacitor. An anode made of an aluminum foil having an aluminum oxide film on the surface;
A cathode made of aluminum foil;
An aluminum electrolytic capacitor comprising a separator that holds an electrolytic solution disposed between an anode and a cathode,
The said electrolytic solution is an electrolytic solution for aluminum electrolytic capacitors of any one of Claims 1-9, The aluminum electrolytic capacitor characterized by the above-mentioned.

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