JP4582798B2 - Electrolytic capacitor driving electrolyte and electrolytic capacitor using the same - Google Patents

Description

  The present invention relates to an improvement of an electrolytic solution for driving an electrolytic capacitor (hereinafter referred to as an electrolytic solution). Even when the specific resistance is high and the amount of water is large, the electrode foil is long-term in a wide temperature range. The present invention relates to an electrolytic solution for driving an electrolytic capacitor capable of suppressing a hydration deterioration reaction and having good product reliability, and an electrolytic capacitor using the electrolytic solution.

  An electrolytic capacitor is one of general electric components, and is widely used in various electric products and electronic products mainly for power supply circuits and digital circuit noise filters.

  In general, an aluminum electrolytic capacitor is formed by subjecting a high-purity aluminum foil to an electrochemical etching treatment to increase the surface area, followed by a chemical conversion treatment in a chemical conversion solution such as an aqueous ammonium borate solution, an aqueous solution of ammonium adipate, or an aqueous solution of ammonium phosphate. A capacitor element obtained by inserting and winding a separator between an anode foil having an oxide film formed on the etched foil surface and a cathode foil etched with a high-purity aluminum foil is impregnated with an electrolytic solution. And after accommodating in a metal cylindrical case, it is comprised by sealing an opening part with elastic rubber and drawing a sealing part.

  In recent years, with the progress of digitalization of electronic components, the demand for low loss and low impedance of electrolytic capacitors is increasing, and the electrolyte used for electrolytic capacitors is being developed for lowering the specific resistance. Yes.

  Conventional low-pressure electrolytes have been prepared by dissolving ammonium salts such as adipic acid and benzoic acid as electrolytes in a mixed solvent containing ethylene glycol as a main solvent and about 10% of water added thereto. The specific resistance of such an electrolyte is about 150 Ω · cm.

  In the electrolytic capacitor, means for reducing the impedance by various methods other than the reduction of the specific resistance of the electrolytic solution are employed. For example, a method of increasing the electrode area accommodated in the electrolytic capacitor or a method of reducing the density of the separator is used, but the former cannot cope with downsizing of the capacitor, and the latter does not reduce the tensile strength of the separator. Since short-circuit resistance is lowered, these methods cannot achieve a significant reduction in impedance.

In addition, a method for reducing the specific resistance of the electrolytic solution by increasing the amount of water in the electrolytic solution has been proposed (see, for example, Patent Documents 1 and 2).
Japanese Patent No. 3366267 Japanese Patent No. 3366268

  However, in an electrolytic capacitor using an electrolytic solution containing a large amount of water, aluminum used as an electrode foil elutes and reacts with moisture in the electrolytic solution (hydration reaction) to form aluminum hydroxide on the foil surface. Precipitate. When this reaction is repeated, the electrode foil deteriorates, causing a significant deterioration in the characteristics of the capacitor. When the hydration reaction further proceeds, the internal pressure of the capacitor rises due to the hydrogen gas generated as a result of the elution of aluminum, leading to the operation of the safety valve (valve operation) and the function of the capacitor is lost.

  Although it is well known that phosphoric acid has an inhibitory effect on such electrode foil degradation, it is not sufficient. This is because when phosphoric acid is added to the electrolytic solution, phosphoric acid reacts with aluminum ions to form a highly water-resistant aluminum phosphate film on the surface of the electrode foil, thereby suppressing deterioration of the electrode foil. This is because phosphoric acid gradually disappears and hydration deterioration cannot be sufficiently suppressed.

In order to suppress such deterioration of the electrode foil, the hydration reaction of the aluminum electrode foil is suppressed by adding an electrolyte such as carboxylic acid, carboxylate, and inorganic acid and a chelate compound to the electrolyte containing a large amount of water. As a result, attempts have been made to extend the life of electrolytic capacitors (see, for example, Patent Document 3).
Japanese Patent No. 3623139

  A chelating agent is a compound that forms a chelate complex that is a cyclic structure containing a metal by coordination with a metal ion. When this chelating agent is added to the electrolytic solution, a chelate complex is formed with the aluminum ions eluted from the electrode foil, so that the reaction between phosphoric acid and aluminum ions in the electrolytic solution is suppressed, and long-term It is thought that the hydration reaction inhibitory effect can be maintained.

However, the ability of the chelating agent to form a chelate complex varies greatly depending on the chelating agent structure, and conventionally used ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), triethylenetetraminehexaacetic acid (TTHA), ethylenediaminetetrakis. When a large amount of a chelating agent having a high chelate complex formation rate (high chelate stability) such as (methylenephosphonic acid) (EDTPO) or the like is added, the aluminum electrode foil is liable to undergo a dissolution reaction, thereby prolonging the life of the chelating agent. There is a problem that the effect cannot be obtained sufficiently.

  Even when using an electrolytic solution having a low specific resistance and a large amount of water, the present invention keeps the phosphoric acid in the electrolytic solution at an optimum amount and suppresses the hydration deterioration reaction of the electrode foil for a long time. It is an object.

  It is another object of the present invention to provide an electrolytic capacitor that has a low impedance and realizes a long life by using the electrolytic solution according to the present invention.

  The present invention has been found as a result of various studies in order to solve the above-mentioned problems, and focuses on the characteristics of a specific alkyldiaminetetraacetic acid and intends to apply the characteristics to an electrolytic solution.

  The electrolytic solution for driving the electrolytic capacitor of the present invention comprises: a mixed solvent composed of 10 to 80 wt% organic solvent and 90 to 20 wt% water; and at least one electrolyte selected from carboxylic acid and carboxylate And at least one phosphoric acid compound and at least one selected from alkyldiaminetetraacetic acid represented by the following [Chemical Formula 1] and a salt thereof as a chelating agent.

[N in the formula represents an integer of 3 to 7. ]
As the chelating agent represented by [Chemical Formula 1], 1,3-propanediaminetetraacetic acid, 1,4-butanediaminetetraacetic acid, 1,5-pentanediaminetetraacetic acid, 1,6-hexanediaminetetraacetic acid, 1, There is 7-heptanediaminetetraacetic acid, and as these salts, metal salts such as aluminum, iron, copper, calcium, magnesium, titanium, tantalum, ammonium salts, amine salts, and the like can be used. A plurality of these chelating agents may be used in combination.

  As the organic solvent, one or more solvents selected from a protic solvent and an aprotic solvent can be used. Examples of the protonic solvent include methyl alcohol, ethyl alcohol, butyl alcohol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, glycerin and the like, and among these, ethylene glycol is preferable. Examples of aprotic solvents include lactone compounds such as γ-butyrolactone.

  As the electrolyte used in the present invention, one or more electrolytes selected from carboxylic acids and carboxylates can be used. Carboxylic acids that can be used include formic acid, acetic acid, oxalic acid, propionic acid, benzoic acid, malonic acid, succinic acid, glutaric acid, adipic acid, fumaric acid, maleic acid, phthalic acid, azelaic acid, citric acid and their ammonium. Salts, sodium salts, potassium salts and amine salts. Among these, formic acid and adipic acid are suitable for realizing both low resistivity and life characteristics.

  Examples of the phosphoric acid compound used in the present invention include orthophosphoric acid, phosphorous acid, and hypophosphorous acid, and examples of condensed phosphoric acids include pyrophosphoric acid, tripolyphosphoric acid, tetrapolyphosphoric acid, metaphosphoric acid, and hexametaphosphoric acid. Examples of acid esters include monomethyl phosphate, dimethyl phosphate, monoethyl phosphate, diethyl phosphate, monopropyl phosphate, dipropyl phosphate, monoethylene glycol phosphate, and diethylene glycol phosphate. As the salt of the phosphoric acid compound, ammonium salt, sodium salt, potassium salt, amine salt and the like can be used, and among these, ammonium salt is preferably used.

  The addition amount of the phosphoric acid compound is preferably 0.1 to 2.0 wt% with respect to the total electrolyte weight, and when it is less than 0.1 wt%, the effect of extending the life of the electrolytic capacitor can be sufficiently obtained. Moreover, since it will deviate from an optimal value when it exceeds 2.0 wt%, life characteristics will be reduced conversely.

The amount of alkyldiaminetetraacetic acid and its salt added is preferably 0.01 to 2.0 wt% with respect to the total electrolyte weight. When the added amount is less than 0.01 wt%, the effect of extending the life of the electrolytic capacitor is hardly recognized, and when it exceeds 2.0 wt%, it deviates from the optimum value. become.

  Furthermore, various additives generally used as capacitor driving electrolytes can be added to the above electrolyte for the purpose of reducing leakage current, improving withstand voltage, gas absorption, and the like. Examples of additives include sugars such as glucose, fructose, mannitol, xylose, galactose, pentaerythritol, polymer compounds such as polyvinyl alcohol, polyethylene glycol, polypropylene glycol, nitrophenol, nitrobenzoic acid, nitroacetophenone, nitroanisole, dinitro Examples thereof include nitro compounds such as benzoic acid and nitrobenzyl alcohol, and silane coupling agents.

  In addition, other chelating agents can be used in combination with the alkyldiaminetetraacetic acid of the present invention. Examples of chelating agents that can be used in combination include citric acid, tartaric acid, gluconic acid, malic acid, lactic acid, glycolic acid, α-hydroxybutyric acid, hydroxymalonic acid, α-methylmalic acid, dihydroxytartaric acid and the like, and γ-resorcylic acid , Β-resorcylic acid, trihydroxybenzoic acid, hydroxyphthalic acid, dihydroxyphthalic acid, phenol tricarboxylic acid, aromatic hydroxycarboxylic acids such as aurintricarboxylic acid, ethylenediaminediacetic acid, ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA) ), Glycol ether diamine tetraacetic acid (GEDTA), diethylenetriaminepentaacetic acid (DTPA), hydroxyethylethylenediaminetriacetic acid (HEDTA), triethylenetetraminehexaacetic acid (TTHA), trans-1,2- Aminocyclohexane-N, N, N ′, N′-tetraacetic acid (CyDTA), ethylenediaminetetrakis (methylenephosphonic acid) (EDTPO), ethylenediamine-N, N′-bis (methylenephosphonic acid), hydroxyethylethylenediaminetriacetic acid ( EDTA-OH), 1,3-diamino-2-hydroxypropanetetraacetic acid (DPTA-OH), 1,2-propanediaminetetraacetic acid (1,2-PDTA), aminopolycarboxylic such as dihydroxyethylglycine (DHEG) Mention may be made of acids. The amount added when used in combination is preferably 0.01 to 0.4 wt%, and the total amount of all chelating agents including alkyldiaminetetraacetic acid is preferably 0.02 to 2.0 wt%.

  The chelating agent contained in the electrolytic solution of the present invention has a lower chelate stability than the conventionally used aminopolycarboxylic acid and has the ability to complex with aluminum ions eluted in the electrolytic solution. It is considered that there is no excessive chelating action and the aluminum electrode foil is not dissolved.

Therefore, the product using the electrolytic solution described in the present invention can maintain the phosphoric acid in the electrolytic solution for a longer period of time compared to the electrolytic solution using aminopolycarboxylic acids conventionally used. With this, the product life can be extended.

The electrolytic capacitor of the present invention is obtained by subjecting a high-purity aluminum foil to an electrochemical etching treatment to increase the surface area, followed by a chemical conversion treatment in a chemical conversion solution such as an aqueous ammonium borate solution, an aqueous solution of ammonium adipate, or an aqueous solution of ammonium phosphate. A capacitor element obtained by inserting and winding a separator between an anode foil having an oxide film formed on the etched foil surface and a cathode foil etched with a high-purity aluminum foil is impregnated with an electrolytic solution. Then, after being housed in a metal cylindrical case, the opening is sealed with elastic rubber and the sealed portion is drawn, and the electrolytic solution of the present invention is used as the electrolytic solution.
The electrolytic solution of the present invention has a large amount of water added, and also dissolves alkyldiaminetetraacetic acid having 3 to 7 carbon atoms or a salt thereof. A good electrolytic capacitor can be obtained.

  Examples of the present invention will be specifically described below. In addition, the Example given below is for illustrating this invention, and this invention is not limited to the following content.

A method for manufacturing a wound electrolytic capacitor used in the examples will be described below.
After high-purity aluminum foil is electrochemically etched to increase the surface area, it is subjected to chemical conversion treatment in a chemical conversion solution such as ammonium borate aqueous solution, ammonium adipate aqueous solution, or ammonium phosphate aqueous solution. A capacitor element was produced by inserting and winding a separator between an anode foil on which an oxide film was formed and a cathode foil obtained by etching a high-purity aluminum foil.
Then, after impregnating the capacitor element with an electrolytic solution having the composition described in Table 1, it was stored in a metal bottomed cylindrical case, and then the opening was sealed with elastic rubber, and the sealing part was drawn. A wound electrolytic capacitor (6.3 WV-1000 μF) was produced.

  The value of specific resistance at 30 ° C. of the electrolyte used is also shown in Table 1.

  10 electrolytic capacitors each having a rating of 6.3 V-1000 μF (φ10 × 12.5 mmL) were produced using the electrolytic solution in Table 1, and the capacitance and leakage current were DC 6.3 V at 65 ° C. and 105 ° C. A load test was performed. After 2000 hours and 4000 hours of reliability test, the electrolyte in the product was collected by centrifugation to measure the amount of phosphoric acid in the electrolyte of the test product, and the stannous chloride method described in JIS-K-0101 Then, orthophosphate ions were measured. The measurement results are shown in Table 2.

  As shown in Table 2, in the conventional examples 1 to 3 in which the alkyldiaminetetraacetic acid according to the present invention is not added, the amount of phosphoric acid in the electrolyte solution tends to decrease with time at 65 ° C., and 2000 at 105 ° C. Reduced to below detection limit over time. In addition, in the conventional examples 4 to 6 to which ethylenediaminetetraacetic acid or diethylenetriaminepentaacetic acid, which is not a chelating agent according to the present invention, was added, the amount of phosphoric acid in the electrolyte remained with time as compared with the conventional examples 1 to 3, but 105 It decreases to below the detection limit at 4000 ° C.

On the other hand, among Examples 1-21 to which alkyldiaminetetraacetic acid according to the present invention was added, Examples 2-5, Examples 8-11, and Example 14 in which the addition amount was in the range of 0.01 to 2.0 wt%. In -17 and Examples 19-21, the phosphoric acid amount in electrolyte solution is maintained over a long period of time in a wide temperature range compared with a prior art example.
However, in Example 1, Example 7 and Example 13 in which the addition amount of the alkyldiaminetetraacetic acid is 0.005 wt%, the amount of active phosphoric acid is detected when 65 ° C.-4000 hours and 105 ° C.-2000 hours have elapsed. It has decreased to below the limit, and the effect of adding alkyldiaminetetraacetic acid cannot be sufficiently obtained. On the other hand, the amount of phosphoric acid in the electrolyte decreased to below the detection limit when 65 ° C.-4000 hours and 105 ° C.-2000 hours passed even in Example 6, Example 12 and Example 18 where the addition amount was 3.0 wt%. Therefore, it can be seen that the addition amount of alkyldiaminetetraacetic acid is preferably 0.01 to 2.0 wt%.

  Tables 3 and 4 show the results of reliability tests at 65 ° C. and 105 ° C., respectively.

In Table 3, Conventional Examples 1 to 3 in which no alkyldiaminetetraacetic acid was added, Examples 1, 7 and 13 with an alkyldiaminetetraacetic acid addition amount of 0.005 wt%, and an alkyldiaminetetraacetic acid addition amount. 0 wt% of Examples 6, 12, and 18 resulted in valve actuation within 4000 hours of test time.
Moreover, in the conventional examples 4-6 which added the ethylenediaminetetraacetic acid and the diethylenetriaminepentaacetic acid which are not the chelating agent by this invention, it came to valve operation within 4000 hours of test time.
On the other hand, in Examples 2 to 5, Examples 8 to 11, Examples 14 to 17, and Examples 19 to 21 in which the alkyldiaminetetraacetic acid was 0.01 to 2.0 wt%, the valve operation was performed even at a test time of 4000 hours. Good characteristics are maintained without exhibiting.

Also in Table 4, Examples 1 to 7 in which Conventional Examples 1 to 3 in which alkyldiaminetetraacetic acid is not added, alkyldiaminetetraacetic acid addition amount 0.005 wt%, alkyldiaminetetraacetic acid addition amount In Examples 6, 12 and 18 of 3.0 wt%, the deterioration reaction was severe and the valve operation was reached within a test time of 2000 hours. However, the alkyldiamine tetraacetic acid was 0.01 to 2.0 wt%. In Examples 2 to 5, Examples 8 to 11, Examples 14 to 17, and Examples 19 to 21, deterioration is suppressed and the effect of extending the life is obtained.
From the above results, it can be seen that the addition amount of alkyldiaminetetraacetic acid is preferably 0.01 to 2.0 wt%.

  Moreover, if the total addition amount of alkyldiaminetetraacetic acid is within the range of 0.01 to 2.0 wt% from Example 21, the same effect may be obtained even if several types of alkyldiaminetetraacetic acid having 3 to 7 carbon atoms are used in combination. An effect is obtained.

  As described above, according to the present invention, it is possible to put to practical use an electrolytic capacitor having a low impedance and good life characteristics.

In addition, when the water content in the solvent is less than 20% (8.9 / (8.9 + 79.6) = 0.10) as compared with Comparative Example 1, the specific resistance is 160 Ω · cm, which does not serve the purpose of lowering the impedance of the capacitor. . Further, when the water content in the solvent exceeds 90 wt% (82.0 / (82.0 + 6.5) = 0.93) as compared with Comparative Example 2, the effect of increasing the reliability cannot be obtained. Therefore, the solvent of the electrolytic solution according to the present invention is preferably a mixed solvent composed of 10 to 80 wt% organic solvent and 90 to 20 wt% water.
Further, as is apparent from the results for Comparative Example 3 in Tables 3 and 4, when n = 8 in [Chemical Formula 1], valve operation occurs at a test time of 4000 hours, so the range of n = 3 to 7 Is appropriate.

  In addition, the present invention is not limited to the above-described embodiments, and an electrolytic solution in which various solutes exemplified above are dissolved alone or plurally, and a general additive used in an electrolytic solution for driving an electrolytic capacitor are added. The electrolytic solution had the same effect as the above example.

Claims (6)

A mixed solvent composed of 10 to 80 wt% of an organic solvent and 90 to 20 wt% of water, at least one electrolyte selected from carboxylic acid and carboxylate, at least one phosphate compound, and a chelating agent As an electrolytic solution for driving an electrolytic capacitor, comprising at least one selected from alkyldiaminetetraacetic acid represented by the following [Chemical Formula 1] and salts thereof.

[N in the formula represents an integer of 3 to 7. ] An electrolytic solution for driving an electrolytic capacitor, wherein the organic solvent is at least one solvent selected from a protonic solvent and an aprotic solvent. The carboxylic acid and carboxylate are formic acid, acetic acid, oxalic acid, propionic acid, benzoic acid, malonic acid, succinic acid, glutaric acid, adipic acid, fumaric acid, maleic acid, phthalic acid, azelaic acid, citric acid, and 3. The electrolytic solution for driving an electrolytic capacitor according to claim 1, wherein the electrolytic solution is selected from the group consisting of an ammonium salt, a sodium salt, a potassium salt, and an amine salt. The phosphoric acid compound is selected from the group consisting of orthophosphoric acid, phosphorous acid, hypophosphorous acid, condensed phosphoric acids, phosphoric esters and salts thereof. The electrolytic solution for driving an electrolytic capacitor according to any one of the above. 5. The electrolytic solution for driving an electrolytic capacitor according to claim 1, comprising 0.01 to 2.0 wt% of the alkyldiaminetetraacetic acid or a salt thereof. 6. An electrolytic capacitor characterized in that the driving electrolytic solution used is the electrolytic solution for driving an electrolytic capacitor according to any one of claims 1 to 5.