electrolytic capacitor

Abstract

To provide an electrolytic capacitor arranged to have low impedance by increase of water content and having a structure which satisfies the requirement of a withstand voltage of 400 V or higher and which enables the increase in long-term reliability.SOLUTION: An electrolytic capacitor 1 comprises a liquid electrolyte 2e containing ethylene glycol, water of 10-30 mass%, and an amine salt of carboxylic acid of 1-12 mass%, with 0.01-2 mass% of any one or more kinds of ammonium hypophosphite, amine hypophosphite, and hypophosphorous acid added thereto. The carboxylic acid is a polyvalent carboxylic acid having a chain hydrocarbon skeleton and a molecular weight of 140-500. In addition to the above structure, the electrolytic capacitor has any one or more kinds of phosphoric acid, ammonium phosphate, and phosphoric acid amine salt added thereto.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electrolytic capacitor. [Background technology]

[0002] For example, an electrolytic capacitor is configured such that a capacitor element is formed by arranging an anode foil and a cathode foil, each electrically connected to a terminal, with a separator interposed between them, and an electrolyte is introduced into the capacitor element. Aluminum electrolytic capacitors use an oxide film formed on the surface of the aluminum foil by electrochemical surface treatment as a dielectric, and have excellent self-repair properties.

[0003] For example, there is growing demand for medium- to high-voltage electrolytic capacitors for use in LED lighting, power supply circuits, etc. The challenge for medium- to high-voltage electrolytic capacitors is to achieve both low impedance and high reliability.

[0004] Conventionally, an electrolyte solution for electrolytic capacitors has been proposed that contains ethylene glycol as the main solvent, 5 to 7 wt % water, 7 to 15 wt % ammonium adipate, and 0.2 to 0.5 wt % hypophosphorous acid (Patent Document 1: JP-B-62-8004).Also proposed is an electrolyte solution for electrolytic capacitors that contains ethylene glycol as the main solvent, 5 to 10 wt % water, 5 to 10 wt % ammonium benzoate, 0.5 to 2 wt % ammonium p-nitrobenzoate, and 0.5 to 4 wt % ammonium hypophosphite (Patent Document 2: JP-A-6-151251). An electrolytic capacitor has been proposed that contains ethylene glycol as an electrolyte, as well as 10 to 50 wt % water and 10 wt % triethylamine benzoate (Patent Document 3: Japanese Patent Laid-Open Publication No. 2002-270473).

[0005] Another proposed electrolytic capacitor uses ethylene glycol as the main solvent in its electrolyte, containing 5 to 20% by weight of water and 14 to 22% by weight of diethylamine azelate (Patent Document 4: JP 2011-071238 A). Another proposed electrolyte uses ethylene glycol as the main solvent, containing 20% ​​by weight of water, 10% by weight of triethylamine salt, 5% by weight of ammonium adipate, 0.5% by weight of ammonium hypophosphite, and 0.3% by weight of tributyl phosphate (Patent Document 5: JP 2005-039245 A). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 62-8004 [Patent Document 2] Japanese Patent Application Publication No. 6-151251 [Patent Document 3] Japanese Patent Application Laid-Open No. 2002-270473 [Patent Document 4] Japanese Patent Application Laid-Open No. 2011-071238 [Patent Document 5] Japanese Patent Application Laid-Open No. 2005-039245 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the configurations of Patent Documents 1 to 3 have the problem that, if the water content is high, the anode and cathode foils of the electrolytic capacitor undergo a hydration reaction at high temperatures, generating gas, which increases internal pressure and leads to defects. This also leads to deterioration of the anode and cathode foils, which in turn leads to deterioration of the capacitor characteristics and shortens the lifespan of the electrolytic capacitor. In this regard, the configuration of Patent Document 4 uses diethylamine azelate as the electrolyte, and the configuration of Patent Document 5 uses triethylamine salt as the electrolyte. Therefore, both configurations have superior thermal stability compared to the configurations of Patent Documents 1 to 3. Furthermore, the inclusion of diethylamine azelate or triethylamine salt suppresses the hydration reaction of the electrode foil (especially the cathode foil) caused by a large amount of water to some extent. However, the configurations of Patent Documents 4 and 5 do not achieve both good chemical conversion properties and high voltage resistance. It has been found that, depending on the conditions of use of the electrolytic capacitor, problems such as accelerated anode foil deterioration and insufficient voltage resistance can occur.

[0008] In recent years, there has been an increasing demand for electrolytic capacitors that have low impedance, high withstand voltage, and long life. In particular, there is a market demand for electrolytic capacitors with a withstand voltage of 400 V or more and that maintain good characteristics over a wide temperature range even after being left unloaded under high-temperature conditions. However, the electrolytic capacitors that employ the conventional techniques disclosed in Patent Documents 1 to 5 do not meet these high demands. [Means for solving the problem]

[0009] The present invention has been made in consideration of the above circumstances, and aims to provide an electrolytic capacitor having a configuration that increases the water content to achieve low impedance, satisfies a withstand voltage of 400 V or more, and is capable of improving long-term reliability.

[0010] In one embodiment, the above problem is solved by the solution disclosed below.

[0011] The electrolytic capacitor of the present invention comprises a capacitor element having an anode foil on which an oxide film is formed, a cathode foil, and a separator disposed between the anode foil and the cathode foil, and an electrolytic solution introduced into the capacitor element, the electrolytic solution comprising ethylene glycol and 10 to 1500 vol% ammonium hydroxide. 15 The composition is characterized in that it contains % by mass of water and 1 to 9% by mass of an amine salt of a carboxylic acid, and that 0.01 to 2% by mass of one or more of ammonium hypophosphite, amine hypophosphite, and hypophosphorous acid is added, the carboxylic acid being a polycarboxylic acid having a chain hydrocarbon skeleton and a molecular weight of 140 to 240, and that in addition to the above composition, one or more of phosphoric acid, ammonium phosphate, and amine phosphate is added.

[0012] This configuration achieves sufficiently low impedance by containing 10% or more water by weight, while maintaining a water content of 30% or less by weight. This prevents problems caused by gas generation and increased internal pressure due to hydration reactions with the electrode foil at high temperatures, thereby suppressing the progression of performance degradation due to electrode foil degradation. Furthermore, the use of a polycarboxylic acid with a chain hydrocarbon skeleton and a molecular weight of 140-500, combined with a polycarboxylic acid amine salt content of 1-12% by weight, achieves a withstand voltage of 400 V or higher. Furthermore, the addition of 0.01-2% by weight of one or more of ammonium hypophosphite, amine hypophosphite, and hypophosphorous acid, ensures sufficient adhesion and protection to the anode and cathode foils, prevents excess hypophosphorous acid or its salt, and further improves conversion performance. In particular, the addition of phosphoric acid or its salt in addition to hypophosphorous acid or its salt effectively suppresses hydration reactions of the anode and cathode foils. [Effects of the Invention]

[0013] According to the present invention, the water content in the electrolyte is increased within an appropriate range to reduce impedance, while the concentration of the amine salt of a polycarboxylic acid is appropriately reduced and hypophosphorous acid or its salt is added, thereby achieving a high withstand voltage and good chemical conversion properties, and achieving good life characteristics by suppressing deterioration of the anode foil and cathode foil. Therefore, an electrolytic capacitor having a configuration that satisfies all of the requirements of low impedance, high withstand voltage, and long life can be realized. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a graph showing a comparison between examples according to an embodiment of the present invention and comparative examples in terms of the relationship between the content of the amine salt of a polycarboxylic acid in the electrolyte and the time it takes to reach 400 V in a spark voltage measurement test at room temperature. [Figure 2] FIG. 2 is a graph showing a comparison between the content of the amine salt of polycarboxylic acid in the electrolyte and the maximum voltage reached in a spark voltage measurement test at room temperature for examples according to an embodiment of the present invention and comparative examples. [Figure 3] FIG. 3 is a partial cross-sectional view showing the schematic structure of the electrolytic capacitor according to the embodiment of the present invention as viewed from the side. DETAILED DESCRIPTION OF THE INVENTION

[0015] An embodiment of the present invention will be described in detail below. As shown in Fig. 3, an electrolytic capacitor 1 includes a wound capacitor element 2 containing an electrolyte solution 2e, lead terminals 5, a sealing body 3 with two through holes, and a bottomed case 4 that houses the capacitor element 2, with the open side of the case 4 sealed by the sealing body 3. The case 4 is cylindrical and bottomed, and is made of a metal such as aluminum. The sealing body 3 is highly airtight to prevent the intrusion of moisture and the scattering of oxide film repair substances, and has a roughly cylindrical shape that matches the inner shape of the case 4.

[0016] The anode foil 2a is made of a valve metal such as aluminum, and its surface is roughened by etching, and then an oxide film is formed by chemical conversion treatment. The cathode foil is made of a valve metal such as aluminum, and its surface is roughened by etching, and then an oxide film is formed by natural oxidation or chemical conversion treatment.

[0017] In this embodiment, as an example, the anode foil 2a has a film withstand voltage and a capacitance per unit projected area of ​​300 [V·μF / cm 2 ] or more is used. This allows for the realization of a small and / or high-capacity electrolytic capacitor, and by increasing the water content in the electrolyte, it is possible to reduce the size while maintaining low impedance. Furthermore, it is expected that the oxide film repair performance of the electrolyte 2e will be improved, especially in the vicinity of the anode foil. Taking these advantages into consideration, it is recommended that the product of the film withstand voltage and the capacitance per unit projected area of ​​the anode foil 2a be 350 [V·μF / cm 2 ] or more, and 400 [V·μF / cm 2 Here, the film withstand voltage and capacitance of the aluminum foil are both values ​​according to the method described in EIAJ RC-2364A.

[0018] A separator made of a known material and capable of retaining an electrolyte is disposed between the anode foil 2a and the cathode foil 2b, and the capacitor element 2 is impregnated with the electrolyte 2e.

[0019] Electrolyte solution 2e contains ethylene glycol, 10 to 30% by mass of water, and 1 to 12% by mass of an amine salt of a polycarboxylic acid, with 0.01 to 2% by mass of hypophosphorous acid or its salt, the polycarboxylic acid having a chain hydrocarbon skeleton and a molecular weight of 140 to 500. The inclusion of electrolyte solution 2e results in electrolytic capacitor 1 having a configuration that satisfies all of the requirements of low impedance, high withstand voltage, and long life.

[0020] Here, in order to achieve a lower impedance while further enhancing the effect of inhibiting the hydration reaction of the electrode foil, the content of the amine salt of the polycarboxylic acid in the electrolyte solution 2e may be set to 3 [mass %] or more, 6 [mass %] or more, or 9 [mass %] or more.

[0021] In addition, we also attempted to evaluate the case where the content of the amine salt of polycarboxylic acid was less than 1 [mass%], but the specific resistance of the electrolyte increased, and it was not possible to sufficiently reduce the impedance. Furthermore, as a result of evaluating the case where the content of the amine salt of polycarboxylic acid was more than 12 [mass%], it was found that adding hypophosphorous acid or its salt to the electrolyte did not significantly improve the conversion properties (see Reference Examples 1 and 2 described below).

[0022] To achieve lower impedance, the water content in the electrolytic solution 2e may be set to 13% by mass or more, or 16% by mass or more. To achieve both better conversion properties and high withstand voltage, the water content in the electrolytic solution 2e may be set to 25% by mass or less, or 20% by mass or less.

[0023] Although evaluation was also attempted when the water content was less than 10% by mass, the specific resistance of the electrolyte increased, and it was not possible to sufficiently reduce the impedance. Furthermore, when the water content was more than 30% by mass, the reduction rate of the time to reach 400 V was a negative value (see Reference Examples 3 and 4 described below).

[0024] Examples of the amine salt of a polycarboxylic acid include dimethylamine adipate, diethylamine adipate, dimethylamine azelaate, diethylamine azelaate, dimethylamine sebacate, diethylamine sebacate, ethyldimethylamine sebacate, dimethylamine 2-methylnonanedioate, diethylamine 2-methylnonanedioate, dimethylamine 3-tert-butylhexanedioate, diethylamine 3-tert-butylhexanedioate, dimethylamine 1,6-decanedicarboxylic acid, diethylamine 1,6-decanedicarboxylic acid, dimethylamine brassylate, dimethylamine octadecenedioate, diethylamine octadecenedioate, ethyldimethylamine octadecenedioate, dimethylamine 12-vinyl-8-octadecenedioate, dimethylamine dimethyloctadecadienetetracarboxylate, diethylamine dimethyloctadecadienetetracarboxylate, and other known amine salts of polycarboxylic acids.

[0025] Examples of polycarboxylic acids having a chain hydrocarbon skeleton and a molecular weight of 140 to 500 include adipic acid (molecular weight 146.1), azelaic acid (molecular weight 188.2), sebacic acid (molecular weight 202.3), 1,6-decanedicarboxylic acid (molecular weight 230.3), 5,6-decanedicarboxylic acid (molecular weight 230.3), 1,10-decanedicarboxylic acid (molecular weight 230.3), 2-methylnonanedioic acid (molecular weight 202.3), 4-methylnonanedioic acid ( Examples of suitable carboxylic acids include 2,4-dimethyl-4-methoxycarbonyl-undecanedioic acid (molecular weight 302.4), 2,4,6-trimethyl-4,6-dimethoxycarbonyl-tridecanedioic acid (molecular weight 402.5), 8,9-dimethyl-8,9-dimethoxycarbonyl-hexadecanedioic acid (molecular weight 430.5), and dimethyloctadecanetetracarboxylic acid (molecular weight 458.6). In addition to the above, polycarboxylic acids having a chain hydrocarbon skeleton and a molecular weight of 140 to 500 can also be used.

[0026] Here, in consideration of ease of solubility in ethylene glycol or water and low impedance characteristics, the molecular weight of the polycarboxylic acid is more preferably 240 or less.

[0027] Furthermore, evaluations were also conducted on polycarboxylic acids with a molecular weight of less than 140, but sufficient voltage resistance characteristics were not obtained. Preparations were also attempted on polycarboxylic acids with a molecular weight of more than 500, but sufficient solubility could not be maintained at low temperatures, and the specific resistance of the electrolyte solution increased, making it impossible to sufficiently reduce impedance.

[0028] The amount of one or more of ammonium hypophosphite, amine hypophosphite, and hypophosphorous acid added is more effectively in the range of 0.03 to 1.5 [mass %], and even more effectively in the range of 0.05 to 1 [mass %].

[0029] The results also showed that the content of hypophosphorous acid or its salts was less than 0.01% by mass, but no sufficient improvement in chemical conversion properties was obtained.The results also showed that the content of hypophosphorous acid or its salts was more than 2% by mass, but no further improvement in chemical conversion properties was obtained, and no sufficient voltage resistance characteristics were obtained.

[0030] In order to stabilize the voltage resistance characteristics, a voltage resistance improver such as a polyether-based compound may be added to the electrolyte solution 2e. Examples of polyether-based voltage resistance improvers include polyethylene glycol, polypropylene glycol, and other known polyether-based voltage resistance improvers, including branched polyethers. Furthermore, other voltage resistance improvers may be added to the electrolyte solution 2e, such as polyvinyl alcohol, polysiloxane, sugar alcohols (e.g., mannitol), and other known voltage resistance improvers. One or more types of voltage resistance improvers may be added.

[0031] To further stabilize the conversion properties, in addition to one or more of ammonium hypophosphite, amine hypophosphite, and hypophosphorous acid, a phosphorus-based compound other than those mentioned above may be added to the electrolyte solution 2e. Examples of phosphorus-based compounds other than hypophosphorous acid or its salts include phosphoric acid or its salts (e.g., phosphoric acid, ammonium phosphate, amine salt of phosphoric acid), phosphorous acid or its salts (e.g., phosphorous acid, ammonium phosphite, amine salt of phosphorous acid), phosphate esters (e.g., methyl phosphate ester, ethyl phosphate ester, dimethyl phosphate ester, diethyl phosphate ester, trimethyl phosphate ester, triethyl phosphate ester), and other known phosphorus-based compounds. In particular, adding phosphoric acid or its salts in addition to hypophosphorous acid or its salts is more preferable because it provides an excellent effect of suppressing hydration reactions of the anode foil and cathode foil.

[0032] In addition to the above, an aromatic nitro compound may be added to the electrolyte solution 2e. Examples of the aromatic nitro compound include nitroacetophenone, nitrobenzoic acid, nitrobenzyl alcohol, nitrophenol, nitrobenzene, nitroxylene, and other known aromatic nitro compounds.

[0033] The electrolyte used in the electrolyte solution 2e may include ammonium salts in addition to amine salts. To further improve thermal stability and the effect of suppressing electrode foil deterioration, the total ammonium salt content in the electrolyte solution 2e may be set to 5% by mass or less, 4% by mass or less, or 3% by mass or less. Furthermore, to further stabilize good voltage resistance characteristics, the total content of all amine salts and all ammonium salts in the electrolyte solution 2e may be set to 15% by mass or less.

[0034] Next, examples, reference examples, and comparative examples of the electrolyte solution according to this embodiment, and the results of performance evaluations required when applying these electrolyte solutions to electrolytic capacitors will be described below.

[0035] [Examples 1 to 6] The electrolyte solution 2e in Examples 1 to 6 contains ethylene glycol, water, and 1 to 12% by mass of an amine salt of a polycarboxylic acid, with 0.01 to 2% by mass of hypophosphorous acid or its salt. Spark voltage measurements were performed on each of the electrolyte solutions 2e prepared in the Examples to evaluate the time to reach 400V (seconds) and the maximum voltage (V). The composition of each electrolyte solution and the performance evaluation results are shown in Table 1 below.

[0036] [Table 1]

[0037] [Reference examples 1~2] The electrolyte solutions of Reference Examples 1 and 2 contain ethylene glycol, water, and 14 to 20% by mass of an amine salt of a polycarboxylic acid, with 0.01 to 2% by mass of hypophosphorous acid or its salt. Spark voltage measurements were performed on each of the prepared electrolyte solutions to evaluate the time to reach 400 V (seconds) and the maximum voltage (V). The composition of each electrolyte solution and the performance evaluation results are shown in Table 2 below.

[0038] [Table 2]

[0039] [Comparative Examples 1 to 8] The electrolytes of Comparative Examples 1 to 8 contain ethylene glycol, water, and 1 to 20% by mass of an amine salt of a polycarboxylic acid. However, hypophosphorous acid or its salts are not added. Spark voltage measurements were performed on each of the prepared electrolytes of Comparative Examples to evaluate the time to reach 400 V (seconds) and the maximum voltage (V). The composition of each electrolyte and the performance evaluation results are shown in Tables 3 and 4 below.

[0040] [Table 3]

[0041] [Table 4]

[0042] FIG. 1 is a graph showing a comparison of the relationship between the content of the amine salt of a polycarboxylic acid in the electrolyte and the time to reach 400 V for each of the electrolytes of Examples 1 to 5, Comparative Examples 1 to 5, and Comparative Examples 7 and 8 described above.

[0043] According to Tables 1, 3, 4, and FIG. 1, Examples 1 to 5, in which the content of the amine salt of polycarboxylic acid was increased or decreased, all reached a voltage of 400 V in a short time, with little fluctuation in the time, and were stable. On the other hand, in Comparative Examples 1 to 5 and 6, when the content of the amine salt of polycarboxylic acid was 14% by mass or less, the time to reach 400 V increased significantly, with large fluctuations in the time, and the results were unstable. Furthermore, compared to Comparative Examples 1 to 5 and 6, Examples 1 to 5 and 6 achieved a significant reduction in the time to reach 400 V. Furthermore, compared to Comparative Examples 7 and 8, Examples 1 to 5 achieved a reduction in the time to reach 400 V. Therefore, when the content of the amine salt of polycarboxylic acid in the electrolyte was 1 to 12% by mass, the effect of improving the conversion properties by adding hypophosphorous acid or its salt to the electrolyte was significant.

[0044] According to Tables 2 and 4, the time to reach 400 V in Reference Examples 1 and 2 was reduced by less than 20% compared to Comparative Examples 7 and 8. This indicates that when the content of the amine salt of a polycarboxylic acid in the electrolyte exceeds 12% by mass, adding hypophosphorous acid or its salt to the electrolyte does not significantly improve the conversion properties.

[0045] In addition, we also attempted to evaluate cases where the content of the amine salt of polycarboxylic acid was less than 1 [mass%], but the specific resistance of the electrolyte increased, and it was not possible to sufficiently reduce the impedance. We also evaluated cases where the content of hypophosphorous acid or its salt was less than 0.01 [mass%], but we were unable to obtain a sufficient improvement in chemical conversion properties. We also evaluated cases where the content of hypophosphorous acid or its salt was more than 2 [mass%], but we were unable to obtain a further improvement in chemical conversion properties and sufficient voltage resistance characteristics.

[0046] [Examples 7 to 8] The electrolyte solutions of Examples 7 and 8 contain ethylene glycol, water, and 1 to 12% by mass of an amine salt of a polycarboxylic acid, with 0.01 to 2% by mass of hypophosphorous acid or its salt. Spark voltage measurements were performed on each of the electrolyte solutions 2e prepared in the examples, and the time to reach 400 V (seconds) and the maximum voltage (V) were evaluated. The composition of each electrolyte solution and the performance evaluation results are shown in Table 5 below.

[0047] [Table 5]

[0048] [Comparative Examples 9 to 10] The electrolytes of Comparative Examples 9 and 10 contain ethylene glycol, water, and 1 to 12% by mass of an amine salt of a polycarboxylic acid. However, hypophosphorous acid or its salts are not added. Spark voltage measurements were performed on each of the prepared electrolytes of Comparative Examples to evaluate the time to reach 400 V (seconds) and the maximum voltage (V). The composition of each electrolyte and the performance evaluation results are shown in Table 6 below.

[0049] [Table 6]

[0050] Examples 7 and 8 and Comparative Examples 9 and 10 all share the commonality of using an electrolyte solution containing 6% by mass of dimethylamine azelate in a solvent consisting of ethylene glycol and water. The electrolyte solutions of Comparative Examples 9 and 10 differ from the electrolyte solution of Example 7 in that hypophosphorous acid is replaced with phosphoric acid or phosphorous acid.

[0051] According to Tables 5 and 6, Examples 7 and 8, in which hypophosphorous acid was added, both achieved a significant reduction in the time to reach 400 V compared to Comparative Example 9, in which phosphorous acid was added without hypophosphorous acid, and Comparative Example 10, in which phosphoric acid was added without hypophosphorous acid. Therefore, a significant effect of improving chemical conversion properties can be achieved by the synergistic effect of adding 0.01 to 2 mass% of one or more of ammonium hypophosphite, amine hypophosphite, and hypophosphorous acid while setting the content of the amine salt of polycarboxylic acid in the electrolyte to 1 to 12 mass%.

[0052] On the other hand, even when the content of the amine salt of a polycarboxylic acid in the electrolyte is 1 to 12 [mass%], phosphorous acid or phosphoric acid cannot replace hypophosphorous acid or its salt, so little improvement in chemical conversion properties can be expected. Furthermore, compared to Example 8, in which hypophosphorous acid was added but no phosphoric acid was added, Example 7, in which both hypophosphorous acid and phosphoric acid were added, further shortened the time to reach 400 V. Therefore, the synergistic effect of adding both hypophosphorous acid or its salt and phosphoric acid or its salt to the electrolyte while keeping the content of the amine salt of a polycarboxylic acid in the electrolyte at 1 to 12 [mass%] provides an even more significant improvement in chemical conversion properties.

[0053] 2 is a graph showing a comparison of the relationship between the content of the amine salt of polycarboxylic acid in the electrolyte and the maximum voltage for each of the electrolytes of Examples 1 to 5, Comparative Examples 1 to 5, and Comparative Examples 7 and 8. For example, if the maximum voltage is 440 V or higher, an electrolytic capacitor with a withstand voltage of 400 V or higher can be realized. For example, if the maximum voltage is 440 V or higher, the rated voltage of the electrolytic capacitor can be set to 400 V or higher.

[0054] According to Tables 1, 3, 4, and FIG. 2, Examples 1 to 5 all have a maximum voltage of 440 V or higher. Comparative Examples 1 to 4 have a maximum voltage of 440 V or higher. However, Comparative Examples 5, 7, and 8 have a maximum voltage below 440 V. Therefore, by adding hypophosphorous acid or its salt to the electrolyte and setting the content of the amine salt of a polycarboxylic acid in the electrolyte to 1 to 12 mass %, it is possible to achieve a maximum voltage of 440 V or higher, and, as described above, the time required to reach 400 V can be significantly reduced.

[0055] Next, examples and comparative examples in which the type of amine salt of polycarboxylic acid was changed, and the results of performance evaluations required when applying these electrolyte solutions to electrolytic capacitors will be described below.

[0056] [Examples 9 to 27] The electrolyte 2e of Examples 9 to 27 contained ethylene glycol, 10% by mass of water, and 6% by mass of a modified amine salt of a polycarboxylic acid, with 0.3% by mass of hypophosphorous acid or its salt added. Spark voltage measurements were performed on each of the electrolytes 2e prepared in the Examples, and the time to reach 400 V (seconds) and the maximum voltage (V) were evaluated. The composition of each electrolyte and the performance evaluation results are shown in Table 7 below.

[0057] [Table 7]

[0058] [Comparative Examples 11 to 29] The electrolytes of Comparative Examples 11 to 29 contained ethylene glycol, 10% by mass of water, and 6% by mass of a modified amine salt of a polycarboxylic acid. However, hypophosphorous acid or its salts were not added. Spark voltage measurements were performed on each of the prepared electrolytes of the Comparative Examples to evaluate the time to reach 400 V (seconds) and the maximum voltage (V). The composition of each electrolyte and the performance evaluation results are shown in Table 8 below.

[0059] [Table 8]

[0060] According to Tables 7 and 8, in all of Examples 9 to 27, the time to reach a voltage of 400 [V] was stable with little fluctuation, and the time to reach a voltage of 400 [V] was significantly shorter than in Comparative Examples 11 to 29. Therefore, even when the type of amine salt of polycarboxylic acid was changed, the effect of improving the conversion property by adding hypophosphorous acid or its salt to the electrolyte was remarkable.

[0061] Furthermore, evaluations were also conducted on polycarboxylic acids with a molecular weight of less than 140, but sufficient voltage resistance characteristics were not obtained. Preparations were also attempted on polycarboxylic acids with a molecular weight of more than 500, but sufficient solubility could not be maintained at low temperatures, and the specific resistance of the electrolyte solution increased, making it impossible to sufficiently reduce impedance.

[0062] Next, examples and reference examples in which the water content was changed will be described below.

[0063] Electrolyte solutions 2e of Examples 28 to 32 and Reference Examples 3 and 4 each contained ethylene glycol, water, and 9% by mass of an amine salt of a polycarboxylic acid, with 0.3% by mass of hypophosphorous acid or its salt added. Spark voltage measurements were performed on each of the prepared electrolyte solutions to evaluate the time (seconds) to reach 400V. Here, the time (seconds) to reach 400V for each of electrolyte solutions 2e of the Examples and each of the Reference Examples was designated as T1. Spark voltage measurements were then performed on each of the electrolyte solutions under the same conditions as above, except that no hypophosphorous acid or its salt was added. The time (seconds) to reach 400V for each electrolyte solution was designated as T2, and the reduction rate (%) in the time to reach 400V based on the 400V time T2 was calculated (400V reduction rate = 100 × (T2 - T1) / T2). The results are shown in Table 9 below.

[0064] [Table 9]

[0065] According to Table 9, in all of Examples 28 to 32, the reduction rate of the time to reach 400V was 20% or more. On the other hand, in all of Reference Examples 3 and 4, the reduction rate of the time to reach 400V was a negative value. Therefore, by changing the water content within the range of 10 to 30% by mass and adding an appropriate amount of hypophosphorous acid or its salt to the electrolyte solution 2e, a significant effect of improving the chemical conversion property can be obtained through a synergistic effect.

[0066] An evaluation was also attempted when the water content was less than 10% by mass, but the specific resistance of the electrolyte solution increased, and the impedance could not be reduced sufficiently.

[0067] Next, the results of performance evaluation required when applying an anode foil 2a in which the product of the film withstand voltage and the capacitance per unit projected area is changed to an electrolytic capacitor will be described below.

[0068] The electrolyte solutions 2e of Examples 33 and 34 each contained ethylene glycol, water, and 12% by mass of an amine salt of a polycarboxylic acid, with 0.3% by mass of hypophosphorous acid or its salt added. Spark voltage measurements were performed on each of the electrolyte solutions 2e of Examples 33 and 34 to evaluate the time to reach 400V (seconds). The time to reach 400V for each of the electrolyte solutions 2e of Examples 33 and 34 was designated T3. Spark voltage measurements were then performed on each of the electrolyte solutions under the same conditions as above, except that no hypophosphorous acid or its salt was added, to evaluate the time to reach 400V (seconds). The time to reach 400V for each electrolyte was designated T4, and the percentage reduction in the time to reach 400V (% reduction in the time to reach 400V) based on the 400V time T4 was calculated (400V reduction = 100 × (T4 - T3) / T4). The results are shown in Table 10 below.

[0069] [Table 10]

[0070] According to Table 10, in all of Examples 33 and 34, the reduction rate of the time to reach 400 V was 20% or more. This indicates that even when the product of the film withstand voltage and the capacitance per unit projected area of ​​the anode foil is less than 300, adding an appropriate amount of hypophosphorous acid or its salt to the electrolyte 2e can achieve a significant effect of improving the conversion properties. Furthermore, the reduction rate of the time to reach 400 V in Example 33 is approximately 1.26 times greater than that in Example 34. Therefore, particularly when the product of the film withstand voltage and the capacitance per unit projected area is less than 300 [V·μF / cm 2 ] By using the above anode foil and adding hypophosphorous acid or its salt to the electrolyte 2e, a synergistic effect can be obtained, which results in a more significant improvement in the conversion properties.

[0071] The present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the scope of the present invention. [Explanation of symbols]

[0072] 1 electrolytic capacitor 2 Capacitor elements 2a anode foil 2e electrolyte 3 Sealing body 4 cases 5 Lead terminal

Claims

1. A capacitor element comprising an anode foil having an oxide film formed thereon, a cathode foil, and a separator disposed between the anode foil and the cathode foil, and an electrolytic solution introduced into the capacitor element, wherein the electrolytic solution contains ethylene glycol, 10 to 15 mass % of water, and 1 to 9 mass % of an amine salt of a carboxylic acid, and further contains 0.01 to 2 mass % of one or more of ammonium hypophosphite, amine hypophosphite, and hypophosphorous acid, the carboxylic acid being a polycarboxylic acid having a chain hydrocarbon skeleton and a molecular weight of 140 to 240, and further contains one or more of phosphoric acid, ammonium phosphate, and amine phosphate in addition to the above configuration. An electrolytic capacitor characterized by:

2. The anode foil has a product of the withstand voltage of the film and the capacitance per unit projected area of ​​300 V·μF / cm 2 The above aluminum foil is used, and the withstand voltage is 400V or more.

2. The electrolytic capacitor according to claim 1,

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