Gelling agent for capacitor electrolyte, and electrolyte for electrolytic capacitors using the same, and electrolytic capacitor

Abstract

The object of this invention is to provide a gelling agent for capacitor electrolytes that can be used to obtain electrolytic capacitors with excellent impedance characteristics and lifespan characteristics. [Solution] By using a polymerizable monomer containing polyoxyalkylene (poly)glyceryl ether methacrylate as a gelling agent in the electrolyte for capacitors, electrolytic capacitors with superior impedance characteristics and lifespan characteristics compared to those using general-purpose additives such as PEG can be obtained.

Description

Technical Field

[0001] The present invention relates to an electrolytic solution for an electrolytic capacitor and an electrolytic capacitor.

Background Art

[0002] An aluminum electrolytic capacitor is formed by winding an anode electrode foil having an insulating oxide film layer formed on the surface of roughened aluminum and a cathode electrode foil for current collection through electrolytic paper to form a capacitor element, impregnating it with an electrolytic solution, and housing it in an outer case. The electrolytic solution intervenes between the dielectric layer formed on the anode foil and the current-collecting cathode foil, and its resistance component is inserted in series into the electrolytic capacitor, and it is known that the characteristics of the electrolytic solution are a major factor affecting the characteristics of the capacitor.

[0003] Generally, an electrolytic solution for an aluminum electrolytic capacitor is a solution obtained by dissolving an electrolyte composed of an inorganic acid such as boric acid or phosphoric acid, an organic acid such as a higher dicarboxylic acid, or an ammonium salt thereof in an organic solvent such as ethylene glycol or γ-butyrolactone. It is known that the withstand voltage is improved by adding polyethylene glycol (PEG) or polyvinyl alcohol (PVA) to the electrolytic solution (Patent Documents 1 and 2). However, in recent years, in in-vehicle applications where the demand for aluminum electrolytic capacitors is increasing, the requirements for the impedance characteristics and high-temperature stability (long-life characteristics) of aluminum electrolytic capacitors have been increasing. When using general-purpose additives such as PEG and PVA, although an improvement in safety (product reliability) due to an improvement in withstand voltage can be expected, the impedance characteristics and life characteristics of the capacitor are insufficient for recent required performance.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

[0005] The object of this invention is to provide an electrolyte for capacitors that can be used to obtain electrolytic capacitors with excellent impedance characteristics and lifespan characteristics. [Means for solving the problem]

[0006] We discovered that by using a polymerizable monomer containing polyoxyalkylene (poly)glyceryl ether methacrylate as a gelling agent in the electrolyte for capacitors, we can obtain an electrolytic capacitor with superior impedance characteristics and lifespan characteristics compared to the general-purpose additive PEG, thus completing the present invention. [Effects of the Invention]

[0007] By using the gelling agent for capacitor electrolytes of the present invention, it is possible to manufacture an electrolyte for aluminum electrolytic capacitors that has excellent impedance characteristics and good lifespan characteristics. [Modes for carrying out the invention]

[0008] The embodiments for implementing this description will be explained in more detail below, but the scope of the present invention is not limited to these embodiments, and modified embodiments that do not impair the spirit of the present invention also belong to the present invention. The "~" indicating the range includes both an upper and lower limit.

[0009] The polymerizable monomer used in the gelling agent of the present invention comprises at least one polyoxyalkylene (poly)glyceryl ether methacrylate (hereinafter referred to as PGAO methacrylate). In this specification, "(poly)glycerin" means "glycerin" and / or "polyglycerin". Other polymerizable monomers may include monofunctional monomers such as 2-hydroxyethyl methacrylate, 2-hydroxyethyl methacrylamide, and N-(3-dimethylaminopropyl) methacrylamide, and polyfunctional monomers such as 1,6-hexanediol dimethacrylate, polyethylene glycol dimethacrylate, polypropylene glycol dimethacrylate, glycerin dimethacrylate, trimethylolpropane trimethacrylate, and dipentaerythritol EO-modified polymethacrylate.

[0010] The PGAO methacrylate is a compound in which polyoxyalkylene (poly)glyceryl ether and methacrylic acid are ester-bonded, and its functional group equivalent is preferably 450 to 780 g / eq., and more preferably 500 to 700 g / eq. When the functional group equivalent is 450 g / eq. or more, it has good compatibility with the electrolyte and forms a uniform gel-like electrolyte, resulting in an electrolytic capacitor with good impedance characteristics. When the acrylic equivalent is 780 g / eq. or less, it has a sufficient crosslinking density to maintain the shape of the gel even in high-temperature environments, resulting in an electrolytic capacitor with good lifetime characteristics. The functional group equivalent is a numerical value representing the molecular weight per methacryloyl group, and was calculated from the saponification value SV (mgKOH / g) of PGAO methacrylate using Formula 1. (Formula 1) Functional group equivalent (g / eq.)=56110 / SV

[0011] The aforementioned polyoxyalkylene (poly)glyceryl ether is a compound obtained by adding an alkylene oxide to the hydroxyl group of (poly)glycerin. Examples of alkylene oxides include ethylene oxide, propylene oxide, 1,2-butylene oxide, and 2,3-butylene oxide, and it is particularly preferable to use one or more selected from ethylene oxide and propylene oxide.

[0012] The (poly)glycerin constituting the polyoxyalkylene (poly)glyceryl ether has a structure in which the hydroxyl groups of glycerin are linked by ether bonds through dehydration condensation. The ether bonds may be linear or branched, and may also contain intramolecularly condensed cyclic compounds. The (poly)glycerin used preferably has an average degree of polymerization of 1 to 20, and more preferably 3 to 15. By setting the average degree of polymerization of (poly)glycerin to 3 or higher, the number of functional groups per molecule increases, resulting in a higher crosslinking density, which allows for the production of capacitors with excellent impedance characteristics and long-term characteristics. Here, the average degree of polymerization is the average degree of polymerization (n) of polyglycerin calculated from the hydroxyl value (OHV) by the end group analysis method. Specifically, the average degree of polymerization (n) is calculated from the following equations (Equation 2) and (Equation 3). (Formula 2) Molecular weight=74n+18 (Formula 3) OHV=56110(n+2) / molecular weight In the above (Equation 2), OHV is a numerical value that serves as an indicator of the number of hydroxyl groups (OH groups) contained in (poly)glycerin, and refers to the number of milligrams of potassium hydroxide required to neutralize the acetic acid necessary to acetylate the free OH groups contained in 1 g of (poly)glycerin. The number of milligrams of potassium hydroxide is calculated in accordance with the "Standard Test Methods for Analysis of Fats and Oils, 2013 Edition," edited by the Japan Oil Chemists' Society. Specific examples of (poly)glycerin include glycerin, diglycerin, triglycerin, tetraglycerin, hexaglycerin, and decaglycerin. Commercially available products include diglycerin S, PGL-S, polyglycerin #310, polyglycerin #500, and polyglycerin #750 (all manufactured by Sakamoto Pharmaceutical Co., Ltd.).

[0013] The polyoxyalkylene (poly)glyceryl ether is preferably hydroxyl valued at 30 to 240, and more preferably 60 to 240. Specific examples of polyoxyalkylene (poly)glyceryl ethers include polyoxyethylene (40) glyceryl ether, polyoxyethylene (20) diglyceryl ether, polyoxyethylene (40) diglyceryl ether, polyoxyethylene (60) diglyceryl ether, polyoxyethylene (80) diglyceryl ether, polyoxyethylene (100) diglyceryl ether, polyoxyethylene (120) diglyceryl ether, polyoxyethylene (60) tetraglyceryl ether, and polyoxyethylene (120) tetraglyceryl ether. Examples include, but are not limited to, ethers, polyoxyethylene (60) decaglyceryl ether, polyoxyethylene (120) decaglyceryl ether, polyoxypropylene (24) diglyceryl ether, polyoxypropylene (14) polyoxyethylene (100) diglyceryl ether, polyoxypropylene (25) diglyceryl ether, polyoxypropylene (24) polyoxyethylene (60) tetraglyceryl ether, and polyoxypropylene (48) polyoxyethylene (240) decaglyceryl ether.

[0014] There are no particular limitations on the method for producing the PGAO methacrylate. For example, there is a dehydration esterification method in which a polyoxyalkylene (poly)glyceryl ether, obtained by adding an arbitrary amount of alkylene oxide to a specific (poly)glycerin in a known manner, is reacted with methacrylic acid to the terminal hydroxyl group of the polyoxyalkylene (poly)glyceryl ether, and the resulting water is removed from the system while obtaining an esterified product; and there is a transesterification method in which a methacrylic acid ester of a lower alcohol is reacted with the terminal hydroxyl group of the polyoxyalkylene (poly)glyceryl ether, and the resulting lower alcohol is removed from the system while obtaining an esterified product.

[0015] The electrolyte of the present invention preferably contains 5% to 30% by weight of PGAO methacrylate, more preferably 10% to 25% by weight, and most preferably 10% to 20% by weight. By having a methacrylate content of 5% to 30% by weight, an aluminum electrolytic capacitor with good impedance characteristics and lifespan characteristics can be obtained.

[0016] The electrolyte of the present invention may contain PGAO methacrylate, as well as various organic solvents, electrolytes, and additives. Examples of organic solvents include, but are not limited to, ethylene glycol, γ-butyrolactone, and glycerin. Examples of electrolytes include organic acids, inorganic acids, or salts thereof. Examples of organic acids or salts thereof include formic acid, acetic acid, propionic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, 1,10-decanedicarboxylic acid, 1,6-decanedicarboxylic acid, 5,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, 7-vinylhexadecene-1,16-dicarboxylic acid, maleic acid, benzoic acid, phthalic acid, and their ammonium salts and amine salts. Furthermore, examples of inorganic acids or salts thereof include carbonic acid, hypophosphorous acid, phosphorous acid, phosphoric acid, boric acid, perchloric acid, and their ammonium salts and amine salts. However, they are not limited to these. Examples of additives include, but are not limited to, polyhydric alcohols such as mannitol, hydrophilic polymer compounds such as polyvinyl alcohol and polyvinylpyrrolidone, metal oxides such as silicon dioxide and aluminosilicate, nitro compounds such as p-nitrobenzoic acid and p-nitrophenol, and water.

[0017] For polymerization of polymerizable monomers, it is preferable to use a water-soluble radical polymerization initiator. Known water-soluble radical polymerization initiators include, for example, peroxide-based polymerization initiators such as potassium persulfate, ammonium persulfate, t-butyl hydroperoxide, and hydrogen peroxide, and azo-based radical polymerization initiators such as 2,2′-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide] and 2,2′-azobis[2-methyl-N-(imidazolin-2-yl)-propane]. When using an oxidative polymerization initiator, redox polymerization may be carried out in combination with a reducing agent such as sodium sulfite, sodium bisulfite, iron(II) sulfate, or L-ascorbic acid. These initiators may be used alone or in combination of two or more. The amount of these thermal polymerization initiators added is not limited as long as a gel-like electrolyte can be obtained, but from the viewpoint of the electrical properties of the gel-like electrolyte, 0.001 to 20 parts by weight per 100 parts by weight of polymerizable monomer is preferred.

[0018] When using azo polymerization initiators, it is preferable to use azo polymerization initiators with a 10-hour half-life temperature of 40 to 100°C, particularly 60 to 90°C. Examples of polymerization initiators include 2,2′-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide], 2,2′-azobis[2-(2-imidazolin-2-yl)propane], 2,2′-azobis[N-(2-carboxyethyl)-2-methylpropionamidine], 2,2′-azobis(2-methylpropanamide oxime), 2,2′-azobis(2-amidinopropane) dihydrochloride, and 2,2′-azobis[2-(2-imidazolin-2 Examples include 2,2′-azobis[2-(5-methyl-2-imidazolin-2-yl)propane] sulfate, 2,2′-azobis[2-(5-methyl-2-imidazolin-2-yl)propane] dihydrochloride, 2,2′-azobis[2-(3,4,5,6-tetrahydropyrimidine-2-yl)propane] dihydrochloride, and 2,2′-azobis[2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane] dihydrochloride.

[0019] The method for preparing the electrolytic solution is not particularly limited. For example, a gelled electrolytic solution can be obtained by blending a polymerizable monomer and a polymerization initiator and polymerizing the methacryloyl group by heating or light irradiation. When used as the electrolytic solution for an electrolytic capacitor, since it is difficult to impregnate a gelled electrolytic solution into a generally used wound capacitor element, after impregnating the capacitor element with an electrolytic solution containing a polymerizable monomer and a polymerization initiator, an electrolytic capacitor using a gelled electrolytic solution can be manufactured by a method of polymerizing and gelling by heating in an aging process. At this time, the gelling of the electrolytic solution due to the polymerization of the polymerizable monomer may be carried out before the aging of the electrolytic capacitor, may be carried out after the aging, or may be carried out by a method of polymerizing stepwise before and after the aging. Further, after applying an electrolytic solution containing a polymerizable monomer and a polymerization initiator to an anodic oxidized aluminum foil and / or a cathode aluminum foil for an electrolytic capacitor and polymerizing by heating or light irradiation to form a sheet-like gelled electrolytic solution on the electrode foil, an electrolytic capacitor containing the gelled electrolytic solution can be produced by lamination or winding.

Examples

[0020] Next, the present invention will be described in detail with reference to Examples and Comparative Examples, but the present invention is not limited only to these Examples. Examples and Comparative Examples of the present invention are shown below. However, % is based on weight.

[0021] (Example 1) A reaction vessel equipped with a thermometer, a stirrer, a Dean-Stark apparatus, and an air blowing tube was charged with polyoxyethylene polyglyceryl ether PGEO1 (average degree of polymerization of polyglycerol: 2, hydroxyl value: 117 mg KOH / g), toluene, p-toluenesulfonic acid, hydroquinone monomethyl ether, copper(II) chloride, sodium hypophosphite, and methacrylic acid. While stirring under air blowing, the temperature was raised to a toluene reflux atmosphere, and a dehydration esterification reaction was carried out over about 8 hours. After the reaction was completed, it was washed with alkaline water and then with water, and the toluene in the organic layer was distilled off under reduced pressure to obtain polyoxyethylene polyglyceryl ether acrylate M1 (functional group equivalent: 544 g / eq.). Using M1 as a gelling agent, an electrolyte (diammonium 1,7-octanedicarboxylate), ethylene glycol, and ion-exchanged water were blended at the ratios shown in Table 1 to prepare an electrolytic solution. A polymerization initiator (2,2′-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide]) at 0.1 wt% was added to the prepared electrolytic solution, the temperature was adjusted to 25°C, and it was impregnated into a wound element for an aluminum electrolytic capacitor (φ12 mm × 20 mmH, rated voltage: 400 V, rated capacitance: 22 μF). The impregnation of the electrolytic solution was repeated 4 times by holding it under a reduced pressure of 6.7 kPa for 2 minutes and then returning to normal pressure. The capacitor element impregnated with the electrolytic solution was placed in an aluminum case, a sealing rubber was passed through the lead wire portion at the upper part of the element, and it was sealed using a necking device (manufactured by Takizawa Co., Ltd.). The sealed electrolytic capacitor was preheated in a constant temperature bath at 65°C for 30 minutes, and then the lead wire of the capacitor was connected to a DC power supply (PL-650-0.1: manufactured by Matsusada Precision Co., Ltd.) to carry out an aging treatment. In the aging treatment, a current of 2 mA was applied at 65°C, and after the voltage reached 420 V, it was held at a constant voltage of 420 V for 60 minutes. The electrolytic solution containing the gelling agent and the polymerization initiator described in the examples maintains a liquid state during impregnation, but undergoes thermal polymerization and gelation by heating in the aging process.

[0022] (Measurement of Electrical Characteristics (Initial Characteristics) of Capacitor) The electrical characteristics of the electrolytic capacitors fabricated using the method described above were measured using the following method. Using an LCR meter (ZM2376: manufactured by NF Circuit Block Co., Ltd.), the capacitance at 120 Hz and the equivalent series resistance (ESR) at 100 kHz were measured under conditions of 25°C, a voltage of 0.5 V, and a DC bias of 1.0 V. The results of the evaluation according to the following criteria are shown in Table 1. In the evaluation criteria, ◎ or ○ indicates good characteristics, ◎ indicates particularly excellent characteristics, and × indicates insufficient performance. <Evaluation Criteria> Capacitance (μF) ○: Rated ±10% (19.8~24.2), ×: Over Rated ±10% ESR (Ω) ◎: Less than 2.0, ○: 2.0 to less than 3.0, ×: 3.0 or higher

[0023] (Evaluation of capacitor lifespan characteristics) The life characteristics of the electrolytic capacitors fabricated in Example 1 were evaluated by the following method. The electrolytic capacitors were left undisturbed in a high-temperature environment of 125°C, and their electrical characteristics after 16 days (384 hours; equivalent to approximately 1500 hours at 105°C) were measured under the same conditions as the initial characteristics. The evaluation of life characteristics was performed using the initial electrical characteristics (capacitance: C0, ESR: R0) and the electrical characteristics after storage at 125°C (capacitance: C0). L ESR:R L From the above, the rate of change in capacitance: ΔC (%) and the rate of increase in ESR: ΔESR (mΩ / h) were calculated using Equations 4 and 5, and evaluated according to the following criteria. In the evaluation criteria, ◎ or ○ indicates good characteristics, ◎ indicates particularly excellent, and × indicates insufficient performance. (Formula 4)ΔC(%)=[(C L -C0) / C0]×100 (Equation 5) ΔESR(mΩ / h) = 1000 × (R L -R0) / 384 <Evaluation Criteria> ΔC(%) ◎: Less than ±1.0, ○: Less than ±2.0, ×: ±2.0 or more ΔESR (mΩ / h) ◎: Less than 4.0, ○: 4.0 to less than 5.5, ×: 5.5 or higher

[0024] (Example 2) A dehydration esterification reaction was carried out in the same manner as in Example 1, except that polyoxyethylene polyglyceryl ether PGEO2 (average degree of polymerization of polyglycerin 4, hydroxyl value 114 mg KOH / g) was used instead of PGEO1 to obtain polyoxyethylene polyglyceryl ether methacrylate M2 (functional group equivalent 573 g / eq.). A capacitor was fabricated in the same manner as in Example 1, except that M2 was used instead of M1 as the gelling agent, and the initial characteristics and lifetime characteristics were evaluated. The evaluation results are shown in Table 1.

[0025] (Example 3) Except for using polyoxyethylene polyglyceryl ether PGEO3 (average degree of polymerization of polyglycerin 10, hydroxyl value 116 mg KOH / g) instead of PGEO1, a dehydration esterification reaction was carried out in the same manner as in Example 1 to obtain polyoxyethylene polyglyceryl ether methacrylate M3 (functional group equivalent 548 g / eq.). Capacitors were fabricated in the same manner as in Example 1, except for using M3 instead of M1 as the gelling agent, and their initial characteristics and lifetime characteristics were evaluated. The evaluation results are shown in Table 1.

[0026] (Comparative example) Electrolytic capacitors were fabricated in the same manner as in Example 1, except that polyethylene glycol 1000 (PEG1000) was used as an additive instead of a gelling agent, and no polymerization initiator was added. Initial characteristics and lifetime characteristics were then evaluated. The evaluation results are shown in Table 1.

[0027] [Table 1]

[0028] In Examples 1-3, which used PGAO methacrylate of the present invention as a gelling agent, the ESR of the electrolytic capacitors at 25°C was significantly lower and the impedance characteristics were clearly better compared to the comparative example which used PEG1000 instead of the gelling agent. Furthermore, in terms of lifetime characteristics, Examples 1-3 showed less change in electrical characteristics after high-temperature storage and were superior to the comparative example. From these results, it is clear that by using PGAO methacrylate as a gelling agent for the electrolyte and producing an electrolytic capacitor as a gel-like electrolyte by polymerization, an electrolytic capacitor with excellent impedance characteristics and good lifetime characteristics can be obtained.

Claims

1. A gelling agent for capacitor electrolytes comprising a polymerizable monomer, characterized in that the polymerizable monomer contains polyoxyalkylene (poly)glyceryl ether methacrylate, which is obtained by methacrylate modification of the terminal groups of polyoxyalkylene (poly)glyceryl ether.

2. The gelling agent for capacitor electrolyte according to claim 1, characterized in that a polymerization initiator is added to the capacitor electrolyte to polymerize methacryloyl groups.

3. The gelling agent for capacitor electrolyte according to claim 1 or 2, wherein the (poly)glycerin constituting the polyoxyalkylene (poly)glyceryl ether has an average degree of polymerization of 1 to 20.

4. The gelling agent for capacitor electrolyte according to claim 1, wherein the alkylene oxide constituting the polyoxyalkylene (poly)glyceryl ether is one or more selected from ethylene oxide or propylene oxide.

5. The gelling agent for capacitor electrolyte according to claim 1, wherein the functional group equivalent of the polyoxyalkylene (poly)glyceryl ether methacrylate is 450 to 780 g / eq.

6. An electrolyte for an electrolytic capacitor using the gelling agent described in claim 1.

7. An electrolyte for an electrolytic capacitor comprising an electrolyte, a polymerizable monomer, and a polymerization initiator, wherein the polymerizable monomer contains polyoxyalkylene (poly)glyceryl ether methacrylate obtained by methacrylate modification of the terminal groups of polyoxyalkylene (poly)glyceryl ether.

8. An aluminum electrolytic capacitor using the electrolyte described in claim 6 or claim 7.

9. A method for preparing an electrolyte for a capacitor according to claim 7, characterized in that a polymerizable monomer and a polymerization initiator are combined to polymerize a methacryloyl group.

10. A method for manufacturing an aluminum electrolytic capacitor using an electrolyte prepared by the method of claim 9.

Images