JP2002110469A - Electrolyte for electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolyte having a superior high-temperature life characteristic and impedance characteristic. SOLUTION: One or more kinds of polyatomic alcohol complex compounds of boric acid obtained from polyatomic alcohol of boric acid are dissolved in a solvent which is mainly formed of ethylene glycol and contains 7-50 wt.% of water. Then, organic carboxylic acids are added by 5-40 wt.% of the total quantity of the boric acid, and in addition, 1-hydroxyethylidene-1,1-diphosphonic acid is added. By using this electrolyte, an electrolytic capacitor having a superior life characteristic and impedance characteristic can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolytic solution for electrolytic capacitors, and more particularly to an electrolytic solution for medium and high pressures.

[0002]

2. Description of the Related Art An electrolytic solution for an electrolytic capacitor uses a valve metal having an insulating oxide film formed on the surface such as aluminum or tantalum for an anode electrode, and uses the oxide film layer as a dielectric material. An electrolyte for forming an electrolyte layer is brought into contact with the surface of the substrate, and a current collecting electrode usually called a cathode is arranged.

As described above, the electrolytic solution for an electrolytic capacitor directly contacts the dielectric layer and acts as a true cathode. That is, the electrolytic solution is interposed between the dielectric of the electrolytic capacitor and the collector cathode, and the resistance of the electrolytic solution is inserted in series with the electrolytic capacitor. Therefore, the characteristics of the electrolytic solution are a major factor affecting the characteristics of the electrolytic capacitor.

[0004] In the prior art of electrolytic capacitors, since an electrolysis solution for medium and high pressures can obtain a relatively high spark voltage, an organic carboxylic acid such as sebacic acid or azelaic acid is used using ethylene glycol as a solvent. In some cases, however, since these have low solubility, crystals tend to precipitate at low temperatures, and the disadvantage of deteriorating the low-temperature characteristics of the capacitor cannot be avoided. Furthermore, Japanese Patent Publication No. 60-1
There is an example using butyloctane diacid as a solute as shown in Japanese Patent No. 3296, and an example using 5,6-decanedicarboxylic acid as a solute as shown in Japanese Patent Publication No. 63-15738. Electrolyte solutions using these organic carboxylic acids or salts thereof have high sparking voltage and conductivity, and high solubility, and thus have good low-temperature characteristics.

[0005]

However, in these electrolytes, the esterification reaction proceeds between the hydroxyl group of ethylene glycol and the carboxyl group of the organic carboxylic acid, and the conductivity decreases due to the decrease of ions. Tanδ of the electrolytic capacitor increases. Moreover,
The organic carboxylic acid forms a complex with aluminum on the surface of the electrode foil, resulting in a decrease in the effective area of the electrode foil, and a phenomenon that the capacitance decreases. For this reason, there is a problem that the life characteristics of the electrolytic capacitor at high temperatures are not sufficient.

Further, in recent years, there has been an increasing demand for lower impedance in electronic equipment using a switching power supply.

Accordingly, an object of the present invention is to provide a medium-to-high pressure electrolytic solution having good high-temperature life characteristics, that is, good tan δ and capacitance characteristics, and good impedance characteristics.

[0008]

In order to solve the above-mentioned problems, an electrolytic solution for an electrolytic capacitor according to the present invention comprises boric acid and a polyhydric alcohol in a solvent mainly composed of ethylene glycol and containing 7 to 50% by weight of water. , A 1,6-decanedicarboxylic acid, 5,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, 7-
Methyl-7-methoxycarbonyl-1,9-decanedicarboxylic acid, 7,9-dimethyl-7,9-dimethoxycarbonyl-1,11-dodecanedicarboxylic acid, 7,8-dimethyl-7,8-dimethoxycarbonyl-1 At least one or more organic carboxylic acid compounds or salts thereof selected from 14,14-tetradecanedicarboxylic acid, sebacic acid and azelaic acid in an amount of 5 to 40% by weight of the total amount of boric acid
And 1-hydroxyethylidene-1,1-diphosphonic acid is further added.

Further, the polyhydric alcohol in the polyhydric alcohol complex compound of boric acid in the electrolytic solution may be erythritol,
It is a sugar alcohol selected from arabbit, adnit, sorbit, mannitol, dursit, and tarit.

[0010] One or more polyoxyalkylene polyhydric alcohol ether compounds obtained by polymerizing ethylene oxide and / or propylene oxide with a polyhydric alcohol are added to the electrolyte solution. It is characterized by the following.

[0011] Further, one or more aromatic nitro compounds are added to the electrolyte.

Further, the above-mentioned electrolytic solution has a general formula:

Embedded image Wherein R ₁ and R ₂ each represent an alkyl group having 1 to 18 carbon atoms or a hydrogen atom which may be the same or different, and at least one is alkyl. And one or more phosphorous acids are added.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The electrolytic solution for an electrolytic capacitor of the present invention mainly comprises a polyhydric alcohol complex compound of boric acid or a salt thereof (hereinafter referred to as polyhydric alcohol complex compounds of boric acid) obtained from boric acid and a polyhydric alcohol. Solute. And, as polyhydric alcohol in the polyhydric alcohol complex compound of boric acid, ethylene glycol, propylene glycol, trimethylolpropane, trimethylolethane, pentaerythritol, polyvinyl alcohol and the like, and further, trit, tetrit, pentite, hexit, Sugar alcohols such as petite, octit, nonit, desit, dodecit and the like can be mentioned.

Here, the polyhydric alcohol complex compounds of boric acid are obtained by synthesizing boric acid and polyhydric alcohol. When mixing and preparing an electrolytic solution, boric acid and polyhydric alcohol are added to ethylene glycol. It can also be obtained by mixing quantitatively, dissolving by heating, and synthesizing in an electrolytic solution.

And 1,6-decanedicarboxylic acid,
5,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, 7-methyl-7-methoxycarbonyl-1,9
-Decanedicarboxylic acid, 7,9-dimethyl-7,9-dimethoxycarbonyl-1,11-dodecanedicarboxylic acid, 7,8-dimethyl-7,8-dimethoxycarbonyl-1,14-tetradecanedicarboxylic acid, sebacic acid,
At least one or more organic carboxylic acid compounds or salts thereof (hereinafter, organic carboxylic acids) selected from azelaic acid are added in an amount of 5 to 40% by weight, preferably 10 to 25% by weight of the total amount of the boric acid. Here, the total amount of boric acid refers to the total amount of boric acid used at that time, although the polyhydric alcohol complex compounds of boric acid are prepared from boric acid and polyhydric alcohol, as described above.

Then, ethylene glycol is mainly used and 7
Using a solvent containing 50 to 50% by weight of water;
Hydroxyethylidene-1,1-diphosphonic acid is used.

The above electrolyte of the present invention has high-temperature life characteristics,
That is, the stability of the conductivity, the capacitance characteristic, and the leakage current characteristic at a high temperature is good, and the impedance characteristic is also good. The reason is presumed to be as follows.

The polyalcohol complex compound of boric acid, which is a main solute of the electrolytic solution of the present invention and obtained from boric acid and polyhydric alcohol, has an electric conductivity by an esterification reaction with ethylene glycol like an organic carboxylic acid. There is no such thing as lowering. In addition, since a complex with aluminum is not formed, the capacitance does not decrease, and therefore, the life characteristics at high temperatures are good. Here, if only boric acid is used, there is a problem that the conductivity decreases and the leakage current increases in a high-temperature test, but polyhydric alcohol complex compounds of boric acid do not have such disadvantages. It is because boric acid which became borate anion in the electrolyte is taken in the anodic oxide film at high temperature, the concentration of borate anion in the electrolyte decreases,
The conductivity of the electrolytic solution decreases, and furthermore, the borate anion incorporated in the oxide film reacts with the oxide film, dissolving the oxide film and increasing the leakage current. However, since the polyhydric alcohol complex compounds of boric acid of the present invention have a large molecular size, they are not taken into the oxide film, so that the electric conductivity does not decrease and the leakage current increases. It is considered that this is due to the absence of any.

Since the above-mentioned organic carboxylic acids are added in an amount of 5 to 40% by weight based on the total amount of boric acid, the ability of the electrolyte to repair the oxide film, ie, the chemical conversion, is improved, and the spark voltage and the leakage current are improved. Since the characteristics are improved and good chemical conversion properties are maintained for a long time, the leakage current characteristics in the life test are further improved.

Furthermore, the above-mentioned electrolytic solution has excellent overvoltage characteristics when an overvoltage is applied to the electrolytic capacitor, that is, excellent safety. Normally, when an overvoltage is applied to a capacitor, an anodic oxidation reaction occurs, the current increases, and heat generation and generation of hydrogen gas occur. Here, in the conventional electrolytic solution using an organic carboxylic acid, the anodic oxidation reaction is slow at the beginning when an overvoltage is applied, and the reaction becomes explosive on the way.
Since a large current flows due to the explosive reaction, the possibility of occurrence of a short circuit increases. However, in the electrolytic solution of the present invention containing polyalcohol complex compounds of boric acid as a main solute, when an overvoltage is applied, the anodic oxidation reaction proceeds from the beginning, the current increases, and heat generation and generation of hydrogen gas occur. Occurs, and due to this heat generation and generated gas,
Since the safety valve operates and the electrolytic solution evaporates to be in an open state, high safety can be achieved. Although the reason is not clear in the electrolytic solution of the present invention, the addition of the organic carboxylic acid in the range of 5 to 40% by weight of the total amount of boric acid does not lower the overvoltage characteristic.

In the electrolytic solution of the present invention, the organic carboxylic acid contains 5 to 40% by weight, preferably 10 to 25% by weight of the total amount of the boric acid.
Although it is added by weight%, since the situation is as described above, if it is less than this range, the effect of improving the leakage current characteristics during the initial and life tests is reduced. If the ratio exceeds this range, the spark voltage decreases, and the conductivity decreases due to the decrease in anions due to the esterification reaction of organic carboxylic acids with ethylene glycol during the life test, so that the life characteristics deteriorate.

The content of the solute comprising the polyhydric alcohol complex compound of boric acid and the organic carboxylic acid in the electrolyte is 3 to 50% by weight, preferably 5 to 20% by weight.
It is. Below this range, the ion concentration is low, and above this range, the mobility of ions decreases due to an increase in the viscosity of the electrolyte, resulting in a significant decrease in conductivity.

Then, ammonia gas is injected and added to the electrolyte solution thus formed to adjust the pH, whereby the electrolyte solution of the present invention is formed.

Here, as the polyhydric alcohol in the polyhydric alcohol complex compound of boric acid, a sugar alcohol having a cis-position hydroxyl group such as erythritol, arabbit, adnit, sorbit, mannitol, dulcit, and talit is used. A reduction in conductivity at high temperatures can be suppressed, and a rise in the internal pressure of the capacitor is small. This is because when a sugar alcohol having a cis-position hydroxyl group is used, the two cis-position hydroxyl groups are bonded to boric acid,
It is considered that a more stable boric acid complex compound is formed at a high temperature, and that gas generation due to hydration deterioration is suppressed. Although the reason is not clear, the spark voltage can be increased. Here, among these sugar alcohols having a hydroxyl group at the cis position, mannitol is the most preferable. The content of the sugar alcohol having a cis-position hydroxyl group is 0.4% by weight to 1 part of boric acid.
To 3.0, preferably 1.0 to 2.0. Below this range, the conductivity at high temperatures will increase, and beyond this range the initial conductivity will decrease.

The salts of the polyhydric alcohol complex compound of boric acid and the salts of the organic carboxylic acid compounds in the present invention include ammonium salts, amine salts, quaternary ammonium salts and quaternary ammonium salts of cyclic amidine compounds. Examples of the amine constituting the amine salt include primary amines (methylamine, ethylamine, propylamine, butylamine,
Ethylenediamine, monoethanolamine, etc., secondary amine (dimethylamine, diethylamine, dipropylamine, ethylmethylamine, diphenylamine, diethanolamine, etc.), tertiary amine (trimethylamine, triethylamine, tributylamine, 1,8-diazabicyclo (5, 4,0) -undecene-7, triethanolamine, etc.). Of these, ammonium salts are preferred.

The solvent mainly contains ethylene glycol and contains 7 to 50% by weight of water. By mainly containing ethylene glycol and containing 7 to 50% by weight of water, the impedance of an electrolytic capacitor using the same can be reduced. Furthermore, a protic polar solvent, an aprotic solvent, or water can be added as a secondary solvent for the purpose of improving low temperature characteristics, reducing specific resistance, and the like. As the 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, etc.). Examples of aprotic solvents include amides (N-methylformamide, N, N-dimethylformamide, N-ethylformamide, N, N-dimethylformamide, N-methylacetamide, hexamethylphosphoramide, etc.),
Lactones, cyclic amides, carbonates (γ-butyrolactone, N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate and the like), nitriles (acetonitrile) oxides (dimethylsulfoxide and the like) are typical examples.

Since 1-hydroxyethylidene-1,1-diphosphonic acid is used as an additive, deterioration of the characteristics of the electrolytic capacitor due to hydration deterioration of the electrode foil can be suppressed.

As described above, the electrolytic solution of the present invention has stable characteristics at high temperatures and good impedance characteristics. Therefore, by using the electrolytic solution of the present invention, it is possible to obtain an electrolytic capacitor having good life characteristics such as a change in dielectric loss, a change in capacitance, a change in leakage current, and the like at a high temperature, and a good impedance characteristic.

Then, a nonionic surfactant and a polyoxyalkylene polyhydric alcohol ether compound obtained by polymerizing ethylene oxide and / or propylene oxide with a polyhydric alcohol are added to the electrolytic solution, whereby the electrolytic solution is The spark voltage can be improved. This makes it possible to reduce the short-circuit rate at the time of re-chemical formation, and it becomes suitable as an electrolyte for a high-voltage capacitor. In addition, since the nonionic surfactant has a property of foaming during impregnation, considering the workability at the time of impregnation, polyoxyalkylene polyoxyalkylene obtained by polymerizing ethylene oxide and / or propylene oxide with a polyhydric alcohol is used. Dihydric alcohol ether compounds are preferred.

Examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, alkylallyl formaldehyde condensed polyoxyethylene ether, polyoxyethylene polyoxypropylene alkyl ether, and polyoxyethylene of glycerin fatty acid ester. Ether, polyoxyethylene ether of sorbitan fatty acid ester, polyoxyethylene ether of sorbitol fatty acid ester, fatty acid ester of polyethylene glycol, hydrophilic silicone oil and the like.

The polyhydric alcohol of the polyoxyalkylene polyhydric alcohol ether compound obtained by polymerizing ethylene oxide and / or propylene oxide on the polyhydric alcohol includes ethylene glycol, propylene glycol,
Glycerin, pentaerythritol, sorbit, polyglycerin, trimethylolpropane, trimethylolethane and the like can be mentioned. Of these, glycerin,
Pentaerythritol, sorbit, polyglycerin,
Trimethylolpropane and trimethylolethane are preferred.

The addition amount of the nonionic surfactant and polyoxyalkylene polyhydric alcohol ether compound is 0.1%.
-15% by weight, preferably 0.5-10% by weight. Below this range, the effect decreases, and beyond this range,
Conductivity decreases. Here, the polyoxyalkylene polyhydric alcohol ether compound has an average molecular weight of 1
In the case of 000 or more, the effect is high, so the addition amount may be small.

Further, by adding an aromatic nitro compound to the electrolytic solution, an increase in the internal pressure of the capacitor can be suppressed, and the life characteristics of the capacitor can be improved. This is considered to be due to a reduction reaction of the nitro group with the hydrogen gas generated inside the capacitor. The addition amount of the aromatic nitro compound is 0.01
To 7.0% by weight, preferably 0.1 to 5.0% by weight. If it is less than this range, the effect decreases, and if it exceeds this range, the conductivity of the electrolytic solution decreases.

Specific examples of the aromatic nitro compound include nitrophenol, dinitrophenol, nitrobenzoic acid, nitrotoluene, dinitrotoluene, nitroxylene, nitrobenzene, dinitrobenzene, nitrobenzyl alcohol, nitroacetophenone, nitroanisole, dimethoxynitrobenzene, and nitrobenzene. Examples include aniline, nitrophenetol, nitrophthalic acid, 2- (nitrophenoxy) ethanol and the like.

Further, by adding an acidic alkyl phosphate compound represented by the formula (2), phosphoric acid, and phosphorous acid to the electrolytic solution, it is possible to suppress an increase in leakage current at high temperature of the capacitor. This seems to be due to the effect of these additives on hydration deterioration of the anodic oxide film generated when the capacitor is left for a long time. The addition amount of phosphoric acid or phosphorous acid is 0.01 to 1.0% by weight, preferably 0.1 to 0.5% by weight. The amount of the acidic alkyl phosphate compound to be added is 0.01 to 5.0% by weight, preferably 0.1 to 3.0% by weight. If it is less than this range, the effect decreases, and if it exceeds this range, the spark voltage decreases.

Embodiments of the present invention will be described below.

Table 1 shows the compositions of the electrolytic solutions for electrolytic capacitors in Examples of the present invention and Comparative Examples. (Table 2) shows 400 V-330 μF using the electrolytes of the examples and comparative examples in (Table 1).
2 shows the initial characteristics of the electrolytic capacitor of Example 1 and the characteristics of the electrolytic capacitor 2000 hours after the rated voltage was applied at 105 ° C.

[0037]

[Table 1]

[0038]

[Table 2]

[0039]

[Table 3]

As can be seen from Tables 1 to 3, the electrolytic capacitors of Examples have lower impedance characteristics than those of Comparative Example 3 in which a solvent containing no water is used. Is small. Also, there is little change in the height dimension of the product. In comparison, Comparative Examples 1 and 2, in which 1-hydroxyethylidene-1,1-diphosphonic acid was not added, were all open, and Comparative Example 4, in which no organic carboxylic acid compound was contained, had characteristics after the life test. Deterioration is remarkable.

[0041]

As described above, the electrolytic solution of the present invention comprises a polyhydric alcohol complex of boric acid obtained from a polyhydric alcohol of boric acid in a solvent mainly composed of ethylene glycol and containing 7 to 50% by weight of water. One or more compounds are dissolved, and organic carboxylic acids are added in an amount of 5 to 40% by weight based on the total amount of boric acid.
Further, it is an electrolytic solution to which 1-hydroxyethylidene-1,1-diphosphonic acid is added, and has good high-temperature and long-life characteristics and good impedance characteristics. Therefore, by using the electrolytic solution of the present invention, it is possible to obtain an electrolytic capacitor having good life characteristics and good impedance characteristics, having a small change in capacity, a change in tan δ, and a change in leakage current after a life test.

Claims (5)

[Claims] (1) ethylene glycol as a main component;
In a solvent containing boric acid and polyhydric alcohol, at least one polyhydric alcohol complex compound of boric acid or a salt thereof is dissolved in a solvent containing 1% by weight of 1,6-decanedicarboxylic acid, 5,6, -Decanedicarboxylic acid, 1,7-octanedicarboxylic acid, 7-methyl-7-methoxycarbonyl-1,9-decanedicarboxylic acid, 7,9-dimethyl-
At least one or more selected from 7,9-dimethoxycarbonyl-1,11-dodecanedicarboxylic acid, 7,8-dimethyl-7,8-dimethoxycarbonyl-1,14-tetradecanedicarboxylic acid, sebacic acid and azelaic acid An electrolytic solution for an electrolytic capacitor to which an organic carboxylic acid compound or a salt thereof is added in an amount of 5 to 40% by weight based on the total amount of boric acid, and 1-hydroxyethylidene-1,1-diphosphonic acid is further added. 2. The polyhydric alcohol in the polyhydric alcohol complex compound of boric acid according to claim 1, wherein the polyhydric alcohol is a cis-position sugar alcohol selected from erythritol, arabbit, adnit, sorbit, mannitol, dursit, and tarit. Electrolyte for electrolytic capacitors. 3. The electrolysis according to claim 1, wherein at least one polyoxyalkylene polyhydric alcohol ether compound obtained by polymerizing ethylene oxide and / or propylene oxide with a nonionic surfactant or polyhydric alcohol is added. Electrolyte for capacitors. 4. The method according to claim 1, wherein at least one aromatic nitro compound is added.
The electrolytic solution for an electrolytic capacitor according to claim 1. 5. A compound of the general formula: (Wherein, R ₁ and R ₂ each represent an alkyl group having 1 to 18 carbon atoms, which may be the same or different, or a hydrogen atom, and at least one of them is alkyl.) The electrolytic solution for an electrolytic capacitor according to claim 1, wherein one or more phosphorous acids are added.