JPH04350920A - Electrolyte for electrolytic capacitor - Google Patents

Abstract

PURPOSE:To provide an electrolyte for an electrolytic capacitor which improves the voltage resistance property remarkably while maintaining conductivity by adding a specified derivative of polyvinyl alcohol to an electrolyte for an electrolytic capacitor. CONSTITUTION:Hydroxyethylalkylated polyvinyl alcohol is added to an electrolyte for an electrolytic capacitor wherein an organic polar solvent is a main solvent and organic acid or inorganic acid or its salt is a solute.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to the improvement of electrolytic solutions for electrolytic capacitors, and more specifically, the present invention relates to the improvement of electrolytic solutions for electrolytic capacitors. Concerning improvements in electrolytes for capacitors.

0002

[Prior Art] Electrolytic capacitors are small, large capacity, inexpensive, and have excellent characteristics such as smoothing rectified output.
It is one of the important components of electronic equipment, and generally an aluminum film whose surface has been changed into an oxide film by electrolytic oxidation is used as an anode, and an electrolyte is interposed between it and the current collector cathode, using this oxide film as a dielectric. It is made by During use, the oxide film is constantly regenerated, so it is stable, but if it is not used for a long time, for example, regeneration becomes insufficient and it deteriorates.

In the chemical reactions that occur during use of electrolytic capacitors, the electrolyte forms an ionic conductor that is a medium for ion transport. Charges move at the interface between the electrolyte and the electrode as the electrode reaction progresses, an oxidation reaction progresses at the anode surface, a reduction reaction progresses at the cathode surface, and at the same time, ions move through the electrolyte, which is an ionic conductor. Current flows. Therefore, the electrical conductivity of the electrolytic solution reflects the characteristics of the electrolytic solution as an ionic conductor in the chemical reactions that occur during use of the electrolytic capacitor, and is one of the important indicators for evaluating the overall performance of the capacitor.

[0004] Since electrolytic capacitors are used while undergoing chemical reactions, their characteristics greatly depend on the properties of the electrolyte. Maintaining a steady state of the chemical reaction that occurs between the aluminum electrode, which has an oxide film on its surface, and the electrolyte, and maintaining the aluminum oxide film, which serves as a dielectric, in good condition is important for stabilizing performance. If the chemical steady state is disturbed due to an incorrect method, for example, due to an excessively high voltage load, the aluminum oxide film will be destroyed and eventually the insulation will be broken.

[0005] Scintillation is a phenomenon in which the load voltage of a capacitor increases and the physical properties of the dielectric material change due to the high voltage load, and the electrochemical state fluctuates as a result of temporal changes in dielectric constant. The voltage at which this is observed can be used as a scintillation voltage (spark voltage) as a measure of the voltage resistance of the capacitor, and the higher the scintillation voltage (spark voltage), the greater the voltage resistance of the capacitor. This can be easily measured by immersing an unformed aluminum foil of an appropriate size in the electrolytic solution to be measured, without assembling the final capacitor product.

[0006] In conventional electrolytic solutions for general electrolytic capacitors, an acid such as boric acid or a salt thereof is added as a main solute in order to obtain high voltage resistance. Also,
In addition to these, attempts have been made to improve the electrolytic solution for electrolytic capacitors and obtain high voltage resistance by adding various additives.

[0007] Additives for obtaining high voltage resistance include:
For example, addition of sulfamic acid (Japanese Patent Publication No. 49-8296
No. 3), addition of suberic acid (JP-A-49-13386)
No. 0), addition of dodecyl phosphate (JP-A-49-7365)
No. 9), addition of alkyl phosphoric acid (JP-A-52-153)
No. 154), addition of diphosphorous acid (JP-A-57-1419)
No. 13), use of boric acid-mannite system (JP-A-57-
60829), the use of boric acid-mannitol-polyvinyl alcohol system (Japanese Patent Application Laid-open No. 177915-1982), and the addition of modified silicone oil (Japanese Patent Application Laid-open No. 175722-1999), etc. The maintained voltage resistance could not necessarily be sufficiently improved.

[0008]

[Problems to be Solved by the Invention] Several attempts have been made to improve the properties of certain electrolytic solutions by adding polyvinyl alcohol to them. As a prior art using polyvinyl alcohol, for example, Japanese Patent Publication No. 37-15
No. 073, JP-A-49-121162, JP-A-52
-129963 and JP-A-60-91618 can be exemplified.

[0009] As a result of paying attention to the properties of this polyvinyl alcohol and continuing to study the effects of adding various derivatives thereof to electrolyte solutions for electrolytic capacitors, we found that:
We have discovered that certain specific derivatives can significantly improve withstand voltage characteristics while maintaining electrical conductivity.

[0010] Accordingly, an object of the present invention is to provide an electrolytic solution for electrolytic capacitors which has significantly improved dielectric strength characteristics while maintaining electrical conductivity by adding a predetermined derivative of polyvinyl alcohol.

[0011]

[Means for Solving the Problems] According to the present invention, hydroxyethyl alkylated polyvinyl alcohol is added to an electrolytic solution for an electrolytic capacitor using an organic polar solvent as a main solvent and an organic acid or an inorganic acid or a salt thereof as a solute. An electrolytic solution for an electrolytic capacitor is provided.

[0012] Hydroxyethyl alkylated polyvinyl alcohol can be obtained, for example, as one of its synthetic methods as follows.

Vinyl alkyl ether and vinyl acetate monomer are reacted in the presence of benzoyl peroxide to obtain a vinyl acetate vinyl alkyl ether copolymer. The obtained copolymer is saponified with an alkali to obtain a vinyl alcohol vinyl alkyl ether copolymer. Furthermore, by allowing ethylene oxide (or ethylene chlorohydrin) to act on this copolymer in the presence of an alkali catalyst,
Hydroxyethyl alkylated polyvinyl alcohol is obtained.

Specific examples of solvents that can be used alone or in combination as the organic polar solvent of the electrolytic solution include the following: Protic polar solvents ethanol, propanol, butanol, pentanol, hexanol, cycloprotic polar solvents Monohydric alcohols such as butanol, cyclopentanol, cyclohexanol, and benzyl alcohol; polyhydric alcohols such as ethylene glycol, propylene glycol, glycerin, methoxyethanol, ethoxyethanol, methoxypropylene glycol, dimethoxypropanol, methyl cellosolve, and ethyl cellosolve. and alcohol ethers, aprotic polar solvents N-methylformamide, N,N-dimethylformamide, N-ethylformamide, N,N-diethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylacetamide , N,N-diethylacetamide, amide solvents such as hexamethylphosphoric amide, lactones such as γ-butyrolactone, N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, isobutylene carbonate, cyclic amide solvents, acetonitrile Nitrile solvents such as, oxide solvents such as dimethyl sulfoxide.

[0015] Specific examples of electrolytes that can be used alone or in combination in the electrolyte of organic acids, inorganic acids, or salts thereof include the following: organic acids formic acid, acetic acid, propionic acid, Aliphatic monocarboxylic acids such as enanthic acid, malonic acid, succinic acid, glutaric acid, adipic acid, methylmalonic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, maleic acid, citraconic acid, and itacone Aliphatic dicarboxylic acids such as benzoic acid, phthalic acid, salicylic acid, toluic acid, aromatic carboxylic acids such as pyromellitic acid, inorganic acids such as boric acid, phosphoric acid, silicic acid, HBF4, HPF6, ammonium ammonium (NH4+), monoalkylammoniums such as methylammonium, ethylammonium, and propylammonium; dialkylammoniums such as dimethylammonium, diethylammonium, ethylmethylammonium, and dibutylammonium; trialkylammoniums such as trimethylammonium, triethylammonium, and tributylammonium; Quaternary ammoniums such as ammonium, tetramethylammonium, triethylmethylammonium, tributylammonium, tetraethylammonium, and N,N-dimethylpyrrolidinium, as well as other phosphoniums and arsoniums can also be used.

The organic polar solvent of the electrolytic solution for an electrolytic capacitor according to the present invention can be the above-mentioned protic polar solvent or aprotic polar solvent alone or any mixed solvent, and the amount of the organic polar solvent in the electrolytic solution for an electrolytic capacitor according to the present invention is By mixing water in an amount of about 0.1 to 10 parts by weight, if necessary, it is possible to further improve the reduction in electrical conductivity and the chemical formation property (oxidation film forming property). It is preferable that 1.0 to 40 parts by weight of an organic or inorganic acid or a salt thereof to be used as a solute be dissolved in such a solvent system.

Preferably, 1.0 to 10 parts by weight, more preferably 1.0 to 5.0 parts by weight of the above-mentioned hydroxyethyl alkylated polyvinyl alcohol is added to the electrolytic solution consisting of such a solute-solvent system. As a result, an electrolytic solution for an electrolytic capacitor can be obtained that can improve the withstand voltage characteristics while maintaining the electrical conductivity.

[0018]

[Operation] How does hydroxyethyl alkylated polyvinyl alcohol, which is a unique additive added to the electrolytic solution for electrolytic capacitors disclosed in the present invention, act in the electrolytic solution for electrolytic capacitors?The mechanism of its action itself is unclear. It's not clear. However, the electrolytic solution for an electrolytic capacitor according to the present invention does not contribute in some way to stabilizing the chemical steady state of the electrochemical reaction system consisting of the anode, cathode, aluminum oxide film dielectric, and electrolyte of the electrolytic capacitor. It is estimated that there are.

As described above, since an electrolytic capacitor is used while undergoing a chemical reaction, its characteristics largely depend on the properties of the electrolyte. It is important to maintain a steady state of the chemical reaction that occurs between the aluminum electrode, which has an oxide film on its surface, and the electrolyte, and to maintain the aluminum oxide film, which serves as a dielectric, in a good condition to stabilize performance.

In the present invention, it is presumed that by adding hydroxyethyl alkylated polyvinyl alcohol, which is a unique additive, the entire electrolytic capacitor, which is an electrochemical reaction system, is stabilized and provides good capacitor characteristics. Ru.

[0021]

According to the present invention, there is provided an electrolytic solution for electrolytic capacitors which has significantly improved dielectric strength characteristics while maintaining electrical conductivity by adding a specified derivative of polyvinyl alcohol.

[0022]

[Examples] The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to the following Examples.

In the following examples, hydroxyethyl alkylated polyvinyl alcohol used in the present invention includes:
Those shown by the following symbols having different contents of alkoxyl group, methoxyl group, ethoxyl group and hydroxypropoxyl group were used: A: Alkoxyl group, methoxyl group content 5-10% Hydroxypropoxyl group content 60-65 % viscosity (20
CPS at °C) 15.5B: Alkoxyl group, ethoxyl group content 15-20% Hydroxypropoxyl group content 75-80% Viscosity (CPS at 20 °C)
7.5C: Alkoxyl group, methoxyl group content 20~
25% Hydroxypropoxyl group content 60-65% Viscosity (CPS at 20°C) 25.0 Note that the viscosity is 2
% aqueous solution. A predetermined amount of these hydroxyethyl alkylated polyvinyl alcohols was added to a predetermined solvent and solute to prepare an electrolytic solution for an electrolytic capacitor. The electrolytic capacitor was manufactured by a conventional method.

The electrical conductivity and withstand voltage after addition of the hydroxyethyl alkylated polyvinyl alcohol according to the present invention (Examples 1 to 4) and the electrical conductivity and withstand voltage before addition (Comparative Examples 1 to 4) are shown below. The withstand voltage is 315V, 22μF capacitor element is impregnated,
Measured at mA.

Example 1 and Comparative Example 1 Electrolyte composition (Figures in parentheses are parts by weight. Solvent: Ethylene glycol (100) Solute: Ammonium benzoate (15), Benzoic acid (3), Boric acid (2) Additive: A (1.5) The measurement results of conductivity and withstand voltage were as follows. The voltage resistance of Example 1 was increased by 20% compared to Comparative Example 1.

Example 2 and Comparative Example 2 Electrolyte composition (Figures in parentheses are parts by weight. Solvent: Ethylene glycol (100), water (3) Solute: Monoammonium azelaate (10), boric acid (2) Additive: B (2) The measurement results of electrical conductivity and withstand voltage were as follows. The voltage resistance of Example 2 increased by 27% compared to Comparative Example 2.

Example 3 and Comparative Example 3 Electrolyte composition () Parts by weight Solvent: γ-Butyrolactone (60), Methyl Cellosolve (15), Ethylene Glycol (10) Solute:
Monotetramethylammonium phthalate (15), boric acid (2) Additive: B (2) The measurement results of electrical conductivity and withstand voltage were as follows. The voltage resistance of Example 3 increased by 13% compared to Comparative Example 3.

Example 4 and Comparative Example 4 Electrolyte composition (Figures in parentheses indicate parts by weight of solvent: γ-butyrolactone (60), methylcellosolve (10), ethylene glycol (15) Solute:
Tetraethylammonium benzoate (15), boric acid (
2) Mannitol (2) Additive: C (1.5) The measurement results of electrical conductivity and withstand voltage were as follows. The voltage resistance of Example 4 increased by 42% compared to Comparative Example 4.

From the above results, according to the present invention, by adding a specified derivative of polyvinyl alcohol,
It can be seen that an electrolytic solution for electrolytic capacitors can be obtained which has significantly improved voltage resistance characteristics while maintaining electrical conductivity.

Claims (1)

[Claims] 1. An electrolyte for electrolytic capacitors, characterized in that hydroxyethyl alkylated polyvinyl alcohol is added to an electrolytic solution for electrolytic capacitors, the main solvent being an organic polar solvent and the solute being an organic acid or an inorganic acid or a salt thereof. liquid.