JPH0419689B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] This invention relates to the improvement of electrolytic capacitors, and in particular to the development of highly reliable electrolytic capacitors that can suppress inconveniences such as deterioration of electrical characteristics and short circuit accidents, and maintain excellent characteristics over a long period of time. Concerning capacitors. [Background of the Invention] Electrolytic capacitors use an insulating film-forming metal (also called valve metal) such as aluminum for the anode electrode, and the surface of this electrode metal is anodized, etc.
A capacitor element with an insulating oxide film layer as a dielectric material formed and facing a cathode electrode for current collection through a separator is impregnated with an electrolyte solution and is housed in an exterior case. The exterior case opening is sealed with an elastic member such as. The cathode electrode of an electrolytic capacitor exists simply to collect current, and functions as a true cathode when the electrolytic solution impregnated into the capacitor element comes into contact with the insulating oxide film that is the dielectric. The electrolytic solution also has a so-called chemical conversion action that repairs the oxide film by reacting with the deteriorated or defective portions of the insulating oxide film. The electrolytic capacitor element impregnated with the electrolytic solution is maintained sealed from the outside by the exterior member. The exterior has a structure in which the capacitor element is usually housed in a metal exterior case, and the opening of the exterior case is sealed with a sealant. Various natural or synthetic rubbers are usually used for the sealing body, but these various rubber materials are
Various compounds are usually blended for vulcanization and to improve various properties. This sealing rubber comes into contact with the electrolyte inside the electrolytic capacitor, but depending on the combination of the solvent of the electrolyte and the sealing member, various compounds blended in the sealing member may be mixed into the solvent. extracted,
It may react with solutes in the electrode or electrolyte, causing corrosion or property deterioration. [Prior art] In recent years, electrolytic solutions with high electrical conductivity have been developed, and among these electrolytic solutions, an electrolytic solution in which a tetraalkylammonium salt is dissolved as a solute in an aprotic solvent exhibits high electrical conductivity. Since then, it has been developed as an electrolyte for low-loss, low-impedance electrolytic capacitors (for example, Japanese Patent Application No. 60-237628). In addition, sealing rubbers are required to have excellent weather resistance, heat aging resistance, chemical resistance, and electrical properties in order to maintain stable properties for long periods of time at high temperatures. Butyl rubber is a synthetic rubber with a low degree of unsaturation made by copolymerizing isobutylene and a small amount of isoprene in a solvent such as methyl chloride at low temperatures.It satisfies the above conditions and has recently been used as a sealing rubber for high-performance electrolytic capacitors. It is used. Butyl rubber, which is used as the sealing rubber for electrolytic capacitors, is mainly subjected to quinoid vulcanization, which has excellent heat resistance. In this quinoid vulcanization, lead oxide, red lead, is added as a vulcanization accelerating aid. . Lead oxides such as lead red do not directly affect the characteristics of electrolytic capacitors, but when combined with an electrolyte solution in which a tetraalkylammonium salt is dissolved in the above-mentioned aprotic solvent and placed at high temperatures, the electrolyte It was discovered that the lead oxide extracted from the reactor reacts with the aluminum of the electrode, depositing metallic lead on the surface of the electrode, separator, and sealing rubber. When current flows through this metal lead, it causes an increase in leakage current and a short circuit accident. [Problems to be solved by the invention] This invention prevents short-circuit accidents that occur when an electrolyte in which a tetraalkylammonium salt is dissolved in an aprotic solvent and a sealing rubber containing lead oxide are used as a sealing material. The purpose of the present invention is to provide an electrolytic capacitor with excellent electrical characteristics and high reliability. [Means for Solving the Problems] The present invention provides an electrolytic capacitor in which butyl rubber containing lead oxide is used for all or a part of the exterior, in which the electrolyte is contained in a solvent mainly composed of an aprotic solvent. The method is characterized by using an electrolytic solution in which a tetraalkylammonium salt is dissolved as a main solute and an aromatic nitro compound is added. Nitro compounds are added to electrolyte solutions, for example, for the purpose of improving low-temperature characteristics (Japanese Patent Publication No. 54-93443), and for suppressing internal hydrogen gas generation (Japanese Patent Publication No. 1983-1989). 14300, Japanese Patent Publication No. 51-7296, Japanese Patent Publication No. 53-42110);
No. 45049), and those aimed at preventing corrosion caused by halogen-based cleaning agents (Japanese Patent Application Laid-Open No. 60-7119) are known. However, all of these conventional techniques were directed to electrolytes whose main solvent was a proton solvent such as ethylene glycol. The inventor focused on the precipitation phenomenon of metallic lead that occurs in the combination of a sealing rubber containing lead oxide and an electrolytic solution mainly composed of an aprotic solvent and containing a tetraalkylammonium salt as the main solute.
In order to prevent the precipitation of metallic lead, we have found that adding an aromatic nitro compound to the electrolytic solution is effective in preventing the precipitation of lead oxide as metallic lead. [Function] The aprotic solvent has a strong dissolving power and acts on various rubbers that come into contact with the electrolyte to extract various compounds added to the rubber. The lead compounds contained in the sealing rubber are extracted into the electrolyte when it comes into contact with the electrolyte.
Metallic lead is precipitated by causing a reaction with the aluminum electrode and reducing the lead oxide (conversely, oxidizing the aluminum). This reaction proceeds according to the formula: Pb ²⁺ +2/3Al→Pb(M)+2/3Al ³⁺ ↓ (actually Al ₂ O ₃ ), and metallic lead is formed. However, when an aromatic nitro compound is added as in this invention, the precipitated metallic lead becomes 2Pb(M)+φ−NO ₂ 2H ⁺ → 2Pb ²⁺ +φ−NH ₂ ↓ (actually PbO) (however, φ (phenyl group), it is dissolved and exists in the state of lead ions, which do not exhibit electrical conductivity, and are thought to act to prevent short circuit accidents and increases in leakage current. Aromatic nitro compounds added to the basic electrolyte include nitrobenzoic acid (including isomers), nitrophenol (including isomers), dinitrophenol, trinitrophenol, 3-nitrophthalic acid, 4-nitrophthalic acid, picrin. Examples include acids. In this invention, examples of the aprotic solvent of the basic electrolyte used include N-methylformamide, N,
Acid amides such as N-dimethylformamide, N-ethylformamide, N,N-diethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylacetamide, and N,N-diethylacetamide. Lactones such as γ-butyrolactone and γ-valerolactone. Carbonates such as propylene carbonate and ethylene carbonate. Nitriles such as acetonitrile, propionitrile, and benzonitrile. Other examples include N-methyl-2-pyrrolidone and dimethyl sulfoxide. Examples of tetraalkylammonium salts of solutes include quaternary alkylammonium phenols such as tetraethylammonium phenolate and tetrabutylammonium phenolate. Quaternary alkylammonium aliphatic saturated monocarboxylic acids such as tetrabutylammonium formate, tetraethylammonium acetate, tetramethylammonium propinate, tetrabutylammonium butyrate. Quaternary alkylammonium 1,3 diketones such as tetramethylammonium acetyl cisetonate, tetraethylammonium benzoylacetonate, and tetrabutylammonium diphenylacetylacetonate. Quaternary alkylammonium unsaturated dicarboxylic acids such as tetraethylammonium maleate and tetrabutylammonium itaconate. Examples include quaternary alkylammonium of aliphatic dicarboxylic acids such as tetramethylammonium adipate and tetraethylammonium succinate. These solvents, solutes, and additives are not limited to those mentioned above. [Example] The present invention will be described below with reference to Examples. First, as basic electrolytes, five types of electrolytes were prepared by dissolving a tetraalkylammonium salt in an aprotic solvent and adding an aromatic nitro compound. The composition of this electrolyte is shown below. Note that the composition ratio is in parts by weight. Present invention example 1 N,N-dimethylformamide 90 Tetramethylammonium phenolate 10 p-nitrobenzoic acid 0.5 Present invention example 2 N-methylformamide 90 Tetrabutylammonium formate 10 m-nitrobenzoic acid 0.5 Present invention example 3 γ- Butyrolactone 90 Tetraethylammonium maleate 10 p-nitrophenol 0.5 Invention example 4 Propion carbonate 90 Tetrabutylammonium succinate 10 m-nitrophenol 0.5 Invention example 5 Acetonitrile 90 Tetrabutylammonium acetylacetonate 10 3-nitrophthalic acid 0.5 These electrolyzed Comparative Examples 1 to 5 were prepared by removing the nitro compound from the liquid, corresponding to Examples 1 to 5 of the present invention. On the other hand, for the sealing rubber, quinoid vulcanized butyl rubber was used. The composition of this butyl rubber is as follows. Blending ratio (polymerization part) Butyl rubber batch (Exxon Butyl 268) 100 Carbon HAF 30 Calcined clay 90 Stearic acid 1 p-quinone dioxime 2 Lead Red 7.5 Dibenzothiazyl disulfide 4 And using these electrolyte and sealing rubber , created an aluminum electrolytic capacitor with a rated voltage of 10V and a capacitance of 100μF. Next, 10 of each of these electrolytic capacitors were subjected to a life test at a high temperature of 110°C by applying the rated voltage. After 1000 hours, the sample electrolytic capacitor was disassembled and the inner surface of the sealing rubber was examined using a microscope. The presence or absence of lead precipitation was investigated. The results are shown in the table below.

〔Effect of the invention〕

As described above, according to the present invention, lead compounds contained in the sealing rubber of an electrolytic capacitor are extracted by the electrolytic solution and precipitated as metallic lead, thereby preventing an increase in leakage current and the occurrence of short circuit accidents. I can,
It is possible to improve the reliability of electrolytic capacitors and maintain stable characteristics over a long period of time.

Claims (1)

[Claims] 1. In an electrolytic capacitor formed by sealing a capacitor element impregnated with an electrolytic solution using butyl rubber containing lead oxide for all or part of the exterior, the electrolytic solution is placed in a solvent mainly consisting of an aprotic solvent. An electrolytic capacitor characterized by using an electrolytic solution in which a tetraalkylammonium salt is dissolved as a main solute and an aromatic nitro compound is added.