JPH0419690B2 - - 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. [Prior art] 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. In addition, the sealing rubber used to seal the electrolyte-impregnated capacitor element inside the outer case is made of various types such as natural rubber (NR), styrene butadiene rubber (SBR), butyl rubber, and ethylene propylene rubber (EPDM). Natural or synthetic rubber is used. These rubbers are blended with various substances for vulcanization, acceleration of vulcanization, and improvement of rubber physical properties. Among these compounding agents, metal oxides such as red lead oxide and zinc oxide come into contact with the electrolyte inside the electrolytic capacitor, but they do not interact with the solvent of the electrolyte. Due to the combination of It may cause short circuit or characteristic deterioration. [Problems to be Solved by the Invention] In this invention, zinc ions or lead ions extracted into the electrolyte are reduced when they come into contact with the aluminum of the electrode, and are deposited on the surface of the electrode or in the fibers of the separator as metallic zinc or metallic lead. Deposition on the internal surface of the sealing rubber may cause an increase in leakage current,
Suppressing the causes of short circuit accidents,
The purpose is to obtain an electrolytic capacitor with excellent electrical characteristics and high reliability. [Means for Solving the Problems] The present invention is made by sealing a capacitor element impregnated with an electrolyte using a rubber exterior member containing zinc oxide or lead oxide for all or part of the exterior. In the electrolytic capacitor, the electrolytic solution is dissolved in a solvent mainly composed of ethylene glycol with a carboxylic acid or a salt thereof as a main solute,
It is characterized by the use of an electrolytic solution containing an aromatic nitro compound. 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);
45049) and one aimed at preventing corrosion caused by halogen-based cleaning agents (Japanese Patent Application Laid-Open No. 60-7119). However, none of these conventional techniques focuses on the metal precipitation phenomenon that occurs in the combination of the sealing rubber and the electrolytic solution of a specific composition and attempts to prevent this precipitation phenomenon. The inventor discovered that metallic zinc and metallic lead are produced by combining a sealing rubber containing zinc oxide or lead oxide with an electrolytic solution in which carboxylic acid or its salt is dissolved as a main solute in ethylene glycol as a main solvent. It has also been discovered that adding an aromatic nitro compound to the electrolytic solution is effective in preventing zinc oxide or lead oxide from precipitating as metal. [Operation] When the sealing rubber comes into contact with the electrolyte, various compounding materials added to the rubber are extracted by the solvent of the electrolyte. When the zinc oxide or lead oxide contained in the sealing rubber comes into contact with the electrolyte, it is extracted into the electrolyte, reacts with the aluminum electrode, and is reduced (conversely, aluminum is oxidized).
As a result, zinc and lead are precipitated. This reaction proceeds according to the formula M ⁿ⁺ +n/3Al→M+n/3Al ³⁺ ↓ (actually Al ₂ O ₃ ), and zinc or lead (M) is precipitated. However ^, when ^an aromatic nitro compound is added as in this invention, the _precipitated zinc or _lead ( _M ) becomes Phenyl group M is lead, zinc M ⁿ⁺ is redissolved and exists in the state of metal ions due to the reaction of lead ions and zinc ions, and does not exhibit electrical conductivity, resulting in short circuit accidents and increased leakage current. It is thought that it acts to prevent Here, the aromatic nitro compounds added to the basic electrolyte include nitrobenzoic acid, nitrophenol, dinitrophenol, trinitrophenol, 3-nitrophthalic acid, 4-nitrophthalic acid,
An example is picric acid. Further, the basic electrolytic solution used in the present invention may be a solvent consisting of ethylene glycol alone or a mixed solvent consisting mainly of ethylene glycol and other solvents. Furthermore, examples of the solute carboxylic acid include aliphatic monocarboxylic acids, aromatic monocarboxylic acids, aliphatic dicarboxylic acids, aromatic dicarboxylic acids, aliphatic oxycarboxylic acids, and aromatic oxycarboxylic acids. Examples of the salts include ammonium salts, primary amine salts, secondary amine salts, tertiary amine salts, and quaternary ammonium salts of these carboxylic acids. These solutes may be used alone or in combination of two or more. [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 carboxylic acid or its salt in ethylene glycol and adding an aromatic nitro compound.
The composition of this electrolyte is shown below. Note that the composition ratio is in parts by weight. Electrolyte example 1 Ethylene glycol 90 Ammonium maleate 10 p-Nitrobenzoic acid 0.5 Electrolyte example 2 Ethylene glycol 90 Ammonium benzoate 10 Dinitrophenol 0.5 Electrolyte example 3 Ethylene glycol 90 Ammonium 1,6-decanedicarboxylate 10 p-Nitro Phenol 0.5 Electrolyte example 4 Ethylene glycol 90 Monoethanolamine formate 10 Nitrophthalic acid 0.5 Electrolyte example 5 Ethylene glycol 90 Diethylamine salicylate 10 Picric acid 0.5 And the composition of these electrolyte examples excluding aromatic nitro compounds is as follows. A comparative example was prepared corresponding to the invention example. On the other hand, sealing rubbers were also vulcanized in various rubber batches containing zinc oxide or lead oxide, respectively, as shown below, to create sealing bodies for electrolytic capacitors. The blending ratio (parts by weight) is shown below. (Formulation 1) Natural rubber 100 HAF carbon black 50 Zinc white 5 Stearic acid 3 Antioxidant D 1 Sulfur 2.5 Accelerator DM 0.7 (Formulation 2) SBR rubber 100 HAF carbon black 50 Zinc white 3 Stearic acid 2 Antioxidant D 1 Sulfur Yellow 2 Accelerator CZ 1 (Formulation 3) Natural rubber 60 SBR rubber 40 HAF carbon black 50 Zinc white 5 Stearic acid 1 Vulcanization accelerator CBS 0.7 Sulfur Yellow 2.3 Antioxidant D 1 Process oil 3.8 (Formulation 4) Butyl rubber 100 HAF carbon Black 30 Calcined clay 90 Stearic acid 1 p-quinone dioxime 2 Red lead 7.5 Dibenzothiazyl disulfide 4 (Formulation 5) EDPM rubber 100 EPC Black 10 White text 25 Dixie clay 100 Paraffin 5 Zinc white 5 DCP 2.7 Sulfur 0.32 An aluminum electrolytic capacitor with a rated voltage of 10 V and a capacitance of 100 μF was created by combining each of these electrolytes and sealing rubbers. Next, we applied the rated voltage (10V) to each of these 10 electrolytic capacitors and conducted a life test at a high temperature of 110°C. After 1000 hours, the sample electrolytic capacitor was disassembled and the inner surface of the sealing rubber were observed using a microscope to check for the presence or absence of metal precipitation. The results are shown in Table 1 (examples of the present invention) and Table 2 (conventional examples) below.

【table】

〔Effect of the invention〕

As described above, according to the present invention, zinc oxide or lead oxide contained in the sealing rubber of an electrolytic capacitor is extracted by the electrolytic solution and precipitated as zinc or lead, resulting in an increase in leakage current and short circuit accidents. This makes it possible to prevent the occurrence of the electrolytic capacitor, improve the reliability of the electrolytic capacitor, and maintain stable characteristics for 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 a rubber exterior member containing zinc oxide or lead oxide in all or a part of the exterior, the electrolyte mainly contains ethylene glycol. An electrolytic capacitor characterized by using an electrolytic solution in which a carboxylic acid or a salt thereof is dissolved as a main solute in a solvent, and an aromatic nitro compound is added thereto.