JPH0257329B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] This invention relates to improvement of electrolytic capacitors, and particularly to improvement of corrosion resistance properties of electrolytic capacitors. [Prior art] Electrolytic capacitors use a film-forming metal such as aluminum or tantalum as an anode, and an insulating oxide film that serves as a dielectric is formed on the surface of the anode by anodizing treatment, and the oxide film is used as a cathode. A capacitor element is formed by arranging metals of the same type or other metals and winding or layering them with a separator such as paper or porous plastic interposed between these electrodes. The drawing shows an example of the element structure of an aluminum electrolytic capacitor with a general winding structure.A strip-shaped aluminum anode foil 2 is etched on its surface to enlarge its surface, and an anode is placed on its upper surface. A dielectric oxide film layer is formed by the oxidation treatment. A strip-shaped aluminum cathode foil 3 is similarly arranged opposite to the anode foil 2, and a separator paper 4 slightly wider than the electrode foil is sandwiched between the anode foil 2 and the cathode foil 3. A capacitor element 1 is formed by winding it into a cylindrical shape. Note that the lead 5 is connected to the electrode foils 2 and 3 of the capacitor element 1.
It is attached to each electrode foil and pulled out from the winding end surface of the capacitor element 1 in order to make an electrical connection between the capacitor element 1 and the outside. Then, this capacitor element is impregnated with an electrolytic solution, provided with means for extending electrodes to the outside, and then covered with an outer case made of metal, resin, or the like, or with a means such as resin molding, thereby forming an electrolytic capacitor. In an electrolytic capacitor, the dielectric is an oxide film formed on the surface of a film-forming metal as an anode, and when the electrolyte comes into contact with this oxide film, it functions as a capacitor. In other words, the electrolyte functions as a true cathode. Furthermore, the electrolytic solution has the function of acting on the deteriorated portions of this oxide film and repairing the film. This means that an anodic oxidation reaction is always occurring locally at the contact surface between the oxide film and the electrolyte. However, when chlorine ions are present at the site of this anodic oxidation reaction, aluminum combines with chlorine to form aluminum chloride, which is further hydrolyzed to form aluminum hydroxide. The chlorine ions then act as if they were a catalyst, accelerating the corrosion of aluminum, causing an increase in leakage current, an increase in internal pressure, etc., and eventually breaking the internal leads, completely impairing the functionality of the electrolytic capacitor. . Electrolytic capacitors use a film-forming metal such as aluminum or tantalum as an anode, and an insulating oxide film that becomes a dielectric is formed on the surface of this anode by anodizing, and a similar or other material without an oxide film is used as a cathode. A capacitor element is formed by arranging metals facing each other and winding or stacking them in layers with a separator such as paper or porous plastic interposed between these electrodes. The drawing shows an example of the element structure of an aluminum electrolytic capacitor with a general winding structure.A strip-shaped aluminum anode foil 2 is etched on its surface to enlarge its surface, and an anode is placed on its upper surface. A dielectric oxide film layer is formed by the oxidation treatment. A strip-shaped aluminum cathode foil 3 is similarly arranged opposite to the anode foil 2, and a separator paper 4 slightly wider than the electrode foil is sandwiched between the anode foil 2 and the cathode foil 3. A capacitor element 1 is formed by winding it into a cylindrical shape. Note that the lead 5 is connected to the electrode foils 2 and 3 of the capacitor element 1.
It is attached to each electrode foil and pulled out from the winding end surface of the capacitor element 1 in order to make an electrical connection between the capacitor element 1 and the outside. Then, this capacitor element is impregnated with an electrolytic solution, provided with means for extending electrodes to the outside, and then covered with an outer case made of metal, resin, or the like, or with a means such as resin molding, thereby forming an electrolytic capacitor. In an electrolytic capacitor, the dielectric is an oxide film formed on the surface of a film-forming metal as an anode, and when the electrolyte comes into contact with this oxide film, it functions as a capacitor. In other words, the electrolyte functions as a true cathode. Furthermore, the electrolytic solution has the function of acting on the deteriorated portions of this oxide film and repairing the film. This means that an anodic oxidation reaction is always occurring locally at the contact surface between the oxide film and the electrolyte. However, when chlorine ions are present at the site of this anodic oxidation reaction, aluminum combines with chlorine to form aluminum chloride, which is further hydrolyzed to form aluminum hydroxide. The chlorine ions then act as if they were a catalyst, accelerating the corrosion of aluminum, causing an increase in leakage current, an increase in internal pressure, etc., and eventually breaking the internal leads, completely impairing the functionality of the electrolytic capacitor. . Therefore, the presence of chlorine must be eliminated as much as possible inside the electrolytic capacitor. However, since the electrode foil is etched with chlorine in hydrochloric acid or an aqueous sodium chloride solution, it is extremely difficult to completely remove chlorine. There is also a possibility that chlorine ions may enter during the manufacturing process. Furthermore, electrolytic capacitors are attached to printed wiring boards by soldering, but since a halogen-based cleaning agent such as trichloroethane is used to clean the board after soldering, the remaining cleaning agent may be left behind on the sealing part of the electrolytic capacitor or on the lead drawer. It can also penetrate into the interior and cause corrosion. Therefore, in order to obtain a highly reliable electrolytic capacitor, a means for suppressing corrosion is required. [Problems to be Solved by the Invention] Against this conventional technical background, the purpose of the present invention is to prevent corrosion caused by chlorine remaining inside or entering from the outside, and to obtain a highly reliable electrolytic capacitor. It is in. [Means for Solving the Problems] The present invention provides a capacitor in which a separator is interposed between an anode electrode and a cathode electrode and impregnated with an electrolytic solution, in which the capacitor element contains a mixture of bismuthate and antimonic acid. It is characterized by the fact that [Function] Although the detailed reason is not clear, bismuth acid has an excellent ability to adsorb anions such as chlorine. Furthermore, antimonic acid is known to selectively adsorb cations, particularly alkali metal ions including sodium ions. Therefore, the inventor focused on the characteristics of these two compounds, and by making them exist in a mixture, both cations and anions can be removed from the chlorine present in the capacitor in the form of sodium chloride. The aim is to increase the efficiency of chloride ion capture by selectively adsorbing chloride ions. First, we will show an experimental example in which the ability of a mixture of bismuthate and antimonic acid to capture chloride ions was confirmed. In the experiment, a certain amount of chlorine ions were added to an electrolytic solution for electrolytic capacitors in which maleic acid and triethylamine were dissolved in N,N-dimethylformamide, and a mixture of bismuthate and antimonic acid was added thereto and left for a predetermined period of time. The subsequent change in chloride ion concentration was investigated. The experimental conditions were such that the chloride ion concentration of the electrolyte was
Add sodium chloride to 100ppm,
The bismuthate and antimonic acid shown in Table 1 were mixed in the mixture in the proportions shown in the table, and the remaining amount of chlorine ions was measured after the mixture was left at 60°C for 20 hours. Note that since both the mixed bismuthate and antimonic acid were insoluble in the electrolytic solution, stirring was performed every 2 hours.

【table】

〔Example〕

Next, we will present the results of an investigation into corrosion suppression using actual electrolytic capacitors manufactured. The manufactured electrolytic capacitor is a normal electrolytic capacitor made by winding a band-shaped aluminum electrode with separator paper, and has a rated voltage of 63V, a capacitance of 10μF,
It has external dimensions of 10φ x 12.5mm. In an embodiment of the present invention, a slurry made by mixing equal amounts of bismuthate and antimonic acid and adding water is applied to the surface of a separator paper made of Manila fiber paper, and after drying. It was wound together with electrode foil to form a capacitor element. The electrolytic solution used was an N,N-dimethylformamide-maleic acid based electrolytic solution and had the following composition. N,N-dimethylformamide 84 wt% Maleic acid 9 wt% Triethylamine 7 wt% Sodium chloride was dissolved in this electrolyte and adjusted to a concentration of 100 ppm with chlorine ions.
After impregnating the capacitor element with this electrolytic solution, it was housed in an exterior case, and the opening was sealed with a sealing member to complete an electrolytic capacitor. A lifespan test was performed on this electrolytic capacitor by applying a voltage of 63V at 110°C, and the rate of corrosion was observed. As a comparative example, a capacitor element wound with ordinary separator paper not coated with a mixture of bismuthate and antimonic acid was impregnated with the same electrolyte and subjected to the same life test. The results are shown in Table 2.

〔Effect of the invention〕

As described above, according to the present invention, corrosion caused by chlorine in electrolytic capacitors is suppressed, thereby preventing fatal problems for electrolytic capacitors such as an increase in leakage current due to corrosion, disconnection of internal leads, and opening of valves in the sealing part. Accidents can be prevented from occurring, and an extremely reliable electrolytic capacitor can be obtained.

[Brief explanation of drawings]

The drawing is an explanatory diagram showing an electrolytic capacitor element having a wound structure. 1... Capacitor element, 2... Anode foil, 3...
Cathode foil, 4... separator paper, 5... lead.

Claims (1)

[Scope of Claims] 1. An electrolytic capacitor in which a separator is interposed between an anode electrode and a cathode electrode, and a capacitor element impregnated with an electrolyte is housed inside an outer case, wherein the capacitor element contains bismuthate and antimonic acid. An electrolytic capacitor characterized by containing a mixture of. 2. The electrolytic capacitor according to claim 1, wherein the mixture of bismuthate and antimonic acid is applied to an electrode or a separator of a capacitor element. 3. The electrolytic capacitor according to claim 1, wherein the mixture of bismuthate and antimonic acid is mixed in the electrolyte in the capacitor element.