JPH0240208B2 - DENKAIKONDENSA - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present 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 opposite 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 the structure of a general electrolytic capacitor, in which a cylindrical capacitor element 1 is formed by layering aluminum band-shaped electrode foils for both the anode and cathode and a separator, and winding the electrode foils for the anode and cathode. It is housed in a bottom cylindrical outer case 2, and the opening of the outer case 2 is closed with a disc-shaped elastic sealing body 3 made of an elastic material such as various synthetic rubbers or elastic plastics, and the opening end of the outer case 2 is wrapped around the opening. It is tightened and sealed. Note that an internal lead 4 protrudes from the upper end of the capacitor element 1 and is electrically connected to both the anode and cathode electrodes. The internal leads 4 are inserted into through holes 5 provided in the elastic sealing body 33, and external leads 6 for electrical connection with the outside are connected to their tips. In addition to this structure, although not shown, a sealing body having a structure in which a sheet of an elastic member is bonded to a hard insulating plate-like member in place of the elastic sealing body 3 is also generally used. In this electrolytic capacitor, the dielectric is an oxide film formed on the surface of the film-forming metal as the anode, and when the electrolyte comes into contact with this oxide film, it acts as a true cathode and has the function of a capacitor. . 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 causing the electrolytic capacitor to lose its functionality due to internal lead breakage, etc. . Therefore, the presence of chlorine must be eliminated as much as possible inside the electrolytic capacitor. However, many additives such as cross-linking agents, cross-linking accelerators, and anti-aging agents are added to elastic sealing bodies made of various synthetic rubbers in order to maintain and improve the sealing function.
The impurities in this may contain chlorine, which may cause corrosion. Conventionally, as a countermeasure to this problem, additives such as those mentioned above are not included. It has been proposed to use urethane rubber, polyoffine-based thermoplastic elastomers, and the like for the sealing bodies of electrolytic capacitors. However,
These sealing bodies are not practical in terms of heat resistance, cost, etc. In addition, electrolytic capacitors are attached to printed circuit boards by soldering, and halogen-based cleaning agents such as trichloroethane are used to clean the board after soldering, so residual cleaning agents may be left behind on the sealing body of the electrolytic capacitor. It may also seep into the interior through the lead extraction area and cause corrosion. As a countermeasure to this, fluororubber, which has strong resistance to halogen-based cleaning agents, is dispersed in the rubber of the sealing body.
Although there is a method of increasing the distance through which the cleaning agent actually reaches the inside of the electrolytic capacitor, it is not practical because it is not effective and there are problems in terms of cost. In addition, coating resin on the outer surface of the sealing body has also been practiced, but this method has drawbacks such as complicating the manufacturing process and increasing the overall length of the product. As described above, electrolytic capacitors are extremely susceptible to chlorine, so in order to obtain highly reliable electrolytic capacitors, means for suppressing corrosion are required. [Problems to be Solved by the Invention] Against this conventional technical background, the present invention provides a highly reliable electrolytic capacitor that prevents corrosion caused by chlorine contained in the sealing body or chlorine that enters from the outside. It's about getting. [Means for Solving the Problems] The present invention involves interposing a separator between an anode electrode and a cathode electrode, storing a capacitor element impregnated with an electrolyte inside an outer case, and sealing the opening of the outer case with a sealing member. The sealed electrolytic capacitor is characterized in that the sealing member contains bismuthate and antimonic acid. [Function] Bismuth acid has an excellent ability to adsorb anions such as chlorine, although the detailed reason is not clear. On the other hand, 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,
For example, by selectively adsorbing both cations and anions of chlorine present in the sealing body in the form of aluminum chloride, the efficiency of trapping chlorine ions is increased. Furthermore, it is presumed that chloride ions are captured in the form of bismuth acid, but bismuth acid is not obtained as a simple substance, but only in the form of a salt with an alkali metal. Therefore, it is considered that by coexistence with antimonic acid, the cations of bismuthate are captured by antimonic acid, and the capture of chloride ions in the form of bismuth acid is promoted. [Example] Next, we will show the results of an investigation into inhibition of corrosion by manufacturing an actual electrolytic capacitor. In the experiment, a certain amount of chlorine ions were added to the elastic sealant material of an electrolytic capacitor, and in the case of the present invention, the above-mentioned corrosion inhibiting substance was also added to produce an elastic sealant, which was then attached to the electrolytic capacitor. A lifespan test was conducted to determine the rate of corrosion occurrence. The fabricated electrolytic capacitor has the usual structure shown in Figure 1, in which a band-shaped aluminum electrode is wound together with separator paper, impregnated with electrolyte, and stored in an external case.The rated voltage is 400V, the capacitance is 4.7μF,
External dimensions are 10φ x 30mm. The elastic sealant was made of ethylene propylene terpolymer (EPT), and sodium chloride was added at the material stage to adjust the chloride ion concentration to 300 ppm. In the comparative examples shown in the table below, a product vulcanized and molded with this composition was used as an elastic sealant.
In addition, in this invention example, bismuthate and antimonic acid as shown in the table are added to the EPT raw material.
Each was further added at a ratio of 1.5 wt%, and the product was vulcanized and used as an elastic sealant. A lifespan test was then performed on this electrolytic capacitor by applying a voltage of 400V at 110°C, and the rate of corrosion was observed. The results are shown in the table below.

〔Effect of the invention〕

As described above, according to the present invention, chlorine ions contained as impurities in the sealing member of an electrolytic capacitor or chlorine ions contained in substrate cleaning agents and the like and entering the electrolytic capacitor from the outside are removed from bismuth acid. Since it is captured by salt and antimonic acid, corrosion of electrolytic capacitors caused by chlorine can be suppressed. As a result, it is possible to prevent fatal accidents such as an increase in leakage current of the electrolytic capacitor, breakage of internal leads, and opening of the sealing part, and it is possible to obtain an extremely reliable electrolytic capacitor.

[Brief explanation of drawings]

The drawing is a cross-sectional view showing the structure of a general electrolytic capacitor. 1...Capacitor element, 2...Exterior case, 3
...Elastic sealing body, 4...Internal lead, 5...Through hole, 6...External lead.

Claims (1)

[Claims] 1. An electrolytic capacitor in which a separator is interposed between an anode electrode and a cathode electrode, a capacitor element impregnated with an electrolyte is housed inside an exterior case, and an opening of the exterior case is sealed with a sealing member, wherein the sealing member is made of bismuth. An electrolytic capacitor characterized by containing an acid salt and antimonic acid.