JPS61156716A - Electrolytic capacitor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to improvements in electrolytic capacitors, and particularly to improvements in corrosion resistance properties of electrolytic capacitors.

[Conventional technology]

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 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 -a-like winding structure. A dielectric oxide film layer is formed by anodizing.

A strip-shaped aluminum cathode foil 3 is similarly arranged opposite to this anode foil 2, and between these anode foil 2 and cathode foil 3 there is a separator 4 that is slightly wider than the electrode foil.
is sandwiched and wound into a cylindrical shape to form a capacitor element l.
is formed. Note that the lead 5 is connected to the capacitor element 1.
It is attached to each electrode foil and drawn out from the winding end surface of the capacitor element 1 in order to electrically connect the electrode foil 2.3 with the outside.

Then, this capacitor element is impregnated with an electrolytic solution, provided with a means for drawing out the electrodes to the outside, and then covered with an outer case made of metal, resin, etc., or with means such as resin molding.
Becomes 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. In addition, chlorine ions act as if they were catalysts, accelerating the corrosion of aluminum, increasing leakage current, and
This starts with an increase in internal pressure, and eventually leads to a breakage of internal leads, which completely impairs 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. Furthermore, electrolytic capacitors are attached to printed wiring boards by soldering, but since this soldering uses halogen-based cleaning agents such as trichloroethane to clean the board afterward, residual cleaning agents may be left behind on the sealing parts of the electrolytic capacitors or on the leads. It may seep into the interior through the drawer and cause corrosion.

[Problem that the invention seeks to solve]

SUMMARY OF THE INVENTION The present invention aims to prevent corrosion caused by chlorine remaining inside or entering from the outside, and to provide a highly reliable electrolytic capacitor.

[Means for solving problems]

This invention is characterized in that a separator is interposed between an anode electrode and a cathode electrode, and a capacitor element impregnated with an electrolytic solution contains bismuth oxide.

[Effect]

Bismuth oxide, ie, bismuth oxide, or bismuth acid salt has an excellent ability to adsorb anions such as chlorine, although the detailed reason for this is not clear. This invention focuses on this and attempts to capture chlorine ions in the electrolyte by making bismuth oxide exist inside the capacitor element.

First, we will show an experimental example in which we confirmed the ability of bismuth oxide to capture chloride ions.

In the experiment, a certain amount of chlorine ions were added to an electrolytic solution for an electrolytic capacitor in which maleic acid and triethylamine were dissolved in N,N-dimethylformamide, and bismuth oxide was added thereto. The concentration change was investigated.

The experimental conditions were that the chlorine ion concentration of the electrolyte was 1100
Sodium chloride was added to the solution so as to give a ppm of sodium chloride, and the bismuth oxide shown in Table 1 was mixed therein, and the remaining amount of chlorine ions was measured after the mixture was left at 60° C. for 20 hours. In addition,
Since all of the mixed bismuth oxides were insoluble in the electrolytic solution, stirring was performed every 2 hours.

As can be seen from these experimental examples, the chlorine ion concentration of the electrolytic solution mixed with bismuth oxide, which was initially adjusted to 1100 pp, decreased to around 1/2 after a predetermined period of time, and the chlorine ions were oxidized by bismuth oxide. This indicates that it has been adsorbed to something.

〔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 in which a band-shaped aluminum electrode is wound together with separator paper, and has a rated voltage of 63 V, a capacitance of 1110 μF, and an external dimension of lO.
It has a diameter of 12.5 m. In an example of the present invention, bismuth oxide made into a slurry by adding water was applied to the surface of a separator paper made of manila fiber paper, dried, and then wound together with an 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% 1t% Maleic acid 9wt% Triethylamine 7wt% Sodium chloride was dissolved in this electrolytic solution and adjusted to a concentration of 1100 pp 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 life test was conducted on this electrolytic capacitor by applying a voltage of 63 V at 110° C., and the rate of occurrence of corrosion was observed. As a comparative example, a capacitor element wound with ordinary separator paper not coated with bismuth oxide was impregnated with the same electrolyte and subjected to the same life test. The results are shown in Table 2.

Table 2 As is clear from the results, in all of the examples in which the bismuth oxide of the present invention was applied to the separator paper, the occurrence of corrosion was extremely low compared to the cases in which no application was made, and the bismuth oxide corroded. It can be seen that it is effective in suppressing it.

In addition to the bismuth oxide mentioned in this example, other forms of bismuth oxide or salts of bismuth acid can also be used to similarly adsorb chlorine ions and have the effect of suppressing corrosion of the electrolytic capacitor.

In addition, in this example, bismuth oxide was made into a slurry and applied to the separator paper so that bismuth oxide was present in the capacitor element, but the means for containing the bismuth oxide is not limited to this. Alternatively, the coating may be applied to the electrode foil side.

Alternatively, instead of making it into a slurry, a powdered material may be wound with NK cloth between the electrode foil and the separator paper at the same time as winding the capacitor element. Further, although this bismuth oxide is insoluble in the electrolytic solution, it may be dispersed in the electrolytic solution and impregnated into the capacitor element.

(Effects of the Invention) As described above, according to the present invention, corrosion of electrolytic capacitors due to chlorine is suppressed, which can be fatal to electrolytic capacitors such as increased leakage current, disconnection of internal leads, and opening of valves due to corrosion. This makes it possible to prevent the occurrence of accidents, and to obtain an electrolytic capacitor with extremely high reliability.

[Brief explanation of drawings]

The drawing shows an electrolytic capacitor element with a wound structure.
It is an explanatory diagram. DESCRIPTION OF SYMBOLS 1... Capacitor element, 2... Anode foil, 3... Cathode foil, 4... Separator paper, 5... Lead.

Claims (3)

[Claims] (1) A separator is interposed between the anode electrode and the cathode electrode,
1. An electrolytic capacitor comprising a capacitor element impregnated with an electrolytic solution housed inside an exterior case, characterized in that the capacitor element contains bismuth oxide. (2) The electrolytic capacitor according to claim (1), wherein the bismuth oxide is applied to an electrode or a separator of a capacitor element. (3) The electrolytic capacitor according to claim (1), wherein the bismuth oxide is mixed with an electrolyte in the capacitor element.