JPH0658870B2 - Aluminum electrolytic capacitor - Google Patents

Description

TECHNICAL FIELD The present invention relates to an aluminum electrolytic capacitor having improved leakage current deterioration characteristics.

(Prior Art) Generally, in an aluminum electrolytic capacitor, an aluminum tab for drawing is joined to an anode foil having an anodic oxide film and a cathode foil having no anodic oxide film, and then the capacitor element is wound by interposing a separator therebetween. Is formed, and the capacitor element is impregnated with an electrolytic solution and hermetically sealed in a case. This electrolytic capacitor is subjected to a voltage treatment called aging in order to reduce the leakage current.

Such electrolytic capacitors are used in various electronic devices such as communication devices and measuring devices. The performance of these electronic devices is greatly related to the electrical characteristics of the electrolytic capacitors, and especially the long-term deterioration of leakage current is small. Electrolytic capacitors with long life and high reliability are required.

However, when an aluminum electrolytic capacitor is left unloaded at high temperature for a long time, the leakage current increases, and in some cases, the aluminum oxide film may be remarkably destroyed and the insulating property may deteriorate. It is considered that this is because the electrolytic solution enclosed in the case reacts with the oxide film to deteriorate the oxide film.

(Problems to be Solved by the Invention) As a method for preventing such deterioration of an oxide film, 10
Regarding a low voltage capacitor of 0 V or less, JP-A-54-1
Many methods have been proposed as shown in Japanese Patent No. 36651, Japanese Patent Laid-Open No. 62-145808 and the like. In these methods, various additives are added to the electrolytic solution, and some effects have been confirmed. For medium- and high-voltage capacitors having a voltage of 100 V or more, JP-A-62-6615 and JP-A-63-7613 have been proposed as a method for adding an additive to an electrolytic solution, but the effect is still insufficient. Further, even if the water content in the electrolytic solution is reduced, the deterioration of the oxide film can be suppressed, but it is difficult to reduce the water content to a certain amount or less due to restrictions on other properties such as chemical conversion and specific resistance.

Also, the cause of the increase in leakage current is mainly the deterioration of the anode foil, but even if the deterioration of the oxide film is suppressed by the additive contained in the electrolytic solution, the additive is always concentrated near the anode foil. However, the amount of additive had to be increased.

The present invention has been made in view of the above problems, and an object thereof is to efficiently suppress deterioration of the anode foil.

(Means for Solving the Problem) In the present invention according to the above object, a cathode foil and an anode foil on which an anodized film is formed are wound with a separator interposed, and a capacitor element impregnated with an electrolytic solution is used as a case. In a sealed aluminum electrolytic capacitor, on at least the surface of the anode foil on which the anodized film is formed,
It is characterized in that one or more phosphorus compounds are attached to pyrophosphoric acid or salts thereof.

In the present invention, the cathode foil and the anode foil on which the anodized film is formed are wound with a separator interposed, and in an aluminum electrolytic capacitor in which a capacitor element impregnated with an electrolytic solution is sealed in a case, the anode foil of It is characterized in that an adduct compound containing phosphorus such as urea phosphate is attached to at least the surface on which the anodized film is formed.

(Function) The deterioration of the aluminum oxide film is generally considered to be associated with the hydration reaction. However, since the amount of water in the electrolytic solution is about several% of the total amount of the electrolytic solution, it is impossible to attribute the deterioration of the oxide film to a simple hydration reaction. As a result of research, the inventors have found that an adduct compound containing pyrophosphoric acid or a salt thereof or phosphorus such as urea phosphate suppresses deterioration of an oxide film. The effect of these phosphorus compounds is increased by positioning them as close as possible to the oxide film. Therefore, in the present invention, it is attached to the anode foil. On the other hand, it was found that when the phosphorus compound is adhered only on the cathode foil, not only the leakage current suppressing effect but also the opposite effect is produced. It is believed that this is because the phosphorus compound is separated from the anode foil and that any product resulting from the reaction of the phosphorus compound with the cathode foil adversely affects the anode foil.

Further, since the phosphorus compound has an action of promoting the formation of an oxide film, the leakage current during aging is reduced quickly,
The aging time can also be shortened.

(Examples) Hereinafter, the present invention will be described in detail based on Examples.

In this embodiment, the electrolytic capacitor is formed by forming an anode foil having an anodized film and an aluminum tab on a cathode foil having no anodized film formed thereon, and then winding with a separator interposed therebetween to form a capacitor element, The capacitor element is formed by impregnating it with an electrolytic solution and sealing it in a case. Before being wound on the capacitor element, a phosphorus compound is deposited on the anodized film of the anode foil as described later.

Solvents for the electrolytic solution include alcohols such as ethylene glycol and diethylene glycol, glycol ethers such as ethylene glycol monomethyl ether, esters such as ethylene glycol monomethyl acetate, N,
Although polar organic solvents such as acid amides such as N'-dimethylformamide, nitriles such as acetonitrile, or cyclic esters such as γ-butyrolactone can be used, it is particularly preferable to use ethylene glycol or γ-butyrolactone as a main solvent. It is suitable.

As the solute, at least one of carboxylic acids such as succinic acid, adipic acid and azelaic acid or a salt thereof, or aromatic carboxylic acids such as benzoic acid, salicylic acid and phthalic acid or a salt thereof is dissolved.

Table 1 shows the composition of the treatment liquid used in the treatment for adhering the phosphorus compound to the anode foil according to the present invention. First, the 250 WV anode foil having the oxide film formed thereon was immersed in the treatment liquid shown in Table 1 at 30 ° C. for 60 seconds and then dried. next,
This anode foil was cut into a predetermined width, a lead wire was connected, and then the anode foil and a separator were wound together to produce a capacitor element. This capacitor element was impregnated with a driving electrolytic solution and sealed in an aluminum case with a rubber sealing body to manufacture an electrolytic capacitor rated at 250 WV and 33 μF.

As Conventional Example 1, a capacitor was manufactured using an anode foil that was not treated as in the example.

In addition, as a comparative example, a capacitor was manufactured using a cathode foil, not a cathode foil, to which a phosphorus compound was attached.
The composition of the cathode foil treatment liquid is also shown in Table 1.

For each 20 types of electrolytic capacitors produced, 1
Changes in leakage current when a high temperature no-load test was performed at 05 ° C. for 1000 hours are shown in FIGS.

FIG. 1 is a comparison of the leakage currents of the non-treated conventional example and Examples 1 to 3 treated with ammonium pyrophosphate. Example 1
No. 3 had good characteristics with less increase in leakage current than the conventional example. Further, the higher the concentration of the treatment liquid, the smaller the change in leakage current.

FIG. 2 shows changes in leakage current between a conventional example which is not treated and Examples 4 to 6 which are treated with urea phosphate. Similar to the first to third embodiments, the fourth to sixth embodiments have a smaller increase in leakage current than the conventional example and have good characteristics. Further, as in Examples 1 to 3, the higher the concentration of the treatment liquid, the smaller the change in leakage current.

FIG. 3 is a comparison of changes in leakage current between Comparative Examples 1 to 3 in which the cathode foil was treated with hypophosphorous acid and the conventional example. It can be seen that when the phosphorus compound is attached to the cathode foil, the deterioration of the leakage current is larger than that in the case of no treatment.

FIG. 4 shows the relationship between the amount of phosphorus compound attached to the anode foil and the leakage current of the capacitor after 1000 hours at 105 ° C. for ammonium pyrophosphate. It was found that the leakage current can be reduced when the amount of adhesion to the anode foil is 50 mg / m ² or more, and the higher the concentration, the greater the effect.

In the above-mentioned Examples, the immersion in the treatment liquid was described as the method for adhering the phosphorus compound, but other methods such as applying fine crystals of the phosphorus compound using a binder or the like can also be adopted. In addition, the case before cutting is shown as the step of attaching the phosphorus compound to the anode foil,
It is also possible to attach the anode foil after cutting and connecting the lead wire and before winding. In this case, since the phosphorus compound can be attached to the cut end portion of the anode foil or the lead wire connecting portion, the formation of an oxide film during aging can be assisted and the aging time can be shortened.

(Effect of the invention) As described above, according to the present invention, the anode foil contains one or more phosphorus compounds of pyrophosphoric acid or hypophosphorous acid or salts thereof, or phosphorus such as urea phosphate. By attaching the adduct compound, the deterioration of the leakage current of the capacitor can be prevented.

[Brief description of drawings]

FIG. 1 is a diagram showing changes in leakage current in a high temperature no-load test of capacitors according to Examples 1 to 3, and FIG. 2 is a diagram showing changes in leakage current for Examples 4 to 6 similarly. Third
The figure is a diagram showing changes in leakage current in a high temperature no-load test of capacitors according to Comparative Examples 1 to 3. Figure 4 shows the amount of ammonium pyrophosphate and capacitor 1 attached to the anode foil.
It is a figure which shows the relationship with a leakage current after 05 degreeC and 1000 hours.

Claims (2)

[Claims] 1. An aluminum electrolytic capacitor in which a cathode foil and an anode foil on which an anodized film is formed are wound with a separator interposed, and a capacitor element impregnated with an electrolytic solution is hermetically sealed in a case. An aluminum electrolytic capacitor, wherein one or more phosphorus compounds of pyrophosphoric acid or salts thereof are attached to at least the surface on which the anodized film is formed. 2. An aluminum electrolytic capacitor in which a cathode foil and an anode foil on which an anodized film is formed are wound with a separator interposed, and a capacitor element impregnated with an electrolytic solution is hermetically sealed in a case. An aluminum electrolytic capacitor, wherein an adduct compound containing phosphorus such as urea phosphate is attached to at least a surface on which an anodized film is formed.