JPH0744130B2 - Method for forming anode foil for electrolytic capacitors - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for forming an anode foil for an electrolytic capacitor, and more specifically, to obtain an anode foil having excellent water resistance and high capacitance. It relates to the chemical conversion method.

[Conventional technology]

In order to obtain this type of anode foil, first, the aluminum foil is etched, then the aluminum foil is boiled in pure water, or the etched aluminum foil is directly immersed in a prescribed chemical conversion solution. So that anodic oxidation is performed. In that case, conventionally, an aqueous solution of ammonium phosphate, an aqueous solution of ammonium adipate, or a mixed solution thereof has been used as the chemical conversion liquid.

[Problems to be Solved by the Invention]

However, in the case of using the ammonium phosphate aqueous solution alone, the water resistance is good, but the electrostatic capacity is low, the use range is limited, and it is not suitable for miniaturized products. In addition, phosphoric acid formation often causes generation of aluminum hydroxide, which causes liquid contamination. Therefore, aluminum hydroxide adheres to the surface of the electrode foil, which may cause a problem when the anode lead is caulked.

On the other hand, in the case of the aqueous solution of ammonium adipate, although the elution of aluminum was small, there was a problem in terms of water resistance.

Therefore, a mixed solution of phosphoric acid and adipic acid was also investigated. According to this, although the chemical conversion solution was prevented from being contaminated, the electrostatic capacity was not so different from that of the phosphorylated chemical solution alone.

The present invention has been made in view of such conventional circumstances,
It is an object of the present invention to provide a method for forming an anode foil for an electrolytic capacitor, which is excellent in water resistance and has a high capacitance.

[Means for Solving the Problems]

To achieve the above object, in the present invention, after the etched aluminum foil is boiled in pure water, or the etched aluminum foil is directly exposed to phosphorous acid or a salt thereof in an aqueous ammonium adipate solution or It is characterized in that it is immersed in a chemical conversion solution to which hypophosphorous acid or a salt thereof is added for anodic oxidation.

The preferable addition amount of phosphorous acid or a salt thereof or hypophosphorous acid or a salt thereof is ammonium adipate 1 to
It is 0.01 to 1 wt% with respect to a 20 wt% aqueous solution. Addition amount is 0.0
If it is less than 1% by weight, the effect of addition is not obtained, and if it exceeds 1% by weight, the leakage current increases remarkably and it cannot be used.

〔Example〕

Next, examples of the present invention will be described together with comparative examples. In each of the following examples, the anode foil has a purity of 99.99%.
A 90 μm thick etched and boiled aluminum foil was used.

First, Examples 1 and 2 and Comparative Example when forming voltage is 33V
1 and 2 will be described.

«Example 1» Aluminum foil was immersed in a chemical conversion liquid having a liquid temperature of 80 ° C. in which 0.3 wt% of ammonium phosphite was added to a 10 wt% aqueous solution of ammonium adipate, and a current having a current density of 30 mA / cm ² was applied, and a conversion voltage of 33 V As a result, the same voltage was applied for 15 minutes to perform anodization.

It was washed with water and dried, and the electrostatic capacitance of this formed foil was measured and found to be 27.1 μF / cm ² . Also, the leakage current (LC) is 4
It was 9 μA.

«Example 2» Aluminum foil was immersed in a chemical solution having a liquid temperature of 80 ° C. in which ammonium hypophosphite was added at 0.5 wt% to an aqueous solution of ammonium adipate at 10 wt%, and a current having a current density of 30 mA / cm ² was flowed to generate a chemical conversion voltage. At 33 V, the same voltage was applied for 15 minutes to perform anodization.

It was 31.9 μF / cm ² when the electrostatic capacity of this formed foil was measured after washing with water and drying. The leakage current (LC) is 5
It was 0 μA.

<Comparative Example 1> An aluminum foil was immersed in a chemical conversion solution containing a 0.2 wt% ammonium phosphate aqueous solution at a liquid temperature of 80 ° C., a current having a current density of 30 mA / cm ² was applied, and the formation voltage was 33 V, and the same voltage was applied for 15 minutes. Then, anodization was performed.

It was 24.8 μF / cm ² when the electrostatic capacity of this formed foil was washed with water and dried. Also, the leakage current (LC) is 4
It was 6 μA.

<Comparative Example 2> Ammonium adipate 10 wt% and ammonium phosphate 0.2 w
The aluminum foil is immersed in a chemical conversion solution consisting of a t% mixed aqueous solution at a liquid temperature of 80 ° C, a current density of 30 mA / cm ² is applied, and a formation voltage of 33 V is applied for 15 minutes to perform anodization. It was

It was 25.3 μF / cm ² when the electrostatic capacity of this formed foil was washed with water and dried. The leakage current (LC) is 6
It was 0 μA.

Next, Examples 3 and 4 and Comparative Example when forming voltage is 82V
3 and 4 will be explained.

<< Example 3 >> 0.1 wt% phosphorous acid was added to an aqueous solution of 10 wt% ammonium adipate.
%, The aluminum foil was immersed in a chemical conversion solution having a liquid temperature of 80 ° C., a current density of 30 mA / cm ² was applied, and the formation voltage was 82 V, and the same voltage was applied for 15 minutes to perform anodization.

It was washed with water and dried, and the capacitance of this formed foil was measured and found to be 8.49 μF / cm ² . The leakage current (LC) is 9
It was 4 μA.

«Example 4» Aluminum foil was immersed in a chemical conversion liquid having a liquid temperature of 80 ° C. in which ammonium hypophosphite was added at 0.2 wt% to a 10 wt% ammonium adipate aqueous solution, and a current having a current density of 30 mA / cm ² was applied to the chemical conversion voltage. At 82 V, the same voltage was applied for 15 minutes to perform anodization.

It was washed with water and dried, and the capacitance of this formed foil was measured and found to be 9.16 μF / cm ² . The leakage current (LC) is 8
It was 0 μA.

<Comparative Example 3> An aluminum foil was immersed in a chemical conversion liquid containing a 0.1 wt% ammonium phosphate solution at a liquid temperature of 80 ° C, a current having a current density of 30 mA / cm ² was applied, and the formation voltage was set to 82 V, and the same voltage was applied for 15 minutes. Then, anodization was performed.

It was washed with water and dried, and the capacitance of this formed foil was measured and found to be 6.89 μF / cm ² . The leakage current (LC) is 8
It was 3 μA.

<Comparative Example 4> Ammonium adipate 10 wt% and ammonium phosphate 0.3 w
The aluminum foil is immersed in a chemical conversion liquid consisting of a t% mixed solution at a liquid temperature of 80 ° C, a current density of 30 mA / cm ² is applied, and a formation voltage of 82 V is applied for 15 minutes for anodization. It was

It was washed with water and dried, and the capacitance of this formed foil was measured and found to be 7.15 μF / cm ² . The leakage current (LC) is 8
It was 5 μA.

In order to facilitate comparison, the capacitance value and leakage current value for each of the above examples are shown in the following table. Also, for reference, the rate of increase in capacitance with respect to Comparative Examples 1 and 3 using ammonium phosphate and the reforming time (second) after boiling for 1 hour with pure water for each example are additionally shown in the table. Here, the re-forming time means the time until the desired formation voltage is reached by punching the formation foil into a size of 1 cm × 5 cm, boiling it with pure water for 1 hour, and then applying 1 mA in the formation solution. .

[Effects of the Invention] As described above, according to the present invention, the capacitance can be increased by about 9 to 33% as compared with the case of using the phosphoric acid oxidizing solution alone. It also has excellent water resistance. Further, the generation of aluminum hydroxide is small, and therefore the stain of the chemical conversion liquid can be prevented. Also, the reforming time is reduced by about 20%, which can suppress the increase of leakage current in the storage of the electrolytic capacitor.

Claims (2)

[Claims] 1. An etched aluminum foil is boiled in pure water, or the etched aluminum foil is directly treated with phosphorous acid or a salt thereof or hypophosphorous acid or a salt thereof in an aqueous ammonium adipate solution. A method of forming an anode foil for an electrolytic capacitor, which comprises immersing in an added chemical solution and anodizing. 2. The chemical conversion solution is ammonium adipate 1
The method for forming an anode foil for an electrolytic capacitor according to claim 1, wherein 0.01 to 1 wt% of phosphorous acid or a salt thereof or hypophosphorous acid or a salt thereof is added to an aqueous solution of 20 wt%.