JP3371362B2 - Method for producing electrode foil for aluminum electrolytic capacitor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an electrode foil for an aluminum electrolytic capacitor, particularly an aluminum foil for a cathode and a low voltage aluminum foil for an anode.

[0002]

2. Description of the Related Art Conventionally, an electrode foil for an aluminum electrolytic capacitor is an etched foil roughened by chemical or electrochemical etching in an aqueous solution containing chloride, and chlorine ions remaining on the etched foil are dechlorinated. After that, in the case of the aluminum foil for the cathode, it is manufactured by performing a treatment for forming a stabilizing film on the surface of the etched foil, and for the aluminum foil for the anode, performing a treatment for forming an oxide film by chemical conversion treatment. As the dechlorination treatment, a method of performing chemical treatment with an acid aqueous solution of phosphoric acid, sulfuric acid, nitric acid or the like, or as disclosed in Japanese Patent Publication No. 63-16480, electrochemically removes chlorine ions in a nitric acid aqueous solution. Methods of removing are known.

[0003]

However, with the recent miniaturization of aluminum electrolytic capacitors, it is necessary to increase the capacitance per unit area. Therefore, the etched foil is further roughened to have a fine etch pit structure. Have come to possess. In order to remove the residual chlorine ions from the finely roughened aluminum foil by the conventional method, dechlorination treatment must be strongly performed, resulting in the dissolution of fine etch pits. ,
On the contrary, there is a disadvantage that the capacitance is reduced.

[0004]

In order to solve the above-mentioned conventional inconveniences, the present invention is to dechlorinate aluminum foil after roughening it by chemical or electrochemical etching in an aqueous solution containing chloride. When carrying out the ion treatment, the dechlorination treatment step is divided into two stages, a front stage and a rear stage, and in the front stage, it is immersed in an aqueous solution of an inorganic acid such as phosphoric acid, sulfuric acid or nitric acid, and in the rear stage, Oxalic acid,
It is characterized by being immersed in an aqueous solution of an organic acid such as citric acid or tartaric acid.

In the above, in the case of phosphoric acid, sulfuric acid or nitric acid used in the preceding stage, the concentration of the aqueous solution is preferably 0.5 w.
In the range of t% to 30 wt% and the temperature of the aqueous solution is 20
If the concentration and temperature are lower than the above range, the chlorine ion removing effect cannot be obtained. It brings about a decrease in electric capacity.

In the case of oxalic acid, citric acid or tartaric acid used in the latter stage, the concentration in the aqueous solution is preferably 0.2 w.
In the range of t% to 10 wt% and the temperature of the aqueous solution is 30
It is in the range of ℃ to 90 ℃. If the concentration and temperature are lower than this range, the chlorine ion removal effect cannot be obtained. Brings capacity reduction.

[0007]

As described above, according to the present invention, since the dechlorination treatment is carried out in two steps by changing the kind of acid, the conventional dechlorination treatment carried out in one step in a constant inorganic acid aqueous solution. Compared to the treatment, chlorine ions not removed by the dechlorination treatment with the inorganic acid aqueous solution are effectively removed by the subsequent organic acid aqueous solution treatment, and the aluminum is less dissolved, so the capacitance is also reduced. Can be reduced.

[0008]

EXAMPLES Examples of the present invention will be described in detail below. Example 1 (1) An etching process using an aluminum foil having a purity of 99.9% and a thickness of 90 μm,
5.5wt% chlorine, 1.5wt% phosphoric acid and 0.5w
Etching was carried out for 18 minutes with a triangular wave alternating current having a current density of 120 mA / cm 2 at 10 Hz in an electrolytic solution of 18 ° C. which was composed of an aqueous solution containing t% nitric acid and 2.0 wt% aluminum chloride, and washed with ion exchange water. (2) Dechlorination treatment step After performing the dechlorination treatment at 60 ° C. in a 5.0 wt% sulfuric acid aqueous solution for 2 minutes, and then immersing in a 1.0 wt% oxalic acid aqueous solution at 50 ° C. for 1 minute 30 seconds. Then, the subsequent dechlorination treatment was performed and the product was washed with ion-exchanged water.

Example 2 (1) Etching step The same as in Example 1 (2) Dechlorination ion treatment step After the dechlorination ion treatment of the previous stage was performed in a 5.0 wt% phosphoric acid aqueous solution at 40 ° C. for 2 minutes, 2.0 wt% at 75 ° C
It was immersed in an aqueous citric acid solution for 5 minutes to carry out dechlorination ion treatment in the latter stage, and washed with ion-exchanged water.

Example 3 (1) Etching process Same as in Example 1 (2) Dechlorination ion treatment process After the dechlorination ion treatment of the previous stage was performed for 1 minute 30 seconds in a 5.0 wt% nitric acid aqueous solution at 60 ° C. , 85 ° C 2.0w
It was dipped in a t% tartaric acid aqueous solution for 5 minutes, subjected to dechlorination ion treatment in the latter stage, and washed with ion-exchanged water.

Comparative Example 1 (1) Etching Step Same as Example 1 (2) Dechlorination Ion Treatment Step After immersion in a 5.0 wt% sulfuric acid aqueous solution at 60 ° C. for 2 minutes and 3 minutes, washing with ion-exchanged water did.

Comparative Example 2 (1) Etching Step Same as Example 1 (2) Dechlorination Treatment Step 2 minutes and 3 in a 5.0 wt% phosphoric acid aqueous solution at 40 ° C.
After soaking for a minute, it was washed with ion-exchanged water.

Comparative Example 3 (1) Etching Step Same as Example 1 (2) Dechlorination Ionizing Step After immersion in a 5.0 wt% nitric acid aqueous solution at 60 ° C. for 1 minute 30 seconds and 2 minutes, ion-exchanged water Washed with.

The amounts of chlorine ions remaining on the surfaces of the etched foils obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were measured by the silver nitrate nephelometry. Further, the same foil was subjected to 20 V chemical formation in a commonly used aqueous solution of ammonium adipate, the electrostatic capacity was measured, and the results are shown in the table.

[0015]

[Table 1]

As is apparent from Table 1, Examples 1 to 3
The amount of residual ions in the etched foil obtained in 1. was 1.
0 mg / m2, 1.2 mg / m2 and 1.0 mg / m2
And each of them showed a significant decrease as compared to the residual chlorine ion amount of the etched foils obtained in Comparative Examples 1 to 3.

When the one-step dechlorination treatment shown in Comparative Examples 1 to 3 is performed, when the immersion time in the acid aqueous solution is prolonged, the amount of residual chlorine ions is reduced but the electrostatic capacity is also reduced, and The decrease in the amount of chlorine ions is small and still high.

[0018]

As described above, according to the present invention, the chlorine ions remaining in the etched foil can be effectively reduced, and an electrode foil having a small amount of residual chlorine ions despite having the same capacity can be manufactured. be able to. In addition, dechlorination treatment can be easily achieved without requiring special equipment.

Further, in the present invention, since the latter step is soaked in an organic acid aqueous solution for dechlorination treatment, the inorganic acid ions such as phosphoric acid, sulfuric acid or nitric acid used in the previous step are removed from the surface of the etched foil, Further, oxalic acid, citric acid or tartaric acid used in the subsequent stage is easily decomposed by heat treatment at a relatively low temperature of 250 ° C. or lower, so that unnecessary acid ions can be easily removed from the surface of the etched foil. Have the advantage of.

Claims (3)

(57) [Claims] 1. When the aluminum foil is roughened by chemical or electrochemical etching in an aqueous solution containing chloride and then subjected to dechlorinating ion treatment, the dechlorinating ion treatment step is performed in two stages, a first stage and a second stage. And in the previous stage,
An aluminum electrolytic capacitor characterized by being dipped in an aqueous solution of an inorganic acid such as phosphoric acid, sulfuric acid, nitric acid, and in the latter step by being dipped in an aqueous solution of an organic acid such as oxalic acid, citric acid, tartaric acid. Of manufacturing electrode foil for automobile. 2. The concentration of phosphoric acid, sulfuric acid or nitric acid in an aqueous solution of phosphoric acid, sulfuric acid or nitric acid is 0.5 wt% to 30.
It is in the range of wt% and the temperature of the aqueous solution is 20 ° C to 80
The method for producing an electrode foil for an aluminum electrolytic capacitor according to claim 1, which is in the range of ° C. 3. The concentration of oxalic acid, citric acid or tartaric acid in an aqueous solution of oxalic acid, citric acid or tartaric acid is 0.
2 wt% to 10 wt% and the temperature of the aqueous solution is 30
The method for producing an electrode foil for an aluminum electrolytic capacitor according to claim 1 or 2, wherein the temperature is in the range of ℃ to 90 ℃.