JPH11354387A - Manufacture of electrode foil for aluminum electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively remove chlorine ion, when a dechlorine-ion process is performed after the surface of an aluminum foil is roughened by chemical etching, etc., submerging the foil in the water solution of inorganic acid such as phosphoric acid, sulfuric acid, etc., at a first stage, and submerging it in the water solution of organic acid such as oxalic acid, citric acid, etc., at a second stage. SOLUTION: The surface of an aluminum foil is roughened by chemical or electro-chemical etching in a water solution containing chloride, and then dechlorine-ion process is performed. Here, the dechlorine-ion process is divided into a first stage and a second stage, and at the first stage it is submerged in the water solution of inorganic acid such as phosphoric acid sulfuric acid nitric acid, etc., while at the second stage it is submerged in the water solution of organic acid such as oxalic acid, citric acid, tartaric acid, etc. Here, the concentration of phosphoric acid, sulfuric acid, etc., in the water solution comprising them is 0.5-30 wt.% while the temperature of water solution is 20-80 deg.C. The concentration of oxalic acid, citric acid, etc., in the water solution comprising them is 2-10 wt.% while the temperature of water solution is 30-90 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an electrode foil for an aluminum electrolytic capacitor, in particular, an aluminum foil for a cathode and a low-pressure aluminum foil for an anode.

[0002]

2. Description of the Related Art Conventionally, an electrode foil for an aluminum electrolytic capacitor has been obtained by removing an etched foil which has been roughened by chemical or electrochemical etching in an aqueous solution containing a chloride and removing chlorine ions remaining on the etched foil. After that, in the case of aluminum foil for the cathode, it is manufactured by performing a process of forming a stabilized film on the surface of the etched foil, and in the case of an aluminum foil for the anode, a process of forming an oxide film by a chemical conversion process. As the dechlorinating ion treatment, a method of performing chemical treatment with an aqueous acid solution of phosphoric acid, sulfuric acid, nitric acid, or the like, or as described in JP-B-63-16480, electrochemically converts chloride ions into an aqueous nitric acid solution. Methods of removing are known.

[0003]

However, in recent years, it has been necessary to increase the capacitance per unit area in accordance with the miniaturization of aluminum electrolytic capacitors. Therefore, the etched foil has been further roughened to form a fine etch pit structure. I have. In order to remove residual chlorine ions from such a finely roughened aluminum foil by a conventional method, dechlorination ion treatment must be performed strongly, and as a result, fine etch pits are dissolved. ,
On the contrary, there is a disadvantage that the capacitance is reduced.

[0004]

SUMMARY OF THE INVENTION In order to solve the above-mentioned disadvantages, the present invention provides a method in which an aluminum foil is roughened by chemical or electrochemical etching in an aqueous solution containing chloride and then dechlorinated. When performing the ion treatment, the dechlorination ion treatment process is divided into two stages, a former stage and a latter stage, and in the former stage, the process is immersed in an aqueous solution of an inorganic acid such as phosphoric acid, sulfuric acid, and nitric acid. 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 step, the concentration of the aqueous solution is preferably 0.5 W
t% to 30 wt% and the temperature of the aqueous solution is 20%.
If the concentration and the temperature are lower than the above ranges, the effect of removing chloride ions cannot be obtained. This results in a decrease in capacitance.

The concentration of oxalic acid, citric acid or tartaric acid used in the latter stage in the aqueous solution is preferably 0.2 watts.
t% to 10 wt%, and the temperature of the aqueous solution is 30%.
If the concentration and temperature are lower than this range, the effect of removing chloride ions cannot be obtained. This results in reduced capacity.

[0007]

As described above, according to the present invention, since the dechlorination ion treatment is performed in two stages by changing the kind of acid, the conventional dechlorination ion treatment in one stage in a fixed inorganic acid aqueous solution is performed. Compared to the treatment, chlorine ions that were not removed by the dechlorination ion treatment with the inorganic acid aqueous solution are effectively removed by the subsequent organic acid aqueous solution treatment, and the dissolution of aluminum is less, so the capacitance is also reduced. Can be reduced.

[0008]

Embodiments of the present invention will be described below in detail. Example 1 (1) Etching Step An aluminum foil having a purity of 99.9% and a thickness of 90 μm was
5.5 wt% chlorine, 1.5 wt% phosphoric acid and 0.5 w
Etching was performed for 18 minutes with a triangular wave alternating current of 10 Hz and a current density of 120 mA / cm 2 in an electrolytic solution at 18 ° C. consisting of an aqueous solution containing t% nitric acid and 2.0 wt% aluminum chloride, and washed with ion-exchanged water. (2) Dechlorination Ion Treatment Step After performing the pre-dechlorination ion treatment in a 5.0 wt% sulfuric acid aqueous solution at 60 ° C. for 2 minutes, it was immersed in a 1.0 wt% oxalic acid aqueous solution at 50 ° C. for 1 minute and 30 seconds. Then, a subsequent dechlorination ion treatment was performed, and the resultant was washed with ion-exchanged water.

Example 2 (1) Etching step Same as in Example 1 (2) Dechlorination ion treatment step After performing the predechlorination ion treatment in a 5.0 wt% aqueous phosphoric acid solution at 40 ° C. for 2 minutes, 2.0wt% at 75 ℃
Then, the substrate was immersed in a citric acid aqueous solution for 5 minutes to perform a subsequent dechlorination ion treatment, and washed with ion-exchanged water.

Example 3 (1) Etching step Same as in Example 1 (2) Dechlorination ion treatment step After performing the pre-dechlorination ion treatment in a 5.0 wt% nitric acid aqueous solution at 60 ° C. for 1 minute and 30 seconds. , 85w, 2.0w
It was immersed in a t% aqueous solution of tartaric acid for 5 minutes to perform a subsequent dechlorination ion treatment, and washed with ion-exchanged water.

Comparative Example 1 (1) Etching step Same as in Example 1 (2) Dechlorinating 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 exchange water did.

Comparative Example 2 (1) Etching step Same as in Example 1 (2) Dechlorinating ion treatment step 2 minutes in a 5.0 wt% phosphoric acid aqueous solution at 40 ° C.
After immersion for a minute, it was washed with ion-exchanged water.

Comparative Example 3 (1) Etching step Same as in Example 1 (2) Dechlorinating ion treatment step After immersing in a 5.0 wt% nitric acid aqueous solution at 60 ° C. for 1 minute 30 seconds and 2 minutes, ion-exchanged water And washed.

The amount of chloride ions remaining on the surfaces of the etched foils obtained in Examples 1 to 3 and Comparative Examples 1 to 3 was measured by a silver nitrate turbidimetric method. The same foil was subjected to 20 V chemical conversion in a commonly used aqueous solution of ammonium adipate, and its capacitance was measured. The results are shown in the table.

[0015]

[Table 1]

As 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
In each case, the amount significantly decreased as compared with the amount of residual chlorine ions in the etched foils obtained in Comparative Examples 1 to 3.

In the case where the one-stage dechlorination treatment shown in Comparative Examples 1 to 3 is performed, if the immersion time in an acid aqueous solution is lengthened, the amount of residual chloride ions decreases, but the capacitance also decreases. The decrease in the amount of chloride ions is slight and still shows a high value.

[0018]

As described above, according to the present invention, it is possible to effectively reduce the chlorine ions remaining in the etched foil, and to manufacture an electrode foil having a small residual chlorine ion amount despite the same capacity. be able to. Further, the dechlorination treatment can be easily achieved without requiring any special equipment.

Further, in the present invention, since the dechlorination ion treatment is carried out by immersing in an organic acid aqueous solution in the latter stage, the inorganic acid ions such as phosphoric acid, sulfuric acid or nitric acid used in the former stage are removed from the etched foil surface, Oxalic acid, citric acid, or tartaric acid used in the subsequent stage can be easily decomposed by heat treatment at a relatively low temperature of 250 ° C. or less, so that unnecessary acid ions can be easily removed from the etched foil surface. Has the advantage of

Claims (3)

[Claims] 1. When performing dechlorination ion treatment after roughening an aluminum foil in an aqueous solution containing chloride by chemical or electrochemical etching, a dechlorination ion treatment step is performed in two stages, a first stage and a second stage. And in the first stage,
An aluminum electrolytic capacitor characterized by being immersed in an aqueous solution of an inorganic acid such as phosphoric acid, sulfuric acid, nitric acid, etc. Of manufacturing electrode foil for use. 2. The concentration of phosphoric acid, sulfuric acid or nitric acid in an aqueous solution comprising phosphoric acid, sulfuric acid or nitric acid is 0.5 wt% to 30 wt.
wt%, and the temperature of the aqueous solution is from 20 ° C to 80 ° C.
The method for producing an electrode foil for an aluminum electrolytic capacitor according to claim 1, wherein the temperature is in the range of ° C. 3. An aqueous solution comprising oxalic acid, citric acid or tartaric acid having a concentration of oxalic acid, citric acid or tartaric acid of 0.3.
2 wt% to 10 wt%, and the aqueous solution temperature is 30 wt%.
The method for producing an electrode foil for an aluminum electrolytic capacitor according to claim 1 or 2, wherein the temperature is in a range of from 0C to 90C.