JPH1187186A - Etching method for electrode foil for aluminum electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an etching method in which a pit diameter can be expanded to a diameter suitable for a chemical conversion voltage, by a method wherein, in a later-stage etching process, an etching operation is performed in an electrolytic solution which is composed of, at least, one kind out of sulfuric acid and nitric acid and, after that, an etching operation is performed in an acid aqueous solution which is composed of, at least, one kind out of hydrochloric acid and sulfuric acid. SOLUTION: In a later-stage etching process, an etching operation is performed electrochemically in an electrolytic solution which is composed of at least one kind out of sulfuric acid and nitric acid, and, after that, a chemical etching operation is performed in an acid aqueous solution which is composed of,at least, one kind out of hydrocholic acid and sulfuric acid. In this case, the concentration of the electrolytic solution which is composed of, at least, one kind out of sulfuric acid and nitric acid is set in a range of 0.5 to 9 wt.%, and a solution temperature is set in a range of 50 to 80 deg.C. In addition, 0.1 to 0.5 wt.% of an additive which is composed of, at least, one kind out of oxalic acid, phosphoric acid and acetic acid is added to the electrolytic solution which is composed of at least one kind out of sulfuric acid and nitric acid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for etching an electrode foil for an aluminum electrolytic capacitor, and more particularly to a method for etching an electrode foil for an aluminum electrolytic capacitor for high pressure.

[0002]

2. Description of the Related Art Generally, an aluminum electrolytic capacitor has an anode foil in which an oxide film serving as a dielectric is formed on a surface of an aluminum foil whose effective surface area is enlarged by an etching process and a cathode foil, and a separator is interposed therebetween. To form a capacitor element, impregnating the capacitor element with a driving electrolyte, and sealing the capacitor element in a metal case.

[0003] The etching of the aluminum foil in the aluminum electrolytic capacitor described above is roughened by corroding the surface of the aluminum foil. In general, an acid for forming a film such as sulfuric acid, nitric acid, phosphoric acid, oxalic acid is added. It is performed chemically or electrochemically in a chloride solution. The reason for roughening the surface of the aluminum foil by this etching is based on the fact that the capacitance of the aluminum electrolytic capacitor is proportional to the surface area of the aluminum foil, and by increasing the capacitance per unit area, Aluminum electrolytic capacitors can be reduced in size and weight.

In particular, for electrode foils for medium and high pressures, it is necessary to enlarge the pits generated in the first etching step to a pit diameter suitable for the formation voltage in the second etching step, and it is important how to efficiently increase the pit diameter. It will be a point. Conventionally, pits are generated by electric etching in an acidic solution containing chlorine ions in the first etching step, and chemical dissolution is performed in a high-temperature acidic solution in the second etching step, or
No. 8, JP-A-3-101213, JP-A-3-101213
As described in JP-A-136226, a technique for enlarging the diameter of a pit by performing electric etching in an acidic solution containing nitrate ions has been considered to be effective.

[0005]

However, in the above-mentioned prior art, it is difficult to enlarge the pits generated by the DC etching in the pre-etching step to the pit diameter suitable for the formation voltage by the etching method in the post-etching step. That is the actual situation. The reason for this is that the pit diameter generated by DC etching in the pre-etching process varies, and the pit diameter in the post-etching process increases when chemical dissolution is performed in a high-temperature acidic solution. Causes a variation in distribution. For this reason, it is conceivable that all the pits generated by the DC etching in the previous etching step are not used, but are filled by the formation in the next chemical formation step, and become invalid. In the method of expanding the pit diameter by electric etching in an acidic solution containing nitrate ions, the pit diameter becomes uniform, but the pit diameter is not expanded to a suitable pit diameter for the formation voltage, resulting in a low capacitance. I was

The present invention solves the above-mentioned conventional problems. In a subsequent etching step for increasing the pit diameter, the pit diameter is made uniform and the pit diameter suitable for the formation voltage can be increased. It is an object of the present invention to provide a method for etching an electrode foil for an aluminum electrolytic capacitor which can increase the capacitance of the electrode foil.

[0007]

In order to achieve the above object, the present invention provides a method for etching an electrode foil for an aluminum electrolytic capacitor, comprising: a pre-etching step of forming pits by electrochemically etching an aluminum foil;
A post-etching step of enlarging the pits generated by the pre-etching step to a pit diameter suitable for the formation voltage, wherein the post-etching step is performed in an electrolytic solution of at least one type of sulfuric acid or nitric acid. Etching is performed in an acidic aqueous solution of at least one kind of hydrochloric acid or sulfuric acid. According to this etching method, the pit diameter is increased in a subsequent etching step for enlarging the pit diameter. And the pit diameter suitable for the formation voltage can be increased to increase the capacitance per unit area.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention comprises a pre-etching step of forming pits by electrochemically etching an aluminum foil, and a pit formed by the pre-etching step. A post-etching step of expanding to a pit diameter suitable for the voltage, wherein the post-etching step electrochemically etches in at least one or more of an electrolytic solution of sulfuric acid or nitric acid, and then performs etching of hydrochloric acid or sulfuric acid. At least one
According to this etching method, electrochemical etching is performed in at least one or more kinds of electrolytes of sulfuric acid or nitric acid in a subsequent etching step. Therefore, the triangular pyramid pit shape generated in the previous etching step can be made into a pit shape having a cylindrical shape and a uniform diameter, and after that, in at least one kind of acidic aqueous solution of hydrochloric acid or sulfuric acid. Since the chemical etching is performed in the pit, the pit diameter suitable for the formation voltage can be surely enlarged, thereby preventing the pit from being filled with the oxide film of the formation in the next formation process. Therefore, the capacitance per unit area can be increased.

According to a second aspect of the present invention, the concentration of at least one type of electrolyte solution of sulfuric acid or nitric acid is 0.5 to 9%.
%, And the solution temperature is set in the range of 50 to 80 ° C. According to this method, the concentration of the electrolyte is set in the range of 0.5 to 9% by weight, and Temperature 5
By setting the temperature in the range of 0 to 80 ° C., the influence of impurities and grain boundaries in the aluminum foil can be reduced and the overdissolution of the etching can be controlled, so that the pit diameter is uniform and the pit diameter is suitable for the formation voltage. The enlargement is performed effectively, and the capacitance per unit area can be increased.

According to a third aspect of the present invention, at least one additive of oxalic acid, phosphoric acid, and acetic acid is added to at least one or more electrolytes of sulfuric acid or nitric acid in an amount of 0.1 to 0.5% by weight. According to this method, by setting the amount of the additive in the range of 0.1 to 0.5% by weight, overdissolution of the etching can be effectively suppressed. Is effectively made uniform and enlarged, and a higher capacitance can be obtained.

According to a fourth aspect of the present invention, the concentration of at least one kind of acidic aqueous solution of hydrochloric acid or sulfuric acid for performing chemical etching is set in a range of 3 to 10% by weight, and the concentration is 3% by weight or less. In the case of, the density is too low to increase the pit diameter, while the density is 10
If it is more than 10% by weight, the density is too high to control the enlargement of the pit diameter.
The concentration of the acidic aqueous solution is preferably in the range of 3 to 10% by weight.

Hereinafter, specific embodiments of the present invention will be described. Embodiment Mode 1 Purity is 99.98% and thickness is 100
A pretreatment is performed by immersing the aluminum foil having a thickness of 0.5 μm in an aqueous solution of sodium hydroxide having a concentration of 0.5% by weight, and then containing hydrochloric acid and sulfuric acid having a concentration of 10% by weight and having a liquid temperature of 8%.
Pre-etching is performed in which a pit is generated by electrochemically etching the aluminum foil by applying a direct current having a current density of 20 A / dm ² to the aluminum foil pre-treated in an acidic aqueous solution at 5 ° C. for 200 seconds. Was.

[0013] Thereafter, as post-etching, in which the pits generated by the pre-etching are enlarged to a pit diameter suitable for the formation voltage, as shown in Table 1, the liquid temperature, the composition, and the concentration were changed, respectively. A current density of 10 A was applied to the aluminum foil that was pre-etched in the electrolyte of No. 13.
/ Dm ² is applied electrochemically by applying a direct current of 400 s for 400 seconds, and then the aluminum is subjected to the electrochemical etching in a hydrochloric acid aqueous solution having a concentration of 10% by weight and a liquid temperature of 60 ° C. The foil was immersed for 200 seconds to perform chemical etching.

Each of the etched foils subjected to the second-stage etching in the electrolyte solutions No. 1 to No. 13 was subjected to 600 V chemical conversion in a boric acid aqueous solution having a concentration of 8% by weight and a liquid temperature of 90 ° C. Thereafter, the capacitance and the bending strength of each of these samples (measured once per reciprocation under the conditions of 1.0 mmR, 50 g load, and bending angle of 90 °) were measured.
The measurement results are shown in (Table 1).

Table 1 shows Comparative Example 1 in which hydrochloric acid was used instead of nitric acid having the composition of No. 13, and electrochemical etching was performed under the same electrochemical etching conditions as in No. 13. FIG. 3 shows Comparative Example 2 in which no subsequent chemical etching was performed, and Comparative Examples 1 and 2 were also subjected to post-etching in the electrolyte solutions of Nos. 1 to 13 respectively. As in the case of the foil, a 600 V chemical conversion was performed in a boric acid aqueous solution having a concentration of 8% by weight and a liquid temperature of 90 ° C., and thereafter, the capacitance and the bending strength (1.0 mm
R, a load of 50 g, and a bending angle of 90 degrees under one reciprocation). The measurement results are shown in (Table 1).

[0016]

[Table 1]

As is clear from Table 1, the electrochemical etching conditions in the latter etching step are such that the concentration of the electrolytic solution using sulfuric acid or nitric acid is in the range of 0.5 to 9% by weight.
In addition, when the liquid temperature is in the range of 50 to 80 ° C., those having excellent capacitance and bending strength can be obtained.

(Embodiment 2) The purity is 99.98%,
A pretreatment is performed by immersing an aluminum foil having a thickness of 100 μm in an aqueous solution of sodium hydroxide having a concentration of 0.5% by weight. The pre-etching was performed in which a pit was generated by applying a direct current having a current density of 20 A / dm ² for 200 seconds to the aluminum foil pretreated in the acidic aqueous solution for 200 seconds to electrochemically etch the aluminum foil.

Then, as a post-stage etching for expanding the pits generated by the pre-stage etching to a pit diameter suitable for the formation voltage, the composition and the concentration as shown in (Table 2) were applied to an electrolyte composed of nitric acid having a concentration of 8% by weight. N which changed each
o. A direct current having a current density of 10 A / dm ² was applied to the aluminum foil that had been subjected to the first stage etching in an electrolyte solution having a temperature of 70 ° C. to which an additive of No. 14 to No. 22 was added for 400 seconds to electrochemically Etching was performed, and then the aluminum foil subjected to the electrochemical etching was immersed in a hydrochloric acid aqueous solution having a concentration of 10% by weight and a liquid temperature of 60 ° C. for 200 seconds to perform chemical etching.

Then, for each of the etched foils that were subjected to the second-stage etching in the electrolytes of Nos. 14 to 22,
A 600 V chemical conversion was carried out in a boric acid aqueous solution having a concentration of 8% by weight and a liquid temperature of 90 ° C. Thereafter, the capacitance and bending strength (1.0 mmR, 50 g load, bending angle 90 Under the condition of 1 degree). The measurement results are shown in (Table 2).

[0021]

[Table 2]

As is clear from Table 2, the amount of at least one additive of oxalic acid, phosphoric acid and acetic acid added to at least one electrolyte solution of sulfuric acid or nitric acid is 0.1 to 0. By adding in the range of 0.5% by weight, overdissolution of etching is effectively suppressed, and a higher capacitance can be obtained.

(Embodiment 3) The purity is 99.98%,
A pretreatment is performed by immersing an aluminum foil having a thickness of 100 μm in an aqueous solution of sodium hydroxide having a concentration of 0.5% by weight, and then containing hydrochloric acid and sulfuric acid having a concentration of 10% by weight, respectively, and a liquid temperature of 85 ° C. The pre-etching was performed in which a pit was generated by applying a direct current having a current density of 20 A / dm ² for 200 seconds to the aluminum foil pretreated in the acidic aqueous solution for 200 seconds to electrochemically etch the aluminum foil.

After that, it was produced by the pre-etching.
The second step is to enlarge the pit to a pit diameter suitable for the formation voltage.
As a solution, a solution temperature of 7% by weight of nitric acid was used.
Aluminum pre-etched in electrolyte at 0 ° C
Current density of 10A / dm on foil ^TwoDC current for 400 seconds
To perform electrochemical etching, and then
Change the composition and concentration as shown in 3), and
Is 60 ° C. in an acidic aqueous solution of No. 23 to No. 29.
20 aluminum foils that have been electrochemically etched
Chemical etching was performed by immersion for 0 seconds.

Then, for each of the etched foils subjected to the chemical etching in the acidic aqueous solutions No. 23 to No. 29, a 600 V chemical conversion was carried out in a boric acid aqueous solution having a concentration of 8% by weight and a liquid temperature of 90 ° C. After that, the capacitance and the bending strength (one reciprocation per one cycle under the conditions of 1.0 mmR, 50 g load, and bending angle of 90 degrees) were measured for each of these samples. The measurement results are shown in (Table 3).

[0026]

[Table 3]

As is clear from Table 3, when the concentration of the acidic aqueous solution comprising hydrochloric acid or sulfuric acid for chemical etching is in the range of 3 to 10% by weight, a higher capacitance can be obtained.

The acidic aqueous solution used for the chemical etching may be a mixed aqueous solution of hydrochloric acid and sulfuric acid as long as its concentration is in the range of 3 to 10% by weight. We have confirmed that the same effect can be obtained.

[0029]

As described above, the method for etching an electrode foil for an aluminum electrolytic capacitor according to the present invention comprises a pre-etching step of forming pits by electrochemically etching an aluminum foil, and a pre-etching step formed by this pre-etching step. A post-etching step of enlarging the pits to a pit diameter suitable for the formation voltage, wherein the post-etching step electrochemically etches in at least one or more of an electrolytic solution of sulfuric acid or nitric acid, According to this etching method, electrochemical etching is performed in an electrolytic solution of at least one of sulfuric acid or nitric acid in a subsequent etching step in an acidic aqueous solution of at least one of hydrochloric acid and sulfuric acid. Etching is performed in the previous stage. Since the triangular pyramid pit shape can be formed into a cylindrical and uniform pit shape, and thereafter, chemical etching is performed in an acidic aqueous solution of at least one kind of hydrochloric acid or sulfuric acid. It is possible to reliably increase the pit diameter to a voltage suitable for the voltage, thereby preventing the pits from being buried with the oxide film formed in the next chemical conversion step, and thereby increasing the capacitance per unit area. Can be done.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuaki Nakanishi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (4)

[Claims] 1. A pre-etching step of generating pits by electrochemically etching an aluminum foil, and a post-etching step of expanding the pits generated in the pre-etching step to a pit diameter suitable for a formation voltage. The post-etching step includes electrochemically etching in at least one or more kinds of electrolytic solution of sulfuric acid or nitric acid, and thereafter performing chemical etching in at least one or more kinds of acidic aqueous solution of hydrochloric acid or sulfuric acid. Method for etching electrode foil for aluminum electrolytic capacitors. 2. The method according to claim 1, wherein the concentration of at least one of sulfuric acid and nitric acid is set in the range of 0.5 to 9% by weight.
The method for etching an electrode foil for an aluminum electrolytic capacitor according to claim 1, wherein the liquid temperature is set in a range of 50 to 80C. 3. The method according to claim 1, wherein at least one additive of oxalic acid, phosphoric acid, and acetic acid is added in an amount of 0.1 to 0.5% by weight to at least one electrolyte solution of sulfuric acid or nitric acid. The method for etching an electrode foil for an aluminum electrolytic capacitor as described in the above. 4. The concentration of at least one kind of acidic aqueous solution of hydrochloric acid or sulfuric acid for performing chemical etching is adjusted to 3-10.
2. The method for etching an electrode foil for an aluminum electrolytic capacitor according to claim 1, wherein the etching rate is set in a range of% by weight.