JPH0719733B2 - Method for etching aluminum foil for electrolytic capacitors - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for etching an aluminum foil for an electrolytic capacitor, and more specifically to a method for etching an electrode foil for an aluminum electrolytic capacitor for low voltage.

[Conventional technology]

Generally, the low-voltage electrode foil is etched by an AC etching method in which an AC current is passed in an aqueous solution containing chlorine ions. Industrially, a continuous etching method in which an electrode is arranged in an etching tank and an aluminum foil is moved in the tank at a constant speed is adopted.

In that case, the ideal current distribution in the etching tank is such that the current suddenly rises almost at the same time as the aluminum foil enters the tank, and a current having a constant current density flows immediately. That is, if the current sharply rises at the same time as the etching starts, the chlorine ions sufficiently accelerated by the electric field attack the aluminum foil surface,
This is because a large number of fine corrosion starting points (pits) are formed and a high surface expansion ratio can be obtained. On the other hand, when the rise of the current is delayed, the number of the corrosion starting points is formed without sufficiently accelerating the chlorine ions, so that the number of the starting points is small, and as a result, a small number of relatively large corrosion holes are formed. It grows, and sufficient surface expansion ratio cannot be obtained.

[Problems to be Solved by the Invention]

However, in the actual manufacturing process by the continuous etching method, when the aluminum foil rushes into the liquid surface of the electrolytic solution, the resistance of the natural oxide film existing on the surface of the aluminum foil hinders the rapid rise of the current, and Has a current distribution such that the current gradually increases. Therefore, there is a problem that the starting point of corrosion is reduced and a sufficient surface expansion ratio cannot be obtained.

[Means for Solving the Problems]

To solve the above problems, in the present invention, while continuously dipping the aluminum foil in the electrolytic solution at a predetermined speed, prior to etching the aluminum foil by applying an alternating current, the aluminum foil is electrolyzed. Preliminary AC etching (hereinafter referred to as preliminary etching) is performed in a liquid at a current density higher than that at the time of etching for a predetermined time.

That is, as illustrated in FIG. 1, the first electrolytic cell 1 and the second electrolytic cell 2 are prepared, and the aluminum foil A
Is first pre-etched in the first electrolytic cell 1,
Next, the main etching is performed by immersing in the second electrolytic bath 2.
In this case, the current density in the preliminary etching is set higher than that in the main etching as described above. The etching time of the preliminary etching is preferably in the range of 1 to 8 seconds. In the illustrated example, a pair of electrode plates 1a and 1b are arranged so as to sandwich the aluminum foil A in the first electrolytic bath 1 for pre-etching.
The AC power supply 3 is connected between a and 1b. In addition, in the second electrolytic cell 2 for the main etching, three electrode plates 2a to
The two AC power supplies 2c are arranged so that the aluminum foil A is sandwiched between them and are in synchronization with each other.
a and 4b are prepared. Then, in the figure, one AC power supply is provided between the middle electrode plate 2b and the left electrode plate 2a.
4a is connected, and the other AC power source 4b is connected between the middle electrode plate 2b and the right electrode plate 2c.

Although the basic example of the present invention has been described above with the main etching step as one-step etching, the main etching step may be multi-step etching such as two-step etching or three-step etching.

[Action]

By this preliminary etching, the natural oxide film on the surface of the aluminum foil is removed to the extent that its resistance can be ignored.

Example 1 First, the aluminum foil was first treated with HCl 7 wt%, AlCl ₃ 1 wt%, H ₃ PO ₄
In a pre-etching liquid having a liquid temperature of 30 ° C. at 1 wt%, pre-etching was performed for 5 seconds with each alternating current (frequency 30 Hz) having a current density of 200, 300, 400, 500, 600, 800, 1000 mA / cm ² . Then, for each of them, in the same etching solution as the preliminary etching solution, the current density of 250 mA /
The main etching was performed for 10 minutes with an alternating current of cm ² and a frequency of 30 Hz. Table 1 shows the relationship between the preliminary etching current density (mA / cm ² ) and the electrostatic capacity (μF / cm ² ). Table 2 shows the relationship between the preliminary etching current density (mA / cm ² ) and the number of times the bending test was performed.

<< Example 2 >> In the same pre-etching solution as in Example 1, the current density of the alternating current (frequency: 30 Hz) was set to 500 mA / cm ² , and 1 to 10
The preliminary etching was performed by increasing the etching time in units of 1 second until the second. Then, each of them was subjected to the main etching under the same conditions as in the above-mentioned Example 1. Table 3 shows the relationship between the preliminary etching time (sec) and the electrostatic capacity (μF / cm ² ). Table 4 shows the relationship between the pre-etching time and the number of times the bending test was performed.

Example 3 First, the aluminum foil was treated with HCl 10 wt%, AlCl ₃ 1 wt%, HNO ₃
Current density of 200,300,400,500,600,800,1000mA / cm ^{2 in} 1wt%, H ₃ PO ₄ 1wt% in pre-etching solution at 25 ℃
Pre-etching was performed for 5 seconds with each alternating current (frequency 15 Hz). Then, each of them was subjected to the main etching under the same conditions as in the above-mentioned Example 1. The preliminary etching current density (mA / cm ² ) and capacitance (μF /
The relationship with cm ² ) is shown in Table 5. Table 6 shows the relationship between the preliminary etching current density (mA / cm ² ) and the number of times the bending test was performed.

Example 4 In the same pre-etching solution as in Example 3, the current density of the alternating current (frequency: 15 Hz) was set to 500 mA / cm ² , and 1 to 10
The preliminary etching was performed by increasing the etching time in units of 1 second until the second. Then, each of them was subjected to the main etching under the same conditions as in the above-mentioned Example 1. Table 7 shows the relationship between the preliminary etching time (sec) and the electrostatic capacity (μF / cm ² ). Table 8 shows the relationship between the preliminary etching time and the number of times the bending test was performed.

[Comparative Example 1] An aluminum foil was treated with HCl without pre-etching.
The current density of the alternating current (frequency 30Hz) was measured in an etching solution containing 7wt%, AlCl ₃ 1wt%, H ₃ PO ₄ 1wt% and a liquid temperature of 30 ℃.
Etching was performed at 250 mA / cm ² for 10 minutes. At this time, the electrostatic capacity was 15.0 μF / cm ² , and the bending test was performed 15 times.

Next, a case where the main etching after the preliminary etching has multiple stages will be described. Here, Example 5 and Comparative Example 2 in the case of using three stages will be described below.

Example 5 In the same pre-etching solution as in Example 3, pre-etching was performed for 3 seconds at an alternating current (frequency 20 Hz) current density of 500 mA / cm ² . Then, at the same etching solution as in Example 1 at a liquid temperature of 30 ° C., a current density of 250 mA / cm
^2. The first stage of the main etching was performed for 4 minutes with an alternating current having a frequency of 30 Hz. Then, the second etching of the main etching was performed for 4 minutes with the same main etching solution at a liquid temperature of 25 ° C. and an alternating current with a current density of 200 mA / cm ² and a frequency of 25 Hz. Furthermore, the same main etching solution,
At the liquid temperature of 20 ° C., the third stage of the main etching was performed for 4 minutes with an alternating current having a current density of 150 mA / cm ² and a frequency of 20 Hz.

Comparative Example 2 The same three-step etching as the main etching of Example 5 was performed without preliminary etching.

Table 9 shows the relationship between the electrostatic capacity (μF / cm ² ) and the service life of the bending test in Example 5 and Comparative Example 2.

It can be seen from Table 9 that the preliminary etching has a sufficient effect even if the main etching is multi-stage etching.

For reference, the preliminary etching current density (mA / cm ² ) corresponding to Table 1 of Example 1 and Table 5 of Example 3 is shown in FIG.
The graph of electrostatic capacity (μF / cm ² ) is shown. Further, FIG. 3 shows a graph of the pre-etching current density versus the number of times the bending test was performed (times) corresponding to Table 2 of Example 1 and Table 6 of Example 3. FIG. 4 shows a graph of pre-etching time (sec) versus capacitance corresponding to Table 3 of Example 2 and Table 7 of Example 4. Further, FIG. 5 shows a graph of the pre-etching time versus the number of times the bending test is performed corresponding to Table 4 of Example 2 and Table 8 of Example 4.

From the graphs of FIGS. 2 and 3, the current density during the pre-etching is higher than the current density of the main etching, and from the graphs of FIGS. 4 and 5, the pre-etching time is within the range of 1 to 8 seconds. It will be appreciated that it is preferable.

〔The invention's effect〕

As described above, according to the present invention, prior to the main etching, pre-etching is performed to remove the natural oxide film on the surface of the aluminum foil to such an extent that its resistance can be ignored. A fine corrosion starting point (pit) is formed, and a high surface expansion ratio can be obtained. Also, an aluminum foil for an electrolytic capacitor, which is excellent in mechanical strength, can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing an example of an etching apparatus used for carrying out the present invention, FIG. 2 is a graph showing the relationship between pre-etching current density and capacitance, and FIG. 3 is pre-etching. A graph showing the relationship between the current density and the number of times the bending test is used, FIG. 4 is a graph showing the relationship between the pre-etching time and the capacitance, and FIG. 5 is the relationship between the pre-etching time and the number of times the bending test is used. It is a graph showing. In the figure, 1 is a first electrolytic cell and 2 is a second electrolytic cell.

Front page continuation (72) Inventor Ryuji Kawasaki, 2-2-1 Tsujido Shinmachi, Fujisawa-shi, Kanagawa Elner Co., Ltd. (72) Inventor Akira Yoshii 2-2-1 Tsujido Shinmachi, Fujisawa, Kanagawa Elner Co., Ltd. (72) Inventor Eiji Endo Marunouchi 2-1-2 Marunouchi, Chiyoda-ku, Tokyo Asahi Glass Co., Ltd. (72) Inventor Junjiro Iwamoto 2-1-2 Marunouchi, Chiyoda-ku, Tokyo Asahi Glass Co., Ltd.

Claims (2)

[Claims] 1. A method of etching an aluminum foil for an electrolytic capacitor, wherein an aluminum foil is continuously dipped in an electrolytic solution at a predetermined rate while an alternating current is applied to etch the aluminum foil. A method for etching an aluminum foil for an electrolytic capacitor, characterized in that the aluminum foil is preliminarily subjected to AC etching in an electrolytic solution at a current density higher than the current density at the time of etching for a predetermined time. 2. The method for etching an aluminum foil for an electrolytic capacitor according to claim 1, wherein the etching time of the preliminary AC etching is 1 to 8 seconds.