JP2673312B2 - Method for manufacturing aluminum electrode foil for electrolytic capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a method for manufacturing an aluminum electrode foil for an electrolytic capacitor, which has a high capacitance and is excellent in mechanical strength.

[Prior art]

2. Description of the Related Art Conventionally, the surface of an aluminum electrode foil for an electrolytic capacitor has been subjected to etching treatment in order to increase its capacitance. This etching treatment is performed by immersing the aluminum foil in an electrolytic solution and applying a current to the aluminum foil. At this time, as the current, a direct current with a constant current magnitude, an alternating current with a constant current magnitude, or a rectangular wave with a continuous current magnitude is used. When a rectangular wave is used, conventionally, the etching process is performed at the same frequency from the start of etching to the end of etching. The aluminum electrode foil for electrolytic capacitors obtained by such an etching treatment has a cross section in a state as shown in FIG. That is, the boundary between the etched etched portion and the unetched unetched portion has a saw-tooth shape.

As described above, when the etched portion and the unetched portion are sawtooth-shaped, the resulting aluminum electrode foil for electrolytic capacitors has low mechanical strength, that is, tensile strength. There is. This is because when the aluminum electrode foil for an electrolytic capacitor is pulled, stress concentrates on the non-etched portion where the etched portion has entered, and is easily cut. Therefore, the present inventor tried to make the boundary between the etched portion and the unetched portion linear. As a result, it was surprisingly found that the boundary between the etched portion and the unetched portion becomes linear by decreasing the frequency of the rectangular wave as the etching progresses. Then, the inventors have invented that if the boundary between the etched portion and the non-etched portion is made linear, the electrostatic capacitance also increases. The present invention has been made based on such findings.

Means and Action for Solving the Problems

That is, the present invention, the aluminum foil is immersed in the electrolytic solution,
In a method for producing an aluminum electrode foil for an electrolytic capacitor, which applies a rectangular wave current to the aluminum foil for etching, the frequency of the rectangular wave is increased at the start of etching,
After that, the present invention relates to a method for manufacturing an aluminum electrode foil for an electrolytic capacitor, which is characterized in that the frequency of the rectangular wave is sequentially lowered and the etching process is advanced. As the aluminum foil used in the present invention, any aluminum foil conventionally used for capacitors can be adopted. Specifically, a hard or soft aluminum foil having a purity of 99.9% or more can be used. As the electrolytic solution for immersing the aluminum foil, a conventionally known electrolytic solution can be adopted, and for example, an acid aqueous solution or an alkaline aqueous solution can be used. This electrolytic solution may be used at room temperature or may be heated to about 30 to 60 ° C. before use. As the rectangular wave used in the present invention, a value in which the magnitude of the current continuously changes, for example, a value that changes in a binary manner or a value that changes in a three to six value is used. Specifically, a current value of + A and -A is alternately taken (Fig. 3),
Alternating current values of + A and 0 (4th
(See FIG. 5) and the like, which sequentially adopts + A, 0, -A, and 0 as current values are used. The characteristic feature of the present invention lies in that the frequency of the rectangular wave is increased at the start of etching, and then the frequency is sequentially decreased. That is, the frequency is sequentially decreased in such a manner that the etching starts at the first stage and then the second stage, the third stage, and the fourth stage. The frequency at each stage may be a frequency that is conventionally used. Specifically, the frequency of the rectangular wave in the first stage is
About 30 to 50 Hz or more is preferable, the second stage lowers the frequency by about 10 to 20 Hz than the first stage, and the third stage lowers the frequency by about 10 to 20 Hz than the second stage, and the etching proceeds sequentially. Let Also, the time of the first stage and the second stage,
Although it can be set as appropriate, it is preferable to set the intermediate stage time to the longest. This is because this method makes the boundary between the etched portion and the unetched portion more linear. In addition, the magnitude of the electric current may be the same as that conventionally used, specifically,
About 40 A / dm ² is preferable. The aluminum electrode foil for an electrolytic capacitor obtained by the above method has a linear boundary between the etched portion and the unetched portion, has excellent mechanical strength, and has a high electrostatic capacity. The aluminum electrode foil for electrolytic capacitors obtained by the method of the present invention can be suitably used for both a cathode and an anode.

【Example】

First, hard aluminum foil with a purity of 99.9% and a thickness of 90μ
It was immersed in the etching solution shown in the table. Then, as shown in Table 2, the frequency of the rectangular wave was sequentially decreased at the current density shown in Table 1 in the order of the first step → the second step → the third step (Examples 1 to 3). . The type of the rectangular wave used was that shown in FIG. For comparison, a test was conducted in which the frequency of the rectangular wave was not changed at all (Comparative Examples 1 and 2) and a test in which the frequency of the rectangular wave was increased as the etching treatment proceeded (Comparative Example 3). The electrostatic capacity (μF / cm ² ) of the aluminum electrode foils for electrolytic capacitors obtained in Examples 1 to 3 and Comparative Examples 1 to 3 was measured. The method of measuring the dielectric capacitance After etching under the conditions shown in Table 1, similarly, immersing the electrode foil in a 5% aqueous solution of boric acid, caustic at 20v. It was measured. Further, the obtained aluminum electrode foil was annealed at 450 ° C. for 1 minute, and the tensile strength (kg / cm) was measured. The results are shown in Table 2. As is clear from this result, the method according to the example It can be seen that the aluminum electrode foil for electrolytic capacitors obtained in 1. has higher capacitance and tensile strength than the aluminum electrode foil for electrolytic capacitors obtained by the method according to the comparative example.

【The invention's effect】

As described above, the aluminum electrode foil for an electrolytic capacitor obtained by the method according to the present invention has a high electrostatic capacity and a high tensile strength. Therefore, the aluminum electrode foil for electrolytic capacitors obtained by the method according to the present invention has the effect of reducing the risk of damage when incorporated as a capacitor, and having excellent performance even after being formed into a capacitor. is there.

[Brief description of the drawings]

FIG. 1 is a photograph of the metal structure of the cross section of the aluminum electrode foil for electrolytic capacitors obtained by the method according to Comparative Example 1, and FIG. 2 is the aluminum for electrolytic capacitors obtained by the method according to Example 1. It is a photograph of the metal structure of the cross section of the electrode foil. FIGS. 3, 4, and 5 illustrate the types of square waves that can be used in the present invention.

Claims (1)

(57) [Claims] 1. A method of manufacturing an aluminum electrode foil for an electrolytic capacitor, which comprises immersing an aluminum foil in an electrolytic solution and applying a rectangular wave current to the aluminum foil for etching.
A method of manufacturing an aluminum electrode foil for an electrolytic capacitor, which comprises increasing the frequency of a rectangular wave at the start of etching and then gradually decreasing the frequency of the rectangular wave to proceed with an etching process.