JP3180954B2 - Manufacturing method of aluminum foil for electrolytic capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a method for producing an aluminum foil for an electrolytic capacitor, which can obtain an electrode foil having good etching properties and high capacitance.

2. Description of the Related Art Conventionally, aluminum foil for electrolytic capacitors has been manufactured by the following method. That is, the surface of the aluminum ingot is chamfered, and then subjected to a homogenization treatment, then hot-rolled, and repeatedly subjected to cold rolling on the obtained aluminum plate to produce an aluminum foil for an electrolytic capacitor. I have. Cold rolling is performed in several passes, and an aluminum plate having a thickness of 3 to 8 mm becomes an aluminum foil for an electrolytic capacitor having a thickness of 20 to 100 μm. The aluminum foil for an electrolytic capacitor manufactured in this manner is subjected to an etching treatment to form micropores on the surface of the aluminum foil, thereby increasing the surface area of the aluminum foil, thereby providing an electrolytic foil having a high capacitance. You get. However, the aluminum foil for an electrolytic capacitor manufactured by the conventional method cannot sufficiently increase the surface area of the aluminum foil even by etching. This is because a thick oxide film is formed on the surface of the obtained aluminum foil for an electrolytic capacitor, and even when the etching process is performed, it is difficult to uniformly form micropores in the thickness direction of the oxide film. For this reason, the obtained aluminum foil for electrolytic capacitors is dissolved and washed with an alkaline aqueous solution or an acidic aqueous solution,
Attempts have been made to reduce the thickness of the oxide film by removing the oxide film. However, the surface of the obtained aluminum foil for an electrolytic capacitor may be roughened and the etching property may be reduced.

[Problems to be solved by the invention]

The present inventors have conducted various studies on the formation of an oxide film, and as a result, the oxide film on the surface of the aluminum foil is formed unevenly during hot rolling, and grows during cold rolling to have a large thickness. I found out. Then, it was thought that the removal of the oxide film would prevent the formation of a thick oxide film on the aluminum foil surface in a subsequent step.
Therefore, the present inventor did not dissolve and wash the obtained aluminum foil for an electrolytic capacitor with an alkaline aqueous solution or an acidic aqueous solution. When dissolved and washed with an alkaline aqueous solution or an acidic aqueous solution,
It has been found that the formation of a thick oxide film is prevented and that the surface of the aluminum foil does not remain rough. The present invention has been made based on such findings.

Means and Action for Solving the Problems

That is, the present invention provides a method for producing an aluminum foil for an electrolytic capacitor by repeatedly performing cold rolling on an aluminum plate, wherein the thickness (t) of the aluminum plate is expressed by the following expression: 5.5t ₀ ≦
After cold rolling to a thickness satisfying t ≦ 20t ₀ (where t ₀ indicates the thickness of the obtained aluminum foil for an electrolytic capacitor), the surface of the aluminum plate is dissolved and washed with an alkaline aqueous solution. The present invention further relates to a method for producing an aluminum foil for an electrolytic capacitor, wherein the method further comprises cold rolling. In the present invention, first, an aluminum plate is manufactured by a conventionally known method. That is, an aluminum ingot is prepared, the surface of the ingot is chamfered, homogenized, and then hot-rolled to produce an aluminum plate having a thickness of 3 to 8 mm. As the aluminum ingot, one having a purity suitable for producing an aluminum foil for an electrolytic capacitor is used, and specifically, one having an aluminum purity of 99.7% or more is used. Further, the surface facing, homogenizing treatment, and hot rolling are performed under conventionally employed conditions. Next, the aluminum plate is subjected to cold rolling. Cold rolling is performed in several passes, and the aluminum plate gradually becomes thinner, and is adjusted to a thickness suitable for an aluminum foil for an electrolytic capacitor, generally 20 to 100 μm. What is important in the present invention is that the thickness (t) of the aluminum plate is 5.5 to 20 times the thickness (t ₀ ) of the finally obtained aluminum foil for an electrolytic capacitor during the cold rolling. And dissolving and washing the aluminum plate using an alkaline aqueous solution. Therefore, even if the dissolution washing with an alkaline aqueous solution is performed only before cold rolling, an oxide film grows during cold rolling,
The thickness of the oxide film on the surface of the aluminum foil cannot be reduced. Further, even in the middle of the cold rolling, (if thick to the extent that greater than 20t ₀₎ the thickness of the aluminum plate is not sufficiently thin, that reducing the thickness of the oxide film of the aluminum foil surface Can not. Conversely, (if thin less than about 5.5 tons ₀₎ the thickness of the aluminum plate is too thin, the remainder roughened aluminum foil surface, since the etching is deteriorated undesirably. In the present invention, in addition to the dissolution washing with an alkaline aqueous solution during the cold rolling and when the thickness (t) of the aluminum plate is 5.5t ₀ ≦ t ≦ 20t ₀ , Needless to say, melting cleaning and degreasing cleaning after cold rolling may be performed. The alkaline aqueous solution used in the dissolution washing may be a strong alkaline aqueous solution such as an aqueous solution of sodium hydroxide, which may be used in a conventional washing step. After washing, neutralization with an acidic aqueous solution may be performed. As the acidic aqueous solution, a strongly acidic aqueous solution such as a nitric acid aqueous solution or a chromic acid aqueous solution is preferably used. The aluminum foil for an electrolytic capacitor obtained as described above is subjected to an etching treatment to increase the surface area of the aluminum foil, thereby obtaining a high-capacitance electrode foil.

【Example】

Example 1 Aluminum ingot of 99.98% aluminum purity (thickness 4
(00mm x width 1110mm x length 2500mm) 10cm each surface, then homogenized at 600 ℃ x 10 hours, immediately 240 ℃
Was subjected to hot rolling to prepare an aluminum plate having a thickness of 6 mm. Next, cold rolling was repeated, and when the thickness became 0.5 mm, the aluminum plate was passed through a continuous cleaning line to be dissolved and cleaned. The dissolution washing condition was immersion in a 2% sodium hydroxide aqueous solution at 60 ° C. for about 30 seconds. Thereafter, the mixture was neutralized with a 20% aqueous nitric acid solution at room temperature, and then washed with water and dried. Thereafter, the aluminum plate was further cold-rolled to produce an aluminum foil having a thickness of 0.09 mm. Then, the aluminum foil was degreased and washed with a weak alkaline soap water to obtain an aluminum foil for a hard electrolytic capacitor. Example 2 An aluminum foil for a hard electrolytic capacitor was obtained in the same manner as in Example 1, except that an aluminum ingot having a purity of 99.96% aluminum was used. Example 3 The aluminum foil having a thickness of 0.09 mm obtained in Example 1 was
The final annealing was performed in an inert atmosphere at a temperature of 300 ° C. for 20 hours to obtain an aluminum foil for a flexible electrolytic capacitor. Example 4 The aluminum foil having a thickness of 0.09 mm obtained in Example 2 was
The final annealing was performed in an inert atmosphere at a temperature of 300 ° C. for 20 hours to obtain an aluminum foil for a flexible electrolytic capacitor. Comparative Examples 1 to 4 Aluminum foils for electrolytic capacitors were obtained in the same manner as in Examples 1 to 4, except that when the thickness of the aluminum foil became 0.5 mm, the aluminum foil was not passed through the continuous cleaning line. Comparative Example 1 corresponds to Example 1, Comparative Example 2 corresponds to Example 2, Comparative Example 3 corresponds to Example 3, and Comparative Example 4 corresponds to Example 4.
It corresponds to. Electrolytic etching was performed on the aluminum foil for electrolytic capacitors according to Examples 1 to 4 and Comparative Examples 1 to 4 to obtain an electrode foil, and the capacitance was measured. Here, the conditions of the electrolytic etching are as follows. That is, base retention: hydrochloric acid (35
%): C ₂ H ₂ O ₄ .2H ₂ O: AlCl ₃ = 3.5: 0.35: 175g: 175g, liquid temperature 56 ° C, rectangular liquid 30Hz, current density 0.4A / cm
^2. Electrolytic etching was performed under the conditions of 5 minutes. And
The capacitance of the obtained electrode foil was measured at 0 vf. Further, each electrode foil was cut into a strip having a width of 1 cm, and the tensile strength was measured. Table 1 shows the results. As is clear from comparison of Examples 1 to 4 and Comparative Examples 1 to 4 in Table 1, if the surface of the aluminum plate is dissolved and washed during the cold rolling, the capacitance is increased and the electrolytic etching is good. It can be seen that this is being done. Also, the tensile strength of the example is slightly higher than that of the comparative example, and it can be seen that uniform electrolytic etching is performed. Comparative Example 5 An aluminum foil for an electrolytic capacitor was obtained in the same manner as in Example 1 except that the following points were different. The difference is that when the thickness of the aluminum plate is 0.5 mm, cold rolling is further performed without passing through the continuous cleaning line, and the thickness of the aluminum plate is reduced.
It is at the point where it passed through the continuous washing line when it reached 0.2 mm. Comparative Example 6 An aluminum foil for an electrolytic capacitor was obtained in the same manner as in Example 1 except that the following points were different. The difference is that when the thickness of the aluminum plate is 0.5 mm, the thickness of the aluminum plate is 2.0 mm
At the point where it passed through the continuous washing line when The capacitance and tensile strength of the aluminum foil for electrolytic capacitors obtained in Comparative Examples 5 and 6 were measured in the same manner as described above. Table 2 shows the results. As is clear from comparison with the comparative example in Table 2 of Example 1 of Table 1 even when the melting and washing is performed during the cold rolling, the thickness (t) of the aluminum plate is 5.5. t ₀ ≦ t ≦ 20t
₀ (where t ₀ represents the thickness of the obtained aluminum foil for an electrolytic capacitor), if the dissolution cleaning is performed at a thickness that does not satisfy the expression, the oxide film formed on the aluminum foil surface becomes thick, Alternatively, it can be seen that good electrolytic etching is not performed due to roughness remaining on the aluminum foil surface, and the capacitance cannot be sufficiently increased. Example 5 A 1080 mm ingot of JIS H4000 was hot-rolled at a temperature of 240 ° C. to obtain an aluminum plate having a thickness of 3 mm. Next, cold rolling was repeated, and when the thickness became 0.28 mm, under the same conditions as in Example 1, the aluminum plate was dissolved and washed through a continuous washing line, then neutralized, washed with water and dried. After this, the aluminum plate is further cold-rolled to a thickness
An aluminum foil of 0.05 mm was prepared and used as an aluminum foil for a hard electrolytic capacitor. Example 6 Except that the thickness of the final aluminum foil was 0.02 mm,
Under the same conditions as in Example 5, an aluminum foil for a hard electrolytic capacitor was obtained. Comparative Example 7 An aluminum foil for a hard electrolytic capacitor was obtained in the same manner as in Example 5, except that the aluminum foil was not passed through the continuous washing line. Comparative Example 8 An aluminum foil for a hard electrolytic capacitor was obtained in the same manner as in Example 6, except that the aluminum foil was not passed through a continuous washing line. The aluminum foils for electrolytic capacitors according to Examples 5 and 6 and Comparative Examples 7 and 8 were chemically dissolved, and the dissolution loss was measured. Table 3 shows the results. Here, the method for measuring the dissolution loss is as follows. That is, 100mm x 100mm
Was immersed in a 15.5% hydrochloric acid aqueous solution at 50 ° C. for 2.5 minutes, and the value obtained by subtracting the weight after immersion from the weight before immersion was defined as the dissolution loss. As is clear from the comparison between the examples and the comparative examples in Table 3, the obtained aluminum foil for electrolytic capacitors obtained by dissolving and washing during cold rolling has a smaller dissolution loss than that of the comparative example, It can be seen that uneven etching or overdissolution during electrolytic etching is prevented, and the capacitance is increased.

【The invention's effect】

As described above, the method according to the present invention is different from the conventional method for manufacturing an aluminum foil for electrolytic capacitors in that during cold rolling, and when the aluminum plate reaches a specific thickness, the alkaline aqueous solution is used. The surface is dissolved and washed. The thickness of the oxide film present on the surface of the aluminum foil for an electrolytic capacitor obtained by this method is smaller than that of a conventional aluminum foil. Therefore, when the aluminum foil for an electrolytic capacitor obtained by the method of the present invention is electrolytically etched, nuclei are formed at a number of places on the surface at the start of the etching, and the etching proceeds, thereby enabling uniform etching and increasing the surface area. Can also be achieved. Therefore, the electrode foil obtained by etching has an effect of exhibiting high capacitance. Further, since the etching is uniform, there is an effect that the strength can be prevented from lowering due to the uneven etching.

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C22F 1/04-1/057 B21B 1/40 B21B 3/00 C23G 1/22 H01G 9/055

Claims (1)

(57) [Claims] 1. A method for producing an aluminum foil for an electrolytic capacitor by repeatedly performing cold rolling on an aluminum plate, wherein the thickness (t) of the aluminum plate is expressed by the following formula: 5.5t ₀ ≦ t ≦ 20t
₀ (in the formula, t ₀ indicates the thickness of the obtained aluminum foil for an electrolytic capacitor). After cold rolling to a thickness satisfying, the surface of the aluminum plate is dissolved and washed using an alkaline aqueous solution, and then A method for producing an aluminum foil for an electrolytic capacitor, further comprising performing cold rolling.