JPH03257147A - Production of aluminum foil for electrolytic capacitor - Google Patents

Abstract

PURPOSE:To improve the etchability of Al foil and to perform uniform etching by dissolving and washing the surface of an Al sheet with an alkaline aq. soln. at the time when the sheet to be repeatedly cold rolled to obtain foil is cold rolled to a specified thickness. CONSTITUTION:When an Al sheet is repeatedly cold rolled to produce Al foil for an electrolytic capacitor, the sheet is cold rolled to a thickness (t) satisfying an inequality 3.3t0<=t<=20t0 (where t0 is the thickness of the resulting Al foil), the surface of the sheet is dissolved and washed with an alkaline or acidic aq. soln. and the sheet is further cold rolled. By this method, foil with a thinner oxide film on the surface is obtd. When this foil is electrolytically etched, nuclei are formed at many positions of the surface at the beginning of etching, etching proceeds well and uniform etching can be performed. The surface area of the foil is sufficiently increased and the reduction of the strength can be prevented.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method for manufacturing aluminum foil for electrolytic capacitors, which allows obtaining electrode foil with good etching properties and high capacitance.

[Conventional technology]

Conventionally, aluminum foil for electrolytic capacitors has been manufactured by the following method. That is, aluminum foil for electrolytic capacitors is manufactured by face-shaving the surface of an aluminum foil block, then subjecting it to homogenization treatment, hot rolling, and repeatedly cold rolling the obtained aluminum plate. There is. Cold rolling is performed in several steps, and an aluminum plate with a thickness of 3 to 8 μm becomes an aluminum foil for electrolytic capacitors with a thickness of 20 to 100 μm. By etching the aluminum foil for electrolytic capacitors manufactured in this way, micropores are formed on the surface of the aluminum foil, expanding the surface area of the aluminum foil, and thereby creating an electrolytic foil with high capacitance. You get it. However, the surface area of aluminum foil for electrolytic capacitors manufactured by conventional methods cannot be sufficiently increased even when subjected to etching treatment. This is because a thick oxide film is formed on the surface of the obtained aluminum foil for electrolytic capacitors, and even if etched, it is difficult to uniformly form micropores in the thickness direction of the oxide film. For this reason, attempts have been made to reduce the thickness of the oxide film by dissolving and cleaning the obtained aluminum foil for electrolytic capacitors in an alkaline aqueous solution or acidic aqueous solution to remove the oxide film. However, the surface of the obtained aluminum foil for electrolytic capacitors may become rough and the etching properties may deteriorate.

[Question B that the invention attempts to solve]

As a result of various studies conducted by the present inventor regarding the formation of oxide films, it was found that the oxide film on the surface of aluminum foil is formed unevenly during hot rolling, and that it grows during cold rolling and becomes thick. I discovered that. We also thought that removing the oxide film would prevent the formation of a thick oxide film on the surface of the aluminum foil in subsequent steps. Therefore, instead of dissolving and cleaning the obtained aluminum foil for electrolytic capacitors with an alkaline aqueous solution or acidic aqueous solution, the present inventor developed an aluminum plate during cold rolling, which is a process in the middle of manufacturing aluminum foil for electrolytic capacitors. When the aluminum foil was dissolved and cleaned with an aqueous alkali solution or an acidic aqueous solution, it was found that the formation of a thick oxide film was prevented and no roughness remained on the surface of the aluminum foil. The present invention has been made based on such knowledge.

Means for Solving the Problems and Effects That is, the present invention provides a method for manufacturing aluminum foil for an electrolytic capacitor by repeatedly subjecting an aluminum plate to cold rolling, in which the thickness (t) of the aluminum plate is determined by the formula 3. 3to≦t≦20to
(In the formula, f and o indicate the thickness of the obtained aluminum foil for electrolytic capacitors.) After being cold rolled to a thickness that satisfies the following, the surface of the aluminum plate is dissolved and cleaned using an alkaline aqueous solution or an acidic aqueous solution. The present invention relates to a method for manufacturing an aluminum foil for an electrolytic capacitor, which is characterized in that the aluminum foil is further subjected to cold rolling. In the present invention, an aluminum plate is first manufactured by a conventionally known method. That is, an aluminum ingot is prepared, the surface of the ingot is milled, homogenized, and then hot rolled to produce an aluminum plate having a thickness of 3 to 8 pans. As the aluminum ingot, one having a purity suitable for manufacturing aluminum foil for an electrolytic capacitor is used, and specifically, one having an aluminum purity of 99.7% or more is used. Further, surface milling, homogenization treatment, and hot rolling are performed under conventionally employed conditions. Next, the aluminum plate is cold rolled. Cold rolling is carried out in several steps, and the aluminum plate is gradually thinned until it is adjusted to a thickness of 20 to 100 microns, which is suitable for use as aluminum foil for electrolytic capacitors. What is important in the present invention is that during this cold rolling, the thickness (t) of the aluminum plate is 3.3 to 20 times the thickness (to) of the final aluminum foil for electrolytic capacitors. At the time of doubling, the aluminum plate is dissolved and cleaned using an alkaline aqueous solution or an acidic aqueous solution. Therefore, even if dissolving and cleaning with an alkaline aqueous solution or an acidic aqueous solution is performed only before cold rolling, the oxide film will lengthen during cold rolling, and the thickness of the oxide film on the surface of the aluminum foil cannot be reduced. In addition, even during cold rolling, if the thickness of the aluminum sheet is not sufficiently thinned (if it is thick enough to exceed 20 tO), it is difficult to reduce the thickness of the oxide film on the surface of the aluminum foil. Can not. On the other hand, if the thickness of the aluminum plate is too thin (less than 3.3 tO), the surface of the aluminum foil will remain rough and the etching properties will deteriorate, which is not preferable. In addition, in the present invention, in addition to dissolution cleaning with an alkaline aqueous solution or acidic aqueous solution during the cold rolling and when the thickness (t) of the aluminum plate is 3.3to≦t≦20t0, Needless to say, it is also possible to perform dissolution cleaning or degreasing cleaning after cold rolling. The alkaline aqueous solution used in dissolving and cleaning may be a strong alkaline aqueous solution such as a sodium hydroxide aqueous solution, which is used in conventional cleaning processes. Further, the acidic aqueous solution may be a strong acidic aqueous solution such as a nitric acid aqueous solution or a chromic acid aqueous solution, which is used in a conventional cleaning process. Further, a strong alkaline aqueous solution and a strong acidic aqueous solution may be used together. The aluminum foil for electrolytic capacitors obtained as described above is subjected to etching treatment to enlarge the surface area of the aluminum foil, thereby obtaining an electrode foil with high capacitance.

【Example】

Example 1 The surface of an aluminum ingot (thickness: 400 mm x width: 1110 mm x length: 2,500 m) with 99.98% aluminum purity was milled by 10 ci, then homogenized at 600°C for IO hours, and immediately heated to 240″C. An aluminum plate with a thickness of 6 mm was created by hot rolling. Next, cold rolling was repeated, and when the thickness reached 0.5 -, the aluminum plate was passed through a continuous cleaning line and melted and cleaned. The dissolution and cleaning conditions were as follows: immersion in a 2% sodium hydroxide aqueous solution at 60°C for about 30 seconds.Then, the aluminum plate was neutralized with a 20% nitric acid aqueous solution at room temperature, and then washed with water and dried.After this, the aluminum plate was further cooled. Rolled between
An aluminum foil with a thickness of 0.09 mm was created. This aluminum foil was then degreased and washed with slightly alkaline soapy 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 with an aluminum purity of 99.96% was used. Example 3 The aluminum foil with a thickness of 0.09 mm obtained in Example 1 was subjected to final annealing at a temperature of 300° C. for 20 hours in an inert atmosphere to obtain an aluminum foil for a soft electrolytic capacitor. Example 4 The aluminum foil with a thickness of 0.09 m obtained in Example 2 was subjected to final annealing in an inert atmosphere at a temperature of 300° C. for 20 hours to obtain an aluminum foil for a soft electrolytic capacitor. Comparative Examples 1 to 4 Aluminum foils for electrolytic capacitors were obtained in the same manner as Examples 1 to 4, except that the continuous cleaning line was not passed when the aluminum foil had a thickness of 0.5 mm. In addition,
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. Electrolytic etching was performed on the aluminum foils for electrolytic capacitors according to Examples 1 to 4 and Comparative Examples 1 to 4 to obtain electrode foils, and the capacitance was measured. Here, the conditions for electrolytic etching are as follows. That is, distilled: Hydrochloric acid (35%): C! H2O4・
2HtO:^lC1:l = 3.51:0.3i:
175g: In a liquid with a composition of 175g, the liquid temperature is 5.
6°C9 square wave 30Hz, current density 0.4A/ci
Electrolytic etching was carried out under the conditions of , 5 minutes. Then, the capacitance of the obtained electrode foil was measured using Ovf. In addition, each electrode foil was cut into strips with a width of 1 cm, and the tensile strength was also measured. The results are shown in Table 1. (Left below) Table 1 As is clear from comparing Examples 1 to 4 and Comparative Examples 1 to 4 in Table 1, if the surface of the aluminum plate is dissolved and cleaned during cold rolling, the capacitance It can be seen that the electrolytic etching is carried out satisfactorily. Furthermore, the tensile strength of the examples was slightly higher than that of the comparative examples, indicating that uniform electrolytic etching was performed. Comparative Example 5 An aluminum foil for an electrolytic capacitor was obtained in the same manner as in Example 1 except for the following differences. The difference is that when the aluminum plate is 0.5 mm thick, it is cold rolled without passing through the continuous cleaning line, and when the aluminum plate becomes 0.2 mm thick, it is passed through the continuous cleaning line. That's the point. Comparative Example 6 An aluminum foil for an electrolytic capacitor was obtained in the same manner as in Example 1 except for the following differences. The difference is that when the thickness of the aluminum plate is 0.5 mm, it is not passed through the continuous cleaning line, but when the thickness of the aluminum plate is 2.0 m after cold rolling, it is passed through the continuous cleaning line. It is in. The capacitance and tensile strength of the aluminum foils for electrolytic capacitors obtained in Comparative Examples 5 and 6 were measured in the same manner as above. The results are shown in Table 2. Table 2 As is clear from a comparison of Example 1 in Table 1 and Comparative Example in Table 2, even when melt cleaning is performed during cold rolling, the thickness of the aluminum plate (t ) is 3.3to ≦t
, ≦20t0 (in the formula, T0 indicates the thickness of the obtained aluminum foil for electrolytic capacitors). Alternatively, it can be seen that roughness remains on the surface of the aluminum foil, and good electrolytic etching is not performed, making it impossible to sufficiently increase the capacitance. Example 5 A JIS H4000 1080 aluminum ingot was hot rolled at a temperature of 240°C to obtain an aluminum plate with a thickness of 3 mm. Next, cold rolling was repeated, and when the thickness reached 0.28 mm, the aluminum plate was passed through a continuous cleaning line to be dissolved and cleaned under the same conditions as in Example 1, and then neutralized, washed with water, and dried. After this, the aluminum plate is further cold rolled,
An aluminum foil with a thickness of 0.05M was made and used as an aluminum foil for a hard electrolytic capacitor. Example 6 An aluminum foil for a hard electrolytic capacitor was obtained under the same conditions as in Example 5 except that the final thickness of the aluminum foil was 0.02 mm. Comparative Example 7 An aluminum foil for a hard electrolytic capacitor was obtained in the same manner as in Example 5 except that it was not passed through the continuous cleaning line. Comparative Example 8 An aluminum foil for a hard electrolytic capacitor was obtained in the same manner as in Example 6 except that it was not passed through the continuous cleaning line. The aluminum foils for electrolytic capacitors according to Examples 5 and 6 and Comparative Examples 7 and 8 above were chemically dissolved and the weight loss by dissolution was measured. The results are shown in Table 3. Here, the method for measuring the dissolution loss is as follows. That is, a 100m x 100m (7) sample was heated to 50'C (7
) The sample was immersed in a 15.5% hydrochloric acid aqueous solution for 2.5 minutes, and the weight after immersion was subtracted from the weight before immersion, and the value obtained was defined as the weight loss after immersion. Table 3 As is clear from the comparison between the example and the comparative example in Table 3, the aluminum foil for electrolytic capacitors obtained by melting and cleaning during cold rolling has a melting loss that is comparable to that of the comparative example. It can be seen that the capacitance is reduced, non-uniform etching or excessive dissolution is prevented during electrolytic etching, and the capacitance is increased.

【Effect of the invention】

As explained above, the method according to the present invention differs from the conventional method for producing aluminum foil for electrolytic capacitors in that an alkaline aqueous solution is applied during cold rolling and when the aluminum plate reaches a specific thickness. Alternatively, the surface is dissolved and cleaned with an acidic aqueous solution. The aluminum foil for electrolytic capacitors obtained by this method has a thinner oxide film on its surface than conventional aluminum foils. Therefore, when the aluminum foil for electrolytic capacitors obtained by the method of the present invention is electrolytically etched, nuclei are formed at many locations on the surface during the etching process, and the etching progresses, making uniform etching possible and reducing the surface area. It can also be expanded sufficiently. Therefore, the electrode foil obtained by etching has the effect of exhibiting high capacitance. Furthermore, since the etching is uniform, it is possible to prevent a decrease in strength caused by non-uniform etching.

Claims (1)

[Claims] In a method of manufacturing aluminum foil for electrolytic capacitors by repeatedly subjecting an aluminum plate to cold rolling, the thickness (t) of the aluminum plate satisfies the formula 3.3t_0≦t≦20t.
After being cold-rolled to a thickness that satisfies _0 (in the formula, T_0 indicates the thickness of the obtained aluminum foil for electrolytic capacitors), the surface of the aluminum plate is dissolved and cleaned using an alkaline aqueous solution or an acidic aqueous solution. A method for producing aluminum foil for electrolytic capacitors, which comprises further cold rolling.