JP3203665B2 - Manufacturing method of aluminum foil for anode of electrolytic capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an aluminum foil for an anode of an electrolytic capacitor for medium and low pressure, and more particularly to obtaining an anode foil of an electrolytic capacitor having a relatively high capacitance while being a low-purity aluminum foil. And a method for producing an aluminum foil.

[0002]

2. Description of the Related Art Conventionally, a high-purity aluminum foil has been used to obtain an anode foil of an electrolytic capacitor having a high capacitance. Specifically, an aluminum foil having an Al purity of 99.98% or more is used. The reason for this is that when a low-purity aluminum foil is used, coarse precipitates due to impurities are present on the foil surface, and when etching is performed, coarse holes are generated, so that the surface area of the foil cannot be increased. But,
Since high-purity aluminum foil is expensive, the resulting anode foil for electrolytic capacitors also has the disadvantage of being expensive.

[0003]

In order to avoid this drawback, the inventor of the present invention has developed an electrolytic capacitor having the same high capacitance as that of using a high-purity aluminum foil while using a low-purity aluminum foil. Tried to obtain an anode foil for use. First, the present inventors investigated what the surface condition of the low-purity aluminum foil was like. as a result,
On the surface of the low-purity aluminum foil, precipitates due to impurities were present along the grain boundaries of a coarse crystal structure. Then, they found that etching proceeded preferentially along the grain boundaries to form coarse pores, and the surface area of the foil surface did not expand sufficiently. This investigation result suggests that even if there are many impurities, if the crystal structure due to the impurities is fine, coarse pores are not formed, and the surface area of the foil surface is sufficiently increased.

Accordingly, the present inventors have studied various conditions for producing aluminum foil in order to generate a fine crystal structure. As a result, it has been found that, particularly by devising the conditions of hot finish rolling, even if many impurities are present, a fine and uniform crystal structure is generated, and the impurities are finely and uniformly precipitated. Was reached.

[0005]

That is, the present invention relates to Fe0.03
% Or less, Si 0.03% or less, Cu 0.01% or less, Al 99.93 to 99.98
% Of the aluminum ingot is subjected to a homogenization treatment at a temperature of 590 ° C. or more for a time of 3 hours or more, and then subjected to hot rough rolling. The hot finish rolling is performed with a reduction ratio of 85% or more, and the temperature of the aluminum plate at the end of the hot finish rolling is set to 250 to 300 ° C., the aluminum plate is wound up, and then cold rolling is performed. The present invention relates to a method for producing an aluminum foil for an electrolytic capacitor anode.

[0006] The aluminum ingot used in the present invention is Fe
0.03% or less, Si 0.03% or less, Cu 0.01% or less, Al99.93-9
9.98%. If the content of Fe and Si exceeds 0.03%, even if the method according to the present invention is employed, coarse crystals of impurities are generated and coarse holes are formed during etching, which is not preferable. Also, if Cu exceeds 0.01%, overdissolution is likely to occur, and coarse holes are formed during etching,
Not preferred. On the other hand, when Al is less than 99.93, the amount of impurities becomes relatively large, and coarse impurity crystals are likely to be generated, which is not preferable. Conversely, if Al exceeds 99.98%, the resulting aluminum foil becomes expensive,
Does not meet the purpose of the present invention.

The aluminum ingot is subjected to a homogenization treatment at a temperature of 590 ° C. or more for a time of 3 hours or more. Particularly preferably, the homogenization treatment is performed at a temperature of 600 to 630 ° C for a time of 5 to 24 hours. This homogenization treatment is performed to re-dissolve the impurities in the aluminum ingot, ie, the crystallized compound composed of Fe, Si, and Cu. If the temperature condition during the homogenization treatment is lower than 590 ° C., it is particularly not preferable because the Fe-based compound hardly re-dissolves. Even when the time for the homogenization treatment is less than 3 hours, it is not preferable because the Fe-based compound or the like hardly re-dissolves. After this homogenization treatment, hot rough rolling is performed to obtain an aluminum plate having a predetermined thickness. The condition of the hot rough rolling may be a conventionally known general condition.

After hot rough rolling, hot finish rolling is performed under the following specific conditions. That is, in the hot finish rolling step, the rolling reduction in one pass is set to 40% or less, and the total rolling reduction in all passes is set to 85% or more. The rolling reduction in one pass is a reduction rate of the thickness of the aluminum plate when the aluminum plate is passed through a pair of rolling rolls. Therefore, the thickness of the aluminum plate before passing through a pair of rolling rolls and t _1, if the thickness of the aluminum plate after passing through the pair of rolling rolls and a t _2, a reduction ratio (%) = [(t ₁₋ t ₂ ) / t ₁ ] × 100. If the rolling reduction in one pass exceeds 40%, dynamic recrystallization tends to occur, and coarse impurities tend to precipitate, which is not preferable. Further, in order to suppress dynamic recrystallization, it is preferable that the aluminum plate be sufficiently cooled with a coolant for each pass.

[0009] The total rolling reduction in all passes is a reduction rate of the thickness of the aluminum plate after passing the aluminum plate through all the rolling rolls in the hot finish rolling process. Therefore, assuming that the thickness of the aluminum plate before the hot finish rolling step is t _a and the thickness of the aluminum plate after the hot finish rolling is t _z , the total draft (%) =
[(T _a −t _z ) / t _a ] × 100. If the total draft in all passes is less than 85%, the processing strain is too small, and it is difficult to obtain a fine recrystallized structure after the hot finish rolling, which is not preferable. Further, it is preferable that the time from the start of hot finish rolling to the end of hot finish rolling be within 5 minutes. If the hot finish rolling time is too long, dynamic recrystallization occurs in the aluminum plate during hot finish rolling, and coarse impurities are likely to precipitate. In addition, the thickness of the aluminum plate after the hot finish rolling is preferably about 3 to 8 mm.

After the hot finish rolling, the aluminum plate is kept at a temperature of 250 to 300 ° C. and rolled up as it is. The reason why the temperature of the aluminum plate is maintained at 250 to 300 ° C. is to generate a fine recrystallized structure on the surface of the aluminum plate. That is, it is not preferable that the temperature of the aluminum plate is lower than 250 ° C. because a recrystallized structure is hardly generated. On the other hand, when the temperature of the aluminum plate exceeds 300 ° C., the recrystallized structure grows violently, resulting in a coarse crystal structure, which is not preferable. After the aluminum plate is wound up, the aluminum plate cools down naturally.

Thereafter, the rolled-up aluminum plate is rewound and cold-rolled. Cold rolling may be performed under generally employed conditions. By this cold rolling,
The thickness of the aluminum plate is reduced, and an aluminum foil is obtained. The thickness of the aluminum foil can be arbitrarily determined, but is generally about 50 to 100 μm.

[0012]

EXAMPLE First, an aluminum ingot having the composition shown in Table 1 was prepared.

[Table 1]

Using the aluminum ingots shown in Table 1,
Homogenization treatment was performed under the conditions shown in Table 2. Then start temperature 59
Hot rough rolling was performed at 0 ° C. and an end temperature of 500 ° C., and then hot finish rolling was performed at a starting temperature of 500 ° C. and under the conditions shown in Table 2. Thereafter, cold rolling was performed in a conventional manner to obtain an aluminum foil having a thickness of 90 μm.

[Table 2]

This aluminum foil was electrolytically etched under the following conditions. That is, it consists of 3.5% hydrochloric acid and 4.0% oxalic acid
Electrolytic etching was performed in an aqueous solution at 53 ° C. using a rectangular wave having a frequency of 30 Hz at a current density of 0.2 / cm ² for 300 seconds. Then, in a 60 ° C. aqueous solution containing 8.0% boric acid,
A chemical conversion treatment was performed at a voltage of V. The capacitance of the electrode foil thus obtained was measured using an LCR meter 4284A manufactured by YHP. Table 3 shows the results.

[Table 3]

As is clear from the above results, the electrode foil obtained by the method according to the example has a high capacitance, whereas the electrode foil obtained by the method according to the comparative example has a low capacitance. Indicated capacity.

[0016]

As described above, the aluminum foil for an anode of an electrolytic capacitor obtained by the method according to the present invention does not have a coarse crystal structure, despite the low aluminum purity, and a fine crystal is obtained. Many are dispersed uniformly. Therefore,
When the aluminum foil is etched, impurities existing along the fine crystal structure are dissolved, and a large number of fine holes are formed on the surface of the aluminum foil. Accordingly, the surface area of the aluminum foil surface can be sufficiently increased, and the anode foil obtained by etching has an effect of giving a high capacitance equivalent to that when using a high-purity aluminum foil. .

────────────────────────────────────────────────── ⁷ Continuation of the front page (51) Int.Cl. ⁷ Identification code FI C22F 1/00 691 C22F 1/00 691B 691C 694 694A 694B H01G 9/055 H01G 9/04 337 (58) Fields surveyed (Int. Cl ^7, DB name) C22F 1/04 -. 1/057 C22C 21/00 - 21/18 H01G 9/04 - 9/055

Claims (1)

(57) [Claims] 1. Fe0.03% or less, Si0.03% or less, Cu0.01%
Hereinafter, into an aluminum ingot composed of Al 99.93-99.98%,
After performing homogenization treatment at a temperature of 590 ° C. or more for a time of 3 hours or more, hot rough rolling is performed, and then the reduction in one pass is 40% or less and the total reduction in all passes is 85% or more. Performing hot finish rolling, and setting the temperature of the aluminum plate at the end of hot finish rolling to 250 to 300 ° C., winding up the aluminum plate, and then performing cold rolling, the aluminum foil for an electrolytic capacitor anode characterized by performing cold rolling Production method.