JPH06271962A - Aluminum alloy foil for electrolytic capacitor high in strength after etching - Google Patents

Abstract

PURPOSE:To increase the capacitance of aluminum alloy foil after etching treatment and to improve its bending strength by specifying Si, Fe, Cu, Zr, Mo, W and Al. CONSTITUTION:This Al alloy is formed of a compsn. contg., by ppm, <=100 Si and <=100 Fe and furthermore contg. total 0.5 to 10 of one or more kinds among 0.5 to 10 Zr, 0.5 to 10 Mo and 0.5 to 10 W, and the balance Al. The content of Si and Fe is regulated to prevent the self-corrosivity of Al foil. Moreover, the content of Cu is limited to promote the progress of pits and to increase its capacitance. Furthermore, Zr, Mo and W are incorporated in specified ranges to improve its bending strength after etching.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an aluminum alloy foil for electrolytic capacitors, which has high strength after etching.
The present invention relates to an aluminum alloy foil for electrolytic capacitor anodes, which has good etching characteristics and particularly has high bending strength after AC etching.

[0002]

2. Description of the Related Art Electrodes of aluminum electrolytic capacitors are roughened by chemical or electrochemical etching in order to increase the electrode surface area and increase the capacitance per unit volume. Therefore, the aluminum foil used as an electrode must have excellent etching characteristics and form a fine three-dimensional structure with an enlarged surface area by etching. On the other hand, the electrolytic foil is required to have strength, especially tensile strength and bending strength in use, but the strength of the aluminum foil is lowered by performing the etching treatment.

Generally, as the aluminum electrolytic foil, for example, high-purity aluminum having a purity of 99.9% or more is used. However, an aluminum foil having a high aluminum purity is likely to have coarse crystal grains during production, and its mechanical strength tends to be lowered. Therefore, aluminum alloy foils for electrolytic capacitors have been developed in which various alloy elements are added to improve mechanical strength without lowering etching properties.

For example, B is added to control Ti (Japanese Patent Publication No. Sho 62-8492), Ga is contained, and Si,
A material to which Cu and Mg are selectively added (Japanese Patent Publication No. 1-45766) and a material containing Si, Fe and Cu (Japanese Patent Laid-Open No. 2-5
No. 1212), a material to which Zn and Ga are further added (Japanese Patent Laid-Open No. 2-51211), which regulates the purity of aluminum and also Si, Fe, Cu, Mn, B, Ga and Z.
For example, those containing n (JP-A-4-124806) are available.

However, although some of the aluminum foils for electrolytic capacitor electrodes have numerical values of tensile strength, the bending strength has not been examined at all, and they do not always have sufficient bending strength. Absent. According to the research by the inventors, the bending strength after etching in the aluminum foil for electrolytic capacitors is affected by the uniformity of the amount of progress of the etch pits, and there is a constant relationship between the tensile strength and the bending strength after etching. It cannot be said that there is.

The inventors previously developed an aluminum alloy foil for capacitors, which has a high bending strength after etching,
I applied for a patent. This aluminum alloy foil is made of Si, F
e, Cu, Zr and Mo are added as essential alloy components,
Further, although W can be added as a selective component, as a result of further studying the effect of Zr, Mo, and W on the bending strength after etching of the aluminum alloy foil containing Si, Fe, and Cu, these results were obtained. It was found that an aluminum alloy foil for electrolytic capacitors having an industrial value in the field can be obtained by expanding the addition amount of additive components and adding them individually or in combination, and the present invention has been completed.

[0007]

SUMMARY OF THE INVENTION In order to improve the bending strength of an electrode for an electrolytic capacitor, particularly an aluminum foil for an electrolytic capacitor anode after etching, the present invention is directed to the progress of etching, the mechanism for forming an etch pit, and the bending mechanism. It was made as a result of repeated research on factors that affect bending strength, such as the relationship with strength. The purpose is to achieve excellent etching characteristics, especially AC etching characteristics.
Another object of the present invention is to provide an aluminum alloy foil for electrolytic capacitors, which has high bending strength after AC etching.

[0008]

An aluminum alloy foil for electrolytic capacitors, which has a high bending strength after etching according to the present invention for achieving the above object, contains Si100ppm or less, Fe100ppm or less, Cu5-60ppm, and further Z
r0.5-10ppm, Mo0.5-10ppm and W0.5-10ppm
The total amount of Zr, Mo and W is 0.5-10ppm.
And the balance is 99.96 (wt%, the same applies hereinafter) or more of Al and unavoidable impurities.

In etching the electrolytic foil, electrochemical etching is usually used for the aluminum foil for the anode. Direct current and alternating current are applied as the electrolytic current, but they are used properly according to the purpose of the capacitor.When used for high voltage, direct current that produces a large pit is used for so-called high voltage, and used for low voltage. If you do
For so-called low voltage, an alternating current is used that can obtain fine pits.

According to the research conducted by the inventors, the bending strength after etching generally shows a larger value as the uniformity of the amount of progress of the etch pits increases, whether the etching pits are DC etching or AC etching. When it progresses along a line, for example, along a crystal grain boundary, the progress of pits becomes non-uniform and it is easy to break in a bending test. Since the mechanism of the progress of the etch pit differs depending on the components contained in the aluminum foil, it is necessary to study the component composition in order to obtain an aluminum foil having excellent bending strength after etching.

For example, in the AC etching applied to the low-voltage electrolytic foil, a film is formed on the wall of the pit formed during the anode half cycle in the next half cycle, and from the defective portion of the film to the next anode half cycle. Since pits sometimes occur, and the pit formation progresses by repeating this, the conditions for the aluminum foil to have excellent etching characteristics, sufficient capacitance as an electrode for electrolytic capacitors, and high bending strength after etching. It is important that the film formed during the cathode half cycle has an appropriate amount of defects and these defects are not aligned in a particular direction. If the amount of defects is small, the progress of the etch pits tends to be non-uniform, and if the amount of defects is too large, the pits will coalesce or the pits will not progress in the thickness direction of the aluminum foil, reducing the effect of expanding the surface area. The capacitance of is not obtained.

From the above viewpoints, the inventors of the present invention diversify the combinations of the components and compositions for obtaining an aluminum foil for electrolytic capacitors in which uniform etching proceeds, and which has excellent capacitance and bending strength after etching. The present invention has been made through investigations. The significance of each element and the reasons for limitation will be described below.

Si and Fe are elements that are inevitably contained in high-purity aluminum. However, if a large amount of these elements is contained, the aluminum foil becomes more self-corrosive,
The walls of the pits formed by etching are dissolved and the capacitance is reduced. Therefore, it is necessary to limit each to 100 ppm or less, preferably 60 ppm or less.

Cu passivates the walls of the etch pits,
It has a function of promoting the progress of pits, but if it is too large, the self-corrosion property of the foil becomes strong and the capacitance is lowered. The preferable content of Cu is in the range of 5 to 60 ppm, more preferably 10 to 50 ppm. Al must have a purity of 99.96% or more, preferably 99.98% or more. Al
If the purity of the foil becomes low, the self-corrosion property of the foil material becomes strong and the electrostatic capacity is lowered.

Zr, Mo and W make the formation of etch pits by etching uniform and improve the bending strength. In particular, in AC etching, it is effective in causing an appropriate amount of defects in the film formed during the cathode half cycle to improve the distribution of etch pits and to improve the bending strength after etching. The preferred content is Z
r0.5-10ppm, Mo0.5-10ppm, W0.5-10ppm
And the total amount of Zr, Mo and W is in the range of 0.5 to 10 ppm. When Zr, Mo and W are less than 0.5 ppm respectively, the effect of improving the bending strength is small, and when Zr, Mo and W are added alone, these elements are
If it exceeds 10 ppm, the amount of defects increases and the pits do not progress in the thickness direction of the foil, the surface area expansion effect decreases and the capacitance decreases. When two or more kinds are added, Z
When the total amount of r, Mo and W exceeds 10 ppm, the same adverse effect occurs.

[0016]

In the present invention, the amounts of Si and Fe that enhance the self-corrosion property of the aluminum foil are regulated, the content of Cu that promotes the progress of pits and increases the capacitance is limited, and the etch pits are dispersed. Aluminum foil for electrolytic capacitor electrodes containing Zr, Mo and W in a specific range to improve the bending strength after etching and to have excellent capacitance and bending strength after etching due to the interaction of these component elements. Is what you get.

[0017]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples. Example 1 An aluminum alloy having the composition shown in Table 1 was cast into a slab shape by continuous casting, and the cast slab was cast at 600 ° C.
After homogenizing heat treatment at the temperature of 10 hours, hot rolling and cold rolling were performed to obtain a foil with a thickness of 0.1 mm. The obtained foil material is annealed in an argon gas atmosphere at 325 ° C for 1 hour,
The annealed material is 150m in a solution of 300ml / l hydrochloric acid, 24ml / l nitric acid, 1ml / l phosphoric acid at 25 ℃ using 10Hz alternating current.
The etching treatment was performed by energizing the device at a current density of A / cm ² for 10 minutes. The sample after etching was formed into a strip shape having a width of 10 mm, and the bending strength and the capacitance were measured.

The bending strength was measured using a MIT rub resistance tester under a load of 200 gf, a bending radius of 1 mm, a bending angle of 90 ° on one side, and a bending speed of 175 times / min. It was converted to 20 V in an aqueous ammonium solution and measured with an LCR meter. The self-corrosiveness of the foil is
The annealed material before the etching treatment was cut into a size of 50 mm × 50 mm, immersed in 20% hydrochloric acid at 80 ° C. for 10 minutes, and the dissolution amount was measured. The measurement test results are shown in Table 2.

As shown in Table 2, each of the samples prepared according to the examples of the present invention had bending strength,
It can be seen that both the electrostatic capacity shows high performance, the amount of dissolution is small, and the self-corrosion resistance is excellent.

[0020]

[Table 1]

[0021]

[Table 2]

Comparative Example 1 An aluminum alloy having the composition shown in Table 3 was prepared as in Example 1.
In the same manner as in (1), a continuous slab was cast into a slab shape, and the cast slab was homogenized, hot-rolled, cold-rolled and annealed under the same conditions as in Example 1 to obtain a foil material having a thickness of 0.1 mm. did. This foil material was treated with 300 ml / l hydrochloric acid, 24 as in Example 1.
10 ml at a current density of 150 mA / cm ² using an alternating current of 10 Hz in a solution of ml / l nitric acid and 1 ml / l phosphoric acid at 25 ° C.
An alternating current etching process was performed by energizing for a minute.
The sample after the AC etching treatment was formed into a strip shape with a width of 10 mm, and the bending strength was measured using a MIT rub-fatigue tester in the same manner as in Example 1, and the sample was statically formed at 20 V in an ammonium adipate aqueous solution and statically formed. The capacitance was measured and the self-corrosion property was evaluated. The results are shown in Table 4. In addition, in Table 3,
Those under the conditions of the present invention are underlined.

[0023]

[Table 3]

[0024]

[Table 4]

As can be seen from Table 4, the sample No. 1 produced according to the comparative example contained a large amount of Zr + Mo and was
Has a large Zr content and a large total content of Zr + Mo + W, so that there are too many defects that occur in the film formed during the cathode half cycle of AC etching, the etch pits coalesce, and the pits are the thickness of the foil. Since it does not proceed in the direction, the effect of increasing the surface area is reduced, so that both the bending strength and the capacitance are reduced, and the self-corrosion property is also increased. No.3 is Z
Since the contents of r, Mo, and W are small, the progress of the etch pits is not uniform, and the pits are likely to be dispersed along the grain boundaries, resulting in poor bending strength. In No. 4, the total amount of W is
Since it exceeds 10 ppm, the number of defects formed in the film during AC etching causes pit coalescence, resulting in a decrease in bending strength, electrostatic capacity, and self-corrosion. In No. 5, since the amount of Si and Fe exceeds the specified amounts, the walls of the pits formed by etching are dissolved, so that the capacitance is lowered and the bending strength is also lowered. Since No. 6 has a large Cu content, the progress of pits is excessively promoted, the self-corrosion property becomes strong, and the electrostatic capacity becomes poor.

[0026]

As described above, according to the present invention, an aluminum foil for an electrolytic capacitor electrode, particularly an anode, which has an excellent capacitance by etching treatment, particularly AC etching, and has a high bending strength after etching is obtained. Provided.

Claims (1)

[Claims] 1. Si 100 ppm or less, Fe 100 ppm or less, Cu
Including 5-60ppm, Zr0.5-10ppm, Mo0.5
~ 10ppm and W0.5 ~ 10ppm at least one of Z
The total amount of r, Mo, and W is included in the range of 0.5-10ppm, the balance
Aluminum alloy foil for electrolytic capacitors, which has a high strength after etching, consisting of 99.96% (weight% and the same below) Al and inevitable impurities.