JPH0521288A - Aluminum alloy for cathode foil of electrolytic capacitor - Google Patents

Abstract

PURPOSE:To provide aluminum alloy for a cathode foil which avoids the increase of a leakage current and breakage of itself when it is employed as the cathode foil of an electrolytic capacitor while a high electrostatic capacity is provided. CONSTITUTION:50-1500ppm of Mg, 30-150ppm of Ga and 5-100ppm of B are contained in the alloy whose base is aluminum having a purity not less than 99.85% and, further, 50-1500ppm may be contained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy for cathode foil of electrolytic capacitors.

[0002]

2. Description of the Related Art In order to increase the electrostatic capacity of an aluminum electrolytic capacitor and improve its performance, it is necessary to increase the electrostatic capacity of not only the aluminum foil for anode but also the cathode foil.

For this reason, generally, the cathode foil is subjected to a chemical or electrochemical etching treatment to enlarge the effective area to increase the electrostatic capacity per unit volume. Studies have been conducted from the viewpoint of the material composition of the cathode foil to improve it. As a cathode foil having improved etching characteristics, an aluminum alloy cathode foil containing Cu in an amount of 0.1 to 0.5 wt% is known (for example, JP-A-56-13344).
4, JP-A-62-149858).

[0004]

However, when a cathode foil containing Cu is used in an electrolytic capacitor, Cu in the foil is deposited to increase leakage current, which may cause damage to the capacitor body. It turned out to cause the problem.

The present invention has been made in view of the above circumstances and provides a cathode foil which has a high electrostatic capacity but does not cause an increase in leakage current or damage when used in a capacitor. It is an object of the present invention to provide an aluminum alloy for an electrolytic capacitor cathode foil.

[0006]

In order to achieve the above object, an aluminum alloy for a cathode foil according to the present invention is based on an aluminum base metal having a purity of 99.85% or more, and M
g: 50 to 1500 ppm, Ga: 30 to 150 pp
m, B: 5 to 100 ppm, or further Zn: 50
It is characterized by containing ~ 1500 ppm.

In the above description, the base aluminum ingot is limited to those having an Al purity of 99.85% or more. If it is less than 99.85%, elements such as Mg, which will be described below, that act as etching nucleation elements are limited. This is because the effect of increasing the capacitance of the foil cannot be obtained even when it is contained.

When Mg (magnesium) is contained, it forms an Mg ₂ Si intermetallic compound with Si which is unavoidably contained in the alloy. And thereby, suppressing the Si precipitation that causes excessive surface dissolution in the etching treatment for increasing the surface area,
There is an effect that the starting point of etching is appropriately increased to suppress excessive surface dissolution, thereby improving the surface area ratio and eventually increasing the capacitance. However, if it is less than 50 ppm, the above-mentioned effect is insufficient, and it is not possible to improve the surface area ratio and thus the electrostatic capacity. On the other hand, even if the content exceeds 1500 ppm, the amount of surface dissolution also increases, and as a result, not only a sufficient surface expansion ratio cannot be obtained but also the mechanical strength deteriorates due to an increase in corrosion weight loss. Therefore, Mg is 50 to 1500 ppm
Must be contained within the range of. A particularly preferable content of Mg is 60 to 600 ppm.

Since both Ga (gallium) and B (boron) are contained, they have the effect of increasing the etching start point and increasing the capacitance. But,
When Ga is less than 30 ppm or B is less than 5 ppm, these effects are poor, and conversely, when Ga exceeds 150 ppm or B exceeds 100 ppm, mechanical strength is deteriorated due to excessive surface dissolution and increase in corrosion weight loss. Therefore, Ga is 30 to 150 ppm, B is 5 to 100 ppm.
Must be contained in the ppm range. Particularly preferred contents are Ga: 60 to 120 ppm, B: 10 to 6
It is 0 ppm.

Zn which can be optionally contained is 50 to 50%.
When the content is in the range of 1500 ppm, it contributes to increase of electrostatic capacity and improvement of mechanical strength due to increase of etching start point. However, if it is less than 50 ppm, its effect is poor, and conversely, if it exceeds 1500 ppm, electrostatic capacity and strength are deteriorated due to excessive corrosion. A particularly preferable Zn content range is 70 to 300 ppm.

The other impurity elements are in the range of 99.85% aluminum purity. The production of the electrolytic capacitor cathode foil of the aluminum alloy according to the present invention may be carried out by a conventional method, for example, after casting a slab by a vertical or horizontal semi-continuous casting method from molten aluminum,
This slab may be hot-rolled, cold-rolled, and foil-rolled to form a foil having a thickness of about 15 to 60 μm. The thus-produced foil is used as an electrolytic capacitor cathode foil by expanding the effective area of the foil surface by subjecting it to a hard foil or softening it by an annealing treatment and then performing an electrochemical or chemical etching treatment.

[0012]

According to the aluminum alloy for an electrolytic capacitor cathode foil according to the present invention, as will be apparent from the consideration of the examples described later, it does not substantially contain Cu but has a large capacitance. It is possible to provide a cathode foil having the same. Moreover, by not containing Cu substantially,
Even when the cathode foil is used in an electrolytic capacitor, it is possible to avoid the conventional increase in leakage current and the risk of capacitor damage.

[0013]

Embodiments of the present invention will be described below.

A slab is cast by a semi-continuous casting method from an aluminum melt adjusted to have the component amounts shown in Table 1 below, and the slab is subjected to hot rolling, cold rolling and foil rolling according to a conventional method to obtain a thickness. A 50 μm hard foil was produced. Next, this was immersed in a mixed aqueous solution of 7% hydrochloric acid, 0.2% phosphoric acid and 0.2% nitric acid at a temperature of 55 ± 1 ° C. to obtain a current density of 60 A.
Etching was performed for 135 seconds with an alternating current of / dm ² to obtain a cathode foil. Also, the corrosion weight loss due to etching was determined.

Each of the cathode foils obtained above was immersed in a mixed aqueous solution of 5% boric acid and 5% citric acid (temperature: 30 ° C.), and the electrostatic capacity was measured by an AC universal bridge. The results are also shown in Table 1. Note that the corrosion weight loss and the electrostatic capacity are represented by relative comparison, with sample No. 6 being 100%.

[0016]

[Table 1]

As is clear from the results shown in Table 1 above, according to the alloy of the present invention, the capacitance of the cathode foil produced by the alloy is extremely high while the Cu content is kept extremely low. It was confirmed that it can be made very expensive.

Claims (2)

[Claims] 1. A cathode foil for an electrolytic capacitor, which is based on an aluminum base metal having a purity of 99.85% or more and contains Mg: 50 to 1500 ppm, Ga: 30 to 150 ppm, and B: 5 to 100 ppm. Aluminum alloy for. 2. A base of aluminum ingot having a purity of 99.85% or more, containing Mg: 50 to 1500 ppm, Zn: 50 to 1500 ppm, Ga: 30 to 150 ppm, and B: 5 to 100 ppm. Aluminum alloy for electrolytic capacitor cathode foil.