JPH10287944A - Aluminum alloy for electrolytic capacitor anode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum alloy for medium- and low-voltage electrolytic capacitor anode foil, having high bending strength even after being annealed after alternating current etching. SOLUTION: This aluminum alloy has a composition in which the purity of aluminum is regulated to >=99.9 wt.% and the contents of Ti and V are limited to <2 wt.ppm and <2 wt.ppm, respectively, or has a composition in which the purity of aluminum is regulated to >=99.9 wt.% and the contents of Ti, V, and B are limited to <=3 wt.ppm, <=3 wt.ppm, and 2-10 wt.ppm, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an aluminum alloy for an anode of an electrolytic capacitor.

[0002]

2. Description of the Related Art An aluminum foil for an anode of a medium- to low-pressure electrolytic capacitor is assembled as a capacitor after being subjected to AC etching, washing, drying, annealing, chemical conversion treatment and cutting.

[0003]

However, in an etched foil subjected to AC etching, cleaning, drying and annealing, there is a problem that the bending strength is greatly reduced.

An object of the present invention is to provide an aluminum alloy for a medium-to-low pressure electrolytic capacitor anode foil having high bending strength even after annealing after AC etching.

[0005]

The inventor of the present invention has found that the reduction in bending strength, which is a problem of the prior art, is caused by heat treatment at 200 to 300 ° C., such as drying and annealing after AC etching, at crystal grain boundaries. Hydrogen introduced into the aluminum by alternating current etching is diffused to the crystal grain boundaries by heat treatment such as drying and annealing, and the voids are the cause.
It has been found that this occurs due to aggregation.

Therefore, the present inventor has found that it is effective to suppress the decrease in bending strength, in other words, to suppress the diffusion of hydrogen in aluminum during heat treatment in order to suppress voids. Focusing attention, as a result of intensive research, it has been found that diffusion of hydrogen can be suppressed by controlling the contents of Ti and V in aluminum or by adding B.

To achieve the above object, the present invention provides:
The following aluminum alloy for electrolytic capacitor anode foil is provided. That is, it is an aluminum alloy for an anode of an electrolytic capacitor in which the purity of aluminum is 99.9% by weight or more, and the content of Ti is less than 2 ppm by weight and the content of V is less than 2 ppm by weight. The purity of aluminum is 99.9% by weight or more, the content of Ti is 3% by weight or less, the content of V is 3% by weight or less, B
Is limited to 2 to 10 ppm by weight.

The reasons for limiting the composition of each component of the aluminum alloy according to the present invention will be described below. The hydrogen solubility of Ti and V at room temperature is 15000 cc / 100 g or more,
Even if the amount contained in aluminum is as small as a few ppm, it becomes a trap site of hydrogen and generates hydrides.
It is conceivable that, when the temperature rises to a medium to low temperature range of 00 ° C., hydrogen solubility decreases, so that hydrogen is released and the amount of hydrogen diffusion increases.

[0009] B penetrates into and defects in aluminum,
It is conceivable to suppress hydrogen diffusion to obstruct the hydrogen diffusion path.

[0010] The following experiments were performed to verify the above hypothesis. Various aluminum alloys shown in Table 1 were melted, cast, cold-rolled, and then cut into 1 mm × 5 mm × 10 mm as test materials.

[0011]

[Table 1]

The obtained test material was degreased with acetone, immersed in an aqueous solution containing 10% by weight of hydrochloric acid for 5 minutes to activate the surface, and then immersed in an etching solution containing 4% by weight of hydrochloric acid and 0.25% by weight of sulfuric acid. Then, the cathode was charged with hydrogen at an alternating current of 5 Hz (0 to 1 A) for 30 minutes.

Each of the specimens subjected to hydrogen charging was subjected to three levels of heat treatment immediately after hydrogen charging, after vacuum annealing at 200 ° C. for 24 hours, and after vacuum annealing at 400 ° C. for 24 hours. The amount of hydrogen gas released at each annealing level of the test material, that is, the amount of hydrogen diffusion was investigated.

Table 2 shows the results of the investigation on the amount of released hydrogen gas.
(All are relative values with the amount of hydrogen gas immediately after hydrogen charging of each test material as 100)

[0015]

[Table 2]

From the results shown in Table 2, it can be seen that 2 wt ppm or more of Ti and V contained in aluminum increases the amount of diffusion of hydrogen during annealing in a medium to low temperature range around 200 ° C. 3 ppm by weight of Ti therein,
Even if V is included, it is apparent that the addition of B at 2 ppm by weight or more can suppress an increase in the amount of diffusion of hydrogen during annealing in a low-temperature region around 200 ° C.

However, if the B content exceeds 10 ppm by weight, the dissolution during etching becomes non-uniform, so that the added amount of B is 2 to 10 ppm by weight, preferably 3 to 5 ppm by weight.
pm is preferred.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described based on examples. Various aluminum alloys shown in Table 3 were melted, cast, hot and cold rolled and then 0.1 mm × 10 mm × 5
The foil cut to 0 mm was used as a test material.

[0019]

[Table 3]

The obtained test material is degreased with acetone, immersed in an aqueous solution containing 10% by weight of hydrochloric acid for 5 minutes to activate the surface, and then immersed in an etching solution containing 4% by weight of hydrochloric acid and 0.25% by weight of sulfuric acid. And AC 5 Hz (-0.3 to 0.3 A) x 30
Minute AC etching was obtained.

For the test material subjected to AC etching,
After each washing, annealing was performed in the air, and the amount of voids in the cross section was investigated. The annealing temperature and time were set at 300 ° C. × 24 hours to promote void formation.

Table 4 shows the results of the cross-sectional void amount investigation.

[0023]

[Table 4]

From the results shown in Table 4, the content of Ti and V in aluminum of 2 ppm by weight or more is 200 to 3 ppm.
To increase the amount of voids during annealing at 00 ° C. in the low-temperature range, and to add 3 wt ppm of Ti, V in aluminum.
However, it is clear that the addition of 3 wt ppm of B can suppress an increase in the amount of voids during annealing in a medium to low temperature range of 200 to 300 ° C.

[0025]

As described above, by supplying the aluminum alloy of the present invention to an aluminum foil for a low-pressure anode in an electrolytic capacitor, the diffusion of hydrogen during drying and annealing after AC etching can be suppressed. The effect of suppressing generation of voids and contributing to improvement in bending strength is achieved.

[Procedure amendment]

[Submission date] September 16, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0015

[Correction method] Change

[Correction contents]

[0015]

[Table 2]

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tomoaki Isayama 80, Yotsumachi, Omuta-shi, Fukuoka Kyushu Mitsui Aluminum Industry Co., Ltd. (72) Takeshi Fukiharu 80, Yotsumachi, Omuta-shi, Fukuoka Luminium Industry Co., Ltd.

Claims (2)

[Claims] 1. An aluminum alloy for an anode of an electrolytic capacitor, wherein the purity of aluminum is 99.9% by weight or more, and the content of Ti is limited to less than 2 ppm by weight and the content of V is limited to less than 2 ppm by weight. 2. The purity of aluminum is not less than 99.9% by weight, the content of Ti is 3 ppm by weight or less, the content of V is 3 ppm by weight or less, and the content of B is 2 to 10 ppm by weight. Aluminum alloy for restricted electrolytic capacitor anode.