JP3312913B2 - Aluminum foil for electrode 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 an aluminum foil for an electrode of an electrolytic capacitor, and more particularly to a composite type aluminum clad formed by coating both surfaces of a core layer mainly for maintaining mechanical strength with outer layers contributing to surface area expansion. Regarding foil.

[0002] In this specification, "%" means "% by weight".

[0003]

2. Description of the Related Art In recent years, there has been an increasing demand for smaller and lighter electrolytic capacitors. Therefore, it is strongly required that the aluminum foil for an electrode has excellent mechanical strength so that it can be wound up at a high speed with a small radius of curvature, in addition to further improving the capacitance. I have.

[0004] In response to such a demand, a clad foil laminated and integrated with a core layer mainly for maintaining mechanical strength between outer layers of high-purity aluminum which contributes to an increase in the surface area by etching has been hitherto used. Various proposals have been made.

[0005] For example, in Japanese Patent Application Laid-Open No. 51-113154, the core layer is made of aluminum containing more Fe than the outer layer, and the progress of etching pits growing from the surface during etching is included in the core layer. F
e, the core is stopped by an intermetallic, and the core layer is securely left to maintain the mechanical strength of the foil. In Japanese Patent Application Laid-Open No. 62-47110, the core layer is It has been proposed to obtain the same effect as described above by using an aluminum alloy having a lower purity than the outer layer.

[0006]

However, in any of the above-mentioned prior arts, sufficient satisfaction has not yet been obtained with respect to the conflicting demands of the improvement of the capacitance and the improvement of the mechanical strength. It was not something that could be done, but something that needed further improvement.

[0007] The present invention is based on the same improvement means using a clad foil as described above, and further enhances the mechanical strength without impairing the etching property, so that a deep etching layer can be formed. The purpose is to ensure sufficient strength.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is to select Fe and Si as strengthening elements, to include them in a relatively large amount in the core layer, and to make the crystal structure fine. In, without impairing the etching properties,
The mechanical strength and bending strength are increased.

Thus, the present invention relates to Fe: 0.9-1.
An aluminum foil containing 6 % and Si: 0.2 to 0.6 %, the balance being aluminum foil and inevitable impurities is used as a core layer, and a high-purity aluminum outer layer having a purity of 99.9% or more is provided on both surfaces of the core layer. The gist is an aluminum foil for an electrolytic capacitor electrode which is laminated and integrated.

In the core layer, in addition to the above Fe and Si, Ti: 0.005 to 0.1% and / or B: 0.0
01-0.05% may be contained. However, it is preferable that B be contained in the presence of Ti.

In order to secure the bending strength of the foil, it is necessary that the core layer is recrystallized at least after etching and the crystal grain size is set to 50 μm or less.

Hereinafter, each of the above components of the present invention will be described in more detail.

First, the use of high-purity aluminum having a purity of 99.9% or more in the outer layer makes it possible to improve the etching property, and to enhance the effect of enlarging the surface area by electrolytic etching and, consequently, the effect of improving the capacitance. The reason for this is to obtain a small leakage current. Most preferably, aluminum having a purity of 99.99% or more is used.

On the other hand, the main function of the core layer is to ensure the mechanical strength of the aluminum foil even after etching. Therefore, it is necessary that the tensile strength and the bending strength are at least higher than those of the outer layer. For this reason, in the core layer, Fe: 0.9 to 1.6 % and S
i: 0.2 to 0.6 % is contained. These inclusions,
The effects of solid solution strengthening of Fe and Si, particle dispersion strengthening by an intermetallic compound, and strengthening by crystal refinement are also realized .

The core material further preferably contains one or two of Ti and B. Each of these elements is effective in refining solidified crystal grains, but the effect is poor when the content is less than 0.005% Ti and less than 0.001% B; : 0.
If the content exceeds 05%, coarse crystals are formed, and the mechanical strength is rather reduced. The most preferred content range is T
i: 0.01 to 0.03%, B: 0.005 to 0.01
%, And B is more T
It is desirable that i coexist with the content of i in the above range.

The core layer needs to have high tensile strength and bending strength as described above. In order to increase the bending strength, it is desirable that the elongation is large. Therefore, in order to increase the strength and elongation, at least one step is required in the process from etching to forming the capacitor electrode foil.
It is necessary that the core layer be recrystallized by performing heat treatment more than once, and the crystal grain size be reduced to 50 μm or less, preferably 40 μm or less. The heating step for bringing into the recrystallization state may be performed before or after the etching.

In the production of the clad foil according to the present invention, in which the core layer and the outer layer are laminated, the core layer and the outer layer are pressure-bonded by hot rolling, cold-rolled and foil-rolled to a predetermined thickness. It is desirable that the core layer and the outer layer be manufactured separately, but the present invention is not limited to this. For example, the core layer and the outer layer separately manufactured may be joined and integrated via an adhesive.

The cladding ratio between the core layer and the outer layer is not particularly limited in the present invention. Considering the material strength of the core layer, the most advantageous harmony between the capacitance and the mechanical strength is determined. Although it is set as required, it is desirable that the etching pit does not bite into the core material. That is, it is desirable that the thickness of the outer layer be equal to or greater than the depth of the etching layer where the etching pits are formed. Generally, the cladding ratio of the outer layer to the total thickness of the cladding foil [(total thickness of outer layer / total thickness of cladding foil)
× 100] is about 30 to 85%, particularly preferably 5 to 85%.
It is good to be 0-75%.

[0019]

According to the aluminum foil for an electrolytic capacitor electrode of the present invention, etching pits are formed sufficiently deep and densely in the outer layer portion made of a high-purity Al foil by electrolytic etching to sufficiently enlarge the surface area. While the Fe and Si contents of the core layer are
Since the core layer has a high tensile strength and a high bending strength, the core layer can have sufficient mechanical strength even after etching due to the remaining core layer.
Therefore, while the surface area is made as large as possible by etching, and the capacitance is large, the mechanical strength can be made sufficiently excellent, and thus it is more suitable for the demand for lighter and smaller electrolytic capacitors. Can be made compatible. Furthermore, the inclusion of Ti and B in the core layer
Higher tensile strength and bending strength
You.

Also, the recrystallized grains of the core layer are set to 50 μm or less.
If specified, the elongation is large and the bending strength is particularly high.
Is made.

[0021]

Example: Fe: 0.002%, Si: 0.002%,
A high-purity aluminum slab containing 0.002% of Cu and the balance of aluminum and inevitable impurities is
After homogenizing at 0 ° C. for 20 hours, it was hot-rolled to produce a 110 mm-thick outer layer plate.

On the other hand, a slab containing Fe, Si, Ti, and B in various proportions shown in Table 1 and containing 0.01% or less of impurities and the balance of aluminum was formed by hot rolling to a thickness of 80 mm. Was obtained.

Then, the outer layer plate is placed on both sides of the core layer plate, heated to 500 ° C., pressed by hot rolling, cold rolled, and foil rolled to obtain various 90 μm thick clads. A foil was obtained (the thickness of the outer layer was 30 to 32 μm on one side)
m).

With respect to these clad foils, foil-rolled ones in the H18 state and ones subjected to annealing at 300 ° C. for 2 hours ( Example 7 ) were prepared, and all were electrolytically etched under the following conditions. After that, a heat treatment was performed at 400 ° C. for 1 minute. [Etching conditions] Electrolyte: 5% hydrochloric acid + 0.3% phosphoric acid + 0.1% nitric acid Temperature: 55 ° C. Current: 25 A / dm ² · 60 Hz AC Time: 10 minutes And after the above etching and heat treatment With respect to each sample, its tensile strength, bendability, crystal grain size of the core layer were examined, and the capacitance after formation at 20 V was measured.
The results are shown in Table 1 in comparison with Comparative Examples 1 to 3.

In Comparative Examples 1 and 2, the core layer was formed of an aluminum alloy having a composition in which one or both of Fe and Si deviated from the specified amount of the present invention. It was manufactured as a single-layer product made of high-purity aluminum alone having the composition of the outer layer material in the examples.

The capacitance is shown as a ratio when the value of Comparative Example 3 is set to 100.

[0027]

[Table 1]

As shown in Table 1, the aluminum foil for an electrolytic capacitor electrode according to the present invention has a purity of 99.
Single-layer product made of 99% high-purity aluminum (Comparative Example 3)
It was confirmed that the tensile strength and the bendability were further improved while realizing a high capacitance corresponding to.

Continued on the front page (72) Inventor Makoto Yao 6,224 Kaiyamacho, Sakai-shi, Osaka Showa Aluminum Co., Ltd. (72) Inventor Takeshi Nishizaki 6,224 Kaiyamacho, Sakai-shi, Osaka Showa Aluminum Co., Ltd. (72) Inventor Kenji Goshi name 6,224 Kaiyama-cho, Sakai City, Osaka Prefecture Inside Showa Aluminum Co., Ltd. (72) Inventor Masaru Kiryu 6,224 Kaiyama-cho, Sakai City, Osaka Prefecture Inside Showa Aluminum Co., Ltd. (56) References JP-A-55-77986 (JP, A) JP-A-62-47110 (JP, A) JP-A-49-10366 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name ) H01G 9/055 H01G 9/042 C22C 21/00

Claims (3)

(57) [Claims] 1. Fe: 0.9-1.6 % and Si: 0.2
An electrolytic capacitor comprising an aluminum foil containing aluminum and inevitable impurities as a core layer, and a high-purity aluminum outer layer having a purity of 99.9% or more laminated and integrated on both sides of the core layer. Aluminum foil for electrodes. 2. The core layer further comprises Ti: 0.005 to 0.1.
% And B: 0.001 to 0.05% of the aluminum foil for an electrolytic capacitor electrode according to claim 1, which contains one or two of 0.001 to 0.05%. 3. The aluminum foil for an electrolytic capacitor electrode according to claim 1, wherein the recrystallized grain size of the core layer is set to 50 μm or less.