JPH09213586A - Aluminum foil for electrode of electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum foil for electrode of electrolytic capacitor by means of which the capacitance can be increased. SOLUTION: The aluminum foil has aluminum purity of 99.9% or above and contains 15-300ppm of Ag. In addition to Ag, it may contain one kind or more of 0.1-5ppm of Pb, 1-50ppm of Zn, 1-50ppm of Ga, 5-60ppm of Fe, 5-80ppm of Si.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an aluminum foil for an electrode of an electrolytic capacitor.

[0002]

2. Description of the Related Art An Al foil generally used as an electrode material for an aluminum electrolytic capacitor usually has a large effective area to increase the capacitance per unit area.
An electrochemical or chemical etching process is performed.

[0003] However, a sufficient capacitance cannot be obtained simply by etching the foil. For this reason, generally, in the final annealing step after foil rolling, a high temperature heat treatment of about 450 ° C. or higher is performed in order to improve the etching characteristics of the foil by forming a texture having many cubic orientations. In recent years, on the surface layer of Al foil up to 0.1 μm,
Concentration of Pb has also been performed as a nucleus of etch pit generation (Japanese Patent Publication No. 62-42370).

[0004]

However, when the above-mentioned Al foil provided with the Pb-enriched layer was analyzed in detail about the occurrence of etch pits, the occurrence of etch pits was found to be
It is still sparse and non-uniform, and it has not been sufficiently satisfied with the recent demand for higher capacitance of electrolytic capacitors.

The present invention has been made in view of the above technical background, and an object of the present invention is to provide an aluminum foil for an electrolytic capacitor electrode capable of increasing electrostatic capacitance.

[0006]

In order to achieve the above object, the inventors of the present invention have conducted extensive studies and found that the aluminum foil composition was
It was found that by adding g and further various trace elements, the surface area ratio by etching is increased, and a high capacitance foil can be obtained.

The present invention has been made on the basis of such findings, and has an aluminum purity of 99.9% or more,
Ag: 15 to 300 ppm, or Pb: 0.1 to 5 ppm, Zn: 1 to 50 ppm,
Ga: 1 to 50 ppm, Fe: 5 to 60 ppm, Si:
The gist is to contain at least one of 5 to 80 ppm.

The reason why the aluminum purity of the aluminum foil according to the present invention is required to be 99.9% or more is 99.9%.
If the purity is less than%, the growth of etching pits is hindered by the presence of many impurities during etching, and even the presence of Ag within the scope of the present invention makes it impossible to form uniform deep tunnel-shaped etching pits, and therefore the capacitance of This is because a high aluminum foil cannot be obtained. Preferably, the aluminum purity is 99.95% or more.

Ag in the aluminum foil is an element necessary for uniformly distributing pits at a high density during etching. That is, generally, in the initial stage of etching, uneven unevenness of the surface existing on the foil surface, oil, deposits such as roll coating, or those that have been altered cause uneven local dissolution pits, resulting in uneven etching pit density. The property (sparse / dense) occurs, and in the remarkable case, the surface melts like a crater. This non-uniformity remains even after the end of the etching, causing a decrease in capacitance. Therefore, in order to prevent such a problem, attempts have been made to control the non-uniformity factor of the etching pits existing on these surfaces. It has been found that it has the effect of eliminating the locality of the etching pit and forming it at a high density.
If the Ag content is less than 15 ppm, such effect is poor, but if it exceeds 300 ppm, (100) after the final annealing.
Since the occupancy of the crystal plane is reduced, it is not possible to obtain a high capacitance foil. The occupation ratio of the (100) crystal plane is 95
When it is at least%, the capacitance can be increased, but if the Ag content is within the above range, it can be at least 95%. Therefore, the Ag content needs to be 15 to 300 ppm. The preferred lower limit of Ag content is 50 p
pm, the preferred upper limit is 200 ppm.

Further, in the aluminum foil for electrolytic capacitor electrodes according to claim 2, trace elements Pb, Zn, Ga and F are contained.
e and Si contribute to the improvement of the etching characteristics of the foil, respectively, as described in detail below. The presence of one or more of these elements can synergistically increase the capacitance together with the above-described Ag. In addition, these trace elements may be added individually, or may be added in any two or more kinds, and a synergistic effect corresponding to each action can be obtained.

Pb suppresses local solubility in the initial stage of etching and contributes to uniform distribution of etch pits. If the Pb content is 0.1 ppm, the above effect is poor, and if it exceeds 5 ppm, surface dissolution may occur. Therefore, the Pb content needs to be 0.1 to 5 ppm, the preferable lower limit value is 0.3 ppm, and the preferable upper limit value is 2 ppm. Further, since it is an element that exerts an effect in the initial stage of etching, it is preferable that it is present at a high concentration in the surface layer portion of the foil.

When Zn forms a solid solution in the Al matrix, it increases the solubility of the foil, promotes the growth of etching pits, and increases the capacitance. Zn content is 1pp
If it is less than m, the above effect is poor, while if it exceeds 50 ppm, the local solubility is strengthened to prevent the uniform distribution of the etch pits. Therefore, the Zn content is preferably 1 to 50 ppm, the particularly preferable lower limit value is 8 ppm, and the particularly preferable upper limit value is 20 ppm.

Ga is an element which easily segregates at the crystal grain boundaries or sub-grain boundaries and causes an uneven distribution of etch pits by itself, but since Ag makes the size of the sub-grain boundaries fine,
The presence of Ag has the effect of increasing the uniform dispersibility of etch pits. If the Ga content is less than 1 ppm, the above effect is poor, while if it exceeds 50 ppm, the local solubility increases.
Prevents uniform distribution of etch pits. Therefore, the Ga content is preferably 1 to 50 ppm, the particularly preferable lower limit value is 8 ppm, and the particularly preferable upper limit value is 20 ppm.

Fe and Si easily form a compound with Al in the matrix, and by controlling the dispersion state of these elements, the Ag concentration distribution can be made uniform, which in turn makes the etch pit distribution uniform. Can be In such an effect, Fe and Si are equivalent, and at least one kind may be contained. However, if the content is large, it causes overdissolution at the time of etching and the electrostatic capacity is lowered. Therefore, the Fe content is preferably 5 to 60 ppm, the particularly preferable lower limit value is 10 ppm, and the particularly preferable upper limit value is 30 ppm. Further, the Si content is 5
80 ppm is preferable, and a particularly preferable lower limit is 15 pp
m, and a particularly preferable upper limit value is 40 ppm.

[0015]

Next, specific examples of the aluminum foil for an electrolytic capacitor electrode of the present invention will be described.

First, aluminum ingots of various compositions shown in Table 1 are chamfered, followed by hot rolling, cold rolling (including intermediate annealing), and further final annealing, so that the final thickness is 1
An aluminum foil of 00 μm was produced.

Next, each aluminum foil was etched under the following conditions, and the capacitance of the obtained aluminum foil was measured at 250 V in 5% boric acid solution. The results are shown in Table 1 as a relative comparison when the electrostatic capacity of Comparative Example 20 is 100%.

[Etching conditions] Pretreatment liquid composition: 0.01% NaOH, liquid temperature: 30 ° C., time: 60 seconds Primary etching liquid composition: 5% HCl + 10% H ₂ SO ₄ , liquid temperature: 75 ° C. Current density: DC 20A / dm ² , time: 80 seconds Secondary etching liquid composition: 5% HCl, liquid temperature: 75 ° C, current density: DC 5A / dm ² , time: 10 minutes

[Table 1]

From the results shown in Table 1, Ag in the range of the present invention was added to the surface.
It has been confirmed that the product of the present invention containing the above can increase the capacitance as compared with the comparative product which deviates from the scope of the present invention. It was also confirmed that the addition of Pb, Zn, Ga, Fe and Si in a predetermined range synergistically increased the capacitance.

[0020]

The aluminum foil for electrolytic capacitor electrodes according to the present invention basically has an aluminum purity of 99.
Since it is characterized by containing 15% to 300 ppm of Ag at 9% or more, the density of the etch pits is increased, the depth is increased, and the pits are evenly dispersed. You can get a rate. Therefore, it is possible to provide an aluminum foil for an electrolytic capacitor electrode having a large capacitance and excellent electrical characteristics.

In addition to the above Ag, Pb: 0.1
5 ppm, Zn: 1 to 50 ppm, Ga: 1 to 50 pp
m, Fe: 5 to 60 ppm, Si: 5 to 80 ppm, by further containing one or more, the etching characteristics are further improved, and for electrolytic capacitor electrodes having a synergistically large electrostatic capacity and excellent electrical characteristics. Can be made with aluminum foil.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tomoaki Yamanoi, 6-224, Kaiyamacho, Sakai City, Showa Aluminum Co., Ltd.

Claims (2)

[Claims] 1. The aluminum purity is 99.9% or more,
An aluminum foil for an electrolytic capacitor electrode, which contains Ag: 15 to 300 ppm. 2. The aluminum purity is 99.9% or more,
Ag: 15-300ppm, Pb: 0.
1 to 5 ppm, Zn: 1 to 50 ppm, Ga: 1 to 50
ppm, Fe: 5 to 60 ppm, Si: 5 to 80 ppm
An aluminum foil for an electrolytic capacitor electrode, which contains at least one of the above.