JPH0543972A - Aluminum alloy foil for cathode of electrolytic capacitor and its production - Google Patents

Abstract

PURPOSE:To provide aluminum alloy foil for the cathode of an electrolytic capacitor having good etching properties and its manufacturing method. CONSTITUTION:This is aluminum alloy foil constituted of, by weight, 0.001 to 0.10% Mg, 0.001 to 0.05% Zn, <=0.001% Cu, <=0.00l% Ti, <=.002% Ni and the balance Al with inevitable impurities. The preferable manufacturing method of the aluminum alloy foil for the cathode of an electrolytic capacitor is as follows. Namely, an ingot constituted of, by weight, 0.001 to 0.10% Mg, 0.001 to 0.05% Zn, <=0.001% Cu, <=0.001% Ti, <=0.002% Ni and the balance Al with inevitable impurities is prepd. This ingot is subjected to hot rolling and cold rolling to obtain aluminum foil. This aluminum foil is subjected to final annealing under the conditions of temp.-time in the range shown by the hatched line in the figure, by which aluminum alloy foil for the cathode of an electrolytic capacitor can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy foil for electrolytic capacitor cathodes having good etching characteristics and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, an aluminum alloy foil containing 0.1 to 0.5% by weight of Cu has been used as an aluminum alloy foil for a cathode of an electrolytic capacitor. The reason why Cu is contained in a relatively large amount is to improve the etching property of the aluminum alloy foil. However, Cu
When a cathode foil was prepared using an aluminum alloy foil containing a large amount of, there were the following drawbacks. That is, Cu added for improving the etching property, after incorporating the cathode foil into the capacitor, during repeated charging and discharging, elute and precipitate in the electrolytic solution, there is a risk of short-circuiting the cathode and anode. It was Also, in the cathode foil, a natural oxide film may be formed, or a chemical conversion film with a withstand voltage of several volts may be applied.In this case, the additive element such as Cu and the precipitate such as Fe make the film nonuniform. However, there is a drawback in that the reliability of the capacitor deteriorates over time.

For this reason, there has been proposed a method for reducing the amount of Cu added in the aluminum alloy foil for the electrolytic capacitor cathode. For example, it has been proposed that Mg and Mo are added to an aluminum alloy foil so that the etching characteristics do not deteriorate even if the amount of Cu added is reduced (JP-A-62-296410). This utilizes the property that Mg diffuses and concentrates on the foil surface when an aluminum alloy foil is annealed, and thus increases the defective portion of the oxide film. That is, by increasing the number of defects in the oxide film, the initial etching starting point is increased, the density of pits generated by etching is increased, and the reduction of the etching characteristics due to the reduction of the Cu addition amount is attempted. It is a thing.

[0004]

However, even with the method described in the above-mentioned JP-A-62-296410, C
It was not possible to reduce the amount of u added. This means that in the above publication, the amount of Cu added is 0.05 to 0.5% by weight.
It is also clear from the description. Therefore,
The present inventor tried to obtain an aluminum alloy foil having good etching characteristics even when the amount of Cu added was less than 0.05% by weight. As a result, together with Mg having the above characteristics
The inventors have found that the above-mentioned properties of Mg can be further enhanced by using Zn, and have reached the present invention.

[0005]

Means for Solving the Problems That is, the present invention provides Mg0.00
1 to 0.10% by weight, Zn 0.001 to 0.05% by weight, Cu 0.001% by weight
Below, Ti 0.001 wt% or less, Ni 0.002 wt% or less, balance Al
And an aluminum alloy foil for an electrolytic capacitor cathode, which comprises unavoidable impurities, and a method for producing the same.

The addition amount of Mg in the aluminum alloy foil according to the present invention is 0.001 to 0.10% by weight. If the added amount of Mg is less than 0.001% by weight, even if annealed, the diffusion and concentration of Mg on the foil surface is not sufficient, and the etching starting point cannot be increased, which is not preferable. On the other hand, if the addition amount of Mg exceeds 0.10% by weight, the increase of the etching start point becomes too large, the etching becomes excessive, and the surface of the obtained cathode foil easily peels off, which is not preferable.

The amount of Zn added is 0.001 to 0.05% by weight.
Is. Zn lowers the potential of the Al matrix and assists the reaction at the metal oxide interface after the start of etching with Mg concentrated on the foil surface. Therefore, the presence of Zn improves the progress of pits due to etching. If the amount of Zn added is less than 0.001% by weight, the effect of assisting the reaction at the metal oxide interface cannot be sufficiently exerted, which is not preferable. On the other hand, if the amount of Zn added exceeds 0.05% by weight, the reaction at the metal oxide interface becomes excessive, etching becomes excessive, and the surface of the obtained cathode foil is easily peeled off, which is not preferable.

In the aluminum alloy foil according to the present invention,
It is preferable that Cu is not contained as much as possible. this is,
This is because when the capacitor is used as a cathode foil, by repeating charging and discharging, Cu elutes in the electrolytic solution and deposits on the electrode, and the risk of short circuit is avoided. Therefore, the amount of Cu in the aluminum alloy foil is 0.001% by weight or less. When the amount of Cu exceeds 0.001% by weight, there is a risk of short circuit as described above, which is not preferable.

The amount of Ti in the aluminum alloy foil is
0.001% by weight or less. If the amount of Ti exceeds 0.001% by weight, overdissolution may occur during etching, which is not preferable. The amount of Ni in the aluminum alloy foil is 0.002% by weight or less. Since Ni has a higher potential than Al, it promotes the dissolution of Al during etching. However, if it exceeds 0.002% by weight, excessive dissolution may occur during etching, which is not preferable.

In the aluminum alloy foil according to the present invention,
It may contain inevitable impurities usually contained in aluminum ingots. For example, Fe which is usually contained in an amount of about 0.05 to 0.8% by weight and Si which is contained in an amount of about 0.05 to 0.5% by weight may be contained.

The aluminum alloy foil according to the present invention is preferably manufactured by annealing under the following final annealing conditions. That is, on an aluminum foil having a predetermined elemental composition,
It is preferable to perform the final annealing under the conditions of a temperature of 150 to 530 ° C. and a time of 1 minute to 100 hours, and a temperature-time condition within the range shown by the diagonal lines in FIG. When the final annealing is performed under these conditions, Mg existing in the aluminum foil diffuses and concentrates on the foil surface, and the etching characteristics are improved. If the final annealing is performed under conditions outside this range, Mg existing in the aluminum foil is difficult to diffuse and concentrate on the foil surface, and further improvement in etching characteristics tends not to be recognized. In addition,
In FIG. 1, the horizontal axis is time (hr) and is graduated on a logarithmic scale, and the vertical axis is temperature (° C.) and is normally graduated.

[0012]

【Example】

Examples 1 to 19 and Comparative Examples 1 to 6 Aluminum ingots of the elemental composition shown in Table 1 (thickness 400 mm)
Is homogenized at a temperature of 520 ° C. for 25 hours, then rolled at a hot rough rolling start temperature of 480 ° C. and a hot rough rolling end temperature of 400 ° C. using a hot rough rolling machine, and an aluminum plate having a thickness of about 25 mm is obtained. Got This aluminum sheet is hot-finished and rolled at the starting temperature.
Rolling was carried out at 380 ° C with a hot finishing rolling ending temperature of 230 ° C using a hot rolling mill to obtain an aluminum thin plate having a thickness of 3 mm. The thin aluminum plate was wound into a coil, cooled, and then cold rolled to obtain an aluminum foil having a thickness of 0.05 mm.

[Table 1]

This aluminum foil was finally annealed under the conditions shown in Tables 2 and 3 to obtain an aluminum alloy foil for electrolytic capacitors. This aluminum alloy foil was etched under the following etching conditions. Etching is 30
2.8 wt% hydrochloric acid + 7.5 wt% aluminum chloride (hexahydrate) + 0.1 wt% oxalic acid (dihydrate) in water at 10 Hz, using a rectangular wave alternating current at 0.2 A / cm ² It was performed by processing for 210 seconds. Then, after etching, the electrostatic capacity (μF / cm ² ) was measured under the following conditions. That is, the capacitance was measured at 0 vf. In a 8.0 wt% nitric acid solution at 30 ° C. with a 120 Hz series equivalent circuit using an LCR meter. The results are shown in Tables 2 and 3.

[Table 2]

[Table 3] As is clear from Tables 2 and 3, it can be seen that when the aluminum alloy foil according to the example is subjected to etching, it has a higher capacitance than that of the case according to the comparative example.

Examples 20 to 34 The aluminum foils used in the above examples were subjected to final annealing under the conditions shown in Table 4. Then, etching is performed under the same conditions as in the above-mentioned embodiment, and the electrostatic capacity (μF / cm ² )
Was measured. The results are shown in Table 4.

[Table 4] Since the final annealing conditions in Examples 20 to 34 were not subjected to the final annealing under the temperature-time conditions within the range shown by the slanted lines in FIG. 1, the capacitance of the obtained aluminum alloy foils after etching was the same as that in Examples. It was lower than in the cases of 1 to 19.

[0015]

As described above, the aluminum alloy foil for electrolytic capacitor cathodes according to the present invention has a Cu content of 0.
Since it contains only 001% by weight or less, Cu does not easily precipitate even when the cathode foil made using this aluminum alloy foil is incorporated into a capacitor and repeatedly used. Therefore, it is possible to prevent a short circuit of the capacitor due to the deposition of Cu. It also improves etching characteristics
Since Cu and Mg were contained in the aluminum alloy foil instead of Cu, the etching starting point was increased, and the reactivity at the metal oxide interface after the etching was started was improved. Can be formed. Therefore, the surface area of the cathode foil obtained by etching can be sufficiently increased, and the cathode foil having a high capacitance can be obtained.

If the aluminum alloy foil for an electrolytic capacitor cathode according to the present invention is obtained by the method according to claim 2,
The diffusion and concentration of Mg and Zn on the foil surface can be sufficiently achieved, and the etching characteristics can be dramatically improved. Therefore, by etching the aluminum alloy foil for the electrolytic capacitor cathode obtained by the method according to the second aspect, it is possible to obtain a cathode foil having a high capacitance.

[Brief description of drawings]

FIG. 1 shows temperature-time conditions for final annealing when using the method for producing an aluminum alloy foil for an electrolytic capacitor cathode according to claim 2.

Claims (2)

[Claims] 1. Mg 0.001 to 0.10% by weight, Zn 0.001 to 0.05% by weight, Cu 0.001% by weight or less, Ti 0.001% by weight or less, Ni 0.00
An aluminum alloy foil for an electrolytic capacitor cathode, comprising 2% by weight or less and the balance Al and inevitable impurities. 2. Mg 0.001 to 0.10% by weight, Zn 0.001 to 0.05% by weight, Cu 0.001% by weight or less, Ti 0.001% by weight or less, Ni 0.00
After obtaining an aluminum foil using an ingot composed of 2% by weight or less and the balance Al and unavoidable impurities, the aluminum foil is provided with a temperature of 150 to 530 ° C. and a time of 1 minute to 100 hours. The method for producing an aluminum alloy foil for a cathode of an electrolytic capacitor is characterized in that the final annealing is performed under a temperature-time condition within a range indicated by the diagonal line.