JP2005336557A - Aluminum foil for electrolytic capacitor, and electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aluminum foil for an electrolytic capacitor, which gives higher capacitance to the electrolytic capacitor, by preparing more starting points of etching therein, from which pits start growing through an etching reaction. <P>SOLUTION: The aluminum foil for the electrolytic capacitor comprises Si, Fe, Cu, Pb, 0.1 to 100 ppm Ge and 99.9 mass% or more Al. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an aluminum foil for electrolytic capacitors and an electrolytic capacitor provided with the aluminum foil as an electrode.

Aluminum foil used for electrodes of electrolytic capacitors is not limited to anodes and cathodes, but can be used with a rough surface treatment (electrolytic etching) to effectively increase the surface area and thus increase the capacitance. Is common. In order to effectively increase the surface area, it is necessary to generate a large number of pits (corrosion holes) uniformly on the surface of the aluminum foil by electrolytic etching. Currently, in order to improve the uniform corrosiveness of the aluminum foil surface, the oil film formed on the surface by rolling in the middle of the manufacturing process is removed by solvent degreasing or by light soda cleaning. As described in Patent Document 1, a method of adding Fe, Si, Cu, Ni, In, Bi, or the like to an aluminum foil has also been proposed.
JP 2002-173724 A

  However, the aluminum foil for electrolytic capacitors described in Patent Document 1 described above has a problem that the etching start point that is the starting point of pit formation by etching is not sufficient, and the effect of increasing the capacitance is insufficient. .

Therefore, as a result of intensive studies on the alloy composition of the aluminum foil for electrolytic capacitors by the present inventors, by adding a small amount of Ge to the aluminum foil, a unique effect that has never been known until now is expressed. I found.
The present invention has been made in view of the above circumstances, and an aluminum foil for an electrolytic capacitor capable of further increasing an electrostatic capacity by increasing an etching start point which is a starting point of pit formation by etching, and the same It aims at providing the electrolytic capacitor provided with.

In order to achieve the above object, the present invention employs the following configuration.
The aluminum foil for electrolytic capacitors of the present invention contains Si, Fe, Cu, and Pb, and contains Ge in the range of 0.1 ppm to 100 ppm and 99.9% by mass or more of Al. Features.

  According to the aluminum foil for electrolytic capacitors described above, Ge is included in the above range, and this Ge has an effect of enhancing the activity of the aluminum foil surface, so that the number of etching start points can be increased more than before. The surface area can be increased by increasing the number of pits, thereby increasing the capacitance.

Moreover, the aluminum foil for electrolytic capacitors of this invention is an aluminum foil for electrolytic capacitors as described above, Comprising: The cube orientation rate is 80% or more, It is characterized by the above-mentioned.
Since electrolytic etching forms pits effectively in a cube-oriented structure, when the cube orientation ratio is 80% or more, a sufficient number of pits are formed, and the capacitance can be further increased.

Next, the electrolytic capacitor according to the present invention is characterized by including the aluminum foil for electrolytic capacitors described above as an electrode.
According to this configuration, the capacitance of the electrolytic capacitor can be made higher than before.

  According to the aluminum foil for an electrolytic capacitor of the present invention, it is possible to increase the capacitance of the electrolytic capacitor by increasing the etching start point that is the starting point of pit formation by etching.

Hereinafter, embodiments of the present invention will be described in detail.
The aluminum foil for electrolytic capacitors of the present invention contains Si, Fe, Cu, and Pb, and contains Ge in a range of 0.1 ppm to 100 ppm and 99.9% by mass or more of Al. Yes. In this aluminum foil for electrolytic capacitors, the cube orientation ratio is 80% or more. Hereinafter, the reasons for limiting the content of the additive element of the aluminum foil and the cube orientation ratio will be described.

  Ge has the effect of increasing the activity on the surface of the aluminum foil, can increase the number of etching starting points than before, increase the number of pits, increase the surface area, and thereby increase the capacitance. . However, if the content is less than 0.1 ppm, the effect of adding Ge cannot be obtained. On the other hand, if it exceeds 100 ppm, pits are excessively generated, and the capacity improvement effect cannot be obtained due to the coalescence phenomenon between the pits. Accordingly, the Ge content is preferably in the range of 0.1 ppm to 100 ppm, more preferably in the range of 10 ppm to 70 ppm.

Further, the addition effect of Ge can be further increased by adding Si, Fe, Cu, and Pb.
The content of Si and Fe is preferably in the range of 5 ppm to 100 ppm, more preferably in the range of 10 ppm to 50 ppm. If Fe and Si are each less than 5 ppm, the crystal grains tend to grow abnormally, and high-purity aluminum is required, resulting in an increase in cost. On the other hand, if Fe and Si each exceed 100 ppm, the growth of cubic crystals is hindered and the required cubic crystal ratio cannot be obtained.

  Further, Cu is an important element for increasing the loss of dissolution during etching and improving the capacitance. In order to obtain this effect sufficiently, it is desirable to contain as much Cu as possible. In the present invention, the range of 10 ppm to 100 ppm is preferable, and the range of 20 ppm to 60 ppm is more preferable. If the Cu content is less than 10 ppm, the effect of addition cannot be sufficiently obtained. Moreover, when Cu exceeds 100 ppm, the ineffective melt | dissolution part by excessive melt | dissolution will increase and an electrostatic capacitance will fall.

  Further, Pb has a function of weakening the oxide film on the aluminum surface and improving the initial etching property. The Pb content is preferably in the range of 0.1 ppm to 10 ppm, and more preferably in the range of 0.3 ppm to 2 ppm.

  Moreover, it is preferable that one or more elements of Sn, Zn, Zr, and Na are further added to the aluminum foil for electrolytic capacitors of the present invention. These elements have an effect of increasing the number of pits and uniformly dispersing the pits. The total amount of these elements added is preferably 0.5 ppm to 50 ppm, more preferably 2 ppm to 20 ppm.

  Other inevitable impurities increase the ineffective solubility of the aluminum foil, so it is preferable to suppress it as much as possible. However, if it is about 50 ppm or less in total, there is no possibility of inhibiting the effect of adding Ge.

  Moreover, it is preferable that content of Al is 99.9 mass% or more. Decreasing the Al content is not preferable because the leakage current increases and the basic performance as a capacitor is significantly reduced, particularly when used in a medium to high voltage capacitor.

  Next, the aluminum foil of the present invention is required to have a cubic orientation ratio of 80% or more by volume ratio. Since pits are effectively formed in a cube-oriented structure, the lower limit of the cube orientation ratio is determined in order to form a sufficient number of pits. For the same reason, it is more desirable that the cubic orientation ratio is 95% by volume or more.

  In producing the aluminum foil for electrolytic capacitors of the present invention, an aluminum alloy containing the above-described components within the set range and melted can be used. The alloy can be melted by a conventional method, and can be obtained through, for example, melting, casting, homogenizing heat treatment and the like. The alloy obtained as described above is hot-rolled by heating to a high temperature in the form of an ingot. The conditions at the time of hot rolling are not particularly limited, and a sheet material having a thickness of about several mm is obtained by this hot rolling. The sheet material is subsequently cold-rolled to obtain an aluminum alloy foil of about several tens to 100 μm. In addition, you may add degreasing | defatting suitably in the middle of cold press or after completion | finish of cold press. In addition, intermediate annealing may be appropriately added during the cold press. Moreover, when manufacturing aluminum foil, an aluminum thin plate may be obtained by direct continuous rolling, and this may be cold-rolled into a foil.

The aluminum foil obtained as described above is then subjected to a roughening treatment. The roughening treatment is generally performed by electrolytic etching using an electrolytic solution mainly composed of hydrochloric acid, but the present invention is not particularly limited with respect to the specific conditions of the roughening treatment. It can be performed according to conventional methods. In the surface roughening treatment, the pits are formed with high density on the foil by setting the above components, and a high surface roughening rate is obtained. In particular, sufficiently contained Ge increases the etching start point in the roughening treatment, increases the number of pits, and significantly increases the capacitance. Electrolytic etching may be either a direct current method or an alternating current method.

  Further, a voltage-resistant oxide film is formed on the aluminum foil subjected to the roughening treatment. This oxide film is usually formed as an anodized film by chemical conversion treatment. The method of forming this oxide film is not particularly limited in terms of the method and conditions in the present invention, and can be performed, for example, by a conventional method. By incorporating the foil thus obtained as an electrode in an electrolytic capacitor by a conventional method, a capacitor having a high capacitance and a small leakage current can be obtained.

Hereinafter, the present invention will be described in more detail with reference to examples.
Aluminum foils having the compositions shown in Table 1 were produced by ordinary casting, chamfering, homogenizing treatment, hot rolling, and cold rolling. Intermediate annealing and degreasing cleaning were appropriately performed during the process. The thickness of the obtained aluminum foil is 100 μm. This foil was subjected to final annealing in an Ar atmosphere at 550 ° C. for 6 hours. Further, a mixed solution of 1 mol / L hydrochloric acid and 3 mol / L sulfuric acid was used as an electrolytic bath, and electrolysis was performed under conditions of a liquid temperature of 75 ° C., a DC current density of 0.2 A / cm ² , and an electrolysis time of 120 seconds. Next, chemical etching was performed for 7 minutes with 50% nitric acid at 75 ° C., followed by chemical conversion treatment at 270 V, and the capacitance was measured. The capacitance measurement results are shown in Table 1 as relative evaluation with Example 1 as 100%.
In addition, the cubic orientation ratio was obtained by etching the aluminum foil before electrolytic etching treatment using a mixed acid of nitric acid and hydrochloric acid, and the volume ratio was calculated by performing surface analysis (in the used aluminum foil, The cube orientation penetrates the front and back along the thickness direction of the foil, and the volume ratio can be calculated by surface analysis).

As shown in Table 1, in Examples 1 to 14, the content of additive elements and the cube orientation ratio are within the scope of the present invention, so that it can be seen that both exhibit excellent capacitance.
On the other hand, regarding Comparative Example 1 and Comparative Examples 4 to 10, it is considered that the capacitance was lower than that of the Examples because Ge was not added. Further, in Comparative Examples 2 and 3, since the Ge content greatly exceeds 100 ppm, it is considered that the capacitance is lower than that in the Examples.

Claims (3)

  An aluminum foil for an electrolytic capacitor characterized by containing Si, Fe, Cu, Pb, and containing Ge in a range of 0.1 ppm to 100 ppm and Al of 99.9% by mass or more.   2. The aluminum foil for electrolytic capacitors according to claim 1, wherein the cube orientation ratio is 80% or more. An electrolytic capacitor comprising the electrolytic capacitor aluminum foil according to claim 1 as an electrode.