JPH07176454A - Aluminum foil for electrode material and cathode material in electrolytic capacitor - Google Patents

Abstract

PURPOSE:To provide an aluminum foil for a capacitor electrode and a cathode material used in an electrolytic capacitor, along with high electrostatic capacitor realized with a small loss in weight during an etching step. CONSTITUTION:A surface oxide film is formed on aluminum foil, and a pitting corrosion potential to a silver/silver chloride reference electrode in 3.5% NaCl solution at 30 deg.C is not less than -600mV. In addition, an etching step is carried out for the aluminum foil having these characteristics. As a result a cathode material used for an electrolytic capacitor with high electrostatic capacitance can be obtained without deterioration in mechanical characteristics and the like.

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 material of an electrolytic capacitor and a cathode material of an electrolytic capacitor, and in particular, the amount of reduction (dissolution reduction or electrolytic reduction) at the time of etching treatment does not become unnecessarily large and the electrostatic capacitance is reduced. The present invention relates to an aluminum foil for an electrolytic capacitor electrode material capable of increasing the effective area for increasing the electric field, and an electrolytic capacitor cathode material obtained from such an aluminum foil.

[0002]

2. Description of the Related Art In order to improve the performance of an electrolytic capacitor, it is necessary to increase not only the capacitance of the anode material but also the capacitance of the cathode material. Aluminum foil used as an electrode material for electrolytic capacitors is subjected to electrochemical or chemical etching to roughen the surface to improve the electrostatic capacity per unit volume as an electrolytic capacitor, and its effective area is Expansion is common. Further, it is said that increasing the number of etchings, increasing the etching depth, etc. are effective in expanding the effective area.

However, when the etching is advanced to increase the area due to the roughening, the weight loss due to the etching becomes excessive and the improvement of the capacitance with respect to the increase rate of the weight loss is poor, and as a result, the capacitance per unit weight loss is small. The problem arises that the increase of the On the other hand, when the weight loss is excessive, the thickness of the aluminum foil becomes small and the mechanical properties also deteriorate. For these reasons, it is desired to realize an aluminum foil for an electrolytic capacitor electrode material, in which the weight loss during the etching process does not increase more than necessary and a high capacitance can be achieved.

Aluminum foil for electrolytic capacitor electrode materials has been studied from various angles. First, from the aspect of chemical composition, for example, Japanese Patent Publication No. 3-6
No. 1333 specifies the contents of Fe, Si, Cu, etc. in an aluminum foil having a purity of 99.9% or more, and
An aluminum foil for an electrolytic capacitor electrode material has been proposed in which the precipitation amount of Fe or Si is regulated. In addition, Japanese Patent Laid-Open No. 4-1
No. 24806 describes Fe, Si, Cu, Mn, B, Ga and Zn in aluminum foil having a purity of 99.9% or more.
Aluminum foils for electrolytic capacitor electrode materials have been proposed in which the contents of the above are specified. On the other hand, JP-A-5-1487
No. 00 also proposes a technique of performing multi-step electrolytic etching in terms of etching conditions.

By the way, the production of the aluminum foil used as the electrode material of the electrolytic capacitor is carried out in the same manner as the production of general aluminum foil, after soaking treatment, followed by hot rolling and cold rolling and, if necessary, cooling. Annealing is performed before or during hot rolling, but improvements have also been made in terms of these manufacturing conditions. For example, Japanese Patent Laid-Open No. 3-166344
Japanese Patent Laid-Open Publication No. 2003-242242 proposes a method for producing an aluminum foil for an electrolytic capacitor electrode material, which aims to achieve the above object by controlling the heating temperature during the production process. In addition, JP-A-4
No. 88155 proposes a method for producing an aluminum foil for an electrolytic capacitor electrode material, which regulates the annealing temperature, the reduction rate of cold rolling time, and the like.

[0006]

All of the above techniques have been aimed at the realization of an aluminum foil for an electrolytic capacitor electrode material, in which the weight loss during etching does not become unnecessarily large and a high capacitance can be achieved. Although the respective effects have been recognized, the effects are limited in each case, and it is the actual situation that further improvement is desired.

The present invention has been made under the above-mentioned technical background, and an object thereof is to provide an electrolytic capacitor electrode in which a weight loss during etching does not become unnecessarily large and a high electrostatic capacity can be achieved. An object is to provide an aluminum foil for a material, and an electrolytic capacitor cathode material obtained from such an aluminum foil.

[0008]

Means for Solving the Problems The present invention, which has been able to achieve the above object, means that an oxide film is formed on the surface, and silver / silver chloride in a 3.5% NaCl aqueous solution at 30 ° C. is used. It is an aluminum foil for an electrolytic capacitor electrode material, which is characterized in that the pitting potential with respect to the electrode is -600 mV or more. Further, by etching the aluminum foil as described above, an electrolytic capacitor cathode material capable of achieving a high capacitance can be obtained without inconvenience such as deterioration of mechanical properties.

[0009]

As a technique of aluminum foil for electrolytic capacitor electrode material, various techniques have been proposed from the aspects of chemical composition, etching conditions and manufacturing conditions as described above. From a completely different point of view, we have studied to realize an aluminum foil, which is useful as an electrode material for electrolytic capacitors. Then, the present inventors have paid attention to the pitting corrosion potential, which is an index showing the characteristics of the oxide film present on the surface of the aluminum foil, and the dissolution weight loss (electrolytic weight loss) in AC electrolysis, and examined these relationships. As a result, a good correlation was observed between the pitting potential and the electrolytic loss, and in the aluminum foil adjusted to have a pitting potential of a certain value or more, the weight loss during etching was increased more than necessary. It has been found that an aluminum foil which can achieve a high electrostatic capacity and which is extremely useful as an electrode material of an electrolytic capacitor can be realized without doing so and completed the present invention.

FIG. 1 is a graph showing the relationship between the pitting potential for a silver / silver chloride reference electrode (Ag / AgCl) in a 3.5% NaCl aqueous solution at 30 ° C. and the electrolytic weight loss of an aluminum foil. As is clear from this result, when the pitting corrosion potential is -600 mV or more, the electrolytic weight loss is 5.0 g /
It can be seen that m ² or less is extremely suppressed, and there is no difference in the degree. On the other hand, when the pitting potential was less than -600 mV, the electrolytic weight loss was large, and no substantial difference was observed between the aluminum foil having no oxide film on the surface and the electrolytic weight loss.

The reason why the above-described effects are obtained in the present invention has not been completely clarified, but it can be considered as follows. That is, if the pitting corrosion potential of the oxide film on the surface of the aluminum foil becomes higher, the anode polarization resistance becomes larger, so that it is largely polarized toward the anode side during AC constant current electrolytic etching, and as a result, stable at high potential during etching. It is considered that an electrolytic coating can be formed to suppress the electrolytic loss.

The aluminum foil of the present invention has an oxide film formed on its surface. The oxide film may be a generally formed oxide film, such as an aluminum oxide or an aluminum oxide film. It is intended to include any of those containing as a main component a mixture of an oxide and a hydroxide and / or a hydrate. Further, as long as it does not hinder the use as an electrolytic capacitor, it is not limited to the above surface film, and may have an oxide film that is forcibly formed in addition to the above.

The oxide film may be formed by an external preparation and / or an internal preparation. The external preparation may be, for example, an oxidation treatment condition, a cleaning condition after rolling, a cleaning condition at an intermediate stage of rolling, a rolling condition such as a rolling speed and a reduction ratio, and the like, which may be based on these changes. It may be prepared by two or more methods. Further, as the internal preparation, the characteristics of the oxide film to be formed may be adjusted by adjusting the chemical components such as the amount of impurities in the aluminum foil such as Fe and Si, adjusting the annealing conditions, etc. One method or two or more methods may be adopted. However, the method for forming the surface coating is not limited to the above methods. In short, the aluminum foil of the present invention has a pitting potential of −60 with respect to a silver / silver chloride reference electrode in a 3.5% NaCl aqueous solution at 30 ° C.
The point that the voltage is 0 mV or higher is an important configuration, and the method of forming the oxide film formed on the surface is not limited.

The aluminum foil of the present invention preferably has an aluminum purity of 99.94% or more, but the aluminum foil is not limited to this, and if it is within a range that can be used as an electrolytic capacitor, Fe. , Si, etc., and various additive elements proposed so far may be contained.

Since the aluminum foil according to the present invention can achieve a high capacitance without increasing the weight loss during etching more than necessary, it is subjected to an etching treatment as a cathode material of an electrolytic capacitor. As described above, the effect is most exerted when used,
From the viewpoint of increasing the capacitance, the above configuration is also useful in the anode material of the electrolytic capacitor, and after performing the etching treatment on the aluminum foil according to the present invention,
An oxide film may be formed by anodizing treatment, or a conductive metal film may be formed by a sputtering method, an ion plating method or the like, and this may be used as the anode material of the electrolytic capacitor.

The present invention will be described in more detail with reference to the following examples. However, the following examples are not intended to limit the present invention, and any modification of the design in consideration of the contents described in the preceding and the following is the present invention. Are included in the technical scope of.

[0017]

EXAMPLES Aluminum alloys having the chemical composition shown in Table 1 were melted by a general method and subjected to chamfering, homogenizing heat treatment, hot rolling and cold rolling to obtain foils having a thickness of 100 μm as test materials. .

[0018]

[Table 1]

With respect to each of the above-mentioned test materials, the pitting potential was adjusted by changing the steps shown in Table 2 below. At this time, the pitting corrosion potential was measured by immersing the test material in a 3.5% NaCl aqueous solution (degassed) at 30 ° C. for 600 seconds at a sweep speed of 20 mV / min and a current density of 100 μm.
The potential reaching A / cm ² was defined as the pitting potential.

Etching was carried out on each of the test materials for which the pitting potential was adjusted, and the corrosion resistance was evaluated. At this time, etching was carried out by constant current AC electrolysis in 45 ° C., 15% hydrochloric acid-2.5% sulfuric acid aqueous solution. The corrosion resistance was evaluated by electrolyzing for 30 seconds under the conditions of 0.25 A / cm ² and 60 Hz, and then under the conditions of 0.3 A / cm ² and 60 Hz for 30 seconds.
Electrolyze for 2 seconds and measure the electrolytic loss in the latter half of 30 seconds. If the electrolytic loss is 5.0 g / m ² or less, corrosion resistance:
○, more than that was judged to be corrosion resistance: ×. The results are also shown in Table 2, and it can be seen that the aluminum foil according to the present invention has less electrolytic loss.

[0021]

[Table 2]

[0022]

The present invention is configured as described above, and by setting the pitting potential of the oxide film on the surface to a predetermined value or more, the weight loss during etching can be increased without increasing it more than necessary. We were able to achieve an electrostatic capacity, and we were able to realize an aluminum foil that was optimal as an electrode material for electrolytic capacitors.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between pitting potential and electrolytic loss.

Claims (2)

[Claims] 1. An electrolysis having an oxide film formed on the surface thereof, wherein the pitting potential for a silver / silver chloride reference electrode in a 3.5% NaCl aqueous solution at 30 ° C. is −600 mV or more. Aluminum foil for capacitor electrode material. 2. An electrolytic capacitor cathode material obtained by etching the aluminum foil according to claim 1.