JP2578521B2 - Aluminum foil for electrolytic capacitor electrodes - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum foil for an electrolytic capacitor electrode, and more particularly to an aluminum foil used as an anode material for medium and high pressures.

2. Description of the Related Art Generally, an aluminum foil for an electrolytic capacitor electrode is subjected to an electrical or electrochemical etching treatment in order to increase its effective surface area and increase the capacitance per unit area. In order to increase the surface area, many studies have been made on increasing the density of etching pits formed on the foil surface by etching. Among them, from the knowledge that the density of etching pits is greatly affected by the composition and structure of the surface portion of the aluminum foil, as seen in JP-B-62-42370, Pb, Bi, In The usefulness of a technique for allowing one or more elements selected from the group to be contained in a high concentration has been proposed. In the production of such an aluminum foil, as an example, at least one of Pb, In and Bi is applied in the form of a compound to the surface of the aluminum foil, and heat diffusion treatment is performed at a temperature equal to or higher than the melting point of these metals. Then, it is proposed to perform annealing in accordance with a conventional method.

Problems to be Solved by the Invention In the background of the prior art as described above, the present invention includes elements other than those described above which can be contained in a high concentration on the surface of an aluminum foil to effectively contribute to an increase in the area coverage. The purpose of the present invention is to provide an aluminum foil for an electrolytic capacitor electrode capable of increasing the capacitance by searching and finding a range that is most effective in increasing the area coverage from the relationship between the distribution state and the distribution amount. I do.

Means for Solving the Problems According to the present invention, Siu is selected as an element that effectively acts on the increase in the area coverage.

Thus, the present invention provides Fe 5-1,000 ppm, Si 5-1,000 pp
m, containing 5 to 1,000 ppm of Cu, aluminum foil having a composition of remaining Al and unavoidable impurities, and the Si concentration in the surface layer from the surface to a thickness of 0.1 μm is 2 to 250 times the Si content in the foil. An aluminum foil for an electrolytic capacitor electrode characterized by being set to:

In the present invention, Fe5 ~ in the entire aluminum foil
It is well known that the content of 1,000 ppm, Si 5 to 1,000 ppm, and Cu 5 to 1,000 ppm is required. This is because it is hindered by the presence of impurities and cannot form a uniform deep tunnel-like pit, and therefore cannot obtain an aluminum foil having a high capacitance. If it is less than the above lower limit, crystal grains are coarse after final annealing. This is because the number of etching pits is reduced and the effect of improving the capacitance cannot be sufficiently obtained. Preferably Fe8-100ppm, Si8-100pp
m, Cu is preferably in the range of 15 to 60 ppm.

S within 0.1μm thickness from the surface of aluminum foil
Inclusion of i at a high concentration is a main factor for obtaining the effect of increasing the capacitance, and the oxide film on the foil surface has countless fine defects due to the high concentration. In the early stage of the etching, the above-mentioned defective portion becomes the starting point of the etching, and a large number of etching pits are formed. Can be Therefore, the thickness of the surface layer portion of 0.1 μm does not necessarily have a critical significance in terms of the effect itself in the numerical value itself, and the concentration of Si in the surface layer within the thickness range is different from the Si content inside the foil. It has a limiting significance in that it should be 2-250 times. So also
It is not necessary that Si is uniformly distributed in the surface layer portion, but rather it is preferable that Si is unevenly distributed at a higher concentration on the surface portion.

If the Si content in the surface layer is less than twice the Si content in the foil, the density of the etching pits becomes insufficient, and a sufficient effect of increasing the capacitance cannot be obtained.
On the other hand, if the surface layer content of Si exceeds 250 times the internal content, the corrosion resistance of the aluminum foil surface is significantly reduced, leading to the entire melting of the foil surface, and the surface area is rather small. The most preferable range of the Si content in the surface layer is about 5-150 times the Si content inside the foil.

As described above, the production of aluminum foil containing Si at a high concentration in the surface layer is performed by adding a required amount of Si at a stage of dissolving the aluminum base metal, casting, and then hot rolling, cold rolling, and foil in a conventional manner. Rolling, if necessary, further intermediate annealing is performed to make a foil, and this foil is subjected to a heat treatment at 460 to 580 ° C. for 1 to 24 hours, preferably at 485 to 540 ° C. for 2 to 5 hours. can do. Si added to the metal
By the above-mentioned heat treatment, it can be concentrated in the surface layer portion and intensively contained in the surface layer portion within the specified range of the present invention in relation to the amount of addition.

However, the production of the aluminum foil according to the present invention,
Without being limited to the above, an aluminum foil to which substantially no Si is added is applied to the surface as a film having an appropriate thickness by a method such as immersion or vapor deposition in a solution containing silicic acid, and then heat treatment is performed. Thereby, Si may be diffused into the surface layer. Further, the above means may be used in combination.

Effect of the Invention The aluminum foil for an electrode of an electrolytic capacitor according to the present invention is excellent in etching properties, can obtain an extremely large area coverage by etching treatment, and can suppress dissolution of the entire foil surface during the etching.

Therefore, it is possible to have a large capacitance, excellent electrical characteristics, and excellent strength.

Example Pure aluminum ingot having a purity of 99.99% (Fe: 12 ppm, Cu: 35
ppm) of various contents shown in Table 1 (S in aluminum foil)
i content), melt casting, hot rolling,
Cold rolling, foil rolling, intermediate annealing, and foil rolling were sequentially performed to produce an aluminum foil having a thickness of 0.1 mm. The aluminum foil was immersed in various concentrations of sodium silicate solution to give a predetermined amount of Si to the surface, and various types were prepared without the immersion. Next, these aluminum foils were subjected to a final annealing treatment under vacuum at 520 ° C. × 3 hours to obtain various samples as electrode materials for electrolytic capacitors.

In these various samples, the concentration of Si in the surface layer of 0.1 μm from the surface was higher than the Si concentration in the foil excluding the surface layer.
In comparison with the content of, the ratios shown in Table 1 were used.

Next, the above various aluminum foils were heated at a liquid temperature of 85 ° C for 5w.
After performing the first-stage etching for 1 minute and 30 seconds with a direct current having a current density of 20 A / dm ² with an etching solution containing t% hydrochloric acid and 20 wt% sulfuric acid, 5 wt% hydrochloric acid and 0.2 wt% at a liquid temperature of 85 ° C.
The second-stage etching was performed for 9 minutes with a direct current having a current density of 5 A / dm ² using an etching solution containing oxalic acid.

After forming the etched foil to 380 V, the capacitance of each sample was measured, and the capacitance of other various samples was compared with the case where the capacitance of the sample of Comparative Example No. 8 was set to 100%. The ratio was determined. The results are shown in Table 1.

As can be seen from the results in Table 1 above, the electrode foil containing Si in the surface layer portion within the range of the specified amount of the present invention is a foil that does not substantially contain it, and a foil that does not contain Si in the surface layer portion. Or, it has an effect of increasing the capacitance and is excellent in strength as compared with a foil containing Si excessively in the surface layer portion.

Claims (1)

(57) [Claims] (1) Fe5 to 1,000 ppm, Si5 to 1,000 ppm, Cu5 to 1,0
It is composed of aluminum foil having a composition of Al and unavoidable impurities containing 00 ppm, and a thickness of 0.1 μm from the surface.
An aluminum foil for an electrode of an electrolytic capacitor, characterized in that the Si concentration in the surface layer is set to 2 to 250 times the Si content in the foil.