JP2960118B2 - 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 has been proposed to perform annealing according to 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 The present invention selects a rare earth element as an element that effectively acts on the increase in the area coverage.

Thus, the present invention provides an aluminum foil having a purity of 99.9% or more, one or more of the rare earth elements contained in the whole foil in a total amount of 0.2 to 50 ppm, and a thickness of 0.1 μm from the surface.
m, the total content of the rare earth elements in the surface layer up to m is 1.5 to 500 times the content of the inside of the foil excluding the surface layer. Make a summary.

In the present invention, the aluminum purity of the entire aluminum foil requires 99.9% or more, and the content of the rare earth element in the entire foil is limited to 0.2 to 50 ppm,
If the purity is less than the above and the total content of rare earth elements exceeds 50 ppm, the growth of etching pits is inhibited by the presence of many impurities during electrolytic etching, and uniform deep tunnel-like pits cannot be formed. This is because a high-capacity aluminum foil cannot be obtained. On the other hand, when the content of the rare earth element is less than 0.2 ppm, the number of etching pits is small, and a sufficient effect of increasing the capacitance cannot be obtained. Preferably aluminum purity 9
It is preferable to use a material having a rare earth element content of not less than 9.98% and about 1 to 30 ppm.

In order to allow one or more of the rare earth elements to be contained in a high concentration within a thickness of 0.1 μm from the surface of the aluminum foil, a main element for obtaining the effect of increasing the capacitance is The reason why this effect is obtained is that the oxide film on the foil surface has a myriad of fine defects due to the high-concentration content. Points
This is probably because a large number of etching pits are formed, and thereafter the pits progress deeply in a tunnel shape on the inner surface of the foil. Therefore, the thickness of the surface layer
0.1 μm does not necessarily have a critical significance in the effect itself in the numerical value itself, the total content of rare earth elements in the surface layer within its thickness range is 1.5 to 1.5 of its content in the foil excluding the surface layer. The point that it should be 500 times has its limiting significance. Therefore, it is not necessary that the above-mentioned elements are uniformly distributed in the above-mentioned surface layer portion, but it is rather preferable that the above-mentioned element is further unevenly distributed at a high concentration on the surface portion.

Here, rare earth elements are 15 elements with atomic numbers 57 to 71, that is, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, D
y, Ho, Er, Tm, Yb, Lu, and these, plus Y, Sc
It consists of a group of seven elements, and these elements can be evaluated mutually as equivalents in that they effectively contribute to the effect of increasing the surface area by etching the aluminum foil in the present invention. These elements do not need to be used individually as individual elements, and two or more of them can be used in combination. Of course, misch metal (MM) obtained by electrolyzing a mixed chloride of rare earth elements can be used. May be used. Industrially, Y, La, Ce, P
It is preferably used in one or a combination of two or more selected from the group consisting of r, Nd, Sm, and misch metal.

By the way, when the content in the total of the rare earth elements in the surface layer portion is less than 1.5 times the content in the inside of the foil excluding the surface layer portion, the density of etching pits becomes insufficient, and a sufficient effect of increasing the capacitance is obtained. I can't get it.
On the other hand, when the surface layer content of the element exceeds 500 times the content inside the foil, the corrosion resistance of the aluminum foil surface is significantly reduced, and the etching pits are formed at a high density beyond the limit. As a result, the entire surface of the foil is substantially dissolved, and the surface area is rather small. The most preferable range of the total content of one or more rare earth elements in the surface layer is about 5-200 times the content inside the foil.

As described above, at least one of the rare earth elements
The production of aluminum foil containing a high concentration of at least one kind of element is performed by adding one or more of the above rare earth elements in a required amount at the stage of dissolving the aluminum ingot, casting, and then hot rolling according to a conventional method. , Cold rolling, foil rolling, if necessary, further intermediate annealing is performed to make a foil, and this foil is, for example, in vacuum at 460 to 580 ° C for 1 to 24 hours, preferably 475 to 540.
It can be manufactured by subjecting to a heat treatment at a temperature of 2 to 5 hours. The rare earth element added to the base metal is concentrated in the surface layer by the heat treatment, and can be intensively contained in the surface layer 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,
The method is not limited to the above, and one or more of these elements may be separately ion-sputtered, vapor-deposited, or immersed in a liquid containing a rare-earth element on the surface of the aluminum foil to which no rare-earth element is added. It may be applied as a thick film and then diffused into the surface layer by heat treatment. Further, both of 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% (Si: 0.002%, Fe:
0.002%), one or more selected from the rare earth elements are added so as to have the various contents shown in Table 1. After melting and 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. Then, various types were prepared on the surface of this aluminum foil, in which a predetermined amount of a rare earth element was applied by ion sputtering, and in the case where no rare earth element was applied. Then, these aluminum foils are placed under vacuum
A final annealing treatment at 485 ° C. × 3 hours was performed to obtain various samples as electrode materials for electrolytic capacitors.

In each of these samples, the content of one or more of the above rare earth elements in the surface layer portion of 0.1 μm from the surface is shown in Table 1 in comparison with their content in the inside of the foil excluding the surface layer portion. It had the magnification shown together.

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.

Then, after forming the etched foil to 380 V, each capacitance was measured, and the capacitance of the sample of Comparative Example 18 was measured.
The capacitance ratio of other various samples was determined in comparison with the case of 100%. The results are shown in Table 1.

As can be seen from the results in Table 1 above, the electrode foil containing one or more of the rare earth elements in the surface layer portion in the range of the specified amount of the present invention is a foil and a surface layer substantially free of it. It has an effect of increasing the capacitance and is excellent in strength as compared with a foil containing these elements excessively in the portion.

Continuation of the front page (72) Inventor Shozo Umezu 6, 224 Kaiyama-cho, Sakai-shi, Osaka Showa Aluminum Co., Ltd. (58) Field surveyed (Int. Cl. ⁶ , DB name) H01G 9/04 H01G 9 / 045

Claims (1)

(57) [Claims] 1. The foil has an aluminum purity of 99.9% or more, and one or two or more rare earth elements are contained in the whole foil in total.
0.2 to 50 ppm, and the total content of the rare earth elements in the surface layer portion from the surface to a thickness of 0.1 μm is 1.5 to 500 times the content inside the foil excluding the surface layer portion. An aluminum foil for an electrolytic capacitor electrode, characterized in that: