JP3130055B2 - Aluminum foil for electrolytic capacitor electrodes - Google Patents

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 electrolytic capacitor electrode, and more particularly to an aluminum foil used as an anode material for medium and high pressures.

[0002]

2. Description of the Related Art An aluminum foil for an electrode of an electrolytic capacitor is generally formed on the foil surface by an electrical or electrochemical etching process in order to increase the effective surface area and increase the capacitance per unit area. Much research has been done on increasing the density of pits. Above all, 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 at a high density has been proposed. Then, at least one of Pb, In and Bi is applied in the form of a compound to the surface of the aluminum foil, subjected to a thermal diffusion treatment at a temperature equal to or higher than the melting point of these metals, and if necessary, annealed according to a conventional method. It has been proposed.

[0003]

SUMMARY OF THE INVENTION In the background of the prior art as described above, the present invention seeks for an element which can be contained in a high concentration on the surface of an aluminum foil to contribute to an increase in the area coverage. It is another object of the present invention to provide an aluminum foil for an electrolytic capacitor electrode capable of increasing the capacitance by finding a relationship between a distribution state and a distribution amount which is most effective for increasing the surface area.

[0004]

According to the present invention, an etching nucleation element which effectively contributes to the increase of the surface area is selected,
This is intended to be contained in a specific portion of the foil in a specific concentration range in a concentrated state.

[0005] Thus, the present invention provides an aluminum alloy having an aluminum purity of 99.9% or more and Cu, Si, Zn, Mn, Ga,
P, V, Ti, Cr, Ni, Ta, Zr, C, Be, P
b, In, an aluminum foil containing one or more of the rare earth elements, and the above elements are contained in a concentrated state in the surface layer portion of the oxide film formed on the surface of the foil base; The gist of the present invention is an aluminum foil for an electrolytic capacitor electrode, characterized in that the concentration of the element in the surface layer portion of the film is set in the range of 1.2 to 30 in ionic strength ratio with respect to the inner layer portion of the foil substrate.

In the present invention, the reason why the aluminum purity of the entire aluminum foil is required to be 99.9% or more is that if the purity is less than the above, the growth of etching pits during electrolytic etching is hindered by the presence of many impurities. This is because a uniform deep tunnel-like pit cannot be formed, and thus an aluminum foil having a high capacitance cannot be obtained. Preferably aluminum purity 99.98%
It is better to use the above.

[0007] As shown in FIG. 1, at least one type of etching nucleus forming element is contained in the surface layer portion of the oxide film formed on the surface of the foil base in a concentrated state. It is the main element for obtaining the increasing effect.
The reason that this effect is obtained is that the oxide film formed on the surface of the foil substrate due to the high-concentration content has countless fine defects in the surface layer portion, and the defective portions are formed in the initial stage of etching. It is considered that this is because a large number of etching pits are formed and the tunnel progresses deeply in a tunnel shape, so that a larger surface area is obtained.

[0008] The concentration of the above-mentioned elements in the surface layer of the film is 1.2 to 30 as an ionic strength ratio to the inner layer of the foil substrate.
Must be set in the range. If it is less than the lower limit, the density of the etching pits becomes insufficient and an increase in the area coverage cannot be expected. As a result, the pits are united to substantially dissolve the entire foil surface, resulting in a smaller surface area. The most preferable range of the ionic strength ratio is approximately 3 to 25.
It is.

Here, the etching nucleus forming element is C
u, Si, Zn, Mn, Ga, P, V, Ti, Cr, N
i, Ta, Zr, C, Be, Pb, In, and rare earth elements are used. The rare earth elements have atomic numbers 57 to 71.
15 elements, ie, La, Ce, Pr, Nd, Pm,
Sm, Eu, Gd, Tb, Dy, Ho, Er, Im, Y
b, Lu and a group of 17 elements obtained by adding Y and Sc to them. In the present invention, each of the above-mentioned elements can be evaluated as equivalent to each other in that they effectively contribute to the effect of increasing the surface area by etching the aluminum foil. These elements do not need to be used as single elements here, and two or more of them can be used in combination. In the case of a rare earth element, a misch metal (MM) obtained by electrolyzing a mixed chloride thereof may be used, and industrially Y, La, Ce,
1 selected from the group consisting of Pr, Nd, Sm, and Misch Metal
It is preferable to use them in a species or a combination of two or more species.

[0010] As etching nucleation elements, Cu, S
When i, Zn, Mn, and Ga are used, it is desirable to set the concentration of the above elements in the foil inside the foil except for the surface layer of the foil up to 0.1 μm in thickness from the foil surface to a range of 3 to 60 ppm. P, V, Ti, Cr, Ni, Ta, Z
When r, C, and Be are used, the same concentration is set to 1 to 40 pp.
When the range of m, Pb, In, and the rare earth element are adopted, it is desirable to set the same concentration in the range of 0.01 to 3 ppm. In any case, if the amount is less than the lower limit, the formation of the etching nucleus is insufficient, and if the amount exceeds the upper limit, the content is excessively etched.

When Cu, Si, Zn, Mn, and Ga are used, the preferred concentration range is generally 10 to 30 pp.
m, P, V, Ti, Cr, Ni, Ta, Zr, C, Be
The preferred concentration range is approximately 5 when
The preferred concentration range when using 25 ppm, Pb, In, or a rare earth element is approximately 0.2 to 1.5 ppm.
It is.

In order to produce an aluminum foil containing the etching nucleation elements in the above-mentioned concentration range in the above-mentioned distribution state, a required amount of one or more of the above elements is added at the stage of dissolving the aluminum base metal. After the casting, hot rolling and foil rolling are performed according to a conventional method, and if necessary, intermediate annealing is further performed to produce a foil. Then, after washing, this is subjected to an annealing treatment at 450 to 550 ° C. for 1 to 30 hours, preferably at 470 to 520 ° C. for 3 to 10 hours in a vacuum, and the above elements are sputter-plated on the foil surface, wet-plated, Appropriately applied by ion implantation or the like, and this is applied, for example, in vacuum at 300 to 550 ° C. for 0.2 to 1
It can be achieved by performing a reheating treatment for 0 hour, preferably at 400 to 500 ° C. for 1 to 3 hours. The elements added to the base metal and the elements added to the foil surface are concentrated in the outermost layer of the oxide film by the heat treatment, so that they can be intensively contained in the specified range of the present invention.

[0013]

The aluminum foil for an electrolytic capacitor electrode according to the present invention is excellent in etching properties, can obtain an extremely large area coverage by the etching treatment, and especially when the etching treatment is performed without the pre-etching treatment, a large number of aluminum foils can be obtained. Etching pits are formed and a large surface area can be obtained, and the entire surface of the foil surface can be prevented from being dissolved during etching.

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

[0015]

EXAMPLE A pure aluminum ingot of 99.99% purity (S
i: 0.002%, Fe: 0.002%) and Cu, S
i, Zn, Mn, Ga, P, V, Ti, Cr, Ni, T
a, Zr, C, Be, Pb, In, and one or more selected from rare earth elements are added so as to have various contents shown in Tables 1 and 2 and dissolved. After casting, hot rolling, intermediate annealing, and foil rolling were performed to produce an aluminum foil having a thickness of 0.1 mm. Then, this is washed and annealed at 490 ° C. for 4 hours under vacuum, and then a predetermined amount of the above element is applied to the surface of the obtained foil by ion sputtering. Various samples as electrode materials for electrolytic capacitors were obtained by performing a heat treatment.

Subsequently, the above-mentioned various aluminum foils were subjected to a first-stage etching for 60 seconds with a DC current having a current density of 20 A / dm ² using an etching solution containing 5% hydrochloric acid and 15% sulfuric acid at a liquid temperature of 85 ° C. Thereafter, the current density was 5 A / dm ² with an etching solution of 5% hydrochloric acid and 0.1% oxalic acid at 85 ° C.
The second-stage etching was performed for 8 minutes by passing a direct current.

After the etched foil was converted to 380 V, the inner layer of the foil substrate (0.1 mm from the foil surface) in the surface layer of the oxide film formed on the surface of the foil substrate for each sample.
The ion intensity ratio to the primary ion: Ar ⁺ , the beam diameter: 500 μm, the acceleration voltage: 10 kV, and the current: 0.3 μA were measured, and the result was taken as the first value. While shown in Table 2 and Table 2, the respective capacitances were measured, and the capacitance ratios of other various samples were obtained in comparison with the case where the capacitance of the sample of Comparative Example 27 was set to 100%. Are also shown in Tables 1 and 2.

[0018]

[Table 1]

[0019]

[Table 2]

As can be seen from the above results, the electrode foil containing one or more of the etching nucleation elements in the surface layer portion of the oxide film formed on the surface of the foil substrate in the range of the specified amount of the present invention. Has an effect of increasing the capacitance as compared with a foil containing these elements excessively.

[Brief description of the drawings]

FIG. 1 is a graph showing detected ionic strength at a surface portion of an aluminum foil for an electrode for an electrolytic capacitor according to the present invention.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-52-139993 (JP, A) JP-A-59-92518 (JP, A) JP-A-61-117820 (JP, A) JP-A-4- 62822 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01G 9/055 C22C 21/00 H01G 9/042

Claims (4)

(57) [Claims] An aluminum purity of 99.9% or more and Cu, Si, Zn, Mn, Ga, P, V, Ti, C
r, Ni, Ta, Zr, C, Be, Pb, In, and an aluminum foil containing one or more of the rare earth elements, wherein the above elements are oxide films formed on the surface of the foil substrate. Electrolysis characterized in that it is contained in the surface layer portion in a concentrated state, and the concentration of the above-mentioned element in the surface layer portion of the film is set in the range of 1.2 to 30 in ionic strength ratio to the inner layer portion of the foil base. Aluminum foil for capacitor electrodes. 2. An aluminum foil having an aluminum purity of 99.9% or more and containing one or more elements of Cu, Si, Zn, Mn, and Ga, wherein said elements are present on the surface of the foil substrate. The oxide layer is contained in a concentrated state in the surface layer portion of the formed oxide film, and the concentration of the element in the surface layer portion of the film is 1.2% in terms of ionic strength to the inner layer portion of the foil substrate.
~ 30 and a thickness of 0.1μ from the foil surface
m in the foil excluding the surface layer of the foil up to m
An aluminum foil for an electrode of an electrolytic capacitor, which is contained in the range of ppm. 3. An aluminum alloy having an aluminum purity of 99.9% or more and P, V, Ti, Cr, Ni, Ta, Zr, C, Be,
Of the oxide film formed on the surface of the foil substrate in a concentrated state, and the above-described element in the surface layer portion of the film. The concentration of the element is set in the range of 1.2 to 30 in ionic strength ratio to the inner layer of the foil base, and the above element is 1 to 1 in the foil excluding the surface layer of the foil from the foil surface to a thickness of 0.1 μm. An aluminum foil for an electrolytic capacitor electrode, which is contained in a range of 40 ppm. 4. An aluminum foil having an aluminum purity of 99.9% or more and containing one or more of Pb, In and rare earth elements, wherein said elements are formed on the surface of the foil substrate. The oxide layer is contained in the surface layer portion of the oxide film in a concentrated state, and the concentration of the element in the surface layer portion of the oxide film is 1.2 to 30 in ionic strength ratio with respect to the inner layer portion of the foil substrate.
And the above element is contained in the inside of the foil excluding the surface layer of the foil from the foil surface to a thickness of 0.1 μm.
An aluminum foil for an electrolytic capacitor electrode, wherein the aluminum foil is contained in the range of pm.