JPH10308329A - Aluminum foil for electrolytic capacitor and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum foil for an electrolytic capacitor, by which leak current can be reduced without reducing electrostatic capacity during chemical processing. SOLUTION: In an etched aluminum foil whose aluminum purity is 99.9-99.97% (wt.%) and the Fe content is 80-500 ppm, the core part of the etched foil is made of intermetallic compound of Al-Fe and/or Al-Fe-Si dispersed in a matrix, and the intermetallic compound is removed from the surface layer subjected to chemical processing.

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 for an electrolytic capacitor electrode capable of reducing a leakage current after formation, and a method for producing the same.

[0002]

2. Description of the Related Art With the miniaturization of electronic components, it is required to improve the capacitance of aluminum foil for electrolytic capacitors used in electronic components. Various proposals have been made to obtain a larger area coverage.

On the other hand, when an aluminum foil for an electrolytic capacitor electrode is subjected to a chemical conversion treatment after an etching treatment, there is a problem that a leakage current (residual current) occurs. When the leakage current occurs, the capacitance is reduced. Various proposals have been made to reduce the minute current flowing through the film.

Hitherto, high-purity aluminum foil has been used as an aluminum foil for electrolytic capacitor electrodes, and it has been an effective means to increase the aluminum purity of the aluminum foil from the viewpoint of reducing leakage current. In order to reduce costs, the use of aluminum foil with low aluminum purity as an aluminum foil for electrolytic capacitor electrodes has been considered. For example, aluminum foil for anodes has a purity of 99.99% to 99.98%. It is shifting to.

However, when the purity of aluminum decreases, the leakage current during the chemical conversion treatment tends to increase, which leads to a decrease in the performance of the electrolytic capacitor. In general, it is said that the cause of the leakage current is due to the formation of film defects by the intermetallic compound in the chemical conversion film, and many attempts have been made to improve the chemical conversion treatment method to increase the capacitance. The solution has not been reached.

[0006]

In the course of the study on the relationship between the intermetallic compound remaining in the etched etched aluminum foil and the leakage current at the time of formation, the inventors found that Al in the matrix of the etched foil. -Fe
Of the intermetallic compound mainly composed of Al-Fe-Si-based compound, found that the leakage current at the time of chemical conversion treatment increased, and the above-mentioned intermetallic compound remaining in the etched foil was selectively removed. As a result of repeated experiments and studies on a method of performing the method, it was found that these intermetallic compounds can be effectively removed by treating the etched aluminum foil with a specific acid solution.

The present invention has been made based on the above findings, and an object of the present invention is to provide an electrolytic solution having a reduced leakage current during a chemical conversion treatment and improved chemical conversion film characteristics without lowering the capacitance. An object of the present invention is to provide an aluminum foil for a capacitor electrode and a method for manufacturing the same.

[0008]

An aluminum foil for an electrode of an electrolytic capacitor according to the present invention for achieving the above object has an aluminum purity of 99.9 to 99.97% and an Fe content of 99.9% to 99.97%.
An etched aluminum foil containing 80 to 500 ppm of an Al-Fe-based and / or Al-Fe-Si-based intermetallic compound dispersed in a matrix at the core of the etched aluminum foil. The first feature of the surface layer to be subjected to the chemical conversion treatment is that the intermetallic compound is removed, and the aluminum layer has a purity of 9%.
An etched aluminum foil containing 9.9 to 99.97% of Fe and containing 80 to 500 ppm of Fe, and having an etched aluminum core having an average particle size of 3 μm or less in a matrix. A second feature is that a -Fe-based and / or Al-Fe-Si-based intermetallic compound is dispersed, and the surface layer to be subjected to the chemical conversion treatment has the intermetallic compound removed.

The method for producing an aluminum foil for an electrolytic capacitor electrode according to the present invention has an aluminum purity of 99.9 or more.
The first feature is that the intermetallic compound containing 99 to 97 ppm of Fe, containing 80 to 500 ppm of Fe, and removing the intermetallic compound in the surface layer of the etched aluminum foil by an acid solution is then subjected to a chemical conversion treatment.

In addition, the acid solution is 1 to 10 mol / l nitric acid.
And a sulfuric acid of 1 to 5 mol / l at a liquid temperature of 5 to 40 ° C., and immersing the etched aluminum foil in the mixed acid for 10 seconds or more.
1, when the concentration of phosphoric acid is Ymol / L, Y ≦ 2-
The second and third features are to use a mixed acid to which phosphoric acid is added within the range of 0.4X.

Further, the aluminum purity is 99.9-9.
After quenching and solidifying an aluminum melt containing 9.97% of Fe at 80 to 500 ppm at a cooling rate of 100 ° C./s or more to form a rapidly solidified material, the rapidly solidified material is cold-rolled into an aluminum foil, A fourth feature is that the aluminum foil is immersed in an acid solution to remove the intermetallic compound in the surface layer, and then subjected to a chemical conversion treatment.

In the present invention, the purity of aluminum is 9
An aluminum foil containing 9.9 to 99.97% of Fe and 80 to 500 ppm of Fe is applied. When the aluminum purity is less than 99.9% and the Fe content is 500 ppm
When the ratio exceeds the range, impurities increase and the intermetallic compound becomes coarse, so that the dissolution and removal of the intermetallic compound tend to be insufficient. The aluminum foil contains 450 p as an impurity.
pm or less of Si can be contained.

[0013] Al-Fe and / or Al-Fe-Si intermetallic compounds are dispersed in the matrix of the core of the aluminum foil. It is preferable that the fine particles have a fineness of 3 μm or less. By dispersing the intermetallic compound finely, the dissolution and removal thereof can be further facilitated.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The aluminum foil for an electrode of an electrolytic capacitor of the present invention is etched in a solution containing chlorine ions, for example, a hydrochloric acid solution or a mixed acid solution of hydrochloric acid and sulfuric acid, according to a conventional method. The intermetallic compound in the surface layer of the etched aluminum foil is removed by an acid solution.

As the acid solution, nitric acid 1 to 10 mol / l
It is preferable to use a mixed acid consisting of sulfuric acid and sulfuric acid at 1 to 5 mol / l at a liquid temperature of 5 to 40 ° C., and immerse the etched aluminum foil in the mixed acid for 10 seconds or more. Nitric acid concentration is 1mol
If it is less than / l, the dissolution and removal of the intermetallic compound will not be sufficiently performed, and the effect of reducing the leakage current at the time of chemical formation will be small.
If it exceeds 0 mol / l, the dissolution of the etch pits may proceed and the capacitance may decrease.

Sulfuric acid is added to nitric acid in order to suppress the dissolution of the etched foil and to prevent the dissolution of the etch pits or the mechanical detachment of the etched layer. If the sulfuric acid concentration is less than 1 mol / l, the effect is not obtained. If the concentration is more than 5 mol / l, the etch pits may be dissolved due to chemical dissolution, which is not preferable. When the liquid temperature is lower than 5 ° C., it takes too much time to dissolve the intermetallic compound, resulting in poor working efficiency. When the liquid temperature exceeds 40 ° C., the chemical dissolution reaction becomes severe. The immersion time is 10
If the time is less than seconds, it is difficult to sufficiently dissolve and remove the intermetallic compound.

In the mixed acid, dissolution of the etched foil is suppressed,
Phosphoric acid can be added for the purpose of preventing the dissolution of the etch pits or the mechanical detachment of the etching layer. When the sulfuric acid concentration in the mixed acid is X mol / l and the phosphoric acid concentration is Y mol / l, the amount of phosphoric acid is preferably in the range of Y ≦ 2-0.4X. Phosphoric acid concentration is 2-0.4X
When the value exceeds, the capacitance tends to decrease due to chemical dissolution.

In order to make the average particle size of the Al-Fe-based compound and the Al-Fe-Si-based compound dispersed in the matrix of the aluminum foil 3 μm or less, the aluminum purity must be 9 or less.
An aluminum melt containing 9.9 to 99.97% of Fe in an amount of 80 to 500 ppm was subjected to air atomization by 10
A rapidly solidified powder obtained by rapid solidification at a cooling rate of 0 ° C./s or more is solidified to form a rapidly solidified material, or the above aluminum melt is spray-formed by a spray forming method.
After cooling at a cooling rate of 0 ° C./s or more to form a rapidly solidified material, the rapidly solidified material is preferably cold-rolled into an aluminum foil.

After the intermetallic compound in the surface layer of the etched aluminum foil is dissolved and removed with an acid solution, a chemical conversion treatment is performed.
The chemical conversion treatment is performed by anodic oxidation in a neutral solution, for example, an aqueous solution of boric acid or ammonium adipate according to a conventional method, and an oxide film of a dielectric is formed according to the working voltage of the capacitor. Although the voltage of the chemical conversion treatment is not particularly limited, a voltage of 100 V or less is preferable, and the voltage may be 0 V where the chemical conversion treatment is not performed.

[0020]

Hereinafter, examples of the present invention will be described in comparison with comparative examples. Example 1 350 pp Fe with an aluminum purity of 99.92%
m-containing etched aluminum foil having a thickness of 100 μm was immersed in an acid solution having a composition shown in Tables 1 and 2 under the conditions shown in Tables 1 and 2, and 1 liter of pure water was added to 150 g of ammonium adipate. It was immersed in a solution (liquid temperature: 85 ° C.), immediately converted to a current of 70 V at a current density of 0.05 A / cm ² , and kept at a constant current for 15 minutes. After 15 minutes, the current density was measured, and this was defined as the leakage current. After chemical formation, LC
Using an R meter, the capacitance was measured with a parallel equivalent circuit at 120 Hz.

The aluminum foil is produced by subjecting an aluminum ingot produced by ordinary continuous casting to homogenization treatment according to a conventional method, and then performing hot rolling and cold rolling. The aluminum foil is dispersed in a matrix. The average particle size of the Al-Fe-based compound and / or Al-Fe-Si-based compound is 6 µm. As the etched foil, an AC-etched etched aluminum foil having spongy pits was used.

The measured values of the leakage current and the capacitance were evaluated relative to each other by setting the leakage current and the capacitance when the chemical conversion treatment was immediately performed on the etched aluminum foil under the above conditions as 100%. The results are shown in Table 2. As shown in Tables 1 and 2, the etched foil according to the present invention can reduce the leakage current to 85% or less while maintaining the capacitance at 97% or more.

[0023]

[Table 1]

[0024]

[Table 2]

Comparative Example 1 As in Example 1, the aluminum purity was 99.92%
Then, an etched aluminum foil having a thickness of 100 μm and containing 350 ppm of Fe was added to an acid solution having a composition shown in Table 3 in Table 3
Immersed in a solution (liquid temperature: 85 ° C.) obtained by adding 1 liter of pure water to 150 g of ammonium adipate as in Example 1, and immediately immersed in a current density of 0.05 A / cm up to 70 v. ^The mixture was formed at ² and kept at a constant current for 15 minutes. After 15 minutes, the current density was measured, and this was defined as the leakage current. After the formation, use an LCR meter for 120H
z, the capacitance was measured using a parallel equivalent circuit. Note that, as the etched foil, an etched aluminum foil having spongy pits and subjected to AC etching was used.

The measured values of the leakage current and the capacitance were evaluated relative to each other by setting the leakage current and the capacitance when the above-mentioned etched aluminum foil was immediately subjected to the chemical conversion treatment under the above-mentioned conditions to 100%, respectively. Was. As shown in Table 3, when the liquid composition of the acid solution and the immersion conditions were not appropriate, either the effect of reducing the leakage current or the effect of maintaining the high capacitance was inferior.

[0027]

[Table 3] << Table Note >> Test material No. 32 is a conventional one that does not perform immersion treatment in an acid solution.

Example 2, Comparative Example 2 Aluminum purity of 99.91% and 99.93%
Then, an aluminum melt containing up to 610 ppm of Fe was cooled and solidified by a spray forming method to produce a plate material having a thickness of 2 mm. After cold rolling this sheet material to a thickness of 100 μm, AC etching was performed to obtain an etched aluminum foil. The cooling rate is 2 mm
The microstructure of the rapidly solidified plate material was observed and calculated from dendrite arm spacing (DAS) according to the following equation.
D × C ^0.33 = 33.4 (D: DAS (μm), C: cooling rate (° C./s)).

[0029] The etched foil was treated with nitric acid 5 mol / l, sulfuric acid 3
immersion treatment in an acid solution (liquid temperature: 35 ° C.) consisting of 0.5 mol / l and phosphoric acid 0.5 mol / l for 180 seconds, followed by a chemical conversion treatment under the same conditions as in Example 1 and maintained at a constant voltage for 15 minutes. In the same manner as in Example 1, the leakage current and the relative capacitance were evaluated. Table 4 shows the results. When the Fe contents are different, the absolute values of the capacitances after the formation of the etched foils are different. Therefore, a relative comparison was made between test materials having the same Fe content.

[0030]

[Table 4]

As shown in Table 4, the test material No.
No. In Nos. 33 to 36, the capacitance was maintained at 100% or more, and the leakage current could be reduced to 85% or less. In Nos. 37 and 38, since the Fe content is large, the intermetallic compound becomes coarse and large even when rapid solidification is performed, and the dissolution and removal of the intermetallic compound by the acid solution become insufficient. I can't get it.

[0032]

According to the present invention, the intermetallic compound remaining on the etched foil is completely removed, and the aluminum for an electrolytic capacitor electrode can reduce the leakage current without lowering the capacitance during formation. A foil is provided.

──────────────────────────────────────────────────の Continued on front page (51) Int.Cl. ⁶ Identification code FI H01G 9/042 H01G 9/04 331

Claims (6)

[Claims] (1) an aluminum purity of 99.9 to 99.9;
80 to 500 ppm Fe at 7% (% by weight, hereinafter the same)
An etched and etched aluminum foil comprising a core of Al-Fe and / or Al-Fe-Si in a matrix.
An aluminum foil for an electrode of an electrolytic capacitor, characterized in that a system intermetallic compound is dispersed and a surface layer to be subjected to chemical conversion treatment has the intermetallic compound removed. 2. An aluminum purity of 99.9 to 99.9.
An etched aluminum foil containing 80 to 500 ppm of Fe at 7% and having been subjected to an etching treatment, wherein the core of the etched aluminum foil has an average particle size of 3 μm or less in a matrix of an Al—Fe-based material and / or Al-Fe-
An aluminum foil for an electrolytic capacitor electrode, wherein an Si-based intermetallic compound is dispersed, and a surface layer to be subjected to chemical conversion treatment has the intermetallic compound removed. 3. An aluminum purity of 99.9 to 99.9.
7%, containing 80 to 500 ppm of Fe, removing an intermetallic compound in a surface layer portion of the etched aluminum foil by an acid solution, and then subjecting the etched aluminum foil to a chemical conversion treatment. Production method. 4. The acid solution is a mixed acid comprising 1 to 10 mol / l of nitric acid and 1 to 5 mol / l of sulfuric acid at a liquid temperature of 5 to 40 ° C., and immersing the etched aluminum foil in the mixed acid for 10 seconds or more. The method for producing an aluminum foil for an electrolytic capacitor electrode according to claim 3, wherein: 5. The method according to claim 4, wherein the concentration of sulfuric acid in the mixed acid is Xm
ol / l and the phosphoric acid concentration is Ymol / l, Y ≦
The method for producing an aluminum foil for an electrolytic capacitor electrode according to claim 4, wherein a mixed acid to which phosphoric acid is added within a range of 2-0.4X is used. 6. An aluminum purity of 99.9 to 99.9.
A 7% aluminum melt containing 80 to 500 ppm of Fe is rapidly solidified at a cooling rate of 100 ° C./s or more to form a rapidly solidified material, and then the rapidly solidified material is cold-rolled to form an aluminum foil. A method for producing an aluminum foil for an electrolytic capacitor electrode, comprising immersing the foil in an acid solution to remove an intermetallic compound in a surface layer portion, and then performing a chemical conversion treatment.