JPH10172868A - Aluminum electrode foil for electrolytic capacitor and method for producing the same - Google Patents

Abstract

(57) [Problem] To provide an aluminum electrode foil for an electrolytic capacitor in which the capacitance per unit area is increased by increasing the uniformity of the pit diameter and the pit interval on the aluminum electrode foil. The pits are ideally formed by immersing an aluminum foil in an acidic aqueous solution containing hydrochloric acid, sulfuric acid and phosphoric acid, and forming pits on the aluminum foil by etching by applying a DC voltage to the aluminum foil. The distance between two adjacent pits of the aluminum electrode foil arranged hexagonally is L,
As closest pit interval of the shortest pit interval of the interval between each pit adjacent the one pit thereto with actual etched aluminum electrode foil, an average value of the closest pit interval determined for each pit L _a and then when the value of L _a / L is 0.58 or more, or the coefficient of variation of the pit diameter 0.4
The capacitance per unit area is increased to 5 or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode foil for an aluminum electrolytic capacitor, and more particularly to an electrode foil having excellent capacitance characteristics and a method for producing the same.

[0002]

2. Description of the Related Art With the recent miniaturization of electronic devices, smaller and smaller aluminum electrolytic capacitors are required. Therefore, it is an important issue to increase the capacitance per unit area of the electrode foil. This is also important from the viewpoint of resource saving and reduction of raw material costs.

Conventionally, in order to increase the capacitance per unit area of an electrode foil for an aluminum electrolytic capacitor, the aluminum foil is immersed in an acidic or neutral aqueous solution and chemically or electrically etched. Accordingly, a method of increasing the surface area by roughening the surface of the aluminum foil has been used.

[0004] Generally, by performing etching, the surface area is increased and the capacity is increased, but the mechanical strength of the foil is reduced. Therefore, it is important to control the location and shape of the etch pits to be formed to increase the surface area while maintaining the strength of the foil.

[0005] Conventionally, in the production of electrode foil for aluminum electrolytic capacitors for high voltage, an etching method has been used in which a large number of columnar etch pits are formed vertically from the surface of the aluminum foil toward the inside thereof. In this etching method, the surface area is determined by the number of generated pits and the size of each pit diameter. Therefore, the electrode foil obtained by this etching method must be closest-packed so that adjacent pits do not overlap each other, the pit diameter should be the optimum diameter for the formation voltage used, and each pit should be Ideally, it should have a uniform columnar shape rather than a cone.

[0006]

However, the above-described etching method has the following problems. (1) As the etching magnification is increased, the surface area increases in accordance with the etching loss. However, when the etching proceeds to a certain extent, the adjacent etch pits overlap each other, and conversely, the surface area decreases. (2) If the pit diameter varies, pits smaller than a certain diameter will be filled with the chemical conversion film after conversion, which will not only contribute to an increase in capacity but also waste power for formation. (3) From the above, the interval between the generated pits,
Making the pit diameter more than a certain value and making the pit shape uniform columnar are important points in increasing the etching magnification.However, in the conventional technology, ideally the interval and shape of the etch pits generated are ideal. It was difficult to control.

An object of the present invention is to solve the above-mentioned conventional problems, and to improve the etching magnification by making the etch pit interval and the pit diameter uniform, thereby increasing the capacitance per unit area. An object is to provide an electrode foil and a method for manufacturing the same.

[0008]

In order to achieve the above object, an aluminum electrode foil of the present invention is obtained by immersing an aluminum foil in an acidic aqueous solution and applying a DC voltage to the aluminum foil to perform etching. An aluminum electrode foil for an electrolytic capacitor having pits formed on the aluminum foil, the aluminum electrode foil having pits ideally arranged in hexagons, that is, one pit formed on the aluminum electrode foil and six pits adjacent thereto. The distance between two adjacent pits in an aluminum electrode foil having the same distance from each pit is L, and the shortest pit among the distance between one pit of an actual etched aluminum electrode foil and each pit adjacent thereto apart as the closest pit interval, when the average value of the closest pit interval determined for each pit and L _a, the value of L _a / L is 0.58 or more, or pit Wherein the coefficient of variation is 0.45 or less.

According to the aluminum electrode foil of the present invention, the uniformity of the pit diameter and the pit interval is improved,
The capacitance per unit area can be increased.

Next, a method for manufacturing an aluminum electrode foil according to the present invention is a method for manufacturing an aluminum electrode foil according to the present invention, wherein the etching is performed in an acidic aqueous solution containing hydrochloric acid, sulfuric acid and phosphoric acid. It is characterized by the following.

In the method for manufacturing an aluminum electrode foil,
It is preferable that the concentration of phosphate ions is 2.0 to 6.0N.

Further, in the method for manufacturing an aluminum electrode foil, it is preferable that the concentration of sulfate ions is 5.0 to 7.0 N.

In the method for manufacturing an aluminum electrode foil, the concentration of chlorine ions is preferably 0.5 to 2.0 N.

According to the method for manufacturing an aluminum electrode foil of the present invention, the electrode foil is etched in an aqueous solution containing hydrochloric acid, sulfuric acid, and phosphoric acid, thereby improving the uniformity of pit spacing and pit diameter. An electrode foil can be manufactured.

Next, the aluminum electrolytic capacitor of the present invention comprises:
It is characterized by being manufactured using the aluminum electrode foil of the present invention.

According to the aluminum electrolytic capacitor of the present invention, the uniformity of the pit diameter and the pit interval of the aluminum electrode foil is enhanced, so that an excellent frequency characteristic with a small ESR component is obtained.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. In order to increase the capacitance per unit area, it is necessary to increase the etching magnification. However, even if the etching magnification is high, if the pit diameter variation is large, pits smaller than a certain diameter will not fill the pit recesses due to the chemical conversion film after conversion and will not contribute to the capacitance, and the formation power will also be wasted. become. Therefore, the smaller the variation of the pit diameter and the smaller the number of pits buried by the chemical conversion film, the higher the contribution to the capacitance.

From the above, the aluminum electrode foil of the present embodiment was manufactured by focusing on the fact that the aluminum electrode foil having a high degree of contribution to the capacitance has a uniform pit interval and pit diameter. Things.

Therefore, the aluminum electrode foil of the present embodiment has higher uniformity of the pit interval and pit diameter than the conventional aluminum electrode foil. In this embodiment, the pit dispersibility index is used to compare the uniformity of the pit interval, and the variation coefficient is used to compare the uniformity of the pit diameter.

Hereinafter, the pit dispersibility index will be described. The pit dispersibility index is a value representing the ratio of the average closest pit interval of the actual etched foil to the pit interval when the pits of the aluminum electrode foil are ideally arranged in hexagons. Hereinafter, a specific description will be given with reference to the drawings.

First, an ideal hexagonal arrangement will be described. FIG. 1 shows a diagram in which pits of an aluminum electrode foil are ideally arranged in hexagons. With respect to one pit 1, adjacent pits are six pits 2 to 7. The distances between pit 1 and each pit (pits 2 to 6) are all equal to L. This relationship is the same for other pits.

Next, a method of calculating the pit interval L when the pits of the aluminum electrode foil are ideally arranged in hexagons will be described. FIG. 2 is an enlarged view of a portion A in FIG. The three lines connecting the center points of the adjacent pits are all L in length, and thus form an equilateral triangle. This equilateral triangle includes ピ ッ ト pits. The area S _{0 of} this equilateral triangle is represented by the following (Equation 1).

[0023]

(Equation 1)

Let S be the area of the aluminum electrode foil, and this area S
If there are n pits in the equation, the following relationship (Equation 2) is established from the proportional relationship.

[0025]

(Equation 2)

When S ₀ of (Equation 1) is substituted for (Equation 2) and developed, the pit interval L is expressed by the following (Equation 3).

[0027]

(Equation 3)

Therefore, if the area S and the number n of pits are known, the pit interval L in an ideal hexagonal arrangement is
It will be obtained by calculation.

Next, a method of calculating the average closest pit interval of an actual etched foil will be described. FIG. 3 shows an example of a part of the pit distribution of an actual etched foil. The area of the entire aluminum electrode foil is S, and there are n pits in the area S. The coordinates of all pits are known and can be distinguished from other pits. Assuming that the i-th pit coordinate is (x _i , y _i ) and the j-th pit coordinate is (x _j , y _j ), the distance L _ij between the i-th pit and the j-th pit is given by 4).

[0030]

(Equation 4)

The calculated distance between the i-th pit and all other j-th pit, the smallest is the closest pit interval L _i therein. Similarly, i = Request and recently against pit interval L _i also 1 to n. The closest pit interval of the _ith pit is _Li and the average closest pit interval L
_a is represented by the following (Equation 5).

[0032]

(Equation 5)

Using (Equation 3) and (Equation 5), the pit dispersity index V is represented by the following (Equation 6).

[0034]

(Equation 6)

Therefore, the greater the value of the pit dispersibility index, the higher the uniformity of the pit spacing. If the actual etched foil is an ideal hexagonal arrangement, the pit spacing is completely uniform and the pit dispersity index is It becomes 1.

Next, the pit diameter variation coefficient will be described. The pit diameter variation coefficient C is a value obtained by dividing the pit diameter standard deviation s by the average pit diameter value RA. When the i-th pit diameter is R _i , it is expressed by the following (Formula 7).

[0037]

(Equation 7)

This variation coefficient C relatively represents the variation of the pit diameter. If the pit diameter is completely uniform, the pit diameter variation coefficient C becomes zero.

In the following embodiments and examples, the pit dispersibility index and the coefficient of variation of the pit diameter were determined by measuring the coordinates of each pit by applying a scanning electron microscope photograph of the manufactured aluminum electrode foil to an image analyzer. Find equivalent diameter data,
These numerical values were obtained by substituting the numerical values into the above-mentioned mathematical expressions.

Next, the aluminum electrode foil of the present embodiment and the method of manufacturing the same will be specifically described. The aluminum foil used in the present embodiment is a 4N high-purity foil having a uniform crystal orientation. This was immersed in an aqueous solution to which hydrochloric acid, sulfuric acid and phosphoric acid were added, and a DC voltage was applied using the aluminum foil as a positive electrode. After the completion of the first stage etching, a second stage etching for enlarging the pit diameter is performed.
To complete the aluminum electrode foil.

When the chlorine ion concentration was 1.0 N, the sulfate ion concentration was 6.0 N, and the phosphoric acid concentration was changed from 0 N to 10.0 N, the respective values of the pit dispersity index, the pit diameter variation coefficient, and the capacitance were calculated. The results are shown in Table 1 below.

[0042]

[Table 1]

FIG. 4 shows the relationship between the phosphate ion concentration and the capacitance in Table 1. In FIG. 4, the horizontal axis P indicates the phosphate ion concentration, and the vertical axis F indicates the capacitance. Of the aluminum electrode foils shown in Table 1, those having a phosphate ion concentration of 0N are conventional examples, and those having a phosphate ion concentration of 1N to 10N are those of the present embodiment.

In the case of the conventional example, the pit dispersibility index is 0.
In contrast to this, in the case of this embodiment in Table 1, the pit dispersibility index is 0.58 or more or the pit diameter variation coefficient is 0.45 or less. In particular, in the embodiment in which the phosphate ion concentration is 2N to 6N, the pit dispersibility index is 0.58 or more and the pit diameter variation coefficient is 0.45 or less, and as shown in FIG. A large capacitance of 7.0 μF / 10 cm ² or more is ensured.

This is because if the phosphate ion concentration is within the above range, excessive dissolution of the aluminum electrode foil does not occur, and the dispersion of the pit diameter and pit interval is small.
This is probably because there are few pits smaller than a certain diameter.
That is, it is considered that there are few pits which do not contribute to the capacitance in which the concave portions of the pits are filled by the chemical conversion film after the chemical conversion.

In the aluminum electrolytic capacitor using the aluminum electrode foil for an electrolytic capacitor according to the present invention, the uniformity of the pit diameter and the pit interval of the aluminum electrode foil is improved, so that the aluminum electrode foil has a smaller diameter, that is, a smaller resistance. Since there are few large pits, the ESR component is small and the frequency characteristics are excellent.

The chlorine ion concentration and the sulfate ion concentration are not limited to those in the present embodiment, but are 0.5 to 2.0 N for the chloride ion concentration and 5.0 to 5.0 for the sulfate ion concentration.
It may be set within a range of about 7.0N.

[0048]

Embodiments will be described below. In the following examples, the aluminum foil used is a 4N high-purity foil having a uniform crystal orientation, similarly to the above embodiment. This was immersed in an aqueous solution to which hydrochloric acid, sulfuric acid and phosphoric acid were added, and a DC voltage was applied using the aluminum foil as a positive electrode. After the completion of the first-stage etching, the second-stage etching for enlarging the pit diameter was performed, and finally, formation was performed at 520 V to complete an aluminum electrode foil. (Example 1) In Example 1, a chlorine ion concentration of 1.0
N, phosphate ion concentration 4.0N, sulfate ion concentration 5.
0 to 7.0N. In addition, the sulfate ion concentration of 3.0 to 3.0
The thing of 4.0N was made into the comparative example.

Table 2 below shows the values of the pit dispersibility index and the pit diameter variation coefficient at each sulfate ion concentration.

[0050]

[Table 2]

As can be seen from Table 2, good results with a pit dispersibility index of 0.58 or more and a pit diameter variation coefficient of 0.45 or less at any of the sulfate ion concentrations of 5.0 to 7.0 N. was gotten. Table 1 shown in the above embodiment
From such a relationship, if the pit dispersity index and the pit diameter variation coefficient are such values, the capacitance is also 7.0 μF /
A large capacity of 10 cm ² or more is expected. (Embodiment 2) In Embodiment 2, the sulfate ion concentration is 6.0.
N, phosphate ion concentration 4.0N, chloride ion concentration 0.5
２．０2.0 N. The values of the pit dispersibility index and the pit diameter variation coefficient at each chlorine ion concentration are shown in Table 3 below.

[0052]

[Table 3]

As can be seen from Table 3, good results were obtained in which the pit dispersibility index was 0.58 or more and the pit diameter variation coefficient was 0.45 or less at any of the sulfate ion concentrations of 5.0 to 7.0 N. was gotten. Table 1 shown in the above embodiment
From such a relationship, if the pit dispersity index and the pit diameter variation coefficient are such values, the capacitance is also 7.0 μF /
A large capacity of 10 cm ² or more is expected.

[0054]

As described above, according to the aluminum electrode foil for an electrolytic capacitor of the present invention, the capacitance per unit area can be increased by improving the uniformity of the pit diameter and the pit interval.

Further, the aluminum electrolytic capacitor using the aluminum electrode foil for an electrolytic capacitor of the present invention has a small ESR component and excellent frequency characteristics because the uniformity of the pit diameter and the pit interval of the aluminum electrode foil is enhanced. It will be.

According to the method of manufacturing an aluminum electrode foil of the present invention, the electrode foil is etched in an aqueous solution containing hydrochloric acid, sulfuric acid, and phosphoric acid, thereby improving the uniformity of the pit interval and the pit diameter. Aluminum electrode foil can be manufactured.

[Brief description of the drawings]

FIG. 1 is a diagram showing that pits of an aluminum electrode foil are ideally arranged in hexagons.

FIG. 2 is an enlarged view of a portion A in FIG. 1;

FIG. 3 is a diagram showing an example of a part of a pit distribution of an etched foil.

FIG. 4 is a diagram showing a relationship between a phosphate ion concentration P and a capacitance F in one embodiment of the present invention.

[Explanation of symbols]

 1,2,3,4,5,6 pit

 ──────────────────────────────────────────────────の Continuing on the front page (72) Yoshiki Murakami, Inventor 1006 Kadoma, Kazuma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd.

Claims (6)

[Claims] 1. An aluminum electrode foil for an electrolytic capacitor in which pits are formed on the aluminum foil by immersing the aluminum foil in an acidic aqueous solution and applying a DC voltage to the aluminum foil to perform etching. The aluminum electrode foil in which pits are arranged hexagonally, that is, the interval between two adjacent pits in the aluminum electrode foil where the interval between one pit formed on the aluminum electrode foil and each of the six adjacent pits is all equal. L, and the shortest pit interval among the intervals between one pit of the actual etched aluminum electrode foil and each adjacent pit is defined as the closest pit interval.
The average value of the closest pit interval obtained for each pit is L
When _a, aluminum electrode foil, wherein the value of L _a / L is 0.58 or more, or coefficient of variation of the pit diameter is 0.45 or less. 2. The method for producing an aluminum electrode foil according to claim 1, wherein the etching is performed in an acidic aqueous solution containing hydrochloric acid, sulfuric acid and phosphoric acid. 3. A phosphate ion concentration of 2.0 to 6.0 N.
The method for producing an aluminum electrode foil according to claim 2, wherein 4. The method for producing an aluminum electrode foil according to claim 2, wherein the concentration of sulfate ions is 5.0 to 7.0 N. 5. The method for producing an aluminum electrode foil according to claim 2, wherein the concentration of chlorine ions is 0.5 to 2.0 N. 6. An aluminum electrolytic capacitor manufactured using the aluminum electrode foil according to claim 1.