JP3428035B2 - Aluminum foil for anode of ultra-high voltage Al electrolytic capacitor - 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 anode of an ultrahigh voltage Al electrolytic capacitor having a withstand voltage of about 600V or more.

[0002]

2. Description of the Related Art An aluminum foil used as an anode of an Al electrolytic capacitor for medium and high voltage has a large number of tunnel-shaped etching pits formed in an etching process which is usually performed to increase electrostatic capacity. Generally desired. Therefore, in order to increase the number of etching pits, the crystal plane of the aluminum foil is aligned with the (100) plane, and elements such as Pb, Zn, and Bi are collected and concentrated on the surface.

By the way, recently, along with the expansion of applications of Al electrolytic capacitors, development of ultrahigh voltage Al electrolytic capacitors having a withstand voltage of about 600 V or more has been carried out. In order to realize such an ultrahigh pressure, it is necessary to increase the thickness of the chemical conversion film as a dielectric film formed on the aluminum anode foil by the chemical conversion treatment, and therefore it is necessary to reduce the film defects. Also, to increase the capacitance,
It is necessary to increase the number of etching pits and reduce the number of etching pits compared to the conventional medium and high pressure.

[0004]

However, in the above-mentioned aluminum foil which has been conventionally used for medium and high pressure, there are many film defects and the thickness of the chemical conversion film is limited, and many etching pits are generated. Since the pits are bonded to each other and the surface area is reduced, it cannot be used as it is for the Al anode foil for ultrahigh pressure.

The present invention has been made in view of the above technical background, and it is possible to reduce the film defects to form a thick chemical conversion film and to increase the capacitance.
It is an object of the present invention to provide an aluminum foil that can be used as an anode foil for an ultra high voltage Al electrolytic capacitor.

[0006]

In order to achieve the above-mentioned object, the inventor has conducted various experiments and researches, and as a result, the above-mentioned generation of film defects and increase of etching pits were observed in conventional anode foils for medium and high pressure. The inventors have found that this occurs because the content of each element is too large, and based on such findings, the present invention has been completed.

That is, one of the inventions is Fe: 0.1
14 ppm, Si: 0.1 to 20 ppm, Cu: 0.1
~ 20ppm, Ga: 20ppm as an impurity
Hereinafter, an aluminum foil for an anode of an ultra-high voltage Al electrolytic capacitor, characterized in that Zn: 20 ppm or less, B: 10 ppm or less, other impurity elements are individually regulated to 5 ppm or less, and the balance is aluminum, To do.

In the above, Fe, Si, and Cu are elements necessary to secure an appropriate number of etching pits, but if each of them is less than 0.1 ppm, the effect is poor and the cost increases. On the other hand, Fe (iron)
14 ppm, Si (silicon) 20 ppm, Cu
When the content of (copper) exceeds 20 ppm, it causes a film defect when a chemical conversion film is formed and lowers the withstand voltage. Particularly preferably Fe 8 ppm or less, Si 8 ppm or less, Cu1
It is preferable to set it to 0 ppm or less.

Also, if a large amount of other unavoidable impurity elements is contained, it causes a film defect. Specifically, when Ga (gallium) exceeds 20 ppm, Zn (zinc) exceeds 20 ppm, B (boron) exceeds 10 ppm, and any of the other impurity elements exceeds 5 ppm, film defects occur and high breakdown voltage is reached. I can not get sex. Particularly preferably, Ga 10 ppm or less, Zn 10 ppm or less, B5 pp
It is good to regulate to m or less.

It is desirable that the number of solute atoms is small in order not to lower the withstand voltage. However, if these solute atoms exist in Al in the state of intermetallic compounds, they cause a chemical conversion film defect.
Need to be in solid solution.

In order to make the above Fe, Si, Cu, etc. into a solid solution state, the aluminum foil is generally kept at a temperature of about 500 ° C. or higher, or even lower if Fe, Si, Cu, etc. is small. Is heated. However, this heating causes a phenomenon in which the impurity element is concentrated on the foil surface. If the concentration phenomenon is too violent, the surface concentration becomes high, which leads to an increase in etching pits during etching, which easily causes a coupling between the pits and reduces the capacitance.

Therefore, in the present invention, the surface concentration of the aluminum foil is preferably 50 for each element.
It is preferable to control the content to be less than ppm, and particularly 20 ppm or less. If either element exceeds 50 ppm, the number of etching pits increases too much, and the capacitance decreases. Here, the surface concentration means the concentration in the surface layer portion from the surface to a depth of 0.1 μm. It is necessary to regulate the content of solute atoms in order to suppress the surface concentration.

On the other hand, if the entire surface of the aluminum foil is dissolved or local surface dissolution occurs during etching, the number of effective pits becomes too small and the capacitance cannot be increased. Therefore, it is preferable to regulate the surface concentration of solute atoms of the aluminum foil to less than 50 ppm as described above, and more preferably to regulate the oxide film on the surface of the aluminum foil to 3.5 to 8 nm. This oxide film is dissolved at the time of etching, but if the thickness is less than 3.5 nm, it melts too much and the entire surface of the aluminum foil is dissolved. Conversely, if the thickness exceeds 8 nm, it becomes difficult to melt. There are too few pits and the capacitance is small. Therefore, the thickness of the oxide film is 3.5 to
By defining the thickness to 8 nm, an appropriate number of etching pits can be formed and the capacitance can be increased. The most preferable oxide film thickness is 4 to 6 nm.

The surface concentration as described above is measured by etching the aluminum foil with a Na0H solution and then
It can be carried out by dismounting with a NO ₃ solution and chemically analyzing the content in the solution. The oxide film thickness can be measured by the Hunter Hall method.

When the aluminum foil described above is used as an electrode foil for an electrolytic capacitor anode, it is subjected to the same etching as in the conventional case for the purpose of improving the surface expansion ratio, and then is subjected to a chemical conversion treatment, and a dielectric film consisting of a chemical conversion film is formed on the surface thereof. A film is formed. The chemical conversion treatment must be performed at a chemical conversion voltage of 600 V or higher in order to obtain a high breakdown voltage of about 600 V or higher. Other conditions such as the treatment liquid and the liquid temperature are not particularly limited.

[0016]

By containing Fe, Si, and Cu, an appropriate number of large etching pits are formed in the etching process, and the capacitance is increased. Further, since the upper limit values of Fe, Si, and Cu are regulated and the contents of other impurities are regulated, the chemical conversion film defects are reduced, a chemical conversion film having a large thickness is formed, and the withstand voltage increases.

Further, since the surface concentration is regulated, the increase of etching pits due to etching is further suppressed and the capacitance is further increased.

Further, when the thickness of the oxide film formed on the surface is regulated to 3.5 to 8 nm, the entire surface of the aluminum foil or conversely difficult to dissolve is prevented and the insufficient state of the etching pits is prevented. Prevented and more and more moderate number of etching pits are formed.

[0019]

[Examples] Aluminum alloys having various compositions shown in Table 1 were melt-cast and then homogenized at 550 ° C for 3 hours or more, and then hot rolling, cold rolling, and foil rolling were sequentially performed. Then, an Al foil having a thickness of 110 μm was manufactured.

Next, the aluminum foil was heated at a high temperature under various conditions to obtain an aluminum foil for an Al electrolytic capacitor anode having a surface concentration and an oxide film thickness as shown in Table 1.

Next, for each of the above aluminum foils, 5
% Hydrochloric acid, 80 ° C., direct current density 2000 A / m ² , first etching time 60 seconds, then 5% hydrochloric acid, 95 ° C., direct current density 500 A / m ² , etching time 30 minutes, second stage Etching was performed.

Next, the above-mentioned etched foil was treated with 5% boric acid 95%.
Formation of 800 V was performed at a temperature of 30 ° C. and a direct current density of 30 A / m ² .

The capacitance and withstand voltage of each of the obtained anode foils were measured, and the results are shown in Table 1. In addition,
The capacitance is measured with 10% ammonium borate, 30 ° C,
It was performed at 120 Hz, and the relative ratio is shown when the capacitance of Sample No. 7 is 100. The withstand voltage was measured by immersing the foil after chemical formation in pure water at 100 ° C. for 30 minutes,
It was determined by the voltage when a current of 0.3 A / m ² in direct current was applied at 90 ° C. in 5% boric acid.

[0024]

[Table 1]

From the results shown in Table 1 above, it is understood that the practical products (Nos. 1 to 7 ) defined in the scope of the present invention have a large withstand voltage and a large electrostatic capacity. Comparative product No. 8 having an impurity content outside the range of the present invention was presumed to have many film defects and had a low withstand voltage. Further, as can be seen from the product of No. 4, the electrostatic capacity tends to decrease and the withstand voltage tends to decrease as the surface concentration increases. In addition, a product with an oxide film thickness of less than 3.5 nm (No. 5) or 8 nm
It can also be seen that the actual product (No. 7) exceeding the above-mentioned value has a small capacitance.

[0026]

According to the present invention, depending on the above, Fe: 0.1
~1 4 ppm, Si: 0.1~20ppm, Cu: 0.
Containing 1 to 20 ppm, Ga: 20 pp as an impurity
m or less, Zn: 20 ppm or less, B: 10 ppm or less, other impurity elements are individually regulated to 5 ppm or less, and the balance is made of aluminum. A chemical conversion film having a small thickness and a large thickness can be formed, and its withstand voltage can be increased. Moreover, since an appropriate number of large etching pits can be formed, the electrostatic capacity can be increased, and it can be suitable as an anode foil of an electrolytic capacitor for ultrahigh voltage.

In addition, the concentration of each element in the surface layer from the surface to a depth of 1 μm is 50 ppm.
When it is specified to be less than the above, the increase of etching pits due to etching can be further suppressed, and the capacitance can be further increased.

Furthermore, when the thickness of the oxide film formed on the surface is regulated to 3.5 to 8 nm, it is possible to prevent the entire surface of the aluminum foil from being melted and the contrary difficult to melt, so that the etching pits are in an insufficient state. Can be prevented and more and more appropriate number of etching pits can be formed.
The anode of the electrolytic capacitor can be provided.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tomoaki Yamanoi 6224, Kaiyamacho, Sakai City, Osaka Prefecture Showa Aluminum Co., Ltd. (72) Inventor Tadao Fujihira 6224, Kaiyamacho, Sakai City, Osaka Showa Aluminum Incorporated (72) Inventor Takeshi Nishizaki 6-224, Kaiyamacho, Sakai City, Osaka Prefecture Showa Aluminum Co., Ltd. (56) References JP-A-4-124806 (JP, A) JP-A-2-51211 (JP , A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01G 9/042 H01G 9/055

Claims (3)

(57) [Claims] 1. A Fe: 0.1~ 14 ppm, Si: 0.
1 to 20 ppm, containing Cu: 0.1 to 20 ppm,
Ga: 20ppm or less as impurities, Zn: 20ppm
Hereinafter, B: an aluminum foil for an anode of an ultra-high pressure Al electrolytic capacitor, which is regulated to 10 ppm or less, other impurity elements are individually regulated to 5 ppm or less, and the balance is made of aluminum. 2. The aluminum foil for an anode of an ultrahigh voltage Al electrolytic capacitor according to claim 1, wherein the concentration of each element in the surface layer portion from the surface to a depth of 1 μm is regulated to less than 50 ppm. 3. The aluminum foil for an anode of an ultrahigh voltage Al electrolytic capacitor according to claim 2, wherein the thickness of the oxide film formed on the surface is regulated to 3.5 to 8 nm.