JP2809988B2 - Aluminum foil for electrolytic capacitor electrode and etching method thereof - 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 a method for etching the foil.

[0002]

2. Description of the Related Art An aluminum foil generally used as an electrode material for an aluminum electrolytic capacitor generally has an electrochemical area in order to increase its effective area and increase the capacitance per unit area. Alternatively, a chemical etching process is performed.

[0003] However, a sufficient capacitance cannot be obtained simply by etching the foil. For this reason, in the final annealing step after foil rolling, high-temperature heat treatment of about 450 ° C. or higher is generally performed in order to improve the etching characteristics of the foil in a texture having many cubic orientations. However, it has not been possible to sufficiently satisfy the demand for higher capacitance of the electrolytic capacitor.

The present invention has been made in view of such technical background, and an object of the present invention is to provide an aluminum foil for an electrolytic capacitor electrode capable of increasing the capacitance and a method for etching the foil.

[0005]

Means for Solving the Problems In order to achieve the above object, the present inventors have conducted intensive studies and as a result, have increased the etching pit density by providing a surface-concentrated layer of Mg on an aluminum foil having a high cubic orientation occupancy. And that a high capacitance foil can be obtained.

The present invention has been made based on such findings, and one of them is that the aluminum purity is 99.9.
% Or more, the cubic orientation occupancy of the core portion excluding the thickness of 1 μm from the surface is 90% or more, and the Mg concentration of the surface layer portion having a thickness of 1 μm from the surface on at least one side of the foil is 200%.
An aluminum foil for an electrode of an electrolytic capacitor, characterized in that the content is 2,000 ppm.

Another one is to use the above aluminum foil,
HCl (hydrochloric acid): 3 to 10%, H ₂ SO ₄ (sulfuric acid): 1
After performing primary electrolytic etching in an aqueous solution containing 0 to 40% under the conditions of a liquid temperature of 70 to 90 ° C. and a current density of 10 to 40 A / dm ² , HCl: 3 to 10% or further H _2. C ₂ O ₄ (oxalic acid): In an aqueous solution containing 1% or less, liquid temperature: 70 to 95 ° C., current density: 0 to 10 A / d
The gist of the present invention is a method for etching an aluminum foil for an electrolytic capacitor electrode, wherein a secondary electrolytic etching or a chemical etching is performed under the condition of m ² .

The reason why the aluminum purity of the aluminum foil according to the present invention is required to be 99.9% or more is 99.9%.
At a purity of less than 0.1%, the growth of etching pits during etching is hindered by the presence of many impurities, and uniform deep tunnel-shaped etching pits cannot be formed even by the formation of the Mg-concentrated layer in the range of the present invention. This is because an aluminum foil having a high capacitance cannot be obtained. Preferably, the aluminum purity is 99.98% or more.

The cubic orientation occupancy of the core portion excluding the thickness of 1 μm from the surface is specified to be 90% or more because of the combination of the cubic orientation occupancy in such a range and the Mg surface-concentrated layer, and thus high static electricity. This is because the capacitance becomes possible, and if the cubic orientation occupancy is less than 90%, the capacitance cannot be increased.

[0010] Mg in the surface layer of the aluminum foil is an element necessary for obtaining pits uniformly dispersed during etching. That is, in general, in the initial stage of etching, surface irregularities and oil existing on the foil surface, deposits such as roll coating,
Alternatively, non-uniform local dissolving pits are generated due to the deterioration of the pits, resulting in non-uniformity (sparse / dense) of the etching pit density. In a remarkable case, the surface dissolves in a crater shape. This non-uniformity remains even after the end of the etching, causing a decrease in capacitance. Therefore, in order to prevent such disadvantages, attempts have been made to control the non-uniformity of the etching pits present on these surfaces, but the inventors have conducted extensive research on this point,
It has been found that an aluminum foil having a surface-concentrated layer of Mg has an effect of eliminating locality of etching pits.
That is, if there is a surface-concentrated layer of Mg, shallow grooves along the (100) direction are formed in the rolling direction and a direction perpendicular to the rolling direction in the rolling plane at the initial stage of etching, causing surface melting. Next, etching pits grow perpendicularly to the rolling surface from a part of the groove recess. Due to such groove-shaped surface dissolution occurring at the beginning of etching, the surface irregularities, oil, and deposits such as roll coatings on the foil surface, or those that have been altered, are removed and uniformly dispersed from the beginning of etching. Etched pits are generated. In order to obtain such an effect, the Mg concentration is required to be 200 ppm or more in the surface layer portion having a thickness of 1 μm from the surface. However, if it exceeds 2000 ppm, the concentration is too high and remarkable surface melting occurs, and the total thickness of the foil decreases. Therefore, a high capacitance foil cannot be obtained. Therefore, the surface concentration range of the Mg amount is 200 to 20 in the surface layer portion having a thickness of 1 μm from the surface.
Must be 00 ppm. Particularly preferably 500 to
It is good to be 1000 ppm.

The Mg-concentrated layer may be present on at least one side of the foil. Of course, it may exist on both sides. Further, the Mg concentration in the core portion excluding the surface layer having a thickness of 1 μm from the surface is preferably less than 1 ppm. If it exceeds 1 ppm, the effect of forming the Mg-concentrated layer on the surface layer of the foil is diminished, and etching pits may be communicated inside the foil, so that a sufficient area coverage may not be obtained.

As described above, the production of an aluminum foil containing Mg at a high concentration in the surface layer is not particularly limited.
While it is melted and cast as less than 1 pm (more preferably less than 1 ppm), it is cast by adding 200-2000 ppm of Mg when another aluminum ingot is melted, and both aluminum ingots are rolled to a predetermined thickness by rolling. What is necessary is just to clad it. Alternatively, Mg may be separately applied to the surface of the aluminum foil containing no Mg as a film having an appropriate thickness by a method such as ion sputtering, and then heat treatment may be performed to diffuse Mg into the surface layer portion.

The aluminum foil is subjected to an etching treatment to form an electrode material for an electrolytic capacitor. The etching conditions are not particularly limited, but it is preferable to apply the etching method according to the present invention.

This etching method is a two-step process, and the primary etching is performed using an HCl + H ₂ SO ₄ -based electrolytic solution. However, the inventor has set an appropriate H ₂ SO ₄ concentration at the time of the primary etching. It has been found that by setting the content in such a range, the amount of surface dissolution can be appropriately suppressed, and only the uniform dispersibility of the etching pit distribution can be enhanced. That is, HCl
In the + H ₂ SO ₄ liquid composition, the H ₂ SO ₄ concentration is 1
If the concentration is less than 0%, the surface dissolution amount by the Mg-concentrated layer is large, so that a sufficiently high capacitance foil cannot be obtained. If the H ₂ SO ₄ concentration exceeds 40%, the etching pit density becomes too high and the partial etching is performed. Pit coupling occurs and the capacitance decreases. Therefore, in the primary etching process, H ₂ S
The O ₄ concentration is 10 to 40%. Particularly preferably 20 to
35%. At this time, the other primary etching conditions include an HCl concentration for ensuring an etching pit density, a diameter, and a pit length sufficient to obtain a sufficient surface area after the chemical conversion treatment:
3 to 10%, liquid temperature: 70 to 90 ° C, DC current density: 10
４０40 A / dm ² .

Subsequent to the primary etching, a secondary etching is performed for the purpose of increasing the etching pit diameter. The treatment liquid is basically an aqueous solution of hydrochloric acid having a HCl concentration of 3 to 10%, but may be mixed with H ₂ C ₂ O ₄ having a concentration of 1% or less.
The solution temperature may be 70 to 95 ° C., chemical etching without current application may be performed, or DC current density of 10 A / dm.
Electrolytic etching of ² or less may be used. Any deviation from the above treatment conditions in the secondary electrolysis treatment is insufficient for the effect of increasing the etching pit diameter.

By such primary etching and secondary etching, it is possible to obtain an Al foil having a higher capacitance than the conventional method.

[0017]

The Mg-concentrated layer on the surface layer of the foil eliminates the locality of etching pits on the foil surface during etching and promotes uniform formation. Such an action of the Mg-concentrated layer is more effectively exhibited when the Mg concentration in the foil core is less than 1 ppm.

Further, the etching pits are appropriately dispersed by the primary etching process, and the hole diameter is increased by the secondary etching, so that the area coverage is increased.

[0019]

【Example】

(Example 1) Aluminum ingots having various compositions shown in Table 1 were subjected to face milling, then clad-rolled by hot rolling so as to obtain the structure shown in Table 2, and then cold-rolled (including intermediate annealing).
Then, final annealing at 500 ° C. × 10 hours was performed in an inert gas atmosphere. The sample No. 5 in Table 2 was used as a single foil without cladding.

Then, the occupancy of the cubic orientation of the core of each of the obtained aluminum foils was examined. Table 2 shows the results.

Next, after etching was performed under the following conditions, the obtained aluminum foil was placed in a 5% boric acid solution for 25 minutes.
The capacitance when converted to 0 V was measured. The results are shown in Table 2 as a relative comparison when the capacitance of Sample No. 5 is set to 100%.

[Etching conditions] Pre-treatment: none Primary etching solution composition: 5% HCl + 30% H ₂ SO
_4. Liquid temperature: 80 ° C., current density: DC 20 A / dm ² , time: 80 seconds Secondary etching solution composition: 5% HCl + 0.1% H ₂ C
₂ O ₄ , liquid temperature: 80 ° C., current density: DC 5 A / dm ² ,
Time: 10 minutes

[Table 1]

[Table 2] As can be seen from the results in Table 2, it can be confirmed that the product of the present invention having the Mg surface-concentrated layer in the range of the present invention can increase the capacitance as compared with the comparative product deviating from the range of the present invention. Was.

Example 2 For each sample in Table 2 above,
After performing the etching by setting the conditions of the primary etching and the secondary etching as shown in Table 3, the capacitance when the obtained aluminum foil was converted to 250 V in a 5% boric acid solution was measured. The results are shown by relative comparison when the capacitance of sample No. 5 in Table 2 is set to 100%.

[0024]

[Table 3] As can be seen from the results in Table 3 above, it was confirmed that a product that satisfies the conditions of the etching method according to the present invention can increase the capacitance as compared with a comparative product that deviates from the conditions.

[0025]

The aluminum foil for an electrolytic capacitor electrode according to the present invention has an aluminum purity of 99.9% or more.
The cubic orientation occupancy of the core except the thickness of 1 μm from the surface is 9
0% or more, and at least one surface of the foil has a Mg concentration of 200 to 2,000 in a surface layer part 1 μm thick from the surface.
Since it is characterized by ppm, it is excellent in etching property, and an extremely large surface area can be obtained by the etching treatment. Therefore, it is possible to provide an aluminum foil for an electrolytic capacitor electrode having a large capacitance and excellent electrical characteristics.

[0026] According to the etching method of the present invention, the aluminum foil is added with HCl: 3 to 10%,
H ₂ SO ₄ : In an aqueous solution containing 10 to 40%, liquid temperature: 7
After performing primary electrolytic etching under the conditions of 0 to 90 ° C. and current density of 10 to 40 A / dm ² , HCl: 3 to 1
0% or more H ₂ C ₂ O _4: with an aqueous solution containing 1% or less, the liquid temperature: 70 to 95 ° C., a current density: 0~10A /
Since the secondary electrolytic etching or chemical etching is performed under the condition of dm ² , the etching pits can be appropriately dispersed and the hole diameter can be enlarged, and the surface area is increased and the electrolytic capacitor has a large capacitance. An electrode foil can be provided.

In the above, the Mg concentration in the core is 2
When the amount is less than ppm, the effect of the Mg surface-concentrated layer is more effectively exerted, and an aluminum foil having further excellent capacitance can be obtained.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Eizo Isoyama 6,224, Kaiyamacho, Sakai City Showa Aluminum Co., Ltd. (72) Inventor Shigeru Endo, 6224, Kaiyamacho, Sakai City Showa Aluminum Co., Ltd. (56) References JP-A-4-62821 (JP, A) JP-A-5-21288 (JP, A) JP-A-6-41665 (JP, A) JP-A-7-211593 (JP, A) (58) Field surveyed (Int.Cl. ⁶ , DB name) H01G 9/055 H01G 9/04 304

Claims (4)

(57) [Claims] 1. A cubic orientation occupancy ratio of a core portion excluding a thickness of 1 μm from the surface having an aluminum purity of 99.9% or more is 90%.
% Or more, and at least one surface of the foil has a Mg concentration of 200 to 2,000 p.
pm, which is an aluminum foil for an electrode of an electrolytic capacitor. 2. The aluminum foil for an electrode of an electrolytic capacitor according to claim 1, wherein the core has a Mg concentration of less than 2 ppm. 3. The cubic orientation occupancy of a core portion having an aluminum purity of 99.9% or more and excluding a thickness of 1 μm from the surface is 90%.
% Or more, and at least one surface of the foil has a Mg concentration of 200 to 2,000 p.
pm of aluminum foil for electrolytic capacitor electrodes
_{Cl: 3~10%, H 2 SO} 4: in an aqueous solution containing 10-40%, a liquid temperature: 70 to 90 ° C., a current density: 10 to 40
After performing primary electrolytic etching under the condition of A / dm ² , HCl: 3 to 10% or further H ₂ C ₂ O ₄ :
Electrolytic capacitor electrode characterized in that secondary electrolytic etching or chemical etching is performed in an aqueous solution containing 1% or less at a liquid temperature of 70 to 95 ° C. and a current density of 0 to 10 A / dm ^2. Method for etching aluminum foil. 4. The method for etching an aluminum foil for an electrolytic capacitor electrode according to claim 3, wherein the core has a Mg concentration of less than 2 ppm.