JPH08111351A - Aluminum foil for electrode of electrolytic capacitor and production of aluminum electrode foil employing the same - Google Patents

Abstract

PURPOSE: To provide an aluminum foil for the electrode of an electrolytic capacitor in which multiple deep etching pits can be made uniformly at high density by suppressing generation of a local fusion pit in the initial stage of etching and the surface enlarging rate, and thereby the capacitance, is increased. CONSTITUTION: Occupation area of surface crack is 30% or above and the number of protrusions having vertical angle of 140 deg. or lass in the irregular profile on the surface is 20/0.5mm or less in the direction perpendicular to the rolling direction. Occupation area of oil pit on the surface is 30% or above, or alternatively the occupation area of surface crack is 30% or above and the number of protrusions having vertical angle of 140 deg. or less in the irregular profile on the surface may be 20/0.5mm or less in the direction perpendicular to the rolling direction. Preferably, the surface layer of a foil is removed within the range of average thickness of 0.5μm prior to etching.

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 electrolytic capacitor electrodes and a method for producing an aluminum electrode foil for electrolytic capacitors obtained by etching the aluminum foil.

In this specification, the term aluminum is used to include its alloy.

[0003]

2. Description of the Related Art An aluminum foil used as an aluminum electrode material for an electrolytic capacitor is required to have a surface area as large as possible and a large capacitance per unit volume. For this reason, it is generally performed to increase the effective area of the aluminum foil by subjecting it to electrochemical or chemical etching treatment. Further, in order to increase the surface expansion ratio as much as possible, etching pits are formed. Studies have been conducted to generate the particles more uniformly.

For example, in the foil rolling just before the intermediate annealing and just before the finish annealing, the center line average roughness (Ra) in the direction perpendicular to the rolling direction of the foil is adjusted by changing the roll roughness to 0.35 μm or less. Therefore, it has been proposed to increase the degree of accumulation of cubic oriented grains (Japanese Patent Publication No. 1-3.
3546). Furthermore, it is also proposed that the rolling residue or scratches on the surface with respect to the rolling direction of the foil be angled and the center line average roughness (Ra) be set to 0.10 μm or more to prevent coalescence of the tunnel pits in the horizontal direction. (Japanese Patent Laid-Open No. 6-88298)

[0005]

However, in the above-mentioned conventional proposals, local dissolution occurs at the initial stage of etching, and etching pits communicate with each other to form coarse local dissolution pits. There is a problem that it is difficult to obtain the effect of increasing the surface expansion rate.

The present invention has been made in order to solve such a problem, and it is possible to form a large number of deep etching pits uniformly and with high density by suppressing the generation of local dissolution pits in the initial stage of etching. It is an object of the present invention to provide an aluminum foil for an electrode of an electrolytic capacitor, which is capable of achieving a high surface area ratio, that is, an excellent capacitance.

[0007]

For the above-mentioned purpose, the inventor has found that as a result of repeated experiments and research, the etching nuclei are often formed on the uneven portions of the aluminum foil surface. The present invention has been completed as a result of repeating the experiment and the research after obtaining the surface condition of the aluminum foil capable of suppressing the generation of the local dissolution pit in the initial stage of etching after the start.

That is, according to one aspect of the present invention, the number of peaks having an apex angle of 140 degrees or less is 20 in the surface unevenness profile in the surface irregularity profile of 30% or more and in the direction perpendicular to the rolling direction. It is characterized in that the number is 0.5 / mm or less.

In the above, the surface crack is a surface morphology defined in "Classification of Surface Defects of Aluminum and Aluminum Alloys" (published by Japan Institute of Light Metals), and specifically, countless numbers appearing at right angles to the rolling direction. Of fine surface cracks. This surface crack is several μm in terms of an optical microscope.
It is observed as a groove-like defect having a length of several tens of μm. The area occupied by the surface cracks is defined to be 30% or more of the total surface area of the foil. If it is less than 30%, local dissolution pits are often generated in the initial stage of etching, and as a result, a large capacitance cannot be obtained. However, the reason is speculated as follows.

That is, it is presumed that a fine concave shape portion which becomes the nucleus of the initial etching pit is generated by the surface crack and disperses the etching pit, but the area occupied by the surface crack is 30% of the total surface area of the foil. It is presumed that if the value is less than the above, the effect is poor. The particularly preferable surface crack occupying area is 40% or more, and the upper limit is preferably 70%.

Such surface cracks cause an excessive amount of rolling oil drawn into the contact arc between the roll and the plate (foil) during rolling, reduce the amount of reduction per pass, and increase the rolling speed. And the like. Therefore, by adjusting these, the occupied area of surface cracks can be made 30% or more.

Even if the area occupied by surface cracks is 30% or more, if there are many sharp-angled rolling streaks, many local melting pits will occur at the initial stage of etching. Must. Specifically, as shown in FIG. 1, in the direction (Y direction in the figure) perpendicular to the rolling direction of the aluminum foil (1), the apex angle (θ) of the acute peak (2) of 140 degrees or less is formed. It is necessary that the number is 20 or less per 0.5 mm length. Thus, even if the area occupied by surface cracks is 30% or more, the number of acute peaks (2) having an apex angle (θ) of 140 degrees or less in the direction perpendicular to the rolling direction is 20 per 0.5 mm. It is presumed that the presence of more than one of the above causes a large number of local dissolution pits in the initial stage of etching for the following reason.

That is, since the rolling streaks are protrusions (convex shapes) and are arranged along the rolling direction, concentration of electric potential occurs at the very early stage of etching, and local melting pits preferentially occur in streaks. It is supposed to be. Therefore, it is considered that the nonuniformity of the initial etching is suppressed by eliminating the streak-shaped convex portion.

Preferably, the number of acute peaks (2) having an apex angle (θ) of 140 degrees or less in a direction perpendicular to the rolling direction is 10 or less per 0.5 mm. Since such rolling streaks are generated by transferring the polishing streaks of the rolling roll, the number of peaks (2) having an apex angle of 140 degrees or less can be controlled within the above range by controlling the polishing streaks of the rolling roll. . The uneven profile of the foil surface may be measured with a surface roughness meter or the like.

A second aspect of the present invention capable of suppressing the generation of local dissolution pits at the initial stage of etching is an aluminum foil for electrolytic capacitor electrodes, characterized in that the surface area of the oil pits is 30% or more. is there.

Here, the oil pit means a hole formed after the rolling oil is embedded. This oil pit is generally considered to impair the shape of the foil surface, but in the present invention, the oil pit is positively utilized and the occupied area is 30% or more of the entire surface of the foil. As described above, by making the occupied area of the oil pits 30% or more, the occurrence of the local dissolution pits can be suppressed because the oil pits are the very thick part of the oil film, and the contact area with the roll surface is small. As a result, it is speculated that the nuclei of the etching pits that lead to the initial local dissolution pits decrease as the foil surface becomes a free surface. The particularly preferred occupation area of the oil pit is 40% or more, and the upper limit is 70%.
Is preferred.

The oil pit is affected by the deformation resistance of the material and the viscosity of rolling oil. Therefore, the occupied area ratio of the oil pit can be increased by means such as applying the material to the intermediate annealing and then rolling, or rolling with a rolling oil having a high kinematic viscosity.

Further, the occupation area of the oil pit is 30%.
In addition to the above requirements, the area occupied by surface cracks is 30%
By adding the above requirement, it is possible to further suppress the occurrence of local dissolution pits in the initial stage of etching, and to obtain a larger capacitance. Moreover, in addition to the requirements for the occupied area of the oil pit and the occupied area of the surface crack, the number of peaks having an apex angle of 140 degrees or less is 20/0 in the surface unevenness profile in the direction perpendicular to the rolling direction. When the requirement of 0.5 mm or less is added, these act synergistically and the occurrence of local dissolution pits can be further suppressed, and a large capacitance can be obtained. The area occupied by these surface cracks and the apex angle are 1
The requirement regarding the number of peaks of 40 degrees or less is the same as that described above, and thus the description thereof is omitted.

The aluminum foil used in the present invention preferably has an Al purity of 99.9% or more, particularly 99.99%, in order to uniformly grow etching pits.
The above-mentioned high-purity ones are preferable, but not limited to these, as long as they are in a range used for electrolytic capacitors.

The aluminum foil for electrolytic capacitor electrodes according to the present invention is used as an electrode foil after being subjected to an etching treatment for improving the surface expansion rate. Thus, the aluminum foil according to the present invention, whose surface morphology is specified, suppresses the generation of coarse local dissolution pits in the initial stage of etching, but more preferably the surface layer of the aluminum foil before etching. Good to remove. By removing the surface layer of the aluminum foil, substances such as oxides and rolling oil embedded in the surface layer during rolling can be removed, and the above-mentioned surface morphology is more significantly exposed, resulting in coarse local dissolution. This is because the generation of pits can be further suppressed and a larger capacitance can be obtained. However, if the removed thickness is too thick, the surface morphology is impaired and disappears. Therefore, the removed thickness must be set to 0.5 μm or less on average. Particularly preferably, the average value is 0.3 μm or less, and the lower limit value is preferably 0.01 μm on average.

The method of removing the surface layer of the aluminum foil is not particularly limited, but examples thereof include alkali etching and acid etching. Further, it is better to remove the surface layer immediately before the etching in order to perform the etching in a state where the fresh surface after the removal is exposed and further increase the electrostatic capacity.

[0022]

In the aluminum foil for electrolytic capacitor electrodes according to claims 1 to 4, the occurrence of local dissolution pits is suppressed in the initial stage of etching, and a large number of etching pits are formed in a uniformly dispersed state on the entire foil surface and grow. As a result, deep and thick etching pits are formed, and as a result, the surface expansion rate increases and the capacitance increases.

Further, the surface layer of the foil according to any one of claims 1 to 4 is removed in a range of an average thickness of 0.5 μm or less, and then etching is performed, so that the oxidation embedded in the surface layer during rolling is performed. Substances such as rolling stock and rolling oil are removed, and the generation of coarse local dissolution pits is further suppressed.

[0024]

【Example】

(Example 1) Fe: 15 ppm, Si: 25 ppm, C
An ingot of aluminum having an Al purity of 99.99% and containing u: 30 ppm was subjected to chamfering, hot rolling and cold rolling according to a conventional method. During the cold rolling, intermediate annealing was performed under the conditions shown in Table 1. Moreover, about No. 11, the intermediate annealing was not performed.

After cold rolling, foil rolling was carried out by changing the rolling speed, the viscosity of rolling oil, and the surface roughness of the rolls, and a plurality of aluminum foils having different surface morphologies (thickness: 100 μm) were used.
m) was obtained. The rolling speed is 100 to 8 in terms of roll peripheral speed.
The rolling oil used was a mineral oil based on which 5% of alcohol was added, the viscosity was changed between 1.3 and 4 cst, and the surface roughness of the roll was at the center. Line average roughness (Ra) 0.4-0.03μ
It was changed between m.

Next, each aluminum foil was finally annealed at 520 ° C. for 3 hours in an argon atmosphere.

The surface of each aluminum foil obtained as described above was observed by a laser surface roughness meter and a microscope, and the area ratio occupied by surface cracks, the area ratio occupied by oil pits, and the length in the direction perpendicular to the rolling direction were measured. The number of peaks having an apex angle of 140 degrees or less per 5 mm was measured. The results are shown in Table 1.
Shown in

Next, the aluminum foil of each of the above types was subjected to a current density of 20 A / dm ^{2 in} a mixed solution of 5% hydrochloric acid and 10% sulfuric acid (80 ° C.) without removing the surface layer.
After the primary etching for 80 seconds, the secondary etching was subsequently performed in 5% hydrochloric acid (80 ° C.) at a current density of 5 A / dm ² for 10 minutes.

Then, after performing chemical conversion treatment at 380 V in a boric acid bath, the capacitance of each electrode foil was measured. The results are shown in Table 1 as a relative comparison when Comparative Example 1 was set to 100%.

[0030]

[Table 1] Further, when the surface of each aluminum foil was observed after etching, coarse local dissolution pits were generated in the comparative products of Nos. 1 and 2, whereas coarse local dissolution pits were generated in the products of Nos. 3 to 11. It was suppressed.

As can be seen from the above results, it can be confirmed that the product of the present invention can suppress the local dissolution pit and increase the capacitance as compared with the comparative product.

(Example 2) No. of Table 1 in Example 1
The same aluminum foils as 3, 5, 7, and 9 (all of which were carried out) were used, and the surface layer of each aluminum foil was removed with various average removal thicknesses as shown in Table 2. The removal process is
It was carried out by varying the soaking time in 2.5% NaOH (30 ° C.).

Next, each aluminum foil from which the surface layer was removed was immediately etched under the same etching conditions as in Example 1, and then subjected to chemical conversion treatment in a boric acid bath at 380V. Then, the capacitance of each electrode foil was measured. The results are shown in Table 2 as a relative comparison when the capacitance of No. 1 aluminum foil in Table 1 is set to 100.

[0034]

[Table 2] From the results of Table 2 above, it could be confirmed that a larger capacitance can be obtained by removing the surface layer of the aluminum foil over an average thickness of 0.5 μm or less before etching.

[0035]

Since the aluminum foil for electrolytic capacitor electrodes according to claims 1 to 4 defines the surface morphology of the aluminum foil as described above, it is possible to suppress the occurrence of local dissolution pits at the initial stage of etching. It is possible to generate a large number of etching pits in a uniformly dispersed state on the entire foil surface, and these grow to become deep and thick etching pits. As a result, it is possible to increase the surface area ratio and increase the capacitance. .

Further, by removing the surface layer of the aluminum foil according to any one of claims 1 to 4 in a range of an average thickness of 0.5 μm or less, etching is performed,
It is possible to remove substances such as oxides and rolling oil embedded in the surface layer during rolling, the surface morphology is more significantly exposed, and it is possible to further suppress the occurrence of coarse local dissolution pits and to achieve greater static Capacitance can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic enlarged cross-sectional view of a surface of an aluminum foil according to the present invention, which is cut in a direction orthogonal to a rolling direction.

[Explanation of symbols]

 1 ... Aluminum foil 2 ... Mountain

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Toru Kumagai, 6-224, Kaiyamacho, Sakai City, Showa Aluminum Co., Ltd. (72) Inventor: Toyoh Kato, 6-224, Kaiyamacho, Sakai City 72) Inventor Kenji Kenji 6-224, Kaiyamacho, Sakai City, Showa Aluminum Co., Ltd.

Claims (5)

[Claims] 1. The number of peaks having an apex angle of 140 ° or less is 20 / in the surface unevenness profile having an area occupied by surface cracks of 30% or more and in a direction perpendicular to the rolling direction.
Aluminum foil for electrolytic capacitor electrodes, which is 0.5 mm or less. 2. An aluminum foil for an electrolytic capacitor electrode, wherein an occupied area of the oil pit on the surface is 30% or more. 3. An aluminum foil for an electrolytic capacitor electrode, wherein an occupied area of oil pits on the surface is 30% or more and an occupied area of surface cracks is 30% or more. 4. The area occupied by oil pits on the surface is 30% or more, and the area occupied by surface cracks is 30% or more. Further, in the uneven profile of the surface, in the direction perpendicular to the rolling direction, the apex angle is The aluminum foil for electrolytic capacitor electrodes, wherein the number of peaks at 140 degrees or less is 20 / 0.5 mm or less. 5. An aluminum electrode foil for an electrolytic capacitor, characterized in that the surface layer of the foil according to any one of claims 1 to 4 is removed in a range of an average thickness of 0.5 μm or less and then etched. Manufacturing method.