JP3403443B2 - Aluminum foil for electrode of electrolytic capacitor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum foil for an electrolytic capacitor electrode. [0002] In this specification, the term aluminum is used to include its alloy. [0003] 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 to have a large capacitance per unit volume. Therefore, the effective area of the aluminum foil is generally enlarged by performing an electrochemical or chemical etching process. Further, in order to increase the surface area as much as possible, etching pits are formed. Various studies have been made on increasing the depth, thickness, and thickness of the material, such as improvement of the material composition and metal structure, improvement of the etching method, and research on the manufacturing process of the foil. [0004] However, in practice, in the known etching technique, the site of generation of etching nuclei, which forms the basis of the formation of etching pits, is not uniform. Attempting to increase the number of holes causes a disadvantage that the etching pits communicate with each other to form a coarse hole or that the etching pit does not become deep, so that the effect of increasing the area coverage that is sufficiently expected in the result is obtained. There was a problem that it was difficult. SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and makes it possible to form a large number of deep etching pits uniformly and at a high density. The purpose is to provide aluminum foil. [0006] With the above object, the inventor of the present invention has found that, as a result of repeated experiments and studies, the etching nuclei are often formed on the irregularities on the aluminum foil surface. Starting from such knowledge, the present invention was able to be completed as a result of repeating experiments and studies in order to find the irregularities on the aluminum foil surface where etching pits can be uniformly and densely formed. That is, according to the present invention, referring to the reference numerals in the drawings, the roll marks (1) formed of a plurality of strips extending in the rolling direction are formed in parallel on the surface by the transfer of the polishing strips of the rolls. In addition to the roll marks (1), intermittent concave or convex streaks (2) are formed separately from the roll marks (1) in a direction perpendicular or oblique to the rolling direction. (2) The average pitch (P2) in the direction orthogonal to the rolling direction or in the oblique direction is 1-2.
0 μm and when the foil surface is divided into a large number of squares (3) of 20 μm square, the concave or convex streaks (2)
The gist of the present invention is an aluminum foil (A) for an electrolytic capacitor electrode, characterized in that the number of squares in which exists occupies 30% or more of the whole. The aluminum foil (A) has a purity of 99.
A high purity of 99% or more is preferable, but not limited to this, as long as it is within a range used for an electrolytic capacitor. The roll mark (1) and the concave or convex stripes (2) formed on the surface of the aluminum foil (A) are necessary to secure the starting point of the etching pit, that is, the etching nucleus at the time of etching. is there. That is, it is presumed that an etching nucleus is formed around the roll mark (1) and the concave or convex streaks (2). Therefore, by defining the existing state, etching pits are generated in a uniformly dispersed state. Things. The roll mark (1) refers to a concave or convex rolling streak formed by transferring a polishing streak of a rolling roll, and its pitch, height and depth are not particularly limited, but are as uniform as possible. It is desirable. However, if the pitch P1 of the roll mark (1) is too large, the number of etching pits is reduced. Conversely, if the pitch P1 is small, the number of etching pits is too large, and a continuity of adjacent pits is generated, resulting in a large surface area. It becomes difficult to do. Further, the appropriate value of the pitch P1 of the roll mark (1) differs depending on the formation voltage after etching. For example, the pitch of the roll mark (1) may be considerably small in a low-pressure foil having a formation voltage of several tens of volts. Strong roll mark (1)
The average value of the pitch P1 is 1 to 20 .mu.m.
It is about. On the other hand, if the height or depth of the roll mark (1) is not uniform, there is a risk that etching pits are intensively generated in a stripe having a large height or depth, and a local melting phenomenon occurs. Therefore, the preferred height or depth of the roll mark (1) is 1 to 5 μm. Note that the roll mark (1) does not have to completely match its direction with the rolling direction Y, and may be formed in an inclined state with an inclination angle of about 15 degrees or less with respect to the rolling direction Y. The concave streaks or convex streaks (2) formed intermittently on the surface of the aluminum foil (A) in a direction perpendicular to the rolling direction or in an oblique direction are minute ones having a length of about 1 to 50 μm. It is formed mainly by the effect of bringing in rolling oil between the rolling roll and the surface of the aluminum material during rolling. Specifically, by increasing the amount of rolling oil brought in, more concave or convex streaks (2) can be formed. In order to increase the amount of rolling oil brought between the rolling roll and the surface of the aluminum material, for example, the viscosity of the oil may be increased, the rolling speed may be increased, or the oil temperature may be decreased, or these oils may be used. Two or more of the methods may be combined. The pitch P of the concave or convex streaks (2) in a direction perpendicular to the rolling direction or in a diagonal direction.
2 must be specified to an average of 1 to 20 μm.
If the pitch is less than 1 μm, the starting point of the etching pit increases and the area coverage is reduced due to the communication of adjacent pits. On the other hand, if the pitch exceeds 20 μm, the number of etching pits becomes too small, and the effect of increasing the area coverage is also poor. A particularly preferred pitch P2 is 5 to 10 .mu.m on average.
It is. Further, if the amount of the concave streaks or the convex streaks (2) with respect to the foil surface area is too small, the number of etching pits is also reduced and the surface area ratio is reduced. In the present invention, as shown in FIG. The foil surface is divided into a large number of squares (3) of 20 μm square, and the number of squares (hatched in FIG. 2) in which the concave or convex stripes (3) are present is 30% or more of the total number of squares. Occupy and must exist. If the amount is less than 30% of the whole, the number of concave streaks or convex streaks (2) with respect to the entire foil surface becomes too small, and thus the number of etching pits caused by the concave streaks or convex streaks becomes small, Enough area coverage,
The capacitance cannot be obtained. Preferably, the number of squares (3) having concave or convex streaks occupies 70% or more. In the above description, the length of one side of the cell (3) is set to 20 μm. If the length is less than 20 μm, the measurement becomes complicated, and if it exceeds 20 μm, the existence of the concave or convex streaks (2) and the capacitance This is because the correspondence relationship becomes poor. If the rolling conditions such as the rolling speed, the viscosity of the rolling oil, and the temperature are the same, the formation and distribution of the concave or convex streaks (2) can be considered to be substantially uniform over the entire foil surface. Therefore, the measurement of the number of squares (3) on the foil surface does not necessarily have to be performed on the entire surface of the foil. For example, in a 0.1 mm (100 μm) square or other square field of view, a measurement of 20 μm square The fact that the number of squares where the concave or convex streaks (2) exist when divided into squares is 30% or more of all squares in the visual field can be replaced with the ratio to the entire foil surface. During the etching process, it is presumed that the etching starts along the roll mark (1) on the surface of the aluminum foil (A) or around the concave or convex streaks (2). Of the roll marks and concave or convex streaks are formed, deep and thick etching pits are formed in a uniformly dispersed state over the entire foil surface, so that the surface area is increased and the capacitance is increased. Examples: Fe: 15 ppm, Si: 25 ppm, C
u: An ingot of aluminum having a purity of 99.99% containing 30 ppm is subjected to hot rolling and cold rolling in accordance with a conventional method, and then, when performing foil rolling, an annular concave streak along the circumferential direction is formed on the circumferential surface. Was subjected to foil rolling using a plurality of rolls provided in parallel in the axial direction. Then, four types of foils were manufactured by using a plurality of rolls having different concave streaks as rolling rolls and changing the rolling speed and oil temperature during foil rolling as shown in Table 1. The thickness of the aluminum foil was 100 μm, and the rolling oil used was a 6% mineral oil to which 2% of alcohol was added. Next, each aluminum foil was finally annealed at 520 ° C. for 3 hours in an argon atmosphere. When the surface of each of the aluminum foils obtained above was observed with a laser surface roughness meter, convex roll marks extending in the rolling direction were formed in parallel, and in the direction substantially orthogonal to the rolling direction, The minute concave streaks were formed intermittently. Then, the average height and average pitch of the roll marks and the average depth and average pitch of the concave streaks were examined. Also, in an observation field of 0.1 mm square, 20 μm
The number of squares with concave streaks when divided by square squares was counted, and the ratio was determined. Table 1 shows the results. The (100) area ratio of each sample was 90% or more. Next, the above four types of aluminum electrode foils were electrolytically etched in a mixed solution of 5% hydrochloric acid and 20% sulfuric acid (85 ° C.) at a current density of 20 A / dm ² for 2 minutes, and then for 10 minutes. Chemically etched. Then, after a chemical conversion treatment at 380 V in a boric acid bath, the capacitance of each electrode foil was measured. The result was compared with Comparative Example 1 by 10
Table 1 shows a relative comparison when 0% is set. [Table 1] As can be seen from the above results, it was confirmed that the product of the present invention had an increased capacitance as compared with the comparative product. According to the aluminum foil for an electrolytic capacitor electrode according to the present invention, a plurality of roll marks extending in the rolling direction are formed as described above, and the roll marks are formed in a direction orthogonal to the rolling direction or in an oblique direction. Since the intermittent concave or convex streaks are formed, and the average pitch and abundance of the concave or convex streaks are defined, the etching nuclei formed around the roll marks and the concave or convex streaks, A uniform distribution can be formed over the entire foil. Therefore, the etching pits resulting from the erosion of the etching nucleus portion can be formed uniformly and at a high density, and the communication of the etching pits can be prevented.
Each one can be formed thick and deep. As a result, the area expansion ratio of the electrode foil can be remarkably increased, and the capacitance can be increased.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic enlarged plan view of the surface of an aluminum foil according to the present invention. FIG. 2 is a partially enlarged view of FIG. [Description of Signs] A: Aluminum foil 1: Roll mark 2: Concave or convex line 3: Square

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI C25F 3/04 H01G 9/04 346 (72) Inventor Masaru Kiryu 6,224 Kaiyamacho, Sakai City, Osaka Prefecture Showa Aluminum Co., Ltd. (56) References JP-A-5-205983 (JP, A) JP-A-6-145922 (JP, A) JP-A-6-314638 (JP, A) JP-A-56-1520 (JP, A) ( 58) Field surveyed (Int.Cl. ⁷ , DB name) H01G 9/055 C23F 1/00 C23F 1/36 C25F 3/04 C22F 1/04

Claims (1)

(57) [Claims 1] A roll mark (1) composed of a plurality of strips extending in the rolling direction is formed in parallel on the surface by transfer of polishing strips of a roll. In addition to the roll mark (1), an intermittent concave or convex streak (2) oriented in a direction orthogonal to or oblique to the rolling direction is formed. The average pitch (P2) in the direction perpendicular to the rolling direction or in the oblique direction is 1 to 20 m
And when the foil surface is divided into a large number of squares (3) of 20 μm square, the number of squares having the concave or convex streaks (2) occupies 30% or more of the whole. Features Aluminum foil for electrolytic capacitor electrodes.