JP2003272960A - Foil for aluminum electrolytic capacitor electrode and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an electrode foil for an aluminum electrolytic capacitor which has a high electrostatic capacity per unit area. <P>SOLUTION: A non-porous aluminum oxide film of thickness 0.02 to 0.6 μm is formed on a surface layer of an aluminum foil of purity 99.92 to 99.995%, and fine recesses 12 are uniformly formed on the surface of the oxide film. The fine recesses 12 can be formed through indentation by the use of fine projections or through pattern printing by the use of a photoresist. Therefore, in a surface roughing process, pits are uniformly and densely provided, so that the aluminum electrolytic capacitor electrode having a high electrostatic capacity per unit area can be obtained. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an electrode foil for an aluminum electrolytic capacitor and a method for manufacturing the electrode foil.

[0002]

2. Description of the Related Art Generally, an aluminum foil for electrolytic capacitor electrodes is roughened by electrolytic etching in an aqueous solution containing hydrochloric acid in order to obtain a high electrostatic capacity. The characteristics of the current medium- and high-voltage electrode foils are that the crystallographic characteristics of the material are such that the cubic orientation ratio is controlled to 90% or more, and the characteristics of the surface oxide film range from 0.004 μm to 0.006 μm for the oxide film. Is well controlled by. The conventional manufacturing method for these conventional materials is generally hot rolling, cold rolling, intermediate annealing, and finally heat treatment at a high temperature (500 ° C. or higher) in an inert gas atmosphere. In this heat treatment step, it is significant to heat at a high temperature of 500 ° C. or higher in order to obtain a high cubic orientation. However, in order to improve the etching property by the subsequent roughening treatment, the heat treatment step should be performed in an inert gas. It can be said that this is for annealing to reduce the thickness of the oxide film on the surface as much as possible.

[0003]

However, the above conventional materials have many problems as described below. 1) In electrolytic etching, which is a surface roughening step, since the oxide film has defects and the thickness is nonuniform, the etching pits are nonuniformly dispersed. 2) Therefore, in the place where pits are formed with high density, when the roughening progresses, the pits are united with each other and the roughening rate is lowered. Due to the non-uniform properties of the oxide film as described above,
The current situation is that the pit formation becomes non-uniform and a high surface roughening rate and thus a high capacitance cannot be obtained.

Various attempts have been made from the past in order to eliminate the drawbacks of the current product. For example, JP-A-59-16
No. 1808, JP-A-61-288411, JP-A-1-189907, etc., a resist is applied to the surface of an aluminum foil, and the resist is removed only at a position expected at the pit start point. It is proposed to perform roughening etching after forming the pattern, but in that case, the barrier property of the resist is weak and the effect of the already formed thermal oxide film is strong, and the pit It was not possible to uniformly disperse the formation points of. In addition, it is also considered that the surface layer oxide film of the aluminum foil is roughened after being indented by fine projections, but the oxide film is partially covered by the minute recesses formed in the surface layer part. It was difficult to sufficiently improve the formation density of pits because the minute recesses were connected to each other by being damaged.

The present invention has been made in view of the above circumstances, and in the surface roughening treatment, pits can be formed uniformly and at high density to increase the electrostatic capacity per unit area. It is an object to provide an electrode foil and a method for manufacturing the electrode foil.

[0006]

In order to solve the above problems, the invention according to claim 1 of the aluminum electrolytic capacitor electrode foil of the present invention has a purity of 99.92 to 99.995.
% Aluminum foil surface layer, a non-porous aluminum oxide film having a thickness of 0.02 μm to 0.6 μm is formed, and minute recesses are uniformly formed on the surface of the oxide film to roughen the surface. It is characterized by being used for processing.

The invention of an aluminum electrolytic capacitor electrode foil according to a second aspect is characterized in that, in the first aspect of the invention, the minute recesses have a depth of 5 μm or less.

The invention of the method for producing a foil for an aluminum electrolytic capacitor electrode according to claim 3 has a purity of 99.92 to 9
A thickness of 0.02μ on the surface layer of 9.995% aluminum foil
It is characterized in that a non-porous aluminum oxide film having a thickness of m to 0.6 μm is formed and minute concave portions are uniformly formed on the surface of the aluminum foil, and then roughening treatment is performed.

The invention of the method for producing a foil for an aluminum electrolytic capacitor electrode according to claim 4 has a purity of 99.92 to 9
A thickness of 0.02μ on the surface layer of 9.995% aluminum foil
It is characterized in that a non-porous aluminum oxide film having a thickness of m to 0.6 μm is formed, indentation is performed on the surface of the aluminum foil with fine projections, and then roughening treatment is performed.

The invention of the method for producing a foil for an aluminum electrolytic capacitor electrode according to claim 5 has a purity of 99.92 to 9: 9.
An organic resist is printed and formed on the surface of a 9.995% aluminum foil in the pit formation portion, a non-porous aluminum oxide film having a thickness of 0.02 μm to 0.6 μm is formed on the surface layer of the aluminum foil, and the resist is removed. After that, a roughening treatment is performed.

The invention of a method for manufacturing an aluminum electrolytic capacitor electrode foil according to claim 6 is the invention according to any one of claims 3 to 5, wherein the non-porous oxide film is formed by anodic oxidation. It is characterized by

That is, according to the present invention, an oxide film having a high barrier property is formed on the surface of the aluminum foil, and minute recesses are formed at the expected pit formation points by indentation or resist coating to enable uniform pit formation. To improve the capacitance.

The effect of this non-porous oxide film is considered as follows. For example, when this non-porous oxide film is formed and indentation is performed to form a press-in mark at the pit forming location, the pit formation starts at the place of the press-fitting mark at the time of electrolytic etching for roughening. Further, the current tends to flow to other film defect locations, but pits cannot be formed because the portions other than the pit forming portions are covered with the oxide film having a withstand voltage of 10 V or more. Therefore, the pits grow only at the indentation site, and the surface area can be increased. It is considered that uniform pit generation and eventually high capacitance were obtained by making the locations of the minute recesses uniform by the indentation or the like in advance.

The conditions defined in the present invention will be described below.

Aluminum foil purity: 99.92 to 99.
995 mass% The purity of the aluminum foil of the present invention is 99.9.
The reason why the content is 2% by mass or more is that it cannot be applied if the purity is less than that, when used in a medium-high voltage capacitor, the leak current increases and the basic performance as a capacitor deteriorates. Also,
From the viewpoint of generating dislocations at a high density, the purity is 99.
It is 995 mass% or less.

Thickness of non-porous oxide film: 0.02 μm to 0.6 μm When the thickness of the non-porous oxide film is less than 0.02 μm, it does not have sufficient withstand voltage and pits are formed. It becomes difficult to generate it uniformly. On the other hand, if it exceeds 0.6 μm, it takes time to form the non-porous oxide film, and it is impossible to form the fine recesses by clearly dispersing fine recesses due to indentation by fine projections (<1 μm).
The thickness is limited to 2 μm to 0.6 μm. For the same reason as above, a thickness of 0.05 μm or more and 0.2 μm or less is preferable.

Method for forming non-porous oxide film The present invention includes:
The method for forming the non-porous oxide film is not particularly limited, but an anodic oxidation treatment in an aqueous boric acid solution is shown as an efficient and suitable forming method. The thickness can be controlled almost correctly by the voltage applied during anodic oxidation. Since the thickness of the oxide film that grows per 1 V is considered to be 1.4 nm,
In order to form 1 μm, anodic oxidation should be performed at a voltage of 70V.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below. In the present invention, pure aluminum obtained by a conventional method can be used, and as a processing step for obtaining the foil, usually, hot rolling and cold rolling for processing a foil having a predetermined thickness or cold rolling and intermediate heat treatment Including the process. Pure aluminum must be able to ensure the purity of the aluminum foil of the present invention. The amount and type of impurities are not limited as long as these are satisfied, and may contain a trace amount of additional elements. In particular, it is preferable to contain Pb of about 1 ppm, which promotes surface solubility. The foil obtained in the above processing step is an aluminum original foil,
This is a suitable manufacturing method for forming the oxide film of the present invention and forming minute recesses in the oxide film.

The formation of the non-porous oxide film can be suitably performed for anodic oxidation as described above, and the thickness thereof is adjusted to 0.02 μm to 0.6 μm. The thickness of the oxide film is shown as the thickness immediately before the roughening treatment.

One of the methods for forming the minute recesses will be described with reference to FIG. The aluminum foil 1 has a non-porous oxide film 2 formed as a surface layer. On the other hand, a pressing roller 3 is prepared as a tool for forming minute recesses, and a large number of fine protrusions 4 are uniformly formed on the surface of the pressing roller 3. The fine protrusions 4 can be formed on the surface of the pressing roller 3 with photoresist, for example.

When the pressing roller 3 is pressed against the aluminum foil 1, the fine projections 4 are pressed against the non-porous oxide film 2, and the fine recesses (not shown) corresponding to the fine projections 4 are formed in the oxide film 2. Are formed uniformly. In the surface roughening treatment of the aluminum foil 1 in which the minute recesses are formed in this way, the minute recesses function as starting points of the pits,
Pits are uniformly and densely formed on the surface of the aluminum foil 1. By using the aluminum foil as an electrode of an electrolytic capacitor, an electrolytic capacitor having a high capacitance per unit area of the foil can be obtained.

FIG. 2 is a diagram for explaining a method of forming minute recesses in the surface layer of the aluminum foil 10 by another method. Prior to the formation of the non-porous oxide film, the aluminum foil 10 has a resist portion 1 at the planned starting point of the pit on the surface.
1a is formed. As a result, the other part is the non-resist part 11b.
Becomes The resist portion 11a and the non-resist portion 11b can be formed by a conventional method. A non-porous oxide film 10 is formed on the aluminum foil 10 by anodic oxidation or the like.
a is formed. After that, when the resist 11a is removed,
Aluminum foil 10 having minute recesses 12 formed on the surface layer
Is obtained. In the aluminum foil, pits are formed uniformly and with high density during the surface roughening treatment as described above.

The present invention is not particularly limited in terms of the surface roughening treatment and the subsequent chemical conversion treatment conditions, and it can be carried out by a conventional method.

[0024]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples. A high-purity aluminum foil having a purity of 99.92% to 99.995% and a thickness of 100 μm was prepared, and the crystal was subjected to a high temperature treatment to prepare an original foil having a cubic orientation ratio of 90% or more. Next, resist printing was performed as one method. In this resist printing pattern, resist portions are printed at predetermined pitch positions at regular intervals of 1 μm with a diameter of 1.5 μm. After that, a non-porous oxide film of 10 V to 500 V was formed using a boric acid aqueous solution. After that, the resist was removed with a solvent, electrolytic etching as a roughening treatment was performed, and the capacitance was measured.

As another method, a non-porous oxide film was previously formed using the above-mentioned original foil by the same method as described above, and this foil was indented by the method shown in the above-mentioned embodiment. The indentation was made at the same position as the resist printing pattern. After that, roughening treatment was performed and the capacitance was measured. By the above, fine recesses were formed in the surface layer of the aluminum foil, respectively, and the fine recesses had a depth of 1 μm.
Table 1 shows the measurement results of the capacitance.

[0026]

[Table 1]

As is apparent from the table, when the aluminum foil of the present invention is used, a high capacitance is obtained. On the other hand, if the non-porous oxide film is thin (conventional material), even if the minute recesses are formed, there is almost no effect of improving the capacitance. Further, if the thickness of the non-porous oxide film is too large, the effect of improving the capacitance cannot be recognized even if the minute recesses are formed.

[0028]

As described above, the aluminum electrolytic capacitor electrode foil of the present invention has a purity of 99.92.
To 99.995% aluminum foil surface layer, a non-porous aluminum oxide film having a thickness of 0.02 μm to 0.6 μm is formed, and minute recesses are uniformly formed on the surface of the oxide film. Since it is used for the surface roughening treatment, it is possible to obtain an aluminum electrolytic capacitor electrode in which pits are formed uniformly and at a high density during the surface roughening treatment and which has a high capacitance per unit area.

Further, the purity is 99.92 to 99.995%.
The thickness of the aluminum foil surface layer from 0.02μm to 0.6
A non-porous aluminum oxide film having a thickness of μm is formed and fine recesses are uniformly formed on the surface of the aluminum foil, and then roughening treatment is performed or aluminum having a purity of 99.92 to 99.995% is used. Thickness of foil surface layer is 0.02
If a non-porous aluminum oxide film with a thickness of μm to 0.6 μm is formed, and the surface of the aluminum foil is indented by fine protrusions and then roughened, the minute recesses become the starting points of pits. Pits are formed uniformly and with high density during the roughening treatment.

[Brief description of drawings]

FIG. 1 is a diagram showing a manufacturing process of an aluminum foil according to an embodiment of the present invention.

FIG. 2 is a diagram showing a manufacturing process of an aluminum foil according to another embodiment of the same.

[Explanation of symbols]

1 aluminum foil 2 Non-porous oxide film 3 Pressing roller 4 Fine protrusions 10 Aluminum foil 10a non-porous oxide film 11a resist part 11b Non-resist part 12 Minute recess

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01G 9/00 H01G 9/04 346 9/055 9/24 B

Claims (6)

[Claims] 1. An aluminum foil surface layer having a purity of 99.92 to 99.995% and a thickness of 0.02 μm to 0.6 μm.
m non-porous aluminum oxide film is formed and minute recesses are uniformly formed on the surface of the oxide film.
An aluminum electrolytic capacitor electrode foil, characterized in that it is subjected to a roughening treatment. 2. The foil for an aluminum electrolytic capacitor electrode according to claim 1, wherein the minute recesses have a depth of 5 μm or less. 3. An aluminum foil surface layer having a purity of 99.92 to 99.995% and a thickness of 0.02 μm to 0.6 μm.
The method for producing a foil for an aluminum electrolytic capacitor electrode, which comprises: forming a non-porous aluminum oxide film, and forming fine recesses uniformly on the surface of the aluminum foil; and then performing a roughening treatment. . 4. An aluminum foil surface layer having a purity of 99.92 to 99.995% and a thickness of 0.02 μm to 0.6 μm.
1. A method for producing a foil for an aluminum electrolytic capacitor electrode, which comprises forming a non-porous aluminum oxide film, and indenting the surface of the aluminum foil with fine projections, and then roughening the surface. 5. An organic resist is printed on the surface of an aluminum foil having a purity of 99.92 to 99.995% in a pit forming portion, and the aluminum foil surface layer has a thickness of 0.02 μm.
To form a non-porous aluminum oxide film of 0.6 μm from
A method of manufacturing a foil for an aluminum electrolytic capacitor electrode, which comprises performing a roughening treatment after removing the resist. 6. The method for producing an aluminum electrolytic capacitor electrode foil according to claim 3, wherein the non-porous oxide film is formed by anodic oxidation.