JPH06168853A - Aluminum material for electrode of electrolytic capacitor and production thereof - Google Patents

Abstract

PURPOSE:To enhance etching aptitude of Al material for the electrode of electrolytic capacitor by specifying purity of basic material, i.e., Al foil, thickness of oxide formed on the surface, and area rate of crystal texture of Al foil. CONSTITUTION:A rolled Al foil is heated in preheat steep prior to cleaning step quickly at a rate of 50 to 0.2 deg.C/min upto a temperature of 150 to 400 deg.C which is sustained for 10min to 24 hours thus relaxing distorsion of crystal texture sufficiently. When oxide is formed in a short time by raising ambient temperature abruptly in oxidizing step following to cleaning step, crystal face conditioning effect is exhibited in high temperature heating step thus providing a high (100) area rate. This Al material for electrolytic capacitor has purity of 99.99% or above and the thickness of oxide is set in the range of 30 to 70Angstrom .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum material for electrolytic capacitor electrodes and a method for producing the same.

[0002]

2. Description of the Related Art Aluminum foil, which is generally used as an electrode material for aluminum electrolytic capacitors, has a large effective area to increase the capacitance per unit area.
Generally, electrochemical or chemical etching treatment is performed. However, since sufficient capacitance cannot be obtained by simply etching the foil, various treatments are performed to enhance the etching suitability.

As an example of a method for enhancing the etching suitability, after removing the oil content adhering to the surface of the aluminum foil, the heterogeneous oxide film formed by rolling, the altered layer of rolling, etc. by cleaning, the new surface of the aluminum foil is etched. There is a method in which oxidation treatment is performed to form an oxide film having uniform nuclei, and high temperature heating is performed mainly for the purpose of adjusting the (100) crystal orientation of the aluminum foil. In such a method, in order to form a uniform oxide film in the width direction as well as the length direction of the aluminum foil, the oxidation treatment is performed.
It may be continuously performed while unwinding the coiled aluminum foil. In this case, in order to form an oxide film having a predetermined thickness in a short time to shorten the processing time, the temperature rising rate is usually increased to quickly raise the temperature to a predetermined high temperature.

[0004]

However, the aluminum material for electrolytic capacitor electrodes, which has been continuously oxidized by the above-mentioned method, is not always suitable for etching despite the fact that the oxide film has a predetermined thickness. In some cases, it could not be obtained, and in some cases, the surface area ratio after the etching treatment, and further, the capacitance could not be satisfied.

In order to solve the above problems, the present invention has an aluminum material for an electrolytic capacitor electrode excellent in etching suitability and an aluminum material for an electrolytic capacitor electrode which can efficiently produce such an aluminum material in a short time. It is intended to provide a method for manufacturing a material.

[0006]

The inventors have paid attention to the relationship between the temperature condition in the oxidation treatment and the crystal orientation of the aluminum foil after the high temperature heating step, and conducted research from such a viewpoint. As a result, the distortion of the crystal structure caused by the foil rolling is carried over to the high temperature heating step without being relaxed by the rapid temperature rise in the oxidation treatment, and therefore the crystal orientation is sufficiently adjusted to the (100) orientation by the high temperature heating treatment. It was clarified that this was not achieved, and it was concluded that this decrease in the (100) area ratio hinders improvement in etching suitability. Therefore, in the aluminum material for electrolytic capacitor electrodes of the present invention, an oxide film having a thickness of 30 to 70 angstroms is formed on the surface of an aluminum foil having a purity of 99.99% or more, and the (100) crystal structure of the aluminum foil is formed. ) The area ratio is 90% or more.

In the aluminum material for electrolytic capacitor electrodes, the purity of the aluminum foil as the base material is 99.
The reason why it is 99% or more is that it is difficult to manufacture an electrode material having a high (100) area ratio with an aluminum foil containing a large amount of impurities.

The oxide film has a large number of etching nuclei which become etching pits during the etching process, and has an action of improving etching suitability. The thickness of such an oxide film is regulated to 30 to 70 Å by 30
If it is less than angstrom, the etching aptitude is not excellent because the number of etching nuclei is insufficient.
This is because if the thickness exceeds Å, there is a risk that the etching nuclei once generated are erased, and excellent etching suitability cannot be obtained. It is preferably 35 to 50 angstroms. Further, the crystal orientation of the aluminum foil is related to the formation direction and depth of the etching pit,
(00) The area ratio is defined to be 90% or more because if it is less than 90%, the depth of the etching pits formed in the direction orthogonal to the surface of the foil is insufficient and the expansion ratio cannot be expected to be improved. A preferable (100) area ratio is 95% or more.

In addition, the aluminum material for electrolytic capacitor electrodes having the above-mentioned characteristics is obtained by subjecting an aluminum foil having a purity of 99.99% or more to 150 to 400 ° C. after the foil rolling step.
And a heating step at a temperature of 50 to 0.2 ° C./min, and a pre-heat treatment step of holding the temperature for 10 minutes to 24 hours after completion of the heating, and then removing the surface layer of the aluminum foil. An oxidation step of forming an oxide film having a thickness of 10 to 60 angstrom on the new surface of the aluminum foil by heating, and the total thickness of the oxide film is 30.
It can be manufactured by sequentially performing a high temperature heating step of heating the aluminum foil at a high temperature in the range of about 70 Å.

In the method for producing an aluminum material for an electrolytic capacitor electrode, the pre-heat treatment step is carried out for the purpose of eliminating the distortion of the crystal structure of the aluminum foil caused by the foil rolling in the previous step. By raising the temperature to and holding the temperature for a predetermined time, the internal stress caused by the strain is relaxed and the strain is eliminated. In this step, if the rate of temperature rise exceeds 50 ° C./min, the strain cannot be sufficiently eliminated, and (1
00) Area ratio decreases. Further, at a slow rate of less than 0.2 ° C./minute, it takes too much time to raise the temperature to a predetermined temperature, and the production efficiency decreases. Further, if the holding temperature is lower than 150 ° C, the strain resolving ability is insufficient, and if it exceeds 400 ° C, the strain resolving ability is saturated, which is useless. Further, if the holding time at the predetermined temperature is less than 10 minutes, the strain is not sufficiently eliminated, and if it exceeds 24 hours, the strain eliminating ability is saturated, which is useless. Therefore, the temperature rising rate in this step is 50-
0.2 ° C./minute, the holding temperature is 150 to 400 ° C., and the holding time is 10 minutes to 24 hours. Particularly preferable pre-heat treatment conditions are that the temperature rising rate is 4 to 0.3 ° C. /
Min, holding temperature is 250 to 350 ° C, holding time is 2 to 10
It's time. The holding temperature is finally set to (10
0) In order to increase the area ratio, it is desirable that the temperature is higher than the temperature in the oxidation step performed in the subsequent step. In addition, the pre-heat treatment may be performed in two or more stages with different holding temperatures and holding times. In this case, the total holding time needs to be within the above range.

The cleaning step performed after the pre-heat treatment step is a step performed for the purpose of removing the heterogeneous layer on the surface of the aluminum foil. That is, on the aluminum foil surface after foil rolling, oil content, a heterogeneous oxide film formed by rolling is present, and in the vicinity of the aluminum foil surface, a deterioration layer due to rolling or a contamination layer due to roll coating during rolling is present. They exist non-uniformly, and these cause the non-uniformity of the oxide film. Therefore, the heterogeneous layer is removed to promote the formation of a uniform oxide film. However, it is not always necessary to remove the surface of the aluminum foil to a predetermined depth, and the degreasing level, in other words, to remove oil to a level where the contact angle of pure water is 30 ° or less (pure spray OK level). May be Of course, it is desirable to completely remove the non-uniform layer, but in this case, the removal thickness is preferably 5 angstroms or more, and particularly preferably 40 angstroms or more. There is no upper limit, but at about 500 Å, the effect of removing the surface layer is saturated,
Further removal is useless. The specific means for such surface layer removal treatment is not particularly limited. When removing over a predetermined depth, a wet method such as alkali etching or acid etching may be used, or laser processing such as excimer laser (KrF, ArF, XeCl), electron beam processing, ion beam processing, reaction Alternatively, a dry method such as reactive gas etching or plasma etching may be used.

The oxidation step, which is carried out after the cleaning step, is carried out for the purpose of forming an oxide film having a predetermined thickness and having uniform etching nuclei on a new surface of the aluminum foil. The method for forming the oxide film is not particularly limited, but it is preferable to continuously heat the atmosphere while unwinding the coiled aluminum foil in an oxidizing atmosphere. In this case, the temperature of the oxidizing atmosphere is 30 to 4
An oxide film having a thickness of 10 to 60 Å can be formed by rapidly increasing the temperature to 00 ° C. at a rate of 1000 to 50 ° C./minute and heating at the same temperature for 0.5 to 60 minutes.

The high temperature heating step performed after the oxidation step has the main purpose of adjusting the crystal structure of the aluminum foil to the (100) orientation to improve the etching characteristics, and is formed in the previous step. The total thickness of the oxide film should be 30 to 70 angstroms so that the thickness of the oxide film is not excessively increased in this step and the etching nuclei are not erased. The treatment conditions in this high temperature heating step are not particularly limited,
It is desirable to heat in an atmosphere in which water and oxygen are removed as much as possible so as not to increase the thickness of the oxide film too much. Specifically, in an inert gas such as Ar gas or 10 ^-3 T
It is preferable to heat in a vacuum of about or less, and it is desirable that the heating temperature is 300 to 600 ° C. and the heating time is about 10 minutes to 24 hours.

[0014]

The foil-rolled aluminum foil is heated to 150 to 400 ° C. in the pre-heat treatment step before the washing step.
While gradually increasing the temperature at a rate of 0 to 0.2 ° C / min,
By holding the temperature for 10 minutes to 24 hours after completion of the temperature rise, the strain of the crystal structure generated during rolling is sufficiently relaxed. Therefore, since the aluminum foil that has been subjected to this pre-heat treatment has already been free from distortion, even if the oxidizing atmosphere temperature is rapidly raised in the oxidation step after the cleaning step to form an oxide film in a short time, the high temperature heating step The effect of adjusting the crystal plane in (3) sufficiently acts, and a high (100) area ratio is obtained. The aluminum material for electrolytic capacitor electrodes manufactured in this manner has a (100) area ratio of 90% or more, and the purity of the aluminum foil as the base material is 99.9.
Combined with the high value of 9% or more and the final thickness of the oxide film formed on the surface of 30 to 70 angstroms, the etching suitability becomes excellent.

[0015]

EXAMPLES Next, a specific example of the method for producing the aluminum material for electrolytic capacitor electrodes of the present invention will be described.

(Example) First, aluminum having a purity of 99.99% was foil-rolled in a cold manner to a thickness of 100 μm by a conventional method and wound into a coil. Next, this coiled aluminum foil was preheated in a batch type heating furnace for 1 hour.
The temperature was slowly raised to 300 ° C. at a rate of 0 ° C./minute, and heating was continued for 8 hours. Next, this coiled aluminum foil was immersed in a 0.1% caustic soda bath at 30 ° C. for 1 minute to dissolve and remove the surface layer to a depth of 300 Å. Next, while unwinding this coiled aluminum foil in a continuous oxidation treatment furnace,
By rapidly raising the temperature up to 1000 ° C./min for 10 minutes, the oxide film having a thickness of 25 μm was formed. Further, this coiled aluminum foil was heated at a high temperature of 400 ° C. for 5 hours in a vacuum of 10 ⁻⁵ Torr to obtain an aluminum material for electrolytic capacitor electrodes. The oxide film finally had a thickness of 35 μm by the high temperature heat treatment.

(Comparative Example) Each of foil rolling, washing, continuous oxidation, and high temperature heating was carried out in the same manner as in the above-mentioned example except that the pre-heat treatment was not carried out. As a result, the obtained oxide film of the aluminum material for electrolytic capacitor electrodes had the same thickness as that of the example both after the continuous oxidation treatment and after the high temperature heat treatment.

Then, the (100) area ratios of the aluminum materials for electrolytic capacitor electrodes of Examples and Comparative Examples manufactured by the above-mentioned method were examined and the results are shown in Table 1. Further, these aluminum materials for electrolytic capacitor electrodes were subjected to electrolytic etching treatment in 3% hydrochloric acid (85 ° C.) with a current density of 10 A / dm ² for 3 minutes, and then chemically etched with the same solution for 10 minutes. Then, after performing chemical conversion treatment at 350 V in a 5% boric acid bath, the capacitance of each material was measured. The result is
The results are shown in Table 1 by relative comparison with the electrostatic capacity of the comparative example being 100.

[0019]

[Table 1] As is clear from the results shown in Table 1, the aluminum foil for electrolytic capacitor electrodes (100) manufactured through the high temperature heating step is manufactured by gently heating the aluminum foil in the preheat treatment before the rapid heating in the oxidation step.
It is possible to prevent a decrease in the area ratio and to impart excellent etching suitability. As a result, it was found that a high capacitance can be maintained even if the treatment temperature in the oxidation step is rapidly increased to a high temperature in order to form an oxide film having a predetermined thickness in a short time.

[0020]

As described above, according to the method of the present invention,
Before cleaning the foil-rolled aluminum foil and performing the oxide film formation treatment, the temperature should be 50 to 50 ° C until the temperature reaches 150 to 400 ° C.
By performing the pre-heat treatment step of gradually increasing the temperature at a rate of 0.2 ° C./minute and maintaining the temperature for 10 minutes to 24 hours after the completion of the temperature increase, the distortion of the crystal structure generated during rolling can be eliminated. As a result, since the aluminum foil that has been subjected to this pre-heat treatment has already been distorted, even if the oxidation atmosphere temperature is rapidly raised in the oxidation step after the cleaning step to form an oxide film in a short time, high-temperature heating is performed. The (100) area ratio does not decrease through the process. Further, the aluminum material for electrolytic capacitor electrodes of the present invention produced in this manner has a (100) area ratio of 90% or more,
Combined with the fact that the purity of the aluminum foil as the base material is as high as 99.99% or more, and the thickness of the final oxide film formed on the surface is 30 to 70 angstroms, the etching suitability is excellent. It becomes a thing. Therefore,
ADVANTAGE OF THE INVENTION According to this invention, the aluminum material for electrolytic capacitor electrodes which is excellent in etching suitability and has large electrostatic capacitance can be manufactured efficiently.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Eizo Isoyama 6-224 Kaiyamacho, Sakai City, Osaka Prefecture Showa Aluminum Co., Ltd.

Claims (2)

[Claims] 1. An aluminum foil having a purity of 99.99% or more has an oxide film with a thickness of 30 to 70 angstroms formed thereon, and the (100) area ratio of the crystal structure of the aluminum foil is 90% or more. An aluminum material for electrolytic capacitor electrodes, which is characterized by being present. 2. After the foil rolling step, aluminum foil having a purity of 99.99% or more is heated to 150 to 400 ° C. for 50 to 400 ° C.
A pre-heat treatment step of increasing the temperature at 0.2 ° C./minute and holding the temperature at the temperature for 10 minutes to 24 hours after completion of the temperature increase is performed, and then a cleaning step of removing the surface layer of the aluminum foil, and heating the aluminum. 10-thick on the new surface of the foil
An electrolytic capacitor characterized by sequentially performing an oxidation step of forming an oxide film of 60 angstrom and a high temperature heating step of heating the aluminum foil at a high temperature within a range of the total thickness of the oxide film of 30 to 70 angstroms. Manufacturing method of aluminum material for electrodes.