JPH05200406A - Production of aluminum foil for electrolytic capacitor - Google Patents

Abstract

PURPOSE:To contrive producing the aluminum foil for electrolytic capacitors with which excellent etching performance and the high electrostatic capacity are obtainable and which is free from the fluctuation in the electrostatic capacity in a transverse direction. CONSTITUTION:An aluminum slab having >=99.9% purity is used and before the slab is subjected to final finish rolling after hot rolling, the aluminum foil base is subjected to at least one pass of washing for removing the surface layers, by which the flaw-like recessed parts and inclusions, such as Al oxides and carbon, on the foil surfaces are removed. As a result, the generation of the coarse etching pits by the unavoidable local concn. of these recessed parts and inclusions is obviated and the uniform etching pits are formed. In addition, the aluminum foil un-coiled from a coil is continuously subjected to a low-temp. heating treatment prior to final annealing after foil rolling and, therefore, the thickness in the transverse direction of the oxide films formed on the surfaces of the aluminum foil is previously uniformalized and the fluctuation in the electrostatic capacity is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an aluminum foil for electrolytic capacitors.

[0002]

2. Description of the Related Art Al foil, which is generally used as an electrode material for aluminum electrolytic capacitors, is usually subjected to an electrochemical or chemical etching treatment in order to expand its effective area and increase the capacitance per unit area. Is given.

However, a sufficient capacitance cannot be obtained by simply etching the foil. Therefore, generally, in the final annealing step after foil rolling, a high temperature heat treatment of about 450 ° C. or more is performed in order to improve the etching characteristics of the foil with a texture having many cubic orientations, but recently However, it was not possible to obtain sufficient satisfaction for the requirement for high capacitance of the electrolytic capacitor.

Therefore, recently, before the foil rolling process and / or
Alternatively, it has been proposed to degrease the aluminum foil with a cleaning agent containing nitric acid as a main component to form an aluminum foil for electrolytic capacitors (Japanese Patent Laid-Open No. 60-92489).

According to this proposal, since degreasing is performed with a cleaning agent containing nitric acid as a main component, the rolling oil adhering to the surface of the aluminum foil is suppressed while the surface dissolution of the aluminum foil is suppressed, resulting in a large electrostatic capacity after etching. Is said to be obtained.

[0006]

However, even with this prior proposal, there is still a limit to the increase in capacitance.
Moreover, when the aluminum foil that has undergone the final annealing by the high-temperature heat treatment is subjected to etching, there is a drawback that the capacitance varies in the width direction of the aluminum foil.

The present invention has been made in view of the above circumstances, and is an electrolytic capacitor which is excellent in etching performance, can obtain a high capacitance, and can improve the variation in the capacitance in the width direction. The purpose is to provide and provide aluminum foil for use.

[0008]

In order to solve the above problems, the inventors of the present invention have conducted extensive studies, and as a result, first of all, the factor inhibiting the increase in capacitance is not the rolling oil adhered to the foil surface, but the aluminum foil material in the rolling process. It was found that it is due exclusively to the presence of flaw-like recesses formed on the surface and embedded materials such as Al oxide and carbon embedded in the surface. In other words, the flaw-like recesses and embeddings present on the surface of the aluminum foil are one of the factors that form the starting point of the etching pit in the etching process that is generally applied to the aluminum foil for electrolytic capacitors, so disperse them evenly. If it is possible, etching pits can be uniformly generated, which can contribute to an increase in capacitance. However, it is actually extremely difficult to disperse the recesses and the embedded material in a uniform manner, and local concentration is inevitably caused. It has been found that when such local concentration is present, a rough etching pit is formed around it, and on the contrary, a sufficient surface expansion ratio and thus a large electrostatic capacity cannot be obtained. That is, the recesses and the embedded materials rather hinder the uniform generation of the etching pits. Rather, the unevenness and the embedded materials should be reduced as much as possible so that the etching pits can be generated uniformly, and the surface expansion ratio is sufficient. As a result, it was found that a large capacitance can be obtained.

On the other hand, as for the cause of the variation in the width direction of the aluminum foil, the inventor has found by experiments and studies that
It was found that such variations are due to the thickness of the oxide film formed on the surface of the aluminum foil. That is, in actual production, since the aluminum foil is handled in a coiled state after rolling until final annealing, both end portions in the width direction of the coil are more environmentally friendly (temperature, humidity, etc.) than the central portion. It is easily affected, so that the oxide film is thick and the central portion is thin at both ends in the width direction. Therefore, during etching, a difference occurs in the dissolution form between the end portion and the central portion of the aluminum foil, which appears as a variation in electrostatic capacitance. And, the widthwise variation of the oxide film thickness does not occur only during the final annealing, but rather, most of it has already occurred during storage before entering the treatment step, and the variation at this time is the final variation. It was found that it was maintained even during annealing.

The present invention has been made on the basis of such various findings, and further includes hot rolling and cold rolling of an aluminum slab having a purity of 99.9% or more, and further includes final finishing rolling. When manufacturing aluminum foil for electrolytic capacitors by carrying out foil rolling and then final annealing, at least one surface layer removal cleaning is performed on the aluminum foil after the hot rolling and before the final finishing rolling. A method for producing an aluminum foil for electrolytic capacitors is characterized in that the aluminum foil unwound from the coil after the foil rolling and before the final annealing is continuously subjected to a low temperature heat treatment.

First, the purity of aluminum foil is 99.9%.
What is defined above is that if the purity is less than 99.9%, the growth of etching pits during electrolytic etching is hindered by the presence of many impurities, and uniform pits cannot be formed.
Therefore, the effect of increasing the capacitance cannot be obtained.

The aluminum foil for electrolytic capacitors is generally manufactured by carrying out each rolling step of hot rolling, cold rolling, and foil rolling including final finishing rolling, and then carrying out final annealing. Thus, in the rolling step, a large number of elongated recesses having an elongated or elliptical shape with the rolling direction being the length direction are formed on the surface of the aluminum foil. It is considered that the main reason for this is that aluminum oxide such as Al ₂ O ₃ or carbon of the carbonized rolling oil is dragged on the surface of the aluminum foil by the rolling roll. Moreover, these oxides and carbon not only cause flaw-like recesses, but are also embedded in the aluminum foil surface in large numbers by rolling. Therefore, generally, on the surface of an aluminum foil after rolling, a large number of the flaw-like recesses and embedded materials such as aluminum oxide and carbon coexist, and furthermore, local concentration is partially caused. Coarse etching pits are formed in the recesses and the locally concentrated portions of the embedded material in an etching process to be performed later, which rather hinders the increase of the capacitance.

Therefore, in the present invention, the surface layer of the aluminum foil is removed and washed in order to remove the above-mentioned recesses and embedded objects. The thickness of the surface layer removed by this cleaning is preferably 0.01 μm or more. 0.01 μm
If it is less than the above range, the effect of removing the recesses and the embedded substances on the surface is poor. Further, the treatment in which the removal thickness exceeds 5 μm is useless because the existing amount of the recesses and the embedded substances is already small, and therefore it is preferable to set the removal thickness to about 0.01 to 3 μm. The most preferable removal thickness is 0.1 to 1 μm.

The specific treatment method for the surface layer removal cleaning is not particularly limited, but chemical dissolution cleaning with an alkali or an acid is preferable from the viewpoint of the ease of processing. As a desirable condition of this chemical dissolution cleaning, the concentration of the cleaning liquid is 1 to 7%,
Caustic soda with a liquid temperature of 40-70 ° C, a concentration of 10-30%,
Using sulfuric acid with a liquid temperature of 70 to 90 ° C., immersion time: 10 seconds to 1
It is good to set it to about 0 minutes.

The cleaning for removing the surface layer of the aluminum foil must be performed after hot rolling. The reason for this is that many of the above-mentioned recesses and embedded materials are generated by hot rolling. Moreover, it should not be performed after the foil rolling, which is the final rolling step, is completed. The reason for this is as follows. That is,
The generation of etching pits is related not only to the recesses and embedded materials but also to the dislocation density on the foil surface.If the surface layer is removed and washed after the final foil rolling, the high dislocation density portion on the surface layer is removed and etching This is because the number of pits is reduced and the surface expansion ratio and thus the capacitance cannot be increased. Therefore, in order to leave the high dislocation density portion on the surface of the aluminum foil even after the completion of rolling, it is necessary to further perform rolling after removing the surface layer of the foil. Therefore, the cleaning for removing the surface layer must be performed after the hot rolling and before the final finishing rolling step in the foil rolling step. Specifically, it may be performed after hot rolling and before foil rolling (hereinafter referred to as pre-cleaning) or during foil rolling (hereinafter referred to as intermediate cleaning). The pre-cleaning may be performed between hot rolling and cold rolling, during cold rolling, or between cold rolling and foil rolling. Further, the time of the intermediate cleaning may be any after the foil rolling and before the final finish rolling. Moreover, the number of times of cleaning for removing the surface layer may be such that the pre-cleaning or the intermediate cleaning is performed only once, the pre-cleaning may be performed twice or more, the intermediate cleaning may be performed two or more times, and The pre-cleaning and the intermediate cleaning may be mixed and performed once or multiple times. Preferably, in order to effectively remove embeddings and the like, it is preferable to perform intermediate cleaning during the foil rolling, and most preferably, intermediate cleaning is performed immediately before final finish rolling, in which recesses and embeddings are It is desirable in that sufficient removal and formation of high dislocation density portions on the foil surface can be effectively realized.

It should be noted that, after the completion of rolling, a cleaning process (hereinafter referred to as a post-cleaning process) for removing an oil component adhered in the final rolling process or an oxide film produced during the rolling process (hereinafter referred to as a post-cleaning process) is also generated by a low temperature heat treatment described later. It is recommended that the oxide film can be made more uniform and the capacitance can be increased. However, if the thickness of the surface removed by this post-cleaning is too thick, the high dislocation density portion formed on the surface of the aluminum foil will be removed. Therefore, the thickness of the post-cleaning removed should be 300 angstroms or less. Is good. Such degreasing cleaning may be carried out, for example, by using caustic soda having a concentration of 0.01 to 1% and a liquid temperature of 30 to 60 ° C. and immersing it for 5 to 200 seconds.

Thereafter, the aluminum foil is subjected to a low temperature heat treatment before the final annealing. This low-temperature heat treatment is performed by a continuous heat treatment, in other words, a method of continuously treating the aluminum foil unwound from the coil, but may be performed while unwinding the aluminum foil wound on the coil after the final finish rolling. Alternatively, final finishing rolling may be performed while unwinding the aluminum foil wound on the coil, and continuously transferred to the low temperature heat treatment as it is. Prior to such heat treatment, a natural oxide film has already been formed on the aluminum foil, but by carrying out continuous low-temperature heat treatment, the heat treatment will be performed with the entire surface of the foil in direct contact with the atmosphere. In particular, the growth of the oxide film is promoted especially in the widthwise central portion where the thickness of the oxide film is thin, and the thickness of the oxide film is made uniform in the width direction of the foil. The reason for applying such low temperature heating is to uniformly form an oxide film having fine defects in the coil width direction corresponding to the transition of the surface of the aluminum foil formed by finish rolling. Since heating at high temperature decreases the transition density, an oxide film is first formed at low temperature.
That is, the low-temperature heating contributes to the formation of fine defects in the coating, and the continuous treatment contributes to the uniformization of the oxide coating in the coil width direction. Such low temperature heating is preferably performed at a temperature of 30 to 300 ° C.
If the temperature is lower than 30 ° C, the oxide film may grow slowly and may not be uniformized. On the other hand, if the temperature exceeds 300 ° C., the oxide film may grow excessively and hinder the etching performance. Particularly preferably, the temperature is 100 to 200 ° C. Further, the atmosphere of low temperature heating is preferably an oxidizing atmosphere because it enables formation of an oxide film. As an example, an atmosphere in the air or an atmosphere of an inert gas containing oxygen or the like can be cited. The residence time of the aluminum foil in the atmosphere is preferably set to about 5 seconds to 1 hour. If it is less than 5 seconds, the oxide film grows too slowly, and as a result, a uniform oxide film may not be formed. On the other hand, if the residence time exceeds 1 hour, productivity may be significantly reduced. Most preferred residence time is 10
Seconds to 5 minutes. Such continuous low-temperature heat treatment may be performed only once, or may be performed twice or more when it is difficult to form a uniform oxide film once.

The aluminum foil that has been subjected to the continuous low-temperature heat treatment is then subjected to high-temperature final annealing for aligning the crystal grains on the (100) plane. It is considered that in this annealing treatment, the foil structure is improved and the oxide film having fine defects formed by the low temperature heating is inherited in the final annealing. As the heating conditions for the final annealing, conventionally used conditions may be appropriately adopted, but preferably the temperature is 450 to 580 ° C. and the time is 10 seconds to 30 hours. If the temperature is less than 450 ° C. and the time is less than 10 seconds, the effect of improving the structure is small. On the other hand, if the temperature is more than 580 ° C. or the time is more than 30 hours, the effect is saturated and energy is wasted. This is because there is a risk that excessive growth of the oxide film may be caused and the improvement of etching characteristics may be hindered. The processing form may be either batch type or continuous type. In this high temperature heat treatment, an oxide film is further formed on the surface of the aluminum foil on the oxide film formed by the low temperature heat treatment, but the variation of the oxide film thickness in the width direction of the aluminum foil is mainly continuous. Since an oxide film having a uniform thickness formed by the low temperature heat treatment is affected by the low temperature heat treatment, even when the final annealing is performed in a batch method, the thickness of the oxide film is no longer remarkable in the width direction. Variation does not occur. But,
In order to more completely maintain the uniformity of the oxide film thickness formed by the continuous low-temperature heat treatment, it is preferable to adopt the continuous treatment.

The aluminum foil produced as described above is then subjected to a chemical or electrochemical etching treatment to be used as an electrolytic capacitor electrode foil. In this etching process, there are no longer any localized defects such as flaw-like recesses on the foil surface or embedded materials such as Al oxide, and many etching pits are formed at the corresponding positions of the high dislocation density portion on the foil surface. It is formed. In addition, since the oxide film formed on the surface of the aluminum foil has a uniform thickness over the entire width direction, uniform etching is performed during etching, and a stable capacitance without variation can be obtained. ..

The aluminum foil may be used for either the anode or the cathode, but in view of the Al purity of 99.9% or more, it is generally preferable to use it as an anode foil which requires high Al purity. ..

[0021]

Embodiments of the present invention will be described below.

(Example 1) An aluminum slab having a purity of 99.99% was hot-rolled to a thickness of 5 mm according to a conventional method, further cold-rolled to a thickness of 0.4 mm, and then to a thickness of 0.2 mm. Primary foil rolling was performed.

Next, the aluminum foil obtained was concentrated to a concentration of 5
% And a temperature of 50 ° C. for 90 seconds to perform intermediate cleaning for removing the surface layer. The thickness of the surface layer removed by this washing was 1 μm.

Then, final finishing rolling was performed to a thickness of 0.1 mm to obtain an aluminum foil coil having a width of 500 mm.

Next, the aluminum foil was unwound from the coil and continuously heated at low temperature in the atmosphere at 120 ° C. for 5 minutes.

Next, the aluminum foil coil was batchwise applied to a vacuum of 1 × 10 ⁻⁴ Torr or less at 500 ° C. × 5.
A final annealing treatment was performed for a time to obtain a final foil.

(Example 2) An aluminum slab having a purity of 99.99% was hot-rolled to a thickness of 5 mm by an ordinary method, further cold-rolled to a thickness of 0.4 mm, and then to a thickness of 0.2 mm. Primary foil rolling was performed.

Next, the aluminum foil obtained was concentrated to a concentration of 5
% And a temperature of 50 ° C. for 90 seconds to perform intermediate cleaning for removing the surface layer. The thickness of the surface layer removed by this washing was 1 μm.

Then, final finishing rolling was performed to a thickness of 0.1 mm to obtain an aluminum foil coil.

Next, the obtained aluminum foil was treated with a density of 0.
Post-washing was carried out by immersing in 1% caustic soda at a temperature of 50 ° C. for 10 seconds. The thickness of the surface layer removed by this washing is 1
It was 00 angstrom.

Next, the aluminum foil was unwound from the coil and continuously heated at a low temperature in the air at 120 ° C. for 5 minutes.

Next, the aluminum foil coil was batch-processed at a temperature of 500 ° C. × 5 in a vacuum of 1 × 10 ⁻⁴ Torr or less.
A final annealing treatment was performed for a time to obtain a final foil.

(Comparative Example 1) An aluminum foil was produced under the same conditions as in Example 1 except that the intermediate cleaning treatment in Example 1 and the continuous low temperature heating treatment before final annealing were not performed.

The three types of aluminum foils obtained as described above were subjected to 5% hydrochloric acid at 80 ° C. and a current density of 10 A / dm for direct current.
² was electrolytically etched for 7 minutes. Then, after performing chemical conversion treatment in a boric acid bath at 380 ° C., the capacitance of each electrode foil in the widthwise center and both ends was measured. In addition, the measurement position of both ends was a position 50 mm inward from the edge of the foil. The result shows that the capacitance of the central portion of Comparative Example 1 is 100
Table 1 shows the relative comparison in the case of.

[0035]

[Table 1] As can be seen from the results in Table 1, the electrostatic capacity of the product of the present invention, which was subjected to the cleaning for removing the surface layer after the hot rolling and before the final finish rolling, increased in comparison with the comparative product. It is also understood that the continuous low-temperature heat treatment can improve the variation in the electrostatic capacitance in the width direction. Further, it is understood from the comparison between Example 1 and Example 2 that the electrostatic capacity can be further increased by performing the post-cleaning after the final finish rolling.

[0036]

[Function] By the surface layer removal cleaning of the aluminum foil material performed after the hot rolling and before the final finish rolling, flaw-like recesses formed on the surface of the aluminum foil material in the rolling step or Al oxide embedded in the surface, The embedded material such as carbon is removed, and the inevitable local concentration of these recesses and embedded material is eliminated.
Therefore, in the etching process to be performed thereafter, the coarse etching pits generated due to the local concentration of recesses and embedded materials are eliminated, and the high dislocation density portion formed by at least the finish rolling performed after the surface cleaning is eliminated. Etching pits supposed to be based are uniformly formed.

By continuously heat-treating the aluminum foil unwound from the coil after the foil rolling and before the final annealing, the thickness of the oxide film on the foil surface is made uniform and the width direction after etching is reduced. Variations in capacitance are suppressed.

[0038]

According to the present invention, the purity of 99.
After performing hot rolling and cold rolling on an aluminum slab of 9% or more, when performing foil rolling including final finishing rolling to produce an aluminum foil, after the hot rolling and before final finishing rolling, Since the surface of the aluminum foil is removed and washed at least once, a flaw-like recess formed on the surface of the aluminum foil in the rolling step or an Al oxide, carbon, etc. embedded in the surface. The implant can be removed. Therefore, since it is possible to eliminate the rough etching pits caused by the localized concentration of the recessed recesses and the embedded material, which has hindered the formation of the uniform etching pits in the conventional etching process, it is possible to uniformly generate the etching pits. It is possible to form thick and deep etching pits uniformly and with high density over the entire foil surface. As a result, the surface expansion rate of the aluminum foil can be remarkably increased, which in turn can increase the capacitance.

Moreover, since the aluminum foil unwound from the coil after the foil rolling and before the final annealing is continuously subjected to low-temperature heat treatment, the widthwise thickness of the oxide film formed on the surface of the aluminum foil before the final annealing is controlled. It can be homogenized in advance. Therefore, even if the oxide film grows in the subsequent final annealing, the oxide film grows while maintaining the uniform thickness, so that the final aluminum foil can be made with little variation in the oxide film thickness in the width direction of the foil. .. As a result, uniform etching can be performed in the etching process, and a stable aluminum foil for electrolytic capacitors with less variation in capacitance can be obtained.

Further, when the surface layer removal thickness is set to 0.01 μm or more, the recessed portions and embedded materials on the surface of the aluminum foil can be removed more effectively, and the capacitance can be increased more and more. ..

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

Claims (2)

[Claims] 1. An aluminum slab having a purity of 99.9% or more is hot-rolled and cold-rolled, and then foil-rolling including final finishing rolling is performed, and then final annealing is performed for electrolytic capacitors. When manufacturing aluminum foil,
After the hot rolling and before the final finishing rolling, the aluminum foil is subjected to at least one surface layer removal cleaning, and the aluminum foil rewound from the coil after the foil rolling and before the final annealing is continuously cooled at a low temperature. A method for manufacturing an aluminum foil for an electrolytic capacitor, which comprises heat treatment. 2. The method for producing an aluminum foil for an electrolytic capacitor according to claim 1, wherein the surface layer removal thickness is 0.01 μm or more.