JP2006186093A - Aluminum foil for electrolytic capacitor and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide strong aluminum foil for an electrolytic capacitor that has a high rate of presence of a cubic crystal system and can form a deep pit in a depthwise direction. <P>SOLUTION: In the aluminum foil for electrolytic capacitors and the method for manufacturing it; 90% or higher cubic crystal systems are obtained with a purity of 99.9%, the grain shape is extended in a rolling direction, and the aspect ratio of the grain diameter in a direction in parallel with the rolling direction to a direction perpendicular to the rolling direction is set to a range of 1.1-1.5. After heat treatment is made at a temperature of 500-600°C, rolling machining is made again with a working rate of 11-50%. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an aluminum foil for electrolytic capacitors having a cubic crystal ratio of 90% or more and a method for producing the same.

In general, an aluminum electrolytic capacitor is configured such that an anode aluminum foil having an aluminum oxide dielectric film formed on the surface thereof by anodic oxidation and a cathode aluminum foil not subjected to oxidation treatment are opposed to each other with an electrolyte interposed therebetween. As the aluminum foil for the anode, high-purity aluminum having a purity of about 99.99% is usually used, and as the aluminum foil for the cathode, various aluminum alloys having a purity of about 99.2 to 99.8% are usually used. in use.
However, in this type of aluminum electrolytic capacitor, for the purpose of improving its electrostatic capacity, various studies have been made on a small amount of additive elements and manufacturing processes for the anode formed of high-purity aluminum foil. However, not only high pressure but also medium and low pressure electrolytic capacitors are actively used.

Among these, the medium- and high-pressure etching foils for electrolytic capacitors are roughened by making many holes called tunnel pits on the surface, and the characteristics have been improved so that high capacitance can be obtained. Etching technology for obtaining capacity tends to be improved year by year. In addition, recently, it has been demanded to ensure high capacitance and to have practical strength.
However, if the length of the etching pit is simply increased in order to increase the capacity, there is a problem that the foil thickness in the central portion where no pit exists is insufficient and the strength of the foil as a whole is reduced.
Further, the strength of the aluminum foil is almost constant because the aluminum foil is sufficiently softened by the final annealing process at the stage of processing to the target thickness by rolling. Therefore, in order to ensure the strength as an aluminum foil, conventionally, the length of the pits must be adjusted in the etching technique, or the foil thickness itself must be increased to increase the strength, and there has been a restriction on the formation of pits. .

Since the pits formed on the surface of the aluminum foil are perpendicular to the (100) plane of the aluminum crystal, it is necessary to increase the cubic ratio in the aluminum foil crystal in order to obtain high capacity and high strength. There is.
According to the research by the present inventors, in order to grow aluminum cubic crystals, annealing at 200 to 300 ° C. (intermediate annealing) is performed in the middle of cold rolling to grow crystal grains serving as the nucleus of the cubic crystals. After that, rolling (additional rolling) is performed again, and the previous crystal grains are distorted, so that it is necessary to prepare a situation in which cubic crystals preferentially grow during final annealing.

By the way, conventionally, when manufacturing aluminum foil, purity 99.96 mass% or more and cubic orientation rate 60 volume% or more after hot rolling, cold rolling, intermediate annealing, cold rolling, final annealing at 450 ° C. or higher. A manufacturing method is known in which a low annealing process with a cold working rate of 0.3% to 10% is performed on the raw aluminum foil prior to the roughening treatment, followed by final annealing. (See Patent Document 1)
JP 2003-119555 A

In the method described in Patent Document 1, the size of the dislocation structure existing in the surface inner layer portion of the aluminum foil is less than 0.3 μm in terms of the equivalent circle diameter, and the area ratio is 10% or less. In the case where the area ratio is over 8 μm, the area ratio is 10% or less, so that the variation in the size of subgrain boundaries or dislocation cells can be controlled and the uniform generation of pits can be improved. In terms of improving the strength of the foil, a sufficient effect could not be expected.
Further, as described in the above-mentioned Patent Document 1, when the processing rate at the time of rolling is increased, the cubic crystal is recrystallized, and the cubic crystal rate tends to decrease. Therefore, the strength can be increased without decreasing the cubic rate. The advent of technology that can obtain high aluminum foil is desired.

  The present invention has been made in view of the above circumstances, and by controlling the heat treatment after processing, it is possible to perform cold working at a high processing rate without destroying the cubic crystal, the cubic rate is high, and the strength is also high. The purpose is to provide a high aluminum foil for electrolytic capacitors.

As a result of studies conducted in view of the above-mentioned problems, the present inventor has determined that the aspect ratio of the deformed crystal grains is 1 when rolling the aluminum foil in which a cubic crystal ratio of 90% or more is obtained in the process of manufacturing the aluminum foil. By keeping the range of .1 to 1.5, the recrystallized structure can be changed to the rolled structure while maintaining the high cubic rate, and the foil strength can be reduced by changing the crystal grains to the processed structure. The present invention has been reached based on the knowledge that it can be dramatically improved.
In order to achieve the above object, the present invention is made of aluminum having a purity of 99.9% or more, and 90% or more of cubic crystals are obtained, and their grain shape is stretched in the rolling direction. It is an aluminum foil for electrolytic capacitors in which the aspect ratio of the grain size in the direction parallel to the rolling direction with respect to the vertical direction is in the range of 1.1 to 1.5.
In addition, the manufacturing method is characterized in that after heat treatment is performed at a temperature of 500 to 600 ° C., re-rolling is performed at a processing rate of 11 to 50%.
Furthermore, the present invention is characterized by performing annealing for removing dislocations at a temperature of 100 to 300 ° C. for 2 to 12 hours after the rerolling performed at a processing rate of 11 to 50%.

The matters limited in the present invention will be described below.
Aspect ratio of crystal grains When the aspect ratio of the crystal grains is less than 1.1, the amount of deformation of the crystal grains accompanying the rolling is small, so that an improvement in strength cannot be expected. On the other hand, when the aspect ratio of the crystal grains exceeds 1.5, the amount of deformation accompanying the rolling is too large, so that the cubic crystals are partially broken and normal etching cannot be performed.
When the re-rolling process is introduced, dislocations are introduced into the structure of the aluminum foil, and the introduced dislocations may inhibit the growth of pits along with electrolytic etching in the subsequent roughening treatment. Therefore, for such a case, dislocation can be removed by performing a heat treatment at 100 to 300 ° C. for 2 to 12 hours, more preferably at a temperature of 100 to 250 ° C. for 2 to 12 hours.
In terms of removal of dislocations, if heat treatment is performed at a temperature of less than 100 ° C., dislocation removal tends to be insufficient, and if heat treatment is performed at a temperature exceeding 250 ° C., recrystallization starts and the cubic rate decreases. Note that the necessity of this dislocation removal process varies depending on the electrolytic etching conditions to be applied. Therefore, the dislocation removal process is not always necessary and may be omitted.

Next, the aluminum foil to be applied to the present invention will be described in detail.
The aluminum foil for electrolytic capacitors mainly used for medium to high pressure according to the present invention is mainly composed of 99.9% or more pure aluminum.
Here, as an element other than Al contained in the aluminum foil of the present invention, Fe as impurities may be contained in a range of 5 ppm to 50 ppm, Si may be contained in a range of 5 to 50 ppm, and Cu may be contained in an amount of about 1 to 100 ppm. Moreover, you may contain about 5-30 ppm of other inevitable impurities as a total amount.
When the cubic rate of the aluminum foil applied to the present invention is 90% or more and less than 90%, the number of vertically generated pits decreases, resulting in insufficient capacity and strength.

According to the present invention, it is possible to provide an aluminum foil for electrolytic capacitors having a high cubic crystal ratio, capable of forming deep etching pits, and having a high capacity and high strength.
Moreover, when the manufacturing method as in the present invention is employed, an aluminum foil for electrolytic capacitors having an appropriate aspect ratio, a high cubic crystal ratio, and a high strength can be obtained.

  The aluminum foil for electrolytic capacitors obtained by carrying out the present invention is mainly composed of 99.9% or more pure aluminum. In addition, as an example of impurities contained in aluminum that can be applied to the aluminum foil of the present invention, Fe: 5 to 50 ppm, Si: 5 to 50 ppm, Cu: 1 to 100 ppm, and a composition containing about 5 to 30 ppm of other inevitable impurities It may be.

  The aluminum foil for electrolytic capacitors of the present invention is an aluminum foil made of aluminum having a foil thickness in the range of 0.1 to 0.2 mm and a purity of 99.9% or more, and has a cubic crystal ratio of 90% or more.

In this way, the aluminum foil obtained as a predetermined thickness and having a cubic crystal of 90% or more is further rolled to obtain a final target thickness, and obtained as a result of deformation here. The aspect ratio of the crystal grains in the aluminum foil (grain size parallel to the rolling direction / grain size perpendicular to the rolling direction) is set in the range of 1.1 to 1.5. By this rolling process, the crystal grains can be changed from a recrystallized structure to a rolled structure, and thereby the strength as an aluminum foil can be dramatically increased.
In the present embodiment, the cubic crystal ratio is defined as a cubic crystal ratio obtained by taking an area of 30 cm ² from an aluminum foil using an image analysis apparatus and calculating a crystal grain occupancy ratio in the (100) orientation.
Next, in the aluminum foil of this embodiment, when the aspect ratio of the crystal grains is less than 1.1, the strength cannot be improved because the deformation amount of the crystal grains accompanying rolling is small. On the other hand, when the aspect ratio of the crystal grains exceeds 1.5, the amount of deformation accompanying the rolling is too large, so that the cubic crystals are partially broken and normal etching cannot be performed.

By the way, when the re-rolling process performed earlier is introduced, dislocations are introduced into the structure of the aluminum foil, and this introduced dislocation inhibits pit growth accompanying electrolytic etching in the subsequent roughening treatment. In such a case, the aluminum foil after the re-rolling process is heat-treated at 100 to 300 ° C. for 2 to 12 hours, more preferably at a temperature of 100 to 250 ° C. for 2 to 12 hours. The dislocation can be removed by performing
In terms of removal of dislocations, if heat treatment is performed at a temperature of less than 100 ° C., dislocation removal tends to be insufficient, and if heat treatment is performed at a temperature exceeding 250 ° C., recrystallization starts and the cubic rate decreases. Note that the necessity of the dislocation removal process varies depending on the electrolytic etching conditions to be applied. Therefore, the dislocation removal process is not always necessary and may be omitted.

  If the aluminum foil has a foil thickness as described above and a cubic ratio of 90% or more, and the aluminum foil after re-rolling with the above aspect ratio, the roughening treatment for an electrolytic capacitor is performed. Further, over-dissolution and over-precipitation are not further generated, and a more uniform etched surface can be obtained.

An aluminum alloy having a composition of Fe: 10 ppm, Si: 10 ppm, Cu 50 ppm, other inevitable impurities, and the balance Al was melted and cast to obtain a plurality of slabs having a thickness of 600 mm. This slab was subjected to hot rolling, cold rolling, intermediate annealing and cold rolling to obtain an aluminum foil having a thickness of 0.2 mm. When this aluminum foil was heat-treated at 550 ° C. for 6 hours, an aluminum foil having a cubic crystal ratio of 95% could be obtained.
Further, this aluminum foil was subjected to re-rolling to obtain an aluminum foil sample having a thickness shown in Table 1 below. In the obtained aluminum foil sample, the crystal aspect ratio (grain size in the direction parallel to the rolling direction / particle size in the direction perpendicular to the rolling direction) of the aluminum foil sample after rerolling was measured. Moreover, the proof stress of these aluminum foil samples was measured.
The measurement results are summarized in Table 1.
Next, a part of the sample of the aluminum foil after the rerolling was reheated, and further roughened by electrolytic etching under the following conditions, and the capacitance was measured. The results are also shown in Table 1 below.
Etching: 3 mol / l sulfuric acid + 1 mol / l hydrochloric acid: conditions for applying a constant current of 0.2 mA / cm ² for 120 seconds using a solution at 75 ° C.

From the results shown in Table 1, the samples Nos. 1 to 14 have an aspect ratio in the range of 1.1 to 1.5 by changing the processing rate after heat treatment to a range of 13 to 50%. An aluminum foil having a crystallinity of 94% or more and a range of 94 to 96%, excellent proof stress, and high electrostatic capacity could be obtained. Specifically, excellent values in the range of 30 to 58 N / mm ² in the proof stress of each sample and in the range of capacitance of 100 to 104% with respect to Comparative Example 1 were obtained.
Samples Nos. 1 to 6 in Table 1 are samples in which the re-rolling rate after heat treatment is gradually increased in the range of 13 to 50%, but the yield strength can be improved without substantially reducing the cubic rate. It is clear. On the other hand, Comparative Examples 1 and 2 in which the re-rolling rate after heat treatment was 0% or 5% were remarkably insufficient in proof stress. The capacity has dropped significantly.
Samples Nos. 7 to 14 were samples subjected to a reheat treatment temperature, and the proof stress could be maintained at a higher level while maintaining a high cubic crystal ratio.
Next, the difference in strength in the comparison between Examples 1 and 6 is due to work hardening. As a result of promoting recrystallization by reheating, the recrystallized grains can be enlarged.

Claims (3)

  It is made of aluminum with a purity of 99.9% or more, and a cubic crystal ratio of 90% or more is obtained. Their grain shape is elongated in the rolling direction, and the direction parallel to the rolling direction with respect to the direction perpendicular to the rolling direction. The aluminum foil for electrolytic capacitors in which the aspect ratio of the particle diameter is 1.1 to 1.5. It is made of aluminum with a purity of 99.9% or more, and a cubic crystal ratio of 90% or more is obtained. Their grain shape is elongated in the rolling direction, and the direction parallel to the rolling direction with respect to the direction perpendicular to the rolling direction. Is a method for producing an aluminum foil for electrolytic capacitors, wherein the aspect ratio of the particle diameter is 1.1 to 1.5.
A method for producing an aluminum foil for electrolytic capacitors, comprising performing a heat treatment at a processing rate of 11 to 50% after performing a heat treatment at a temperature of 500 to 600 ° C. The method for producing an aluminum foil for an electrolytic capacitor according to claim 2, wherein annealing is performed at a temperature of 100 to 300 ° C for 2 to 12 hours after the rerolling performed at a processing rate of 11 to 50%. .