JP2002173748A - Method for producing high purity aluminum foil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method by which high purity aluminum foil having stable and high cubic orientation ratio can stably be obtained. SOLUTION: A high purity aluminum material having purity of >=99.9% is subjected to primary intermediate annealing at 200 deg.C to 400 deg.C, is thereafter cold-rolled at a working ratio of 5 to 50%, is subsequently subjected to secondary intermediate annealing at 180 deg.C to 350 deg.C, is thereafter cold-rolled at a working ratio of 5 to 30%, and is subsequently subjected to final annealing. The generation of variation in the cubic orientation ratio caused by the difference in the contents of trace impurities in the material and in the production conditions is prevented, so that the aluminum foil having stable and high cubic orientation ratio can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high-purity aluminum foil having a high cubic azimuth ratio and used for an anode foil of an aluminum electrolytic capacitor.

[0002]

2. Description of the Related Art An anode foil for an electrolytic capacitor is generally 99.
Although high-purity aluminum of 9% or more is used, the foil (final foil) which has been finally rolled and annealed by a foil maker is not used as it is, but post-treated.
Capacitor manufacturers apply the chemical treatment or the electrochemical treatment to the plain foil to roughen it and use it for practical use. The reason for performing the surface roughening is that the surface area significantly increased by the surface roughening is directly proportional to the capacitance which is a characteristic of the capacitor, and a high capacitance can be obtained. Processing can be said to be the biggest point that determines the quality of a capacitor. As is well known, the roughened foil is used as an anode by anodizing, that is, coating a dielectric film. The medium and high voltage capacitors have a high formation voltage of 250 V or more, and therefore have a thick dielectric film (>
If the irregularities formed by the surface roughening treatment are very fine (<0.3 μm), they will be buried in the anodic oxide film and the effective surface area will be reduced.

For this reason, the surface roughening treatment for medium and high pressures is usually performed by direct current electrolytic etching to obtain relatively thick pits. The pits formed by the DC electrolytic etching are so-called capillary-shaped pits, and the traveling direction proceeds linearly in a crystallographically determined direction. The direction is parallel to the axis of the cubic crystal, ie, <001>
Direction. For example, assuming that the recrystallized texture of the foil has a cubic orientation, the direction of the pits formed by direct current electrolytic etching proceeds inward perpendicularly to the foil surface. Therefore, pits formed on a plane other than the cubic orientation are formed linearly with pits inclined with respect to the normal to the foil surface. Although the surface roughening rate is approximately proportional to the density and length of the pits to be formed (if the pit diameter is the same), it is empirically known by those skilled in the art that the cubic orientation has the highest surface roughening rate. Know that it is a bearing. It is considered that the reason for this is that the pit density formed in the cubic orientation is higher than the other orientations among the factors affecting the surface roughening rate described above. For this reason, foil manufacturers have been studying manufacturing methods for obtaining a higher cubic orientation than before. At present, it may be considered that the technique described in Japanese Patent Publication No. 54-11242 is generally used. This technology has a cold working degree of 90
% Of the material is partially annealed at a low temperature (around 200 ° C),
After that, final annealing is performed by performing low distortion processing.

[0004]

The above-mentioned conventional method has been used until now, as compared with the previous process, in which the cubic azimuth ratio is increased and the surface roughening ratio is improved. However, the following problems remain. 1. The cubic azimuth ratio of the high-purity 99.992% -purity has a large variation of 90 to 99%. In short, the obtained cubic azimuthal ratio changes due to a slight difference in the manufacturing process or the amount of trace impurities, and is not stable. 2. Further, when the purity reaches 99.9% grade, it becomes 70 to 9
Only a cubic orientation ratio of about 0% can be obtained. That is, Fe, S
When i is 100 ppm or more, a high cubic orientation ratio cannot be obtained by the above conventional method. The above disadvantages were found.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has been made of a high-purity aluminum having a small variation in cubic azimuth ratio depending on the material, and a good cubic azimuth ratio can be obtained even in a material having relatively low purity. It is an object to provide a method for producing a foil.

[0006]

The background that this technique was obtained was obtained based on the following research results. A detailed study of the crystallographic conditions for obtaining a high cubic orientation rate revealed the following. In order to obtain a high cubic orientation ratio, the structure before final rolling is as follows: 1) Cubic orientation grains are present in at least 5% or more. 2) The orientation (R-direction) grains other than the cubic orientation grains should be as small as possible (<5%). 3) The strain amount in the S-orientation, which is the work texture before final annealing, is sufficiently large. It was concluded that the above three conditions were necessary.

In the conventional method, the low-temperature processing and the low-temperature annealing are performed only once. However, in this method, the difference between the trace components contained in aluminum (Fe, Ga,
), The amount of nucleation in the cubic orientation during the intermediate annealing or the amount of strain in the R-orientation and the S-orientation changes, causing a variation in the cubic orientation during the final high-temperature annealing. Was not obtained. However, the primary intermediate annealing before the continuous pass in the final stage according to the present invention and the low reduction rate rolling to be performed thereafter reduce the variation in the primary intermediate annealing and the subsequent low reduction rate rolling, the secondary intermediate annealing, and the subsequent low reduction rate rolling. It can be said that a high cubic azimuth ratio can be obtained very stably by canceling out by the rolling reduction.

More specifically, even when only 1% of the cubic orientation is generated in the primary intermediate annealing, the cubic orientation is grown to 10% in the secondary intermediate annealing. Is not reduced by two passes, a high cubic azimuth ratio can be obtained even with a material of low purity,
And it seems to be stable. In actual practice, 99.
For 993% pure material and 99.9%, intermediate annealing conditions,
Processing rates are slightly different. Those with 99.9% are 99.9%.
It shifts to a higher temperature and a higher pressure reduction side than 993%. The reason for this is that, when the amount of Fe, Si, etc. increases, the number of cubic orientation particles generated by the isothermal IA also decreases, so that the growth of the cubic orientation is promoted toward the high temperature side and by high strain processing. And eliminating the disadvantages of the prior art as described above,
It can be said that the production method capable of obtaining a cubic orientation ratio of 98% or more at 99.993% purity and 90% or more at 99.90% purity was solved by the following steps.

That is, the first invention of the method for producing a high-purity aluminum foil of the present invention is to roll a high-purity aluminum material having a purity of 99.9% or more into a foil having a predetermined thickness by cold rolling. In the method for producing a high-purity aluminum foil in which final annealing is performed on the foil, after performing a primary intermediate annealing of the high-purity aluminum material at 200 to 400 ° C., cold rolling is performed at a processing rate of 5 to 50%. Then, after performing a secondary intermediate annealing of heating to 180 ° C. to 350 ° C., cold rolling is performed at a processing rate of 5 to 30% to form a foil having a predetermined thickness. It is characterized by performing annealing.

[0010] The method for producing a high-purity aluminum foil according to the second invention is the method according to the first invention, wherein the step from the secondary intermediate annealing to the cold rolling is repeated at least twice to obtain the foil having the predetermined thickness. And performing final annealing. A method for producing a high-purity aluminum foil according to a third aspect of the present invention is the method according to the first or second aspect, wherein the final annealing is performed by heating to 500 ° C. or more.

[0011] As described above, prior to the final high-temperature annealing, the present invention comprises a first intermediate annealing and a cold rolling at a predetermined working rate, followed by one or more secondary intermediate annealings and a cold rolling at a predetermined working rate. It is required to perform cold rolling. Hereinafter, the contents specified in the present invention will be described.

High-purity aluminum material: purity of 99.9% or more In the present invention, a high-purity aluminum material having a purity of 99.9% or more is used as a material to be rolled. Even in high-purity aluminum materials, trace amounts of Fe, Si, etc. are contained as unavoidable impurities in production, but in the present invention, as long as the above purity is satisfied, the type and content of each impurity are not particularly limited. .

Primary intermediate annealing: 200 ° C. to 400 ° C. (heating temperature) The above-mentioned high-purity aluminum material is subjected to primary intermediate annealing in a cold rolling step. In the first intermediate annealing, nuclei of crystal grains having a cubic orientation are generated. At this time, if the heating temperature during annealing is less than 200 ° C., the nuclei are not sufficiently generated.
Since the nuclei disappear by recrystallization, the heating temperature of the first intermediate annealing is limited to 200 to 400 ° C. For the same reason as above, it is desirable to set the lower limit to 220 ° C. and the upper limit to 350 ° C.

[0014] In the annealing, it is necessary to select a heating time during which the above effect is sufficiently obtained. Heating during annealing
In addition to a batch furnace with a gradual rise in temperature, a continuous furnace that raises the temperature quickly may be used. For example, in the case of a batch furnace, it is desirable to perform heating for 1 hour or more. This is because the crystal structure does not reach the stable region in less than one hour. In addition, since it enters the stable region within several hours, it is not preferable in terms of production even if heating is performed for a longer time.
It is desirable to set the time as the upper limit. However, the present invention does not exclude heating for more than 10 hours. In a continuous furnace, the heating can be performed by heating for a shorter time.

Cold rolling (after primary intermediate annealing): 5 to 50%
(Working ratio) In the cold rolling after the primary intermediate annealing and before the secondary intermediate annealing, a work strain is given to the material to promote the nuclei to grow as cubic crystal grains in the final annealing. It promotes the formation of new nuclei during intermediate annealing. If the working ratio in this cold rolling is less than 5%, the above-mentioned effects cannot be obtained.
If it exceeds 0%, the cubic orientation nucleus formed at an angle changes to another orientation.
Limited to ~ 50%. For the same reason as above, it is desirable to set the lower limit to 10% and the upper limit to 25%. Note that the number of rolling passes in the cold rolling step is not particularly limited, and the number of passes can be arbitrarily set to one or more as long as the above-mentioned working ratio is satisfied.

Secondary intermediate annealing: 180 ° C. to 350 ° C. (heating temperature) After the above-described primary intermediate annealing and cold rolling at a predetermined working ratio, secondary intermediate annealing is performed. In the primary intermediate annealing, as described above, nuclei that become cubic crystal grains are generated.
It is inevitable that the degree of nucleation varies depending on the material due to the earlier manufacturing process of the material or the slight difference in the content of trace impurities. In the secondary intermediate annealing, the nuclei generated in the primary intermediate annealing are maintained, and new nuclei are generated from the dough. As a result, even in a material in which nucleation in the primary intermediate annealing is not sufficient due to the above-mentioned variation, sufficient nuclei exist in the secondary intermediate annealing. In addition, in the material in which nucleation is sufficiently performed in the first intermediate annealing, the presence of the nucleus is maintained in the second intermediate annealing as described above, and as a result, the variation in the degree of nucleation depending on the material is eliminated. Will be done.

The heating temperature in this secondary intermediate annealing is 1
If the temperature is lower than 80 ° C., the above effect cannot be obtained.
When the temperature exceeds 0 ° C., the nuclei generated in the primary intermediate annealing appear, and the heating temperature in the secondary intermediate annealing is set to 180 to 350 ° C. in order to secure the strain amount in the S orientation and further suppress the R orientation growth. Limited to. Further, the lower limit is set to 220 for the same reason as described above.
° C, and the upper limit is desirably 280 ° C.

Further, as in the case of the primary intermediate annealing, it is necessary to select a heating time in the annealing so that the above-mentioned effect can be sufficiently obtained. The heating during the annealing may be performed in a batch furnace or a continuous furnace. Also, as in the case of the primary annealing, it is desirable to perform heating for one hour or more in the case of a batch furnace. This is because the crystal structure does not reach the stable region in less than 1 hour, and the crystal structure enters the stable region in several hours. It is desirable to set the upper limit. However, as the present invention,
It does not preclude heating over 10 hours. In a continuous furnace, the heating can be performed by heating for a shorter time.

Cold rolling (after secondary intermediate annealing): 5 to 30%
(Working ratio) In the cold rolling after the secondary intermediate annealing, a work strain is given to the material, and the nuclei generated in the primary and secondary intermediate annealings are promoted to grow as cubic crystal grains in the final annealing. . If the working ratio in this cold rolling is less than 5%, the above effect cannot be sufficiently obtained. On the other hand, if it exceeds 30%, the cubic orientation grains rotate too much, making it difficult to return to the original state. The processing rate in the intermediate step is limited to 5 to 30%. For the same reason as above, it is desirable to set the lower limit to 10% and the upper limit to 20%. More preferably, the upper limit is set to 15%. In addition,
In the above-mentioned secondary intermediate annealing and the subsequent cold rolling, it is also possible to repeat these steps as a series of these steps, in which case, in each step, the above-mentioned conditions (annealing temperature, working ratio) It is necessary to meet.

Final Annealing After one or more of the above-mentioned secondary intermediate annealing and cold rolling, final annealing is performed. In the final annealing, crystal grains having a cubic orientation grow by the nuclei generated by the primary and secondary intermediate annealings, and a high-purity aluminum foil having a high cubic orientation ratio is obtained. The temperature of the final annealing is desirably 500 ° C. or higher in order to sufficiently obtain the above-mentioned effect. However, the present invention does not exclude final annealing performed at less than 500 ° C.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. A high-purity aluminum material prepared to have a purity of 99.9% or more can be obtained by a conventional method, and the production method is not particularly limited in the present invention. For example, a hot rolled slab obtained by semi-continuous casting can be used, or a high-purity aluminum material obtained by continuous casting can be used.

The high-purity aluminum material is subjected to a first intermediate annealing in a cold rolling step. The aluminum material to be subjected to the primary intermediate annealing is not limited as long as it has a sheet thickness that takes into account the working ratio in the subsequent cold rolling and the thickness of the foil at the final stage of rolling. The thickness of the sheet is not limited to this, and the timing of the primary intermediate annealing in the cold rolling step can be arbitrarily selected as long as the conditions of the present invention are satisfied. However, in order to more stably obtain a foil having a high cubic orientation ratio, it is desirable that the working ratio in the cold rolling (one or more rolling passes) before the first intermediate annealing is 90% or more. Further, cold rolling in the process of manufacturing the foil is generally composed of sheet rolling and foil rolling, but the cold rolling in the present invention is not limited to any of the above-mentioned rolling, for example, foil It may be one that belongs only to rolling, or one that includes both sheet rolling and foil rolling. That is, the present invention only needs to satisfy cold rolling prior to final annealing.

In the first intermediate annealing, heat treatment is performed in the above-mentioned temperature range. The heat treatment may be any of a batch furnace and a continuous furnace, and the heating time is selected in consideration of the form of the furnace and the like, in consideration of the above-mentioned effects being sufficiently obtained, and having industrial properties. . After the primary intermediate annealing, cold rolling is performed at the above-described predetermined working ratio. The number of rolling passes in the rolling is arbitrary as described above as long as the processing rate specified in the present invention is secured. In the case of a plurality of rolling passes, the working ratio is discussed on the basis of before and after cold rolling.

After the above cold rolling, secondary intermediate annealing is performed. Heat treatment is also performed in the above-mentioned temperature range in the secondary intermediate annealing. The heat treatment is similar to the primary intermediate annealing,
Either a batch furnace or a continuous furnace may be used, and the heating time is selected in consideration of the form of the furnace and the like in view of the fact that the above-mentioned action is sufficiently obtained and that the furnace is industrial. Note that heating may be performed using different furnaces for the primary intermediate annealing and the secondary intermediate annealing. After the secondary intermediate annealing, cold rolling is performed at a working ratio specified in the present invention. The number of rolling passes in the rolling is arbitrary as described above as long as a predetermined processing rate is secured. In the case of a plurality of rolling passes, the working ratio is discussed on the basis of before and after cold rolling.

A series of steps from the secondary intermediate annealing to the cold rolling can be repeated as described above, and the number of repetitions can be appropriately selected. In this case, the heating temperature and the processing rate are performed in each step under the conditions specified in the present invention. By performing the above-described series of steps from the secondary intermediate annealing to the cold rolling once or twice or more, a foil having a predetermined thickness can be obtained. The thickness of the foil is not particularly limited as the present invention, and may be any thickness as long as the foil is rolled in accordance with the thickness required for the foil of the final product.

The aluminum foil rolled to a predetermined thickness as described above is subjected to final annealing. The heating method in the final annealing is not particularly limited, and a batch furnace or a continuous furnace can be appropriately selected. In the present invention, the heating temperature of the final annealing is not particularly limited, but is preferably 500 ° C. or higher as described above. By the final annealing, a large number of crystal grains having a cubic orientation are present, and a high cubic orientation ratio is obtained.

The aluminum foil that has been finally annealed as described above can be subjected to a post-treatment depending on the intended use. When used as an electrolytic capacitor electrode foil, a roughening treatment, a chemical conversion treatment, or the like is performed after the final annealing. These treatments can be performed by a conventional method. Note that, in the present invention, the contents of the steps after the final annealing are not particularly limited, and processing as needed can be appropriately performed according to the use and the like.

The high-purity aluminum foil obtained by the manufacturing method of the present invention has a high cubic azimuthal rate by the above-described manufacturing process. Are uniformly formed at a high density, and have a high surface roughening rate. Therefore, if this is used as a capacitor electrode, a capacitor having a high capacitance per area can be obtained. Therefore, as a use of the aluminum foil obtained by the production method of the present invention, a foil for an electrolytic capacitor electrode is suitable.

[0029]

EXAMPLE Al with a purity of 99.9% or 99.995%
Using ingots, especially for 99.995% ingots, Fe:
The components were adjusted to 10 ppm, Si: 10 ppm, and Cu: 50 ppm, and the components were adjusted to be approximately 99.993%. A rolled material having a thickness of 6 mm was obtained by ordinary production (casting, hot rolling). After cold rolling this rolled material at a predetermined processing rate,
Under the conditions shown in Table 1, primary intermediate annealing and cold rolling (PF in the table)
P), secondary intermediate annealing, and cold rolling (denoted as FP in the table) to obtain a high-purity aluminum foil having a final thickness of 100 µm. In some cases, the above-mentioned secondary intermediate annealing and subsequent cold rolling were repeated twice. The high-purity aluminum foil obtained by the above manufacturing process was subjected to final annealing by heating at 550 ° C. for 5 hours in an inert gas to obtain a foil specimen. For these foil specimens, HCl, HNO ₃
Corrosion in mixed acid at 60 ° C. If the etched surface is a mirror surface, the cubic orientation, if the etched surface is white and diffusely reflected, the other orientation, calculate the area ratio of each with a particle analyzer and calculate the cubic orientation ratio. Calculated. The following table summarizes the results.

[0030]

[Table 1]

[0031]

[Table 2]

As is clear from the table, the test piece obtained by the production method of the present invention shows that when a highly pure material is used,
Aluminum foils with very high cube orientation have been obtained. Even when a material having a relatively low purity is used, a high cubic azimuth ratio is stably obtained.
On the other hand, the foil specimens obtained by the conventional method and the comparative method which deviate from the conditions of the present invention are clearly inferior in cubic azimuth.

[0033]

As described above, according to the method for producing a high-purity aluminum foil of the present invention, a high-purity aluminum material having a purity of 99.9% or more is rolled into a foil having a predetermined thickness by cold rolling. Thereafter, in the method for producing a high-purity aluminum foil in which the foil is subjected to final annealing, the high-purity aluminum material is subjected to primary intermediate annealing at 200 ° C. to 400 ° C., and then cold-processed at a working rate of 5 to 50%. Rolling, and then, after subjecting to a secondary intermediate annealing heating to 180 ° C ~ 350 ° C, cold rolling at a working rate of 5-30% at least once to give a foil of a predetermined thickness, Since the foil is finally annealed, the cubic azimuth does not vary due to the difference in the amount of trace impurities in the material or the difference in the manufacturing conditions, and an aluminum foil having a high cubic azimuth can be obtained stably. If this aluminum foil is used for an electrode of an electrolytic capacitor, a capacitor having a high surface roughness and excellent capacitance can be obtained.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference)

Claims (3)

[Claims] 1. A high-purity aluminum material having a purity of 99.9% or more is rolled into a foil having a predetermined thickness by cold rolling.
In the method for producing a high-purity aluminum foil in which the foil is subjected to final annealing,
After the first intermediate annealing at 0 ° C., cold rolling is performed at a working ratio of 5 to 50%, and then 180 ° C. to 3%.
After performing the secondary intermediate annealing heated to 50 ° C, 5-30%
Cold rolling at a processing rate of to a foil of a predetermined thickness,
A method for producing a high-purity aluminum foil, comprising subjecting the foil to final annealing. 2. The high-purity aluminum according to claim 1, wherein the step of repeating from the secondary intermediate annealing to the cold rolling is repeated twice or more to obtain the foil having the predetermined thickness, and then the final annealing is performed. Manufacturing method of foil 3. The method for producing a high-purity aluminum foil according to claim 1, wherein the final annealing is performed by heating to 500 ° C. or higher.