JPH0489118A - Production of aluminum foil for electrolytic capacitor anode - Google Patents

Abstract

PURPOSE:To obtain a high degree of integration of cube bearings if aluminum having the purity of a base metal for electrolytic capacitors is used by combining the control of recrystallization and temp. at the time of hot rolling and annealing after the hot rolling. CONSTITUTION:After an aluminum cast ingot for electrolytic capacitors is subjected to a homogenization treatment for 4 to 24 hours in a temp. range of 570 to 630 deg.C, the rough hot rolling is started immediately thereafter at about the homogenization treatment temp. The rough hot rolling is ended at 480 to 530 deg.C and the aluminum is rested until the recrystallization is completed. The aluminum is thereafter subjected to finish hot rolling and the hot rolling is ended at <=280 deg.C. Further, the aluminum is subjected to annealing for 1 to 12 hours at 300 to 380 deg.C and is finally subjected to cold rolling, foil rolling and final annealing by the conventional method. The anode foil having good foil characteristics, i.e., the high degree of integration of the cube bearings, high electrostatic capacity and uniform characteristic distribution, is effectively produced by using the aluminum base metal of the purity lower than the purity of the aluminum used heretofore.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing an aluminum foil for an electrolytic capacitor anode, which is electrolytically etched mainly using direct current.

(Problems with conventional technology) Aluminum foils used for electrodes of electrolytic capacitors are etched to increase their effective surface area.

Etching can be roughly divided into those using direct current and those using alternating current. The former is mainly used for high-voltage anode foils with a high conversion voltage of 150 Å or more, and the latter is used for electrolytic etching of low-voltage anode foils with a low conversion voltage of less than 150 Å and cathode foils that are not subjected to chemical conversion treatment. Tunnel-shaped etch bits with a diameter of 1.5 to 3 μm are formed in the aluminum foil electrolytically etched by direct current. The preferential growth direction of tunnel-shaped etch bits is the <100> direction, so in order to efficiently perform tunnel-shaped electrolytic etching and obtain an electrolytic capacitor with high capacitance, the aluminum foil used for the electrode should be <100> perpendicular to the plane
It is required that the degree of accumulation of crystal grain orientations having a direction (hereinafter referred to as "cubic orientation J") (value expressed as a percentage of the ratio of cubic orientation grains to the foil surface) is high. Furthermore, even if the cubic orientation is macroscopically non-uniform, it is not suitable as a highly reliable electrode foil for electrolytic capacitors.

When manufacturing aluminum foil for electrolytic capacitors, which is usually etched with direct current, the following steps are performed. That is, the cast slab is homogenized, hot rolled,
Cold rolling and foil rolling are performed, and finally annealing is performed to obtain an aluminum foil for an electrolytic capacitor. By the way, high
100 > To obtain the degree of azimuth integration, conventional (1) 99
．． Use high purity aluminum of 99% or more. (2)
The final annealing temperature is set to a high temperature of 500°C or higher. (3) Methods such as adding partial annealing and additional rolling before final annealing are effective, according to the Journal of the Japan Institute of Light Metals, Light Metals, 3H19.
81), 675. In order to produce aluminum with a high purity of 99.99% or higher, a method is used in which a 99.7% pure primary metal produced by a molten salt electrolytic refining method is refined by a three-layer molten salt electrolytic refining method. ing. This method requires a large amount of electricity and costs 99.99
% or more, which significantly increased the manufacturing cost of high-purity aluminum, which increased the cost of aluminum foil for electrolytic capacitors. In recent years, 99.9
Aluminum with a purity of 5% or higher can now be produced at a lower cost than the conventional three-layer molten salt electrolytic refining method. Furthermore, improvements in the molten salt electrolytic refining method have made it possible to produce aluminum with a purity of 99.90% or higher. However, when the purity of aluminum decreases, it is difficult to obtain a foil with a high degree of cubic orientation integration using only the above-mentioned method.

(Means for Solving the Problems) The present inventors have diligently researched and developed a manufacturing method that can obtain a high degree of cubic orientation integration when the purity of aluminum is a bare metal for electrolytic capacitors, and recrystallization during hot rolling. They found that the requirements could be met by a combination of temperature control and annealing after hot rolling, and came to invent the following manufacturing method.

That is, (1) After subjecting an aluminum ingot for electrolytic capacitors to homogenization treatment for 4 to 24 hours at a temperature range of 570 to 630°C, rough hot rolling was immediately started at approximately the homogenization treatment temperature. Rough hot rolling was completed at a temperature of ~530°C, left until recrystallization was completed, and then finish hot rolling was completed at a temperature of 280°C or less, and further rolled at 300°C.
Annealing is performed at ~380°C for 1 to 12 hours, and finally cold rolling, foil rolling and final annealing are performed by conventional methods. (2)
570-630℃ for aluminum ingots for electrolytic capacitors
After performing homogenization treatment for 4 to 24 hours, rough hot rolling is immediately started at approximately the homogenization treatment temperature, and rough hot rolling is performed at a reduction rate of 80% or more.

The rough rolling was completed in a temperature range of 480 to 530°C.

Recrystallization is completed by leaving it for 100 to 200 seconds, then finish hot rolling is completed at a temperature of 280°C or less, further annealing is performed at 300 to 380°C for 1 to 12 hours, and finally by a conventional method. Cold rolling 7 Perform foil rolling and final annealing.

(Function) Next, the reason for limiting the manufacturing conditions of the present invention will be explained.

This manufacturing method does not restrict the purity of the aluminum base metal used, as long as it is of the purity used for electrolytic capacitors.
In order to obtain a more uniform distribution of tunnel-shaped etch bits, it is desirable to use a metal having a purity of 99.90% A1 or higher.

Furthermore, 99.90%A1 or more, Fe 300 ppm or less, 5i300 ppm or less, Cu 1009pm
By using the following metals, the effects of the manufacturing method of the present invention become more effective. That is, since Fe is an element that inhibits the growth of cubic orientation, it is desirable that the content be 300 ppm or less. Si promotes the precipitation of Fe and thus alleviates the harmful effects of Fe;
It is desirable to keep it below ppm. Cu is.

It is an element that has the effect of uniformly progressing etching, but if it is contained in a large amount, problems such as over-dissolution will occur during etching, so the content is preferably 100 ppm or less.

The reason why the homogenization treatment was carried out at 570 to 630°C or higher for 4 to 12 hours is because if it is lower than 570°C, the micro-segregation of impurity elements generated during casting cannot be uniformly distributed in solid solution, and even if it is higher than 570°C, the heating time is too long. If the time is less than 4 hours, homogenization is still insufficient, and as a result, the degree of cubic orientation of the final annealed foil is low, and the density varies from place to place. On the other hand, heating above 630°C is convenient for uniformizing the micro-segregation of impurity elements generated during casting, but
The surface oxidation of the ingot becomes significant, causing abnormal etching. Moreover, even if this heating time exceeds 24 hours, the effect will be saturated.

It is also disadvantageous in terms of thermal energy. Therefore 570-630
The homogenization treatment is carried out for 4 to 24 hours at a temperature range of .degree.

After the homogenization treatment, crude hot rolling was started at a high temperature without lowering the temperature, and crude hot rolling was carried out at a rolling reduction of 80% or more.
The rough hot rolling is completed in the temperature range of 80 to 530°C and left until recrystallization is completed.Generally, rolling slabs have a thickness of 300 to 600 mm (most commonly used).
Add a reduction of 80% or more to this, and keep the same thickness as 4
When the rough hot rolling is finished in the temperature range of 80 to 530°C and left to stand.

This is because the crystal grains of the ingot stretched in the rolling direction during rough hot rolling are completely recrystallized in 100 seconds or more. Many of these recrystallized grains have a cubic orientation. If the recrystallization progresses insufficiently, unrecrystallized areas will remain locally, and the cubic orientation of the foil after final annealing will increase. A reduction of less than 80% or a temperature of less than 480°C takes several minutes or more for complete recrystallization, which significantly impedes production and is undesirable. - Blade set hot rolling When the temperature exceeds 530°C, recrystallization progresses easily, but the crystal grains become coarse and the degree of cubic orientation in the foil after final annealing decreases.Also, even if left for more than 200 seconds, recrystallization is already completed. It is meaningless.The upper limit of the rolling reduction does not need to be particularly limited, and it can be up to about 99.5%.Therefore, rough hot rolling is performed at a rolling reduction of 80% or more, and a temperature of 480 to 530°C is used. Finish the rough hot rolling in the range,
100 to 200 to complete recrystallization.
Leave for seconds to recrystallize.

Next, the reason why the finish hot rolling end temperature is set to 280° C. or lower will be explained. In other words, finish hot rolling is performed in 3 to 4 passes from a thickness of 60n+m or less to a thickness at the end of finish hot rolling (3 to 8s+m thickness for boat fishing), but the finish hot rolling temperature is As the temperature decreases, regions with high accumulated strain energy are formed near grain boundaries and in deformation transition zones within grains. And the strain energy is higher near the grain boundaries than in the deformation transition zone.

At the stage of 2 to 3 baths, recrystallized grains with random orientation are generated near grain boundaries. In such a state, the final pass is 28
If the deformation is completed at 0°C or lower, preferably 250 to 280°C, the strain energy will be highest in the deformation transition zone within the 9 grains.

On the other hand, when finishing hot rolling is completed at a temperature exceeding 280° C., there is no difference in the accumulation of strain energy between the vicinity of grain boundaries and the deformation transition zone. As a result, when finish hot-rolling is finished at a temperature of 280°C or lower when finish hot-rolled plate is annealed, recrystallization nuclei with cubic orientation are generated in the deformation transition zone, resulting in cubic-oriented grains. However, if finish hot rolling is completed at a temperature exceeding 280°C, recrystallization nuclei will be generated both near the grain boundaries and in the deformation transition zone, resulting in not only cubic oriented grains but also randomly oriented grains. Since grains are generated, the proportion of cubic oriented grains contained in the annealed plate is reduced accordingly. As a result, the cubic orientation density of the final annealed foil is reduced.

Note that the lower limit of the finish rolling finishing temperature is generally about room temperature, but there is no problem with it being lower than this, and there is no need to specifically limit it.

The reason why the finish hot-rolled plate was annealed at a temperature range of 300 to 380°C for 1 to 12 hours is because below 300°C, it takes a long time to complete recrystallization, and preferential treatment from the deformation transition zone occurs. This is because the formation of recrystallized nuclei becomes difficult to occur, and 3.
This is because even if the temperature is 00° C. or higher, recrystallization is not completely completed in less than 1 hour. Since recrystallization is completed within 12 hours, there is no industrial meaning in annealing for more than 12 hours, and if the annealing temperature exceeds 380°C, recrystallization occurs rapidly and preferential nucleation occurs from the deformation transition zone. I can't get it. Therefore, annealing is performed at 300 to 380°C for 1 to 12 hours.

Cold rolling and foil rolling performed after annealing in finish hot rolling may be conventionally performed steps. The reduction rate is 95
% or more is normal. It is also possible to perform intermediate annealing during cold rolling and foil rolling, and intermediate annealing does not impede the effects of the present invention. Finally, final annealing is performed at a high temperature of 500° C. or higher in vacuum or in an inert atmosphere, but this is also conventionally performed and does not specify any particular conditions for the first step.

(Example) A slab having a chemical composition shown in Table 1 and having a thickness of 400 mm and a width of 1000 mm was obtained by ordinary DC casting.

Table 1 Composition Using a DC slab having the chemical composition shown in Table 1, after performing homogenization treatment, hot rolling, and annealing under the conditions shown in Table 2,
After cold rolling and foil rolling, test materials A-1 to A-1 were obtained.
Foil base materials were created with a thickness of 104 μm for No. 8 and 90 μm thick for B-1 to B-4. The foil was final annealed in vacuum at 550'C for 4 hours, electrolytically etched and chemically treated according to the conditions shown in Table 3, and the quality of the foil was determined by measuring capacitance and cubic density. evaluated. Capacitance measurement was performed by a known bridge method. The results of the evaluation are shown in Table 2. The mark ○ was judged as passing.

"Effects of the Invention" As explained above, the method of manufacturing aluminum foil for electrolytic capacitor anodes according to the present invention uses an aluminum base metal of lower purity than conventionally used, and has good foil characteristics, that is, high cubic shape. This invention is industrially highly effective because an anode foil having azimuthal integration, high capacitance, and uniform characteristic distribution can be efficiently manufactured.

Patent applicant Nippon Light Metal Co., Ltd. Toyo Aluminum Co., Ltd.
Nichikei Giken Co., Ltd. Inventor Masahiko Katano

Claims (2)

[Claims] (1) 570-6 for aluminum ingots for electrolytic capacitors
After homogenization treatment for 4 to 24 hours at a temperature range of 30°C, rough hot rolling is immediately started at approximately the homogenization treatment temperature, and rough hot rolling is completed at a temperature of 480 to 530°C, followed by recrystallization. Leave it until it is completed, then finish hot rolling,
An aluminum foil for electrolytic capacitors, characterized in that the aluminum foil is finished at a temperature of 280°C or lower, further annealed at 300 to 380°C for 1 to 12 hours, and finally cold rolled, foil rolled and final annealed by conventional methods. manufacturing method. (2) 570-6 for aluminum ingots for electrolytic capacitors
After homogenizing at 30°C for 4 to 24 hours, immediately begin rough hot rolling at approximately the homogenizing temperature, perform rough hot rolling at a rolling reduction of 80% or more, and heat to 480 to 530°C.
Rough hot rolling is completed at a temperature range of 100 to 200 seconds to complete recrystallization, then finish hot rolling is completed at a temperature of 280°C or lower, and then 300 to 380°C.
1. A method for producing an aluminum foil for an electrolytic capacitor, which comprises annealing the aluminum foil for 1 to 12 hours, and finally cold rolling, foil rolling, and final annealing by conventional methods.