JPH08296010A - Production of aluminum foil for high voltage of electrolytic capacitor - Google Patents

Abstract

PURPOSE: To provide a method for producing aluminum foil for high voltage of an aluminum foil having etch pits of high density and capable of remarkably increasing capacitance by improving its electrolytic etching properties. CONSTITUTION: The slab of pure aluminum having >=99.90wt.%. purity is subjected to homogenizing treatment at 450 to 620 deg.C for 1 to 20hr and is successively subjected to hot rolling and cold rolling. After that, it is heated at 180 to 260 deg.C for 1 to 20hr, is subjected to process annealing treatment and is next subjected to final cold rolling at 5 to 25% draft. Then, the obtd. aluminum foil is immersed in pure water of 75 to 95 deg.C having <=10μS electric conductivity for 30 to 250sec to form a hydroxide film, which is furthermore heated at 480 to 620 deg.C for 1 to 5hr and is subjected to final annealing. On the surface of the obtd. aluminum foil, γ-Al2 O3 crystals are present by 25 to 1000 pieces/mm<2> . Furthermore, by its immersion into the same pure water, the hydroxide film of 0.010 to 0.200g/m<2> is formed on the surface.

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 an aluminum foil for electrolytic capacitor high voltage, which is capable of producing an electrolytic capacitor which is uniformly and moderately dissolved during etching and has a high capacitance.

[0002]

2. Description of the Related Art In general, aluminum foil for electrolytic capacitors is electrochemically or chemically surface-expanded for the purpose of increasing its capacitance. That is, since the capacitance is proportional to the surface area of the electrode surface due to the characteristics of the capacitor, high density of etch pits is generated and at the same time the pits do not collapse even after an oxide film that can withstand the voltage used is applied. , The pits should be dense.
Therefore, depending on the voltage used, an electrolytic capacitor high-voltage aluminum foil that normally performs direct current electrolysis in a hydrochloric acid-based etching solution to generate high-density etch pits in the direction perpendicular to the foil surface, and an alternating current electrolysis that causes spongy It is divided into aluminum foil for low voltage anode and cathode for electrolytic capacitors that generate etch pits. The two have very different material properties and surface properties. Therefore, even if a foil manufactured for high pressure is used for medium / low voltage anode / cathode, sufficient characteristics cannot be obtained. Further, even if the aluminum foil for medium / low voltage anode / cathode is used for high pressure, sufficient characteristics cannot be obtained.

As described above, the high-voltage aluminum foil is added with a metal nobler than aluminum, such as Pb, Bi, or B, for the purpose of improving the DC etching characteristics, or a metal nobler than this aluminum is added. A treatment for forcibly forming etching nuclei by adhering to the foil surface is carried out. Further, in order to control the crystal orientation of the aluminum foil and increase the occupation rate of the (100) plane, the aluminum foil may be heat-treated at a high temperature of 500 ° C. or higher in a vacuum or an inert gas such as argon gas. Has been done.

However, it is difficult to allow the metal to be present in a uniform dispersed state on the foil surface by the conventional method of adding a metal for forming an etching nucleus to the aluminum foil or adhering it to the foil surface, and thus the etching nucleus is formed. As a result, the number of etching nuclei becomes small, or conversely, the number of etching nuclei concentrates in a part and local dissolution occurs at the time of etching.As a result, good etching performance cannot be obtained and, in turn, sufficient capacitance is not obtained. There was a drawback that it could not be obtained.

The crystal orientation of the aluminum foil is (10
0) Even if a method of heating at high temperature in vacuum or in an inert gas such as argon gas in order to make the occupying ratio of the surface uniform, the same satisfactory etching performance and electrostatic capacity cannot be obtained. It was

Therefore, various studies have been made for the purpose of solving these problems, and as a result, the following aluminum foils have been developed and proposed.

Japanese Unexamined Patent Publication No. 63-116417 discloses a large number of γ-Al ₂ O _{3 on the} surface of an aluminum foil before etching.
There is disclosed an aluminum material for electrolytic capacitors in which etching characteristics are improved by forming an amorphous oxide film in which crystals are uniformly dispersed.

[0008]

However, the above-mentioned conventional aluminum foil has the following problems. That is, the aluminum material for electrolytic capacitors disclosed in Japanese Patent Laid-Open No. 63-116417 is an amorphous oxide in which polymorphic γ-Al ₂ O ₃ crystals are uniformly dispersed on the surface of the aluminum foil before etching. By forming a film, a large number of uniformly dispersed γ-Al ₂ O ₃ crystals are used as etching nuclei to form a uniform etching surface, and a high electrostatic capacity is obtained.

[0009] However, aluminum foil to form an oxide film having such a large number of γ-Al ₂ O ₃ crystal was uniformly dispersed amorphous can not be said to have a necessarily desirable high density etch pit . Therefore, the conventional aluminum foil for electrolytic capacitors cannot be said to have a sufficiently high electrostatic capacity. The inventors of the present application repeated various experiments and studies, and as a result, the aluminum foil manufactured by the method disclosed in the prior art has 10 gamma-Al ₂ O ₃ crystals.
It was found that the number of particles / μm ² exists. As described above, in a foil having about 10 γ-Al ₂ O ₃ crystals / μm ² , there are few starting points for etching, so that it is easy to form an unetched portion and an effect of increasing the capacitance can be obtained. I can't.

The present invention has been made in view of the above problems, and has a high density of etch pits and is capable of improving electrolytic etching property and significantly increasing electrostatic capacity, and thus aluminum for high voltage of an electrolytic capacitor. It is an object to provide a method for manufacturing a foil.

[0011]

The method for producing a high voltage aluminum foil for electrolytic capacitors according to the present invention has a purity of 99.
90% by weight or more of pure aluminum slab
Homogenization treatment at 620 ° C for 1 to 20 hours, hot rolling and cold rolling subsequently, heating at 180 to 260 ° C for 1 to 20 hours to perform intermediate annealing treatment, and then at a rolling reduction of 5 to 25%. Final cold rolling is performed, and then the obtained aluminum foil is immersed in pure water having an electric conductivity of 10 μS or less at 75 to 95 ° C.
It is characterized in that it is immersed for ˜250 seconds and further heated at 480 to 620 ° C. for 1 to 5 hours in vacuum or in an inert gas atmosphere for final annealing treatment. The inert gas includes nitrogen gas in addition to argon gas.

In this case, 25 to 1000 γ-Al ₂ O ₃ crystals existing on the surface of the obtained aluminum foil / m.
It is preferably m ² . Further, it is preferable to form a hydroxide film of 0.010 to 0.200 g / m ^{2 on} the surface by immersion in the pure water.

[0013]

In the present invention, in order to solve the above problems, the number of γ-Al ₂ O ₃ crystals existing on the surface of the aluminum foil is preferably 25 to 1000 crystals / μm ² . The reason why the conventional aluminum foil for electrolytic capacitors has an insufficient capacitance is that the number of γ-Al ₂ O ₃ crystals has been about 10 / μm ^{2 in the} past, as described above.
Therefore, in the present invention, the number of γ-Al ₂ O ₃ crystals is set to exceed 10 / μm ² . In particular, the inventors of the present invention have reasonably covered the entire surface with γ-Al ₂ O ₃ crystals, and the aluminum foil surface has 25 to 1000 pieces / μm ^2.
If the the γ-Al ₂ O ₃ crystals are present, it has been found to have a high density of etch pits. And, in order to obtain such a state, the surface of the foil should have a thickness of 0.010 to 0.200.
A g / m ² hydroxide film may be formed and finally annealed at a temperature of 480 to 620 ° C. for 1 to 5 hours in vacuum or in an inert gas atmosphere such as argon gas. As a result, 25 to 1000 pieces / μm ² of γ-Al ₂ O ₃ crystals can be formed on the foil surface.

In order to obtain an aluminum foil having such a surface condition, the purity of aluminum is 99.9.
A slab consisting of 0% by weight or more of pure aluminum is
It is continuously heated to a temperature of 0 to 620 ° C. for 1 to 20 hours for homogenization treatment, followed by hot rolling and cold rolling, and then at an intermediate annealing. This intermediate annealing is performed at 180 to 260 ° C.
After heating at a temperature of 1 to 20 hours, final cold rolling is performed at a reduction rate of 5 to 25% to obtain a foil having a predetermined product thickness. Then, 0.010 to 0.200 g / m on the surface
² ) Form a hydroxide film, and in vacuum or in an inert gas atmosphere such as argon gas at a temperature of 480-620 ° C for 1-5
Heat for an hour and finally anneal. The manufacturing conditions will be described below.

Purity of aluminum slab: 99.90 weight
The amount of aluminum slab must have a purity of 99.90% by weight or more. If the purity is lower than this, the amount of impurities increases, the occupancy of the (100) plane is less than 90%, and the capacitance decreases. More preferably, 9
Use an aluminum slab with a purity of 9.98% or higher.

Surface condition of aluminum foil: γ-Al ₂ O ₃
The crystals 25-1000 pieces / [mu] m ² foil surface γ-Al ₂ O ₃ crystal 25 to 1000 pieces / [mu] m ²
To exist. A γ-Al ₂ O ₃ crystal of less than 25 pieces / μm ² is not preferable because there are few starting points of the etch pits, unetched portions are easily formed, and the capacitance is lowered. Further, a γ-Al ₂ O ₃ crystal having a density of more than 1000 pieces / μm ² is not preferable because there is a difference in the density, local dissolution is likely to occur, and the capacitance is lowered.

Homogenization treatment conditions: 480-620 ° C., 1-
The homogenization treatment temperature for 20 hours is 480 to 620 ° C. If the temperature is lower than 480 ° C., it becomes difficult for the impurities to form a solid solution in aluminum sufficiently uniformly, and the impurities are likely to precipitate in a later step,
The occupancy rate of the 0) plane becomes 90% or more, and the electrostatic capacity is reduced, which is not preferable. In addition, the homogenization treatment temperature is 62
If the temperature exceeds 0 ° C., coarse crystal grains are likely to be generated, it is difficult to rotate to the (100) plane even in the subsequent rolling treatment, the occupancy of the (100) plane is less than 90%, and the capacitance is lowered. Is generated, which is not preferable. More preferably, the homogenization treatment temperature is 500 to 600 ° C.

The homogenization treatment time is 1 to 20 hours. If the heating time of the homogenization treatment is less than 1 hour, the impurities cannot be sufficiently and solid-dissolved in aluminum, and the impurities are likely to precipitate in the subsequent step, and the occupancy of the (100) plane is 9%.
It is not preferable because it is hard to be 0% or more and the capacitance is lowered. When the homogenization treatment time exceeds 20 hours, coarse crystal grains are likely to be generated, and it is difficult to rotate to the (100) plane even by the subsequent rolling treatment, and the occupancy of the (100) plane is less than 90%, It is not preferable because the capacitance is lowered. More preferably, the homogenization treatment time is 5 to 15 hours.

Intermediate annealing conditions: 180 to 260 ° C., 1-2
After homogenizing for 0 hours , hot rolling is performed, and then cold rolling is performed.
Then, after this cold rolling, intermediate annealing is performed. The intermediate annealing temperature is 180 to 260 ° C. When the intermediate annealing temperature is less than 180 ° C., the crystal grains on the (100) plane hardly grow,
It is not preferable because the occupation ratio of the (00) plane is less than 90% and the electrostatic capacity is lowered. Intermediate processing temperature is 260
When it exceeds ℃, crystal grains other than (100) plane grow,
The occupancy of the (100) plane is unlikely to be 90% or more, and the capacitance is lowered, which is not preferable. More preferably,
The intermediate annealing temperature is 200 to 240 ° C.

The intermediate annealing time is 1 to 20 hours. If the intermediate annealing time is less than 1 hour, the crystal grains of the (100) plane hardly grow, the occupancy of the (100) plane is less than 90%, and the capacitance is lowered, which is not preferable.
When the intermediate annealing time exceeds 20 hours, crystal grains other than the (100) plane grow and the occupancy of the (100) plane does not easily reach 90% or more, and the capacitance decreases. More preferably, the intermediate annealing time is 5 to 15 hours.

Final cold rolling condition: Final cold rolling after intermediate annealing of 5 to 25% reduction . The rolling reduction in the final cold rolling is 5 to 25%. If the rolling reduction is less than 5%, the amount of strain is small, and it becomes difficult to rotate on the (100) plane.
The occupancy of the (0) plane is less than 90%, and the electrostatic capacity is lowered, which is not preferable. When the rolling reduction exceeds 25%, the amount of strain is large, the growth of the planes other than the (100) plane proceeds, the occupation rate of the (100) plane does not easily reach 90% or more, and the capacitance decreases. Therefore, the rolling reduction at the final cold rolling is 5 to 25%, more preferably 10 to 20%.
Is.

Hydroxide film: 0.010 to 0.200 g /
m ^{2 After the} final cold rolling, 0.010 to 10
An Al hydroxide film of 0.200 g / m ² is formed. If the hydroxide film is less than 0.010 g / m ^2, there are only 25 γ-Al ₂ O ₃ crystals on the foil surface and less than 25 μm ² μ3 of γ-Al ₂ O ₃ crystals are present, and the starting point of the etch pit is small. It is not preferable because it is easily formed and the electrostatic capacity is reduced. On the other hand, if the hydroxide film exceeds 0.200 g / m ² , the density of γ-Al ₂ O ₃ crystals is likely to be different, and local dissolution occurs to lower the capacitance, which is not preferable.

As a method of forming a hydroxide film of 0.010 to 0.200 g / m ^{2 on} the surface of the aluminum foil in this way, the conductivity at 75 to 95 ° C. is 10 μS.
The aluminum foil may be immersed in the following pure water for 30 to 250 seconds.

Final annealing treatment conditions: vacuum or inert gas
The final annealing treatment is performed in an atmosphere at 480 to 620 ° C. for 1 to 5 hours in vacuum or in an inert gas such as nitrogen gas or argon gas (oxygen concentration is 20 ppm or less). When annealing at a temperature of 480 to 620 ° C. in the atmosphere,
This is not preferable because the thickness of the oxide film becomes extremely high and the capacitance decreases. The pressure in the furnace is preferably about 1 × 10 ^-2 Torr under vacuum, and about 600 to 760 Torr under an inert gas atmosphere.

The annealing temperature is 480 to 620 ° C. When the annealing temperature is lower than 480 ° C, the occupation ratio of the (100) plane is 90
% Or more and it is difficult to reduce the capacitance, which is not preferable. On the other hand, if the annealing temperature exceeds 620 ° C., diffusion bonding (blocking) between foils occurs, which is not preferable. More preferably, the final annealing temperature is 500-590 ° C.
And

The annealing time is 1 to 5 hours. If the annealing time is less than 1 hour, the occupancy of the (100) plane is unlikely to be 90% or more, and the capacitance is lowered, which is not preferable. If the annealing time exceeds 5 hours, diffusion bonding (blocking) between the foils occurs, which is not preferable. More preferably, the final annealing time is 2 to 4 hours.

[0027]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples. A slab having the purity shown in Table 1 below was produced by a semi-continuous casting method, the slab was subjected to a homogenization treatment in the production process shown in Table 1, hot rolling was performed, and cold rolling was performed while sandwiching intermediate annealing. A foil with a thickness of 100 μm was obtained. Then, the foil (1
000 mm width coil) was dipped to form a hydroxide film, the coil width was adjusted to 500 mm, and the final annealing was performed to obtain an O material. Using the obtained aluminum foil as a sample,
The density of γ-Al ₂ O ₃ crystals on the foil surface, the electrostatic capacity, the weight change value before and after immersion in pure water, and the occupancy of the (100) plane were investigated.

Measurement of weight change before and after immersion in pure water The foil before and after immersion in pure water was sampled in a 150 mm square, and the weight was measured to calculate (weight after immersion in pure water)-(weight before immersion in pure water). Then, this was converted to g / m ² .

Electrolytic etching conditions: Dipped in hydrochloric acid having a concentration of 5% by weight at 85 ° C. to obtain 100 mA.
Direct current etching is performed for 1000 seconds at a current density of / cm ² .

Chemical conversion treatment conditions Phosphoric acid: 0.25 ml and ammonium phosphate: 1.4 g were added to 1 liter of pure water, and the liquid temperature was 85 ± 2.5 ° C.
The formation time was 25 minutes, and the formation treatment was performed at a formation voltage of 375V.

Capacitance measurement In 1 liter of pure water, boric acid: 50 g, citric acid: 50
g and ammonia: 50 ml was added, and the liquid temperature was 30 ± 5.
The measurement was performed using a universal bridge under the conditions of ° C and frequency: 120 Hz. The measurement site is the central part of the coil.

Occupancy rate measurement of (100) plane Macro etching was carried out with hydrochloric acid, nitric acid and hydrofluoric acid,
The area ratio was measured by an image analyzer by comparison with a standard sample prepared in advance. The measurement site is the central part of the coil.

Density measurement of γ-Al ₂ O ₃ crystal on foil surface The foil surface was observed by SEM and photographed at three places.
The density of the γ-Al ₂ O ₃ crystal was determined based on this photograph.
The magnification was 10,000 times, and the density was obtained from the average value at three points. The observation site is the central part of the coil.

[0034]

[Table 1]

[0035]

[Table 2]

Γ-Al on the surface of the obtained aluminum foil
Table 2 shows the measurement results of the ₂ O ₃ crystal density, capacitance, weight change value before and after immersion in pure water, and (100) plane occupancy. As is clear from Table 2, No. 1 according to the embodiment of the present invention. The aluminum foils 1 to 1 have high capacitance. On the other hand, the aluminum foil of the comparative example outside the scope of the present invention has a low capacitance.

[0037]

As described above, since the aluminum foil according to the present invention is excellent in electrolytic etching property, it is possible to manufacture an aluminum foil for high voltage of an electrolytic capacitor having a high capacitance. When applied, it has an industrially remarkable effect that a high-performance electrolytic capacitor can be obtained.

Claims (3)

[Claims] 1. A slab of pure aluminum having a purity of 99.90% by weight or more is homogenized at 450 to 620 ° C. for 1 to 20 hours, followed by hot rolling and cold rolling.
Intermediate annealing treatment is performed by heating at 80 to 260 ° C. for 1 to 20 hours, and then final cold rolling is performed at a reduction rate of 5 to 25%, and then the obtained aluminum foil is subjected to an electrical conductivity of 10 μS at 75 to 95 ° C. An aluminum foil for electrolytic capacitor high voltage, which is characterized in that it is immersed in the following pure water for 30 to 250 seconds and further heated at 480 to 620 ° C. for 1 to 5 hours in a vacuum or an inert gas atmosphere for final annealing treatment. Production method. 2. The aluminum foil for electrolytic capacitor high voltage according to claim 1, wherein the aluminum foil obtained has 25 to 1000 crystals / mm ² of γ-Al ₂ O _{3 on} the surface thereof. Production method. 3. The surface is exposed to 0.0 by immersion in the pure water.
The method for producing an aluminum foil for high voltage of an electrolytic capacitor according to claim 1 or 2, wherein a hydroxide film of 10 to 0.200 g / m ² is formed.