JPH11172389A - Production of aluminum foil for electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing aluminum foil for an electrolytic capacitor in which, at the time of subjecting an aluminum foil coil to annealing treatment, the seizure of the aluminun foil and the discoloration of both edge parts can be prevented, further, the dispersion of capacitance therein is made small, and its productivity is made excellent. SOLUTION: At the time of subjecting aluminum foil for an electric capacitor having >=99.90 wt.% purity to annealing treatment, the annealing treatment is composed of a temp. rising stage in which the atmosphere at least at the time of starting the temp. rising is composed of an inert gas, a holding stage in which the holding temp. lies in the range of 400 to 600 deg.C and a temp. dropping stage. At the point of time in which the temp. in the inert gas atmosphere in the temp. rising stage reaches the range of >=400 deg.C, it is made a vacuum atmosphere of <=10<-1> Torr, the annealing treatment is continued while the vacuum atmosphere is held, and at the optional point of time before the temp. reaches <400 deg.C, the atmosphere is made the one of an inert gas.

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 an electrolytic capacitor,
The present invention relates to a method for annealing aluminum foil.

[0002]

2. Description of the Related Art In general, an aluminum electrolytic capacitor comprises an anode having an aluminum oxide film formed on the surface of an aluminum foil, a cathode having no aluminum oxide film formed thereon, and an electrolytic solution. The aluminum foil for the electrolytic capacitor is a hot or cold rolled pure aluminum slab having a purity of 99.9% or more, which is turned into an aluminum foil having a thickness of about 100 μm. The aluminum foil is subjected to annealing treatment, surface etching treatment, and anode treatment. It is manufactured by performing an oxidation treatment.

[0003] Since the capacitance of an electrolytic capacitor is proportional to the surface area of an electrode, an etching process is performed to increase the surface area of an aluminum foil as an anode. In this etching treatment, a high-density etching pit is formed on the surface of the aluminum foil by immersing the aluminum foil coil in an etching solution containing hydrochloric acid as a main component and applying a current. The formation of the etching pits increases the surface area of the foil. The etched aluminum foil for an electrolytic capacitor has an electrostatic capacity per unit area several tens times that of an untreated aluminum foil for an electrolytic capacitor. Further, as the amount of increase in the surface area due to the etching process is larger, the amount of aluminum foil used for the capacitor can be reduced, which can contribute to downsizing of the capacitor and resource saving of aluminum. For this reason, a method of manufacturing an aluminum foil for an electrolytic capacitor having a larger surface area has been studied.

[0004] In particular, the annealing step is important for the anode foil of the electrolytic capacitor for medium and high pressure. This is because the annealing process increases the occupation ratio of the aluminum (100) plane on the foil surface and aligns the crystal orientation, so that etching pits are formed at a high density on the foil surface, and furthermore, tunnels are formed vertically from the foil surface. This is because the surface area of the aluminum foil increases. From various attempts, it has been found that it is preferable to perform the annealing treatment in a vacuum atmosphere or an inert gas atmosphere, and at present, this method is employed.

[0005]

In the case where all of the above annealing treatments are performed in a vacuum atmosphere, heat from a heat source is mainly transmitted to the outer peripheral portion of the coil because radiant heat transfer is dominant. In addition, there has been a problem that the temperature of the coil surface is locally increased, and the aluminum foil wound in a coil shape in that portion is likely to be seized. In addition, since radiative heat transfer is dominant and there is no medium for conducting heat, there is no heat conduction by convection, there is a problem that a long time is required for the temperature raising and lowering steps and the productivity is extremely low.

On the other hand, when the above-mentioned annealing treatment is all performed in an inert gas atmosphere, it is difficult to remove the rolling oil applied to the surface of the aluminum foil, so that the rolling oil tends to remain. However, there has been a problem that the color is oxidized and discolored. In addition, due to the discoloration, the degree of the etching process differs between the center portion and both end portions of the aluminum foil in the post-etching process, and there is a problem that the capacitance is different in the coil width direction. Further, in this case, both ends of the coil are discarded and only the center portion of the coil is used, so that there is a problem that productivity of the aluminum foil for the electrolytic capacitor is reduced.

Therefore, in order to solve the above-mentioned problems, a method of annealing the aluminum foil after adjusting the inside of the furnace in which the annealing treatment is performed to an inert gas atmosphere of 1 to 500 Torr, or an inert gas or vacuum atmosphere. Then, a method is proposed in which the temperature is maintained at 300 to 350 ° C. for 3 to 6 hours during the temperature raising step of the annealing treatment. However, even with the above-described method, there is basically no change in annealing in an inert gas or vacuum atmosphere, and the above-mentioned problem has not been completely solved. Furthermore, a method of degreasing the rolling oil applied to the aluminum foil and annealing in an inert gas atmosphere is also conceivable, but performing degreasing causes an increase in the number of steps, and lowers the productivity of the aluminum foil for electrolytic capacitors. There were challenges.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and when an aluminum foil coil is subjected to an annealing treatment, it is possible to prevent the aluminum foil from burning or discoloring at both ends and to prevent electrostatic capacity. It is an object of the present invention to provide a method for manufacturing an aluminum foil for an electrolytic capacitor, which has a small variation in the thickness and is excellent in productivity.

[0009]

In order to achieve the above object, the present invention employs the following constitution. The method for producing an aluminum foil for an electrolytic capacitor of the present invention has a purity of 99.
In annealing an aluminum foil for an electrolytic capacitor of 90% by weight or more, the annealing treatment is performed at least in a heating step in which the atmosphere at the start of the heating is an inert gas atmosphere, and a holding temperature of 400 ° C to 600 ° C. a holding step in the range of, consists of a cooling step, wherein at any time after the temperature reaches the range of more than 400 ° C. inert gas atmosphere in the heating step, 10 ^-1 Torr vacuum pressures below The annealing process is continued while maintaining the vacuum atmosphere, and the atmosphere is changed to an inert gas atmosphere at an arbitrary point before the temperature becomes lower than 400 ° C.

The method for producing an aluminum foil for an electrolytic capacitor according to the present invention is the method for producing an aluminum foil for an electrolytic capacitor described above, wherein the temperature holding time for holding the holding temperature is 1 hour or more and 10 hours or less. It is characterized by being a range.

The method for producing an aluminum foil for an electrolytic capacitor according to the present invention is the method for producing an aluminum foil for an electrolytic capacitor described above, wherein the vacuum holding time for maintaining the vacuum atmosphere is 1 hour or more and 10 hours or less. It is characterized by being a range. The method for producing an aluminum foil for an electrolytic capacitor according to the present invention is the method for producing an aluminum foil for an electrolytic capacitor described above, wherein a vacuum atmosphere having a pressure of 10 ^-1 Torr or less is provided before performing the temperature raising step. An inert gas atmosphere is provided later.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. The purity of the aluminum foil used as the raw material of the aluminum foil for electrolytic capacitors is 99.90.
% By weight, more preferably 99.98% by weight or more. When the purity of the aluminum foil is 99.90% by weight or less, the amount of impurities increases, so that the occupation ratio of the aluminum (100) plane on the foil surface by 90% is increased even by annealing.
It is difficult to achieve the above, and the amount of increase in the surface area due to the etching process is small, and the capacitance of the electrolytic capacitor cannot be increased.

As shown in FIG. 1, the annealing treatment in the method for manufacturing an aluminum foil for an electrolytic capacitor includes a heating step,
It consists of a holding step and a cooling step.

In the heating step, the aluminum foil coil is heated at an appropriate heating rate. The atmosphere in the annealing furnace at this time needs to be an inert gas atmosphere at least at the start of temperature rise. As the inert gas, a so-called rare gas such as helium or argon, or nitrogen is used. When the entire temperature rise process is performed in a vacuum atmosphere, radiant heat transfer becomes dominant, heat from the heat source is mainly transmitted to the outer peripheral portion of the coil, and the temperature of the coil locally rises, and the coil is wound. The resulting aluminum foils are liable to burn or roll off, and since there is no medium for conducting heat, it takes a long time to raise the temperature and the productivity of the aluminum foil for electrolytic capacitors is undesirably reduced. In addition, when all steps of the temperature raising step are performed in an air atmosphere, a thick film of aluminum oxide is formed on the surface of the aluminum foil by oxygen in the air, and the etching process is not performed efficiently. This is not preferable because the increase does not occur and the capacitance of the electrolytic capacitor decreases.

Prior to performing the temperature raising step, a vacuum atmosphere having a pressure of preferably 10 ^-1 Torr or less, more preferably 10 ^-2 Torr or less is formed in order to exhaust oxygen in the furnace. An atmosphere is desirable. Pressure 1
At 0 ⁻¹ Torr or higher, the amount of oxygen remaining in the furnace is large, and a thick aluminum oxide film is formed on the surface of the aluminum foil by the annealing treatment, and the etching treatment is not performed efficiently. This is not preferable because the increase does not occur and the capacitance of the electrolytic capacitor decreases.

The holding temperature in the holding step is preferably in the range of 400 ° C. to 600 ° C.
It is more preferable that the temperature be in the range of not less than 580 ° C. If the holding temperature is less than 400 ° C., it is difficult to make the occupation ratio of the aluminum (100) plane of the aluminum foil surface to 90% or more, the increase in the surface area of the aluminum foil due to etching pits is small, and the electrostatic capacitance of the electrolytic capacitor is small. It is not preferable because the capacity cannot be increased.
On the other hand, if the holding temperature exceeds 600 ° C., burning between the aluminum foils occurs, which is not preferable.

The temperature holding time for holding the holding temperature is preferably in the range of 1 hour to 10 hours, preferably 3 hours.
More preferably, the time is in the range of at least 8 hours. If the temperature holding time is less than 1 hour, it is difficult to make the occupation ratio of the aluminum (100) plane of the foil surface to 90% or more, the increase in the surface area of the aluminum foil due to etching pits is small, and the electrostatic capacitance of the electrolytic capacitor is small. It is not preferable because the capacity cannot be increased. On the other hand, if the temperature holding time exceeds 10 hours, burning between the aluminum foils occurs, and the productivity is undesirably reduced.

At any point after the temperature of the inert gas atmosphere reaches a range of 400 ° C. or more in the temperature raising step, 10
It is necessary to use a vacuum atmosphere having a pressure of ^-1 Torr or less. Here, at an arbitrary point, the vacuum atmosphere may be used immediately after the temperature of the inert gas atmosphere reaches 400 ° C., or the vacuum atmosphere may be used after a certain time has elapsed since the temperature reached 400 ° C. It is good. That is, if the temperature reaches a range of 400 ° C. or higher, a vacuum atmosphere may be set in the middle of the temperature raising step as shown in FIG.
Further, as shown in FIG. 3, a vacuum atmosphere may be provided from the beginning or the middle of the holding step. More preferably, the vacuum atmosphere is set at any time after the temperature of the inert gas atmosphere reaches a range of 450 ° C. or higher.

In order to bring the inside of the furnace into a vacuum atmosphere, the inert gas in the furnace is evacuated by a vacuum pump or the like until a predetermined pressure is reached. The pressure in the vacuum atmosphere is preferably as low as possible within a range of 10 ^-1 Torr or less. If the pressure in a vacuum atmosphere exceeds 10 ^-1 Torr, discoloration occurs at both ends of the coil, and the capacitance in the width direction of the aluminum foil is different, which is not preferable.

Further, when the pressure inside the furnace reaches a predetermined pressure,
Subsequently, the annealing process is continued while maintaining the vacuum atmosphere. The vacuum holding time for maintaining the vacuum atmosphere is preferably in the range of 1 hour to 10 hours, more preferably in the range of 3 hours to 8 hours. If the vacuum holding time is less than 1 hour, discoloration occurs at both ends in the width direction of the aluminum foil coil, and the capacitance in the width direction of the aluminum foil differs, which is not preferable. If the vacuum holding time exceeds 10 hours, burning between the aluminum foils occurs, which is not preferable.

However, when the temperature is lowered, at least the temperature is 400 ° C.
At any point before reaching the range below, it is necessary to switch from a vacuum atmosphere to an inert gas atmosphere. Here, at an arbitrary time, the reason is that if the vacuum holding time ends in the middle of the holding step, an inert gas atmosphere may be set in the middle of the holding step as shown in FIG. If the vacuum holding time ends at the beginning or in the middle of the process,
As shown in FIG. 2, an inert gas atmosphere may be set at the beginning or in the middle of the temperature lowering step. Further preferably, the temperature of the inert gas atmosphere is less than 450 ° C., more preferably,
The inert gas atmosphere is preferably set at an arbitrary point after the temperature of the inert gas atmosphere reaches a range of less than 500 ° C.

Here, the inert gas atmosphere is used because when the temperature is lowered in the air, the oxygen in the air forms a thick aluminum oxide film on the foil surface, and the etching process is not performed efficiently. It is not preferable because the surface area is not increased and the capacitance of the electrolytic capacitor is reduced. Also, if the temperature is lowered in a vacuum atmosphere, radiative heat transfer becomes dominant, and the heat of the aluminum foil is not efficiently dissipated because there is no medium to transmit the heat. It is not preferable because the productivity of the aluminum foil is lowered and the roll-up occurs. Here, the term “rolling” means that when the aluminum foil is wound into a roll, the aluminum foil sags below the center of the winding and a space is generated.

In the cooling step, the temperature of the aluminum foil coil is usually lowered by natural cooling or forced cooling.

According to the above-described method for producing an aluminum foil for an electrolytic capacitor, aluminum having a purity of at least 99.90% by weight is annealed, so that the occupancy of the (100) plane of the aluminum foil surface is at least 90%. It is possible to increase the surface area by the etching process, so that the capacitance of the electrolytic capacitor can be increased. According to the method for manufacturing an aluminum foil for an electrolytic capacitor described above, the atmosphere in the temperature raising step is an inert gas atmosphere at least at the start of the temperature raising. Is shortened, so that the productivity of the aluminum foil can be increased. In addition, before performing the above-described temperature raising step, since the inside of the furnace for performing the annealing process is set to a vacuum atmosphere of 10 ^-1 Torr or less and the inert gas is introduced, the amount of oxygen in the furnace is reduced, and the surface of the aluminum foil is reduced. The formation of an aluminum oxide film can be prevented.

According to the method for manufacturing an aluminum foil for an electrolytic capacitor described above, the temperature of the inert gas atmosphere is 400 ° C.
At any point after reaching the above range, 10 ^-1 Torr
Since the vacuum atmosphere having the following pressure is used, discoloration of the aluminum foil can be prevented, and the capacitance can be made uniform in the width direction of the coil. In addition, the holding temperature in the holding step is set to 400 ° C. or more and 600 ° C. or less, and the temperature holding time is set to 1 hour or more and 10 hours or less. The occupancy can be 90% or more.

Further, according to the above-mentioned method for manufacturing an aluminum foil for an electrolytic capacitor, the vacuum atmosphere is changed to an inert gas atmosphere at any time before the temperature becomes lower than 400 ° C., so that the heat of the aluminum foil can be efficiently reduced. The heat can be radiated well, the temperature can be reduced in a short time, the productivity of the aluminum foil for an electrolytic capacitor can be improved, and the aluminum foil can be prevented from rolling down.

[0027]

The present invention will be described below in detail with reference to examples. (Example) Purity 99.99%, thickness 100 μm, width 50
An aluminum foil coil having a weight of 0 mm and a weight of 20 kg was placed in a furnace for annealing treatment, and the inside of the furnace was evacuated by a vacuum pump to a vacuum atmosphere at a pressure of 10 ^-5 to 10 ^-1 Torr, and then argon gas was introduced. did. Next, the temperature is raised to 500 to 550 ° C. at a constant rate, and
After holding for a time, the temperature was lowered. At the same time, the argon gas in the furnace was evacuated with a vacuum pump to obtain a vacuum atmosphere at a pressure of 10 ^-4 Torr. The vacuum atmosphere was an arbitrary point in time when the temperature in the furnace became 400 ° C. or higher, and an arbitrary point in time before the temperature became lower than 400 ° C., and the rest was an argon gas atmosphere. Thus, annealing treatment was performed on the aluminum foil under various conditions to obtain an annealed aluminum foil. Table 1 shows specific annealing conditions.

(Comparative Example) Purity 99.99%, thickness 100
An aluminum foil coil having a thickness of 500 μm, a width of 500 mm and a weight of 20 kg was set in a furnace for annealing treatment, and the inside of the furnace was evacuated by a vacuum pump to a vacuum atmosphere at a pressure of 10 ^{−5 to 1} Torr. Further, depending on the sample, argon gas or air was introduced into the furnace. Next, at a constant heating rate,
The temperature was raised to 630 ° C., the temperature was maintained for 0.5 to 13 hours, and then the temperature was lowered. At the same time, the argon gas in the furnace was evacuated with a vacuum pump to make a vacuum atmosphere with a pressure of 10 ^{-4 to} 760 Torr. The temperature in the furnace is 37
From an arbitrary point when the temperature becomes 0 to 550 ° C. or higher, 370 to 5
It was an arbitrary time before the temperature became lower than 50 ° C. In addition, the evacuation by the vacuum pump was not performed for some samples. Furthermore,
Depending on the sample, after maintaining the vacuum atmosphere, a subsequent vacuum atmosphere or air was introduced. In this way, the aluminum foil is subjected to annealing under various conditions,
An annealed aluminum foil was obtained. Table 1 shows specific annealing conditions.

[0029]

[Table 1]

With respect to the aluminum foil obtained as described above, the discoloration of the edge of the aluminum foil, the thickness of the oxide film, the capacitance and the occupancy of the (100) plane were analyzed and examined as follows. Table 2 shows the results.

(Discoloration of Coil End) The coil was visually observed to check for discoloration. The evaluation was x when there was discoloration, ○ when there was no discoloration, and Δ when the presence or absence of discoloration was not clear. (Thickness of oxide film)
Analyzed by X-ray photoelectron spectroscopy.

(Electrostatic capacity)
After being immersed in an etching solution mainly containing 0 wt% hydrochloric acid, the solution temperature was 80 ° C., and the current density was 100 mA / cm ² (D
C) The etching process was performed under the condition of an etching time of 600 seconds. Next, the etched aluminum foil was treated with 100 g / l boric acid and 1.0 g / ammonium pentaborate.
immersion in an electrolyte solution having a concentration of
After adjusting to 2.5 ° C., formation voltage 270 V, formation time 1
Anodizing treatment was performed under the condition of 0 minutes to form an aluminum oxide film on the surface of the aluminum foil, thereby preparing an aluminum foil for an electrolytic capacitor. The aluminum foil for an electrolytic capacitor is immersed in an electrolytic solution having a concentration of boric acid of 50 g / l and borax of 45 g / l at a liquid temperature of 25 ± 5 ° C.
The capacitance was measured by an LCR meter under the condition of a frequency of 120 Hz.

((100) plane occupation ratio) Macroetching was performed on the annealed aluminum foil using hydrochloric acid, nitric acid and hydrofluoric acid. Next, the occupancy of the (100) plane at the center of the aluminum foil was measured using an image analyzer.

[0034]

[Table 2]

In the aluminum foils of Examples 1 to 5, no discoloration was observed at the ends of the coil, and an oxide film having an appropriate thickness was formed on the surface of the aluminum foil. The occupancy of the (100) plane of the aluminum foil surface is 95% in all cases.
As described above, it can be seen that the capacitance is higher than those of Comparative Examples 1 to 7.

In the aluminum foils of Comparative Examples 1 and 10, since the entire holding process was performed in an argon atmosphere, discoloration occurred at the coil end, a thick oxide film was formed, and the capacitance was reduced. In the aluminum foil of Comparative Example 2, although the discoloration of the coil end portion and the decrease in the capacitance were not recognized,
Since all steps of the annealing treatment were performed in a vacuum atmosphere, seizure between the aluminum foils occurred. In the aluminum foil of Comparative Example 3, the pressure of the vacuum atmosphere was 1 T in the holding step.
Due to the high orr, discoloration occurs at the coil end, a thick oxide film is formed, and the capacitance is reduced.

In the aluminum foils of Comparative Examples 4 and 5, no discoloration of the coil end portion and no decrease in the capacitance were observed, but the time required for the temperature lowering step was reduced because the temperature lowering step was performed in a vacuum atmosphere. It is about 1.5 to 2 times that of Examples 1 to 3 or other comparative examples, and the productivity is very low. The aluminum foils of Comparative Example 6 and Comparative Example 7 were in the air atmosphere in the temperature raising step or the temperature lowering step, the oxide film was formed very thick (measurable by X-ray photoelectron spectroscopy), and the capacitance was significantly large. Is declining.

In the aluminum foil of Comparative Example 8, since the holding time in the holding step was short, the occupancy of the (100) plane was low, the surface area of the aluminum foil surface was small, and the capacitance was low. The aluminum foil of Comparative Example 9 was
In the holding step, since the pressure in the vacuum atmosphere is high, discoloration occurs at the coil end, a thick oxide film is formed, and the capacitance is reduced.

In the aluminum foil of Comparative Example 11, since the furnace pressure before the start of heating was 1 Torr, exhaust was insufficient and oxygen remained in the furnace, and the oxygen oxidized the surface of the aluminum foil. As a result, discoloration occurs, the oxide film is formed thick, and the capacitance is reduced. Comparative Example 1
The aluminum foil of No. 2 has no problem in discoloration, thickness of oxide film, capacitance and occupancy of (100) plane,
Due to the long holding time (13 hours), burning between the aluminum foils occurred.

The aluminum foil of Comparative Example 13 has a low holding temperature (370 ° C.) and thus cannot have a high occupancy of the (100) plane, and thus has a low capacitance.
The aluminum foil of Comparative Example 14 had no problem with discoloration, thickness of oxide film, capacitance, and occupancy of the (100) plane. However, since the holding temperature was high (630 ° C.), the aluminum foils were burned together. There has occurred.

[0041]

As described in detail above, according to the method for manufacturing an aluminum foil for an electrolytic capacitor of the present invention,
When annealing the aluminum foil, the annealing treatment,
A heating step in which the atmosphere at least at the start of heating is an inert gas atmosphere, and a holding temperature of 400 ° C. or more and 600 ° C.
The temperature range of the inert gas atmosphere in the temperature raising step is 400 ° C.
At any point after reaching the above range, 10 ^-1 Torr
Since the annealing treatment is continued while maintaining the vacuum atmosphere under the following pressure and at any time before the temperature reaches a range of less than 400 ° C., the atmosphere is set to an inert gas atmosphere. The occupation ratio of the (100) plane of the surface can be made 90% or more, and the amount of increase in the surface area due to the etching process increases, so that the capacitance of the electrolytic capacitor can be increased. In addition, the seizure and rolling of the aluminum foils are prevented, and the time for raising the temperature is shortened, so that the productivity of the aluminum foil can be increased. Further, the discoloration of the aluminum foil can be prevented, and the capacitance can be made uniform in the width direction of the coil. Furthermore, the heat of the aluminum foil can be efficiently radiated, the temperature can be reduced in a short time, and the productivity of the aluminum foil for an electrolytic capacitor can be improved.

According to the method for manufacturing an aluminum foil for an electrolytic capacitor of the present invention, the holding temperature in the holding step is set to 40.
The temperature is set to 0 ° C. or more and 600 ° C. or less, and the temperature holding time is set to 1 hour or more and 10 hours or less.
The occupancy of the surface can be 90% or more.

According to the method for producing an aluminum foil for an electrolytic capacitor of the present invention, the inside of the furnace is set to a vacuum atmosphere of 10 ^-1 Torr or less before performing the temperature raising step. It is possible to prevent an excessive increase in the thickness of the oxide film, so that a decrease in capacitance can be prevented.

[Brief description of the drawings]

FIG. 1 is a view for explaining a temperature raising step, a holding step, and a temperature lowering step in an annealing treatment of an aluminum foil according to an embodiment of the present invention.

FIG. 2 is a view for explaining a state of an atmosphere in a furnace in an annealing process of an aluminum foil according to an embodiment of the present invention.

FIG. 3 is a view for explaining a state of an atmosphere in a furnace in an annealing process of an aluminum foil according to an embodiment of the present invention.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C22F 1/00 661 C22F 1/00 691B 691 691C 691Z H01G 9/04 346

Claims (4)

[Claims] When performing an annealing process on an aluminum foil for an electrolytic capacitor having a purity of 99.90% by weight or more, the annealing process includes a heating step in which an atmosphere at least at the start of heating is an inert gas atmosphere; A holding step in which the holding temperature is in a range of 400 ° C. or more and 600 ° C. or less; and a temperature lowering step.
At any point after reaching the range above 10 ° C., 10 ⁻¹ Torr
a vacuum atmosphere having a pressure equal to or lower than r, the annealing treatment is continued while maintaining the vacuum atmosphere, and at any time before the temperature becomes lower than 400 ° C., the atmosphere is changed to an inert gas atmosphere. Manufacturing method of aluminum foil for capacitors. 2. The method for producing an aluminum foil for an electrolytic capacitor according to claim 1, wherein a temperature holding time for holding the holding temperature is in a range of 1 hour to 10 hours. 3. The method for producing an aluminum foil for an electrolytic capacitor according to claim 1, wherein the vacuum holding time for maintaining the vacuum atmosphere is in a range of 1 hour to 10 hours. 4. The method according to claim 1, wherein the step of increasing the temperature is 10 ^-1 Torr.
The method for producing an aluminum foil for an electrolytic capacitor according to claim 1, wherein an inert gas atmosphere is formed after a vacuum atmosphere having a pressure of r or less is set.