JP2000204456A - Production of aluminum foil for electrolytic capacitor electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the increase of the capacitance of a capacitor and its miniaturization by improving the surface roughening treating ratio of aluminum foil used for an electrolytic capacitor. SOLUTION: As to the method for producing aluminum foil for an electrolytic capacitor electrode in which aluminum foil is subjected to final annealing and is thereafter subjected to surface roughening treatment, in the temp. rising stage in final annealing, aluminum foil is heated in an oxygen-added reducing atmosphere contg. 0.01 to 1.0% oxygen and 0 to 50% inert gas, and the balance reducing gas, and, subsequently, in a stage including a holding stage, the aluminum foil is heated in an oxygen-nonadded reducing atmosphere contg. 0 to 25% inert gas, and the balance reducing gas and is annealed. Its expansing ratio in surface roughening treatment is improved, the capacitance of an electrolytic capacitor is increased, and its miniaturization is made possible.

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 an electrode of an electrolytic capacitor, and more particularly, to a method suitable for an anode foil for medium and high pressure.

[0002]

2. Description of the Related Art In general, the production of an aluminum foil for an electrolytic capacitor electrode requires a purity of 99.9% or more (for example, a purity of 99.9%).
Pure aluminum of 9.96% or more)
After cold rolling to a thickness of about 100 μm and final annealing, a surface roughening treatment and a predetermined chemical treatment (anodic oxidation) are performed. The surface roughening treatment described above is intended to increase the surface area of the aluminum foil, and is generally performed electrochemically in an electrolytic solution mainly containing hydrochloric acid to form a large number of capillary pits. The individual pits extend perpendicular to the foil surface, resulting in an increase in foil surface area,
Produces higher capacitance than untreated ones. The larger the surface area expansion rate in the roughening, the smaller the amount of foil used when used for the electrode of the capacitor, which can contribute to miniaturization and resource saving. For this reason, capacitor manufacturers are studying the conditions of surface roughening treatment in order to increase the enlargement rate in the surface roughening process. Various studies have been made on foils that provide a ratio (magnification ratio). In order to provide a material capable of obtaining a high surface roughening rate, the present inventor previously changed the atmosphere in the final annealing to a reducing atmosphere from a conventional vacuum or an inert gas atmosphere to a reducing atmosphere. A method for improving the rate has been proposed (Japanese Patent Laid-Open No. Hei 8-222488). According to this method, the oxide film formed on the aluminum foil prior to the surface roughening treatment can be adjusted to an appropriate thickness and crystallization rate, and thus a large number of uniform pits are formed during the surface roughening treatment. It is expected that the surface roughening rate will be improved.

[0003]

The aluminum foil obtained by the above method can be used as an electrolytic capacitor to obtain an electrolytic capacitor having an improved capacitance per unit area. However, the degree of the improvement is lower than theoretically expected, and there is a problem that a sufficient surface roughening rate is not obtained. The present inventor has further researched and pursued the cause of the above-mentioned problem. As a result, the lubricating oil adhering to the rolled material (which eventually becomes aluminum foil) in the rolling process of manufacturing aluminum foil was subjected to final annealing. After that, it remains on the surface of the aluminum foil, which hinders the formation of pits during the surface roughening treatment, and thus causes unevenness of the oxide film.In addition, under the current annealing conditions,
It has been clarified that the pit formation density becomes coarse due to the increase in the thickness, and the surface roughening rate is lowered. The present inventors have completed the present invention based on such findings. That is, the present invention has been made in view of the above circumstances, and appropriately controls the oxide film thickness of the aluminum foil at the time of final annealing, and reliably removes oil adhering to the surface of the aluminum foil at the time of final annealing to obtain a roughened surface. An object of the present invention is to provide a method for producing an aluminum foil for an electrolytic capacitor electrode that can obtain a high surface roughening rate during the treatment.

[0004]

Means for Solving the Problems In order to solve the above problems, a first invention of a method for manufacturing an aluminum foil for an electrode of an electrolytic capacitor according to the present invention is to perform a final annealing on an aluminum foil, followed by a roughening treatment. A method for producing an aluminum foil for an electrolytic capacitor electrode, wherein 0.01 to 1.0% by volume of oxygen and 0 to 5%
The aluminum foil is heated in an oxygen-added reducing atmosphere containing 0% by volume of an inert gas and the balance substantially consisting of a reducing gas. Wherein the aluminum foil is heated and annealed in an oxygen-free reducing atmosphere consisting essentially of a reducing gas.

[0005] In a second aspect of the present invention, the method for producing an aluminum foil for an electrolytic capacitor electrode according to the first aspect is characterized in that the rate of temperature rise in an oxygen-added reducing atmosphere is 200 ° C / hour or less. The method for producing an aluminum foil for an electrolytic capacitor electrode according to the third invention is the method according to the first or second invention, wherein the oxygen-adding reducing atmosphere has a heating temperature of 350 to 350.
It is characterized in that it is maintained until it reaches 500 ° C.

In a fourth aspect of the present invention, there is provided a method for producing an aluminum foil for an electrolytic capacitor electrode according to any one of the first to third aspects, wherein the oxygen concentration is reduced when the oxygen-containing reducing atmosphere is shifted to the oxygen-free reducing atmosphere. Is characterized by providing a transition time for gradually decreasing the time. The method for producing an aluminum foil for an electrolytic capacitor electrode according to a fifth aspect of the present invention is the method according to any one of the first to fourth aspects, wherein the transition to the oxygen-free reducing atmosphere is performed by setting the heating temperature in the temperature increasing process to 500 ° C. It is characterized in that it is performed before crossing.

In a sixth aspect of the present invention, there is provided a method for manufacturing an aluminum foil for an electrolytic capacitor electrode according to any one of the first to fifth aspects, wherein the oxygen concentration in the oxygen-free reducing atmosphere is set to 0.1.
It is characterized in that it is regulated to less than 01% by volume. A method for producing an aluminum foil for an electrolytic capacitor electrode according to a seventh invention is characterized in that, in any one of the first to sixth inventions, the heating temperature in the holding step is set to 500 to 600 ° C.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The aluminum foil used in the present invention preferably has a purity of 99.9% or more, more preferably 99.96% or more. And the manufacturing method up to the final thickness is not particularly limited. The final thickness of the present invention is, of course, not particularly limited. However, the final thickness is usually about 0.1 mm.

[0009] The aluminum foil obtained by the above process is subjected to final annealing. In this annealing, the aluminum foil is heated in a reducing atmosphere through a heating process, a holding process, and a cooling process, and in that process, an atmosphere gas used is changed. That is, as described above, during the heating process, 0.01 to 1.0% by volume of oxygen and 0 to 50%
The aluminum foil is heated in an oxygenated reducing atmosphere comprising a volume% of inert gas and the balance substantially consisting of reducing gas. By containing a small amount of oxygen in the reducing atmosphere as described above, an oxide film of an appropriate thickness is formed on the aluminum foil surface by the reducing action of the reducing gas, and adheres to the aluminum foil surface by the oxidizing action of oxygen. The oil content is oxidized. The oxidized oil is decomposed and gasified in a high-temperature heating state, and is easily separated from the aluminum foil. If the oxygen concentration in the atmosphere is not more than 0.01% by volume, the above effect cannot be sufficiently obtained, and it becomes difficult to reliably remove oil from the surface of the aluminum foil. On the other hand, if too much oxygen is contained, the oxidizing action on the aluminum foil surface becomes excessive, the thickness of the oxide film becomes unnecessarily thick, and the subsequent roughening treatment cannot be performed well. For the same reason, it is desirable to set the lower limit to 0.02% by volume and the upper limit to 0.3% by volume. Due to the above-described appropriate oxygen concentration, an oxide film having an appropriate thickness (for example, 30 to 50 mm thick) on the aluminum foil surface and having no remaining rolling oil is formed.

In the present invention, the oxygen-added reducing atmosphere can be substantially composed of the above-mentioned small amounts of oxygen and a reducing gas. It may be made to be. Further, the inert gas has an effect of effectively removing oxidized oil from the surface of the aluminum foil, and also has an effect of effectively preventing the evaporated oxide oil from re-adhering to the aluminum foil. In order to surely obtain these effects, when an inert gas is contained, the content is desirably 10% by volume or more. However, the inert gas is a reducing gas (especially hydrogen)
Since the thermal conductivity is lower than that of, when the content of the inert gas is too large, the thermal conductivity in the atmosphere is deteriorated and the heating efficiency is reduced. On the other hand, if the content of the inert gas is too large, the content of the reducing gas is relatively too low, and the reducing action is impaired. From these points, the inert gas concentration is 5
The upper limit is 0% by volume. For the same reason, it is desirable to set the upper limit to 25%. In addition, as a reducing gas used in the present invention, hydrogen can be typically cited, but other gases such as CO and hydrocarbons can also be used. However, hydrogen is preferred from the viewpoint of reducing power and thermal conductivity. Examples of the inert gas include Ar and He. Generally, N _{2 is} also positioned as an inert gas. However, in the present invention, a reaction with the aluminum foil may occur in a high temperature region during annealing. It is desirable to use the gas to which it belongs. Note that a slight amount of moisture or impurities is allowed in the atmosphere, but it is desirable that these are as small as possible.

Although the above-mentioned oxygen-added reducing atmosphere is employed in the temperature raising process, it is not essential that the atmosphere be changed to the atmosphere during the entire temperature raising process. However, it is desirable to maintain the atmosphere from the beginning of the temperature rise until the heating temperature reaches 350 to 500 ° C. Note that the heating temperature in the above description indicates an ambient temperature. If the atmosphere is terminated at a heating temperature lower than the above range, the oil adhering to the aluminum foil surface is not sufficiently and reliably removed, and the oxidized oil that has scattered easily adheres again. It is desirable to maintain up to a heating temperature of 350 ° C. or higher. On the other hand, when the above atmosphere is maintained at a considerably high temperature, high-temperature oxidation is excessively promoted, and an oxide film thicker than a desired oxide film is formed on the aluminum foil surface due to the presence of the oxygen-added atmosphere. It will be easier. For this reason, it is desirable that the maintenance of the atmosphere be completed at 500 ° C. or less. Note that the lower limit is preferably 400 ° C. for the same reason.

Therefore, when the temperature range is in the middle of the heating process, it is desirable to remove the oxygen-containing reducing atmosphere during the heating process. The temperature rise during the temperature rise process
The higher the speed, the better the efficiency. However, in the present invention, it is desirable to set the temperature rising rate to 200 ° C./hour or less. This is because if the heating rate is high, the temperature reaches the above-mentioned temperature range before the above-mentioned oxidation and removal of the oil is sufficiently performed, and when the oil is removed from the oxygen-added reducing atmosphere, the oil remains on the aluminum foil surface. It will be left standing. In addition, if the atmosphere is maintained as it is, the temperature further rises, and the above-described problem occurs. Therefore, it is desirable that the heating rate be slow enough to oxidize and remove the oil, that is, 200 ° C./hour or less. After the heating in the oxygen-added reducing atmosphere is completed, the temperature raising rate is increased (for example, over 200 ° C. /
Time) is also possible.

After the above-described oxygen-added reducing gas atmosphere is completed, heating is performed in an oxygen-free reducing atmosphere in a process including a holding process. This means that after oxidizing and removing the oil, it is necessary to perform heating in a reducing atmosphere to which oxygen has not been added in order to uniformly form an oxide film of appropriately adjusted thickness on the aluminum foil surface. Because it becomes.
Here, if oxygen is added to the atmosphere, the temperature is considerably high and the oxidation is excessively advanced, and it becomes difficult to obtain an oxide film having an appropriate thickness. Therefore, in this atmosphere, it is desirable that oxygen is not added and oxygen contained as an impurity is regulated to less than 0.01% by volume.
Further, for the same reason, it is desirable to restrict the oxygen concentration to 0.001% by volume or less.

Further, this atmosphere may contain an inert gas in addition to the reducing gas. A small amount of the inert gas has an effect of preventing the scattered oil from re-adhering to the aluminum foil surface as described above, but on the other hand, lowers the thermal conductivity. In this atmosphere, a sufficient reducing action is required to uniformly form an oxide film having an appropriate thickness on the surface of the aluminum foil. Therefore, in this atmosphere, the reducing gas concentration is set to 75% by volume or more,
Even when an inert gas is added, its concentration is set to 25% by volume or less. For the same reason, the content of the reducing gas is 9
More preferably, the content is 0% by volume or more and the content of the inert gas is 10% by volume or less. The types of the reducing gas and the inert gas are the same as those described in the oxygen-added reducing gas atmosphere. The type of the reducing gas and the type of the inert gas can be changed between the oxygen-containing reducing atmosphere and the oxygen-free reducing atmosphere, but usually the same type is used.

Since it is difficult to immediately transition from the above-described oxygen-free reducing atmosphere to the oxygen-free reducing atmosphere, a transition period for gradually reducing the oxygen concentration from the oxygen-free reducing atmosphere can be provided. This transition period is desirably as short as possible, and it is desirable to transition to an oxygen-free reducing atmosphere until the heating temperature exceeds 500 ° C. This is because, during the transition period, the oxygen concentration is high and the atmosphere becomes considerably high in temperature, so that the oxidizing action becomes excessive and it becomes difficult to form an appropriate oxide film on the aluminum foil surface. The above-mentioned transition can be exemplified by a method in which a reducing gas to which no oxygen is added is gradually introduced into an atmosphere, for example, a heating furnace to lower the overall oxygen concentration. Further, in the above transition, it is possible to gradually decrease the concentration of the inert gas in addition to the concentration of the oxygen. In this case, too, the inert gas is not added to the atmosphere or the inert gas is added. The concentration of the inert gas can be gradually reduced by gradually introducing the reducing gas having a low concentration.

In the holding step after the temperature raising step, the holding and heating temperature is desirably set to 500 to 600 ° C. This is because it is desirable to raise the temperature to 500 ° C. or higher in order to obtain an appropriate oxide film (thickness) and an aluminum material (high cubic orientation structure) in a reducing gas atmosphere. It should be noted that the surface roughening rate in the surface roughening treatment is also improved by increasing the cubic orientation rate of the aluminum material. On the other hand, if the temperature is too high, excess oxygen causes partial seizure between the aluminum foils, so that the holding temperature is desirably 600 ° C. or lower.
Note that the lower limit is 5 in order to increase the cubic orientation in crystal structure.
30 ° C. is preferable, and the upper limit is preferably 580 ° C. for the above-mentioned reason. Further, the holding time is desirably 2 to 8 hours. This is because if the time is less than 2 hours, the cubic orientation ratio is insufficient, and if the time exceeds 8 hours, the above-mentioned foils cause seizure.

It is desirable to maintain an oxygen-free reducing atmosphere throughout the holding process, and it is also desirable to maintain the atmosphere in a high temperature region (for example, 500 ° C. or higher) during the subsequent cooling process. Further, it is desirable that the aluminum foil is not kept in an oxidizing atmosphere until the annealing is completed. Therefore, at a temperature lower than the high temperature range, it is possible to shift the atmosphere from a reducing atmosphere to an inert gas atmosphere. However, even in this atmosphere, the oxygen content is desirably regulated in the same manner as above (for example, less than 0.01% by volume). Note that the reactivity becomes lower in a temperature range lower than the above-mentioned high temperature range, so that, for example, nitrogen gas can be used as the inert gas. In the cooling process, since this annealing is held and heated at a relatively high temperature, if it is rapidly cooled, wrinkles are likely to be generated in the aluminum foil due to thermal stress, and minute cracks and the like also occur in the oxide film, and the rough surface afterwards The homogeneity in the chemical treatment is easily lost. Therefore, in the cooling process, it is desirable to control by furnace cooling or the like so that the cooling rate does not become too fast. Specifically, it is desirable to cool at a cooling rate of 200 ° C./hour or less on average.

The aluminum foil obtained by the above-mentioned final annealing has oil removed from its surface without fail, and has an oxide film having an appropriate thickness uniformly formed on the surface. This aluminum foil can be subjected to a surface roughening treatment by a conventional method. At the time of the surface roughening treatment, high-density and uniform capillary-like pits are formed, and a high surface roughening rate can be obtained. By forming high-density and uniform pits, an electrolytic capacitor using this aluminum foil can have a large capacitance.

[0019]

Embodiments of the present invention will be described below. Pure aluminum having a purity of 99.99% produced by a conventional method was finally cold-rolled to obtain a rolled hard aluminum foil having a thickness of 0.1 mm. This aluminum foil was finally annealed in a heating furnace under the conditions shown in Table 1. At that time, in the inventive materials (Nos. 1 to 12), an oxygen-added reducing atmosphere and an oxygen-free reduced atmosphere were combined, and the comparative materials (Nos.
In 17), annealing was performed in the atmosphere except for the conditions of the invention method. In the method of the present invention, as in the example shown in FIG. 1 (sample No. 1), heating is performed in an oxygen-added reducing atmosphere during the heating process, and then hydrogen gas without added oxygen is introduced into the furnace. Then, the amount of oxygen is gradually reduced, and the atmosphere is shifted to an oxygen-free reducing atmosphere during the temperature raising process, and this atmosphere is maintained during the holding process. Further, in these test materials, cooling is performed after holding and heating.
At a temperature of 300 ° C. or 300 ° C., nitrogen gas was gradually introduced into the furnace, and the inside of the furnace was finally replaced with nitrogen gas.

[0020]

[Table 1]

The aluminum foil obtained as described above includes:
Subsequently, after performing a surface roughening treatment and a chemical conversion treatment under the following conditions, the capacitance was measured. 1. Roughening treatment condition (1) the first step etching conditions (electrolytic etching) electrolyte solution HCl 1 mol / _l H 2 SO ₄ 3 mol _{/ l AlCl 3 · 6H 2 O} 60g / l electrolysis conditions Temperature 75 ° C. Current density 0 0.8 A / cm ² electrolysis time 40 seconds (2) Second stage etching condition (chemical etching) Etching solution (75 ° C.) H ₂ O: HNO ₃ (1: 1) Etching time: 300 seconds

2. Chemical formation conditions (270V) Chemical formation liquid Boric acid 100g / l Ammonium borate 1g / l Condition Temperature 85 ° C Current density 0.1A / cm ² Ultimate voltage 270V

Further, with respect to the test material, Al was dissolved with a bromo-methanol solution, and the oxide film floating on the petri dish was observed with a transmission electron microscope. The oxide film thickness was measured by the following equation using a photoelectron spectrometer (ESCA) manufactured by Shimadzu Corporation. Oxide film thickness (Å) = 23.7 ln (1 ÷ IM / IT) IM: Integrated intensity of metal Al peak IT: Integrated intensity of metal and Al oxide peaks The above measurement results are shown in Table 2.

[0024]

[Table 2]

As is evident from Table 2, by performing the final annealing in an appropriate atmosphere, the capacitance of the aluminum foil is clearly increased. On the other hand, when the oxygen-added reducing atmosphere and the oxygen-free reduced atmosphere were not appropriately combined, a high capacitance could not be obtained.
Also, among the test materials of the present invention, those in which the heating rate, oxygen concentration, inert gas concentration, and atmosphere transition temperature were appropriately adjusted, the increase in capacitance became more remarkable as compared with the other test materials. I was

[0026]

As described above, according to the method for manufacturing an aluminum foil for an electrolytic capacitor electrode of the present invention, the aluminum foil is subjected to a final annealing, and then a roughening treatment is performed. A manufacturing method, wherein a temperature rise in the final annealing is 0.01 to 1.0.
Volume% oxygen and 0-50 volume% inert gas,
The aluminum foil is heated in an oxygen-added reducing atmosphere in which the balance is substantially composed of a reducing gas, and thereafter, at least in a process including a holding process, contains 0 to 25% by volume of an inert gas, and the balance substantially includes the inert gas. Since the aluminum foil is annealed by heating in an oxygen-free reducing atmosphere composed of a reducing gas, oil on the surface of the aluminum foil is reliably removed during annealing, and an appropriate oxide film is formed on the surface. In this manner, a high surface roughening rate can be obtained during the surface roughening treatment. As a result, the capacitance per unit area is significantly increased, and the miniaturization and resource saving of the electrolytic capacitor are achieved. . In addition, since oil is removed at the time of final annealing, there is also an effect that a special cleaning step is not required and production efficiency is improved.

[Brief description of the drawings]

FIG. 1 is a graph showing a change in oxygen content during final annealing in one example of the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) C22F 1/00 691 C22F 1/00 691B H01G 9/04 346

Claims (6)

[Claims] 1. A method for producing an aluminum foil for an electrolytic capacitor electrode, wherein a final annealing is performed on an aluminum foil, and thereafter the aluminum foil is subjected to a surface roughening treatment. % Of oxygen and 0 to 50% by volume of an inert gas, with the balance heating the aluminum foil in an oxygenated reducing atmosphere consisting essentially of a reducing gas. , 0-2
An aluminum foil for an electrolytic capacitor electrode, wherein said aluminum foil is heated and annealed in an oxygen-free reducing atmosphere containing 5% by volume of an inert gas and the balance substantially consisting of a reducing gas. Production method 2. The method for producing an aluminum foil for an electrolytic capacitor electrode according to claim 1, wherein the rate of temperature rise in an oxygen-added reducing atmosphere is 200 ° C./hour or less. 3. The oxygen-added reducing atmosphere has a heating temperature of 3.
The method for producing an aluminum foil for an electrolytic capacitor electrode according to claim 1, wherein the temperature is maintained until the temperature reaches 50 to 500 ° C. 4. 4. The electrolysis according to claim 1, wherein a transition time for gradually reducing the oxygen concentration is provided when shifting from the oxygen-added reducing atmosphere to the oxygen-free reducing atmosphere. Manufacturing method of aluminum foil for capacitor electrode 5. The production of an aluminum foil for an electrolytic capacitor electrode according to claim 1, wherein the oxygen concentration in the oxygen-free reducing atmosphere is regulated to less than 0.01% by volume. Method 6. The heating temperature in the holding step is 500 to 600.
The method for producing an aluminum foil for an electrolytic capacitor electrode according to any one of claims 1 to 5, wherein the temperature is set to ° C.