JP2000204455A - Production of aluminum foil for electrolytic capacitor electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To securely remove oil stuck to the surface of foil and to obtain the structure of a high cubic body orientating ratio by heating an Al foil in a reducing atmosphere contg. oxygen of specified concn. and an inert gas and executing final annealing prior to the surface roughening treatment of the Al foil. SOLUTION: The Al foil of 99.9% purity and about 0.1 mm thickness is heated in a reducing atmosphere contg. 1 to 100 ppm oxygen, 0 to 10% inert gas, and the balance substantial reducing gas and is subjected to final annealing. The holding heating temp. in the final annealing is held to 530 to 620 deg.C. The holding time is desirably controlled to 2 to 10 hr. Moreover, as the reducing gas, hydrogen can be cited. The reducing atmosphere is preferably held even in a cooling stage after the holding stage in the final annealing. In the cooling stage, desirably, the cooling rate is controlled in such a manner that it is not made too fast by furnate cooling or the like, and, concretely, the cooling is executed, derirably, at the cooling rate of <=100 deg.C/hr on the average.

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 is particularly suitable for producing an anode foil for medium pressure 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).

[0003]

However, there is still much room for improvement in the surface roughening rate, and research for improving the surface roughening rate is being continued. One factor for increasing the surface roughening rate is the ratio of the cubic orientation from the material side,
That is, the cubic orientation ratio. In order to increase the cubic orientation, the annealing temperature of the aluminum foil may be increased. However, when the final annealing is performed by heating the aluminum foil to a high temperature, there is a problem that the lubricating oil adhering to the aluminum foil during the manufacturing process (rolling) of the aluminum foil is oxidized at a stretch and burns to the aluminum foil. Then, as proposed by the present inventor (JP-A-8-222488), a method of preventing the above-described oxidation by performing the final annealing in a reducing atmosphere to avoid image sticking can be considered. However, in this method, the lubricating oil attached to the aluminum foil remains on the surface of the aluminum foil even after the final annealing without being oxidized, and this hinders the formation of pits during the surface roughening treatment. There is a problem that the effect of improving the surface roughening rate is offset. On the other hand, in the current annealing in an inert gas-based annealing atmosphere, the coil is baked at a relatively low temperature due to oxidation caused by moisture and the like contained in the material, so that the annealing temperature of the aluminum foil wound in a coil shape is reduced. Was raised only about 520 ° C., and therefore, for example, it was difficult to obtain a foil having a very high cubic orientation ratio (98% or more). This method improves this point and proposes a new annealing atmosphere that can be heated to a considerably high temperature.

The present invention has been made in view of the above circumstances, and appropriately controls the thickness of an oxide film at the time of final annealing and ensures that oil adhering to the aluminum foil surface does not remain after the final annealing. It is an object of the present invention to provide a foil having a high cubic azimuthal rate for obtaining a high surface roughening rate by removing and increasing the final annealing temperature.

[0005]

Means for Solving the Problems To solve the above problems, the first invention of the method for manufacturing an aluminum foil for an electrolytic capacitor electrode according to the present invention is to perform a final annealing on the aluminum foil prior to the surface roughening treatment. In the method for producing an aluminum foil for an electrolytic capacitor electrode, the final annealing is performed in a range of 1 to 1;
The method is characterized in that it is carried out by heating and holding at 530 to 620 ° C. in a reducing atmosphere containing 00 ppm of oxygen and 0 to 10% by volume of an inert gas and the balance substantially consisting of a reducing gas.

According to a second aspect of the present invention, there is provided a method of manufacturing an aluminum foil for an electrolytic capacitor electrode according to the first aspect, wherein the amount of the inert gas in the reducing atmosphere is increased within the range of 0 to 10% by volume during the holding and heating. It is characterized by.

[0007]

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.

[0008] The aluminum foil obtained by the above process is subjected to final annealing in a reducing atmosphere containing a small amount of oxygen. That is, as described above, the volume ratio is 1 to 10
The aluminum foil is heated in a reducing atmosphere containing 0 ppm of oxygen and 0 to 10% of an inert gas and the balance substantially consisting of a reducing gas. 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. 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.

In the present invention, as a factor for suppressing the adhesion of aluminum to each other up to a high temperature region, a method of suppressing the oxidation to suppress the oil content on the surface is considered. For example, by including a trace amount of oxygen in the reducing atmosphere as described above, an oxide film having an appropriate thickness is formed on the aluminum foil surface by the reducing action of the reducing gas, and the aluminum foil surface is oxidized by the oxygen. The attached oil is gradually oxidized. However, since the amount of oxygen is not enough to completely decompose and oxidize the oil in the low temperature range, a slight residual is observed. Higher temperature (5
Above 30.degree. C., preferably <550.degree. C.), decomposition of the oil takes place slowly even with trace amounts of oxygen, and finally at the final (up to 620.degree. C.) temperature the oil is completely oxidized and decomposed. Therefore, according to the present method, since oil remains up to a high temperature, sticking of the coil is suppressed, so that high-temperature annealing can be said to be possible. Since high-temperature annealing can be achieved in this manner, a result of obtaining a high cubic orientation ratio was obtained.

The above phenomenon can be obtained by setting the concentration of oxygen contained in the atmosphere to an appropriate range. In other words, when the annealing temperature (highest) is high, the amount of oxygen added is preferably small because the oil needs to remain at high temperatures, and by limiting the amount, the oil content can be reduced at once from the beginning of holding and heating. Suppresses oxidation. Therefore, the oxygen concentration is set to 100 ppm or less in volume ratio. In addition,
For the same reason, the content is desirably 50 ppm or less. Further, in order to finally oxidize and remove the oil in the holding and heating, the oxygen concentration needs to be 1 ppm or more, and it is desirable to be 10 ppm or more for the same reason.

The reducing atmosphere may contain an inert gas of 10% by volume or less, if desired, as described above. This inert gas adheres to the surface of the aluminum foil and effectively acts to remove oil remaining between the coils after being vaporized in the final annealing.
However, if an excessive amount of inert gas is contained, the reducing power will be impaired and an appropriate oxide film (of an appropriate thickness) will be formed on the aluminum foil surface.
Is difficult to form, so the upper limit of the concentration of the inert gas is 10
% By volume. The inert gas may have a constant concentration during the holding heating, but as described above, the concentration may be increased up to 10% by volume from the middle of the holding heating when the oxidation of the oil proceeds. Alternatively, the inert gas may be introduced midway without including the inert gas. As a result, it is possible to obtain high reducibility at the beginning of the holding heating, to avoid excessive removal of oil, and to suppress sticking of the coil to a high temperature. Furthermore, even if the film is heated in a high temperature region, it becomes possible to finally form an appropriate oxide film including the thickness. The upper limit of the inert gas is desirably 5 % by volume or less for the same reason as described above.
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.

In the holding process of the final annealing, the holding heating temperature is 530 to 620 ° C. This is necessary to obtain a structure with a higher cubic orientation ratio in a reducing gas atmosphere.
This is because a temperature of 30 ° C. or higher is required. By heating at the temperature or higher, the crystal structure of the aluminum foil can be changed to a cubic structure at a high ratio (for example, 95% or higher). The cubic azimuth ratio increases as the holding temperature increases, but if the temperature is too high, partial seizure of the aluminum foils may occur even with this method, so the holding temperature is set to 620 ° C. or lower. Further, the lower limit is preferably higher than 550 ° C. for the same reason, and the upper limit is 6 ° C. for the above-mentioned reason.
00 ° C is desirable. The holding time is 2 to 10
Time is desirable. This is because if it is less than 2 hours, the formation of cubic crystals and the removal of oil are insufficient.
If the time exceeds 10 hours, the above-mentioned foils may cause seizure.

It is desirable to maintain the above-mentioned atmosphere in a high temperature region (for example, 500 ° C. or higher) even in a cooling process after the holding 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. In addition, since reactivity becomes low in a temperature range lower than the high temperature range, for example, nitrogen gas can be used as an 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 100 ° C./hour or less on average.

The aluminum foil obtained by the final annealing has an appropriate thickness of the oxide film (for example, a thickness of 35 to 45).
Å) and a structure having a high cubic azimuth ratio is obtained, and the oil is reliably removed from the surface without seizure. 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.

[0015]

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, the invention materials (Nos. 1 to 9) were annealed in a reducing atmosphere to which a small amount of oxygen was added, and the comparative materials (Nos. 10 to 15) were annealed in the atmosphere under the conditions of the invention method. Alternatively, an inert gas (Ar) atmosphere, a vacuum atmosphere (10 ⁻³ Torr)
Annealed. Inventive material No. In No. 9, the inert gas was not initially contained in the atmosphere, and the inert gas was introduced from the middle of the holding process (at an almost intermediate time).

[0016]

[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

The cubic orientation of the test material was determined by etching using a mixed acid of nitric acid and hydrochloric acid to reveal the cubic orientation, and a surface analysis was performed to calculate the rate. Further, the thickness of the oxide film 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 1. Further, FIG.
2 shows the relationship between the heating temperature in annealing and the cubic orientation of the aluminum foil, and FIG. 2 shows the relationship between the cubic orientation and the capacitance. In addition, comparative material No. 10, 11, 13
2 to 15 were excluded from FIG. 2 because sticking between aluminum foils and remaining oil content, other than the cubic azimuth, affected the capacitance.

As is clear from Table 1, it can be seen that by performing the final annealing in an appropriate atmosphere and heating temperature, the capacitance of the aluminum foil is clearly increased. In particular,
As shown in FIG. 2, the capacitance is further improved by increasing the area ratio of the crystal cubic orientation of the aluminum material. As shown in FIG. 1, the ratio of the cubic structure depends on the holding temperature of the final annealing (the higher the temperature, the larger the ratio). On the other hand, in the comparative material, a high capacitance was not obtained because the atmosphere or the heating temperature of the final annealing was not properly adjusted. That is, the comparative material No. In Nos. 10, 11, 13, and 14, the ratio of the cubic structure was increased by increasing the final annealing temperature. In Nos. 10, 11, and 13, the oxygen content in the atmosphere was excessive, and In No. 14, since the heating temperature was too high, the aluminum foils were stuck together and a high capacitance could not be obtained. In addition, the comparative material No. 12
Although there was no sticking of the aluminum foil and no oil remaining, the cubic orientation rate was low due to the low final annealing temperature, and as a result, the capacitance was low. Further, the comparative material N
o. In No. 15, although the aluminum foil did not stick and the cubic orientation rate was increased by an appropriate final temperature, the oil content remained after the final annealing because the oxygen content in the final annealing was too small. No capacity was obtained. Comparative material No. corresponding to the conventional example. In No. 16, the cubic azimuth ratio was low because the heating temperature was low, and thus a sufficient capacitance could not be obtained.

[0021]

As described above, according to the method for producing an aluminum foil for an electrolytic capacitor electrode of the present invention, the aluminum foil for an electrolytic capacitor electrode is subjected to final annealing prior to the surface roughening treatment. , The final annealing is 1-100 ppm oxygen and 0-10 volume%
High inertia gas, and a high cubic azimuthal rate of the material without seizure of oil because the heating is performed at 530 to 620 ° C. in a reducing atmosphere substantially consisting of a reducing gas. In addition, the oil content is surely removed by the final annealing, so that a high surface roughening rate can be obtained during the surface roughening treatment. As a result, an electrolytic capacitor having a high capacitance per unit area can be obtained. Also, if the amount of the inert gas in the reducing atmosphere is increased within the range of 0 to 10% by volume during the holding and heating, the residual oil on the surface of the aluminum foil can be reduced, and a high surface roughening rate can be obtained. Is obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a final annealing holding heating temperature and a cubic orientation ratio of a material in an example.

FIG. 2 is a graph showing the relationship between the cubic orientation ratio of a material and the capacitance.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22F 1/00 686 C22F 1/00 691Z 691 691B H01G 9/04 346

Claims (2)

[Claims] 1. A method for producing an aluminum foil for an electrolytic capacitor electrode, wherein a final annealing is performed on the aluminum foil prior to the surface roughening treatment, wherein the final annealing includes 1 to 100 ppm of oxygen and 0 to 10% by volume of an inert gas. 530-6 in a reducing atmosphere consisting essentially of a reducing gas.
A method for producing an aluminum foil for an electrode of an electrolytic capacitor, wherein the method is carried out by heating and holding at 20 ° C. 2. The method for producing an aluminum foil for an electrolytic capacitor electrode according to claim 1, wherein the amount of the inert gas in the reducing atmosphere is increased within the range of 0 to 10% by volume during the holding and heating.