JP2006147609A - Manufacturing method of aluminum foil for electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To highly obtain a surface roughening rate of aluminum foil for electrolytic capacitor and to increase capacitor electrostatic capacity while permitting miniaturization. <P>SOLUTION: An exhaust processing process for vacuum-exhausting atmosphere gas in an anealing furnace and making pressure as not more than 100 Pa, and a restoration pressure processing process for introducing inert gas into the annealing furnace after the exhaust processing process and making pressure not less than 10 kPa, are repetitively performed twice or more. Inert gas or reducing gas or both gases are introduced into the annealing furnace as annealing atmosphere gas. The inner part of the annealing furnace is heated, a temperature is raised and annealing is performed. Remaining oxygenated components and oil can securely be removed to the inner part of a rolling up article. An oxide film formed in aluminum foil can be adjusted to appropriate thickness. Thus, a plurality of uniform pits are formed at the time of a surface roughening processing, and the high surface roughening rate can be obtained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing an aluminum foil for electrolytic capacitors, and is particularly suitable for an aluminum foil for an anode.

  In general, in the manufacture of aluminum foil for electrolytic capacitors, pure aluminum with a purity of 99.9% or more is hot and cold rolled to obtain an aluminum foil having a thickness of about 100 μm, which is finally annealed and further roughened. Processing and anodizing are performed. The surface roughening treatment is intended to increase the surface area of the aluminum foil and increase the capacitance. Generally, etching treatment is performed with an electrolytic solution mainly composed of hydrochloric acid to form many pits. Capacitance per unit area can be increased as the surface area is increased by such surface roughening treatment, the amount of aluminum foil used for capacitor electrodes is reduced, and miniaturization and resource saving can be achieved. it can. As described above, since the roughening treatment is greatly related to the performance of the capacitor, various studies have been made by manufacturers.

  For example, for the purpose of providing an aluminum foil with a high roughening rate, that is, a roughening rate, the atmosphere in the final annealing is changed from a conventional vacuum or an inert gas atmosphere to a reducing atmosphere. A method for improving the roughening rate has been proposed (see Patent Document 1). According to this method, the oxide film formed on the aluminum foil has an appropriate thickness prior to the roughening treatment, and the crystallization rate of the oxide film (occupation ratio of the crystalline film in the oxide film) is adjusted. Therefore, it is expected that a large number of uniform pits are formed during the roughening process and the roughening rate is improved.

  In the said patent document 1, when a trace amount oxygen-containing material exists in an annealing furnace, it was made | formed on the assumption that the oxide film on the surface of aluminum foil will be grown and a roughening will be adversely affected. That is, the oxygen-containing material is removed by evacuation in an annealing furnace to suppress the growth of the oxide film.

JP-A-8-222488

By the way, in aluminum foil for electrolytic capacitors, between the aluminum foil stacked like a wound product and the aluminum foil, there remains an oxidizing gas such as oxygen and moisture, and the rolling oil that cannot be removed by washing. Minutes exist. Since these oxidizing gas and residual oil cause the oxide film on the surface of the aluminum foil to grow thick or remain as carbides during the final annealing, the subsequent roughening rate is hindered.
However, the method disclosed in Patent Document 1 has a problem that the oxidizing gas and oil remaining in the overlapped portion of the wound product, particularly the central portion in the width direction, are not sufficiently removed. In addition, it is possible to increase the ultimate vacuum at the time of evacuation or to extend the evacuation time, but in order to increase the vacuum, it is necessary to improve the sealing performance of a high-performance exhaust pump or furnace. . Therefore, a burden is imposed on the cost of equipment and the manufacturing time in productivity, which is not realistic.

   The present invention has been made against the background of the above circumstances, and reliably removes oxidizing gas and oil adhering to the surface of the aluminum foil, appropriately controls the oxide film thickness of the aluminum foil during final annealing, It is an object of the present invention to provide a method for producing an aluminum foil for electrolytic capacitors, which can obtain a high roughening rate during the surface treatment.

  That is, among the methods for producing an aluminum foil for electrolytic capacitors of the present invention, the invention according to claim 1 is a method for producing an aluminum foil for electrolytic capacitors in which final annealing is performed in an annealing furnace prior to the surface roughening treatment, An exhaust treatment step of evacuating the atmosphere gas in the annealing furnace to a pressure of 100 Pa or less, and a re-pressure treatment step of introducing an inert gas into the annealing furnace after the exhaust treatment step to a pressure of 10 kPa or more. Repeated twice or more, and then introduces one or both of an inert gas and a reducing gas as an annealing atmosphere gas into the annealing furnace, and heats the inside of the annealing furnace to perform annealing. And

  The invention of the method for producing an aluminum foil for electrolytic capacitors according to claim 2 is characterized in that, in the invention according to claim 1, the pressure in the final exhaust treatment is 20 Pa or less.

  The invention of the method for producing an aluminum foil for electrolytic capacitors according to claim 3 is the invention according to claim 1 or 2, wherein the inert gas is nitrogen gas or argon gas having a purity of 99.9% or more. Features.

  The invention of the method for producing an aluminum foil for electrolytic capacitors according to claim 4 is the invention according to any one of claims 1 to 3, wherein the reducing gas is hydrogen gas having a purity of 99.9% or more. Features.

  The invention of the method for producing an aluminum foil for electrolytic capacitors according to claim 5 is characterized in that in the invention according to any one of claims 1 to 4, it is carried out after or after the introduction of the annealing atmosphere gas.

  According to the present invention, the oxygen-containing material in the furnace is effectively removed by the exhaust treatment process in which the atmospheric gas in the annealing furnace is evacuated to a pressure of 100 Pa or less. However, only this exhaust treatment does not sufficiently remove the oxidizing gas and oil remaining in the overlapped portion of the wound product. After that, when the inert gas is introduced into the annealing furnace, the inert gas enters the depressurized overlapping portion of the wound product and pushes out some residual gas and oil from the overlapping portion. When the pressure is further reduced, the extruded residual gas and the like are removed, and the oxidizing gas and oil remaining in the overlapped portion are taken out along with the movement of the inert gas molecules. The action of removing residual gas and the like is greatly improved by being discharged to the outside. Residual gas and the like are effectively removed by repeating the above-described decompression and decompression. The final annealing is performed in an atmosphere of one or both of an inert gas and a reducing gas, so that the growth of the oxide film is suppressed and a good roughening rate is obtained in the subsequent roughening treatment. It is done.

The pressure during evacuation is set to 100 Pa or less. When evacuation is completed at a pressure higher than 100 Pa, the removal of oxidizing gas and residual oil becomes insufficient. Further, the pressure is desirably 50 Pa or less, and if it is 20 Pa or less, a better effect can be expected.
The pressure in the final exhaust treatment is desirably 20 Pa or less in order to obtain the above effect more effectively.

  The pressure when introducing the inert gas after evacuation is 10 kPa or more. When the pressure is less than 10 kPa, the inert gas does not sufficiently enter the wound product. This pressure is more preferably 100 kPa or more.

  The number of times of repeating the evacuation treatment step and the step of returning to the inert gas atmosphere is preferably 2 to 4 times. If this repetitive process is not performed and only the exhaust from the atmosphere and the return pressure are performed, the oil and the like are not sufficiently removed. Moreover, even if it repeats 5 times or more, the removal of oil etc. does not advance remarkably further.

  In the final annealing, the gas introduced before or during the temperature increase may be an inert gas or a reducing gas, and is a mixed gas of an inert gas and a reducing gas. Also good. The inert gas is preferably nitrogen gas or argon gas having a purity of 99.9% or more, and the reducing gas is preferably hydrogen gas having a purity of 99.9% or more.

  Moreover, the composition of the aluminum foil used in the present invention is not particularly limited, but usually an aluminum foil for electrolytic capacitors such as a pure aluminum type having a purity of 99% to 99.99% or more or JIS A3003 is used. Among them, the purity is preferably 99.9% or more, and more preferably 99.96% or more. In the production, casting and rolling can adopt the same process as that of a normal aluminum foil until the final thickness is reached. Of course, the manufacturing method is not particularly limited, but the final thickness is usually about 0.1 mm.

  As described above, according to the method for producing an aluminum foil for electrolytic capacitors of the present invention, the method for producing an aluminum foil for electrolytic capacitors in which final annealing is performed in an annealing furnace prior to the surface roughening treatment, the annealing furnace An exhaust treatment process in which the internal atmospheric gas is evacuated to a pressure of 100 Pa or less, and a return pressure treatment process in which an inert gas is introduced into the annealing furnace after the exhaust treatment process to obtain a pressure of 10 kPa or more. After repeating the above, after introducing one or both of an inert gas and a reducing gas as an annealing atmosphere gas into the annealing furnace and heating the temperature inside the annealing furnace to perform annealing, residual oxygen content Ingredients and oil can be reliably removed up to the inside of the wound product, and the oxide film formed on the aluminum foil prior to the roughening treatment can be adjusted to an appropriate thickness. Therefore, a large number of uniform pits are formed during the surface roughening treatment to obtain a high surface roughening rate, and an electrolytic capacitor excellent in capacitance per unit area can be manufactured.

(Embodiment 1)
An embodiment of the present invention will be described below.
Aluminum having a purity of 99.9% or more (for example, 99.99% or more) is cast and rolled by a conventional method, and an aluminum foil is obtained with a final thickness of usually about 0.1 mm. The aluminum foil is subjected to final annealing in an annealing furnace.
At the time of annealing, the atmosphere is exhausted from the inside of the annealing furnace, and the pressure is reduced to 100 Pa or less, preferably 50 Pa or less (exhaust treatment step). Thereafter, an inert gas such as nitrogen gas or argon gas having a purity of 99.9% or more is introduced into the annealing furnace to increase the pressure in the furnace to 10 kPa or more, preferably 100 kPa or more (return pressure treatment step).
If the evacuation process and the inert gas introduction process are repeated twice or more, the remaining oxygen-containing components and oil can be reliably removed from the aluminum foil surface.

After the exhaust treatment and the return pressure treatment are repeated twice or more, one or both of an inert gas and a reducing gas is introduced into the annealing furnace as an annealing atmosphere gas. Although the annealing atmosphere pressure is not limited to a specific one in the present invention, it is desirable to be at least atmospheric pressure (101 kPa) in order to prevent air from entering from the outside. A more desirable range is 105 kPa or more.
Growth of the oxide film during annealing is suppressed by the annealing atmosphere gas, and an oxide film having an appropriate thickness is formed on the surface of the aluminum foil.
At the time of final annealing, the temperature in the furnace is raised to a predetermined temperature. This temperature increase may be performed after the introduction of the annealing atmosphere gas described above or may be performed together with the introduction of the atmosphere gas.

  In addition, the temperature in the final annealing is usually an actual temperature, which is about 280 ° C. to 400 ° C. for the cathode and low pressure anode used for AC electrolytic etching, and about 500 ° C. to 600 ° C. for medium and high pressure anode used for DC electrolytic etching. is there. The holding time in the final annealing is usually about 1h to 10h. Furthermore, the temperature increase rate and the cooling rate in the final annealing are usually about 10 ° C / h to 200 ° C / h.

An embodiment of the present invention will be described below. Aluminum having a purity of 99.99% was cast by a conventional method, slitted through the steps of homogenization treatment, chamfering, hot rolling, and cold rolling to obtain an aluminum foil having a thickness of 110 μm.
As shown in Table 1, the aluminum foil was subjected to final annealing by combining an evacuation process and a return pressure process with different conditions. Moreover, the final annealing was performed about the prior art example and comparative example which do not satisfy | fill the conditions of an exhaust_gas | exhaustion process process of 2 times or more, and a return pressure process process.

In the final annealing, the temperature raising rate was about 100 ° C./h, the substance holding temperature was 560 ° C., and the holding time was about 6 hours. An annealing atmosphere gas was introduced at an average of 20 nm ³ / h after the start of the temperature increase until the end of the holding at the predetermined temperature, and was appropriately evacuated so that the pressure in the gas atmosphere was 103 kPa to 110 kPa. After holding at the predetermined temperature, the process shifted to a cooling step with a cooling rate of about 100 ° C./h. In the cooling step, the exhaust was basically stopped, and the inflow amount of the gas was adjusted so that the furnace pressure became 103 kPa to 110 kPa.
After the solid temperature became 50 ° C. or lower in the cooling step, the annealed aluminum foil was taken out into the atmosphere. When hydrogen gas was present in the furnace, the aluminum foil was taken out after replacing the inside of the furnace with nitrogen gas to ensure safety.
A specimen was collected from the center in the width direction of the obtained aluminum foil, subjected to a roughening treatment and a chemical conversion treatment under the following conditions, and then the capacitance was measured. The measurement results are summarized in Table 2.

1. Roughening conditions (1) First stage etching conditions (DC electrolytic etching)
Electrolytic solution (mixed solution)
HCl 1 mol / l
H ₂ SO ₄ 3 mol / l
Temperature 80 ℃
Current density 0.5A / cm ²
Energizing time 60 seconds (2) Second stage etching conditions (chemical etching)
Etching solution 30% HNO ₃ aqueous solution
Temperature 75 ° C
Time 240 seconds

2. Chemical conversion treatment conditions Implemented at a chemical conversion voltage of 350 Vf according to EIAJ standards.

As is clear from Table 2, it can be seen that the electrostatic capacity of the aluminum foil is clearly increased by repeatedly performing evacuation and return pressure twice or more in the final annealing. Further, among the test materials of the present invention, when the ultimate vacuum at the time of evacuation was high and the return pressure was high, the increase in capacitance was more remarkable.
On the other hand, when the evacuation and the introduction of the inert gas were not repeated twice or more, a high capacitance was not obtained.
Further, in the example where the degree of vacuum reached at the time of evacuation is low and the case where the return pressure is low, the capacitance is only slightly increased even if the evacuation and introduction of the inert gas are repeated.

Claims (5)

  A method for producing an aluminum foil for an electrolytic capacitor in which final annealing is performed in an annealing furnace prior to roughening treatment, wherein the exhaust gas is evacuated to a pressure of 100 Pa or less by evacuating the atmosphere gas in the annealing furnace; After the treatment step, an inert gas is introduced into the annealing furnace and the return pressure treatment step of 10 kPa or more is repeated twice or more, and then the inert gas is used as the annealing atmosphere gas in the annealing furnace. A method for producing an aluminum foil for an electrolytic capacitor, wherein one or both of reducing gases are introduced and the annealing furnace is heated and heated to perform annealing.   2. The method for producing an aluminum foil for an electrolytic capacitor according to claim 1, wherein the pressure in the final exhaust treatment is 20 Pa or less.   The method for producing an aluminum foil for an electrolytic capacitor according to claim 1 or 2, wherein the inert gas is nitrogen gas or argon gas having a purity of 99.9% or more. The said reducing gas is hydrogen gas with a purity of 99.9% or more, The manufacturing method of the aluminum foil for electrolytic capacitors in any one of Claims 1-3 characterized by the above-mentioned.
Production method.   The method for producing an aluminum foil for an electrolytic capacitor according to any one of claims 1 to 4, wherein the temperature rise is performed after or after the introduction of the annealing atmosphere gas.