JPH02156053A - Manufacture of aluminum foil for electrolytic capacitor cathode - Google Patents

Abstract

PURPOSE:To manufacture a high-strength, high-capitance, and high-grade soft Al foil with superior productivity by carrying out annealing at a specific temp. in a continuous annealing furnace at the time of manufacturing an Al foil for electrolytic capacitor cathode. CONSTITUTION:The the time of manufacturing an Al foil for electrolytic capacitor cathode, a slab of Al of 99.8% purity is subjected to soaking treatment and then formed into an Al foil by means of hot rolling and cold rolling, and this Al foil is subjected to short-time annealing by using a continuous heating furnace at 300-500 deg.C for <=3min, cooled down to <=150 deg.C in the continuous heating furnace, and wound up. By this method, the Al foil for cathode having fine crystalline grains and excellent in etching characteristic, strength, and high electrostatic capacity can be obtained.

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for manufacturing an aluminum foil for an electrolytic capacitor cathode, and more particularly to a method that enables improvement in strength and capacitance by improving final annealing. (Prior Art) Aluminum foil for electrolytic capacitors is generally used by enlarging its surface area through etching treatment to increase its capacitance. In particular, aluminum foil for an electrolytic capacitor cathode does not require the formation of an electrically resistant coating by chemical conversion treatment, unlike anode foil, and therefore is subjected to etching treatment to form as fine etched holes as possible. Conventionally, the aluminum material used for such cathode foils has a purity of about 99.80% for boat fishing. The foil has a thickness of 20 to 60 μm and is used as a hard material (H2S) or a tempered soft material (0) depending on the type of etching process. Among these, in the case of soft materials, the final annealing is performed in a batch furnace in the form of a coil in a vacuum or in an atmosphere of an oxygen-free atmospheric gas (such as DX gas) in order to suppress the growth of an oxide film. On the other hand, recently, an attempt to apply the continuous annealing method (CCAL method) to the production of high-pressure anode aluminum foil has been reported,
There is no report on the application of the CAL method to the production of 7/L/minilam foil for cathodes. (Problems to be Solved by the Invention) When producing an aluminum foil for a cathode, particularly a soft material subjected to finish annealing, using the above-mentioned conventional technology, there is the following problem. First, in the conventional batch annealing method, (1) there is variation in etching properties in the width direction, and surface oxidation occurs more severely at the edges than at the center, resulting in poor etching properties and a tendency to lower capacitance. - Differences in heating rate and heating time occur between the coil core and the outer periphery, resulting in variations in etching performance due to surface oxidation conditions and differences in internal structure. ■It takes a lot of time to heat and cool, which reduces productivity. On the other hand, if the continuous annealing method is applied, ■the foil thickness is the aforementioned high-pressure anode aluminum foil (generally 100μ
(By the way, it is 100μI in JP-A No. 60-110854) (about 50μI or less), so the length per coil is longer.
It takes time to unwind and wind up, and there is no particular advantage in improving the productivity described above. ■When the foil thickness becomes thinner, thermal strain occurs during cooling when the foil is annealed at high temperatures for a short period of time, causing wrinkles and other problems in winding. There is a good luck point, and I can't find any examples of it being applied so far. The present invention solves the above-mentioned drawbacks of the prior art and provides a method for manufacturing an aluminum foil for an electrolytic capacitor cathode, particularly by a continuous annealing method, to obtain a high-strength, high-capacity, and high-quality soft material. The purpose is to (Means for Solving the Problems) In order to achieve the above object, the inventors of the present invention conducted extensive research in order to find a method that would allow the continuous annealing method, which had not been attempted in the past, to be applied without any problems. As a result, we have found conditions that allow annealing at a low temperature using a continuous heating furnace, and hereby the present invention has been made. That is, in the method for manufacturing an aluminum foil for an electrolytic capacitor cathode according to the present invention, in the final annealing of the aluminum foil, a continuous heating furnace is used, and short-time annealing is performed at an annealing temperature in the range of 300 ° C. to 500 ° C. and held for less than 3 minutes. It is characterized by this. The present invention will be explained in more detail below. (Function) First, in the present invention relating to the production of aluminum foil for an electrolytic capacitor cathode, it is a premise that a continuous heating furnace is used for final annealing. In a continuous heating furnace, the coil is wound by passing through a heating zone and a cooling zone while being unwound, and equipment called so-called CAL is used. In continuous annealing, since the coil is annealed in a heating zone while being unwound, there is no variation in I direction, coil core, and quality of the outer periphery (oxide film, crystal grains, etc.). Additionally, since the heating rate can be increased, the crystal grains become finer, which improves etching performance. Improved strength can be obtained. Further, since the heating time is short, there are advantages such as suppressing the formation of an oxide film. Next, the annealing temperature is in the range of 300 to 500°C. It is necessary to secure the minimum necessary temperature to perform the softening process, and the temperature of 3
00℃ or higher. If the temperature is lower than 300°C, it is necessary to hold the temperature for a long time, which causes problems in productivity. On the other hand, in order to suppress the growth of the oxide film, it is necessary to perform annealing at a temperature range of 500° C. or lower. If the temperature exceeds 500° C., the oxide film thickness increases and the crystal grains become coarser, resulting in a decrease in etching performance and also being disadvantageous in terms of energy. Preferably, it is easier to obtain stable quality when the temperature is 300 to 450°C, and more preferably 350 to 430°C.
It is ℃. In addition, the heating time is a short heating time of 3 minutes or less. The CAL type allows for shorter heating and cooling times compared to the conventional batch type, but since the coil length is long in the CAL type as well, the longer the heating time, the more the formation of an oxide film will be promoted. It is necessary to carry out the heat treatment in a short time, preferably within 3 minutes, preferably within 1 minute. Also from the viewpoint of improving productivity, it is preferable to increase the line speed and shorten the annealing heating time. Short-time high-temperature heating causes thermal distortion in the width direction of the foil, which causes problems during winding. Therefore, it is preferable to uniformly cool the foil in the width direction in the cooling zone to a low temperature of 150° C. or lower. By cooling uniformly in the width direction to 150° C. or lower, shape defects due to thermal distortion can be suppressed. If the temperature exceeds 150° C., it is likely to be cooled unevenly in the width direction by the atmosphere and by the passing rollers before winding, resulting in problems such as one winding deviation and unwinding. From the viewpoint of productivity, cooling to about 70°C is sufficient. In this regard, in the conventional general CAL system, the temperature in the cooling section is 150°C.
It is only cooled to a relatively high temperature exceeding . In addition, in the continuous annealing described above, the atmosphere may be air (oxidizing atmosphere), and there is no need to intentionally set it to a vacuum or non-oxidizing atmosphere. In addition, the heating rate and cooling rate are usually 1000℃/w.
Although there is no particular restriction on cooling, it is desirable to have a relatively fast cooling rate (1500° C./akin or more) in order to prevent distortion. The foil thickness is suitable for the cathode for electrolytic capacitors, and -
For boat fishing, the thickness is 60 μm or less, and up to about 20 μm. Of course, the aluminum material may be any material as long as it can be used for the above purpose, and the other steps except the final annealing may be the same as conventional ones. Next, examples of the present invention will be shown. (Example) The material used is purity 99.8, which is usually used for cathode foil.
0% aluminum (Si: 0.05vt%, Fe: 0.
10 wt%, including Cu: 0.002 wt%),
The slab was subjected to soaking treatment (540℃ x 6hr),
Immediately, the plate was hot rolled to a thickness of 3.5 mm. Thereafter, cold rolling was performed to a product thickness of 50 μm, and final annealing was performed under the conditions shown in Table 1. The heating rate at CAL is 1000℃/win, and the cooling rate is 1500℃/wi.
It was set as n. The resulting aluminum foil soft material was examined for oxide film thickness, strength, and capacitance, as well as for the occurrence of strain in the board width direction. The results are also listed in Table 1. Note that the oxide film thickness was measured by the capacitance method using an LCR meter. The strength was measured by performing a tensile test on a 15 mm wide aluminum foil on a strip using an Instron tensile tester at a tensile speed of 10 a+m/win, and expressed as a relative value with the value of conventional process material 1 being 100%. Regarding capacitance, samples were electrolytically etched for 2 minutes at a current density of 45 A/dat using AC 50 Hz alternating current in an aqueous solution (7.5% hydrochloric acid, 0.5% oxalic acid in 1a pure water) at a liquid temperature of 60°C. Aqueous solution with a liquid temperature of 30°C (IQ pure water, 50 g of halonic acid, 50 g of citric acid, 501 g of ammonia)
The capacitance was measured using a universal bridge at a measurement frequency of 120 Hz, and expressed as a relative value with the value of conventional process material No. 1 taken as 100%. From Table 1, inventive examples Nα3 to Seed 5 and NO3 all show high strength and high capacitance equal to or higher than conventional examples &1, and it is confirmed that there is no uneven strain in the width direction. Recognize. This indicates that the oxide film has no unevenness, has uniform etching properties, and is of high quality. In addition, productivity is higher than that of the patch type.

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(Effects of the Invention) As detailed above, according to the present invention, continuous annealing can be applied to the production of aluminum foil for an electrolytic capacitor cathode, so the following excellent effects can be obtained. ■ Etching properties are uniform and a cathode foil of stable quality can be obtained. ■ The crystal grains become fine and a cathode foil with excellent etching properties and strength can be obtained. ■ Due to its high strength and high capacitance, it can be made thinner, making the capacitor lighter and smaller. ■ Due to its high strength, it can prevent the etching foil from breaking and improve the etching speed.
Productivity improves. Patent applicant: Patent attorney representing Kobe lK11 Co., Ltd.
Takashi Nakamura

Claims (2)

[Claims] (1) A method for manufacturing an aluminum foil for an electrolytic capacitor cathode, characterized in that in the final annealing of the aluminum foil, short-time annealing is performed at an annealing temperature in the range of 300°C to 500°C for no more than 3 minutes using a continuous heating furnace. . (2) Claim 1 in which the continuous heating furnace is provided with a heating section and a cooling section, and after being cooled to 150° C. or less in the cooling section, the winding is performed.
The method described in.