JPH02200749A - Aluminum foil for electrolytic capacitor cathode and its production - Google Patents

Abstract

PURPOSE:To obtain an Al foil in which the amount of precipitates is limited and which shows high electrostatic capacity after alternating current etching by subjecting a cold rolled high-purity Al stock in which cold draft is specified to final annealing at specific temp. CONSTITUTION:Al of >=99.50% purity is cast, hot-rolled, and cold-rolled at 70-95% cold draft so as to be formed into an Al foil. Subsequently, the above Al foil is subjected to final annealing at 150-300 deg.C, by which the Al foil for electrolytic capacitor cathode in which the amount of precipitates of 0.1-5mum grain size is regulated to 2000-6000 pieces is obtained. By the above control of the amount of precipitates, high electrostatic capacity can be obtained after alternating current etching.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an aluminum foil for an electrolytic capacitor cathode that has a high capacitance after AC etching and a method for producing the same.

[Prior art] The purity of the foil for the cathode of an electrolytic capacitor is 99°50-99.
．． 94ffli1% aluminum is used as pure aluminum or as an aluminum alloy with alloying elements such as Cn4, nickel, and manganese added as required.

Foil production usually involves casting, homogenization, hot rolling, and cold rolling, and if necessary, annealing may be performed after final rolling.

The purpose of the final annealing is to soften the foil, so it is usually carried out at a temperature of 350° C. or higher (above the recrystallization temperature).

In the rolling process of the foil base and foil, intermediate annealing is usually not performed. Normally, intermediate annealing is performed to soften the rolled material when it becomes work-hardened and becomes difficult to roll. However, because the foil material for electrolytic capacitors has a high aluminum purity, it is difficult to roll. This is because it does not harden until it becomes solid. For this reason, the cold rolling ratio is usually 98% or more.

By the way, the capacitance of an electrolytic capacitor is proportional to the surface area of its electrodes. Therefore, aluminum foil for electrodes is chemically or electrochemically etched and roughened to increase its surface area. The etching conditions are determined by the final use of the foil.

Etching can be roughly divided into two types: electrochemical methods and chemical methods. Electrochemical methods can be further divided into methods using direct current and methods using alternating current. Furthermore, alternating current uses various frequencies. Is there a method that changes the current waveform or a method that changes the current waveform? Etching on the production line is performed using these various etching methods alone or in various combinations.

The cathode of an electrolytic capacitor is usually not chemically formed, or even if it is chemically formed, it is formed at an extremely low voltage. Since the bits will not be damaged even if the etching is performed, the AC etching method is selected for the cathode because it can obtain fine bits densely.

On the other hand, the aluminum foil is selected from components or manufacturing processes suitable for various etching conditions. For AC etching, it has been found that performing intermediate annealing during cold rolling improves the capacitance after etching.

(Patent application 1986-145151). This is because the intermediate annealing controls the amount of strain in the final rolled foil, controls the bit generation density during AC etching, and prevents the bits from coalescing with each other.

[Problems to be Solved by the Invention] An object of the present invention is to provide an aluminum foil for an electrolytic capacitor cathode that exhibits high capacitance after AC etching by a novel means different from the above, and a method for manufacturing the same. That is.

[Means for Solving the Problems] As described above, the capacitance of an electrolytic capacitor is proportional to the surface area of the electrode. Therefore, in order to increase the capacitance, it is necessary to enlarge the surface of the foil by etching.

In AC etching, precipitates in aluminum foil (AI
- Intermetallic compounds such as Fe-3t system) affect the formation of etch bits, and if the amount of these precipitates is less than the optimum amount, a sufficient area expansion ratio cannot be obtained, and conversely, if it is too much, the bits may coalesce. As a result, the area enlargement ratio decreases. Therefore, it is necessary to control the amount of precipitates.

Therefore, in order to obtain an aluminum foil for an electrolytic capacitor cathode having a high capacitance, the present inventors have been conducting research on means for controlling the precipitates deposited thereon. As a result, it was discovered that the grain size and amount of precipitation can be controlled by the cold rolling rate and final annealing temperature conditions, leading to the present invention.

That is, the present invention provides (1) an electrolytic capacitor cathode characterized in that it is an aluminum foil with a purity of 99.50% or more, and the amount of precipitates with a particle size of 0°1 to 5 μm is 2000 to 6000 pieces/l1l12; (2) Aluminum foil with a purity of 99°50% or more 70-9
The method for producing an aluminum foil for an electrolytic capacitor cathode according to claim 1, wherein the 5% cold rolled material is finally annealed at a temperature of 150 to 300°C.

In the present invention, the particle size of precipitates in aluminum foil is reduced to 0.
．． The reason why the thickness is 1 to 5 .mu.m is because precipitates smaller than 0.1 .mu.m will not serve as starting points for etch bits, and if they exceed 5 .mu.m, the number of etch bits will be small and the spreading effect will be small.

In the present invention, the number of precipitates is 2000 to 6000/
The reason for setting +as 2 is that if it is less than 2000 pieces/mm2, the number of etch bits will be too small and a sufficient area expansion ratio will not be obtained, and if it exceeds 6000 pieces/11112, the etch bits will coalesce, so the expansion efficiency will be reduced. This is because it does not rise.

In addition, in the method for manufacturing electrolytic capacitor cathode foil of the present invention, a foil with a cold rolling rate of 70 to 95% is used and is final annealed at a temperature of 150 to 300°C; Foil with a rolling rate of less than 70% has a baking rate of 11! It is difficult to form precipitates due to machining regardless of temperature, and there is little strain;
%, dislocation fields Isl will be too large and will precipitate excessively, resulting in bit coalescence during etching.

[Example〕 Hereinafter, the present invention will be explained in more detail with reference to Examples.

99.8596 aluminum containing Si, = 0.0596, Fe-0.07% and other unavoidable impurities was cast, homogenized and hot rolled according to the usual method.
A plate with a thickness of Oan was prepared. Using this lQmi board,
A Q, 1 vst foil with a cold rolling reduction of 50-99% was prepared. The rolling rate was adjusted by performing intermediate annealing at 350°C for 3 hours during rolling.

Then, final annealing was performed at various temperatures from room temperature to 400°C. Using these samples, fl1
It was fixed at 1. The results are shown in Figures 1-3. (AC etching test) In a 12.5% hydrochloric acid and 0.6% phosphoric acid solution at 55°C,
It was etched for 60 seconds at 0.6 A/c- with an alternating current of 0 Hz, washed with water, dried, and then chemically converted in a 15% ammonium adipate solution at 3 V. Then, the capacity was determined in the same solution using an LCR meter. c, Determination of ti product After the foil surface was electrolytically polished in a mixture of sulfuric acid and chromic acid, it was quantified using an image analyzer.

It can be seen from FIGS. 1 to 3 that the aluminum foil within the scope of the present invention has a high capacitance.

[Effects of the Invention] As explained above, according to the configuration of the present invention, AC,
After the capacitance is increased, it is possible to stack aluminum foil for electrolytic condenser cathode.

[Brief explanation of the drawing]

Figure 2 is a graph showing the relationship between annealing temperature and precipitates.
The figure is a graph showing the relationship between precipitation amount and capacitance, and FIG. 3 is a graph showing the relationship between rolling ratio and capacity. 1” 11 patent applicant Sumitomo Light Metal Co., Ltd.

Claims (2)

[Claims] (1) Aluminum foil with a purity of 99.50% or more, and the amount of precipitates with a particle size of 0.1 to 5 μm is 2000 to 6
000 pieces/mm^2 Aluminum foil for electrolytic capacitor cathode. (2) 70-9 of aluminum with purity of 99.50% or more
The method for manufacturing an aluminum foil for an electrolytic capacitor cathode according to claim 1, wherein the 5% cold rolled material is finally annealed at a temperature of 150 to 300°C.