JPH09310136A - Aluminum hard foil for electrolytic capacitor and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce dispersion in the surface of foil at the time of electrolytic etching and to reduce the solubility thereof into an electrolyte by regulating the reflected X-rays intensity ratio in the crystal plane in alminum in which purity is regulated to specified value or above and the crystal grain size width in the surface is regulated to specified value or below to specified value or above. SOLUTION: Aluminum in which purity is regulated to >=99.97% and the crystal grain width in the surface is regulated to <=0.4mm is used. In the case the crystal grain width is <=0.4mm. dispersion in the surface after etching is solved. The reflected X-rays intensity ratio (220) in the (220) plane to the (311) plane in the crystal orientation of the aluminum is regulated to >=1. For regulating the crystal grain width to <=0.4mm and reducing the crystals in the (311) orientation, in the alminum ingot after homogenizing treatment, recrystallization is generated for >= two times in the process of hot rolling. As for the rolling conditions of the hot rolling generating the final recrystallization, the rolling is started so as to regulate the temp. in the inlet side of the sheet, and the temp. in the outlet side is regulated to >=310 deg.C. Cold rolling is executed without annealing treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum hard foil for an electrolytic capacitor and a method for manufacturing the same, for an electrolytic capacitor having less surface unevenness during electrolytic etching and low solubility in an electrolytic solution and good electrolytic etching property. The present invention relates to an aluminum hard foil and a preferable manufacturing method thereof.

[0002]

2. Description of the Related Art Aluminum is used as a capacitor by taking advantage of the fact that a dense oxide film having a withstand voltage is formed on the surface by anodic oxidation and can be used as a dielectric, and that the surface area can be increased by electrochemical etching. Have been. The aluminum used in this capacitor is based on aluminum having a purity of 99.97% or more, preferably 99.98% or more, in the anode foil because of its high electrostatic capacity, and other significant or impurity elements within the necessary range. After compounding and melting, and degassing, removing impurities, etc., cast a slab with a thickness of about 500 mm by DC casting method using a water-cooled mold with open upper and lower parts, solution heat treatment, hot rolling, It is cold-rolled to form a foil with a thickness of about 0.3 mm, and after annealing recrystallization, or further thin rolling without annealing to obtain a foil for electrolytic capacitors with a thickness of about 0.1 mm.

The foil obtained as described above is electrochemically perforated from both sides in an etching process using an acid electrolyte to form a large number of pits to increase the surface area and leave the core portion. As the strength. In the next chemical conversion process, the treatment liquid and conditions are changed to electrochemically form a dielectric oxide film, then cut into product widths, leads are attached, separate paper is sandwiched, and wound to impregnate the electrolyte solution. It is placed in a case and sealed with a sealing material. After that, a voltage is applied to repair the scratches on the dielectric oxide film applied during the processing to complete the product.

By the way, the aluminum foil for electrolytic capacitors is required to have good etching characteristics without surface unevenness because it is precisely manufactured and processed as described above, and the surface area of the foil can be reduced due to the miniaturization of the capacitor. Etching conditions for expansion have become increasingly severe. Aluminum hard foil for low-voltage capacitors, which is used especially for the anode, is manufactured by homogenizing the ingot and then cold rolling it without annealing. It is etched with an electric current. Recently, in order to increase the capacitance of the foil, the concentration of hydrochloric acid in the electrolytic solution tends to be increased, and the time for which the foil is present in the solution tends to be long.

That is, when the above-mentioned treatment is carried out, the amount of chemical dissolution on the surface of the foil in contact with the electrolytic solution is increased, the shape of the pits is destroyed, the capacitance is lowered, and the thickness of the residual core portion is insufficient. Since it causes a lack of mechanical strength, it is necessary to reduce the amount of chemical dissolution so as not to damage the shape of the pit, and there is a demand for an aluminum foil that is resistant to dissolution in an acid electrolyte. Further, it is known that the chemical dissolution is promoted when the aluminum foil has a large amount of impurities, and there is a tendency for high purification. Further, in JP-A-4-333541, from the consideration of the crystal orientation of the foil, (100) with respect to the (110) plane
A proposal has been made for a hard aluminum foil in which the surface ratio (100) / (110) is set to a specific value or less.

[0006]

The above-mentioned aluminum hard foil proposed from the consideration of the crystal orientation in the aluminum foil is effective in terms of chemical dissolution resistance, but the low-pressure aluminum hard foil is visually uneven in surface after etching. Is caused, which is an unfavorable drawback when engaging in etching. Needless to say, a hard aluminum foil for electrolytic capacitors, which has a smaller amount of chemical dissolution, is required.

[0007]

The present invention has succeeded in solving the problems in the prior art as described above, that is, the present inventors have found that the visual surface of an aluminum hard foil for low pressure after etching The unevenness is the remnant of crystal grains after homogenization of the ingot, and as a result of diligent research on how to eliminate this remnant, a hard foil with a crystal grain width of 0.4 mm or less was found after etching. It was found that no visible surface unevenness occurred, and the crystal grain width of the foil was set to 0.4 mm in this way.
The hard foil described below has a rolling texture with many types of crystal orientations, and the (311) orientation in other crystal orientations other than the (200) and (220) orientations in the rolling texture of this aluminum hard foil is The present invention has been completed by finding out that the solubility in an acid-based electrolytic solution, particularly a hydrochloric acid-based electrolytic solution is promoted, and the present invention is completed as follows.

That is, the first aspect of the invention is that the aluminum purity is 99.97% or more, the crystal grain width of the surface is 0.4 mm or less, and the crystal orientation is (2211) with respect to the (311) plane.
The ratio of the reflected X-ray intensity of the (0) plane (220) / (311) is 1.0
The second aspect of the present invention is an aluminum hard foil for an electrolytic capacitor, characterized in that the aluminum purity is 99.97% or more, and the surface crystal grain width is 0.4 mm or less, and (200) plane and (31
The ratio of the reflected X-ray intensity of the (220) plane to the 1) plane (22
The aluminum hard foil for electrolytic capacitors is characterized in that 0) / {(200) + (311)} is 1.0 or more. Furthermore, in the third invention, the aluminum purity is 99.97.
% Or more, the crystal grain width of the surface is 0.4 mm or less, and the (200) plane, (220) plane and (31) of the crystal orientation are
The ratio of the reflected X-ray intensity of the (220) plane to the 1) plane (22
0) / {(200) + (220) + (311)} is 0.4
A fourth aspect of the present invention is an aluminum hard foil for electrolytic capacitors, which is characterized in that the ingot having an aluminum purity of 99.97% or more is hot-rolled after homogenization treatment to obtain a hot-rolled sheet. As a rolling condition for hot rolling in which recrystallization is generated twice or more during hot rolling to generate final recrystallization, the temperature at the entrance side of the plate is set to 400 ° C. or less and rolling is started and the temperature at the exit side is set. A method of manufacturing an aluminum hard foil for an electrolytic capacitor, which comprises performing a cold rolling at a temperature of 310 ° C. or higher and without subsequent annealing treatment.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION
More specifically, the aluminum hard foil for electrolytic capacitors is cold rolled without homogenizing and then annealing the ingot, so that the crystal structure of the ingot after homogenizing treatment is the foil. Will be affected. That is, since it can give a high capacitance, the purity is 99.97%.
As described above, preferably, based on aluminum of 99.98% or more, elements such as Fe, Si, Cu, etc. are blended or limited within a necessary range to be melted, and after degassing, removing impurities, etc., A slab having a thickness of about 500 mm was cast by a DC casting method using a water-cooled mold whose top and bottom were open,
The solution is formed at a temperature of about 0 ° C. Here, the ingot is recrystallized and the recrystallized ingot is then hot rolled. In this hot rolling, the ingot is rolled a plurality of times to a thickness that enables cold rolling.

During a plurality of times of rolling as described above, the crystal grains are stretched in the rolling direction and hot rolling is completed before there is a time margin for recrystallization, but the surface of the rolled plate is assumed to be smooth. If both ends of the hot rolled plate are cut in order to
Recrystallization is completed during this both-end cutting operation. Although the present inventors have found that the surface unevenness of the hard foil after etching is very related to this recrystallization, as described above, the width of the recrystallized grains is more important, and It has been found that when the width is 0.4 mm or less, surface unevenness after etching is eliminated. However, the inventors have also confirmed that in order to reduce the recrystallized grain width to 0.4 mm or less, it is necessary to perform a process of causing recrystallization at least twice in hot rolling. A preferable condition for generating such recrystallization is a hot rolling condition for generating final recrystallization, in which the plate temperature is 40 ° C.
Rolling starts at 0 ° C or lower and ends at a temperature of 310 ° C or higher.

The reason why the above-mentioned recrystallization eliminates the surface unevenness after etching is considered as follows. That is, the crystal grains of the ingot are stretched in the rolling direction during a plurality of rollings, but by recrystallization, new recrystallized grains are generated from the grain boundaries of the crystal grains stretched in the rolling direction and inside the grains. . In the recrystallization at this time, since the processing strain due to rolling becomes the nucleus of the recrystallization, the size is smaller than the crystal grains in the ingot before rolling, and the recrystallization of the ingot crystal grains causes the original grain boundaries to disappear. It will be. In this way, the shadow of the ingot structure, which is the cause of surface unevenness, is eliminated, but since the crystal grains along the crystal grain boundaries of the ingot remain linearly, it is possible to eliminate the surface irregularity in one recrystallization. The effect is not sufficient.

Therefore, in order to secure the phenomenon as described above, it is important to recrystallize at least twice, preferably three times or more, more preferably four times or more. The hot rolling conditions in this case are, as described above, as the rolling conditions of the hot rolling that causes the final recrystallization, the temperature at the inlet side of the plate is 400 ° C. or less, and the temperature at the outlet side is 310 ° C. Since the process ends at the above temperature, the unevenness of the surface can be preferably eliminated by doing so.

The reason why the hot rolling temperature is within the above range is that when the recrystallization temperature exceeds 400 ° C., the amount of impurities is small and the crystal grains become coarse, and the width thereof exceeds 0.4 mm. Further, if the exit temperature is less than 310 ° C., the strain that is the driving force for recrystallization is released to some extent during hot rolling, and recrystallization does not occur in the plate with the driving force thus released. Is. However, when recrystallization is performed twice or more, crystal grains are generated inside and from the grain boundaries of the crystal grains generated along the crystal grain boundaries of the ingot, and further recrystallization on the grain boundaries and on the grain boundaries is repeated to form the ingot. The remnant of the crystal texture in the image disappears properly. As a result, the grain width becomes finer,
It is presumed that this fineness eliminates the visual unevenness of the surface.

The hot-rolled sheet that has been hot-rolled as described above is then cold-rolled to form a hard foil. As described above, the rolling texture of the hard aluminum foil in which recrystallization is generated a plurality of times is: Not only (200) and (220) but (111)
(311) and (422) having various crystallographic orientation planes, among which (200) imparts acid solubility to the aluminum foil and (220) imparts acid solubility resistance. It is known. However, this specific crystal orientation alone cannot define the acid solubility of the aluminum hard foil that has undergone recrystallization a plurality of times. because,
Among the above crystal orientation planes other than (200) and (220) (3
Since (11) gives remarkably acid solubility, (31)
This is because depending on the amount of 1) present, the acid solubility cannot be defined only by defining the quantitative ratio of (200) and (220) in the foil.

Therefore, to define the acid solubility (311)
From the results of various studies by the present inventors, the reflected X-ray intensity ratio (220) / (311) of the (220) plane to the (311) plane of the crystal orientation is 1.0 or more. Or (200) plane and (311) of crystal orientation
Ratio of reflected X-ray intensity of (220) plane to (220) /
{(200) + (311)} is 1.0 or more, or the (200) plane, (220) plane, and (3
The ratio of the reflected X-ray intensity of the (220) plane to the (11) plane (22
0) / {(200) + (220) + (311)} is 0.4
It was found that an aluminum hard foil excellent in acid solubility can be obtained by the above.

In order to reduce the number of crystals in the (311) orientation, for example, the final recrystallization treatment in a plurality of recrystallization treatments in the hot rolling described above is performed at a temperature 400 at the entrance side of the plate.
Rolling is started at a temperature of ℃ or below, and the temperature on the delivery side is set to a temperature of 310 ℃ or higher. As another method, it can be achieved by a combination of the speed of hot rolling and the plate temperature of hot rolling. Therefore, in order to produce a hard aluminum foil for an electrolytic capacitor that has no surface unevenness during etching and is excellent in acid resistance, conditions for eliminating the above-described surface unevenness that occurs during etching and hot rolling conditions for reducing the (311) orientation are required. , The recrystallization is performed twice or more during the hot rolling, and the final recrystallization is generated as the rolling conditions of the hot rolling. The temperature on the side will be 310 ° C. or higher. The upper limit value of (220) / (311) of claim 1 and (220) / {(200) + (311)} of claim 2 is in practical operation of obtaining a foil without surface unevenness.
Although it is about 3.5 to 4.0, the theoretical upper limit value obtained in the present invention becomes infinite if the ideal conditions are grasped. Similarly, (220) / {(200) + (2
20) + (311)} has an actual upper limit value of about 0.9, but the theoretical upper limit value of the present invention is 1.

In the present invention, the above-mentioned crystal orientation is the reflection X
It was measured by the line intensity and was measured by the following method. In the reflection X-ray intensity measurement of CuKα (alpha) rays of the foil, Al (200), (220), (31
While fixing the detector at the position of 1) and rotating the sample in-plane at 80 rpm, rotate the sample in the range of ± 10 ° of each azimuth at a scan speed of 10 ° / min, and in the meantime.
All measurement values measured at 0.02 ° intervals were obtained as the integration degree of each azimuth. The voltage during measurement is 30 kV, the current is 20 mA, the slit width is 1 ° for the divergence slit, and the slit for receiving light.
It is 0.3 mm. Further, the number of repetitions of measurement was set to 5 and the average value was obtained.

The chemical solubility was evaluated by the following method. In order to avoid the influence of the surface oxide film, the foil was dipped in a dilute aqueous solution of hydrofluoric acid at room temperature for 20 seconds, and then the chemical solubility (against acidity) was evaluated under the following conditions. Liquid composition: 2360cc hydrochloric acid, 2640cc pure water Liquid temperature: 80 ° C Immersion time: 180 seconds

Further, the determination of surface unevenness and the measurement of crystal grain width were carried out by the following methods. Surface unevenness determination After immersing the foil in a dilute hydrofluoric acid solution at room temperature for 20 seconds, the foil is kept at 50 ° C for 8 hours.
In a mixed acid solution of 1% HCl and 1% H ₂ SO ₄ , 300 mA /
AC electrolysis at a frequency of 20 Hz was performed for 60 seconds at a current density of cm ² , and the surface unevenness was visually determined. Measurement of Crystal Grain Width The foil was electropolished and anodized in a borofluoric acid solution, and then the crystal grain was observed using a polarizing lens in an optical microscope. Thereafter, the maximum width of the crystal grains in the sample was determined from the photograph.

[0020]

EXAMPLE A concrete example of the present invention will be described. The present inventors prepared an aluminum melt having the composition shown in Table 1 below, and DC-casted the same into an ingot having a thickness of 500 mm.

[0021]

[Table 1]

The ingot obtained as described above was then homogenized at a temperature of 600 ° C. for 4 hours and hot-rolled under various conditions as shown in Table 2 below. None, and thereafter, an aluminum hard foil having a thickness of 90 μm was formed without annealing. The chemical solubility and the reflected X-ray intensity of the obtained hard foil were measured by the above-mentioned measuring methods, and the results are shown in Table 2 below.

[0023]

[Table 2]

That is, in Table 2, Test No. 1 is a comparative example in which the number of recrystallizations during hot rolling was one, and
For the test Nos. 2 and 3, the number of recrystallizations during this hot rolling was twice. Test Nos. 4 and 5 are invention examples satisfying the conditions of the method of the present invention three times, and Test Nos. 6 and 7
Although the number of recrystallizations during hot rolling was 2 in each case, it was a comparative example in which the temperature of the plate as the hot rolling condition for generating the final recrystallization did not satisfy the temperature condition of the present invention, and surface unevenness was observed. , The amount of chemical dissolution was inferior to that of the present invention, and the reflected X-ray intensity ratio and the like were lower than those of Test No. 1.

[0025]

As described above, according to the present invention, there is provided an aluminum hard foil for electrolytic capacitors, which has less surface unevenness during electrolytic etching, has low solubility in an electrolytic solution, and has good electrolytic etching properties. It is an invention that has a great effect industrially because it is possible to appropriately provide a product that immediately responds to the recent trend toward miniaturization of capacitors by establishing the preferable manufacturing method.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masahiko Katano 1-34-1 Kambara, Kambara-cho, Anbara-gun, Shizuoka Prefecture Nippon Light Metal Co., Ltd. Group Technology Center (72) Inventor Zhangyumi Kosuge 1-11 Koike, Inazawa-shi, Aichi No. 1 Nippon Light Metal Co., Ltd. Nagoya factory

Claims (4)

[Claims] 1. The aluminum purity is 99.97% or more,
The crystal grain width of the surface is 0.4 mm or less, and the reflected X-ray intensity ratio (220) / (311) of the (220) plane to the (311) plane of the crystal orientation is 1.0 or more. Aluminum hard foil for electrolytic capacitors. 2. The aluminum purity is 99.97% or more,
The crystal grain width of the surface is 0.4 mm or less, and the reflected X-ray intensity ratio of the (220) plane to the (200) plane and the (311) plane of the crystal orientation is (220) / {(200) + (31
1)} is 1.0 or more, an aluminum hard foil for electrolytic capacitors. 3. The aluminum purity is 99.97% or more,
The crystal grain width of the surface is 0.4 mm or less, and the ratio of the reflected X-ray intensity of the (220) plane to the (200) plane, the (220) plane and the (311) plane of the crystal orientation (220) / {(20
0) + (220) + (311)} is 0.4 or more, an aluminum hard foil for electrolytic capacitors. 4. In obtaining a hot-rolled sheet by hot-rolling an ingot having an aluminum purity of 99.97% or more after homogenization treatment,
The rolling conditions of hot rolling in which recrystallization is generated twice or more during hot rolling to generate the final recrystallization are as follows. 310 ° C
A method for producing an aluminum hard foil for an electrolytic capacitor, which comprises the above temperature and then cold rolling without annealing treatment.