JP3370239B2 - Aluminum hard thin plate for electrolytic capacitor and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum hard thin plate for an electrolytic capacitor and a method for manufacturing the same, and an object thereof is to provide an aluminum hard thin plate for an electrolytic capacitor which has very little surface unevenness during electrolytic etching and a method for manufacturing the same. . The thin plate in the present invention means a foil and a foil.

[0002]

2. Description of the Related Art Aluminum is used as a capacitor by taking advantage of the fact that a dense oxide film withstanding voltage can be formed on the surface by anodic oxidation and can be used as a dielectric, and the surface area can be expanded by electrochemical etching. Has been done. Aluminum used for this capacitor has a purity of 99.97% or more, preferably 99.98% or more, because high capacitance is obtained in the anode foil.
% Aluminum or more as a base, other significant or impurity elements are mixed and melted in the required range, and after degassing, removing impurities, etc., the thickness is increased by the DC casting method using a water-cooled mold with open top and bottom. Cast a slab of about 500 mm,
For solution capacitors, hot-rolling, cold-rolling to make a thin plate with a thickness of about 0.3 mm, and after annealing recrystallization, or further thin rolling without annealing for electrolytic capacitors with a thickness of about 0.1 mm It is a thin plate.

A thickness of about 0.1 mm obtained as described above
The thin plate is electrochemically perforated from both sides in an etching process using an acid-based electrolytic solution to form a large number of pits to increase the surface area, and the core is left to impart strength as a thin plate. 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. Put it in the case and seal it with the sealing material. After that, a voltage is applied to repair the scratches on the dielectric oxide film formed during the processing to obtain a finished product.

Since the aluminum thin plate for electrolytic capacitors is precisely manufactured as described above and etched with an acidic electrolyte, unevenness of the surface, which is not observed by cold rolling, becomes apparent as surface unevenness. Since it has come to be regarded as a defect in quality improvement, a thin plate having no surface unevenness is required. That is, as a method of obtaining a thin plate having less surface unevenness after etching, the present inventors have made recrystallization at least one or more times during hot rolling to refine recrystallized grains, and after passing through a rolling roll. The plate temperature is 300 to 370 ° C, the number of hot rolling passes is 2 or less, and the coil winding plate temperature after the hot rolling is 300 ° C.
A method of obtaining a hard thin plate by performing hot rolling which is less than the above and then performing ordinary cold rolling has been proposed (JP-A-6-1811).
No. 46).

[0005]

However, according to the method disclosed in Japanese Patent Laid-Open No. 6-181146, the crystal width of the obtained hard thin plate is still considerably large, at most about 0.3 mm, It is not always possible to meet such demands, and therefore, there is a demand for a thin plate having no surface unevenness.

[0006]

The present invention has been made by further studying in view of the above-mentioned actual circumstances,
The inventors of the present invention considered that the visual unevenness of the surface of the aluminum hard thin plate after etching was due to the afterimage of the crystal grain after the homogenization treatment of the ingot and the metal structure of the hot rolled sheet. As a result of diligent research on whether or not to remove the thin plate, it was found that the thin plate having a crystal grain width of 0.2 mm or less does not cause visual unevenness on the thin plate after etching. As a method for obtaining a thin plate having, it has been found that it can be obtained by a combination of the rolling reduction and the recrystallization temperature, the present invention has been completed, the purpose of the purpose, the surface unevenness visually after etching is extremely small. The present invention has succeeded in providing an aluminum hard thin plate for an electrolytic capacitor having a small amount and a high electrostatic capacity and a method for manufacturing the same, and the details thereof are as follows.

That is, the first invention is that the total value of Si and Fe is 20 to 150 ppm and the aluminum purity is 9 ppm.
9.97% or more, the width of the crystal grain on the surface of the hard thin plate is 0.2 mm
The following is a hard aluminum thin plate for an electrolytic capacitor characterized by the following.

A second aspect of the present invention is to obtain a hot-rolled sheet by hot rolling after soaking an aluminum ingot having the above-described composition and purity, after rolling at a rolling reduction of 70% or more during a hot rolling step, and then re-rolling. After crystallization, the final hot rolling condition is set to 300 to 420 for the temperature of the hot rolled sheet on the rolling roll entering side.
C, and hot rolling with a reduction rate of 50% or more, and cooling the hot-rolled sheet to a recrystallization temperature or lower while the recrystallized grain width of the surface of the rolled hot-rolled sheet does not exceed 0.2 mm, A method for producing an aluminum hard thin plate for an electrolytic capacitor, which comprises rolling at a temperature not higher than a recrystallization temperature after that.

Further, a third aspect of the invention is to obtain a hot-rolled sheet by hot rolling after soaking an aluminum ingot having the above-described composition and purity, and rolling at a rolling reduction of 70% or more during a hot rolling step. A hot-rolled sheet having a temperature of 400 to 520 ° C. is recrystallized by providing an interruption time of 60 seconds or more to the temperature, and then the final hot rolling condition is set to a temperature of the hot-rolled sheet on the rolling roll side of 300 to 420 C., hot rolling with a rolling reduction of 50% or more, and within 10 seconds after the hot rolled sheet comes into contact with a rolling roll, the hot rolled sheet on the roll exit side is cooled to a temperature of 250 ° C. or lower, and then rolled. A method for producing a hard aluminum thin plate for an electrolytic capacitor, which comprises rolling at a temperature equal to or lower than a recrystallization temperature.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Since the aluminum hard thin plate for electrolytic capacitors as described above is subjected to homogenization treatment of the ingot, hot rolling is performed, and cold rolling is performed without annealing treatment to obtain a hard thin plate. The crystal structure of the subsequent ingot and the metal structure of the hot rolled sheet obtained by hot rolling affect the final product, and the crystal structure of this ingot and the metal structure of the hot rolled sheet are the hard thin plate surface after etching. In the above, the light is recognized as the reflection of the light on each crystal face, and the appearance becomes uneven reflection of the light and is visually judged as the unevenness of the surface. As regenerated during hot rolling to eliminate visually the non-uniform reflection of light by the crystal structure after homogenization treatment of this ingot,
By setting the crystal grain width of the hard thin plate to 0.2 mm or less, it is possible to obtain an aluminum hard thin plate for an electrolytic capacitor with minimal surface unevenness.

The composition is such that the total value of Si and Fe is 20.
To 150ppm, aluminum purity is 99.97
% Or more, preferably 99.98% or more of aluminum. Here, the reason why the total value of Si and Fe is set to 20 ppm or more is that when the content is less than 20 ppm, mechanical strength is insufficient, and the distribution of intermetallic compounds is sparsely distributed, which causes such sparseness during hot rolling. Coarse crystal grains are likely to be generated at locations, and fine recrystallized grains cannot be formed. If it exceeds 150ppm,
The density of the intermetallic compound becomes high, the etching starting point increases too much, the surface of the thin plate is excessively melted, the shape of the pit is destroyed, and the capacitance is lowered. Therefore, the content of Si and Fe is 20 to 150 ppm in total of Si and Fe. Preferably, Si is 15 to 80 ppm and Fe is 10
~ 70 ppm.

If necessary, Cu is added in an amount of 5 to 100 ppm, and a compound containing Cu, such as AlCu or AlCu ₂
And the like are more noble than other compounds in terms of potential, so that the thin plate has good etching properties and the capacitance is improved.
It is preferably 5 to 50 ppm. However, the Cu content is 1
If it exceeds 00 ppm, the starting point of etching increases excessively, the surface of the thin plate is excessively melted, the shape of the pit is destroyed, and the capacitance is lowered.

The aluminum purity is set to 99.97% or more because the elements other than Si, Fe and Cu are Ti, V,
Mn, Cr, Ni, Zn, Ga, etc. are mentioned, but these are elements that increase the etching start point density either singly or as a whole, and if they are contained in large amounts, the surface melting of the thin plate excessively occurs as described above and the Since the electric capacity is lowered, the total amount of these may be regulated by the purity of aluminum. Therefore, the purity of aluminum is 99.97% or more, preferably 99.98.
% Or more.

The aluminum melt whose composition and purity are adjusted as described above is subjected to degassing, impurity removal and the like by a conventional method, and then a water-cooled mold whose upper and lower sides are opened is used.
A slab having a thickness of about 500 mm is cast by the C casting method to obtain an ingot. This ingot is kept at a temperature of about 550 ° C. or higher for about 3 hours or more for solution treatment. Here, the crystal grains of the ingot are recrystallized, and the recrystallized ingot is then hot rolled. In this hot rolling, the ingot is rolled multiple times to a thickness that enables cold rolling. During this rolling of several times, the crystal grains are extended in the rolling direction and hot rolling is completed while there is no time to recrystallize, but in order to make the surface of the rolled plate smooth, hot rolling is performed. In the case where both ends of the plate are cut, recrystallization is completed during this cutting work.

The present inventors have found that the surface unevenness of a hard thin plate after etching is closely related to the recrystallized grains on the surface of the hot-rolled plate after the hot rolling. The grain width is even more important,
It has been found that if it is finely recrystallized to have a thickness of 0.2 mm or less, the uneven surface of the hard thin plate cold-rolled after the etching can be eliminated. In the cold rolling, the crystal grains are only stretched in the rolling direction, and the width dimension does not change.

In order to make the crystal grain width of the hard thin plate as fine as 0.2 mm or less, recrystallization during hot rolling is generated at least twice, and the other recrystallization except the last recrystallization treatment is performed. The crystallization treatment is a treatment for destroying the ingot and the crystal structure after soaking, and by doing so, a uniform and fine recrystallized structure can be obtained. By recrystallizing a hot-rolled sheet that has been hot-rolled with a rolling reduction of 70% or more, the whole is recrystallized finely to form recrystallized grains having a size of about 0.5 mm or less. The rolling reduction referred to here means the total rolling reduction after the recrystallization treatment in the previous step because it is necessary to accumulate strain energy. Further, in this case, if the rolling reduction is less than 70%, the strain energy is not uniform, and a fine and uniform desired recrystallization structure cannot be obtained, and a hard thin plate having a preferable crystal width cannot be obtained even in the subsequent treatment. A preferable value of the rolling reduction is 80% or more.

In the recrystallization during the hot rolling, the temperature of the hot rolled sheet on the roll exit side is preferably 400 to 520 ° C., more preferably 450 to 500 ° C., and the time until the start of the next final hot rolling is 60 seconds. By the above, the hot rolled sheet in which the whole is uniformly and finely recrystallized as described above can be easily obtained. If the temperature is lower than 400 ° C, recrystallization tends to be insufficient, which is not preferable. Again 5
If it exceeds 20 ° C., recrystallized grains tend to grow nonuniformly and large, which is not preferable in any case.

In the final recrystallization treatment, sufficient strain energy is applied to make the driving force of recrystallization sufficient, uniform fine recrystallized grains are generated, and the structure of the ingot and the structure after soaking are caused. The purpose is to eliminate surface unevenness due to uneven light reflection of the hard thin plate, and the hot rolling condition is that the temperature of the hot rolled plate on the rolling roll side is 300 to 42.
Re-crystallized by hot rolling at 0 ° C with a rolling reduction of 50% or more, and the recrystallized grain size during recrystallization growth on the surface of the rolled hot-rolled sheet does not exceed 0.2 mm and is below the recrystallization temperature. It is intended to be cooled. By setting the temperature of the hot-rolled sheet on the rolling roll entering side to 420 ° C. or lower, the growth rate of recrystallized grains is suppressed, and the rolling reduction is set to 50% or more,
Strain energy is applied sufficiently to generate working heat to temporarily raise the temperature of at least the surface layer portion of the hot-rolled sheet to generate fine and uniform recrystallization on the sheet surface. The rolling reduction is preferably 70% or more.

Therefore, by cooling according to the growth rate of the recrystallized grains and stopping the growth, it becomes possible to easily obtain a hot-rolled sheet having a recrystallized grain size of 0.2 mm or less. In order to keep the grain size of recrystallized grains during growth to 0.2 mm or less, the hot rolled sheet should be kept at 250 ° C or less on the exit side of the roll within 10 seconds after the hot rolled sheet comes into contact with the roll on the entrance side. It is preferable to cool to a temperature of 230 ° C. or lower. More than 10 seconds and 250 ℃
If the temperature does not reach below, recrystallized grains grow to 0.2mm
It becomes difficult to obtain the following recrystallized grain size.

The temperature of the hot-rolled plate on the rolling roll entrance side is 420
If it exceeds ℃ and the rolling reduction is less than 50%, the recrystallized grain size is 0.
It becomes difficult to obtain a hot rolled sheet having fine recrystallized grains of 2 mm or less. If the temperature of the hot-rolled sheet on the rolling roll entering side is less than 300 ° C. and the rolling reduction is less than 50%, the temperature is too low to obtain uniform fine recrystallization as described above. In any case, the recrystallized grain width thus obtained is 0.2 mm.
The hot-rolled sheet and the following are rolled after the recrystallization temperature after that,
The grain width remains 0.2 mm or less and is made into a hard thin plate.

The reason why such fine recrystallization eliminates the surface unevenness after etching is considered as follows. That is, the uneven and coarse recrystallized grains recrystallized by the homogenization treatment of the ingot are visually observed on the surface of the hard thin plate after the etching even after the hot rolling and the cold rolling, and the uneven light reflection is visually observed as the surface unevenness. However, it is presumed that the above-mentioned nonuniform reflection of light can be visually observed uniformly by making the crystal grains having a very narrow crystal width over the entire surface.

[0022]

EXAMPLE A molten aluminum having the composition shown in Table 1 below was DC cast into a slab having a thickness of 400 mm.
Soaking treatment was performed at a temperature of 0 ° C. for 7 hours, and then hot rolling was started at about this soaking temperature, and hot rolling was performed under various hot rolling conditions as shown in Table 2 below.

[0023]

[Table 1]

[0024]

[Table 2]

Those hot-rolled under the conditions shown in Table 2 as described above are then cold-rolled without annealing and have a thickness of 0.
A 1 mm hard thin plate is used, and these hard thin plates are subjected to etching treatment under the following electrolytic etching conditions. In addition, electrostatic capacitance measurement and surface unevenness determination conditions, and crystal grain width measurement conditions cause electrostatic capacitance and surface unevenness. The grain width was determined. 1) Electrolytic etching conditions Etching solution: 8 wt% hydrochloric acid + 1 wt% sulfuric acid Etching temperature: 50 ° C Electrolytic waveform: Sine wave AC, frequency 20 Hz Current density: 180 mA / cm2 Electrolysis time: 270 seconds 2) Capacitance measurement Chemical solution: 50 ° C 50 g / l aqueous solution of ammonium dihydrogen adipate Formation voltage: 20 V Capacity measurement: Using a capacitance meter in the same solution at 30 ° C. 3) Electrolytic polishing of foil for measuring crystal grain width, anodic oxidation in borofluoric acid solution, and then optical Crystal grains were observed using a polarizing lens in a microscope. Then, the maximum width of the crystal grain in the sample was obtained from the photograph.

The above-mentioned measurement or judgment results are summarized as shown in Table 3 below, and the samples Nos. 1 to 20 according to the embodiments of the present invention all have a capacitance of 100.
%, The maximum width of crystal grains was 0.2 mm or less, surface unevenness was not visually observed, and the quality was excellent, while the comparative example in which the crystal grain width exceeded 0.2 mm (test number 21-29
And 31) and the comparative example (Sample No. 30) in which the capacitance does not reach 100% even if the crystal grain width is 0.2 mm or less, the surface unevenness is visually observed and the etching characteristics are low. Was known.

[0027]

[Table 3]

[0028]

As described above, according to the present invention, an aluminum hard thin plate for an electrolytic capacitor, which is excellent in quality and has little surface irregularity during electrolytic etching and is not visually observed, is appropriately provided, and a product having excellent etching characteristics is provided. Since it is possible, it is an invention that is industrially highly effective.

Front page continuation (72) Inventor Masahiko Katano 1-34-1 Kambara, Kambara-cho, Anbara-gun, Shizuoka Nippon Light Metal Co., Ltd. Group Technology Center (72) Hidehiko Ishii 1-11-1 Koike, Inazawa, Aichi No. Japan Light Metal Co., Ltd. Nagoya Plant (72) Inventor Fumio Otake 1-11-1 Koike, Inazawa City, Aichi Japan Light Metal Co., Ltd. Nagoya Plant (56) Reference JP-A-4-88153 (JP, A) ( 58) Fields investigated (Int.Cl. ⁷ , DB name) C22C 21/00-21/18 C22F 1/04-1/057 H01G 9/055

Claims (3)

(57) [Claims] 1. The total value of Si and Fe is 20 to 150 pp.
An aluminum hard thin plate for an electrolytic capacitor, characterized in that the width of crystal grains on the surface of the hard thin plate having an aluminum purity of 99.97% or more is 0.2 mm or less. 2. When the aluminum ingot having the composition and aluminum purity of claim 1 is hot rolled after soaking to obtain a hot rolled sheet, a reduction ratio of 70 during the hot rolling step.
% Or more and then recrystallized. Then, the final hot rolling condition is set to 300 to 4 for the hot rolled sheet temperature on the rolling roll entering side.
Hot rolling is performed at 20 ° C. and a rolling reduction of 50% or more, and the hot-rolled sheet is cooled to a recrystallization temperature or lower while the recrystallized grain width on the surface of the rolled hot-rolled sheet does not exceed 0.2 mm. And then rolling at a temperature equal to or lower than the recrystallization temperature after that, a method for producing a hard aluminum thin plate for an electrolytic capacitor. 3. An aluminum ingot having the composition and aluminum purity of claim 1 is soaked and then hot-rolled to obtain a hot-rolled sheet.
% To produce a hot-rolled sheet of 400 to 520 ° C., re-crystallize by providing an interruption time of 60 seconds or more at the temperature, and then the final hot rolling condition is the hot-rolled sheet temperature on the rolling roll entering side. Of 300 to 420 ° C. and hot rolling with a rolling reduction of 50% or more, and within 10 seconds after the hot rolled sheet comes into contact with the rolling roll, the hot rolled sheet on the roll exit side has a temperature of 250 ° C. or less. A method for producing a hard aluminum thin plate for an electrolytic capacitor, which comprises cooling to a temperature below the recrystallization temperature after cooling.