JPH04231442A - Production of aluminum foil for middle-and high-voltage electrolytic condenser anode - Google Patents

Abstract

PURPOSE:To inexpensively obtain annealing foil having a large electrostatic capacity by using an aluminum base metal of about 99.9wt.% purity from which the aluminum foil for middle- and high-voltage electrolytic condenser anodes having the sufficiently large electrostatic capacity cannot heretofore be obtd. by the influence of impurity elements. CONSTITUTION:This process for production consists in starting hot rolling right after an aluminum ingot having >=99.9wt.% purity is subjected to a homogenization treatment for holding for >=3 hours at >=560 deg.C, ending the passage of a temp. region where the temp. falls from 450 deg.C to 350 deg.C within 5 minutes, executing hot rolling in such a manner that the hot rolling end temp. attains <=350 deg.C, subjecting the material to intermediate annealing for >=1 hours in a temp. range of 250 to 350 deg.C before the execution of cold rolling after the hot rolling or during the course of the cold rolling and further executing cold rolling, foil rolling and final annealing.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing aluminum foil for use in electrolytic capacitor anodes.

0002

[Prior Art] Foil for medium and high voltage electrolytic capacitor anodes is made by roughening aluminum foil by direct current etching.
It is manufactured by chemical conversion treatment at a voltage of ~200 V or higher. What this aluminum foil for an anode of an electrolytic capacitor should have is a large capacitance. In the recrystallized texture of the final annealed aluminum foil, (10
0) If there are many so-called cubic crystal grains whose planes are parallel to the surface of the foil and whose [001] direction is parallel to the rolling direction, then when this aluminum foil is etched, it will be perpendicular to the (100) plane. It is a well-known fact that as the density of columnar pits that develop increases, the capacitance increases.

0003

[Problems to be Solved by the Invention] Various methods of manufacturing aluminum foil for electrolytic capacitor anodes have been proposed utilizing the above-mentioned facts. However, in the conventional method, when an aluminum ingot with a purity of about 99.9 wt% is used, the number of cube-oriented crystal grains in the recrystallized texture after final annealing does not increase too much due to the influence of impurity elements, and it is not sufficiently static. It was not possible to obtain an aluminum foil with a large capacitance. Therefore, we use aluminum ingots with a purity of 99.99 wt% or higher, which has an extremely low content of impurity elements such as Fe, Si, and Cu, and use aluminum for electrolytic capacitor anodes in the hot rolling, cold rolling, and final annealing processes. Although the foil is manufactured by this method, there is a problem in that the cost is high because the raw metal is expensive.

0004

[Means for Solving the Problems] The present invention has been made in view of the above problems, and has a purity of 9.
Even in an aluminum foil of about 9.9 wt %, there are many crystals with cubic orientation in the recrystallized texture after final annealing, and therefore the object is to provide an aluminum foil with a large capacitance.

That is, the method for producing aluminum foil for electrolytic capacitor anodes of the present invention involves immediately hot-rolling an aluminum ingot with a purity of 99.9 wt % or more after homogenizing it by holding it at 560° C. or more for 3 hours or more. Start processing,
Passing through the temperature range from 450℃ to 350℃ is completed within 5 minutes, and the hot rolling end temperature is 350℃.
Hot rolling is carried out so as to be as follows, and after hot rolling, before cold rolling or during cold rolling, 250 to 350
It is characterized by performing intermediate annealing in the temperature range of °C for 1 hour or more, and further performing cold rolling, foil rolling, and final annealing.

[0006]

[Function] In the above, the aluminum ingot has a purity of 99.9wt% or more, considering the cost.
What is necessary is to use less than wt%. Purity 99.9wt%
If it is less than 80%, the method of the present invention has the effect of increasing recrystallized grains with cubic orientation, but it is difficult to increase the occupancy of cubic orientation to 80% or more, and it is not suitable for practical use. Further, the aluminum ingot is a continuously cast plate obtained by a continuous casting and rolling method, a slab obtained by a normal manufacturing method, or the like.

[0007] In the present invention, the aluminum ingot is
When homogenization treatment is performed at 60°C or higher for 3 hours, Fe
, Si, and other impurity elements are completely dissolved in aluminum. The reason for limiting the heating temperature and time to 560°C or more and 3 hours or more, respectively, is that below the above lower limits,
This is because solid solution of impurity elements such as Fe and Si becomes incomplete. The above temperature and time are particularly 590-630°C,
Preferably, the time is 5 hours or more.

[0008] Next, hot rolling is carried out such that passing through the temperature range from 450°C to 350°C is completed within 5 minutes and the hot rolling end temperature is 350°C or less. This is because the solid-dissolved impurity elements such as Fe and Si start to precipitate as the temperature decreases during hot rolling, but the precipitates that precipitate during hot rolling are coarse particles with a size exceeding 1 μm. It is something. Precipitation during hot rolling in the composition range of the present invention is significant at 350 to 450°C, so hot rolling is carried out so that the temperature range is passed within 5 minutes and the hot rolling end temperature is 350°C or less. This is because the above precipitation can be virtually suppressed by rolling.

[0009] Next, after hot rolling, before cold rolling or during cold rolling, 1
When intermediate annealing is performed for more than 1 hour, solute elements such as Fe and Si precipitate finely and uniformly, and the solute elements such as Fe and Si materials dissolved in solid solution decrease. Intermediate annealing at 250-350℃
The reason for limiting the temperature range to 1 hour or more is that solute elements such as Fe and Si do not precipitate sufficiently below the lower limits,
On the other hand, if the temperature exceeds the upper limit, the solid solution of the solute elements will progress and will not precipitate uniformly, resulting in fewer recrystallized grains with a cubic orientation formed in the final annealing. Note that the intermediate annealing treatment conditions are particularly preferably 280 to 330°C for 5 hours or more.

[0010] The aluminum plate obtained as described above is made into a foil by cold rolling and foil rolling, and when this aluminum foil is subjected to final annealing, a large number of cubically oriented recrystallized grains are formed. The final annealing temperature is preferably 500° C. or higher because the higher the temperature, the more cubically oriented recrystallized grains are formed. This is because during final annealing, precipitates with a size of 1 μm or less do not affect the formation of recrystallized grains with a cubic orientation, but solute elements such as Fe and Si in solid solution and precipitates with a size of more than 1 μm do not affect the formation of recrystallized grains with a cubic orientation. This is because it is necessary to finely and uniformly precipitate solute elements such as Fe and Si in order to inhibit the formation of oriented recrystallized grains.

As mentioned above, in the homogenization treatment before hot rolling, after the aluminum ingot is heated to a high temperature to dissolve impurity elements such as Fe and Si, coarse precipitates that precipitate during hot rolling. By suppressing the formation of solute elements and performing intermediate annealing at an appropriate temperature range before cold rolling after hot rolling or during cold rolling, an aluminum plate with finely uniform precipitates of solute elements can be cold-rolled. When rolled and foil rolled and subjected to final annealing, a large number of recrystallized grains with cubic orientation are formed. The final annealed aluminum foil is then etched to form an electrolytic capacitor anode foil.

[0012] In the aluminum foil which has been finally annealed as described above, there are extremely many crystals with cubic orientation in the recrystallized texture, so when this aluminum foil is etched, its capacitance becomes extremely large.

[0013]

[Examples] The present invention will be explained in detail below with reference to Examples. An aluminum slab (thickness: 250 mm) having the chemical composition shown in Table 1 was homogenized and hot rolled under various conditions shown in Table 2 to obtain an aluminum plate with a thickness of 3 mm. At that time, spray coolant and heat from 450℃ 3
The time taken to pass through the temperature range until the temperature dropped to 50°C was controlled. Next, after performing intermediate annealing under the conditions shown in Table 2, cold rolling was performed to create an aluminum foil with a thickness of 0.1 mm,
This foil was subjected to a final annealing treatment at 550° C. for 1 hour in a vacuum of 0.05 to 0.001 Torr. The obtained foil was etched with an etching solution containing 50% hydrochloric acid, 47% nitric acid, and 3% hydrofluoric acid to expose crystal grains, and the proportion of cubic orientation in a field of view of 25 x 25 mm was measured. The results are also listed in Table 2.

[0014]

[Table 1]

[0015]

[Table 2]

Table 2 shows that in the aluminum foil of the present invention, the occupancy of crystal grains having cubic orientation is 84% or more, which is an excellent value. On the other hand, comparative aluminum foil No. whose homogenization temperature was lower than 560°C. 6,
Comparative aluminum foil No. whose intermediate annealing temperature is not in the range of 250 to 350°C. 7. Comparative aluminum foil No. 7 without intermediate annealing. 8. After the start of hot rolling 450
Comparative aluminum foils whose passage time in the temperature range from .degree. C. to 350.degree. C. is longer than 5 minutes are all inferior in that the occupancy rate of the crystal grains is 68% or less.

[0017]

As described above, according to the present invention, the purity is 99.
Even if the aluminum foil is about 9wt%, it is possible to have many crystals with cubic orientation in the recrystallized texture after final annealing, so it is possible to obtain an aluminum foil for anodes of medium- and high-voltage electrolytic capacitors with large capacitance. It has remarkable effects such as

Claims (1)

[Claims] [Claim 1] After homogenizing an aluminum ingot with a purity of 99.9 wt% or more and holding it at 560°C or more for 3 hours or more, hot rolling is immediately started, and 450
Hot rolling is carried out so that the passage through the temperature range from ℃ to 350℃ is completed within 5 minutes and the hot rolling end temperature is 350℃ or less, and after hot rolling or before cold rolling. A method for producing an aluminum foil for medium and high voltage electrolytic capacitor anodes, which comprises performing intermediate annealing at a temperature range of 250 to 350° C. for 1 hour or more during rolling, and further performing cold rolling, foil rolling, and final annealing.