JPH04232233A - Production of aluminum foil for anode of electrolytic capacitor - Google Patents

Abstract

PURPOSE:To form an oxidized surface film contg. a large percentage of cubic recrystallized grains and having the same thickness as a film formed in a vacuum annealing furnace by successively subjecting a high purity Al ingot to primary process annealing, secondary process annealing, cold rolling and final annealing under prescribed conditions. CONSTITUTION:An Al ingot having >=99.9wt.% purity is successively subjected to primary process annealing at >=450 deg.C, cooling to <=250 deg.C, secondary process annealing at 250-350 deg.C for 1hr, cold rolling at >=70% draft and final annealing at 250-400 deg.C.

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 anodes of electrolytic capacitors for medium and high voltages is made by roughening aluminum foil by direct current etching.
It is manufactured by chemical conversion treatment at a voltage of ~200V 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, there are many crystal grains with so-called cubic orientation, in which the (100) plane is parallel to the surface of the foil and the [001] direction is parallel to the rolling direction. It is a well-known fact that when this aluminum foil is etched, the density of columnar pits that grow perpendicular to the (100) plane increases, and the capacitance increases.

0003

[Problems to be Solved by the Invention] Various methods of manufacturing aluminum foil for electrolytic capacitor anodes have been studied using 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 an aluminum base metal with a purity of 99.99 wt% or higher, which has extremely low content of impurity elements such as Fe, Si, and Cu, and use aluminum foil for electrolytic capacitor anodes in the hot rolling, cold rolling, and final annealing processes. However, this method has the problem of high costs because the raw metal is expensive. Further, foils produced by conventional methods cannot have a high proportion of cubic-oriented crystal grains unless final annealing is performed at a high temperature of about 500° C. or higher. When final annealing is performed at such a high temperature in a normal atmospheric annealing furnace, there is a problem that significant surface oxidation occurs and etching properties deteriorate. Therefore, a special vacuum annealing furnace or an inert atmosphere annealing furnace must be used for final annealing, which poses a problem of increasing manufacturing costs.

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 aluminum foil with a concentration of about 9.9 wt%, there are many crystals with cubic orientation in the recrystallized texture after final annealing, which provides an aluminum foil with a large capacitance and also prevents surface oxidation even when an atmospheric annealing furnace is used. The purpose of the present invention is to provide a low-cost foil in which many cubic-oriented crystals are formed during final annealing at a low temperature that does not cause any problems.

[0005] The method for producing aluminum foil for electrolytic capacitor anodes of the present invention includes a step of producing foil by rolling from an aluminum ingot with a purity of 99.9 wt% or higher, which includes a first intermediate annealing treatment at a temperature of 450°C or higher. After performing a second intermediate annealing treatment in which the temperature is cooled to 250°C or lower and maintained at a temperature range of 250 to 350°C for 1 hour or more, and further cold rolling is performed at a processing rate of 70% or higher, 4
A method characterized by carrying out final annealing at a temperature of 00 ° C.
After the first intermediate annealing treatment, cold rolling is performed at a processing rate of 1 to 70% at a temperature of 250° C. or lower, and then a second intermediate annealing treatment is performed.

[0006] In the above, the aluminum ingot has a purity of 99.9 wt% or more, considering the cost.
．． It is sufficient to use less than 99 wt%. Purity 99.9
If it is less than wt%, the method of the present invention has the effect of increasing recrystallized grains with cubic orientation, but the occupancy rate of cubic orientation is 80%.
% or more, and is not suitable for practical use. Further, the aluminum material is a continuous cast plate obtained by a continuous casting and rolling method, a slab obtained by a normal manufacturing method, or the like. The present invention is applied to manufacturing aluminum foil for electrolytic capacitor anodes by homogenizing these ingots using conventional methods, hot rolling, cold rolling, intermediate annealing, foil rolling, and final annealing. .

In the present invention, before cold rolling an aluminum plate that has been homogenized and hot rolled by a conventional method, or after cold rolling by about 10 to 70%,
When the first intermediate annealing treatment is performed at a temperature of 450°C or higher, F
Impurity elements such as e and Si are completely dissolved in aluminum. The reason why the heating temperature is limited to 450°C or higher is because
This is because if the temperature is lower than 450° C., solid solution of impurity elements such as Fe and Si will be incomplete. When a batch type furnace is used, the heating and holding time is preferably 1 hour or more in order to completely dissolve impurity elements such as Fe and Si. When using a continuous annealing furnace for the first intermediate annealing treatment, it is difficult to increase the heating holding time due to the structure of the furnace, so the treatment is performed at a temperature of 500°C or higher to completely dissolve the impurity elements. It is preferable to do so.

Next, this is cooled to below 250°C, and Fe,
A state is created in which impurity elements such as Si are in a supersaturated solid solution. If the cooling temperature exceeds 250° C., the degree of supersaturation of impurity elements is low, so the amount of precipitation during the subsequent secondary heating will be small, and the precipitated intermetallic compounds will become coarse. The cooling rate is preferably 10° C./hour or more, particularly 120° C./hour or more, because it is preferable that the impurity elements do not precipitate during cooling and are in supersaturated solid solution.

[0009] Next, when this is subjected to a second intermediate annealing treatment in which the material is held in a temperature range of 300 to 450°C for 1 hour or more, solutes such as Fe and Si that have been supersaturated in solid solution during heating and heating are removed. Fe in which the elements are precipitated finely and uniformly and are dissolved in solid solution.
, the amount of solute elements such as Si decreases. Heating holding temperature 250
The reason why it is limited to the range of ~350℃ is that below the lower limit, F
Solute elements such as e and Si do not precipitate sufficiently, and on the other hand, if the upper limit is exceeded, the solute elements advance into solid solution and do not precipitate uniformly, resulting in fewer cubic-oriented recrystallized grains formed in the final annealing. be. The holding time in the secondary heating is preferably 8 to 120 hours, because the longer the holding time, the more the precipitation progresses, but the coarsening of the precipitates also progresses. During the 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 dissolved in solid solution and precipitates with a size of 1 μm or more do not affect recrystallization with a cubic orientation. In order to inhibit grain formation, it is necessary to precipitate solute elements such as Fe and Si in a fine and uniform manner.

[0010] Furthermore, after the first intermediate annealing treatment, 250°C
If cold rolling is performed at a processing rate of 1 to 70% at the following temperature and a secondary annealing treatment is performed after applying a working strain, the introduction of the working strain during the second intermediate annealing will result in supersaturated The precipitation of dissolved solute elements such as Fe and Si is promoted and the precipitates become fine and uniform. Rolling temperature is 2
The reason why the processing rate is limited to 50°C or less and 1 to 70% is that below the lower limit, the effect is not sufficient, and on the other hand, when the upper limit is exceeded, during processing or secondary annealing treatment,
This is because recrystallization progresses before the solute element starts to precipitate, and the processing strain is released, resulting in no effect. Therefore, in the first annealing treatment and the cold rolling process after cooling, it is necessary to introduce appropriate processing strain within a range that does not cause recrystallization, and the processing temperature is 150°C or less and the processing rate is 3.
~30% is more preferred.

[0011] The aluminum plate that has been subjected to the intermediate treatment as described above is then cold-rolled by 70% or more to obtain a final foil, and then final annealed at a temperature range of 250 to 400°C, resulting in a cubic orientation. A large number of recrystallized grains are formed. The cold working rate before final annealing is limited to 70% or more because if the working rate is less than 70%, recrystallization will not proceed smoothly and the number of crystal grains with cubic orientation will decrease. Final annealing temperature is 2
The reason why the temperature range is limited to 50 to 400°C is that below the lower limit, recrystallization does not complete and the processed structure remains, resulting in fewer crystal grains with cubic orientation, while above the upper limit, surface oxidation progresses significantly. This is because you end up doing it.

[0012] The aluminum foil that has been subjected to the final annealing treatment is then etched to form an anode foil for an electrolytic capacitor.

[0013] Since the final annealed aluminum foil as described above has an extremely large number of crystals with cubic orientation in the recrystallized texture, when this aluminum foil is etched, its capacitance becomes extremely large. Hereinafter, the present invention will be explained in detail with reference to Examples.

[0014]

[Example] An aluminum slab (thickness: 250 mm) having the chemical composition shown in Table 1 was homogenized by holding the chemical composition shown in Table 2 at 600°C for 10 hours, and then immediately hot rolled to reduce the thickness. A 3 mm aluminum plate was obtained. This was subjected to first and second intermediate annealing under the conditions shown in Table 1. Note that the temperature when cold rolling was performed after the first intermediate annealing treatment was the same as the cooling temperature. Then cold rolled to a thickness of 0.1mm.
An aluminum foil was prepared, and this foil was subjected to a final annealing treatment under the conditions shown in Table 1 using an atmospheric furnace. 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. Furthermore, the thickness of the oxide film on the foil surface was measured using an X-ray photoelectron analyzer. The results are also listed in Table 2.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

Effects of the Invention As is clear from Table 2, the aluminum foil produced by the method of the present invention has a larger proportion of cubic-oriented recrystallized grains than aluminum foil produced by other methods, and has surface oxidation. The film thickness is almost the same as that obtained using a vacuum annealing furnace.

Claims (2)

[Claims] Claim 1: In the process of manufacturing electrolytic capacitor anode foil by rolling from an aluminum ingot with a purity of 99.9 wt% or higher, after performing a first intermediate annealing treatment at a temperature of 450°C or higher, the aluminum ingot has a purity of 250°C or lower. Cool to 250
It is characterized by performing a second intermediate annealing treatment held at a temperature range of ℃ to 350℃ for 1 hour or more, further performing cold rolling at a processing rate of 70% or more, and then performing final annealing at a temperature of 250 to 400℃. A method for producing aluminum foil for electrolytic capacitor anodes. 2. In the process of manufacturing electrolytic capacitor anode foil by rolling from an aluminum ingot with a purity of 99.9 wt % or more, after performing a first intermediate annealing treatment at a temperature of 450° C. or higher, the temperature is 250° C. or lower. Cool to 250
After performing cold rolling at a working rate of 1 to 70% at a temperature below A method for manufacturing an aluminum foil for an electrolytic capacitor anode, which comprises performing intermediate rolling and then final annealing at a temperature of 250 to 400°C.