JP2639553B2 - Manufacturing method of aluminum foil for electrolytic capacitors - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for producing an aluminum foil for a medium-to-low pressure electrolytic capacitor, which is particularly advantageous when producing an aluminum foil for a medium-to-low pressure electrolytic capacitor. Things.

"Problems to be solved by the prior art and the invention" As is well known, in the production of conventional aluminum foil for medium and low voltage electrolytic capacitors, 9
It was common knowledge that aluminum bullion with a purity of more than 9.99% had to be used.

The above is not necessarily based on theoretically clear backing.In fact, aluminum foil actually obtained from low-pure ingots is electrolytically etched to roughen the surface, Even if it is used, impurities cause various inconveniences at the time of surface roughening, and it is difficult to guarantee the low efficiency.

Conventionally, in order to provide a capacitor foil having a stable performance, further refinement of a base metal and improvement of an etching treatment technique to be applied later to an aluminum foil have been mainly performed.

The present inventor considers that the improvement of the performance of the capacitor foil due to the high purity of the aluminum ingot is contrary to the social trend in which cost reduction is required, and in the stage of rolling the aluminum ingot, The inventors of the present invention have conducted studies to suppress the adverse effects of impurities on the performance of the capacitor foil, and have reached the present invention.

[Means for Solving the Problems] A method for producing a rolled aluminum foil after soaking an ingot from an aluminum ingot having a purity of 99.90 to 99.99% at a temperature of 550 ° C. or more and 650 ° C. or less, Hot rolled or intermediate annealing immediately before hot rolling to 400 ° C
After the temperature was raised as described above and the temperature of the rolled material was lowered from 400 ° C. to 250 ° C. within 2 minutes to complete this step,
A method for producing an aluminum foil for a medium-to-low pressure electrolytic capacitor, characterized in that the cold rolling is performed while maintaining the temperature at 0 ° C. or lower.

Here, it is assumed that the final cold rolling step may include performing a plurality of steps of cold rolling in a plurality of passes in the production of the target aluminum foil. This clearly clarifies that cold rolling refers to the final cold rolling referred to herein. Therefore, when the intended aluminum foil is obtained by performing the cold rolling step only once, it goes without saying that this cold rolling refers to the final cold rolling referred to herein.

In addition, immediately before the final cold rolling, hot rolling or intermediate annealing itself is only a step usually performed conventionally, and furthermore, hot rolling to raise the temperature of the rolled material to 400 ° C. or more This is something that has been done in the past.

However, conventionally, temperature conditions from hot rolling or intermediate annealing immediately before the final cold rolling to final cold rolling have been almost incoherent.

In the present invention, hot rolling immediately before the final cold rolling,
Or, in the intermediate annealing just before the final cold rolling, rolled material
After the temperature is raised to 400 ° C or higher, in the subsequent stages (including the latter half of hot rolling and intermediate annealing),
It is essential to shorten the time of exposure to the temperature range of ° C.

[Operation] Conventionally, when performing intermediate annealing, regardless of whether or not it is intermediate annealing immediately before final cold rolling, it is usually performed at a temperature of less than 400 ° C., for example, around 350 ° C.

However, when the intermediate annealing immediately before the final cold rolling is performed at 250 ° C. to 400 ° C., even if impurities are uniformly dissolved in the rolled material in the previous stage, the rolled material is Long exposure to the temperature range of 250 ° C to 400 ° C causes impurities to precipitate out and remain on the aluminum foil for capacitors as it is, which inconveniences later etching and adversely affects the performance of aluminum foil for capacitors did.

In the present invention, the step immediately before the final cold rolling, the step is not limited to hot rolling, even in the case of intermediate annealing, to avoid the temperature range of 250 ° C. ~ 400 ° C., One is for the above reasons.

On the other hand, the rolled material, by raising the temperature to a temperature of 400 ° C. or higher, can even be a rolled material in which the impurities are uniformly dissolved, even if it contains impurities precipitated so far. .

In the present invention, it is for this reason that the rolled material is heated to 400 ° C. or higher by hot rolling or intermediate annealing immediately before the final cold rolling.

Also, in order to uniformly dissolve the impurities, even in the case of a rolled material once heated and maintained at a temperature of 400 ° C. or higher by hot rolling or intermediate annealing, it may be used in hot finish rolling in the latter half of hot rolling. Was exposed to the range of 250 ° C to 400 ° C for a long time,
For the reasons described above, impurities are likely to preferentially precipitate in the structure of the rolled material.

Therefore, in the present invention, from 400 ℃ of rolled material of 400 ℃ or more
This step was completed by rapidly lowering the temperature to 250 ° C., and the final cold rolling was performed.

In addition, the rate of temperature decrease from 400 ° C to 250 ° C,
Although it is difficult to grasp critically, the time of the rolled material exposed to about 400 ° C. to 250 ° C. may be set within 2 minutes.

As described above, in the present invention, after the temperature is raised to 400 ° C. or higher by hot rolling or intermediate annealing immediately before final cold rolling, the rolled material is not exposed to the temperature range of 250 ° C. to 400 ° C. for a long time in the subsequent stage. It is important to do so. However, more desirably, the present invention is not limited to any step after hot rolling, and the temperature of the rolled material between 250 ° C. and 400 ° C. should be quickly raised and lowered to be implemented. This is because, once the precipitated impurities are dissolved in the rolled material by raising the temperature of the rolled material to 400 ° C. or higher, it is difficult to completely complete them.

In addition to the above, in the past, the soaking temperature was generally as low as around 500 ° C., but according to the experiments of the present inventors, the range of the soaking temperature from 550 ° C. to 650 ° C. exerted an influence on the performance of the aluminum foil for capacitors. It is appropriate to suppress the adverse effects of impurities as one factor.

This soaking temperature is more important as the purity of the aluminum ingot is lower, and when using an ingot with a purity of about 99.90 to 99.97%, the soaking temperature is desirably set to 580 ° C or higher and 650 ° C or lower, And soaking time is 4
It is desirable that the time be longer than the time.

"Examples" Examples 1 to 9 and conventional methods 1 to 3 According to the following Table 1, a 400 mm thick ingot was soaked and then rolled to a thickness of 20 mm (20 m / min) by a hot roughing mill.
After further adjusting the temperature, the coil was rolled up to a thickness of 4 mm (60 mm / min) by a hot finish rolling mill to coil up. Then, cold rolling was performed with or without intermediate annealing to obtain an aluminum foil for an electrolytic capacitor having a thickness of 0.1 mm.

In the meantime, the intermediate annealing was performed in a continuous manner in the case of the present embodiment. However, in the case of the conventional method, a batch manner (a method of raising, holding, and lowering the temperature of the rolled material with the coil up)
It was done in.

The electrolytic etching treatment and the subsequent measurement of the capacitance were performed in the following manner.

That is, first, an etching treatment was performed under the following conditions.

Electrolyte composition; mixed aqueous solution consisting of 5% hydrochloric acid and 4.2% oxalic acid Etching temperature; 54 ± 1 ° C Current density (square wave); 40 A / dm ² 30 Hz Etching time; 5 minutes After etching, these foils were distilled water. After washing with 0.5% nitric acid aqueous solution and drying sufficiently, the foil is cut into two foils A and B each having a size of 10 mm × 20 mm, and the foils A and B are subjected to a chemical conversion treatment under the following conditions. Was formed.

Chemical conversion solution; boric acid 100g + sodium tetraborate 8.25g + pure water 1
1 Chemical formation temperature; 70 ° C Chemical formation time; 20 minutes Chemical formation voltage; 80 V Thereafter, two foils A and B each having a dielectric film formed thereon are paired and opposed to each other in a 5% aqueous ammonium borate solution at 20 ° C. And the capacitance (CV product) was measured by an AC bridge.

Examples 10 to 16 and Comparative Examples 1 and 2 According to the following Table 2, after soaking an ingot having a thickness of about 400 mm, it was rolled to a thickness of about 20 to 25 mm by a hot rough rolling mill (20 to 25 mm).
mm / min), and after further adjusting the temperature, it was rolled to a thickness of about 3 to 5 mm (60 to 70 mm / min) by a hot finish rolling mill and coiled up. Then, cold rolling was performed with or without intermediate annealing to obtain an aluminum foil for an electrolytic capacitor having a thickness of 0.08 to 0.12 mm.

 The intermediate annealing was performed in a continuous manner.

Further, the electrolytic etching treatment and the subsequent measurement of the capacitance were performed in the same manner as in Examples 1 to 9. However, in Table 2 Note 1) - Note 6), N ₂ gas atmosphere either prior to electrolysis, in which was conducted at the following temperature.

That is, Note 1) and Note 2) are 300 ° C, Note 3), Note 4) and Note 5) are 450 ° C, and Note 6) is 350 ° C.

For the ingots used in Examples 10 to 16 and Comparative Examples 1 and 2, the contents of trace elements other than A1 were measured just in case. The results were as shown in Table 3 below.

[Effects of the Invention] As described above, according to the present invention, the influence of impurities contained in the raw material aluminum ingot is minimized, and a high capacitance with good reproducibility is obtained even from a low-purity ingot. It is possible to provide the indicated capacitor foil.

In particular, the soaking temperature is set at 550 ° C or higher and 650 ° C or lower, and in all steps from the start of hot rolling to the final cold rolling, the time required for raising and lowering the temperature of the rolled material between 250 ° C and 400 ° C is quickly increased. The implementation of the present invention in the following mode (the above-described Examples 1 to 6 and the like correspond thereto) is desirable for achieving the above-mentioned effects to the maximum.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Osamu Matsui 61-8 Sasaya, Yamadera-cho, Kusatsu-shi, Shiga Japan Foil Co., Ltd. Shiga Factory (72) Inventor Toshio Saito 61-8-8 Sasaya, Yamadera-cho, Kusatsu-shi, Shiga Japan (56) References JP-A-63-137505 (JP, A) JP-A-58-1046 (JP, A) JP-A-59-25943 (JP, A)

Claims (1)

(57) [Claims] 1. A method for producing an aluminum foil for a medium-to-low pressure electrolytic capacitor, comprising: soaking an ingot from aluminum ingot having a purity of 99.90 to 99.99% at a temperature of 550 ° C. or more and 650 ° C. or less; The temperature of the rolled material is raised to 400 ° C. or more by hot rolling or intermediate annealing immediately before the final cold rolling, and the temperature drop of the rolled material from 400 ° C. to 250 ° C.
A method for producing an aluminum foil for a medium-to-low pressure electrolytic capacitor, wherein the step is performed within 250 minutes, and after completing this step, the final cold rolling is performed while maintaining the temperature at 250 ° C. or lower.