JP2005268427A - Method for manufacturing etching foil for aluminum electrode capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly productive etching method for realizing the increase of the capacitance of an etching foil for an aluminum electrode capacitor. <P>SOLUTION: In this etching process for roughening aluminum or an aluminum alloy foil by AC application in etching solution containing chlorine ion; the waveform of AC currents is constituted of principal waveform and complementary waveform, the main waveform is AC waveform of 2 cycles or more, the frequency of complementary waveform is made higher than the frequency of principal waveform, and the complementary waveform is AC waveform of 2 to 10 cycles. The AC waveform is repeated while the impression time of the principal waveform is 1 to 30 seconds, and the rate of the maximum amplitude of the complementary waveform to the maximum amplitude of the principal waveform is 0.5 to 1.2. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing an aluminum electrolytic capacitor etching foil (hereinafter referred to as an etching foil).

In manufacturing the etching foil, in order to increase the effective surface area and increase the capacitance of the electrolytic capacitor, the etching process is performed by applying direct current or alternating current in a solution containing hydrochloric acid.
Conventionally, chemical etching, electrolytic etching, and the like have been employed for the etching process, but electrolytic etching using an alternating current is widely performed for the low-pressure anode foil (see, for example, Non-Patent Document 1).
By Isaya Nagata, “Electrolyte cathode aluminum electrolytic capacitor (aluminum dry electrolytic capacitor augmented and revised edition, published by Nihon Densetsu Kogyo Co., Ltd., February 24, 1997, second edition, first edition) p.226-228, p.236 ~ 239

The effective enlargement ratio has been improved by the inventive method and ingenuity of the etching method, and it has become possible to manufacture high-capacity etching foils.In recent years, however, the need for miniaturization of capacitors has increased more than ever. It is necessary to increase the capacity.
In order to increase the capacity of the etching foil, it is necessary to increase the capacity per thickness, and while the ingenuity and improvement of the etching solution composition are performed, many inventions relating to the frequency and waveform of the AC power supply used have been made. Yes.
For example, a technique is disclosed in which AC etching at frequencies lower than commercial frequencies of 50 Hz and 60 Hz is effective (see, for example, Patent Document 1).
Further, it has been reported that the effective area expansion magnification can be increased by devising the waveform of the alternating current as compared to a current waveform having a simple shape such as a sine wave or a rectangular wave (see, for example, Patent Document 2).
Further, a method has been developed in which the etching is divided into a front stage and a rear stage, and the frequency is sequentially lowered (see, for example, Patent Document 3) and the current density is successively increased.
A technique is also disclosed in which an etching magnification can be increased by using an alternating current having a waveform in which a low frequency and a high frequency are alternately repeated every cycle (see, for example, Patent Document 4).
Japanese Examined Patent Publication No. 54-43177 JP 58-22390 A JP-A-2-239610 Japanese Patent Publication No. 5-61767

As described above, the method of regulating the frequency of alternating current or improving the waveform shape increases the surface area as the amount of aluminum dissolved increases, but even if the amount of dissolution increases after a certain point, The surface area is rather reduced.
Here, in the etching method using an alternating current, a thin hydrated film or a hydroxide film generally formed by a reduction reaction or a chemical reaction exists on the surface of the applied aluminum foil. The generated defect point is the starting point of corrosion.
Under the etching conditions using alternating current with positive and negative symmetric waveforms, these films have essentially different reactions on the positive and negative sides, causing a shift in the reduction reaction or chemical reaction. The amount of film changes. As a result, with the progress of etching, appropriate defect points are hardly formed even when an alternating current is applied.
If the method of changing the magnitude of the alternating current for each etching stage is improved as compared with the case of using a single stage, the surface area increases gradually as the etching progresses.

Considering the ideal current waveform shape, it is necessary to make the current waveform on the positive side and the negative side asymmetric, and a method of etching by changing the current density and application time on the positive side and the negative side has been proposed. However, it is necessary to apply a current directly to the aluminum foil, and there is a problem that a large current cannot flow.
Further, the interval of one cycle in the method using an alternating current having a waveform in which a low frequency and a high frequency are alternately repeated every cycle is not appropriate when aiming at further higher magnification.
Furthermore, methods for applying a film by applying an anodic oxidation method or a heat oxidation method in the middle of the etching process have been studied, but the film formed by these methods is too uniform or has many irregularities. For example, it was not always effective as a film in the etching process.
Due to the above-described problems, there has been a demand for an etching method that has a high productivity and is capable of increasing the capacity of the etching foil because the surface area is unlikely to decrease even when etching proceeds.

The present invention solves the above-mentioned problem, and in an etching step of roughening aluminum or aluminum alloy foil by applying an alternating current in an etching solution containing chlorine ions,
The waveform of the AC current is composed of a main waveform and a sub waveform, the main waveform is an AC waveform of 2 cycles or more, and the sub waveform is a higher frequency than the main waveform and an AC waveform of 2 to 10 cycles. It is the manufacturing method of the etching foil for aluminum electrolytic capacitors characterized.

  Further, the AC waveform is a repetitive waveform in which the application time of the main waveform is 1 to 30 seconds.

The ratio of the maximum amplitude of the sub waveform to the maximum amplitude of the main waveform is 0.5 to 1.2.
In this etching method, the film generated in the main waveform (waveform A) of the etching progress is appropriately modified and generated by the sub-waveform (waveform B). Moreover, since it is a positive / negative symmetrical alternating current and it is not necessary to apply a current directly to the aluminum foil, high productivity can be realized.

As described above, as an alternating current, a main waveform (waveform A) composed of an alternating waveform of two cycles or more and a sub waveform (waveform B) composed of an alternating waveform of 2 to 10 cycles at a higher frequency than the main waveform, By alternately applying the main waveform for an application time of 1 to 30 seconds, the capacity of the etching foil can be increased as compared with the case where an alternating current having a single waveform is used.
That is, by appropriately modifying and generating the film generated in the main waveform A, which is the main component of the etching, by the sub waveform B, etching with high etching efficiency proceeds, and as a result, the amount of aluminum dissolved increases. Even so, the increase in effective surface area is not suppressed, and an etching foil having a high electrostatic capacity can be obtained.
Moreover, it can be used with an alternating current having a positive / negative symmetrical waveform. In other words, it is not necessary to apply a current directly to the aluminum foil by changing to an asymmetric waveform to eliminate the reaction between the positive side and the negative side, and changing the current density and application time. It can be used as it is, and productivity can be improved.

Hereinafter, the present invention will be specifically described.
AC electrolytic etching was performed at 30 ° C. in an electrolytic solution containing 6.0 wt% hydrochloric acid and 1.0 wt% phosphoric acid using a hard material of aluminum foil having a purity of 99.86% and a thickness of 50 μm. Etching was performed with the main waveform A and the sub waveform B under the conditions shown in Table 1 as the alternating current.
Next, the etching foil was washed with pure water, subjected to chemical washing treatment with a 3.0 wt% phosphoric acid aqueous solution at 45 ° C. for 2 minutes, and washed with pure water.
Then, after forming 20V in 10 wt% ammonium adipate aqueous solution, the electrostatic capacity was measured, and the results shown in Table 1 were obtained.

Under the electrolysis conditions shown in Table 1, the maximum amplitude of the applied current and the amount of electricity were the same in the comparative example and the conventional example. For the conventional example, a single sine wave with a frequency of 10 Hz was used as an alternating current.
For Examples 1 to 15, an alternating current having a main waveform A with an application time t at the frequency shown in Table 1 and an alternating current repeating the sub waveform B of the frequency shown in Table 1 by the number of cycles n were alternately applied. AC current was used.
An example of the waveform of Examples 1-6 is shown in FIG.

In Examples 1 to 6, the application time t of the main waveform A is changed between 0.1 and 60 seconds, and t = 0.1 seconds (Example 1) and t = 60 seconds (Examples). In 6), since the effect of improving the capacitance is not observed as compared with the conventional example, t is preferably 1 to 30 seconds.
In Examples 4 and 7 to 10, when the difference due to the number of cycles n of the sub-waveform B in one repetitive waveform is compared, when n = 1 (Example 7) and n = 15 (Example 10), compared to the conventional example. The cycle number n is preferably 2 to 10 because the effect of improving the capacitance is not observed.
In Example 8, 11-14, when the difference by the ratio of the maximum amplitude of the sub waveform B to the maximum amplitude of the main waveform A is compared, Example 11 of 0.2 and Example 14 of 1.5 are conventional examples. In view of the fact that no effect is observed, the range of 0.5 to 1.2 is preferred.
In Examples 4 and 15, the frequency of the sub waveform B with respect to the frequency of 10 Hz of the main waveform A is preferably 15 Hz and 20 Hz. However, when the frequency of the sub waveform B is 2 Hz and 5 Hz which are lower than the frequency of the main waveform A as in Comparative Examples 1 and 2, the capacitance decreases.

In addition, this invention is not limited to the said Example, You may combine with a well-known etching method, various electric current waveforms, the etching method made multistage.
In the above embodiment, sine waves are used for the main waveform A and the sub waveform B. However, the same effect can be obtained by applying various basic waveforms such as a rectangular wave, a triangular wave, and a trapezoidal wave.
Further, the basic waveform of the main waveform A and the sub waveform B may be different from each other.
Further, as the etching progresses, the surface state of the aluminum foil changes, so it is more effective to divide the etching into a plurality of stages and change the conditions for both the main waveform A and the sub waveform B for each stage. is there. Specifically, the application time t of the main waveform A may be shortened as the etching progresses, that is, the latter half of the stage.

It is a waveform diagram of an alternating current according to an embodiment of the present invention.

Claims (3)

In the etching step of roughening aluminum or aluminum alloy foil by applying an alternating current in an etching solution containing chlorine ions,
The waveform of the AC current is composed of a main waveform and a sub waveform, the main waveform is an AC waveform of 2 cycles or more, and the sub waveform is a higher frequency than the main waveform and an AC waveform of 2 to 10 cycles. A method for producing an etching foil for an aluminum electrolytic capacitor.   The method for producing an etching foil for an aluminum electrolytic capacitor, wherein the AC waveform according to claim 1 is a repetitive waveform in which the application time of the main waveform is 1 to 30 seconds.   A method for producing an etching foil for an aluminum electrolytic capacitor, wherein the ratio of the maximum amplitude of the sub waveform to the maximum amplitude of the main waveform according to claim 1 is 0.5 to 1.2.

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