JP2802730B2 - Etching method of aluminum foil for electrolytic capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for etching an aluminum foil used for an electrolytic capacitor.

[0002]

2. Description of the Related Art Generally, in the production of aluminum foil for electrolytic capacitors, electrolytic etching is performed in order to increase the effective surface area. The power supply current used for the electrolytic etching includes a direct current and an alternating current. When etching a cathode foil or an anode foil for low pressure, an alternating current that can obtain a fine corrosion pit shape is widely used. In order to reduce the size of the electrolytic capacitor, it is necessary to increase the effective area expansion ratio of the etching foil, and the composition of the etching solution is devised and improved, while the frequency of the AC power supply used, sine wave, square wave , A triangular wave, a trapezoidal wave, a distortion wave and the like. In addition, the method of etching by changing the current density and the application time of the positive half cycle and the negative half cycle of the applied AC current and dividing the etching into the former stage and the latter stage, performing the etching with the DC current in the former stage, and performing the latter stage In the former case, the positive and negative current waveforms are asymmetric, which is an advantage of the AC etching method.
The indirect electric induction method in which an aluminum foil is disposed between two electrodes and current is applied cannot be performed, and electric induction must be performed directly from the aluminum foil. In the latter case, the etching equipment must be divided into two. There is a problem.

[0003]

SUMMARY OF THE INVENTION By devising and improving an etching method using an alternating current, the effective enlargement magnification is improved.
Although it has become possible to manufacture high-capacity etched foil, on the other hand, the mechanical strength of the etched foil, represented by tensile strength and bending strength, is reduced, and it becomes brittle and easily cut when used in chemical formation. Therefore, this is a major problem when winding the capacitor element. However, the necessity of miniaturizing the capacitor is increasing more than before, and it is necessary to further increase the capacity of the etched foil. To increase the effective enlargement ratio while maintaining the mechanical strength of the etched foil,
It is an extremely difficult task to simultaneously solve conflicting relations in characteristics. One solution to this problem is to further increase the capacitance per corrosion loss (hereinafter referred to as etching efficiency). That is,
Even in the case of an etched foil having the same capacitance, in the case of a foil having a high etching efficiency, the corrosion loss is small and a large number of unetched core portions remain, so that the foil has high mechanical strength. Further, even if the corrosion loss is the same and the mechanical strength is the same, an etched foil having a high etching efficiency becomes a foil having a high capacitance. Therefore, an object of the present invention is to develop an etching method with high etching efficiency in order to solve the above-mentioned difficult problem.

[0004]

In order to achieve the above object, the present inventor has focused on a pit formation mechanism such as pit initiation, extension, and enlargement occurring during the positive half cycle of etching by an alternating current. Assuming that each stage of pit growth occurs in a different time zone during the positive half cycle, as a result of repeated studies, as shown in FIG. 1, two half waves having the same or different amplitudes during the half cycle are generated. A rest period in which a small current is applied to the positive side or the negative side within 0/15 within 1/15 of the maximum amplitude between two half-waves [time of rest period (hereinafter, t ₀ )] / When the etching is performed with the alternating current provided in the range of 0.18 to 0.85 in [half cycle time (hereinafter, T)], the etching efficiency is higher than that in the conventional etching with a single waveform. I found
That is, when etching is performed with an alternating current in which [amplitude of the preceding half-wave (hereinafter, a ₁ )] / [amplitude of the subsequent half-wave (hereinafter, a ₂ )] is in the range of 0.4 to 4.0, the cathode foil In addition, it has been found that fine pits suitable for the range of 5V to 140V formation are formed at high density, furthermore, unnecessary corrosion for pit formation is reduced, and a foil with high etching efficiency can be manufactured. When a ₁ / a ₂ is larger than 4.0, fine pits suitable for low voltage formation are formed, but the etching efficiency is reduced. Also, a ₁ / a ₂ is equal to 0.
If it is less than 4, thick pits suitable for forming a high voltage are formed, but also in this case, the etching efficiency is slightly reduced. From these, it occurs prior to the start elongation of pits in a high density in the half-wave (W _1), considering the pit generated in the half-wave (W ₂₎ by the previous half-wave (W ₁₎ after becomes thick ,
The effect is well understood.

Next, when the rest period between two half-waves exceeds to / T in the range of 0.18 to 0.85, the etching efficiency decreases. Since the etching efficiency is improved by providing an appropriate rest period, during the rest period, the etched foil surface, the already formed pit inner wall, and the previous half wave (W ₁ )
A film is formed on the inner wall of the pit formed by the above process, and when the pit is enlarged by the subsequent half-wave (W ₂ ), the weak points of the foil surface and the inner wall of the pit are repaired, and the pit can be efficiently expanded. Understood. Further, the current applied during this pause period is preferably 0, and when a current exceeding 1/15 of the maximum amplitude is applied to both the positive side and the negative side, the etching efficiency is reduced. The effect provided is understood. Next, when the ratio of the application time of the preceding half-wave (hereinafter, t ₁ ) to the application time of the subsequent half-wave (hereinafter, t ₂ ) is less than 0.5 at t ₁ / t ₂ , or 3. When the value exceeds 0, the etching efficiency decreases. In order for the pit onset and extension by the _first half-wave (W ₁ ) and the pit expansion by the _second half-wave (W ₂ ) to occur effectively, the optimal value should be set to the ratio of the application time of each half-wave. It is understood that there is. In the present invention, when the electrolyte temperature is lower than 5 ° C. or higher than 50 ° C., when the frequency is lower than 1.0 Hz or higher than 30 Hz, and when the current density is 25 mA /
If it is less than ² cm ² or more than 450 mA / cm ² , the increase in capacitance due to the increase in corrosion loss is reduced, and the etching efficiency is reduced, so that the effect of the present invention cannot be seen.

[0006]

The present invention will be specifically described below with reference to examples and comparative examples. Example 1 A soft material of aluminum foil having a purity of 99.86% and a thickness of 50 μm was used, and 4.5% by weight of hydrochloric acid and 0.9% by weight of phosphoric acid.
% And aluminum chloride at 45 ° C. in an electrolytic solution containing 2.0 wt%. As an alternating current, FIG. Using the waveform of A, a ₁ / a ₂ = 3.45, t ₁ / t ₂ =
2.67, t ₀ /T=0.45, frequency 15.0 Hz
And the current density was 280 mA / cm ² . Then, after washing with pure water, 3 V in an aqueous solution of ammonium adipate.
Was performed, and the capacitance was measured. Comparative Example 1 Using the same aluminum foil and electrolytic solution as in Example 1,
Etching was performed at 45 ° C. as an alternating current with a triangular wave having a frequency of 33.0 Hz at a current density of 280 mA / cm ² , and the same formation as in Example 1 was performed to measure the capacitance. In FIG. 2, the vertical axis represents the 3V formation capacitance (μF / cm ² ), and the horizontal axis represents the corrosion loss (g / m ² ). The 3V formation static of the etched foil obtained in Example 1 and Comparative Example 1 is shown. 4 is a graph showing an etching efficiency in a capacitance. Referring to FIG. 2, when the etching efficiency is compared with the same corrosion weight loss, the capacitance of Example 1 is higher than that of Comparative Example 1. For example, when compared with the corrosion weight loss of 30 g / m ² , the capacitance of Comparative Example 1 is 98 μF / cm 2. Example ² vs. ²
Was 113 μF / cm ² .

Example 2 A soft material of aluminum foil having a purity of 99.98% and a thickness of 100 μm was used, and 4.0 wt% of hydrochloric acid and 1.5 w of phosphoric acid were used.
t%, nitric acid 0.6 wt%, aluminum chloride 4.2
Etching was performed at 18 ° C. in an electrolytic solution containing wt%. As an alternating current, FIG. Using the waveform of B, a ₁ / a ₂ =
2.0, a ₃ / a ₁ = 0.025, t ₁ / t ₂ = 1.4
0, t _o /T=0.40, and the frequency was 5.0 Hz.
After etching at a current density of 140 mA / cm ² and washing with pure water, normal chemical conversion at 20 V was performed in an aqueous solution of ammonium adipate. Comparative Example 2 Using the same aluminum foil and electrolytic solution as in Example 2,
Etching was performed at a current density of 140 mA / cm ² with a sine wave having a frequency of 12.0 Hz as an alternating current at 18 ° C., and the same formation as in Example 2 was performed. FIG. 3 is a graph comparing the etching efficiencies of the etched foils obtained in Example 2 and Comparative Example 2 at a capacitance of 20 V formed. Referring to FIG. 3 and comparing with the same corrosion weight loss, 20
The V-formation capacitance is higher than the capacitance of Comparative Example 2, and for example, when compared at a corrosion loss of 90 g / m ² ,
In contrast to F ² / cm ² , Example 2 had 42 μF / cm ² .

Example 3 A soft material of aluminum foil having a purity of 99.98% and a thickness of 70 μm was used, containing 4.5% by weight of hydrochloric acid and 0.9% by weight of oxalic acid.
%, Nitric acid 0.5wt%, aluminum chloride 2.0w
Etching was performed at 35 ° C. in an electrolytic solution containing t%. As an alternating current, FIG. Using the waveform of C, a ₁ / a ₂ = 1.1
1, a ₃ / a ₁ = 0.03, t ₁ / t ₂ = 2.13, t
_{o /} T = 0.53, and the frequency was 10.5 Hz. After etching at a current density of 276 mA / cm ² and washing with pure water, normal conversion of 40 V was performed in an aqueous solution of ammonium adipate. Comparative Example 3 Using the same aluminum foil and electrolytic solution as in Example 3,
Etching was performed at 35 ° C. as an alternating current with a single triangular wave having a frequency of 24.0 Hz at a current density of 276 mA / cm ² , and the same chemical conversion as in Example 3 was performed. FIG. 4 is a graph comparing the etching efficiencies of the etched foils obtained in Example 3 and Comparative Example 3 at 40 V chemical conversion capacitance. FIG.
, And the same corrosion amount is compared, 40
The V-formation capacitance was higher than the capacitance of Comparative Example 3, and the capacitance of Example 3 was 10.3 at a corrosion loss of 50 g / m ² .
3 μF / cm ² was higher than 9.0 μF / cm ² of Comparative Example 3.

Example 4 Using a soft material of aluminum foil having a purity of 99.98% and a thickness of 80 μm, 9.0 wt% of hydrochloric acid and 0.4 w of oxalic acid were used.
t%, sulfuric acid 0.08 wt%, aluminum chloride 2.
Etching was performed at 25 ° C. in an electrolytic solution containing 0 wt%. As an alternating current, FIG. Using the waveform of D, a ₁ / a ₂ =
_{0.67, t 1 / t 2 =} 1.0, t o /T=0.7, was 7.0Hz frequency. Current density of 270 mA / cm ²
After washing with pure water, a normal chemical conversion at 80 V was performed in an aqueous solution of ammonium adipate. Comparative Example 4 Using the same aluminum foil and electrolytic solution as in Example 4,
Etching was performed at 25 ° C. with a single trapezoidal wave having a frequency of 10.5 Hz as an alternating current at a current density of 132 mA / cm ² , and the same formation as in Example 4 was performed. FIG. 5 shows the fourth embodiment.
9 is a graph comparing the etching efficiencies of the etched foils obtained in Comparative Example 4 and Comparative Example 4 at 80 V chemical conversion capacitance. Referring to FIG. 5, when compared at the same corrosion weight loss, the 80 V chemical conversion capacitance of Example 4 is higher than the capacitance of Comparative Example 4, and the capacitance of Example 4 at a corrosion weight loss of 70 g / m ² is 5.7μF / cm ² and Comparative example 5.0μF / cm ² from 14
%it was high.

The bending strength and tensile strength of the foils etched in Examples 1, 2, 3, and 4 and Comparative Examples 1, 2, 3, and 4 were measured. As shown in Table 1, according to the etching method of the present invention, it is possible to produce a foil having a high capacitance with the same corrosion loss and the same mechanical strength.

[Table 1. In addition to the alternating current waveforms shown in the _{first, second, third} and fourth embodiments, the same effect can be obtained with a square wave or a distorted wave, and the former half wave (W ₁ ) and the latter half wave (W ₂ ) are different. The same effect was obtained with a combination of different waveforms.

[0011]

As described above, according to the present invention, two half-waves are included in a half-period, and the amplitude between the two half-waves is 0 or a minute current is on the positive side or the negative side and is 1 / the maximum amplitude. 1
By using an alternating current having a rest period applied within 5 as an etching power source, a foil having high etching efficiency can be manufactured, and the effective enlargement ratio can be increased without lowering the mechanical strength. Further, since two half waves are provided in a half cycle to improve the etching efficiency by dividing the pit forming process of one cycle of the alternating current into the former stage and the latter stage, it is not necessary to divide the etching equipment into two. It is also suitable for rationalizing production equipment. The foil produced according to the present invention contributes to the miniaturization of the electrolytic capacitor as a cathode foil and an anode foil for low pressure.

[Brief description of the drawings]

FIG. 1A is a diagram showing an alternating current waveform in Example 1.

FIG. 1B is a diagram showing an alternating current waveform in the second embodiment.

FIG. 1C is a diagram showing an AC current waveform in the third embodiment.

FIG. 1D is a diagram showing an AC current waveform in Example 4.

FIG. 2 is a comparison of the etching efficiency of the foils obtained in Example 1 and Comparative Example 1 at 3V formation capacitance.

FIG. 3 shows a comparison of the etching efficiency of the foils obtained in Example 2 and Comparative Example 2 at 20V chemical conversion capacitance.

FIG. 4 is a comparison of the etching efficiency of the foils obtained in Example 3 and Comparative Example 3 at 40V formation capacitance.

FIG. 5 is a comparison of the etching efficiency of the foils obtained in Example 4 and Comparative Example 4 at 80V formation capacitance.

[Table 1]

Claims (5)

(57) [Claims] 1. A method of manufacturing an aluminum foil for an electrolytic capacitor, wherein an alternating current is applied to an aluminum foil in an electrolytic solution containing chlorine ions to perform etching, wherein the alternating current has a waveform during a positive half cycle and a negative half cycle. Any one or all of the amplitude and the application time include two half-waves that are the same or different, and the amplitude is 0 or a minute current is applied to the positive or negative side within 1/15 of the maximum amplitude. A method for etching an aluminum foil for an electrolytic capacitor, wherein a rest period is provided between each half-wave. 2. The method according to claim 1, wherein two half-waves in the half-cycle of the alternating current are one of a sine wave, a triangular wave, a trapezoidal wave, a square wave, and a distorted wave. 2. The method for etching an aluminum foil for an electrolytic capacitor according to claim 1, wherein the ratio of (the amplitude of the former half wave) / (the amplitude of the latter half wave) is in the range of 0.4 to 4.0. 3. In the half cycle of the alternating current, the ratio of the application time of the previous half wave to the application time of the subsequent half wave is (the application time of the previous half wave) / (the application time of the subsequent half wave) is 0. 3. The method for etching an aluminum foil for an electrolytic capacitor according to claim 1, wherein the thickness is in the range of 0.5 to 3.0. 4. In a half cycle of the alternating current, the amplitude is 0 or less, and a minute current is present on the positive or negative side at 1/15 of the maximum amplitude.
4. The electrolysis according to claim 1, wherein a rest period applied within two half-waves is set to 0.18 to 0.85 by (pause time) / (half cycle time). Method for etching aluminum foil for capacitors. 5. The electrolytic solution is an aqueous solution containing chloride ions as a main component and further containing phosphate ions, sulfate ions, nitrate ions, oxalate ions or the like alone or in combination, and has a temperature of 5 ° C. to 50 ° C. claims a range frequencies in these electrolyte solution and applying an alternating current the current density is in the range of 25mA / cm ² of 450 mA / cm ² to the aluminum foil at 30Hz in the range of 1.0Hz The method for etching an aluminum foil for an electrolytic capacitor according to 1, 2, 3, or 4.