JPH07235456A - Etching method of aluminum foil for electrolytic capacitor - Google Patents

Abstract

PURPOSE:To enhance the etching efficiency by providing two half waves where at leant one or all of the waveform, amplitude and applying time is identical or different and setting a pause interval for applying a positive or negative microcurrent having an amplitude equal to zero or within a specific ratio to the maximum amplitude between respective half waves. CONSTITUTION:Two half waves, where at least one or all of the waveform, amplitude and applying time is identical or different, are provided within the positive or negative half period of AC current. A pause interval for applying a microcurrent having amplitude equal to zero or within 1/15 of maximum amplitude to the positive or negative side is set between respective half waves. Consequently, the etching efficiency can be enhanced and useless corrosion can be reduced.

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 aluminum foil used for electrolytic capacitors.

[0002]

2. Description of the Related Art Generally, in the production of aluminum foil for electrolytic capacitors, electrolytic etching is carried out for the purpose of expanding its effective surface area. The power supply current used for this electrolytic etching includes direct current and alternating current, but in the case of etching the cathode foil or the low voltage anode foil, an alternating current that produces a fine corrosion pit shape is widely used. In order to realize the downsizing of electrolytic capacitors, it is necessary to increase the effective surface expansion ratio of the etching foil, and while the composition of the etching solution is devised and improved, the frequency of the AC power supply used, sine wave and square wave are used. Inventions relating to waveforms such as a triangular wave, a trapezoidal wave, and a distorted wave have been made. 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 alternating current to be applied and the etching are divided into the front stage and the rear stage, and the direct current is used for the etching in the front stage Although a method of etching with an alternating current has been developed in the above, in the former case, the current waveforms on the positive and negative sides are asymmetrical, which is an advantage of the alternating etching method.
The indirect electricity introduction method of applying an electric current by arranging aluminum foil between two electrodes cannot be performed, and electricity must be introduced directly from the aluminum foil. In the latter case, the etching equipment must be divided into two. There is a problem.

[0003]

The effective surface enlargement ratio is improved by devising and improving the etching method using an alternating current.
It has become possible to manufacture high-capacity etched foil, but on the other hand, the mechanical strength of the etched foil, which is represented by tensile strength and bending strength, decreases, and it becomes brittle and easy to cut when used for chemical conversion. Therefore, it becomes a big problem when winding the capacitor element. However, the need for capacitor miniaturization is increasing more than ever before, and it is necessary to further increase the capacitance of the etched foil. To increase the effective surface expansion ratio while maintaining the mechanical strength of the etched foil,
It is to solve at the same time conflicting characteristics, which is extremely difficult. One of the solutions to this problem is to further increase the electrostatic capacity per corrosion weight 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 amount of corrosion loss is small, and a large amount of unetched core remains, so that the foil has high mechanical strength. Further, an etched foil having the same corrosion weight loss and high mechanical strength and high etching efficiency has high electrostatic capacity. Therefore, the present invention aims to develop an etching method with high etching efficiency in order to solve the above-mentioned difficult problems.

[0004]

In order to achieve the above object, the inventor of the present invention has focused on a pit formation mechanism such as pit start, extension, and expansion that occurs in the positive half cycle of etching by an alternating current. As a result of repeated studies assuming that each stage of growth of these pits occurs in different time domains in the positive half cycle, two half waves of the same or different amplitude are generated in the half cycle as shown in Fig. 1. A quiescent period is included between the two half-waves and has an amplitude of 0 or a minute current is applied to the positive or negative side within 1/15 of the maximum amplitude [pause period time (hereinafter, t ₀ )] / When etching with an alternating current provided in the range of 0.18 to 0.85 for [half cycle time (hereinafter, T)], the etching efficiency is higher than that of the conventional single waveform etching. Found out.
That is, when etching is performed with an alternating current having a [amplitude of front half wave (hereinafter, a ₁ )] / [amplitude of rear half wave (hereinafter, a ₂ )] in a range of 0.4 to 4.0, the cathode foil It has been found that fine pits suitable for the range of 5V to 140V formation are formed at high density, and less wasted corrosion is required for forming the pits, and a foil with high etching efficiency can be manufactured. If 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 0.
If it is less than 4, thick pits suitable for high voltage formation are formed, but in this case as well, the etching efficiency is slightly lowered. 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 the two half waves exceeds the range of 0.18 to 0.85 in to / T, the etching efficiency decreases. Since etching efficiency is improved by providing a proper rest period, the surface of the etched foil, the inner wall of the pit already formed and the front half-wave (W ₁ ) during this rest period are improved.
A film is formed on the inner wall of the pit formed by the method, and when the pit is expanded by a later half-wave (W ₂ ), the weak points on the foil surface and the inner wall of the pit are repaired to enable efficient expansion of the pit. To be understood. In addition, the current applied during the rest period is preferably 0, and if the current is applied in excess of 1/15 of the maximum amplitude on both the positive side and the negative side, the etching efficiency is lowered, and therefore the rest period is also set. The effect provided is understood. Next, when the ratio of the application time of the former half wave (hereinafter, t ₁ ) and the application time of the latter half wave (hereinafter, t ₂ ) is less than 0.5 at t ₁ / t ₂ , or 3. If it exceeds 0 and becomes large, the etching efficiency decreases. This means that in order for the start and extension of the pit by the front half wave (W ₁ ) and the expansion of the pit by the rear half wave (W ₂ ) to occur effectively, the optimum value for the ratio of the application time of each half wave is Understood to be. In the present invention, when the electrolyte temperature is lower than 5 ° C or higher than 50 ° C, the frequency is lower than 1.0 Hz or higher than 30 Hz, and the current density is 25 mA /
When it is less than cm ² or more than 450 mA / cm ² , the increase in electrostatic capacitance due to the increase in corrosion weight loss is lowered and the etching efficiency is lowered, so that the effect of the present invention cannot be seen.

[0006]

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples. Example 1 Using a soft material of aluminum foil having a purity of 99.86% and a thickness of 50 μm, hydrochloric acid was 4.5 wt% and phosphoric acid was 0.9 wt.
%, Aluminum chloride was etched at 45 ° C. in an electrolyte solution containing 2.0 wt%. As an alternating current, Figure 1. 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 ammonium adipate aqueous solution
The usual chemical conversion 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 a current density of 280 mA / cm ² with a triangular wave having a frequency of 33.0 Hz as an alternating current at 45 ° C., and the same formation as in Example 1 was performed to measure the capacitance. In FIG. 2, the vertical axis shows the 3V conversion capacitance (μF / cm ² ) and the horizontal axis shows the corrosion weight loss (g / m ² ), and the etched foils obtained in Example 1 and Comparative Example 1 are subjected to 3V formation. It is a graph which shows the etching efficiency in electric capacity. Referring to FIG. 2, when the etching efficiencies are compared at the same corrosion weight loss, the capacitance of Example 1 is higher than that of Comparative Example 1. For example, when the corrosion weight loss is 30 g / m ² , the capacitance of Comparative Example 1 is 98 μF / cm 2. ² against Example 1
Was 113 μF / cm ² .

Example 2 Using a soft material of aluminum foil having a purity of 99.98% and a thickness of 100 μm, hydrochloric acid was 4.0 wt% and phosphoric acid was 1.5 w.
t%, nitric acid 0.6 wt%, aluminum chloride 4.2
Etching was performed at 18 ° C. in an electrolyte 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, it was the frequency with 5.0Hz.
After etching at a current density of 140 mA / cm ² and washing with pure water, a conventional chemical conversion of 20 V was carried out 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 20V conversion capacitance. As shown in FIG. 3, when comparing the same corrosion weight loss, 20
The V formation capacitance is higher than that of Comparative Example 2. For example, when comparing with corrosion weight loss of 90 g / m ² , 38 μ of Comparative Example 2 is obtained.
In Example 2, it was 42 μF / cm ² with respect to F ² / cm ² .

Example 3 Using a soft material of aluminum foil having a purity of 99.98% and a thickness of 70 μm, 4.5 wt% of hydrochloric acid and 0.9 wt of oxalic acid.
%, Nitric acid 0.5 wt%, aluminum chloride 2.0 w
Etching was performed at 35 ° C. in an electrolytic solution containing t%. As an alternating current, Figure 1. 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, a conventional chemical 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 a current density of 276 mA / cm ² with a single triangular wave having a frequency of 24.0 Hz as an alternating current at 35 ° C., and the same formation 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 a 40 V conversion capacitance. Figure 4
When comparing the same amount of corrosion with reference to FIG.
The V formation capacitance is higher than the capacitance of Comparative Example 3, and at a corrosion weight loss of 50 g / m ² , the capacitance of Example 3 is 10.
It was 3 μF / cm ² and 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, hydrochloric acid was 9.0 wt% and oxalic acid was 0.4 w.
t%, sulfuric acid 0.08 wt%, aluminum chloride 2.
Etching was performed at 25 ° C. in an electrolyte solution containing 0 wt%. As an alternating current, Figure 1. 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
Etching was performed on the substrate, and the substrate was washed with pure water, and then subjected to a conventional chemical conversion of 80 V in an aqueous ammonium adipate solution. Comparative Example 4 Using the same aluminum foil and electrolytic solution as in Example 4,
Etching was carried out at a current density of 132 mA / cm ² with a single trapezoidal wave having a frequency of 10.5 Hz as an alternating current at 25 ° C., and the same formation as in Example 4 was performed. FIG. 5 shows the fourth embodiment.
6 is a graph comparing etching efficiencies of the etched foils obtained in Comparative Example 4 with 80 V chemical conversion capacitance. Referring to FIG. 5, when comparing with the same corrosion weight loss, the 80V formation capacitance of Example 4 is higher than the capacitance of Comparative Example 4, and at a corrosion weight loss of 70 g / m ² , the capacitance of Example 4 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, 4 and Comparative Examples 1, 2, 3, 4 were measured. As shown in Table 1, according to the etching method of the present invention, it is possible to manufacture a foil having the same corrosion weight loss and a high capacitance even if the mechanical strength is the same.

[Table 1. Besides the AC current waveforms shown in Examples 1, 2, 3 and 4, the same effect can be obtained with a square wave or a distorted wave, and the front half wave (W ₁ ) and the rear 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, the half-cycle includes two half-waves and the amplitude between the two half-waves is 0 or the minute current is 1 / maximum of the maximum amplitude on the positive or negative side. 1
By using an alternating current with a rest period applied within 5 as an etching power source, it is possible to manufacture a foil with high etching efficiency, and it is possible to increase the effective surface expansion ratio without lowering the mechanical strength. Also, since two half waves are provided in the half cycle and the pit formation process of one cycle of the alternating current is divided into the front stage and the rear stage to improve the etching efficiency, it is not necessary to divide the etching equipment into two. It is also suitable for rationalizing production equipment. The foil produced by the present invention contributes to downsizing of an electrolytic capacitor as a cathode foil and a low voltage anode foil.

[Brief description of drawings]

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

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

FIG. 1C is a diagram showing an alternating current waveform according to the third embodiment.

FIG. 1D is a diagram showing an alternating current waveform according to the fourth embodiment.

FIG. 2 is a comparison of etching efficiencies of the foils obtained in Example 1 and Comparative Example 1 in 3V conversion capacitance.

FIG. 3 is a comparison of etching efficiencies of foils obtained in Example 2 and Comparative Example 2 at a 20V conversion capacitance.

FIG. 4 is a comparison of etching efficiencies of foils obtained in Example 3 and Comparative Example 3 at a 40 V conversion capacitance.

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

[Table 1]

Claims (5)

[Claims] 1. A method of manufacturing an aluminum foil for an electrolytic capacitor, wherein an aluminum foil is etched by applying an alternating current in an electrolytic solution containing chlorine ions, wherein the alternating current has a waveform during positive and negative half cycles. , Any one of the amplitude and the application time or all of them have the same or different half waves, and the amplitude is 0 or a minute current is applied to the positive side or the negative side within 1/15 of the maximum amplitude. A method for etching aluminum foil for electrolytic capacitors, characterized in that a rest period is provided between each half wave. 2. The 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, and the amplitude of the front half wave and the amplitude of the rear half wave. The method for etching an aluminum foil for an electrolytic capacitor according to claim 1, wherein a ratio of (amplitude of front half wave) / (amplitude of rear half wave) is in the range of 0.4 to 4.0. 3. The ratio of the application time of the front half wave to the application time of the subsequent half wave in the half cycle of the alternating current is (the application time of the front half wave) / (the application time of the rear half wave) is 0. The method for etching an aluminum foil for an electrolytic capacitor according to claim 1 or 2, wherein the etching rate is in the range of 0.5 to 3.0. 4. In a half cycle of an alternating current, the amplitude is 0 or, and a small current on the positive side or the negative side is 1/15 of the maximum amplitude.
The electrolysis according to claim 1, 2 or 3, wherein a rest period applied within is provided between two half waves by (rest period time) / (half cycle time) from 0.18 to 0.85. Method for etching aluminum foil for capacitors. 5. The electrolytic solution is an aqueous solution containing chlorine ions as a main component and phosphate ions, sulfate ions, nitrate ions, oxalate ions or the like alone or in combination, and the temperature is 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 1. A method for etching an aluminum foil for an electrolytic capacitor according to 1, 2, 3 or 4.