JPH07326547A - Manufacture of cathode foil for aluminum electrolytic capacitor - Google Patents

Abstract

PURPOSE:To provide aluminum cathode foil for electrolytic capacitors, which prevents the decrease in capapcitance and short circuits. CONSTITUTION:A manufacturing method includes a step of subjecting aluminum foil 28 including impurity copper to DC electrolytic etching and/or chemical in an etching container 23, a step of removing copper material deposited on the aluminum foil 28 during the etching in a copper removing container 25. After the copper deposited on the aluminum foil is oxidized by heat treatment in a furnace 24, and the copper is dissolved by an acid and removed in the copper removing container 25.

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 a cathode foil for aluminum electrolytic capacitors used in various electronic devices.

[0002]

2. Description of the Related Art Miniaturization and high reliability of aluminum electrolytic capacitors have been promoted in order to miniaturize electronic devices and increase reliability. For this purpose, it is necessary to increase the capacity and reliability of the aluminum foil.For the cathode foil, it is necessary to improve the capacity and reduce the amount of copper remaining on the surface of the aluminum foil after etching, which greatly affects the reliability of the product. is important.

A conventional method for manufacturing a cathode foil for an aluminum electrolytic capacitor will be described below. FIG. 8 shows an outline of the manufacturing process of a conventional cathode foil for aluminum electrolytic capacitors. In FIG. 8, 1 is an unwinding roll, 2 is a pretreatment bath, 3 is an etching bath, 4 is a copper removing bath, 5 is a post-treatment bath, 6 is a winding roll, 7 is an aluminum foil, 8 is a DC power supply,
Reference numeral 9 is a cathode plate, and 10 is a drying furnace.

As the aluminum foil 7, 0.1% copper as an impurity is used.
Aluminum foil having a thickness of 20% to 50 μm containing 1% is used, and after the surface of the aluminum foil 7 has been cleaned by pretreatment in the pretreatment tank 2, it contains a trace amount of additive and
At the same time as immersing in the etching bath 3 having a hydrochloric acid-based etching solution heated to 90 ° C., the aluminum foil 7 is used as an anode, and the cathode plates 9 arranged in parallel on both sides of the aluminum foil 7 are used as a cathode, and a direct current is supplied from a DC power source 8. Is applied to chemically and electrically etch the surface of the aluminum foil 7 to increase the surface area.

By the etching in this etching step, aluminum and copper are dissolved out in the etching solution and are present in the etching solution as aluminum ions and copper ions. Then, during this etching, some copper ions are deposited as copper on the cathode plate 9, and some of the remaining copper ions are deposited as copper on the surface of the aluminum foil 7, and the copper removal step 4 of the next step is performed as it is. Be brought in.

Next, decoppering for removing the copper deposited on the surface of the aluminum foil 7 is performed in the copper removing tank 4.
Then, a copper removing step is performed in which the aluminum foil 7 from which hydrochloric acid has been removed by washing with pure water is immersed in a solution of nitric acid or the like to dissolve and remove copper. After that, the cathode foil was manufactured through the post-treatment in the post-treatment tank 5 and the drying process in the drying furnace 10.

[0007]

However, in the above-mentioned conventional method for manufacturing a cathode foil, aluminum is also dissolved at the same time when copper is dissolved and removed by an acid, so that the pits formed by etching are partially dissolved by this dissolution. It is destroyed and the capacitance decreases. In addition, if the removal of copper is insufficient, when a product is made using such a cathode foil with insufficient removal of copper, the product remains when a reverse voltage (+ is applied to the product) is applied to the product. Copper dissolves out as copper ions and deposits on the anode. While repeating this, the cathode and the anode were electrically connected, and there was a possibility that the product would have a short circuit defect.

The present invention solves the above-mentioned problems of the prior art, and it is possible to prevent a decrease in capacitance and
It is an object of the present invention to provide a method for manufacturing a cathode foil for an aluminum electrolytic capacitor, which can reduce short-circuit defects of the product.

[0009]

In order to achieve the above object, a method of manufacturing a cathode foil for an aluminum electrolytic capacitor according to the present invention comprises applying at least one of direct current electrolytic etching or chemical etching to an aluminum foil containing copper as an impurity. It has an etching step to perform and a decoppering step to remove copper deposited on the surface of the aluminum foil during etching in this etching step. This decoppering step oxidizes the copper deposited on the surface of the aluminum foil and then dissolves it with an acid. It is designed to be removed.

[0010]

According to the method for manufacturing a cathode foil for an aluminum electrolytic capacitor of the present invention, the copper deposited on the surface of the aluminum foil is removed in the copper removal step of removing the copper deposited on the surface of the aluminum foil during the etching step. Is oxidized and then removed by dissolving with acid.Because the copper deposited on the surface of the aluminum foil is oxidized before decoppering, copper with a noble electrode potential is usually used. Oxidation causes the electrode potential to become base, which causes the copper deposited on the surface of the aluminum foil to dissolve more easily in the acid after oxidation before aluminum, so copper is removed by acid as in conventional methods. In doing so, aluminum is not melted at the same time and the pits formed by etching are not destroyed by this melting, so that the capacitance is not lowered.

Further, the copper deposited on the surface of the aluminum foil is not easily dissolved by the acid after oxidation and does not remain on the surface of the cathode foil. Even when the reverse voltage is applied, copper ions are not deposited on the anode as in the conventional case, and thus short-circuit defects of the product can be reduced as compared with the conventional case.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

(Embodiment 1) FIG. 1 shows an outline of a manufacturing process of a cathode foil for an aluminum electrolytic capacitor according to Embodiment 1 of the present invention. In FIG. 1, 21 is an unwinding roll and 22 is a pretreatment. Tank, 23 is an etching tank, 24 is a heat treatment furnace, 24a is a heater for heating, 25 is a copper removing tank, 26 is a post-treatment tank, 27 is a winding roll, 28 is aluminum foil, 29
Is a DC power source, 30 is a cathode plate, and 31 is a drying oven.

The aluminum foil 28 has a purity of 99.3% and contains 0.3% of copper as an impurity, and has a thickness of 50 μm and a width of 50 cm.
The aluminum foil of No. 2 was used, and after the surface of the aluminum foil 28 was cleaned by pretreatment in the pretreatment tank 22, about 20% hydrochloric acid-based etching solution containing a trace amount of an additive and heated to 80 ° C. or higher. The aluminum foil 28 is immersed in an etching bath 23 having a space for about 10 seconds for chemical etching, and at the same time, the aluminum foil 28 is used as an anode and a cathode plate 30 arranged parallel to both sides of the aluminum foil 28 is used as a cathode from a DC power supply 29. By applying a direct current having a current density of 0.2 to 0.3 A / cm ² to perform electrolytic etching, the aluminum foil 28
Etching was performed to increase the surface area of the.

The aluminum foil 28 that has undergone this etching process is heat-treated through a heat treatment furnace 24 having a heater 24a for heating. In this case, the temperature in the atmosphere of the heat treatment furnace 24 is set to 100 to 500 ° C. By heat-treating the aluminum foil 28 at this temperature for 5 to 10 seconds,
Aluminum foil 2 during etching in the etching process
The copper deposited on the surface of No. 8 was oxidized. After this, aluminum foil 2
Copper removal for removing the copper deposited on the surface of No. 8 was performed in the copper removal tank 25. In this copper removing tank 25, a copper removing step is carried out in which the aluminum foil 28 from which hydrochloric acid has been removed by washing with water in a pure water tank is immersed in a heated solution of about 15% nitric acid for 10 to 80 seconds to dissolve and remove copper. It was Then, after this, the cathode foil was manufactured through the post-treatment in the post-treatment tank 26 and the drying process in the drying furnace 31.

In the method of manufacturing the cathode foil of the above-mentioned Example 1, when etching is performed in the etching step,
Aluminum and copper are dissolved in the etching solution, and are present in the etching solution as aluminum ions and copper ions. During this etching, some copper ions are deposited as copper on the cathode plate 30, and some of the remaining copper ions are aluminum foil 2.
Although copper is deposited on the surface of No. 8, in the first embodiment, the aluminum foil 28 is passed through the heat treatment furnace 24 to be heat-treated after the etching process is completed.
The copper deposited on the surface of the aluminum foil 28 is oxidized by this heat treatment, and the electrode potential of copper becomes base due to this heat treatment. Therefore, in the next copper removal step in the copper removal tank 25, the aluminum foil 28 is not treated with nitric acid or the like. When copper is dissolved and removed by immersion in a liquid, copper is easily dissolved before aluminum, so aluminum is simultaneously dissolved when copper is removed by acid as in the past. The dissolution does not destroy the pits formed by etching, so that the capacitance does not decrease.

Further, the copper deposited on the surface of the aluminum foil 28 is easily dissolved by the acid after oxidation and does not remain on the surface of the cathode foil. Even when a reverse voltage is applied, copper ions are no longer deposited on the anode foil as in the conventional case,
As a result, the short circuit defect of the product can be reduced as compared with the conventional product.

FIG. 2 shows the relationship between the heat treatment temperature of the etched aluminum foil 28 and the amount of copper remaining on the surface of the aluminum foil 28. As is clear from FIG. 2, the heat treatment temperature increases. The amount of copper remaining on the surface of the aluminum foil 28 is reduced. And this heat treatment temperature is 4
The optimum temperature is from 00 to 500 ° C. That is, there is a problem that copper removal is insufficient at 400 ° C. or lower,
On the other hand, when the temperature is 500 ° C. or higher, the foil is softened and easily cut, resulting in an increase in process defects. Therefore, the range of the heat treatment temperature is preferably 400 to 500 ° C.

(Embodiment 2) FIG. 3 shows an outline of a manufacturing process of a cathode foil for an aluminum electrolytic capacitor in Embodiment 2 of the present invention. The same parts as those in Embodiment 1 of the present invention described above are designated by the same reference numerals. Only the different points will be described. That is, in the second embodiment of the present invention, the etching bath 2
An ultraviolet irradiator 32 having an ultraviolet lamp group 32a for irradiating ultraviolet rays is provided between the No. 3 and the copper removing tank 25.

In the second embodiment, the surface of the aluminum foil 28 is pretreated in the pretreatment tank 22, and after being etched in the etching tank 23, it is passed through the ultraviolet irradiation device 32 and passed through the ultraviolet irradiation device 32 at a wavelength of 312 nm and an intensity of 100 μW / cm. By irradiating the aluminum foil 28 with the ultraviolet rays of ² for 10 seconds,
Ozone generated at that time oxidizes the copper deposited on the surface of the aluminum foil 28 during the etching in the etching step, and then removes copper for removing the copper deposited on the surface of the aluminum foil 28 by removing copper. After that, the cathode foil was manufactured through the post-treatment by the post-treatment tank 26 and the drying step by the drying furnace 31 as in Example 1.

In the method of manufacturing the cathode foil of the second embodiment, after the etching process is completed, the aluminum foil 28 is passed through the ultraviolet irradiation device 32 to irradiate the aluminum foil 28 with ultraviolet rays. The copper deposited on the surface of 28 is oxidized by this ultraviolet irradiation, and the electrode potential of copper becomes base by this oxidation. Therefore, in the next copper removing step in the copper removing tank 25, the aluminum foil 28 is treated with a liquid such as nitric acid. When the copper is immersed in the solution to remove the copper, the copper is easily dissolved before the aluminum. Therefore, the second embodiment also has the same effect as the first embodiment. .

FIG. 4 illustrates the etched aluminum foil 28.
Table of irradiation energy amount of ultraviolet rays and aluminum foil 28
It shows the relationship with the amount of copper remaining on the surface.
As is clear from the above, the amount of residual copper is the irradiation energy of ultraviolet rays.
-The amount is 1 mJ / cm²(Light intensity 100 μW / cm²The light of
It is very equivalent to the case of irradiation for 10 seconds)
Therefore, the irradiation energy of ultraviolet rays is reduced.
-The amount is 1 mJ / cm ²The above is the practical range, and light intensity
What can shorten the processing time by increasing the degree
Is.

(Embodiment 3) FIG. 5 shows an outline of a manufacturing process of a cathode foil for an aluminum electrolytic capacitor in Embodiment 3 of the present invention. The same parts as those of Embodiment 1 of the present invention described above are designated by the same reference numerals. Only the different points will be described. That is, in the third embodiment of the present invention, the etching bath 2
3 and the copper removal tank 25, a hydrogen peroxide solution aqueous solution tank 33
Is provided.

In the third embodiment, the surface of the aluminum foil 28 is pretreated in the pretreatment bath 22 and etched in the etching bath 23, and then the concentration is set to 1 to 4% and the temperatures are 30 ° C. and 50 ° C. By immersing the aluminum foil 28 in the hydrogen peroxide aqueous solution tank 33 set for about 30 seconds, the aluminum foil 28 is etched during the etching in the etching step.
The copper removed on the surface of the aluminum foil 28 is removed by oxidizing the copper deposited on the surface of the aluminum foil 28.
After that, the cathode foil was manufactured through the post-treatment by the post-treatment tank 26 and the drying step by the drying furnace 31 as in Example 1.

In the method of manufacturing the cathode foil of Example 3 described above, since the aluminum foil 28 is immersed in the hydrogen peroxide solution aqueous solution tank 33 after the etching step is completed, the aluminum foil 28 is deposited on the surface of the aluminum foil 28. The copper thus formed is oxidized by being immersed in the hydrogen peroxide aqueous solution tank 33, and the electrode potential of the copper becomes base due to this oxidation. Therefore, in the next copper removing step in the copper removing tank 25, the aluminum foil 28 is not covered with nitric acid or the like. When the copper is dissolved and removed by immersion in the liquid, the copper is easily dissolved before the aluminum. Therefore, the third embodiment also has the same effect as the first embodiment. is there.

FIG. 6 shows the relationship between the concentration and temperature of the hydrogen peroxide solution and the amount of copper remaining on the surface of the aluminum foil 28. As is clear from this FIG. As the temperature increases, the amount of copper remaining on the surface of the aluminum foil 28 decreases.

(Embodiment 4) FIG. 7 shows an outline of a manufacturing process of a cathode foil for an aluminum electrolytic capacitor in Embodiment 4 of the present invention. The same parts as those in Embodiment 1 of the present invention described above are designated by the same reference numerals. Only the different points will be described. That is, in Example 4 of the present invention, the etching bath 2
A chemical conversion tank 34 having a chemical conversion DC power supply 34a is provided between the No. 3 and the copper removal tank 25.

In Example 4, the surface of the aluminum foil 28 was pretreated in the pretreatment bath 22 and etched in the etching bath 23, and then the aluminum foil 28 was placed in the chemical conversion bath 34 using a 10% aqueous solution of ammonium adipate as the chemical conversion liquid. The aluminum foil 28 is passed through and the aluminum foil 28 is supplied from the chemical conversion DC power source 34a.
Is formed as an anode by applying a DC voltage in the range of 1 to 5 V to oxidize the copper deposited on the surface of the aluminum foil 28 during the etching in the etching step,
After that, copper removal for removing the copper deposited on the surface of the aluminum foil 28 is performed in the copper removal tank 25. After that, after the post-treatment by the post-treatment tank 26 as in the first embodiment, A cathode foil was manufactured through a drying process in the drying oven 31.

In the method of manufacturing the cathode foil of Example 4 described above, since the aluminum foil 28 is passed through the chemical conversion tank 34 to be formed after the etching process, the surface of the aluminum foil 28 is formed. The copper deposited on the aluminum foil 28 is oxidized by the chemical conversion in the chemical conversion tank 34, and the electrode potential of the copper becomes base due to this oxidation. Therefore, in the next copper removal step in the copper removal tank 25, the aluminum foil 28 is treated with a liquid such as nitric acid. When the copper is soaked in to dissolve and remove the copper, the copper is dissolved before the aluminum. Therefore, the fourth embodiment also has the same effect as the first embodiment.

Next, a method for measuring the copper remaining on the surface of the aluminum foil forming the cathode foil will be described. That is, each of the cathode foils obtained in Examples 1, 2, 3, 4 of the present invention and the conventional method was heat-treated in air at 500 ° C. for 5 minutes to oxidize the surface, and this was heated to 40 ° C. The copper oxide on the surface was dissolved in a nitric acid solution by immersing it in a warm 15% nitric acid aqueous solution for 5 minutes. Then, the copper dissolved in this nitric acid solution was quantitatively analyzed using an atomic absorption spectrophotometric method and converted into a sample area to obtain the amount of copper on the surface. The results are shown in (Table 1).

[0031]

[Table 1]

As is clear from (Table 1), the capacitance of the cathode foils obtained in Examples 1, 2, 3 and 4 of the present invention is higher than that of the cathode foils obtained by the conventional method. In addition, the residual copper amount in Examples 1, 2, 3, 4 of the present invention is much smaller than that in the conventional method.

[0033]

As described above, the method for producing a cathode foil for an aluminum electrolytic capacitor according to the present invention can be applied to the surface of the aluminum foil in the decoppering step of removing the copper deposited on the surface of the aluminum foil during the etching step. After oxidizing the deposited copper, it was dissolved in acid to remove it.
Since the copper deposited on the surface of the aluminum foil is oxidized before decoppering, the electrode potential of copper, which normally has a noble electrode potential, becomes base due to oxidation, which causes the copper to deposit on the surface of the aluminum foil. Copper is more easily dissolved in the acid after oxidation before aluminum, so that aluminum is simultaneously dissolved when the copper is dissolved and removed by acid as in the conventional case, and this dissolution is formed by etching. Since the pits are not destroyed, the capacitance is not reduced. In addition, since the copper deposited on the surface of the aluminum foil is not easily dissolved by the acid after oxidation and remains on the surface of the cathode foil, the reverse voltage to the product when using this cathode foil as a product Even when the voltage is applied, copper ions will not be deposited on the anode as in the conventional case, whereby the short circuit defect of the product can be reduced as compared with the conventional case.

[Brief description of drawings]

FIG. 1 is a schematic view showing a manufacturing process of a cathode foil for an aluminum electrolytic capacitor according to a first embodiment of the present invention.

2 is a characteristic diagram showing the relationship between the heat treatment temperature of the etched aluminum foil and the amount of copper remaining on the surface of the aluminum foil in Example 1. FIG.

FIG. 3 is a schematic view showing a manufacturing process of a cathode foil for an aluminum electrolytic capacitor according to a second embodiment of the present invention.

FIG. 4 is a characteristic diagram showing the relationship between the irradiation energy amount of ultraviolet rays applied to the etched aluminum foil and the amount of copper remaining on the surface of the aluminum foil in Example 2;

FIG. 5 is a schematic view showing a manufacturing process of a cathode foil for an aluminum electrolytic capacitor according to a third embodiment of the present invention.

FIG. 6 is a characteristic diagram showing the relationship between the concentration and temperature of hydrogen peroxide solution and the amount of copper remaining on the surface of the aluminum foil in Example 3;

FIG. 7 is a schematic view showing a manufacturing process of a cathode foil for an aluminum electrolytic capacitor in Example 4 of the present invention.

FIG. 8 is a schematic view showing a manufacturing process of a conventional cathode foil for an aluminum electrolytic capacitor.

[Explanation of symbols]

 23 etching tank 24 heat treatment furnace 25 copper removal tank 28 aluminum foil 32 ultraviolet irradiation device 33 hydrogen peroxide aqueous solution tank 34 chemical conversion tank

Claims (5)

[Claims] 1. An etching step of performing at least one of direct current electrolytic etching and chemical etching on an aluminum foil containing copper as an impurity, and decoppering for removing copper deposited on the surface of the aluminum foil at the time of etching in this etching step. The method for producing a cathode foil for an aluminum electrolytic capacitor comprises a step of removing copper that has been deposited on the surface of an aluminum foil by oxidizing the copper deposited on the surface of the aluminum foil and then removing it by dissolving with an acid. 2. The method for producing a cathode foil for an aluminum electrolytic capacitor according to claim 1, wherein the oxidation of copper in the copper removal step is performed by heat treating the aluminum foil. 3. The method for producing a cathode foil for an aluminum electrolytic capacitor according to claim 1, wherein the oxidation of copper in the copper removal step is performed by irradiating the aluminum foil with ultraviolet rays. 4. The method for producing a cathode foil for an aluminum electrolytic capacitor according to claim 1, wherein the oxidation of copper in the copper removing step is performed by immersing the aluminum foil in a hydrogen peroxide solution. 5. The method for producing a cathode foil for an aluminum electrolytic capacitor according to claim 1, wherein the oxidation of copper in the copper removal step is performed by forming an aluminum foil.