JPH11307399A - Manufacture of electrode foil for aluminum electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of electrode foil for aluminum electrolytic capacitor with high electrostatic capacity per unit area, particularly in forming it with high voltage. SOLUTION: A pre-processing process of an aluminum original foil, an etching pit generation process and an etching pit enlargement process are provided. A DC current is applied continuously in the etching pit generation process and an immersion processing is executed in same etching fluid. The quantity of electricity applied in the etching pit enlargement process is set so as to be 200%-400% of the quantity of electricity applied in the etching pit generation process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum electrolytic capacitor electrode foil used for various electronic devices, and particularly to an anode aluminum foil etching technique suitable for high-pressure formation. The present invention relates to a method for manufacturing an electrode foil.

[0002]

2. Description of the Related Art In recent years, with the miniaturization and high reliability of sets, the needs (miniaturization, cost reduction) of users for aluminum electrolytic capacitors have been rapidly increasing.
Electrode foils for aluminum electrolytic capacitors (hereinafter referred to as electrode foils), which greatly influence the performance of aluminum electrolytic capacitors, also need to have higher capacitance per unit area than ever before. In addition, with the recent expansion of the overseas market and the market of large-sized products for industrial use, cost reduction has become an issue particularly for products in a region where the working voltage is particularly high among capacitors.

[0003] A conventional method of manufacturing this type of electrode foil will be described below. Electrode foils are used to increase the effective surface area by electrochemically or chemically etching aluminum foil in order to reduce the size of aluminum electrolytic capacitors. Various etching methods are used to increase this surface area. In general, aluminum foil is inserted continuously into several different etching tanks, and the surface area of the aluminum foil is gradually increased by applying current or chemically dissolving in each etching tank. ,
Etching is performed by performing final cleaning.

[0004] Then, in the next step, a process of forming a chemical conversion film in accordance with the working voltage of the product is performed. However, if the formation voltage is different, the appropriate pit shape is different, so that the pit shape is controlled according to the formation voltage. It becomes important.
Therefore, conventionally, there has been a great demand for an electrode foil for forming at a formation voltage from the latter half of the 200V range to the 400V range, so that it is necessary to extract the capacitance as disclosed in Japanese Patent Publication No. 3-69168. In order to ensure a high pit density, the manufacturing method focuses on the etching process in the etching pit generation step, and the manufacturing method uses a relatively small amount of current applied in the etching pit expansion step. there were.

[0005]

However, in the above-mentioned conventional manufacturing method, many etching pits which are buried in the chemical conversion film when formed at a high voltage, particularly at a voltage of 500 V or more, remain, and as a result, the capacity is insufficient. However, there has been a problem that the power consumption per unit capacity in the chemical conversion step also increases due to no extraction. In addition, since the ratio of the amount of current applied in the etching pit generation step is relatively large, it is necessary to increase the number of etching tanks so as not to impair the productivity, so that it is susceptible to the unavoidable interruption of the current that occurs during the process. In addition, the lengths of the tunnel-like pits generated in the etching pit generation step become uneven, and it was difficult to obtain a high capacitance while maintaining the strength of the electrode foil.

The present invention solves the above-mentioned conventional problems. In particular, when forming at a high pressure, the capacitance per unit area is high while maintaining the strength of the electrode foil, and the power consumption in the forming step is high. It is an object of the present invention to provide a method for manufacturing an electrode foil for an aluminum electrolytic capacitor, which also has an effect of reducing the above.

[0007]

In order to solve this problem, a method for producing an electrode foil for an aluminum electrolytic capacitor according to the present invention comprises a pretreatment step of immersing an aluminum foil in an aqueous solution containing an acid having a film-forming function. After the pretreatment step, the aluminum foil is immersed in an etching solution and subjected to etching by applying a direct current, and the etched foil is then placed in the etching solution used for the etching for a predetermined time. The etching pit generating step of dipping, and the etching foil after the etching pit generating step is immersed in an acidic aqueous solution having a low chemical solubility containing sulfuric acid or nitric acid as a main component and the amount of electricity applied in the etching pit generating step is applied. A manufacturing method comprising an etching pit enlargement step of applying 200 to 400% of electricity to the etching foil; Are as hereinbefore, according to the present invention, particularly in the case of chemical conversion at high pressure may also be a capacitance per unit area is high and also obtain the effect of reducing the power consumption in the conversion process.

[0008]

DETAILED DESCRIPTION OF THE INVENTION The invention according to claim 1 of the present invention comprises a pretreatment step of immersing an aluminum foil in an aqueous solution containing an acid having a film-forming function, and an aluminum foil finished with the pretreatment step. An etching pit generating step of immersing the foil in an etching solution and applying a direct current to perform etching, and subsequently immersing the etched foil in the etching solution used for the etching for a predetermined time; The etching foil after the generation step is immersed in an acidic aqueous solution containing sulfuric acid or nitric acid as a main component and having low chemical solubility, and the amount of electricity of 200 to 400% of the amount of electricity applied in the etching pit generation step is applied to the etching foil. This is a method of manufacturing an electrode foil for aluminum electrolytic capacitors, which consists of a step of expanding the applied etching pits. According to the manufacturing method, since the pretreatment is performed on the aluminum foil before the etching pit generation step in the previous stage, the influence of the non-uniform natural oxide film present on the surface of the aluminum foil is reduced. , Whereby the etching pits are uniformly generated.

According to a second aspect of the present invention, in the first aspect of the present invention, the time during which the etching foil is immersed in the etching solution in the etching pit generation step is set such that a direct current is applied to the aluminum raw foil in the etching pit generation step. According to this manufacturing method, the tunnel-like etching pit generated during the application of the direct current in the former stage had a sharp tip, but the chemical immersion By the treatment, it is shaped into a shape close to a columnar shape, and the treatment in the subsequent etching pit enlargement step can be performed efficiently, so that the capacitance per unit area of the electrode foil can be increased.

According to a third aspect of the present invention, in the first or second aspect of the invention, when a direct current is applied to the aluminum foil in the etching pit enlargement step, the application of the current is interrupted at predetermined intervals. The dormant state is provided intermittently. According to this manufacturing method, the liquid exchange inside the etching pit is promoted during the current interruption,
By maintaining the reaction resistance between the side surface of the etching pit and the etching solution sufficiently large compared to the liquid resistance inside the etching pit, and maintaining the dissolution rate of the side surface of the etching pit almost constant in the length direction of the etching pit,
This has the effect that the expansion of the etching pit can be advanced in a shape close to an ideal columnar shape.

According to a fourth aspect of the present invention, in the first aspect of the present invention, before the etching pit enlargement process, the shape of the etching pit is made cylindrical beforehand. According to this manufacturing method, the conical etching pit generated in the previous etching is shaped into a cylindrical etching pit by using an electrochemical reaction. In addition, the dissolution reaction proceeds uniformly along the side wall of the etching pit, and greatly contributes to the increase in the capacitance of the electrode foil.

Hereinafter, specific embodiments of the present invention will be described. (Embodiment 1) 99.9989% purity, 100 μm thickness
m, an aluminum foil having a (100) plane crystal orientation ratio of 90% or more is subjected to a pretreatment of immersing in an aqueous solution containing phosphoric acid or sulfuric acid for 1 minute, and then mainly containing hydrochloric acid, and then adding oxalic acid,
A direct current having a current density of 20 A / dm ² was applied in an acidic aqueous solution at 85 ° C.
For 2 seconds, etching pit generation processing was performed. Here, in the etching pit generation step, a comparison was made between the case where the current interruption for 5 seconds was performed during the current application and the case where the current interruption was not performed.

Thereafter, the substrate is immersed in an acidic aqueous solution containing sulfuric acid or nitric acid as a main component and having low chemical solubility, and a current density of 10 A
/ Dm ² DC current application time from 360 seconds to 1080
The etching pit was enlarged in a range of seconds. In the etching pit enlargement step, 3
The current was interrupted for 5 seconds at 0 second intervals. This promotes liquid exchange inside the etching pit during current interruption, and maintains a state where the reaction resistance between the side surface of the etching pit and the etching liquid is sufficiently large compared to the liquid resistance inside the etching pit,
By maintaining the dissolution rate on the side surface of the etching pit substantially constant in the length direction of the etching pit, the present invention is intended to promote the expansion of the etching pit in a shape close to a column which is considered to be ideal.

In the pretreatment step, an acid having a film-forming function, for example, phosphoric acid or sulfuric acid can be used, and other known methods may be used. In addition, in the etching pit generation step at the preceding stage, the application of a direct current is performed continuously, so that the length of the tunnel-like etching pit generated in the etching pit generation step becomes relatively uniform,
After that, since the immersion treatment was performed in the same etching solution, the shape of the tunnel-like etching pit generated in the previous stage was sharpened as shown in FIG. 2 and is shaped like a column, so that the processing in the subsequent etching pit enlargement process is performed efficiently, and a high capacitance can be obtained while maintaining the strength of the electrode foil. .

In the subsequent step of expanding the etching pits, a sufficient amount of electricity is applied to the etching pits generated in the preceding step, taking into account the reaction to the formation of high pressure, so that the etching pits are expanded. This reduces the rate at which the pits are filled with the chemical conversion film, thereby increasing the capacitance of the electrode foil and preventing an increase in power consumption in the chemical conversion step.

If the amount of electricity applied in the etching pit enlargement step is less than 200% of that in the etching pit generation step, the diameter of the etching pit is not sufficiently enlarged. The number of invalid pits (which do not contribute to an increase in the capacitance) in which the etching pits are buried increases, and the effect does not appear. On the other hand, when the amount of electricity applied in the etching pit enlargement step is more than 400% of the etching pit generation step,
Of the generated etching pits, the adjacent etching pits are crushed with each other, so that the effective effective etching pit density is reduced, and the capacitance is rather reduced.

The surface of the thus obtained electrode foil after etching is washed with a 9% aqueous solution of nitric acid at 50 ° C. for 1 minute, and then subjected to a chemical conversion at 600 V in a 8% aqueous solution of boric acid at 90 ° C. The results of measuring the capacitance, bending strength (one time per reciprocation under the conditions of 1.0 mmR, 50 g load, and 90 ° bending angle) and the chemical power consumption index per capacity of each of the samples were shown as ( It is shown in Table 1).

[0018]

[Table 1]

As is clear from Table 1, the current is continuously applied without interrupting the current in the etching pit generating step, and the applied electric quantity in the etching pit expanding step is the applied electric quantity in the etching pit generating step. In the range of 200% to 400%, the effects of increasing the capacitance and reducing the power consumption during the formation can be recognized as compared with the conventional case. In addition, if DC current is continuously applied in the etching pit generation step, the length of the generated tunnel-like etching pits is considered to be relatively uniform, and high static electricity is maintained while maintaining the strength of the electrode foil. You can get the capacity.

On the other hand, if the DC current applied in the etching pit generation step is interrupted on the way, the length of the aforementioned tunnel-shaped etching pits becomes irregular, which leads to a decrease in the bending strength of the electrode foil. When the amount of electricity applied in the etching pit enlargement step is less than 200% of the etching pit generation step, the diameter of the etching pit is not sufficiently enlarged. The number of invalid pits increases and the effect does not appear. On the other hand, the amount of electricity applied in the etching pit enlargement process is 40
If it is more than 0%, among the generated etching pits, the adjacent etching pits will crush each other and the effective etching pit density will decrease, so that the capacitance will decrease.

(Embodiment 2) An aluminum raw foil having a purity of 99.989%, a thickness of 100 μm, and a (100) plane crystal orientation ratio of 90% or more is placed in an aqueous solution containing phosphoric acid or sulfuric acid.
A pretreatment of immersion for about 1 minute, followed by a direct current having a current density of 20 A / dm ^{2 in} an acidic aqueous solution at 85 ° C. containing hydrochloric acid as a main component and an additive having a film-forming function such as oxalic acid and sulfuric acid at 120 ° C. for 120 minutes. The process of generating an etching pit is performed by continuously applying for 2 seconds, and the time of immersion processing in the same etching solution (hereinafter referred to as a pre-stage etching solution) used therein is set to 0.
Seconds to 600 seconds. Then, it is immersed in an acidic aqueous solution containing sulfuric acid or nitric acid as a main component and having a low chemical solubility, and the total application time of a direct current having a current density of 10 A / dm ² is set to 4 hours.
The etching pit enlargement process was performed for 80 seconds. In the etching pit enlargement process, the current was interrupted for 30 seconds at intervals of 30 seconds.

Table 2 shows 9%, 50% of the surface of the electrode foil after the completion of etching obtained in the second embodiment.
After washing in an aqueous solution of nitric acid at 1 ° C. for 1 minute, a 600 V chemical conversion was performed in an aqueous solution of 8% and 90 ° C. boric acid, and the capacitance, bending strength (1.0 mmR, 50 g load, bending angle) Table 1 shows the results of the measurement under the condition of 90 degrees and one reciprocation.

[0023]

[Table 2]

As apparent from Table 2, the immersion time in the pre-etching solution is 100% of the current application time in the pre-stage.
When the number is smaller, the tip of the tunnel-shaped etching pit generated during the application of the direct current in the previous stage remains sharp as shown in FIG. 1, and is shaped into a column as shown in FIG. 2 by the chemical immersion treatment. No effect is seen in the efficiency of the processing in the subsequent etching pit enlargement step. When the immersion time is more than 400% of the current application time,
Since the effective dissolution of the electrode foil surface is promoted and the adjacent etching pits are crushed with each other, the effective etching pit density is reduced, and the capacitance is rather reduced. Therefore, the immersion time after the continuous application of the direct current to the pre-etching solution is set to 100% or more of the current application time to 400%.
%, The capacitance per unit area of the electrode foil can be increased.

(Embodiment 3) An aluminum foil having a purity of 99.9989%, a thickness of 100 μm, and a (100) plane crystal orientation ratio of 90% or more is placed in an aqueous solution containing phosphoric acid or sulfuric acid.
A pretreatment of immersion for about 1 minute, followed by a direct current having a current density of 20 A / dm ^{2 in} an acidic aqueous solution at 85 ° C. containing hydrochloric acid as a main component and an additive having a film-forming function such as oxalic acid and sulfuric acid at 120 ° C. for 120 minutes. The process of generating an etching pit is performed by continuously applying for 2 seconds, and the time of immersion processing in the same etching solution (hereinafter referred to as a pre-stage etching solution) used therein is set to 0.
Seconds to 480 seconds. Then, it is immersed in an acidic aqueous solution containing sulfuric acid or nitric acid as a main component and having a low chemical solubility, and the total application time of a direct current having a current density of 10 A / dm ² is set to 9 hours.
60 seconds. In the etching pit enlargement step, the current was interrupted for 30 seconds at intervals of 30 seconds.

Here, when the etching pit is enlarged while the etching pit remains in the shape shown in FIG.
In this state, the diameter of the etching pit is enlarged while the shape of the etching pit is inherited, and the effect of increasing the capacitance of the electrode foil is not observed as compared with the case of FIG. 2 to FIG.

The surface of the thus obtained electrode foil after etching is washed with a 9% aqueous solution of nitric acid at 50 ° C. for 1 minute, and then subjected to a chemical conversion at 600 V in a 8% aqueous solution of boric acid at 90 ° C. Table 3 shows the results of measuring the capacitance and bending strength (one reciprocation per reciprocation under the conditions of 1.0 mmR, 50 g load, and 90 ° bending angle) for each sample.

[0028]

[Table 3]

As apparent from (Table 3), even when the total application time of the direct current having a current density of 10 A / dm ² in the etching pit enlargement step was set to 960 seconds, the value shown in (Table 2) was obtained. Similarly, the immersion time after continuous application of DC current to the former etching solution is set to 100% of the current application time.
By controlling it to at least 400%, the capacitance per unit area of the electrode foil can be increased.

[0030]

As described above, the method for producing an electrode foil for an aluminum electrolytic capacitor according to the present invention comprises a pretreatment step of an aluminum foil, an etching pit generation step, and an etching pit expansion step. After a current is continuously applied and then immersion treatment is performed in the same etching solution, the amount of electricity applied in the etching pit enlargement step is set to 200% or more and 400% or less of the electricity applied in the etching pit generation step. According to this manufacturing method, the pretreatment is performed on the aluminum foil before the etching pit generation step in the preceding stage, so that the non-uniform natural oxidation existing on the surface of the aluminum foil is uneven. The effect of the film will be mitigated, whereby the etching pits will be generated uniformly. In addition, in the preceding etching pit generation step, direct current is continuously applied, so that the length of the tunnel-like etching pit generated in the etching pit generation step is relatively uniform, and the strength of the electrode foil is reduced. A high capacitance can be obtained while maintaining the same. After that, since the immersion treatment was performed in the same etching solution, the shape of the tunnel-like etching pit generated in the previous stage was sharpened as shown in FIG. As a result, the shape is approximated to a columnar shape, and the processing in the subsequent etching pit expansion step is efficiently performed, and a high capacitance can be obtained while maintaining the strength of the electrode foil. In addition, in the etching pit enlargement process in the later stage, a sufficient amount of electricity is applied to the etching pit generated in the previous stage in consideration of coping with high-pressure formation, and the etching pit is enlarged. The filling ratio of the film is reduced, whereby the capacitance of the electrode foil can be increased, and the power consumption in the chemical conversion step can be prevented from increasing.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a pit shape immediately after pre-etching (generation of etching pits) of an electrode foil for an aluminum electrolytic capacitor of the present invention.

FIG. 2 is a schematic cross-sectional view of a pit shape when the pit shape is shaped immediately after the previous stage etching (occurrence of etching pit).

FIG. 3 is a schematic cross-sectional view of a pit shape when a post-stage etching (etching pit enlargement process) is performed on an electrode foil having an etching pit cross section having the shape of FIG. 2;

FIG. 4 is a schematic cross-sectional view of a pit shape when a post-stage etching (etching pit enlargement process) is performed on an electrode foil having an etching pit cross section of FIG.

[Explanation of symbols]

 1 Surface of electrode foil 2 Tip of etching pit of electrode foil

Claims (4)

[Claims] 1. A pretreatment step of dipping an aluminum foil in an aqueous solution containing an acid having a film-forming function, and dipping the aluminum foil after the pretreatment step in an etching solution to apply a direct current. An etching pit is generated by immersing the etched foil in the etching solution used for the etching for a predetermined time, and the etching foil having undergone the etching pit generation is mainly composed of sulfuric acid or nitric acid. 200 to 4 of the amount of electricity applied in the etching pit generation step by dipping in an acidic aqueous solution having low chemical solubility
A method for manufacturing an electrode foil for an aluminum electrolytic capacitor, comprising a step of enlarging an etching pit by applying 00% of electricity to an etching foil. 2. The method according to claim 1, wherein the time during which the etching foil is immersed in the etching solution in the etching pit generation step is 100 to 400% of the time during which a direct current is applied to the aluminum foil in the etching pit generation step. Manufacturing method of electrode foil for aluminum electrolytic capacitor. 3. The method according to claim 1, wherein when applying a direct current to the aluminum foil in the etching pit enlargement step, a pause state for interrupting the current application at predetermined intervals is provided intermittently. Manufacturing method of electrode foil for aluminum electrolytic capacitor. 4. Before the etching pit enlargement processing step,
The method for producing an electrode foil for an aluminum electrolytic capacitor according to any one of claims 1 to 3, wherein the shape of the etching pit is previously made cylindrical before performing the etching pit enlargement process.