JP2009105242A - Method of manufacturing electrode foil for electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an electrode foil for an electrolytic capacitor of raised electrostatic capacitance. <P>SOLUTION: The method of manufacturing the electrode foil for an electrolytic capacitor includes an etching step with an aluminum foil, an immersion step in which the aluminum foil is immerged in a processing liquid at least once, a thermal treatment step, and a chemical formation step. In the immersion step, micro bubbles are generated in any step liquid when performing a cleaning step of removing ion sticking to the aluminum foil and a hydration treatment step in which the aluminum foil is immersed in the processing liquid for forming a hydrate film. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing an electrode foil for an aluminum electrolytic capacitor, and particularly to a processing technique after etching an aluminum foil.

In the aluminum electrolytic capacitor, with the demand for miniaturization, the electrode foil is required to improve the capacitance.
In order to meet such demands, conventionally, an aluminum foil is chemically etched (electroless etching) and / or electrochemically etched in an etching solution in which nitric acid or phosphoric acid is mixed with an aqueous solution of hydrochloric acid and sulfuric acid. (Electrolytic etching) to increase the effective surface area, and then perform a cleaning process, a hydration process, and a chemical conversion process to remove chloride ions, sulfide ions, etc. adhering to the etching foil. High anode foil is obtained.
Here, the purpose of the hydration process is to improve the film quality of the anodized film formed in the chemical conversion process by forming a hydrated film on the surface of the aluminum foil (for example, see Non-Patent Document 1). .

Isaya Nagata, “Electrolytic Cathode Aluminum Electrolytic Capacitor”, Nihon Denki Kogyo Kogyo Co., Ltd., February 24, 1997, Second Edition, First Printing, P265-271

  However, the electrolytic capacitor is required to be further miniaturized, and accordingly, an anode foil having a higher capacitance is required. However, in the conventional manufacturing method, the etching pit is made fine by increasing the etching magnification. Even if it is deepened, there is a problem that the capacitance of the anode foil cannot be increased to a level that can meet such requirements.

  In view of the above problems, an object of the present invention is to provide a method for producing an electrode foil for an electrolytic capacitor that can further increase the capacitance.

In order to solve the above problems, the inventors of the present application have made various studies. As a result, when the etching magnification is increased, the etching pits become finer and deeper. It was found that the cleaning process of ions and the hydration process were not performed reliably, and a good quality anodic oxide film could not be formed.
That is, the smaller the diameter of the etching pit, the more difficult it is for the processing solution to enter and exit and exchange between the inside of the aluminum foil (the back of the etching pit) and the surface side in contact with the solution. Washing and hydration will not be performed sufficiently.

  The present invention has been achieved on the basis of such knowledge. At least, an etching process for chemically and / or electrochemically etching an aluminum foil, and after the etching process, the aluminum foil is used as a treatment liquid. In the method for producing an electrode foil for an electrolytic capacitor having a dipping step of dipping more than once and a chemical conversion step of anodizing the surface of the aluminum foil after the dipping step, at least one of the dipping steps. The process is characterized in that the microbubbles are generated in the treatment liquid and immersed.

  In the present invention, as the dipping step, the aluminum foil is dipped in a processing solution, and a cleaning step for removing ions attached to the aluminum foil in the etching step, and after the cleaning step, the aluminum foil is used as a processing solution. A hydration treatment step of immersing and forming a hydrated film on the foil surface. In this case, the microbubbles are generated in the treatment liquid in both the washing step and the hydration treatment step. It is preferable to make it.

“Microbubbles” are bubbles having a diameter of 100 μm or less, for example, 10 μm to several tens of μm, and can be formed by a pressure-reduced pressure method or a gas-liquid shear method.
In the pressure-reduced pressure method, a large amount of gas is dissolved under high pressure and re-bubbled by reducing pressure.
On the other hand, in the gas-liquid shearing method, a vortex is created, and the gas is finally cut and pulverized while entraining the gas.
The microbubbles formed by either method have a very slow rising speed compared to normal bubbles, have excellent dissolution capability, and have various self-pressurization effects due to the high internal pressure. It has features such as drawing out crushing phenomena that can decompose chemical substances.

When microbubbles are generated in the processing liquid in the immersion process such as the cleaning process and the hydration processing process, stirring of the processing liquid inside the etching pit is promoted by the microbubbles, and the processing liquid penetrates into the pit details. Since it promotes, chlorine ions and sulfate ions adhering and remaining inside the pit are washed out, and the washing process can be sufficiently performed.
In addition, since the penetration of moisture into the pit details is promoted, the hydration treatment can be performed sufficiently and uniformly.
Therefore, at the time of chemical conversion, an anodic oxide film having a good film quality can be formed uniformly, and an electrode foil having a high capacitance can be obtained.

  In the present invention, in both the washing step and the hydration treatment step, the treatment liquid is preferably immersed at a temperature of 40 to 60 ° C.

  The present invention can also be applied to a manufacturing method in which a heat treatment step is performed after the dipping step and before the chemical conversion step.

  In this invention, when generating the said microbubble, it is preferable to spray the said microbubble toward both surfaces of the said aluminum foil. If comprised in this way, even if an etching pit is fine and deep, it can wash | clean and hydrate evenly to the detail of an etching pit, and can form a quality anodic oxide film.

  In the present invention, the more microbubbles are generated, the more effective.

In the present invention, when microbubbles are generated in the treatment liquid in the immersion process such as the washing process and the hydration treatment process, the stirring of the treatment liquid inside the etching pit is promoted by the microbubbles, and the treatment into the pit is performed. Since the penetration of the liquid is promoted, chlorine ions and sulfate ions adhering to and remaining in the pit are washed out, and the washing process can be sufficiently performed.
Further, since the penetration of moisture into the pit details is promoted, the hydration process can be performed uniformly.
Therefore, since the washing treatment or the hydration treatment can be performed sufficiently and uniformly, a uniform and good quality anodic oxide film can be formed at the time of chemical conversion, and a high capacitance can be obtained.
Here, when the bubble diameter of the microbubbles exceeds 100 μm, there is only an agitation effect of the solution (bulk) in the treatment tank due to the bubble rise, and the agitation of the treatment liquid into the pit is less likely to occur. Therefore, the cleaning process cannot be performed sufficiently, and the hydration process in the pits cannot be performed uniformly, which is not preferable.

  FIG. 1 is an explanatory diagram of a dipping process in a method for producing an electrode foil for an electrolytic capacitor to which the present invention is applied.

In order to manufacture an anode foil (electrolytic capacitor electrode foil) used for an electrolytic capacitor for low pressure, first, in an etching process, chemical and chemicals are mixed in an etching solution in which nitric acid or phosphoric acid is mixed with an aqueous solution of hydrochloric acid and sulfuric acid. Electrochemical etching is performed to enlarge the effective surface area.
When manufacturing an etching foil for an electrolytic capacitor for low pressure as the anode foil, electrolytic etching using alternating current is frequently used.

Next, an immersion process is performed in which the aluminum foil is immersed in the treatment liquid at least once.
As this immersion process, in this embodiment, the aluminum foil (etching foil) is immersed in water or an acidic treatment solution to remove ions such as chloride ions and sulfide ions attached to the aluminum foil in the etching process. After the step and the cleaning step, a hydration treatment step is performed in which the aluminum foil is immersed in a neutral, weakly acidic or weakly alkaline treatment solution to form a thin hydrated film on the surface of the aluminum foil.
Here, a water washing step may be provided between the washing step and the hydration treatment step.

  Next, in the heat treatment step, for example, a heat treatment at a temperature of 400 ° C. is performed on the etching foil.

  Next, in the chemical conversion step, using an aqueous solution of ammonium adipate or the like, anodization is performed on the surface of the aluminum foil to form an anodized film serving as a dielectric.

In such a manufacturing method, when an etching process is performed, as shown in FIG. 1, etching pits are formed on the surface (both sides) of the aluminum foil, and a metal core remains in the center in the thickness direction of the aluminum foil.
Here, in order to obtain an anode foil having a high capacitance, the etching magnification is increased to grow the etching pit finely and deeply.
As a result, in the immersion process (cleaning process and hydration process) performed after the etching process, there is no replacement of the processing solution inside and outside the etching pit, and chloride ions, sulfide ions, etc. that have penetrated to the details Cleaning removal and hydration treatment are not performed. As a result, a good quality anodic oxide film cannot be formed.

  Therefore, in this embodiment, microbubbles are generated in the processing liquid. At that time, micro bubbles are sprayed toward both sides of the aluminum foil. Such microbubbles are bubbles having a diameter of several tens of μm or less, for example, 10 μm to several tens of μm, and promote the replacement of the processing liquid inside and outside the etching pit.

  Hereinafter, based on an Example, this invention is demonstrated more concretely.

[Examples 1 to 5]
The etched low-pressure aluminum foil is immersed in a cleaning treatment solution for removing deposits and a hydration treatment solution for 1 minute each. When performing this washing | cleaning process and a hydration process process, as demonstrated with reference to FIG. 1, the microbubble was generated in the process liquid and the microbubble was sprayed toward both surfaces of the aluminum foil.
Microbubbles were generated by a gas-liquid shear method. Specifically, in a tank different from the immersion tank, a vortex is created in the processing liquid heated to the temperature described below, and the air is blown and crushed while being blown, and then processed from the spout provided in the immersion tank. Microbubbles were sprayed on the aluminum foil together with the liquid.
In this example, the treatment liquid for cleaning was a 10 wt% nitric acid aqueous solution at a treatment liquid temperature of 60 ° C., and the treatment liquid for hydration treatment was a 0.03 wt% potassium hydroxide aqueous solution.
In this example, as shown in Table 1, the temperature of the hydration solution was set to 20 ° C., 40 ° C., 50 ° C., 60 ° C., and 65 ° C.

  Next, in the heat treatment step, the etching foil was subjected to heat treatment at a temperature of 400 ° C. for 5 minutes.

  Next, in a chemical conversion solution in which 80 g / L of ammonium adipate and 1.5 g / L of adipic acid were dissolved, a voltage was applied at 85 ± 2 ° C. to increase the voltage to 22 V, followed by depolarization, Re-chemical conversion treatment etc. were performed and chemical conversion foil (electrode foil for electrolytic capacitors) was obtained.

(Comparative Examples 1-5)
As Comparative Examples 1 to 5, chemical conversion foils were obtained under the same conditions as in Examples 1 to 5. However, the washing step and the hydration treatment step were performed without generating microbubbles in the treatment liquid.

[Evaluation results]
Next, the electrostatic capacitance of the chemical conversion foil of said Examples 1-5 and Comparative Examples 1-5 was measured. The results are shown in Table 1.

  As is clear from Table 1, when performing the cleaning step and the hydration treatment step on the etching foil, in Examples 2 to 4 in which microbubbles were generated, a higher capacitance was obtained compared to Comparative Examples 2 to 4. be able to.

That is, it is understood that a high capacitance can be obtained at a temperature of 40 to 60 ° C. in the treatment liquid in the dipping process (cleaning process and hydration process).
When the temperature of the treatment liquid is less than 40 ° C., for example, when the temperature is 20 ° C., the effect is small (Example 1). Thus, there is a tendency that the electrostatic capacity cannot be improved reliably (Example 5). Therefore, the temperature of the treatment liquid is preferably in the range of 40 to 60 ° C. (Examples 2 to 4).

  In addition, although only the comparison by the temperature of a process liquid was described this time, about a process liquid, pH 5-11, immersion process time 0.5-1.0 minute, and about heat processing temperature 250-400 degreeC for 5 minutes. If it is within the range, it has been confirmed that the same effect can be obtained.

  In the above embodiment, an aqueous nitric acid solution is used as the cleaning treatment solution and an aqueous potassium hydroxide solution is used as the hydrating treatment solution. However, an aqueous solution of phosphoric acid, oxalic acid, and sulfuric acid is used as the cleaning treatment solution. The same effect can be obtained even when sodium hydroxide is used in the treatment liquid for hydration treatment.

In the above embodiment, microbubbles are used in both the washing step and the hydration treatment step. However, the effect can be obtained even if only one of the washing step and the hydration treatment step is described above. Just as you did.
In the above embodiment, the example in which the present invention is applied to the manufacture of an electrode foil for electrolytic capacitors for low pressure has been mainly described. However, the present invention may be applied to the manufacture of an electrode foil for electrolytic capacitors of medium to high pressure. In this case, electrolytic etching using direct current is frequently used. Further, a method in which electrolytic etching and electroless etching are combined may be employed.

It is explanatory drawing of the immersion process in the manufacturing method of the electrode foil for electrolytic capacitors to which this invention is applied.

Claims (6)

at least,
An etching step of chemically and / or electrochemically etching the aluminum foil;
After the etching step, an immersion step of immersing the aluminum foil in the treatment liquid at least once;
After the dipping step, a chemical conversion step of anodizing the surface of the aluminum foil,
In the manufacturing method of the electrode foil for electrolytic capacitors having
A method for producing an electrode foil for an electrolytic capacitor, characterized in that microbubbles are generated in the treatment liquid and immersed in at least one of the immersion steps. As the immersion step, the aluminum foil is immersed in a treatment liquid, a cleaning step for removing ions attached to the aluminum foil in the etching step, and after the cleaning step, the aluminum foil is immersed in a treatment solution, A hydration process for forming a hydrated film on the foil surface,
The method for producing an electrode foil for an electrolytic capacitor according to claim 1, wherein the microbubbles are generated in a treatment liquid in both the washing step and the hydration treatment step.   3. The method for producing an electrode foil for an electrolytic capacitor according to claim 2, wherein in both the washing step and the hydration treatment step, the treatment solution is immersed at a liquid temperature of 40 to 60 ° C.   4. The method for producing an electrode foil for an electrolytic capacitor according to claim 2, wherein a heat treatment step for heat-treating the etching foil is provided after the dipping step and before the chemical conversion step. 5.   The method for producing an electrode foil for an electrolytic capacitor according to any one of claims 1 to 4, wherein when the microbubbles are generated, the microbubbles are sprayed toward both surfaces of the aluminum foil.   The method for producing an electrode foil for an electrolytic capacitor according to claim 1, wherein a bubble having a bubble diameter of 100 μm or less is generated as the microbubble.

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