JPH08115854A - Method for manufacturing electrode foil for aluminum electrolytic capacitor - Google Patents

Abstract

PURPOSE: To easily manufacture an electrode foil with a large effective area, namely a large capacity per unit area by controlling a pit occurrence starting point when manufacturing an electrode foil for aluminum electrolytic capacitor. CONSTITUTION: Aluminum foil is dipped into a solution containing metal which is electrochemically more precious than aluminum as the pretreatment process of etching and a metal which is more precious than aluminum is uniformly deposited and adhered on the surface of the aluminum foil for making the adhesion part of metal as a pit occurrence starting point.

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 an electrode foil for aluminum electrolytic capacitors.

[0002]

2. Description of the Related Art In recent years, with the miniaturization and high reliability of electronic equipment, there has been a strong demand for miniaturization of the user's needs for aluminum electrolytic capacitors. Therefore, the electrode foil for aluminum electrolytic capacitors is more than ever before. It is necessary to increase the electrostatic capacity per unit area (hereinafter referred to as capacity).

A conventional method for manufacturing an electrode foil for an aluminum electrolytic capacitor will be described below with reference to the drawings.

FIG. 6 shows a manufacturing process of a conventional electrode foil for an aluminum electrolytic capacitor. In order to miniaturize the aluminum electrolytic capacitor, the aluminum foil is electrochemically or chemically etched to increase its effective surface area. Various etching methods have been conventionally researched to increase the effective surface area.However, generally, the aluminum foil is first treated as a pretreatment step immediately after the introduction of the aluminum foil to remove dirt and dust such as oil. After immersing in the cleaning solution for cleaning, it is continuously inserted into several different etching tanks, and the etching is performed to gradually increase the surface area of the aluminum foil by applying a current or chemically dissolving in each etching tank. In the post-treatment step, final washing is carried out and then dried, and this is wound to produce an electrode foil. Particularly, in order to obtain an electrode foil having a large effective surface area, how to uniformly generate many pits on the foil surface is an important point.

[0005]

In the prior art,
The capacity expansion, that is, the control of pit generation, is usually achieved by devising an etching solution or etching current.
The pretreatment step only plays a role of cleaning, and in some cases, the pretreatment step itself may be omitted.

It is known that the generation and distribution of pits are generally very strongly influenced by the surface condition of the aluminum foil as a raw material, particularly the degree of non-uniformity of the surface coating on the foil surface. However, in the prior art, no means has been developed to completely remove the influence of the surface coating or to make the surface coating uniform. Therefore, there is a limit in the control of pit generation, especially in the uniformity of pit generation. .

That is, when etching is carried out only by performing no treatment shown in FIG. 7 or pretreatment by a conventional method, the generation of the pits 13 is strongly influenced by the strength of the surface film of the aluminum foil 10, The distribution becomes non-uniform such that the weak portion 11 of the surface film is dense and the strong portion 12 of the surface film is sparse.

The present invention is to solve the above-mentioned problems, and to improve the surface of the aluminum foil at the stage of pretreatment of the aluminum foil to remove the influence of unevenness of the surface film and to make the pits uniform. Provided is a method for producing a high-capacity electrode foil for an aluminum electrolytic capacitor by controlling the pit density.

[0009]

In order to achieve the above object, the method for producing an electrode foil for an aluminum electrolytic capacitor according to the present invention uses an aluminum foil which is electrochemically more noble than aluminum as a pretreatment step for etching. This is a method of immersing in a solution containing the above and depositing and adhering these metals in the form of dots or islands on the surface of the aluminum foil.

[0010]

[Function] As described above, when the aluminum foil is immersed in a solution containing a metal that is more precious than aluminum, aluminum, which generally has a higher ionization tendency, elutes into the solution, and instead, a metal that is more precious than aluminum is deposited on the surface of the aluminum foil. The phenomenon of uniform deposition and adhesion occurs. After that, when this aluminum foil is etched, a kind of partial battery is formed because the redox potential is different between the metal that is more precious than the deposited aluminum and the aluminum around it.
The aluminum around the precious metal melts out preferentially over the rest. That is, the portion where the metal, which is more precious than aluminum, adheres serves as the starting point of the pit. Here, since the metal, which is more precious than aluminum, is uniformly deposited and adhered on the surface of the aluminum foil, the pits are uniformly generated.
The density of the pits also depends on the amount of metal that is more noble than aluminum that deposits and adheres to the aluminum foil.

When a current is applied with the aluminum foil as a negative electrode while the aluminum foil is immersed in a solution containing a metal nobler than aluminum, aluminum hardly elutes, but a metal nobler than aluminum is not plated. According to the principle, it deposits and adheres to the surface of the aluminum foil and becomes the starting point of the pit.

[0012]

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

FIGS. 5 (a), 5 (b) and 5 (c) show how the surface of the aluminum foil changes when processed according to the present invention. At the stage of no treatment or pretreatment by a conventional method, that is, washing treatment, a non-uniform surface coating in which the strong strength portion 2 and the weak strength portion 3 are mixed is present on the surface of the aluminum foil 1. When this aluminum foil 1 is dipped in a solution containing a metal nobler than aluminum according to the present invention, the metal 4 nobler than aluminum is uniformly deposited on the surface of the aluminum foil 1. Then, when the aluminum foil 1 is etched, the pits 5 are generated mainly from the metal 4, which is noble as much as aluminum deposited and deposited on the surface of the aluminum foil. That is, the pits 5 are uniformly generated without being influenced by the nonuniformity of the surface film of the aluminum foil 1.

FIG. 1 is a process drawing of an embodiment of a method for manufacturing an electrode foil for an aluminum electrolytic capacitor according to the present invention. In FIG. 1 showing the present invention, the pretreatment process after the introduction of the aluminum foil is a dipping treatment in a solution containing a metal nobler than aluminum. After this pretreatment step, etching is carried out, washing is performed as a posttreatment, and after drying, the electrode foil for an aluminum electrolytic capacitor is manufactured by winding the foil.
(Table 1) and (Table 2) show the capacitance characteristics of the electrode foil manufactured according to the present invention. (Table 1) shows the case where the aluminum foil was immersed in a solution containing Cu, which is a metal more noble than aluminum, at room temperature for 1 minute, and then etched and formed, and (Table 2) is nobler than aluminum. This is the result of chemical conversion after immersion in a solution containing Zn as a metal for 1 minute and then etching at a current density 6 times that in the case of (Table 1). The formation voltage is 520 V in both cases (Table 1) and (Table 2).

[0015]

[Table 1]

[0016]

[Table 2]

From (Table 1) and (Table 2), it is expected that there is an optimum value for the concentration of a metal that is more precious than aluminum.
When the concentration of the noble metal is extremely lower than that of aluminum, the amount of these metals deposited and deposited on the surface of the aluminum foil is too small, so that the starting point of the pit does not increase and the effect cannot be obtained. On the contrary, if the concentration is too high, the adhesion amount will be too large and the density of the pit starting point will be too dense, so when the pit diameter is increased according to the formation voltage, the pits will stick to each other and will not contribute to the capacity expansion. . When the aluminum foil is immersed in a solution containing a metal nobler than the aluminum, the amount of the metal nobler than the aluminum deposited and adhered to the surface of the aluminum foil depends on the concentration of these metals, the ionization tendency, the type of the solution, and the type of the solution. Although it depends on the temperature, the immersion time, etc., the concentration of the metal which is effective in expanding the capacity is generally about 0.
It is from 1 ppm to 50,000 ppm.

In FIG. 1, the conventional cleaning treatment is not performed as the pretreatment, but only the immersion treatment in a metal nobler than aluminum is performed. However, if necessary, a cleaning treatment with a thin alkaline solution or a commercially available cleaning liquid is performed. After performing the above step, the immersion treatment may be performed in a solution containing a metal nobler than aluminum.

FIG. 2 shows an embodiment of the present invention in which an electric current is applied while the aluminum foil is immersed in a solution containing a metal nobler than aluminum. At this time, the electric current may be continuously applied while the aluminum foil is immersed in the solution, or may be applied for a partial time during the immersion as shown in FIG. 3 to combine with the chemical treatment.

In FIG. 2, 6 is a pretreatment tank in which a solution 7 containing a metal nobler than aluminum is injected, and the aluminum foil 1 is immersed in this solution 7 via a roller 8. An electrode 9 is arranged around the aluminum foil 1 in the solution 7, and a current is applied to the electrode 9 and the aluminum foil 1 from a power source 10. A current may be applied to the aluminum foil 1 with the aluminum foil as a positive electrode or with a negative electrode.

However, when the aluminum foil 1 is used as a positive electrode and a current is applied, the deposited metal falls off from the surface of the aluminum foil 1 as the surrounding aluminum melts in the range where the etching of the aluminum foil 1 occurs violently during the pretreatment. Then, it is no longer used as a pit starting point, so it is necessary to keep the applied amount within a range where the etching of the aluminum foil 1 does not occur violently.

FIG. 3 shows the behavior of the potential sweep of the aluminum foil in an acid solution containing hydrochloric acid as a main component. When the potential is swept from the natural potential to the anode side, an inflection point as shown in the figure appears. , At a potential higher than that, the current increases rapidly. It has been clarified by observation with a scanning electron microscope that the foil surface is severely etched at a potential above this inflection point, and conversely, in order to suppress etching, it must be below the current reaching this inflection point. It can be said that it does not. The magnitude of the current at this inflection point depends on the conditions of the solution, the purity of the aluminum foil, etc., but it was about 0.05 A / cm ² as confirmed by us. Therefore, the magnitude of the current applied to the aluminum foil as the positive electrode must be 0.05 A / cm ² or less.

FIG. 4 shows an embodiment of the present invention in which an aluminum foil is immersed in a solution containing a metal nobler than aluminum and then heat-treated. This heat treatment oxidizes the aluminum foil and the metal that is more precious than the aluminum deposited and adhered to the surface of the aluminum foil. Etching is less likely to occur around the noble metal than aluminum oxidized by this treatment compared to the case when it is not oxidized. Therefore, if appropriate heat treatment conditions are selected, the aluminum foil contains a noble metal more than aluminum. While increasing the starting point of pit generation compared to the conventional case where immersion treatment in solution is not performed,
Oxidation of a metal that is more precious than aluminum can prevent the formation of excessive pits.

In FIG. 4, the cleaning treatment is performed before the immersion treatment in the solution containing a metal nobler than aluminum, but this may be omitted. In addition, in order to remove the surface film on the surface of the aluminum foil after heat treatment,
An extremely weak surface treatment may be performed with a thin NaOH solution or the like as long as the deposited metal does not fall off.

In the above embodiments, Cu and Zn have been described as metals that are more precious than aluminum.
Other than this, Pb, Fe, Ni, Sn can also be used.

[0026]

As described above, by immersing an aluminum foil in a solution containing a metal nobler than aluminum as a pretreatment for etching, the metal nobler than aluminum is uniformly deposited and adhered on the surface of the aluminum foil. This is the starting point for the pit. At this time, the density of the pit starting points can be controlled to an optimum value by selecting conditions such as the kind and concentration of a metal that is more noble than aluminum in an appropriate range, and as a result, the capacity of the electrode foil increases.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram in a method for manufacturing an electrode foil for an aluminum electrolytic capacitor according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of a method for applying a current to an aluminum foil of the present invention.

FIG. 3 is a characteristic diagram of the potential sweep of the aluminum foil showing the upper limit current value applied by the present invention.

FIG. 4 is a manufacturing process diagram of a method for manufacturing an electrode foil for an aluminum electrolytic capacitor according to another embodiment of the present invention.

FIG. 5 is an enlarged view showing changes in the surface of the aluminum foil applied with the present invention.

FIG. 6 is a manufacturing process diagram of a conventional method for manufacturing an electrode foil for an aluminum electrolytic capacitor.

FIG. 7 is an enlarged view of the surface of the aluminum foil after etching by the conventional manufacturing method.

[Explanation of symbols]

 1 Aluminum foil 2 Strong surface film part 3 Weak surface film part 4 Metal noble than aluminum 5 Pit 6 Pretreatment tank 7 Solution 8 Roller 9 Electrode 10 Power supply

Claims (6)

[Claims] 1. Before the step of etching the aluminum foil, the aluminum foil is immersed in a solution containing a metal that is electrochemically more noble than aluminum so that the surface of the aluminum foil is more electrochemically noble than the aluminum. A method for manufacturing an electrode foil for an aluminum electrolytic capacitor, which comprises a pretreatment step of depositing and depositing metal in the form of dots or islands. 2. The aluminum electrolysis according to claim 1, wherein a weak current of 0.05 A / cm ² or less is applied to the aluminum foil immersed in a solution containing a metal electrochemically more noble than aluminum with the aluminum foil as a positive electrode. Method for manufacturing capacitor electrode foil. 3. The method for producing an electrode foil for an aluminum electrolytic capacitor according to claim 1, wherein a current is applied to the aluminum foil immersed in a solution containing a metal electrochemically more noble than aluminum with the aluminum foil as a negative electrode. 4. The method for producing an electrode foil for an aluminum electrolytic capacitor according to claim 1, wherein at least one of Cu, Zn, Pb, Fe, Ni, and Sn is used as the metal electrochemically more noble than aluminum. 5. The method for producing an electrode foil for an aluminum electrolytic capacitor according to claim 1, wherein a liquid containing 0.1 ppm to 50000 ppm of a metal electrochemically more noble than aluminum is used. 6. The method for producing an electrode foil for an aluminum electrolytic capacitor according to claim 1, wherein the aluminum foil is immersed in a solution containing a metal electrochemically more noble than aluminum and then heat-treated.