JPH08264390A - Manufacture of electrode foil for aluminum electrolytic capacitor - Google Patents

Abstract

PURPOSE: To provide a method for manufacturing an electrode foil for an aluminum electrolytic capacitor by which an electrode foil with a large electrostatic capacity per unit area can be manufactured. CONSTITUTION: In a method for manufacturing an electrode foil for an aluminum electrolytic capacitor wherein etching is performed in two stages, a prestage and a poststage, a pretreatment is conducted by applying cathode current in an acid aqueous solution including one or more kinds of metallic ions which have higher natural electrode potential than aluminum before a prestage etching is conducted and the total concentration of the metallic ions is controlled to a range of 1-100ppm.

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 an aluminum electrolytic capacitor, and more particularly to a technique for etching an anode aluminum foil for medium and high voltage.

[0002]

2. Description of the Related Art In recent years, the need for aluminum electrolytic capacitors (miniaturization, cost reduction) has rapidly increased due to the miniaturization and high reliability of sets. Also referred to as electrode foil), it is necessary to increase the capacitance per unit area more than ever before.

A conventional method for manufacturing an electrode foil will be described below. In order to miniaturize the aluminum electrolytic capacitor, an electrode foil is used that has an effective surface area enlarged by electrochemically or chemically etching the aluminum foil. Various etching methods have been studied to expand this surface area, but in general, aluminum foil is continuously inserted into several different etching tanks and the surface area of the aluminum foil is changed by applying current or chemical dissolution in each etching tank. Is gradually expanded, and a final wash is performed. In particular, how efficiently and uniformly pits are generated from the surface of the aluminum raw foil, which is uneven due to trace impurities, natural oxide film, rolling scratches, etc., is an important point for increasing the capacitance per unit area. Becomes Conventionally, iron, silicon, magnesium, or their intermetallic compounds are uniformly dispersed on the surface during the rolling and annealing step of the aluminum raw foil to increase the starting point of etching, and then in an acidic aqueous solution containing chloride ions. Pits were generated by the electric etching of.

[0004]

However, the above-mentioned conventional technique is affected by inevitable impurities contained in the aluminum raw foil, rolling oil, rolling scratches, etc., and pits are uniformly generated from the surface of the aluminum raw foil. It was difficult to do.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a method of manufacturing an electrode foil for an aluminum electrolytic capacitor, which can manufacture an electrode foil having a high capacitance per unit area. To do.

[0006]

In order to achieve the above object, the method for producing an electrode foil for an aluminum electrolytic capacitor of the present invention is produced by dividing the etching treatment into at least two steps, a first step and a second step. In the method for manufacturing an electrode foil for an aluminum electrolytic capacitor, a cathode current is applied to the aluminum original foil in an acidic aqueous solution containing at least one metal ion having a higher natural electrode potential than aluminum before performing the etching in the first step. Pretreatment is performed and the total concentration of the metal ions is set to 1 to 100 ppm.

[0007]

According to the above-mentioned manufacturing method, a cathode current is applied to the aluminum original foil in an acidic aqueous solution containing at least one metal ion having a higher natural electrode potential than that of aluminum before the etching of the former stage. Along with pretreatment, the total concentration of the metal ions is set to 1 to 100 ppm. Conventionally, if these metal ions were contained in the pretreatment liquid or the etching liquid, the surface dissolution of the aluminum raw foil was prevented. It was said that it is not possible to expect an increase in the capacitance due to the promotion, but as a result of various studies this time, if the concentration of these metal ions is appropriately controlled, it is rather expected that the pit density will increase and the capacitance will increase. I found what I could do. The mechanism is as follows.

The liquid in the treatment tank usually causes forced convection by a circulation pump, where these metal ions are uniformly dissolved and dispersed in the liquid. When a cathode current is applied to the aluminum foil that passes through the treatment tank, the aluminum foil has a negative potential with respect to the liquid, so metal ions with a positive charge are forcibly adsorbed on the aluminum foil surface. . Without pretreatment, the pit density and distribution after initial etching tends to be non-uniform due to the influence of the non-uniform natural oxide film existing on the surface of the aluminum original foil. However, if the pretreatment of the present invention is carried out, a part of the natural oxide film is dissolved by the acid, and the adsorbed metal ions form a weak part of the film, that is, a defect part, which becomes the starting point of the pit, and thus the aluminum original foil Pits are uniformly and densely formed on the surface, and an electrode foil having a high capacitance per unit area can be obtained.

The present invention is expected to be effective even if the immersion treatment is performed as it is without applying a cathode current, because a local battery is formed due to the potential difference between the aluminum ion and the metal ion and the metal ion is adsorbed on the surface of the aluminum original foil. However, the application of a cathode current is more effective because the dissolution reaction of the aluminum substrate is relaxed and the adsorption of metal ions is further promoted.

[0010]

Embodiments of the present invention will be described below.

In an aluminum raw foil having a purity of 99.98% and a thickness of 100 μm, a lead acid and a zinc ion were added to a mixed acid of 1% by weight hydrochloric acid and 2% by weight nitric acid in a liquid at 50 ° C.
The cathode current of dm ² is applied for 180 seconds for pretreatment,
Subsequently, acidic aqueous solution at 85 ° C (hydrochloric acid 10%, sulfuric acid 10%)
Immersion in the inside, direct current with a current density of 20 A / dm ² was applied for 250 seconds to perform the etching treatment of the previous stage, and then the concentration of 10%,
It is washed with nitric acid at 60 ° C., then immersed in a 5% hydrochloric acid aqueous solution at 80 ° C., and a direct current with a current density of 10 A / dm ² is applied to 600 ° C.
It is applied for 2 seconds to perform the etching process in the latter stage, that is, the final stage.

(Comparative Example) The same aluminum original foil as in the above example was used for the same etching, but the concentration of metal ions having a higher natural electrode potential than that of aluminum added to the pretreatment liquid, that is, lead ion and zinc ion concentration. Of which the total sum is less than 1 ppm is used.

The etching foils according to the above-mentioned comparative examples and the respective examples of the present invention were immersed in a 10% nitric acid aqueous solution at 50 ° C.
After washing for 5 minutes, 500% in an aqueous solution of 8% boric acid at 90 ° C
V formation was performed, and the capacitance and bending strength of each of the samples (measured once per reciprocation under the conditions of 1.0 mmR, 50 g load and bending angle of 90 degrees) were measured (Table 1). Shown in.

[0014]

[Table 1]

In this (Table 1), the electrode foil characteristics due to the difference in the metal ion concentration having a higher natural electrode potential than that of aluminum in the pretreatment liquid are shown. It is possible to increase the pit density on the surface and increase the capacitance per unit area by controlling the total sum of the concentrations of 1 to 100 ppm. In this case, when the total concentration of metal ions is lower than 1 ppm as in the comparative example, the amount of metal ions adsorbed on the surface of the aluminum raw foil during the pretreatment is small, and the effect of the present invention is hard to appear. On the other hand, the total concentration of metal ions is too high,
If it exceeds ppm, the metal ions are excessively adsorbed on the aluminum surface, the surface dissolution is promoted in the next etching step, and it becomes difficult to control the dissolution loss, and the capacitance is rather reduced.

In the examples and comparative examples of the present invention, the ratio of the amount of electric etching in the subsequent stage to the total amount of dissolved etching is 55%, but when chemical conversion is performed at medium and high voltage (200 to 650 V), the ratio is 55%. Is preferably controlled to 20 to 60%. In this case, if it is less than 20%, the pit diameter is not sufficiently expanded, and the number of ineffective pits (which do not contribute to the increase in electrostatic capacity) in which the pits are filled with the chemical conversion film increases. If there are many pits, the adjacent pits will be crushed, and the capacitance will be reduced.

As described above, the conventional method (comparative example) was carried out by performing the pretreatment in which the cathode current was applied to the aluminum original foil in the acidic solution containing 1 to 100 ppm of metal ions having a higher natural electrode potential than that of aluminum. ) Has a capacitance of about 1
It increased by 0%.

In the above-mentioned embodiments of the present invention, data of lead ions and zinc ions are shown as an example of metal ions having a higher natural electrode potential than aluminum, but other metal ions,
For example, even if copper, nickel, tin, silver or the like is used, substantially the same result as the above-mentioned embodiment of the present invention can be obtained. Also,
Although an example using a mixed acid of hydrochloric acid and nitric acid was shown as the acidic aqueous solution, hydrochloric acid alone or nitric acid alone may be used, and phosphoric acid, sulfuric acid, oxalic acid, etc. may be used under the condition that the aluminum surface is not extremely oxidized to form an excessive film. Even if it is used, almost the same effect can be obtained.

[0019]

As described above, according to the method for producing an electrode foil for an aluminum electrolytic capacitor of the present invention, at least one metal ion having a higher natural electrode potential than that of aluminum is contained before the etching of the previous stage. Pretreatment is performed by applying a cathode current to the aluminum foil in an acidic aqueous solution and the total concentration of metal ions is set to 1 to 100 ppm. Electric current is applied to the surface of the aluminum foil, which causes a large number of defects in the natural oxide film to be generated, which allows pits to be formed uniformly and at high density from the surface of the aluminum foil. The surface area of the electrode foil can be expanded to increase its capacitance. In addition, this increase in capacitance reduces the size of the aluminum electrolytic capacitor,
This can contribute to cost reduction.

Claims (3)

[Claims] 1. A method of manufacturing an electrode foil for an aluminum electrolytic capacitor, which is manufactured by performing at least two steps, a first step and a second step, in which the natural electrode potential is higher than that of aluminum before the first step etching. Pretreatment by applying a cathode current to an aluminum raw foil in an acidic aqueous solution containing at least one metal ion, and the total concentration of the metal ions is set to 1 to 100 ppm. Method for manufacturing capacitor electrode foil. 2. The method for producing an electrode foil for an aluminum electrolytic capacitor according to claim 1, wherein the acid used for the pretreatment is hydrochloric acid, nitric acid, or a mixed acid thereof. 3. The method for producing an electrode foil for an aluminum electrolytic capacitor according to claim 1, wherein the proportion of the etching amount in the latter stage is 20 to 60% of the total etching dissolution amount.