JPH02296315A - Manufacture of electrode foil for aluminum electrolytic capacitor - Google Patents

Abstract

PURPOSE:To obtain high capacitance stably by applying alkaline immersion treatment as pretreatment, and next performing AC etching treatment to slowly raise initial current density. CONSTITUTION:Alkaline immersion treatment is executed as pretreatment, and next AC etching treatment to slowly raise the initial current density is done, whereupon etched holes arise from near impurities dispersed on the surface of an aluminum foil. By performing public AC etching after etched holes are generated selectively on the surface of the aluminum foil, capacitance increases linearly as compared with the quantity of electricity. Hereby, an electrode foil having high capacitance can be manufactured stably.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method of manufacturing an electrode foil for an aluminum electrolytic capacitor.

BACKGROUND OF THE INVENTION Aluminum electrolytic capacitors are generally constructed by winding aluminum electrode foil together with insulating paper and impregnating it with electrolyte. The electrode foil for aluminum electrolytic capacitors is roughened by electrochemically or chemically etching the surface in a solution containing chlorine ions, and the capacitance of light per unit area is increased by 2. Page We have achieved miniaturization and weight reduction of aluminum electrolytic capacitors. In this etching process, a certain amount of electricity (
Normally 50 coulombs/cr! ), the capacitance increases linearly with the increase in the amount of aluminum dissolved, but beyond that amount of electricity, the increase in capacitance slows down even if the amount of aluminum dissolved increases, and even if excessive etching treatment If it progresses, it may even decrease. this is,
This is because as the number of corrosion holes near the surface continues to increase, adjacent corrosion holes become connected and grow into large corrosion holes, which reduces the fine irregularities that are effective in increasing capacitance. This tendency is remarkable in AC etching, which provides a finer uneven surface than DC etching.

In order to eliminate such adverse effects, various studies have been carried out in the past, including the following regarding pre-treatment conditions for etching:
For example, the invention disclosed in Japanese Unexamined Patent Publication No. 33-299309 is known. In the method disclosed in this publication, in order to form a protective film on the surface of aluminum, phosphoric acid, After performing pretreatment with one type of aqueous solution of sulfuric acid and chromic acid, an alternating current etching process is performed in which the initial current density is gradually increased.

Problems to be Solved by the Invention According to the above-mentioned conventional method, although it has the effect of increasing the capacitance linearly by increasing the amount of dissolved aluminum,
The formation of a protective film through pretreatment is easily affected by the raw aluminum foil, and as a result, there has been a problem in that a stable capacitance cannot be obtained.

The present invention solves these conventional problems,
It is an object of the present invention to provide a method for manufacturing a tlf<foil for aluminum electrolytic capacitors, which provides a more stable capacitance than before.

Means for Solving the Problems In order to achieve the above objects, the method for manufacturing electrode foil for aluminum electrolytic capacitors of the present invention includes performing an alkaline immersion treatment as a pretreatment, and then gradually increasing the initial current density to an alternating current. This is an etching process.

Function The aluminum foil that is the object of the present invention has a purity of 99.9% or more obtained by ordinary rolling, and contains trace amounts of Cu as well as Sl as impurities.

It contains Fe and the like.

In the present invention, an alkali immersion treatment is performed as a pretreatment for etching, and through this process, aluminum, which makes up most of the surface of the aluminum foil, dissolves in the alkali, while impurities such as Fe and Cu do not react with the alkali. As a result, impurity elements become apparent in some places on the surface of the aluminum.

By gradually increasing the current density in the subsequent alternating current etching process, corrosion holes are generated near the impurities dispersed on the surface of the aluminum foil.

The above reactions will be reproducible as long as the amount of impurities in the aluminum foil is normal and controlled and will be influenced by a variable factor, the amount of the initial natural oxide layer on the aluminum foil. There isn't.

After selectively generating corrosion holes on the surface of the aluminum foil in this way, by performing a known AC etching method, the capacitance increases linearly in proportion to the amount of electricity, and a large electrostatic Capacity can be stably obtained.

EXAMPLE Hereinafter, an example of the present invention will be described while comparing it with a conventional example.

Conventional example 1 (etching liquid) B%HO (1+2%A110e5
(Etching conditions) 36℃ sine wave eoHzO, 3A/
Ca Etching time: 420 seconds Conventional example 2 (method of Japanese Patent Publication No. 63-299309) The etching solution and etching conditions are the same as those of Conventional Example 1. The current was started for 6 volts and 7 seconds.

The etching solution and etching conditions of the present invention are the same as those of the conventional example 1, and after immersion in a 60° C. 3 wt % NILOH aqueous solution as a pretreatment, the current at the initial stage of etching is started for 7 seconds.

Table 1 shows the capacitance per unit area when six types of aluminum foils from different lots were subjected to the three types of treatments and then subjected to chemical conversion treatment at 70V.

(Hereinafter, blank) As is clear from Table 1, the capacitance of the inventive example is not affected by the aluminum foil compared to the conventional example, and a higher value can be obtained on average.

Effects of the Invention As described above, the method for manufacturing electrode foil for aluminum electrolytic capacitors of the present invention has an excellent feature in that electrode foil with high capacitance can be stably manufactured compared to conventional methods. It has the following.

Claims (1)

[Claims] A method for manufacturing an electrode foil for an aluminum electrolytic capacitor, characterized by performing an alkali immersion treatment as a pretreatment, and then performing an AC etching treatment to gradually increase the initial current density.