JPS60170928A - Method of producing electrode foil for aluminum electrolytic condenser - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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.

Structure of the conventional example and its problems This conventional aluminum electrolytic capacitor is made of aluminum foil and insulating paper, which has been electrolytically etched in an electrolytic solution containing chlorine ions to increase the effective surface area, and then has a dielectric oxide film applied. It is constructed by winding and impregnating it with a driving electrolyte.

The effect of expanding the surface area of electrode foil by electrolytic etching depends on many factors, such as etching current waveform, current density, etching solution type, concentration, temperature, additive type and concentration, etching pre-treatment, intermediate treatment, post-treatment, etc. It is known that it is affected by the type of aluminum raw material.

Among them, studies on current waveforms have been conducted for a long time, and direct current, alternating current, and pulsed current are usually used industrially.

Various etching methods using pulsed current waveforms have been studied, and methods using pulsed current waveforms in an electrolytic solution containing chloride ions are known.

Also known is a method in which etching is carried out using a pulsed current waveform in an electrolytic solution containing chloride ions and chromate ions as an additive.

In these methods, aluminum foil is electrolytically etched using a rectangular waveform as the current waveform. In the case of a rectangular wave, the current value suddenly drops from the set value to zero, but studies are also being conducted regarding the fall time of the current waveform.

Furthermore, using hydrochloric acid as the electrolyte, a waveform in which the fall of the current waveform does not suddenly become zero from a set value, but suddenly falls at an intermediate value, and then gradually becomes zero is being considered.

Conventionally, it has been known that in order to expand the effective surface area of aluminum foil by performing electrolytic etching, it is effective to repeatedly perform melting and film formation. This is because by forming a film, new corrosion holes can always be created during the next melting process.

Conventionally, a hydrochloric acid electrolyte has been used as the electrolyte.

In an acidic electrolyte, in order to form a film on the aluminum surface, a cathode current must be passed through the aluminum foil as a cathode and the counter electrode as an anode.

When a cathode current flows, hydrogen ions near the surface of the aluminum foil are ring-formed and become hydrogen gas, so the hydrogen ion concentration decreases near the surface and the pH increases. As a result, a film of aluminum hydroxide is formed on the surface of the aluminum foil. The situation is shown in C,Dyer,R,S,',
Alwitt: Journal of Electr.
chemical Soc, 128[2:]300
, 1981.

Conventional methods require the flow of anode and cathode currents, require both positive and negative pulses, and require the use of a bidirectional pulsed power supply. Compared to a unidirectional pulse power supply, a bidirectional pulse power supply requires equivalent circuits in both the positive and negative directions, making the power supply circuit more complex and costly.]
・It has the disadvantage of inviting an amplifier.

Furthermore, since hydrochloric acid is used, chemical dissolution proceeds at the same time as electrical dissolution due to electric current. Chemical dissolution has the property of preferentially dissolving the convex portions on the uneven surface of aluminum foil, so corrosion holes cannot penetrate deeper than a certain level. As a result, there is a limit to the surface magnification that can be obtained, and the target effective surface area cannot be obtained.

Furthermore, when an acidic electrolyte such as hydrochloric acid is used, dissolved aluminum combines with the hydrochloric acid and dissolves into the solution as aluminum chloride. As etching progresses, the amount of free hydrochloric acid in the electrolyte gradually decreases, so hydrochloric acid must be periodically replenished, making it difficult to maintain a constant electrolyte concentration. .

Purpose of the Invention The present invention eliminates such conventional drawbacks, and uses a neutral aqueous solution that is not subject to chemical dissolution as an electrolyte.
The purpose of this invention is to manufacture a high-magnification electrode foil for an aluminum electrolytic capacitor using a pulsed current having a trapezoidal current waveform with a slow fall time.

Structure of the Invention In order to achieve this object, the present invention provides a solution containing chloride ions such as common salt, ammonium chloride, potassium chloride, etc. having a pH of 4 to 8.
Using an aqueous solution of as an electrolyte, between an aluminum foil and a counter electrode, and using the aluminum foil as an anode, the current waveform rises rapidly from zero to the set current at less than o, sm S, and the current set as the first stage. A constant current flows to maintain the current value for a reset time, and in the second stage, a decreasing current flows so that the current value gradually reaches zero after 2 to 6 times the current rise time, and in the third stage, the current value decreases to zero. In a pulse current waveform that repeatedly maintains a zero state, the frequency is 10 to 100) (z, and the sum of the times of the first stage and the second stage is 2 times the time of the third stage.
The purpose is to electrolytically etch an aluminum foil using a current waveform that is ~5 times as large as that of the conventional one, to obtain an electrode foil with a high magnification.

This configuration achieves the objectives of the invention as detailed below. In other words, since the conventional method uses hydrochloric acid, a two-way power source with positive and negative power is used.
Since the present invention uses a near-neutral electrolyte with a pH of 4 to 8, a unidirectional power source only in the forward direction is required, which simplifies the power supply circuit and reduces power supply costs.

The reason for this is that in an electrolytic solution with a pH of 4 to 8, the current simply becomes zero, and an aluminum hydroxide film is formed on the surface of the aluminum foil, making it unnecessary to flow a cathode current.

Since the present invention uses a neutral electrolyte, there is no chemical dissolution that occurs in the conventional case. As a result, corrosion holes can progress deeper, which has a positive effect on expanding the surface area.

In addition, in an electrolytic solution near neutrality (pH 4 to 8), dissolved aluminum reacts with water to form white crystals and precipitate as aluminum hydroxide. Therefore, if the precipitate is filtered, the effective chlorine ion concentration in the solution is always constant, and the electrolyte has the advantage that it can be recycled and used many times, making it economical.

Although the electrochemical explanation for the fact that better results are obtained when the rate of falling current is somewhat slower in the pulsed current waveform is not yet clear, the inventors have found that the It is believed that gradual electric double discharge at the interface between aluminum and electrolyte will have a better effect on expanding the surface area.

Description of examples An embodiment of the present invention will be described below with reference to the drawings.

[Example 1] Fig. 1A shows the study results regarding the fall time of pulse current.
- Shown in C.

On the horizontal side, the fall time (ΔtOFF) of the current waveform shown in FIG. 1B was delayed as shown in FIG. 1C, and the effect of the fall time on the wavefront magnification was investigated. The method of investigation is to obtain a waveform by amplifying the output of a function gelator that can generate arbitrary waveforms.

As is clear from FIG. 1A, as ΔtOFF is made slower, an increase in wavefront magnification is obtained in the range of ΔtOFF/ΔtON (rise time) from 2 to 6.

[Example 2] Fig. 2 shows the results of an investigation regarding the frequency of the pulse current waveform. As for the pulse waveform, good results are obtained in the frequency range of 10 to 100 Hz, as is clear from ΔtOFF/ΔtON in FIG.

[Example 3] FIG. 3 shows the relationship between the wavefront magnification and the ratio of the times t11 t21 t3 of each of the first, second, and third stages of the pulse current waveform.

It can be seen that a high wavefront magnification is obtained when t1+t2/t3 is 2 to 6 times.

Although the present examples were all conducted using 10% saline, similar effects can be obtained with potassium chloride and ammonium chloride.

Effects of the Invention As described above, according to the method of manufacturing an electrode foil for an aluminum electrolytic capacitor of the present invention, an electrode foil for an aluminum electrolytic capacitor with a high magnification can be produced by performing electrolytic ennodding using a pulse current with a slow fall. is obtained, thereby achieving the effect of reducing the size and cost of the aluminum electrolytic capacitor.

Figure 1 (8~(q) is a diagram showing the influence of the current rise time and fall time on the wavefront magnification, Figure 2 is a diagram showing the influence of the frequency of the pulse number form on the expansion magnification, FIG. 3 is a diagram showing the influence of the on-time and off-time of the pulse current on the wavefront magnification.

Name of agent: Patent attorney Toshio Nakao and 1 other person - Gangko Shikakuya Y@Kibei-ku, Figure 3, 1゛

Claims (5)

[Claims] (1) Using a neutral aqueous solution containing chlorine ions with a pH of 4 to 8 as an electrolyte, a pulse current is applied between the aluminum foil and the counter electrode so that the potential of the aluminum foil with respect to the counter electrode becomes positive or zero. During melting, the current value rapidly rises from zero to the set current value below 'o, e; A decreasing current flows such that the current value gradually becomes zero after 2 to 6 times the rise time, and the third
A method for manufacturing an electrode foil for an aluminum electrolytic capacitor, characterized in that in the step, the current value is maintained at zero, and electrolytic etching is performed using a pulsed current waveform that repeats this pattern. (2) The method for manufacturing an electrode foil for an aluminum electrolytic capacitor according to claim 1, wherein the frequency of the pulse current waveform is 10 to 100 degrees. (3) Manufacturing an electrode foil for an aluminum electrolytic capacitor according to claim 1, wherein the sum of the times of the first stage and the second stage is 2 to 6 times the time of the third stage. Method. (4) The electrode for an aluminum electrolytic capacitor according to claim 1, characterized in that the aqueous solution containing chloride ions and having a pH of 4 to 8 uses one of common salt, ammonium chloride, potassium chloride, or a mixture thereof. Method of manufacturing foil. (5) The method for manufacturing an electrode foil for an aluminum electrolytic capacitor according to claim 1, wherein the electrolyte is an aqueous solution having a concentration of 5 to 20%.