JPS60169130A - 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 is applicable to electrolytic capacitors, especially for medium and high voltage (100W,
This invention relates to a method for etching aluminum foil for anodes (V6 or higher).

Conventional configuration and its problems Conventional aluminum electrolytic capacitors of this type need to be improved, their capacitance increased, or downsized.

In order to reduce the price and improve other characteristics, aluminum electrode foils are used that have been subjected to etching treatment to increase the surface area.

Various methods have been considered and implemented to expand the surface area of electrode foils for aluminum electrolytic capacitors, and the most common method is electrolytic etching of aluminum anodically in an aqueous chloride solution such as di-salt hydrochloric acid. A method is being taken to do so.

By the way, the manufacturing conditions for aluminum electrolytic capacitors, especially as etched foils for medium and high voltages, are that a very thick anodic oxide film is formed by chemical conversion treatment after etching, and very fine etched bits on the aluminum foil surface are formed. The setting is made so that the irregularities (on the aluminum surface and inside thereof caused by etching) will not be filled in and become unable to contribute to the etching magnification. In other words, the ideal etching bit diameter of the electrode foil for medium and high voltage is 1.3 μm (when used in the formation voltage EOOV switching), and the etching pits are tunnel pins (the etching pits penetrate from the front surface to the back surface of the aluminum foil). is generally considered to be the ideal state.

As a result of various studies aimed at achieving the ideal etching pit state, the present inventors added film-forming substances such as oxalic acid, sulfuric acid, phosphoric acid, and boric acid to an aqueous hydrochloric acid solution as the first stage of etching, and fixed the etching using a direct current. After this, a second stage of etching is performed using sodium chloride or potassium chloride, which is a metal chloride that has a greater tendency to ionize than aluminum.
Electrode foils have been manufactured through a process in which direct current etching is performed using an aqueous solution of ammonium chloride or the like, and an intermediate step is performed two to six times to completely form an oxide film on the foil surface by heat treatment or chemical treatment.

However, with conventional etching methods, surface dissolution often progresses as etching progresses, and the trench etching bit diameter is too small for the formation voltage, making it difficult to obtain sufficient surface enlargement magnification (
(hereinafter referred to as magnification) cannot be obtained, or even if the magnification is increased, the shape of the etching bits is not controlled and the etching pits propagate in a branched manner in directions other than the depth direction inside the foil, significantly reducing the strength of the electrode foil. This has been a problem, and has been a major hindrance in achieving miniaturization of aluminum electrolytic capacitors by improving the electrode foil magnification.

Here, an example of the conventional etching method will be explained in more detail as follows.

That is, conventionally, the first stage was etched with a direct current in a hydrochloric acid solution;
When the second stage is etched with direct current in a hydrochloric acid solution (see Example 1 in Figures 1 and 2) or when the second stage is chemically etched in a hydrochloric acid solution (see Example 1 in Figures 1 and 2). Refer to Example 3), the advantages are that the etching focus of the electrode foil is tunneled and the mechanical strength of the electrode foil is excellent.
The disadvantage is that even if the dissolution loss is increased, the capacity is saturated at an early stage and a high magnification cannot be obtained. This is because when hydrochloric acid is used as an etching solution, even if a film-forming substance is added to the surface of the electrode foil, the activation of the aluminum surface progresses as the amount of dissolution of aluminum increases due to etching, and etching progresses in a surface dissolution manner. However, the etching pits on the foil surface are destroyed, and bits branching in the lateral direction other than the tunnel direction are hardly generated.

Next, conventionally, the first stage was etched with a direct current in a hydrochloric acid solution, and the second stage was etched with a direct current in a neutral etching solution consisting of ammonium chloride or a chloride of a metal that has a greater tendency to ionize than aluminum (Fig. 1). , Example 2) in Figure 2 has the advantage of obtaining a high magnification, but the disadvantage is that the mechanical strength of the foil sharply decreases as the melt loss of aluminum increases, so the melt loss is 8" f /
crit was the limit, and any further increase in magnification was restricted.

This is because the oxide film formed on the foil surface in the neutral etching solution is thick, and therefore the oxide film on the surface causes non-uniformity in surface activity over a relatively wide range on the foil surface. At the same time, the etched pits grow in the direction of the tunnel (depth) of the foil, and at the same time new etched pits are generated from active points caused by non-uniform surface activity. This is because the etching pits develop as branched etching bits in the vertical and lateral directions, and further grow excessively, causing the etching pits to connect with each other, making it impossible to maintain the mechanical strength of the electrode foil.

In the case of a neutral etching solution that has not been washed, non-uniformity in surface activity tends to occur over a relatively wide range, so compared to the case of a hydrochloric acid etching solution, the ability to completely dissolve the focus diameter inside the etching pit is lower. Since the dissolution tends to concentrate at the tip of the etching pit, the diameter of the etching bit becomes smaller, and when an anodic oxide film is formed later, many etching pits that do not contribute to the magnification occur, which is a problem that hinders the improvement of the magnification. It had become.

Purpose of the Invention The present invention solves these conventional problems, and while suppressing surface dissolution during etching, the etching bit can be moved in the depth direction perpendicular to the foil and in the lateral direction perpendicular to this. By growing the electrode foil under controlled conditions and adjusting the shape of the etching bit according to the voltage used, it is possible to increase the magnification of the electrode foil.
The purpose is to achieve high strength and simultaneously satisfy the above contradictory characteristics required for miniaturization of aluminum electrolytic capacitors.

DESCRIPTION OF THE INVENTION To achieve this object, the present invention provides a method for applying a direct current in an etching solution in which at least one film-forming substance selected from oxalic acid, sulfuric acid, phosphoric acid, boric acid, or a salt thereof is added to an aqueous hydrochloric acid solution or an aqueous solution thereof. It has a first stage etching process in which etching is carried out by applying electricity, and a second stage etching process in which etching is carried out by passing a direct current in an etching solution consisting of a metal chloride or ammonium chloride, which has a greater tendency to ionize than aluminum. In the third stage etching, an aqueous hydrochloric acid solution, a solution prepared by adding at least one film-forming substance selected from oxalic acid, sulfuric acid, phosphoric acid, boric acid, or their salts to the aqueous solution, or an aqueous nitric acid solution is used as the etching solution. He invented an effective method of chemical etching.

Here, in particular, the second stage etching conventionally consisted of direct current etching alone using a hydrochloric acid etching solution, chemical etching alone using a hydrochloric acid etching solution, or direct current etching alone using a neutral etching solution. A combination of current etching and chemical etching using a hydrochloric acid etching solution was used to take advantage of the advantages of each etching method while separating the etching functions to increase effectiveness.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention, particularly basic methods, will be described.

First, as a second step, we will develop the basic structure of the etching bit shape (tunneling in the depth direction of the etching bit and branching bits in the vertical direction) to increase the magnification by direct current etching using a neutral etching solution. number and length), and furthermore, following this, a new third
As a step, chemical etching using a hydrochloric acid etching solution increases the amount of dissolution loss compared to the conventional method without significantly reducing the mechanical strength of the foil, increases the capacity by increasing the bit diameter of the etching bit according to the forming voltage, and improves the tunneling of the tunnel bit. We discovered that it is possible to effectively improve the

Describing in more detail the overall structure of etching for the purpose of fully and effectively performing this etching function, the etching method consists of three steps as shown below.

That is, in the first stage, pores formed on the foil surface by the oxidizing additive are applied under conditions of applying a current at a high current density higher than the pitting corrosion potential in high-temperature hydrochloric acid containing the oxidizing additive. By utilizing the unevenness of the oxidized film, the etching points are generated uniformly and densely. The oxide film formed on the foil surface by the additive acts as an anti-corrosion film, which promotes unevenness of the surface condition between the etching bit generation point and the foil surface, and the pore dissolution rate is faster than the surface dissolution rate. The etching bit is advanced in the depth direction under prevailing conditions to tunnel the etching pit.

In the second stage, a current is applied at a low current density in a high-temperature aqueous solution of a neutral salt containing chloride ions, and the oxide film formed on the foil surface by the solution is used as an anti-corrosion film to protect the inside of the etching bit. Under the dominant etching conditions, where the surface dissolution rate is faster than the surface dissolution rate, the etching bit is tunneled in the depth direction and the etching bit is tunneled in the depth direction. Corrosion progresses in the vertical direction. Here, we create a situation that makes it easier to suppress surface corrosion than when using a hydrochloric acid solution.
A function to generate and grow a small amount of etching bits not only in the depth direction but also in the direction perpendicular to the depth direction while preventing surface dissolution, and simultaneously expanding the diameter of all etching bits formed. fulfill.

In the third stage, under the conditions of immersion treatment in high temperature hydrochloric acid containing an oxidizing additive, the oxide film formed on the foil surface by the oxidizing additive is used as an anti-corrosion film, and the inner wall surface of the etching bit and the foil surface are The etching progresses in the radial direction of the etching bit by making the surface condition non-uniform with respect to the upper surface, making the dissolution rate inside the etching bit faster and more dominant than the dissolution on the surface.

Here, etching of the inner wall of the tunnel bit can be promoted and progressed more uniformly than in the case of electroetching in a chloride solution, and the generation and growth of new etched bits in directions other than the direction in which the diameter of the etched tunnel bit is expanded is completely suppressed. By doing so, it becomes possible to expand and adjust the etching bit diameter according to the intended voltage used for all etching bits generated. Moreover, this makes it possible to maintain the penetrability of the etched tunnel bit after chemical formation, and it is possible to obtain high capacitance and low jan δ.

Figure 4 shows a comparison of the differences in the etching bit shapes formed by the conventional etching method (Example 2) and the etching method according to the present invention (Example 4) (Relationship between the etching bit diameter and the number of bits by the etching method). ), which shows that the etching bit diameter is enlarged by the etching method of the present invention.

Specific examples based on the present invention will be shown below.

[Example-1] An aluminum annealing track with a purity of 99.99% and a thickness of 10o/1m was used as a sample, and the first stage etching was performed using an aqueous solution of 6% hydrochloric acid and 0.03% oxalic acid at a liquid temperature of 8o''C. So, the current density is 1cs
After applying a direct current of o mA/crA for 80 seconds,
Etching foil was etched by applying a direct current with a current density of 40 mA/7 for 10 minutes in the same aqueous solution.
After 70V chemical formation, the results of measurements on etching weight loss and capacitance 2 strength are shown below.The foil strength is based on the bending strength.1. oR.

With a load of 200g and a bending angle of 9o, one reciprocation was made once.

[Example-2] Using the same sample as in Example 1, the first stage etching was performed at ts
After adding %HCIKo, o% oxalic acid and applying a direct current (i780 seconds) at a current density of 150 mA/cut in an aqueous solution at a solution temperature of so'C, the second stage etching was performed using a diammonium chloride solution at a solution temperature of 90°C. Current density 80mA/cn in aqueous solution of
Table 2 shows the results of measurements of etching dissolution loss, capacitance, and strength after chemical conversion in a boric acid solution at 370 V for etching foils that were subjected to a DC gold application of 1 for 4 minutes.

[Example-3] Using the same sample as Example 1, the first stage etching was 6% in total.
After adding 0.03% oxalic acid to hydrochloric acid and applying a direct current with a current density of 150 mA/cnl for 80 seconds in an aqueous solution with a liquid temperature of 80'C, the second stage etching was performed by adding 0.03% oxalic acid to 6% hydrochloric acid.
Etching foil that was chemically dissolved by immersion in an aqueous solution containing oxalic acid at a temperature of 90''C for 6 minutes was chemically converted in a boric acid solution at 370V, and the etching dissolution loss and capacitance were 2.
Table 3 shows the results of measuring strength.

(Table 3) [Example 4] Using the same sample as Example 1, the first stage etching was 6%.
After the second stage etching was carried out using an aqueous solution containing 0.03% oxalic acid in hydrochloric acid at a temperature of 80°C and applying a direct current with a current density of 150 mA/shoulder for 70 seconds, the second stage etching was carried out at a diammonium chloride solution temperature of eo'. After applying a direct current with a current density of 80 mA/cni for 3 minutes and 30 seconds using an aqueous solution of c, the third stage etching was performed at 6%
After adding 0.03% oxalic acid to hydrochloric acid and chemically etching it in an aqueous solution with a liquid temperature of 90°C (refer to Figure 3 for the relationship between chemical etching temperature, weight loss, and capacity) at 370V, the etching dissolution weight loss, Table 4 shows the results of measurements for capacitance 2 intensity.

(Table 4) As shown in Table 4, by using the etching method of the present invention, even if the dissolution loss is increased in this way, the capacity can be increased proportionally without becoming saturated, and at the same time, the strength can be increased. It became possible to maintain the (Fig. 1, 2
(See Example 4 in the figure) Effects of the Invention As described above, the capacitance value can be increased by 8 to 25% compared to when etching is performed using the electrode foil method for aluminum electrolytic capacitors of the present invention. It becomes possible to downsize the capacitor, and at the same time, when used as a capacitor product, the jan δ can be lowered by 20 inches compared to the conventional product. Furthermore, running costs can be reduced by reducing the cost of incidental equipment required for production and the power consumption of the etching method.

[Brief explanation of drawings]

Figure 1 is a characteristic diagram showing the relationship between dissolution loss and capacitance by each etching method listed in Examples 1 to 4, and Figure 2 is the same (dissolution loss by each etching method listed in Examples 1 to 4). FIG. 3 is a characteristic diagram showing the relationship between chemical etching temperature/loss and capacitance according to the present invention, and FIG. FIG. 7 is a characteristic diagram showing the relationship between the etching pit diameter and the number of pits according to the etching method according to the invention (Example 4). Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure @2 Figure @ζlUX t (tn?/cmf) Figure 3 Figure 4

Claims (1)

[Claims] An aqueous solution of hydrochloric acid, or an aqueous solution containing oxalic acid or sulfuric acid. A first stage etching step in which etching is carried out by passing a direct current in an etching solution containing at least one film-forming substance selected from phosphoric acid, boric acid, or their salts, and a chloride of a metal that has a greater tendency to ionize than aluminum. or a second stage etching process in which etching is carried out by passing a direct current in an etching solution made of ammonium chloride, and a third stage etching process in which a hydrochloric acid aqueous solution or oxalic acid, sulfuric acid, phosphoric acid, or boric acid is added to the aqueous solution. A method for producing an electrode foil for an aluminum electrolytic capacitor, characterized in that chemical etching is performed using a solution containing at least one film-forming substance among these salts or a nitric acid aqueous solution as an etching solution.