JPH02114620A - Manufacture of electrode foil for aluminum electrolytic capacitor - Google Patents

Abstract

PURPOSE:To manufacture the title electrode foil for aluminum electrolytic capacitor capable of expanding the surface space thereof while conserving the mechanical strength of the electrode foil by a method wherein, during the first and the second phase etching processes, more than one time of intermediate processing to melt a hydroxide film on the surface of aluminum in a specified water solution is performed during the halfway stage of the second phase etching process. CONSTITUTION:When the two phase etching process comprising the first and the second phase is to be performed, the first phase etching procese is performed as a DC etching process on a water solution containing 0.01-5% of at least one kind out of porus filming oxide comprising 2-15% of hydrochloric acid as well as sulfuric acid, oxalic acid and phosphoric acid; the second phase etching process is performed as the DC etching process in another water solution containing 0.1-10% of at least one kind out of neutral salt containing Cl<->, sodium chloride, ammonium chloride and potassium chloride; while at least more than one time of intermediate processing to melt a hydroxide film on the surface of aluminum in the water solution containing 0.01-15% of at least one kind out of fluoric acid, hydrochloric acid is performed during the halfway stage of the second phase etching process. Through these procedures, the surface space can be expanded in proportion to the decreased amount of melted aluminum.

Description

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

BACKGROUND OF THE INVENTION Electrode foils for aluminum electrolytic capacitors (hereinafter referred to as electrode foils) are made by electrochemically or chemically etching aluminum foil to enlarge its surface area in order to reduce the size of capacitors.

Various etching methods have been studied to increase this surface area, and conventionally for this purpose.

It has been practiced to divide enching into two or more stages. That is, in the first stage etching, etching pits are generated using an aqueous solution of hydrochloric acid and porous film forming acid, and then in the second stage etching, c7! The surface area has been expanded by suppressing surface dissolution and further generating and growing etching bits by using a neutral salt aqueous solution containing .

Problems to be Solved by the Invention In the conventional method, there was a problem in the effect of enlarging the surface area after the second stage of etching. That is, in the second stage of etching, in order to suppress surface dissolution that occurs as etching progresses,
Surface dissolution has been prevented using a neutral salt aqueous solution containing CI, but in this aqueous solution, the number and dispersion of film defects on the surface, which are likely to cause etching pits on the hydroxide film, are insufficient, resulting in etching. The generation and growth of pits concentrates on localized areas on the surface, which not only reduces the surface area expansion effect but also causes a new problem of impairing the mechanical strength of the electrode foil. For this reason, when using electrode foils to downsize aluminum electrolytic capacitors, the effect of increasing the surface area is insufficient, which has been a problem.

The present invention solves the above-mentioned problems, and aims to provide a method for manufacturing an electrode foil for an aluminum electrolytic capacitor that can increase the surface area while maintaining the mechanical strength of the electrode foil.

Means to solve problems In order to achieve this objective, the present invention provides the first stage.

When performing etching in two stages, the first
Stage etching with 2-15% hydrochloric acid, sulfuric acid, and oxalic acid.

After performing direct current etching in an aqueous solution containing 0.01 to 5% of at least one of porous film forming acids consisting of phosphoric acid, the second stage etching is performed using neutral salts containing Cl, sodium chloride, and ammonium chloride. .

Direct current etching is performed in an aqueous solution containing 0.1 to 10% of at least one of potassium chloride, and in the middle of this second stage etching, an aqueous solution containing 0.01 to 15% of at least one of hydrochloric acid and hydrochloric acid. In this process, an intermediate treatment for dissolving the hydroxide film on the aluminum surface is performed at least once.

According to the present invention, etching pits can be grown as etching progresses without causing surface dissolution or loss of mechanical strength, and the surface area can be expanded in proportion to the aluminum dissolution loss. The effects of each etching process will be explained below.

(First Stage Etching) In order to form etching pits with high density and uniformity, it is necessary to add an appropriate concentration of hydrochloric acid and an acid capable of forming a porous film. If the hydrochloric acid concentration is less than 2%, the etching effect will be small, and if it exceeds 15%, the entire surface will be dissolved. Therefore, it is in the range of 2 to 15%, and 3 is particularly preferable.
~8%.

The amount of acid that can form a porous film, whether it is sulfuric acid, oxalic acid, or phosphoric acid, is less than 0.01%, the formation of a porous film is insufficient, and if it exceeds 5%, the film is not formed. The reaction becomes stronger, and the growth of the generated etch pits in the length direction is suppressed. Therefore, in the range of 0.01 to 6%,
Particularly preferred is 0.05-1%. Within this preferred range, a porous film with high-density and uniform pores is formed on the aluminum surface, and r4 erodes the pores to form etching pits. Since the portion is covered with a film, surface dissolution is suppressed, resulting in formation of highly dense and uniform etching pits. The temperature of the etching solution also has an important effect;
If it is less than 0, the etching effect will be small, and if it exceeds 100°C, the entire surface will be dissolved. Therefore, within the range of 60 to 100'C, particularly preferred is 70 to 90'C. Further, if the current density is less than 3 A/dm2, the etching effect will be small, and if it exceeds 70 A/dm2, the entire surface will be dissolved.

Therefore, within the range of 3 to 70 A/dm2, particularly preferred is 10 to 40 A/dm2.

(Second stage etching) The second stage etching is carried out after the first stage etching and is combined with an intermediate treatment to suppress surface dissolution while further generating etching pits. Grow the pit. For this reason,
Neutral salt containing C1-.

Etching is required in an aqueous solution containing at least one of sodium chloride, ammonium chloride, and potassium chloride. In the case of an aqueous solution of any of these neutral salts, if the concentration is less than 0.1%, the etching effect is small;
If it exceeds 0%, total surface dissolution occurs. Therefore, 0.
Within the range of 1 to 10%, particularly preferred is 1 to 3%. By combining this with intermediate treatment within such a suitable range, it is possible to generate new etching pits with almost no surface dissolution, and at the same time it is possible to grow the etched bits generated in the first stage etching. be. In the second stage etching, as in the first stage etching, the liquid temperature is within the range of 50 to 100°C, and particularly preferably 70°C.
The current density is within the range of 3 to 70 μm/dm 2 , particularly preferably 4 to 20 μm/dm 2 .

(Intermediate Processing) In the present invention, intermediate processing is performed in the middle of the second stage etching. This process continues the process in which a new etching focus was generated in the first stage of etching, and the surface area expansion progressed in proportion to the decrease in aluminum dissolution, and the second stage of etching also expanded the surface area. This is done not only to saturate the amount of aluminum melted but also to increase it proportionally. This has the effect of preventing the etching from concentrating in the second stage of etching, making the etching bits larger than necessary, destroying adjacent etching bits, or causing surface dissolution.

That is, even in the second stage etching, new etching bits are uniformly generated and grown. In the present invention, the hydroxide film formed on the aluminum surface by an aqueous solution of a neutral salt containing C1 in the second stage etching causes a greater number of film defects, which are the starting points for etching bits, to exist in a more uniformly dispersed manner than in the past. buoyant acid, which can dissolve the hydroxide film formed on the aluminum surface during the second stage etching and further generate film defects;
Perform chemical treatment with hydrochloric acid. The concentration of the processing liquid is 0.01%
If it is less than 15%, the effect of dissolving the surface hydroxide film will be small, and if it exceeds 15%, the surface hydroxide film will be dissolved so much that no hydroxide film will exist, and the number of starting points for etching bits will decrease when etching is performed next time. It ends up. Therefore o,
Within the range of 01 to 15%, particularly preferred is 01 to 6%. Further, if the liquid temperature is below 20°C, the effect of dissolving the surface hydroxide film is small, and if it exceeds 90°C, the surface hydroxide film will be dissolved too much, and the effect of generating etching bits will be reduced. Therefore, within the range of 20 to 90°C, particularly preferred is 40 to 70°C.

Here, the intermediate treatment according to the present invention can be repeatedly performed in the middle of the second stage etching, and by repeatedly performing the intermediate treatment, the surface area enlarging effect can be increased in proportion to the number of times of treatment.

Example Examples of the present invention will be described below along with comparative examples.

The sample has a purity of 99.99% and a thickness of io.

High-purity annealed aluminum with a diameter of μm was used.

<Comparative example> After the first stage etching was carried out using an aqueous solution containing 7% hydrochloric acid and 0.1% sulfuric acid at a temperature of 80°C and applying a direct current with a current density of 20 μm/dm2 for 90 seconds, the second stage etching Etching was carried out using an aqueous solution containing 5% sodium chloride at a temperature of 80°C at a current density of 1o.
The test is carried out by applying a direct current of 2 pm/dv for 320 seconds.

<Example> After the first stage etching was performed in the same manner as in the comparative example, the second stage etching was performed using an aqueous solution containing 5% sodium chloride and a liquid temperature of aoC, and applying a direct current at a current density of 10 μm/dm2 for 120 seconds.
Next, immersion treatment was performed for 3 seconds in an aqueous solution containing 1% hydrochloric acid at a temperature of 6°C, and then a second stage etching was performed again in an aqueous solution containing 6% sodium chloride at a temperature of 80°C at a current density of 10 A/d.
This is done by applying a direct current of 2 for 200 seconds.

After etching foils according to the above comparative examples and examples of the present invention were subjected to 37Qv chemical conversion in a boric acid aqueous solution, the capacitance and bending strength (1, oR) of each sample were determined.

200! ? 1 in one round trip under load and bending angle of 90'
The results are shown in Table 1.

Table 1 Effects of the Invention As described above, according to the manufacturing method of the present invention, uniform etching pits with a high density and an appropriate etching pit diameter can be produced in proportion to the weight loss of aluminum lamb melted. This makes it possible to manufacture electrode foil for aluminum electrolytic capacitors that has a very large surface area expansion effect.

Claims (3)

[Claims] (1) When etching is performed in two or more stages, the first stage and the second stage, an aqueous solution containing 0.01 to 15% of at least one of hydrochloric acid and hydrochloric acid is added in the middle of the second stage etching. A method for manufacturing an electrode foil for an aluminum electrolytic capacitor, comprising performing at least one intermediate treatment for dissolving a hydroxide film on the aluminum surface. (2) The first stage etching is direct current etching in an aqueous solution containing 2 to 15% hydrochloric acid and 0.01 to 5% of at least one of porous film forming acids consisting of sulfuric acid, oxalic acid, and phosphoric acid. A method for manufacturing an electrode foil for an aluminum electrolytic capacitor according to claim 1. (3) The second stage etching is direct current etching in an aqueous solution containing 0.1 to 10% of at least one of neutral salts containing Cl^-, sodium chloride, ammonium chloride, and potassium chloride. 1. The method for producing an electrode foil for an aluminum electrolytic capacitor according to 1.