JP2621079B2 - Method of forming electrode foil for aluminum electrolytic capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a method for forming an electrode foil for an aluminum electrolytic capacitor.

(Prior Art) In the manufacture of an electrode foil for an aluminum electrolytic capacitor, in order to increase the water resistance of an oxide film, the electrode foil is immersed in a phosphoric acid solution (hereinafter referred to as P treatment). The P treatment time of this electrode foil is usually 1 to 10 minutes, but if this P treatment is continued for a long time, white aluminum phosphate scale is generated. This aluminum scale not only floats in the phosphoric acid solution but also firmly adheres to the inner wall of the P treatment tank. There is no good way to prevent this, and at present, it is common practice to periodically stop the chemical conversion machine and mechanically scrape it off or dissolve it with alkali. And we are spending a lot of time on this work.

(Problems to be Solved by the Invention) As described above, there is no appropriate means for preventing or removing aluminum phosphate scale generated in the P processing solution, and the method depends on mechanical removal or dissolution. There were problems such as processing cost, reduction of work, and the like.

[Constitution of the Invention] (Means for Solving the Problems) In the method for forming an electrode foil for an aluminum electrolytic capacitor according to the present invention, aminotrimethylphosphonic acid or a salt thereof from which chlorine has been removed is used as a scale inhibitor, and this is used as phosphoric acid. Is added to a solution having a main composition to form a treatment liquid, and a depolarization treatment step of immersing the electrode foil in the treatment liquid is provided, and the chlorine removal is performed by steam distillation. Or aminotrimethylphosphonic acid or a salt thereof.

(Function) The method for forming an electrode foil for an aluminum electrolytic capacitor according to the present invention comprises adding a chlorine-removed aminotrimethylphosphonic acid or a salt thereof to a solution containing phosphoric acid as a main component and using the solution as a treatment liquid. Although the amount of aluminum phosphate scale generated is small and the time until the generation is greatly delayed to substantially prevent the generation, aminotrimethylphosphonic acid as an inhibitor has three methylphosphonic acid groups in which a nitrogen atom is a nitrogen atom. Move freely from the base point, the terminal hydroxyl group captures Al ³⁺ in the liquid and forms a strong chelate structure, but the theoretical amount required to form the chelate (weight ratio Al / scale inhibitor = 1 / 5.5 ) Because it achieves scale prevention with a much smaller amount than
It is thought that there is a bond other than this chelate.

It is a phenomenon (threshold effect) peculiar to the scale inhibitor, which adsorbs to the growth points such as dimer, trimer ions and small crystal nuclei, thereby changing the crystal growth pattern and delaying the scale crystal growth. It is considered to be one that is significantly distorted. That is, the crystal growth rate decreases, the adhesion to the inner wall of the tank also slows, and the adhesion to the inner wall changes due to the distortion of the crystal structure, and the scale decreases.

Aminotrimethylphosphonic acid has the structure shown in FIG. 1, and aminotrimethylphosphonate has X in FIG.
Na, K, NH ₄

However, since aminotrimethylphosphonic acid uses chloride as a starting material as a raw material, a liquid having a concentration of 50% usually contains 0.3 to 1.0% of chlorine. When 20 ppm of this aminotrimethylphosphonic acid is added to the P-treated solution, the chlorine becomes 120 to 400 ppb, far exceeding the allowable chlorine content of 50 ppb.

Generally, chlorine easily erodes the aluminum oxide film, as represented by Al ₂ O ₃ + 6Cl ⁻ → 2AlCl ₃ + 3O ²⁻ , and is the most harmful to chemical conversion foils. This will shorten the life of the capacitor.

It is fully expected that chlorine contained in this aminotrimethylphosphonic acid or its salt will enter the oxide film during the P treatment, and therefore, removal of this chlorine is an absolute condition.

The present inventors have conducted intensive studies on this method for removing chlorine, and have found that steam distillation is optimal. The term “steam distillation” as used herein means that steam is blown into a solution to perform distillation purification and impurity removal at a low temperature. For example,
By passing 10 to 50 times the amount of water vapor to 50% concentration of aminotrimethylphosphonic acid, chlorine is reduced to 1/5 to 1/2.
Can be reduced to zero.

This dechlorinated aminotrimethylsulfonic acid or its salt has no difference in its scale prevention ability as compared with the non-dechlorinated one, and even if it is added to the P treatment tank, it does not affect the properties of the chemical conversion foil. Do not give.

(Example) Example Product name: DiQuest 2000 (manufactured by Mitsubishi Monsanto, concentration: 49%) 100 g (76 ml) was placed in a steam distillation vessel as a scale inhibitor, and after passing 20 times the amount of steam to the steam distillation vessel. Is shown in Table 1.

As is clear from Table 1, the amount of chlorine in the trade name: Demand 2000 used as an inhibitor by steam distillation can be reduced to an allowable value or less (50 ppb).

A batch test for the scale prevention of the dechlorination demand 2000 obtained as described above was conducted. 3% in Erlenmeyer flask
100 ml of phosphoric acid and 0.6 g of 330V conversion foil (cut into 5 mm squares) were added, and a predetermined amount of Diquest 2000 from which chlorine had been removed as described above was added. The temperature was maintained at 85 ° C. and stirred with a magnetic stirrer. Table 2 shows the time until scale generation and the amount of precipitate generated.

As is clear from Table 2, by adding Diquest 2000 to the phosphoric acid solution, it is possible to delay the time until scale generation and reduce the amount of precipitate generated.

Example 2 Next, a test was performed in which phosphoric acid was continuously supplied and the chemical conversion foil was replaced at predetermined time intervals. 800 ml of a 3% phosphoric acid solution containing 20 ppm of the same quest 2000 as in Example 1 was placed in a beaker with an overflow tube at 800 ml, and the above phosphoric acid solution was supplied at 1.2 ml / min. It overflowed. Immerse 4cm x 6cm 300V conversion foil for 4h
The foil was replaced every time. The temperature was kept at 70 ° C. and the mixture was stirred with a magnetic stirrer. In addition, test pieces (Ti plate, 1 cmW x 4 cml x 0.4 mm
t) was immersed in the solution. Table 3 shows the time until scale generation and the amount of adhesion to the test piece.

As is evident from Table 3, when Diquest 2000 was added, the time until scale generation became longer and the amount of adhesion was extremely small. In this test,
Since the concentration of phosphoric acid increased with time, the time until scale generation was relatively shortened. However, when the concentration of phosphoric acid was kept constant, a further effect of addition was expected.

Example 3 The results of examining the characteristic values of the chemical conversion foil prepared by adding Diquest 2000 to the P treatment liquid are described below. 0.1M maintained at 30 ° C
In an aqueous solution of ammonium pentaborate, a constant current of 50 A / cm ²
Was applied and reached 49 V, and then kept at that voltage for 10 minutes. After washing with water, the treatment was carried out with and without the addition of Diquest 2000 during the P treatment, and re-formation was performed by maintaining a constant voltage to prepare a chemical conversion foil. Table 4 shows the characteristic values of the chemical conversion foil.

As is apparent from Table 4, there is no problem in the electrical characteristics of the chemical conversion foil even when Diquest 2000 is added.

In the above embodiment, the case where only phosphoric acid is used as the treatment liquid has been described, but the same effect can be obtained when a substance other than phosphoric acid is added.

It is obvious that the removal of chlorine in aminotrimethylphosphonic acid or a salt thereof may be carried out beforehand.

[Effect of the Invention] In the method for forming an electrode foil for an aluminum electrolytic capacitor, the use of aminotrimethylphosphonic acid or a salt thereof subjected to dechlorination treatment in the P treatment tank delays the amount of scale generation and the time until generation. Therefore, the chemical conversion machine does not have to be stopped for a long time until the scale is generated, and effects such as having no influence on the characteristics of the electrode foil even when such a treatment is performed are exhibited.

[Brief description of the drawings]

FIG. 1 is a structural formula of aminotrimethylphosphonic acid or a salt thereof used in the present invention.

Continued on the front page (72) Inventor Shunichi Osawa 1-1, Sachimachi, Nagai-shi, Yamagata Prefecture Inside Marcon Electronics Co., Ltd. (72) Inventor Masashi 1-1, Sachimachi, Nagai-shi, Yamagata Prefecture Inside Marcon Electronics Co., Ltd. Examiner Koji Osawa

Claims (2)

(57) [Claims] 1. A depolarizing step in which a chlorine-removed aminotrimethylphosphonic acid or a salt thereof is added to a solution containing phosphoric acid as a main composition to form a treatment solution, and an electrode foil is immersed in the treatment solution. A method for forming an electrode foil for an aluminum electrolytic capacitor, comprising: 2. The method for forming an electrode foil for an aluminum electrolytic capacitor according to claim 1, wherein aminotrimethylphosphonic acid from which chlorine has been removed by steam distillation is used.