JPS6045280B2 - Formation method of aluminum anodic oxide film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming an aluminum anodic oxide film.

Generally, aluminum foil contains impurities such as copper and iron to varying degrees, and when these contents are large, the chemical formability of aluminum is severely impaired.

This has been well known for a long time. The present invention aims to provide a method that can obtain chemical conversion properties and chemical conversion film properties equivalent to those of high-purity aluminum foil, even with a primary electrolytic aluminum foil of low purity. Application of the method of the present invention is extremely useful in manufacturing aluminum electrolytic capacitors whose purity is directly related to electrical properties.

When manufacturing aluminum electrolytic capacitors, the aluminum foil for electrodes is usually etched to increase the effective surface area, and then boric acid-ammonium borate or borax is mixed in an aqueous solution to form a non-porous oxide film. The anode electrode foil was produced by immersing it in an electrolyte for chemical formation, and performing chemical formation using a DC voltage. For example, 75V) 500mA
- When chemical formation is performed using a DC constant voltage constant current power supply set at a constant voltage, the voltage and current change as shown in the figure as time passes, and both approach a constant value. However, if the purity of the aluminum foil to be anodized is low, not only will the anodizing time t1 become significantly longer, but the current 1
R also becomes larger. More specifically, in the case of 99.8% pure aluminum and 99.99% pure aluminum foil, the former requires a formation time of 14 minutes, 308 minutes, while the latter requires only 9 minutes (8 minutes). In addition, the IR is 45n1A in the former case, and 8.5m in the latter case.
A, the higher the purity of the aluminum foil, the better its chemical formability and the less leakage current can be obtained.
The present invention eliminates these drawbacks of low-purity aluminum foil and realizes an anodizing treatment that can form an oxide film with good chemical conversion properties and low leakage current even if the purity is not as high as that of current aluminum foil. It is something.

Specifically, before anodizing the aluminum foil, the aluminum foil is immersed in a dilute solution of aluminum alkoxides, dried, and then immersed in boiling water to form a layer of alkoxide hydrolyzate on the surface of the aluminum foil. is formed, heat treated, and then subjected to normal anodization. in this case,
The main reactions that occur on the surface of aluminum foil are thought to be as follows. Therefore, through this treatment, the surface of the aluminum foil is coated with extremely pure aluminum oxide produced by decomposition of aluminum alkoxide.

More specifically, aluminum foil is immersed in an aluminum alkoxide solution with a concentration of 1 to 10%, air-dried in the air, then placed in boiling water and boiled for about 3 minutes, and then heated at 400°C for 3 minutes. It is fired and then undergoes chemical conversion treatment. In this case, the concentration of alkoxides is 1 to 10%. Suitable organic solvents can include ethyl alcohol, propyl alcohol, toluene, hexane, xylene, and mixtures thereof. In addition, the alkoxides include aluminum prooxide, aluminum isopropoxide, side, aluminum-n-
Butoxide, aluminum-tertiary butoxide, or two or more thereof can be used. In addition, the actual chemical conversion is performed using acids such as boric acid, phthalic acid, citric acid, tartaric acid, adipic acid, benzoic acid, maleic acid, succinic acid, and ascorbic acid, which are known to form a nonporous oxide film on the aluminum surface. It is carried out in aqueous solutions of various acids, their salts, or two or more thereof. Examples and comparative examples will be described below. [
Comparative example] 5g of adipic acid was dissolved in 1000ml of water, and aqueous ammonia was added to this solution to adjust the pH to 6.
An electrolytic solution for chemical formation was obtained.

This chemical solution was kept at a temperature of 60°C, and a low-purity aluminum foil with an apparent surface area of 2 x 5 cfi obtained by etching was immersed in it, and a constant voltage was adjusted to 73 V 1500 mA using a 5 x 15 cIt platinum plate as a counter electrode. Chemical conversion treatment was performed using a constant current device. As a result, the formation time was 14 minutes 3
08, leakage current 1R was 45rnA. Fluorescent X-ray analysis results of the low-purity aluminum foil used at this time showed 99.29% aluminum, 0.34% copper, and 0.00% iron.
32%, and silicon was 0.05%. [Example] The same low-purity aluminum foil as in the comparative example was immersed in a toluene solution of 2% aluminum isopropoxide for 1 to 2 seconds, and then air-dried in the air.

After that, the aluminum foil was immersed in warm water adjusted to a temperature of 95°C for 3 minutes, and N [
Decomposition of 0CH2(CH3)]3→A1[0H)CO was observed. Then, this was baked in air at 400° C. for 3 minutes to complete the pretreatment of the aluminum foil. When the aluminum foil obtained in this way was chemically formed under the same chemical formation conditions as the comparative example, the formation time Ti was 7 minutes, and the leakage current was 1.
A result of R8.9mA was obtained. As is clear from this, according to the method of the present invention, not only the formation time is greatly shortened, but also the leakage current of the chemically treated aluminum foil is significantly reduced. Furthermore, for comparison, an apparent surface area of 2×5C71! was added to the same chemical solution as the comparative example!
High purity aluminum foil (purity 99)
．． 994%), and chemical conversion treatment was performed using a constant voltage and constant current device adjusted to 73V1500n1A using a 5×Bd platinum plate as a counter electrode. As a result, Kasei Jihai, 9 minutes and 3 minutes
C@7, leakage current 1R is &? I got a result of A. Comparing this with the results of Examples, it can be seen how effective the method of the present invention is. For both Examples and Comparative Examples, the leakage current after the first chemical formation is shown to simplify the explanation, but for actual capacitor foils, the chemical formation and heat treatment are repeated several times while stopping the chemical formation as appropriate. This process is then completed to create a chemically formed foil with a smaller leakage current.

Even in this case, the above-mentioned significant difference is not completely different.

[Brief Description of the Drawings] The figure shows an example of the relationship between the formation time of aluminum foil, the formation voltage, and the leakage current.

Claims (1)

[Claims] 1. An aluminum foil is immersed in a dilute solution of aluminum alkoxides dissolved in an organic solvent, and then dried;
The aluminum foil is then immersed in boiling water to form a hydrolyzate layer of alkoxides on the surface of the aluminum foil, further heat-treated, and then an aluminum anodized film is obtained using an electrolyte for aluminum chemical conversion. Formation method of aluminum anodic oxide film. 2. The method is characterized in that one or more of aluminum propoxide, aluminum isopropoxide, aluminum n-butoxide, and aluminum tert-butoxide is used as the aluminum alkoxide to be dissolved in the organic solvent. A method for forming an aluminum anodic oxide film according to claim 1. 3 The concentration of a dilute solution of aluminum alkoxides is 1
~10%, and the organic solvent is comprised of one or more of ethyl alcohol, propyl alcohol, toluene, hexane, and xylene. Or the method for forming an aluminum anodic oxide film according to item 2. 4 As a chemical electrolyte, one or more of boric acid, phthalic acid, citric acid, adipic acid, tartaric acid, succinic acid, lactic acid, malic acid, maleic acid, ascorbic acid, and their respective salts. The method for forming an aluminum anodic oxide film according to claim 1, characterized in that an aqueous solution of the mixture is used.