JPS5846559B2 - Method for producing milky white film on aluminum or aluminum alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a milky white film on aluminum or an aluminum alloy (hereinafter both simply referred to as aluminum).

Conventionally, the Ematal method and the chromic acid method are well known as methods for producing a milky white film on the surface of aluminum. Of these, the Ematal method is a method for producing a milky white film on the surface of aluminum. Since it is a method of anodizing, the chemicals used are expensive, and the cost of the film is high because electrolysis must be carried out at a high voltage.In contrast, the chromic acid method Although the cost of the film is lower than that of chromic acid, it is not used much at present because it uses chromic acid and may cause chemical pollution.

In order to solve the above-mentioned drawbacks, the method of the present invention attempts to obtain a white ceramic-like milky white film on the surface of aluminum, similar to the ematal method or the chromic acid method, without using expensive or dangerous chemicals or high voltage. The aluminum on which a normal anodic oxide film has been formed is temporarily sealed in a hot water bath with a bath temperature of 50 to 100°C for up to 30 minutes, and then heated to a voltage of 5 to 15 V in a sulfuric acid electrolytic bath. It is characterized by performing AC electrolytic treatment.

Below, each step of the method for producing a milky white film on aluminum according to the present invention will be explained more specifically and in detail.In the first step of forming an anodic oxide film, aluminum is usually anodized using a sulfuric acid electrolyte. process,
A sulfuric acid anodic oxide film is formed on the surface of aluminum, but the thickness of the film needs to be 5 microns or more.

In a thin film of 5 microns or less, current easily flows during the sulfuric acid alternating current electrolysis treatment in the subsequent process, making it difficult to form a complete milky-white film, which may result in an uneven film.

In the next temporary sealing process, the anodic oxide film formed on the aluminum surface in the previous process is properly sealed, and if the degree of sealing is weak, AC electrolytic treatment is performed in the post process. Since current flows easily and a normal AC film is generated, it does not result in a milky white film.

On the other hand, if the degree of pore sealing is strong, no current will flow in the subsequent AC electrolytic treatment, making AC electrolysis impossible.

Therefore, in order to obtain a film having an appropriate degree of sealing, the hot water washing conditions require a shorter immersion time if the bath temperature is higher, and a longer immersion time if the bath temperature is lower.

Generally, immersion treatment at a temperature of 50 to 100°C for 10 to 30 minutes is appropriate, and immersion treatment may also be performed in a bath containing nickel acetate as a pore sealing agent.

In the final AC electrolytic treatment step, the anodic oxide film sealed in the temporary sealing step is subjected to AC electrolysis in a sulfuric acid electrolytic bath. Since the holes are sealed, even when AC voltage is applied,
At the initial stage of energization, no current flows, but after a certain amount of time, a so-called "recovery phenomenon" occurs in which current begins to flow, and this recovery phenomenon makes it possible to form a milky white film.

In this case, a milky-white film will be obtained if it takes more than 20 minutes for the current density to reach IA/dm2 due to the recovery phenomenon, and a film that takes less than 20 minutes for the current density of the recovery current to reach IA/dm3. In this case, only an uneven milky white film is produced, and a uniform milky white film cannot be obtained.

As mentioned above, the alternating current electrolytic treatment of this step is characterized by the current recovery taking a long time, and is closely related to the sealing treatment conditions.

In other words, when the sealing degree of the film is weak, the current recovery occurs in a very short time, but when the current is restored over a long period of time, an AC film is generated and the substrate surface is roughened, causing the film to deteriorate due to diffuse reflection. If it is milky white and the current recovers in a short time, only an AC film is produced and no effect of roughening the substrate surface occurs.

As a result of film peeling experiments using a mixed solution of phosphoric acid and chromic acid, we found that when the current recovered over a long period of time, the surface of the substrate itself became rough, whereas on the other hand, the current recovered in a short time. It was confirmed that the surface of the film was not roughened.

In addition, in order to prolong the current recovery time, the AC voltage during electrolytic treatment has a large influence, and the voltage magnitude should be 5 to 1
5V is good, and around 10V is best.

In this case, if the voltage is below 5V, no current will flow;
If the current density exceeds 50 V, the current density recovers quickly to IA/d 711.2, so only an AC film is generated, and therefore, of course, no roughening of the substrate occurs.
The phenomenon of film peeling is more likely to occur.

Other points to keep in mind in this process are that the sulfuric acid aqueous solution used in the AC electrolytic treatment bath has a concentration of 10 to 30%
% is appropriate; if the sulfuric acid concentration is too low, the solubility of the film will be poor and it will take too long for the current to recover; on the other hand, if the sulfuric acid concentration is too high, the recovery time will be shortened.

Moreover, the appropriate bath temperature is 18 to 22°C.

As the temperature rises, the time for current recovery becomes shorter; conversely, when the temperature is lower, the time for current recovery becomes too long, which is inappropriate; considering these conditions, the time for current recovery is
Approximately 30 minutes is most appropriate.

As mentioned above, according to the method of the present invention, when producing a milky white film on the surface of aluminum, expensive chemicals such as titanium potassium oxalate or dangerous chemicals that cause pollution such as chromic acid are not used at all. It is possible to easily obtain a milky-white film with an even and beautiful color by performing electrolytic treatment at low voltage without the use of aluminum.Coupled with the low cost of the film, aluminum film is It has a remarkable effect on processing.

Next, specific examples of the method for producing a milky white film according to the present invention will be described, but the method of the present invention is not limited thereto.

Example 1 An aluminum material (60638-T5) was degreased for 5 minutes at 60°C in a commercially available phosphoric acid degreaser 2 multi-aqueous solution, and then 50g/piece was immersed in a caustic soda aqueous solution for 5 minutes at 50°C. etching at 20% of room temperature.
Neutralization treatment was performed by immersing it in a nitric acid aqueous solution for 2 minutes.

The aluminum material pretreated in this way was heated to a bath temperature of 20°C.
, was anodized in a 150 g/l sulfuric acid aqueous solution to obtain a 15 μm thick anodic oxide film on the surface of the aluminum material.

Next, this was immersed in pure water at 70°C for 20 minutes to temporarily seal the holes, and then the bath temperature was 20°C.
/, ff A carbon plate was used as a counter electrode in an aqueous sulfuric acid solution, and a commercially available AC current (60 cycles) of 10 V was applied.

When the current was first applied, no current flowed at all, but after IO minutes, the current gradually began to flow, and after 30 minutes, when the current density reached I A / d m2, the current was stopped, and the aluminum material It had a beautiful milky white film.

Example 2 After subjecting an aluminum material (IlooP-HI3) to the same pretreatment as in Example 1, a bath temperature of 20°C and 150 fl/l was applied.
An anodic oxidation treatment was performed in an aqueous sulfuric acid solution to obtain a 15 μm anodic oxide film on the surface of the aluminum material.

Next, 5 g of this was immersed in an aqueous nickel acetate solution at 80°C for 10 minutes.
A lead plate was used as a counter electrode in a sulfuric acid aqueous solution, and a commercially available AC current (60 cycles) of 8 V was applied.

At first, no current flowed, but after 7 minutes, the current gradually started flowing, and after 26 minutes, the current density reached IA.
When the current supply was stopped when the temperature reached /dm2, the aluminum material exhibited a beautiful milky white film.

Claims (1)

[Claims] 1 Aluminum or aluminum alloy on which a normal anodic oxide film has been formed is heated in a hot water bath with a bath temperature of 50 to 100°C.
1. A method for producing a milky white film on aluminum or an aluminum alloy, which comprises performing a temporary sealing treatment for less than 0 minutes, and then performing an AC electrolytic treatment at 5 to 15 V in a sulfuric acid electrolytic bath.