JPS5920759B2 - Coloring method for aluminum or aluminum alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a novel method for coloring aluminum by depositing white metal hydroxide on aluminum or aluminum alloy (hereinafter simply referred to as aluminum) that has been subjected to anodizing treatment. Regarding the law.

Conventionally, the DC electrolysis method (Sumika method) and AC electrolysis method (Asada method) are generally well known as methods for electrolytically coloring aluminum that has been subjected to anodizing treatment. The treated aluminum is subjected to direct current cathode electrolysis or alternating current electrolysis in a metal salt aqueous solution,
This is a so-called "electrolytic coloring method" in which the metal salt is deposited as metal particles in the pores of the anodic oxide film.

In this coloring method, metal particles are precipitated and distributed unevenly in the film pores, so commonly used metal salts such as nickel and tin can only produce cold, bronze, or black coloring. A method for obtaining a white colored film is to precipitate calcium and barium salts as sulfates, peroxides, and carbonates in the pores of the anodic oxide film by electrolyzing in an aqueous hydroxide solution. (Japanese Unexamined Patent Publication No. 50-37631) has been proposed.

However, with this method, the amount of precipitated white compounds is small, so when hydration sealing treatment is applied to this method, the transparency increases as the hydration sealing progresses, resulting in an opaque and deep white color. The disadvantage is that it cannot be done. On the other hand, as a result of extensive research into a method for coloring aluminum white using a coloring mechanism that is completely different from the conventional method, the inventors of the present invention discovered that after anodizing aluminum o 2 , a method was developed to further thicken the barrier layer. After applying film thickening treatment and then immersing in an acidic aqueous solution, aluminum, titanium, zinc,
When direct current cathodic electrolysis is performed in an aqueous solution containing one or more metal salts selected from lead and stannic metal salts, a large amount of white metal hydroxide is deposited in the pores of the anodic oxide stone film. We have newly discovered that the hydroxide appears as a colored color, and that even when hydration and pore sealing treatment is applied to it, a thick white film with no change in opacity can be obtained.

The method of the present invention was developed based on such knowledge, and involves performing anodization treatment on aluminum, and further performing a method similar to the porous type anodization treatment in an electrolyte solution that forms a barrier film. After increasing the barrier layer thickness by electrolyzing at a high voltage, the anode is immersed in an acidic aqueous solution containing one or more of sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, and oxalic acid with a concentration of 1 to 30%. Expanding the pore size of the oxide film,
Next, direct current cathode electrolysis is performed in an aqueous solution containing one or more metal salts selected from aluminum, titanium, zinc, lead, and stannic metal salts to precipitate white metal hydroxide in the pores of the anodic oxide film, It is characterized by a white film on the aluminum surface.

This precipitated lead hydroxide is not only a stable inorganic compound, but also aluminum hydroxide, titanium hydroxide, zinc hydroxide, and tin hydroxide are all stable white inorganic compounds, so they cannot be used as conventional metal particles. This is a new aluminum coloring method that is completely different from previous methods, and it is possible to obtain a beautiful white colored film that cannot be obtained with the electrolytic coloring method or the method of JP-A-50-137631. be. Next, the method of coloring aluminum according to the present invention will be explained in detail.
) Porous anodic oxide film process.

2) Barrier layer thickness increasing treatment step.

3) Immersion step in acidic aqueous solution.

4) Direct current cathodic electrolysis step in an aqueous solution containing one or more metal salts selected from aluminum, titanium, zinc, lead, and stannic metal salts.

Since coloring is carried out in the following order, each step will be explained step by step.

1) Porous anodic oxide film process In the coloring method of the present invention, a porous anodic oxide film is first formed on the aluminum surface. When the coloring method of the present invention is applied to an anodic oxide film with strong coloring such as, the coloring will be a mixture of white and brownish colors, which is of course not very desirable. There are no particular restrictions as long as the method is other than those commonly used and can form a transparent film, for example, in a single or mixed bath of sulfuric acid, oxalic acid, etc.

Any method of producing an anodic oxide film by direct current or alternating current superimposed electrolysis can be applied to this step. 2) Barrier layer thickness increasing treatment step In this step, the aluminum treated with the porous anodic oxide film is electrolytically treated at a voltage higher than the anodic oxidation treatment voltage in a barrier type film forming bath. Increases the thickness of the barrier layer at the bottom of the oxide film, widens the allowable range of immersion time and temperature in the next acidic aqueous solution, and facilitates the precipitation of aluminum, titanium-zinc, lead, and stannic hydroxides. The purpose is to

Therefore, there are no special restrictions on the bath conditions used for this, but in order to thicken the barrier layer of the anodized film, barrier type baths such as boric acid, ammonium borate, citric acid, tartaric acid and malic acid are generally used. It is sufficient to apply a voltage higher than the porous type anodizing treatment voltage in the electrolytic bath in which the film is formed, and it is appropriate to conduct the electrolytic treatment at an electrolytic voltage of 200 V or less and for a period of 0.5 minutes or more to about 10 minutes.

In this case, if the electrolytic voltage is lower than the porous anodizing treatment voltage, the barrier layer thickness will not increase and the purpose of this process cannot be achieved.The appropriate voltage for this process depends on the bath composition, electrolysis time Although it varies depending on the bath temperature, etc., it is 20
An electrolytic treatment of 0 V or less can be sufficiently effective, and if the electrolytic voltage is increased more than necessary, the electrolytic voltage in the subsequent DC cathode electrolysis will become high, which is not preferable from an economical point of view.

Regarding electrolysis time, baths with slow current drop after electrolysis,
For example, in a bath such as boric acid, the proper time for barrier layer electrolysis is long, whereas in a bath with a fast current drop, the process of increasing the barrier layer thickness is completed in a short time. An electrolysis time of 10 minutes satisfactorily achieves the purpose of this step.

3) Immersion step in acidic aqueous solution The coloring by metal hydroxides of aluminum, titanium, zinc, lead, and stannic, which is a feature of the present invention, is different from conventional "electrolytic coloring" by precipitation of metal particles9. The coloring components of the metal become metal hydroxides and precipitate into the pores of the film, so it is impossible to obtain a white film of sufficient density unless the pore volume of the film is increased.Therefore, in this process, porous type The purpose of this is to increase the pore volume by perforating the pore walls of the anodic oxide film, which has been subjected to a treatment to increase the barrier layer thickness after anodizing treatment, and is immersed in an acidic aqueous solution. If this is not done, the pore volume of the film is small, so that aluminum, titanium, zinc, lead and stannic will not be precipitated as their hydroxides by direct current cathode electrolysis, and therefore a white film will not be obtained.

On the other hand, an anodized film that has been subjected to a process to increase the barrier layer thickness after porous anodizing is further immersed in an acidic aqueous solution to penetrate the pore walls of the film. When the pore volume is increased, aluminum, titanium, zinc, lead, and tin are sufficiently precipitated in the film pores as their hydroxides by subjecting them to direct current cathode electrolysis.
A white film is obtained. There are no special restrictions on the acidic aqueous solution used in this step, but acids such as sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, and oxalic acid are suitable in order to uniformly dissolve and increase the pore volume. The conditions necessary for the treatment vary depending on the composition, temperature, concentration and immersion time, as well as the conditions for forming the anodic oxide film and the voltage and time of the barrier layer thickness increasing treatment.

That is, in order to obtain a pore volume that allows the hydroxides of aluminum, titanium, zinc, lead, and stannic to be precipitated by optical spectroscopy, the composition of the bath such as phosphoric acid, hydrochloric acid, nitric acid, and sulfuric acid must be soluble in the film. It is strong and can be processed in a relatively short time, but
Since oxalic acid and the like have weak film solubility, the processing time becomes long.

Furthermore, the temperature of the processing bath has a strong influence on the processing time, with high temperatures requiring a short time and conversely low temperatures requiring a long time. 9 On the other hand, at low concentrations, the time becomes shorter, but
In this case, if the treatment is performed at a low concentration of 10 t) or less, the bath tends to age due to film dissolution, resulting in poor bath sustainability.

In addition, although it varies depending on the bath composition, when the concentration is higher than 30%, there is an economical problem due to loss of liquid carried out. For the above reasons, this step may be carried out under economically advantageous conditions by appropriately adjusting the composition, concentration, treatment time, etc. of the bath used, taking into account productivity and the like.

4) DC cathode electrolysis step In this step, the type of coloring bath and electrolysis waveform are essential requirements for the reasons described in the following sections (a) and (b).

(a) Type of coloring bath: A water solution containing one or more selected from aluminum, titanium, zinc lead, and stannic metal salts.

The type of coloring bath in this process is limited to a water solution containing one or more selected from metal salts of aluminum, titanium, zinc, lead, and stannic salts. In an aqueous solution, it does not precipitate into the film pores as a stable white metal hydroxide, and even if it precipitates as white, it quickly undergoes a chemical change in the air and discolors, or the metal particles are aluminum. This is because it either adheres to the surface of the surface as a smut.

(b) Electrolytic waveform: Performed at a DC cathode. The coloring mechanism of the present invention is such that the pH increases by direct current cathodic electrolysis in an aqueous solution containing one or more metal salts selected from aluminum, titanium zinc, lead, and stannic metal salts. Titanium, zinc, lead, and tin are precipitated in the pores of the film as white hydroxides. However, if alternating current electrolysis is performed in an aqueous solution containing one or more metal salts selected from aluminum, titanium, zinc, lead, and stannic metal salts, aluminum undergoes repeated anode and cathode polarization. At times, the pH at the interface between aluminum and the aqueous solution begins to rise, but then the anodic polarization occurs immediately, and in order to suppress the pH rise, aluminum, zinc, lead, and tin are added to the metals into the film pores. It cannot be precipitated as a hydroxide. For this reason, the present invention is different from the conventional so-called "electrolytic coloring method" and JP-A-50-376.
It is clear that this is a new and excellent method for coloring aluminum, which is different from the invention of No. 31.

Specific examples of the coloring method according to the present invention are listed below, but the present invention is not necessarily limited to these examples.

Example 1 An aluminum alloy plate (6063S) was pretreated by a conventional method and heated in a 1509/l sulfuric acid bath at a bath temperature of 20°C and a current density of 1.
．． Anodized at 6A/Dm2 for 30 minutes to a thickness of 15
After obtaining a μm thick anodic oxide film, electrolytic treatment was performed for 10 minutes at a voltage of 80 V using the sample as an anode using a barrier layer thickness increasing treatment bath under the following conditions, and further using an acidic aqueous solution under the following conditions. After immersion for 5 minutes, electrolysis was carried out for 1 minute at a current density of 1 A/Dm2 using the sample as a cathode using a colored solution under the following conditions, and a white film was obtained due to precipitation of aluminum hydroxide into the pores of the anodic oxide film. It was done.

Example 2 An aluminum alloy plate (6063S) was pretreated in a conventional manner, and subjected to anodizing treatment to increase the thickness of the barrier layer and immersion treatment in an acidic aqueous solution under the same conditions as Example 1, and then subjected to the following treatment. When the sample was electrolyzed for 1 minute at a current density of 2 A/Dm2 using the colored liquid as a cathode, a white film was obtained due to the precipitation of titanium hydroxide into the pores of the anodic oxide film.

Example 3 An aluminum alloy plate (6063S) was pretreated by a conventional method and anodized under the same conditions as in Example 1. After that, a barrier layer thickness increasing treatment was performed under the following conditions, and the sample was used as an anode. After electrolytic treatment at a voltage of 120 V for 1 minute, and further immersion in an acidic aqueous solution under the following conditions for 7 minutes, electrolysis was performed for 30 seconds in a colored solution of 2A/Dm2 under the following conditions, resulting in hydroxylation in the pores of the anodized film. A white film was obtained due to zinc precipitation.

Example 4 An aluminum alloy plate (6063S) was pretreated in a conventional manner and subjected to anodizing treatment to increase the thickness of the barrier layer and immersion treatment in acidic aqueous solution under the same conditions as in Example 3, and then subjected to the following treatment. When the sample was electrolyzed for 1 minute at a current density of 2 A/Dm2 using the colored solution as the negative electrode, a white film was obtained due to precipitation of lead hydroxide into the pores of the anodic oxide film.

Example 5 An aluminum alloy plate (6063S) was pretreated by a conventional method and subjected to anodizing treatment to increase the barrier layer thickness and immersion treatment in an acidic aqueous solution under the same conditions as in Example 3. When the sample was electrolyzed for 30 seconds at a current density of 6 A/Dm2 using a colored solution as a negative electrode, a white film was obtained due to precipitation of stannic hydroxide into the pores of the anodic oxide film.

Example 6 An aluminum plate (99.2%) was pretreated by a conventional method,
After anodizing treatment, barrier layer thickness increasing treatment, and immersion treatment in an acidic aqueous solution under the same conditions as in Example 1, a current density of 2 was applied using a colored liquid under the following conditions, with the sample as a negative electrode.
When electrolyzed at A/Dm2 for 1 minute, a white film was obtained due to precipitation of aluminum hydroxide and zinc hydroxide into the pores of the anodic oxide film.

As described above, if the method of the present invention is applied to coloring aluminum, the coloring components can be mixed into the stable hydroxides of aluminum titanium, zinc, lead, and tin. Because it can be precipitated as
A stable white film can be obtained, which is completely different from the coloring method of No. 7631, and together with the high productivity, it exhibits a remarkable effect on white coloring of aluminum.

Claims (1)

[Claims] 1 Aluminum or aluminum alloy that has been previously subjected to porous anodizing treatment is electrolytically treated in a barrier type film forming bath at a voltage higher than that of the anodizing treatment to increase the barrier layer thickness, and then sulfuric acid, It is immersed in an acidic aqueous solution with a concentration of 1 to 30% containing one or more of nitric acid, hydrochloric acid, phosphoric acid, and oxalic acid, and then aluminum, titanium,
Aluminum or aluminum characterized by performing direct current cathodic electrolysis in an aqueous solution containing one or more metal salts selected from zinc, lead, and stannic metal salts to precipitate white metal hydroxide in the pores of the anodic oxide film. Coloring method for aluminum alloys.