JP2000355795A - Surface treatment of aluminum and aluminum alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to form a normal coating film free of discoloration by chemically forming an anodically oxidized film on the surface of an aluminum alloy, electrically preparing the micropore structure of the film, depositing metal ions on the bottoms of micropores, neutralizing the inside of the micropores and subjecting the surface to cation electrodeposition coating by cathode deposition type acrylic resin coating. SOLUTION: The stage yields the oxidized film by an anodic oxidation treatment with DC or pulse waveforms by an aqueous solution containing at least >=1 kind of selected sulfuric acid, oxalic acid, chromic acid, phosphoric acid and aromatic sulfonic acid and executes an AC electrolysis with the same aqueous solution at lower voltage. In succession, the alloy is subjected to the AC electrolysis with the aqueous solution containing >=1 kind of Sn, Co, Ni, Cu and Fe, then to the AC electrolysis with the aqueous solution containing at least >=1 kind of ammonium acetate and ammonium sulfate. Finally, the aluminum alloy side is subjected to the DC electrolysis with the aqueous solution containing a cathode deposition type acrylic resin. The transparent coating film which maintains the color tones of multicolor electrolytic coloration and has excellent quality may be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment method for aluminum and an aluminum alloy (hereinafter, referred to as an aluminum alloy), and more particularly to a composite film treatment in which an anodized film colored by an electrolytic coloring method is electrodeposited.

[0002]

2. Description of the Related Art Extruded and rolled aluminum alloy materials are formed into an anodic oxide film in an aqueous solution of sulfuric acid, phosphoric acid, chromic acid, oxalic acid, aromatic sulfonic acid, etc., and then tin, nickel, There is a method in which alternating current electrolysis is carried out in an acidic aqueous solution containing metal ions such as cobalt and electrolytic coloring is performed, and then a coating film is formed by electrophoresis in an acrylic paint-based water-soluble paint which is generally called electrodeposition coating. Widely implemented.

[0003] In this electrodeposition coating method, there are an anion electrodeposition coating in which a product is used as an anode and electrolysis is performed using an anodic deposition type electrodeposition paint (the paint is charged to an anion), and a product is used as a cathode and a cathode is used. There is a cationic electrodeposition coating (electrically charged cations) that performs electrolysis using a deposition type electrodeposition coating.

Conventionally, when an anodic oxide film is formed on an aluminum alloy and electrodeposition coating is performed continuously, it is considered that a normal coating film cannot be formed unless anion electrodeposition coating is performed with the aluminum alloy side as an anode. I was

[0005] The reason is that when the aluminum alloy side is used as a cathode, the anodized film formed as a base treatment is destroyed by gasification of hydrogen ions (H ⁺ ) in an aqueous solution.

However, after forming an anodic oxide film on an aluminum alloy, the pore structure such as the pore diameter of the anodic oxide film is electrolytically adjusted, and then electrolytically colored in an aqueous solution containing metal ions. When the transparent anion electrodeposition coating is performed after adopting the secondary electrolytic coloring method), there is a technical problem that the color tone of the anodic oxide film changes due to the electrolytic coloring.

The reason is that the multicolor electrolytic coloring method uses the method shown in FIG.
As shown in the schematic diagram of FIG. 3, a coloration method is used in which a color is formed by interference between the optical path C2 reflected by the metal ions 2 deposited in the anodic oxide film 6 and the optical path C1 reflected by the aluminum alloy surface. It is considered that the aluminum alloy 1 becomes an anode at the time of coating, metal ions are partially eluted, and interference light changes.

[0008]

The problem to be solved by the present invention is to provide a method of forming an anodized film on an aluminum alloy, electrolytic coloring by a multicolor electrolytic coloring method, and then performing transparent electrodeposition coating. An object of the present invention is to provide a method for surface treatment of an aluminum alloy capable of forming a normal coating film without discoloration.

[0009]

The method for treating the surface of an aluminum alloy according to the present invention includes the following steps.

First step: An anodic oxidation film is obtained by anodic oxidation using an aqueous solution containing at least one of sulfuric acid, aromatic sulfonic acid, oxalic acid, chromic acid and phosphoric acid by DC or pulse waveform. . Second step: AC electrolysis is performed with an aqueous solution containing at least one of sulfuric acid, aromatic sulfonic acid, oxalic acid, chromic acid, and phosphoric acid at a voltage lower than the final voltage in the first step. Third step: AC electrolysis is performed with an aqueous solution containing at least one or more salts of Sn, Co, Ni, Cu, and Fe metals. Fourth step: AC electrolysis is performed with an aqueous solution containing at least one of ammonium acetate and ammonium sulfate. Fifth step: In an aqueous solution containing a cathode deposition type acrylic resin,
DC electrolysis is performed on the aluminum alloy side at the cathode.

Next, each step will be described in detail.

The first step is to form an anodic oxide film on the surface of the aluminum alloy. Therefore, it is usually degreased and washed, and if necessary, subjected to etching treatment, pickling treatment and the like. Electrolysis is performed with a direct current or a pulse waveform using the aluminum alloy as an anode and a lead plate, graphite or the like as a cathode.

The electrolyte used is sulfuric acid,
Aqueous solutions of oxalic acid, chromic acid, phosphoric acid, aromatic sulfonic acids and the like are widely known.

The second step aims at adjusting the pore diameter of the anodic oxide film and the thickness of the barrier layer for generating interference light in the subsequent electrolytic coloring.

There have been proposed various methods of adjusting the film. The method of broadly dividing the pore diameter at the bottom of the pore (JP-A-6-49688) and the method of forming the pore bottom at a branched fine hole (Patent) No. 2534805
No.).

In the type in which the diameter of the bottom of the pore is enlarged, the anodic oxide film in the first step is formed by using an electrolytic solution having a high solubility such as a sulfuric acid aqueous solution and then weakly dissolving a phosphoric acid aqueous solution or the like in the subsequent film adjusting solution. With this electrolytic solution, the pore diameter at the bottom is increased and the thickness of the barrier layer is adjusted.

On the other hand, in the type in which the pores are formed as branched micropores at the bottom of the pore, the anodic oxidation treatment voltage is reduced at a fixed rate with respect to the treatment voltage in the first step, or the film is adjusted by AC electrolytic treatment or the like. However, in order to stably obtain various color tones in the next third step, it is desirable to carry out AC electrolysis at a voltage lower than the final voltage in the first step. This is because the barrier layer 4 shown in FIG. 1 becomes uniform. Further, as the electrolytic solution to be used, aqueous solutions of sulfuric acid, oxalic acid, chromic acid, phosphoric acid, aromatic sulfonic acid and the like are widely known.

In the third electrolytic coloring step, Sn, Cu,
In an aqueous solution containing a metal salt such as Ni, Co, and Fe, alternating current electrolysis is performed using graphite, an aluminum alloy, stainless steel, or the like as a counter electrode.

The electrolytic neutralization step of the fourth step is the most characteristic part of the present invention together with the fifth step, and its purpose is to neutralize the electrolytic solution in the pores generated in the first to third steps. And
The object is to enable cationic coating in the next fifth step.

Specifically, ammonium acetate, 1-10
g / l aqueous solution, preferably 1 to 5 g / l aqueous solution at a voltage of 5 to 20 V for 30 to 300 seconds, preferably 3
Perform AC electrolysis treatment for 0 to 180 seconds.

This is because the neutralizing effect cannot be obtained if the conditions are less than the respective conditions, and the anodic oxide film is broken if the upper limit is exceeded.

Or 1 to 20 g of ammonium sulfate /
1, preferably 5 to 10 g / l aqueous solution, and the other conditions are the same as above.

The cationic electrodeposition coating in the fifth step is a cathodic deposition type acrylic coating, specifically, a cationic acrylic copolymer resin and a blocked isocyanate type curing agent are treated with an organic acid such as acetic acid and lactic acid and water with a disperser or a homogenizer. It is obtained by mixing with a mixer such as a mixer.

At this time, the amount of water is adjusted so that the solid content becomes 50 to 250 g / l. If the amount is less than 50 g / l, the efficiency of forming a coating film decreases, and if it exceeds 250 g / l, the throwing power decreases.

The graphite is used as a counter electrode in such a water-soluble paint, and the voltage is 60 to
Electrolyze at 120V, preferably 80-100V.

When the voltage exceeds 100 V, the anodic oxide film is destroyed, and when the voltage becomes 60 V or less, the formation of the coating film becomes extremely slow.

The electrolysis time is set in accordance with the predetermined coating film thickness. When the coating film thickness is 20 μm, it takes 2 to 3 minutes.

As described above, conventionally, when the cationic electrodeposition was applied after the first to third steps, the anodic oxide film was destroyed, and a normal electrodeposition coating film could not be obtained. In the fourth step, the acid content in the pore is neutralized, and in the fifth step, gasification of hydrogen ions can be prevented by performing cation coating by low-voltage electrolysis, without breaking the anodized film. And, without elution of metal ions in the electrolytic coloring step, appearance design, corrosion resistance, weather resistance,
Thus, a surface treatment method for an aluminum alloy having excellent water resistance has been obtained.

A sufficient water washing step is provided between each step, especially before the fifth step at 60-80 ° C. for 30-600.
Second water washing is not desirable, and after the cationic coating in the fifth step, it is desirable to wash with a paint mouth liquid and then wash with pure water.

Further, in order to ensure sufficient coating film performance,
After the electrodeposition coating, it is baked and dried at 160 to 180 ° C. for 10 to 30 minutes.

[0031]

[Example 1] Aluminum alloy JIS A6
063S-T5, thickness 3mm, width 30mm x length 300
mm aluminum alloy plate was washed with an industrial weak alkaline detergent at 50 ° C. for 5 minutes, and after washing with water, sodium hydroxide 10
0 g / l, etching treatment at 50 ° C. × 3 minutes, washing with water, nitric acid 150 g / l, pickling with 20 ° C. × 1 minute, washing with water, sulfuric acid 200 g / l, counter electrode lead plate, DC voltage 14 V
Anodizing treatment was performed at 0 ° C. for 30 minutes to obtain a 10 μm anodic oxide film (first step).

Next, as a second step, 5 V, 20 ° C. × 1 using an AC power source in the anodizing tank used in the first step.
The anodic oxide film structure was adjusted by electrolysis for minutes.

In the present embodiment, the electrolytic solution of the first step was used as it is in the second step, so that water washing between the steps was omitted. However, the aqueous solution of anodic oxidation by direct current and the aqueous solution of alternating current electrolysis were different. In this case, it is desirable to provide water washing between steps.

In the third step, stannous sulfate 10 g /
1, an aqueous solution containing tartaric acid 20 g / l and sulfuric acid 15 g / l was subjected to electrolytic coloring at an alternating voltage of 12 V at 25 ° C. for 60 seconds to obtain a gray colored anodic oxide film.

As the fourth step, 2 g of ammonium acetate /
The solution was subjected to electrolytic neutralization treatment in an aqueous solution at an alternating voltage of 10 V and 20 ° C. for 3 minutes, washed with water, and then washed with deionized water at 70 ° C. for 3 minutes.

In the fifth step, the cationic paint solid component 15
After electrolysis at 0 g / l and DC voltage of 80 V at 25 ° C. for 3 minutes, the film was washed with water and baked and dried at 160 ° C. for 20 minutes. As a result, a transparent coating film of 15 μm was obtained, and the gray color did not change at all.

Example 2 Aluminum Alloy JIS A
5052P, board thickness 1.5 mm, width 100 mm x length 20
0mm plate material is thinner washed and phosphoric acid 1100g /
l, an aqueous solution containing 30 g / l of nitric acid was subjected to a chemical polishing treatment at 98 ° C. for 60 seconds, and then washed with water.
l, sulfosalicylic acid 100 g / l, aluminum impurity 3 g
/ L aqueous solution, the counter electrode graphite DC current density 1
Anodizing treatment was performed at 00 A / m ² at 25 ° C. for 30 minutes.
At a final voltage of 15 V, a 10 μm anodic oxide film was obtained.

Next, the graphite plate was subjected to electrolytic treatment with an aqueous solution of 150 g / l sulfuric acid at the opposite electrode at an AC voltage of 4 V × 20 ° C. × 120 seconds to prepare a film, and then washed with water.

Next, nickel sulfate 30 g / l, boric acid 3
When subjected to electrolytic coloring with an aqueous solution of 0 g / l at an alternating voltage of 15 V × 25 ° C. × 60 seconds, a vivid green color tone was obtained.

Next, the resultant was subjected to a neutralization treatment with an aqueous solution of ammonium sulfate of 7 g / l at 10 V × 25 ° C. × 120 seconds by alternating current electrolysis, washed with water, and washed with deionized water at 80 ° C. × 2 minutes with hot water.

Next, the same liquid as in Example 1 was applied by electrodeposition at 100 V × 2 minutes, washed with water and baked and dried. As a result, a normal transparent coating film of 12 μm was obtained without discoloration of the green color tone.

Example 3 Aluminum Alloy JIS A
1100S, board thickness 3mm, width 30mm x length 300mm
Alcohol exfoliates the extruded shape of
g / l, etching treatment at 40 ° C. × 3 minutes, washing with water, pickling with nitric acid 150 g / l, 20 ° C. × 1 minute, washing with water, and then using a saturated oxalic acid aqueous solution at 25 ° C. and a pulse waveform of 20 V ×
Anodizing treatment was performed for 30 minutes to obtain an anodized film of 7 μm (first step).

In the second to fifth process steps, the same processing as in Example 1 was performed, and as a result, a translucent gray tone was obtained.

[Comparative Example] For comparison, the first to third steps were treated in the same manner as in [Example 1], the fourth step was omitted, and the fifth step was the same as in [Example 1]. When cationic electrodeposition was applied, the anodic oxide film was broken, and a normal coating film could not be obtained.

[0045]

According to the surface treatment method for an aluminum alloy according to the present invention, a transparent coating film having excellent quality can be formed while maintaining the color tone of the multicolor electrolytic coloring.

In the evaluation of the adhesion of the coating film, 40 ° C. × 50
After immersion in deionized water for 0 hour, a cross-cut adhesion test was carried out. As a result, no peeling occurred per 100 squares.

[Brief description of the drawings]

FIG. 1 is a schematic view showing the principle of multicolor electrolytic coloring in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Aluminum alloy 2 Metal ion deposited at the bottom of pore 3 Pore 4 Barrier layer 5 Transparent coating film 6 Anodized film C1, C2 Optical path

Claims (1)

[Claims] 1. A method for treating a surface of an aluminum alloy through at least the following steps. (1) Anodizing step of forming an anodized film on the surface of the aluminum alloy. (2) An electrolytic adjustment step of a fine pore structure of the anodic oxide film. (3) An electrolytic coloring step of depositing metal ions on the bottom of the fine pores. (4) An electrolytic neutralization step for neutralizing the inside of the fine pore. (5) A cationic electrodeposition coating process using a cathode deposition type acrylic resin coating.