JPH0820894A - Surface treatment of aluminum or its alloy - Google Patents

Abstract

PURPOSE:To give wear resistance, corrosion resistance, water repellency and oil repellency by using Al or Al alloy as an anode and electrolyzing successively with an oxalic acid aq. solution, a sulfuric acid aq. solution and a perfluoroalkyl compound aq. solution to form a porous anodically oxidized film on the surface. CONSTITUTION:A porous anodically oxidized film having 10-20mum thickness is formed by using Al or Al alloy as the anode and primarily electrolyzing in the aq. solution consisting essentially of oxalic acid, sulfuric acid or chromic acid. Next, an anodically oxidized film 30-60mum in thickness and having funnel shaped fine pores is formed by using the treated Al or the alloy as the anode and secondarily electrolyzing in the aq. solution consisting essentially of sulfuric acid. After that, tertiary electrolysis is executed by using the treated Al or the alloy as the anode in the aq. solution containing the perfluoroalkyl compound. As a result, a perfluoroalkyl compound film filled in the fine pores, having anchor effect is 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 or its alloys by coating the surface of aluminum or its alloys with a perfluoroalkyl compound.

[0002]

2. Description of the Related Art A surface treatment method is known in which aluminum or its alloy is anodized to form a corrosion resistant oxide film on the surface of aluminum or its alloy. However, since the oxide film formed by this treatment method is porous, aluminum or its alloy has a high friction coefficient on the surface and is inferior in wear resistance. Therefore, a surface treatment method of aluminum or its alloy has been proposed in which the surface of the anodic oxide film is further coated with a perfluoroalkyl compound (for example, Japanese Patent Publication No. 60-15718). This method uses aluminum or its alloy as an anode and forms a porous anodic oxide film on the surface of aluminum or its alloy with a primary electrolytic solution of sulfuric acid, oxalic acid, phosphoric acid, or chromic acid. This is a method of performing secondary electrolysis in an electrolytic solution of an aqueous solution containing a perfluoroalkyl compound. According to this method, corrosion resistance and abrasion resistance are improved, and water repellency and oil repellency are also improved.

[0003]

In the above method, the thickness of the coating and the diameter of the fine pores in the coating differ depending on the type of acid used in the electrolytic solution for the primary electrolysis of aluminum or its alloy. For example, when sulfuric acid is used as the primary electrolytic solution, a relatively thick film of about 30 to 60 μm can be formed, but the fine pores formed in the film have an extremely small diameter of about 0.010 to 0.015 μm. Met. On the other hand, when oxalic acid, phosphoric acid or chromic acid is used as the primary electrolytic solution, relatively large pores of about 0.015 to 0.040 μm are formed in the film, but the rate of formation of the film is Lately, its thickness was 20 μm or less. Therefore, when the perfluoroalkyl compound is filled in the micropores during the secondary electrolysis, when sulfuric acid is used as the primary electrolytic solution, there is a problem that the perfluoroalkyl compound hardly enters the micropores because the micropores are extremely small. there were. Further, when oxalic acid, phosphoric acid or chromic acid was used as the primary electrolytic solution, the productivity was poor and it was difficult to form a film having a thickness of 30 μm or more, which is practically required.

The object of the present invention is to adsorb a sufficient amount of perfluoroalkyl compound on the inner surface of the fine pores of the anodized film or to fill the fine pores, and to form an oxide film of a sufficient thickness for practical use. Another object of the present invention is to provide a surface treatment method for aluminum or its alloy, which imparts wear resistance, corrosion resistance, water repellency and oil repellency to the alloy.

[0005]

In order to achieve the above object, the surface treatment method for aluminum or its alloy according to the present invention comprises aluminum or its alloy as an anode and oxalic acid, phosphoric acid or chromic acid as a main component. Primary electrolysis in an aqueous solution, and the secondary electrolysis is performed in an aqueous solution containing sulfuric acid as a main component using this primary electrolysis-treated aluminum or its alloy as an anode, and then this secondary electrolysis-treated aluminum or its alloy is used as an anode in a perfluoroalkyl group. It is a method of forming a porous anodic oxide film on the surface of aluminum or its alloy by tertiary electrolysis in an aqueous solution containing a compound.

The present invention will be described in detail below. The work piece of the present invention is not limited to a pure aluminum material, but includes its alloy. As an aluminum alloy, Al-Cu-Mg system, Al-
Si-based, Al-Zn-Mg-Cu-based processing alloy, Al
-Cu-Si system, Al-Si system, Al-Cu-Ni-M
Examples include g-based, Al-Mg-based, and Al-Si-Cu-Ni-Mg-based casting alloys. The perfluoroalkyl compound of the present invention includes a perfluoroalkyl compound monomer and a polymer thereof, that is, a perfluoroalkyl compound polymer. Examples of this monomer include: N-alkyl-N-perfluoroalkylsulfonyl glycine potassium salt (trade name: EF-112, manufactured by Tochem Products Co., Ltd.), ammonium perfluoroalkyl sulfonate (trade name: EF-). 104, manufactured by Tochem Products Co., Ltd.,-Perfluoroalkylsulfonic acid lithium salt (trade name: EF-105, manufactured by Tochem Products Co., Ltd.), N-alkyl-N-acryloxyethyl perfluoroalkylsulfonic acid amide. (Product name: EF-125M,
Tochem Products Co., Ltd., N-alkyl-N-methacryloxyethyl perfluoroalkylsulfonic acid amide (trade name: EF-135)
M, manufactured by Tochem Products Co., Ltd.-Perfluorocarboxylic acid (trade name: EF-201,
Tochem Products Co., Ltd. ・ Ammonium salt of perfluorocarboxylic acid (trade name: E
F-204, manufactured by Tochem Products Co., Ltd., and the like. Examples of this polymer are: -Polyoxyalkylene glycol monoester acrylate-Perfluoroalkylsulfonyl acrylate-N
-Alkylaminoethyl copolymer (trade name: EF-35
2 or EF-802, manufactured by Tochem Products Co., Ltd.).

To produce this aluminum or its alloy, electrolysis is performed three times on this workpiece. The primary electrolysis uses an aqueous solution containing oxalic acid, phosphoric acid, and chromic acid as a main component as an electrolytic solution, the secondary electrolysis uses an aqueous solution containing sulfuric acid as a main component as an electrolytic solution, and the third electrolysis uses an aqueous solution containing a perfluoroalkyl compound. To use. Both electrolysis is performed by anodizing the work piece in the electrolytic solution with a constant current. By the primary electrolysis and the secondary electrolysis, an anodic oxide film is formed on the surface of the base aluminum or its alloy. The temperature of the electrolytic solution at the time of electrolysis may be room temperature, but may be heated in the case of a perfluoroalkyl compound monomer having low solubility. Also the current density during electrolysis is any electrolyte is adjusted to a range of a few mA / dm ² ~ Number 1000 mA / dm ² at a direct current electrolysis, preferably 5000 mA / dm ² or less.

[0008]

When the primary electrolysis is performed using oxalic acid, phosphoric acid or chromic acid as the electrolytic solution, an anodized film having a thickness of about 10 to 20 μm is formed, and the film has a relatively large size of about 0.015 to 0.040 μm. Fine pores of diameter are formed. Then, when secondary electrolysis is performed using sulfuric acid as an electrolytic solution, an anodized film is formed even inside the workpiece, the thickness of the film increases, and the fine pores formed by the primary electrolysis deeply extend. After the secondary electrolysis, the thickness of the coating becomes about 30 to 60 μm, the upper pore diameter is about 0.04 to 0.05 μm, and the lower pore diameter is 0.01.
Just funnel-shaped pores of about 0 to 0.015 μm are formed in the film. When tertiary electrolysis is performed in this state, the perfluoroalkyl compound easily penetrates into the fine pores and is adsorbed on the entire inner surface or filled in the whole fine pores. Further, a layer made of a perfluoroalkyl compound is also formed on the surface of the film excluding the fine pores. The perfluoroalkyl compound adsorbed on the film imparts wear resistance, corrosion resistance, water repellency and oil repellency to the work piece. Further, when the perfluoroalkyl compound is in the form of a polymer, an anchor effect occurs on the adsorption surface of the work piece, and wear resistance and corrosion resistance are further improved.

[0009]

EXAMPLES Next, examples of the present invention will be described together with comparative examples. <Example 1> A5052 material (5
Five pieces (0 × 20 × 2 mm) were prepared as the workpieces. After degreasing these objects to be processed, they are placed in an electrolytic solution of a 3 wt% oxalic acid solution at 20 ° C., and the objects to be processed are subjected to primary electrolysis at a direct current of 3 A / dm ² for 5 minutes to remove the objects to be processed. A porous anodic oxide film was formed on the surface. The work piece having the oxide film formed thereon is washed with water to sufficiently remove the attached water, and then the work piece is placed in an electrolyte solution of 15 wt% H ₂ SO ₄ at 10 ° C., and the work piece is immersed in this electrolyte solution. 3 at DC 3 A / dm ²
Secondary electrolysis was performed for 0 minutes to further form a porous anodic oxide film on the surface of the workpiece. Again, after sufficiently removing the attached water from the work piece, a 0.5 wt% perfluoroalkyl compound monomer (trade name: EF-112, manufactured by Tochem Products Co., Ltd.) aqueous solution was used as an electrolytic solution to make the work piece an anode. West,
Using an aluminum plate as the counter electrode, DC 50 mA / dm ²
Thirdly electrolyzed for 10 minutes. Adhering water was sufficiently removed from the workpiece and the surface of the oxide film of the workpiece was coated with a perfluoroalkyl compound.

<Embodiment 2> As an electrolytic solution for tertiary electrolysis,
The surface of the oxide film of the work piece was treated with a perfluoroalkyl compound in the same manner as in Example 1 except that an aqueous solution of 0.5 wt% perfluoroalkyl compound polymer (trade name: EF-352, manufactured by Tochem Products Co., Ltd.) was used. Coated.

<Embodiment 3> As an electrolytic solution for tertiary electrolysis,
The surface of the oxide film of the work piece was treated with a perfluoroalkyl compound in the same manner as in Example 1 except that a 0.5 wt% perfluoroalkyl compound polymer (trade name: EF-802, manufactured by Tochem Products, Inc.) aqueous solution was used. Coated.

<Embodiment 4> In the electrolytic solution consisting of a 4 wt% phosphoric acid solution at 20 ° C., the same five workpieces as in Embodiment 1 were subjected to primary electrolysis at DC 50 V for 5 minutes to form a surface of the workpiece. The surface of the oxide film of the workpiece was coated with a perfluoroalkyl compound in the same manner as in Example 1 except that the porous anodic oxide film was formed.

<Embodiment 5> In the electrolytic solution consisting of a 3 wt% chromic acid solution at 20 ° C., the same five workpieces as in Embodiment 1 were subjected to primary electrolysis at DC 50 V for 5 minutes to form the surface of the workpiece. The surface of the oxide film of the workpiece was coated with a perfluoroalkyl compound in the same manner as in Example 1 except that the porous anodic oxide film was formed.

<Comparative Example 1> The same five aluminum alloys as in Example 1 were used as the workpieces and 10% of 15 wt% H ₂ SO ₄ was used.
Immersing in the electrolytic solution at ℃, the work piece is DC 3A in this electrolytic solution.
Primary electrolysis was performed for 30 minutes at / dm ² to form a porous anodic oxide film on the surface of the workpiece. After sufficiently removing the attached water from the work piece, 0.5 w of perfluoroalkylcarboxylic acid salt (trade name: Surflon s 111, made by Asahi Glass Co., Ltd.)
An aqueous solution containing t% was prepared, and a workpiece having an oxide film formed thereon was used as an electrolytic solution as an anode, and an aluminum plate was used as a counter electrode, and secondary electrolysis was performed at 10 ° C. at a direct current of 50 mA / dm ² for 10 minutes. The surface of the oxide film of the work piece was coated with a perfluoroalkyl compound.

<Comparative Test and Evaluation> Using the surface-treated workpieces of Examples 1 to 5 and Comparative Example 1 as test pieces, a wear test was conducted with an Ogoshi-type wear tester. This wear test is a test in which a disk of ferrous steel is rotated and a test piece is pressed against the circumferential surface of the rotating disk to measure the amount of wear. That is, the amount of wear on the surface of the test piece was measured and the average value of the five pieces was obtained. Table 1 shows the wear amount of each test piece when the wear amount of Example 1 was set to 1.

[0016]

[Table 1]

As is clear from Table 1, the workpieces of Examples 1 to 5 had about 4 to 5 times less wear than the workpieces of Comparative Example 1 and were excellent in wear resistance. . In particular, it was found that Examples 2 and 3 in which the perfluoroalkyl compound polymer was used were superior to Examples 1, 4 and 5 in which the perfluoroalkyl compound monomer was used, in that the abrasion amount was smaller.

[0018]

As described above, according to the conventional surface treatment method, the perfluoroalkyl compound is not sufficiently filled in the fine pores, or the oxide film having a practically sufficient thickness is not formed on aluminum or its alloy. According to the surface treatment method of the present invention, a sufficient amount of perfluoroalkyl compound is adsorbed on or filled in the inner surface of the fine pores of the anodized film, and an oxide film having a practically sufficient thickness is formed. Which results in aluminum or its alloys having high wear resistance, corrosion resistance, water repellency and oil repellency.

Claims (1)

[Claims] 1. Aluminum or an alloy thereof is used as an anode for primary electrolysis in an aqueous solution containing oxalic acid, phosphoric acid or chromic acid as a main component, and aluminum or an alloy thereof subjected to the primary electrolysis is used as an anode and sulfuric acid is used as a main component. After secondary electrolysis in an aqueous solution, the secondary electrolyzed aluminum or its alloy is used as an anode for tertiary electrolysis in an aqueous solution containing a perfluoroalkyl compound to form a porous anodic oxide film on the surface of the aluminum or its alloy. Surface treatment method for aluminum or its alloy.