JPS5956594A - Method for coloring aluminum - Google Patents

Abstract

PURPOSE:To enable electrolytic coloring using an aqueous soln. of a silicate, by anodically reoxidizing an Al or Al alloy member having a formed porous anodic oxide film on the surface in an aqueous soln. of silicate having a specified concn. CONSTITUTION:An Al or Al alloy member is anodically oxidized by a conventional method to form a porous anodic oxide film on the surface. After well washing the film, the member is immersed in an aqueous soln. of sodium silicate having >=2.0 molar ratio and 0.05-2.0g/l concn., and it is anodically reoxidized as an anode at >=120V voltage. By the reoxidation colloidal silicic acid is deposited in the micropores in said anodic oxide film to color the film gray. Potassium or lithium silicate may be used in place of sodium silicate.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrolytic tinting power method for aluminum or aluminum alloys (hereinafter both will be collectively referred to as aluminum) using an aqueous silicate solution.

Conventionally, when aluminum is anodized in water glass, an anion agglomeration film is formed, which causes a discharge.
It is said that a porous film cannot be obtained. Similarly, even if aluminum is re-anodized in a water glass solution to eliminate the porous oxide film created in a sulfuric acid bath, an anion aggregation film is formed and silicic acid is precipitated in the pores of the oxide film. do not. Therefore, even after re-anodizing, no change in the appearance of the sample is visually observed.

The inventor of the present application has repeatedly studied the relationship between the composition of silicate, the aqueous solution temperature JW, and the re-anodization of aluminum with a porous oxide film. discovered that the film was colored gray and completed the present invention.

An object of the present invention is to provide a method for coloring aluminum in a grayish color using a silicate water-resistant liquid that has not been previously available.

That is, after forming a porous anodic oxide skin on aluminum or aluminum alloy, the molar specific force is 2p.
The gist of the invention is to perform re-anodization at a voltage of 120 V or more in an aqueous solution with a concentration of α05 g/l-2.0 g/l.

JP-A-50-78535 describes a method of electrolytically tinning aluminum with an aqueous silicate solution, which involves forming a chemical conversion film on aluminum and reducing the molar ratio α5 to about 10% on I2L. This method uses a highly concentrated aqueous silicate solution to form an inorganic composite film containing a chemical conversion film and silicic acid, which is different from the present invention.

To explain the present invention, a porous anodic oxide film is formed on aluminum which has been degreased and cleaned by a conventional method using a sulfuric acid method or the like, and then re-anodized in a silicate aqueous solution DL. The silicate used in the present invention has a molar ratio of 2 or more, that is, M
a O・n S 102 (M'alkali metal atom), SiO□, / ht 20 molar ratio 1) is z
It must be O or less. Since the aqueous solution of the or-1-silicate with n == 0-5 and the meta-silicate with n = 1 is highly alkaline, it may dissolve the primary film and become 1-layer. Since the p IT tfi binding ability is weak, anion aggregation is likely to occur, making it unsuitable. Examples of silicates used in the present invention include lithium salt!
, tNa, 0-28in3. Na30-38+02
．． There are Na2O, 4SiO3, etc., and potassium salt Suzu1
1 salt can be used as well. As a potassium salt
I< , (] ・2SiO,,,](20・3Si
O,,,K 20 ・4 SiOp↓1112 ”)・25i02 for lithium salt. Li , IO・3
S i(J p + I' + 20・4 S+ 0
．． 2nd prize is mentioned.

Next, the degree of θ of the gaic acid salt aqueous solution is 0.051/1
~2. Oget ) range force ttJT: b <, 0-
05 V'i Below is f4'7 color failure], so there is an inappropriate guess, zOg//l CJ l.

In this case, the precipitation of the silicate co-hydrogen into the pores of the oxide film is insufficient, and similarly, insufficient color development can be obtained. This is because silicate anions adsorb to the surface of the oxide film and close the pores.
It is thought that Ih impairs the precipitation of silicic acid colloid into f'L.

During re-anodizing electrolysis, in order to obtain uniform coloration (i) in which silicate cocoids were deposited on the porous skin, constant current electrolysis with a lower current density was used, rather than constant voltage electrolysis. In addition, the applied voltage for re-anodizing electrolysis is preferably 1
20Vl near and above are required. If the applied voltage is lower than 120 Å, one layer of burrs in the porous coating may be reformed, and the silicic acid colloid is deposited at a voltage higher than 120 Å. In other words, if it is 120■ or more,
An anodic decomposition reaction of water occurs on the barrier layer, and the hydrogen ions generated during this process neutralize silicate anions and precipitate into the pores as silicate colloids.

Hereinafter, the present invention will be specifically explained using examples.

Aluminum with a purity of 99.5 (, TJiS II 40
00 no 10504'! ), length 100 mm, jM
A specimen of 100 m +n and thickness 1.2111 II+ was prepared and soaked in 15% sulfuric acid aqueous solution T overnight at a temperature of 20°C.
A porous oxide film of 15/jm was formed by constant current electrolysis using IZEE 17V.

Test 1-1 was thoroughly washed (after washing, the molar ratio was 2.0, 3.
1-lium silicate aqueous bay of 0 and 40; molar ratio 30
Potassium silicate, an aqueous solution and a solution of sudzu silicate with a molar ratio of 30 were mixed with water, and a stainless steel plate was used as the counter electrode.
Re-anodization electrolysis was performed at 20°C. Note that the concentration of the silicate aqueous solution was 0.5 g/L in all cases.

Re-anodizing electrolysis is performed at a DC current density of 0-05 A/d.
A force current electrolysis of m2 was carried out. The voltage increased with the electrolysis time, and the maximum voltage was 150V or 200V. What is the maximum voltage situation? If the IL solution is continued, the current will go to 1). In this situation], the solution to re-anodizing 9 was found in each magazine 14 (I got stuck and carried out the process for 5 minutes!).

Even if the type of electrolytic bath is different, the maximum type H', 150 V
Similarly, when the specimen is grayish white (not colored and the maximum voltage
At 00V, each magazine was colored gray-black.

The specimen is colored gray because the silicic acid colloid deposited in the pores of the porous film scatters light. In addition,
When X-ray micro-arylizer analysis was performed on the cross-section of Test 11, it was confirmed that γr41- of silicon with a multiplicity of 1i was observed in the cases of potassium silicate and sutiuno silicate, as well as in the case of helium silicate. However, no effect of different cations was observed.

Comparative Example Test No. 1 was used to pierce the same anodic oxide film as that used in the example, and the concentration of sodium silicate 11 aqueous solution with a molar ratio of 2.0 was α03 gel and 3.0. Re-anodizing electrolysis was performed using Ovl as an electrolytic bath.

In either case, the silvery white color was the same as that of a normal sulfuric acid anodized film, and the same color as that without re-anodizing electrolysis did not occur.

In addition, using the same sample J1 as in the example, re-anodizing electrolysis was performed under the condition (4) of the example using 1-lium silicate at a molar ratio of 1.0. The thickness of the film was 12μI11, resulting in a decrease in film thickness of 3μm.Furthermore, when 1-lium silicate with a molar ratio of 0.5 was used, a decrease in film thickness of 35μm11 occurred. Ruled.

Patent applicant [] Honkei Metal Co., Ltd. Attorney: Keiji Matsunaga

Claims (1)

[Claims] 1. After forming a porous anodic oxide film on aluminum or aluminum alloy, apply it to 120V in an aqueous solution with a molar ratio of 30 or more and a concentration of 005g/x to zOν.
A coloring strength method for aluminum characterized by re-anodizing at a voltage higher than or equal to the above.