JPH0633267A - Surface treating liquid for aluminum - Google Patents

Abstract

PURPOSE:To obtain the surface treating agent for aluminum which consists of an aq. soln. containing ferric nitrate or an aq. soln. further added with sulfuric acid, nitric acid and phosphoric acid and is suitable especially to remove surface passivity before etching. CONSTITUTION:This surface treating agent consists of an aq. soln. containing ferric nitrate or an aq. soln. containing ferric nitrate and >=1 kind of inorg. acid among sulfuric acid. nitric acid and phosphoric acid. The treating agent has nearly no malodor, and has low corrosion property and low danger, and the passivity of the aluminum surface is removed completely by the short time treatment. Therefore, etching proceeds quickly, the generation of pitting corrosion and the formation of black smut is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to surface treatment of aluminum, and more particularly to surface treatment before etching.

[0002]

2. Description of the Related Art A passivation, which is usually a thin oxide film, is formed on the surface of aluminum, which causes the following etching inhibition.

(1) Since an abrupt reaction is started after the passivation is nonuniformly removed by the etching solution, the reaction start time cannot be predicted and it is difficult to control the etching time. (2) When the passive state is partially removed, only the removed portion is preferentially etched, resulting in a non-uniform finish. (3) Pitting corrosion occurs due to local reaction or heat generation, and black smut is generated.

As means for solving these problems,
It is effective to remove the surface passivation before etching, but hitherto no treatment agent suitable for removing the passivation has been available.

Although there are examples of using borofluoric acid, borofluoric acid is highly corrosive to equipment materials, highly dangerous to humans, and difficult to treat wastewater.

[0006]

Means for Solving the Problems The inventors of the present invention have made earnest studies on a surface treatment agent for aluminum which does not have the above-mentioned drawbacks, and as a result, an aqueous solution containing ferric nitrate before etching or ferric nitrate. And either sulfuric acid, nitric acid, or phosphoric acid 1
When aluminum is treated with an aqueous solution containing one or more inorganic acids, the passivation is removed from the aluminum surface and etching proceeds rapidly. Furthermore, this treatment liquid has almost no odor and is corrosive and dangerous. It was found that the properties are low and the processing time is extremely short, and the present invention has been completed.

That is, according to the present invention, an aqueous solution containing ferric nitrate or ferric nitrate and any one of sulfuric acid, nitric acid and phosphoric acid is used.
The present invention relates to a surface treatment liquid for aluminum, which comprises an aqueous solution containing one or more inorganic acids.

The ferric nitrate contained in the aluminum surface-treating solution of the present invention is preferably 5 to 30% in terms of an anhydride, and if it is lower than this, the treatment requires a long time and is not practical. On the other hand, if it is higher than this, crystals tend to precipitate, which may cause a problem in handling.

The inorganic acid to be contained in the aluminum surface treatment liquid of the present invention is contained for the purpose of preventing the formation of hydroxide and increasing the treatment speed, but if the content is too large, the passive state is only removed. However, since the etching may proceed and the aluminum surface may be roughened, the preferable content is 0 to 10%. still,
Phosphoric acid has the effect of preventing the formation of a passive state again.

Further, in order to remove the oil film and the like adhering to the aluminum surface, it is preferable to add a surface active agent such as polyoxyalkylene glycol which is a nonionic surface active agent. The content of the surfactant is not particularly limited, but it is preferably 2% or less in the aqueous solution in consideration of the content and the performance.

In using the surface treatment liquid of the present invention,
Either dipping or spraying can be used. The treatment temperature is preferably 20 ° C. or higher in consideration of the treatment time, and is preferably 50 ° C. or lower from the viewpoints of water evaporation, equipment maintenance, and the like. Further, the treatment time varies depending on other conditions, for example, the treatment temperature and the composition of the treatment liquid, but it is preferably 1 to 5 minutes in view of production efficiency.

The use of the surface treatment liquid of the present invention is not limited to the surface treatment before etching, and it is also used for the surface treatment before coating an etching resist, for example.

[0013]

EXAMPLES The present invention will be described in detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. The raw material mixing ratios in the following examples are weight ratios.

Example 1 40 parts of ferric nitrate nonahydrate and 5 parts of sulfuric acid were dissolved in 55 parts of water. Immerse an aluminum test piece in the above treatment liquid and keep it at 45 ℃
After being treated for 5 minutes, it was washed with water and dried. Then, 20 ℃
When etching was carried out by immersing in a ferric chloride aqueous solution having a specific gravity of 1.4, etching started immediately after the immersion. 1
There was no pitting corrosion on the aluminum surface of the test piece which had been washed with water and dried after etching for 1 minute, and no generation of black smut was observed.

Examples 2 to 6 Aluminum test pieces were treated with the treatment agents shown in Table 1 under the conditions shown in the same table, and then etched under the same conditions as in Example 1. In all cases, the etching was started immediately after the immersion, and the surface of the test piece had no pitting corrosion and no smut was formed.

[0016]

[Table 1]

Comparative Example 1 An aluminum test piece was washed with water, dried, and then etched under the same conditions as in Example 1. The etching started abruptly 1 minute and 30 seconds after the immersion. After etching for another 30 seconds, pitting corrosion was observed on the surface of the test piece which was washed with water and dried, and black smut was generated.

[0018]

When aluminum is treated with the surface treatment solution of the present invention, etching can proceed rapidly and pitting corrosion and black smut formation can be prevented. Furthermore, the treatment liquid of the present invention has almost no odor, is less corrosive and less dangerous, and can completely remove the passive state in a short treatment time.

Claims (1)

[Claims] 1. A surface treatment liquid for aluminum comprising an aqueous solution containing ferric nitrate or an aqueous solution containing ferric nitrate and one or more inorganic acids selected from sulfuric acid, nitric acid and phosphoric acid.