JPS6123879B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for electrolytically coloring aluminum or its alloys, and more specifically to a method for electrolytically coloring aluminum or its alloys, which enables a desired color tone to be obtained in a shorter time with a small current in the electrolytic coloring process. Conventionally, the method of immersing an anodized film of aluminum or its alloy in an electrolytic bath containing a metal salt and applying alternating current to color it is a well-known technique known as the Asada method, and is widely practiced in industry. The metal salts most commonly used in the Asada method are nickel, tin, and other salts, and when colored, they all give a bronze-like color tone. The colored oxide film obtained in this way has excellent weather resistance, so
Coupled with its color, it is widely used in building materials such as curtain walls and satsushi. However, in order to obtain a deep color tone using metal salts such as nickel or tin, it usually requires a long coloring time of 15 minutes or more and a current of 2 to 10 A per ¹ m2, which increases productivity and From the viewpoint of saving the amount of electricity used, there has been a demand for the development of improved methods. As a result of the inventor's intensive research with the purpose of solving or improving the drawbacks of the above-mentioned prior art,
By introducing an intermediate step of immersing aluminum or its alloy in a specific aqueous solution prior to the secondary electrolytic coloring of aluminum or its alloy, the secondary electrolytic coloring process can be completed in a shorter time and with a smaller current. We have found that it can be implemented, and have completed the present invention. That is, the present invention provides a method for secondary electrolytically coloring an anodic oxide film of aluminum or its alloy by alternating current in an electrolytic bath containing a metal salt, in which an anodic oxide film has already been formed before carrying out the secondary electrolytic coloring. The method is characterized in that the aluminum or its alloy is immersed in an aqueous solution containing a zinc compound and a mineral acid for a certain period of time. Generally, the electrolytic coloring process for aluminum or its alloys is carried out in the order of degreasing, water washing, etching, water washing, smut removal, water washing, anodizing, water washing, electrolytic coloring, water washing, sealing, and water washing, and the electrolytic coloring bath composition is tin compound 5~10g/, mineral acid 20~30g/
g/, nickel compound 10-20g/, organic acid 5
~15g/. The coloring conditions depending on the bath composition and the resulting color tone are as shown in the table below.

[Table] As is clear from this table, in order to obtain a deep color using conventional coloring methods, electrolytic coloring had to take a long time of 15 minutes or more. In the electrolytic coloring method according to the present invention, in the series of steps as described above, intermediate treatment and water washing steps are inserted after anodization and subsequent water washing, and then electrolytic coloring is performed. The intermediate treatment step is immersion for a certain period of time in an aqueous solution containing a zinc compound and a mineral acid as described above, and the zinc compound used therein is preferably Zn(OH) ₂ .
Further, as the mineral acid, phosphoric acid, hydrochloric acid, nitric acid, sulfuric acid, chromic acid, etc. can be used, but phosphoric acid is particularly preferred. The concentrations of these zinc compounds and mineral acids in the aqueous solution can be appropriately selected within a wide range, but from a practical standpoint, the zinc compounds are 5 to 15 g/concentration, and the mineral acids are 50 to 50 g/concentration.
150g/is appropriate. In addition, the temperature of the treatment aqueous solution is preferably in the range of 20 to 30°C, while the immersion time depends on the type and concentration of the zinc compound and mineral acid used.
Although it varies depending on the temperature of the treated aqueous solution, etc., from a practical standpoint, a range of 10 to 25 minutes is suitable. Examples of the present invention will be shown below. Example 1 The target color tone was a bronze color with a color measurement value (L value) of 26 by a color difference meter, and a sample with no intermediate treatment under the following coloring conditions and a sample with intermediate treatment under the following intermediate treatment conditions were subjected to secondary coloring. Electrolytic coloring was carried out. Intermediate treatment conditions (a) Bath composition Zinc compound 10g/phosphoric acid 100g/ (b) Immersion conditions Liquid temperature 25°C Time 20 minutes Coloring conditions (a) Voltage (AC)

[Table] (b) Bath composition Stannous sulfate 8g / Sulfuric acid 25g / Nickel sulfate 15g / Cresol sulfonic acid 10g / (c) Bath temperature 20±1℃ Coloring time and L value after coloring for each sample ( Figure 1 shows the relationship between brightness and brightness. That is, the coloring voltage and coloring time required to obtain the target bronze color tone are as follows.

[Table] That is, it can be seen that when intermediate treatment is used to obtain the same brightness, coloring at a lower voltage and for a shorter time is sufficient. Example 2 Regarding the influence of differences in intermediate treatment time on the shading (lightness) of the color tone after coloring, under the intermediate treatment conditions of Example 1, only the immersion time was 0 minutes (no intermediate treatment)
A coloring test was conducted for 5, 10, 15, 20, 25, and 30 minutes, and the coloring voltage was changed to 13, 15, and 18V, respectively. The results are shown in FIG. As is clear from this figure, it was found that the color becomes darker (that is, the L value decreases) with the intermediate treatment than with the intermediate treatment. In one example, it previously took 7 minutes at 18V AC to obtain a dark bronze color with an L value of 19, but by applying intermediate processing, it can now be obtained in 2 minutes at 18V and 5 minutes at 10V. Therefore, by applying the intermediate treatment according to the present invention, the voltage for electrolytic coloring can be reduced by 3 to 3 to obtain the same color density compared to the case where the conventional intermediate treatment is not performed.
Since it is possible to reduce the voltage by 8V and at the same time shorten the coloring time by 1.5 to 3 minutes, it is possible to significantly reduce the required power.

[Brief explanation of the drawing]

Figure 1 shows the coloring time and the obtained lightness (L
Figure 2 is a graph showing the relationship between intermediate processing time and lightness (L value) after coloring.

Claims (1)

[Scope of Claims] 1. A method of secondary electrolytically coloring an anodic oxide film of aluminum or its alloy by alternating current in an electrolytic bath containing a metal salt, in which an anodic oxide film is already formed prior to carrying out the secondary electrolytic coloring. A method for electrolytically coloring aluminum or its alloy, which comprises immersing the aluminum or its alloy in an aqueous solution containing a zinc compound and a mineral acid for a certain period of time. 2. The method according to claim 1, wherein the mineral acid is phosphoric acid, and the electrolytic coloring method for aluminum or its alloy. 3. The method according to claim 1, wherein the zinc compound is Zn(OH) _2. The electrolytic coloring method for aluminum or its alloy.