JPS582599B2 - Coloring method for anodic oxide films on aluminum and its alloys using current reversal electrolysis - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to coloring of anodic oxide films of aluminum and its alloys, in which sulfur compounds are accumulated in the film by a negative current of current reversal electrolysis, and metal salts are heated after forming the film. It is colored by immersion in a solution or by sealing after immersion, and the repetition period of current reversal, reversal ratio,
This is a method in which the anodic oxide film is colored in various colors by changing the concentration of the electrolyte, the thickness of the film, the type of metal salt, etc.

Generally, anodic oxide films on aluminum and its alloys are porous and can be easily colored using the pores. Taking advantage of this property, they are currently widely used in decorative items, equipment parts, kitchen items, building materials, etc. There is.

A commonly used method for coloring anodic oxide films is to adsorb organic dyes into the viewing pores of the film, but the colored films produced by this method have poor light resistance and cannot be exposed to sunlight. It cannot be used for parts and materials that
If it is lightly colored, it has the disadvantage that it will fade even indoors.

The following methods are available to compensate for these shortcomings.

(1) Alloy method: This is a method in which an alloy element that easily develops color through anodization is added to the aluminum material used to form the film, and the anodic oxide film is formed into a natural color, but the color tone varies depending on the alloy element. It has the drawbacks of being limited in color and not producing color unless it is a thick film.

(2) Method using electrolyte: This method uses an alloy that easily develops color as in (1), and also uses a special electrolyte that easily develops color during film formation.It has excellent light resistance, but the electrolyte Compared to sulfuric acid electrolytes, however, they are more complex to manage and more expensive, require high voltage and high current density for film formation, and have drawbacks such as the limited variety of color tones that can be obtained.

(3) Secondary AC electrolysis method (patent application publication 1715-1970)
No.): This method involves forming an anodic oxide film in an electrolytic solution such as sulfuric acid, and then performing alternating current electrolysis in a solution containing heavy metal salts to color the film.
This is the most commonly used method for coloring building materials.

However, in this method, the liquid composition of the secondary electrolyte is complex and the control range of electrolysis is narrow, making operation and management difficult, and the color tone tends to vary.

In addition, in order to obtain products with many different color tones, an electrolytic cell and a power source are required for each color tone, resulting in high equipment costs.

(4) Coloring method using heavy metal salts after AC/DC superposition electrolysis (Patent Application Publication No. 1983-9805): This method involves subjecting aluminum or aluminum alloy to AC/DC superposition anodic oxidation in an electrolytic solution containing sulfuric acid, and then immersing it in a heavy metal solution. The color is then developed by performing a sealing treatment, and the operation and equipment are simpler than the secondary AC electrolytic method, but as shown in Table 1, the properties of the film make it easier to use the commonly used DC method. Furthermore, as shown in Table 2, it takes a long time to form a film in order to color it.

The reason for this is that, as shown in FIG. 2, in the AC/DC superposition method, the voltage for passing a negative current is low, and as a result, less sulfur compounds are produced in the film, making it difficult to color the film.

If the direct current component is made smaller and the superimposed alternating current component is made larger, the coloring property will be improved, but as it approaches an alternating current waveform with a large inversion ratio, only a thin film with low hardness and poor properties will be obtained, similar to the alternating current method.

In addition to these drawbacks, in the AC/DC superimposition method, it is necessary to adjust the voltage and current for each of DC and AC, and it is difficult to control the negative current, which is the most important for coloring the film. Due to drawbacks such as the complicated structure and wiring of the electrolytic cell, the coloring operation is simple, but it is not widely used at present.

(From Electrochemistry VOL 27 P674 (1959)) In the present invention, during anodic oxide film formation, the polarity is periodically changed and a negative current is passed at a reversal ratio of 50% or less, and the film formation is interrupted, thereby polarization and We have developed a method to obtain a hard film at high speed while suppressing the heat generated by electrolysis, namely, a new anodic oxidation method proposed in Patent Application Publication No. 131932/1988, ``Anodic oxidation of aluminum and its alloys by current reversal electrolysis.'' As a result of investigating the coloring method of anodized film using metal salt solution, it was found that a highly hard film could be obtained at high speed.
It has been found that it is possible to form a film in a very advantageous manner in a wide variety of colors by forming a film in a short period of time.

That is, the purpose of the present invention is to change the polarity periodically, perform current reversal, flow a negative current, and interrupt film formation, thereby suppressing heat generation due to polarization and electrolysis, and increasing thickness and thickness at high speed at high temperatures. In addition to obtaining a film with high hardness, the sulfur compounds that are accumulated in the film are effectively generated by reduction of the sulfuric acid electrolyte with a small reversal ratio and large negative voltage, and the film has excellent properties by reacting with the sulfur compounds. immersed in a metal salt solution that produces sulfides,
This provides a method for easily coloring in various tones.

The present invention uses current reversal electrolysis to periodically change the polarity of aluminum and its alloys in sulfuric acid or an electrolytic solution containing sulfuric acid. In other words, a positive current produces an anodic oxide film, and a negative current causes sulfur compounds to accumulate in the film. Nickel, cobalt, lead,
The anodic oxide film can be colored in various tones by immersing it in a solution containing metal salts such as silver, copper, or zinc, or by performing a sealing treatment after immersing it in a metal salt solution. be.

The major features of the present invention are (1) It is possible to color aluminum and its alloys very easily by forming an anodic oxide film on aluminum or its alloys in conventional sulfuric acid or an electrolytic solution containing sulfuric acid, and then immersing it in a heated metal salt solution. .

In addition, if the material is lightly colored, coloring and pore sealing can be performed at the same time using a pore sealing solution containing a metal salt.

(2) Under electrolytic conditions of high temperature and high current density, a smooth film with high hardness can be formed at high speed, and a dark color can be easily obtained by forming the film in a short time.

(3) Coloring in various tones is possible by changing the inversion ratio and repetition period of changing the polarity and flowing a negative current, and by selecting the metal salts.

(4) As shown in Figure 3, compared to the AC/DC superposition method, the current reversal method can obtain a large negative current with a small reversal ratio, and by controlling the negative voltage, it is easy to adjust the negative current that governs coloring. Therefore, variations in color tone are reduced, and as shown in FIG. 4, the electrolytic cell and wiring are simple and easy to put into practical use.

etc. are mentioned. Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Aluminum material 6063 Electrolyte 15% by weight of sulfuric acid Bath temperature 25°C Current reversal conditions Repetition period 13.3Hz Positive current density 4A/dm2 Film formation time 20min A film formed under the above conditions using a carbon plate as a counter electrode was heated at 95°C.
The color tone of the film immersed for 10 minutes in a 2 g/l lead acetate solution kept at 0.degree. C. was as shown in Table 3.

According to this method, a thick film with greater hardness can be obtained than with the direct current method, and as the inversion ratio is increased, the coloring becomes darker.

In addition, when the reversal ratio is increased, the rest time of film formation becomes longer and the hardness of the film tends to decrease.This tendency is particularly strong in AC and AC/DC weights where the reversal ratio is large (reversal ratio 50%), but when the current In the reversal method, the reversal ratio is 14.3%
Even if the negative current density is as low as 1.2A/dm2, it is as large as 2
Even with a short film formation time of 0 minutes, a deep coloring could be achieved.

Example 2 Aluminum material 6063 Electrolyte 15% by weight of sulfuric acid Bath temperature 25°C Current reversal conditions Reversal ratio 15% Positive current density 4 A/dm2 Film formation time 20 min Under the above conditions, chemical formation was performed by changing the repetition period of current reversal. The coatings were immersed for 20 minutes in a 20 g/l nickel sulfate solution maintained at 95° C., resulting in the color tones listed in Table 4.

At a repetition period of 20 Hz to 100 Hz, black coloring is obtained with almost no change in color tone.

At repetition cycles of 10 Hz or less, the negative current decreases and the coloring tends to become lighter, and at 200 Hz or more, the film thickness decreases to 5.
It becomes lighter and the coloring becomes lighter.

From these facts, the color tone can be changed by changing the repetition period of current reversal, and by setting the repetition period to 10 to 20 Hz, a hard film was obtained at a high temperature of 25°C.

Example 3 Aluminum material 6063 Electrolyte Sulfuric acid 15% by weight Bath temperature 25°C Current reversal conditions Repetition period 17.1Hz Reversal ratio 20% Positive current density 4A/dm2 Negative current density 1.3A/dm2 Under the above conditions, formation time After chemically forming coatings with different thicknesses by changing the conditions, the color tone and properties of the coatings colored under the same conditions as in Example 2 were as shown in Table 5.

As can be seen from this example, when the film was thin, it had a light stainless steel color tone, and as the film became thicker, the color tone became darker.

When the film thickness was 40.1 μm or more, it became jet black, and a deep color tone that could not be obtained with organic dyes or other coloring methods was obtained.

Example 4 Aluminum material 1080 Electrolyte 15% by weight sulfuric acid 35% by weight sulfuric acid + 10 g/l oxalic acid bath temperature 25°C Current reversal conditions Reversal ratio 14.3% Repetition period 13.3Hz Positive current density 4A/dm2 Negative current density 1 .2A/dm2 Film formation time 20 min Under the above conditions, the chemically formed films were immersed in various metal salt solutions at the boiling point for 20 minutes, and as a result, the color tones shown in Table 6 were obtained.

Films chemically formed in a sulfuric acid monooxalic acid mixed bath other than a sulfuric acid bath were also colored in almost the same tone as the sulfuric acid film, and by changing the metal salt solution, colored films with various tones were obtained.

Furthermore, if a hole treatment liquid containing a metal salt is used, coloring and hole sealing can be performed at the same time, although the color is pale.

Example 5 After film formation under the same conditions as Example 4, the temperature was maintained at 60°C.
After being immersed in a metal salt solution for 5 minutes, a boiling water sealing treatment was performed, resulting in coloring as shown in Table 7.

The coloring of the film becomes lighter as the temperature of the metal salt solution decreases, and almost no coloration is observed below 50°C, but if the sealing treatment is performed at a temperature close to the boiling point after immersion in the metal salt solution, Coloring with almost the same tone as coloring with only metal salt solution at high temperature was achieved.

[Brief explanation of the drawing]

Figure 1 is the voltage waveform of the AC/DC superposition method, Figure 2 is the structure and wiring diagram of an electrolytic cell for the AC/DC superposition method, Figure 3 is the voltage waveform of the current thickness inversion method of this invention, and Figure 4 is the G1 current inversion method. FIG. 2 is a structure and wiring diagram of an electric beak tank. Explanation of the main symbols in the drawings, 1: DC power supply, 2: AC power supply,
3: Electrolytic cell, 4: Carbon plate, 5: Aluminum product,
6: Current reversal power supply.

Claims (1)

[Claims] 1 By periodically changing the polarity of aluminum and its alloys in sulfuric acid or an electrolytic solution containing sulfuric acid at a frequency of 0.1 Hz or more to perform current reversal, and by changing the reversal ratio and negative voltage not exceeding 50%. Controlling the negative current and accumulating sulfur compounds in the film while performing film formation, and then coloring by immersing it in a heated metal salt solution, or by sealing after immersion in the metal salt solution. A method for coloring an anodic oxide film of aluminum and its alloys, characterized in that: