JPS6148597B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improvement in a method for coloring an anodized film of aluminum or its alloy by subjecting it to secondary electrolytic treatment using an electrolytic bath containing a metal salt and alternating current. A method of coloring an anodized film of aluminum or its alloy by subjecting it to secondary electrolytic treatment using an electrolytic bath containing a metal salt and alternating current is already known and practiced. However, this method has problems with variations in the thickness of the strong positive oxide film and variations in the activity of the film pores.
Also, the coloring becomes uneven or the desired coloring cannot be obtained due to the suitability of the secondary electrolytic treatment conditions, etc.
It had drawbacks such as being prone to spalling (peeling of the film). In particular, prevention of non-uniform coloring, that is, the occurrence of color differences, has been an important issue. The present inventor has conducted various studies on a method for coloring an anodic oxide film of aluminum or its alloy by secondary electrolytic treatment using a metal salt-containing electrolytic bath and alternating current, and has found that uneven coloring can be extremely effectively prevented. They have succeeded in developing the method of the present invention. That is, the present invention provides a method for coloring an anodic oxide film of aluminum or its alloy by secondary electrolytic treatment using a metal salt-containing electrolytic bath and alternating current. Preliminary electrolytic treatment is performed by applying a low voltage alternating current that does not cause precipitation of metal components for at least 20 seconds, and then secondary electrolytic treatment is performed by increasing the alternating current voltage to a voltage at which metal components are precipitated. The AC voltage is increased in two or more multi-stage steps, and the amount of current in the direction of the anodic oxide film used as a cathode during secondary electrolytic treatment is controlled so that it does not increase over time while the same AC voltage is applied. This is a method for electrolytically coloring an anodic oxide film of aluminum or its alloy. In the present invention, the anodized film of aluminum or its alloy to be colored refers to the process of electrolytically treating aluminum or its alloy using direct current or alternating current in various electrolytic baths to form a porous anodic oxide film on the surface of aluminum or its alloy. A film has been formed. The anodic oxide film of aluminum or its alloy (hereinafter sometimes referred to as "aluminum anodic oxide film" or simply "anodized film") and the method of forming the anodic oxide film are well known to those skilled in the art. Since this is a technical matter, detailed explanation thereof will be omitted. Conventional methods (such as the Asada method) in which the anodic oxide film is colored by secondary electrolytic treatment using an electrolytic bath containing metal salts and alternating current, generally involve applying an AC voltage of about 8 to 10 V to the anodic oxide film in the electrolytic bath. This conventional method has the drawbacks that coloring tends to be uneven and spalling tends to occur as described above. The attached FIG. 1 shows the current in the direction of the anodized film as the cathode during the secondary electrolytic treatment in a typical operation of the conventional method (herein, this may be referred to as "current in the direction"). This figure illustrates the change over time. As is clear from Fig. 1, when a constant AC voltage of about 8 to 10 V is applied to start the secondary electrolytic treatment, the amount of current in the direction increases after the first peak, when the applied AC voltage remains the same (8 to 10 V). ~10V), it gradually increases over time. That is, the current variation angle (di/dt) in the direction (in the formula, i represents the amount of current and t represents time) gradually becomes more positive over time. According to the research conducted by the present inventors, it is believed that the reason why non-uniform coloring tends to occur in the conventional method is due to a significant increase in the amount of current in this direction. The method for electrolytically coloring an aluminum anodic oxide film of the present invention is on par with conventional methods (such as the Asada method) in that the anodic oxide film is subjected to a secondary electrolytic treatment using an electrolytic bath containing a metal salt and alternating current. However, in the electrolytic coloring method of the present invention, (i) prior to the secondary electrolytic treatment, the anodic oxide film is coated in a metal salt-containing electrolytic bath for at least 20 seconds at a low voltage alternating current that does not cause precipitation of metal components; Preliminary electrolytic treatment for 60 seconds,
(ii) The AC voltage for secondary electrolytic treatment is not increased all at once, but is carried out in multiple stages of two or more, and (iii) The anodic oxide film during secondary electrolytic treatment is used as a cathode. This method is an improvement over the conventional method in that the amount of current in the direction (that is, the current in the direction) is controlled so that it does not increase over time while the same alternating current voltage is applied. Generally, the thickness of the barrier layer in the anodic oxide film is not uniform in each part, and this is thought to be an important cause of uneven coloring in the secondary electrolytic treatment, that is, the occurrence of color differences. Therefore, if the preliminary electrolytic treatment (i) is carried out, the thick part of the barrier layer will be partially dissolved and removed, and the thickness of the barrier layer will be made uniform, so that the coloring of the secondary electrolytic treated film will be made uniform. It is thought that this contributes to In addition, when the AC voltage is increased all at once in secondary electrolytic treatment, the current concentrates in specific pores of the anodic oxide film, causing segregation of metal components, and once segregation of metal components occurs, the segregation As a result, uneven coloring occurs.
it is conceivable that. However, in the present invention, (ii)
Because the alternating current voltage for secondary electrolytic treatment is not raised all at once, but is carried out sequentially in two or more multisteps, the current in the direction is concentrated in specific holes, and therefore the metal components are segregated. can effectively prevent the above (i)
It is thought that, together with the preliminary electrolytic treatment, uneven coloring can be prevented. Furthermore, since the increase in the amount of current in the direction over time is considered to be an important cause of non-uniform coloring as described above, in the present invention (iii) the amount of current in the direction increases over time while the same AC voltage is applied. It is controlled so that it does not increase. In the present invention, in order to (iii) prevent the amount of current in the direction from increasing over time while applying the same AC voltage, perform the preliminary electrolytic treatment in (i) and increase the AC voltage increase in (ii). By taking steps, you can often achieve your goals. In particular, if the increase in the alternating current voltage (ii) is carried out successively in a sufficient number of stages, the increase in the amount of current over time can be extremely effectively prevented. However, if it is detected that the amount of current in the direction increases over time while the same AC voltage is being applied, measures such as temporarily lowering the applied AC voltage to a certain extent should be used. Also, it is possible to effectively prevent the amount of current in the direction from increasing over time. Note that since the color tone depends on the total amount of current in the directions, even if the voltage during the secondary electrolytic treatment is temporarily lowered, the color tone can be adjusted by extending the treatment time, etc. In this way, in the present invention, the amount of current in the direction (iii) during the secondary electrolytic treatment is controlled so as not to increase over time while the same AC voltage is applied. It is desirable to constantly or continuously measure the current in the direction of , or to constantly measure the current variation angle (di/dt) of the current in the direction. Note that if the value of the current fluctuation angle (di/dt) is positive, the amount of current tends to increase over time, and if the value is negative, it tends to decrease over time.
In order to prevent the amount of current from increasing over time, the value of the current variation angle (di/dt) may be set to 0 or a negative value. Such a current fluctuation angle can be easily measured using a commercially available current fluctuation range detector. Incidentally, the tendency of the amount of current in the direction to increase or decrease over time can also be predicted by examining the current waveform.
For example, if the waveform of the current in the direction a or b in Fig. 2 is
If the waveform slopes upward to the right, as shown in Figure 2, it can be predicted that the current amount will eventually tend to increase; if the waveform slopes downward to the right, as shown in c or d in Figure 2, the current amount will tend to increase. It can be predicted that the number will eventually start to decline. The metal salt used in the metal salt-containing electrolytic bath of the present invention includes various metal salts similar to those used in conventional methods. Examples include salts of various metals such as iron, nickel, cobalt, chromium, tin, copper, silver, gold, zinc, vanadium, titanium, cadmium, and manganese. In some cases, two or more of these metal salts may be used in combination. Furthermore, it is desirable to add a small amount of acid such as boric acid, sulfuric acid, hydrochloric acid, and phosphoric acid to the metal salt-containing electrolytic bath to maintain the pH of the bath at an acidic level. Moreover, when adding sulfuric acid, magnesium sulfate is added, and when adding hydrochloric acid, magnesium chloride is added at the same time. moreover,
The metal salt-containing electrolytic bath contains various other additives,
For example, chelating agents such as glycine and iminodiacetic acid can be added. The metal salt concentration in the electrolytic bath is usually 5 to 100 g/, preferably 30 to 50 g/
, the pH of the bath is 3-6, preferably 3.0-4.5. Regarding the preliminary electrolytic treatment conditions in the present invention,
The AC voltage used is a low voltage within a range that does not cause precipitation of metal components, and is usually 4.5V or less, preferably 4 to 1V. The pre-electrolytic treatment voltage can also be increased in multiple steps. For example, it is possible to first perform preliminary electrolytic treatment at 2V for a certain period of time, then increase the voltage to 4V, and further perform preliminary electrolytic treatment for a certain period of time. The pre-electrolysis treatment time is at least 20 seconds, preferably
60 seconds to several minutes. The temperature of the electrolytic bath is 0 to 50°C, preferably 10 to 30°C. Regarding the secondary electrolytic treatment conditions in the present invention,
The alternating current voltage is usually 5 to 15 V, preferably 6 to 12 V, and as described above, the alternating voltage is increased in multiple steps of two or more times. The secondary electrolytic treatment time is usually several minutes to several tens of minutes in total, preferably 4
Minutes to 20 minutes. Bath temperature is 0-50℃, preferably
The temperature is 10-30℃. For example, nickel, carbon, tin, etc. are used for both the preliminary electrolytic treatment and the secondary electrolytic treatment. Next, the present invention will be further explained in detail by giving Examples and Comparative Examples. Comparative Examples 1 to 5 Examples 1 to 10 First, aluminum alloy material (Alco standard 63S)
was subjected to an anodic oxide film treatment (primary electrolytic treatment) using direct current under the following conditions to produce an anodic oxide film. Electrolytic bath Aqueous sulfuric acid solution bath containing 180 g of H ₂ SO ₄ Temperature: 20°C Current density: 2 to 3 A/dm ² Electrolytic treatment time: 10 to 20 minutes Film thickness: 10μ Next, aluminum on which the obtained anodic oxide film was formed Alloy material (30cm x 8cm x 0.3cm) 6
A pure nickel board (30cm x
8 cm x 1 cm), and in the electrolytic bath described below, AC voltage was applied in the manner shown in Table 1, and 50 cycles of AC were applied at each predetermined voltage for each predetermined time to perform treatment. Electrolytic bath composition Nickel sulfate (as NiSO ₄ ) 100g/ stannous sulfate (as SnSO ₄ ) 10g/ citric acid 10g/ sulfuric acid (as H ₂ SO ₄ ) 20g/ In addition, the applied voltages of 2V and 4V in each example are This is the applied voltage for preliminary electrolytic treatment, and the applied voltage of 6 V or more is the applied voltage for secondary electrolytic treatment. The direction and amount of electric current in each example and the properties of the colored film obtained were as shown in Table 1. In Comparative Example 1, secondary electrolytic treatment was performed by applying an AC voltage of 10 V all at once according to the conventional method, but the directional current curve in this case showed a change over time as shown in Figure 1. , the amount of current in the direction gradually increased as time progressed. Also, Comparative Examples 2 to 4
Also, the amount of current in the direction increased over time at any applied voltage in the secondary electrolytic treatment. The colored films obtained in Comparative Examples 1 to 4 were all extremely non-uniform in coloring. On the other hand, in the secondary electrolytic treatments in Examples 1 to 10, the directional current did not increase over time while the same AC voltage was applied, and the coloring of the obtained films was extremely uniform. . The attached FIGS. 3, 4, 5, and 6 are representative examples of Example 3, Example 4, and Example 4, respectively.
12 illustrates current curves of each applied AC voltage and direction in Comparative Example 3 and Comparative Example 4. In Figures 3 and 4, the current in the direction slightly increased over time when a voltage of 4V, which is the preliminary electrolytic treatment voltage, was applied, but the current in the direction increased when a voltage of 6V or higher, which is the secondary electrolytic treatment voltage, was applied. There was no increase over time. On the other hand, in FIGS. 5 and 6 of the comparative example, the current in the direction gradually increased over time when a voltage of 10 V, which is the secondary electrolytic treatment voltage, was applied.

【table】

[Table] Example 11 An electrolytic bath with the following composition was used as an AC electrolytic bath,
As an AC application method, 2V (120 seconds) → 4V (120 seconds)
Electrolytic treatment was performed while applying alternating current (seconds) → 6V (90 seconds) → 8V (240 seconds), and the other treatment was carried out in the same manner as in Example 1. As a result, a colored film uniformly colored in light pink was obtained. Obtained. Also, no increase in directional current over time was observed when voltages of 6V and 8V were applied. Electrolytic bath composition Nickel sulfate (as NiSO ₄ ) 100g/ Copper sulfate (as CuSO ₄ ) 20g/ Sulfuric acid (as H ₂ SO ₄ ) 5g/ Comparative example 6 As an AC application method, 2V (120 seconds) → 4V (120
seconds) → 6V (90 seconds) → 8V (90 seconds) → 12V (150 seconds)
When the treatment was carried out in the same manner as in Example 11 using the application method described above, the current in the direction increased over time when an AC voltage of 12 V was applied. Although the film was red in color, the coloring was extremely uneven.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the change in directional current over time in a known secondary electrolytic treatment (Comparative Example 1) of an anodic oxide film. 2A to 2B show model waveforms of several examples of current waveforms in AC secondary electrolytic treatment of an anodic oxide film. Figures 3 and 4
FIG. 5, and FIG. 6 are drawings showing changes over time in current curves of each AC applied voltage and direction in Example 3, Example 4, Comparative Example 3, and Comparative Example 4, respectively.

Claims (1)

[Claims] 1. In a method of coloring an anodic oxide film of aluminum or its alloy by secondary electrolytic treatment using an electrolytic bath containing a metal salt and alternating current, the anodic oxide film is first treated in the electrolytic bath at a low voltage at which metal components do not precipitate. A preliminary electrolytic treatment is performed by applying an alternating current of
The increase in AC voltage for performing the secondary electrolytic treatment is carried out in multiple steps of two or more times, and the amount of current in the direction of the anodic oxide film used as the cathode during the secondary electrolytic treatment is maintained while the same AC voltage is being applied. 1. A method for electrolytically coloring an anodic oxide film of aluminum or its alloy, which method is controlled to prevent coloring from increasing over time.