JPH0240755B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for electrolytically coloring aluminum or aluminum alloy (hereinafter simply referred to as "aluminum"), and more specifically, a method for electrolytically coloring aluminum that has been subjected to anodizing treatment. The present invention relates to a method for efficiently applying uniform and beautiful coloring to an aluminum surface by applying a positive voltage with a specific intermittent waveform for pretreatment.

[Prior art and problems to be solved by the invention]

Various methods have been proposed to improve coverage and coloring speed when electrolytically coloring aluminum. For example, in order to improve the coverage of coloring, there are methods for making various improvements to the electrolyte (Japanese Patent Publication No. 11119/1986), and methods for increasing the voltage applied during electrolytic coloring (Japanese Patent Publication No. 11119/1983). 54-23663, Japanese Patent Publication No. 58-46557, Japanese Patent Application Laid-open No. 145798/1982), or a method of carrying out a specific direct current anodic electrolysis prior to electrolytic coloring (Japanese Patent Publication No. 1983)
-32064 Publication, Special Publication No. 54-13859, Special Publication Sho
54-25898, Japanese Patent Publication No. 54-23664, Japanese Patent Publication No. 58-52037, Japanese Patent Publication No. 58-39237). In addition, in order to improve the coloring speed of electrolytic coloring, a method of modifying the electrolytic solution (Special Public Interest Publication in 1983-
11119, Japanese Patent Publication No. 11119, Japanese Patent Publication No. 54-23663) or a method of modifying the return electrode (Japanese Patent Publication No. 13440, 1987).

However, in general, in the electrolytic coloring method, and in particular in the AC electrolytic coloring method, the above-mentioned devices improve one of the coverage and coloring speed, but the other is not sufficiently improved. Rather, it shows a decreasing trend.

Therefore, the present inventors have conducted extensive research in order to overcome the drawbacks of the above-mentioned conventional techniques and to develop a method that can simultaneously improve coverage and coloring speed.

[Means for solving problems]

As a result, they found that the objective could be achieved by pre-treating anodic oxidized aluminum by applying a positive voltage with a specific intermittent waveform, and then subjecting it to electrolytic coloring. The present invention was completed based on this knowledge.

That is, in electrolytically coloring aluminum subjected to anodizing treatment in an electrolytic coloring liquid containing a metal salt, the present invention uses the positive half of two substantially continuous sine waves of the same shape in the electrolytic coloring liquid. Preprocessing is performed by applying a voltage of a waveform in which the initial part of the phase angle of the positive half wave of a wave or a sine wave is repeated through a substantial rest part, or a waveform in which these are superimposed. The present invention provides a method for electrolytically coloring aluminum, which is characterized by electrolytically coloring aluminum in an electrolytically coloring solution.

The aluminum used in the method of the present invention has its surface subjected to anodic oxidation treatment. The anodic oxidation treatment carried out here may be carried out by a conventionally widely used method. Usually, the surface of aluminum is degreased and cleaned, and this is used as an anode, and aluminum, graphite, etc. is used as a cathode, and sulfuric acid, oxalic acid, etc.
This is carried out by applying direct current in an acidic electrolyte such as sulfamic acid.

In the method of the present invention, it is necessary to pre-treat aluminum that has been anodized as described above in an electrolytic coloring solution prior to electrolytic coloring.

In general, when modifying a barrier layer formed by anodizing, the thicker the modified barrier layer is, the less the influence of the barrier layer during anodizing will be, which is advantageous for electrolytic coloring. In addition, the higher the peak value of the applied voltage, the thicker the modified barrier layer becomes. However, when applying a normal DC voltage to modify the barrier layer, if too high a voltage is applied, part of the barrier layer will become thicker. There is a problem that the applied voltage cannot be withstood and current leaks locally. This leak can be avoided by significantly increasing the pressure increase rate (for example, instantaneous pressure increase) and immediately stopping it, but this method has the problem that the barrier layer cannot be uniformly modified.

Therefore, in the method of the present invention, by intermittently applying a positive voltage during the pretreatment stage, the barrier layer can be modified thickly and uniformly without leaking current even at high voltages.

Therefore, in the preliminary treatment of the present invention, it is necessary to perform electrolytic treatment by applying a voltage with a specific intermittent waveform that satisfies the above requirements. The voltage waveform used herein is a waveform in which two substantially consecutive identical positive voltage waveforms are repeated with a substantial pause. Specific examples of such voltage waveforms include those shown in FIGS. 1 to 6. In Figure 1, there are two consecutive positive half waves of a sine wave, and these two consecutive positive half waves are repeated with a pause in between, creating an intermittent waveform. Also, in Figure 2, positive double half-waves similar to those in Figure 1 are repeated at regular intervals, but between these double half-waves there is a negative double-half wave with extremely low voltage. waves exist. However, since the voltage of this negative double half-wave is extremely small, it does not actually affect the modification of the barrier layer of the anodic oxide film, and constitutes a substantial rest portion.

The voltage waveforms shown in FIGS. 1 and 2 can be formed from a half-wave sine wave and incomplete rectification using a transformer or slider control.

Furthermore, FIG. 3 shows an intermittent waveform in which two continuous positive waves are repeated with a resting part in between, which is a waveform in which the initial part of the phase angle of the positive half wave of a sine wave is cut. Since the initial part of the phase angle of each positive wave is cut off, these two successive positive waves are not completely continuous with each other, but can be considered to be substantially continuous. Furthermore, in Fig. 4, two consecutive positive waves similar to those in Fig. 3 are repeated at a constant period, but in the resting part, two consecutive positive waves are applied so small that they do not affect the modification of the barrier layer of the anodic oxide film. There is a negative wave, which constitutes a substantial rest part.

Note that the voltage waveforms shown in FIGS. 3 and 4 can be formed from a half wave of a sine wave and incomplete rectification by thyristor control.

On the other hand, the voltage waveform shown in FIG.
The voltage waveform shown in FIG. 6 is a superimposition of the voltage waveforms shown in FIG. 2 and FIG. 4.

As described above, the voltage waveform applied in the preprocessing of the present invention is a waveform in which two consecutive positive waves are repeated with a pause portion. Here, there is no particular restriction on the length of the pause portion (correctly speaking, the substantial pause portion), that is, the pause time, and it may be the same as the application time of the double positive wave, or may be longer or shorter than that. Good too. However, usually the ratio between the application time T ₁ and the pause time T ₂ of the double positive wave is T ₁ :T ₂ =1:0.1-10, preferably 1:0.5-2. Further, the maximum value V _P of the applied voltage is influenced by the type of voltage waveform used, the ratio of the pause time, etc., and cannot be unambiguously determined, but it is usually 30 to 100V, preferably 40 to 80V.

In the preliminary treatment in the method of the present invention, electrolytic treatment is carried out by applying a voltage having the waveform as described above, but there are no particular restrictions on the current application time, voltage increase rate, etc. at this time. However, the energization time is usually 5 seconds to 5 minutes, preferably 30 seconds to 3 minutes,
Boosting rate is 0.1~10V/sec, preferably 0.5~5V/sec.
Seconds.

Note that the method of the present invention uses the above-mentioned double positive waves for pretreatment, but if a single positive wave intermittent voltage waveform is used here, a biased current will flow in the transformer and heating will occur due to iron loss. Otherwise, the excitation current may cause problems such as adverse effects on the primary-side measuring instruments. However, such problems can be avoided by using intermittent waves of two consecutive positive waves as in the method of the present invention.

In the method of the present invention, after the above-mentioned preliminary treatment is carried out in an electrolytic coloring solution, the electrolytic coloring treatment is subsequently carried out in the same solution.

The electrolytic coloring treatment performed here may be performed by an alternating current electrolytic coloring method that has been widely used in the past. The electrolytic coloring solution used in this case contains various metal salts depending on the purpose. Specific examples of these metal salts include nickel, cobalt, copper, silver, selenium, iron,
Sulfates and nitrates of metals such as molybdenum and tin,
These include phosphate, hydrochloride, oxalate, acetate, and tartrate.

The conditions for electrolytic coloring, such as the alternating current voltage to be applied, the current application time, and the liquid temperature, may be appropriately selected as in the usual case. However, in the method of the present invention, since the barrier layer has been sufficiently modified by the above-mentioned pretreatment, coloring can be carried out at high voltage and the coloring speed is fast, so electrolytic coloring can be carried out in a relatively short time. Can be done.

〔Effect of the invention〕

According to the method of the present invention, the barrier layer of the anodic oxide film on the aluminum surface is sufficiently modified through pre-treatment to form a uniform barrier layer that can withstand high voltage, so electrolytic coloring does not occur at high voltages due to spalling. The process progresses quickly and with good coverage, and a uniform electrolytically colored film is formed in a short time.

In particular, in the method of the present invention, since intermittent double positive waves are used in the pretreatment, the effect of modifying the barrier layer is significantly large, and as a result, coverage and coloring speed are significantly improved.

〔Example〕

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

In addition, the test pieces and test equipment in Examples 1 and 2 and Comparative Examples 1 to 4 are as follows.

That is, first, we used an aluminum plate called A-1100-H14 (height 100 mm x width 180 mm) as a test piece, and used it in a Hull cell test device as shown in Figure 9 (however, it was made with a more acute angle than the Hull cell test device for metal fittings). The horizontal section is 80mm at the top, 250mm at the bottom,
It was suspended in a trapezoidal container with a height of 80 mm. In addition,
The coloring state after electrolytic coloring is determined using Hunter lightness (L
Value) was evaluated. Here, part A shows the part of the test piece 2 closer to the counter electrode 3, and part B shows the part of the test piece 2.
The far side part is shown on the opposite pole 3.

Example 1 An electrolytic coloring solution containing 90 g of nickel sulfate hexahydrate, 100 g of magnesium sulfate heptahydrate, 40 g of boric acid, and 3 g of tartaric acid and having a pH of 5.0 was placed in the test apparatus, and anodized in it. Using a nickel plate as the counter electrode, the treated test piece was subjected to two positive half-waves (peak value 60V) and a negative double half-wave with the voltage waveform shown in Figure 2 using the power supply shown in Figure 7. (peak value - 10V) at a boost rate of 1V (peak value - 10V)
Preliminary treatment was performed by applying electricity under the conditions of V _P )/sec and a holding time of 5 seconds.

Next, after this preliminary treatment, the power source shown in FIG. 7 was switched to the alternating current side, and an alternating current electrolytic coloring treatment was performed under conditions of a voltage of 32 V and a current application time of 4 minutes.

As a result, the L value for part A is 30.8, and for part B
29.9, and the entire test piece was finished in a uniform bronze color.

Comparative Example 1 In Example 1, without performing pretreatment,
The same procedure as in Example 1 was carried out except that the AC electrolytic coloring treatment was performed under the conditions of a voltage of 13 V and a current application time of 10 minutes.

As a result, the L value for part A is 28.8, and for part B
39.2, part A was colored bronze, part B was colored gold, and the coloring was obviously non-uniform.

Comparative Example 2 When the voltage was increased to 40 V at a rate of 0.3 V/sec using normal direct current instead of the pretreatment of Example 1, the current suddenly increased. Therefore, using the electrolytic coloring solution of Example 1, a DC current was applied at 26 V for 15 seconds, and then an AC electrolytic coloring treatment was performed at a voltage of 20 V and a current application time of 8 minutes.

As a result, the L value for part A is 29.0 and for part B
35.3, the A part was dark and the B part was light, resulting in non-uniform coloring.

Example 2 8 g of stannous sulfate, 15 g of sulfuric acid, and antioxidant (product name: Stana Keep, Yuki Shoji Co., Ltd.)
An electrolytic coloring solution containing 3 g/ml of (manufactured by) was placed in the test device, and the anodized test piece was placed in the test device.
Using the power supply shown in Fig. 8 with carbon as the counter electrode, a voltage consisting of two positive half-waves and a pause time of the same length as the two half-waves with the voltage waveform shown in Fig. 5 is applied to V _P The voltage was raised uniformly over 35 seconds until it reached 55V, and a pretreatment was performed with a holding time of 5 seconds.

After this preliminary treatment, the power source shown in FIG. 8 was switched to the alternating current side, and an alternating current electrolytic coloring treatment was performed under conditions of a voltage of 27 V and a current application time of 4 minutes.

As a result, the L value for part A is 32.8 and for part B.
31.9, and the entire test piece was finished in a uniform deep bronze color.

Comparative Example 3 In Example 2, without performing pretreatment,
The same procedure as in Example 2 was carried out except that the AC electrolytic coloring treatment was performed under the conditions of a voltage of 14 V and a current application time of 3 minutes.

As a result, the L value for part A is 22.9 and for part B
55.5, the A part was a deep bronze color, and the B part was almost uncolored.

Comparative Example 4 Instead of the pretreatment of Example 2, normal direct current was used to increase the pressure in the same electrolytically colored solution as in Example 2.
The voltage was increased to 25V at a rate of 0.3V/second and the current was applied for 10 seconds. Thereafter, AC electrolytic coloring treatment was performed under conditions of a voltage of 20 V and a current application time of 3 minutes.

As a result, the L value for part A is 25.4, and for part B
28.5, the A part was a dark bronze color and the B part was a pale bronze color, resulting in non-uniform coloring. Moreover, compared to Example 2, the overall finish was pale.

[Brief explanation of drawings]

1 to 6 are examples of voltage waveforms used in the pretreatment of the method of the present invention. FIG. 7 is a circuit diagram of the power supply used in the first embodiment, and FIG. 8 is a circuit diagram of the power supply used in the second embodiment. FIG. 9 is a plan view showing the apparatus used in Examples 1 and 2 and Comparative Examples 1 to 4, and the test piece installed therein. 1 in the diagram
indicates the test device, 2 indicates the test piece, and 3 indicates the counter electrode.

Claims (1)

[Claims] 1. When anodized aluminum or aluminum alloy is electrolytically colored in an electrolytic coloring solution containing a metal salt, the positive half of two substantially continuous sine waves of the same shape is generated in the electrolytic coloring solution. Preprocessing is performed by applying a voltage of a waveform in which the initial part of the phase angle of the positive half wave of a wave or a sine wave is repeated through a substantial rest part, or a waveform in which these are superimposed. A method for electrolytically coloring aluminum or an aluminum alloy, which comprises electrolytically coloring aluminum or an aluminum alloy in an electrolytically colored solution.