JP3379482B2 - Electrolytic coloring of aluminum material - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolytic coloring method for an aluminum material (hereinafter, simply referred to as "aluminum material") made of aluminum or an aluminum alloy that has been subjected to an anodic oxide film treatment. Aluminum that can produce an aluminum material colored in a uniform color tone by suppressing not only the color tone variation within the same current-carrying lot but also the color tone variation that easily occurs between the current-carrying lots during electrolytic coloring treatment The present invention relates to an electrolytic coloring method for materials.

[0002]

2. Description of the Related Art Aluminum materials are frequently used in many fields such as building materials, vehicle parts, and furniture because of their excellent workability and corrosion resistance. Ni, Co, C for the purpose of enhancing the effect
Electrolytic coloring is performed in which an aluminum material is colored by electrolyzing in an electrolytic solution containing a soluble metal salt such as u or Sn to deposit an electrolytic product of these metal salts in a porous anodic oxide film.

As a treatment method for electrolytically coloring the aluminum material, an alternating current electrolytic coloring treatment (Asada method) in which an alternating current is applied to the electrolytic solution for electrolysis, and a direct current method in which a direct current is applied to the electrolytic solution for electrolysis Decolorization treatment is known,
It is known that the latter DC electrolytic coloring treatment can obtain sufficiently uniform coloring, especially when performing dark electrolytic coloring such as black.

On the other hand, the former method of AC electrolytic coloring has a problem that uneven coloring occurs in the depressions and protrusions, especially when the aluminum material has a complicated shape. Therefore, conventionally, various methods for solving this problem have been proposed, for example, before subjecting an aluminum material to an alternating current electrolytic coloring treatment, a direct current is applied in the same electrolytic coloring treatment bath with the aluminum material as an anode. There is a method of conducting a coloring pretreatment for energizing, and a constant voltage electrolysis in which energization is performed for a certain period of time while keeping the voltage value of a direct current constant (Japanese Patent Publication No. 54-23,664, etc.) is known.

This coloring pretreatment by constant voltage electrolysis is carried out by applying a direct current having a constant voltage value for a certain period of time.
It aims to eliminate uneven coloring by making the film resistance value of each part of the anodized film of aluminum material uniform so that a relatively uniform current flows through the film during the next AC electrolytic coloring treatment. This is an industrially acceptable method when electrolytically coloring an aluminum material in a relatively dark color.

As another method, when electrolytically coloring an aluminum material, energization and stopping are repeated intermittently over a plurality of stages, and at this time, the processing voltage of the next stage is more than that of the preceding stage. It has been proposed to achieve a stable color tone by sequentially setting it higher (Japanese Patent Laid-Open No. 8-41685).
Issue). According to this method, not only a stable color tone but also the black coloring time can be shortened, and the influence of trace impurities can be suppressed to prevent white streak defects.

However, although any of the above methods can achieve a relatively stable color tone in the same electrified lot, it is possible to completely suppress the color tone variation that occurs between the electrified lots. This is not possible, and it is difficult to manufacture an aluminum material that is colored in a uniform color tone between each electrified lot. This tendency is not so problematic when electrolytically coloring a relatively dark color tone, but is remarkable when electrolytically coloring a relatively light color tone, and industrially produces an electrolytically colored aluminum material. Is a problem in doing.

[0008]

Therefore, the inventors of the present invention prevent coloring unevenness that occurs between the current-carrying lots as much as possible during AC electrolytic coloring treatment of an aluminum material, and color the aluminum material with a uniform color tone. As a result of diligent study on a method capable of stably producing an aluminum material, by performing a pre-coloring treatment to be performed prior to the AC electrolytic coloring treatment up to a preset final reaching voltage value and final reaching current value, comparatively It has been found that a uniform color tone can be achieved between each electrified lot even when light color electrolytic coloring is applied.

That is, according to the investigations and studies by the present inventors, it is considered that the variation in color tone between the respective electrified lots occurs when the aluminum material is subjected to the AC electrolytic coloring treatment for the following reason. To be For example, when performing an AC electrolytic coloring treatment of an aluminum material, when performing a coloring pretreatment by constant current electrolysis in the same electrolytic coloring treatment bath as the coloring pretreatment, the electrolytic voltage in this coloring pretreatment is the electrolytic coloring treatment bath. Temperature and pH, and further, the washing time and the pH of the washing bath when the aluminum material immersed in this electrolytic coloring treatment bath is washed in the washing process after the anodizing treatment (hereinafter, these conditions are summarized. "Bath conditions") and changes according to changes in these bath conditions.

By the way, in the coloring pretreatment by constant current electrolysis, the electrolytic voltage is mainly determined by the resistance of the electrolytic coloring treatment bath and the resistance of the anodic oxide film on the surface of the aluminum material immersed in the electrolytic coloring treatment bath. Among these, the variation of the resistance of the electrolytic coloring treatment bath between each energized lot is not so large as about 0.1 to 0.2 V at the maximum when converted into the equivalent voltage, and the variation of the electrolytic voltage in the coloring pretreatment is mainly It is thought that this is due to the resistance of the film. The anodic oxide film on the surface of the aluminum material is a so-called "barrier layer" made of a dense alumina formed on the aluminum substrate of the aluminum material, and a porous layer formed on the barrier layer. However, most of the resistance of this film depends on the barrier layer.

Further, the efficiency of the barrier layer generated in the pretreatment for coloring by constant current electrolysis is the apparent efficiency expressed by the ratio of the actual increased amount in consideration of the dissolution of the barrier layer to the theoretical generated amount with the current efficiency of 100%. (Increase / theoretical production) is considered to be about 60%, and
Since the chemical dissolution rate of the barrier layer is affected by the change in bath conditions, the apparent efficiency changes under the influence of the bath conditions as well as the electrolytic voltage in the coloring pretreatment, and as a result, the aluminum material The resistance of the film on the surface will change between each electrified lot.

However, in the conventional coloring pretreatment by constant current electrolysis in which the current value of the direct current is kept constant for a certain period of time, the "electrolysis voltage in the coloring pretreatment which occurs due to the above-mentioned change in bath conditions occurs. Of the aluminum material surface and the variation of the resistance of the film on the aluminum material surface, the electrolytic voltage fluctuates within the energizing time, and as a result, the generation of the barrier layer on the aluminum material surface cannot be completely controlled. It was not possible to make the current distribution of the film No. 1 uniform.

Therefore, in order to obtain a uniform color tone between each energized lot, it is conceivable to strictly control the bath conditions described above and eliminate the influence of these bath conditions. It is difficult to strictly control industrially, and variations in bath conditions are unavoidable within the control range.In particular, when electrolytically coloring a relatively pale color, it is possible to completely suppress variations in color tone between each electrified lot. It is impossible to do.

As a result of studies on how to industrially solve this problem, the present inventors have found that the thickness of the barrier layer of the anodic oxide film produced and adjusted in the coloring pretreatment is the coloring pretreatment. In the case of coloring pretreatment by constant current electrolysis, for example, it is proportional to the final reaching voltage value in the case of coloring pretreatment by constant current electrolysis, so that the thickness of this barrier layer is The inventors have completed the present invention by finding that it is directly related to the color tone of electrolytic coloring applied to a material.

Therefore, an object of the present invention is to prevent coloring unevenness occurring not only in one energized lot but also between energized lots during AC electrolytic coloring treatment of aluminum material as much as possible. An object of the present invention is to provide an electrolytic coloring method for an aluminum material, which can industrially and stably produce an aluminum material colored in a uniform color tone.

[0016]

That is, according to the present invention, an aluminum material made of aluminum or an aluminum alloy subjected to anodizing treatment is immersed in an electrolytic coloring treatment bath containing a soluble metal salt, and this aluminum material is used as an anode. As a pre-coloring treatment for energizing a direct current waveform as, then in the electrolytic coloring method of aluminum material to be subjected to alternating-current electrolytic coloring treatment in the same electrolytic coloring treatment bath, the final reaching voltage value and the final reaching current value set in advance for the coloring pre-treatment. This is an electrolytic coloring method for aluminum materials that is performed up to the specified value.

In the present invention, the aluminum material to be electrolytically colored is not particularly limited, and sulfuric acid, oxalic acid, sulfonic acid, etc. can be used as an electrolytic bath as in the case of the conventional anodic oxide film treatment. Using an aqueous acid solution such as chromic acid, an aluminum material made of normal aluminum or an aluminum alloy is used as an anode, and a direct current or an alternating current or a current superposed with a direct current is applied to this to form an anodized film on the surface of the aluminum material. It is obtained by merging.

The electrolytic coloring treatment bath containing a soluble metal salt for pre-coloring treatment and AC electrolytic coloring treatment on the aluminum material thus obtained is not particularly limited, and any conventional electrolytic coloring treatment bath can be used. The same may be applied, for example, as a soluble metal salt, nickel (Ni), cobalt (Co),
Copper (Cu), tin (Sn), chromium (Cr), magnesium (M
g), iron (Fe), cadmium (Cd), titanium (Ti), manganese (Mn), molybdenum (Mo), calcium (Ca),
Inorganic acid salts such as sulfates, nitrates, phosphates, hydrochlorides, chromates, etc. of metals such as vanadium (Ba), lead (Pb), zinc (Zn), etc., oxalates, acetates, tartrates, etc. The organic acid salts thereof and the like can be mentioned.

If desired, the electrolytic coloring treatment bath further contains dithionite salts such as sodium dithionite and zinc dithionite, ammonium thiosulfate and thiosulfate for the purpose of further improving the degree of coloring. Thiosulfates such as sodium sulfate,
Add additives such as bisulfite such as sodium bisulfite, sulfite such as sulfurous acid and sodium sulfite, and strong reducing compounds such as thioglycolic acid such as thioglycolic acid and ammonium thioglycolate. Good.

In the present invention, the pre-coloring treatment to be performed prior to the AC electrolytic coloring treatment is to immerse an aluminum material in an electrolytic coloring treatment bath and use this aluminum material as an anode to form a DC waveform (that is, DC or AC / DC superimposed wave). Energize the
The process ends when the voltage value (the peak voltage value when the DC waveform is the AC / DC superposed wave) and the current value at this time reach the preset final reaching voltage value and final reaching current value.

As a specific method for carrying out this pre-coloring treatment, for example, in the case of constant current electrolysis which is carried out by passing a current having a constant current value, the direct current is maintained while the current value is kept at a preset final reaching current value. It is preferable that the coloring pretreatment be terminated when the voltage value at this time reaches a preset final reaching voltage value. In this constant-current pretreatment, in the initial stage of energization, the barrier layer of the aluminum material film is relatively thin, and the current preferentially flows in the portion having a small resistance and the portion having a small distance from the cathode and a small resistance of the bath. The thickness of the barrier layer in this portion is compensated or becomes relatively thicker than the other portions by the amount corresponding to the difference in resistance, and a uniform anode current distribution is obtained when the final reached voltage value is reached. .

On the other hand, in the case where this pre-coloring treatment is carried out by constant voltage electrolysis by passing a current of a constant voltage value, normally, when an electric current of a final reaching voltage value set in advance from the beginning is passed at the beginning of energization, an overcurrent is generated. There is a danger of flowing. Therefore, in order to prevent this overcurrent from flowing, in the initial stage of energization, energization of the DC waveform is started at a voltage value lower than the preset ultimate voltage value,
After that, when the current value has settled down, the voltage value is switched to the final reaching voltage value, and this constant voltage electrolysis is continued until the preset final reaching current value is reached.

Here, the setting of the final reaching voltage value and the final reaching current value in the pre-coloring treatment differs depending on what kind of color tone the aluminum material needs to be obtained as a product, and electrolytic coloring with a relatively pale color tone is performed. In this case, it is better to set the final reaching voltage value to 30 to 50V, and conversely,
When performing electrolytic coloring with a relatively dark color tone, it is preferable to set the final reaching voltage value to 20 to 30 V, and to set the final reaching current value in the range of ^{20 to} 50 A / m ^2. .

After the coloring pretreatment is completed in this way,
In the present invention, the same electrolytic coloring treatment bath is used as it is, and an alternating current or alternating / direct superposition waveform is applied to the aluminum material to perform the alternating electrolytic coloring treatment. In this case, the method of AC electrolytic coloring treatment is not particularly limited and can be carried out in the same manner as the conventional method, but the peak voltage of the AC or AC / DC superposed waveform used is preferably for the following reason. The final reaching voltage of 0.
55 to 0.8 times, more preferably 0.6 of the final reached voltage
It is preferable to set it to 5 to 0.75 times. If the peak voltage of the AC or AC / DC superposed waveform used is lower than 0.55 times the final reaching voltage set in advance in the coloring pretreatment, no coloring occurs or the coloring speed becomes extremely slow.
When it is higher than 8 times, it becomes difficult to keep the current value constant during the AC electrolytic coloring treatment, and it becomes impossible to obtain a uniform color tone even if the treatment time is kept constant.

According to the research conducted by the present inventors, this point can be understood as follows. That is, in the electrolytic coloring treatment, a color tone is provided by the metal species in the bath being deposited in the film by the reduction reaction. Therefore,
Making the color tone uniform is nothing but making the current distribution of the aluminum material uniform when electrolytically coloring the aluminum material as the cathode.

When the current-controlled coloring pretreatment in which the final voltage is regulated by using the aluminum material as the anode is performed, the film resistance corresponding to the bath resistance of each part is formed. Therefore, the current distribution of the aluminum material at the end of the coloring pretreatment is completed. Can be made uniform.

However, when the AC waveform is subsequently energized to perform the AC electrolytic coloring treatment, if the peak voltage of this AC waveform is equal to or higher than the final voltage in the current control coloring pretreatment, the coloring pretreatment is completed. Although the current distribution of the aluminum material is uniform at that time, the current distribution of the aluminum material during the AC electrolytic coloring treatment is not uniform and the color tone is not uniform. This is because the film resistance itself has a property that the resistance value varies depending on the current direction, and the resistance value when the aluminum material serves as the cathode is smaller than when it is the anode.

As a result of studying this problem, the inventors of the present invention have found that the change in the film resistance during the AC electrolytic coloring treatment shows that the final voltage during the current-controlled coloring pretreatment and the peak of the AC waveform during the AC electrolytic coloring treatment. Depends on the ratio between the voltage and
We found that there is a close relationship. That is, first, a current-controlled coloring pretreatment in which a final voltage is regulated and a direct current is applied is performed, and subsequently, in the same electrolytic coloring treatment bath, 0.55 to 0.8 times the final voltage at the time of the current-controlled coloring pretreatment. By applying a voltage-controlled AC waveform with a peak voltage of 1 to perform AC electrolytic coloring treatment, it is possible to obtain a uniform current distribution corresponding to the change in film resistance at the end of the pretreatment for coloring, and to obtain a uniform color tone. Obtainable.

In the actual operation, in order to improve the productivity, it is necessary to select a voltage as high as possible within the range of 0.55 to 0.8 times the final voltage, and this color tone is uniform. In order to satisfy both the productivity and the productivity improvement, more preferably, the aluminum material after the current-controlled coloring pretreatment arranged in the electrolytic coloring treatment bath is scanned with an AC voltage, and the obtained voltage-current curve It is desirable to find the boundary voltage E ₀ given by the intersection of the extension lines of the flat region and the rising region and set the peak voltage during the AC electrolytic coloring treatment to this boundary voltage E ₀ . The boundary voltage E ₀ is 0.65 to 0.
It becomes about 75 times, and it fluctuates slightly depending on the coloring pretreatment conditions and other conditions (conditions of difference in anodic oxide film treatment, subsequent washing conditions, etc.), but finally as the optimum peak voltage of AC or AC / DC superimposed waveform. It is uniquely determined.

According to the method of the present invention, the barrier layer grows preferentially in the initial and middle stages of the pretreatment for coloring because the current easily flows in the portion close to the counter electrode, and the film of the film grows as the barrier layer grows. The resistance increases, which suppresses the ease of current flow in this portion. That is, since the barrier layer grows preferentially in the portion where the current easily flows in the pre-coloring treatment, the difference in the ease of the current flow due to the position is eliminated in the AC electrolytic coloring treatment, and the aluminum in the same electrified lot is eliminated. The current flows through the entire surface of the material with a uniform current distribution, and variations in color tone within the same lot are eliminated.

Further, in the method of the present invention, since the above-mentioned pre-coloring treatment is carried out up to the preset final reaching voltage value and final reaching current value, even if the bath conditions vary between the energized lots, this coloring pre-treatment is carried out. The state of the barrier layer that is finally adjusted by each of the current-carrying lots becomes uniform, and the current flows through the entire surface of the aluminum material with a uniform current distribution between the current-carrying lots. Variations in color tone are eliminated.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be specifically described below based on test examples, examples and comparative examples.

Example 1 A6063S-T5 was used as an aluminum material,
20% H ₂ SO ₄ , 100A / m ² × 30 minutes, anodized film treatment is performed and the film thickness is 1 on the surface of aluminum material.
An anodized film having a thickness of 0 μm was formed and then washed with water in an acidic bath having a pH of 5 for 5 minutes to obtain an aluminum material.

Next, an electrolytic coloring treatment bath having a composition of CuSO ₄ : 25 g / liter and H ₂ SO ₄ : 5 g / liter was constructed, and the aluminum material was used as an anode to obtain a current density of 25 A / m ² and a bath temperature of 25. ℃, and the ultimate voltage 20
The current-controlled coloring pretreatment was performed under the condition of V. The processing time at this time was about 20 seconds.

After the current-controlled coloring pretreatment is completed in this way, 0 V is set as the starting point in the same electrolytic coloring bath.
Scanning was performed by increasing the AC peak voltage at a speed of V / sec to obtain a voltage-current curve. The result is as shown in FIG. 1. When the boundary voltage E ₀ is obtained from the intersection of the extension lines of the flat region and the rising region, the boundary voltage E ₀ is 14
It was V.

Further, the peak voltage of the commercial alternating current is set to 14 V which is the boundary voltage E _{0 in} the same electrolytic coloring treatment bath, and 10
An alternating current electrolytic coloring treatment was performed by energizing for 0 seconds to obtain an aluminum material electrolytically colored pink. The obtained electrolytically colored aluminum material was subjected to color measurement to determine the uniformity of color tone (color difference: ΔE ^* _ab ) within the same electrified lot.

Further, the anodic oxide film treatment, the current-controlled coloring pretreatment and the alternating current electrolytic coloring treatment are repeated under the same conditions as above, and the electrolytically colored aluminum material obtained in the same manner as above is subjected to colorimetric measurement to obtain the difference between each electrified lot. Uniformity of color tone (color difference:
ΔE ^* _ab ) was determined. The results are shown in Table 1.

Example 2 Before current-controlled coloring was carried out in the same manner as in Example 1 except that the treatment conditions of the current-controlled coloring pretreatment and the commercial AC peak voltage in the AC electrolytic coloring treatment were carried out under the conditions shown in Table 1. Treatment and AC electrolytic coloring treatment were performed to obtain an electrolytically colored aluminum material. The obtained electrolytically colored aluminum material was examined for uniformity of color tone in the same manner as in Example 1.
The results are shown in Table 1.

Example 3 An aluminum material which was anodized by the same material and method as in Example 1 was used, and the same electrolytic coloring bath as in Example 1 was used. The aluminum material was used as an anode and the initial voltage was 15V. Apply a direct current, then the current density is 32 A / m
^{When the} voltage dropped to ² , the voltage was switched to 20 V, and constant voltage coloring pretreatment was performed until the final current density reached 25 A / m ² .

After the constant voltage coloring pretreatment was completed in this way, a commercial countercurrent voltage was scanned in the same electrolytic coloring treatment bath as in Example 1 to obtain a voltage-current curve. The result was the same as in Example 1, and the boundary voltage E ₀ obtained from the intersection of the extension lines of the flat region and the rising region was 14V.

Further, the peak voltage of the commercial alternating current is set to 14 V which is the boundary voltage E _{0 in} the same electrolytic coloring treatment bath, and 10
An alternating current electrolytic coloring treatment was performed by energizing for 0 seconds to obtain an aluminum material electrolytically colored pink. The obtained electrolytically colored aluminum material was subjected to color measurement, and the uniformity of color tone (color difference: ΔE ^* _ab ) in the same electrified lot was determined every time.
The results are shown in Table 1.

Comparative Example 1 An AC electrolytic coloring treatment was carried out under the same conditions as in Example 1 without the current-controlled coloring pretreatment to obtain an electrolytically colored aluminum material. The obtained electrolytically colored aluminum material was examined for uniformity of color tone in the same manner as in Example 1. The results are shown in Table 1.
Shown in.

Comparative Examples 2 to 3 Current control was carried out in the same manner as in Example 1 except that the treatment conditions of the current control coloring pretreatment and the commercial AC peak voltage in the AC electrolytic coloring treatment were carried out under the conditions shown in Table 1. Pre-coloring treatment and AC electrolytic coloring treatment were performed to obtain an electrolytically colored aluminum material. The obtained electrolytically colored aluminum material was examined for uniformity of color tone in the same manner as in Example 1.
The results are shown in Table 1.

Comparative Example 4 A constant voltage coloring pretreatment was performed under the conditions of an electrolytic voltage of 30 V and a treatment time of 30 seconds, and then an AC electrolytic coloring treatment was performed under the same conditions as in Example 2 to obtain an electrolytically colored aluminum material.
The obtained electrolytically colored aluminum material was examined for uniformity of color tone in the same manner as in Example 1. The results are shown in Table 1.

[0045]

[Table 1]

[0046]

EFFECTS OF THE INVENTION According to the present invention, in AC electrolytic coloring treatment of aluminum material, not only the uniformity of color tone in the same energized lot but also coloring unevenness occurring between energized lots can be prevented as much as possible. Therefore, an aluminum material colored in a uniform color tone can be industrially and stably manufactured.

[Brief description of drawings]

FIG. 1 is a graph showing a voltage-current curve when a boundary voltage E ₀ is obtained in Example 1.

Continuation of the front page (56) Reference JP-A-5-331688 (JP, A) Patent 3266084 (JP, B2) JP-B 54-23664 (JP, B1) (58) Fields investigated (Int.Cl. ⁷⁾ , DB name) C25D 11/22

Claims (3)

(57) [Claims] 1. A coloring pretreatment in which an aluminum material made of anodized aluminum or an aluminum alloy is immersed in an electrolytic coloring treatment bath containing a soluble metal salt, and the aluminum material is used as an anode to apply a DC waveform. In the electrolytic coloring method of an aluminum material, which is then subjected to AC electrolytic coloring treatment in the same electrolytic coloring treatment bath, the above coloring pretreatment is performed by changing the voltage and the current, and finally setting a final reaching voltage value and a final reaching current value. An electrolytic coloring method for aluminum materials, which is characterized by carrying out up to. 2. The pre-coloring treatment is a process in which a voltage value is preset.
The energization of the DC waveform is started at a value lower than the final voltage value, and the next
Switch to the final voltage value before switching on the DC waveform.
This is a voltage electrolysis, and this constant voltage electrolysis is set in advance.
The method for electrolytically coloring an aluminum material according to claim 1, wherein the method is carried out until the reaching current value is reached . 3. A coloring pretreatment placed in an electrolytic coloring treatment bath.
The resulting aluminum material was scanned with an AC voltage and the
Each extension of the flat region and the rising region in the pressure-current curve
The boundary voltage E ₀ given by the intersection of the lines is calculated to determine the AC electrolytic coloring process.
Contract to control the peak voltage at the time of operation to the boundary voltage E ₀ or less.
The electrolytic coloring method for an aluminum material according to claim 2 .