JPH0542519B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) This invention relates to a method for electrolytic coloring of chromium alloys, in particular chromium alloys having one or more main metals of iron, cobalt and nickel, such as stainless steel. The present invention relates to an electrolytic coloring method for chromium alloys, in which the surface of chromium alloys is colored by electrolytic treatment.

(Prior Art) A conventional electrolytic coloring method for chromium alloys is disclosed, for example, in Japanese Patent Publication No. 32621/1983. In this method, stainless steel as a chromium alloy is immersed in an aqueous solution containing chromic acid and sulfuric acid, and the stainless steel is subjected to anodic electrolysis treatment to form a porous oxide film on the surface of the stainless steel. This is a method of coloring the surface.

The present inventor has discovered that in such a conventional electrolytic coloring method for chromium alloys, the color tone of the formed oxide film can be adjusted based on the current density and treatment time of the anodic electrolytic treatment. An electrolytic coloring method for alloys was proposed.

(Problems to be Solved by the Invention) In the conventional electrolytic coloring method and the electrolytic coloring method proposed by the present inventor, as the treatment time of the anodic electrolytic treatment passes, the color tone of the oxide film formed rapidly changes. Therefore, it is difficult to adjust this tone and the reproducibility of the tone is poor. Moreover, in this electrolytic coloring method for chromium alloys, the oxide film formed did not have sufficient wear resistance or corrosion resistance, that is, its strength was low.

On the other hand, the present inventor has developed an oxidation method for coloring the surface of a chromium alloy by alternately repeating anodic electrolytic treatment and cathodic electrolytic treatment on the chromium alloy in an aqueous solution containing a chromium compound and sulfuric acid. We proposed an electrolytic coloring method for chromium alloys that forms a strong film.

However, with the electrolytic coloring method for chromium alloys proposed by the present inventors, no attention has yet been paid to adjusting the color tone of the oxide film formed. Moreover, the strength of the formed oxide film is low, and it may peel off when it comes into contact with other objects.

Therefore, the main object of the present invention is to provide a method for electrolytic coloring of chromium alloys, which can adjust the color tone of the oxide film formed on the surface of the chromium alloy and improve the strength of the oxide film. That's true.

(Means for Solving the Problems) The present invention is an electrolytic coloring method for a chromium alloy, which colors a chromium alloy by electrolytically treating the chromium alloy. A step of preparing an aqueous solution containing sulfuric acid, and adding 0.05 to 0.05 to a chromium alloy in this aqueous solution.
Anodic electrolytic treatment and cathodic electrolytic treatment for 1 second or more each with a current density of 2 A/dm ² are repeated two or more times each, and the current density and treatment of each of the anodic electrolytic treatment and cathodic electrolytic treatment are The process of forming an oxide film on the surface of the chromium alloy by adjusting the color tone of the oxide film by changing the time and number of repetitions, and oxidizing the chromium alloy with the oxide film in an aqueous solution. This is an electrolytic coloring method for chromium alloys, which includes a step of performing cathodic electrolytic treatment with a current density of 0.5 to 5 A/dm ² that is higher than the current density of cathodic electrolytic treatment in the step of forming a film.

(Function) In the process of forming an oxide film on the surface of a chromium alloy, the oxidation formed by changing the current density, treatment time, and number of repetitions of each of the anodic electrolytic treatment and cathodic electrolytic treatment in that process. The color tone of the film is adjusted. Furthermore, the current density is higher than that of cathodic electrolytic treatment in the process of forming an oxide film on chromium alloy in an aqueous solution.
The oxide film formed on the surface of the chromium alloy is hardened by performing cathodic electrolytic treatment with a current having a current density of 0.5 to 5 A/dm ² or more.

(Effects of the Invention) According to the present invention, the color tone of the oxide film formed on the surface of the chromium alloy can be adjusted and the strength of the oxide film can be improved.

Furthermore, since the aqueous solution for forming an oxide film on the surface of the chromium alloy and the aqueous solution for curing the formed oxide film are the same aqueous solution, the aqueous solution in one bath can be used to form an oxide film on the surface of the chromium alloy. The color tone of the oxide film can be adjusted, and the strength of the oxide film can be increased.

Therefore, the industrial significance of this invention is extremely large.

The above objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

(Example) Fig. 1A and Fig. 1B show an example of an apparatus for carrying out the present invention, Fig. 1A is an illustrative diagram of the entire device, and Fig. 1B is an illustrative diagram showing a bath and its surrounding parts. It is.

This device 10 includes a constant current power supply 12 . This constant current power supply 12 has an input terminal, for example, an AC
By connecting a 100 to 200V power supply,
An arbitrary constant current is output from the output end. In addition, in this constant current power supply 12, for example, 0 to
It is possible to output a constant DC current with an arbitrary current value of 10.0 A, and for example, a current with a current density of 0 to 10.0 A/dm ² can be passed through a conductor with a current passing area of 1 dm ² .

The output terminal of the constant current power supply 12 is connected to the input terminal of the polarity change switch 14. This polarity change switch 14 is for changing the polarity of the current input to its input terminal as it is or with the lapse of an arbitrary period of time, and outputting it from its output terminal.

Therefore, the polarity of the constant current input to the input terminal of the polarity change switch 14 is switched from its output terminal as an arbitrary time elapses as shown in FIGS. 2A to 2D, for example. A current or a current with a constant polarity as shown in FIG. 3 is output. In addition, Fig. 2A and Fig. 2B
The figure shows the relationship between time and current value when the current value of the constant current input to the polarity change switch is 0.1A, and in Figures 2C and 2D, the constant current value input to the polarity change switch is shown. The relationship between time and current value when the current value is 0.5A is shown, and furthermore,
In Figures 2A and 2C, the polarity of the constant current is 10
Figures 2B and 2D show the relationship between time and current value when the polarity of the constant current is switched every 36 seconds.
Shows the relationship between current values. Also, in Figure 3, the current value of the constant current input to the polarity change switch is 2.0A.
and shows the relationship between time and current value when the time is 500 seconds.

One output end of the polarity change switch 14 is connected to the plate 20 to be colored via an ammeter 16 connected in series, such as a digital display or an analog display, and a copper connector 18a. This plate to be colored 2
For example, SUS304 stainless steel,
A chromium alloy such as SUS430 stainless steel is used.

Note that the plate 20 to be colored is preferably subjected to treatments such as degreasing treatment, water washing treatment, and neutralization treatment as pretreatments for the electrolytic coloring treatment. This degreasing treatment is carried out by immersing the plate 20 to be colored, such as a stainless steel plate made of a chromium alloy, in a sodium orthosilicate solution at, for example, 70°C. Further, the water washing treatment is performed by, for example, ultrasonically washing the plate 20 to be colored in a water bath. Furthermore, as a neutralization treatment, the plate 20 to be colored is, for example, 20%
This is done by immersion in _HNO3 solution for 30-60 seconds.

On the other hand, the other output end of the polarity change switch 14 is connected to the colored plate 20 through a copper connector 18b.
It is connected to a return electrode plate 22 as a counter electrode. Although the return electrode plate 22 is made of lead in this embodiment, it may be made of other conductive metals such as platinum, titanium, niobium, carbon, and stainless steel.

The plate 20 to be colored and the counter electrode plate 22 are arranged to face each other at a predetermined interval in the aqueous solution 26 in the bath 24.

Further, the aqueous solution 26 stored in the bath 24 contains, for example, 250 g/of chromic acid as a main ingredient and 490 g/of sulfuric acid as an electrolyte.

In addition, as a preferable example of the aqueous solution 26 in this invention, the aqueous solution containing 50-500 g/of chromic acid and 300-1000 g// of sulfuric acid is mentioned.

In other words, if the amount of chromic acid contained in an aqueous solution is less than 50 g, the process of forming an oxide film and the process of curing the oxide film will take too much time, making it unusable.
If the value exceeds 2, it becomes difficult to dissolve chromic acid, which is economically disadvantageous, and the aqueous solution 2 in this invention
It is preferable that the chromic acid contained in No. 6 be contained within the above-mentioned range.

Furthermore, sulfuric acid contained in an aqueous solution
If the value is less than 300g/, the electrolytic treatment reaction will be too slow to be used for practical purposes, and if it exceeds 1000g/, the surface of the plate to be colored will dissolve and a porous oxide film will form on the surface of the plate to be colored. Therefore, the sulfuric acid contained in the aqueous solution 26 in the present invention is preferably contained within the above-mentioned range.

Furthermore, preferably chromic acid is added at 200 to 400 g/
and an aqueous solution containing 400 to 600 g/sulfuric acid.

Note that as the main ingredient of the aqueous solution 26, a chromium compound such as chromate or dichromic acid can be used instead of chromic acid.

In the present invention, in the aqueous solution 26 containing the above-mentioned base material and sulfuric acid, for example, a chromium alloy such as stainless steel (plate 20 to be colored) is coated with 0.05 to
By alternately repeating anodic electrolytic treatment and cathodic electrolytic treatment for 1 second or more each at a current density ^of 2 A/dm 2 two or more times,
An oxide film was formed on the surface of the chromium alloy. In this case, the color tone of the formed oxide film was adjusted by changing the current density, treatment time, and number of repetitions of each of the anodic electrolytic treatment and the cathodic electrolytic treatment for forming the oxide film. Furthermore, the chromium alloy on which the oxide film has been formed is subjected to cathode electrolysis treatment in an aqueous solution 26 at a current density of 0.5 to 5 A/dm ² that is higher than the current density of the cathode electrolysis treatment for forming the oxide film. In particular, the oxide film was hardened.

Experimental example 1 First, chromic acid 250g/and sulfuric acid 490g/
A solution containing was prepared. Furthermore, samples 1 to 18
We prepared 18 SUS304 stainless steel plates.

Then, these stainless steel plates were electrolytically treated in the above-mentioned solution under the conditions shown in Attached Table 1.
Samples 1 to 18 were obtained. In this case, as shown in Attached Table 1
A ₁ , A ₂ , T ₁ , T ₂ , N, A ₃ and T ₃ are the values shown below, respectively.

A ₁ : Current density of anodic electrolytic treatment [A/dm ² ] A ₂ : Current density of cathodic electrolytic treatment [A/dm ² ] T ₁ : Time of one anodic electrolytic treatment [seconds] T ₂ : One time of cathode electrolysis Electrolytic treatment time [seconds] N: Number of times of alternately repeated anodic electrolytic treatment and cathodic electrolytic treatment [times] A ₃ : Current density of subsequent cathodic electrolytic treatment [A/d
m ² ] T ₃ : Subsequent cathodic electrolytic treatment time [minutes] That is, for all samples 1 to 18, first, anodic electrolytic treatment and cathodic electrolytic treatment were repeated alternately to form an oxide film on the stainless steel plate. I went. In this case, especially samples 1 to
For No. 16, anodic electrolytic treatment and cathodic electrolytic treatment were alternately repeated two or more times for at least 1 second each at a current density of 0.05 to 2 [A/dm ² ]. Further, for Samples 17 and 18, anodic electrolytic treatment and cathodic electrolytic treatment were alternately repeated by a method outside the scope of the present invention.

At this stage, the color tone and hardness of the oxide film formed on the surface of each sample 1 to 18 was examined. In this case, the color tone is
~18 was examined by visual inspection. Incidentally, those that were not colored were indicated with a "-".
In addition, the hardness was measured by rubbing the surface of each sample 1 to 18 with an eraser, and if the color tone of that part changed significantly after 100 rubbings, it was marked with an "x" as not suitable for practical use. , the color tone of the area remained almost unchanged even after being rubbed several hundred times.
Items that can be put to practical use are marked with an “〇”. The experimental results are shown as Evaluation 1 in Attached Table 1.

From this experimental result, even if the treatment time ((T ₁ + T ₂ )N) for forming an oxide film is the same, the current density of the anodic electrolytic treatment and the cathodic electrolytic treatment, each treatment time, or their It has been found that by changing the number of repetitions, the color tone of the oxide film formed can be changed. For example, in Samples 1 to 7, a "blue" oxide film is formed, and in Samples 1 to 7, a "brown" oxide film is formed. Furthermore, it was found that the strength of the formed oxide film in this state was not sufficient for practical use.

Samples 1 to 16 on which such oxide films were formed were subjected to subsequent cathodic electrolysis treatment in an aqueous solution 26. In this case, the cathodic electrolytic treatment was carried out at a current density of 0.05 to 5 A/dm ² that was higher than the current density of the cathodic electrolytic treatment used to form the oxide film.

Samples 1 to 16 subjected to cathodic electrolytic treatment were examined for color tone and hardness of their oxide films. In this case, color tone and hardness were examined in the same manner as described above. The results of this experiment are shown in Evaluation 2 of Appendix 1.

From the results of this experiment, it was found that the color tone was hardly changed by this cathodic electrolytic treatment. Furthermore, it was found that the formed oxide film had sufficient hardness and could withstand practical use.

Therefore, from the above experimental results, it is possible to adjust the color tone of the oxide film formed on the surface of the stainless steel plate by the method within the scope of the present invention.
Moreover, it can be seen that the strength of the oxide film can be improved.

In addition, samples 1 to 4 having oxide films of the same color tone (blue) were examined for their brightness (brightness and darkness) by measuring them with a color difference meter CR-100 manufactured by Minolta Co., Ltd. Then, if sample 1 is used as a reference, the "blue" of sample 2 is bright, the "blue" of sample 3 is dark, and the "blue" of sample 4 is
was bright and hot. In this way, in this invention,
It is also possible to adjust the brightness and chroma of the oxide film that is formed.

Experimental Example 2 In this experiment, when oxide films were formed on the surfaces of a plurality of stainless steel plates using the same method within the scope of the present invention, the reproducibility of the color tone of the oxide films was examined.

In this experiment, first, five samples 2-1,
2-2, 2-3, 2-4 and 2-5 were obtained. Then, the L, a, and b values of each sample were measured using the color difference meter described above. The experimental results are shown in Attached Table 2. Furthermore, the ΔE values based on sample 2-1 are shown in Attached Table 2.

From this experimental result, the ΔE of the five samples is 1.5
Therefore, it can be said that there is almost no color difference between the five samples. Therefore, it can be seen that the method within the scope of the present invention provides good reproducibility of the color tone of the oxide film.

Experimental Example 3 In this experimental example, samples 31 to 52 were obtained by forming an oxide film on a stainless steel plate under the conditions shown in Attached Table 3, and then performing cathodic electrolysis treatment on the stainless steel plate on which the oxide film was formed. .

In this case, for sample 31, 0.2A/d
An oxide film was formed by alternately repeating anodic electrolytic treatment for 60 seconds and cathodic electrolytic treatment (120 seconds) 10 times at a current density of m ² . Similarly, samples 32 to 52 were alternately subjected to anodic electrolytic treatment and cathodic electrolytic treatment to form oxide films. Furthermore, after forming the oxide film, for samples 31-34, 49 and 50,
sample at a current density of 0.4A/dm2 or ^less .
For 35 to 48, 51 and 52, the current density is higher than the current density of the cathodic electrolytic treatment when forming the oxide film.
With a current density of 0.5-5A/ ^dm2 , respectively,
Cathode electrolysis treatment was performed.

Regarding samples 31 to 52 obtained in this way,
The color tone and hardness of the oxide film were examined. The color tone and hardness were examined in the same manner as in Experimental Example 1 above. The results of this experiment are shown in Evaluation 3 of Appendix 3.

As is clear from the results of this experiment, it can be seen that if the conditions for forming an oxide film are kept constant, oxide films with the same color tone can be formed. Furthermore, it can be seen that the oxide film is cured if the cathode electrolytic treatment is performed with a current density of 0.5 to 5 A/dm ² that is higher than the current density of the cathodic electrolytic treatment used to form the oxide film.

In addition, in each of the above-mentioned Experimental Examples 1, 2, and 3, using the electrolytic apparatus shown in FIG. 1A and FIG. 1B,
Got the sample.

[Brief explanation of the drawing]

1A and 1B show an example of an apparatus for carrying out the present invention, with FIG. 1A being an illustrative view of the entire device, and FIG. 1B being an illustrative view showing a bath and its surrounding parts. 2A to 2D and FIG. 3 each show an example of the output current of the polarity change switch when a constant current is input to the polarity change switch. In the figure, 10 is a device, 12 is a constant current power supply,
14 is a polarity change switch, 16 is an ammeter, 18a
and 18b is a connector, 20 is a stainless steel plate, 2
2 is a return electrode, 24 is a bath, and 26 is an aqueous solution.

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Claims (1)

[Scope of Claims] 1. An electrolytic coloring method for a chromium alloy in which the chromium alloy is colored by electrolytically treating the chromium alloy, the method comprising preparing an aqueous solution containing a chromium compound as a main ingredient and containing sulfuric acid. a step of adding 0.05 to 0.05 to the chromium alloy in the aqueous solution;
Anodic electrolytic treatment and cathodic electrolytic treatment for 1 second or more each at a current density of 2 A/dm ² are repeated alternately two or more times, and the current density of each of the anodic electrolytic treatment and cathodic electrolytic treatment, A step of forming an oxide film on the surface of the chromium alloy by adjusting the color tone of the oxide film by changing the treatment time and the number of repetitions thereof, and a step of forming an oxide film on the chromium alloy on which the oxide film is formed,
In the aqueous solution, the current density is higher than the current density of the cathodic electrolytic treatment in the step of forming the oxide film, and
A method for electrolytic coloring of chromium alloys, comprising the step of cathodic electrolytic treatment with a current density of 0.5 to 5 A/ ^dm2 . 2. The method for electrolytic coloring of a chromium alloy according to claim 1, wherein the chromium compound includes chromic acid, chromate, and dichromic acid.