JPH0230391B2 - SUTENRESUKONOCHAKUSHOKUHANNOTEISHIHOHO - Google Patents

Description

[Detailed description of the invention]

The present invention is a method for coloring reaction of stainless steel in order to stop the coloring reaction in a coloring liquid during the coloring process of stainless steel, and to obtain colored stainless steel with little color difference and excellent reproducibility with respect to a certain target color. This relates to a method of stopping the system. Because colored stainless steel has a luxurious appearance, it has come to be widely used in furniture, daily necessities, and construction materials in recent years, and coloring technology has progressed rapidly and numerous patents have been published. It's starting to look like this. Among them, the production of colored stainless steel by JP-A No. 48-11243 ``Processing of Chromium Alloys'' and JP-A No. 49-21339 ``Processing of Chromium Alloys'' has achieved a desired color tone with good reproducibility and durability. Materials with good abrasion properties began to be produced industrially. The content of the above invention is that a mixed aqueous solution consisting of chromic acid and sulfuric acid as a coloring liquid (hereinafter referred to as a coloring liquid)
Stainless steel is immersed in the liquid, and the oxidation reaction on the stainless steel surface that occurs at the interface between the stainless steel and the colored liquid and the potential difference between a reference electrode (a saturated aqueous electrode or a platinum electrode) are measured. The coloring potential-coloring time curve shown in Fig. 1 is used to obtain the desired coloring tone from the inflection point A to its extension point B.
The desired coloring tone is determined by the degree of change B-A, and the stainless steel is immediately taken out of the coloring solution once the desired coloring potential, point B, is reached. However, in order to completely stop the coloring reaction of stainless steel, it is necessary to remove the colored liquid from the surface of the stainless steel and to lower the surface temperature of the stainless steel. For this reason, the current common method for stopping the coloring reaction is to wash the stainless steel with water immediately after removing it from the coloring liquid to remove the coloring liquid on the surface of the stainless steel and lower the surface temperature. However, with this method, stainless steel It has become difficult to obtain a constant color tone because considerable temporal and environmental variations occur from the time the color is removed from the coloring liquid until the coloring reaction stops. Furthermore, in JP-A-49-21339, a method similar to that described in JP-A-48-11243 is described in which a direct current is applied so that the stainless steel that is to be colored becomes an anode during the coloring process. There is also a method to obtain a more accurate index of the potential difference by measuring the potential difference between the stainless steel and the reference electrode and stopping the DC electrolysis when the desired potential difference is reached. The coloring reaction proceeds while the steel is immersed in the coloring liquid. The present inventors have conducted extensive research in order to solve the above-mentioned problems with the conventional coloring control method in which the stainless steel is immediately removed from the coloring solution to stop the coloring reaction after coloring to the desired color tone. As a result, as a coloring control method in which temporal and environmental variations from the end of coloring until the coloring reaction completely stops have no effect on the reproducibility of the colored tone, stainless steel that stops the coloring reaction in the coloring liquid has been developed. They discovered a coloring control method and completed the present invention. The gist of the present invention relates to a method for stopping a coloring reaction in which the coloring reaction is immediately stopped in a coloring solution after coloring is completed in order to improve the reproducibility of the color tone of stainless steel. The coloring reaction is an anodic reaction (M
→M ^Z+ +Ze ^- ) and cathodic reaction of film formation (HCrO ₄ ^- +7H ⁺ +
3e ^- →Cr ³⁺ +4H ₂ O) and hydrolysis reaction (M ^Z+ +Cr ³⁺ +H ₂ O→MCrO+
2H ⁺ ) occurs simultaneously, forming a colored film. To stop the coloring reaction, external energy is applied to the stainless steel that has been polarized at the anode as the coloring reaction progresses, and the stainless steel is polarized at the cathode and electrically neutralized. As soon as the set potential difference is reached, a metal less base than stainless steel, such as Pb, is added to the coloring solution.
By electrically shorting Fe, Mo, etc., stainless steel is instantaneously polarized as a cathode, forcing the coloring reaction to shift from an oxidation reaction to a reduction reaction. In particular, since Pb is usually used in the lining of the coloring tank, the entire coloring tank can be used as a Pb counter electrode, so there is no need to install a counter electrode in the coloring liquid. As described above, according to the present invention, the coloring reaction of stainless steel is stopped at the same time as the coloring is completed, and a color tone with a small color difference and excellent reproducibility with respect to a fixed target color can be obtained. The scope of the present invention is applicable to austenitic stainless steel, ferritic stainless steel, and stainless steel with various surface finishes (BA finish, HL finish), and the coloring reaction can be stopped by this treatment method. Next, the present invention will be explained in detail. Chromic anhydride (250g/), sulfuric acid (500g/)
A mixed aqueous solution (colored liquid) containing both of the above was heated to 80°C, and a platinum reference electrode and a Pb counter electrode were placed in this colored liquid, and the stainless steel was immersed therein for coloring. It is preferable that this counter electrode is a metal that is base to stainless steel and is insoluble in the coloring liquid, but even if it is not insoluble, it is possible to do so by immersing it in the coloring liquid only when the coloring reaction is stopped. Yes, Pb,
Either Fe or Mo may be used. First, we measured the oxidation reaction on the stainless steel surface and the potential difference between the platinum reference electrode.
As soon as the desired coloring potential was reached, the stainless steel was electrically short-circuited with the Pb counter electrode to polarize the stainless steel as a cathode, and the stainless steel in this state was taken out of the coloring solution and washed with water. After washing with water, the short circuit between the stainless steel and the Pb counter electrode was removed, hardening treatment was performed, and the material was washed with water and dried. The color tone was measured using a color analyzer [manufactured by Hitachi, Ltd., Model 307 Light Diffuser, BaSO ₄ white plate standard] in accordance with the conditions of JIS Z 8722. Examples according to the present invention are shown below. The sample material is SUS304 stainless steel HL material (1.5mm
thickness), and the sample size was set at three levels ((1)100
×100mm, (2)300×300mm, (3)700×700mm) Extracted Pb
Lined coloring tank [300W×1000H×
1200L (mm)] under the above-mentioned coloring treatment conditions. In order to obtain a green color tone, B-
The coloring potential difference of A was set to 19.5 mV, and at the same time as the desired coloring potential difference was reached, an electrical short circuit was made with a clip to the coloring bath, and the stainless steel was instantaneously polarized to the cathode. FIG. 2 shows the change in the coloring potential-coloring time curve at this point. colored potential difference
When B'-A' reached 19.5 mV and a short circuit was made to the color bath, the potential difference between the stainless steel and platinum reference electrodes instantly dropped to the cathode side. Therefore, as soon as the coloring potential reached 19.5 mV, the stainless steel was short-circuited to the coloring bath, and in this state, the stainless steel was taken out from the coloring solution, washed with water, and then hardened. On the other hand, in order to compare the treatment effect of the present invention with the conventional method, coloring treatment was carried out at a coloring potential difference of 19.5 mV, and as soon as the desired potential difference was reached, the stainless steel was taken out from the coloring solution, washed with water, and then hardened. Ta. Figure 3 shows the results of measuring the color difference between the three levels of colorants for the treated material according to the present invention and the conventionally treated material (comparative material) using a color analyzer as a chromaticity index characteristic curve diagram of a value and b value. show.
Arrows in the figure indicate the progress of the coloring reaction.

[Table] As a result, the coloring reaction progresses as the sample size increases for materials treated using the conventional method. This is because as the sample size increases, the heat capacity of stainless steel increases, so the coloring reaction progresses until the stainless steel is removed from the coloring liquid and the coloring reaction is stopped. On the other hand, the treated material according to the present invention showed almost the same position for each sample size, indicating that the coloring reaction was stopped and the coloring reproducibility was improved by the treatment method of the present invention. Based on the results of the above examples, we investigated (1) cessation of coloring reaction in colored tones other than green, and (2) cessation of coloring reaction when the surface finish of stainless steel was changed from HL material to BA material. This will be explained in the following example. The coloring conditions are the same as those in the previous example. The test materials are HL material [1.5×100×100 (mm)] and
BA material [0.4 x 100 x 100 (mm)] was used. The coloring tone is the coloring potential difference B-A in Figure 1 of 6.0 mV and 12.0
mV, 15.0 mV, and 19.5 mV, and 10 sheets each were colored in four colors: blue, gold, red, and green. The coloring reaction termination treatment was carried out in the same way as in the previous example, when the desired coloring potential difference B''-A'' was reached, the stainless steel was short-circuited with the coloring bath using a clip, and the stainless steel was taken out from the coloring solution in that state. Further, a treated material taken out from the colored solution at the same time as the desired potential difference was reached at the coloring potential difference B-A in FIG. 1 was used as a comparative material. The color tone of the treated materials was measured using the color analyzer mentioned above, and the measurement results were expressed as L value, a value, and b value.
Expressed as a value. Coloring treatment is 10 times for each tone.
Repeat the process several times and measure the L, a, and b values.
The standard deviation value of each of the L, a, and b values was determined and used as an index of color difference variation. The results are shown in the table below.

[Table] As shown in the table, in all color tones, the treated material according to the present invention has smaller standard deviations of L, a, and b values than the conventionally processed material, indicating that the variation in color difference is small. In this way, in the method of the present invention, the target coloring tone,
Even if the surface finish of the stainless steel differs, the coloring reproducibility is improved. To summarize the present invention as described above, when the potential difference between the stainless steel in the coloring solution and the platinum reference electrode reaches the desired potential difference B''-A'', the stainless steel and the coloring tank (Pb lining) are connected. When the stainless steel is instantaneously polarized to the cathode by an electrical short circuit, and when the stainless steel is taken out of the coloring liquid in that state, the coloring reaction stops and the color tone is better reproducible than that produced by conventional coloring processes. A colored tone is obtained. And the treatment method according to the invention can be carried out regardless of the color toning agent and the surface finishing agent for stainless steel. The present invention not only requires no equipment or energy consumption, but is also extremely easy to manufacture. This method stops the coloring reaction and provides better reproducibility of color tone than conventional methods.

[Brief explanation of drawings]

Figure 1 is a coloring potential-coloring time curve diagram, Figure 2 is a coloring potential curve diagram for stopping the coloring reaction according to the present invention, and Figure 3 is a chromatographic diagram of the color measurement results of the treated material according to the present invention and the conventional method. FIG. A...Inflection point, B...Coloring end point, B-A...
Coloring potential difference, A′...inflection point, B′...coloring end point,
B′−A′……Coloring potential difference.

Claims (1)

[Claims] 1. In a mixed aqueous solution of chromic acid and sulfuric acid, a colored stainless steel is electrically short-circuited with a metal that is more base than the stainless steel, and the stainless steel is polarized as a cathode to cause a coloring reaction. How to stop. 2. The method for stopping a coloring reaction of stainless steel according to claim 1, wherein the base metal is Pb. 3. The method for stopping a coloring reaction of stainless steel according to claim 1, wherein the base metal is Fe.