Method for forming a zinc-colored coating by anodizing and zinc-colored plate using the same

Abstract

To provide a zinc-colored coating that allows for the formation of an oxide film of a thickness exhibiting interference colors on the zinc surface by optimizing the anodic oxidation conditions. [Solution] An anodic electrification system comprising a cathode 30 connected to the negative terminal of a DC power supply 50 and an anode 40 connected to the positive terminal of the DC power supply 50, wherein a sample to be colored is placed on the anode 40, and the cathode 30 and anode 40 are immersed in an electrolyte 20, wherein the DC voltage applied to the cathode 30 and anode 40 is within a range in which an oxide film by anodic electrification can stably grow on the surface of the sample to be colored, the electrolyte 20 is an organic solvent in which a solute is dissolved in an amount that does not corrode the zinc sample to be colored, and by adjusting the DC voltage applied to the cathode 30 and anode 40, an anodic oxide film of a thickness that generates interference colors is formed on the zinc sample located on the anode 40.

Description

Technical Field

[0001] The present invention relates to a method for forming a zinc-colored film by anodic oxidation and a zinc-colored plate using the same.

Background Art

[0002] Zinc is plated on the surface of steel materials to become galvanized steel. Galvanized steel can exhibit high corrosion resistance due to its sacrificial anticorrosion effect and protective film effect, and is mainly used in outdoor atmospheric corrosion environments. For the above reasons, although galvanized steel is exposed to the eyes of many people outdoors, in most cases it is used with the plated surface as it is, and there is no option other than the silver appearance. It is considered that the functionality of zinc plating can be further enhanced by coloring the zinc plating surface and imparting design properties.

[0003] On the other hand, there is an anodic oxidation method as a technique for coloring aluminum-based materials, titanium-based materials, magnesium-based materials, stainless steel, etc. [for example, Non-Patent Documents 1 and 2]. The color obtained by the anodic oxidation method is the interference effect of light due to the growth of the transparent oxide film, and the thickness of the oxide film on the above-mentioned metal materials needs to fall within an integer multiple (up to about 3 times) or one over an integer multiple (up to about 1 / 3) of the visible light wavelength according to the Bragg reflection condition. Regarding zinc, there have been many reports on anodic oxidation since long ago, but the purpose has not been coloring, and most of them have been aimed at improving the characteristics of alkaline batteries [Non-Patent Document 3]. The colors obtained when zinc is anodized are only two types, black and white [Non-Patent Document 4]. There are Patent Documents 1 and 2 as report examples of producing zinc oxide films other than black and white by anodic oxidation, but there is still no example of coloring treatment over the entire range of RGB. In other words, anodizing is a known method for coloring the surface of zinc to give it a decorative appearance [see Patent Documents 1 and 2]. However, Patent Documents 1 and 2 limit the range of coloring to dark colors ranging from bluish-black to black, and the plating solution contains heavy metal ions such as Co (cobalt), Ni (nickel), and Mo (molybdenum), which presents the problem of burdensome wastewater treatment. Furthermore, Patent Documents 3-5 disclose examples of anodizing for aluminum alloys. However, regarding zinc alloys, this is merely an armchair invention stating that it can be applied as a substitute alloy for aluminum alloys, and it is not the case that the anodizing treatment for aluminum alloys can be directly applied to zinc alloys to achieve coloring. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Special Publication No. 61-38276 [Patent Document 2] Special Publication No. 61-60915 [Patent Document 3] WO2020 / 166240, paragraph numbers 0026, 0062 [Patent Document 4] Japanese Patent Publication No. 2020 / 97794, paragraph numbers 0040, 0146 [Patent Document 5] Special Publication No. 2017 / 525601, Paragraph Number 0009 [Non-patent literature]

[0005] [Non-Patent Document 1] Keisuke Kino, Anodizing and Electrolytic Coloring of Titanium Materials, Surface Technology, Vol. 73, No. 1, pp. 38-40 (2022) [Non-Patent Document 2] Yoshio Shoji, Coloring Method for Stainless Steel, Metal Surface Technology, Vol. 9, No. 1, pp. 29-32 (1958) [Non-Patent Document 3] Yasuhide Yamaguchi, Masatoshi Yamazaki, Sachio Yoshihara, and Takashi Shirakashi; Electrochemistry and Industrial Physical Chemistry, Vol. 64, No. 5, pp. 373-377 (1996) [Non-Patent Document 4] RW Powers, MW Breiter, Journal of the Electrochemical Society, Vol. 116, pp. 719-729 (1969) [Overview of the project] [Problems that the invention aims to solve]

[0006] In anodic oxidation, only black or white oxide films can be formed on the zinc surface, and the conditions for obtaining the so-called seven colors of the rainbow, which belong to the visible light region, have not been clarified. This is thought to be because, in anodic oxidation in aqueous solution, the oxide film of zinc grows too much and falls outside the region that exhibits interference colors (approximately 90 nm to 400 nm, but considering up to m=2 under Bragg's reflection conditions, i.e., up to secondary interference).

[0007] The present invention solves the problems of the above-mentioned prior art and aims to provide a zinc-colored coating that allows for the formation of an oxide film of a thickness exhibiting interference colors on the zinc surface by optimizing the anodic oxidation conditions, thereby enabling coloring of the zinc surface. [Means for solving the problem]

[0008] The inventors of the present invention conceived of the present invention by considering whether it would be possible to color the surface of zinc by forming an oxide film of a thickness that exhibits interference colors on the zinc surface. Here, anodizing is an electrochemical process that forms and grows an oxide film on a metal surface. It is a method in which the target metal is placed as the anode and a counter material as the cathode in an electrolyte solution, and a voltage or current is applied between the two electrodes.

[0009] [1] The formation of a zinc colored film by anodizing according to the present invention is, for example, as shown in Figure 1, an anodic electrification system comprising a cathode 30 to which the negative electrode of a DC power supply 50 is connected, and an anode 40 to which the positive electrode of a DC power supply 50 is connected, wherein the sample to be colored is placed on the anode 40, and the cathode 30 and anode 40 are immersed in an electrolyte 20, wherein the DC voltage applied to the cathode 30 and anode 40 is within a range in which the oxide film by anodic electrification can stably grow on the surface of the sample to be colored, the electrolyte 20 is an organic solvent in which a solute is dissolved in an amount that does not corrode the zinc sample to be colored, and by adjusting the DC voltage applied to the cathode 30 and anode 40, an anodic oxide film of a thickness that generates interference colors is formed on the zinc sample located on the anode 40.

[0010] [2] In the formation of a zinc-colored coating by anodic oxidation of the present invention [1], preferably the electrolyte 20 is a solution containing a mixture of ethanol, methanol, isopropanol, ethylene glycol, γ-butyrolactone as an organic solvent, at least one alkali salt selected from the group consisting of sodium hydroxide, calcium hydroxide, potassium hydroxide, magnesium hydroxide, aluminum hydroxide, ammonium hydroxide, lithium hydroxide, and beryllium hydroxide as a solute, and distilled water in a volume % of 50% or less. [3] In the formation of a zinc-colored coating by anodic oxidation of the present invention [2], preferably the electrical conductivity of the electrolyte is 100 [μS / cm] or more and 6000 [μS / cm] or less. [4] In the formation of a zinc-colored coating by anodizing according to the present invention [2], preferably the DC voltage applied to the DC power supply 50 is in the range of 0.5V to 500V, more preferably in the range of 10V to 100V, and most preferably in the range of 20V to 50V. [5] In the formation of a zinc-colored coating by anodic oxidation of the present invention [1], the temperature of the solution is preferably -15°C to 200°C (from the melting point to the boiling point of ethylene glycol), and more preferably 10°C to 50°C. [6] In the formation of the zinc-colored film by anodic oxidation of the present invention [2], preferably, the sample to be colored may be any one of pure zinc, zinc-plated steel, Zn-Al plated steel, Zn-Al-Mg plated steel, and Zn-Ni plated steel.

[0011] [7] The zinc-colored plate by anodic oxidation of the present invention is, for example, as shown in FIG. 2, a zinc-colored plate on which an anodic oxide film with a film thickness of 120 nm or more and 280 nm or less is formed.

Advantages of the Invention

[0012] According to the method for forming a zinc-colored film by anodic oxidation of the present invention, by using an organic solvent in the solution, the electrical conductivity of the solution can be appropriately controlled, and the growth of the oxide film during anodic oxidation can be controlled within the film thickness range where interference colors occur. The applied voltage and the temperature of the solution are also factors that affect the control of the film thickness range. According to the method for forming a zinc-colored film by anodic oxidation of the present invention, colors (red, orange, yellow, green, blue-green, blue, purple) in the visible light region can be developed on the zinc surface in addition to the silver color as-plated and the black and white colors by conventional anodic oxidation, enhancing the designability of zinc and zinc-plated steel.

Brief Description of the Drawings

[0013] [Figure 1] It is a diagram for explaining the principle of anodic oxidation treatment. [Figure 2] It is a surface photograph of a sample when anodic oxidation is performed at room temperature using a solution obtained by adding calcium hydroxide powder to ethylene glycol as a solution for zinc-colored film treatment by anodic oxidation showing an embodiment of the present invention. [Figure 3] It is a surface photograph of a sample when anodic oxidation is performed at 30 °C using a solution obtained by adding calcium hydroxide powder to ethylene glycol as a solution showing an embodiment of the present invention. [Figure 4] It is a surface photograph of a sample when anodic oxidation is performed at 40 °C using a solution obtained by adding calcium hydroxide powder to ethylene glycol as a solution showing an embodiment and a comparative example of the present invention. [Figure 5]This is a comparative example, showing a photograph of the sample surface after anodic oxidation at 50°C using a solution of ethylene glycol with added calcium hydroxide powder. [Figure 6] This is a comparative example, showing a photograph of the sample surface after anodic oxidation was performed at room temperature and 100V using ethylene glycol as the solution. [Figure 7] This is a comparative example, showing a photograph of the sample surface after anodic oxidation at room temperature and 80V using a solution of ethylene glycol with distilled water added. [Figure 8] This is a comparative example, showing a photograph of the sample surface after anodic oxidation at room temperature using a solution of ethylene glycol with saturated calcium hydroxide added. [Figure 9] This is a comparative example, showing a photograph of the sample surface after anodic oxidation at room temperature using a saturated calcium hydroxide solution. [Figure 10] This is a photograph of the sample surface after anodic oxidation at room temperature using a solution of ethylene glycol with added sodium hydroxide powder. [Figure 11] This figure shows the relationship between applied voltage and hue when anodizing is performed at room temperature using a solution of ethylene glycol with added calcium hydroxide powder. [Figure 12] This is a schematic diagram of Bragg's reflection conditions. [Figure 13] This figure shows the relationship between applied voltage and hue when anodizing is performed at room temperature using a solution of ethylene glycol with added sodium hydroxide powder. [Modes for carrying out the invention]

[0014] Figure 1 is a diagram illustrating the principle of anodic oxidation. In the diagram, the electrolytic cell 10 contains an electrolyte 20, and the cathode 30 and anode 40 are immersed in the electrolyte 20. The cathode 30 has a portion that contacts the electrolyte 20 and is provided with a wire connected to the negative terminal of the DC power supply 50. The anode 40 is provided with a wire connected to the positive terminal of the DC power supply 50. The DC power supply 50 supplies a DC current between the cathode 30 and the anode 40, and is connected to an ammeter 60 and a voltmeter 70.

[0015] The process of anodizing using the anode electrification system configured in this way is as follows: The DC power supply 50 draws electrons from the anode 40 and has the driving force to move ions in the electrolyte 20, causing a chemical reaction to occur simultaneously in both the cathode 30 and the anode 40. When electrons are taken from the metallic zinc of the anode, Zn 2+ This forms a cation, which then dissolves into the electrolyte 20. In the case of anodic oxidation, the Zn produced in the reaction of equation (1) dissolves into the electrolyte 20. 2+ It forms an anodic oxide film while moving within the film and dissolving in the electrolyte. Zn → Zn 2+ +2e (1) When the electrolyte contains NaOH, the reaction that forms the anodic oxide film produces sodium tetrahydroxozincate Na2[Zn(OH)4] as shown in equation (2), which is either incorporated into the film or dissolved in the electrolyte. Zn 2+ +2NaOH+2H2O→Na2[Zn(OH)4]+H2(2)

[0016] The processing conditions for an anodic oxide coating to become a white film require sufficient oxygen ions relative to zinc ions. By using a low alkali concentration (less than 0.3 N) and a high applied voltage (20 V or higher), a white zinc oxide film with a stoichiometric composition can be grown. On the other hand, an anodized coating becomes a black film when ZnOx contains an excess of metallic zinc where x is less than 0.8, which absorbs visible light and turns black. The first processing condition for a black film is when the electrolysis voltage is low, such as 5V or less, and although zinc is electrolytically oxidized, the oxidation is insufficient and oxygen is deficient in stoichiometric ratio. The second processing condition for a black film is when the alkali concentration is high (for example, 0.5N or higher), and even with a high electrolysis voltage, the chemical dissolution of zinc or zinc oxide takes precedence, so the zinc is not completely oxidized and zinc atoms are generated within the crystal. See Yasuhide Yamaguchi, Masatoshi Yamazaki, Sachio Yoshihara, and Takashi Shirakashi, "Electrolytic Conditions and Film Formation Process in the Anodization of Zinc," Electrochemistry, Vol. 64, p. 373 (1996).

[0017] Therefore, in the anodic oxidation of the present invention, in order to control the growth of the oxide film during anodic oxidation to a film thickness range in which interference colors occur, it is necessary to control the film thickness to be thinner than the white or black film mentioned above, and to find conditions in which the oxide film growth becomes so thin that it cannot be seen with the naked eye (or no oxide film is formed on the surface). The conditions investigated in the anodic oxidation process of this invention are (a) the solution, (b) the applied voltage, (c) the solution temperature, and (d) the zinc material. Details of each condition are shown below. (a) Solution The solution used was the same as that used in electrolyte solution 20, and consisted of ethylene glycol (Fujifilm Wako Pure Chemical Industries, reagent grade) as an organic solvent, calcium hydroxide (Fujifilm Wako Pure Chemical Industries, reagent grade) and sodium hydroxide (Fujifilm Wako Pure Chemical Industries, reagent grade) as solutes, and distilled water as a solvent. A mixture of these was used as the test solution. Furthermore, the organic solvent is not limited to ethylene glycol; ethanol, methanol, isopropanol, or ethylene glycol may also be used. Alternatively, a mixture of alkali salts such as sodium hydroxide, calcium hydroxide, and potassium hydroxide, and distilled water with a volume percentage of 50% or less may be used as the solute.

[0018] (i) DC applied voltage A DC power supply (PK-80M, Matsusada Precision) was used for the DC power supply 50. In this embodiment, the applied DC voltage was between 10V and 100V due to the output voltage of the DC power supply, but it is not limited to this range and may be between 0.5V and 500V. (c) As for the solution temperature, the temperature of the electrolyte 20 was set to room temperature (25°C) to 50°C, but it is not limited to this, and may be -15°C to 200°C (from the melting point to the boiling point of ethylene glycol). (e) As the zinc material to be colored, pure zinc plate (99.2%, Niraco Co., Ltd.) was used, but it is not limited to this, and pure zinc, galvanized steel, Zn-Al plated steel, Zn-Al-Mg plated steel, or Zn-Ni plated steel may also be used. In this specification, the upper and lower limits are considered to be within a numerical range unless otherwise explicitly stated. That is, the upper limit to the lower limit means greater than or equal to the lower limit and less than or equal to the upper limit. [Examples]

[0019] In all of the following anodizing experiments, a pure zinc plate (99.2%, Niraco Co., Ltd.) was used as the sample, and a platinum wire was used as the counter electrode.

[0020] Figure 2 shows a photograph of the sample surface when anodizing was performed at room temperature using a solution of ethylene glycol with calcium hydroxide powder added as the solution for treating a zinc colored film by anodizing, as in one embodiment of the present invention. The mixing ratio of ethylene glycol to calcium hydroxide powder was 500 mL of ethylene glycol to 5 g of calcium hydroxide. Discoloration of the sample surface was observed at applied voltages from 10 V to 100 V, and clear chromatic colors were seen from 20 V onwards (hereafter, colors other than white and black are defined as chromatic colors). The chromatic colors observed here and those shown in Figures 3 to 10 are thought to be light interference colors produced by the growth of the oxide film on the zinc surface due to anodizing.

[0021] Figure 3 shows a photograph of the sample surface when anodizing was performed at 30°C using a solution of ethylene glycol with calcium hydroxide powder added as the basis for one embodiment of the present invention. The mixing ratio of ethylene glycol to calcium hydroxide powder was 500 mL of ethylene glycol to 5 g of calcium hydroxide. As with the procedure performed at room temperature, discoloration of the sample surface was observed at applied voltages from 10 V to 100 V, and a clear chromatic color was observed from 30 V onwards.

[0022] Figure 4 shows one embodiment and a comparative example of the present invention. The image shows the surface of a sample after anodic oxidation at 40°C using a solution of ethylene glycol with calcium hydroxide powder added. The mixing ratio of ethylene glycol to calcium hydroxide powder was 500 mL of ethylene glycol to 5 g of calcium hydroxide. Discoloration of the sample surface was observed at applied voltages from 10 V to 100 V. However, no clear chromatic color was observed at 10 V and 100 V, and a black oxide film was formed at 100 V. On the other hand, yellow coloration was observed at 50 V.

[0023] Figure 5 shows a comparative example, which is a photograph of the sample surface after anodic oxidation at 50°C using a solution of ethylene glycol with added calcium hydroxide powder. The mixing ratio of ethylene glycol to calcium hydroxide powder was 500 mL of ethylene glycol to 5 g of calcium hydroxide. Discoloration of the sample surface was observed at applied voltages from 10 V to 100 V, but no chromatic color was observed at any voltage, and the formation of a black oxide film was observed.

[0024] Figure 6 shows a comparative example, which is a photograph of the sample surface after anodic oxidation using ethylene glycol as the solution at room temperature and 100V. No discoloration of the sample surface due to anodic oxidation was observed.

[0025] Figure 7 shows a comparative example, which is a photograph of the sample surface after anodic oxidation at room temperature and 80V using a solution of ethylene glycol with distilled water added. The mixing ratio of ethylene glycol to distilled water was 490 mL of ethylene glycol to 10 mL of distilled water. No discoloration of the sample surface was observed due to anodic oxidation.

[0026] Figure 8 shows a comparative example, which is a photograph of the sample surface after anodic oxidation at room temperature using a solution of ethylene glycol with saturated calcium hydroxide added. The mixing ratio of ethylene glycol to saturated calcium hydroxide solution was 490 mL of ethylene glycol to 10 mL of saturated calcium hydroxide solution. At 10 V, no discoloration of the sample surface due to anodic oxidation was observed, and at 50 V and 80 V, discoloration of the sample surface was observed, but no chromatic color was observed.

[0027] Figure 9 shows a comparative example, which is a photograph of the sample surface after anodic oxidation at room temperature using a saturated calcium hydroxide solution. Discoloration of the sample surface was observed under both 20V and 50V conditions, but a black oxide film was formed at 20V and a white oxide film at 50V, both of which were the same color as the oxide film of zinc reported previously.

[0028] Figure 10 shows a photograph of the sample surface after anodic oxidation at room temperature using a solution of ethylene glycol with added sodium hydroxide powder. The mixing ratio of ethylene glycol to sodium hydroxide powder was 500 mL of ethylene glycol to 5 g of sodium hydroxide powder. No discoloration was observed on the sample surface at an applied voltage of 10 V. Discoloration was observed on the sample surface from 20 V to 100 V, and clear chromatic coloration was observed from 40 V onwards. Compared to Figure 2, the same color was not produced even with the same applied voltage (for example, at 80V, ethylene glycol + calcium hydroxide produced purple, while ethylene glycol + sodium hydroxide produced yellow), clearly indicating that the color produced is influenced by the solute added to the ethylene glycol.

[0029] To investigate the discoloration and appearance of chromatic colors on the sample surface, the electrical conductivity of each solution was measured using an electrical conductivity meter (LAQUAtwin, HORIBA). First, the electrical conductivity of ethylene glycol was less than 1 μS / cm (below the detection limit). For ethylene glycol with saturated calcium hydroxide solution added, the conductivity was 18 μS / cm; for ethylene glycol with calcium hydroxide added, it was 647 μS / cm; for ethylene glycol with sodium hydroxide added, it was 1800 μS / cm; and for saturated calcium hydroxide solution, it was 6790 μS / cm. Here, the calcium ion concentration of ethylene glycol with saturated calcium hydroxide solution added is 0.023 mol / L, since saturated calcium hydroxide solution is 0.17 wt%, and when the total volume is adjusted to 500 mL, it becomes 0.023 mol / L. The calcium ion concentration of ethylene glycol with calcium hydroxide added is 0.135 mol / L. As shown in Figures 6 and 8, no surface change was observed after anodizing with ethylene glycol and ethylene glycol with saturated calcium hydroxide solution. Under the conditions using saturated calcium hydroxide solution, only black and white surfaces were obtained (no chromatic surfaces were obtained). Therefore, it became clear that within the processing temperature and applied voltage range of this embodiment, it is necessary to control the electrical conductivity of the solution to preferably 100 [μS / cm] to 6000 [μS / cm], and more preferably 500 [μS / cm] to 3000 [μS / cm].

[0030] To quantitatively evaluate the relationship between the obtained color, the solution, and the applied voltage, the obtained color was quantified as H (Hue). The following analysis was performed for quantification. 1) Five points were randomly selected from the photographs of the sample surface, and the RGB values ​​of those points were determined using Photoshop (Adobe). 2) The obtained RGB values ​​were normalized by dividing them by their respective maximum values ​​(255). 3) The H value for each point was calculated using normalized RGB values. The method for calculating H is as follows: 3-a) Among the normalized RGB values ​​(hereinafter referred to as positive R, positive G, and positive B), the largest value is M and the smallest value is m. 3-i) If positive R = M, then H = 60 × ((positive G - positive B) / (Mm)) If positive G = M, then H = 60 × ((positive B - positive R) / (Mm)) + 120 If positive B = M, then H = 60 × ((positive R - positive G) / (Mm)) + 240 Here, the RGB (Red-Green-Blue) color system represents a standard method of representing colors when handling shapes, images, and videos on computers. It is a combination of three colors, taking the first letters of Red, Green, and Blue. With RGB, the more colors you mix, the brighter the color becomes. It is also called "additive mixing" or "additive color mixing." Hue is based on the Munsell color system (see JIS Z 8721) and represents color using three components: Hue, Saturation, and Value. It is one of the HSV color systems, where Hue takes values ​​from 0 to 360, with 0 being red, 120 being green, 240 being blue, and 360 being red again. Saturation takes values ​​from 0 to 1, with 0 being gray (a colorless color from white to black) and 1 being a vivid color. Value (or intensity) also takes values ​​from 0 to 1, with 0 being black and 1 being white. RGB and HSV can be converted to and from each other using a program such as GMIP.

[0031] Figure 11 shows the relationship between applied voltage and hue when anodizing was performed at room temperature using a solution of ethylene glycol with added calcium hydroxide powder. The mixing ratio of ethylene glycol to calcium hydroxide powder was 500 mL of ethylene glycol to 5 g of calcium hydroxide. A clear linear relationship was obtained between applied voltage and hue in the ranges of 20V to 50V and 60V to 100V. The result for 60V appears to deviate from the linear relationship at first glance, but since the hue cycles every 360, adding 360 to the hue for 60V places it on the linear relationship between 70V and 100V. Therefore, a linear relationship between voltage and hue was obtained in the range of 60V to 100V.

[0032] As shown in Figure 12, if we consider a thin, transparent zinc oxide film on a zinc substrate and light is incident at an angle θ, then according to Bragg's reflection condition, the path difference between the light reflected on the zinc oxide film and the light reflected on the zinc substrate can be expressed as mλ = 2ndsinθ, where d is the thickness of the zinc oxide film. Here, m is the order of reflection, λ is the wavelength of light, n is the refractive index of the zinc oxide film, d is the thickness of the zinc oxide film, and θ is the angle of incidence of light, which is equal to the angle of reflection. The order of reflection is expressed as a natural number greater than or equal to 1, with m=1 being called first-order interference and m=2 being called second-order interference. As m increases, the thickness of the oxide film increases, but mixing of reflected light, absorption of light by the oxide film, and phase changes of light become more likely, making it difficult to produce chromatic colors. In other words, the appearance of interference colors of light due to metal oxide films is almost always first-order or second-order interference.

[0033] In Figure 11, it is thought that a thinner oxide film is formed at lower applied voltages, so of the two linear relationships, the lower potential side is thought to represent primary interference, and the higher potential side represents secondary interference. Furthermore, it is known that the refractive index n of a metal oxide film is approximately 2, and using this value, the thickness of the oxide film formed on the zinc surface by anodizing is estimated to be approximately 120 nm to 280 nm in the range of 20 V to 100 V.

[0034] Figure 13 shows the relationship between applied voltage and hue when anodizing was performed at room temperature using a solution of ethylene glycol with added sodium hydroxide powder. Here, a single linear relationship was obtained in the range of 20V to 100V. Since the electrical conductivity of the solution with added calcium hydroxide powder and the solution with added sodium hydroxide differed, it is thought that the thickness of the zinc oxide film formed changed, resulting in a single linear relationship. In this case, it is thought that only primary interference occurred, and the thickness of the oxide film formed on the zinc surface can be estimated to be approximately 120nm to 190nm in the range of 20V to 100V.

[0035] In the above embodiment, a solution of ethylene glycol with sodium hydroxide powder was used, and anodizing was performed at room temperature with an applied voltage within a predetermined range. However, the present invention is not limited thereto. For example, the solution may be methanol, isopropanol, ethylene glycol, γ-butyrolactone, etc., with an alkali salt powder such as calcium hydroxide or potassium hydroxide added. The alkali salt powder may also contain a mixture of distilled water at a volume percentage of 50% or less. [Industrial applicability]

[0036] According to the formation of a zinc-colored coating by anodizing according to the present invention, in addition to the silver color of the plated surface and the black and white colors obtained by conventional anodizing, it is possible to produce colors in the visible light range (red, orange, yellow, green, blue-green, blue, purple) on the zinc surface, thereby enhancing the design of zinc and galvanized steel, and thus improving the aesthetics of zinc-colored plates. [Explanation of Symbols]

[0037] 10 Electrolytic cell 20. Electrolyte (organic solvent + conductive solute) 30 cathode 40 Anode (Zn) 50 DC power supply 60 ammeter 70 Voltmeter

Claims

1. The cathode to which the negative terminal of the DC power supply is connected, The anode to which the positive terminal of the DC power supply is connected, and the sample to be colored is placed on the anode, In an anodic electrification system comprising an electrolyte in which the cathode and anode are immersed, The DC voltage applied between the cathode and anode is within a range that allows the oxide film produced by anodic electrification to grow stably on the surface of the sample to be colored. The electrolyte is an organic solvent in which a solute is dissolved in such an amount that it does not corrode the zinc sample to be colored. By adjusting the DC voltage applied between the cathode and anode, an anodic oxide film of a thickness that generates interference colors is formed on the zinc surface, which is the sample to be colored, located at the anode. A method for forming a zinc-colored coating by anodizing.

2. The aforementioned electrolyte is Organic solvents include ethanol, methanol, isopropanol, ethylene glycol, γ-butyrolactone, The solution contains a mixture of at least one alkali salt selected from the group consisting of sodium hydroxide, calcium hydroxide, potassium hydroxide, magnesium hydroxide, aluminum hydroxide, ammonium hydroxide, lithium hydroxide, and beryllium hydroxide, and distilled water in a volume percentage of 50% or less. A method for forming a zinc-colored coating by anodizing according to claim 1.

3. The electrical conductivity of the electrolyte is 100 [μS / cm] or more and 6000 [μS / cm]. The method for forming a zinc-colored coating by anodizing according to claim 2.

4. The method for forming a zinc-colored coating by anodizing according to claim 2, wherein the DC voltage of the DC power supply is in the range of 0.5V to 500V.

5. The solution temperature ranges from -15°C to 200°C. The method for forming a zinc-colored coating by anodizing according to claim 2.

6. The sample to be colored is one of the following: pure zinc, galvanized steel, Zn-Al plated steel, Zn-Al-Mg plated steel, or Zn-Ni plated steel. A method for forming a zinc-colored coating by anodizing according to claim 1.

7. A zinc-colored plate having an anodic oxide film with a thickness of 120 nm to 280 nm formed on it.

Images