Method for producing colored metal product

Abstract

[Problem] To provide a method whereby it is possible to easily color a metal surface. [Solution] A method for producing a metal product of titanium or of a titanium alloy having a colored surface, the method including: a grinding step in which the surface of the titanium or titanium alloy is ground from one or more directions using a disk grinder or a grindstone; and a coloring step in which the positive electrode of a power supply is connected to the titanium or titanium alloy, the negative electrode is connected to a liquid-absorbing member holding an electrolytic solution, and the color of the surface is changed by bringing the liquid-absorbing member into contact with the ground surface. As a result, it is possible to obtain a metal product in which the surface appears to shine differently depending on the viewing direction.

Description

Manufacturing method for colored metal products

[0001] The present invention relates to a method for producing colored metal products. The metal products produced by the present invention can be used, for example, for signs.

[0002] It has been known for some time that an anodized film is formed by using a light metal or an alloy thereof immersed in an electrolyte as an anode, thereby coloring the surface and imparting a design feature (see, for example, Patent Document 1).

[0003] Furthermore, Patent Document 2 proposes a method for coloring titanium or the like, in which titanium or a titanium alloy material is immersed in an oxidizing molten bath.

[0004] JP 2006-183065 JP 01-000279

[0005] However, when the anodizing method is performed by immersing a metal or the like in an electrolyte as in Patent Document 1, electrolysis equipment is required, which increases the equipment cost, and it is considered technically difficult to continuously color multiple metal members.

[0006] Furthermore, Patent Document 2 discloses that one or a mixture of two or more of nitrates, dichromates, permanganates, and hydroxides is used as the melt for use in the coloring method for titanium, etc. However, the melts listed therein are corrosive to the skin, carcinogenic, or may cause fires or explosions when reacting with flammable substances, and therefore all of them are highly dangerous substances and difficult to handle.

[0007] Therefore, a main object of the present invention is to propose a method for coloring a metal surface more easily.

[0008] The present invention relates to a method for producing a colored metal product. Specifically, the metal product is a colored surface of a transition metal or an alloy material containing a transition metal as a main component (hereinafter simply referred to as "metal, etc."). Examples of the metal, etc. include titanium or a titanium alloy. In the present invention, the surface of the metal, etc. is first ground from one or more directions using a disc grinder or a grinding wheel (grinding process). Next, the positive electrode of a power source is connected to the metal, etc., and the negative electrode of the power source is connected to a liquid-absorbent member holding an electrolyte. The liquid-absorbent member is then brought into contact with the ground metal, etc. surface to discolor the surface (coloring process). That is, the metal, etc. connected to the positive electrode of the power source becomes the anode, and a colored anodic oxide coating is formed on the surface of the metal, etc., upon contact with the cathode side of the electrolyte held in the liquid-absorbent member. The liquid-absorbent member is not particularly limited, and commercially available sponges, brushes, and other materials capable of temporarily holding liquid may be used.

[0009] Transition metals such as titanium are known to form colorless, transparent oxide films on their surfaces, and the stability of these oxide films provides excellent corrosion resistance. Therefore, in the present invention, the colorless, transparent oxide film is first removed by grinding the surface of the metal or the like. Then, the metal or the like is connected to the positive electrode of a power source, and an absorbent member holding an electrolyte is connected to the negative electrode of the power source. The absorbent member is then brought into contact with the ground surface of the metal or the like, thereby re-forming a colored oxide film on the surface of the metal or the like. This allows the surface of the metal or the like to be colored without immersing the metal or the like in an electrolyte. In particular, since the absorbent member is brought into contact with the metal or the like in the present invention, the surface of the metal or the like can be colored with the same sensation as drawing or coloring a picture while holding the absorbent member by hand. Furthermore, by deeply scratching the surface of the metal or the like using a disc grinder or a grindstone to form fine irregularities and then coloring it using the above procedure, the surface of the metal or the like diffuses light in various directions, making the surface of the metal or the like appear sparkling. As a result, the present invention can provide colored metal products with novel designs that are different from conventional designs.

[0010] In the present invention, the grinding step preferably grinds the surface of the metal or the like from three or more directions, and more preferably from five or more directions. By grinding the surface of the metal or the like from three or more directions (or five or more directions), the surface of the metal or the like appears to shine differently depending on the direction from which it is viewed. For this reason, for example, if a metal product colored by the method of the present invention is used for a signboard, the metal surface will appear to sparkle when a viewer looks at the signboard while walking by.

[0011] In the present invention, it is preferable that the surface of the metal or the like is ground multiple times using grinding members with different grit sizes in the grinding process. By using grinding members with different grit sizes in the grinding process, the depth and state of scratches (irregularities) on the surface of the metal or the like become diverse. This results in a diverse light reflection on the surface of the metal or the like, which can further attract the interest of viewers.

[0012] In the present invention, the transition metal is preferably titanium, and the alloy material is preferably a titanium alloy. Titanium or titanium alloys change color beautifully when exposed to an electrolyte after removing the colorless and transparent oxide film. Therefore, when using a metal product for a signboard, for example, titanium or titanium alloys are suitable.

[0013] In the present invention, the electrolyte is preferably a sodium bicarbonate aqueous solution (sodium bicarbonate water). Although sodium carbonate aqueous solution is alkaline, it has long been commonly used as a food additive and detergent, and is relatively safe for the human body, making it an easy-to-handle material when manually coloring metal products. Because sodium bicarbonate aqueous solution is weakly alkaline, it is generally resistant to discoloration even when applied to the surface of titanium or the like while a voltage is applied. Therefore, as described above, in the present invention, as a pretreatment before applying the sodium bicarbonate aqueous solution, the surface of titanium or the like is ground to remove the oxide film and to create fine irregularities on the surface to increase the surface area. This makes it easier to color the surface of titanium or the like using a weakly alkaline sodium bicarbonate aqueous solution.

[0014] In the present invention, the voltage of the power supply is preferably 5 to 110 V. By adjusting the voltage applied to the metal or the like from the power supply, the color of the surface of the metal or the like can be adjusted.

[0015] In the present invention, the coloring step preferably includes using a liquid-absorbent member to bring the electrolyte solution into uneven contact with the surface of the metal, etc. By intentionally bringing the electrolyte solution into uneven contact with the surface of the metal, etc. to form uneven coloring, the color of the surface of the metal, etc. becomes more diverse, which can further attract the interest of viewers.

[0016] In the present invention, the surface of a metal product is colored, for example, blue. For example, when titanium or a titanium alloy is applied as an anode with a voltage of approximately 30 V and then attached to an electrolyte, a beautiful blue color is produced. Note that "blue" refers to a color with an L* value of 10 or more, an a* value of -80 to 15, and a b* value of -15 or less in the Lab color system. While it is preferable for the entire colored surface of the metal product to be blue, this is not necessarily the case; it is sufficient if at least a portion of the surface is blue. However, by adjusting the voltage applied to the titanium or titanium alloy, it is also possible to color it yellow, orange, red, or purple.

[0017] According to the present invention, metal surfaces can be easily colored.

[0018] Fig. 1 is a schematic diagram showing a coloring process according to one embodiment of the present invention, and Fig. 2 is a photograph showing a metal product colored according to an embodiment of the present invention.

[0019] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the embodiments described below, and includes appropriate modifications of the embodiments described below within the scope obvious to those skilled in the art.

[0020] The present invention relates to a method for manufacturing colored metal products. The present invention can be applied to, for example, the manufacture of metal signboards. Specifically, the letters, figures, symbols, etc. that make up the signboard can be molded from metal, and the molded metal can be colored. In addition, the present invention can be used for coloring the surfaces of various metal products.

[0021] The metal products to be colored by the present invention are products made of metals whose surfaces can be discolored by applying a voltage to the anode and then applying an electrolyte. Such metals are primarily transition metals or alloys containing transition metals as their primary component. Transition metals are metal elements belonging to the d-block of the periodic table. Examples of transition metals that can be colored by an electrolyte include, but are not limited to, titanium, aluminum, iron, copper, zinc, and chromium. Among these, titanium, copper, or chromium is preferred, with titanium being particularly preferred. Furthermore, an alloy material primarily containing a transition metal refers to a material containing 80% or more by mass of the transition metal as the primary component. Examples of transition metal alloys that can be colored by an electrolyte include, but are not limited to, titanium alloys, aluminum alloys, iron alloys, copper alloys, zinc alloys, and chromium alloys. Among these, titanium alloys, copper alloys, or chromium alloys are preferred, with titanium alloys being particularly preferred. Examples of titanium alloys are Ti-6Al-4V (Grade 5), Ti-3Al-2.5V (Grade 9), Ti-6Al-7Nb (Grade 23), Ti-5Al-2.5Fe (Grade 24), Ti-0.5Pd (Grade 7), Ti-0.5Ru (Grade 21), and Ti-0.5Ni-0.5Cu.

[0022] The method for manufacturing a metal product according to the present invention mainly includes a grinding step and a coloring step.

[0023] The grinding process is primarily performed to remove the colorless, transparent oxide film formed on the surface of metals and the like, and to form minute irregularities on the surface to increase its surface area, thereby accelerating the discoloration reaction caused by an alkaline aqueous solution in the subsequent coloring process. Furthermore, the grinding process creates fine scratches on the surface of metals and the like, allowing light to diffuse from the surface. The grinding process uses a processing tool capable of grinding the surface of hard metals. A metal processing disc grinder or grinding wheel can be used as the processing tool.

[0024] In the grinding process, it is preferable to grind the surface of the metal or the like from three or more directions. In particular, it is more preferable to grind the surface of the metal or the like in four or more directions, and even more preferable to grind in five or more directions. The grinding direction of the metal is the linear direction connecting the start point and the end point of grinding. When there are multiple grinding directions, the angle between one grinding direction and the adjacent grinding direction is preferably 180 / n degrees ± 10 degrees, where n is the number of grinding directions. For example, when there are two grinding directions, it is preferable that the angle between the first grinding direction and the next grinding direction is 90 degrees ± 10 degrees. Furthermore, when there are five grinding directions, it is preferable that the angle between one grinding direction and the adjacent grinding direction is 36 degrees ± 10 degrees. It is also possible to perform grinding more than twice along the same grinding direction. Furthermore, grinding may be performed back and forth along the same direction.

[0025] Furthermore, in the grinding process, it is preferable to grind the surface of the metal or the like multiple times using grinding members with different grit sizes. For example, when grinding the surface of the metal or the like from multiple directions, the grit size of the grinding members may be different when grinding in one direction and when grinding in another direction. For example, when grinding in five directions, the grit size of the grinding members may be different for each direction. Alternatively, when grinding the surface of the metal or the like from multiple directions, the grit size of the grinding members may be different when grinding more than once along a certain direction. For example, when grinding in five directions, grinding in each of the five directions may be performed with a grinding member of a first grit size, and then grinding again in each of the five directions with a grinding member of a second grit size. The grit size of the grinding members may be adjusted to an appropriate grit size depending on the hardness and properties of the metal or the like to be colored, or the desired surface shine.

[0026] Furthermore, the depth of the irregularities (scratches) imparted to the surface of the metal or the like during the grinding process is preferably about 0.1 to 5 mm, and particularly preferably about 0.5 to 3 mm. The depth of the irregularities can be measured, for example, by photographing the surface of the metal or the like after grinding using a microscope (manufactured by KEYENCE Corporation, product name "One-Shot 3D Measuring Macroscope VR-3100") and then using image analysis software (manufactured by the same company, product name "VR-H1A"). Specifically, a "contour curve" is calculated from the cross-sectional curve of the height profile, and two upwardly convex inflection points on this contour curve and the minimum value between these inflection points are determined. The minimum depth value Min and the average value of the depth values ​​at the two inflection points are defined as the maximum depth value Max, and the depth of the irregularities = maximum value Max - minimum value Min.

[0027] Next, in the coloring step, a voltage is applied to the metal or the like to make it an anode, and an electrolyte is applied to the surface of the ground metal or the like to discolor the surface. This coloring step is preferably performed after the grinding step, but before a thick, colorless, transparent oxide film is formed on the surface of the metal or the like. Specifically, the coloring step is preferably performed immediately after the grinding step (within 1 hour), but may also be performed within 48 hours or 24 hours.

[0028] FIG. 1 schematically illustrates a method for performing a coloring process in one embodiment of the present invention. In the example shown in FIG. 1, a metal plate 10 made of titanium or the like, a power source 20, two clip-equipped conductive members (alligator clips) 30 and 40, and a liquid-absorbent member 50 such as a sponge are prepared. The liquid-absorbent member 50 is soaked in an electrolyte (alkaline aqueous solution). A first conductive member 30 is connected to the positive terminal of the power source 20, and the metal plate 10 is clamped by the clips at its tip. A second conductive member 40 is connected to the negative terminal of the power source, and the liquid-absorbent member 50 is clamped by the clips at its tip. In this state, a voltage is applied from the power source 20 to the metal plate 10 and the liquid-absorbent member 50, so that when the liquid-absorbent member 50 comes into contact with the metal plate 10, a current flows between them. In this state, the metal plate 10 serves as the anode, and the clips clamping the liquid-absorbent member 50 serve as the cathode. As a result, a colored oxide film is formed on the metal plate 10 at the portion where the electrolyte has come into contact with the liquid-absorbent member 50, and the surface gradually discolors. When the liquid-absorbent member 50 starts to dry out, the electrolyte can be replenished.

[0029] Examples of alkaline aqueous solutions retained in the absorbent member during the coloring process include aqueous sodium bicarbonate (sodium bicarbonate solution), aqueous sodium hydroxide, aqueous potassium hydroxide, aqueous ammonia, aqueous sodium carbonate, and aqueous potassium carbonate. These alkaline aqueous solutions are generally readily available and therefore suitable for the method of manufacturing a metal product according to the present invention. Strongly alkaline aqueous solutions are difficult to handle manually during the coloring process, so it is preferable to use an alkaline aqueous solution with a weak alkaline pH of 8 to 11, with a pH of 8 to 10 being particularly preferred. The pH of the alkaline aqueous solution can be adjusted by adjusting the alkaline compound dissolved in water or the concentration of the alkaline compound in the aqueous solution.

[0030] In the coloring process, it is preferable to retain the electrolyte in an absorbent member and then manually contact the absorbent member with the surface of the metal or the like to apply the electrolyte to the metal or the like. As the absorbent member, a sponge or a brush is preferably used, but cloth, nonwoven fabric, paper towel, etc. may also be used. By coloring the surface of the metal or the like using an absorbent member soaked in the electrolyte, the coloring process can be easily performed with the same feeling as painting a picture. Instead of uniformly applying the electrolyte to the surface of the metal or the like, it is preferable to apply the electrolyte to the surface of the metal or the like unevenly using an absorbent member. In other words, it is preferable to leave a mottled pattern or band-like color unevenness on the surface of the metal or the like. Immersing the metal or the like in the electrolyte will uniformly color its surface, but applying the electrolyte to the surface of the metal or the like using an absorbent member such as a sponge as described above makes it easier to create such color unevenness.

[0031] Furthermore, the color of the surface of a metal or the like can be adjusted by adjusting the voltage of the power supply. The power supply voltage may be 5 to 110 V, preferably 5 to 40 V, and particularly preferably 5 to 30 V. For example, when titanium is used as the metal or the like, the surface of the titanium will be yellow at 5 to 10 V, orange to red at 10 to 15 V, reddish purple to light purple at 15 to 20 V, and blue to light blue at 20 to 30 V. It is preferable to use a DC stabilized power supply as the power supply.

[0032] In one embodiment of the present invention, the metal to be colored may be titanium or a titanium alloy, and a sodium bicarbonate solution may be selected as the electrolyte (alkaline aqueous solution). The sodium bicarbonate solution is applied to the titanium or titanium alloy that has undergone the grinding process described above using an absorbent material (sponge). The concentration of the sodium bicarbonate solution is preferably 5-50%, more preferably 9-30%. For example, the pH of the sodium bicarbonate solution is 8.2 at 5% concentration, 8.26 at 9%, 8.5 at 30%, and 8.7 at 50% concentration. For example, if a voltage of 25-35 V is applied to the ground titanium or titanium alloy to make it an anode, and the sodium bicarbonate solution from the cathode side is applied to the surface, the surface will exhibit a vivid blue color. Furthermore, because the surface is ground from multiple directions, the blue glow appears different depending on the viewing angle.

[0033] After the grinding and coloring steps, a coating may be applied to protect the surface of the colored metal, etc. (coating step). In this coating step, a coating agent is preferably applied to the surface of the metal, etc. Examples of the coating agent include a fluorine coating agent, a silicone coating agent, a UV-curable coating agent, an epoxy coating agent, an acrylic coating agent, and a ceramic coating agent, which are transparent to visible light.

[0034] Next, the method for manufacturing a metal product according to the present invention will be described in more detail with reference to examples.

[0035] In this example, a metal plate made of pure titanium (TP340, pure titanium type 2) was used as the metal to be colored. The surface of this metal plate was ground using a disc grinder. During grinding, the grinding wheel of the disc grinder was rotated while the grinding wheel was applied to the metal plate at an angle of approximately 45 degrees. Grinding using the disc grinder was performed multiple times in five directions, changing the direction. Furthermore, three types of grinding wheels with different grit sizes were used for each direction. The grinding wheels were used in order of coarse grit size, followed by gradually finer grit sizes. The grinding wheels used were WONDER SHARP #46, WONDER SHARP #60, and WONDER SHARP #120, in that order (all manufactured by TKX Corporation).

[0036] Next, in this example, a sodium bicarbonate solution (sodium bicarbonate water) was used as the electrolyte. The sodium bicarbonate solution was prepared by dissolving 10% sodium bicarbonate in 100% water to create an approximately 9% aqueous solution. The pH of this sodium bicarbonate solution was approximately 8.26. A sponge was thoroughly saturated with this sodium bicarbonate solution. A metal plate was clamped with an alligator clip connected to the positive terminal of a power source, and the sponge was clamped with another alligator clip connected to the negative terminal of the power source, and a voltage was applied from the power source. The power source voltage was set to 30 V. In this state, the sponge was brought into contact with the metal plate, depositing the sodium bicarbonate solution (electrolyte) on the surface of the metal plate. The contact time between the sponge and the metal plate was approximately 1 second. This resulted in a blue discoloration of the surface of the pure titanium metal plate. The metal plate was then cut out to form the desired letters, resulting in a metal product.

[0037] Figure 1 is a photograph of the metal product obtained through the above process, taken with a digital camera. The photograph is originally a color photograph, and the metal product appears blue, but for the sake of illustration, it is a monochrome photograph. The color photograph of the metal product taken with a digital camera (taken with an iPhone (registered trademark) 15 Pro) was imported into a computer, and the surface color of the metal product contained in the photograph was analyzed. For example, the color shades shown in the color code below were extracted. The values ​​in parentheses indicate the L*, a*, and b* values ​​in the Lab color system.・#23406e (L*=27, a*= 5, b*=-30) ・#386cb3 (L*=45, a*= 6, b*=-43) ・#29549a (L*=36, a*=10, b*=-43) ・#4f5d74 (L*=39, a*= 1, b*=-15)・#1e2d4d (L*=19, a*= 5, b*=-22) ・#446c96 (L*=44, a*=-1, b*=-27) ・#5c8ccc (L*=57, a*= 2, b*=-38) ・#2c4e85 (L*=33, a*= 7, b*=-35)・#385cac (L*=40, a*=14, b*=-47) ・#162c5d (L*=19, a*=10, b*=-32) ・#365c89 (L*=38, a*=1, b*=-29) As can be seen, the surface of the metal product obtained in this example is blue. Furthermore, as can be seen from the photograph shown in Figure 1, the surface of the metal product shines brightly like a mottled pattern, and the shine changes depending on the angle and direction from which it is viewed.

[0038] In the above example, pure titanium was used as the metal to be colored and a sodium bicarbonate aqueous solution was used as the electrolyte, but it is expected that discoloration will also occur if other alkaline aqueous solutions (especially weak alkaline ones) are applied to other transition metals or alloys containing them as the main component in the same manner. It is also expected that the color of the metal plate surface can be adjusted by adjusting the voltage of the power supply.

[0039] In the above, in order to express the contents of the present invention, the present specification has described the embodiments and examples of the present invention with reference to the drawings. However, the present invention is not limited to the above embodiments and examples, and includes modifications and improvements that are obvious to those skilled in the art based on the matters described in the present specification.

[0040] REFERENCE SIGNS LIST 10: Metal plate 20: Power source 30: First current-carrying member 40: Second current-carrying member 50: Liquid-absorbent member

Claims

1. A method for manufacturing a metal product made of titanium or titanium alloy with a colored surface, comprising: a grinding step in which the surface is ground from one or more directions using a disc grinder or grinding stone; and a coloring step in which the positive terminal of a power source is connected to the titanium or titanium alloy, the negative terminal of the power source is connected to a liquid-absorbent member holding an electrolyte which is an aqueous solution of sodium bicarbonate, and the liquid-absorbent member is brought into contact with the ground surface to discolor the surface, thereby causing the surface to appear to shine differently depending on the viewing direction.

2. The manufacturing method according to claim 1, wherein the grinding step grinds the surface from three or more directions.

3. The manufacturing method according to claim 1, wherein the grinding step involves grinding the surface multiple times using grinding members with different grain sizes.

4. The manufacturing method according to claim 1, wherein the voltage of the power supply is 5 to 110V.

5. The manufacturing method according to claim 1, wherein the coloring step includes applying the electrolyte non-uniformly to the surface using the liquid-absorbent member.

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