Manufacturing method of colored metal products

Abstract

To provide a method for easily coloring a metal surface. [Solution] A method for manufacturing a metal product made of a transition metal or an alloy material containing it as its main component with a colored surface includes a grinding step in which the surface is ground from one or more directions, and a coloring step in which the positive electrode of a power source is connected to the transition metal or alloy material and the negative electrode is connected to an absorbent member holding an electrolyte, and the absorbent member is brought into contact with the ground surface to discolor the surface.

Description

[Technical field]

[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 signage. [Background technology]

[0002] 2. Description of the Related Art It has been known in the past to form an anodic oxide film 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 (eg, Patent Document 1).

[0003] Moreover, 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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2006-183065 A [Patent Document 2] Japanese Patent Application Publication No. 01-000279 Summary of the Invention [Problem to be solved by the invention]

[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 costs, and it is considered technically difficult to continuously color multiple metal members.

[0006] Also, in Patent Document 2, one or a mixture of two or more of nitrates, dichromates, permanganates, and hydroxides is used as the molten material in the coloring method for titanium, etc. However, the molten materials listed therein are corrosive and carcinogenic to the skin, or may cause fires or explosions when reacted 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 provide a method for coloring a metal surface more easily. [Means for solving the problem]

[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 the transition metal as a main component (hereinafter also simply referred to as "metal, etc."). In the present invention, the surface of the metal, etc. is first ground from one or more directions (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, and the liquid-absorbent member is brought into contact with the ground surface of the metal, etc., to discolor the surface (coloring process). That is, since the metal, etc. connected to the positive electrode of the power source becomes the anode, a colored anodic oxide film is formed on the surface of the metal, etc. by contacting the electrolyte on the cathode side held in the liquid-absorbent member. Note that the liquid-absorbent member is not particularly limited, and a commercially available member capable of temporarily holding liquid, such as a sponge or a brush, may be used.

[0009] It is known that a colorless and transparent oxide film is formed on the surface of transition metals such as titanium, and the stability of the oxide film gives the metals excellent corrosion resistance. Therefore, in the present invention, the colorless and 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 the power source, and a liquid-absorbent member holding an electrolyte is connected to the negative electrode of the power source, and the liquid-absorbent member is brought into contact with the ground surface of the metal or the like, thereby forming a colored oxide film again 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 liquid-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 a feeling similar to drawing or coloring a picture. In addition, by deeply scratching the surface of the metal or the like to form fine irregularities and then coloring it in the above procedure, the surface of the metal or the like diffuses light in various directions, so that the surface of the metal or the like appears to sparkle. As a result, according to the present invention, a colored metal product with a novel design different from the conventional design can be provided.

[0010] In the present invention, in the grinding step, it is preferable to grind the surface of the metal or the like from three or more directions, and it is particularly preferable to grind from five or more directions. In this way, by grinding the surface of the metal or the like from three or more directions (or five or more directions), the way the light shines on the surface of the metal or the like changes depending on the direction from which it is viewed. For this reason, for example, by using a metal product colored by the method of the present invention as 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 to grind the surface of the metal or the like multiple times using grinding members with different grain sizes in the grinding process. By using grinding members with different grain sizes in the grinding process, the depth and state of scratches (unevenness) on the surface of the metal or the like become diverse. This makes the surface of the metal or the like reflect light in a diverse manner, which can further attract the interest of the viewer.

[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 as a signboard, it is preferable to use titanium or titanium alloys.

[0013] In the present invention, the electrolyte is preferably an aqueous solution of sodium bicarbonate (sodium bicarbonate solution). Although an aqueous solution of sodium carbonate is alkaline, it has been commonly used as a food additive or detergent for a long time and is relatively safe for the human body, so it can be said to be an easy-to-handle material when coloring metal products.

[0014] In the present invention, the voltage of the power supply is preferably 5 to 110 V. By adjusting the voltage applied from the power supply to the metal or the like, 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 with a voltage of about 30 V as an anode and is attached to an electrolyte, it will exhibit a beautiful blue color. Note that "blue" means 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. Note that it is preferable that the colored surface of the metal product is entirely blue, but this is not necessarily required, and it is sufficient that the surface is at least partially blue. However, it is also possible to color the titanium or titanium alloy in yellow, orange, red, or purple by adjusting the voltage applied to the titanium or titanium alloy. Effect of the Invention

[0017] According to the present invention, metal surfaces can be colored in a simple manner. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic diagram showing a coloring step in one embodiment of the present invention. [Diagram 2] FIG. 2 is a photograph showing a metal product colored according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, the 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 a colored metal product. The present invention can be applied to, for example, the manufacture of a metal signboard. Specifically, the letters, figures, symbols, etc. that constitute 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 product to be colored by the present invention is a product made of a metal that can be used as an anode by applying a voltage and discolored by applying an electrolyte. Such metals are mainly transition metals or alloy materials mainly composed of transition metals. A transition metal is a metal element belonging to the d block in 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 them, the metal to be colored by the present invention is preferably titanium, copper, or chromium, and more preferably titanium. In addition, an alloy material mainly composed of a transition metal means one containing 80 mass% or more of the transition metal as the main component. Examples of alloy materials of transition metals that can be colored by an electrolyte include, but are not limited to, titanium alloys, aluminum alloys, iron alloys, copper alloys, suballoys, and chromium alloys. Among them, the alloy materials to be colored by the present invention are preferably titanium alloys, copper alloys, or chromium alloys, and more preferably titanium alloys. 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 mainly performed for the purpose of removing the colorless and transparent oxide film formed on the surface of the metal, etc., and also for the purpose of forming minute irregularities on the surface to increase the surface area, thereby accelerating the discoloration reaction caused by an alkaline aqueous solution in the subsequent coloring process. In addition, by making fine scratches on the surface of the metal, etc., in the grinding process, it becomes possible to diffuse light on the surface. In the grinding process, a processing member capable of grinding the surface of a hard metal is used. As the processing member, a disk grinder or a grinding wheel for metal processing may be used.

[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 that the grinding direction of the surface of the metal or the like is four or more directions, and particularly preferably five or more directions. The grinding direction of the metal is a linear direction connecting the start point and the end point of grinding. When there are multiple grinding directions, the angle between a certain grinding direction and the adjacent grinding direction may be 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 direction in which the first grinding is performed and the direction in which the next grinding is performed is 90 degrees ± 10 degrees. In addition, when there are five grinding directions, it is preferable that the angle between a certain grinding direction and the adjacent grinding direction is 36 degrees ± 10 degrees. In addition, grinding can be performed two or more degrees along the same grinding direction. Furthermore, grinding may be performed back and forth along the same direction.

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

[0026] In addition, the depth of the irregularities (scratches) given to the surface of the metal or the like in 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, product name "One Shot 3D Measuring Macroscope VR-3100") and using the photographed image as an 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 inflection points that are upwardly convex on this contour curve and the minimum value between these inflection points are obtained, and the minimum value Min of the depth and the average value of the depth values ​​of the two inflection points are set as the maximum value Max of the depth, 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 ground surface of the metal or the like to discolor the surface. This coloring step is preferably performed after the grinding step described above, but before a colorless, transparent, thick oxide film is formed on the surface of the metal or the like again. Specifically, the coloring step is preferably performed immediately after the grinding step (within 1 hour), but may be performed within 48 hours or 24 hours.

[0028] FIG. 1 is a schematic diagram showing a method of 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, 40, and a liquid-absorbent member 50 such as a sponge are prepared. In addition, the liquid-absorbent member 50 is soaked with an electrolyte (alkaline aqueous solution). A first conductive member 30 is connected to the positive electrode of the power source 20, and the metal plate 10 is sandwiched between the clips at the ends. A second conductive member 40 is connected to the negative electrode of the power source, and the liquid-absorbent member 50 is sandwiched between the clips at the ends. 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 a current flows between the two when the liquid-absorbent member 50 comes into contact with the metal plate 10. In this state, the metal plate 10 becomes the anode, and the clips sandwiching the liquid-absorbent member 50 become the cathode. As a result, a colored oxide film is formed on the metal plate 10 at the portion where the electrolyte is attached through contact with the electrolyte-absorbent member 50, and the surface gradually becomes discolored. When the electrolyte-absorbent member 50 becomes dry, it is sufficient to replenish the electrolyte.

[0029] Examples of the alkaline aqueous solution to be retained in the liquid-absorbent member in the coloring step include an aqueous sodium hydrogen carbonate solution (sodium bicarbonate solution), an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, an aqueous ammonia solution, an aqueous sodium carbonate solution, and an aqueous potassium carbonate solution. These alkaline aqueous solutions are generally easy to obtain, and therefore suitable for the manufacturing method of the metal product according to the present invention. If the alkaline aqueous solution is strongly alkaline, it will be difficult to handle it manually in the coloring step. Therefore, it is preferable to use an alkaline aqueous solution that is weakly alkaline, with a pH of 8 to 11, and particularly preferably a pH of 8 to 10. The pH of the alkaline aqueous solution can be adjusted by adjusting the concentration of the alkaline compound dissolved in water or the alkaline compound in the aqueous solution.

[0030] In the coloring process, it is preferable to hold the electrolyte in the liquid-absorbent member, and then manually contact the liquid-absorbent member with the surface of the metal or the like to attach the electrolyte to the metal or the like. As the liquid-absorbent member, it is preferable to use a sponge or a brush, but it may also be cloth, nonwoven fabric, paper towel, or the like. By coloring the surface of the metal or the like using the liquid-absorbent member soaked in the electrolyte in this way, the coloring work can be easily performed as if painting a picture. In addition, instead of uniformly attaching the electrolyte to the surface of the metal or the like, it is preferable to attach the electrolyte to the surface of the metal or the like unevenly using the liquid-absorbent member. In other words, it is preferable to leave a spotted pattern or a band-like color unevenness on the surface of the metal or the like. When the metal or the like is immersed in the electrolyte, the surface is uniformly colored, but by attaching the electrolyte to the surface of the metal or the like using a liquid-absorbent member such as a sponge as described above, it becomes easy to express such color unevenness.

[0031] The color of the surface of the metal or the like can be adjusted by adjusting the voltage of the power supply. The voltage of the power supply 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 becomes 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 is titanium or a titanium alloy, and an aqueous solution of sodium bicarbonate is selected as the electrolyte (alkaline aqueous solution). The aqueous solution of sodium bicarbonate is applied to the titanium or titanium alloy that has been subjected to the grinding process described above using a liquid-absorbing member (sponge). The concentration of the aqueous solution of sodium bicarbonate is preferably 5 to 50%, more preferably 9 to 30%. For example, the pH of the aqueous solution of sodium bicarbonate is 8.2 at a concentration of 5%, 8.26 at a concentration of 9%, 8.5 at a concentration of 30%, and 8.7 at a concentration of 50%. For example, when a voltage of 25 to 35 V is applied to the ground titanium or titanium alloy to make it an anode and the aqueous solution of sodium bicarbonate on the cathode side is applied to the surface, the surface will take on a vivid blue color. In addition, since the surface is ground from multiple directions, the blue shines differently depending on the viewing direction.

[0033] After the grinding and coloring steps, a coating may be applied to protect the surface of the colored metal or the like (coating step). In this coating step, it is preferable to apply a coating agent to the surface of the metal or the like. As the coating agent, it is preferable to use a coating agent that is transparent to visible light, such as a fluorine coating agent, a silicone coating agent, a UV-curable coating agent, an epoxy coating agent, an acrylic coating agent, or a ceramic coating agent. EXAMPLES

[0034] Next, the method for manufacturing a metal product according to the present invention will be described more specifically 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. A grinding process was performed on the surface of this metal plate using a disc grinder. In the grinding process, the grinding wheel of the disc grinder was rotated and applied to the metal plate at an angle of about 45 degrees to grind it. Grinding with the disc grinder was performed multiple times in each of five directions while changing the direction. In addition, three types of grinding wheels with different grain sizes were used for each direction of the disc grinder. The grinding wheels were used in order from coarse to fine. The grinding wheels were WONDER SHARP #46, WONDER SHARP #60, and WONDER SHARP #120, in that order (all manufactured by TKX Corporation).

[0036] Next, in this embodiment, sodium bicarbonate solution (sodium bicarbonate water) was used as the electrolyte. The sodium bicarbonate solution was prepared by dissolving 10% sodium bicarbonate in the amount of water (100%) to create an aqueous solution with a concentration of about 9%. The pH of this sodium bicarbonate aqueous solution was about 8.26. The sodium bicarbonate aqueous solution was thoroughly soaked into the sponge. In addition, a metal plate was clamped with an alligator clip connected to the positive pole of a power source, and a sponge was clamped with another alligator clip connected to the negative pole of the power source, and a voltage was applied from the power source. The voltage of the power source was set to 30V. In this state, the sponge was brought into contact with the metal plate, so that the sodium bicarbonate aqueous solution (electrolyte) was attached to the surface of the metal plate. The contact time between the sponge and the metal plate was about 1 second. As a result, the surface of the metal plate made of pure titanium turned blue. After that, the metal plate was processed to cut out predetermined characters, and a metal product was made.

[0037] Figure 1 is a photograph of the metal product obtained through the above process taken with a digital camera. Originally, the photograph was a color photograph and the metal product would be blue, but due to the nature of the drawing, it is a monochrome photograph. The color photograph (taken with an iPhone (registered trademark) 15 Pro) of the metal product taken with a digital camera was imported into a computer and the color of the surface of the metal product contained in the photograph was analyzed, and the color of the color code shown below, for example, was extracted. Note that the values ​​in parentheses indicate the L* value, a* value, and b* value 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 from the above, the surface of the metal product obtained in this example is blue in color. 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 way it shines varies depending on the viewing angle and direction.

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

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

Claims

1. A method for producing a surface-colored titanium or titanium alloy metal product, comprising the steps of: a grinding step of grinding the surface from multiple directions using a disc grinder or a grinding wheel; A coloring step includes connecting a positive electrode of a power source to the titanium or titanium alloy, connecting a negative electrode of the power source to a liquid-absorbent member that holds an electrolyte solution that is an aqueous solution of sodium bicarbonate, and bringing the liquid-absorbent member into contact with the ground surface to discolor the surface. This method is for producing a metal product in which the surface of the product appears to shine differently depending on the viewing direction.

2. The grinding step grinds the surface from three or more directions. The method of claim 1 .

3. The grinding step grinds the surface multiple times with grinding members having different grain sizes. The method according to claim 1 or 2.

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

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

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