Method for producing metal member

Abstract

To provide a method for producing a metal member which enables the surface color tone to be easily controlled in a desired manner.SOLUTION: A metal member 1 has a substrate 2 composed of a metal, a transparent layer 3 composed of a substance that transmits visible light and provided on the substrate 2, and a reflective layer 4 provided on the transparent layer 3. The reflective layer 4 is configured to reflect a portion of light incident on the reflective layer 4. A method for producing the metal member 1 includes: a surface texture adjustment step for adjusting the surface texture of the substrate so that the developed area ratio Sdr of the substrate 2 becomes a desired value; a transparent layer formation step for forming the transparent layer 3 having a thickness of 15 nm or more and 600 nm or less on the substrate 2 after performing the surface texture adjustment step; and a reflective layer formation step for forming the reflective layer 4 having a thickness of 2 nm or more and 30 nm or less on the transparent layer 3 after performing the transparent layer formation step.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a metal member.

Background Art

[0002] Metal members may be used in applications that require high design quality, such as building materials and the casings of electronic devices. The surface of this type of metal member may be colored for the purpose of enhancing its design quality. When imparting a colored tone to the surface of a metal member, paint is often used. However, paint contains organic substances that are liable to deteriorate due to various causes such as ultraviolet irradiation. Therefore, a colored member having a colored tone imparted by paint has a problem in that peeling, fading, and deterioration of the paint film are likely to occur during use.

[0003] In contrast, a technique has been proposed in which a colored tone is imparted to the surface of a member without using paint by utilizing light interference. For example, Patent Document 1 describes an interference color-developing metal body including a metal substrate capable of forming a transparent anodic oxide film, a barrier layer formed on the surface thereof, and a light-reflective layer having a film thickness of 0.5 to 100 nm formed on the barrier layer.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, when attempting to color the surface of a metal member by utilizing light interference, it may be difficult to control the surface color tone in a desired manner. For example, even when attempting to obtain a metal member exhibiting a specific color tone, the hue of the surface of the metal body may change when the angle of the observer's line of sight with respect to the surface of the metal member is changed.

[0006] In recent years, in order to further enhance the design quality of metal members, metal members that exhibit different hues according to the angle of the observer's line of sight with respect to the surface have been desired. However, despite attempts to obtain such metal members, the change in hue when the angle of the observer's line of sight with respect to the surface of the metal member is changed may be small.

[0007] The present invention has been made in view of such a background, and aims to provide a method for manufacturing a metal member capable of easily controlling the surface color tone in a desired manner.

Means for Solving the Problems

[0008] One aspect of the present invention is a method for manufacturing a metal member having a base material made of metal, a transparent layer made of a substance that transmits visible light and provided on the base material, and a reflective layer provided on the transparent layer, wherein the reflective layer is configured to reflect a part of the light incident on the reflective layer, the method comprising: a surface property adjustment step of adjusting the surface property of the base material so that the developed area ratio Sdr of the base material becomes a desired value; after performing the surface property adjustment step, a transparent layer formation step of forming the transparent layer having a thickness of 15 nm or more and 600 nm or less on the base material; after performing the transparent layer formation step, a reflective layer formation step of forming the reflective layer having a thickness of 2 nm or more and 30 nm or less on the transparent layer.

Effects of the Invention

[0009] In the method for manufacturing the metal member, after adjusting the surface property of the base material so that the developed area ratio Sdr of the base material becomes a desired value, a transparent layer is formed on the base material. Thereby, the developed area ratio Sdr of the interface between the base material and the transparent layer can be adjusted to a desired value. Then, by forming the reflective layer on the transparent layer after adjusting the developed area ratio Sdr of the interface to a desired value in this way, the surface color tone of the metal member can be easily controlled in a desired manner.

[0010] Therefore, according to the above aspect, a method for manufacturing a metal member capable of easily controlling the surface color tone to a desired mode can be provided.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0012] Each step of the method for manufacturing the metal member will be described.

[0013] 〔Surface Property Adjustment Step〕 In the manufacturing method, first, a surface property adjustment step is performed to adjust the surface property of the base material so that the developed area ratio Sdr becomes a desired value. The base material used in the surface property adjustment step is made of metal. As the metal constituting the base material, for example, metals exhibiting achromatic colors such as white, gray, off-white, and silver-white can be preferably used. Examples of metals exhibiting such color tones include iron, iron alloys, aluminum, aluminum alloys, titanium, and titanium alloys. By using an achromatic metal as the base material of the metal member, the influence of the color tone of the base material on the color tone of the metal member can be reduced, and a metal member having a desired color tone can be obtained more easily.

[0014] As the metal constituting the base material, it is preferable to use aluminum, an aluminum alloy, titanium, or a titanium alloy. Since these metals have low chroma, the influence of the color tone of the base material on the color tone of the metal member can be further reduced. Furthermore, by performing anodizing treatment on the base material made of these metals, a transparent layer made of an oxide can be easily formed on the surface of the base material. Among these metals, from the viewpoint of reducing the material cost, the metal constituting the base material is more preferably aluminum or an aluminum alloy.

[0015] The materials of aluminum and aluminum alloys constituting the base material are not particularly limited and can be appropriately selected according to the use of the metal member and the required mechanical properties, etc. For example, when high strength is required for the metal member, it is preferable to use a base material made of a 5000 series alloy or a 6000 series alloy. Further, when excellent design properties are required for the metal member, it is preferable to use a base material made of 1000 series aluminum or a 6000 series alloy in which coloring by anodic oxidation treatment hardly occurs.

[0016] In the surface property adjustment step, it is preferable to adjust the surface property of the base material by performing one or more processes selected from the group consisting of rolling the base material using a pair of rolling rolls, extrusion processing of extruding the base material from an extrusion die, and polishing processing of polishing the surface of the base material. By performing these processes alone or in appropriate combination, the developed area ratio Sdr of the surface of the base material can be more easily adjusted to a desired value.

[0017] The method of adjusting the surface property of the base material by the above-described processes is more specifically as follows. For example, when performing rolling processing, the surface property of the rolling roll is reflected in the surface property of the base material after rolling. Therefore, when attempting to increase the developed area ratio Sdr of the surface of the base material by rolling processing, the base material may be rolled using a rolling roll having a large developed area ratio Sdr on the surface. Further, when attempting to decrease the developed area ratio Sdr of the surface of the base material by rolling processing, the base material may be rolled using a rolling roll having a small developed area ratio Sdr on the surface.

[0018] When performing extrusion processing, the surface property of the surface of the extrusion die that contacts the base material is reflected in the surface property of the base material after extrusion. Therefore, when attempting to increase the developed area ratio Sdr of the surface of the base material by extrusion processing, the base material may be rolled using an extrusion die having a large developed area ratio Sdr on the surface. Further, when attempting to decrease the developed area ratio Sdr of the surface of the base material by extrusion processing, the base material may be rolled using an extrusion die having a small developed area ratio Sdr on the surface.

[0019] As a polishing method in polishing, known polishing methods such as mechanical polishing that performs polishing using an abrasive, electrolytic polishing that performs polishing by electrochemically dissolving the surface of the base material, and chemical polishing that performs polishing by chemically dissolving the surface of the base material can be adopted. When performing polishing, the known polishing methods may be used alone or in appropriate combination according to the desired value of the developed area ratio Sdr.

[0020] For example, when attempting to increase the developed area ratio Sdr of the surface of the base material by polishing, mechanical polishing may be performed using abrasive grains with a large particle size. Also, when attempting to decrease the developed area ratio Sdr of the surface of the base material by polishing, a method of performing mechanical polishing using abrasive grains with a small particle size, or methods such as electrolytic polishing and chemical polishing may be adopted.

[0021] The developed area ratio Sdr of the surface of the base material after performing the surface property adjustment step may be appropriately set according to the desired aspect of the color tone on the surface of the metal member. For example, when attempting to obtain a metal member whose hue changes according to the angle of the observer's line of sight with respect to the surface of the metal member, the surface property of the base material may be adjusted so that the developed area ratio Sdr of the surface of the base material is 0.7% or less. From the viewpoint of more surely obtaining such an effect, the developed area ratio Sdr of the surface of the base material after performing the surface property adjustment step is preferably 0.5% or less, more preferably 0.3% or less, even more preferably 0.2% or less, particularly preferably 0.1% or less, and most preferably 0.05% or less.

[0022] Also, for example, when trying to obtain a metal member with a small change in hue even when the angle of the observer's line of sight with respect to the surface of the metal member changes, the surface property of the base material may be adjusted so that the developed area ratio Sdr of the surface of the base material is 1% or more. From the viewpoint of more surely obtaining such an effect, the developed area ratio Sdr of the surface of the base material after performing the surface property adjustment step is preferably 3% or more, more preferably 5% or more, and even more preferably 10% or more. On the other hand, when the developed area ratio Sdr of the surface of the base material becomes excessively high, light is likely to be scattered at the interface between the base material and the transparent layer or on the surface of the reflective layer, and the surface of the metal member may not show an interference color. By setting the developed area ratio Sdr of the surface of the base material to 100% or less, more preferably 70% or less, even more preferably 60% or less, and particularly preferably 50% or less, such a problem can be easily avoided.

[0023] When trying to obtain a metal member with a small change in hue even when the angle of the observer's line of sight with respect to the surface of the metal member changes, in constructing the preferable range of the developed area ratio Sdr of the interface, the upper limit and the lower limit of the developed area ratio Sdr described above can be arbitrarily combined. For example, the developed area ratio Sdr of the interface between the base material and the transparent layer may be 1% or more and 100% or less, 1% or more and 70% or less, 3% or more and 70% or less, 5% or more and 60% or less, or 10% or more and 50% or less.

[0024] The developed area ratio Sdr of the surface of the base material described above is measured by a method conforming to ISO 25178:2021. For measuring the developed area ratio Sdr, for example, a non-contact surface roughness measuring device such as a laser microscope or a white interference microscope can be used.

[0025] 〔Transparent layer formation step〕 After adjusting the surface properties of the substrate in the surface property adjustment step, a transparent layer forming step is performed to form a transparent layer having a thickness of 15 nm or more and 600 nm or less on the substrate. By setting the thickness of the transparent layer within the specific range, when the light reflected by the reflective layer of the metal member and the light reflected by the substrate are interfered with, light waves having wavelengths in the visible light region can be enhanced. As a result, the metal member can be colored in various color tones.

[0026] The substance constituting the transparent layer may be an organic substance or an inorganic substance. The transparent layer is preferably composed of an inorganic substance. A transparent layer made of an inorganic substance is less likely to deteriorate against temperature changes, humidity changes, sunlight irradiation, etc. during the use of the metal member, and can maintain optical properties over a longer period. Therefore, by providing a transparent layer made of an inorganic substance on the substrate, the color tone of the metal member can be maintained over a longer period.

[0027] Also, the transparent layer is preferably composed of an oxide of the metal constituting the substrate. Since metal oxides are less likely to deteriorate against temperature changes, humidity changes, sunlight exposure, etc., by providing a transparent layer made of an oxide on the substrate, the color tone of the metal member can be maintained over a longer period. Furthermore, in this case, since the transparent layer can be grown from the substrate surface by performing anodic oxidation treatment on the substrate, the formation of gaps and the inclusion of foreign substances at the interface between the substrate and the transparent layer can be prevented. As a result, the occurrence of unevenness and defects in the color tone of the metal member can be more effectively suppressed.

[0028] In the transparent layer formation step, it is preferable to form a transparent layer on the substrate by anodization. When anodization is performed on the substrate, dissolution of the surface of the substrate and formation of the transparent layer proceed simultaneously. Further, dissolution of the surface of the substrate and formation of the transparent layer proceed uniformly on the surface of the substrate. Therefore, the developed area ratio Sdr of the interface between the surface of the substrate and the transparent layer after anodization is generally equal to the developed area ratio Sdr of the surface of the substrate before anodization. Further, when forming the transparent layer by anodization, the thickness of the transparent layer can be adjusted by adjusting the applied voltage. For example, when performing anodization by direct current electrolysis, the thickness of the transparent layer can be increased by increasing the applied voltage.

[0029] The electrolytic solution used for anodization may be a weakly acidic electrolytic solution or a weakly basic electrolytic solution. More specifically, as the weakly acidic electrolytic solution, for example, phosphates, borates, adipic acid, etc. are used as electrolytes, and an electrolytic solution with a pH of 3.5 or more and 7 or less can be used. Further, as the weakly basic electrolytic solution, for example, borates and phosphates are used as electrolytes, and an electrolytic solution with a pH of 7 or more and 8 or less can be used.

[0030] Further, the treatment method in anodization is preferably any one of direct current electrolysis performed by applying a voltage of 10 V or more and 400 V or less, alternating current electrolysis performed by applying a voltage such that the peak voltage is 10 V or more and 400 V or less, or pulse electrolysis. The transparent layer formed in this way is composed of an oxide of the metal constituting the substrate and has no pores, so light scattering in the transparent layer can be further reduced. Therefore, by performing anodization by the above-described treatment method, a metal member having vivid colored appearance can be obtained more easily.

[0031] The developed area ratio Sdr of the interface between the substrate and the transparent layer after the transparent layer formation step is approximately the same as the developed area ratio Sdr of the surface of the substrate after the surface property adjustment step. Therefore, when the surface property of the substrate is adjusted so that the developed area ratio Sdr of the substrate surface becomes 0.7% or less in the surface property adjustment step, the developed area ratio Sdr of the interface between the substrate and the transparent layer after the transparent layer formation step becomes 0.7% or less. By setting the developed area ratio Sdr of the interface between the substrate and the transparent layer to 0.7% or less, it is possible to obtain a metal member whose hue changes according to the angle of the observer's line of sight with respect to the surface of the metal member. For example, the following reasons can be considered for this.

[0032] Since the interface with a small developed area ratio Sdr is relatively smooth, it is considered that the incident light incident on the metal member from the light source is reflected at the interface between the substrate and the transparent layer generally in the direction corresponding to the incident angle. At this time, since the optical path length of the light reflected from the interface in the direction of the observer's line of sight is generally uniform, it is considered that the phase of the light reflected from the interface in the direction of the observer's line of sight also becomes generally uniform. In addition, since the length of the optical path length of the reflected light reflected at the interface changes according to the reflection angle, it is considered that when the direction of the observer's line of sight with respect to the surface of the metal member changes, the phase of the light reflected in the direction of the line of sight also changes. And it is considered that the reflected light having different phases according to the reflection angle in this way interferes with the reflected light reflected on the surface of the reflective layer, etc., so that the metal member can be colored with a color tone having different hues according to the angle of the observer's line of sight with respect to its surface.

[0033] Also, in the surface property adjustment step, when the surface property of the substrate is adjusted so that the developed area ratio Sdr of the substrate surface becomes 1% or more, the developed area ratio Sdr of the interface between the substrate and the transparent layer after the transparent layer formation step becomes 1% or more. By setting the developed area ratio Sdr of the interface between the substrate and the transparent layer to 1% or more, it is possible to obtain a metal member with a small change in hue even when the angle of the observer's line of sight with respect to the surface of the metal member changes. For example, the following reasons can be considered for this.

[0034] Since the interface with a large spreading area ratio Sdr is relatively rough, it is considered that the incident light incident on the metal member from the light source is reflected in various directions. Therefore, it is considered that the light reflected from the interface in the direction of the observer's line of sight includes light reflected from different positions on the interface. And if the reflection positions on the interface are different, the optical path lengths from the interface to the reflective layer are also different. Therefore, it is considered that the light reflected from the interface in the direction of the observer's line of sight includes light having various phases.

[0035] In addition, the reflected light reflected at the interface interferes with the reflected light reflected at the surface of the reflective layer and the like. At this time, since the reflected light reflected at the interface includes light having various phases, on the surface of the metal member, regardless of the direction of the observer's line of sight, the light having the average phase in the reflected light reflected at the interface and the reflected light reflected at the surface of the reflective layer and the like It is considered that an interference color generated by interference appears. As a result of the above, it is considered that even when the angle of the observer's line of sight with respect to the surface of the metal member changes, the change in the hue of the surface of the metal member can be reduced.

[0036] 〔Reflective layer forming step〕 After forming a transparent layer on the base material in the transparent layer forming step, a reflective layer forming step is performed to form a reflective layer having a thickness of 2 nm or more and 30 nm or less on the transparent layer. The reflective layer has the property of reflecting a part of the incident light incident on the metal member. By providing such a reflective layer on the transparent layer, the light reflected by the reflective layer and the light reflected at the interface between the base material and the transparent layer can be interfered to make the metal member emit various color tones. From the viewpoint of further enhancing the chroma of the metal member and emitting a more vivid color tone, the average value of the spectral transmittance of the reflective layer in the wavelength range of 400 nm or more and 700 nm or less is preferably 2% or more and 80% or less, more preferably 20% or more and 70% or less, and further preferably 30% or more and 60% or less.

[0037] The average value of the spectral transmittance of the reflective layer described above can be calculated by the following method. First, measure the spectral transmittance of the reflective layer at a plurality of wavelengths within the range of 400 nm or more and 700 nm or less in wavelength. At this time, from the viewpoint of calculating the average value of the spectral transmittance of the reflective layer more accurately, it is preferable to measure the spectral transmittance of the reflective layer at a plurality of wavelengths determined so that the wavelength intervals are constant. Also, the interval between the wavelengths at which the spectral transmittance is measured is preferably, for example, 20 nm or less. The value obtained by arithmetically averaging the spectral transmittances at the plurality of wavelengths obtained as described above is taken as the average value of the spectral transmittance of the reflective layer.

[0038] The reflective layer may be composed of, for example, a metal or a metal compound. Also, the reflective layer may contain both a metal and a metal compound. When the reflective layer is composed of a metal and / or a metal compound, the thickness of the reflective layer is preferably 2 nm or more and 30 nm or less. In this case, the average value of the spectral transmittance of the reflective layer can be more easily adjusted within the specific range.

[0039] As the metal constituting the reflective layer, for example, aluminum, copper, silver, platinum, etc. can be used. Also, as the metal compound constituting the reflective layer, for example, copper oxide, silver sulfide, etc. can be used. Among these, from the viewpoint of more surely obtaining the above-described effects, it is preferable that the reflective layer contains copper atoms or silver atoms.

[0040] Also, it is more preferable that the reflective layer contains a metal compound. Since the metal compound is less likely to deteriorate in the atmosphere, the optical properties of the reflective layer can be maintained for a longer period. Therefore, by providing a reflective layer made of a metal containing a metal compound on the transparent layer, the vivid color tone of the metal member can be maintained for a longer period. From the viewpoint of more surely obtaining such an effect, it is preferable that the reflective layer contains copper oxide or silver sulfide, and more preferably contains copper oxide.

[0041] From the perspective of more surely imparting the above-described optical properties to the reflective layer, it is preferable that the reflective layer contains a plurality of crystal grains. Further, it is more preferable that the average grain size of the crystal grains contained in the reflective layer is 3 nm or more and 15 nm or less.

[0042] The average grain size of the above-described crystal grains is a value calculated as follows. First, the cross-section of the reflective layer is observed using a high-resolution transmission electron microscope to obtain an electron microscope image of the reflective layer. Next, the equivalent circle diameter of the crystal grains existing in the electron microscope image, that is, the diameter of a circle equal to the cross-sectional area of the crystal grains is calculated. The arithmetic mean value of the equivalent circle diameters of the crystal grains thus obtained is taken as the average grain size of the crystal grains.

[0043] In the reflective layer forming step, it is preferable to form the reflective layer on the transparent layer by a sputtering method. In this case, a reflective layer having desired optical properties can be formed more easily. As the sputtering method, it is preferable to employ DC sputtering or RF sputtering, more preferably to employ DC sputtering, and even more preferably to employ DC magnetron sputtering. In this case, the variation in the thickness of the reflective layer formed on the transparent layer can be further reduced, and crystal grains can be more easily formed in the reflective layer. Further, according to these sputtering methods, the grain size of the crystal grains in the reflective layer can be more easily controlled. Therefore, by performing the sputtering method by the above-described processing method, a reflective layer having desired optical properties can be more easily formed on the transparent layer, and a metallic member having vivid colored appearance can be more easily obtained.

[0044] As the atmosphere gas in the chamber in DC magnetron sputtering, for example, argon can be used. In this case, the degree of vacuum in the chamber is set to 0.05 Pa or more and 5 Pa or less, and the current density applied to the sputtering target is 0.1 mA / cm 2 or more and 7 mA / cm 2It is preferable to do as follows. By performing DC magnetron sputtering under such conditions, a reflective layer having desired optical properties can be more easily formed on the transparent layer.

[0045] 〔Protective layer forming step〕 The manufacturing method may have a protective layer forming step of forming a protective layer made of a substance that transmits visible light on the reflective layer after forming the reflective layer in the reflective layer forming step. By providing a protective layer on the reflective layer, deterioration of the reflective layer due to reaction with oxygen, moisture, sulfur content, etc. in the atmosphere can be suppressed over a longer period, and the vivid colored appearance of the metal member can be maintained over a longer period.

[0046] The substance constituting the protective layer may be an organic substance or an inorganic substance. As the protective layer, for example, transparent resins such as acrylic resin, methacrylic resin, polycarbonate resin, nitrocellulose resin, and organic glass can be preferably used.

Example

[0047] An example of the manufacturing method of the metal member will be described with reference to FIG. 1. As shown in FIG. 1, the metal member 1 obtained by the method of this example has a base material 2 made of metal, a transparent layer 3 made of a substance that transmits visible light and provided on the base material 2, and a reflective layer 4 provided on the transparent layer 3. The transparent layer 3 is made of a substance that transmits visible light and has a thickness of 15 nm or more and 600 nm or less. The reflective layer 4 is configured to be able to reflect a part of the visible light incident on the reflective layer 4 and has a thickness of 2 nm or more and 30 nm or less.

[0048] An example of the manufacturing method of the metal member 1 of this example will be described. In manufacturing the metal member 1 of this example, first, base materials A to F shown in Table 1 are prepared. The base materials A to F are all aluminum plates having a chemical composition represented by alloy number A1050 and have the developed area ratio Sdr shown in Table 1.

[0049] Base material A can be obtained, for example, by polishing the surface of an aluminum plate in multiple steps while changing the type of abrasive, and performing polishing using a finishing abrasive ("SUPERFINISH FINAL LIQUID" manufactured by KULZER) in the final step. Base material B can be obtained, for example, by polishing the surface of an aluminum plate in multiple steps while changing the type of abrasive, performing polishing using an abrasive ("MetaDi (registered trademark) Supreme 3μm" manufactured by BUEHLER) containing diamond abrasive grains with a particle size of 3 μm and a lubricant ("DP-Lubricant Red" manufactured by Strothaus) in the final step, and then performing electrolytic polishing for 2 minutes.

[0050] Base material C can be obtained, for example, by rolling an aluminum plate using a roll with a small surface roughness. Base materials D to F can be obtained, for example, by polishing the surface of an aluminum plate in multiple steps while changing the type of abrasive, and performing polishing using abrasive paper holding abrasive grains with the particle sizes shown in Table 1 in the final step.

[0051] Next, after performing pretreatment such as cleaning on base materials A to F, anodic oxidation treatment is performed on the base materials to form a barrier-type anodic oxide film as a transparent layer on the surface of the base materials. As the treatment method in the anodic oxidation treatment, direct current electrolysis is adopted, and the applied voltage is increased to the values shown in Tables 2 to 4 over 2.5 minutes from the start of the treatment. Also, in the anodic oxidation treatment, a weakly basic electrolyte solution containing 0.5 mol / L boric acid and 0.05 mol / L sodium tetraborate is used as the electrolyte. The temperature of the electrolyte solution in the anodic oxidation treatment is set to 20°C. The thickness of the transparent layer formed under such conditions is as shown in Tables 2 to 4. Also, the developed area ratio Sdr of the interface 21 (see Figure 1) between the transparent layer and the base material formed under such conditions is approximately equal to the developed area ratio Sdr of the surface of the base material after the surface property adjustment step.

[0052] Thereafter, a sputtering process is performed to form a reflective layer made of copper on the transparent layer. The thickness of the reflective layer is 5 nm, and the average value of the spectral transmittance of the reflective layer in the wavelength range of 400 nm or more and 700 nm or less is 56.6%. As the processing method in the sputtering process, DC magnetron sputtering can be adopted. Also, argon is used as the atmospheric gas in the chamber in DC magnetron sputtering, the degree of vacuum in the chamber is set to 0.05 Pa or more and 5 Pa or less, and the current density applied to the sputtering target is 0.1 mA / cm 2 or more and 7 mA / cm 2 or less. Note that the method for measuring the spectral transmittance of the reflective layer will be described later.

[0053] As described above, test materials A1 to F1 shown in Table 2, test materials A2 to F2 shown in Table 3, and test materials A3 to F3 shown in Table 4 can be obtained.

[0054] Next, the method for evaluating the average value of the spectral transmittance of the reflective layer and the color tone of the metal members shown in Tables 2 to 4 will be described.

[0055] 〔Average value of the spectral transmittance of the reflective layer〕 A reflective layer is formed on a glass substrate by the same processing method as the sputtering process for each test material, and the spectral transmittance of this reflective layer at various wavelengths is measured at 10 nm intervals within the range from 400 nm to 700 nm in wavelength. Note that the light source used in the measurement of the spectral transmittance is Supplementary Illuminant C defined in JIS Z8720:2012. Also, the geometric conditions during measurement are the geometric conditions f represented by the symbol 0°:di in JIS Z8722:2009 (that is, the condition of irradiating light from the direction where the angle with respect to the normal of the surface of the transmission layer is 0° and collecting all transmitted light including the directly transmitted light), and the measurement area with a diameter of 30 mm is irradiated with light.

[0056] The spectral transmittance at each wavelength obtained by the above method includes, in addition to the contribution of light absorption etc. in the reflective layer, the contribution of light absorption etc. in the glass substrate. The spectral transmittance T of only the reflective layer ris the spectral transmittance T at each wavelength obtained by measuring the reflective layer on the glass substrate m and the spectral transmittance of the glass substrate at each wavelength is T glass Using these, it can be calculated based on the following formula (1). T r = T m × (100 / T glass ) ···(1)

[0057] As described above, after correcting the measured spectral transmittance T at each wavelength to exclude the influence of the glass substrate, the arithmetic mean of the corrected spectral transmittance T m can be obtained to obtain the average value of the spectral transmittance of the reflective layer. r

[0058] 〔Change in color tone of metal member〕 The change in the color tone of the metal member is evaluated based on the gradation of the digital photograph and the result of visual observation when the surface of the metal member is observed from various directions. The evaluation device 5 used for evaluating the change in color tone has, as shown in FIG. 2, a photographing table 51 configured to be able to change the tilt angle with respect to the horizontal plane, and a camera 52 disposed vertically above the photographing table 51. As the camera 52, a single-lens reflex camera "EOS (registered trademark) 8000D" manufactured by Canon Inc. is used, and photography is performed with the ISO sensitivity automatically set (AUTO), the F value set to 8, and the exposure time set to 0.5 seconds.

[0059] In performing the evaluation, first, place the test specimen T on the photographing stage 51 with the surface of the photographing stage 51 being horizontal. Then, irradiate white light from above the test specimen T to make the illuminance on the surface of the test specimen T 900 lux or more. As the light source, use an LED bar (Toshiba Lighting & Technology, LEEM-40523N-01) attached to an LED bar type fixture (Toshiba Lighting & Technology, LEET-41201-LS9), and set the distance from the light source to the test specimen to 2 m or more. Also, while avoiding the white light being blocked by the camera 52, irradiate the white light from a direction as close as possible to vertically above the test specimen T, and thus install the light source at a position where the straight line connecting the center of the light source and the center of the test specimen T is inclined by about 10° to 40° with respect to the vertical direction. In this state, photograph the test specimen T with the camera 52 under the above-described photographing conditions to obtain a digital photograph of the test specimen T. Perform the above operations by inclining the photographing stage 51 to change the angle of the surface of the test specimen T with respect to the horizontal plane to 15°, 30°, 45°, 60°, and 75°, and photograph digital photographs at each angle.

[0060] Table 2 shows the results represented as RGB values in the sRGB color space and the results judged visually for the color tone at the center of the digital photograph thus obtained. Also, in the "ΔRGB ave " column of Table 2, the average value of the change amounts of the RGB values calculated by the following formula (2) is described using the above-described RGB values.

[0061]

Equation

[0062] In the formula (2), R k is the gradation of the R channel at the center of the digital photograph taken with the angle of the surface of the test specimen with respect to the horizontal plane set to k°, G k is the gradation of the G channel at the center of the digital photograph taken with the angle of the test specimen set to k°, and B kIt is the gradation of the B channel at the center of the digital photograph taken with the angle of the test material set to k°. R, G, and B are each an integer of 0 or more and 255 or less, and the higher the luminance of each channel, the larger the values of R, G, and B.

[0063] As can be understood from the above formula (2), ΔRGB ave is the value obtained by averaging the amount of change in the gradation of each channel when the angle of the surface of the test material changes by 15°. Therefore, the larger the value of ΔRGB ave is, the greater the change in color tone when the angle of the photographing table is changed.

[0064] [Table 1]

[0065] [Table 2]

[0066] [Table 3]

[0067] [Table 4]

[0068] As shown in Table 2, the test materials A1 to C1 have a base material whose surface properties are adjusted so that the developed area ratio Sdr is relatively small in the surface property adjustment step. Therefore, these test materials are likely to have a large change in the hue of the surface of the test material when the angle of the observer's line of sight with respect to the surface changes. Therefore, the surfaces of the test materials A1 to C1 exhibit color tones having different hues depending on the angle of the observer's line of sight with respect to the surface.

[0069] In addition, test specimens D1 to F1 have a base material whose surface properties are adjusted so that the developed area ratio Sdr is relatively large in the surface property adjustment step. Therefore, in these test specimens, when the angle of the observer's line of sight with respect to the surface changes, the change in the hue of the surface of the test specimen tends to be small. Therefore, test specimens D1 to F1 exhibit a color tone having generally the same hue even when the angle of the observer's line of sight with respect to the surface changes.

[0070] In addition, as can be understood from Table 3, test specimens A2 to C2 and test specimens A3 to C3 having the same configuration as test specimens A1 to C1 except that the thickness of the transparent layer is different exhibit different hues depending on the angle of the observer's line of sight with respect to the surface, similar to test specimens A1 to C1.

[0071] Similarly, test specimens D2 to F2 and test specimens D3 to F3 shown in Table 4 also have the same configuration as test specimens D1 to F1 except that the thickness of the transparent layer is different. Therefore, they exhibit a color tone having generally the same hue even when the angle of the observer's line of sight with respect to the surface of the test specimen changes.

[0072] From the above results, it can be understood that by adjusting the developed area ratio Sdr of the surface of the base material to a desired value in the surface property adjustment step, the color tone of the surface of the metal member can be controlled in a desired manner.

[0073] As described above, specific embodiments of the method for manufacturing a metal member according to the present invention have been described based on the examples. However, the embodiments of the method for manufacturing a metal member according to the present invention are not limited to the embodiments of the examples, and the configuration can be appropriately changed without departing from the spirit of the present invention.

[0074] For example, the method for manufacturing the metal member can take the following aspects (1) to (8).

[0075] (1) A method for manufacturing a metal member having a base material made of metal, a transparent layer made of a substance that transmits visible light and provided on the base material, and a reflective layer provided on the transparent layer, wherein the reflective layer is configured to reflect a part of the light incident on the reflective layer. A surface property adjustment step of adjusting the surface property of the base material so that the developed area ratio Sdr of the base material becomes a desired value; After performing the surface property adjustment step, a transparent layer forming step of forming the transparent layer having a thickness of 15 nm or more and 600 nm or less on the base material; After performing the transparent layer forming step, a reflective layer forming step of forming the reflective layer having a thickness of 2 nm or more and 30 nm or less on the transparent layer, a method for manufacturing a metal member.

[0076] 〔2〕In the surface property adjustment step, the surface property of the base material is adjusted by performing one or more processes selected from the group consisting of rolling the base material using a pair of rolling rolls, extrusion processing of extruding the base material from an extrusion die, and polishing processing of polishing the surface of the base material. The method for manufacturing a metal member according to 〔1〕. 〔3〕In the reflective layer forming step, the reflective layer is formed on the transparent layer by a sputtering method. The method for manufacturing a metal member according to 〔1〕 or 〔2〕. 〔4〕The method for manufacturing a metal member according to any one of 〔1〕 to 〔3〕, wherein the reflective layer contains copper atoms or silver atoms.

[0077] 〔5〕In the transparent layer forming step, the transparent layer is formed on the base material by performing anodic oxidation treatment under any of the conditions of direct current electrolysis performed by applying a voltage of 10 V or more and 400 V or less, alternating current electrolysis performed by applying a voltage so that the peak voltage is 10 V or more and 400 V or less, or pulse electrolysis. The method for manufacturing a metal member according to any one of 〔1〕 to 〔4〕. 〔6〕The method for manufacturing a metal member has a protective layer forming step of forming a protective layer made of a substance that transmits visible light on the reflective layer after performing the reflective layer forming step. The method for manufacturing a metal member according to any one of 〔1〕 to 〔5〕.

[0078] 〔7〕In the surface property adjustment step, the surface property of the base material is adjusted so that the developed area ratio Sdr of the surface of the base material becomes 0.7% or less. The method for manufacturing a metal member according to any one of 〔1〕 to 〔6〕. 〔8〕The manufacturing method of the metal member according to any one of 〔1〕~〔6〕, wherein in the surface property adjustment step, the surface property of the base material is adjusted so that the developed area ratio Sdr of the surface of the base material is 1% or more.

Explanation of symbols

[0079] 1 Metal member 2 Base material 3 Transparent layer 4 Reflective layer

Claims

1. A manufacturing method of a metal member, comprising a base material made of metal, a transparent layer made of a substance that transmits visible light and provided on the base material, and a reflective layer provided on the transparent layer, wherein the reflective layer is configured to reflect a part of the light incident on the reflective layer, a surface property adjustment step of adjusting the surface property of the base material so that the developed area ratio Sdr of the base material becomes a desired value; a transparent layer forming step of forming the transparent layer having a thickness of 15 nm or more and 600 nm or less on the base material after performing the surface property adjustment step; a reflective layer forming step of forming the reflective layer having a thickness of 2 nm or more and 30 nm or less on the transparent layer after performing the transparent layer forming step.

2. The manufacturing method of the metal member according to claim 1, wherein in the surface property adjustment step, the surface property of the base material is adjusted by performing one or more processes selected from the group consisting of rolling the base material using a pair of rolling rolls, extrusion molding the base material from an extrusion die, and polishing the surface of the base material.

3. The manufacturing method of the metal member according to claim 1 or 2, wherein in the reflective layer forming step, the reflective layer is formed on the transparent layer by a sputtering method.

4. The manufacturing method of the metal member according to claim 1 or 2, wherein the reflective layer contains copper atoms or silver atoms.

5. The manufacturing method of the metal member according to claim 1 or 2, wherein in the transparent layer forming step, the transparent layer is formed on the base material by anodizing under any of the conditions of direct current electrolysis performed by applying a voltage of 10 V or more and 400 V or less, alternating current electrolysis performed by applying a voltage so that the peak voltage is 10 V or more and 400 V or less, or pulse electrolysis.

6. The manufacturing method of the metal member according to claim 1 or 2, further comprising a protective layer forming step of forming a protective layer made of a substance that transmits visible light on the reflective layer after performing the reflective layer forming step.

7. The manufacturing method of the metal member according to claim 1 or 2, wherein in the surface property adjustment step, the surface property of the base material is adjusted so that the developed area ratio Sdr of the surface of the base material becomes 0.7% or less.

8. The manufacturing method of the metal member according to claim 1 or 2, wherein in the surface property adjustment step, the surface property of the base material is adjusted so that the developed area ratio Sdr of the surface of the base material becomes 1% or more.

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