JP5146948B2 - Metal surface processing method - Google Patents

Description

  The present invention relates to a metal surface processing apparatus and method, and, for example, to an apparatus and method for applying heat to a metal surface by irradiating a laser beam and thereby coloring the surface.

  In general, it is known that when a metal is heated in an electric furnace or the like, the metal is oxidized and colors such as rainbow, gold, and black are attached to the metal surface. It is also known that there are a gas torch, plasma, laser, electron beam, etc. used for bonding cutting as a heating method. Among these, the laser is easy to control energy, and can be heated locally in the atmosphere by focusing on a limited area. Therefore, it can be used for processing such as forming and coloring a surface modification layer on the metal surface, and some proposals have been made regarding the technique and mechanism.

  For example, a method (Patent Document 1) in which a metal surface is engraved with a periodic structure composed of fine irregularities and made to appear as if it is colored rainbow by interference of reflected light, or an oxide film is formed on the metal surface, There are known methods (Patent Documents 2, 3, 4 and Non-Patent Documents 1, 2, etc.) that show various colors by interference of light between the oxide film and the surface of the metal base material under the oxide film.

  In addition, after applying a coating (liquid) containing a metal colloid having a nano-level size to a metal surface, the laser beam is irradiated to agglomerate the metal colloid, and various colors such as gold are used for marking. A laser color marking method (Patent Document 5) is also known.

  In addition, a number of laser engraving machines comprising a pulse laser and a galvanometer scanning mirror are on the market. In these apparatuses, the surface layer is usually removed using laser ablation and deformation by local heating and melting is used to form a concavo-convex structure in a one-dimensional array on the metal surface for inscription. ing.

JP-A-6-212451 JP-A-7-61198 Japanese Patent Laid-Open No. 2004-250786 JP 2005-200730 A JP 2003-94181 A Soma et al., Surface Technology, 1994, Vol. 45, pp. 67-72 Tanabe et al., Transactions of the Japan Society of Mechanical Engineers (C), 2003, 69, 685, 246-251 Asahikawa Industrial Technology Center News, 1996, No. 12, page 3

  However, there are various problems with the metal surface coloring techniques described in the above-mentioned documents. In other words, the technique described in Patent Document 1 for forming a fine periodic concavo-convex structure with a laser on a metal surface effectively utilizes the removal of a surface layer using laser ablation or deformation by local heating. However, this method forms a periodic concavo-convex structure acting as a diffraction grating on the metal surface to give a rainbow color, and does not give a specific color. In Patent Document 1, the type of laser light is not specified, and it is described in the embodiment that an Nd: YAG laser having a wavelength of 1.06 micrometers belonging to the infrared region is used.

  Patent Document 2 also mentions a coloring and patterning method using a laser. This patent relates to a technique for performing desired coloring using interference of a metal oxide film by setting each of a laser beam current, a repetition frequency, an integrated light amount, an irradiation time, and an air temperature to predetermined values in laser irradiation. Is formed in a recess formed by a laser engraving machine. In this patent, the type of laser light is not specified, and it is described in the embodiment that an Nd: YAG laser having a wavelength of 1.06 micrometers belonging to the infrared region is used for irradiation. Although this patent is different from Patent Document 1 in that a desired color can be obtained, the number of conditions to be set for this purpose is large and complicated. Further, the concave portions formed by the laser are colored. This indicates that the surface layer is removed at the time of forming the colored portion, and there is a problem that scattered matters are generated during the coloring process to contaminate the surroundings. Another problem is that dirt or the like is likely to accumulate in the recess. Furthermore, in this coloring method, it is specified that the color is developed by the interference of light between the metal base material and the oxide film formed thereon. In such coloring using light interference, the thickness of the oxide film is very thin and easily damaged, and the color appearance changes depending on the angle of illumination light and the angle at which the colored part is viewed. is there.

  Patent Document 3 also proposes a pattern coloring (color marking) method for forming an oxide film by laser irradiation on a metal surface. The phenomenon of coloring by laser itself has already been disclosed in Patent Document 1 or Non-Patent Documents 1 and 3, etc., but in this patent, the color of the metal surface uniformly colored by heat treatment at 200 ° C. or higher is It is characterized by being changed by a reducing action by reheating by irradiating a laser. In addition, techniques using atmospheric gases such as hydrogen, ammonia, carbon monoxide are also introduced. Since a primary coloring process is required, the number of coloring steps is increased. When an atmospheric gas is used, an apparatus for controlling the atmosphere is required, and handling of hydrogen, ammonia, carbon monoxide and the like is dangerous. In addition, since the color development uses reduction by laser irradiation, there is a problem that the color development state obtained by the surface layer state generated by the primary treatment is limited. In this patent as well, it is clearly stated that the principle of color development is the interference of light between the surface of the metal base material and the oxide film, and there are problems that the film is easily damaged and the visible color changes depending on the viewing angle.

  Patent Document 4 discloses a method for obtaining a condition for forming an oxide film having a desired thickness on a metal surface using a neural network. Although a technology that enables strict management of the film thickness created by appropriately managing many irradiation conditions has been introduced, conditions to be set are required, but there are improvements in the number of conditions. Therefore, the procedure for drawing a pattern composed of a plurality of colors is complicated. In Non-Patent Document 2 in which this method is introduced, the laser beam scanning speed, irradiation energy, and number of irradiations are controlled in a composite manner to obtain a desired coloration. The need for irradiation is indicated. The reason why the number of irradiations must be increased in this way is because the absorption rate of the infrared laser with respect to the metal is poor.

  Patent Document 5 introduces a laser color marking technique that utilizes agglomeration of metal colloids by applying a paint having a metal colloid having a nano-level size and irradiating laser light. However, this method requires the preparation of metal colloids with nano-sized sizes, application to the surface, and removal of non-aggregated metal colloids after laser treatment, resulting in a large number of processes and a large amount of waste liquid. Is a problem.

  The present invention has been made in view of such a situation, and realizes stable color development that does not vary in color depending on the viewing direction and angle, regardless of light diffraction or interference, and a metal surface with a relatively simple process. Processing is realized.

  In order to solve the above problems, in the present invention, the surface modification layer is efficiently formed by irradiating the metal surface with laser light in the ultraviolet region where the reflectance of the metal material decreases. In other words, the laser beam to be irradiated is in the ultraviolet region with a wavelength of 100 nm or more and 400 nm or less. The ultraviolet laser beam is condensed and the condensed laser beam is scanned two-dimensionally on the metal surface. Irradiation is performed to form a surface modification layer on the metal surface. The condensing regions of the ultraviolet laser light are scanned so as to overlap each other.

  Further, in the present invention, the irradiation conditions including the irradiation energy of the ultraviolet laser beam, the number of times of scanning of the laser beam, and the scanning speed of the laser beam are controlled according to the color to be colored on the metal surface. For example, the control of the irradiation condition is executed by acquiring the irradiation condition corresponding to the desired color from the irradiation condition table that defines the irradiation condition corresponding to the color to be colored on the metal surface.

  Further, the ultraviolet laser beam may be irradiated in a state where the metal surface is exposed to a predetermined atmospheric gas that is not harmful to the human body.

The irradiation energy contained in the irradiation conditions is preferably 0.1 J / cm ² or more 10J / cm ² or less.

  Further features of the present invention will become apparent from the best mode for carrying out the present invention and the accompanying drawings.

  According to the present invention, it is possible to realize stable color development that does not vary in color depending on the viewing direction and angle, regardless of light diffraction and interference. Further, according to the present invention, it is possible to realize metal surface processing with a relatively simple process.

  The present invention relates to a marking method and apparatus for marking by coloring by forming a surface modification layer such as a layer made of a metal oxide on the surface only by irradiating the surface of various metal materials with a laser beam. Is.

  Hereinafter, embodiments and examples of the present invention will be described with reference to the accompanying drawings. However, it should be noted that this embodiment is merely an example for realizing the present invention and does not limit the present invention. In each drawing, the same reference numerals are assigned to common components.

<Concept of the present invention>
First, the concept of the present invention will be described. In the present invention, laser light is applied to a metal thin film such as plating formed on the surface of various metals, iron, chromium, nickel, copper, tin, zinc, titanium, or an alloy made of these, or the surface of other materials, Irradiation is performed at a light energy density so that an oxide layer with a sufficient thickness is formed on the surface, and the irradiation position is scanned two-dimensionally so that the irradiated regions overlap each other. Laser irradiation is performed on the entire region to form a surface modification layer.

  The wavelength of the laser beam used on the metal surface is preferably 100 nm (more preferably 190 nm) or more and 400 nm or less, corresponding to the ultraviolet region where the reflectance of the metal is known to decrease. In addition, when irradiating the entire specific area by scanning the irradiation position two-dimensionally, the number of pulses to be irradiated becomes very large, so laser oscillation is performed at a high pulse repetition frequency of 1000 times (1 kHz) or more per second. It is preferable to use a laser light source capable of

In order to obtain a sufficient energy density for forming the modified layer (oxide film), it is necessary to focus the laser beam using a lens or a mirror. The size of light collection depends on the irradiation energy obtained by the laser light source, but a typical energy density used for coloring is 0.1 to 10 J / cm ² . If the energy density is too high, the surface layer may be removed by ablation, and the irradiated part may become a concave portion. Therefore, it is necessary to set the energy density below a threshold at which ablation occurs.

  Laser light scanning is performed once to five times so as to obtain a desired coloration, but in order to shorten the process time, the scanning speed or It is preferable to set the conditions for controlling the coloring by the energy density.

<Configuration of metal surface processing equipment>
FIG. 1 is a diagram showing a schematic configuration of a metal surface processing apparatus 100 according to an embodiment of the present invention. As shown in FIG. 1, the metal surface processing apparatus 100 is an apparatus for coloring the surface of the metal sample plate 8, and includes an ultraviolet laser light source 1 that emits an ultraviolet laser light 10, an output of the laser light 10, A variable output device 2 for changing the number of times of irradiation, a shutter 4 for stopping laser irradiation and setting a laser irradiation range, and a laser for scanning the metal surface with the laser 10 in the set laser irradiation range Optical scanning device (galvano scanning mirror) 5, output device 2, shutter 4, control device 4 for controlling laser light scanning device 5, condensing lens 6 for condensing laser light 10, lens 6 A lens protection cover 7 for preventing laser light reflection on the lens and protecting the lens surface, and a metal sample plate fixing stage 9 for mounting the metal sample plate 8.

  In the metal surface processing apparatus 100, the operator inputs data indicating the coloring range and color type such as drawing data on the surface of the metal sample plate 8 to the control apparatus 3 by the operator. Based on the coloring range, the metal type of the metal sample plate 8, the data of the color to be colored, and the like, the control device 3, for example, obtains a table of each embodiment described later (a table stored in a memory (not shown)). The laser beam 10 output, irradiation range, number of irradiations, scanning speed (moving speed of the focused spot), etc. are determined. Then, based on these determined laser irradiation conditions, the laser beam 10 is irradiated onto the surface of the metal sample plate 8, an oxide film is formed, and surface coloring is realized.

  In the metal surface processing apparatus 100 of FIG. 1, the laser beam 10 is scanned two-dimensionally using a galvano scanning mirror with respect to the scanning of the condensing position. As shown, a method of scanning the light collection position on the sample by moving the stage 11 to which the metal sample to be irradiated is fixed without moving the laser beam 10 may be used. At this time, in the metal surface processing apparatus 200, the speed at which the light collection position is scanned by the stage on which the metal sample is fixed is controlled by the external control apparatus 3.

  Further, as described above, the irradiation energy can be controlled by the output variable device 2 while keeping the output of the laser constant, but an excitation laser diode constituting the laser light source 1 or The current value supplied to the lamp may be controlled and changed. Also, the irradiation energy may be controlled by controlling the timing of the Q switch when the Q switch oscillates.

  It is necessary to scan the condensing position over the entire region where the surface modification layer is formed by scanning in a two-dimensional manner with the condensing regions overlapping each other. In this case, scanning as shown in FIG. 3 can be performed.

<Procedure for coloring>
FIG. 4 is a process diagram for explaining a coloring process procedure for the surface of the metal sample plate 8 using the metal surface processing apparatus 100 or 200 shown in FIG. 1 or 2. First, a metal sample plate (metal piece) 8 to be colored is prepared (process P1). As the metal sample plate 8 to be colored, for example, an iron-based metal such as stainless steel, copper, zinc, titanium, chromium, nickel, or an alloy made of them can be used. Also, use an alloy prepared by mixing a metal material with a predetermined element (indium, tin, zinc, titanium, etc.), or disperse a predetermined element on the metal surface (for example, by PVD, CVD, ion implantation, etc.) Alternatively, a metal obtained by plating the above metal on the surface of another metal or other material may be used. If such an alloy or a metal with elements dispersed on the surface is used, it is possible to color the surface of aluminum or the like, which is usually difficult to produce an oxide film.

  Subsequently, the processed surface of the metal sample plate 8 prepared in Process 1 is mirror-polished (Process 2). The mirror finish can make the energy absorbed by the metal surface uniform, and can be finished finely. However, this process 2 is not essential and can be colored without a mirror finish. Further, the prepared metal plate is washed to remove dust, oil, polishing debris, etc. adhering to the metal plate (process 3).

  Also, an oxygen gas flow is prepared as necessary, and an atmospheric gas (a gas that does not harm the human body, such as oxygen gas or nitrogen gas) is injected onto the metal sample plate 8 (process 4). Since the atmospheric gas is injected to promote the generation of an oxide film, the process 4 is not an essential process. Then, the ultraviolet laser light source 1 is started up and the optical system is adjusted according to the thickness of the metal sample plate 8 (the distance from the lens 6 to the surface of the metal sample plate 8 is adjusted to a predetermined distance). In addition, the laser irradiation conditions such as how many times the energy density is irradiated with the laser are determined (process 5). Since the color varies depending on the progress of oxidation, the energy density and the number of irradiations of the laser beam vary depending on the desired color. This laser irradiation condition (including irradiation energy, number of irradiations, irradiation range, scanning speed, etc.) is determined with reference to a table shown in an example described later.

  Laser irradiation is performed on the surface of the metal sample plate 8 under the laser irradiation conditions determined in Process 5 (Process 6).

Note that an ultraviolet laser has a higher absorptance with respect to a metal surface than an infrared laser, so that an oxide film can be formed on a metal surface and colored even if the energy density is somewhat low. However, if the energy density is too low, an oxide such as a nonconductive film is formed on the metal surface, and oxidation on the metal surface will not proceed even if laser irradiation is performed further. In such a case, the conventional iridescent coloring by light interference is possible, but stable coloring in which the color does not vary depending on the viewing angle cannot be realized. Therefore, a certain degree of density even ultraviolet laser, for example, preferably laser irradiation at an energy density of 0.1 J / cm ² or more 10J / cm ² or less as described above.

  Moreover, in the process 4, when injecting atmospheric gas, the metal processing apparatus 100 or 200 needs to be equipped with the structure shown by FIG. That is, a configuration in which a specific atmospheric gas such as oxygen gas is blown (FIG. 5A) or a configuration in which a specific atmospheric gas is introduced into an atmosphere control mechanism having a window that transmits laser light (FIG. 5B) is employed. be able to. By doing in this way, the surface modification layer, such as a single or several metal nitride and a metal oxide, can be formed in the surface using reaction with atmospheric gas.

  By the processing as described above, an oxide film (oxide layer) having a thickness of 50 nm or more can be formed in a specified region / part of the surface of the metal sample plate 8. If the oxide film has such a thickness, the possibility of breakage is very low.

  Hereinafter, the results of actual coloring using the method described in this embodiment will be described as examples.

Using the apparatus shown in FIG. 1, a laser beam was irradiated on a SUS304 plate mirror-polished in the atmosphere. Laser light pumped Q-switch Nd: YVO ₄ laser was scanned with a galvanoscanning mirror while oscillating pulsed light of the fourth harmonic (wavelength 266 nm) at a repetition frequency of 30 kHz, and condensed by a plano-convex lens with a focal length of 350 mm. The SUS304 plate was installed in a place where a focused spot with a diameter of about 50 μm was obtained, and the focused spot was moved from 76 mm to 247 mm per second on the SUS304 plate. The energy density of the laser to be irradiated is set to 3.1 J / cm ² , and the entire region consisting of a 7 mm square is repeated by repeating a linear movement of 7 mm while shifting it in a direction perpendicular to the moving direction at intervals of 7.5 μm. Was irradiated with laser. By repeating this irradiation twice, the coloring shown in Table 1 was obtained according to the moving speed of the focused spot on the surface.

Using the apparatus shown in FIG. 1, a laser beam was irradiated on a SUS304 plate mirror-polished in the atmosphere. The pulsed light of the fourth harmonic (wavelength 266 nm) of the laser diode excitation Q-switch Nd: YVO ₄ laser was scanned with a galvano scanning mirror while oscillating at a repetition frequency of 30 kHz, and condensed by a plano-convex lens having a focal length of 400 mm. The SUS304 plate was installed in a place where a focused spot having a diameter of about 50 μm was obtained. Laser irradiation to the entire area of a 7 mm square by moving the focused spot on a SUS304 plate at 95 mm per second and repeating a 7 mm linear movement while shifting in a direction perpendicular to the moving direction at 7.5 μm intervals. Went. This operation was repeated twice to change the energy density of the irradiated laser from 0.9 J / cm ² to 3.1 J / cm ² . The coloring shown in Table 2 was obtained according to the energy density to be irradiated.

  Using the apparatus shown in FIG. 1, the apparatus shown in FIG. 3 is used to irradiate a SUS304 plate mirror-polished in an oxygen atmosphere formed by circulating about 3 L of oxygen gas through the space above the sample. It was. Other irradiation conditions are the same as in Example 1. The coloring shown in Table 3 was obtained according to the moving speed of the focused spot.

Using the apparatus shown in FIG. 1, the laser beam was irradiated on the SUS304 plate in the atmosphere. Laser diode excitation Q-switch Nd: YVO ₄ Laser 3rd harmonic (wavelength 355 nm) pulsed light is oscillated at a repetition rate of 30 kHz, scanned by a galvano scanning mirror, and condensed by an f-θ lens with a working distance of 15 cm. did. The SUS304 plate was installed in a place where a focused spot having a diameter of about 100 μm was obtained, and the focused spot was moved from 50 mm to 250 mm per second on the SUS304 plate. By setting the energy density of the laser to be irradiated to 0.6 J / cm ² and repeating the linear movement of 7 mm while shifting it in a direction perpendicular to the moving direction at intervals of 7.5 μm, the entire area consisting of a square of 7 mm square Was irradiated with laser. By repeating this irradiation three times, the coloring shown in Table 4 was obtained according to the moving speed of the focused spot on the surface.

The apparatus shown in FIG. 1 was used to irradiate various metal plates with laser light in the atmosphere. Laser light pumped Q-switch Nd: YVO ₄ laser was scanned with a galvanometer scanning mirror while oscillating pulsed light of the fourth harmonic (wavelength 266 nm) at a repetition frequency of 30 kHz, and condensed by a plano-convex lens with a focal length of 400 mm. The SUS304 plate is installed in a place where a focused spot with a diameter of about 70 μm can be obtained, and the focused spot is moved at 254 mm per second on the SUS304 plate, and the 7 mm linear movement is perpendicular to the moving direction at intervals of 9.5 μm. By repeating while shifting, laser irradiation was performed on the entire area of a 7 mm square. This operation was repeated 5 times, and the energy density of the laser to be irradiated is changed from 0.8 J / cm ² to 1.8 J / cm ^2. The coloring shown in Table 5 to Table 7 was obtained according to the energy density to be irradiated. In Tables 6 and 7, the irradiation energy of (1) to (10) corresponds to the irradiation energy of (1) to (10) in Table 5.

  The present invention can be used not only for manufacturing decorative crafts, but also for marking characters and patterns with various colors on the surface of plates or parts made of various metals or plated with various metals. Therefore, it can be used for identification of metal tools such as metal parts and medical instruments, as well as for display and plate manufacturing at work sites. Further, it can be used in a wide range of fields such as the automobile industry, the IT industry, and the electronic parts industry that have conventionally used laser color marking.

<Summary>
Conventionally, in order to induce the formation of a modified layer by laser irradiation on a metal surface and obtain a predetermined coloration, a number of conditions such as laser light irradiation intensity, scanning speed, repetition frequency, number of irradiations, and temperature are combined. Had to be set manually. For this reason, the procedure for drawing a pattern composed of a plurality of colors is very complicated.

  On the other hand, in the method of the present invention, an ultraviolet laser having a wavelength of 100 nm or more and 400 nm or less is used, and the laser beam irradiation energy, the scanning speed, and / or the number of scans (irradiation) that can be easily controlled are set. A variety of colors can be obtained just by controlling. The irradiation energy, the number of scans, or the scan speed can be input to the control device together with information on the figure to be drawn. Therefore, setting values can be entered and changed during drawing of a figure consisting of multiple colors. It is possible to perform automatically without performing it, and efficient marking becomes possible.

  Further, since the coloring obtained by the present invention is realized by an oxide film having a sufficient thickness, the coloring does not change depending on the direction in which the illumination light strikes or the viewing direction.

  Furthermore, in the present invention, a pretreatment such as forming a surface layer in advance is not required, and a modified layer can be formed on the metal surface without forced heating or cooling. Therefore, the coloring process can be made relatively simple.

  In the present invention, when the metal surface is irradiated with ultraviolet laser light, the metal material is placed in the atmosphere or in a specific atmosphere that does not harm the human body such as oxygen and nitrogen, or is safe to handle, A surface modification layer such as a single or a plurality of metal nitrides or metal oxides is formed on the surface by utilizing the reaction with the atmospheric gas. These surface modified layers can be used as a colored layer. Therefore, the processed portion is not a concave portion, and a mark such as a character, a picture, or a symbol can be provided on the metal surface by coloring that does not change depending on the angle at which the illumination light strikes and the viewing angle.

It is a figure which shows schematic structure of the metal surface processing apparatus by embodiment of this invention. It is a figure which shows schematic structure of the metal surface processing apparatus by another embodiment of this invention. It is a figure which shows the example of the method of scanning a laser beam two-dimensionally in the state which has a condensing area | region overlapping each other. It is a figure which shows the procedure of metal surface processing. It is a figure which shows the mechanism which forms a surface modification layer using reaction with specific atmospheric gas.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ultraviolet laser light source 2 Output variable device 3 Control apparatus 4 Shutter 5 Laser beam scanning device (galvano scanning mirror)
6 Condensing Lens 7 Lens Protective Cover 8 Metal Sample Plate 9 Metal Sample Plate Fixing Stage 10 Laser Light 11 Sample Scanning Device 12 Condensing Spot 13 Surface Modification Layer Forming Area 14 Gas Cylinder 15 Gas Transport Tube 16 Gas Outlet 17 Atmospheric gas 18 Valve 19 Laser light transmission window 20 Gas inlet 21 Gas outlet

Claims (3)

A metal surface processing method of irradiating a metal surface with laser light and performing a coloring process on at least a part of the metal surface,
A first step of emitting laser light in an ultraviolet region having a wavelength of 100 nm to 400 nm;
The laser light by condensed by the condenser lens, forming a condensing region which has an irradiation energy density of a the spot diameter is 50μm or more 100μm or less, and 0.1 J / cm ² or more 3.1 J / cm ² or less A second step of:
The laser light condensed by the condenser lens is adjacent to the laser light spot diameter and the laser light so that the light condensing area of the laser light overlaps in a direction perpendicular to the scanning direction of the laser light. A third step of irradiating while scanning the metal surface two-dimensionally , defining a scanning line drawing interval and a scanning speed of the laser beam ,
A metal surface processing method characterized by forming a surface modification layer on the metal surface to color the metal surface without forming a recess . In accordance with the color to be colored on the metal surface, irradiation conditions including the irradiation energy of the laser beam and the number of scans of the laser beam in the third step are determined ,
The number of scans, the metal surface treatment method according to claim 1 which is selected in the range of 2 to 5 times, characterized in Rukoto. The metal surface processing method according to claim 2 , wherein irradiation conditions including a scanning speed of the laser beam scanning are determined according to a color to be colored on the metal surface.

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