JPH0811309B2 - Iridescent color processing method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rainbow color forming method for forming a pattern or a region on a surface of a metal material, in which the hue of reflection gloss varies in a rainbow-like manner depending on the angle of incident light or the direction of viewing. And is preferably used as a surface decoration means for ornaments, household appliances, industrial articles, and the like.

[0002]

2. Description of the Related Art When fine irregularities of about 1 μm or less close to the wavelength range of visible light are densely formed on the surface of a material such as metal, the surface acts like a diffraction grating to disperse incident light. Since it is reflected by the reflected light, the hue of the reflected gloss changes in various colors like rainbow depending on the direction of the incident light and the viewing angle. Therefore, such fine concavo-convex processing is extremely promising as a decorating means for giving a beautiful multicolor variable coloring which cannot be achieved by painting or chemical coloring on the material surface.

However, in the usual laser processing means which has been frequently used for processing various materials such as metal in recent years, the minimum spot diameter which can be converged by the condenser lens is generally several μm to 10 μm. 1μ as above
It is impossible to form fine irregularities of m or less. Even if the spot diameter is narrowed down to about 1 μm, one groove can be formed by one scanning, so it takes a huge amount of processing time to form the concave and convex portions in a width or a surface shape visible to the naked eye. Will be required.

Therefore, the inventors of the present invention first disclosed in Japanese Patent Laid-Open No. 2-2
No. 63589 and Japanese Patent Laid-Open No. 3-94986 propose an epoch-making means of forming fine unevenness corresponding to the intensity distribution of the interference fringes of the interference light on the metal surface by irradiating the interference light of the laser. That is, according to these proposed means, the intensity of the laser light is melted in the bright part of the interference fringes,
By setting the energy density to evaporate, unevenness with concaves in the bright part and convexes in the dark part is formed on the metal surface. It is possible to form the concavo-convex stripes of a book at once.

[0005]

However, in the above-mentioned proposed means, since the laser light is emitted as the interference light,
Bright pattern components in a low-order multimode laser beam are overlapped with each other, or a plurality of beams divided from a single laser beam are overlapped with each other (Japanese Patent Application No. 1-84326).
No.) or a part of the laser beam is laterally displaced and superimposed on the original beam component (Japanese Patent Application No. 1-229567).
No.), and the restrictions on the model and device configuration of the laser oscillator used for that purpose are large, and it is difficult to adjust the optical system to perform the above division and displacement, and a laser beam with good coherence is selected. However, the clarity of the interference pattern could not be sufficiently enhanced, and there was a limit to the improvement in the sharpness of the iridescent color.

However, as a result of further studies conducted by the present inventors, even if pulsed laser light which is not used as interference light in advance is used, the metal surface is transformed into a specific state during the irradiation, thereby causing interference on the irradiation surface. In the same way as the above, finally, fine irregularities with the bright portion of the interference fringes being concave and the dark portion being convex are formed, and the coherence of the laser light is extremely good, and a very vivid rainbow color is produced. It was clarified that a decoration process that causes the above can be applied, and the present invention was completed.

[0007]

That is, the rainbow coloring processing method according to claim 1 of the present invention is such that the pulsed laser light L converged on the surface of a workpiece W made of a metal material in a reactive gas. By irradiating the same position with multiple pulses so that a thin film P made of a reaction product of the metal component and the gas component is formed on the surface of the workpiece W before the irradiation. After the irradiation, the laser beam La propagating in the surface direction using the thin film P as a waveguide and the irradiation laser beam l are caused to interfere with each other, and fine irregularities G corresponding to the intensity distribution of the interference fringes are formed on the surface of the workpiece W. It adopts the structure to be formed.

A second aspect of the present invention, in the iridescent color processing method according to the first aspect, employs a configuration in which the pulsed laser light L is irradiated at a position shallower than the focal point F of the converging means S in one direction. It was done.

A third aspect of the present invention is the above-mentioned claim 1 or 2.
In the iridescent color processing method, the workpiece W has a thermal conductivity of 1
The structure is a metal material of 00 W / m · K or less.

According to a fourth aspect of the present invention, in the rainbow coloring processing method according to any one of the first to third aspects, the pulse laser light L is a single mode laser beam.

According to a fifth aspect of the present invention, in the iridescent color processing method according to any one of the first to fourth aspects, a configuration is adopted in which the fine irregularities G are continuously formed while scanning the pulsed laser light L. Is.

According to a sixth aspect of the present invention, in the iridescent coloring method by the scanning method according to the fifth aspect, a circular lens of the laser light L is beamed by interposing a cylindrical lens SL in the optical path of the laser light L. This is a structure in which a beam pattern that is long in the direction orthogonal to the scanning direction is used.

[0013]

Detailed Configuration and Operation of the Invention When the pulsed laser light L focused on the surface of the workpiece W made of a metal material is irradiated in a reactive gas so that a large number of pulses hit the same position, the irradiation is performed before the irradiation. As shown in FIG. 1 (A), the metal component of the workpiece W heated by
A film P of the reactant is formed on the surface of the workpiece W. Then, when the refractive index of the coating P is higher than the refractive index of the material on both sides, that is, the material metal of the workpiece W and the atmospheric gas, the coating P is, so to speak, flattened (plate-shaped) in the core portion of the optical fiber. It corresponds to the one described above and acts as a waveguide.

When the surface on which the film P has been formed is further irradiated with the pulsed laser light L, a part La of the laser light is minute as shown by the arrow in FIG. From the scratches and crystal grain boundaries into the thin film P and travels in the surface direction, and the laser light La that travels in the surface direction interferes with the radiated laser light L to cause interference fringes on the surface of the workpiece W. Cause At this time, the intensity of the laser light L is set to a power density sufficient to melt and evaporate the surface in the bright portion of the interference fringes, so that the surface of the workpiece W is exposed as shown in FIG. Fine irregularities G are formed in which the bright portion of the interference fringe is concave and the dark portion is convex.

It should be noted that, as shown in FIG. 2, most of the laser light La propagating in the in-plane direction actually travels out of the thin film P. Needless to say, when the thin film P does not exist, the irradiated laser light L is not absorbed. Minutes simply reflect according to Snell's law, and do not propagate in the plane direction, so no interference occurs.

The groove spacing Δx of the formed fine concavities and convexities G is given by Δx = λ / sin θ, assuming that the laser beams L and La having the wavelength λ intersect at an angle θ and interfere with each other. Since θ is 90 degrees, sin θ = 1,
Δx = λ, that is, the same as the wavelength of the irradiation laser beam. Therefore, the fine irregularities G are composed of irregular stripes having an extremely fine pitch of about 1 μm or less, which is close to the wavelength range of visible light. The iridescent color whose color shade changes variously depending on the direction of incident light and the viewing angle is generated.

Therefore, the laser light L traveling in the above-mentioned plane direction
Since there is almost no optical path difference (distance difference) from the laser light source to the interference position between the laser light L and the irradiating laser light L, the microscopic unevenness G at the initial stage of formation serves as a grating coupler and is a thin film of the waveguide. Since it acts so as to enhance the efficiency of introducing the laser light La into P, and a single mode laser beam can be used, it is possible to generate very clear interference fringes in the entire irradiation spot, and to form a fine pattern. The unevenness G provides a highly vivid rainbow color.

Theoretically, if the laser light La propagating through the thin film P travels in the surface direction even for one pitch of the interference fringes, it will interfere with the irradiation laser light L. This one pitch is about 1 μm or Since the width is shorter than that, most substances that are normally opaque within this width behave as transparent. Therefore, the thin film P serving as the waveguide does not have to be a transparent substance in the general concept, but naturally, it is strongest when the intensity ratio of the irradiation laser light L and the laser light La traveling through the waveguide is 1: 1. It will cause interference,
Good interference fringes cannot be obtained with substances that have too much light attenuation.

In such an iridescent coloring process, fine unevenness G is obtained for each range of the irradiation spot without changing the irradiation position of the laser beam L.
However, a scanning method in which fine irregularities are continuously formed while scanning with laser light is more preferable. That is, in this scanning method, the laser light L
The scanning speed is set so that the pulse of # 1 hits the same position on the workpiece a number of times, but as shown in FIG. 3, the thin film P of the waveguide is formed in the first half of the moving direction of the moving irradiation spot, Fine irregularities G are finished by melting and evaporation corresponding to the interference fringes at the part. In this case, the laser light La propagating through the thin film P is very efficient in the thin film P by using the fine unevenness G already formed in the latter half portion as a grating coupler even if it does not penetrate into the thin film P from minute scratches or crystal grain boundaries. Since it can enter, the interference with the irradiation laser beam L becomes stronger than that in the method of processing with the irradiation spot stopped, and a clearer fine unevenness G can be formed.

As the pulsed laser light L to be applied, the laser beam emitted from the laser oscillator is used by being converged through a converging means such as a convex lens or a concave mirror, but a general laser processing device for metal processing is used. In this case, if the irradiation surface is located near the focus of the converging means, the entire area of the irradiation spot will be melted and evaporated uniformly as in the ordinary groove cutting process, so that clear fine irregularities G corresponding to the interference fringes will be formed. In order to form the laser beam, it is necessary to set the irradiation so that the irradiation is performed at a position deviated from the focal point in one direction at a shallow depth. FIG. 4 exemplifies the above-mentioned processing conditions. The range of Z ₀ including the focal point F of the lens S that converges the pulsed laser light L is the damaged area,
Above and below that are suitable processing areas Z ₁ and Z ₂ .

By the way, since the laser light L emitted from the laser oscillator is generally a beam pattern having a circular cross section, in the processing of the scanning system, the laser light passes with a wider width toward the central portion of the processing line. The groove formation conditions are different between the central part and both sides, and when the beam intensity is strong, the fine irregularities in the central part of the processing line are easily collapsed due to excess energy, while when the beam intensity is weak, the fine irregularities in the peripheral part of the processing line Tends to become unclear due to lack of energy, and it is difficult to form uniform fine irregularities on the entire processing line. However, as shown in FIG. 5, if the cylindrical lens SL is interposed in the optical path of the laser light L such that the longitudinal direction thereof is orthogonal to the beam scanning direction, the circular beam pattern is long in the direction orthogonal to the scanning direction. Since it is converted into a beam pattern, the difference in the width of the irradiation spot along the scanning direction between the central part and both sides of the processing line becomes small, the irradiation energy in the line width direction is equalized, and the irradiation spot is scanned as a whole. Since the width along the direction is narrow, it is possible to prevent more than necessary laser light from hitting the fine unevenness formed during scanning, and thus it is possible to form uniform and clear fine unevenness G over the entire width of the processing line. Becomes

Incidentally, DP in FIG. 5 is a Dope prism interposed in the optical path of the laser beam, and has the function of rotating the transmitted image at a double angle without rotating the plane of polarization by the rotation thereof. Therefore, when the fine irregularities G are formed by the scanning method with the cylindrical lens SL interposed, the vector direction of movement is calculated based on the movement command in the XY directions of the laser beam, and the dope prism DP is set based on this. By controlling the rotation, it is possible to adjust such that the major axis direction of the long beam pattern formed by the cylindrical lens SL is always orthogonal to the scanning direction.

The metal material of the workpiece W is not particularly limited as long as it can form a film of high refractive index to serve as a waveguide by various gas phase reactions under heating by laser light irradiation. However, those having a low thermal conductivity are more preferable.
That is, in this iridescent color processing, the surface irradiated with the laser light L is melted and evaporated according to the pattern of the interference fringes, that is, the bright portions of the interference fringes are concave and the dark portions are convex, and the fine irregularities are formed. Because it is left on the surface, the material being processed is heated rapidly.
It needs to be rapidly cooled, and therefore the lower the thermal conductivity is, the better the fine irregularities G are likely to be formed.

However, as a suitable metal material when using a general laser beam having a pulse width of about 50 to 200, the thermal conductivity [W / m · K] is added in parentheses, for example, nichrome. Alloy (13), stainless steel (Cr18-N
i8 15), titanium (20), silicon steel (25), N
i-Cr steel (33 with Ni3.6-Cr0.8), platinum iridium (31 with Pt90-Ir10), platinum rhodium (46 with Pt90-Rh10), carbon steel (C0.8-M).
n is 50), platinum (72), chromium (87), nickel (94) and the like having a thermal conductivity [W / m · K] of 100 or less. Among these, the thermal conductivity is particularly 50.
The following are preferred: However, the shorter the pulse width of the laser light, the easier the rapid heating / cooling is likely to occur. Therefore, there is a difference in the upper limit of the thermal conductivity of the applicable metal material depending on the type of laser used. For example, a laser having a pulse width of 10 ns or less When light is used, it is possible to process even a metal material having the thermal conductivity of about several hundreds.

On the other hand, the conditions of the pulsed laser light used are that the pulse width is short due to the rapid heating / cooling described above, the repetition of the pulse is faster than the drawing speed, and the single mode (TEM ₀₀ ). In particular, the intensity distribution of laser light is closer to a trapezoidal mode than a Gaussian distribution. At present, as a laser satisfying such conditions, a CW (continuous oscillation) pumped YAG laser with a Q switch (pulse width of about 100 ns, repetition rate K) is used.
Hz, oscillation wavelength 1.06 μm), pulse excitation YAG laser (pulse width 1
0 ns or less, repetition about 500 Hz), pulse excitation carbon dioxide laser (repetition about 1 KHz, oscillation wavelength 10.
6 μm), excimer laser (pulse width 2 to 50 ns, repetition of about 1 KHz, oscillation wavelength = ultraviolet, ArF = 0.1
93 μm, KrF = 0.249 μm, XeCl = 0.3
08 μm, XeF = 0.351 μm), ruby laser (repeating about 500 Hz, oscillation wavelength 0.6943 μ)
m), titanium sapphire laser (oscillation wavelength 0.68 ~
Variable up to 1.1 μm) and the like. Of these, a CW (continuous oscillation) pumped YAG laser with a Q switch is particularly recommended because it repeats quickly and has an appropriate oscillation wavelength and pulse width.

[0026]

Example 1 A pulsed laser beam of a linearly polarized Q-switched Nd: YAG laser (single mode, wavelength 1.06 μm, pulse width 100 ns, laser output 0.5 mJ) can be irradiated by pulse by pulse operation. With the configuration, the irradiation position is set to 8 mm above the focal point of the objective lens, and the power density of this pulsed laser light at the irradiation position is 22M.
Concentrated to W / cm ² and mirror-polished 18-
When one pulse was repeatedly irradiated in air at the same position on the surface of the 8 stainless steel plate, the surface in the irradiation spot was gradually oxidized, and Cr ₂ O _{3 serving} as a waveguide was mainly used (Ni
An oxide film containing O) is formed, and a group of minute grooves corresponding to the bright part of the interference fringes starts to be shallowly formed after 34 times of irradiation, and the depth of the groove increases as the number of times of irradiation increases. After about 100 times, good fine irregularities were uniformly formed on the entire surface of the spot having a diameter of about 90 μm. The fine irregularities had a groove width of about 0.5 μm, a groove depth of 0.03 to 0.04 μm, and a pitch of about 1 μm, and produced a very clear iridescent color. However, when the pulsed laser light was further irradiated, the groove disappeared from the center of the irradiation spot, and this disappeared region gradually expanded to the periphery.

The power density of the pulsed laser light is set to 2
When processed in the same manner with 8 MW / cm ² , a groove group started to be formed after 34 times of irradiation, and fine unevenness was formed in a size of about 110 μm after about 70 times of irradiation. It became slightly blurred. Further, when the power density was set to 18 MW / cm ² , the coloring due to the oxide film on the surface was only darkened up to 100 times of irradiation, but the deep groove group that was suddenly completed in the center of the irradiation spot in the subsequent irradiation. This groove group rapidly expanded with the number of irradiations, but when it exceeded 170 times, the grooves tended to disappear gradually from the central portion of the irradiation spot.

Example 2 A mirror-polished metallic titanium plate was used in place of the stainless steel plate used in Example 1, the processing atmosphere was nitrogen gas (1 atm), and the power density at the irradiation position was 28 MW / cm ^2.
When the irradiation was repeated one pulse at a time on the same position on the surface of the metal titanium plate except that the setting was made so that the surface inside the irradiation spot was gradually nitrided and A TiN nitride film is formed, and a group of fine grooves corresponding to the bright part of the interference fringes starts to be shallowly formed by the irradiation number of 45 times, and the groove depth increases as the irradiation number increases, and the irradiation number of about 100 Good fine irregularities were uniformly formed on the entire surface of the spot having a diameter of about 90 μm. The fine irregularities have a groove width of about 0.5 μm and a groove depth of 0.03 to 0.04 μ.
m, pitch about 1 μm, and very vivid iridescent color was produced.

Example 3 The same Q-switched Nd: YAG laser as in Example 1 was used, the irradiation position was set to 8 mm above the focal point of the objective lens, and the power density was set to 22 MW / cm ^2, and the light was condensed in air. Pulsed laser light (repeated 2KH
z) was continuously irradiated to the same position of a mirror-polished 18-8 stainless steel plate in the air at a speed at which a pulse hits about 100 times, and a line image of a predetermined pattern was drawn. Fine irregularities in which grooves having a width of about 0.5 μm were densely aggregated at a pitch of about 1 μm were formed on the entire surface. This line drawing is composed of lines showing a variety of iridescent reflection gloss under both sunlight and indoor illumination light, and the shade of the reflection gloss changes variously depending on the illumination direction and the viewing angle. there were.

Example 4 Using the same Q-switched Nd: YAG laser as in Example 1,
As shown in FIG. 5, a cylindrical lens SL and a dope prism DP are interposed in the optical path of the laser light,
When the surface of the mirror-polished stainless steel plate is irradiated with the pulsed laser beam while scanning it under the same conditions as in Example 3, the controller controls the rotation of the Dope prism to constantly scan the major axis direction of the elliptical irradiation beam pattern. Scanning was performed so as to be orthogonal to the direction, and a line drawing having a predetermined pattern was drawn. as a result,
Finer concavities and convexities are formed over the entire line width of about 0.3 mm, in which grooves with a width of about 0.5 μm are densely gathered at a pitch of about 1 μm substantially in parallel with the line width direction. A line drawing composed of lines showing a reflection gloss that changes to a different rainbow color was obtained.

Example 5 The same Q-switched Nd: YAG laser as in Example 1 was used, the irradiation position was set to 7 mm above the focal point of the objective lens, and the power density was set to 28 MW / cm ² , respectively. Pulsed laser light (repeated 2 KHz) focused at atmospheric pressure) was continuously irradiated while scanning the same position of the mirror-polished metal titanium plate at a speed at which the pulse hits about 100 times, and a line drawing of a predetermined pattern was drawn. , About 90
Grooves with a width of about 0.5 μm have a pitch of about 1 in the entire line width of
The fine asperities densely gathered at μm were formed. This line drawing is composed of lines showing a variety of iridescent reflection gloss under both sunlight and indoor illumination light, and the shade of the reflection gloss changes variously depending on the illumination direction and the viewing angle. there were.

The present invention is not limited to the above-mentioned embodiments, and metal materials other than those used in these embodiments can be processed and the Q-switched Nd: YAG laser exemplified for forming fine irregularities can be used. It is needless to say that various pulse laser oscillators other than those (preferably those having a small pulse width) can be used.

[0033]

According to the iridescent color processing method of claim 1,
It is possible to easily form irregularities consisting of fine and dense grooves with a mutual interval of about 1 μm or less corresponding to the interference fringes of laser light on the surface of the work piece, and the reflection gloss causes the incident light to be incident on the basis of the fine irregularities. It is possible to inexpensively provide a processed product having a beautiful decoration that is composed of lines and surfaces that change in a rainbow-like manner depending on the direction and viewing angle. Further, in this processing method, a part of the irradiation laser light is propagated in the surface direction in the subsequent stage of the irradiation by the waveguide formed on the surface of the workpiece before the irradiation of the pulsed laser light, and the propagating laser light is propagated. And the irradiation laser light interfere with each other to form fine irregularities corresponding to the intensity distribution of the interference fringes, so there is no need to intervene a special interference mechanism in the optical path of the laser light or the laser oscillator itself, and the laser processing device In addition to the simple structure, there is an advantage that the interference is high and the fine irregularities to be formed cause iridescent color development with extremely high definition.

According to the iridescent color processing method of the second aspect, there is an advantage that it is possible to avoid the uniformization due to melting in the irradiation spot of the pulsed laser light and to form fine fine irregularities corresponding to the interference fringes. .

According to the iridescent color processing method of the third and fourth aspects, there is an advantage that it is easy to form clearer fine irregularities.

According to the iridescent color processing method of claim 5, it is possible to draw a line of an arbitrary pattern composed of a fine uneven surface on the surface of the workpiece by scanning the laser beam, and the fine unevenness is irradiated. It has the advantage that it becomes clearer than the method of processing with the spot stopped, and that it is easy to decorate the metal surface with line drawings, characters, etc. that produce a very vivid rainbow color.

According to the iridescent color processing method of claim 6, particularly when fine irregularities are continuously formed by a scanning method,
Irradiation energy in the width direction of the processing line is equalized, and it is possible to prevent more than necessary laser light from striking the fine irregularities formed during scanning, so that the entire fine width of the processing line is evenly and clearly defined. Is formed, and there is an advantage that decorations such as line drawings and characters that generate more vivid rainbow colors can be applied.

[Brief description of drawings]

FIG. 1 is a schematic vertical cross-sectional view for explaining a mechanism of forming fine irregularities in the iridescent color processing method of the present invention in the order of steps A to C.

FIG. 2 is a schematic vertical cross-sectional view showing a forming process of a fine unevenness by a scanning method in the processing method.

FIG. 3 is a schematic vertical sectional view showing a propagation state of laser light through a waveguide in the same processing method.

FIG. 4 is a schematic diagram showing a processing region of laser light used for forming fine irregularities in the processing method.

FIG. 5 is a schematic front view showing an example in which a cylindrical lens is used to form fine unevenness in the processing method.

[Explanation of symbols]

 W Workpiece P Thin film used as waveguide of laser light L Irradiated laser light La Laser light propagating in waveguide S lens (converging means) F focus G fine unevenness SL cylindrical lens

Front page continuation (72) Inventor Tokihiko Oshima 1-9-1, Jokoji, Amagasaki City, Hyogo Prefecture Osaka Fuji Kogyo Co., Ltd. (72) Inventor Shigeichi Hirata 1-9-1, Jokoji, Amagasaki, Hyogo Prefecture Incorporated (72) Inventor Yoshikazu Okano 1-9-1, Jokoji Temple, Amagasaki City, Hyogo Prefecture Osaka Fuji Industry Co., Ltd.

Claims (6)

[Claims] 1. By irradiating a surface of an object to be processed made of a metal material with a focused pulsed laser light so that a large number of pulses hit the same position in a reactive gas,
Before the irradiation, a thin film made of a reaction product of the metal component and the gas component is formed on the surface of the workpiece, and at the latter stage of the irradiation, laser light propagating in the surface direction is used as the thin film as a waveguide. A method for iridescent coloring, which comprises causing interference with laser light to form fine irregularities corresponding to the intensity distribution of the interference fringes on the surface of the workpiece. 2. The rainbow color developing method according to claim 1, wherein the pulsed laser light is applied at a position shifted in one direction in a depth direction from a focus of the converging means. 3. The iridescent color processing method according to claim 1, wherein the workpiece is a metal material having a thermal conductivity of 100 W / m · K or less. 4. The iridescent color processing method according to claim 1, wherein the pulsed laser light is a single-mode laser beam. 5. The iridescent color processing method according to claim 1, wherein fine irregularities are continuously formed while scanning with a pulsed laser beam. 6. The iridescent color processing according to claim 5, wherein the circular beam of the laser light is converted into a long beam pattern in a direction orthogonal to the beam scanning direction by interposing a cylindrical lens in the optical path of the laser light. Method.