JPWO2009136597A1 - Structure, structure forming method, and laser beam irradiation apparatus - Google Patents

Abstract

Even if it is a material which does not have photosensitivity, while being able to form a periodic structure inside a base material, the periodic structure can be formed with a cheaper laser apparatus. Minute cavities 12 were formed in a three-dimensional periodic arrangement inside the substrate 11 so as to cause light diffraction.

Description

  The present invention relates to a structure having a light control function using an optical phenomenon such as diffraction and interference, a method for forming the structure, and a laser beam irradiation apparatus for forming the structure, and more particularly, a laser beam irradiation apparatus. The present invention relates to a structure in which a periodic structure formed inside by irradiation exhibits a structural color, a structure forming method, and a laser beam irradiation apparatus.

In recent years, chemical coloring using pigment substances is becoming unacceptable from the viewpoints of recyclability and environmental suitability. A structural color that develops by using phenomena such as light diffraction and interference by forming a fine periodic structure is important as an alternative technique.
However, the two-dimensional periodic structure formed on the surface of the material does not have resistance to scratches and dirt that cause color development to be weakened.

In order to provide resistance to scratches and dirt, it is necessary to form a fine periodic structure inside the substance.
In addition, by forming a three-dimensional fine periodic structure inside the substance, it is possible to improve the coloring efficiency and provide coloring selectivity.
The following technique has been proposed as a method of forming this three-dimensional fine periodic structure.
For example, a three-dimensional photonic crystal in which a plurality of layers including a refractive index periodic structure are periodically stacked, and a plurality of layers formed by a rectangular lattice, a hole made of a predetermined medium, a columnar structure, etc. are sequentially cycled. Laminated layers have been proposed (see, for example, Patent Document 1).

However, since this proposed technique is formed by vapor deposition or etching, the process is complicated and takes time.
Therefore, a technique for forming a three-dimensional fine periodic structure by laser irradiation has been proposed (see, for example, Patent Documents 2 and 3).
According to this proposed technique, the process can be simplified and the processing time can be shortened.

However, the techniques described in Patent Documents 2 and 3 described above have the following problems.
For example, the object of the technique described in Patent Document 2 is a photoresist material (photo-curing resin), and the object of the technique described in Patent Document 3 is a photosensitive material (photothermal refractive index capable of multiphoton exposure). Glass that causes a change). For this reason, it could not be used for a material having no photosensitivity.

  In addition, since an ultrashort pulse (femtosecond) laser is used for the laser device, there are problems such as difficulty in adjusting the irradiation optical system and an expensive laser device.

  The present invention has been made to solve the above-described problem. Even if the material does not have photosensitivity, the periodic structure can be formed inside the base material, and the periodic structure can be formed with a less expensive laser device. An object of the present invention is to provide a structure, a structure forming method, and a laser beam irradiation apparatus that can form the structure.

JP 2007-148365 A JP 2003-84158 A Japanese Patent Laid-Open No. 2004-126312

  In order to achieve this object, the structure of the present invention has a configuration in which minute cavities are periodically arranged in a three-dimensional manner inside the substrate so as to cause light diffraction.

  The structure forming method of the present invention is a method of irradiating a base material with light and forming microscopic cavities three-dimensionally and periodically inside the base material.

  The laser light irradiation apparatus of the present invention is a laser light irradiation apparatus that irradiates a substrate with light, and the number of irradiation pulses so that a cavity is formed in the substrate in a periodic array that causes light diffraction. And / or a laser oscillator having a function of adjusting the laser output.

According to the structure, the structure forming method, and the laser beam irradiation apparatus of the present invention, since the periodic structure is formed inside the base material, it can have resistance to scratches and dirt, which cause weakening of color development. .
In addition, since the periodic structure is formed by light irradiation, it can be performed under atmospheric pressure. Moreover, the periodic structure can be formed without performing pre-processing or post-processing.
Furthermore, since the base material is irradiated with light showing transparency to form a periodic structure, the base material may not have photosensitivity.

In addition, since the number of irradiation pulses and the laser output need only be adjusted as the function of the laser device, a structure can be manufactured using a laser device that is inexpensive and easy to adjust the irradiation optical system.
Furthermore, since a large number of cavities are formed in a three-dimensional periodic arrangement, the coloring efficiency can be improved by increasing the period in the depth direction.

It is sectional drawing which represented the structure of the structure of this embodiment typically. 2 is a transmission microscopic observation image of the surface of the structure when the structure is viewed from above (A direction in FIG. 1). It is the transmission microscope observation image inside a structure in depth 5 micrometers when seeing a structure from upper direction (A direction of FIG. 1). It is a SEM observation image which expanded and showed the section of a structure. It is an arrangement | sequence diagram of the periodic structure (or diffractive surface) for demonstrating Bragg's law. It is a schematic perspective view which shows the structure of a laser beam irradiation apparatus. It is a schematic diagram which shows the mode of the division | segmentation into five light beams in a beam splitter. It is a schematic diagram which shows the interference area | region (three-dimensional periodic light intensity distribution) of the light irradiated to a base material. It is a graph which shows the transmission spectrum of the extending | stretching PET sheet | seat which is a base material.

  Hereinafter, preferred embodiments of a structure, a structure forming method, and a laser beam irradiation apparatus according to the present invention will be described with reference to the drawings.

[Structure]
First, an embodiment of a structure of the present invention will be described with reference to FIGS.
FIG. 1 is a cross-sectional view schematically showing the structure of the structure according to this embodiment. FIG. 2 is a transmission microscope observation image when the structure is viewed from the top surface (direction A in FIG. 1). FIG. 3 is a transmission microscope observation image at a depth of about 5 μm when the structure is viewed from above. FIG. 4 is an SEM observation image when the cross section of the structure is enlarged.

As shown in FIGS. 1 to 4, a large number of minute cavities 12 are formed inside the base material 11 of the structure 10.
One cavity portion 12 has a shape approximate to a spherical shape or a capsule shape, and has a long diameter of about 1 μm.

The cavity 12 is formed in a portion of the structure 10 that is irradiated with light.
Within the irradiation range (in the same plane), a plurality of hollow portions 12 are formed as shown in FIGS.
The plurality of cavities 12 are formed at substantially equal intervals in the surface direction and the depth direction within the light irradiation range. That is, the plurality of hollow portions 12 are formed in a three-dimensional periodic array.
Each of the plurality of cavities 12 formed at a certain depth in the depth direction and each of the plurality of cavities 12 formed at the next depth are directly above the light irradiation range (A in FIG. 1). It is formed at a position that does not overlap when viewed from the direction.

  Here, the three-dimensional periodic structure is considered to be a multilayer structure in which the in-plane two-dimensional periodic structure and the two-dimensional periodic structure forming surface are periodically arranged in the depth direction (see FIG. 5). A diffraction phenomenon occurs on the two-dimensional periodic structure forming surface (referred to as a diffraction surface), and colors are generated in different colors depending on the incident angle of light and the observation angle. Here, the diffraction phenomenon also occurs in each diffraction surface existing at a position having a different depth. At this time, if the phase of the diffracted light from each surface is not aligned, the color development becomes weak, but if the phases are aligned, the color development becomes strong. That is, an interference phenomenon derived from the multilayer structure occurs. Specifically, color development becomes stronger with light having a wavelength in accordance with the Bragg reflection equation (Equation 1) below.

mλ = 2D (n ² −sin ² θ) ^1/2 (Expression 1)

In Equation 1, m is the diffraction order, λ is the wavelength, D is the distance between the diffraction surfaces, n is the refractive index of the substance, and θ is the observation angle with the normal angle of the sample surface being 0 °.
The structure in which the minute cavities 12 are periodically arranged in three dimensions is formed to match the three-dimensional periodic intensity distribution during light irradiation. The three-dimensional periodic intensity distribution is generated by five-beam interference. At this time, the period in the surface direction and the depth direction of the periodic intensity distribution is different depending on the intersection angle of the light beams.
That is, a three-dimensional periodic structure with a different period can be formed by varying the crossing angle at the time of five-beam interference. As a result, the wavelength of the light at which the diffraction phenomenon caused by the three-dimensional periodic structure and the interference phenomenon are established, that is, the color development can be controlled.

  The “regular arrangement that expresses structural color” in the present invention means that the grating period is close to the visible light wavelength (about 400 nm to 700 nm), and is about 2.0 μm or less. At this time, since visible light is strongly diffracted, structural colors are observed.

  2 and FIG. 3 and the cross-sectional SEM observation image of FIG. 4 are obtained by using a PET stretched sheet as the structure 10. However, the structure 10 is not limited to this, and may be a substance in which the cavity 12 is formed inside by light irradiation.

(Base material)
The base material 11 refers to a member that serves as a base of the structure 10.
For the base material 11, for example, a polymer compound such as polystyrene, polyethylene, polypropylene, polycarbonate, nylon resin, acrylic resin, vinyl chloride resin, phenol resin, BK7, optical glass such as quartz, soda glass, or the like is used as a material. Can do. In particular, a polyester compound such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), and polytrimethylene terephthalate (PTT) can be used as a suitable material. Moreover, for the base material 11, for example, a polymer compound obtained by kneading a plurality of types, a copolymerized polymer compound, or a polymer compound to which an appropriate additive is added can be used.
In addition, the base material 11 is not restricted to the above-mentioned material, A conventionally well-known arbitrary suitable material can be used. However, it is necessary to form the cavity 12 by light irradiation.

[Laser irradiation equipment]
Next, a laser beam irradiation apparatus will be described with reference to FIG.
FIG. 2 is a schematic perspective view showing the configuration of the laser beam irradiation apparatus.

  The laser beam irradiation device 20 is a device for forming the cavity 12 in the structure 10 (base material 11). As shown in the figure, a laser oscillator 21, a beam splitter 22, a collimator element 23, , A light beam selecting element 24 and a light collecting element 25 are provided.

Here, the laser oscillator 21 is a device that outputs laser light. For example, a nanosecond laser or a picosecond laser such as a YAG laser, a YVO ₄ laser, or a YLF laser can be used. These pulse lasers have a repetition frequency of several Hz to several tens of MHz, and emit energy stored during this repetition period in a very short time width of several ps to several tens ns. Therefore, a high peak power can be efficiently obtained from a small input energy. It is difficult to adjust the irradiation optical system and the apparatus is expensive, but a femtosecond laser such as a Ti: sapphire laser can also be used. In addition, a nanosecond pulse laser is particularly desirable because irradiation can be performed for a time width suitable for forming a cavity in laser light irradiation.

The laser oscillator 21 has a function of adjusting the number of irradiation pulses. The laser oscillator 21 can also control the energy density (fluence: energy per irradiation area of one pulse) by adjusting the output of the laser.
The energy density can be controlled not only by adjusting the laser output in the laser oscillator 21, but also by changing the irradiation beam diameter with the same laser output.
In addition, in order to form a periodic structure inside the irradiated material, it is necessary for light to be irradiated to enter the material. It is desirable to use light of a wavelength having an appropriate transmittance in the irradiated material so that the irradiated light is not absorbed at the extreme surface.

The beam splitter 22 is a transmissive optical element that diffracts because fine concave portions or convex portions are periodically carved on the surface, and divides the laser light into a plurality of light beams.
In particular, as shown in FIGS. 6 and 7, the beam splitter 22 divides laser light into at least 5 light fluxes including at least a central light beam (zero-order light) and a peripheral light beam (primary light) of four light beams. Divide into

As the collimator element 23, for example, a synthetic quartz plano-convex lens having a focal length of 200 mm can be used. In this case, the collimator element 23 is placed at a position 200 mm from the beam splitter 22. The collimator element 23 passes a plurality of light beams divided by the beam splitter 22.
The light beam selection element 24 can be a mask that is placed at a position where the light beam that has passed through the collimator element 23 is focused, blocks a light beam that is unnecessary for interference among a plurality of light beams, and allows only the necessary light beam to pass. The necessary light beams are five light beams of a central light beam (0th order light) and a peripheral light beam (primary light).

As the condensing element 25, for example, a synthetic quartz plano-convex lens having a focal length of 100 mm can be used, and the five light beams that have passed through the light beam selecting element 24 are condensed, and the five light beams intersect and interfere with each other. As shown in FIG. 8, the interfering region has a high intensity region distribution, and the substrate 11 is irradiated with light in this region.
In the interference region, the substrate 11 is irradiated with light having a three-dimensional periodic intensity distribution. This is realized by irradiating with the five-beam interference of the central light beam (zero-order light) and the peripheral light beam (primary light).

At this time, it is important that the intensity of the central light beam (zero-order light) and the intensity of the surrounding light beam (primary light) are close to each other. However, they need not be equal. For example, if the intensity of the zero-order light is too strong, it is equivalent to laser irradiation of a single light beam, and if the intensity of the primary light is too strong, it becomes equal to interference of four light beams, and the required three-dimensional periodic intensity is required. This is because no distribution can occur.
When a transmission type diffraction grating is used for the beam splitter, the distribution of the intensity of each light beam varies depending on the combination of the fine pattern of the transmission type diffraction grating and the laser wavelength used. In this way, the intensity of each light beam can be adjusted. However, what is used as a beam splitter is not limited to a transmissive diffraction grating.
As the collimator element 23 and the condensing element 25, an optical element such as a Fresnel lens or a GRIN (Graded-Index) lens can be used in addition to a convex lens.

Moreover, in order to form a periodic structure inside the base material 11, it is necessary for the light to irradiate to enter the material. In order to prevent the irradiation light from being absorbed at the extreme surface, light having a wavelength having an appropriate transmittance in the base material 11 is used.
Here, whether or not the substrate 11 has a transmissive property with respect to the wavelength is determined as follows.
For a specific wavelength, the light transmittance of the base material 11 is “transmittance” of 70% or more, the transmissivity is 10% or more and less than 70% “semi-transparent”, and the transmittance is less than 10%. Impermeability ".
When the base material 11 shows transparency with respect to a certain wavelength, the light enters the base material. On the other hand, in the case of showing impermeability, light only enters the vicinity of the surface of the substrate 11.

  Specifically, as shown in FIG. 9, when the substrate 11 is a PET sheet, light having a wavelength of about 330 nm or more (for example, a YAG laser) is included as light included in the wavelength region where the substrate 11 exhibits transparency. The third harmonic (355 nm) is irradiated to form the cavity 12.

[Method of forming structure]
Next, a method for forming the structure according to this embodiment will be described.
By irradiating light having a three-dimensional periodic intensity distribution, the cavity 12 is formed inside the substrate 11.
The light is light having a wavelength included in a wavelength region in which the substrate 11 exhibits transparency.

Further, as shown in FIGS. 6 and 8, the five light beams that have passed through the light beam selecting element 24 are collected by the light collecting element 25, and the base material 11 is irradiated with light in a region where these five light beams intersect and interfere with each other. .
In the interference region, since five light beams including the central light beam interfere with each other in the optical system of the laser light irradiation apparatus 20, light having a three-dimensional periodic intensity distribution can be irradiated. Thereby, the cavity part 12 can be formed in the base material 11 by a periodic arrangement.
At this time, it is necessary to irradiate the substrate 11 with a sufficiently high irradiation energy density to form the cavity 12. When the irradiation energy density is low, light is simply transmitted and the cavity 12 is not formed. Moreover, it is not preferable that the irradiation energy density is too high. If the irradiation energy density is too high, the periodic structure to be formed is destroyed or the base material 11 is burnt. The irradiation energy density required for forming the cavity 12 varies depending on the base material 11. Moreover, even if it is the light contained in the wavelength range which shows transparency, if the wavelength to be used differs, the irradiation energy density required for formation of the cavity part 12 will differ according to the difference in the transmittance | permeability.

Here, the case where PET is used for the substrate 11 will be described as an example.
The irradiation energy density in normal processing using light having a wavelength of 266 nm showing impermeability is 20 mJ / cm ² . When light having a wavelength of 355 nm showing transparency is used, the cavity 12 is not formed even if irradiation is performed with the same irradiation energy density of 20 mJ / cm ² . In order to form the cavity 12, the irradiation energy density needs to be 300 mJ / cm ² or more and 1000 mJ / cm ² or less. To better form a cavity 12, in particular, 500 mJ / cm ² or more 850mJ / cm ² or less is preferable.
Thus, when the substrate 11 irradiates light with a wavelength of 355 nm showing transparency with PET, irradiation is performed with an irradiation energy density of about 15 to 50 times that when using light with a wavelength of 266 nm showing normal impermeability. Then, the inventor's experiment revealed that the cavity 12 can be formed.

[Example of structure formation]
Next, examples of structure formation will be described.
The light beam of the Q-switch pulse YAG laser third harmonic (wavelength 355 nm) was split into a plurality of light beams by passing through the beam splitter 22. At this time, when the intensity of the 0th-order light is 1, the intensity of the 1st-order light is 3.6.
Each luminous flux was allowed to pass through the collimator element 23, and the luminous flux selection element 24 placed at the focal point blocked the luminous flux unnecessary for interference, and only the necessary luminous flux (five luminous flux) was allowed to pass. The light beam that passed through was condensed using the condensing element 25, and the light beams crossed and caused interference. At this time, the crossing angle between the 0th order light and the 1st order light was 12.6 °. Irradiate to a biaxially stretched PET sheet (transmittance 82.3% @ 355 nm) in the interfering region.
The specifications of the pulse YAG laser were a pulse width of 5 ns and a repetition frequency of 10 Hz.
As a result of irradiating one pulse at an irradiation energy density of 500 mJ / cm ² , a structure in which minute cavities 12 were three-dimensionally arranged inside the stretched PET sheet was observed. The structure observed at this time had a period in the plane direction of about 1.5 μm and a period in the depth direction of about 3.7 μm.

As described above, according to the structure, the structure forming method, and the laser beam irradiation apparatus of the present embodiment, by irradiating light having a three-dimensional periodic intensity distribution, The cavity 12 can be formed in a three-dimensional periodic arrangement.
Since the hollow portion 12 is formed inside the base material 11, it can have resistance to scratches and dirt that cause weakening of color development.

In addition, since the periodic structure is formed by light irradiation, it can be performed under atmospheric pressure. Moreover, the periodic structure can be formed without performing pre-processing or post-processing.
Furthermore, since the base material 11 is irradiated with light having transparency to form a periodic structure, the base material 11 may not have photosensitivity.

Further, as the function of the laser beam irradiation apparatus 20, it is only necessary to be able to adjust the number of irradiation pulses and the laser output. Therefore, a structure can be manufactured using the laser beam irradiation apparatus 20 that is inexpensive and easy to adjust the irradiation optical system.
Furthermore, since a large number of cavities 12 are formed in a three-dimensional periodic arrangement, the coloring efficiency can be improved by increasing the period in the depth direction.

The preferred embodiments of the structure, the structure forming method, and the laser beam irradiation apparatus of the present invention have been described above. However, the structure, the structure forming method, and the laser beam irradiation apparatus according to the present invention are limited to the above-described embodiments. It goes without saying that various modifications can be made within the scope of the present invention.
For example, in the above-described embodiment, the stretched PET sheet is given as a specific example of the base material, but the base material is not limited to the stretched PET sheet, and base materials formed of various materials and shapes may be adopted. it can.

  Since the present invention relates to a structure having a periodic structure inside the substrate, the present invention can be used for products formed of a material capable of forming the periodic structure.

DESCRIPTION OF SYMBOLS 10 Structure 11 Base material 12 Cavity part 20 Laser beam irradiation apparatus 21 Laser oscillator 22 Beam splitter

Claims (19)

A structure characterized in that minute cavities are periodically arranged in a three-dimensional manner inside a substrate so as to cause light diffraction. The structure according to claim 1, wherein the periodic arrangement of the hollow portions has a regular arrangement that expresses a structural color. The said base material is a polyester compound. The structure of Claim 1 or 2 characterized by the above-mentioned. The structure according to any one of claims 1 to 3, wherein the periodic array of the hollow portions is formed by light irradiation. The structure according to claim 4, wherein the light is light included in a wavelength region in which the base material exhibits transparency. The structure according to claim 4 or 5, wherein the light is irradiated so as to generate a three-dimensional periodic intensity distribution. The structure according to any one of claims 4 to 6, wherein the light is nanosecond pulse laser light. A structure forming method, comprising: irradiating a base material with light to form microscopic cavities in a three-dimensional periodic array inside the base material. The structure forming method according to claim 8, wherein the base material is a polyester compound. The structure forming method according to claim 8 or 9, wherein the light is light included in a wavelength region in which the base material exhibits transparency. The structure forming method according to claim 8, wherein the light is irradiated so as to generate a three-dimensional periodic intensity distribution. The structure forming method according to claim 11, wherein the light is nanosecond pulse laser light. A laser light irradiation device for irradiating a substrate with light,
A laser light irradiation apparatus comprising a laser oscillator having a function of adjusting the number of irradiation pulses and / or the laser output so that a cavity is formed in a periodic arrangement that causes light diffraction inside the base material. . The laser light irradiation apparatus according to claim 13, wherein the laser oscillator is a nanosecond pulse laser. The laser beam irradiation apparatus according to claim 13 or 14, further comprising an optical system that generates light having a three-dimensional periodic intensity distribution and irradiates the substrate. The optical system is configured to divide the light output from the laser oscillator into five light beams and irradiate light so that a region where the five light beams interfere becomes the base material. 15. The laser beam irradiation apparatus according to 15. The laser beam irradiation apparatus according to claim 15 or 16, wherein the optical system includes a beam splitter, a collimator element, a light beam selection element, and a condensing element. The laser light irradiation apparatus according to claim 16 or 17, wherein the optical system has a mechanism for adjusting the intensity of each of the divided light beams. The laser beam irradiation apparatus according to claim 17 or 18, wherein the intensity of each light beam divided by changing the beam splitter can be adjusted.