JP5040152B2 - Structure, structure forming method and structure forming apparatus - Google Patents

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 structure forming apparatus for executing the formation method, and in particular, a void is formed in a substance. In addition, the present invention relates to a structure that expresses a structural color by a periodic structure formed at the interface of the gap, a method for forming the structure, and a structure forming apparatus.

In recent years, chemical coloring using pigment substances is becoming unacceptable from the viewpoints of recyclability and environmental suitability. Therefore, a structural color that develops color by using phenomena such as light diffraction and interference by forming a fine structure is important as an alternative technique.
Examples of the cause of this structural color include thin film interference, multilayer film interference, light scattering phenomenon, diffraction grating, and photonic crystal.

It is difficult to artificially express such a structural color, and there are few examples that have been put to practical use industrially.
As one of the few examples, for example, a method of forming a fine periodic structure by light irradiation and expressing a structural color has been proposed.

As a method for forming a fine periodic structure by the light irradiation, for example, there is LIPS (Laser Induced Periodic Structures) (for example, see Non-Patent Document 1). This is a fine periodic structure formed in a self-organized manner on the material surface by laser irradiation.
As another example, for example, a technique of writing a diffraction grating inside glass with a femtosecond laser is disclosed (for example, see Non-Patent Document 2).
Sylvain Lazare, “Large scale excimer laser production of submicron periodic structures on polymer surface.” Applied Surface Science 69 (1993) 31-37 North-ol. Journal of Laser Society Vol.30 No.2 Hideo Hosono, Kenichi Kawamura “Femtosecond laser interaction with transparent materials: Processing of periodic nanostructures into transparent materials by single pulse interference” Laser Association, May 2005, p . 7-12

However, there are three requirements for industrially putting structural colors into practical use: resistance to scratches and stains that impair color development, high coloration efficiency, and low cost production. It is not easy to meet.
For example, the technique disclosed in Non-Patent Document 1 generates a fine periodic structure on the surface of a substance, but the periodic structure formed on the surface causes light diffraction or weakening of color development. There was a problem that there was no resistance to scratches and dirt.

  On the other hand, since the technique disclosed in Non-Patent Document 2 writes a diffraction grating inside the glass, there is no problem of resistance such as scratches. However, since it can be formed only at one place for each laser irradiation, it takes a very long time to decorate a wide area, and there is a problem in productivity.

  The present invention has been considered in view of the above circumstances, and satisfies the requirements for industrially applying the structural color, and can improve the productivity by forming a fine periodic structure at high speed. Another object is to provide a structure forming method and a structure forming apparatus.

In order to achieve this object, in the structure of the present invention, a periodic structure that causes light diffraction is formed at the interface of one gap, and the periodic structure has a regular arrangement that expresses a structural color. A plurality of voids are formed inside the substance .
When the structure has such a configuration, it is possible to satisfy the requirement for industrially putting the structural color into practical use.
For example, since a fine periodic structure is formed inside the substance, it can be resistant to scratches and dirt. In addition, since the periodic structure is three-dimensionally formed, it is possible to increase the color development efficiency. Furthermore, since a plurality of voids can be formed in a wide range by performing light irradiation for a short time, such as by irradiating several laser beams, high-speed production is possible and manufacturing is possible at low cost. In this way, it is possible to satisfy the requirements for industrially putting structural colors into practical use.

  Furthermore, the coloring principle is based on the fine periodic structure formed inside the substance, not on the basis of chemical coloring such as pigments and dyes. For this reason, if it melts, it can erase easily. Therefore, it can contribute as decoration technology, such as a plastic container excellent in recyclability.

Further, if the structure has such a structure, a structural color can be expressed by a regular arrangement of the periodic structure. Thereby, the novel decoration technique which did not exist conventionally can be proposed.

In addition, the structure of the present invention can be configured such that a plurality of voids are formed at different depths from the surface of the substance.
When the structure has such a configuration, each of the plurality of gaps functions as a diffraction grating, and can be colored in different colors depending on the incident angle of light and the observation angle.
That is, a plurality of gaps are generated at random positions and at different depths within the range irradiated with light. For this reason, a periodic structure is formed three-dimensionally over the entire irradiation range (three-dimensional periodic structure), and the color development can be dramatically improved.

Further, the method of forming the structure of the present invention is irradiated with light structure using the structure forming apparatus, inside to form a void portion of the structure, at the interface of one air gap, the optical diffraction A periodic structure is formed, the periodic structure has a regular arrangement that expresses a structural color, and a plurality of voids can be formed inside the structure .
If the structure is formed by such a method, a space having a periodic structure that causes light diffraction at the interface can be formed inside the material by irradiating the material with light. Thereby, the structural color which satisfy | filled the requirements put into practical use industrially is realizable.

In the structure forming method of the present invention, the structure forming apparatus can perform light irradiation so as to generate a periodic intensity distribution.
When such a method is used for forming the structure, a periodic light intensity distribution is generated, so that a void having a periodic structure can be formed at the interface.

As described above, according to the present invention, it is possible to realize a structural color that satisfies the requirements for industrial use.
In addition, it can contribute as a decoration technique for plastic containers and the like having excellent recyclability.

Hereinafter, preferred embodiments of a structure, a structure forming method, and a structure forming apparatus according to the present invention will be described with reference to the drawings.
In the present embodiment, “decoration” means including coloring the package body in a chromatic color, blocking light so that light in a specific wavelength region does not pass inside the package body, and the like. .

[Structure]
First, an embodiment of the structure of the present invention will be described with reference to FIGS. 1 (a) to 1 (c) and FIG.
FIGS. 1A to 1C are views showing the structure of the structure according to the present embodiment, in which FIG. 1A is a perspective view showing the appearance of the structure, and FIG. Microscopic observation image (magnified view in the direction A of FIG. 1A) in which the portion irradiated with light in the body is enlarged, FIG. 2C is an enlarged longitudinal section of the portion irradiated with light in the structure. It is a microscopic observation image (B direction expanded sectional view of the figure (a)). FIG. 2 is a schematic diagram abstractly showing the enlarged cross-sectional view of FIG.

As shown in FIGS. 1B to 1C and FIG. 2, a gap 11 is formed inside the structure 10.
One gap portion 11 has a substantially copper bowl shape and has a long diameter of about 40 μm.
The void 11 is formed such that the radial direction of the copper bowl shape is substantially parallel to the surface direction of the structure 10 and the thickness direction of the copper bowl shape is substantially parallel to the thickness direction of the structure 10.

As shown in FIG. 2, the interface of the gap 11 has a periodic structure that causes light diffraction. And the periodic structure has the regular arrangement | sequence which expresses a structural color.
One period of the periodic structure is about 2 μm. This periodic structure is formed over the entire interface of the gap 11.

As shown in FIG. 1A, the gap 11 having such a shape is formed in a portion of the structure 10 that is irradiated with light.
Within the range irradiated with the light (in the same plane), a plurality of gaps 11 are formed as shown in FIGS.
The plurality of gaps 11 are formed at random positions in the lateral direction within the light irradiation range, and are formed at different depths from the light irradiation surface.

Here, as shown in FIG. 3, the individual gaps 11 having different depths from the surface within the same plane serve as a diffraction grating, and the structure differs depending on the incident angle of light and the observation angle. Color is developed (hereinafter, a surface on which the individual voids 11 exist within the same plane is referred to as a diffraction plane).
When there are diffractive surfaces at different depths, that is, in multiple layers, diffraction occurs at each diffractive surface. 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. Specifically, color development becomes stronger with light having a wavelength according to the following Bragg reflection formula (Formula 1).

    mλ = 2D (n2-sin2θ) 1/2 (Expression 1)

In this equation, 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 where the normal angle of the sample surface is 0 °.
If it is possible to form the structure 10 having the diffractive surfaces existing at equal intervals, the structure 10 can be colored only with light having a specific wavelength satisfying Equation 1. Further, when the diffractive surface is increased, the intensity of diffracted light is increased, so that the color development becomes stronger.
As described above, a photonic crystal having a three-dimensional periodic structure is known as a material that develops color according to Bragg's law.

  In addition, the microscopic observation image of FIG.1 (b), (c) uses a PET3x3 stretched sheet as a structure. However, the structure is not limited to this, and may be a substance in which a void is formed inside by light irradiation.

[Structure forming apparatus]
Next, the structure forming apparatus will be described with reference to FIGS.
FIG. 4 is a schematic diagram illustrating a configuration of a structure forming apparatus for forming a gap in a sample (structure), and FIG. 5 is a schematic perspective view illustrating a configuration of an interference optical system in the structure forming apparatus. is there.
As shown in FIGS. 4 and 5, the structure forming apparatus 20 includes a laser oscillator 21, a mirror 22, a concave lens 23, a convex lens 24, a microlens array 25, a mask 26, and a convex lens 27. Yes.

  Here, the laser oscillator 21 is a device that outputs a laser. For example, a femtosecond laser such as a YAG laser, a YVO4 laser, a YLF laser, or a Ti: sapphire laser that performs Q-switch oscillation can be used. These pulse lasers have a repetition frequency of several Hz to several tens kHz, and emit energy stored during this repetition period in a very short time width of several fs to several tens ns. Therefore, a high peak power can be efficiently obtained from a small input energy.

  Further, in order to form a periodic structure inside the sample 30, it is sufficient to irradiate about 5 to 20 laser beams, and the required time is about several seconds. Thereby, high-speed production becomes possible, and a product that expresses a structural color can be manufactured at low cost. In addition, the use of a light source with a high repetition frequency can further reduce the time.

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 by adjusting the laser output in the laser oscillator 21 and using, for example, a lens that has the same incident beam output and can reduce the diameter of the focused beam.
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 mirror 22 reflects the laser light output from the laser oscillator 21. In FIG. 4, two mirrors 22 are provided, but the number is not limited to two, and an arbitrary number can be provided.

The concave lens 23 enlarges the laser beam diameter. The convex lens 24 sets the enlarged laser beam diameter to a desired diameter. The microlens array 25 divides the laser into a number of light beams. The mask 26 selects some of the divided light beams. The convex lens 27 collects the light beam selected by the mask 26.
The relationship between the division of the laser by the microlens array 25 and the selection of the light beam by the mask 26 will be described in “Interference pattern forming method” described later.

[Method of forming structure]
(Generation method of periodic light intensity distribution)
Next, a method for generating a periodic light intensity distribution will be described with reference to FIGS.
The generation of the periodic light intensity distribution includes the following three methods.
As a first method, there is a method of generating a periodic light intensity distribution by interference between incident light and interface reflected light as shown in FIG.
As a second method, there is a method of irradiating a single light beam having a periodic light intensity distribution as shown in FIG.
As a third method, there is a method of generating a periodic light intensity distribution by multi-beam interference as shown in FIG.
The light irradiation having the periodic intensity distribution can be realized by exposure with a parallel light beam using the mask 26 having an opening periodically or by irradiation in an interference region where a plurality of light beams intersect.

(Changing the periodic structure pattern)
Next, the change of the periodic structure pattern will be described.
The following method is mentioned as a method of changing a periodic structure pattern.
For example, there is a method of changing the opening position of the mask 26.
In addition, the focal length of the convex lens 27 immediately before the substance is changed.
With such a configuration, irradiation can be performed in a substance interference region.

(Interference pattern formation method)
Next, a method for forming an interference pattern when functioning as a light control element will be described with reference to FIGS.
From the relationship between the light beam splitting by the microlens array 25 and the opening of the mask 26, the interference patterns recorded on the sample 30 are as shown in FIGS.
For example, as shown in FIG. 5A, the laser is divided into 36 (6 × 6) light beams by the microlens array 25, and among them, a light beam positioned vertically 2−2 and vertically 5−horizontal 5 When the light beam located at the position corresponding to the opening of the mask 26 passes, the interference pattern of oblique stripes is recorded on the sample 30.

  Also, for example, as shown in FIG. 5B, the laser is divided into 25 (5 × 5) light beams by the microlens array 25, among which vertical 2−horizontal 2, vertical 2−horizontal 4, vertical 4 -When the light beams positioned in the horizontal 2 and vertical 4-horizontal 4 respectively pass through the openings of the mask 26, a fine dot interference pattern is recorded on the sample 30.

  Further, for example, as shown in FIG. 5C, the laser is divided into 25 (5 × 5) light beams by the microlens array 25, among which vertical 2−horizontal 2, vertical 2−horizontal 4, vertical 3 -When the light fluxes located in the horizontal 3, vertical 4-horizontal 2, and vertical 4-horizontal 4 have passed through corresponding to the openings of the mask 26, a slightly rough interference pattern of dots is recorded on the sample 30.

  In this manner, the interference pattern varies depending on the combination of the division pattern of the microlens array 25 and the opening pattern of the mask 26. Thereby, optical information can be recorded as a kind of barcode using diffraction.

[Example of structure formation]
Next, an example of structure formation will be described with reference to FIG.
Example 1
The laser output from the laser oscillator 21 is magnified by the concave lens 23, and is split into a large number of light beams by passing this one light beam (φ27 mm diameter) through the microlens array 25.
Only a necessary light beam is allowed to pass through the mask 26, is condensed using a convex lens 27 having a focal length of 50 mm, and the light beams are superimposed and interfered.

In the interfered area, the biaxially stretched PET sheet (sample 30) was irradiated.
The wavelength of the YAG laser light is 355 mm, the pulse width is 5 ns, and the repetition frequency is 10 Hz.
One unit of the micro lens array 25 is a convex lens having a 4 mm square and a focal length of 120 mm.

The average light power irradiated was 70 mW and the irradiation area was 1.7 mm square, so the light power density per unit area was 2.4 W / cm ² .
As a result of 20 irradiations with this optical system, voids 11 were formed inside the stretched PET sheet, and a two-dimensional periodic structure with a period of 2 μm was formed at the interface. And the structural color by this periodic structure was observed.

(Example 2)
In the same manner as in Example 1, the injection-molded PET sheet (sample 30) was irradiated.
When 20 shots were irradiated, voids 11 were formed inside the sheet, and a two-dimensional periodic structure with a period of 2 μm was formed at the interface.

(Example 3)
The wavelength of the YAG laser light was 532 nm, and the PEN sheet that was biaxially stretched was irradiated in the same manner as in Example 1 by changing the light flux passing through the mask 26.
The average optical power irradiated was 140 mW and the irradiation area was 1.7 mm square, so the optical power density per unit area was 4.8 W / cm ² .
When 10 shots were irradiated, voids 11 were formed inside the sheet, and a two-dimensional periodic structure with a period of 2 μm was formed at the interface.

In addition, when the space | gap part 11 is formed on the conditions of Example 1, a microscopic observation image as shown in FIG. 1 can be obtained.
However, the conditions for forming the gap 11 are not limited to the above-described first to third embodiments.

For example, under the conditions of YAG-THG (355 nm), 247 mJ / cm ² , and 30 shots, the void 11 when a PET-INJ sheet was used for the sample 30 was formed in a shape as shown in FIG.
Further, under the conditions of YAG-SHG (532 nm), 500 mJ / cm ² , and 10 shots, the void 11 when a PET stretched sheet was used for the sample 30 was formed in a shape as shown in FIG.

[Comparison with comparative example]
Next, a comparison between the structure of the present embodiment and the comparative example will be described with reference to FIGS.
By the way, as a technique for forming a color by forming a plurality of minute cavities inside a substance, there is Japanese Patent Application Laid-Open No. 2004-359344 “Plastic Packaging and its Decorating Method” (hereinafter referred to as “Comparative Example”).
Here, the comparative example and the structure of the present embodiment are compared to clarify the differences.

(1) The structure to be formed is different.
In the comparative example, cavities formed by vaporization due to heat generation are arranged according to a periodic light intensity distribution.
On the other hand, in the present invention, a void portion is formed by a photochemical reaction between a laser beam and a substance, and a periodic structure is formed at the interface according to a periodic light intensity distribution. The voids may not be formed periodically.

Each structure of the cavity part of these comparative examples and the space | gap part of this invention is shown in FIG.
As shown in the figure, each of the cavity portions of the comparative example is formed in a substantially spherical shape, and the arrangement of a large number of cavity portions forms a periodic array structure to enable decoration.
On the other hand, the voids of the present invention (examples) have a periodic structure formed at the interface thereof, and the periodic structure has a regular arrangement that expresses a structural color, enabling decoration.

(2) The sample is different.
In the comparative example, since heat generated by laser light irradiation is used, a light absorbing heat generating agent for efficiently converting light energy into heat energy is kneaded.
On the other hand, no special additive is required in the present invention.
The difference between these samples is shown in FIG. As shown in the figure, in the comparative example, a light-absorbing exothermic agent-kneaded PET injection molded sheet (1.5 mm thickness) is used as a sample, and the transmittance is 0% at a wavelength of 355 nm. At this time, light has entered the inside of the substance, and as a result of exponential decay, the transmittance becomes 0%. On the other hand, in the present invention (Example), a biaxially stretched PET sheet (150 μm thick) was used as a sample, and the transmittance was 83%.

(3) The formation principle is different.
The comparative example is a method using heat generated by laser light irradiation. On the other hand, the present invention forms a structure by irradiation with laser light, and does not use heat generation.
Here, FIG. 12 shows an example of laser light irradiation conditions in the present invention and a condition in the third embodiment described in the background art of Japanese Patent Application Laid-Open No. 2004-359344 as a comparative example. In the figure, the horizontal axis indicates fluence (light energy per irradiation area of one pulse), and the vertical axis indicates the number of irradiation pulses.

In the figure, a circle indicates a condition for forming the void 11 in the structure of the present invention, a mark x indicates a condition for which the void 11 is not formed, and a mark indicates a condition for forming the cavity in the comparative example. Respectively.
As shown in the figure, the forming method of the present invention is characterized by a smaller number of irradiation pulses than the comparative example. This is because heat generation is not used for formation.
Moreover, it turns out that the formation method of this invention has less fluence than a comparative example.

As described above, according to the structure, the structure forming method, and the structure forming apparatus of the present embodiment, the irradiation material is irradiated with light having a periodic intensity distribution, so that voids are formed inside the irradiation material. A periodic structure that coincides with the periodic intensity distribution of the irradiated light can be formed at the interface of the gap.
As a result, it can be resistant to scratches and stains that cause the color development to be weakened, and the color development can be dramatically improved by forming in three dimensions, and the formation time can be shortened. By doing so, productivity can be improved. In this way, it is possible to decorate a material having excellent recyclability while satisfying the requirement for industrially putting structural colors into practical use.

In addition, since the structure of the present invention does not use a colorant by chemical coloring such as a pigment or a dye, the amount of the chemical substance used can be reduced, so that the structure has a small environmental load.
Furthermore, since the structure of the present invention is decorated with a periodic structure formed at the interface of the gap, it can be easily decolored by heating and kneading (re-pelletizing) during recycling. Therefore, although it is decorated when used as a container, it is colorless and transparent after reprocessing, so that recyclability is very good.
In addition, unlike chemical coloring, a vivid color tone having deep colors and gloss can be obtained, which is also effective for differentiation of products due to a decoration effect.

The preferred embodiments of the structure, the structure forming method, and the structure forming apparatus of the present invention have been described above. However, the structure, the structure forming method, and the structure forming apparatus according to the present invention are limited to the above-described embodiments. Needless to say, the present invention is not limited, and various modifications can be made within the scope of the present invention.
For example, in the above-described embodiment, PET is used as a sample, but this PET can be applied as a material for a package such as a container, a cup, a pouch, a tray, or a tube container. In this case, the present invention is provided as a decorating technique for a plastic container excellent in recyclability.

  Since this invention is invention for implement | achieving the expression of a structural color industrially, it can be utilized for the field | area where the substance which requires a decoration is used.

It is a figure which shows the structure of the structure of this invention, Comprising: (a) is a perspective view which shows the external appearance of a structure, (b) is a microscopic observation image (( (a) A direction enlarged view) and (c) are microscopic observation images (B direction enlarged cross sectional view of (a)) in which the longitudinal cross section of the portion irradiated with light in the structure is enlarged. It is the schematic diagram which represented the expanded sectional view of FIG.1 (c) abstractly. It is an array figure of a diffraction grating for explaining Bragg's law. It is the schematic which shows the structure of a structure formation apparatus. It is a typical perspective view which shows the structure of an interference optical system among structure formation apparatuses. FIG. 6 is a diagram illustrating a method for generating a periodic light intensity distribution, where (a) illustrates a method for generating a periodic light intensity distribution by interference between incident light and interface reflected light, and (b) illustrates a period. The figure which shows the method of irradiating the light of the single light beam which has typical light intensity distribution, (c) is a figure which shows the method of generating periodic light intensity distribution by multi-beam interference. It is a figure which shows the formation method of an interference pattern when it is made to function as a light control element. It is a figure which shows the formation state of the space | gap part 11 when using a PET-INJ sheet | seat for the sample 30 on the conditions of YAG-THG (355 nm), 247 mJ / cm < ² >, 30shots. It is a figure which shows the formation state of the space | gap part 11 when a PET stretched sheet is used for the sample 30 on the conditions of YAG-SHG (532 nm), 500 mJ / cm < ² >, 10shots. It is a table | surface which shows the planar observation image and cross-sectional schematic diagram about the space | gap part of this invention, and the cavity part of a comparative example. It is a graph which shows the comparison of the sample and transmittance | permeability about this invention and a comparative example. It is a graph which shows the comparison with the laser beam irradiation conditions in the Example of this invention, and the laser beam irradiation conditions in a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Structure 11 Space | gap part 20 Structure formation apparatus 21 Laser oscillator 25 Micro lens array 26 Mask

Claims (4)

A periodic structure that causes light diffraction is formed at the interface of one gap,
The periodic structure has a regular arrangement expressing a structural color;
A structure in which a plurality of voids are formed inside a substance. The structure according to claim 1, wherein the plurality of voids are formed at different depths from the surface of the substance. Irradiating the structure with light using a structure forming apparatus to form a void inside the structure,
A periodic structure that causes light diffraction is formed at the interface of one of the gaps,
The periodic structure has a regular arrangement expressing a structural color;
A method of forming a structure, wherein a plurality of the voids are formed inside the structure. The structure forming method according to claim 3, wherein the structure forming apparatus performs light irradiation so as to generate a periodic intensity distribution.