JP7463733B2 - Color-developing structure and method for producing the color-developing structure - Google Patents

Description

The present invention relates to a color-developing structure that exhibits structural color and a method for manufacturing the color-developing structure.

Structural colors, which are often observed in natural creatures such as Morpho butterflies, are colors that are visible due to optical phenomena caused by the minute structure of an object, such as light diffraction, interference, and scattering. For example, structural colors caused by multilayer interference are produced when light is reflected at the interface between adjacent thin films and the reflected light interferes. Multilayer interference is one of the principles behind the coloring of Morpho butterfly wings. In addition to multilayer interference, the minute uneven structure of the wing surface causes light scattering and diffraction, resulting in a vivid blue color that can be seen from a wide observation angle.

As a structure for artificially reproducing structural colors like those of the wings of a Morpho butterfly, a structure has been proposed in which a multilayer film layer is laminated on the surface of a substrate having fine irregularities arranged in an uneven manner, as described in Patent Document 1. In a structure in which a multilayer film layer is laminated on a flat surface, the wavelength of the reflected light seen changes significantly depending on the observation angle, and therefore the color seen changes significantly depending on the observation angle. In contrast, in the structure of Patent Document 1, the reflected light is intensified by interference and spreads in multiple directions due to the irregular irregularities, so the color changes gradually depending on the observation angle. As a result, a structure that exhibits a specific color at a wide observation angle, like the wings of a Morpho butterfly, is realized.

JP 2005-153192 A

However, in the manufacturing process of a multilayer film, it is necessary to stack multiple thin films in order with precise film thicknesses so that thin films made of different materials are adjacent to each other. Therefore, the load required to manufacture a structure in which multiple film layers are stacked on a fine uneven structure as described above is large.

The present invention aims to provide a color-producing structure that has a simple configuration and can suppress color changes caused by changes in the observation angle, and a method for manufacturing the color-producing structure.

The color-developing structure that solves the above problem includes a concave-convex layer having a concave-convex structure, and a dielectric layer made of a single thin film that has a surface shape that follows the concave-convex structure and emits reflected light that is enhanced by interference, and the convex parts that make up the concave-convex structure have a step shape of one or more steps from a plane on which the base of the convex part is located, and when viewed from a viewpoint facing the surface of the concave-convex layer, the pattern that the convex parts make up includes a pattern consisting of a collection of multiple graphic elements whose length along a first direction is less than a subwavelength and whose length along a second direction perpendicular to the first direction is greater than the length along the first direction, and the standard deviation of the length along the second direction of the multiple graphic elements is greater than the standard deviation of the length along the first direction, and the extinction coefficient in the visible region of the material of the dielectric layer has the smallest value in the wavelength range of the dominant color in the reflected light and the largest value outside the wavelength range of the dominant color.

The color-developing structure that solves the above problem includes a concave-convex layer having a concave-convex structure, and a dielectric layer made of a single thin film that has a surface shape that follows the concave-convex structure and emits reflected light that is enhanced by interference, the convex parts that make up the concave-convex structure have a step shape of one or more steps from a plane on which the base of the convex part is located, and when viewed from a viewpoint facing the surface of the concave-convex layer, the pattern made up of the convex parts includes a pattern consisting of a collection of multiple geometric elements whose length along a first direction is less than a subwavelength and whose length along a second direction perpendicular to the first direction is greater than the length along the first direction, and the standard deviation of the length along the second direction of the multiple geometric elements is greater than the standard deviation of the length along the first direction, and the dielectric layer is made of a metal compound that is any one of a metal oxide, a metal nitride, and a metal oxynitride, and the metal compound has a composition in which the metal element is in excess of the stoichiometric composition.

According to the above configuration, since the dielectric layer that generates interference is a single thin film, the color-producing structure can be constructed more simply than when a multi-layer film is used, and the burden required for manufacturing the color-producing structure is reduced. In addition, since the dielectric layer is absorptive of light other than the dominant color in the visible range, light in the wavelength range in which it is absorptive is prevented from being included in the reflected light from the color-producing structure. Therefore, the clarity of the dominant color exhibited by the color-producing structure is enhanced.

In the aforementioned configuration, the dielectric layer may be made of titanium oxide, and the titanium oxide may contain more titanium than in a stoichiometric composition.
According to the above-mentioned configuration, a dielectric layer having an absorption property for light other than the dominant color in the visible region is suitably realized.

In the above-described configuration, the dielectric layer may be in contact with the uneven layer, and may further include a reflective layer located on the opposite side of the dielectric layer to the uneven layer and having a function of enhancing the intensity of the reflected light.
According to the above-mentioned configuration, the intensity of reflected light is increased in the coloring structure observed from the side where the concave-convex layer is located relative to the dielectric layer, thereby improving the visibility of the color exhibited by the coloring structure.

In the above-described configuration, a reflective layer may be provided between the concave-convex layer and the dielectric layer, the reflective layer having a function of enhancing the intensity of the reflected light.
According to the above-mentioned configuration, the intensity of reflected light is increased in the coloring structure observed from the side where the dielectric layer is located relative to the concave-convex layer, thereby improving the visibility of the color exhibited by the coloring structure.

In the aforementioned configuration, the dielectric layer may have a thickness of not less than 10 nm and not more than 10 μm.
In the aforementioned configuration, the refractive index of the material of the dielectric layer may be greater than 1.5 and less than or equal to 3.0.
According to each of the above configurations, optical interference in the dielectric layer is easily and suitably generated.

In the above configuration, the reflective layer may have a reflectance of 30% or more for light transmitted through the dielectric layer.
In the above configuration, the reflective layer may be made of a metal material.
In the aforementioned configuration, the reflective layer may have a thickness of 50 nm or more.
According to each of the above configurations, the intensity of the reflected light is further increased.

In the above configuration, a substrate supporting the concave-convex layer may be further provided.
According to the above configuration, it is easy to apply the imprint method to the formation of the concave-convex structure.

In the above configuration, when the uneven structure is viewed from a viewpoint facing the surface of the uneven layer, the pattern formed by the convex portion is a pattern in which a first pattern consisting of a set of the graphic elements and a second pattern consisting of a plurality of strip-shaped regions extending along the second direction and aligned along the first direction are superimposed, and in the second pattern, the arrangement interval of the strip-shaped regions along the first direction is not constant in the plurality of strip-shaped regions, and the average value of the arrangement interval in the plurality of strip-shaped regions is equal to or greater than 1/2 of the minimum wavelength in the wavelength range included in the light incident on the dielectric layer, and the convex portion may have a multi-step shape in which a convex portion element having a predetermined height and an ...

According to the above configuration, the uneven structure provides a diffusion effect and a diffraction effect for the reflected light. As a result, the reflected light enhanced by interference, i.e., the dominant color, can be observed at a wide observation angle, and the increased intensity of this reflected light allows the visual perception of a glossy, vivid color.

A method for manufacturing a color-developing structure that solves the above problem includes the steps of forming an intaglio plate, transferring the intaglio plate's intaglio plate's intaglio plate using an imprinting method to form a resin layer having an intaglio structure on a substrate, and forming a dielectric layer made of a single-layer thin film that has a surface shape that follows the intaglio structure and emits reflected light that is enhanced by interference, from a material whose extinction coefficient in the visible range is the smallest in the wavelength range of the dominant color of the reflected light and the largest outside the wavelength range of the dominant color. The convex portions that make up the intaglio structure have a step shape with one or more steps from a plane on which the bases of the convex portions are located, and when viewed from a viewpoint facing the surface of the resin layer, the pattern made up of the convex portions includes a pattern consisting of a set of multiple graphic elements whose length along a first direction is less than a subwavelength and whose length along a second direction perpendicular to the first direction is greater than the length along the first direction, and the standard deviation of the length along the second direction in the multiple graphic elements is greater than the standard deviation of the length along the first direction.

The method for manufacturing a color-developing structure that solves the above problem includes the steps of forming an intaglio plate, forming a resin layer having an intaglio structure on a substrate by transferring the intaglio plate intaglio using an imprinting method, and forming a dielectric layer consisting of a single-layer thin film that has a surface shape that follows the intaglio structure and emits reflected light that is intensified by interference from a metal compound that is any one of metal oxides, metal nitrides, and metal oxynitrides, and has a composition in which the metal element is in excess of the stoichiometric composition. The convex portions that constitute the intaglio structure have a step shape of one or more steps from a plane on which the bases of the convex portions are located, and the pattern constituted by the convex portions includes a pattern consisting of a set of multiple graphic elements whose length along a first direction is equal to or less than a subwavelength and whose length along a second direction perpendicular to the first direction is equal to or greater than the length along the first direction, and the standard deviation of the length along the second direction in the multiple graphic elements is greater than the standard deviation of the length along the first direction.

According to the above manufacturing method, the dielectric layer that causes interference is a single thin film, so compared to the case where a multi-layer film is used, the color-developing structure can be constructed more simply, and the burden required for manufacturing the color-developing structure can be reduced. In addition, since the uneven structure is formed using the imprinting method, an uneven layer having fine unevenness can be formed conveniently and easily.

The present invention makes it possible to suppress color changes caused by changes in the observation angle with a simple configuration.

FIG. 2 is a diagram showing a cross-sectional structure of a coloring structure having a first uneven structure according to a first embodiment of the coloring structure. 1A is a plan view of a first uneven surface structure of a color-developing structure according to a first embodiment, and FIG. 1B is a cross-sectional view of the first uneven surface structure of the color-developing structure according to a first embodiment. FIG. 4 is a cross-sectional view of a coloring structure having a concave-convex structure of a second structure in the coloring structure of the first embodiment. Regarding the color-developing structure of the first embodiment, (a) is a diagram showing the planar structure of the uneven structure consisting only of second convex elements, and (b) is a diagram showing the cross-sectional structure of the uneven structure consisting only of second convex elements. 4A is a plan view of the concave-convex structure of the second structure of the color-developing structure of the first embodiment, and FIG. 4B is a cross-sectional view of the concave-convex structure of the second structure. FIG. 1 shows the variation of the refractive index and extinction coefficient of _TiO2 as a function of wavelength. FIG. 2 shows the variation of the refractive index and extinction coefficient of TiO _x as a function of wavelength. FIG. 2 is a graph showing the change in refractive index and extinction coefficient of aluminum as a function of wavelength. FIG. 2 is a graph showing the change in refractive index and extinction coefficient of polyethylene terephthalate as a function of wavelength. FIG. 13 is a diagram showing the wavelength of reflected light when _TiO2 and _TiOx are used. FIG. 11 is a diagram showing a cross-sectional structure of a coloring structure according to a second embodiment of the coloring structure; FIG. 13 is a diagram showing a cross-sectional structure of a color-producing structure according to a modified example.

First Embodiment
A first embodiment of a color-emitting structure and a method for manufacturing the color-emitting structure will be described with reference to Figures 1 to 10. The incident light and reflected light that the color-emitting structure targets are light in the visible region. In the following description, light in the visible region refers to light in the wavelength range of 360 nm or more and 830 nm or less.

[Configuration of color-developing structure]
As shown in FIG. 1, the color-developing structure 10 includes a substrate 12 , a resin layer 13 which is an example of a concave-convex layer, a dielectric layer 14 , and a reflective layer 15 .

The substrate 12 is a flat layer and supports the resin layer 13. The substrate 12 is made of a material that transmits light in the entire visible range, that is, a material that is transparent to light in the visible range. For example, the substrate 12 may be a synthetic quartz substrate or a film made of a resin such as polyethylene terephthalate (PET). From the viewpoint of increasing the flexibility of the color-developing structure 10, the substrate 12 is preferably a resin film. The thickness of the substrate 12 is, for example, 10 μm or more and 100 μm or less.

The resin layer 13 has an uneven structure on the surface opposite to the surface in contact with the substrate 12. The uneven structure of the resin layer 13 includes a plurality of irregularly arranged convex portions. The resin layer 13 is made of a resin that transmits light in the entire visible range, that is, a resin that is transparent to light in the visible range. For example, a thermosetting resin or a photosetting resin is used as the resin material for the resin layer 13.

The dielectric layer 14 covers the surface of the resin layer 13 and has a surface shape that follows the uneven structure of the resin layer 13. The dielectric layer 14 is a layer consisting of a single thin film made of a dielectric, and emits reflected light that is enhanced by interference. The dielectric layer 14 is made of any of metal oxides, metal nitrides, and metal oxynitrides. In order to favorably cause optical interference in the dielectric layer 14, the refractive index of the material of the dielectric layer 14 is preferably greater than 1.5 and less than or equal to 3.0, and the film thickness of the dielectric layer 14 is preferably greater than or equal to 10 nm and less than or equal to 10 μm. The material and film thickness of the dielectric layer 14 may be selected according to the desired color to be developed by the color-developing structure 10.

The reflective layer 15 is in contact with the dielectric layer 14 on the side opposite the resin layer 13 with respect to the dielectric layer 14. The reflective layer 15 has a surface shape that follows the uneven structure of the surface of the dielectric layer 14. The reflective layer 15 has the function of increasing the intensity of the reflected light that is enhanced by interference and emitted. As long as it is possible to realize a reflective layer 15 with a reflectance greater than the transmittance in the visible range, the material and film thickness are not limited, but in order to further increase the intensity of the reflected light, it is preferable that the reflective layer 15 is made of a metal material, and the film thickness of the reflective layer 15 is preferably 50 nm or more.

The color-forming structure 10 of the first embodiment is observed from the side where the substrate 12 is located relative to the resin layer 13, with the light that enters the color-forming structure 10 from the side where the substrate 12 is located relative to the resin layer 13 being regarded as incident light. In other words, the color-forming structure 10 is observed from the side where the resin layer 13 is located relative to the dielectric layer 14.

When the incident light that has passed through the substrate 12 and the resin layer 13 enters the dielectric layer 14, the dielectric layer 14 emits reflected light due to thin film interference. That is, the light reflected at the interface between the dielectric layer 14 and the resin layer 13 and the light reflected at the interface between the dielectric layer 14 and the reflective layer 15 interfere with each other, and light in an enhanced wavelength range is emitted. By positioning the reflective layer 15 on the opposite side of the dielectric layer 14 from the resin layer 13, the intensity of the reflected light emitted toward the observer is greater than when the reflective layer 15 is not provided. The reflected light that has been enhanced by interference is scattered by the irregular unevenness of the resin layer 13 and emitted in multiple directions, so that the color changes depending on the observation angle are gradual.

To increase the intensity of the reflected light, it is preferable that the reflectance of light at the interface between the dielectric layer 14 and the reflective layer 15, i.e., the reflectance of light transmitted through the dielectric layer 14 at the reflective layer 15, is 30% or more.

In the above configuration, the refractive index of the material of the dielectric layer 14 is n1, the refractive index of the material of the resin layer 13 is n2, and the refractive index of the material of the reflective layer 15 is n3. When n1>n2 and n1>n3, the following formula (1) is satisfied for wavelengths in the visible region where constructive interference occurs. In the following formula (1), d is the film thickness of the dielectric layer 14, m is 0 or any positive integer, θ is the angle of incidence of the incident light, and λ is the wavelength of the incident light.
2×n1×d×cosθ=(1/2+m)λ (1)

When n1>n2 and n1<n3, the following formula (2) is satisfied for wavelengths in the visible region where constructive interference occurs: In formula (2), d is the film thickness of the dielectric layer 14, m is any positive integer, θ is the angle of incidence of the incident light, and λ is the wavelength of the incident light.
2 × n1 × d × cos θ = m × λ ... (2)

If the above formula (1) or (2) is satisfied, the reflected light is enhanced by thin film interference.

Here, generally, the dielectric layer for generating single-layer thin-film interference or multilayer interference is composed of a material that transmits light in the entire visible range, i.e., a material that is transparent to light in the entire visible range, in order to increase the reflected component. However, since the wavelength range of reflected light due to single-layer thin-film interference does not have as steep a peak as the wavelength range of reflected light due to multilayer interference, the wavelength selectivity of the reflected light tends to be low, and as a result, the vividness of the color visually recognized as reflected light tends to be low. In other words, conventional dielectric layers that generate single-layer thin-film interference were not suitable for use in structures for producing a specific color.

In this embodiment, the dielectric layer 14 is configured so that it absorbs at least a portion of the light in the visible region other than the dominant color of the reflected light from the dielectric layer 14. The dominant color of the reflected light is the color that corresponds to the wavelength range in which the reflected light has the greatest intensity as a result of optical interference. The dominant color is visible in the color-producing structure 10.

In detail, in the visible region, the extinction coefficient k of the material of the dielectric layer 14 has the smallest value in the wavelength range of the dominant color of the reflected light, and has the largest value outside the wavelength range of the dominant color. For example, in the wavelength range of the dominant color of the reflected light, the extinction coefficient k of the material of the dielectric layer 14 is 0, and the extinction coefficient k of the material increases with distance from that wavelength range.

Such a dielectric layer 14 can be realized by using as its material a metal oxide, metal nitride, or metal oxynitride having a composition in which the metal element is in excess of the stoichiometric composition. When these metal compounds have a stoichiometric composition, they transmit light in the entire visible range. The minimum value of the extinction coefficient k of a metal compound tends to shift toward lower wavelengths as the metal element becomes more excessive. The extinction coefficient k of a metal increases as the wavelength increases.

According to the color-producing structure 10 of this embodiment, at least a portion of light in the visible region other than the dominant color of the reflected light from the dielectric layer 14 is absorbed by the dielectric layer 14. Therefore, light of the incident light other than the dominant color of the reflected light, i.e., light of a color different from the color desired to be produced by the color-producing structure 10, is prevented from being reflected by the color-producing structure 10 and being visually recognized by the observer. As a result, the specific color desired to be produced by the color-producing structure 10 becomes more clearly visible.

[Configuration of uneven structure]
The uneven structure of the resin layer 13 will be described in detail. Either of the first structure or the second structure can be applied as the uneven structure, and each of these two structures will be described. Fig. 1 shows a coloring structure 10A, which is a coloring structure 10 having the uneven structure of the first structure. The uneven structure of the first structure is composed of a plurality of convex portions 13a and concave portions 13b, which are regions between the plurality of convex portions 13a.

<First Structure>
The uneven structure of the first structure will be described in detail with reference to Fig. 2. Fig. 2(a) is a plan view of the resin layer 13 as viewed from a viewpoint opposite to its surface, and Fig. 2(b) is a cross-sectional view of the resin layer 13 taken along line II-II in Fig. 2(a). In Fig. 2(a), the protrusions 13a constituting the uneven structure are indicated by dots.

As shown in FIG. 2(a), the first direction Dx and the second direction Dy are directions included in a plane along the direction in which the resin layer 13 spreads, and are perpendicular to the first direction Dx and the second direction Dy. The plane is a surface perpendicular to the thickness direction of the resin layer 13.

When the resin layer 13 is viewed from a viewpoint opposite to its surface, the pattern formed by the convex portions 13a is a pattern consisting of a collection of multiple rectangles R indicated by dashed lines. The rectangles R are an example of a geometric element. The rectangles R have a shape that extends in the second direction Dy, and the length d2 of the rectangles R in the second direction Dy is greater than or equal to the length d1 of the first direction Dx. The multiple rectangles R are arranged so as not to overlap in either the first direction Dx or the second direction Dy.

The length d1 of the multiple rectangles R in the first direction Dx is constant. The arrangement interval of the multiple rectangles R in the first direction Dx is d1, that is, the multiple rectangles R are arranged in the first direction Dx at a period of d1.

On the other hand, the length d2 in the second direction Dy of the multiple rectangles R is irregular, and the length d2 of each rectangle R is a value selected from a population having a predetermined standard deviation. This population preferably follows a normal distribution. A pattern consisting of multiple rectangles R is formed, for example, by temporarily laying out multiple rectangles R having lengths d2 distributed with a predetermined standard deviation in a predetermined area, and determining whether or not each rectangle R is actually placed according to a certain probability, thereby setting areas where rectangles R are placed and areas where rectangles R are not placed. In order to efficiently scatter reflected light from the dielectric layer 14, it is preferable that the length d2 has a distribution with an average value of 4.13 μm or less and a standard deviation of 1 μm or less.

The region in which the rectangles R are arranged is the region in which the convex portion 13a is arranged, and when adjacent rectangles R are in contact with each other, one convex portion 13a is arranged in one region in which the regions in which the rectangles R are arranged are joined. In this configuration, the length of the convex portion 13a in the first direction Dx is an integer multiple of the length d1 of the rectangles R.

In order to prevent rainbow-colored light from scattering due to unevenness, the length d1 in the first direction Dx of the rectangle R is set to be equal to or less than the wavelength of light in the visible region. In other words, the length d1 is equal to or less than the subwavelength, i.e., equal to or less than the wavelength range of the incident light. That is, the length d1 is preferably equal to or less than 830 nm, and more preferably equal to or less than 700 nm. Furthermore, the length d1 is preferably smaller than the wavelength range of the dominant color of the reflected light in the dielectric layer 14. For example, when the color-producing structure 10 is used to produce blue color, the length d1 is preferably about 300 nm, when the color-producing structure 10 is used to produce green color, the length d1 is preferably about 400 nm, and when the color-producing structure 10 is used to produce red color, the length d1 is preferably about 460 nm.

To increase the spread of the reflected light from the dielectric layer 14, i.e., to increase the scattering effect of the reflected light, it is preferable that the uneven structure has many undulations, and it is preferable that the ratio of the area occupied by the convex portions 13a per unit area is 40% or more and 60% or less when viewed from a viewpoint facing the surface of the resin layer 13. For example, it is preferable that the ratio of the area of the convex portions 13a to the area of the concave portions 13b per unit area is 1:1 when viewed from a viewpoint facing the surface of the resin layer 13.

2(b), the height h1 of the convex portion 13a is constant, and the convex portion 13a has a one-step shape from the plane on which the base of the convex portion 13a is located. The height h1 of the convex portion 13a may be set according to the desired color to be produced by the color-producing structure 10, i.e., the wavelength range desired to be reflected from the color-producing structure 10. If the height h1 of the convex portion 13a is greater than the surface roughness of the dielectric layer 14 on the convex portion 13a and the concave portion 13b, the scattering effect of the reflected light can be obtained.

However, in order to suppress the interference of light caused by reflection from the unevenness, it is preferable that the height h1 is equal to or less than 1/2 the wavelength of light in the visible region, i.e., 413 nm or less. Furthermore, in order to suppress the above-mentioned interference of light, it is even more preferable that the height h1 is equal to or less than 1/2 the wavelength range of the dominant color of the reflected light in the dielectric layer 14.

In addition, if the height h1 is excessively large, the scattering effect of the reflected light due to the unevenness becomes too high, and the intensity of the reflected light tends to decrease, so the height h1 is preferably 10 nm or more and 200 nm or less. For example, in a blue color-producing structure 10, in order to obtain effective light diffusion, the height h1 is preferably approximately 40 nm or more and 130 nm or less, and in order to prevent the scattering effect from becoming too high, the height h1 is preferably 100 nm or less.

The rectangles R may be arranged so that two rectangles R arranged along the first direction Dx overlap each other to form a pattern of the convex portion 13a. That is, the rectangles R may be arranged in the first direction Dx at intervals smaller than the length d1, and the intervals between the rectangles R may not be constant. In the overlapping portion of the rectangles R, one convex portion 13a is located in one area where the areas where the rectangles R are arranged are joined. In this case, the length of the convex portion 13a in the first direction Dx is different from an integer multiple of the length d1 of the rectangle R. The length d1 of the rectangle R may not be constant, and it is sufficient that the length d2 of each rectangle R is equal to or greater than the length d1, and the standard deviation of the length d2 of the multiple rectangles R is greater than the standard deviation of the length d1. With such a configuration, the scattering effect of the reflected light can be obtained.

<Second Structure>
3 shows a color-forming structure 10B which is a color-forming structure 10 having a concave-convex structure of the second structure. The configuration in which the resin layer 13 has the concave-convex structure of the first structure and the configuration in which the resin layer 13 has the concave-convex structure of the second structure are common to each other except for the configuration of the concave-convex structure in the color-forming structure 10.
The convex portion 13c constituting the uneven structure of the second structure has a structure in which a first convex portion element having a configuration similar to that of the convex portion 13a of the first structure and a second convex portion element extending in a strip shape are superimposed in the thickness direction of the resin layer 13.

According to the color-producing structure 10A having the uneven structure of the first structure, the change in the color observed due to the observation angle is gradual due to the scattering effect of the reflected light, but the vividness of the color observed is reduced due to the decrease in the intensity of the reflected light caused by scattering. Depending on the application of the color-producing structure 10, a sheet that allows more vivid colors to be observed at a wide observation angle may be required. The second convex elements in the second structure are arranged so that the incident light is strongly diffracted in a specific direction, and the light scattering effect based on the first convex elements and the light diffraction effect based on the second convex elements realize a color-producing structure 10B that allows more vivid colors to be observed at a wide observation angle.

The configuration of the second convex element will be described with reference to Figure 4. Figure 4(a) is a plan view of a concave-convex structure consisting of only the second convex element, and Figure 4(b) is a cross-sectional view taken along line IV-IV in Figure 4(a). In Figure 4(a), the second convex element is indicated by dots.

As shown in FIG. 4(a), in a plan view, the second convex element 13Eb has a strip shape extending at a constant width along the second direction Dy, and the multiple second convex elements 13Eb are arranged at intervals along the first direction Dx. In other words, the pattern formed by the second convex elements 13Eb is a pattern consisting of multiple strip-shaped regions extending along the second direction Dy and arranged along the first direction Dx. The length d3 of the second convex element 13Eb in the first direction Dx may be the same as or different from the length d1 of the rectangle R that determines the pattern of the first convex element.

The arrangement interval de of the second convex elements 13Eb in the first direction Dx, i.e., the arrangement interval of the stripe region in the first direction Dx, is set so that at least a part of the reflected light on the surface of the uneven structure constituted by the second convex elements 13Eb is observed as first-order diffracted light. In other words, the first-order diffracted light is diffracted light whose diffraction order m is 1 or -1. That is, when the incident angle of the incident light is θ, the reflection angle of the reflected light is φ, and the wavelength of the diffracted light is λ, the arrangement interval de satisfies de ≧ λ / (sinθ + sinφ). For example, when a visible ray with λ = 360 nm is targeted, the arrangement interval de of the second convex elements 13Eb may be 180 nm or more, that is, the arrangement interval de may be 1/2 or more of the minimum wavelength in the wavelength range contained in the incident light. The arrangement interval de is the distance along the first direction Dx between the ends of two adjacent second convex elements 13Eb, and is the distance between the ends located on the same side of the second convex elements 13Eb in the first direction Dx.

The periodicity of the pattern formed by the second convex elements 13Eb is reflected in the periodicity of the uneven structure of the resin layer 13. When the arrangement interval de of the multiple second convex elements 13Eb is constant, the diffraction phenomenon on the outermost surface of the dielectric layer 14 causes reflected light of a specific wavelength to be emitted from the dielectric layer 14 at a specific angle. The reflection intensity of the light due to this diffraction is much stronger than the reflection intensity of the reflected light caused by the light scattering effect based on the first convex elements, so light with a metallic luster is visible, but at the same time, the diffraction causes dispersion, and the visible color changes depending on the change in the observation angle.

Therefore, even if the structure of the dielectric layer 14 and the first convex element is designed to obtain a color-producing structure 10 that exhibits a blue color, if the arrangement interval de of the second convex elements 13Eb is set to a constant value of about 400 nm to 5 μm, strong green to red light due to diffraction will be observed depending on the observation angle. In contrast, if the arrangement interval de of the second convex elements 13Eb is increased to about 50 μm, for example, the range of angles at which light in the visible range is diffracted will be narrowed, making it difficult to visually recognize color changes due to diffraction, but light with a metallic luster-like shine will be observed only at certain observation angles.

Therefore, if the arrangement interval de is not set to a constant value, and the pattern of the second convex element 13Eb is a pattern in which multiple periodic structures with different periods are superimposed, multiple wavelengths of light will mix in the reflected light due to diffraction, making it difficult to see the highly monochromatic light that is dispersed. Therefore, glossy, vivid colors can be observed at a wide observation angle. In this case, the arrangement interval de is selected, for example, from the range of 360 nm or more and 5 μm or less, and the average value of the arrangement interval de of the multiple second convex elements 13Eb should be 1/2 or more of the minimum wavelength in the wavelength range contained in the incident light.

However, as the standard deviation of the arrangement interval de increases, the arrangement of the second convex elements 13Eb becomes irregular, the scattering effect becomes dominant, and it becomes difficult to obtain strong reflection due to diffraction. Therefore, it is preferable to determine the arrangement interval de of the second convex elements 13Eb so that the reflected light due to diffraction is emitted in a range similar to the range in which the light spreads, depending on the angle at which the light spreads due to the light scattering effect based on the first convex elements. For example, if the reflected blue light is emitted in a range of ±40° with respect to the incident angle, the arrangement interval de in the pattern of the second convex elements 13Eb is set so that its average value is approximately 1 μm or more and 5 μm or less, and the standard deviation is approximately 1 μm. This causes the reflected light due to diffraction to be generated at an angle similar to the angle at which the light spreads due to the light scattering effect based on the first convex elements.

In other words, the uneven structure based on multiple second convex elements 13Eb is different from a structure for diffracting and extracting light of a specific wavelength range, and is a structure for emitting light of various wavelength ranges in a specified angle range using diffraction due to the dispersion of the array spacing de.

Furthermore, in order to generate a diffraction phenomenon with a longer period, a square region with one side of 10 μm to 100 μm may be used as the unit region, and the pattern of the second convex elements 13Eb for each unit region may have an arrangement interval de with an average value of approximately 1 μm to 5 μm and a standard deviation of approximately 1 μm. Note that the multiple unit regions may include a region in which the arrangement interval de is a constant value within the range of 1 μm to 5 μm. Even if a unit region with a constant arrangement interval de exists, if the arrangement interval de varies with a standard deviation of approximately 1 μm in this unit region and any of the unit regions adjacent to it, an effect equivalent to that of a configuration in which the arrangement interval de varies in all unit regions can be expected in terms of the resolution of the human eye.

The second convex elements 13Eb shown in FIG. 4 have periodicity due to the arrangement interval de only in the first direction Dx. The light scattering effect based on the first convex elements acts mainly on the light reflected in the direction along the first direction Dx in a plan view of the color-developing structure 10, but may also partially affect the light reflected in the direction along the second direction Dy. Therefore, the second convex elements 13Eb may also have periodicity in the second direction Dy. In other words, the pattern of the second convex elements 13Eb may be a pattern in which multiple strip-shaped regions extending in the second direction Dy are aligned along each of the first direction Dx and the second direction Dy.

In such a pattern of the second convex elements 13Eb, for example, the arrangement intervals along the first direction Dx and the arrangement intervals along the second direction Dy of the strip region may each have a variation such that the average value of each is 1 μm or more and 100 μm or less. Furthermore, depending on the difference between the influence of the light scattering effect based on the first convex elements on the first direction Dx and the influence of the light scattering effect on the second direction Dy, the average value of the arrangement intervals along the first direction Dx and the average value of the arrangement intervals along the second direction Dy may be different from each other, and the standard deviation of the arrangement intervals along the first direction Dx and the standard deviation of the arrangement intervals along the second direction Dy may be different from each other.

As shown in FIG. 4(b), the height h2 of the second convex element 13Eb may be greater than the surface roughness of the dielectric layer 14 on the convex portion 13c and the concave portion 13b. However, as the height h2 increases, the diffraction effect based on the second convex element 13Eb becomes more dominant in the effect of the uneven structure on the reflected light, making it difficult to obtain the light scattering effect based on the first convex element. Therefore, it is preferable that the height h2 is approximately the same as the height h1 of the first convex element, and the height h2 may be equal to the height h1. For example, the height h1 of the first convex element and the height h2 of the second convex element 13Eb are preferably in the range of 10 nm to 200 nm, and in the color-developing structure 10 that exhibits blue, the height h1 of the first convex element and the height h2 of the second convex element 13Eb are preferably in the range of 10 nm to 130 nm.

The uneven structure of the second structure will be described in detail with reference to Figure 5. Figure 5(a) is a plan view of the resin layer 13 as viewed from a viewpoint opposite to its surface, and Figure 5(b) is a cross-sectional view of the resin layer 13 taken along line V-V in Figure 5(a). In Figure 5(a), the pattern formed by the first convex element and the pattern formed by the second convex element are shown with dots of different densities.

As shown in FIG. 5(a), when the resin layer 13 is viewed from a viewpoint facing its surface, the pattern formed by the convex portion 13c is a pattern in which a first pattern formed by the first convex portion element 13Ea and a second pattern formed by the second convex portion element 13Eb are superimposed. That is, the region in which the convex portion 13c is located includes a region S1 formed only by the first convex portion element 13Ea, a region S2 in which the first convex portion element 13Ea and the second convex portion element 13Eb are superimposed, and a region S3 formed only by the second convex portion element 13Eb. In FIG. 5, the first convex portion element 13Ea and the second convex portion element 13Eb are superimposed so that their ends are aligned in the first direction Dx, but this is not limited to such a configuration, and the end of the first convex portion element 13Ea and the end of the second convex portion element 13Eb may be misaligned.

As shown in FIG. 5B, in region S1, the height of convex portion 13c is the height h1 of first convex portion element 13Ea. In region S2, the height of convex portion 13c is the sum of the height h1 of first convex portion element 13Ea and the height h2 of second convex portion element 13Eb. In region S3, the height of convex portion 13c is the height h2 of second convex portion element 13Eb. In this way, convex portion 13c has a multi-stage shape in which first convex portion element 13Ea, whose projection image in the thickness direction of resin layer 13 constitutes a first pattern and has a predetermined height h1, and second convex portion element 13Eb, whose projection image in the thickness direction constitutes a second pattern and has a predetermined height h2, are stacked in the height direction. Incidentally, the convex portion 13c can be considered as the first convex element 13Ea having the second convex element 13Eb stacked on top of it, or the first convex element 13Ea having the second convex element 13Eb stacked on top of it, starting from the base of the convex portion 13c.

The pattern formed by the first convex element 13Ea and the pattern formed by the second convex element 13Eb may be arranged so that the first convex element 13Ea and the second convex element 13Eb do not overlap. Even with such a structure, the light scattering effect based on the first convex element 13Ea and the light diffraction effect based on the second convex element 13Eb can be obtained. However, if the first convex element 13Ea and the second convex element 13Eb are arranged so that they do not overlap each other, the area in which the first convex element 13Ea can be arranged per unit area becomes smaller than that of the first structure, and the light scattering effect decreases. Therefore, in order to increase the light scattering effect and diffraction effect based on the convex elements 13Ea and 13Eb, it is preferable to overlap the first convex element 13Ea and the second convex element 13Eb to form the convex 13c into a multi-step shape, as shown in FIG. 5.

[Characteristics of the dielectric layer]
The characteristics of the dielectric layer 14 will be described using the results of a simulation. In the simulation, when the color-producing structure 10 is caused to produce blue color, the wavelength range of reflected light was obtained for each of the cases where titanium oxide (TiO ₂ ) of stoichiometric composition was used as the material of the dielectric layer 14 and where titanium oxide (TiO _x : 0<x<2) having an excess of metal elements compared to the stoichiometric composition was used. In other words, _{TiO x} is titanium oxide in a state where oxygen is deficient in TiO _2. In addition, in the simulation, aluminum was used as the material of the reflective layer 15.

First, Fig. 6 to Fig. 8 show the refractive index n and extinction coefficient k of the materials of the dielectric layer 14 and the reflective layer 15. Fig. 6 shows the refractive index n and extinction coefficient k of _TiO2 , Fig. 7 shows the refractive index n and extinction coefficient k of _TiOx formed so as to have oxygen deficiency, and Fig. 8 shows the refractive index n and extinction coefficient k of aluminum. Fig. 9 shows the refractive index n and extinction coefficient k of polyethylene terephthalate used as the substrate 12. Figs. 6, 8, and 9 show standard values of commercially available products, and Fig. 7 shows actual measured values.

As shown in FIG. 6, for TiO ₂ , the extinction coefficient k is 0 in the entire visible region, that is, TiO ₂ transmits light in the entire visible region. On the other hand, as shown in FIG. 7, for TiO _x , the extinction coefficient k is 0 in the wavelength region of about 410 nm to about 450 nm, which is a part of the wavelength region of blue light, and the extinction coefficient k increases as it moves away from the wavelength region. For example, the extinction coefficient k in the wavelength region of about 750 nm or more is around 0.05. In this way, in titanium oxide in which the metal element is in excess of the stoichiometric composition, the extinction coefficient k is smallest in the wavelength region of blue light, and is larger in the wavelength region other than blue light than the wavelength region of blue light. The extinction coefficient k is maximum in the wavelength region of red light in the visible region. Note that, as shown in FIG. 6 and FIG. 7, there is no difference in the refractive index n between TiO ₂ and TiO _x .

For each of _TiO2 and _TiOx , the incident angle of incident light was set to 30°, the thickness of the reflective layer 15 was set to 0.1 μm, and the optimal thickness at which the dominant color of the reflected light from the laminate of the dielectric layer 14 and the reflective layer 15 was blue was searched for using a genetic algorithm. As a result, the thickness of _TiO2 suitable for blue coloring was 0.0682 μm, and the thickness of _TiOx suitable for blue coloring was 0.0624 μm.

When _TiO2 and _TiOx were used as the material of the dielectric layer 14, the thickness of the dielectric layer 14 was set to a thickness suitable for blue coloring, and the thickness of the reflective layer 15 was set to 0.1 μm, and the wavelength range of the reflected light from the laminate of the dielectric layer 14 and the reflective layer 15 was obtained. Figure 10 shows the results. Note that Figure 10 also shows the wavelength range of the reflected light in the multilayer film layer that emits blue color as a reference value. This multilayer film layer is an alternating laminate of _TiO2 thin films and _SiO2 thin films.

As shown in Fig. 10, when the dielectric layer 14 made of a single thin film is used, the intensity of reflected light in the wavelength range other than blue light, that is, the wavelength range corresponding to a color different from the dominant color, is greater than when the multi-layer film is used. However, when comparing the case where _TiO2 is used as the material of the dielectric layer 14 with the case where _TiOx is used, the intensity of reflected light in the wavelength range other than blue light is lower when _TiOx is used. This is because, as described above, the extinction coefficient k of _TiOx is greater than the extinction coefficient k of _TiO2 in the wavelength range other than blue light. That is, the dielectric layer 14 made of _TiOx has the ability to absorb light other than blue light, and as a result, the intensity of reflected light in the wavelength range other than blue light, in other words, the wavelength range longer than the wavelength range of blue light, is lower than when _TiO2 , which does not have the ability to absorb light in the entire visible range, is used.

Therefore, when using a dielectric layer 14 made of a single thin film, the reflected light contains less light of colors other than blue when TiO _x is used than when TiO ₂ is used, and as a result, the reflected blue light is more easily recognized. In other words, a more vivid blue color is observed.

In addition, when _TiO2 and _TiOx were used, the same results were obtained when the thickness of the dielectric layer 14 was unified to the thickness of _TiO2 suitable for blue coloring, and when the thickness of the dielectric layer 14 was unified to the thickness of _TiOx suitable for blue coloring. That is, when _TiOx was used, the intensity of reflected light in wavelength ranges other than blue light was lower.

[Method of manufacturing color-developing structure]
A method for producing the color-forming structure 10 will now be described.
First, a resin layer 13 is formed on a substrate 12. For example, a nanoimprint method is used as a method for forming the uneven structure of the resin layer 13. For example, when forming the uneven structure of the resin layer 13 by a photo-nanoimprint method, a coating liquid containing a material for the resin layer 13 is applied to a surface on which the unevenness is formed of a mold, which is an intaglio plate having an inverted unevenness of the unevenness to be formed. A photocurable resin is used as the material for the resin layer 13. The method for applying the coating liquid is not particularly limited, and any known coating method such as an inkjet method, a spray method, a bar coating method, a roll coating method, a slit coating method, or a gravure coating method may be used.

Next, the substrate 12 is placed on the surface of the layer made of the coating liquid, and light is irradiated from the substrate 12 side or the mold side while the substrate 12 and the mold are pressed against each other. The mold is then released from the layer made of the cured resin and the substrate 12. As a result, the irregularities of the mold are transferred to the resin, forming a resin layer 13 with an irregular surface, and a laminate made of the substrate 12 and the resin layer 13 is formed. The mold is made of, for example, synthetic quartz or silicon, and is formed using known microfabrication techniques such as lithography and dry etching, which irradiate light or a charged particle beam.

The coating liquid may be applied to the surface of the substrate 12, and light may be irradiated while a mold is pressed against the layer of coating liquid on the substrate 12. Also, a thermal nanoimprinting method may be used instead of the photo-nanoimprinting method.

Then, a dielectric layer 14 is formed on the uneven surface of the resin layer 13. Furthermore, a reflective layer 15 is formed on the surface of the dielectric layer 14. The dielectric layer 14 and the reflective layer 15 are formed by known thin film formation techniques such as sputtering or vacuum deposition depending on the material. This forms the color-producing structure 10.

By adjusting the amount of material introduced during deposition of the dielectric layer 14, it is possible to produce a metal compound having a composition in which the metal element is in excess of the stoichiometric composition. For example, when forming a dielectric layer 14 made of a metal oxide, the oxygen flow rate can be reduced compared to when forming a thin film having a stoichiometric composition, thereby forming a dielectric layer 14 having a composition in which the metal element is in excess.

The color-producing structure 10 of this embodiment has a dielectric layer 14 made of a single thin film as a layer that generates interference, so that it has a simpler configuration and requires fewer thin films than a structure that has a multilayer film as a layer that generates interference. Also, compared to a structure that has a multilayer film, the effect that a manufacturing error in the thickness of a single thin film has on the coloring of the color-producing structure 10 is smaller. Therefore, it is possible to reduce the burden required for manufacturing the color-producing structure 10, and it is easy to obtain the desired coloring.

As described above, according to the first embodiment, the following effects can be obtained.
(1) Since the dielectric layer 14 that generates interference is a single thin film, the color-producing structure 10 can be constructed more simply than when a multi-layer film is used. Therefore, the color-producing structure 10 has a reduced color change caused by the change in observation angle due to the light scattering effect of the irregular unevenness, and the burden required for its manufacture is reduced.

(2) The dielectric layer 14 absorbs light in the visible range other than the dominant color of the reflected light, so that light in this absorbent wavelength range is prevented from being included in the reflected light from the color-producing structure 10. This enhances the clarity of the dominant color exhibited by the color-producing structure 10.

Specifically, the extinction coefficient k in the visible region of the material of the dielectric layer 14 has the smallest value in the wavelength range of the dominant color of the reflected light in the dielectric layer 14, and has the largest value outside the wavelength range of the dominant color. In addition, the dielectric layer 14 is made of a metal compound that is any one of a metal oxide, a metal nitride, and a metal oxynitride, and the metal compound has a composition in which the metal element is in excess of the stoichiometric composition. As a result, the above-mentioned effects are obtained.

(3) The color-producing structure 10 includes a reflective layer 15 located on the opposite side of the dielectric layer 14 from the resin layer 13. This increases the intensity of reflected light in the color-producing structure 10 observed from the side where the resin layer 13 is located relative to the dielectric layer 14. This increases the visibility of the color exhibited by the color-producing structure 10.

(4) The dielectric layer 14 has a thickness of 10 nm or more and 10 μm or less, and the material of the dielectric layer 14 has a refractive index of more than 1.5 and not more than 3.0, which favorably facilitates optical interference in the dielectric layer 14.

(5) The reflectance of the light transmitted through the dielectric layer 14 in the reflective layer 15 is 30% or more, the reflective layer 15 is made of a metal material, and the reflective layer 15 has a thickness of 50 nm or more, which further increases the intensity of the reflected light.

(6) In the case where the resin layer 13 has the second uneven structure, the uneven structure provides a diffusion effect and a diffraction effect for the reflected light. As a result, the reflected light enhanced by interference, i.e., the dominant color, can be observed at a wide observation angle, and the increased intensity of this reflected light allows the visual perception of a glossy, vivid color.

(7) Since the uneven structure of the resin layer 13 is formed using the imprinting method, the resin layer 13 having fine unevenness can be suitably and easily formed. Furthermore, if the color-developing structure 10 is configured to include a substrate 12 that supports the resin layer 13, the imprinting method can be easily applied.

Second Embodiment
A second embodiment of the color-emitting structure and the method for manufacturing the color-emitting structure will be described with reference to Fig. 11. In the second embodiment, the positional relationship between the dielectric layer and the reflective layer is different from that of the first embodiment. In the following, the differences between the second embodiment and the first embodiment will be mainly described, and the same reference numerals will be used to designate the same components as those in the first embodiment, and the description thereof will be omitted.

As shown in FIG. 11, in the color-producing structure 11 of the second embodiment, the reflective layer 15 is in contact with the resin layer 13, and the dielectric layer 14 is located on the opposite side of the reflective layer 15 to the resin layer 13. That is, in the color-producing structure 11 of the second embodiment, the positions of the dielectric layer 14 and the reflective layer 15 with respect to the resin layer 13 are opposite to those of the first embodiment, and the reflective layer 15 is sandwiched between the resin layer 13 and the dielectric layer 14. The dielectric layer 14 is the outermost layer of the color-producing structure 11 and is in contact with the air layer.

In the second embodiment, either the first structure or the second structure described in the first embodiment can be applied as the uneven structure of the resin layer 13. FIG. 11 illustrates an example in which the resin layer 13 has an uneven structure of the second structure. The configurations of the substrate 12 and the resin layer 13 in the second embodiment are the same as those in the first embodiment.

The reflective layer 15 covers the surface of the resin layer 13 and has a surface shape that follows the uneven structure of the resin layer 13. The dielectric layer 14 has a surface shape that follows the uneven structure of the surface of the reflective layer 15, that is, has a surface shape that follows the uneven structure of the resin layer 13. The configuration other than the positional relationship between the dielectric layer 14 and the reflective layer 15, that is, the materials and characteristics of the dielectric layer 14 and the reflective layer 15, are the same as those in the first embodiment.

Moreover, the method for manufacturing the color-producing structure 11 is the same as that of the first embodiment, except that the order of forming the dielectric layer 14 and the reflective layer 15 is reversed.
The color-forming structure 11 of the second embodiment is observed from the side opposite the substrate 12 to the resin layer 13, i.e., the side where the dielectric layer 14 is located relative to the resin layer 13, with light entering the color-forming structure 11 from the side opposite the substrate 12 to the resin layer 13 being regarded as incident light.

When light is incident on the dielectric layer 14, the dielectric layer 14 emits reflected light due to thin film interference. That is, light reflected at the interface between the dielectric layer 14 and the air layer and light reflected at the interface between the dielectric layer 14 and the reflective layer 15 interfere with each other, resulting in the emission of light in an enhanced wavelength range. By positioning the reflective layer 15 on the same side of the dielectric layer 14 as the resin layer 13, the intensity of the reflected light emitted toward the observer is greater than when the reflective layer 15 is not provided. The reflected light enhanced by interference is then scattered by the irregular unevenness and emitted in multiple directions, resulting in a gradual change in color depending on the observation angle.

In the above configuration, the refractive index of the material of the dielectric layer 14 is n1, the refractive index of air is n4, and the refractive index of the material of the reflective layer 15 is n3. When n1>n4 and n1>n3, the following formula (3) is satisfied for wavelengths in the visible region where constructive interference occurs. In the following formula (3), d is the film thickness of the dielectric layer 14, m is 0 or any positive integer, θ is the angle of incidence of the incident light, and λ is the wavelength of the incident light.
2×n1×d×cosθ=(1/2+m)λ (3)

Furthermore, when n4<n1<n3, the following formula (4) is satisfied for wavelengths in the visible region where constructive interference occurs: In formula (4), d is the film thickness of the dielectric layer 14, m is any positive integer, θ is the angle of incidence of the incident light, and λ is the wavelength of the incident light.
2 × n1 × d × cos θ = m × λ ... (4)

If the above formula (3) or (4) is satisfied, the reflected light is preferably enhanced by thin film interference.

In the second embodiment, the material of the dielectric layer 14 is a metal oxide, metal nitride, or metal oxynitride having a composition in which the metal element is in excess of the stoichiometric composition. In the visible region, the extinction coefficient k of the material of the dielectric layer 14 has the smallest value in the wavelength range of the dominant color of the reflected light in the dielectric layer 14, and has the largest value outside the wavelength range of the dominant color.

Therefore, at least a portion of the light in the visible region other than the dominant color of the reflected light from the dielectric layer 14 is absorbed by the dielectric layer 14. As a result, light of the incident light other than the dominant color of the reflected light, i.e., light of a color different from the color desired to be produced by the color-producing structure 11, is prevented from being reflected by the color-producing structure 11 and being perceived by the observer, so that the specific color desired to be produced by the color-producing structure 11 can be more clearly perceived.

As described above, according to the second embodiment, in addition to the advantages (1), (2), and (4) to (7) of the first embodiment, the following advantages can be obtained.
(8) The color-producing structure 11 includes a reflective layer 15 located between the dielectric layer 14 and the resin layer 13. This increases the intensity of reflected light in the color-producing structure 11 observed from the side of the resin layer 13 where the dielectric layer 14 is located. This increases the visibility of the color exhibited by the color-producing structure 11.

[Modification]
Each of the above-described embodiments can be modified and implemented as follows.
The color-developing structure may have an absorbing layer instead of the reflecting layer 15. The absorbing layer is located behind the dielectric layer 14 as viewed from the observer. For example, when the color-developing structure is observed from the side where the dielectric layer 14 is located with respect to the resin layer 13, as shown in FIG. 12, the absorbing layer 16 covers the surface of the substrate 12 opposite to the resin layer 13. The absorbing layer 16 absorbs at least a part of light in the visible region other than the dominant color of the reflected light in the dielectric layer 14. The absorbing layer 16 may be a black layer containing a black pigment or the like, and absorb light in the entire visible region. By providing the absorbing layer, light in a wavelength range different from the wavelength range of the dominant color of the reflected light in the dielectric layer 14 is prevented from being reflected at the interfaces of the layers inside the color-developing structure and the interfaces between the color-developing structure and its outside and being emitted toward the observer. Therefore, the clarity of the dominant color visually recognized in the color-developing structure is improved.

In addition, when the color-developing structure is observed from the side where the dielectric layer 14 is located relative to the resin layer 13, a reflective layer may be provided at the position of the absorbing layer 16 in FIG. 12, that is, at a position covering the surface of the substrate 12 opposite the resin layer 13, instead of between the resin layer 13 and the dielectric layer 14. Even if light other than the dominant color is mixed in the light that is transmitted through the dielectric layer 14, the resin layer 13, and the substrate 12 and reflected by the reflective layer, the dielectric layer 14 has the ability to absorb light other than the dominant color, so that light other than the dominant color is prevented from being emitted toward the observer. As a result, the reflective layer contributes to further increasing the intensity of the dominant color light in the reflected light.

The color-developing structure may further include layers different from those described in the above embodiments and modified examples, such as a protective layer that constitutes the outermost part of the color-developing structure on the side opposite the substrate 12, or a layer that has an ultraviolet absorbing function.

- An uneven structure may be formed on the substrate 12, and the substrate 12 may function as an uneven layer. In other words, a functional layer such as a dielectric layer 14 or a reflective layer 15 may be laminated on the surface of the substrate 12 having an uneven structure. In this case, the uneven structure is formed, for example, by using a dry etching method.

The figures constituting the pattern formed by the convex portions 13a in the first structure of the concave-convex structure in the concave-convex layer, and the pattern formed by the first convex portion elements 13Ea in the second structure are not limited to rectangles. The figures constituting these patterns may be ellipses, etc., and in short, they may be graphic elements having a shape whose length along the second direction Dy is equal to or greater than the length along the first direction Dx. Furthermore, it is sufficient that the length d1 in the first direction Dx and the length d2 in the second direction Dy of the graphic elements satisfy the various conditions described in the explanation of the first structure.

The convex portions constituting the concave-convex structure of the concave-convex layer may have a configuration in which the width in the first direction Dx gradually decreases from the base to the top. With such a configuration, the dielectric layer 14 and the reflective layer 15 are easily formed on the convex portions. In this case, the length d1 and the length d3 in the first direction Dx are determined by the pattern formed by the bottom surface of the convex portions.

- The use of the color-developing structure is not particularly limited. The color-developing structure may be attached to an article for decoration or for the purpose of preventing counterfeiting. In each use, the color-developing structure may be applied to a seal member and then attached to the article, or may be applied to a transfer sheet and then transferred to the article.

[Example]
The above-mentioned color-forming structure and its manufacturing method will be described with reference to a specific example. The color-forming structure of this example has a structure corresponding to that of the first embodiment.

First, a mold for forming a concave-convex structure was formed using the optical imprinting method. Since light with a wavelength of 365 nm is used as the light to be irradiated in the optical nanoimprinting method, synthetic quartz that transmits light of this wavelength was used as the mold material. The mold was formed by forming an inverted concave-convex structure of the concave-convex structure to be formed in the resin layer on a synthetic quartz substrate using electron beam lithography and dry etching methods. The concave-convex structure to be formed is the concave-convex structure of the second structure. Optool HD-1100 (manufactured by Daikin Industries) was applied to the surface of the mold as a release agent.

Next, a photocurable resin was applied to a PET film that had been treated to make one side easier to adhere, and the surface of the mold on which the irregularities were formed was pressed against the resin, and the resin was cured by irradiating it with light of a wavelength of 365 nm. The cured resin and PET film were then peeled off from the mold. This resulted in a laminate of a resin layer with an irregular structure and the PET film substrate.

Next, a single layer of titanium oxide film with a thickness of 60 nm was formed as a dielectric layer on the uneven surface of the resulting laminate of the resin layer and the substrate by sputtering. At this time, the flow rate of oxygen introduced into the chamber was adjusted so that the titanium oxide film was formed so that the metal elements were in excess of the stoichiometric composition. Furthermore, a single layer of aluminum film with a thickness of 100 nm was formed as a reflective layer on the upper surface of the dielectric layer by sputtering.

This resulted in the color-developing structure of the example. The color-developing structure of the example was observed from the side where the resin layer was located relative to the dielectric layer. When observed from a direction inclined at 30 degrees to the direction perpendicular to the surface of the substrate, a glossy blue color was clearly visible.

In addition, the angle dependency of the reflected light emitted on the side of the dielectric layer where the resin layer is located was measured. When white light was incident on the color-producing structure at an incident angle of 30°, scattered light was observed in the range of ±30° from the specularly reflected light.

Dx...first direction, Dy...second direction, 10, 11...color-developing structure, 12...substrate, 13...resin layer, 13a, 13c...protrusions, 13b...recesses, 13Ea...first protrusion element, 13Eb...second protrusion element, 14...dielectric layer, 15...reflective layer.

Claims (10)

A concave-convex layer having a concave-convex structure;
a dielectric layer made of a single thin film having a surface shape conforming to the uneven structure and emitting reflected light enhanced by interference;
the convex portions constituting the uneven structure have a step shape with one or more steps from a plane on which the bases of the convex portions are located, and when viewed from a viewpoint facing the surface of the uneven layer, the pattern constituted by the convex portions includes a pattern consisting of a set of a plurality of rectangular geometric elements, each having a length along a first direction that is equal to or less than a sub-wavelength and a length along a second direction perpendicular to the first direction that is equal to or greater than the length along the first direction, and the standard deviation of the lengths along the second direction in the plurality of geometric elements is greater than the standard deviation of the lengths along the first direction,
The dielectric layer is made of titanium oxide, and the titanium oxide contains more titanium than in a stoichiometric composition.
Chromogenic structure. the dielectric layer is in contact with the uneven layer,
The color-producing structure according to claim 1 , further comprising a reflective layer located on the opposite side of the dielectric layer from the concave-convex layer and having a function of enhancing an intensity of the reflected light. The color-producing structure according to claim 1 , further comprising a reflective layer located between the concave-convex layer and the dielectric layer, the reflective layer having a function of enhancing an intensity of the reflected light. The color-developing structure according to claim 1 , wherein the dielectric layer has a thickness of 10 nm or more and 10 μm or less. 5. The color-forming structure according to claim 1 , wherein the refractive index of the material of the dielectric layer is greater than 1.5 and less than or equal to 3.0. 4. The color-developing structure according to claim 2 , wherein the reflectance of the reflective layer for light transmitted through the dielectric layer is 30% or more. The color-developing structure according to claim 2 , wherein the reflective layer is made of a metal material. The color-forming structure according to claim 2 , 3 , 6 or 7 , wherein the reflective layer has a thickness of 50 nm or more. The color-developing structure according to claim 1 , further comprising a substrate supporting the uneven layer. forming an intaglio;
forming a resin layer having a relief structure on a substrate by transferring the relief patterns of the intaglio plate using an imprinting method;
forming a dielectric layer consisting of a single thin film having a surface shape following the unevenness structure and emitting reflected light enhanced by interference, from titanium oxide containing more titanium than in a stoichiometric composition , wherein the convex portions constituting the unevenness structure have a step shape with one or more steps from a plane on which the bases of the convex portions are located, and when viewed from a viewpoint facing the surface of the resin layer, a pattern constituted by the convex portions includes a pattern consisting of a collection of a plurality of rectangular geometric elements whose length along a first direction is equal to or less than a sub-wavelength and whose length along a second direction perpendicular to the first direction is equal to or greater than the length along the first direction, and wherein a standard deviation of the length along the second direction for the plurality of geometric elements is greater than the standard deviation of the length along the first direction.