Optical element and authentication body

Abstract

To provide an optical element allowing easy verification of authenticity, and a certification body.SOLUTION: A lattice pattern positioned in a first region includes lattice groups GPG repeated along a first direction D1. The lattice group GPG includes a first lattice structure, a third lattice structure and a fourth lattice structure, and in each lattice group GPG, the first lattice structure, the third lattice structure and the fourth lattice structure are arranged along the first direction D1. The first lattice structure, the third lattice structure and the fourth lattice structure have tangential angles different from each other. The first lattice structure, the third lattice structure and the fourth lattice structure have lattice periods different from each other. Differences among the lattice periods of the first lattice structure, the third lattice structure and the fourth lattice structure are less than 20 nm.SELECTED DRAWING: Figure 38

Description

[Technical field]

[0001] Each embodiment of the present invention relates to an optical element and an authentication body. This application claims priority based on Japanese Patent Application No. 2018-053546, filed in Japan on March 20, 2018, the contents of which are incorporated herein by reference. [Background technology]

[0002] For the purpose of preventing counterfeiting of securities such as gift certificates, banknotes, and credit cards, and for the purpose of protecting the brands of products, optical elements using holograms, diffraction gratings, multilayer interference films, etc. are attached to these articles. Since it is not easy to manufacture such optical elements, the optical elements have the effect of preventing counterfeiting of the articles to which they are attached.

[0003] As the above-mentioned optical element, when verifying the authenticity of the optical element, an optical element that can be verified only by visual inspection without using a special verification tool is widely used. Among them, an optical element that changes the color of the optical element or the image displayed by the optical element depending on the angle at which the optical element is observed is widely used. Among these, an optical element that changes the color depending on the angle at which the optical element is observed can be a diffraction grating or a multilayer interference film as described above.

[0004] A diffraction grating and a multilayer interference film have a characteristic that the color of the optical element visually recognized by an observer changes continuously when the angle at which the optical element is observed is changed. Since a plurality of colors are observed by the observer in this manner, it is difficult to clearly define the color that should be visually recognized in determining whether the optical element is a genuine optical element in authenticity verification. In addition, it is difficult for the observer to know the appropriate angle range for observing the optical element in authenticity verification.

[0005] In order to solve these problems, a lattice structure is used as an optical element that emits a predetermined color. The period of the fine structure in the lattice structure is equal to or less than the wavelength of visible light. The lattice structure has a characteristic that, among the light incident on the lattice structure, only light of a specific wavelength is emitted in the direction of regular reflection due to a phenomenon called guided mode resonance. Therefore, when an observer observes an optical element from a direction other than the direction of regular reflection, the lattice structure makes it impossible to visually recognize light having a predetermined color in the optical element. Therefore, unlike a diffraction grating or a multilayer interference film, the lattice structure can specify the angle at which the optical element should be observed and the color that is visually recognized at that angle. As a result, a method for verifying the authenticity of an optical element can be described. An example of an optical element for preventing counterfeiting using such a sub-wavelength lattice structure is the optical element described in Patent Document 1. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2013-527938 Summary of the Invention [Problem to be solved by the invention]

[0007] In the optical element described in Patent Document 1, the optical element is viewed at a first angle at which a first color is visually recognized, and then the optical element is rotated around a normal to the plane on which the optical element extends as a rotation axis. Then, the optical element is viewed at a second angle at which a second color is visually recognized, thereby verifying the authenticity of the optical element.

[0008] Here, the hand movement performed by the observer to rotate the optical element is not as natural as other movements, such as tilting the optical element. Therefore, the workability of the verification work by the observer is likely to be low, and therefore the efficiency of the verification is likely to be low. In addition, as described above, the sub-wavelength grating emits light having a predetermined color only in the specular reflection direction. Therefore, at the moment when the observer picks up the optical element, or at the moment when the observer places the optical element on a flat surface and then observes the optical element, the observer is unlikely to be able to visually recognize the color exhibited by the optical element. In other words, at such a moment, the observer is unlikely to observe the optical element in the specular reflection direction. Therefore, the observer needs to find an angle at which the color exhibited by the optical element can be visually recognized, rotate the optical element, and further find an angle at which another color exhibited by the optical element can be visually recognized even after rotating the optical element. As a result, it takes time for the observer to verify the authenticity of the optical element, so there is a demand for an optical element that can more easily verify the authenticity.

[0009] An object of the present invention is to provide an optical element and an authentication body that enable easy verification of authenticity. [Means for solving the problem]

[0010] The optical element for solving the above problem includes a first layer, a second layer in contact with the first layer, and a third layer in contact with the second layer, each of which has light transmissivity. The first layer is a resin layer having a first refractive index, has a first surface in contact with the second layer, and includes a grating structure formed by concaves and convexities on at least a part of the first surface, the second layer is a dielectric layer having a second refractive index higher than the first refractive index, and has an uneven shape following the grating structure, and the third layer is a resin layer having a third refractive index lower than the second refractive index. The first surface has an uneven surface, and the grating structure includes a first grating structure and a second grating structure, and the uneven surface includes a first region in which the first grating structure is located, and a second region in which the second grating structure is located, which is in contact with the first region or is disposed away from the first region in a plan view facing the first surface. The azimuth angle of the first grating structure and the azimuth angle of the second grating structure are equal to each other, the grating periods of the first grating structure and the second grating structure are 250 nm or more and 500 nm or less, and the difference between the grating period of the first grating structure and the grating period of the second grating structure is 20 nm or more.

[0011] The grating pattern located in the first region includes a grating group repeated along the first direction. The grating group includes the first grating structure, a third grating structure, and a fourth grating structure, and in each grating group, the first grating structure, the third grating structure, and the fourth grating structure are arranged along the first direction. The first grating structure, the third grating structure, and the fourth grating structure have a shape in which one peak is sandwiched between two valleys in a cross-sectional structure along the first direction, and the angle formed by a tangent to a slope connecting one of the valleys and the peak and a straight line connecting the valleys is a tangent angle. The first grating structure, the third grating structure, and the fourth grating structure have different tangent angles. The first grating structure, the third grating structure, and the fourth grating structure have different grating periods, and the difference in the grating periods in the first grating structure, the third grating structure, and the fourth grating structure is smaller than 20 nm.

[0012] According to the above configuration, in both the first grating structure and the second grating structure, the appearance and disappearance of the colors due to each grating structure occur simultaneously. Therefore, in verifying the authenticity of the optical element, it is possible to grasp at once whether the optical element has a first region exhibiting a color due to the first grating structure and a second region exhibiting a color due to the second grating structure. Therefore, the authenticity of the optical element can be verified more easily than when verifying whether the optical element has a state in which the optical element exhibits two colors by rotating the optical element.

[0013] In the above optical element, the second region may further include a third region located away from the first region and between the first region and the second region, and when the optical element is observed at a certain observation angle from the light source side in a state in which light is irradiated from a light source located on the opposite side of the second layer from the third layer, the optical element may have a state in which the color exhibited by the third region is different from both the color exhibited by the first region and the color exhibited by the second region.

[0014] According to the above configuration, since the optical element has a third region, an observer of the optical element can more clearly recognize the boundary between the first region and the second region than if the optical element did not have the third region.

[0015] The third region may be formed by a flat surface on the first surface of the first layer, and the average roughness Sa of the flat surface may be 20 μm or less. According to the above configuration, the light incident on the third region is reflected in a specular reflection direction, and the third region exhibits a white color. This makes the boundary between the first region and the second region, which display a specific color in the specular reflection direction due to guided mode resonance, clearer.

[0016] In the optical element, the third region may include a scattering structure or an anti-reflection structure having directivity in a direction different from the specular reflection direction of light incident on the third region. According to the above configuration, the third region exhibits black in the specular reflection direction. This makes the boundary between the first region and the second region, which display a specific color in the specular reflection direction by waveguide mode resonance, clearer.

[0017] In the optical element, the third region may have a constant width. According to the above configuration, the boundary between the first region and the second region can be uniformly emphasized by the third region. The optical element is likely to have a flat impression and is likely to give a strong impression. If the third region is linear, the impression is likely to be sharp. Furthermore, if the third region is curved, the optical element is likely to give a soft impression.

[0018] In the optical element, the third region may include a first portion and a second portion, and the width of the first portion may be different from the width of the second portion. According to the above configuration, the different widths of the third region tend to give the optical element an elegant impression. In particular, when combined with a curve, it gives a rhythmic impression. Furthermore, when the change in width is continuous, it tends to give a natural appearance.

[0019] In the optical element, the width of the third region may be 30 μm or more and 3000 μm or less. According to the above configuration, since the width of the third region is 30 μm or more, the observer can visually recognize the third region. Furthermore, since the width of the third region is 3000 μm or less, the third region is prevented from being more noticeable than the first and second regions.

[0020] In the above optical element, the first region and the second region are each 0.1 mm 2 The first region and the second region may each include a plurality of cells partitioned to have the following areas, and the first region and the second region may include cells in which the lattice structure is located in at least a portion of the cells.

[0021] According to the above configuration, the luminance of the cell can be changed by changing the area ratio of the lattice structure in each cell.

[0022] The optical element may further include a resin layer located on the first layer opposite to the second layer, and the hardness of the first layer may be higher than the hardness of the resin layer and the hardness of the third layer.

[0023] According to the above configuration, an external force acting on the optical element can be absorbed by the resin layer and the third layer, thereby preventing the shape of the lattice structure of the first layer from being changed by the external force.

[0024] In the optical element, the first layer may be formed of an ultraviolet curable resin, the thickness of the first layer may be 1 μm or more and 10 μm or less, and the resin layer and the third layer may be formed of a thermoplastic resin. With the above configuration, the shape of the lattice structure of the first layer is more prevented from being changed by an external force.

[0025] The optical element may further include a resin layer located on the opposite side of the first layer from the second layer, and at least one of the first layer, the third layer, and the resin layer may contain a filler, and the average particle size of the filler may be 400 nm or less. According to the above configuration, the range of the emission angle of the light emitted from the optical element is wider than when each layer does not contain a filler. Therefore, the range of observation angles at which the observer can observe the color exhibited by the optical element is wider.

[0026] The authentication body for solving the above problem includes the above optical element, and the optical element covers the identification information. Effect of the Invention

[0027] According to the present invention, the authenticity of the optical element and the authenticator can be easily verified. [Brief description of the drawings]

[0028] [Figure 1]1 is a cross-sectional view illustrating a schematic structure of an optical element according to a first embodiment of the present invention. [Diagram 2] 1 is a plan view illustrating a schematic external appearance of an optical element according to a first embodiment of the present invention. [Diagram 3] 1 is a plan view illustrating a schematic structure of an optical element according to a first embodiment of the present invention. [Figure 4] FIG. 2 is a plan view illustrating the azimuthal angle in a cell of the present invention. [Diagram 5] 4 is a cross-sectional view illustrating a schematic structure in a cross section taken along line I-I and line II-II in FIG. 3. [Figure 6] FIG. 1 is a cross-sectional view illustrating a schematic operation of the optical element according to the first embodiment of the present invention. [Figure 7] FIG. 1 is a perspective view illustrating a relationship between the wavelength and the azimuth angle of light emitted from a grating structure of the present invention. [Figure 8] FIG. 1 is a perspective view illustrating a relationship between the wavelength and the azimuth angle of light emitted from a grating structure of the present invention. [Figure 9] FIG. 1 is a perspective view illustrating a structure of an optical element according to a first embodiment of the present invention. [Figure 10] 1 illustrates a schematic diagram of the operation of a first embodiment of the present invention. [Figure 11] 1 illustrates a schematic diagram of the operation of a first embodiment of the present invention. [Figure 12] FIG. 3A is a plan view illustrating a schematic structure of a boundary region according to a first embodiment of the present invention; FIG. 3B is a cross-sectional view taken along lines III-III and IV-IV. [Figure 13] FIG. 2A is a plan view illustrating a schematic structure of a boundary region according to a first embodiment of the present invention, and FIG. 2B is a cross-sectional view taken along line VV. [Figure 14] FIG. 6A is a plan view illustrating a schematic structure of a boundary region according to a first embodiment of the present invention, and FIG. 6B is a cross-sectional view taken along line VI-VI. [Figure 15] FIG. 1 is a schematic diagram illustrating the configuration of a color measuring device for an optical element according to the present invention. [Figure 16] 4 is a graph showing optical characteristics of the structure according to the first embodiment of the present invention. [Figure 17]4 is a graph showing optical characteristics of the structure according to the first embodiment of the present invention. [Figure 18] 4 is a graph showing optical characteristics of the structure according to the first embodiment of the present invention. [Figure 19] 4 is a graph showing optical characteristics of the structure according to the first embodiment of the present invention. [Figure 20] FIG. 2 is a chromaticity diagram showing the optical characteristics of the structure according to the first embodiment of the present invention. [Figure 21] FIG. 2 is a chromaticity diagram showing the optical characteristics of the structure according to the first embodiment of the present invention. [Figure 22] 4 is a graph showing optical characteristics of the structure according to the first embodiment of the present invention. [Diagram 23] 4 is a graph showing optical characteristics of the structure according to the first embodiment of the present invention. [Figure 24] 4 is a graph showing optical characteristics of the structure according to the first embodiment of the present invention. [Diagram 25] FIG. 2 is a plan view illustrating a boundary region according to the first embodiment of the present invention. [Figure 26] FIG. 2 is a plan view illustrating a schematic configuration of a region according to the first embodiment of the present invention. [Figure 27] FIG. 2 is a plan view illustrating a schematic configuration of a region according to the first embodiment of the present invention. [Figure 28] FIG. 2 is a plan view illustrating a schematic configuration of a region according to the first embodiment of the present invention. [Figure 29] FIG. 2 is a plan view illustrating a schematic configuration of a region according to the first embodiment of the present invention. [Diagram 30] 1 is a plan view illustrating a structure of a first embodiment of the present invention; [Diagram 31] 31 is a cross-sectional view illustrating a structure in a cross section taken along line VII-VII in FIG. 30. [Diagram 32] 31 is a cross-sectional view illustrating a structure in a cross section taken along line VII-VII in FIG. 30. [Diagram 33] 1A and 1B are a plan view and a cross-sectional view illustrating the structure of each region of an optical element according to a first embodiment of the present invention. [Diagram 34]1A and 1B are a plan view and a cross-sectional view illustrating the structure of each region of an optical element according to a first embodiment of the present invention. [Diagram 35] FIG. 4 is a plan view illustrating a structure of another example of the first embodiment of the present invention together with an enlarged view. [Diagram 36] FIG. 6 is a cross-sectional view illustrating, together with an enlarged view, a structure of an optical element according to a second embodiment of the present invention. [Figure 37] FIG. 11 is a cross-sectional view illustrating a structure of another example of the optical element according to the second embodiment of the present invention. [Figure 38] FIG. 11 is a cross-sectional view illustrating a structure of another example of the optical element according to the second embodiment of the present invention. [Figure 39] FIG. 11 is a cross-sectional view illustrating a schematic structure of an optical element according to a third embodiment of the present invention. [Diagram 40] FIG. 11 is a cross-sectional view illustrating a schematic structure of a first example of an optical element according to a fourth embodiment of the present invention. [Diagram 41] FIG. 13 is a cross-sectional view illustrating a schematic structure of a second example of the optical element according to the fourth embodiment of the present invention. [Diagram 42] FIG. 13 is a cross-sectional view illustrating a schematic structure of a first example of an optical element according to a fifth embodiment of the present invention. [Diagram 43] FIG. 13 is a cross-sectional view illustrating a layer structure of an optical element according to a fifth embodiment of the present invention. [Diagram 44] FIG. 23 is a cross-sectional view illustrating a structure of a first example of an optical element according to a sixth embodiment of the present invention. [Diagram 45] 13A and 13B are schematic diagrams illustrating the operation of a first example of an optical element according to a sixth embodiment of the present invention. [Figure 46] FIG. 23 is a plan view illustrating a first state in a first example of an optical element according to a sixth embodiment of the present invention. [Figure 47] FIG. 23 is a plan view illustrating a second state in a first example of an optical element according to a sixth embodiment of the present invention. [Figure 48] FIG. 23 is a plan view illustrating a third state in a first example of the optical element according to the sixth embodiment of the present invention. [Figure 49]FIG. 23 is a plan view illustrating a fourth state in a first example of the optical element according to the sixth embodiment of the present invention. [Figure 50] FIG. 23 is a cross-sectional view illustrating a structure of a second example of the optical element according to the sixth embodiment of the present invention. [Figure 51] FIG. 13 is a cross-sectional view illustrating a structure of a first example of an optical element according to a seventh embodiment of the present invention. [Figure 52] FIG. 23 is a cross-sectional view illustrating a structure of a second example of the optical element according to the seventh embodiment of the present invention. [Figure 53] FIG. 23 is a cross-sectional view illustrating a structure of a third example of the optical element according to the seventh embodiment of the present invention. [Figure 54] FIG. 23 is a cross-sectional view illustrating a structure of a fourth example of the optical element according to the seventh embodiment of the present invention. [Figure 55] FIG. 13 is a cross-sectional view illustrating the structure of a transfer foil according to an eighth embodiment of the present invention. [Figure 56] FIG. 13 is a cross-sectional view illustrating a structure of an optical element according to a ninth embodiment of the present invention. [Figure 57] FIG. 13 is a plan view illustrating a schematic structure of a card to which an optical element according to a ninth embodiment of the present invention is applied. [Figure 58] FIG. 13 is a plan view illustrating a structure of an optical element according to a ninth embodiment of the present invention. [Figure 59] FIG. 23 is a plan view illustrating a schematic structure of an authentication body according to a tenth embodiment of the present invention. [Figure 60] 59 is a cross-sectional view illustrating a structure in a cross section taken along line XIV-XIV in FIG. 58. [Figure 61] FIG. 23 is a cross-sectional view illustrating a schematic structure of an authenticator according to an eleventh embodiment of the present invention. [Figure 62] 23 is a schematic diagram illustrating the operation of a first example of an authenticator according to an eleventh embodiment of the present invention; [Figure 63] 23 is a schematic diagram illustrating the operation of a first example of an authenticator according to an eleventh embodiment of the present invention; [Figure 64] 23 is a schematic diagram illustrating the operation of a first example of an authenticator according to an eleventh embodiment of the present invention; [Figure 65] 23 is a schematic diagram illustrating the operation of a first example of an authenticator according to an eleventh embodiment of the present invention; [Figure 66] 23 is a schematic diagram illustrating the operation of a second example of an authenticator according to an eleventh embodiment of the present invention; [Figure 67] 23 is a schematic diagram illustrating the operation of a second example of an authenticator according to an eleventh embodiment of the present invention; [Figure 68] 23 is a schematic diagram illustrating the operation of a second example of an authenticator according to an eleventh embodiment of the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] [First embodiment] A first embodiment of the optical element of the present invention will be described with reference to FIG. 1 to FIG. 35. In each drawing, all components exhibiting the same or similar functions are given the same reference numerals, and duplicated descriptions are omitted. In addition, the embodiments of the present invention of the present disclosure are a group of embodiments based on a unique single invention from the background. In addition, each aspect of the present disclosure is an aspect of a group of embodiments based on a single invention. Each configuration of the present disclosure can have each aspect of the present disclosure. Each feature of the present disclosure can be combined to form each configuration. Therefore, each feature of the present disclosure, each configuration of the present disclosure, each aspect of the present disclosure, and each embodiment of the present disclosure can be combined, and the combination has a synergistic function and can exhibit a synergistic effect.

[0030] As shown in FIG. 1, the optical element 10 includes a first layer 11, a second layer 12 in contact with the first layer 11, and a third layer 13 in contact with the second layer 12. Each layer has light transmissivity. The optical element 10 can be the whole or a part of a security seal. In other words, the security seal can include the optical element 10. The optical element 10 can also be a visible motif. The security seal can be in the form of a patch, a stripe, an overlay, or a sticker. The optical element 10 is irradiated with light from a light source located on the opposite side of the second layer 12 from the third layer 13, and is observed from the opposite side of the second layer 12 from the third layer 13. In the optical element 10, the surface of the first layer 11 opposite the surface in contact with the second layer 12 is an observation surface 10S observed by an observer.

[0031] The first layer 11 is a resin layer having a first refractive index n1. The first layer 11 includes a lattice structure 11G on at least a part of a surface 11S in contact with the second layer 12. The surface 11S is an example of a first surface. The second layer 12 has an uneven shape following the lattice structure 11G. The second layer 12 is a dielectric layer having a second refractive index n2 higher than the first refractive index n1. The third layer 13 is a resin layer having a third refractive index n3 lower than the second refractive index n2. A plurality of lattice structures 11G, which are minimum structural units composed of recesses and protrusions, are arranged in one direction and spread on the surface 11S as a lattice pattern GP. The lattice pattern GP can be formed as an uneven surface of the surface 11S. The lattice period of the lattice structure 11G is a sub-wavelength of a visible wavelength of 250 nm or more and 500 nm or less, for example, 400 nm.

[0032] The refractive index n1 of the first layer 11 may be the same as or different from the refractive index n3 of the third layer 13. The difference between the refractive index n1 of the first layer 11 and the refractive index n3 of the third layer 13 can be 0.2 or less, and further can be 0.1 or less. If the difference between the refractive index n1 of the first layer 11 and the refractive index n3 of the third layer 13 is 0.2 or less, the saturation is easily increased. If the difference between the refractive index n1 of the first layer 11 and the refractive index n3 of the third layer 13 is 0.1 or less, the saturation approaches the maximum. The difference between the refractive index n1 of the first layer 11 and the refractive index n2 of the second layer 12, and the difference between the refractive index n3 of the third layer 13 and the refractive index n2 of the second layer 12 are preferably 0.3 or more, and more preferably 0.5 or more.

[0033] In the surface 11S of the first layer 11, the region where the lattice structure 11G is located is an uneven surface. That is, the surface 11S has an uneven surface. In this embodiment, the entire surface 11S is an uneven surface, but only a part of the surface 11S may be an uneven surface.

[0034] FIG. 2 shows the appearance of the optical element 10 in a plan view facing the observation surface 10S. The optical element 10 includes a motif region 11S1 and a background region 11S2. The motif region 11S1 is an example of a first region, and the background region 11S2 is an example of a second region. The motif region 11S1 is formed of a plurality of image elements 11R1, 11R2, 11R3, 11R4, and 11R5. The background region 11S2 is formed of pattern elements 11P1 and 11P2. The motif region 11S1 is a region having a contour that is a main element in the entire design, such as a character, a sign, an object shape, or a symbol, and has a specific meaning. On the other hand, the background region 11S2 is a region that does not have a special meaning, and may be a stripe shape as in the example of FIG. 2, or may be a figure such as another geometric pattern.

[0035] The motif region 11S1 and the background region 11S2 are adjacent to each other via the boundary region 11S3. The boundary region 11S3 is an example of a third region. When the optical element 10 is observed at a certain observation angle, the color of the boundary region 11S3 of the optical element 10 is different from both the color of the motif region 11S1 and the color of the background region 11S2. Since the optical element 10 has the boundary region 11S3, it is possible for an observer of the optical element 10 to more clearly recognize the boundary between the motif region 11S1 and the background region 11S2 compared to a case where the optical element 10 does not have the boundary region 11S3. The optical element 10 does not need to have the boundary region 11S3. When the optical element 10 does not have the boundary region 11S3, the motif region 11S1 and the background region 11S2 are in contact with each other.

[0036] 3 is an enlarged view of a part of the optical element 10 shown in FIG. 2. A plurality of cells Px are defined in the motif region 11S1, the background region 11S2, and the boundary region 11S3. The area of ​​each cell Px is 0.1 mm 2 It is preferable that the length of each side of the cell Px is 0.3 mm or less. A plurality of cells Px are arranged without gaps over the entire surface 11S of the first layer 11. In the present embodiment, in a plan view facing the surface 11S, each cell Px has a square shape, but the cell Px may have an equilateral triangular shape, a regular hexagonal shape, or the like. Also, each cell Px may have a polygonal shape and a shape including sides having different lengths. In the cell Px, the length of one side is preferably 0.3 mm or less. It is more preferable that the length of one side is 0.08 mm or less. In this case, since the length of one side of the cell Px is a value smaller than the resolution of the human eye, each cell Px is not visually recognized by the observer. This allows the optical element 10 to display a high-resolution image.

[0037] In the following, for convenience of illustration and explanation, the surface 11S of the first layer 11, that is, the surface of the first layer 11 that forms the interface with the second layer 12, will be described using a structure in a plan view facing the observation surface 10S. Also, in FIG. 3, for convenience of illustration, the direction in which the lattice pattern GP extends is shown by a straight line. Here, as an example, a case is shown in which the lattice directions of the lattice structures arranged in the image element 11R1 and the pattern element 11P2 adjacent to the boundary region 11S3 in the cell Px in a region at least 300 μm away from the outline of the boundary region 11S3 are orthogonal to each other. Note that as long as the lattice directions in the cell Px are parallel or orthogonal to each other, the combination of the lattice directions can be arbitrary.

[0038] The definition of the azimuth angle representing the lattice direction will be described with reference to FIG. As shown in FIG. 4, any direction along the observation surface 10S of the optical element 10 is the X direction, and the direction perpendicular to the X direction is the Y direction. In this embodiment, the X direction is the reference direction for the azimuth angle, and the angle formed between the X direction and the direction in which the lattice structure extends is the azimuth angle φ. Therefore, the azimuth angle φ in the first cell Px1 is 0°, and the azimuth angle φ in the second cell Px2 is 45°. In addition, the azimuth angle φ in the third cell Px3 is 90°, and the azimuth angle φ in the fourth cell Px4 is 135°. Note that the X direction often coincides with the horizontal direction of the optical element 10, and in that case, the azimuth angle φ of the lattice structure used is preferably 0°, 90°, or 0° and 90°. By adopting such a design, the optical element 10 can be easily manufactured, and the production efficiency of the optical element 10 can be improved. When the difference between the azimuth angle of the first grating structure and the azimuth angle of the second grating structure is 1° or less, the respective azimuth angles can be defined as being equal.

[0039] 5 shows the cross-sectional structure of the lattice structure 11G along the lines I-I and II-II in FIG. 3. In FIG. 5, for convenience of illustration, the cross-sectional structure of the first lattice structure 11G1 arranged in the image element and the cross-sectional structure of the second lattice structure 11G2 arranged in the pattern element are shown side by side in the vertical direction of the paper. Note that the cross-sectional structure of each lattice structure is shown typically as the cross-sectional structure of the lattice structure located in one cell Px. Also, in FIG. 5, for convenience of illustration, each lattice structure is shown as a surface constituting a convex portion protruding in a direction away from the flat surface.

[0040] As shown in Fig. 5, in each grating pattern GP, ​​the distance between adjacent grating structures is the grating period d. The grating period in the first grating structure 11G1 is the first period d1, and the grating period in the second grating structure 11G2 is the second period d2. In this embodiment, the first period d1 is smaller than the second period d2, but the first period d1 may be larger than the second period d2. In this embodiment, the grating structure is a minimum unit structure having a convex portion and a concave portion, and a pattern in which the grating structure is repeated in one direction is the grating pattern GP.

[0041] When the grating direction of the first grating structure 11G1 and the grating direction of the second grating structure 11G2 are mutually orthogonal, the first period d1 and the second period d2 may be the same or different. On the other hand, when the grating direction of the first grating structure 11G1 and the grating direction of the second grating structure 11G2 are parallel to each other, it is preferable that the first period d1 and the second period d2 are different. In either case, the optical element 10 is configured to satisfy formula (1). |d1(n21-R)-d2(n22-R)|≧25 ... formula (1)

[0042] In equation (1), n21 is the effective refractive index of the virtual layer 12V for incident light in the region where the first lattice structure 11G1 is arranged, n22 is the effective refractive index of the virtual layer 12V for incident light in the region where the second lattice structure 11G2 is arranged, and R is a constant determined by the refractive index n1 of the first layer 11 and the angle θ of the incident light.

[0043] In addition, the color difference ΔE*ab between the average color value L*a*b* of the motif region 11S1 and the average color value L*a*b* of the background region 11S2 can be equal to or greater than 13. The average color value L*a*b* can be any color value L*a*b* within a range of, for example, a diameter of 3 mm.

[0044] FIG. 6 is a schematic diagram showing how light is incident on the area where the lattice structure 11G is arranged in the optical element 10. The incident light IL is incident on the second layer 12 from the first layer 11 side at an incident angle θ. The second layer 12 corresponds to the shape of the lattice structure 11G, but it is known that in a fine structure below the visible wavelength, i.e., a sub-wavelength lattice, the area where the lattice structure exists can be regarded as a two-dimensional planar layer having a constant thickness in the z direction, i.e., a virtual layer 12V. The refractive index neff of this virtual layer 12V is called the effective refractive index or effective refractive index, and its value differs depending on the polarization direction (optical anisotropy). The optical anisotropy that occurs when the structure has a directionality, as in this case, is called structural birefringence, and the effective refractive index differs depending on the relationship between the incident light and the direction of the structure.

[0045] FIG. 7 shows a perspective view of the lattice structure 11G with an azimuth angle φ of 0°. Meanwhile, FIG. 8 shows a perspective view of the lattice structure 11G with an azimuth angle φ of 90°. In this embodiment, the lattice structure is rectangular for convenience of illustration, but may be wavy. Among the polarized light components contained in the incident light to the lattice structure 11G, the polarized light whose electric field oscillates perpendicularly to the incident plane of the lattice structure 11G is s-polarized light. In contrast, the polarized light whose electric field oscillates parallel to the incident plane of the lattice structure 11G is p-polarized light. Note that the incident plane is perpendicular to the plane on which the lattice structure spreads and is a plane that includes the incident light and the reflected light. In addition, each of the s-polarized light and the p-polarized light does not depend on the azimuth angle φ of the lattice structure 11G. In other words, the incident light incident on the lattice structure 11G shown in FIG. 7 and the incident light incident on the lattice structure 11G shown in FIG. 8 include s-polarized light and p-polarized light.

[0046] Here, in a structure having grooves such as the lattice structure 11G, optical anisotropy occurs due to the relationship between the direction in which the grooves extend, that is, the azimuth angle φ and the vibration direction of the electric field, as described above. In the light incident on the lattice structure 11G, the component whose electric field vibration direction is parallel to the azimuth angle φ of the lattice structure 11G is a TE wave. On the other hand, in the light incident on the lattice structure 11G, the component whose electric field vibration direction is perpendicular to the azimuth angle φ of the lattice structure 11G is a TM wave. As described above with reference to FIG. 7, in the lattice structure 11G with an azimuth angle φ of 0°, p-polarized light, whose electric field vibration direction is parallel to the azimuth angle φ of the lattice structure 11G, is equal to a TE wave. In contrast, in the lattice structure 11G with an azimuth angle φ of 90°, p-polarized light, whose electric field vibration direction is perpendicular to the azimuth angle φ of the lattice structure 11G, is equal to a TM wave.

[0047] With reference to FIG. 9, the effective refractive index of the virtual layer 12V will be described using a simple model in which the grating structure 11G has a rectangular shape. As shown in Figure 9, the refractive index of the regions corresponding to the convex portions of the lattice structure with a period d is na, the refractive index of the regions corresponding to the concave portions is nb, the width of the period d occupied by the convex portions is a, and the width of the concave portions is b. If the occupancy rate of the convex portions with respect to the period d is F, the effective refractive index neff for the TE wave and TM wave of the incident light is expressed by formula (2) and formula (3), respectively.

[0048]

number

[0049]

number

[0050] The process of deriving the above formula (1) will be described below. In formula (1), both the effective refractive index n21 and the effective refractive index n22 are treated as including the refractive indexes for both the TE wave and the TM wave. As described above, the values ​​of the effective refractive index n21 and the effective refractive index n22 change depending on the azimuth angle φ of the lattice structure 11G. Here, in order for guided mode resonance to occur in the lattice structure 11G, it is necessary to satisfy the phase matching conditions expressed by the following formulas (4) to (7). Light of a specific wavelength for which this formula holds is propagated through the virtual layer 12V and emitted toward the observer. Note that in a lattice structure formed on a flat surface as shown in FIG. 6, the incident angle θ of the incident light IL and the exit angle θ of the exit light EL are equal, that is, a specific color is observed as zero-order diffracted light at the regular reflection angle.

[0051] kn1sinθ+mK=β … Equation (4) k=2π / λ … Equation (5) K=2π / d … Equation (6) β=(2π / λ)·neff… Equation (7)

[0052] Here, k is the wave number, n1 is the refractive index of the first layer 11, θ is the angle of light incident on the virtual layer 12V, m is the diffraction order, λ is the resonance wavelength, K is the reciprocal lattice vector, d is the lattice period, β is the propagation constant, and neff is the effective refractive index.

[0053] By substituting equations (5) to (7) into equation (4), equation (8) is derived. d(neff-R)=mλ … Equation (8) The refractive index n1 and the incident angle θ are constant when the material and the incident angle are fixed, so here n1sinθ is treated as a constant R. Since it is mainly the first-order diffracted light that contributes to the guided mode resonance, m can be set to 1 in equation 8. For the first grating structure 11G1 and the second grating structure 11G2, if the resonance wavelengths λ derived from equation (8) are λ1 and λ2, respectively, then equation (9) holds. |λ1-λ2|=|d1(n21-R)-d2(n22-R)|… Equation (9)

[0054] In the visible wavelength range, when there is a wavelength difference of 25 nm or more, which is wider than the relatively narrow wavelength range corresponding to a specific color, such as yellow-green, yellow, and orange, the difference in color can be perceived between two areas displayed in two colors. Therefore, by providing the first grating structure 11G1 and the second grating structure 11G2 in the image element and the pattern element such that the right side of the formula (9) is 25 or more, the difference in color can be perceived, and the greater the wavelength difference |λ1-λ2|, the clearer the difference in color becomes. Note that the effective refractive index of the TE wave parallel to the azimuth angle of the grating structure is higher than that of the TM wave perpendicular to the azimuth angle of the grating structure due to the structure, and the refractive index difference between the virtual layer 12V and the first layer 11 is larger, so that the intensity of the specific wavelength emitted in the regular reflection direction is high, and it can be said that the optical effect is dominant.

[0055] The optical element 10 described above with reference to FIG. 3 can have the first grating structure 11G1 shown in FIG. 7 in the image element 11R1, and the second grating structure 11G2 shown in FIG. 8 in the pattern element 11P2. In this case, the state in which the image element 11R1 exhibits the first color and the pattern element 11P2 exhibits the second color is the initial position in the relative positions of the optical element 10, the observer, and the light source. When the optical element 10 is rotated 90° from the initial position with the normal line of the optical element 10 as the rotation axis, in the image element 11R1, the s-polarized light corresponds to the TE wave, and the p-polarized light corresponds to the TM wave. In contrast, in the pattern element 11P2, the s-polarized light corresponds to the TM wave, and the p-polarized light corresponds to the TE wave. As a result, the image element 11R1 exhibits the second color, and the pattern element 11P2 exhibits the first color. Therefore, the observer perceives that the rotation of optical element 10 has inverted the colors exhibited by image element 11R1 and pattern element 11P2.

[0056] As described above, it is preferable that the azimuth angle φ of the first grating structure 11G1 and the azimuth angle φ of the second grating structure 11G2 are 90° or less for the following reasons. The observation angle is the angle formed by the observation surface 10S of the optical element 10 and a plane including the line of sight of the observer. The observation angle at which the color presented by the grating structure is visible is determined by the relative positions of the light source, the observer, and the optical element 10. Therefore, even if the azimuth angle φ of the first grating structure 11G1 and the azimuth angle φ of the second grating structure 11G2 are different from each other, the observation angle at which the color presented by the first grating structure 11G1 is visible and the observation angle at which the color presented by the second grating structure 11G2 is visible are equal to each other. In other words, the observation angle at which the color presented by each grating structure 11G1, 11G2 appears and the observation angle at which the color presented by each grating structure 11G1, 11G2 disappears are equal to each other between the two gratings.

[0057] When the difference between the azimuth angle φ of the first grating structure 11G1 and the azimuth angle φ of the second grating structure 11G2 is 90°, the wavelength of the zero-order diffracted light emitted from the first grating structure 11G1 and the wavelength of the zero-order diffracted light emitted from the second grating structure 11G2 are different from each other. As a result, the first color exhibited by the first grating structure 11G1 and the second color exhibited by the second grating structure 11G2 are different from each other. When the difference between the azimuth angle φ of the first grating structure 11G1 and the azimuth angle φ of the second grating structure 11G2 is set to an angle included in the range of more than 0° and less than 90°, at least one of the first grating structure 11G1 and the second grating structure 11G2 exhibits an intermediate color between the first color and the second color. The color exhibited by the first grating structure 11G1 and the color exhibited by the second grating structure 11G2 change according to the difference in the azimuth angle φ. Therefore, depending on the difference between the azimuth angle φ of the first lattice structure 11G1 and the azimuth angle φ of the second lattice structure 11G2, it is possible to gradually change the color exhibited by each cell Px arranged in one direction, or to suddenly change the color exhibited by each cell Px between adjacent cells Px.

[0058] In addition, in the lattice structure 11G, when the difference between the azimuth angle φ in the first lattice structure 11G1 and the azimuth angle φ in the second lattice structure 11G2 is set to 90°, the difference between the wavelength of the light emitted by the first lattice structure 11G1 and the wavelength of the light emitted by the second lattice structure 11G2 becomes the largest.

[0059] 10, in the optical element 10, for example, when the light source LS and the observer OB are positioned symmetrically with respect to the normal to the observation surface 10S on a plane perpendicular to the observation surface 10S of the optical element 10, the observer OB can visually recognize the zero-order diffracted light emitted by the optical element 10. In other words, the optical element 10 can emit light with a wavelength according to the lattice period of the lattice structure 11G in the direction of regular reflection of the incident light from the light source LS.

[0060] As described above, in this embodiment, the grating period of the grating structure is set to be equal to or less than the visible wavelength, particularly 250 nm to 500 nm. However, the grating period for emitting only light having a specific wavelength due to zero-order diffracted light in a specific direction varies depending on the refractive index of the grating structure and the incidence angle of the incident light incident on the grating structure. Below, the conditions for the grating structure to emit only zero-order diffracted light, in other words, the conditions for the sub-wavelength grating not to emit first-order diffracted light, will be described.

[0061] It is known that the following equation (10) holds true for a reflective diffraction grating. sinθ1+sinθ2 = mλ / nd … Equation (10) In equation (10), θ1 is the angle of incidence of the incident light to the diffraction grating, θ2 is the diffraction angle of the diffracted light emitted by the diffraction grating, m is the diffraction order of the diffracted light, λ is the wavelength, n is the refractive index of the diffraction grating, and d is the grating period of the diffraction grating.

[0062] Here, consider the first-order diffracted light when it is assumed that the refractive index n is 1 and light is incident perpendicular to the plane on which the diffraction grating is arranged. In this case, the incident angle θ1 is 0° and the diffraction order m is 1. Therefore, by substituting these values ​​into equation (10), the following equation (11) is derived.

[0063] sinθ2 = λ / d … Equation (11) Since sinθ2 is between -1 and 1, when the right-hand side (λ / d) in equation (11) is greater than 1, equation (11) does not hold. In other words, when the right-hand side (λ / d) is greater than 1, no first-order diffracted light is emitted from the diffraction grating. Therefore, under the above-mentioned premise, when the grating period of the diffraction grating is smaller than the wavelength, the diffraction grating emits only zero-order diffracted light.

[0064] On the other hand, if the refractive index is not 1 and the incident angle θ1 is not 0°, the diffraction grating may emit diffracted light of an order other than the zeroth order. For example, consider the first-order diffracted light assuming that the incident angle θ1 is 30° and the wavelength λ is 600 nm. In this case, the incident angle θ1 is 30°, the wavelength λ is 600 nm, and the diffraction order m is 1. Therefore, by substituting these values ​​into equation (10), the following equation (12) is derived.

[0065] 1 / 2 + sinθ2 =600 / nd … Equation (12) Since sinθ2 is -1 or more and 1 or less, the left side of equation (12) (1 / 2 + sinθ2) is -0.5 or more and 1.5 or less, and when the product of the refractive index n and the grating period d is 0 or more and 400 or less, the diffraction grating emits first-order diffracted light depending on the combination of the refractive index n and the grating period d. For example, the combination (n, d) of the refractive index n and the grating period d when the first-order diffracted light is emitted is as follows:

[0066] (n,d) = (1,400), (1.5,200), (2,100) In this way, depending on the refractive index n of the diffraction grating, even if the grating period d of the diffraction grating is equal to or less than the wavelength λ, first-order diffracted light or higher-order diffracted light may be emitted. In other words, by adjusting the grating period d and the refractive index n of the diffraction grating, it is possible to configure the diffraction grating so that the diffraction grating emits zero-order diffracted light but does not emit diffracted light of orders higher than the zero-order diffracted light.

[0067] On the other hand, by designing the diffraction angle θ2 of the first-order diffracted light to be much larger than the diffraction angle θ2 of the zeroth-order diffracted light, it is possible to configure the diffraction grating so that the zeroth-order diffracted light is visible to the observer while the first-order diffracted light is not visible to the observer when the relative position of the diffraction grating with respect to the observer is fixed. This increases the degree of freedom in the selection of the material forming the diffraction grating and the degree of freedom in the grating period of the diffraction grating.

[0068] 11, with the light source LS and the viewpoint of the observer OB fixed, the optical element 10 is tilted so that the above-mentioned plane and the optical element 10 intersect at an angle other than perpendicular. In this case, the optical element 10 does not emit zero-order diffracted light in the direction of the line of sight of the observer OB, so the observer cannot see the light of the specific wavelength emitted by the optical element 10. In other words, the observer cannot see the color presented by the optical element 10.

[0069] In the optical element 10, the appearance and disappearance of colors due to each lattice structure occur simultaneously in both the first lattice structure 11G1 and the second lattice structure 11G2. Therefore, the entire optical element 10 switches between a state in which a specific color is exhibited and a state in which a specific color is not exhibited. Therefore, in verifying the authenticity of the optical element 10, it is possible to grasp at once whether the optical element 10 has a motif region 11S1 exhibiting a color derived from the first lattice structure 11G1 and a background region 11S2 exhibiting a color derived from the second lattice structure 11G2. As a result, the authenticity of the optical element 10 can be verified more easily than when verifying whether the optical element 10 has a state in which the optical element 10 exhibits two colors by rotating the optical element 10.

[0070] The structure of boundary region 11S3 will be described with reference to Figures 12 to 14. In Figures 12 to 14, (a) shows a schematic structure along the XY plane in boundary region 11S3, and (b) shows a cross-sectional structure along the cross-section indication line in (a).

[0071] FIG. 12 shows an example of an omnidirectional scattering structure. As shown in Fig. 12, the omnidirectional scattering structure has an irregular structure having irregular widths and heights. For convenience of illustration, the structures are arranged randomly in the X and Y directions in Fig. 12, but the structures may be formed in a completely random uneven structure regardless of the direction. This omnidirectional scattering structure may be formed simultaneously in a process of forming the lattice structure of the motif region 11S1 and the lattice structure of the background region 11S2, or may be physically generated when the laminate including the first layer 11 to the third layer 13 is transferred or laminated to another substrate.

[0072] FIG. 13 shows an example of a directional scattering structure. As shown in FIG. 13, in the directional scattering structure, the width and height of the structure are irregular, but the direction in which the structures are arranged is uniform. If an observer is observing from the front of the paper, when light is incident from the back of the paper to the front of the paper in the cross-sectional view of the structure shown in FIG. 13, the scattered light enters the observer's side and is perceived as white. On the other hand, when light is incident from the left of the paper to the right of the paper in the cross-sectional view of the structure, the light is weak even when observed from the emission direction, and the scattering structure appears substantially black or gray. In other words, depending on which direction the directional scattering structure is provided in when the optical element 10 is viewed in a plane, the boundary region can be displayed in white or black. For example, according to a scattering structure having directivity in a direction different from the regular reflection direction of light incident on the boundary region 11S3, the third region is black in the regular reflection direction. This makes the boundary between the motif region 11S1 and the background region 11S2, which display a specific color in the regular reflection direction by waveguide mode resonance, clearer.

[0073] FIG. 14 shows an example of an anti-reflection structure represented by a moth-eye structure. As shown in Figure 14, the principle behind the anti-reflection effect of the moth-eye structure is that by providing a nano-order needle-like structure, the refractive index around the structure changes gradually, so that the reflection and refraction of incident light becomes extremely small, resulting in the appearance of black. Figure 14 shows an example of a square arrangement of cone-shaped structures, but any fine structure in which the cross-sectional area of ​​the structure in the XY directions changes in the Z direction will do, and the arrangement is not limited to a square arrangement.

[0074] Also, a lattice structure 11G may be provided in the boundary region 11S3. In this case, a color of a specific wavelength is displayed in the boundary region 11S3 as in the motif region 11S1 and background region 11S2. The color difference ΔE*ab between the average color value L*a*b* in the boundary region 11S3 and the average color value L*a*b* in at least one of the image elements and the pattern elements adjacent to the boundary region 11S3 can be 13 or more. As long as this condition is satisfied, the lattice structure 11G provided in the boundary region 11S3 is arbitrary.

[0075] It is preferable that the lattice structure 11G disposed in the boundary region 11S3 extends in the vertical direction in a plan view facing the optical element 10, i.e., the lattice structure 11G has an azimuth angle φ of 90°. The optical characteristics differ when the azimuth angle φ of the lattice structure 11G is 0° and when it is 90°.

[0076] The characteristics of the lattice structure 11G due to the difference in the azimuth angle will be described with reference to Figs. 15 to 24. Figs. 16 to 24 are examples of results obtained by an experiment. The experiment relates to the color measurement results of samples in which the conditions were varied in increments of 20 nm from 300 nm to 500 nm in lattice period d. The samples were in the form of a laminate including the first layer 11 to the third layer 13 laminated with a base material. For each condition, a lattice structure 11G with a constant lattice period d was provided on a 5 mm square plane, and color measurement was performed by obtaining the spectral reflectance in the case of α incidence where light was incident parallel to the lattice direction as shown in Fig. 7, and in the case of β incidence where light was incident perpendicular to the lattice direction as shown in Fig. 8.

[0077] The measurement was carried out using an optical system as shown in Figure 15. The optical system was prepared so that the angle of incidence and the angle of reception on the sample were equal, and the reflected light was received from an area of ​​approximately 4 mmφ on the surface of the sample placed in the sample holder, and the reflected light was measured. The basic angle of incidence and angle of reception was 30 degrees. The spectrometer obtains the spectral reflectance spectrum as raw data, as shown in Figures 16 and 17, which will be referred to later. Tristimulus values ​​XYZ are derived from the reflectance of the object for each wavelength, the spectral characteristics of the light source, and human visual sensitivity, and these are then converted into various color values ​​such as those in the L*a*b* color system.

[0078] By performing measurements on the image elements and the pattern elements using the method shown in FIG. 15, the respective resonance wavelengths λ1 and λ2 can be obtained. That is, the relationship between the difference in the resonance wavelengths λ1 and λ2 and the difference in the structural period, as shown in formula (9), can be experimentally obtained. Thus, from the experimental results shown in FIG. 15, it can be seen that the difference in the resonance wavelengths λ1 and λ2 is 25 nm, and the difference in the structural period corresponds to 20 nm. In other words, strictly speaking, the relationship between the difference in the resonance wavelengths λ1 and λ2 and the structural period can be formulated by formula (9), but in practice, since the difference in the resonance wavelengths λ1 and λ2 and the difference in the structural period are linear, an approximation can be obtained using the experimental value. This approximation depends on the observation angle and the material of the structure, but since the realistic observation angle and the material of the structure are similar, it is sufficiently practical in most realistic configurations.

[0079] 16 and 17 show spectral reflectance spectra obtained by measuring samples with different grating periods d under α incidence and β incidence conditions, which have different relationships between the grating direction and the incidence direction of the grating structure 11G. Fig. 16 shows the spectral reflectance spectrum obtained under the α incidence condition, and Fig. 17 shows the spectral reflectance spectrum obtained under the β incidence condition.

[0080] FIG. 18 shows the relationship between the grating period d of the grating structure 11G and the reflection peak wavelength for the results of FIGS. As shown in Fig. 18, the relationship between the grating period d and the reflection peak wavelength is linear for both α incidence and β incidence. However, while there is a consistent change in the case of α incidence, the relationship between the two changes at the boundary between 360 nm and 380 nm in the grating period in the case of β incidence. This means that the grating structure 11G with α incidence is easier to control in terms of design and manufacturing.

[0081] FIG. 19 shows the relationship between the grating period d of the grating structure 11G and the peak reflectance for the results of FIGS. As shown in Figure 19, α incidence generally has a higher reflectance than β incidence. This is because, in Figure 17, the reflection peak of lattice structure 11G with fine lattice period d appears on the short wavelength side as well as on the long wavelength side, which is the main component. This can be said to be due to the influence of polarization that occurs due to the relationship between the lattice direction and the incidence direction. In a structural design that results in α incidence, the higher the reflectance at the wavelength corresponding to the main hue, the stronger the color development of the displayed color and the higher the visibility.

[0082] Figures 20 and 21 show the results of converting the spectral reflectances shown in Figures 16 and 17 into color values. Figure 20 shows a u'v' chromaticity diagram based on CIE1976. Figure 21 shows an ab chromaticity diagram of the CIE Lab color system. In both cases, the starting point of the arrows on the chromaticity diagram is the color value with a lattice period of 300 nm, and the lattice period increases by 20 nm along the lines connecting the plots. For α incidence and β incidence, the former is generally located outside the chromaticity diagram and has a higher saturation than the latter. The higher the saturation, the stronger the color of each hue is perceived, so α incidence, i.e., providing a lattice structure in which the lattice direction and the incidence direction are parallel, provides higher visibility.

[0083] Figure 22 shows the grating periods d that produce similar hues for α incidence and β incidence for wavelengths corresponding to blue, green, and red, extracted from Figure 21, and overlaid with the corresponding spectral reflectance spectra from Figures 16 and 17. The spectrum with a peak near 450 nm is blue, the spectrum with a peak near 500 nm is green, and the spectrum with a peak near 650 nm is red. The solid line spectrum shows the results for α incidence, and the dashed line spectrum shows the results for β incidence. Comparing the solid and dashed lines for each wavelength, it is easy to see that there are differences in reflectance, as mentioned above.

[0084] 23 and 24 show the spectral reflectance spectra for α incidence and β incidence, respectively, when the measured specular reflection angle is changed from 30° to 20° and 40°. FIG. 23 shows the spectral reflectance spectrum for α incidence, and FIG. 24 shows the spectral reflectance spectrum for β incidence. Comparing the fluctuation range S1 and fluctuation range S2 of the center of the peak wavelength at specular reflection angles of 20° to 40°, the fluctuation range S2 for β incidence is larger. That is, when an observer is instructed to observe the optical element 10 at a specular reflection angle, with β incidence, the hue seen may vary significantly depending on the observation angle even with the same specular reflection. On the other hand, since the amount of hue fluctuation is relatively small in the case of α incidence, the angle dependency of the observed color can be reduced by designing the structure to obtain α incidence.

[0085] The phenomenon in which the color changes depending on the specular reflection angle can be explained by the phase matching condition in formula (4) above. When the incident angle θ changes, the resonant wavelength λ changes because the grating period d is constant. When the grating direction and the incident direction are parallel as shown in Figure 7, F in formulas (2) and (3) does not change even if the incident angle θ changes, that is, the effective refractive index does not change, so the change in the resonant wavelength λ is small. On the other hand, when the grating direction and the incident direction are perpendicular as shown in Figure 8, F changes depending on the incident angle θ. In particular, when the thickness of the dielectric layer of the second layer 12 has a distribution with respect to the shape of the grating structure formed on the interface between the first layer 11 and the second layer 12, F is likely to change, and the variation in the effective refractive index due to the incident angle θ may become large.

[0086] As described above, it can be said that α incidence, i.e., providing a lattice structure in which the lattice direction and the incidence direction are parallel, is superior in terms of visibility and color stability. In general, the optical element 10 is often observed under an illumination environment in which light hits it from directly above or from the upper front side. In light of this, the state in which α incidence occurs is when the azimuth angle of the lattice structure 11G is 90°, i.e., vertical, as seen from the observer, as shown in FIG. 7. Another advantage of using such a lattice direction is that diffracted light is less likely to enter the observer's eyes. As a result, when observing the optical element 10 while tilting it, the gaze can be focused only on the motif region 11S1 and background region 11S2 that are originally intended to be shown.

[0087] In addition, when the azimuth angle is 90° in all of the lattice structures 11G arranged in the motif region 11S1, the background region 11S2, and the boundary region 11S3, there are the following advantages in manufacturing. For example, when manufacturing a film having such a lattice structure 11G, a method of manufacturing the film by applying heat and pressure to a thermoplastic resin or an ultraviolet curing resin on a metal plate on which the lattice structure 11G is formed, filling the structure of the metal plate with the resin, and curing the resin can be considered. When mass-producing the optical element 10, there is a method of winding a metal plate around a roll and embossing a long film, but in these processes, if the flow direction of the film and the direction of the lattice structure are parallel, the moldability is high and the desired optical effect is easily obtained, and furthermore, defects such as the resin being taken up by the metal plate and the plate becoming unusable immediately are less likely to occur.

[0088] FIG. 25 shows one embodiment of the boundary region 11S3. As shown in Figure 25(a), boundary region 11S3 has a contour at the portion adjacent to image element 11R1 and at the portion adjacent to pattern element 11P1, and the distance between any point on this contour and the point perpendicular to the tangent at that point and intersects with the other contour is defined as the width Wb of boundary region 11S3.

[0089] As shown in FIG. 25(b), the width Wb may be constant throughout the boundary region. This allows the boundary between the motif region 11S1 and the background region 11S2 to be uniformly emphasized by the boundary region 11S3. This allows the optical element 10 to have a flat impression and to give a strong impression. In particular, if the boundary region 11S3 is linear, the impression is likely to be sharp. Note that the curved boundary region 11S3 tends to give the optical element 10 a soft impression.

[0090] Alternatively, as shown in FIG. 25(c), the width of the boundary region 11S3 may vary locally to include the width Wb1 and the width Wb2. That is, the boundary region 11S3 may include a first portion and a second portion, and the width Wb1 of the first portion may be different from the width Wb2 of the second portion. This improves the aesthetics of the optical element 10 by varying the width of the boundary region 11S3. The different widths of the boundary region 11S3 tend to give the optical element 10 an elegant impression. In particular, when combined with a curve, it creates a rhythmic impression. Furthermore, when the change in width Wb is continuous, it tends to have a natural appearance.

[0091] The width of the boundary region 11S3 can be 30 μm or more and 3000 μm or less. When the width of the boundary region 11S3 is 30 μm or more, the observer can visually recognize the boundary region 11S3. Also, when the width of the boundary region 11S3 is 3000 μm or less, the boundary region 11S3 is prevented from being more noticeable than the motif region 11S1 and the background region 11S2. In particular, when the width of the boundary region 11S3 is 30 μm or more and less than 300 μm, a dense line can be drawn, so that the boundary region 11S3 can be used as a supplementary boundary line. On the other hand, when the width of the boundary region 11S3 is 300 μm or more and 3000 μm or less, the width is thick enough to be resolved by the human eye, so that the boundary region 11S3 can be used as a boundary line between regions, particularly a boundary between different patterns.

[0092] With reference to Figs. 26 to 29, modified examples regarding the arrangement of the motif region 11S1, the background region 11S2, and the boundary region 11S3 will be described. In Fig. 26, the motif region 11S1 is formed from three image elements, and a boundary region 11S3 is provided on the periphery of the motif region 11S1. The boundary region 11S3 and the background region 11S2 may not have the lattice structure 11G, and may be a substantially flat surface with an average roughness Sa of 20 μm or less. By using such a structure, when a symbol such as a national flag is displayed, the area other than the motif region 11S1 is white, so that the image of the symbol is not lost and the design to be shown can be emphasized.

[0093] 27 shows an example in which the motif region 11S1 is formed from multiple image elements that are not in contact with each other. In such a case, each image element may be regarded as a motif region 11S1, and each may be provided with a boundary region 11S3. Even with such a structure, the boundary region 11S3 clearly displays the outline of each image element, and as a result, it is possible to impress the viewer with the overall shape of the motif region 11S1.

[0094] Fig. 28 shows an example in which background region 11S2 and boundary region 11S3 are not present in part of the outline of motif region 11S1. As Fig. 28 shows, even if the outline of motif region 11S1 is not completely surrounded as in Fig. 27, the outline of motif region 11S1 can be recognized at the edge of the area where the design is placed, so boundary region 11S3 is not necessary. However, if the color of motif region 11S1 and the outside of the design region are similar, providing boundary region 11S3 to highlight the outline makes it easier to recognize the motif shape.

[0095] FIG. 29 shows an example in which the entire design region is filled with the motif region 11S1. As shown in FIG. 29, even if a figure appears meaningless at first glance, if it is arranged throughout the design and has the meaning of a "pattern" in itself, each "pattern" may be treated as a motif region 11S1. In this case, if a boundary region 11S3 is provided for each motif region 11S1, the region on the surface 11S where the motif region 11S1 is not located may be treated as a background region 11S2. If a boundary region 11S3 is not provided in consideration of the appearance of the entire design, the area between adjacent motif regions 11S1 may be regarded as a background region 11S2, or the region on the surface 11S where the motif region 11S1 is not located may be regarded as a boundary region 11S3. If the distance between the nearest points of multiple motif regions 11S1 is 1 mm or less, the motif regions 11S1 can be defined as being adjacent to each other.

[0096] A modified example of the lattice structure 11G will be described with reference to FIGS. Fig. 30 shows a lattice structure 11G arranged on the XY plane at an azimuth angle φ. The cross-sectional shape of the lattice structure 11G taken along line VII-VII in Fig. 30, which is perpendicular to the lattice structure 11G, is shown in Figs. 31 and 32.

[0097] The structure shown in Fig. 31 is the basic structure. In Fig. 31, the height of the convex portion is Hp, and the height of the concave portion is Hv, and the distance H between the height Hp and the height Hv is the structural height. When the center position CL between the convex portion and the concave portion is used as a reference, the width of the convex portion above the center position CL is dp, and the width of the concave portion below the center position CL is dv. In the example of Fig. 31, the width dp and the width dv are equal to each other.

[0098] On the other hand, the structure shown in Fig. 32 is a modified example of the structure shown in Fig. 31. In the structure shown in Fig. 32, the width dp of the convex portion and the width dv of the concave portion based on the central position CL are different from each other. The above-mentioned effective refractive index changes depending on the ratio of the width dp to the width dv. When the effective refractive index changes, the resonant wavelength λ that satisfies the phase matching conditions shown in equations (4) to (7) changes, and therefore the observed color changes.

[0099] In this way, the observed color changes depending on the values ​​of the variables included in the phase matching condition. Figures 31 and 32 show the ratio of the widths of the convex and concave portions of the grating structure 11G, but the effective refractive index also changes depending on the azimuth angle φ and grating period d of the grating structure 11G.

[0100] Furthermore, even under certain conditions that satisfy the phase matching condition, the interference state of the light reflected from the convex and concave portions differs depending on the structural height H of the lattice structure 11G, and the intensity of the observed light, in other words, the saturation, which is a variable equivalent to shading, changes.

[0101] By varying at least one of these variables, the hue and shade of the motif region 11S1, background region 11S2, and boundary region 11S3 can be changed, allowing for free color expression. An example is shown in Figure 33. For the image elements 11R1 and 11R2 forming the motif region 11S1 and the pattern elements 11P1 and 11P2 forming the background region 11S2, the cells Px arranged in the X direction and their cross-sectional shapes are shown. Figure 33(a) shows the planar structure of the image element 11R1 and its cross-sectional structure along line VIII-VIII, Figure 33(b) shows the planar structure of the image element 11R2 and its cross-sectional structure along line IX-IX, Figure 33(c) shows the planar structure of the pattern element 11P1 and its cross-sectional structure along line X-X, and Figure 33(d) shows the planar structure of the pattern element 11P2 and its cross-sectional structure along line XI-XI.

[0102] In this example, the lattice structure 11G of the cell Px is uniform within each element, giving it the appearance of being solidly painted in a particular color. However, the cross section along the line VIII-VIII to the line XI-XI differs for each element. For example, the lattice period d of the lattice structure 11G of the image element 11R1 and the image element 11R2 are different (d1>d2), but the structural heights H are equal to each other (H1=H2). In contrast, the azimuth angle φ of the pattern elements is different from that of the image elements. Furthermore, the lattice period d of the lattice structure 11G of the pattern element 11P1 and the pattern element 11P2 are equal (d3=d4), but the structural heights H are different (H3 <H4)。

[0103] FIG. 34 shows another modified example of the optical element 10. For the image element 11R1 and the pattern element 11P1, the cells Px arranged in the X direction and the Y direction and their cross-sectional shapes are shown. FIG. 34(a) shows the planar structure of the image element 11R1 and the cross-sectional structure along the line XII-XII, and FIG. 34(b) shows the planar structure of the pattern element 11P1 and the cross-sectional structure along the line XIII-XIII. In this example, the grating period d is partially changed within the image element 11R1. In the cross section along the line XII-XII, the structural height H1 is constant, and the grating period d1 and the grating period d2 are different from each other.

[0104] In addition, in the pattern element 11P1, the lattice period d is constant, and the structural height H3 and the structural height H4 are different from each other. In this way, by changing any of the azimuth angle, the lattice period, the structural height, and the ratio of the concave and convex parts of the lattice structure in the element, it is possible to impart a gradation or a shade to the hue. For example, when the optical element 10 displays a petal as shown in FIG. 2, it is possible to express a pseudo three-dimensional effect by changing the shade of the hue from the center of the petal to the outside.

[0105] Fig. 35 shows another example of the optical element 10 of this embodiment. Like Fig. 3, Fig. 35 shows the structure of the optical element 10 in a plan view facing the observation surface 10S. As shown in Fig. 35, the multiple cells Px may include cells Px having a first lattice structure 11G1 located in a part of each cell Px in a plan view facing the surface 11S. In the example described above with reference to Fig. 3, the first lattice structure 11G1 is located in the entirety of each cell Px. This is not limited to the above, and the first lattice structure 11G1 may be located in only a part of each cell Px. In each cell Px, the ratio of the area of ​​the first lattice structure 11G1 to the area of ​​the cell Px is the area ratio. The multiple cells Px may include cells Px having different area ratios.

[0106] The higher the area ratio of each cell Px, the higher the luminance of each cell Px. Therefore, by including a plurality of cells Px with different area ratios, it is possible to form luminance shading in the same hue in the color exhibited by the motif region 11S1. The area ratio may also be gradually changed. This makes it possible to display a pseudo three-dimensional image in the motif region 11S1. In this case, the area ratio can be determined according to the level of luminance, i.e., the gradation value, of the three-dimensional image to be displayed by the motif region 11S1.

[0107] Moreover, the optical element 10 includes the motif region 11S1 and the background region 11S2, but does not include the boundary region 11S3. In the optical element 10, the motif region 11S1 and the background region 11S2 are in contact with each other.

[0108] In this embodiment, the optical element 10 includes a portion where the area ratio of the cells Px decreases along the direction from the center of the motif region 11S1 toward the outer edge of the motif region 11S1, and the area ratio is smallest at the outer edge of the motif region 11S1.

[0109] [Second embodiment] A second embodiment of the optical element will be described with reference to Figs. 36 to 38. The optical element of the second embodiment of the present invention has a different shape of the grating pattern having the grating structure compared to the optical element of the first embodiment. Therefore, while these differences will be described in detail below, the configuration of the optical element of the second embodiment corresponding to the optical element of the first embodiment will be given the same reference numerals as in the first embodiment, and detailed description thereof will be omitted. Note that in Figs. 36 to 38 referred to below, for convenience of illustration, the grating structure is shown as a structure in which convex portions protruding in a direction away from the flat surface are arranged. In addition, in the optical element of the second embodiment, the color of the grating structure observed by the observer may be based on diffracted light of a higher order than the zeroth order diffracted light. Therefore, in the following, the angle at which the effect of the grating structure to produce color appears most efficiently is referred to as the mth order, and the diffracted light at the mth order is referred to as the mth order diffracted light.

[0110] As described above, the lattice pattern includes a plurality of lattice structures 11G. The direction in which the plurality of lattice structures are arranged is the first direction D1, and the direction perpendicular to the first direction D1 is the second direction D2. In each lattice structure, the shape in a cross section along the first direction D1 and perpendicular to the plane in which the first layer 11 extends is the cross-sectional shape. In each lattice pattern, lattice groups are repeatedly arranged. In the lattice group, two or more lattice structures having different cross-sectional shapes are arranged along the second direction D2. Hereinafter, the optical element of this embodiment will be described in more detail.

[0111] 36, similar to the optical element 10 of the first embodiment, the optical element 20 includes a first layer 11, a second layer 12, and a third layer 13. The optical element 20 includes three portions in the first direction D1. That is, the optical element 20 includes a first portion 20A, a second portion 20B, and a third portion 20C. The first portion 20A, the second portion 20B, and the third portion 20C are arranged in the order shown in the drawing in the direction in which the lattice structures are arranged.

[0112] In the lattice pattern, the lattice structures 11G belonging to each portion have the same cross-sectional shape. However, the cross-sectional shapes of the lattice structures belonging to each portion are different from each other between the portions. In the lattice pattern, the portion belonging to the first portion 20A is the first lattice 20AG, the portion belonging to the second portion 20B is the second lattice 20BG, and the portion belonging to the third portion 20C is the third lattice 20CG.

[0113] The first lattice 20AG includes a plurality of first lattice structures AGP. The plurality of first lattice structures AGP are repeated along the first direction D1. The cross-sectional shape of the first lattice 20AG is wavy. The lattice period of the first lattice 20AG is a first period d1. The first lattice structure AGP has a shape in which one peak is sandwiched between two valleys in a cross section along the first direction D1. The first lattice structure AGP has a slope connecting one valley and the peak, and a slope connecting the peak and the other valley. Each slope has an inclination with respect to the plane in which the first layer 11 extends.

[0114] In a cross section along the first direction D1, the angle formed by a tangent to one of the inclined surfaces and a straight line connecting the multiple valleys is a first tangent angle θ1. The straight line connecting the multiple valleys is a straight line that is approximately parallel to the surface of the first layer 11. The first tangent angle θ1 is equal to the angle formed by the plane on which the first layer 11 extends and the inclined surface.

[0115] The second lattice 20BG includes a plurality of second lattice structures BGP. The plurality of second lattice structures BGP are repeated along the first direction D1. The cross-sectional shape of the second lattice 20BG is wavy. The lattice period of the second lattice 20BG is the second period d2. The second period d2 is equal to the first period d1. The second lattice structure BGP has a shape in which one peak is sandwiched between two valleys in a cross section along the first direction D1, similar to the first lattice structure AGP. The second lattice structure BGP has a slope connecting one valley and the peak, and a slope connecting the peak and the other valley. Each slope has an inclination with respect to the plane in which the first layer 11 extends.

[0116] In a cross section along the first direction D1, the angle formed by a tangent to one of the inclined surfaces and a straight line connecting the multiple valleys is the second tangent angle θ2. The second tangent angle θ2 is an angle different from the first tangent angle θ1. The second tangent angle θ2 is equal to the angle formed by the plane on which the first layer 11 spreads and the inclined surface. In this embodiment, the second tangent angle θ2 is smaller than the first tangent angle θ1. On the other hand, as described above, the second period d2 of the second lattice 20BG is equal to the first lattice period d1 of the first lattice 20AG. Therefore, in a cross section along the first direction D1, the cross-sectional shape of the second lattice structure BGP and the cross-sectional shape of the first lattice structure AGP are different from each other.

[0117] The third lattice 20CG includes a plurality of third lattice structures CGP. The plurality of third lattice structures CGP are repeated along the first direction D1. The cross-sectional shape of the third lattice 20CG is wavy. The lattice period of the third lattice 20CG is a third period d3. The third period d3 is equal to the first period d1 and the second period d2. The third lattice structure CGP has a shape in which one peak is sandwiched between two valleys in a cross section along the first direction D1, similar to the first lattice structure AGP. The third lattice structure CGP has a slope connecting one valley and a peak, and a slope connecting a peak and the other valley. Each slope has an inclination with respect to the plane in which the first layer 11 extends.

[0118] In a cross section along the first direction D1, the angle formed by a tangent to one of the inclined surfaces and a straight line connecting the valleys is the third tangent angle θ3. The third tangent angle θ3 is an angle different from the first tangent angle θ1 and also different from the second tangent angle θ2. The third tangent angle θ3 is equal to the angle formed by the plane on which the first layer 11 spreads and the inclined surface. In this embodiment, the third tangent angle θ3 is smaller than the first tangent angle θ1 and smaller than the second tangent angle θ2. On the other hand, as described above, the third period d3 of the third lattice 20CG is equal to the first period d1 and the second period d2. Therefore, in a cross section along the first direction D1, the cross-sectional shape of the third lattice structure CGP is different from both the cross-sectional shape of the first lattice structure AGP and the cross-sectional shape of the second lattice structure BGP.

[0119] That is, in this embodiment, the above-described cross-sectional shape of each lattice pattern includes an inclined surface with an inclination with respect to the plane on which the first layer 11 extends. The plurality of lattice patterns include lattice structures in which the inclination angles of the inclined surface with respect to the first layer 11 are different from one another.

[0120] According to such a grating pattern, the angle at which the light incident on the optical element 20 is diffracted can be changed by changing the tangent angles θ1, θ2, θ3 at each inclined surface. That is, by making the tangent angles θ1, θ2, θ3 different between the first grating 20AG, the second grating 20BG, and the third grating 20CG, the angles at which the m-th order diffracted light is emitted from each of the gratings 20AG, 20BG, and 20CG can be made different from each other. This makes it possible to widen the range of angles at which the m-th order diffracted light is emitted compared to a case where the tangent angles are the same across the entirety of the multiple grating patterns. In other words, it is possible to widen the range of observation angles at which the observer can observe the m-th order diffracted light. Note that, since the gratings 20AG, 20BG, and 20CG have different cross-sectional shapes but the same grating period, the colors exhibited by each of the gratings 20AG, 20BG, and 20CG are approximately the same. Therefore, the collection of the m-th order diffracted light emitted from each of the gratings 20AG, 20BG, and 20CG does not generate white light.

[0121] In the first direction D1, the width of each of the gratings 20AG, 20BG, 20CG can be 300 μm or less, and further, can be 85 μm or less. By making the width of each of the gratings 20AG, 20BG, 20CG 300 μm or less, the resolution of the human eye cannot separate each of the gratings 20AG, 20BG, 20CG. Therefore, the observer cannot recognize that each of the gratings 20AG, 20BG, 20CG diffracts light at different angles.

[0122] It is generally known that the distance that a person with a visual acuity of 1.0 can separate with 1 minute of vision from a position 5 m away from an object of observation is 1.454 mm. This matter is explained using the Landolt ring. Note that 1 minute is 1 / 60 of 1°. Assuming that an observer observes the optical element 20 from a position 30 cm away from the optical element 20, the distance that can be separated by the observer's eyes, i.e., the resolution R, can be derived from the following formula (13).

[0123] R = 1454 × (30 / 500) (μm) … Equation (13) In addition, in the right side of formula (13), the unit of the first term is μm, and the unit of the second term is cm. From formula (13), the resolution R is 87.24 μm. Therefore, if the width of each of the gratings 20AG, 20BG, 20CG is 85 μm or less, it is possible to increase the certainty that the resolution of the human eye cannot resolve each of the gratings 20AG, 20BG, 20CG. Therefore, if the width of each of the gratings 20AG, 20BG, 20CG is 85 μm or less, it is easy to suppress unnaturalness in the image such as jaggies.

[0124] The cross-sectional shape of each of the grating structures AGP, BGP, and CGP is a wave shape having different tangent angles, so that the direction in which the m-th order diffracted light is emitted can be controlled by the tangent angle. On the other hand, when the cross-sectional shape of the grating structure is a rectangle composed of a plane parallel to the surface of the optical element 20 and a plane perpendicular to the surface, the m-th order diffracted light, i.e., the zeroth order diffracted light, is emitted in the direction of regular reflection of the incident light. For example, when the incident angle of the incident light on the surface of the optical element 20 is 45°, the exit angle of the regular reflection light is also 45°. Therefore, the observer cannot observe the light emitted by the optical element 20 unless he observes the optical element 20 from a direction with an observation angle of 45°.

[0125] When the optical element 20 is observed at the emission angle of the specular reflection light, the specular reflection light of the light emitted from the light source toward the optical element 20 is also observed by the observer. Therefore, the observer may have difficulty in visually recognizing the light emitted by the lattice structure. Furthermore, depending on the relative position of the light source with respect to the optical element 20, it may be difficult to observe the optical element 20 from the angle of specular reflection. In this respect, since the direction in which the m-th order diffracted light is emitted can be controlled by the tangent angle, the degree of freedom of the angle at which the optical element 20 emits the m-th order diffracted light is increased. Therefore, it is possible to solve the above-mentioned problem.

[0126] A grating pattern including three grating structures may have the following structure: As shown in Fig. 37, the lattice pattern includes a first lattice structure AGP, a second lattice structure BGP, and a third lattice structure CGP. The first lattice structure AGP, the second lattice structure BGP, and the third lattice structure CGP are arranged in the order shown along the first direction D1. As a result, the first lattice structure AGP, the second lattice structure BGP, and the third lattice structure CGP form one lattice group GPG. In the lattice pattern, a plurality of lattice groups GPG are repeated along the first direction D1.

[0127] In the first direction D1, the first lattice structure AGP has a lattice period of a first period d1, the second lattice structure BGP has a lattice period of a second period d2, and the third lattice structure CGP has a lattice period of a third period d3. The first period d1, the second period d2, and the third period d3 are equal to each other.

[0128] In the first direction D1, the period D of the grating group GPG is preferably 20 μm or more. The larger the period D of the grating group GPG, the more diffracted light of higher orders is included within the same observation angle. In other words, the larger the period D of the grating group GPG, the narrower the range of observation angles in which diffracted light of the same order is included. This reduces the difference between the observation angle of the m-th order diffracted light and the observation angle of other diffracted lights, allowing the observer to view multiple diffracted lights simultaneously with the m-th order diffracted light. This expands the range of observation angles in which the observer can view the light emitted from the optical element 20.

[0129] For example, as described above, in a diffraction grating having a rectangular cross-sectional shape, when the angle between the incident light and the normal to the diffraction grating is angle α and the angle between the diffracted light and the normal to the diffraction grating is angle β, the following formula (14) holds true, where angle α is the angle of incidence and angle β is the angle of diffraction.

[0130] d(sinα+sinβ) = mλ … Equation (14) In equation (14), d is the period of the diffraction grating, m is the diffraction order, and λ is the wavelength of light. The units of period and wavelength are nm. In the grating structure 11G shown in FIG. 37, the period d corresponds to the period D of the grating group GPG described above. In equation (14), when the angle α is set to 45°, the wavelength λ is set to 500 nm, and the period d is set to 5000 nm, the diffraction order m and angle β are determined as follows:

[0131] (m,β) = (1,-37.4), (2,-30.5), (3,-24.0)… Furthermore, when the period d is changed to 10,000 nm, the diffraction order m and angle β are determined as follows.

[0132] (m,β) = (1,-41.1), (2,-37.4), (3,-33.9)… Furthermore, when the period d is changed to 20,000 nm, the diffraction order m and angle β are determined as follows.

[0133] (m,β) = (1,-43.0), (2,-41.1), (3,-39.2)… In this way, the larger the period d, the smaller the difference in angle β between the diffracted lights of different diffraction orders.

[0134] Here, it is assumed that the pupil diameter of the human eye is 5 mm, and the observer observes the optical element 20 from a distance of 30 cm. In this case, the light emitted from a certain point on the optical element 20, which is included within an observation angle of about 1°, enters the observer's eye. That is, the observer visually recognizes the result of integrating the light within an observation angle of about 1°. In other words, if diffracted light having a specific wavelength is included within the range of an observation angle of about 1°, the diffraction efficiency becomes high within this range of observation angle. In addition, when the observer observes while tilting the optical element 20 so that the observation angle changes, the color exhibited by the optical element 20 is maintained as a specific color while the observer changes the observation angle by 2° or more, so that the observer can easily recognize the color exhibited by the optical element 20. Therefore, the optical element 20 can have the above-mentioned effect if it is configured to emit at least two diffracted lights of different orders within a range of 2° in the observation angle. In this respect, the period D of the optical element 20 can have the above-mentioned effect as long as it is 20 μm or more.

[0135] A grating pattern including three grating structures may have the following structure: As shown in Fig. 38, the lattice structure 11G includes a first lattice structure AGP, a second lattice structure BGP, and a third lattice structure CGP. The first lattice structure AGP, the second lattice structure BGP, and the third lattice structure CGP are arranged in the order shown along the first direction D1. As a result, the first lattice structure AGP, the second lattice structure BGP, and the third lattice structure CGP form one lattice group GPG. In the lattice pattern, a plurality of lattice groups GPG are repeated along the first direction D1.

[0136] The grating period of the first grating structure AGP is the first period d1, the grating period of the second grating structure BGP is the second period d2, and the grating period of the third grating structure CGP is the third period d3. The first period d1, the second period d2, and the third period d3 are different from each other. The difference in the grating period between the grating structures adjacent to each other in the first direction D1 can be smaller than 20 nm. For example, it is possible to set the first period d1 to 300 nm, the second period d2 to 310 nm, and the third period d3 to 290 nm.

[0137] Since the grating structures have different grating periods, the diffraction angles of the grating structures are different. The smaller the difference in grating period between the grating structures, the smaller the difference in diffraction angle. As described above, if the difference in grating period between adjacent grating structures in the first direction D1 is smaller than 20 nm, the diffraction angles of the m-th order diffracted light emitted from each grating structure are almost equal to each other. This makes it impossible for the observer to separate the m-th order diffracted light emitted from each grating structure. Therefore, the observation angle at which the observer can observe the light emitted from the optical element 20 can be expanded.

[0138] As described above, according to the second embodiment of the optical element, the following effects can be obtained. (1) Compared to a case where a plurality of lattice patterns have the same cross-sectional shape along the first direction D1, the observation angle at which a viewer can visually recognize the light emitted from the lattice structure 11G can be widened.

[0139] (2) In multiple lattice patterns, compared to when the inclination angles of the slopes included in the cross-sectional shape along the first direction D1 are the same, the observation angle at which an observer can see the light emitted from the lattice structure 11G can be widened depending on the difference in inclination angles between the lattice patterns.

[0140] [Modification of the second embodiment] The above-described second embodiment can be modified and implemented as follows. [Cross-sectional shape] The lattice structure 11G may include lattice structures having different cross-sectional shapes. The cross-sectional shapes may include four or more types of lattice structures. The multiple types of lattice structures may be positioned randomly within the lattice pattern.

[0141] The cross-sectional shape of the lattice structure 11G is not limited to the wavy shape described above. Even if the lattice structure 11G has a shape other than the wavy shape, the pattern lattice can include lattice structures having different cross-sectional shapes, thereby providing an effect equivalent to the above-mentioned (1).

[0142] [Third embodiment] A third embodiment of the optical element will be described with reference to Fig. 39. The optical element of the third embodiment of the present invention differs from the optical element 10 of the first embodiment in that the first layer contains a filler. Therefore, while these differences will be described in detail below, the configuration of the optical element of the third embodiment that corresponds to the optical element of the first embodiment will be given the same reference numerals as in the first embodiment, and detailed description thereof will be omitted.

[0143] As shown in FIG. 39, the first layer 11 of the optical element 30 contains fillers 31 dispersed in the resin forming the first layer 11. The average particle size of the fillers 31 is 400 nm or less. At least a part of the light incident on the first layer 11 is scattered by the fillers dispersed in the first layer 11. Therefore, the light incident on the lattice structure 11G contains light having different angles of incidence. As a result, each lattice structure 11G included in the lattice pattern GP reflects light in a direction of regular reflection according to the angle of incidence of the light incident on the lattice structure 11G. The light reflected by the lattice structure 11G is emitted to the outside of the optical element 30 without being scattered by the fillers 31 or after being scattered by the fillers 31. Therefore, the range of the emission angle of the light emitted from the optical element 30 is wider than when the first layer 11 does not contain a filler. As a result, the range of observation angles at which the observer can observe the color presented by the optical element 30 is wider.

[0144] As described above, the average particle size of the filler 31 can be 400 nm or less. This suppresses the occurrence of Mie scattering, and thus the transparency of the first layer 11 is increased to a certain extent. The shape of the filler 31 is not limited to a spherical shape. Therefore, in this embodiment, the average value of a plurality of diameters that can be specified for each filler 31 is the average particle size of each filler 31. Here, the following is known regarding the relationship between the size of the scatterer such as the filler 31 and the actual scattering state. When the average particle size of the scatterer is in the range of 400 nm or more and 700 nm or less, Mie scattering occurs due to the scatterer. In Mie scattering, light included in the visible range is scattered to the same extent regardless of the wavelength of the light, so that the light scattered by Mie scattering is visually recognized as light having a white color. In Mie scattering, the scattering angle of light is affected by the particle size of the scatterer. In Mie scattering, the larger the particle size of the scatterer, the stronger the scattering in the forward direction in the traveling direction of the light.

[0145] In contrast, Rayleigh scattering occurs when the scatterers are smaller than 1 / 10 of the wavelength of light. In Rayleigh scattering, the direction in which the light is scattered does not depend on the particle size of the scatterers. In Rayleigh scattering, light is scattered in a distribution that forms a figure eight in the direction of light travel, regardless of the particle size of the scatterers. Also, in Rayleigh scattering, the shorter the wavelength of light, the stronger the light scattering.

[0146] When transparency is required for the first layer 11 in which the scatterers, filler 31, are dispersed as in this embodiment, the average particle size of the filler 31 must be at least equal to or less than the wavelength of light, and the scattering of the filler 31 must be Rayleigh scattering. In this case, the average particle size of the filler 31 can be 400 nm or less. When the average particle size of the filler 31 is D and the wavelength of light is λ, the scattering cross section α can be calculated by the following formula (15).

[0147] α =πD / λ … Equation (15) By using formula (15), it is possible to easily determine whether the scattering phenomenon caused by the filler 31 is Rayleigh scattering or Mie scattering. It is known that when the scattering cross section α is 0.4 or more, Rayleigh scattering mainly occurs, whereas when the scattering cross section α is greater than 0.4 and less than 3, Mie scattering mainly occurs. Therefore, when the light incident on the filler 31 is light in the visible range and the wavelength of the light is, for example, 400 nm, if the average particle size of the filler 31 is 50 nm or less, Rayleigh scattering can be mainly caused by the filler 31. As a result, the light incident on the first layer 11 can be scattered by the filler 31 while the transparency of the first layer 11 is high.

[0148] As described above, according to the optical element of the third embodiment, the following effects can be obtained. (3) Compared to when the first layer 11 does not contain a filler, the range of emission angles of light emitted from the optical element 30 is wider. Therefore, the range of observation angles at which an observer can observe the color exhibited by the optical element 30 is wider.

[0149] [Fourth embodiment] A fourth embodiment of the optical element will be described with reference to Fig. 40 and Fig. 41. The optical element of the fourth embodiment of the present invention is different from the optical element 10 of the first embodiment in the state of the surface of the third layer 13 opposite to the surface in contact with the second layer 12. Therefore, while these differences will be described in detail below, the configurations of the optical element of the third embodiment corresponding to those of the optical element 10 of the first embodiment will be denoted by the same reference numerals and detailed description thereof will be omitted. Also, a first example and a second example of the fourth embodiment will be described in order below.

[0150] [Example 1] 40, in the optical element 40, the third layer 13 is an adhesive layer having thermoplastic properties. The third layer 13 contains filler 41 dispersed in a portion closer to the surface opposite to the surface in contact with the second layer 12 than the center in the thickness direction of the third layer 13. In the third layer 13, the surface in contact with the second layer 12 is the front surface 13F, and the surface opposite to the front surface 13F is the back surface 13R. In the third layer 13, as described above, the filler 41 is preferably located closer to the back surface 13R than the center in the thickness direction of the third layer 13, and is preferably located in the vicinity of the back surface 13R.

[0151] As described above, the third layer 13 is an adhesive layer having thermoplasticity. The material for forming the third layer 13 can be an adhesive having thermoplasticity. Since the third layer 13 is an adhesive layer having thermoplasticity, the optical element 40 can be transferred to the transferee by applying heat and pressure to the optical element 40 while the third layer 13 is in contact with the transferee. At this time, the heat and pressure applied to the third layer 13 cause unevenness due to the filler 41 on the back surface 13R of the third layer 13, and thus unevenness is also caused on the front surface 13F of the third layer 13. As a result, unevenness is also caused in the first layer 11 and the second layer 12 in the portion overlapping the unevenness formed on the third layer 13 when viewed from the thickness direction of the optical element 40. As a result, unevenness due to the filler 41 is added to the lattice pattern GP at the interface between the first layer 11 and the second layer 12. The transferee can be, for example, a bill, a passport, or a card.

[0152] The unevenness at the interface between the first layer 11 and the second layer 12 can be adjusted by the size of the filler 41, the thickness of each of the layers 11, 12, and 13, and the heat and pressure conditions when the optical element 40 is transferred.

[0153] Since the grating pattern GP has irregularities caused by the filler 41, the grating structures 11G constituting the grating pattern GP include grating structures 11G having different angles of incidence of light to the grating structure 11G. Each grating structure 11G reflects the m-th order diffracted light at an exit angle corresponding to the angle of incidence of light in the grating structure 11G. The range of exit angles at which each grating structure 11G emits the m-th order diffracted light varies depending on the curvature of the irregularities imparted to each grating structure 11G. In other words, the observation angle at which the observer can observe the color exhibited by the grating pattern GP varies depending on the curvature of the irregularities imparted to each grating structure 11G.

[0154] As described above, it is preferable that the color exhibited by the optical element 40 is maintained within a range of observation angles of 2° or more. On the other hand, if the range of observation angles at which the color exhibited by the optical element 40 can be observed is too wide, the intensity of the light emitted by the optical element 40 at each observation angle will be low. Therefore, the range of observation angles at which the color exhibited by the optical element 40 can be observed is preferably 2° to 10°, and more preferably 2° to 5°. It is preferable that the emission angles of the m-th order diffracted light emitted by all grating patterns GP are included in this range of observation angles.

[0155] Therefore, it is preferable that the curvature of the unevenness caused by the filler 41 is not excessively large. The following two methods can prevent the curvature of the unevenness caused by the filler 41 from becoming excessively large. In the first method, the filler 41 is uniformly dispersed in the third layer 13, and the heat and pressure conditions in the transfer are adjusted so that the curvature of the unevenness does not become excessively large. In the second method, a filler having a flat shape is used as the filler 41, instead of a filler having a spherical shape, and the filler 41 is dispersed in the third layer 13 so that the diameter of the filler 41 is small in the thickness direction of the third layer 13.

[0156] [Example 2] 41, the optical element 40 further includes a fourth layer 42 in contact with the third layer 13. The fourth layer 42 includes a surface 42F in contact with the third layer 13. The surface 42F includes projections and recesses.

[0157] The unevenness on the surface 42F of the fourth layer 42 can be formed by various methods. For example, when the third layer 13 is transferred to the fourth layer 42, which is a transferee, the unevenness can be formed on the surface 42F of the fourth layer 42 so as to follow the third layer 13 deformed by heat and pressure. In this case, an adhesive layer having thermoplasticity can be used for the third layer 13. Also, for example, paper or a resin film can be used for the fourth layer 42. Alternatively, unevenness can be formed on the surface 42F of the fourth layer 42 by dispersing fine particles or fibers in the fourth layer 42. Also, unevenness can be generated on the surface 42F of the fourth layer 42 by degassing or unevenness that occurs when the fourth layer 42 is formed. In the second example, as in the first example, unevenness caused by the surface 42F of the fourth layer 42 can be added to the lattice structure 11G. Therefore, the optical element 40 of the second example can also obtain the same effect as the optical element 40 of the first example.

[0158] When the fourth layer 42 is the transferred body and contains fine particles, it is preferable that the average particle size of the fine particles is approximately the same as the thickness of the adhesive layer, the third layer 13. In addition, by adjusting the heat and pressure conditions in the transfer onto the fourth layer 42, the unevenness imparted to the lattice structure 11G can be prevented from becoming excessively large.

[0159] Also, the fourth layer 42 in which the fibers are dispersed can be a paper fourth layer 42. In this case, the fibers constituting the fourth layer 42 are arranged parallel to the surface 42F of the fourth layer 42. The pulp fibers have a diameter of 20 μm or more and 50 μm or less, and a length of about 1 mm or more and 5 mm or less. Therefore, the unevenness imparted to the lattice pattern GP may become excessively large. In contrast, the cellulose nanofibers have a diameter of 4 nm or more and 100 nm or less, and a length of about 5 μm or more. Therefore, the unevenness imparted to the lattice structure 11G is prevented from becoming excessively large. The cellulose nanofibers are fibers obtained by decomposing pulp fibers.

[0160] As described above, according to the optical element of the fourth embodiment, the following effects can be obtained. (4) Since the unevenness caused by the filler 41 is imparted to the lattice pattern GP, ​​the plurality of lattice structures 11G can include lattice structures 11G in which the angles of incidence of light with respect to the lattice structure 11G are different from one another. This makes it possible to widen the observation angle at which the light emitted from the lattice pattern GP is observed, since the angles of emission from the lattice structure 11G are also different.

[0161] (5) Since the unevenness caused by the surface 42F of the fourth layer 42 is imparted to the lattice pattern GP, ​​the plurality of lattice structures 11G can include lattice structures 11G in which the angles of incidence of light with respect to the lattice structure 11G are different from one another. This allows the exit angles in the lattice structures 11G to also differ, making it possible to widen the observation angle at which the light exiting from the lattice pattern GP is observed.

[0162] [Fifth embodiment] A fifth embodiment of the optical element will be described with reference to Figures 42 and 43. The optical element of the fifth embodiment of the present invention is different from the optical element of the first embodiment in that it includes a resin layer in addition to the first to third layers. Therefore, while these differences will be described in detail below, the configurations of the optical element of the fifth embodiment that correspond to the optical element 10 of the first embodiment will be denoted by the same reference numerals as those of the optical element 10 of the first embodiment, and detailed description thereof will be omitted.

[0163] [Example 1] As shown in FIG. 42, the optical element 50 includes a resin layer 14 on the side of the first layer 11 opposite to the second layer 12. The resin layer 14 is in contact with the first layer 11. The hardness of the first layer 11 is higher than the hardness of the third layer 13 and the hardness of the resin layer 14. In the laminate of these layers, the thickness of the second layer 12 is smaller than the thicknesses of the other layers. Therefore, the hardness of the second layer 12 is omitted because it can be considered not to have much effect on the characteristics of the optical element 50.

[0164] For example, when manufacturing a medium such as a card having the first layer 11, the second layer 12, the third layer, and the resin layer 14, the minute unevenness of each layer and the unevenness of the filler may be imparted to the lattice pattern GP when laminating the layers forming the card. At this time, since the resin layer 14 and the third layer 13 are formed of a material having a relatively high elasticity, the resin layer 14 and the third layer can absorb external forces. In addition, by forming the first layer 11 from a material having a higher hardness than these layers, it is possible to prevent the influence of the minute unevenness from occurring in the area of ​​the lattice pattern GP even when a force is applied to the laminate from the outside. This prevents the shape of the lattice structure 11G of the lattice pattern GP from being deformed, thereby maintaining the purity of the color and the intensity of the coloring observed in a specific direction.

[0165] In order to achieve the above hardness, the material forming the first layer 11 may be an ultraviolet curable resin, and the material forming the third layer 13 and the resin layer 14 may be a thermoplastic resin. Furthermore, by making the thickness of the first layer 11 thicker than the structural height of the lattice structure 11G formed in the first layer 11, the effect of the hardness of the first layer 11 can be further enhanced. The thickness of the first layer 11 can be 1 μm or more and 10 μm or less.

[0166] The resin layer 14 may contain the above-mentioned filler. [Example 2] FIG. 43 shows an example of the structure of a card 50C including the structure of the first example.

[0167] In the example shown in Fig. 43, for example, the first layer 11 is a molding layer, the second layer 12 is a reflective layer, the third layer 13 is an adhesive layer, and the resin layer 14 is a peeling layer. These laminates are transferred to the printing layer 16, and then the white layer 17 and the printing layer 16 are laminated in this order on the printing layer 16. Then, the protective layer 15 is laminated on each of the resin layer 14, which is the uppermost layer, and the printing layer 16, which is the lowermost layer. In this way, it is possible to obtain the card 50C shown in Fig. 43.

[0168] The printing layer 16 is formed of a material that turns black by reacting to, for example, a laser beam. The printing layer 16 can be formed of a material that turns black when carbonized by a laser beam. Identification information and biometric information such as a facial image can be printed on the printing layer 16 after the above-mentioned lamination. In addition, it is preferable to use a highly heat-resistant base material made of polycarbonate or the like for the white layer 17. The surface of the white layer 17 may be printed.

[0169] The protective layer 15 has an uneven surface in contact with the resin layer 14. As a result, after the above-mentioned lamination, the card 50C is given the effect of scattering the light incident on the card 50C through the protective layer 15. This makes it possible to expand the range of observation angles at which the observer can visually recognize the light emitted from the card 50C. At this time, the first layer 11 can have at least one of the hardness and thickness described in the first example. This makes it possible to expand the angle range at which the light is observed while suppressing the effect of the unevenness of the protective layer 15 on the shape of the lattice pattern GP, ​​that is, while maintaining the clear hue of the light emitted from the card 50C.

[0170] [Sixth embodiment] A sixth embodiment of the optical element will be described with reference to Fig. 44 to Fig. 50. The optical element of the sixth embodiment of the present invention is different from the optical element of the first embodiment in that it includes a relief layer having a relief surface. Therefore, while these differences will be described in detail below, the configurations of the optical element of the sixth embodiment corresponding to the optical element 10 of the first embodiment will be denoted by the same reference numerals as those of the optical element 10 of the first embodiment, and detailed description thereof will be omitted. Two examples of the optical element of the sixth embodiment will be described in order below.

[0171] [Example 1] [Optical element configuration] The configuration of the first example of the optical element will be described with reference to FIG.

[0172] As shown in FIG. 44, the optical element 60 includes a first layer 11, a second layer 12 in contact with the first layer 11, and a third layer 13 in contact with the second layer 12, similar to the optical element 10 of the first embodiment described above. The first layer 11 is a resin layer including a lattice structure 11G on at least a part of a back surface 11R in contact with the second layer 12. The back surface 11R is an example of a first surface. For convenience of illustration, FIG. 44 shows a cross-sectional shape in which the lattice structure 11G is located on the entire back surface 11R, but in the optical element 60 of this embodiment, the lattice structure 11G is formed on a part of the back surface 11R.

[0173] In the second layer 12, a front surface 12F in contact with the rear surface 11R of the first layer 11 has an uneven shape following the lattice structure 11G. The front surface 12F is an example of a second surface. The second layer 12 is a layer made of a dielectric material having a refractive index higher than that of the first layer 11. The third layer 13 is a layer made of a resin having a refractive index lower than that of the second layer 12.

[0174] The optical element 60 includes a relief layer including a relief surface 13Re different from the rear surface 11R and the front surface 12F. The relief surface 13Re includes a plurality of reflecting surfaces, and the pitch between adjacent reflecting surfaces is larger than the pitch of the lattice structure 11G. In this embodiment, the relief layer is the above-mentioned third layer 13. More specifically, in the third layer 13, the rear surface 13R, which is the surface in contact with the fourth layer 61, is the relief surface 13Re.

[0175] 44, for convenience of illustration, the relief surface 13Re is located on the entire back surface 13R, but in the optical element 60 of this embodiment, the relief surface 13Re is located on a part of the back surface 13R. Moreover, the relief surface 13Re is formed at a position on the back surface 13R that overlaps with the lattice structure 11G when viewed from the thickness direction of the optical element 60.

[0176] The lattice structure 11G displays a colored image exhibiting a color specific to the lattice period of the lattice structure 11G in a reflection direction including the regular reflection direction. The relief surface 13Re displays a reflection image by white reflected light in a reflection direction including a direction different from the regular reflection direction. The optical element 60 has a first state in which it does not display a colored image or a reflected image, a second state in which it mainly displays a colored image, a third state in which it mainly displays a reflected image, and a fourth state in which it mainly displays a colored image and a reflected image. The angle formed by the plane in which the optical element 60 extends and the plane including the line of sight of the observer is the observation angle. The optical element 60 has one of the respective states depending on the observation angle.

[0177] The optical element 60 further includes a fourth layer 61. The fourth layer 61 may be a reflective layer or a refractive layer. When the fourth layer 61 is a refractive layer, the refractive index of the fourth layer 61 is different from that of the third layer 13. Since the refractive index of the fourth layer 61 is different from that of the third layer 13, the fourth layer 61 can increase the reflectance at the relief surface 13Re. In two adjacent layers, the reflectance at the interface is determined by the difference in refractive index between the two layers. Therefore, since the refractive index of the fourth layer 61 is different from that of the third layer 13, the same effect as when the fourth layer 61 is a reflective layer can be obtained.

[0178] As described above, the optical element 60 is observed from the side opposite to the third layer 13 with respect to the second layer 12. Therefore, the fourth layer 61 may or may not have optical transparency. The fourth layer 61 may be composed of a single layer or may be composed of multiple layers. When the fourth layer 61 is a refractive layer and composed of multiple layers, the fourth layer 61 may include a layer with a relatively low refractive index and a layer with a relatively high refractive index.

[0179] The relief surface 13Re includes a plurality of reflecting surfaces as described above. The relief surface 13Re displays a reflected image formed by white light by at least one of scattering and reflection. The relief surface 13Re includes a plurality of reflecting surfaces as described above, and the plurality of reflecting surfaces may be arranged in a predetermined order or may be arranged irregularly within the relief surface 13Re. In the relief surface 13Re, the emission direction of the light emitted by the relief surface 13Re can be controlled by the orientation and angle of each reflecting surface.

[0180] The lattice structure 11G emits light in a range of emission directions including the above-mentioned specular reflection direction. Of the light emitted by the lattice structure 11G, the intensity of the light emitted in the specular reflection direction is the highest. In contrast, the relief surface 13Re emits light in a range of emission directions including directions other than the specular reflection direction. Of the light emitted by the relief surface 13Re, the intensity of the light emitted in a direction other than the specular reflection direction is the highest. In other words, the orientation and angle of the reflection surface of the relief surface 13Re are set so that, of the light emitted by the relief surface 13Re, the intensity of the light emitted in a direction other than the specular reflection direction is the highest.

[0181] In the relief surface 13Re, the period of the reflective surface may be greater than 400 nm and less than or equal to 1000 nm, or may be greater than 1000 nm. In order to prevent the relief surface 13Re from emitting diffracted light, the period of the reflective surface is preferably greater than 1000 nm. In the relief surface 13Re, for example, the shape in a cross section perpendicular to the extending direction of the reflective surface may be sawtooth.

[0182] The colored image displayed by the lattice structure 11G is an image formed by light of a specific wavelength included in the wavelength of visible light. The colored image includes, for example, chromatic images such as a red image, a green image, and a blue image. When the lattice structure 11G displays a red image, the light emitted by the lattice structure 11G includes, for example, light with a wavelength of 620 nm or more and 750 nm or less. When the lattice structure 11G displays a green image, the light emitted by the lattice structure 11G includes, for example, light with a wavelength of 495 nm or more and 570 nm or less. When the lattice structure 11G displays a blue image, the light emitted by the lattice structure 11G includes, for example, light with a wavelength of 450 nm or more and 495 nm or less. Note that the lattice structure 11G displaying a colored image is synonymous with the lattice structure 11G exhibiting a chromatic color.

[0183] The reflected image displayed by the relief surface 13Re is an image formed by white light caused by reflection or scattering on the relief surface 13Re. In other words, the reflected image displayed by the relief surface 13Re is an achromatic image, an image having no hue. The relief surface 13Re may be configured so that the intensities of the white light emitted from each position are different from each other. This allows the relief surface 13Re to display a specific image by the difference in the intensity of the white light, in other words, the difference in brightness. Note that the relief surface 13Re displaying a reflected image is synonymous with the relief surface 13Re exhibiting an achromatic color.

[0184] [Function of optical elements] The function of the optical element 60 will be described with reference to FIGS. As shown in FIG. 45, the angle at which the incident light IL emitted by the light source LS is incident on the optical element 60 is the incident angle α, and the angle at which the emitted light EL emitted by the optical element 60 is emitted is the emission angle β. The angle formed by the plane including the line of sight of the observer OB and the plane on which the optical element 60 spreads is the observation angle θOB. The above-mentioned regular reflection direction is the direction in which the emitted light EL is emitted at an emission angle β having the same magnitude as the incident angle α. In the optical element 60, the lattice structure 11G displays a colored image in a reflection direction including the regular reflection direction, while the relief surface 13Re displays a reflection image by white light in a reflection direction including a direction different from the regular reflection direction. The optical element 60 has one of the following four states according to the observation angle θOB.

[0185] In this embodiment, an example will be described in which the colored image displayed by the lattice structure 11G has a moon shape, and the reflected image displayed by the relief surface 13Re has a star shape. However, the shape of the colored image displayed by the lattice structure 11G and the shape of the reflected image displayed by the relief surface 13Re can be any shape. The image displayed by the lattice structure 11G is a first image, and the image displayed by the relief surface 13Re is a second image.

[0186] FIG. 46 shows the optical element 60 in a first state. 46, in the first state of the optical element 60, both the first image P1 and the second image P2 disappear in the optical element 60. In the first state, the luminance of the light for forming the first image P1 and the luminance of the light for forming the second image P2 are low enough that the first image P1 and the second image P2 are not distinguished by the observer OB. In other words, at the observation angle θOB at which the observer OB observes the optical element 60, the luminance of the light reflected by the lattice structure 11G and the light reflected by the relief surface 13Re are both low compared to the reflected light of the medium to which the optical element 60 is attached, so that the first image P1 and the second image P2 are not distinguished by the observer OB.

[0187] FIG. 47 shows the optical element 60 in a second state. 47, in the second state of the optical element 60, the first image P1 appears in the optical element 60, and the second image P2 disappears. The appearance of the first image P1 means that the optical element 60 displays the first image P1 in a state in which the luminance of light in the first image P1 is higher than the luminance of light in the second image P2. Therefore, the second state includes a state in which the first image P1 is discerned, while the second image P2 is not discerned. The second state also includes a state in which the first image P1 and the second image P2 appear in the optical element 60, and the luminance of light in the first image P1 is higher than the luminance of light in the second image P2.

[0188] In other words, at the observation angle θOB at which the observer OB observes the optical element 60, the observer can easily perceive the light reflected by the lattice structure 11G, but cannot easily perceive the light reflected by the relief surface 13Re.

[0189] FIG. 48 shows the optical element 60 in a third state. 48, in the third state of the optical element 60, a second image P2 appears in the optical element 60. The appearance of the second image P2 means that the luminance of light in the second image P2 is higher than the luminance of light in the first image P1, and the optical element 60 displays at least the second image P2. Therefore, the third state includes a state in which the second image P2 is identified, while the first image P1 is not identified. The third state also includes a state in which the optical element 60 displays the second image P2 and the first image P1, and the luminance of light in the second image P2 is higher than the luminance of light in the first image P1.

[0190] In other words, at the observation angle θOB at which the observer OB observes the optical element 60, the brightness of the light reflected by the relief surface 13Re is sufficient for the observer to distinguish an image, but the brightness of the light reflected by the lattice structure 11G is not sufficient for the observer to distinguish an image.

[0191] FIG. 49 shows the optical element 60 in a fourth state. As shown in FIG. 49, in the fourth state of the optical element 60, both the first image P1 and the second image P2 appear in the optical element 60. When both the first image P1 and the second image P2 appear, the first image P1 and the second image P2 of the optical element 60 are identified by the observer. In this state, the luminance of the light in the first image P1 may be substantially equal to the luminance of the light in the second image P2. In other words, at the observation angle θOB at which the observer OB observes the optical element 50, the intensity of the light reflected by the lattice structure 11G and the light reflected by the relief surface 13Re is such that the observer OB can distinguish them. Note that the optical element 60 only needs to have the first state to the third state, and the fourth state is not essential for the optical element 60.

[0192] In this way, the optical element 60 displays a reflected image formed by white reflected light, i.e., an achromatic image, and a colored image formed by light having a specific wavelength, i.e., a chromatic image. Here, in distinguishing between an achromatic image and a chromatic image, there is less individual variation in distinguishing between the two images, compared to distinguishing between an achromatic first image and an achromatic second image, or between a chromatic first image and a chromatic second image. Therefore, in the optical element 60, there is less individual variation in verifying the authenticity, and the criteria for verifying the authenticity are easier to clarify, compared to a case in which the authenticity of the optical element 60 is verified based on two chromatic images or two achromatic images.

[0193] The optical element 60 also includes a second state in which the first image P1 is mainly displayed, a third state in which the second image P2 is mainly displayed, and a first state in which neither the first image P1 nor the second image P2 is displayed. Here, the second state or the third state and the first state are contrasting states, so that individual differences are unlikely to occur in distinguishing between the second state or the third state and the fourth state. Therefore, individual differences are unlikely to occur in verifying authenticity, and the criteria for verifying authenticity can be easily described.

[0194] [Example 2] A second example of the optical element 60 will be described with reference to FIG. 50, the optical element 60 of the second example includes a first layer 11, a second layer 12, and a third layer 13, similar to the optical element 60 of the first example. Meanwhile, in the optical element 60 of the second example, the second layer 12 is a relief layer. The second layer 12 includes a relief surface 12Re as the surface opposite to the front surface 12F of the second layer 12, that is, the back surface 12R. Note that, although the relief surface 12Re is located on the entire back surface 12R in FIG. 50, the relief surface 12Re may be located on the entire back surface 12R or only on a part of the back surface 12R.

[0195] In the optical element 60 of the second example, a colored image can be displayed by the light reflected by the lattice structure 11G due to the difference between the refractive index of the first layer 11 and the refractive index of the second layer 12. Also, in the optical element 60 of the second example, a reflected image can be displayed by the light reflected by the relief surface 12Re due to the difference between the refractive index of the second layer 12 and the refractive index of the third layer 13.

[0196] In the second example of the optical element 60, the surface of the third layer 13 opposite to the surface in contact with the second layer 12 may be a flat surface, or may have a shape that follows the unevenness of the relief surface 12Re of the second layer 12.

[0197] As described above, according to the sixth embodiment of the optical element, the following effects can be obtained. (6) Since the optical element 60 displays a colored image and a reflected image using white light, there is little individual difference in distinguishing between the two images. Therefore, with the optical element 60, there is little individual difference in verifying authenticity, and the criteria for verifying authenticity can be easily described.

[0198] (7) Since the second layer 12 includes the lattice structure 11G and the relief surface 12Re, the reflectance at the lattice structure 11G can be increased due to the difference between the refractive index of the first layer 11 and the refractive index of the second layer 12, and the reflectance at the relief surface 12Re can be increased due to the difference between the refractive index of the second layer 12 and the refractive index of the third layer 13.

[0199] [Modification of the sixth embodiment] The sixth embodiment described above can be modified and implemented as follows. [Relief layer] In the optical element 60, the first layer 11 may be a relief layer. That is, in the first layer 11, the surface opposite to the surface including the lattice structure 11G may include a relief surface. In this case, too, the effect equivalent to the above-mentioned (6) can be obtained.

[0200] In the optical element 60 of the second example, the surface of the third layer 13 that is in contact with the relief surface 12Re has a shape that follows the shape of the relief surface 12Re. Therefore, the surface of the third layer 13 can also function as a relief surface.

[0201] [Seventh embodiment] A seventh embodiment of the optical element will be described with reference to Fig. 51 to Fig. 54. The optical element of the seventh embodiment of the present invention is different from the optical element 60 of the sixth embodiment in that layers other than the first layer 11, the second layer 12, and the third layer 13 are relief layers. Therefore, while these differences will be described in detail below, the configurations of the optical element of the seventh embodiment that correspond to the optical element 60 of the sixth embodiment will be given the same reference numerals as in the sixth embodiment, and detailed description thereof will be omitted. Four examples of the optical element of the seventh embodiment will be described in order below.

[0202] [Example 1] A first example of an optical element will be described with reference to FIG. As shown in FIG. 51, the optical element 70 includes a first layer 11, a second layer 12, and a third layer 13. The optical element 70 further includes a relief layer 71 including a relief surface 71Re. The relief surface 71Re is a surface different from the rear surface 11R and the front surface 12F described above. The relief surface 71Re includes a plurality of reflective surfaces, and the pitch between adjacent reflective surfaces is larger than the pitch of the lattice structure 11G. The relief surface 71Re is included in the rear surface 71R of the relief layer 71.

[0203] The optical element 70 further includes a reflective layer 72 and an adhesive layer 73. The reflective layer 72 is in contact with the relief surface 71Re and has a shape that follows the unevenness of the relief surface 71Re. The adhesive layer 73 is in contact with the reflective layer 72 on the side opposite to the relief layer 71 with respect to the reflective layer 72. In the optical element 70, the third layer 13 functions as an adhesive layer. As a result, the multilayer body composed of the first layer 11 and the second layer 12 is attached to the relief layer 71 by the third layer 13. Therefore, in the optical element 70, the lattice structure 11G and the relief surface 71Re overlap when viewed from the thickness direction of the optical element 70.

[0204] The adhesive layer 73 may be located on the entire surface of the reflective layer 72 opposite to the surface in contact with the relief layer 71, or may be located on a part of the surface. According to the first example optical element 70, it is possible to separately manufacture a first multilayer body formed of the first layer 11, the second layer 12, and the third layer 13, and a second multilayer body formed of the relief layer 71, the reflective layer 72, and the adhesive layer 73. Moreover, according to the first example optical element 70, it is possible to attach the optical element 70 to an object to be adhered using the adhesive layer 73.

[0205] [Example 2] A second example of an optical element will be described with reference to FIG. As shown in FIG. 52, the optical element 70 includes a relief layer 71, a reflective layer 72, and an adhesive layer 73 in addition to the first layer 11, the second layer 12, and the third layer 13, as in the optical element 70 of the first example described above. The optical element 70 of the second example further includes a substrate 74 between the third layer 13 and the relief layer 71. In a pair of adjacent surfaces of the substrate 74, the third layer 13 is located on one surface, and the relief layer 71 is located on the other surface. The substrate 74 has optical transparency. The substrate 74 can function as a support layer for the first layer 11 and the relief layer 71 formed on the substrate 74 during the manufacture of the optical element 70. The optical element 70 of the second example is observed from the substrate 74 side with respect to the relief layer 71.

[0206] [Example 3] A third example of an optical element will be described with reference to FIG. As shown in FIG. 53, the optical element 70 includes a relief layer 71, a reflective layer 72, and an adhesive layer 73 in addition to the first layer 11, the second layer 12, and the third layer 13, as in the optical element 70 of the first example described above. The optical element 70 of the third example further includes a first substrate 75 and a second substrate 76. The first substrate 75 is located between the third layer 13 and the relief layer 71. The third layer 13 functions as an adhesive layer, and thus the multilayer body composed of the first layer 11 and the second layer 12 is adhered to the first substrate 75 by the third layer 13. The adhesive layer 73 is adhered to the second substrate 76. The first substrate 75 has light transmittance. On the other hand, the second substrate 76 may or may not have light transmittance.

[0207] A first multilayer body composed of the first layer 11, the second layer 12, and the third layer 13 is located in a part of the first substrate 75 in a plan view facing the lattice structure 11G. A second multilayer body including the relief layer 71, the reflective layer 72, and the adhesive layer 73 is located in a part of the second substrate 76 in a plan view facing the relief surface 71Re. When viewed in the thickness direction of the optical element 70, the first layer 11 overlaps the relief layer 71.

[0208] [Example 4] A fourth example of an optical element will be described with reference to FIG. 54, like the optical element 70 of the first example, the optical element 70 includes a relief layer 71, a reflective layer 72, and an adhesive layer 73 in addition to the first layer 11, the second layer 12, and the third layer 13. The optical element 70 further includes a first substrate 75 and a second substrate 76. The third layer 13 functions as an adhesive layer, and is adhered to the relief layer 71. The adhesive layer 73 is adhered to the second substrate 76.

[0209] The above-mentioned first multilayer body is located in a part of the first substrate 75 in a plan view corresponding to the lattice structure 11G. The second multilayer body is located in a part of the second substrate 76 in a plan view facing the relief surface 71Re. When viewed from the thickness direction of the optical element 70, the first layer 11 overlaps the relief layer 71.

[0210] The optical element 70 is observed from the reflective layer 72 side with respect to the adhesive layer 73. Therefore, the first base material 75 has light transmitting properties. On the other hand, the second base material 76 may or may not have light transmitting properties.

[0211] In the first to fourth examples of the optical element 70, the base material may be paper, plastic film, or the like. The base material may be printed. Alternatively, the base material may be a multi-layer body, and at least some of the layers constituting the base material may be printed.

[0212] As described above, according to the optical element of the seventh embodiment, in addition to the above-mentioned effect (6), the following effect can be obtained. (8) Since the layers other than the first layer 11, the second layer 12, and the third layer 13 are relief layers having a relief surface, the design freedom of the relief layer is increased.

[0213] [Modification of the Seventh Embodiment] The seventh embodiment described above can be modified and implemented as follows. [Base material] In the optical element 70 of the first to fourth examples, in a plan view facing the grating structure 11G, each base material may be smaller than at least one of the first multilayer body and the second multilayer body.

[0214] The first multilayer body including the first layer 11 and the second multilayer body including the relief layer 71 may be embedded between two substrates. In other words, each of the first multilayer body and the second multilayer body may be laminated in a state where it is sandwiched between two substrates.

[0215] Each substrate may be a laser coloring layer that develops color when irradiated with a laser beam, and substrate 74 in the first example may include information recorded on substrate 74 by irradiation with a laser beam.

[0216] In the optical element 70 of the third example, at least one of the first substrate 75 and the second substrate 76 can include information recorded by irradiation with a laser beam. When the first substrate 75 includes information, the second image displayed by the relief surface 71Re and the information included in the first substrate 75 are overlapped when viewed from the thickness direction of the optical element 70, so that only a part of the second image is visible. This increases the resistance of the optical element 70 to counterfeiting. On the other hand, when the second substrate 76 includes information, the entire first image displayed by the lattice structure 11G and the entire second image displayed by the relief surface are visible when viewed from the thickness direction of the optical element 70.

[0217] In the optical element 70 of the third example, when the first substrate 75 contains information, the first image displayed by the lattice structure 11G and the second image displayed by the relief surface 71Re are superimposed on the information contained in the first substrate 75, so that only a part of the first image and a part of the second image are visible when viewed from the thickness direction of the optical element 70. This increases the resistance of the optical element 70 to counterfeiting. In contrast, when the second substrate 76 contains information, the entire first image displayed by the lattice structure 11G and the entire second image displayed by the relief surface are visible when viewed from the thickness direction of the optical element 70.

[0218] [Eighth embodiment] A transfer foil including an optical element will be described with reference to Fig. 55. In the eighth embodiment of the present invention, a case in which the optical element included in the transfer foil is a first example of the optical element 60 of the sixth embodiment will be described as an example of the transfer foil.

[0219] As shown in FIG. 55, the transfer foil 80 includes an adhesive body including an optical element 60 and an adhesive layer 81 for adhering the optical element 60 to a transfer target body. The transfer foil 80 further includes a support layer 82 and a peeling layer 83. In the transfer foil 80, the support layer 82, the peeling layer 83, the optical element 60, and the adhesive layer 81 are stacked in the order described above. The optical element 60 after being transferred to the transfer target body is observed from the opposite side of the peeling layer 83 to the optical element 60. Therefore, the peeling layer 83 has optical transparency. On the other hand, since the peeling layer 83 is peeled off from the support layer 82 when the optical element 60 is transferred, the support layer 82 may or may not have optical transparency.

[0220] The transfer foil 80 includes a lattice structure 11G and a relief surface 13Re. Therefore, the optical element 60 displaying the first image P1 and the second image P2 can be transferred to the transfer target object by only transferring a part of the transfer foil 80. The optical element 60 can be transferred by, for example, a hot stamping method.

[0221] [Modification of the eighth embodiment] [Transfer foil] It is possible to prepare a first transfer foil including a lattice structure 11G and a second transfer foil including a relief surface 13Re, and form an optical element using the two transfer foils. In this case, a part of the first transfer foil and a part of the second transfer foil are transferred to the transferred body so that the lattice structure 11G included in the first transfer foil and the relief surface 13Re included in the second transfer foil overlap when viewed from the thickness direction of the optical element. In this case, when forming the optical element, it is necessary to align the position where the part of the first transfer foil is transferred with the position where the part of the second transfer foil is transferred. Therefore, the optical element is more resistant to counterfeiting.

[0222] [Optical elements] The transfer foil may include the optical element 10 of the first embodiment, the optical element 20 of the second embodiment, the optical element 30 of the third embodiment, and the optical element 40 of the fourth embodiment, instead of the optical element 60 described above. The transfer foil may also include the optical element 60 of the second example in the sixth embodiment, and the optical elements 70 of the first and second examples in the seventh embodiment, instead of the optical element 60 described above.

[0223] [Ninth embodiment] An optical element according to a ninth embodiment will be described with reference to Fig. 56 to Fig. 58. The ninth embodiment of the present invention is different from the sixth embodiment in that the relief surface in the sixth embodiment is provided on the same surface as the grating structure.

[0224] As shown in FIG. 56, in the optical element 90, the first layer 91 has a lattice structure 11G and a relief surface 11Re at the interface with the second layer 12. In the optical element 90, for example, a lattice region SA1 in which the lattice structure 11G is formed and a relief region SA2 in which the relief surface 11Re is formed are alternately arranged. In FIG. 56, for convenience of illustration, the first layer 11 has one lattice region SA1 and one relief region SA2, and the rear surface 11R of the first layer 11 does not have any region other than the lattice region SA1 and the relief region SA2. However, the number and arrangement of the lattice regions SA1 and the relief regions SA2 are changed depending on the image displayed by the optical element 90.

[0225] Like the above-mentioned relief surface 71Re, the relief surface 11Re includes a plurality of reflecting surfaces. The width of the structure including each reflecting surface may be greater than the width of the lattice structure 11G, and the height of the structure including each reflecting surface may be greater than the height of the lattice structure 11G. Alternatively, the width of the structure including the reflecting surface may be equal to the width of the lattice structure 11G, and the height of the structure including the reflecting surface may be equal to the height of the lattice structure 11G. However, the colors displayed by the relief surface 11Re are mainly achromatic colors, and the relief surface 11Re displays an image at an observation angle different from the observation angle at which a colored image is displayed by the lattice structure 11G.

[0226] As described above, the shape of the relief surface 11Re in a cross section perpendicular to the extending direction of the reflection surface may be, for example, sawtooth. When the structure including the reflection surface is large enough that diffracted light is not generated on the relief surface 11Re, the pitch of the reflection surfaces adjacent to each other on the relief surface 11Re may be substantially constant, so that the relief surface 11Re can reflect white light in a specific direction. On the other hand, when the structure including the reflection surface is small enough that diffracted light is generated on the relief surface 11Re, for example, structures having different sizes may be mixed in the relief surface 11Re, and the diffracted light caused by the structures of each size may be mixed to display white light on the optical element 90.

[0227] Fig. 57(a) shows an example of a first image P1 displayed by the optical element 90 through the lattice structure 11G, and Fig. 57(b) shows an example of a second image P2 displayed by the optical element 90 through the relief surface 11Re. Fig. 57 shows the planar structure of a card 90C to which the optical element 90 is applied, together with a third image P3 possessed by the card 90C. The third image P3 includes identification information for identifying the owner of the card 90C. The third image P3 includes, for example, the owner's face image, name, ID number, and other identification information.

[0228] As shown in Fig. 57(a), the optical element 90 can display a symbol meaning euro as the first image P1. As shown in Fig. 57(b), the optical element 90 can display a character string meaning euro (EURO) as the second image P2. The optical element 90 can display a part of the first image P1 and a part of the second image P2 in the region A. That is, in the region A, a part of the lattice structure 11G for displaying the first image P1 and a part of the relief surface 11Re for displaying the second image P2 are located.

[0229] As shown in FIG. 58, in the region A, there are arranged cells in which the lattice structure 11G is located and cells in which the structure including the reflective surface that forms the relief surface 11Re is located. As shown in FIG. 58(a), the cells Px and Pxr may be arranged in a checkerboard pattern. As shown in FIG. 58(b), the cells Px and Pxr may be arranged in a striped pattern. As shown in FIG. 58(c), the cells Px and Pxr may be arranged such that one cell Pxr is surrounded by eight cells Px. In addition, in the region A, the arrangement of the cells Px and Pxr and the ratio of the area of ​​the cells Px to the area of ​​the cells Pxr can be changed according to the image displayed by the optical element 90. For example, when it is desired to emphasize a part of the first image P1 more than a part of the second image P2 in the region A, the proportion of the cells Px in the region A may be made larger than the proportion of the cells Pxr.

[0230] [Tenth embodiment] An authenticator according to a tenth embodiment of the present invention will be described with reference to Fig. 59 and Fig. 60. A card, which is an example of an authenticator, will be described below. Examples of cards include an ID card, a driver's license, a membership card, and a credit card. The card includes the third example of the optical element 70 according to the seventh embodiment as a part of the card.

[0231] [Card configuration] 59, card 100 has a two-dimensional plate shape in a plan view facing front surface 100F of card 100. Card 100 displays first image 101, second image 102, and third image 103 via front surface 100F. Card 100 also displays first image P1 and second image P2 via front surface 100F.

[0232] In this embodiment, the first image 101 includes a face image 101a and a background image 101b. The face image 101a is an image showing the face of the owner of the card 100. The background image 101b includes the face image 101a therein and constitutes the background of the face image 101a. The second image 102 includes information about the owner of the card 100. The second image 102 includes information expressed by letters and numbers. The third image 103 includes information about the card 100. The information included in the third image 103 is the name of the card 100. The face image 101a and the second image 102 are identification information that identifies the owner of the card. Note that it is sufficient for the card 100 to be able to display the first image P1 and the second image P2 through the front surface 100F. The above-mentioned images are examples of images that the card 100 can display.

[0233] FIG. 60 shows a cross-sectional structure of the card 100 taken along line XIV-XIV in FIG. As shown in FIG. 60, a card 100, which is an example of an authenticator, includes an optical element 70. The optical element 70 may cover the identification information. In the optical element 70 included in the card 100, a first multilayer body including a first layer 11, a second layer 12, and a third layer 13 further includes a release layer 78. The release layer 78 covers the first layer 11. A second multilayer body including a relief layer 71, a reflective layer 72, and an adhesive layer 73 further includes a release layer 79. The release layer 79 covers the relief layer 71. In the optical element 70, the second multilayer body is covered by a first substrate 75.

[0234] The entire second base material 76 has a characteristic of developing color when irradiated with a laser beam before being irradiated with the laser beam. The second base material 76 of the card 100 includes a first coloring section 76a which develops color when irradiated with a laser beam, and a second coloring section 76b. The first coloring section 76a is a section which displays a facial image 101a, and the second coloring section 76b is a section which displays a second image 102.

[0235] The card 100 includes a white layer 111, a lower protective layer 112, and an upper protective layer 113. The white layer 111 is a layer colored white, and is in contact with the second base material 76. A printing 114 is applied to a portion of the surface of the white layer 111 that is in contact with the second base material 76. When viewed in the thickness direction of the card 100, the printing 114 is located in an area that overlaps with the first coloring portion 76a. The printing 114 displays a background image 101b.

[0236] The lower protective layer 112 is located on the surface of the white layer 111 opposite to the surface in contact with the second base material 76. The upper protective layer 113 covers the first base material 75, and contains a first multilayer body between the upper protective layer 113 and the first base material 75. The upper protective layer 113 has light transparency. On the other hand, the lower protective layer 112 may or may not have light transparency.

[0237] [Modification of the tenth embodiment] [Authentication Body] The authenticator is not limited to a card but may be embodied as any other authenticator used to authenticate the owner, such as a passport.

[0238] [Optical elements] The authenticated body may include the optical element 10 of the first embodiment, the optical element 20 of the second embodiment, the optical element 30 of the third embodiment, the optical element 40 of the fourth embodiment, the optical element 60 of the sixth embodiment, and the optical element 90 of the ninth embodiment, instead of the optical element 70 described above. Also, the authenticated body may include the optical element 70 in the first, second, and fourth examples of the seventh embodiment, instead of the optical element 70 described above.

[0239] [Eleventh embodiment] An authenticator according to an eleventh embodiment of the present invention will be described with reference to Figures 61 to 68. In the following, another example of a card will be described as an example of an authenticator.

[0240] [Card configuration] The configuration of the card will be described with reference to Fig. 61. As an example of the card, a card including the optical element 10 of the first embodiment will be described, but the card is not limited to the optical element 10 of the first embodiment, and may include the optical element in each of the second to ninth embodiments.

[0241] The card 120 further includes a display layer 121 in addition to the first layer 11, the second layer 12, and the third layer 13. The display layer 121 can display predetermined information. The display layer 121 can display the predetermined information using, for example, letters, numbers, figures, and QR codes (registered trademark). The card 120 includes a front surface 120F as the surface of the first layer 11 opposite to the surface in contact with the second layer 12.

[0242] The display layer 121 can display predetermined information by printing on the display surface 121F that contacts the third layer 13. The method of printing on the display surface 121F can be, for example, letterpress printing, gravure printing, offset printing, or screen printing. The ink used for printing can be functional ink. The functional ink can be ink that changes color depending on the type or state of the light source that irradiates the card 120, and ink that changes color or gloss depending on the observation angle of the observer. The ink that changes color depending on the type or state of the light source can be phosphorescent ink and photochromic ink. The ink that changes color or gloss depending on the observation angle can be pearl ink, magnetic ink, and color shift ink.

[0243] The phosphorescent ink has a function of absorbing and storing light energy emitted from sunlight or fluorescent lamps, and gradually emitting light in the dark. The photochromic ink is an ink that reacts to ultraviolet light and develops a color. The photochromic ink has a function of exhibiting different colors such as red, blue, purple, and yellow depending on the amount of ultraviolet light irradiated on the photochromic ink. The pearl ink is an ink to which a pearl pigment is added. The luster of the pearl ink changes depending on the observation angle. The pearl ink contains a pearl pigment formed from polarized pearl as the pearl pigment, and therefore the color tone also changes depending on the observation angle. With the functional ink, it is easy to check whether the color of the print formed on the display surface 121F changes. Therefore, the authenticity of the card 120 can be reliably verified based on the color of the print.

[0244] The method of printing on display surface 121F may be an inkjet method, a thermal printer method, a laser method, or the like. With these methods, it is possible to set the information to be formed on display surface 121F for each card 120. For this reason, it is preferable that the pattern or the like common to multiple cards 120 is printed at a relatively high speed by the above-mentioned printing method, and the identification information identified by each card 120 is printed using the inkjet method, the thermal printer method, the laser method, or the like.

[0245] As described above, the optical element included in the card 120 is not limited to the optical element 10 of the first embodiment, and may be the optical element in each of the fifth and sixth embodiments. That is, the card 120 may be capable of displaying the first image P1 displayed by the lattice structure 11G, the second image P2 displayed by the relief surface, and the third image displayed by the display layer 121. In such a card 120, when the luminance of the first image P1 and the luminance of the second image P2 are sufficiently high, the third image is difficult to view at each of the observation angles at which the first image P1 is displayed and the observation angle at which the second image P2 is displayed. On the other hand, the third image is viewed at an observation angle at which neither the first image P1 nor the second image P2 is displayed. Therefore, the viewer can view the third image.

[0246] The observation angle at which each of the first image P1, the second image P2, and the third image is visible can be set arbitrarily depending on the observation angle at which each of the first image P1 and the second image P2 appears, i.e., the shape of the lattice structure 11G and the relief surface.

[0247] In the card 120, the multilayer body composed of the first layer 11, the second layer 12, and the third layer 13 can have a transmittance of 70% or more in the direction in which the three layers are stacked. This makes it easier to view the image displayed by the card 120. In this case, particularly when the optical element, which is a multilayer body composed of the first layer 11, the second layer 12, and the third layer 13, covers the identification information, the ease of identification is improved. For example, Article 195 of the Road Transport Vehicle Safety Standards requires that the transmittance of each of the front glass and side glass of an automobile be 70% or more. In view of these standards, it can be said that it is preferable for the transmittance of the transparent body through which the light for displaying the information passes to be 70% or more in order for people to clearly and reliably view the information.

[0248] The transmittance of the transparent multilayer body can be measured using a spectrophotometer. In the environment in which the card 120 is observed, it is assumed that the light source is sunlight or a fluorescent lamp. Therefore, it is preferable to measure the transmittance at a wavelength of 500 nm as the transmittance of the multilayer body used in the card 100. It is preferable to measure the transmittance of the multilayer body by a method conforming to JIS K7375:2008 "Method of determining total light transmittance and total light reflectance of plastics."

[0249] [Card Functions] The operation of card 120 will be described with reference to Fig. 62 to Fig. 68. The operation of a first example of card 120 and the operation of a second example of card 120 will be described below in order. Note that the first example of card 120 includes an optical element including lattice structure 11G and a relief surface, and is configured so that the authenticity of card 120 is verified by the observer's visual inspection. In contrast, the second example of card 120 includes an optical element including lattice structure 11G but not a relief surface, and is configured so that the authenticity of card 120 is verified by a verifier.

[0250] [Example 1] The operation of the first example of the card 120 will be described with reference to Figures 62 to 65. FIG. 62 shows a schematic diagram of a method in which an observer OB visually verifies the authenticity of a card 120. In FIG.

[0251] As shown in FIG. 62, the observer OB visually recognizes the card 120 while holding the card 120 in his / her hand. The reference plane Ph0 is a plane on which the card 120 is placed when the observer OB starts observing the card 120. The reference plane Ph0 is a reference plane when verifying the authenticity of the card 120. The observer OB tilts the card 120 placed on the reference plane Ph0 so that it is aligned with each of the first plane Ph1, the second plane Ph2, and the third plane Ph3. The observer OB observes the card 120 when the card 120 is positioned on each of the planes Ph1, Ph2, and Ph3. The angle formed by the reference plane Ph0 and the first plane Ph1 is the first angle θ1, the angle formed by the reference plane Ph0 and the second plane Ph2 is the second angle θ2, and the angle formed by the reference plane Ph0 and the third plane Ph3 is the third angle θ3. The first angle θ1 is greater than the second angle θ2 and the third angle θ3, and the second angle θ2 is greater than the third angle θ3.

[0252] The light source LS is located on the opposite side of the card 120 from the observer OB. In other words, the light source LS is located in front of the observer OB. The light source LS, the card 120, and the observer OB are arranged in relative positions such that the light of the light source LS incident on the card 120 is reflected by the card 120 toward the observer OB. When observing the card 120, it is preferable that light from a point light source is incident on the card 120 from one direction. However, in reality, when observing the card 120, light from a fluorescent lamp or external light is incident on the card 120 from various directions. Even in this case, if the light incident on the card 120 includes light reflected by the card 120 toward the observer OB, the luminance of the light emitted from the card 120 is reduced, but the observer OB can view the information displayed by the card 120.

[0253] Fig. 63 to Fig. 65 respectively show images displayed by the card 120. Fig. 63 shows an image displayed by the card 120 when the card 120 is placed on the first plane Ph1, and Fig. 64 shows an image displayed by the card 120 when the card 120 is placed on the second plane Ph2. Fig. 65 shows an image displayed by the card 120 when the card 120 is placed on the third plane Ph3. The card 120 is configured to be capable of displaying a first image P1, a second image P2, and a third image P3.

[0254] 63, when the observer OB places the card 120 on the first plane Ph1, the card 120 displays only the third image P3. The third image P3 includes identification information for identifying the owner of the card 120. The third image P3 includes, for example, the owner's facial photograph, name, ID number, and other identification information. When the observer OB places the card 120 on the first plane Ph1, the card 120 displays the entire third image P3 to the outside via the front surface 120F.

[0255] 64, when the observer OB places the card 120 on the second plane Ph2, the card 120 displays the second image P2. In a plan view facing the front surface 120F of the card 120, the second image P2 overlaps with a part of the third image P3. Therefore, in this embodiment, a part of the third image P3 is hidden by the second image P2. Note that the brightness of the second image P2 may be such that it does not completely hide a part of the third image P3.

[0256] As shown in FIG. 64, when the observer OB places the card 120 on the third plane Ph3, the card 120 displays the first image P1. On the other hand, the card 120 does not display the second image P2. In a plan view facing the front surface 120F of the card 120, the first image P1 overlaps with a part of the third image P3. Therefore, in this embodiment, a part of the third image P3 is hidden by the first image P1. Note that the brightness of the first image P1 may be such that it does not completely hide a part of the third image P3.

[0257] In this way, when the observer OB tilts the card 120 forward with respect to the reference plane Ph0, the card 120 displays the first image P1 and the second image P2 according to the position of the card 120. In other words, when the observer OB brings the front surface 120F of the card 120 closer to the observer OB in the observation space while keeping the position of the portion of the card 120 held by the observer OB substantially fixed, the card 120 displays the first image P1 and the second image P2 according to the position of the card 120.

[0258] Note that even if the observer OB tilts the card 120 left or right, for example, with the second plane Ph2 as the reference plane, the observer OB can still view the first image P1 and the second image P2 displayed by the card 120. In other words, even if the observer OB tilts the card 120 in the observation space without substantially changing the distance between the front surface 120F of the card 120 and the observer OB, the observer OB can still view the first image P1 and the second image P2. However, while the observer OB can easily view the second image P2, the observer OB can only view the first image P1 under limited observation conditions for the following reasons.

[0259] As described above, the first image P1 is only viewed by the observer OB when the light source LS and the observer OB are positioned at symmetric angles with respect to a plane including a normal to the surface of the card 120. Therefore, when the card 120 is tilted left or right with the second plane Ph2 as a reference, the angle formed by the second plane Ph2 and the reference plane Ph0 must be the third angle θ3. Here, the second plane Ph2 is a plane on which the observer OB places the card 120 when he or she unconsciously picks up the card 120. Therefore, the probability that the angle formed by the second plane Ph2 and the reference plane Ph0 coincides with the third angle θ3 is low. In contrast, when the observer OB tilts the card 120 back and forth with respect to the reference plane Ph0, the observer OB is highly likely to place the card 120 on the third plane Ph3.

[0260] Therefore, when observing the card 120, it is preferable that the observer OB tilts the card 120 back and forth with the light source LS positioned diagonally above the plane including the line of sight of the observer OB. This increases the probability that the observer OB observes both the first image P1 and the second image P2. This makes it easier for the observer OB to accurately verify the authenticity of the card 120.

[0261] [Example 2] The operation of the second example of the card 120 will be described with reference to Figures 66 to 68. FIG. 66 shows diagrammatically how the authenticity of the card 120 is verified by a verifier V.

[0262] As shown in Fig. 66, an environment for verifying the authenticity of the card 120 is set so that light from a light source LS is incident on the surface 120F of the card 120 at an incident angle α, and the reflected light reflected at an exit angle β is input to the verifier V. The verifier V may be, for example, a camera capable of reading an image, or a sensor capable of reading the distribution of brightness. The verifier V may be any device capable of processing each of the first image P1 and the second image P2 as an image or optical information such as brightness.

[0263] Fig. 67 shows an image displayed by a genuine card 120. Meanwhile, Fig. 68 shows an image displayed by a counterfeit card 200. Note that Figs. 67 and 68 show images displayed by each of the cards 120 and 200 under specific viewing conditions.

[0264] As FIG. 66 shows, the genuine card 120 shows a QR code P3a as part of the third image P3. In contrast, the fake card 200 displays the QR code P3a as part of the third image P3, and also displays the first image P1 through the surface 200F. Here, the verifier V determines that the card 120 is genuine when it reads the QR code P3a displayed by the card 100 under the above-mentioned observation conditions. In this case, the card 120 displays the QR code P3a as part of the third image P3, and the QR code P3a does not overlap with other images, so the verifier V determines that the card 120 is genuine. In contrast, the card 200 displays the QR code P3a as part of the third image P3, but displays the first image P1 so as to overlap the QR code P3a when viewed from the thickness direction of the card 120. In other words, the information read by the verifier V includes information other than the QR code. Therefore, the verifier V determines that the card 200 is fake.

[0265] In this embodiment, the QR code P3a is exemplified as the code displayed by the card 120, 200, but the code displayed by the card 120, 200 may be another code that can be read by the verifier V. The other code may be, for example, a barcode. Note that for verification by the verifier V, the first image P1 or the second image P2 may be used instead of the third image P3.

[0266] Furthermore, in the above example, the position of the verifier V is fixed at one location, but the verifier V may be movable and may read the light emitted from the card 120 at an angle γ different from the emission angle β in addition to the emission angle β described above. In this case, the authenticity of the card 120 can be verified in two stages by using two pieces of information obtained at different angles. This can further increase the accuracy of determining whether the card is authentic or counterfeit.

[0267] [Optical element forming materials] Materials that can be used to form the optical element will be described below. In the following, materials for forming each of the first layer 11, the second layer 12, and the third layer 13 of the optical element will be described.

[0268] [1st and 3rd layers] The material for forming each of the first layer 11 and the third layer 13 may essentially contain the following various resins. For example, poly(meth)acrylic resin, polyurethane resin, fluorine resin, silicone resin, polyimide resin, epoxy resin, polyethylene resin, polypropylene resin, methacrylic resin, polymethylpentene resin, cyclic polyolefin resin, polystyrene resin, polyvinyl chloride resin, polycarbonate resin, polyester resin, polyamide resin, polyamideimide resin, polyarylphthalate resin, polysulfone resin, polyphenylene sulfide resin, polyethersulfone resin, polyethylene naphthalate resin, polyetherimide resin, acetal resin, and cellulose resin may be used as the material for forming the first layer and the third layer. Only one of these resins may be used as the material for forming the first layer and the third layer, or two or more may be mixed or compounded. The materials for forming the first layer 11 and the third layer 13 may include at least one of a curing agent, a plasticizer, a dispersant, various leveling agents, an ultraviolet absorber, an antioxidant, a viscosity modifier, a lubricant, and a light stabilizer.

[0269] Methods for forming each of the first layer 11 and the third layer 13 include, for example, a thermal embossing method, a casting method, and a photopolymer method. In the photopolymer method, a radiation curable resin is poured between a flat substrate such as a plastic film and a metal stamper. The radiation curable resin is cured by irradiation with radiation, and then the cured resin film is peeled off from the metal stamper together with the substrate. The photopolymer method is preferable because it has a higher transfer accuracy of the fine uneven structure and is also excellent in heat resistance and chemical resistance, compared to the pressing method and casting method that use thermoplastic resin.

[0270] [Second layer] As described above, the material for forming the second layer 12 can be a dielectric material having optical transparency. The dielectric material can be a metal, a metal compound, a silicon compound, or a mixture of these. The dielectric material can be, for example, ZnS, ZnO, ZnSe, SiN x , SiO x , Ti x O x , Ta2O5, Cr2O3, ZrO2, Nb2O5, and ITO.

[0271] The method for forming the second layer 12 may be, for example, a physical vapor deposition method or a chemical vapor deposition method. Examples of the physical vapor deposition method that may be used include a vacuum deposition method, a sputtering method, an ion plating method, and an ion cluster beam method. Examples of the chemical vapor deposition method that may be used include a plasma chemical vapor deposition method, a thermal chemical vapor deposition method, and a photochemical vapor deposition method. The vacuum deposition method is easy to increase productivity. The ion plating method is easy to form a good quality reflective layer. The film formation conditions for the physical vapor deposition method and the chemical vapor deposition method may be selected according to the material for forming the reflective layer.

[0272] The second layer 12 can also be formed by using various printing methods, casting methods, die coating methods, etc. In this case, the second layer 12 can be formed by using a resin in which at least one of the above-mentioned dielectric materials is dispersed.

[0273] [Test example] [Test Example 1] Example 1 will be described below. Example 1 is a test example corresponding to the authenticator of the above-mentioned tenth embodiment. In test example 1, a first transfer foil including a first layer 11 and a second transfer foil including a relief layer 71 were prepared. Then, a part of the first transfer foil was transferred to a first substrate 75, and a part of the second transfer foil was transferred to a second substrate 76. A substrate that develops color when irradiated with a laser beam was used as the second substrate 76. The first substrate 75 and the second substrate 76 were laminated together to obtain an ID card as the authenticator of test example 1.

[0274] More specifically, when the first transfer foil was manufactured, a PET film (Lumirror (registered trademark), Toray Industries, Inc.) having a thickness of 38 μm was first prepared as a support layer. A release layer was obtained by applying an ink for a release layer to one surface of the support layer and drying the ink for a release layer. The thickness of the release layer 78 was 1 μm. Next, the ink for the first layer was applied onto the release layer 78 by gravure printing, and then the ink for the first layer was dried. The thickness of the ink for the first layer after drying was 2 μm. Then, a master plate for forming the lattice structure 11G was pressed against the dried ink for the first layer to form the lattice structure 11G. Note that during molding, the pressing pressure was 2 kgf / cm. 2 The press temperature was set to 80° C., and the press speed was set to 10 m / min.

[0275] At the same time as molding, the ink for the first layer was irradiated with ultraviolet light from the side opposite to the release layer 78. A high-pressure mercury lamp was used for the ultraviolet light irradiation, and the output of the high-pressure mercury lamp was 300 mJ / cm. 2 The temperature was set to 120°C. The ink for the first layer was cured to obtain the first layer 11. A TiO2 film having a thickness of 50 nm was formed on the first layer 11 by vacuum deposition. The second layer 12 was obtained. Next, the ink for the adhesive layer was applied and dried to obtain the third layer 13 having a thickness of 2.5 μm or more and 4 μm or less and functioning as an adhesive layer. The drying temperature was set to 120°C and the drying time was set to 45 seconds. When forming the second transfer foil, the same method as that for the first transfer foil was used, except that the original plate used for forming the relief surface 71Re was different from the original plate used for forming the lattice structure 11G.

[0276] As the above-mentioned release layer ink, first layer ink, relief layer ink, third layer ink, and adhesive layer ink, inks having the following compositions were used. [Ink for peeling layer] Acrylic resin 70.0 parts by weight Methyl ethyl ketone 30.0 parts by mass [Ink for 1st layer / Ink for relief layer] UV-curable acrylic acrylate resin 70.0 parts by weight Methyl ethyl ketone 30.0 parts by mass [Third layer ink / adhesive layer ink] Urethane resin 50.0 parts by weight Silica filler 10.0 parts by mass Methyl ethyl ketone 40.0 parts by mass

[0277] As the first substrate 75, a transparent polycarbonate substrate (LEXAN SD8B14, manufactured by SABIC) (LEXAN is a registered trademark) having a thickness of 100 μm was prepared. As the second substrate 76, a polycarbonate substrate (LEXAN SD8B94, manufactured by SABIC) having a thickness of 100 μm and which develops color when irradiated with a laser beam was prepared. After the first transfer foil was transferred to the first substrate 75, the support layer was removed. Also, after the second transfer foil was transferred to the second substrate 76, the support layer was removed. During the transfer, an electric hot stamp machine was used, the temperature of the surface in contact with the transfer foil was set to 120° C., and the pressure was 1.05 t / cm. 2 and the pressurizing time was set to 1 second.

[0278] Next, a white resin film (LEXAN SD8B24, manufactured by SAVIC) having a thickness of 400 μm was prepared as the white layer 111. A transparent resin film (LEXAN SD8B14) having a thickness of 100 μm was prepared as the lower protective layer 112 and the upper protective layer 113. Then, the lower protective layer 112, the white layer 111, the second substrate 76, the first substrate 75, and the upper protective layer 113 were laminated in the stated order. During lamination, the temperature was set to 200° C., and the pressure was 80 N / cm. 2 The time for heating and pressing was set to 25 minutes. Then, a part of the laminated multilayer body was cut into a card shape.

[0279] Using a laser printer, a laser beam with a wavelength of 1064 nm was irradiated onto the multilayer body. This formed a first coloring portion 76a and a second coloring portion 76b on the second substrate 76. As a result, a card was obtained as the authenticator of Test Example 1.

[0280] [Test Example 2] Test Example 2 will be described below. The transfer foil of Test Example 2 is a test example corresponding to the transfer foil of the above-mentioned eighth embodiment. In Test Example 1, first, the same support layer 82 as in Test Example 1 was prepared. A release layer 83 was formed on one surface of the support layer in the same manner as in Test Example 1. Then, a first layer 11 was formed on the release layer 83, and a second layer 12 was formed on the first layer 11 in the same manner as in Test Example 1.

[0281] Next, the ink for the third layer was applied and dried in the same manner as when the ink for the first layer was used to form the first layer 11. Then, a master plate for forming the relief surface 13Re was pressed against the dried ink for the third layer to form the relief surface 13Re. Note that various conditions during molding were set to the same conditions as when the lattice structure 11G was molded.

[0282] Next, a fourth layer 61 was formed on the relief surface 13Re in the same manner as when the second layer 12 was formed. An adhesive layer 81 was formed on the fourth layer 61 in the same manner as when the third layer 13 was formed in Test Example 1. This resulted in the transfer foil of Test Example 2. Note that, for the third layer ink for forming the third layer 13 in Test Example 2, an ink having the same composition as the first layer ink in Test Example 1 was used.

[0283] Although the embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and may include designs within the scope of the present invention and all embodiments that provide effects equivalent to those intended by the present invention. Furthermore, the scope of the present disclosure is not limited to the features of the invention defined by the claims, but includes all of the disclosed features and all combinations of the features.

[0284] The terms "part," "element," "pixel," "segment," "unit," "printed body," and "article" used in this disclosure are physical entities. A physical entity can refer to a material form or a spatial form surrounded by a material. A physical entity can be a structure. A structure can have a specific function. A combination of structures having specific functions can produce a synergistic effect by combining the functions of each structure.

[0285] Terms used in this disclosure, and particularly in the appended claims (e.g., the body of the appended claims), are generally intended as "open" terms (e.g., the term "having" should be interpreted as "having at least," the term "including" should be interpreted as "including but not limited to," etc.

[0286] In addition, when interpreting terms, configurations, features, aspects, and embodiments, drawings should be referred to as necessary. Matters that can be directly and unambiguously derived from the drawings should be the basis for amendment in the same manner as the text.

[0287] Furthermore, where a particular number of introduced claim recitations is intended, such intent shall be expressly recited in the claim, and in the absence of such recitation, such intent does not exist. For example, to aid in understanding, the following appended claims include the use of the introductory phrases "at least one" and "one or more" to introduce the enumeration of claims. However, the use of such phrases should not be construed as meaning that the introduction of a claim recitation with the indefinite article "a" or "an" limits a particular claim that includes such a claim to an embodiment that includes only one such recitation. The opening phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., "a" and / or "an") should be construed to mean at least "at least one" (e.g., "one" or "one or more"). The same applies to the use of express articles used to introduce claim recitations.

[0288] Additional notes regarding the embodiments will be provided. (Appendix 1) An optical element comprising a first layer, a second layer in contact with the first layer, and a third layer in contact with the second layer, each layer having light-transmitting properties, the first layer is a resin layer having a first refractive index, has a first surface in contact with the second layer, and includes a lattice structure formed by recesses and protrusions in at least a part of the first surface; the second layer is a dielectric layer having a second refractive index higher than the first refractive index, and has an uneven shape following the lattice structure; the third layer is a resin layer having a third refractive index lower than the second refractive index, The first surface has an uneven surface, the lattice structure includes a first lattice structure and a second lattice structure; the uneven surface includes a first region in which the first lattice structure is located, and a second region adjacent to the first region in a plan view facing the first surface, and in which the second lattice structure is located, The azimuth angle of the first grating structure and the azimuth angle of the second grating structure are parallel or perpendicular to each other; the grating period of the first grating structure and the second grating structure is 250 nm or more and 500 nm or less; The color difference ΔE*ab between the average color value L*a*b* of the first and second areas is 13 or more. Optical elements.

[0289] (Appendix 2) Further comprising a third region located between the first region and the second region, When the optical element is irradiated with light from a light source located on the opposite side of the second layer from the third layer, the optical element has a state in which the color exhibited by the third region is different from both the color exhibited by the first region and the color exhibited by the second region when the optical element is observed from the light source at a certain observation angle. 2. The optical element according to claim 1.

[0290] (Appendix 3) In at least one of the first region and the second region, any one of an azimuth angle of the grating structure, a grating period of the grating structure, a structural height of the grating structure, and a ratio of concave portions to convex portions of the grating structure is changed. 3. The optical element according to claim 1 or 2.

[0291] (Appendix 4) the third region is formed by a flat surface on the first surface of the first layer; The average roughness Sa of the flat surface is 20 μm or less. 3. The optical element according to claim 2.

[0292] (Appendix 5) The third region includes a scattering structure having directivity in a direction different from the regular reflection direction of light incident on the third region, or an anti-reflection structure. 3. The optical element according to claim 2.

[0293] (Appendix 6) The third region has a constant width. 3. The optical element according to claim 2.

[0294] (Appendix 7) The third region includes a first portion and a second portion, and a width of the first portion is different from a width of the second portion. 3. The optical element according to claim 2.

[0295] (Appendix 8) The width of the third region is 30 μm or more and 3000 μm or less. 3. The optical element according to claim 2.

[0296] (Appendix 9) The first area and the second area are each 0.1 mm 2 The present invention includes a plurality of cells each having an area as follows: The first region and the second region include cells in which the lattice structure is located in at least a portion of the cells. 9. An optical element according to any one of claims 1 to 8.

[0297] (Appendix 10) In each cell, at least one of the first region and the second region includes cells having area ratios different from each other. 10. The optical element according to claim 9.

[0298] (Appendix 11) At least one of the first region and the second region includes a portion in which the area ratio changes gradually. 11. The optical element according to claim 10.

[0299] (Appendix 12) Further, a resin layer is provided on the opposite side of the first layer from the second layer, The hardness of the first layer is higher than the hardness of the resin layer and the hardness of the third layer. 12. An optical element according to any one of claims 1 to 11.

[0300] (Appendix 13) the first layer is formed of an ultraviolet curable resin; The thickness of the first layer is 1 μm or more and 10 μm or less, The resin layer and the third layer are formed of a thermoplastic resin. 13. The optical element according to claim 12.

[0301] (Appendix 14) Further, a resin layer is provided on the opposite side of the first layer from the second layer, At least one of the first layer, the third layer, and the resin layer contains a filler; The average particle size of the filler is 400 nm or less. 12. The optical element according to claim 1 to 11.

[0302] (Appendix 15) 15. An optical element according to claim 1, the optical element covering the identification information. Authentication body. [Explanation of symbols]

[0303] 10, optical element, 30, 40, 50, 60, 70, 90... optical element, 10S... observation surface, 11, 91... first layer, 11G... lattice structure, 11G1... first lattice structure, 11G2... second lattice structure, 11R, 12R, 13R, 71R... back surface, 11Re, 12Re, 13Re, 71Re... relief surface, 11S, 12F, 13F, 42F, 100F... surface, 11S1... motif region, 11S2... background region, 11S3... boundary region, 12... second layer, 12V... virtual layer, 13... third layer, 14... resin layer, 15... protective layer, 16... printing layer, 17... white layer, 20A... first part, 20AG... first lattice , 20B...second part, 20BG...second grating, 20C...third part, 20CG...third grating, 31,41...filler, 42,61...fourth layer, 50C,90C,100...card, 71...relief layer, 72...reflective layer, 73,81...adhesive layer, 74...substrate, 75...first substrate, 76...second substrate, 76a...first color portion, 76b...second color portion, 78,79,83...peeling layer, 80...transfer foil, 82...support layer, 101...first image, 101a...face image, 101b...background image, 102...second image, 103...third image, 111...white layer, 112...lower protective layer, 113...upper protective layer, 114...printing.

Claims

1. An optical element comprising a first layer, a second layer in contact with the first layer, and a third layer in contact with the second layer, each layer having light-transmitting properties, the first layer is a resin layer having a first refractive index, has a first surface in contact with the second layer, and includes a lattice structure formed by recesses and protrusions on at least a part of the first surface; the second layer is a dielectric layer having a second refractive index higher than the first refractive index, and has a concave-convex shape following the lattice structure; the third layer is a resin layer having a third refractive index lower than the second refractive index, The first surface has an uneven surface, the lattice structure includes a first lattice structure and a second lattice structure; the uneven surface includes a first region in which the first lattice structure is located, and a second region in which the second lattice structure is located, the second region being in contact with the first region or spaced apart from the first region in a plan view facing the first surface, an azimuth angle of the first lattice structure and an azimuth angle of the second lattice structure are equal to each other; The grating period of the first grating structure and the second grating structure is 250 nm or more and 500 nm or less, a difference between a grating period of the first grating structure and a grating period of the second grating structure is 20 nm or more; the grating pattern located in the first region includes a grating group repeated along a first direction; the lattice groups include the first lattice structure, the third lattice structure, and the fourth lattice structure, and in each lattice group, the first lattice structure, the third lattice structure, and the fourth lattice structure are aligned along the first direction; The first grating structure, the third grating structure, and the fourth grating structure have grating periods different from one another, and the difference between the grating periods of the first grating structure, the third grating structure, and the fourth grating structure is less than 20 nm. Optical elements.

2. The height of at least one of the first lattice structure, the third lattice structure, and the fourth lattice structure included in the first region is different from the height of the second lattice structure included in the second region. The optical element according to claim 1 .

3. The second region is disposed apart from the first region, Further comprising a third region located between the first region and the second region, When the optical element is irradiated with light from a light source located on the opposite side of the second layer from the third layer, the optical element has a state in which the color exhibited by the third region is different from both the color exhibited by the first region and the color exhibited by the second region when the optical element is observed from the light source at a certain observation angle. The optical element according to claim 1 .

4. the third region is defined by a flat surface on the first surface of the first layer; The average roughness Sa of the flat surface is 20 μm or less. The optical element according to claim 3 .

5. The third region includes a scattering structure having directivity in a direction different from the regular reflection direction of light incident on the third region, or an anti-reflection structure. The optical element according to claim 3 .

6. The third region has a constant width. The optical element according to claim 3 .

7. The third region includes a first portion and a second portion, and a width of the first portion is different from a width of the second portion. The optical element according to claim 3 .

8. The width of the third region is 30 μm or more and 3000 μm or less. The optical element according to claim 3 .

9. The first region and the second region are each 0.1 mm ２ The present invention includes a plurality of cells each having an area as follows: The first region and the second region include cells in which the lattice structure is located in at least a portion of the cells.

9. The optical element according to claim 1 .

10. The resin layer is further provided on the opposite side of the first layer from the second layer, The hardness of the first layer is higher than the hardness of the resin layer and the hardness of the third layer.

10. The optical element according to claim 1 .

11. the first layer is formed of an ultraviolet curable resin; The first layer has a thickness of 1 μm or more and 10 μm or less, The resin layer and the third layer are formed of a thermoplastic resin. The optical element according to claim 10.

12. The resin layer is further provided on the opposite side of the first layer from the second layer, At least one of the first layer, the third layer, and the resin layer contains a filler; The average particle size of the filler is 400 nm or less.

10. The optical element according to claim 1 .

13. The first lattice structure, the third lattice structure, and the fourth lattice structure, in a cross-sectional structure along the first direction, have a shape in which one peak portion is sandwiched between two valley portions, and an angle formed by a tangent to a slope connecting one of the valley portions and the peak portion and a straight line connecting the valley portions is a tangent angle, The tangent angles of the first lattice structure, the third lattice structure, and the fourth lattice structure are different from each other. The optical element according to claim 2 .

14. 14. An optical element according to claim 1, the optical element covering the identification information. Authentication body.

Images