Patent Publication Number: US-2019171028-A1

Title: Display body

Description:
BACKGROUND 
     The present disclosure relates to a display body that displays an image through reflection of light. 
     Certification documents, securities, banknotes, and other objects are required to be counterfeit-resistant. Techniques to increase difficulty in counterfeiting an object include attaching a counterfeit-resistant display body to the object (see Japanese National Phase Laid-Open Patent Publication No. 2008-547040, for example). 
     Techniques to analyze such display bodies have been advanced to develop counterfeit-resistant structures. Techniques to manufacture display bodies have also been diversified to achieve counterfeit-resistant structures. However, the advanced techniques to analyze display bodies make it easier to analyze a display body to counterfeit the display body, and the diversified techniques to manufacture display bodies also facilitate manufacturing of counterfeit products. Thus, elements of display bodies are increasingly sought to have new structures. In particular, there is a high demand for techniques to improve aesthetic appearances of display bodies. 
     SUMMARY 
     It is an objective of the present disclosure to provide a display body with an improved aesthetic appearance. 
     To achieve the foregoing objective, a display body is provided that includes a display surface including one or more display region groups, each including a plurality of display regions. Each display region includes a plurality of reflection surfaces that is configured to reflect light incident on the display surface toward an area including a corresponding one of observation directions that are associated with the respective display region groups. The reflection surfaces are arranged at an average pitch of 1 μm and 300 μm inclusive in a direction in which the reflection surfaces are arranged. In each display region, the reflection surfaces have an identical normal direction associated with the display region so that the reflection surfaces of the display region are configured to form a single image element associated with the display region. The display regions of each display region group include display regions that differ from one another in the normal direction of the reflection surfaces. Each display region group is configured to form, in the associated observation direction, an image that is unique to the display region group and composed of the image elements formed by the display regions of the display region group. 
     In this configuration, each display region forms an image element formed by the light emerging from the reflection surfaces belonging to the display region. The image element is formed by the light emerging from a virtual plane covering the entire display region. Display regions that differ from one another in the normal direction of the reflection surfaces form image elements of mutually different light intensities in the observation direction. The display region group thus displays in the observation direction an image composed of image elements, which have light intensities according to the normal directions of the reflection surfaces of the respective display regions. This improves the aesthetic appearance of the display body. 
     In the above-described display body, the reflection surfaces are preferably arranged at a constant pitch in the direction in which the reflection surfaces are arranged, and the pitch at which the reflection surfaces are preferably arranged is between 1 μm and 300 μm inclusive. 
     In this configuration, the pitch of the reflection surfaces is greater than or equal to 1 μm, so that the reflection surfaces are less likely to produce diffracted light. Further, since the pitch P is less than or equal to 300 μm, the observer of the display body is unlikely to recognize the reflection surfaces. In addition, since the reflection surfaces are at a constant pitch, the advantage obtained by a pitch P of between 1 μm and 300 μm inclusive is achieved over the entire display regions, as compared with a structure in which the reflection surfaces are arranged at different pitches. As such, the image displayed by the display body is more likely to be perceived as the collection of the image elements formed by the respective display regions. 
     In the above-described display body, each reflection surface preferably has a height that is a maximum value of a distance between the reflection surface and the display surface. In each display region, the height of each reflection surface is preferably equal to the heights of the other reflection surfaces. 
     This configuration facilitates the formation of a plurality of reflection surfaces in each display region, as compared with a display region in which reflection surfaces have different heights. 
     In the above-described display body, each display region is preferably polygonal in a plan view of the display surface. 
     This configuration allows the image displayed by the display body to be formed of a combination of polygonal image elements. This helps the image formed by the display body to be perceived as an image representing the curves of a three-dimensional object. 
     In the above-described display body, the display body preferably includes a multilayer interference layer that has a plurality of dielectric layers. Adjacent ones of the dielectric layers that are in contact with each other in a direction in which the dielectric layers are preferably layered have different refractive indices so that the multilayer interference layer is configured to reflect light having a certain wavelength, and the multilayer interference layer preferably has a surface that includes the reflection surfaces. 
     This configuration allows the display body to display an image having a color corresponding to the wavelength of the light reflected by the multilayer interference layer. 
     In the above-described display body, the display surface preferably includes a plurality of pixels, and each display region is preferably one of the pixels. 
     This configuration allows the structure of each display region to be designed based on a raster image. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view showing the planar structure of a display body of an embodiment. 
         FIG. 2  is an enlarged plan view showing a display region group. 
         FIG. 3  is a perspective view showing the structure of a reflection element of a display region. 
         FIG. 4  is a perspective view showing the structure of a plurality of reflection elements of a display region. 
         FIG. 5  is a cross-sectional view showing the structure of the reflection elements of the display region. 
         FIG. 6  is a diagram for illustrating the operation of the reflection surfaces of the display region. 
         FIG. 7  is a diagram for illustrating the operation of a display body. 
         FIG. 8  is a schematic view showing the relationship between an incident angle and an emergence angle at an example of a reflection surface. 
         FIG. 9  is a schematic view showing the relationship between an incident angle and an emergence angle at an example of a reflection surface. 
         FIG. 10  is a perspective view showing the structure of an example of a reflection element. 
         FIG. 11  is a perspective view showing the structure of an example of a reflection element. 
         FIG. 12  is a schematic view showing the relationship between an incident angle and a diffraction angle at an example of a reflection element. 
         FIG. 13  is a schematic view showing the relationship between an incident angle and a diffraction angle at an example of a reflection element. 
         FIG. 14  is a cross-sectional view showing the cross-sectional structure of a display region of a display body of a modification. 
         FIG. 15  is a cross-sectional view showing the cross-sectional structure of a display region of a display body of a modification. 
         FIG. 16  is a perspective view showing the structure of a reflection surface of a display body of a modification. 
         FIG. 17  is a cross-sectional view showing the cross-sectional structure of a display region of a display body of a modification. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODYMENTS 
     Referring to  FIGS. 1 to 13 , an embodiment of a display body is now described. In the following descriptions, the structure of the display body, the operation of the display body, and then a method for manufacturing the display body are described. 
     [Structure of Display Body] 
     Referring to  FIGS. 1 to 6 , the structure of the display body is now described. 
     As shown in  FIG. 1 , a display body  10  have a display surface  10 S including one display region group  11 G. The display region group  11 G forms an image unique to the display region group  11 G in a single observation direction associated with the display region group  11 G. 
     The image unique to the display region group  11 G is displayed on the display surface  10 S of the display body  10 . The display surface  10 S includes only one display region group  11 G. However, the display surface  10 S may include a plurality of display region groups  11 G, and the images unique to the respective display region groups  11 G may be displayed on the display surface  10 S. That is, the display surface  10 S may display a plurality of images. The display surface  10 S may be flat or curved. 
     In a plan view of the display surface  10 S, the display region group  11 G has a heart shape. The shape of the display region group  11 G may be any of a character, a graphics, a symbol, and an illustration. In a plan view of the display surface  10 S, the outline of the display region group  11 G is substantially identical with the outline of the image formed by the display region group  11 G. 
     As shown in  FIG. 2 , the display region group  11 G includes a plurality of display regions  11 . Each display region  11  has a polygonal shape in a plan view of the display surface  10 S. Each display region  11  may have a triangular shape, which is an example of a polygonal shape. The shape of each display region  11  is not limited to a triangular shape and may be a quadrangular shape, or a pentagonal shape. In the display region group  11 G, the plurality of display regions  11  may include display regions  11  of different shapes. In this case, the shapes of the display regions  11  may include two or more different types of polygonal shapes, such as a triangular shape, a quadrangular shape, and a pentagonal shape. 
     The plurality of display regions  11  of the display region group  11 G includes different types of display regions  11  that differ from one another in at least one of shape and size. In the display region group  11 G, each display region  11  is in contact with adjacent display regions  11 . That is, in the display region group  11 G, two adjacent display regions  11  share one of the sides defining the display regions  11 . 
     The image displayed by the display body  10  is a vector image, which is represented by a collection of regions represented by vectors, in other words, display regions  11 . 
     Each display region  11  preferably has an area that allows the observer of the display body  10  to perceive the display region  11 . The area of each display region  11  is preferably between 0.1 mm 2  and 0.5 mm 2  inclusive, for example. 
     Referring to  FIG. 3 , each display region  11  includes reflection elements  21  each including one reflection surface  21 S. Each reflection element  21  extends in one direction along the two-dimensional plane in which the display surface  10 S extends. The reflection surface  21 S is an optical surface extending along a plane intersecting with the display surface  10 S. An inclination angle θ is formed by the reflection surface  21 S and the display surface  10 S. The inclination angles θ of the display region  11  are uniform, and the inclination angles θ are typically constant. Each reflection surface  21 S is a specular surface, which specularly reflects visible light. The light incident on the reflection surface  21 S is regularly reflected in a direction corresponding to the inclination angle θ. 
     The angle formed by the normal direction of the reflection surface  21 S and the traveling direction of the light incident on the reflection surface  21 S is the incident angle of light. The incident angles of the incident light on the reflection surfaces  21 S are in a given range. Each reflection surface  21 S is shaped so as to reflect the light that is incident on the reflection surface  21 S. In addition, each reflection surface  21 S is shaped such that the reflection angle of light emerging from the reflection surface  21 S, or the emergence angle, corresponds to the observation direction DO, which is common to multiple reflection surfaces  21 S. 
     Each reflection element  21  may be a projection forming a triangular prism on the display surface  10 S, or may be a depression having a reflection surface  21 S in the display surface  10 S. The reflection surface  21 S may be a flat or non-flat surface forming an inclination angle θ with the display surface  10 S. A non-flat reflection surface  21 S may be a surface including minute projections and depressions or may be a curved surface. The inclination angle θ of a non-flat reflection surface  21 S may be the inclination angle of a flat reference surface that approximates the non-flat reflection surface  21 S. 
     The reflection surface  21 S of each reflection element  21  may be the surface of a multilayer interference layer. The multilayer interference layer includes a plurality of dielectric layers. Adjacent dielectric layers that are in contact with each other in the direction in which the dielectric layers are layered have different refractive indices, allowing the multilayer interference layer to reflect light having a certain wavelength. In other words, the display body  10  may include a multilayer interference layer, and the multilayer interference layer may include the reflection surfaces  21 S of reflection elements  21 . 
     This allows the display body  10  to display an image having a color corresponding to the wavelength of the light reflected by the multilayer interference layer. 
     Adjacent dielectric layers in the multilayer interference layer have different refractive indices, so that the light incident on the multilayer interference layer is reflected at each interface between dielectric layers. The interference between the light rays reflected at different interfaces intensifies or weakens the light rays of given wavelengths. The multilayer interference layer thus produces light of a certain wavelength. 
     For example, the multilayer interference layer may include a plurality of lamination units, each including one high refractive index layer and one low refractive index layer. The high refractive index layer may be made of tantalum oxide, and the low refractive index layer may be made of silicon oxide. 
     As shown in  FIG. 4 , each display region  11  includes a plurality of reflection surfaces  21 S. Each reflection surface  21 S reflects the incident light on the display surface  10 S toward an area including a single observation direction DO associated with the display region group  11 G. The reflection surfaces  21 S are arranged at a pitch P of between 1 μm and 300 μm inclusive in the direction in which the reflection surfaces  21 S are arranged. In addition to the plurality of reflection surfaces  21 S, each display region  11  typically includes vertical surfaces, inclined surfaces, flat surfaces, and scattering surfaces. The vertical surfaces and the inclined surfaces connect the reflection surfaces  21 S to the display surface  10 S, and the flat surfaces and the scattering surfaces are located in the regions that are free of reflection surfaces  21 S in a plan view of the display surface  10 S. When the reflection surfaces  21 S are connected to the display surface  10 S by vertical surfaces, the areas of the reflection surfaces  21 S in the display region  11  are maximized. When the display regions  11  include inclined surfaces or flat surfaces, the areas of the reflection surfaces  21 S may be varied by varying the angles of the inclined surfaces or the areas of the flat surfaces in display regions  11 . Scattering surfaces in a display region  11  allow the areas of the reflection surfaces  21 S to vary and also enable the display region  11  to produce scattering light in a direction that differs from the reflection surfaces  21 S. The variation in area of the reflection surfaces  21 S of display regions  11  results in different amounts of light reflected at the display regions  11 . 
     Further, the display body may include a display region  11  that has vertical surfaces and a display region  11  that has inclined surfaces, flat surfaces, or scattering surfaces. This allows the areas of the reflection surfaces  21 S in display regions  11  to vary, enabling the display regions  11  to produce different amounts of reflection light. This adds variety to the expression. 
     The pitch P of the display body  10  is greater than or equal to 1 μm, so that the reflection surfaces  21 S do not produce diffracted light. As such, the image displayed by the display body  10  is formed by white light that is regularly reflected by the reflection surfaces  21 S. In addition, the pitch P is less than or equal to 300 μm and therefore smaller than the resolution of human eyes. The reflection surfaces  21 S of the display regions  11  are unlikely to be recognized by the observer of the display body  10 . 
     Further, the reflection surfaces  21 S may be arranged at a constant pitch P. In this case, the advantage obtained by a pitch P of between 1 μm and 300 μm inclusive is achieved over the entire display regions  11 , as compared with a structure in which the reflection surfaces  21 S are at different pitches P. As such, the image displayed by the display body  10  is more likely to be perceived as the collection of the image elements formed by the respective display regions  11 . 
     In each display region  11 , the reflection surfaces  21 S have an identical normal direction DN associated with the display region  11 . Each reflection surface  21 S reflects light in the observation direction DO. In one display region  11 , the normal direction DN of a reflection surface  21 S is identical with the normal directions DN of the other reflection surfaces  21 S. In a plan view of a display region  11 , the normal direction DN of a reflection surface  21 S is the direction in which the reflection surface  21 S is oriented. 
     A display region group  11 G includes display regions  11  that differ from one another in the normal direction DN of the reflection surfaces  21 S. That is, one display region group  11 G includes various normal directions DN of reflection surfaces  21 S. In other words, a plurality of display regions  11  includes display regions  11  that differ from one another in the normal direction DN of the reflection surfaces  21 S. 
     As described above, in a plan view of the display surface  10 S, each display region  11  is triangular. The sides of a display region  11  are shared with three other display regions  11  surrounding the display region  11 . The normal direction DN of the reflection surfaces  21 S of a display region  11  is preferably different from the normal directions DN of the reflection surfaces  21 S of the display regions  11  that share sides with the display region  11 . Among a display region  11  and the three display regions  11  sharing the sides of the display region  11 , at least two display regions  11  may have reflection surfaces  21 S that are identical in normal direction DN. 
     That is, a display region  11  preferably differs from the display regions  11  surrounding the display region  11  in the normal direction DN of the reflection surfaces  21 S. This enables the image formed by the display body  10  to be easily perceived as a three-dimensional image. In addition, a normal direction DN of the reflection surfaces  21 S of each display region  11  is preferably within the group of the normal directions DN of the reflection surfaces  21 S of the plural display regions  11  surrounding the display region  11 . Namely, the normal direction DN can be expressed as a sum of the normal directions DN of the group. When the normal direction DN is the sum of the normal directions DN of the group, the coefficients of the normal directions DN are positive values. This allows the display body  10  to display a more natural three-dimensional image. Not all the display regions  11  of the display body  10  do not have to satisfy the conditions described above as long as some of the display regions  11  satisfy the conditions. 
     In each reflection element  21 , the height H of the reflection surface  21 S is the maximum value of the distance between the reflection surface  21 S and the display surface  10 S, or the section of the display region  11  that serves as the display surface  10 S. In each display region  11 , the height H of a reflection surface  21 S may be equal to the height H of the other reflection surfaces  21 S. 
     When all the reflection surfaces  21 S in a display region  11  have the same height H, it is easy to form reflection surfaces  21 S in the display region  11 , as compared with a structure in which reflection surfaces  21 S have different heights H. 
     In addition, when all reflection surfaces  21 S have the same height H, the reflection surfaces  21 S are likely to be shaped with high accuracy in the step of forming the reflection surfaces  21 S. 
       FIG. 5  shows the cross-sectional structure of reflection elements  21  in a plane defined by the direction in which the reflection elements  21  are arranged and the height direction of the reflection elements  21 . 
     As shown in  FIG. 5 , one display region  11  includes the four reflection elements  21  arranged in one direction. As described above, the four reflection elements  21  are equal in inclination angle θ and height. In the cross section along the plane defined by the direction in which the reflection elements  21  are arranged and the height direction of the reflection elements  21 , each reflection element  21  has the shape of a regular triangle. 
     Referring to  FIG. 6 , in the display region  11 , the normal directions DN of the reflection surfaces  21 S are identical and associated with the display region  11 . Accordingly, the reflection surfaces  21 S reflect light in the observation direction DO, so that the reflection surfaces  21 S of the display region  11  form one image element PICa associated with the display region  11 . 
     The reflection surfaces  21 S of the display region  11  form one image element PICa, which has the shape of the collection of the reflection surfaces  21 S combined in the direction in which the reflection surfaces  21 S are arranged. That is, the area of the image element PICa is equal to the sum of the areas of the reflection surfaces  21 S, and the inclination angle θ between the image element PICa and the display region  11 , or the display surface  10 S, is equal to the inclination angle θ between the reflection surfaces  21 S and the display surface  10 S. Further, the height HP of the image element PICa is the maximum value of the distance between the image element PICa and the display surface  10 S. The height HP is equal to the value obtained by multiplying the height H of a reflection surface  21 S by the number of the reflection surfaces  21 S. 
     Each display region  11  forms one image element PICa, which is formed by the light emerging from the reflection surfaces  21 S of the display region  11 . The image element PICa is formed by the light emerging from a virtual plane, which covers the entire display region  11  and forms a predetermined angle with the display region  11 . 
     The pitch P of the reflection surfaces  21 S is greater than or equal to 1 μm, so that the reflection surfaces  21 S do not produce diffracted light. This facilitates the formation of one image element PICa by the light emerging from the reflection surfaces  21 S. In addition, the pitch P of the reflection surfaces  21 S is less than or equal to 300 μm, so that each reflection surface  21 S itself is unlikely to be recognized by the observer. The observer can therefore easily perceive the image element PICa. 
     The display region  11  shown in  FIGS. 4 to 6  includes four reflection elements  21 . However, the number of reflection elements  21 , or reflection surfaces  21 S, in one display region  11  may be less than or equal to 3, or greater than or equal to 5. The display regions  11  forming the display region group  11 G may include display regions  11  that vary in the number of reflection surfaces  21 S. 
     [Working of Display Body] Referring to  FIGS. 7 to 13 , the operation of the display body is now described. In  FIG. 7 , the intensity of light in the image formed by the display region group  11 G is expressed by the gradation of colors of the display region group  11 G. In this gradation of colors of the image in  FIG. 7 , a section in the image with a lower light intensity has a darker color. 
     As shown in  FIG. 7 , when light is incident on the display surface  10 S of the display body  10  from a given direction, a plurality of reflection surfaces  21 S of the display region group  11 G forms a heart-shaped image PIC in the observation direction DO. 
     The display regions  11  of the display region group  11 G each form a single image element PICa. The normal direction DN of the reflection surfaces  21 S in each display region  11  is unique to the display region  11 . The normal direction DN of the reflection surfaces  21 S in each display region  11  determines the intensity per unit area of the light emerging from the reflection surfaces  21 S in the observation direction DO. That is, the intensity of light of each image element PICa depends on the normal direction DN of the reflection surfaces  21 S forming the image element PICa. 
     [Relationship between Light Amount and Normal Direction of Reflection Surface] 
     With reference to  FIGS. 8 and 9 , the relationship between the normal direction DN of a reflection surface  21 S and the amount per unit area of the light emerging from the reflection surface  21 S is now described in detail.  FIG. 8  shows an example of a reflection surface  21 S of a display region  11 . The reflection surface  21 S and the display region  11  form a first inclination angle θ 1 .  FIG. 9  shows an example of a reflection surface  21 S of another display region  11 . The reflection surface  21 S and the display region  11  form a second inclination angle θ 2 . The second inclination angle θ 2  is larger than the first inclination angle θ 1 . 
     As shown in  FIG. 8 , incident light IL is incident from a given direction onto the reflection surface  21 S having the first inclination angle θ 1 . The incident angle of the incident light IL is formed by the direction of the incident light IL and the normal direction DN of the reflection surface  21 S. The emergence angle is formed by the normal direction DN and the emergent light emerging from the reflection surface  21 S. 
     The incident angle of the incident light IL on the reflection surface  21 S is a first incident angle θα 1 , and the emergence angle of first regular reflection light RL 1  at the reflection surface  21 S is a first emergence angle θβ 1 . The first incident angle θα 1  is equal to the first emergence angle θβ 1 . Of the light reflected at the reflection surface  21 S, the light emerging in the observation direction DO is a first light component PL 1 , and the emergence angle of the first light component PL 1  is a first emergence angle θγ 1 . 
     As shown in  FIG. 9 , on the reflection surface  21 S having the second inclination angle θ 2 , the incident angle of incident light IL is a second incident angle θα 2 , which is smaller than the first incident angle θα 1 . The emergence angle of second regular reflection light RL 2  at the reflection surface  21 S is a second emergence angle θβ 2 . The second emergence angle θβ 2  is equal to the second incident angle θα 2  and therefore smaller than the first emergence angle θβ 1 . Of the light reflected at the reflection surface  21 S, the light emerging in the observation direction DO is a second light component PL 2 , and the emergence angle of the second light component PL 2  is a second emergence angle θγ 2 . 
     When a light component emerges from a reflection surface  21 S in a given direction, the smaller the difference between the emergence angle of the light component and the emergence angle of the regular reflection light, the larger the amount of light per unit area of the light component. The difference between the first emergence angle θβ 1  and the first emergence angle θγ 1  at the reflection surface  21 S having the first inclination angle θ 1  is larger than the difference between the second emergence angle θβ 2  and the second emergence angle θγ 2  at the reflection surface  21 S having the second inclination angle θ 2 . As such, the first light component PL 1  has a smaller light amount per unit area than the second light component PL 2 . 
     Consequently, in the image PIC formed by the display region group  11 G, the image element PICa formed by a display region  11  including reflection surfaces  21 S having the second inclination angle θ 2  is brighter than the image element PICa formed by a display region  11  including reflection surfaces  21 S having the first inclination angle θ 1 . This allows the display region group  11 G to form the shaded image PIC, which is composed of image elements PICa varying in brightness, or the amount of light per unit area. 
     The display body  10  thus forms the single image PIC in the observation direction DO. The image PIC is composed of various image elements PICa, each having a light amount per unit area corresponding to the normal direction DN of the reflection surfaces  21 S of the display region  11 . The display body  10  forms the three-dimensional image composed of image elements PICa, which vary in light amount. This improves the aesthetic appearance of the display body  10 . 
     Each display region  11  is polygonal, and the image PIC displayed by the display body  10  is formed by the combination of polygonal image elements PICa. Consequently, the image formed by the display body  10  is likely to be perceived as an image representing the curves of a three-dimensional object. 
     [Relationship between Azimuth Angle and Inclination Angle] 
     The difference in light amount between the display regions  11  can also be explained using the relationship between the azimuth angle and the inclination angle of a reflection element. Referring to  FIGS. 10 to 13 , the relationship between the azimuth angle of a reflection element and the inclination angle formed by the reflection surface and the display surface will be described. For the convenience of illustration,  FIGS. 10 and 11  each show only one of the reflection elements of a display region. 
     Referring to  FIG. 10 , display regions  11  include a first region  11 A. The first region  11 A includes a plurality of first reflection elements  21   a  arranged in a first direction D 1 , which is a single direction. The first reflection elements  21   a  extend in a second direction D 2 , which is perpendicular to the first direction Dl. A third direction D 3 , which is perpendicular to the first and second directions D 1  and D 2 , is the height direction of the first reflection elements  21   a . Each first reflection element  21   a  includes a first reflection surface  21 Sa, which serves as a reflection surface. 
     Referring to  FIG. 11 , display regions  11  include a second region  11 B. The second region  11 B includes a plurality of second reflection elements  21   b  arranged in a direction intersecting with the direction in which the first reflection elements  21   a  are arranged. Each second reflection element  21   b  extends in the direction perpendicular to the direction in which the second reflection elements  21   b  are arranged. Each second reflection element  21   b  includes a second reflection surface  21 Sb, which serves as a reflection surface. 
     The first reflection elements  21   a  are identical to the second reflection elements  21   b  in shape. In a cross section along a plane defined by the direction in which the reflection elements are arranged in each display region and the height direction of the reflection elements, the inclination angle θ of the first reflection elements  21   a  is equal to the inclination angle θ of the second reflection elements  21   b . The first and second reflection elements  21   a  and  21   b  have the first inclination angle θ 1 . 
     On the other hand, the first reflection element  21   a  differs from the second reflection element  21   b  in the azimuth angle of the reflection surface. The azimuth angle is formed by the direction of the projection of the normal to the reflection surface onto the display surface  10 S and a reference direction, which is one direction along the display surface  10 S. The first reflection surface  21 Sa differs from the second reflection surface  21 Sb in azimuth angle. When the second reflection element  21   b  is rotated about a rotation axis extending in the height direction of the second reflection element  21   b  and passing through the centroid of the second reflection element  21   b , the orientation of the second reflection element  21   b  becomes the same as the orientation of the first reflection element  21   a.    
       FIG. 12  shows the cross-sectional structure of the first reflection element  21   a  along a plane defined by the first and third directions D 1  and D 3 .  FIG. 13  shows the cross-sectional structure of the second reflection element  21   b  along a plane defined by the first and third directions D 1  and D 3 . The following descriptions are given referring to  FIGS. 12 and 13  simultaneously for the convenience of description. 
     As described above, the first reflection element  21   a  differs from the second reflection element  21   b  in azimuth angle. As shown in  FIGS. 12 and 13 , in cross sections along the plane defined by the first and third directions D 1  and D 3 , the first inclination angle θ 1  of the first reflection element  21   a  differs from the second inclination angle θ 2  of the second reflection elements  21   b . The second inclination angle θ 2  is smaller than the first inclination angle θ 1 . The larger the difference between the azimuth angle of the first reflection element  21   a  and the azimuth angle of the second reflection element  21   b , the smaller the second inclination angle θ 2 . 
     The inclination angle formed by each reflection surface may be sized such that the traveling direction of diffracted light of the m-th order (m is an integer of 1 or more), which is produced by the reflection surface and has a certain wavelength, coincides with or differs from the traveling direction of the light specularly reflected by the reflection surface. When the traveling direction of the m-th order diffracted light coincides with the traveling direction of the specularly reflected light, the m-th order diffracted light travels in the reflection direction DK. 
     An incident angle α is formed by the traveling direction of incident light on the reflection surface of a reflection element and the direction of the normal to the display surface  10 S. At the first reflection element  21   a , the traveling direction of the m-th order diffracted light and the normal direction of the display surface  10 S form a first diffraction angle β 1 . At the second reflection element  21   b , the traveling direction of the m-th order diffracted light and the normal direction of the display surface  10 S form a second diffraction angle β 2 . When the diffracted light produced by a reflection element has a certain wavelength λ, the incident angle α, the diffraction angle β, and the inclination angle θ satisfy Equations (1) and (2) below. In Equation (1), m is an integer of 1 or more. 
       sinα+sinβ=mλ  Equation (1)
 
       θ=(α−β)/2   Equation (2)
 
     As described above, when the inclination angle θ is sized such that the traveling direction of the m-th order diffracted light coincides with the traveling direction of the specular reflection light, the reflection surface diffracts the m-th order diffracted light having a certain wavelength λ with high diffraction efficiency. For example, the reflection surface converts white incident light into colored light in the reflection direction DK with high conversion efficiency. As a result, the image displayed in the reflection direction DK is formed by the light diffracted with high diffraction efficiency, so that the image has increased visibility. 
     Assuming that light rays are incident on two reflection surfaces at the same incident angle, when the two reflection surfaces have different inclination angles, the diffracted rays produced at the reflection surfaces have different traveling directions, or reflection directions DK. 
     Specifically, based on Equation (2), the diffraction angle β is obtained from Equation (3) using the inclination angle θ and the incident angle α. 
       β=α−2θ  Equation (3)
 
     As is apparent from Equation (3), when the incident angle α is fixed, varying the inclination angle θ of a reflection surface varies the diffraction angle β. As described above, the first inclination angle θ 1  of the first reflection surface  21 Sa is larger than the second inclination angle θ 2  of the second reflection surface  21 Sb. The first diffraction angle β 1  is therefore smaller than the second diffraction angle β 2 . 
     Different azimuth angles of reflection surfaces result in different inclination angles of the reflection surfaces in cross sections along the same plane. As a result, the diffracted rays that are produced at the reflection surfaces and have a certain wavelength λ travel in different directions. Thus, the images formed by the light reflected by the reflection surfaces are displayed in different directions. Accordingly, when the observer views the display body from a given direction, the image elements PICa formed by the respective display regions  11  vary in brightness. 
     [Method for Manufacturing Display Body] 
     The method for manufacturing the display body  10  includes, for example, a step of forming an uneven structure layer and a step of forming a reflection layer on a surface of the uneven structure layer. The step of forming an uneven structure layer duplicates an uneven structure layer from an original plate, for example. 
     The original plate is produced by applying a photosensitive resist, or photosensitive resin, to one surface of a planar substrate, exposing a part of the photosensitive resin to a beam, and then developing the photosensitive resin. A metal stamper is produced from the original plate by electroplating, for example, and an uneven structure layer is duplicated using this metal stamper as the matrix. The metal stamper may also be obtained by cutting a metal substrate using lathe technique. 
     The uneven structure layer may be formed by a method such as a heat embossing method, a casting method, or a photopolymer method. The photopolymer method introduces a radiation-curing resin into the gap between a flat substrate, such as a plastic film, and the metal stamper. Then, the method cures the radiation-curing resin by radiation and removes the cured resin layer from the metal stamper together with the substrate. The photopolymer method produces reflection elements  21  with high structural accuracy, heat resistance, and chemical resistance and is thus more desirable than a pressing method and a casting method, which use a thermosetting resin. 
     The uneven structure layer may be made of various resins. The material of the uneven structure layer may contain 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 photostabilizer. 
     Examples of the resins include poly(methyl methacrylate) resin, polyurethane resin, fluorine resin, silicone resin, polyimide resin, epoxy resin, polyethylene resin, polypropylene resin, methacrylate resin, polymethyl pentene resin, cyclic polyolefin resin, polystyrene resin such as styrene acrylonitrile copolymer (AS resin) and acrylonitrile butadiene styrene copolymer (ABS resin), polyvinyl chloride resin, polycarbonate resin, polyester resin, polyamide resin, polyamide imide resin, polyaryl phthalate resin, polysulfone resin, polyphenylene sulfide resin, polyether sulfone resin, linethylene naphthalate resin, polyether imide resin, acetal resin, and a cellulose resin. These resins may be used independently or in combination to form the uneven structure layer. 
     The step of forming the reflection layer may use a physical vapor deposition method or a chemical vapor deposition method, for example. Examples of physical vapor deposition methods include a vacuum deposition method, a sputtering method, an ion plating method, and an ion cluster beam method. Examples of chemical vapor deposition methods include a plasma chemical vapor deposition method, a thermal chemical vapor deposition method, and a photochemical vapor deposition method. 
     Of these methods, the vacuum evaporation method and the ion plating method are preferable over the others. These methods have higher productivity and produce desirable reflection layers. The conditions for forming film in a physical vapor deposition method or a chemical vapor deposition method may be selected according to the material of the reflection layer. 
     The reflection layer may be made of a metal or an alloy. The metal may be aluminum, gold, silver, platinum, nickel, tin, chromium, or zirconium, and the alloy may be an alloy of these metals. Further, when the reflection layer is the multilayer interference layer described above, the dielectric layers forming the reflection layer may be made of zinc oxide or zinc sulfide, for example. The reflection layer is preferably made of aluminum or silver since they have higher reflectivities for the visible light region than other materials. 
     The display body of the above-described embodiment has the following advantages. 
     (1) The single image PIC is formed in the observation direction DO by a plurality of image elements PICa, each having a light intensity corresponding to the normal direction DN of the reflection surfaces  21 S of the display region  11 . This improves the aesthetic appearance of the display body  10 . 
     (2) The reflection surfaces  21 S are arranged at a pitch P of greater than or equal to 1 μm, so that the reflection surfaces  21 S are unlikely to produce diffracted light. Further, since the pitch P is less than or equal to 300 μm, the observer of the display body  10  is unlikely to recognize the reflection surfaces  21 S. 
     (3) When the reflection surfaces  21 S are arranged at a constant pitch P, the advantage obtained by a pitch P of between 1 μm and 300 μm inclusive is achieved over the entire display regions  11 , as compared with a configuration in which the pitch P of the reflection surfaces  21 S is varied. As such, the image PIC displayed by the display body  10  is more likely to be perceived as the collection of the image elements PICa formed by the respective display regions  11 . 
     (4) As compared with a configuration in which the reflection surfaces  21 S in each display region  11  have different heights H, a plurality of reflection surfaces  21 S is easily formed in each display region  11 . 
     (5) Each display region  11  is polygonal, and the image PIC of the display body  10  is formed by the combination of the polygonal image elements PICa. This helps the image PIC formed by the display body  10  to be perceived as an image representing the curves of a three-dimensional object. 
     (6) When the reflection surface  21 S is the surface of a multilayer interference layer, the display body  10  can display an image PIC that has the color according to the wavelength of light reflected by the multilayer interference layer. 
     The above-described embodiment may be modified as follows. 
     The display surface  10 S may include a plurality of pixels, and each display region  11  may be a single pixel. The plurality of pixels may be arranged on the display surface  10 S in a matrix. The image displayed by the display body  10  is not limited to a vector image and may be a raster image composed of repeated pixels, which are unit regions. 
     This configuration has the following advantage. 
     (7) The structure of each display region may be designed based on a raster image. 
     The shape of each display region  11  is not limited to polygonal and may be a shape defined by a curve or a shape defined by a curve and a straight line. A shape defined by a curve may be a circular shape or an elliptical shape, and a shape defined by a curve and a straight line may be a semicircular shape or a semi-elliptical shape. A plurality of display regions may include, in addition to a display region having a polygonal shape, at least one of a display region having a shape defined by a curve and a display region having a shape defined by a curve and a straight line. Alternatively, the plurality of display regions may include both of a display region having a shape defined by a curve and a display region having a shape defined by a curve and a straight line. 
     This structure achieves an advantage equivalent to advantage (1) as long as the normal directions of the reflection surfaces of each display region are identical, each display region forms a single image element associated with the display region, and the display body forms in the observation direction an image that is unique to the display body and composed of a plurality of image elements. 
     In a display region  11 , the reflection elements  21  may be identical in inclination angle θ but vary in height H. This configuration achieves an advantage equivalent to advantage (1) as long as the normal directions of the reflection surfaces of each display region are identical, each display region forms a single image element associated with the display region, and the display body forms in the observation direction an image that is unique to the display body and composed of a plurality of image elements. 
     Referring to  FIGS. 14 and 15 , this configuration is described in detail.  FIGS. 14 and 15  each show the cross-sectional structure of reflection elements of a display region  11  in a plane defined by the first direction D 1 , in which the reflection elements are arranged, and the third direction D 3 , which is the height direction of the reflection elements. 
       FIG. 14  shows a display region  11 C that includes first reflection elements  21   a , second reflection elements  21   b , and third reflection elements  21   c . The first to third reflection elements  21   a ,  21   b  and  21   c  have the same inclination angle θ. On the other hand, a first reflection element  21   a , a second reflection elements  21   b , and a third reflection element  21   c  have oblique sides of mutually different lengths in a cross section along a plane defined by the first and third directions D 1  and D 3 . In other words, the reflection elements vary in the length in the first direction D 1  and the length in the third direction D 3 . 
     In the first direction D 1 , the width of the first reflection elements  21   a  is the largest, and the width of the third reflection elements  21   c  is the smallest. The width of the second reflection elements  21   b  is between the width of the first reflection elements  21   a  and the width of the third reflection elements  21   c . In the third direction D 3 , the height of the first reflection elements  21   a  is the largest, and the height of the third reflection elements  21   c  is the smallest. The height of the second reflection elements  21   b  is between the height of the first reflection elements  21   a  and the height of the third reflection elements  21   c.    
     The display region  11 C includes six reflection elements. In the display region  11 C, a first reflection element  21   a , a second reflection element  21   b , and a third reflection element  21   c  are arranged in this order along the first direction Dl. In the display region  11 C, first to third reflection elements  21   a ,  21   b  and  21   c  form one periodicity. This reduces the likelihood that the arrangement of reflection elements produces diffracted light, as compared with a configuration in which all the reflection elements of one display region  11 C have the same width in the first direction D 1 . 
       FIG. 15  shows a display region  11 D that includes a first reflection element  21   a , a second reflection element  21   b , a third reflection element  21   c , a fourth reflection element  21   d , and a fifth reflection element  21   d . The first to fifth reflection elements  21   a  to  21   d  have the same inclination angle θ. On the other hand, the first to fifth reflection elements  21   a  to  21   d  have oblique sides of mutually different lengths in a cross section defined by the first and third directions D 1  and D 3 . In other words, of the first to fifth reflection elements  21   a  to  21   d , the width in the first direction D 1  of one reflection element differs from the widths in the first direction D 1  of the other reflection elements, and the height in the third direction D 3  of one reflection element differs from the heights in the third direction D 3  of the other reflection elements. Of the five reflection elements, the third reflection element  21   c  is the smallest in width in the first direction D 1  and height in the third direction D 3 , followed by the second reflection element  21   b , the fifth reflection element  21   d , the first reflection element  21   a , and then the fourth reflection element  21   d . This configuration further reduces the likelihood that the arrangement of reflection elements produces diffracted light. 
     The reflection surfaces  21 S do not have to be arranged at a constant pitch P, as long as the average value of the pitches P of reflection surfaces  21 S is between 1 μm and 300 μm inclusive. In this configuration, the minimum value and the maximum value of the pitches P are preferably between 1 μm and 300 μm inclusive, and the mode value of the pitches P is preferably between 1 μm and 300 μm inclusive. Further, the display body may include a display region  11  in which reflection surfaces  21 S are arranged at a constant pitch P and a display region  11  in which the pitch P of the reflection surfaces  21 S is varied. 
     When the reflection surfaces  21 S are arranged at an average pitch P of between 1 μm and 300 μm inclusive, the advantage obtained by a pitch P of greater than or equal to 1 μm and the advantage obtained by a pitch P of less than or equal to 300 μm can be achieved to some extent in the display regions. As such, it is still possible to have advantage (1) described above. 
     A reflection element  21  may include more than one reflection surface  21 S and may include two reflection surfaces. 
     As shown in  FIG. 16 , a reflection element  31  may include a first reflection surface  31 S 1  and a second reflection surface  31 S 2 . One side of the first reflection surface  31 S 1  is shared with the second reflection surface  31 S 2 . The first reflection surface  31 S 1  and the display surface  10 S form a first inclination angle θa, and the second reflection surface  31 S 2  and the display surface  10 S form a second inclination angle θb. The first inclination angle θa is smaller than the second inclination angle θb. However, the first inclination angle θa may be larger than or equal to the second inclination angle θb. 
     In this configuration, one display region having a plurality of reflection elements  31  may form a single image element associated with the display region in the observation direction using a set of first reflection surfaces  31 S 1  having the same orientation or a set of second reflection surfaces  31 S 2  having the same orientation. Advantage (1) described above is thus achieved. 
       FIG. 17  shows the cross-sectional structure of reflection elements  21  along a plane defined by the first and third directions D 1  and D 3 . 
     As shown in  FIG. 17 , each reflection element  21  includes a base surface  21 Su extending along the display surface  10 S and a side surface  21 Ss connected to the reflection surface  21 S and the base surface  21 Su. The line of intersection between the side surface  21 Ss and the base surface  21 Su is a base surface end line, and the line of intersection between the reflection surface  21 S and the base surface  21 Su is a front end line. The inclination angle θ at the base surface end line, or the angle formed by the base surface  21 Su and the side surface  21 Ss, is a base surface inclination angle θA. The inclination angle θ at the front end line, or the angle formed by the reflection surface  21 S and the base surface  21 Su, is a front end inclination angle θB. In the display region  11 , the base surface inclination angle θA may be larger than the front end inclination angle θB. In addition, the base surface inclination angles θA and the front end inclination angles θB may decrease monotonically in the direction from the front end line to the base surface end line of a reflection element  21 . Alternatively, the base surface inclination angle θA may be smaller than the front end inclination angle Bθ. In addition, the base surface inclination angles θA and the front end inclination angles θB may increase monotonically in the direction from the front end line to the base surface end line of a reflection element  21 . 
     In this configuration, the side surface  21 Ss of each reflection element  21  may function as a reflection surface  21 S. 
     DESCRIPTION OF THE REFERENCE NUMERALS 
       10  . . . Display body;  10 S . . . Display surface:  11 ,  11 C,  11 D . . . Display region;  11 A . . . First region;  11 B . . . Second region;  11 G . . . Display region group;  21 ,  31  . . . Reflection element;  21   a  . . . First reflection element;  21   b  . . . Second reflection element;  21   c  . . .Third reflection element;  21   d  . . . Fourth reflection element;  21   d  . . . Fifth reflection element;  21 S . . . Reflection surface;  21 Sa,  31 S 1  . . . First reflection surface;  21 sb,  31 S 2  . . . Second reflection surface;  21 Ss . . . Side surface;  21 Su . . . Base surface; PIC . . . Image; PICa . . . Image element