JP2012118216A - Image display body and information medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-definition image display body capable of displaying a wide-field image, changing and stereoscopic image as an image with high reproducibility and gradation expression.SOLUTION: An image display body 20 is disposed, on one surface of a display base material, with a plurality of pixels 22 into a matrix, and displays an image from the plurality of pixels. Each pixel is provided with a diffraction optical element 21 in which a function of emitting diffraction light to a predetermined range is uniform in the pixel, and the area of the diffraction optical element 21 in each pixel is set according to image information to be displayed.

Description

  The present invention relates to an image display body and an information medium having a highly secure anti-counterfeit function that is easy to determine with the naked eye.

  Cards and securities such as passports, credit cards, ID cards, gift certificates, and checks should be difficult to counterfeit because they may be used maliciously if they are handed over to someone else. It is. For this reason, this type of card / securities is made in a state where it is difficult to counterfeit or counterfeit itself, and a label that can be easily distinguished from counterfeit or counterfeit is attached to suppress counterfeiting. ing.

  In particular, in recent years, the problem is that counterfeit products are distributed not only in the above-mentioned cards and securities but also in brand products, and the demand for forgery prevention technology used in securities and the like is increasing.

  Conventionally, a diffraction grating pattern is known as a forgery prevention technique. The diffraction grating pattern can change the pattern or display a three-dimensional image according to the observation angle by controlling the direction, angle, brightness, and the like of diffracting light (for example, Patent Documents). 1 and 2).

  As a method for producing an original plate of the diffraction grating pattern, an XY stage on which a flat substrate coated with an electron beam resist is placed is moved under the control of a computer using an electron beam exposure apparatus. There is a method of forming a diffraction grating pattern on the surface of a substrate (see, for example, Patent Document 3).

Here, as a parameter for forming the diffraction grating,
(1) Spatial frequency of diffraction grating (pitch of grating line)
(2) Direction of diffraction grating (direction of grating line)
(3) There are three such as the drawing area of the diffraction grating (arrangement of the diffraction grating pattern).

  Then, the color that the diffraction grating pattern appears to shine with respect to the fixed point changes according to the parameter (1), and the direction that the diffraction grating pattern appears to shine changes according to the parameter (2). Further, the display pattern (picture, character, etc.) and brightness are determined according to the parameter (3) (for example, see Patent Document 4).

  Therefore, the surface of the substrate on which the diffraction grating pattern is to be formed is divided into small regions of about several tens to several hundreds of μm, and the various parameters described above are changed in each divided region, thereby expressing pictures, characters, etc. Can do.

  A metal stamper is produced from the original plate having a concavo-convex shape produced as described above by a method such as electroforming. Then, using the produced metal stamper as a matrix, a thermoplastic resin or a photocurable resin is applied onto a transparent substrate, the metal stamper is adhered, and the resin is softened or cured by applying heat or light. Duplicate the pattern.

  Since the replicated pattern is normally transparent, after providing a light reflecting layer by vapor deposition of a metal or dielectric thin film layer such as aluminum, an adhesive layer is formed on a substrate such as paper or plastic film. And a protective layer for preventing a printed layer or a pattern layer from being soiled or scratched as necessary, thereby producing cards and securities.

Japanese Patent No. 2508387 Japanese Patent No. 2745902 JP 2000-39508 A Japanese Patent No. 2137005

  By the way, in the image display body using the diffraction grating pattern as described above, as a method for displaying an image with a wide viewing zone, changing (an image that changes according to the observation angle), and a three-dimensional image, diffraction gratings having different grating angles are used. There is a method of juxtaposing the same shape as a diffraction grating and a method of constructing a collection of a plurality of lines in which curves of the same shape are arranged at regular intervals, but in the case of gradation expression using such a diffraction grating structure pattern, Depending on the trimming position, the desired image may not be obtained.

  The present invention has been made in view of the circumstances as described above, and displays a wide viewing area image, a changing image, and a stereoscopic image as an image with gradation expression with higher reproducibility, and authenticity determination with the naked eye. An object of the present invention is to provide an image display body and an information medium having an anti-counterfeit function with high security that can be used.

In order to solve the above problems, an image display body according to the present invention is an image display body in which a plurality of pixels are arranged in a matrix on one surface of a display substrate, and an image is displayed from the plurality of pixels. ,
Each pixel is provided with a diffractive optical element having a function of emitting diffracted light within a predetermined range within the pixel, and the diffractive optical element of each pixel is in accordance with the image information to be displayed. An image with gradation expression is displayed by setting the area.

  In addition, an information medium according to the present invention includes a sheet-like article on which predetermined information is displayed, and the image display body added to a required portion of a surface portion of the sheet-like article. .

  ADVANTAGE OF THE INVENTION According to this invention, the high quality image display body which can display a wide viewing-zone image, changing, and a three-dimensional image as an image with gradation expression with more reproducibility can be provided.

  Further, according to the present invention, it is possible to provide an information medium including an image display body having a highly secure anti-counterfeit function capable of determining authenticity with the naked eye.

1 is a plan view schematically showing an information medium according to an embodiment of the present invention. The top view for demonstrating schematically the image display body concerning the embodiment of the present invention. The top view for demonstrating schematically the image display body which concerns on other embodiment of this invention. The top view for demonstrating the relationship between the pattern of a diffraction grating, and the diffracted light emission direction. The figure which shows the image obtained by Fourier-transforming the structural pattern as an example of a diffractive optical element, and the said structural pattern. The figure which shows the image obtained by Fourier-transforming the structural pattern as the other example of a diffractive optical element, and the said structural pattern. The figure which shows the image obtained by Fourier-transforming the structural pattern as the further another example of a diffractive optical element, and the said structural pattern. The figure which shows the image obtained by Fourier-transforming the structural pattern employable for the diffractive optical element of this invention, and the said structural pattern. The figure which shows the relationship between the magnitude | size of the opening of a diffractive optical element, the wavelength of incident light, and light intensity distribution. The figure which shows the relationship between another magnitude | size of the opening of a diffractive optical element, the wavelength of incident light, and light intensity distribution. The figure which shows the relationship between the still another magnitude | size of the opening of a diffractive optical element, the wavelength of incident light, and light intensity distribution. The figure which shows the relationship between the integrated value of the light intensity which injects into an observer's pupil, and the peak value of light intensity. The figure explaining the relationship between the emission angle of the diffracted light which a diffractive optical element inject | emits, and the intensity distribution of diffracted light. The top view for demonstrating schematically the image display body concerning the embodiment of the present invention. The top view which shows roughly the information medium which concerns on other embodiment of this invention. The top view which shows roughly the information medium which concerns on other embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the drawings. In all the drawings, components having similar or substantially equivalent functions are denoted by the same reference numerals, and redundant description thereof is omitted.

FIG. 1 is a plan view schematically showing an information medium according to an embodiment of the present invention.
This information medium 100 is a personal authentication medium composed of a booklet such as a passport, for example, and depicts an open booklet.

  The information medium 100 includes a signature 1 and a cover 2. The signature 1 is formed, for example, so that one sheet piece 11 or a bundle of a plurality of sheet pieces 11 is folded in two. On the piece of paper 11, face images 11a and 11b including the same person, an image 12 such as a character string, a code, and a mark, and an image 13 such as a background pattern are applied. This piece of paper 11 incorporates not only the images but also an IC (Integrated Circuit) chip in which personal information is recorded and an antenna that enables non-contact communication of read / write data with the IC chip. May be.

  The cover 2 is folded in the same manner as the signature 1. The signature 1 and the cover 2 are both folded in two, and are integrated by binding or the like at the positions of the folds.

  As a result, when the booklet is folded and closed, the cover 2 is in a state in which the folded signature 1 is sandwiched and becomes a pocket-size personal authentication medium that is folded in half.

  Although the cover 2 is not shown, for example, an image including personal information is displayed. This personal information includes personal authentication information used for personal authentication. This personal information can be classified into, for example, biological information and non-biological personal information.

  The biological information is unique to the solid among the characteristics of the biological body. Typically, biological information is information that can be identified by an optical technique. For example, the biometric information is at least one image or pattern of a face, fingerprint, vein, and iris.

  Non-biological personal information is personal information other than biological information. The non-biological personal information is, for example, at least one of name, date of birth, age, blood type, sex, nationality, address, permanent address, telephone number, affiliation, and status. The non-biological personal information may include characters input by typing, may include characters input by hand reading such as signatures, or may include both of them.

  In FIG. 1, images 11a, 12 and 13 displayed on the cover 2 are images that are displayed using light absorption. Specifically, the images 11a, 12 and 13 are images that are visible when illuminated with white light and observed with the naked eye. If at least one of these images 11a, 12 and 13 is provided, the other one or more may be omitted.

  The images 11a, 12 and 13 can be composed of, for example, a dye or a pigment. In this case, as a means for forming the images 11a, 12 and 13, a thermal transfer recording method using a thermal head, an ink jet recording method, an electrophotographic method, or a combination of two or more thereof can be used. The images 11a, 12 and 13 can be formed by forming a layer containing a heat-sensitive color former and drawing with a laser beam on this layer. Further, a combination of the above two image forming methods may be used.

  At least a part of the images 12 and 13 may be formed by a thermal transfer recording method using a hot stamp, may be formed by a printing method, or may be formed using a combination thereof.

  On the other hand, the image 11b is an image displayed by the hologram and / or the diffraction grating. For example, the image 11b can be formed by sequentially performing thermal transfer recording using a thermal head and thermal transfer recording using a hot stamp or a thermal roll.

  The image 11a and the image 11b include face images of the same person. The face image included in the image 11a and the face image included in the image 11b may be the same or different. The face image included in the image 11a and the face image included in the image 11b may have the same or different dimensions. Each of the image 11a and the image 11b may include other biological information instead of the face image, and may further include biological information other than the face image in addition to the face image.

  The image 11b may include non-biological personal information instead of the biological information, and may further include non-biological personal information in addition to the biological information. Further, the image 11b may include non-personal information instead of personal information, and may further include non-personal information in addition to the personal information.

  The image 12 includes non-biological personal information and non-personal information. The image 12 is composed of, for example, one or more of characters, symbols, codes, and marks.

  The image 13 is a background pattern. For example, when the image 13 and at least one of the images 11a and 11b are combined, the information medium 100 can be more easily altered.

  FIG. 2 is a plan view for schematically explaining the image display body 20 according to the embodiment of the present invention. In the following description, the image display body 20 described with reference to FIGS. 2 to 8 and FIG. 14 will be described on the assumption that it is added as a label for forgery prevention or personal identification to a required portion of the information medium. is there.

  The diffractive optical elements 21a and 21b shown in FIG. 2 are diffractive gratings composed of general linear gratings, and do not have a function of emitting diffracted light in a predetermined range. Used for explanation.

  The image display body 20 shown in FIG. 2A includes a pixel 22 and a non-pixel region 23. The pixel 22 includes a diffractive optical element 21a. The diffractive optical element 21a includes a plurality of grooves or streaks (diffraction gratings). In FIG. 2, 31 indicates illumination (including illumination by a white light source such as a fluorescent lamp, sunlight, and incandescent lamp), and 32a and 32b indicate, for example, the observation angle of the observer.

  The angle of the diffraction grating and the angle of the observation direction are assumed to be a positive direction counterclockwise from the X-axis direction, and the angle is represented by 0 ° to 180 °. The same applies to the following description. Also, the direction perpendicular to the XY plane is taken as the Z axis, and the direction from the back side to the front side of the paper is taken as the positive direction of the Z axis.

  The angle of the diffraction grating of the diffractive optical element 21a shown in the figure is 0 °. Therefore, since the observation angle 32a of the observer is oriented in a direction parallel to the YZ plane, the diffracted light from the diffractive optical element 21a can be observed.

  Similarly, the image display body 20 shown in FIG. 2B includes a pixel 22 and a non-pixel region 23. The pixel 22 includes a diffractive optical element 21b. The diffractive optical element 21b includes a diffraction grating, and its angle is 0 °.

  Since the observation angle 32b by the observer is oriented in the direction parallel to the YZ plane, the diffracted light from the diffractive optical element 21b can be observed.

  By the way, when the area of the diffractive optical element 21a is 100%, the area of the diffractive optical element 21b is 50%. Under this condition, for example, assuming that the amount of incident light per unit area from the illumination 31 to the diffractive optical elements 21a and 21b is the same, the amount of diffracted light emitted from the diffractive optical element 21b is the amount of diffraction emitted from the diffractive optical element 21a. 50% of the amount of light. Therefore, the diffractive optical element 21b that can be observed at the observation angle 32b by the observer can be perceived as darker than the diffractive optical element 21a that can be observed at the observation angle 32a. That is, the brightness of the image that can be observed can be changed by changing the area of the diffractive optical element.

  Therefore, if, for example, three types of pixels are arranged in the same image display body 20, that is, the pixel 22 having the diffractive optical element 21a, the pixel 22 having the diffractive optical element 21b, and the pixel 22 having no diffractive optical element. It is possible to set at least three pixel brightness levels. This means that an image with gradation expression can be displayed by setting the area of each diffractive optical element included in each pixel included in the image display body 20 in accordance with the information of the image to be displayed. Image representation can be realized.

  In addition, as an example of the structure of the diffractive optical element, it can be produced by a structure in which an uneven structure forming layer, a reflective layer, and a protective layer are laminated in order. The concavo-convex structure forming layer is a transparent layer having a plurality of grooves as diffraction gratings formed on one main surface. As a material for the transparent layer, a resin such as a thermoplastic resin can be used.

  Examples of the material for the concavo-convex structure forming layer include thermoplastic resins such as polyurethane resin, polycarbonate resin, polystyrene resin and polyvinyl chloride resin, unsaturated polyester resin, melamine resin, epoxy resin, urethane acrylate, urethane methacrylate, polyol acrylate, Thermosetting resins such as polyol methacrylate, melamine acrylate, melamine methacrylate, triazine acrylate and triazine methacrylate, mixtures thereof, or thermoformable materials having radically polymerizable unsaturated groups can be used. You may form an uneven | corrugated structure formation layer using resin which has photocurability.

  The reflective layer is formed on the concavo-convex structure forming layer. The reflective layer covers at least a part of the surface of the concavo-convex structure forming layer provided with the plurality of grooves. Although the reflective layer can be omitted, providing the reflective layer improves the visibility of the image displayed by the diffraction grating.

  As the reflective layer, a transparent reflective layer or an opaque metal reflective layer can be used. The reflective layer can be formed by, for example, a vacuum film forming method such as vacuum deposition or sputtering. When the reflective layer contains a resin, the reflective layer may be formed by applying or printing.

  When a transparent reflective layer is used as the reflective layer, even when a pattern such as a pattern and characters is arranged on the back side of the reflective layer, it can be visually recognized from the front side of the image display body described later. On the other hand, when an opaque metal reflective layer is used as the reflective layer, it is possible to display an image with high brightness and excellent visibility.

  As the transparent reflective layer, for example, a layer made of a transparent material having a refractive index different from that of the concavo-convex structure forming layer can be used. The transparent reflective layer made of a transparent material may have a single layer structure or a multilayer structure. In the latter case, the transparent reflective layer may be designed so as to repeatedly cause reflection interference. As this transparent material, for example, a transparent dielectric such as zinc sulfide and titanium dioxide can be used.

  Alternatively, a metal layer having a thickness of less than 20 nm may be used as the transparent reflective layer. As a material of the metal layer, for example, a single metal such as chromium, nickel, aluminum, iron, titanium, silver, gold, and copper, or an alloy thereof can be used.

  As the opaque metal reflection layer, the same metal layer as described above for the transparent reflection layer can be used except that it is thicker. The opaque metal reflective layer may be a continuous film. Alternatively, the opaque metal reflective layer may be patterned. For example, at least a part of the opaque metal reflective layer may be patterned to display halftone dots, lines, other graphics, or a combination thereof on the image display body. Such a pattern can be used for authenticity determination of the information medium 100, for example.

  A layer containing a transparent resin and particles dispersed therein may be used as the transparent reflective layer or the opaque reflective layer. As the particles, for example, particles made of a metal material such as a single metal and an alloy, or particles made of a transparent dielectric such as a transparent metal oxide and a transparent resin can be used. In the transparent resin, flakes may be dispersed instead of dispersing the particles.

  The protective layer faces the reflective layer with the concavo-convex structure forming layer interposed therebetween. The protective layer is made of, for example, a resin, has optical transparency, and is typically transparent. As this resin, for example, an acrylic resin, a urethane resin, or an epoxy resin can be used. Note that the protective layer can be omitted.

  FIG. 3 is a plan view for schematically explaining an image display body 20 according to another embodiment of the present invention.

  Each of the image display bodies 20 shown in FIGS. 3A, 3B, and 3C includes a pixel 22 and a non-pixel region 23, and each pixel 22 has a diffractive optical element 21c, 21d, 21e, respectively. It has. These diffractive optical elements 21c, 21d, and 21e are diffractive gratings composed of general linear gratings, but have no function of emitting diffracted light in a predetermined range to be described later. It is used for simple explanation.

  In general, if the size of the pixel, that is, the size of the diffractive optical element provided in the pixel is made smaller than the resolution of the eye of the observer, the shape of the diffractive optical element itself cannot be visually recognized. Therefore, assuming that the diffractive optical elements 21c, 21d, and 21e can be observed with the same brightness, the image display bodies 20 shown in FIGS. 3A, 3B, and 3C can be observed as the same image. it can. In other words, the shape of the diffractive optical element itself is not limited to the square shown in FIG. 2, but may be a rectangle, a circle, a triangle, a trapezoid, a star, or the like shown in FIG. 3, and the shape is arbitrary.

  The fact that the shape of the diffractive optical element itself may be arbitrary means that the forgery prevention effect can be enhanced if the shape is characterized. That is, it can be observed as a general diffracted light during normal observation, but can be differentiated from a counterfeit product or a counterfeit product if the shape of the diffracted light emission region can be viewed only during microscopic observation.

  FIG. 4 is a plan view for explaining the relationship between the diffraction grating pattern and the diffracted light emission direction.

  The gratings of the diffractive optical element 21f shown in FIG. 4A are straight lines parallel to the same direction (X axis in this figure), and are arranged at regular intervals in the Y axis direction. In this case, the diffracted light exit direction 24f is parallel to the Y axis.

  On the other hand, the gratings of the diffractive optical element 21g shown in FIG. 4B are curved and are arranged at a constant interval in the Y-axis direction. At this time, the diffracted light emission direction 24g has a certain range corresponding to the shape of the curve because the grating is curved. This means that the diffracted light emission range can be variably set to a desired range by controlling the shape of the curve.

  In FIG. 4B, the diffracted light emission direction 24g is shown from the diffractive optical element 21g as shown by the arrow in the figure, but the range of the diffracted light emission direction 24g is schematic. Therefore, the diffracted light exit direction 24g as shown in the figure is not obtained from the structure of the diffractive optical element 21g as shown.

  FIG. 5 is a diagram showing a structure pattern of a diffractive optical element and a Fourier transform image. FIG. 4A shows a structural pattern of the diffractive optical element 21g, and FIG. 4B shows a Fourier transform image 25g obtained by Fourier transforming the structural pattern of the diffractive optical element 21g shown in FIG. FIG. Note that the Fourier transform in optics indicates the distribution of diffracted light by Fraunhofer diffraction.

  As shown in the Fourier transform image 25g in FIG. 5B, the emission direction of the diffracted light has a certain range in the X-axis direction.

  FIG. 6 is a diagram showing a structure pattern and a Fourier transform image of a diffractive optical element different from FIG. FIG. 4A shows a structural pattern of the diffractive optical element 21h, and FIG. 4B shows a Fourier transform image 25h obtained by Fourier transforming the structural pattern of the diffractive optical element 21h shown in FIG. FIG. As shown in the Fourier transform image 25h, the emission direction of the diffracted light has a certain range in the X-axis direction.

  The diffractive optical element 21h shown in FIG. 6A has a structure pattern obtained by trimming a part of the diffractive optical element 21g shown in FIG.

  Therefore, when the Fourier transform image 25g of FIG. 5B and the Fourier transform image 25h of FIG. 6B are compared, the emission ranges of the diffracted light by the diffractive optical elements 21g and 21h are different.

  As described above, gradation representation of an image can be performed by changing the area of the diffractive optical element. However, in the case of the diffractive optical element 21g, the emission range of the diffracted light varies depending on the trimming position when changing the area. . That is, when gradation expression is performed using a structure pattern as shown in the diffractive optical element 21g, an image as desired may not be obtained depending on the trimming position.

  FIG. 7 is a diagram showing a structure pattern and a Fourier transform image of a diffractive optical element different from those shown in FIGS. FIG. 4A shows a structural pattern of the diffractive optical element 21i, and FIG. 4B shows a Fourier transform image 25i obtained by Fourier transforming the structural pattern of the diffractive optical element 21i shown in FIG. FIG. As shown in the Fourier transform image 25i, the exit direction of the diffracted light has a certain range in the X-axis direction.

  The diffractive optical element 21i shown in FIG. 7A is an image obtained by trimming the diffractive optical element 21g in FIG. 5A, and the trimming position is different from that of the diffractive optical element 21h in FIG.

  Comparing the Fourier transform image 25i shown in FIG. 7B and the Fourier transform image 25g shown in FIG. 5B, it can be seen that the range in which the diffracted light is emitted has not changed. That is, in the case of the trimming shown in FIG. 7B, it can be used for displaying an image with gradation expression without causing any abnormality in the viewing zone.

  However, on the other hand, when an image is displayed by disposing a pixel including the diffractive optical element 21i, a portion where the diffractive optical element is present and a portion where the diffractive optical element is present are densely formed in the Y-axis direction. At this time, since the presence or absence of the diffractive optical element is in a stripe shape, uneven distribution of the diffracted light intensity or the like is generated by the regular stripe, and an unintended visual effect may be observed.

  Note that the diffractive optical elements 21g, 21h, and 21i illustrated in FIGS. 5 to 7 do not depend on the form of the present invention because the function of emitting diffracted light is not uniform within the pixel.

  Accordingly, as described with reference to FIGS. 5 to 7, in the case of a curved structure pattern generally used for the purpose of image display with a wide viewing area or stereoscopic image display, gradation expression can be expressed simply by changing the area. It turns out to be difficult.

  FIG. 8 is a diagram showing a structure pattern that can be employed in the diffractive optical element of the present invention and a Fourier transform image of the structure pattern. FIG. 4A shows a structural pattern of the diffractive optical element 21j, and FIG. 4B shows a Fourier transform image 25j obtained by Fourier transforming the structural pattern of the diffractive optical element 21j shown in FIG. FIG.

  As shown in the Fourier transform image 25j, the diffracted light exit direction has a certain range in the X-axis direction.

  In the case of the diffractive optical element 21j, the emission range of the diffracted light and the intensity distribution of the diffracted light in the emission range do not vary greatly depending on the trimming position, and the function of emitting the diffracted light is uniform within the pixel. .

  Incidentally, the entrance pupil diameter of each of the left and right eyes of the observer is generally 2 to 8 mm, and the distance between the display surface of the image display body and the first surface is 500 mm. In this case, the prospective angle of each of the left and right eyes is 0.2 to 0.9 °. Therefore, when the range of emission of the diffracted light in the first surface is 2 ° or more, it becomes possible to secure a viewing area that is twice or more than this expected angle, and stable image display can be performed.

  However, if the emission range is, for example, 1 ° or less, the scattering component of the emitted light becomes weak, so that the uniformity of the diffracted light emission function in the diffractive optical element cannot be sufficiently obtained, and the area of the diffractive optical element is changed. It becomes difficult to control the emission direction and intensity distribution of the emitted light.

  Therefore, if the diffracted light emission range is 2 ° or more, the uniformity of the diffracted light emission function within the diffractive optical element can be sufficiently obtained, and natural gradation expression is obtained when the area of the diffractive optical element is changed. It has been confirmed by experiments that can be observed.

  Here, as an upper limit of the range of injection, the wider the range that can be visually recognized, the easier it is to perceive visual effects. On the other hand, as the emission range is narrower, the emission light is concentrated in a narrower range, so that it appears brighter. In an experiment, if the angle range is, for example, 10 ° or less, sufficient brightness can be obtained. It has been confirmed.

  In other words, according to the present invention, gradation display can be performed without restriction in wide-area image display and stereoscopic image display using diffracted light, and thus it is possible to provide a higher-quality image display body. It becomes.

  In FIG. 2, when the area of the diffractive optical element 21a is 100%, the area of the diffractive optical element 21b is 50%.

  At this time, if the amount of incident light per unit area from the illumination 31 is the same, the amount of diffracted light emitted by the diffractive optical element 21b is 50% of the amount of diffracted light emitted by the diffractive optical element 21a. As described above.

  However, it cannot be said that the diffracted light actually entering the observer's eyes also changes in proportion to the amount of diffracted light, that is, the area of the diffractive optical element. This is because the diffracted light emitted from the diffractive optical element is not only diffracted by the structural pattern of the diffractive optical element but also diffracted when the size of the diffractive optical element is the aperture.

  Therefore, the larger the area of the diffractive optical element, the narrower the spread of diffracted light, and the smaller the area of the diffractive optical element, the wider the spread of diffracted light. That is, as the area of the diffractive optical element is smaller, not only the amount of incident light simply decreases, but also the intensity of the incident diffracted light intensity decreases.

  Here, for example, consider an example in which the shape of the diffractive optical element is rectangular.

  The intensity distribution of Fraunhofer diffraction from a rectangular opening is expressed by the following formula (1). For easy understanding, diffraction by single-wavelength coherent light is used.

I (x, y) = A ² dx ² dy ² sinc ² {(dx / λR) x}
sinc ² {(dy / λR) y} (1)
In the above equation (1), I is the light intensity distribution on the observation surface (x, y), dx and dy are the lengths of the horizontal and vertical sides of the aperture, λ is the wavelength of light, and R is the distance from the observation surface. And the sinc function is sinc (x) = sin (πx) / πx. A is a variable related to the amplitude of light, but may be considered as a constant here.

  The discussion using single-wavelength coherent light here refers to the light intensity in consideration of the wavelength and the size of the light source under normal illumination (illumination with a white light source such as a fluorescent lamp, sunlight, or incandescent lamp). The distribution I (x, y) may be integrated according to the wavelength and the size of the light source.

  That is, the basic tendency can be estimated from the light intensity distribution in the case of single-wavelength coherent light expressed by the above equation (1).

  Specifically, the results of the trial calculation of the light intensity distribution in the diffraction at the aperture when the size of the aperture is 5 × 5 μm, 3 × 3 μm, 1 × 1 μm and 400 nm and 600 nm light is incident, It is shown in FIGS. The emission angle is set to 0 ° of the regular reflection light. 9 to 11 show cross sections on the x-axis.

  The relative light intensity has a peak value of 1 in the case of an opening of 1 × 1 μm, and in any case, the intensity per unit area of incident light is uniform.

  That is, from the above formula (1), in the case of a rectangular aperture, it can be seen that the peak of the light intensity is proportional to the square of the aperture area. Therefore, when the diffractive optical element is rectangular, the peak of the diffracted light intensity is found to be proportional to the square of the area of the diffractive optical element from the above equation (1). For this purpose, it is understood that the area of the diffractive optical element may be doubled.

  As described above, since the entrance pupil diameter of each of the left and right eyes of the observer is generally 2 to 8 mm, it is assumed that the distance between the display surface of the image display body and the first surface is 500 mm. The prospective angle of each of the left and right eyes is 0.2 to 0.9 °. As will be described later, each diffractive optical element cannot be distinguished if the size of the diffractive optical element is less than the resolution of the eye of the observer. Therefore, the diffractive optical element does not need to be extremely small, and generally has a rectangular shape with a side of about several tens of μm.

  As is clear from the above equation (1) and FIGS. 9 to 11, it can be seen that the larger the aperture size, the narrower the light intensity distribution from the peak and the more concentrated the intensity of the diffracted light. Therefore, since the observer perceives a very narrow range with an expected angle of 0.2 to 0.9 °, it can be approximated that the perceived light intensity is proportional to the peak of the diffracted light. .

  From the above equation (1), the following equation (2) can be derived as an integral value of the light intensity incident on the observer's pupil.

I _int = ∬A ² dx ² dy ² sinc ² {(dx / λR) x}
sinc ² {(dy / λR) y} (2)
In the above equation (2), if the observer's pupil diameter is r, I _int is the integrated value of the light intensity at x ² + y ² ≦ (r / 2) ² .

Here, FIG. 12 shows the relationship between I _int and the peak value of light intensity, that is, I (0,0) in the above equation (1). Note that λ = 500 nm, R = 500 mm, and r = 5 mm.

  In the plot of FIG. 12, the diffractive optical element has a rectangular shape, and its size is 2 × 2 μm, 4 × 4 μm, 6 × 6 μm, 8 × 8 μm, 10 × 10 μm, 20 × 20 μm, 30 × 30 μm, 40 ×. The values are at 40 μm, and the relative values are all set to 1 at 10 × 10 μm.

As is clear from FIG. 12, I _int and I (0,0) are in a proportional relationship. That is, it can be said that the intensity of incident light perceived by the observer is proportional to the peak value of the light intensity distribution.

  Therefore, if the area of the diffractive optical element is determined so that the gradation value of the image to be displayed and the peak of the diffracted light intensity are proportional, for example, if the shape of the diffractive optical element is rectangular, the above equation (1) is used. Accordingly, it is possible to provide an image display body that displays an image in which the gradation value of the image information is accurately reproduced.

  FIG. 13 is a diagram schematically showing the intensity distribution of diffracted light. That is, FIG. 13 shows the intensity distribution C1 of the diffracted light emitted from the diffractive optical element 21g shown in FIG. 5A and the intensity distribution C2 of the diffracted light emitted from the diffractive optical element 21j shown in FIG. I'm drawing. The illustrated emission angle indicates an angle formed between a point on a straight line connecting the left and right eyes of the observer in the first plane and the image display body.

  FIG. 13 is a diagram for schematically explaining the relationship between the emission angle of the diffracted light and the intensity distribution. When the intensity distribution of the diffracted light emitted by the diffractive optical elements 21g and 21j is as depicted in C1 and C2. Is not limited. Further, C1 and C2 are illustrated with the maximum value of each as 100%, and cannot be compared as a difference between absolute values.

  Here, when C1 and C2 are compared, C1 has a narrow angle range in which the intensity is large, and the intensity tends to decrease greatly as it deviates from the center of the angle range of the diffracted light emission angle. On the other hand, C2 has a wide angle range in which the intensity is high, and an angle range in which the intensity is low in the diffracted light emission angle range is narrow.

  This difference arises from the difference in the structure pattern.

  The diffractive optical element 21j has a uniform function of emitting diffracted light in the plane. Such a structure can be designed by, for example, a computer generated hologram method. The computer generated hologram has a diffractive structure having a random phase. By adopting such a structure, it is possible to easily and accurately produce a structure having a uniform function of emitting diffracted light, and thus it is possible to provide an image display body that displays a higher-quality image. It becomes.

  By the way, when the observer observes the state of the image display body at a position 500 mm away from his / her own eye, generally, the resolution of a human eye with a visual acuity of 1.0 is 1 minute. Due to limitations, structures of 145 μm or less cannot be decomposed. Therefore, when the length of the long side of the pixel is 145 μm or less, the pixels cannot be decomposed. Therefore, by setting the length of the long side of the pixel to 145 μm or less, it is possible to provide an image display body that displays a higher quality image.

  FIG. 14 is a plan view for schematically explaining the image display body according to the embodiment of the present invention.

  Each of the image display bodies 20 shown in FIGS. 14A and 14B includes a pixel 22 and a non-pixel region 23. The pixel 22 includes a pixel 22 having a diffractive optical element 21k and a pixel 22 having a diffractive optical element 21l. The structural patterns of the diffractive optical elements 21k and 21l are both linear, but since this does not have a function of emitting diffracted light in a predetermined range, it will be briefly described from the viewpoint of understanding. It was used for this purpose.

  In FIG. 14A, the pixels 22 having the diffractive optical elements 21k and 21l are arranged in a checkered pattern, but in FIG. 14B, they are alternately arranged in a stripe pattern.

  As shown in FIG. 14, a plurality of images can be displayed by arranging a large number of pixels having different diffracted light emission directions on the same plane. In FIG. 14, a checkered pattern and a stripe pattern are shown as pixel arrangement methods having different diffracted light emission directions, but the arrangement method is not necessarily regular and may be random.

  By the way, for example, when comparing a case where a single image is displayed and a case where two images are displayed by changing, when two images are displayed by changing, the area allocated to display one image is larger. This is 1/2 of the case of displaying a single image. However, since the remaining half of the area has pixels arranged to emit light in different directions, the observer can double the size of the pixel compared to displaying a single image. Observe as there is.

  That is, when two or more images are displayed, the number of pixels in appearance decreases, and the image quality decreases.

  Regarding the point that the apparent number of pixels decreases, it is possible to improve the number of pixels by reducing the size of the pixels. However, when displaying an image with a structural pattern such as the diffractive optical element 21g shown in FIG. 5A, for example, as described above, the diffractive optical element according to the present invention (for example, the diffractive optical element 21j shown in FIG. 8A). The unevenness of the intensity distribution of the diffracted light is larger than that, and the tendency becomes more remarkable as the pixel size is reduced.

  In that respect, in the case of the structural pattern according to the present invention, it can be said that the unevenness of the intensity distribution of the diffracted light does not increase or the tendency to increase by reducing the pixel size is small.

  Therefore, according to the present invention, it is possible to use gradation expression without restriction when displaying a wide viewing area image using diffracted light, particularly when displaying two or more images, and the intensity distribution of diffracted light. Therefore, it is possible to provide a higher-quality image display body.

  In particular, when visualizing at least two images at the same time as a stereoscopic image, if the intensity distribution of the diffracted light is highly uneven, the viewing area for viewing images with different brightness between the left and right eyes is widened. Therefore, according to the present invention, in a wide viewing area image display using diffracted light, in particular, when two or more images are displayed and the observer views as a stereoscopic image, the gradation expression can be used without restriction. In addition, since unevenness in the intensity distribution of diffracted light can be reduced, an image display body and an information medium with higher image quality can be provided.

  Here, it is assumed that the length of the line segment connecting the left and right eyes of the observer is 65 mm, and the distance between the image display body and the first surface (the surface including the left and right eyes of the observer) is 500 mm. In this case, the angle formed by the eyes of the left and right eyes of the observer is 7.4 °. Therefore, if the angle range on the first surface of the diffracted light emitted from the diffractive optical element is 7.4 ° or less, the same image does not enter the left and right eyes simultaneously. Therefore, it is possible to prevent the parallax image to be viewed by one eye from becoming noise of the parallax image to be viewed by the other eye.

  Therefore, by setting the angle range on the first surface of the diffracted light emitted from the diffractive optical element to 7.4 ° or less, it is possible to provide an image display body that displays a higher-quality stereoscopic image.

  The above description has been given by taking the information medium 100 (see FIG. 1) as a passport as an example, but it can also be applied to other information media other than the passport. For example, the above-described technique can be applied to various cards such as a visa and an ID card.

  FIG. 15 is a plan view schematically showing an information medium according to another embodiment of the present invention.

  The information medium 200 is a magnetic card, and a printed layer 52 and a strip-shaped magnetic recording layer 53 are formed on a base material 51 made of, for example, plastic. Furthermore, the image display body 20 is affixed on the base material 51 as an anti-counterfeit or personal identification label.

  Therefore, the information medium 200 includes the image display body 20. Therefore, forgery or imitation of the information medium 200 becomes difficult.

  FIG. 16 is a plan view schematically showing an information medium according to still another embodiment of the present invention.

  In the information medium 300, a printed layer 54 made of a person image is formed on the surface portion of the substrate 51. Furthermore, the image display body 20 is affixed to the base material 51 as an anti-counterfeiting or identification label, and the image of the image display body 20 is also a person image like the print layer 54.

  In the case of this information medium 300, the print image of the print layer 54 and the image of the display body 10 are the same. In this case, if the print image of the print layer 54 and the image of the image display body 20 are the same (actual), even if the information on the print image of the print layer 54 is falsified, Since the information of the image display body 20 must be the same, the image display body 20 also needs to be tampered with the same pattern, and forgery or imitation becomes more difficult than the information medium 200 shown in FIG.

  Further, since the authenticity can be determined by comparing the print image of the print layer 54 and the image of the image display body 20, more accurate authentication can be performed for the examiner who performs personal identification. Moreover, since the authenticity determination method is to compare images and is a relatively simple method, not only the examiner but anyone can easily determine the authenticity.

  The image display body 20 included in the information medium 300 shown in FIG. 16 is composed of an image made up of a person image. In this case, forgery or imitation of the personal authentication medium can be made more difficult, but it can also be applied to information media other than the personal authentication medium.

  The material of the substrate 51 of the image display body 20 to be attached to the information media 100 to 300 may not be paper such as natural paper and synthetic paper. For example, polyethylene terephthalate resin (thermoplastic PET), polyvinyl chloride resin, thermosetting polyester resin, polycarbonate resin, synthetic resin such as polymethacrylic resin and polystyrene resin, ceramics such as glass, ceramic and porcelain, or single metal and It may be a metal material such as an alloy.

  In the above embodiment, the personal authentication medium such as a passport and an ID card is exemplified as the information medium. However, the technology relating to the information medium 100 to 300 can be easily applied to information media other than the personal authentication medium. It is. That is, it goes without saying that the technique described above can be used for purposes other than personal authentication, such as individual authentication.

  In addition, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention.

  DESCRIPTION OF SYMBOLS 1 ... Signature, 2 ... Cover, 11 ... Paper piece, 11a, 11b ... Face image, 12, 13 ... Image, 20 ... Image display body, 21a-21l ... Diffractive optical element, 22 ... Pixel, 23 ... Non-pixel area | region, 24f, 24g ... Diffraction light exit direction, 25g-25j ... Fourier transform image, 31 ... Illumination, 32a-32e ... Observer observation angle, 51 ... Substrate, 52 ... Print layer, 53 ... Magnetic recording layer, 54 ... Print Layer, 100, 200, 300 ... Information medium.

Claims (11)

A plurality of pixels are arranged in a matrix on one side of the display substrate, and an image display body that displays an image from the plurality of pixels,
Each of the pixels is provided with a diffractive optical element having a uniform function of emitting diffracted light within a predetermined range within the pixel,
An image display body which displays an image with gradation expression by setting an area of the diffractive optical element in each pixel according to the image information to be displayed.   2. The image according to claim 1, wherein the predetermined range is an angle range of 2 ° or more in a first plane parallel to a straight line connecting the left and right eyes of an observer who perceives the image. Display body.   When setting the area of the diffractive optical element so that the peak size of the diffracted light intensity is proportional to the gradation value of the image to be displayed, the diffracted light from the aperture when the size of the diffractive optical element is the aperture The image display body according to claim 1, wherein an area of the diffractive optical element is set so as to compensate for the spread of the diffractive optical element.   4. The diffractive optical element has a concavo-convex structure, and the plurality of concave portions and / or convex portions are a plurality of grooves or streaks made of a computer generated hologram. The image display body according to one item.   The image according to any one of claims 1 to 4, wherein each pixel cannot be disassembled by an observer's eyes by setting the length of the long side of the pixel to 145 µm or less. Display body. When displaying a plurality of images by arranging the plurality of pixels,
The individual images are composed of the plurality of pixels including the diffractive optical element that has the same emission range of diffracted light,
The image display body according to any one of claims 1 to 5, wherein different images have different diffracted light emission ranges.   The image display body according to claim 6, wherein the image display body can be viewed as a stereoscopic image by simultaneously viewing at least two of the plurality of images.   The image display body according to claim 7, wherein an angle range of the diffracted light emitted from the diffractive optical element on the first surface is 7.4 ° or less.   A sheet-like article on which predetermined information is displayed, and an image display body according to any one of claims 1 to 8, which is added to a required portion of a surface portion of the sheet-like article. Information media.   The predetermined information displayed on the sheet-like article is an image including personal information printed, printed or colored, and the image displayed on the image display body is the same as the image displayed on the sheet-like article. The information medium according to claim 9, wherein:   The information medium according to claim 9 or 10, wherein the image including the personal information is a face image.

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