JP2006327129A - Information recording medium and concealed information detector therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an information recording medium which hardly causes forgery, and to surely decode concealed information from the information recording medium. <P>SOLUTION: The information recording medium is composed of a substrate 11 and an information holding layer 12 which is laminated on the substrate 11; the layer 12 is equipped with a light-reflecting layer 124; a surface of the layer 12 is divided into many areas, so that diffraction grating elements 12a, 12b, etc. can be arranged in the divided areas; the elements 12a, 12b, etc. are composed of diffraction grating which is provided in an irregular shape on the surface of the light-reflecting layer; the directions of the reflected and diffracted light of at least some of the diffraction grating elements are set as the whole or a part of the concealed information; and a center-line surface roughness Ra of the surface of the substrate 11 is 1.0 or more. Irregularities constituting the diffraction grating and irregularities of the substrate 11 are superposed on one another, so that the forgery can be hardly performed. Additionally, the concealed information can be surely decoded by using a prescribed surface light source. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an information recording medium that holds confidential information that cannot be recognized with the naked eye, and a detection device that detects the presence and content of this information. The secret information according to the present invention is held by a reflective diffraction grating provided on the surface of the substrate, and the secret information is reproduced by the direction of the reflected diffracted light.

  An information recording medium in which a reflection type diffraction grating is provided on the surface of the substrate and the secret information is held in the diffraction grating, and the secret information is reproduced in the direction of the reflected diffraction light generated in response to the irradiation light from a specific light source is known. It is.

  Such an information recording medium is generally manufactured using a transfer technique, and the confidential information is used as an information recording medium, that is, authentication information for authenticating the authenticity of a product.

  The transfer foil 9 is, for example, as shown in the cross-sectional view of FIG. 6A. 6A, reference numeral 91 denotes a transfer foil substrate. A protective layer 93, a light reflection layer 94, and an adhesive layer 95 are sequentially laminated on the transfer foil substrate 91 with a release layer 92 interposed therebetween. Yes. The protective layer 93 is made of a transparent resin, and the light reflecting layer 94 is provided on the protective layer 93 by vacuum film formation. The light reflecting layer 94 is made of a metal such as aluminum or copper or a transparent material having a refractive index different from that of the protective layer 93 so that light is reflected at the boundary between the protective layer 93 and the light reflecting layer 94. It is configured.

  The perspective view seen from the base material 91 side is shown in FIG. 6B. As shown in FIG. 6B, the surface of the transfer foil 9 is divided into a number of regions. In each of these many regions, a diffraction grating is arranged in a concavo-convex shape on the boundary surface between the protective layer 93 and the light reflecting layer 94 (hereinafter, the diffraction grating provided in each of these regions is referred to as “diffraction”. Called "lattice elements"). When the diffraction grating elements 9a, 9b,... Are irradiated with light, the wavelength and irradiation direction of the irradiation light, the direction and pitch (or spatial frequency) of the diffraction grating provided in the diffraction grating elements 9a, 9b,. Reflected diffracted light is generated in the corresponding diffraction direction.

  Some or all of these diffraction grating elements 9a, 9b,... Hold confidential information that cannot be recognized with the naked eye. This information is read from a predetermined point light source to the diffraction grating elements. Is reproduced by the diffraction direction of the reflected diffracted light generated in response to the reading light beam. Then, the entire secret information is constituted by a combination of diffraction directions of the reflected diffracted light. For example, each of the diffraction grating elements 9a, 9b,... Is constituted by one of two types of diffraction gratings having different diffraction directions, and binary data of 1 or 0 is associated with each diffraction grating. The entire confidential information can be configured by a combination of value data. Examples of confidential information include authentication information that ensures the authenticity of a product (substrate) described later.

  Then, an information recording medium is obtained by transferring the transfer foil onto the product (substrate) 8 (see FIG. 6C). Various products (substrates) 8 are used, for example, plastic products such as plastic cards. Then, on this product (substrate), it is possible to decode the confidential information by irradiating reading light from a predetermined point light source, receiving reflected diffracted light with an optical sensor and analyzing with a CPU. is there.

  However, since the diffraction direction of the reflected diffracted light is determined by the wavelength and irradiation direction of the reading light beam, and the direction and pitch (spatial frequency) of the diffraction grating, if the position of the point light source that irradiates the reading light beam and the position of the optical sensor are known, Based on these positions, the information recording medium can be forged.

  The present invention has been made based on such circumstances, and an object thereof is to provide an information recording medium that makes it more difficult to counterfeit. Another object of the present invention is to provide a detection device that can reliably read and decode confidential information from such an information recording medium.

That is, the invention according to claim 1 includes a substrate and an information holding layer laminated on the substrate, and the information holding layer includes a light reflecting layer.
The information holding layer surface is divided into a number of regions, and a diffraction grating element is disposed in each of the number of regions.
This diffraction grating element is composed of a diffraction grating provided in the form of irregularities on the surface of the light reflection layer, and the direction of the reflected diffraction light of at least some of the diffraction grating elements of this diffraction grating element is the secret information. In the information recording medium to be all or part of,
A center line surface roughness Ra based on JIS B0601-1994 of the substrate surface is 1.0 or more.

  According to the first aspect of the present invention, since the center line surface roughness Ra of the substrate surface is as large as 1.0 or more, the information holding layer laminated on the surface is also deformed along the unevenness of the substrate surface. The diffraction grating provided in the form is also deformed. For this reason, even if the reading light beam is emitted from a single point light source, the diffraction direction of the reflected diffracted light generated in response to the reading light beam is different from the predetermined diffraction direction and is detected by the optical sensor. Can not do it. For this reason, the counterfeiting becomes more difficult. Such confidential information can be reliably read and decoded by a detection device to be described later.

  Next, in the invention described in claim 2, the secret information is dispersed and held in each of the plurality of diffraction grating elements, and all the diffraction directions of the reflected diffraction light from the plurality of diffraction grating elements are accurately detected. Unless this is done, it is impossible to decipher confidential information.

That is, the invention described in claim 2 is based on the invention described in claim 1,
There are a plurality of diffraction grating elements in which the direction of the reflected diffracted light is part of the confidential information,
All of the secret information is constituted by the entire reflected diffraction light of the plurality of diffraction grating elements.

  According to the second aspect of the present invention, since all of the secret information is constituted by the entire reflected diffracted light of the plurality of diffraction grating elements, the concealment is performed unless the entire reflected diffracted light of these diffraction grating elements is detected. The whole information cannot be deciphered. However, since the surface of the substrate has irregularities, and the irregularities are reflected in the diffraction grating and the diffraction grating is deformed, the reflected diffracted light of these multiple diffraction grating elements is reflected by the reading light from a single point light source. It is difficult to detect. For this reason, it is difficult to detect all of the confidential information. The part of the confidential information is, for example, a signal such as “1” or “0”, which is a part of the binary data, and the whole of the confidential information is, for example, “1” or “0”. This is information having a meaning that is configured by combining these signals.

  Next, in the invention described in claim 3, the reading light for reproducing the secret information of the plurality of diffraction grating elements is made different depending on the diffraction grating elements, thereby making it more difficult to forge.

That is, the invention described in claim 3 is based on the invention described in claim 2,
Among the plurality of diffraction grating elements, a specific diffraction grating element reproduces a part of the confidential information by irradiating light from a specific light source to the diffraction grating element,
The other diffraction grating element is characterized in that a part of the confidential information is reproduced by irradiating light from a light source arranged in a direction different from the specific light source to the diffraction grating element. is there.

  According to the third aspect of the present invention, since the light source required for reproducing the secret information differs depending on the diffraction grating element, the counterfeiting becomes more difficult.

  Next, the invention according to claim 4 includes a diffraction grating element that holds confidential information mixed in a diffraction grating element that does not hold confidential information, and the diffraction grating element that holds the confidential information. It hides the existence and its location, thus making it more difficult to counterfeit.

That is, the invention according to claim 4 is based on the inventions according to claims 1 to 3,
The entire diffraction grating element represents a visible image.

  Next, the invention described in claim 5 relates to a detection apparatus that can read the confidential information reliably using the information recording medium described in claim 1.

That is, the invention described in claim 5
A substrate and an information holding layer laminated on the substrate, the information holding layer including a light reflecting layer;
The information holding layer surface is divided into a number of regions, and a diffraction grating element is disposed in each of the number of regions.
This diffraction grating element is composed of a diffraction grating provided in a concavo-convex shape on the surface of the light reflection layer, and at least some of the diffraction grating elements conceal the direction of the reflected diffraction light. An apparatus for detecting the confidential information from an information recording medium as all or part of information,
A light source for irradiating the information recording medium with light;
In the secret information detection device comprising the reading means for detecting the reflected diffracted light generated in response to the irradiation light from the light source,
The light source comprises a surface light source;
L is a line connecting the end of the surface light source and the center of the diffraction grating element having the secret information, and M is a line connecting the end of the surface light source on the opposite side and the center of the diffraction grating element having the secret information. In this case, the angle formed by L and M is 5 degrees or more.

  According to the invention described in claim 5, the light source that irradiates the diffraction grating element with the light source is a surface light source, and the area thereof is a line connecting the end of the surface light source and the center of the diffraction grating element having the secret information. Is a large area such that the angle formed by L and M is 5 degrees or more, where L is the line connecting the end of the opposite surface light source and the center of the diffraction grating element having the secret information. Thus, the diffraction grating element is irradiated with reading light from various directions, and reflected diffracted light generated from the diffraction grating element is also emitted in various diffraction directions. For this reason, even if the substrate surface has irregularities and the diffraction grating of the diffraction grating element is deformed reflecting the irregularities of the substrate, the reflected diffracted light surely reaches the reading means, and the reading and decoding are performed. Is possible.

In addition, when the substrate is flat, even when the center line average roughness Ra of the substrate surface is 1.0, if the angle formed by L and M is 5 degrees or more, it can be read accurately. . On the other hand, when the angle is less than 5 degrees, the confidential information may not be accurately read when the center line average roughness Ra of the substrate surface is 1.0.

  According to the first aspect of the present invention, even if the reading light beam is irradiated from a single point light source, it cannot be detected by the optical sensor, and the counterfeiting becomes more difficult.

  According to the second aspect of the present invention, the entire confidential information cannot be decoded unless the entire reflected diffracted light of the diffraction grating element is detected. However, it is difficult to detect the reflected diffracted light of the plurality of diffraction grating elements with the reading light from a single point light source, and the counterfeiting becomes more difficult.

  According to the third aspect of the present invention, since the light source required for reproducing the secret information differs depending on the diffraction grating element, the counterfeiting becomes more difficult.

  According to the invention described in claim 4, since the diffraction grating element that does not hold the secret information is mixed with the diffraction grating element that holds the secret information, and the presence / absence and the position thereof are hidden, the forgery thereof. Becomes even more difficult.

  According to the fifth aspect of the present invention, since the light source for irradiating the diffraction grating element is a surface light source and the area is large, the diffraction grating of the diffraction grating element is deformed to reflect the substrate unevenness. However, the reflected diffracted light reliably reaches the reading means, and can be read and decoded.

  As shown in the cross-sectional view of FIG. 1, the information recording medium 1 according to the present invention includes a substrate 11 and an information holding layer 12 that is laminated on the substrate 11 and holds confidential information. is there. The substrate 11 may be arbitrary, but it needs to have a large surface irregularity in order to make it difficult to read confidential information and prevent its counterfeiting. Specifically, the center line surface roughness Ra based on JIS B0601-1994 is 1.0 or more. The larger the centerline surface roughness, the more difficult it is to read and counterfeit, but it is also difficult to reproduce confidential information. Therefore, the surface roughness Ra is preferably 10 or less.

  As such a board | substrate 11, what uses paper as a material can be illustrated, for example. Since some papers have various surface roughnesses, those having appropriate surface roughnesses may be selected and used from these various paper materials. The selection can be easily performed based on JIS B0601-1994.

  Various products can be used as the substrate 11 made of this paper. For example, this paper product itself requires a counterfeit prevention function, such as banknotes, securities such as checks and gift certificates, various certificates such as bankbooks, passports, and the like. Moreover, the case where the substrate 11 is used as a packaging material and the contents packaged by the packaging material requires a forgery prevention function can be suitably used.

  Next, the information holding layer 12 proves the authenticity of the substrate 1 by the confidential information held. When the substrate 11 is a bill, a securities, various certificates, etc., the authenticity of the substrate 11 itself can be proved by the presence of confidential information, otherwise it can be determined to be counterfeit. Moreover, when the board | substrate 11 is a packaging material, the authenticity of the content packaged with this board | substrate (packaging material) 11 can be discriminate | determined.

  This secret information cannot be read with the naked eye but can be read using a specific detection device, and is held in the information holding layer 12 in the following manner.

  That is, the information holding layer 12 includes at least a light reflecting layer 124. As will be described later, the light reflecting layer 124 has a concavo-convex shape, and the concavo-convex forms a reflective diffraction grating, and the direction of the reflected diffracted light is all or part of the secret information. In addition, the unevenness of the light reflecting layer 124 reflects the random unevenness of the surface of the substrate 11, and thus the unevenness constituting the diffraction grating and the unevenness of the surface of the substrate 11 are superimposed to make it difficult to reproduce the secret information. Yes. The information recording medium shown in FIG. 1 includes an adhesive layer 125 that adheres the light reflecting layer 124 to the substrate 11. In this manner, another layer is interposed between the substrate 11 and the light reflecting layer 124. Even in this case, the intervening layer must be capable of reflecting the unevenness of the surface of the substrate 11 to the unevenness of the light reflecting layer 124. In FIG. 1, reference numeral 123 denotes a protective layer that protects the light reflecting layer 124 from scratches and dirt.

  As shown in the perspective view of FIG. 2, the surface of the information holding layer 12 is divided into a number of regions, and diffraction grating elements 12a, 12b,. The diffraction grating elements 12a, 12b,... Are composed of the diffraction gratings, and at least some of the diffraction grating elements 12a among the many diffraction grating elements 12a, 12b,. Holding a part. The other diffraction grating elements 12x, 12y,... Are dummy and do not hold confidential information. The dummy diffraction grating elements 12x, 12y,... Are mixed to conceal the presence and position of the diffraction grating element 12a that holds confidential information. In addition, when each of these many diffraction grating elements 12a, 12b,... Including the dummy diffraction grating elements 12x, 12y,. It is possible to display a beautiful visible image that changes, and to conceal confidential information in this beautiful visible image, and to make it more difficult to find its presence and position. Further, the size of the diffraction grating elements 12a, 12b,... May be arbitrary, but it is desirable that the diffraction grating elements 12a, 12b,. If it does not reach 1 mm, the secret information may not be clearly read with the naked eye.

  Then, the diffraction grating element 12a that holds the confidential information is irradiated with irradiation light from the specific light source 2, and the direction of the reflected diffraction light generated in response thereto is detected to read the presence and content of the confidential information. Can do. As the light source 2, it is necessary to use a surface light source having an illumination light angle range θ of 5 degrees or more as shown in FIG. Note that the illumination light angle range θ here is L for the line connecting the end of the surface light source and the center of the diffraction grating element 12a having the secret information, and the end of the surface light source on the opposite side and the secret information. The line connecting the center of the diffraction grating element 12a is M, and the angle between L and M is defined as M. In FIG. 3, the normal line set at the center of the diffraction grating element 12a is taken as the z axis, and the x axis and the y axis perpendicular to each other in the plane including the diffraction grating element 12a are taken. When the surface light source is projected onto the zx plane including the axis, the lines connecting both ends of the projected figure and the center of the diffraction grating element 12a are L and M, respectively. The L and M intersect at the center of the diffraction grating element 12a, and the intersecting angle is defined as an illumination light angle range θ. The same applies to the case where the surface light source 2 is projected onto a zy plane (a plane including the z axis and the y axis) orthogonal thereto.

As described above, random irregularities of the substrate 1 are superimposed on the irregularities of the light reflecting layer 124 constituting the diffraction grating, and the diffraction direction varies due to the irregularities of the substrate 11. For this reason, when a point light source or a surface light source with an illumination light angle range of less than 5 degrees is used as the light source, it is difficult to reliably detect the diffracted light. On the other hand, when a surface light source having an illumination light angle range of 5 degrees or more is used as a light source, the diffraction grating element 12a is irradiated with reading light from various directions, and the reflected diffraction light generated from the diffraction grating element 12a is also various. The light is emitted in the diffraction direction. For this reason, even if the diffraction grating of the diffraction grating element 12a is deformed reflecting the irregularities of the substrate, the reflected diffracted light reliably reaches the reading means, and can be read and decoded. For this reason, it is difficult to forge the information recording medium 1 with a point light source or the like, and on the other hand, the surface light source having an illumination light angle range of 5 degrees or more is used as a light source to reliably detect the diffracted light and reproduce the secret information. Is possible.

  The reflected diffracted light can be detected, for example, by arranging a photosensor at a predetermined position. It is also possible to place a projection screen at a predetermined position, emit the diffracted light onto the screen, and photograph the presence or absence of the light spot thus obtained with a camera or the like. It is also possible to collect the reflected diffracted light in the form of an image on the screen and capture the obtained image to read confidential information.

  It is also possible to provide a plurality of diffraction grating elements 12a, 12b,... That hold a part of the confidential information, and to configure the entire confidential information by the reflected diffracted light of the plurality of diffraction grating elements 12a, 12b,. Is possible. In this case, the secret diffraction information is detected by emitting the reflected diffracted light of the plurality of diffraction grating elements 12a, 12b,. Is possible. In FIG. 4, four diffraction grating elements 12a, 12b, 12c, and 12d are used as diffraction grating elements that hold a part of confidential information, and are emitted in response to irradiation light from the same surface light source 2. FIG. 5 is an explanatory diagram showing a method of irradiating the projected screen 3 with the four reflected diffracted lights and photographing the light spot with a camera 4 or the like. In the figure, reference numeral 5 denotes a determination means such as a CPU.

  The part of the confidential information is, for example, a signal such as “1” or “0” which is a part of the binary data. The whole of the confidential information is, for example, “1” or “0”. The information is composed of signals and has meaning.

  When the reflected diffracted light is focused on the screen 3 in the form of an image, a part of the image is reproduced with the reflected diffracted light of some of the diffraction grating elements 12a and the reflected diffraction of the other diffraction grating elements 12b. It is also possible to reproduce other parts of the image with light and read the confidential information as a whole. As an image, for example, a kanji character composed of hen and tsukuri can be exemplified, and as a part thereof, hen or tsukuri can be exemplified.

  Further, the secret information can be reproduced by irradiating each of the plurality of diffraction grating elements 12a, 12b,... With reading light from surface light sources arranged in different directions. That is, among the plurality of diffraction grating elements, some of the diffraction grating elements 12a and 12b are irradiated with light from a specific light source 21 to reproduce a part of the secret information, and are transmitted to the other diffraction grating elements 12c and 12d. On the other hand, light is emitted from a light source 22 arranged in a direction different from the specific light source 21 to reproduce a part of the confidential information. FIG. 5 is an explanatory diagram showing this state. The diffraction grating elements 12a and 12b are irradiated with reading light from the light source 21, while the diffraction grating elements 12c and 12d are irradiated with reading light from the light source 22 to reflect and diffract. It is generating light. Note that the reflected diffraction light from these diffraction grating elements 12 a, 12 b, 12 c, and 12 d is irradiated on the projection screen 3 and is photographed by the camera 4 through the lens 6. In the figure, reference numerals 71 and 72 denote switching means for switching between the light sources 21 and 22.

Next, a method for manufacturing the information recording medium according to the present invention will be described. The information recording medium according to the present invention can be manufactured by a known method in addition to the substrate 11 having a center line surface roughness Ra of 1.0 or more based on JIS B0601-1994. That is, first, a master is manufactured. In the master, a resist is applied on a base material, the resist layer is divided into a large number of regions, and diffraction grating irregularities are provided on the resist layer surface in each region. This unevenness is possible by the well-known two-beam interference method or electron beam drawing method. In the case of the two-beam interference method, it is necessary to use a photoresist as the resist, and in the case of the electron beam drawing method, it is necessary to use an EB resist. Since the unevenness constitutes a diffraction grating of the information recording medium, it is necessary to design the reflection diffraction direction in advance. And the process which reverses the unevenness | corrugation of the surface is repeated from the obtained original disk, and a practical version is manufactured. This practical version accurately reflects the unevenness of the master.

  On the other hand, a release layer and a protective layer are applied in this order on the transfer foil substrate. As the transfer foil substrate, for example, a plastic film such as a polyester film can be used. Moreover, a silicone resin can be used as a peeling layer. As the protective layer, a highly transparent resin is preferable. For example, an acrylic resin can be used.

  Then, the practical version is hot-pressed to transfer the surface irregularities to the protective layer surface. Next, a light reflecting layer is formed on the uneven surface. As the light reflecting layer, metals such as aluminum and copper can be used. It is also possible to use a transparent material having a refractive index different from that of the protective layer. Examples of such a transparent material include titanium oxide and zinc sulfide. These light reflecting layers are desirably provided by a vacuum film forming method such as vacuum deposition or sputtering. In addition, after providing a light reflection layer on the surface of the protective layer, it is also possible to transfer the unevenness by heat-pressing the practical plate on the surface of the light reflection layer.

  Next, an adhesive layer is applied to the surface of the light reflecting layer to obtain a transfer foil. Then, this transfer foil is overlaid on the substrate, the adhesive layer, the light reflection layer and the protective layer are transferred, and the transfer foil base material and the release layer are peeled off to obtain an information recording medium.

  The secret information detection apparatus according to the present invention can be manufactured by arranging and fixing a surface light source and a reading unit corresponding to the diffraction grating element of the information recording medium.

<Test Example 1>
A plastic film was used as a foil base material, a release layer and a protective layer were provided on the foil base material, and a practical plate separately produced on the protective layer was hot-pressed to transfer irregularities to the surface of the protective layer. The unevenness constitutes a vertical diffraction grating and a horizontal diffraction grating. The diffraction grating is a square having a length of 5 mm and a width of 5 mm. Next, aluminum was vacuum-deposited on this surface to provide a light reflecting layer, and an adhesive layer was further applied to produce a transfer foil.

  The transfer foil thus obtained was placed on a smooth substrate, and the adhesive layer, light reflecting layer and protective layer were transferred. Then, it was confirmed that the reading light was irradiated from a predetermined direction and the reflected diffracted light was emitted in the predetermined direction. The following test was performed with the reading light irradiation direction as the reference irradiation direction and the emission direction as the reference diffraction direction.

  That is, the transfer foil was stacked on a paper having a center line surface roughness Ra of 2.34 μm based on JIS B0601-1994, and the adhesive layer, the light reflecting layer, and the protective layer were transferred.

  The diffraction grating on the paper thus obtained was irradiated with reading light from a surface light source, and the diffraction direction of the reflected diffracted light was examined. That is, a surface light source was arranged in the reference reading direction, and a part of the surface light source was covered with a mask to change the area of the surface light source. And the illumination light angle range was computed from the area of this surface light source.

<Test Example 2>
The test was performed in the same manner as in Example 1 except that a substrate having a centerline surface roughness Ra of 1.48 was used.

<Test Example 3>
Example 1 except that a rectangular grating having a length of 2.5 mm and a width of 2.5 mm was used as the diffraction grating.
The test was conducted in the same manner as above.

<Test Example 4>
The test was performed in the same manner as in Example 3 except that a substrate having a centerline surface roughness Ra of 1.48 was used.

<Discussion>
The results of Test Examples 1 to 4 are shown in Table 1.

表１の結果から、回折格子の大きさが１ｍｍ×１ｍｍの場合について、回折光が観察できる照明光角度範囲を算出した。この結果、Ｒａ＝２．３４μｍの場合には１７．６度、Ｒａ＝１．４８μｍの場合には９．６度であることが分かった。

From the results in Table 1, the illumination light angle range in which the diffracted light can be observed was calculated when the size of the diffraction grating was 1 mm × 1 mm. As a result, it was found that when Ra = 2.34 μm, it was 17.6 degrees, and when Ra = 1.48 μm, it was 9.6 degrees.

  Next, based on this calculation result, an illumination light angle range in which the diffracted light can be observed was calculated for the case where the magnitude of diffraction is 1 mm × 1 mm and Ra = 1.0 μm. As a result, it was confirmed to be 5.1 degrees.

Sectional drawing of the information recording medium which concerns on embodiment of this invention. 1 is a perspective view of an information recording medium according to an embodiment of the present invention. Explanatory drawing explaining the confidential information reading method in embodiment of this invention. Explanatory drawing explaining the confidential information reading method in other embodiment of this invention. Explanatory drawing explaining the confidential information reading method in other embodiment of this invention. FIG. 6A is a cross-sectional view of a conventional transfer foil having confidential information. FIG. 6B is a perspective view thereof. FIG. 6C is a cross-sectional view of an information recording medium obtained by transfer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Information recording medium 11 ... Board | substrate 12 ... Information holding layer 124 ... Light reflection layers 12a, 12b, 12c, 12d ... Diffraction grating elements 12x, 12y holding secret information Dummy diffraction grating elements 2, 21, 22 ... Light source 3 Projection screen 3
4. Camera θ ... Illumination light angle range

Claims (5)

A substrate and an information holding layer laminated on the substrate, the information holding layer including a light reflecting layer;
The information holding layer surface is divided into a number of regions, and a diffraction grating element is disposed in each of the number of regions.
This diffraction grating element is composed of a diffraction grating provided in the form of irregularities on the surface of the light reflection layer, and the direction of the reflected diffraction light of at least some of the diffraction grating elements of this diffraction grating element is the secret information. In the information recording medium to be all or part of,
A center line surface roughness Ra based on JIS B0601-1994 on the surface of the substrate is 1.0 or more. There are a plurality of diffraction grating elements in which the direction of the reflected diffracted light is part of the confidential information,
3. The information recording medium according to claim 1, wherein all of the secret information is constituted by the whole reflected diffraction light of the plurality of diffraction grating elements. Among the plurality of diffraction grating elements, a specific diffraction grating element reproduces a part of the confidential information by irradiating light from a specific light source to the diffraction grating element,
The other diffraction grating element reproduces a part of the confidential information by irradiating light from a light source arranged in a direction different from the specific light source to the diffraction grating element. 2. The information recording medium according to 2.   The information recording medium according to claim 1, wherein the entire diffraction grating element represents a visible image. A substrate and an information holding layer laminated on the substrate, the information holding layer including a light reflecting layer;
The information holding layer surface is divided into a number of regions, and a diffraction grating element is disposed in each of the number of regions.
This diffraction grating element is composed of a diffraction grating provided in a concavo-convex shape on the surface of the light reflection layer, and at least some of the diffraction grating elements conceal the direction of the reflected diffraction light. An apparatus for detecting the confidential information from an information recording medium as all or part of information,
A light source for irradiating the information recording medium with light;
In the secret information detection device comprising the reading means for detecting the reflected diffracted light generated in response to the irradiation light from the light source,
The light source comprises a surface light source;
L is a line connecting the end of the surface light source and the center of the diffraction grating element having the secret information, and M is a line connecting the end of the surface light source on the opposite side and the center of the diffraction grating element having the secret information. , The secret information detection apparatus characterized in that the angle formed by L and M is 5 degrees or more.

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