JP2017062506A - Diffraction grating recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diffraction grating recording medium having high forgery preventing property and higher reliability from viewpoint of security.SOLUTION: A diffraction grating recording medium 3 includes: a first recording part 31 that includes a first unit cell 11a for an observation image having a first light-diffracting structure for an observation image and a second unit cell 12a for an observation image having a second light-diffracting structure for an observation image; and a second recording part that includes a first unit cell 2R for a hidden image having a first light-diffracting structure for a hidden image, a second unit cell 2G for a hidden image having a second light-diffracting structure for a hidden image, and a third unit cell 2B for a hidden image having a third light-diffracting structure for a hidden image. A grating pitch of the first unit cell 11a for an observation image and of the second unit cell 12a for an observation image is equal to or greater than a wavelength of visible light; and a grating pitch of the first unit cell 2R for a hidden image, a grating pitch of the second unit cell 2G for a hidden image, and a grating pitch of the third unit cell 2B for a hidden image are equal to or less than a wavelength of visible light.SELECTED DRAWING: Figure 10

Description

  The present invention relates to a diffraction grating recording medium that prevents forgery of an article by being attached or transferred to the article or the like.

  Conventionally, various anti-counterfeiting measures have been taken for goods that require anti-counterfeiting as well as authentication such as cards such as cash cards, credit cards, check cards, cash vouchers, identification cards, important documents, etc. ing. For example, in a credit card, a rainbow hologram composed of a relief hologram having a metal reflection layer is provided on the surface of the card as an authentication structure for visually checking the authenticity of the card. Such a hologram recording apparatus is disclosed in Patent Document 1.

Japanese Patent Publication No. 60-30948 Japanese Patent Laid-Open No. 2004-212927

  However, a diffraction grating such as a hologram having a relatively coarse grating pitch can be produced relatively easily by two-beam interference or the dot matrix method. Therefore, there is a possibility that a diffraction grating having a level similar to that at first glance may be easily produced.

  The present invention provides a diffraction grating recording medium having high anti-counterfeiting properties and higher security and reliability.

  The diffraction grating recording medium of the present invention that achieves the above object includes a first observation image unit cell having a first observation image light diffraction structure and a second observation image having a second observation image light diffraction structure. A first recording portion including a unit cell, a first hidden image unit cell having a first hidden image light diffraction structure, and a second hidden image unit having a second hidden image light diffraction structure. A second recording portion including a cell and a second recording portion including a third hidden image unit cell having a third hidden image light diffraction structure, and the first observation image unit cell. And the lattice pitch of the second observation image unit cell is not less than the wavelength of visible light, the lattice pitch of the first hidden image unit cell, the lattice pitch of the second hidden image unit cell, and The lattice pitch of the third hidden image unit cell is a wave of visible light. Characterized in that it is less.

  The grating pitch of the first hidden image unit cell is formed so that the wavelength of the first-order diffracted light is a wavelength corresponding to red, and the grating pitch of the second hidden image unit cell is the first-order diffraction The wavelength of light is formed so as to be a wavelength corresponding to green, and the grating pitch of the third hidden image unit cell is formed so that the wavelength of the first-order diffracted light is a wavelength corresponding to blue. Features.

  Further, the first hidden image unit cell, the second hidden image unit cell, and the third hidden image unit cell are arbitrarily uniformly formed at the same ratio, and It has an area corresponding to the luminance ratio of the color of the unit cell.

  Further, the second recording portion is smaller than the first recording portion and is formed in a straight line parallel to the first recording portion.

  According to the present invention, it is possible to provide a diffraction grating recording medium having high anti-counterfeiting properties and higher security.

It is a figure which shows the image data of the original image of 1st Embodiment. It is a figure which shows the unit cell of each part of the image data of 1st Embodiment. It is a figure which shows the image data of the color hidden image of 1st Embodiment. It is a figure which shows the unit cell of each color of the color hidden image of 1st Embodiment. It is a figure which shows the relationship between the light source with respect to a diffraction grating, and an observer. It is a figure which shows the 1st observation state of the light source with respect to a diffraction grating, and an observer. It is a figure which shows the light source with respect to a diffraction grating, and the 2nd observation state of an observer. It is a figure which shows the relationship of the brightness | luminance of the unit cell of each color of the arbitrary parts of the color hidden image of 1st Embodiment. It is a figure which shows the relationship of the unit cell area of each color of the arbitrary parts of the color hidden image of 1st Embodiment. It is a figure which shows the diffraction grating recording medium of 1st Embodiment. It is the figure which expanded the part of the area | region A of FIG. It is the figure which expanded the part of the area | region B of FIG. It is the figure which expanded the part of the area | region C of FIG. It is the figure which expanded the part of the area | region D of FIG. It is a figure which shows a part of diffraction grating recording medium of 2nd Embodiment. It is the figure which observed the hidden image of the diffraction grating recording medium of 1st Embodiment.

  The diffraction grating recording medium according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram illustrating image data of an original image 1 according to the first embodiment.

  The original image 1 of the first embodiment is a symbol produced as electronic information on a computer, and includes a first symbol portion 11, a second symbol portion 12, and a third symbol portion 13.

  FIG. 2 is a diagram illustrating a unit cell of each part of the image data according to the first embodiment.

  FIG. 2A shows a first observation image unit cell 11 a corresponding to the first symbol portion 11. The first observation image unit cell 11a corresponding to the first symbol portion 11 is formed with a lattice pitch of 1.0 μm and a lattice angle of 45 °. FIG. 2B shows a second observation image unit cell 12 a corresponding to the second symbol portion 12. The second observation image unit cell 12a corresponding to the second symbol portion 12 is formed with a lattice pitch of 1.0 μm and a lattice angle of 0 °. FIG. 2C shows a third observation image unit cell 13 a corresponding to the third symbol portion 13. The third observation image unit cell 13a corresponding to the third symbol portion 13 is formed with a lattice pitch of 1.0 μm and a lattice angle of 90 °.

  As shown in FIG. 1, the original image 1 has three types of parts, a first symbol part 11, a second symbol part 12, and a third symbol part 13 in the first embodiment. However, what is necessary is just to have the 1st symbol part 11 at least.

  FIG. 3 is a diagram illustrating image data of the color hidden image 2 according to the first embodiment.

  As shown in FIG. 3, the color hidden image 2 of the first embodiment is preferably a color image, figure, character, or the like that can be confirmed only under a predetermined viewing condition. The color hidden image 2 is embedded in the original image 1 shown in FIG. 1 so as not to impair the characteristics of the original image 1 and is different from the visible original image 1.

  FIG. 4 is a diagram illustrating a unit cell of each color of the color hidden image 2 according to the first embodiment.

  FIG. 4A shows a red unit cell 2R as a first hidden image unit cell constituting the red color of the color hidden image 2. FIG. FIG. 4B shows a green unit cell 2G as a second hidden image unit cell constituting the green color of the color hidden image 2. Further, FIG. 4C shows a blue unit cell 2B as a third hidden image unit cell constituting the blue color of the color hidden image 2.

  Next, the lattice pitch of the color unit cell for each color will be described.

  5 is a diagram showing the relationship between the light source L and the observer E with respect to the diffraction grating D, FIG. 6 is a diagram showing the case of the first observation state, and FIG. 7 is a diagram showing the case of the second observation state.

When the incident angle of the light L ₁ from the light source L with respect to the diffraction grating D is θ1, and the observer E observes the diffraction grating pattern by the diffraction grating D at the position of the diffraction angle θ2, when the diffraction order is n, Equation (1) holds.
λ = d (sin θ1 + sin θ2) / n (1)
here,
λ is the wavelength of the diffracted light,
d is the grating pitch of the diffraction grating,
θ1 is the incident angle,
θ2 is the diffraction angle,
n is the order of diffraction,
It is.

  In the present embodiment, as shown in FIG. 6, normally, a first observation state in which a human can easily observe the original image 1 and a second observation for confirming the color hidden image 2 as shown in FIG. Set the status.

In the first observation state, as shown in FIG. 6, the incident light L ₁ from the light source is incident on the diffraction grating D at an incident angle θ ₁ = 0 °. In this case, the first-order diffracted light at the portion of the diffraction grating D where the grating pitch d = 1 μm is diffracted as indicated by a solid line a ₁₁ when λ = 400 nm, and is diffracted as indicated by a broken line b ₁₁ when λ = 700 nm.

  Since the lattice pitch d of the first observation image unit cell 11a, the second observation image unit cell 12a, and the third observation image unit cell 13a shown in FIG. 2 is set to 1 μm, the observer If it is the range of 1st area | region (alpha), the original image 1 shown in FIG. 1 can be observed easily.

However, the first-order diffracted light in the portion of the diffraction grating D where the grating pitch d = 400 nm is diffracted as indicated by the solid line a ₂₁ when λ = 400 nm, and does not exist when λ = 700 nm, according to Equation (1). Since the lattice pitch d of the hidden image unit cell 2a shown in FIG. 4 is set to 400 nm, the observer observes the hidden image 2 shown in FIG. 3 in both cases of λ = 400 nm and λ = 700 nm. I can't.

In the second observation state, as shown in FIG. 7, the incident light L ₁ from the light source is incident on the diffraction grating D at an incident angle θ ₁ = 90 °. In this case, the first-order diffracted light at the portion of the diffraction grating D where the grating pitch d = 1 μm is diffracted as indicated by a solid line a ₁₁ when λ = 400 nm, and is diffracted as indicated by a broken line b ₁₁ when λ = 700 nm. Further, the second-order diffracted light at the grating pitch d = 1 μm of the diffraction grating D is diffracted as indicated by a solid line a ₁₂ when λ = 400 nm, and is diffracted as indicated by a broken line b ₁₂ when λ = 700 nm.

  Since the lattice pitch d of the first observation image unit cell 11a, the second observation image unit cell 12a, and the third observation image unit cell 13a shown in FIG. 2 is set to 1 μm, the observer If it is the range of 1st area | region (alpha) and 2nd area | region (beta), the original image 1 shown in FIG. 1 can be observed easily.

Next, the first-order diffracted light in the portion of the diffraction grating D where the grating pitch d = 400 nm is diffracted as indicated by a solid line a ₂₁ when λ = 400 nm, and is diffracted as indicated by a broken line b ₂₁ when λ = 700 nm. Since the lattice pitch d of the hidden image unit cell 2a shown in FIG. 4 is set to 400 nm, the observer can observe the hidden image 2 within the range of the third region γ. However, in practice, in the third b region γ ₂ that overlaps the second region β, it overlaps with the original image 1 shown in FIG. 1, and the hidden image 2 shown in FIG. 3 can hardly be observed. Therefore, the hidden image 2 shown in FIG. 3 can be observed in the 3a region γ ₁ .

In the case of the red unit cell 2R constituting the red color of the color hidden image 2, the grating pitch d _R may be set so that the wavelength λ of the first-order diffracted light is about 670 nm which is the red wavelength λ _R. In the second observation state shown in FIG. 7, in order to set the wavelength λ of the first-order diffracted light to about 670 nm which is the red wavelength λ _R , the grating pitch d _R of the red unit cell 2R is , 400 nm may be set. In general, the wavelength λ _R corresponding to red is 625 nm to 740 nm.

Next, in the case of the green unit cell 2G constituting the green color of the color hidden image 2, the grating pitch d _G may be set so that the wavelength λ of the first-order diffracted light is about 555 nm, which is the green wavelength λ _G. In the second observation state shown in FIG. 7, in order to set the wavelength λ of the first-order diffracted light to about 555 nm, which is the green wavelength λ _G , the lattice pitch d _G of the green unit cell 2G is , 330 nm may be set. In general, the wavelength λ _G corresponding to green is 500 nm to 565 nm.

Then, when the blue unit cell 2B constituting the blue color hidden image 2, may be set grating pitch d _B as the wavelength lambda of the primary diffracted light is about 454nm is a blue wavelength lambda _B. In the second observation state shown in FIG. 7, in order to make the wavelength lambda of the primary diffracted light at about 454nm is a blue wavelength lambda _B, from equation (1), the grating pitch d _B of the blue unit cell. 2B What is necessary is just to set with 270 nm. In general, the wavelength λ _B corresponding to blue is 450 nm to 485 nm.

Furthermore, 400 nm of the grating pitch d _R of the red unit cell 2R, when the grating pitch d _G of the green unit cell 2G 330 nm, and the grating pitch d _B of the blue unit cell 2B is set to 270 nm, from equation (1), first In this observation state, the wavelength λ of each first-order diffracted light is 280 nm or less, and visible light is not diffracted, so that it is difficult to observe.

  Furthermore, since the lattice pitch d of the first observation image unit cell 11a, the second observation image unit cell 12a, and the third observation image unit cell 13a that diffracts the original image 1 is set to 1 μm, From equation (1), in the second observation state, a diffraction image by the second-order diffracted light is generated. However, although the wavelength of the second-order diffracted light is 850 nm, since the light intensity of the second-order diffracted light is about several percent compared to the first-order diffracted light, the original image 1 by the second-order diffracted light is dark and difficult to observe.

  As described above, the hidden image cannot be observed in a normal observation state, but can be observed only when observed at a predetermined angle. Therefore, the anti-counterfeiting property is higher than the conventional technology, and the security is also reliable. It is possible to provide a higher diffraction grating recording medium.

  Further, the grating pitch of the red unit cell 2R is formed so that the wavelength of the first-order diffracted light is a wavelength corresponding to red, and the grating pitch of the green unit cell 2G is the wavelength corresponding to the wavelength of the first-order diffracted light is green. The grating pitch of the blue unit cell 2B is formed so that the wavelength of the first-order diffracted light is a wavelength corresponding to blue, so that the hidden image can be reproduced in color.

  Next, a method for obtaining the area of the color unit cell for each color of the color hidden image will be described.

  FIG. 8 is a diagram showing the luminance relationship of each color unit cell of an arbitrary portion of the color hidden image of the first embodiment, and FIG. 9 is an area of each color unit cell of an arbitrary portion of the color hidden image of the first embodiment. It is a figure which shows the relationship.

  The red unit cell 2R, the green unit cell 2G, and the blue unit cell 2B are uniformly formed at the same ratio in the color hidden image 2. The red unit cell 2R, the green unit cell 2G, and the blue unit cell 2B have an R value, G value, or B value corresponding to the color selected from the R value, G value, or B value of the color hidden image 2. It has an area corresponding to the luminance.

  For example, first, a red unit cell 2R, a green unit cell 2G, and a blue unit cell 2B, which are formed at an arbitrarily uniform ratio, are applied to each unit cell. Next, the luminance for each color of each unit cell of the color hidden image 2 is obtained.

  Next, the ratio of the luminance of the color applied to each unit cell with respect to the luminance maximum value 255 is obtained. For example, the green unit cell 2G in the upper left of FIG. 8 takes a value of G = 10 out of R = 10, G = 10, and B = 220, and is 10/255. Further, the blue unit cell 2B in the lower right of FIG. 8 takes a value of B = 220 out of R = 10, G = 10, and B = 220, and is 220/255.

  Next, as shown in FIG. 9, each unit cell is formed by determining the area of each unit cell in accordance with the obtained luminance ratio of the color applied to each unit cell. For example, since the green unit cell 2G in the upper left of FIG. 8 has a ratio of 10/255, as shown in the upper left of FIG. 9, the total area is 10/255. Further, since the blue unit cell 2B in the lower right in FIG. 8 has a ratio of 220/255, as shown in the lower right in FIG. 9, the total area is 220/255.

  Thus, the red unit cell 2R, the green unit cell 2G, and the blue unit cell 2B have areas according to the ratio of the luminance of the color applied to each unit cell with respect to the luminance maximum value 255 of the color hidden image 2. It is possible to reproduce a beautiful color hidden image like a photograph.

  FIG. 10 is a diagram showing the diffraction grating recording medium 3 of the first embodiment, and FIG. 11 is an enlarged view of a region A in FIG.

  As shown in FIG. 10, in the diffraction grating recording medium 3, the diffraction grating forming the color hidden image 2 shown in FIG. 3 is embedded in the diffraction grating forming the original image 1 shown in FIG. It is a medium recorded on

  The diffraction grating recording medium 3 divides the first recording portion 31 corresponding to the original image 1 shown in FIG. 1 and the second recording portion 32 corresponding to the color hidden image 2 shown in FIG. It is arranged. For example, as shown in FIG. 11, in this embodiment, the ratio of the first recording portion 31 and the second recording portion 32 in the diffraction grating recording medium 3 is set at an area ratio of 5: 1. The ratio of the first recording portion 31 and the second recording portion 32 is preferably about 5: 1 to 10: 1.

  Thus, since the second recording portion 32 is smaller than the first recording portion 31 and is formed in a straight line parallel to the first recording portion 31, the original image 1 in the first observation state. It is possible to make it easy to see the color hidden image 2 in the second observation state without impairing the reproduced image.

  Next, each part of the diffraction grating recording medium 3 will be described.

  FIG. 11 is an enlarged view of a region A in FIG.

  Region A is a portion corresponding to the first symbol portion 11 of the original image 1 that does not include the color hidden image 2. In the first recording portion 31 of the area A, a first observation image unit cell 11 a is formed in a portion corresponding to the first symbol portion 11 of the original image 1. Further, since the area A does not include the color hidden image 2, the second recording portion 32 of the area A is a blank cell 32S.

  Instead of the blank cell 32S, the first observation image unit cell 11a may be formed. When the blank cell 32S is formed, there is a possibility that the blank cell 32S portion looks like a boundary. However, by forming the first observation image unit cell 11a, a blank appears as a boundary. The possibility can be prevented. Further, it may be a diffraction grating cell having a pitch equal to or less than the wavelength of visible light and having a grating angle of about 90 ° with respect to the observation direction. In this case, there is no first-order diffracted light, but since the cell is not blank, the possibility of appearing as a boundary can be prevented.

  FIG. 12 is an enlarged view of a region B in FIG.

  Region B has both a portion corresponding to the first symbol portion 11 of the original image 1 including the color hidden image 2 and a portion corresponding to the first symbol portion 11 of the original image 1 not including the color hidden image 2. .

  In the first recording portion 31 of the region B, the first observation image unit cell 11a is formed in a portion corresponding to the first symbol portion 11 of the original image 1. In the second recording portion 32 including the color hidden image 2 in the region B, a red unit cell 2R, a green unit cell 2G, and a blue unit cell 2B are formed. Further, the second recording portion 32 that does not include the color hidden image 2 in the region B is a blank cell 32S.

  Instead of the blank cell 32S, the first observation image unit cell 11a may be formed. When the blank cell 32S is formed, there is a possibility that the blank cell 32S portion looks like a boundary. However, by forming the first observation image unit cell 11a, a blank appears as a boundary. The possibility can be prevented. Further, it may be a diffraction grating cell having a pitch equal to or less than the wavelength of visible light and having a grating angle of about 90 ° with respect to the observation direction. In this case, there is no first-order diffracted light, but since the cell is not blank, the possibility of appearing as a boundary can be prevented.

  FIG. 13 is an enlarged view of a region C in FIG.

  A region C includes a portion corresponding to the first symbol portion 11 of the original image 1 including the color hidden image 2, a portion corresponding to the second symbol portion 12 of the original image 1 including the color hidden image 2, and the color hidden image 2. And a portion corresponding to the first symbol portion 11 of the original image 1 not including the color hidden portion 2 and a portion corresponding to the second symbol portion 12 of the original image 1 not including the color hidden image 2.

  In the first recording portion 31 of the area C, a first observation image unit cell 11a is formed in a portion corresponding to the first symbol portion 11 of the original image 1, and the second symbol portion 12 of the original image 1 is formed. A second observation image unit cell 12a is formed in the portion corresponding to.

  Further, in the second recording portion 32 including the color hidden image 2 in the area C, a red unit cell 2R, a green unit cell 2G, and a blue unit cell 2B are formed. Further, the second recording portion 32 not including the color hidden image 2 in the area C is a blank cell 32S.

  Note that the first observation image unit cell 11a is formed in a portion corresponding to the first symbol portion 11 of the original image 1 and not the blank cell 32S, and corresponds to the second symbol portion 12 of the original image 1. A second observation image unit cell 12a may be formed in the portion. When the blank cell 32S is formed, there is a possibility that the blank cell 32S part looks like a boundary, but the first observation image unit cell 11a or the second observation image unit cell 12a is formed. Can prevent the possibility of seeing white space like a border. Further, it may be a diffraction grating cell having a pitch equal to or less than the wavelength of visible light and having a grating angle of about 90 ° with respect to the observation direction. In this case, there is no first-order diffracted light, but since the cell is not blank, the possibility of appearing as a boundary can be prevented.

  FIG. 14 is an enlarged view of a region D in FIG.

  A region D includes a portion corresponding to the second symbol portion 12 of the original image 1 including the color hidden image 2, a portion corresponding to the third symbol portion 13 of the original image 1 including the color hidden image 2, and the color hidden image 2. And a portion corresponding to the second symbol portion 12 of the original image 1 not including the color hidden image 2 and a portion corresponding to the third symbol portion 13 of the original image 1 not including the color hidden image 2.

  In the first recording portion 31 of the area D, the second observation image unit cell 12a is formed in the portion corresponding to the second symbol portion 12 of the original image 1, and the portion corresponding to the third symbol portion 13 The third observation image unit cell 13a is formed. Further, in the second recording portion 32 including the color hidden image 2 in the area C, a red unit cell 2R, a green unit cell 2G, and a blue unit cell 2B are formed. Further, the second recording portion 32 not including the color hidden image 2 in the area C is a blank cell 32S.

  Note that the second observation image unit cell 12a is formed in a portion corresponding to the second symbol portion 12 of the original image 1 without forming the blank cell 32S, and corresponds to the third symbol portion 13 of the original image 1. A third observation image unit cell 13a may be formed in the portion. When the blank cell 32S is formed, the portion of the blank cell 32S may look like a boundary, but the second observation image unit cell 12a or the third observation image unit cell 13a is formed. Can prevent the possibility of seeing white space like a border. Further, it may be a diffraction grating cell having a pitch equal to or less than the wavelength of visible light and having a grating angle of about 90 ° with respect to the observation direction. In this case, there is no first-order diffracted light, but since the cell is not blank, the possibility of appearing as a boundary can be prevented.

  FIG. 15 is a diagram illustrating the diffraction grating recording medium 3 according to the second embodiment.

  In the first embodiment, as shown in FIGS. 11 to 14, the second recording portion 32 on the straight line is formed in the first recording portion 31 in a horizontal arrangement, but as shown in FIG. 15, As a second embodiment, the first recording portion 31 may be formed by arranging the second recording portion 32 on a straight line inclined.

  FIG. 16 is a view obtained by observing a hidden image of the diffraction grating recording medium of the first embodiment.

  The case where the formed diffraction grating recording medium 3 is observed in the first observation state and the second observation state will be described.

  First, when the diffraction grating recording medium 3 is observed in the first observation state shown in FIG. 6, the observer can observe the original image 1 shown in FIG. In the first state, the color hidden image 2 cannot be observed.

  Next, when the diffraction grating recording medium 3 is observed in the second observation state shown in FIG. 7, the observer sees the bright color hidden image 2 in the dark original image 1 as shown in FIG. It is possible to observe as follows.

  Next, a method for using the diffraction grating recording medium 3 of the present embodiment will be described.

  Usually, as the diffraction grating recording medium 3 used by being attached to a printed material or the like, a reflection type diffraction grating is used in which a metal reflective film is provided by vapor deposition or the like on the relief surface or plane of a diffraction grating having an uneven relief structure. Other than that, a reflection type is provided by providing a metal reflection film on the back surface of an amplitude type diffraction grating whose amplitude changes periodically or a phase type diffraction grating whose refractive index changes periodically. You may use the diffraction grating, the volume type diffraction grating etc. which comprised the diffraction grating by the interference fringe in the volume type photosensitive material.

  Of course, it is possible to use a transmission type instead of a reflection type, and the diffraction grating may be a transmission type diffraction grating.

  The diffraction grating recording medium 3 can be configured in various forms such as a transfer foil, a label, and a film. In the case of a transfer foil form, it can be applied to, for example, gift certificates, credit cards, packages, etc., in the case of a label form, it can be applied to packages such as software, cartridges, pharmaceuticals, etc., and in the case of a film form, For example, the film can be micro-slit to a width of about 1 to 2 mm, and the sheet can be made into paper together to prevent forgery. In the case of the label form, a brittle layer is interposed in the layer structure, and when the label is peeled off for counterfeiting, the label is peeled off from the brittle layer and the display body is peeled off for counterfeiting. Can be difficult (brittle label).

  When the diffraction grating recording medium 3 including the hidden image 2 by the light diffraction structure of the present embodiment is configured in each form of a transfer foil, a label, a brittle label, and a film, It is the same as that described in 2nd grade.

  Although the diffraction grating recording medium has been described based on several embodiments, the present invention is not limited to these embodiments, and various modifications can be made.

DESCRIPTION OF SYMBOLS 1 ... Original image 11 ... 1st symbol part 11a ... 1st observation image unit cell 12 ... 2nd symbol part 12a ... 2nd observation image unit cell 13 ... 3rd symbol part 13a ... 3rd Observation image unit cell 2 ... Color hidden image 2R ... Red unit cell (first hidden image unit cell)
2G: Green unit cell (second hidden image unit cell)
2B: Blue unit cell (third hidden image unit cell)
3 ... Diffraction grating recording medium 31 ... First recording portion 32 ... Second recording portion

A first observation image unit cell having a first observation image light diffraction structure for forming an original image and a second observation image unit cell having a second observation image light diffraction structure for forming an original image; A first recording portion comprising:
A first hidden image unit cell having a first hidden image light diffraction structure for forming a hidden image; a second hidden image unit cell having a second hidden image light diffraction structure for forming a hidden image; And a second recording portion including a third hidden image unit cell having a third hidden image light diffraction structure for forming a hidden image, and embedded in the first recording portion;
With
The lattice pitch of the first observation image unit cell and the second observation image unit cell is not less than the wavelength of visible light,
The first hidden image for the unit cell of the lattice pitch, the grating pitch of the second hidden image for the unit cell, and the grating pitch of the third hidden image for the unit cell state, and are less than the wavelength visible light,
The second recording portion is smaller than the first recording portion and formed in a straight line parallel to the first recording portion;
Of the second recording portion, cells that do not form the hidden image other than the first hidden image unit cell, the second hidden image unit cell, and the third hidden image unit cell are: The first observation image unit cell, the second observation image unit cell, or a diffraction grating cell having a pitch less than the wavelength of visible light and having a grating angle different from the observation direction. Diffraction grating recording medium.

Claims (4)

A first recording portion including a first observation image unit cell having a first observation image light diffraction structure and a second observation image unit cell having a second observation image light diffraction structure;
A first hidden image unit cell having a first hidden image light diffraction structure, a second recording portion including a second hidden image unit cell having a second hidden image light diffraction structure, and a third A second recording portion comprising a third hidden image unit cell having a hidden image light diffraction structure;
With
The lattice pitch of the first observation image unit cell and the second observation image unit cell is not less than the wavelength of visible light,
The lattice pitch of the first hidden image unit cell, the lattice pitch of the second hidden image unit cell, and the lattice pitch of the third hidden image unit cell are less than or equal to the wavelength of visible light. A diffraction grating recording medium. The grating pitch of the first hidden image unit cell is formed such that the wavelength of the first-order diffracted light is a wavelength corresponding to red,
The grating pitch of the second hidden image unit cell is formed such that the wavelength of the first-order diffracted light is a wavelength corresponding to green,
2. The diffraction grating recording medium according to claim 1, wherein the grating pitch of the third hidden image unit cell is formed such that the wavelength of the first-order diffracted light is a wavelength corresponding to blue. The first hidden image unit cell, the second hidden image unit cell, and the third hidden image unit cell are:
3. The diffraction grating recording medium according to claim 2, wherein the diffraction grating recording medium is formed in an arbitrarily uniform ratio and has an area corresponding to the ratio of the luminance of the color of each unit cell to the maximum luminance value. The second recording portion is smaller than the first recording portion and formed in a straight line parallel to the first recording portion. The diffraction grating recording medium according to one.

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