JP2004021909A - Method for discriminating hidden pattern of optical diffraction structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a discriminating method for a hidden pattern which is highly effective in counterfeit prevention and cannot easily be discriminated by a visual means. <P>SOLUTION: In the method for discriminating a hidden pattern by using a discrimination pattern formed on the surface of a transparent film, the hidden pattern is a pattern of optical diffraction structure characterized in that the optical diffraction structure forming a design with a plane pattern, comprising a first pattern and a second pattern of fine striation of diffraction grating, incorporated in N pieces of plane pattern consisting of diffraction grating and forming a design is divided into reticula and the respective reticulum composes N+1 pixels in relation to the design, while the discrimination pattern is a pattern of striation parallelling the striation constituting the hidden pattern. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for determining a hidden pattern using a light diffraction structure that is difficult to determine in a normal visual recognition state.
[0002]
[Prior art]
2. Description of the Related Art In recent years, cases of counterfeiting of high-value bills and gift certificates with a color copier have frequently occurred.
For this reason, high-value bills and gift certificates incorporate small dots and fine lines, which cannot be read by a sensor of a color copier, in a pattern designed with the same reflection density in a part of the design. As a result, when trying to copy these high-value banknotes and gift certificates with a color copier, the scanner of the copier reads small dots and thin lines, and the portions are white and discriminated as copy products. .
[0003]
In addition, a method of discriminating a copy product by providing a shining metal portion in a part of the design of a printed material has been implemented.
Such a metal portion reflects 100% of the incident light, so that the copy machine reproduces the portion in black. As an embodiment, for example, a gold thread is sewn on a surface layer of paper to perform a copy check.
[0004]
In addition, a metal deposition process is performed on the uneven surface of the optical diffraction structure duplicated with a transparent resin, and thermal transfer is performed to a part of a printing area, thereby preventing copying by a copying machine. This light diffractive structure is used as a means for preventing counterfeiting of the thermally transferred printed material itself while trying to suppress fraud by copying by the reflection effect of the metal surface. Optical diffraction structures are often used as countermeasures against counterfeiting of vouchers due to the need for advanced manufacturing techniques.
However, with the improvement of the manufacturing technology, it has become possible to manufacture an optical diffraction structure that is close to the real thing at first glance.
In order to check for such counterfeit products, a technology has been disclosed in which a hidden pattern that is difficult to distinguish is incorporated in the light diffraction structure, and the authenticity is determined by the determination pattern formed on the determination tool. There is a problem that the pattern itself is slightly visually recognized depending on the viewing angle.
[0005]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION The present invention has been made in view of such a problem, and provides a method for determining a hidden pattern that has a large forgery prevention effect and is extremely difficult to visually recognize by a visual observation unit.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, there is provided a method for determining a hidden pattern by a light diffraction structure, the method comprising: determining a hidden pattern based on a determination pattern formed on a surface of a transparent film. And
The hidden pattern is composed of a diffraction grating, and has N face patterns forming a pattern,
In a light diffraction structure formed of fine stripes formed by a diffraction grating and incorporating a surface pattern composed of a first pattern and a second pattern to form a pattern, the light diffraction structure forming the pattern is divided into meshes. A pattern by an optical diffraction structure, wherein each mesh is composed of N + 1 pixels corresponding to the symbol,
The discrimination pattern is a striped pattern formed in parallel with the stripes forming the hidden pattern.
[0007]
According to a second aspect of the present invention, in the first aspect, the discrimination pattern is any one of a parallel line, a halftone dot, and a diffraction grating having the same pitch and the same line width as the stripes of the hidden pattern. , Photolithography, etching, printing, and transfer.
[0008]
According to a third aspect of the present invention, in the second aspect, the discrimination pattern by the diffraction grating is formed at the same diffraction angle and pitch as the stripes forming the hidden pattern. Things.
[0009]
According to a fourth aspect of the present invention, in the second aspect of the invention, the discrimination pattern based on the parallel lines and the halftone dots is characterized in that the colored portion is formed of a transparent material. .
[0010]
According to a fifth aspect of the present invention, in the second aspect of the present invention, in the discrimination pattern based on the parallel lines and the halftone dots, the width of the colored portion is formed so that the width of the transmission portion is narrower, and the colored portion is other than black. Characterized by being formed of the above material.
[0011]
According to a sixth aspect of the present invention, in the third aspect, the density of the stripes formed in the determination pattern is 5 stripes / mm or more.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a method of determining a hidden pattern by the light diffraction structure of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram for explaining a method of determining a hidden pattern by a light diffraction structure using a determination tool, and FIG. 2 is a diagram for explaining an example of a printed matter to which a light diffraction structure having a hidden pattern is transferred. FIG. 3 is an enlarged view of the hidden pattern partial region of FIG. 2, FIG. 4 is an explanatory diagram of various discriminating patterns, and FIG. 5 is an explanatory diagram of an example of a layer configuration based on a cross section of a discriminating tool for discriminating hidden patterns. 6, FIG. 6 is a diagram showing a discrimination pattern by holding a discrimination pattern over the hidden pattern shown in FIG. 2, FIG. 7 is a diagram for explaining a modification of FIG. 6, and FIG. 9 is a diagram in which the hidden pattern shown in FIG. 8 is determined, FIG. 10 is a diagram for explaining a set of two bands forming a pair, and FIG. To explain the density Figure 12 is a diagram for explaining an example of a diffraction grating formed in a band.
[0013]
Many anti-counterfeiting media using a light diffraction structure have a light diffraction structure including a hidden pattern formed at a predetermined position on a printed material in order to prevent counterfeiting or copying. The method of formation is such that an extremely thin resin having irregularities is blown to a predetermined size by heat and formed on a printed material such as paper by a heat-reactive adhesive.
Rarely, it is punched out to a predetermined size with the light diffraction structure formed on the base film, and is formed on a printed material with an adhesive or an adhesive together with the base film.
[0014]
Examples of printed matter that may not be forged or copied are banknotes, gift certificates, admission tickets, gift certificates, bills, checks, and the like.
These prints include a technique that cannot be duplicated without special techniques in the printing itself, and are double-protected against forgery and misuse by copying.
[0015]
In FIG. 1, the light diffraction structure 2 is formed on the surface of the printed material 3 via an adhesive 23.
The light diffractive structure 2 is formed on a base film and adhered to a printed material as it is, or only the light diffractive structure formed in a thin curtain shape of resin is transferred to the printed material by a thermal transfer method or the like. May have been.
When a hidden pattern discriminating tool (hereinafter referred to as a discriminating tool) 1 is approached at a predetermined angle with respect to a printed material 3 when discriminating a hidden pattern invisible to the optical diffraction structure, the hidden pattern is determined. It is displayed on the discriminator 1 in a moiré state. When the hidden pattern displayed on the discrimination tool 1 is a predetermined pattern, the printed matter is determined to be a legitimate product (genuine product) supplied from a correct supplier.
The discriminator uses a transparent material for the base material because the light applied to the light diffraction structure 2 of the printed matter must pass through the discriminator 1 and reach the "eyes" of the observer. Is done. Further, since the discriminating tool is frequently used, a tool in which a base material is fixed with a strong frame material is often used. This frame member has a handle or the like to prevent the transparent base material of the discrimination tool 1 from being stained with fingerprints or oil.
[0016]
When the hidden pattern is determined, the hidden pattern determination tool 1 is determined by approaching the printed pattern 3 on which the optical diffraction structure 2 is formed so as to be in close contact.
Although it is possible to determine the hidden pattern from the above-mentioned state of contact to a certain distance, it is not possible to determine that the distance between the light diffraction structure 2 and the discriminating tool 1 is too large due to the use of the moire phenomenon. It becomes difficult.
Further, since the hidden pattern of the light diffraction structure 2 and the light for generating the discrimination pattern by the discriminator 1 are incident on the discriminator 1 from the direction of the "eye" shown in FIG. It is preferable that the substrate to be transparent has a high degree of transparency, and a pattern is formed so that incident light is not obstructed by a discrimination pattern formed on the substrate.
[0017]
The hidden pattern will be described with reference to FIG. 2 and FIG.
In FIG. 2, when the lower end of the printed matter 3 is placed in a horizontal state and the hidden pattern partial area 4 in FIG. 2 is enlarged, pixels as shown in FIG. 3 are incorporated.
The light diffraction structure 2 shown in FIG. 2 includes a first surface pattern 5 partitioned into a symbol pattern and a second partial pattern 6.
The two partial regions are further formed of finely divided regions divided into a mesh shape. The pixels forming the mesh-shaped fine area are the second pattern 22 shown in FIG. 3 and the first pattern 21 on the background thereof.
[0018]
As shown in FIG. 2, when the pattern of the light diffraction structure is composed of only the first surface pattern 21 and the second surface pattern 22, the design is often a flat design such as a logo mark, and is visually observed. In this case, only the "star (second surface pattern 6)" of a uniform color, which is the logo mark, can be visually recognized.
The pattern used is not limited to an image or a logo mark, but may be a gradation or a simple pattern incorporated as a background.
[0019]
As shown in FIG. 3, the first pattern 21 and the second pattern 22 that constitute the second surface pattern 6 are constituted by a plurality of fine stripes formed by a diffraction grating, and An angle 11 formed by stripes constituting the first pattern is 45 degrees with respect to a line (hereinafter, referred to as a horizontal line) 13 parallel to a line connecting the left and right eyes, and the second pattern is a hidden pattern. Is formed so that the angle 12 formed by the pattern of FIG.
With respect to the horizontal line 13, the angle 11 formed by the stripes forming the first pattern is 45 degrees, and the angle 12 formed by the second pattern is 135 degrees, but the angle between the first pattern and the second pattern is Alternatively, the angle 11 formed by the stripes forming the first pattern may be set to 135 degrees, and the angle 12 formed by the second pattern may be set to 45 degrees.
The hiding effect does not change even if the angles of 45 degrees and 135 degrees change by about ± 5 degrees.
[0020]
In the above description, it can be seen that the first pattern 21 and the second pattern 22 are incorporated so that the stripes constituting each become 90 degrees, but include the allowable angle at which the hiding effect does not change. In this case, it can be seen that it is sufficient to incorporate the device within a range of 90 degrees plus or minus 10 degrees.
In the embodiment shown in FIG. 3, an alphabet "H" is incorporated as a second pattern 22 as a hidden pattern.
The second pattern 22 is incorporated so as to be indistinguishable in a normal visual recognition state, and cannot be confirmed without a special confirmation pattern. Thus, the second pattern 22, the hidden pattern, is incorporated into the first pattern 21 in a state that is extremely difficult to duplicate.
[0021]
In the case where the hidden pattern is used in a practical state, if the second surface pattern 6 is incorporated into the simple first surface pattern 5 as shown in FIG. Therefore, in some cases, a design such as a hologram is provided as a partial region in the entire region, the region of the first pattern 21 is provided in a harmonized form, and the second pattern 22 is incorporated.
[0022]
Although not shown, the second pattern may be bordered by a stripe having a period shifted by a half period from the period of the stripes forming the pattern. When the second pattern is determined by the edging, there is an effect of making it easy to determine.
[0023]
One embodiment of various discrimination patterns will be described with reference to FIG.
The discrimination patterns a, b, c, and d shown in FIG. 4 formed on the surface of the transparent base material are brought close to the surface of the hidden pattern to generate a discriminated image based on the hidden pattern.
FIG. 4A shows a discrimination pattern based on a line having a stripe angle 15 of 45 degrees with respect to the horizontal line. The lines are connected by a pair of a transparent band and a colored band. The width of the transparent band and the width of the colored band may be the same or different.
As described above, the light for discriminating the hidden pattern is the light transmitted through the discriminator, so that the width of the colored band formed on the discriminator is smaller than the width of the transparent band, so that more light is emitted. Get in. When the discrimination pattern is formed by printing or etching, a bright material, a transparent dye, or a transparent material can be used for the colored portion.
[0024]
FIG. 4B shows a discrimination pattern based on a line having a stripe angle 16 of 135 degrees with respect to the horizontal line. The content of the determination pattern conforms to FIG.
[0025]
FIG. 4C is a discrimination pattern using a diffraction grating in which the fringe angle 17 is 45 degrees with respect to the horizontal line. The pattern formation by the diffraction grating will be described in detail with reference to FIGS. 10, 11, and 12.
[0026]
FIG. 4D shows a discrimination pattern based on a halftone dot having a stripe angle 18 of 135 degrees with respect to the horizontal line.
A halftone dot is composed of a point where a transparent part and a colored part are independent, or a point where two parts are connected in a chain, and a (chain) line connecting the transparent parts and a colored part. The (chain-like) lines connecting the parts are formed in pairs. The paired bands are formed at an angle of 135 degrees. Regarding the configuration of the halftone dots and the transparent portion, it conforms to FIG.
[0027]
FIG. 5 is a cross-sectional view of the discriminator in which the discrimination pattern of FIG. 4C is formed along the band on which the diffraction grating is formed.
The discriminator has a transparent adhesive layer 102 and a light diffraction structure layer 101 formed on the surface of a transparent substrate 103 made of a synthetic resin or the like. A transparent reflection layer may be provided on the adhesive side of the light diffraction structure layer 101. A protective layer is provided on the outermost surface of the light diffraction structure layer 101 to protect the light diffraction structure from abrasion.
The transparent substrate 103 is made of a plastic such as polyethylene terephthalate (hereinafter, referred to as polyester) having a thickness of 100 to 250 μm, acrylic, or the like, and is previously formed of an acrylic resin via a vinyl acetate-based or acrylic-based thermoplastic adhesive (102). The light diffraction structure coated with the resin protective layer 100 is transferred by heat.
As another manufacturing method, the light diffraction structure can be formed of a resin such as acrylic on the surface of polyester treated with an adhesive by the matrix of the light diffraction structure. Also in this case, a protective layer is provided on the outermost surface.
[0028]
A method of determining a hidden pattern by the light diffraction structure using the determination tool will be described with reference to FIGS. 6, 7, 8, and 9. The discrimination pattern used here uses the pattern shown in FIG.
FIG. 6 shows the alignment of the bottom of the discrimination pattern shown in FIG. 4A with the horizontal line 13 of the light diffraction structure composed of the first pattern 21 and the second pattern (hidden pattern) 22 shown in FIG. 7 shows an image (discrimination pattern) displayed on the discrimination tool when the discrimination tool is brought into close contact with the surface of the light diffraction structure.
In the state shown in FIG. 2, the hidden pattern “H” that could not be determined clearly appears.
[0029]
When the discriminating tool described with reference to FIG. 6 is moved along the horizontal line of the printed matter on which the optical structure is formed, a deformation pattern due to moire as shown in FIG. 7 appears. Returns to the discrimination pattern as shown in FIG.
[0030]
In FIGS. 6 and 7, the hidden pattern (22) of the alphabet "H" is determined. In FIGS. 8 and 9, the hidden pattern (32) of the kanji character "Shinsei" is determined.
As shown in FIG. 8, a second pattern 32 is incorporated as a hidden pattern in the first pattern 31. In the state shown in FIG. 8, the first pattern 32 cannot be distinguished, but the second pattern 32 can be distinguished only by using the decision pattern by the decision tool.
[0031]
Next, an example in which the discrimination pattern formed on the discrimination tool is a fringe by a diffraction grating will be described with reference to FIG.
The stripes (a pair of bands) 230 are formed by connecting two bands of a band 210 on which an optical diffraction structure is formed and a band 220 on which a light diffraction structure having a different diffraction angle or pitch is formed with respect to the band 220. It is configured in the state where it was done. The stripes are displayed as rising to the left as the band 210, which indicates that the diffraction grating forming the light diffraction structure is formed at an angle to the left with respect to the length direction of the band.
Further, the band 220 indicates that the stripe is displayed to the right ascending, but the diffraction grating forming the optical diffraction structure is formed to the right ascending with respect to the length direction of the band.
[0032]
As described above, the two bands formed by the diffraction grating at different diffraction angles or pitches form a pair to form stripes, thereby forming the first pattern and the second pattern.
As shown in FIG. 11, the density of the strips constituting the above-mentioned stripes should be 5 or more per 1 mm as shown in FIG. The preference has been found in the inventors' experiments.
The upper limit is related to the width and length of the pits constituting the diffraction grating, and is not particularly limited by the inventor.
[0033]
Referring to FIG. 12, fringes formed by the diffraction grating will be described.
FIG. 12 is an enlarged view of the portion A of the band 210 constituting the stripe, and a plurality of structural units 2100 of the diffraction grating are formed inside the band 210.
These constituent units 2100 are regularly arranged in one band at the same diffraction angle and the same pitch.
For example, the band 210 and the band 220 are arranged at an angle α (14) with respect to the length direction of the band even if the pitch of the constituent units of the formed diffraction grating is the same. In contrast, the strips 220 are arranged at an angle β (not shown) with respect to the length direction of the strip.
[0034]
As described above, when changing the characteristics of a pair of bands, there are a method of changing the formation angle (diffraction angle) of the structural unit 2100 with respect to the band 210 and the band 220 and a method of changing the pitch.
For example, even if the diffraction grating formed in the band 220 has the same angle as the diffraction angle of the band 210 shown in FIG. 12, the number of pits formed for a certain length is changed to be different from the band 210. The hiding effect of the second pattern can also be enhanced by connecting the belt 210 and the belt 220.
As an example of setting the pitch of the structural units of the diffraction grating or the diffraction angle, for example, with respect to the band 210, the pitch of the structural units 2100 is a, and the diffraction angle is α. On the other hand, for the band 220, the pitch of the constituent units 2100 is b, and the diffraction angle is α.
Conversely, with respect to the band 210, the pitch of the constituent units 2100 is a, and the diffraction angle is α. On the other hand, for the band 220, the pitch of the constituent units 2100 is a, and the diffraction angle is β.
When the fringe is formed by changing the two elements of the diffraction angle and the pitch of the diffraction grating, one of the elements is made the same and the other element is changed.
An equivalent effect can be obtained by a combination in which two elements are respectively changed.
[0035]
Stripes are formed by the bands on which the diffraction grating is formed in this manner, and a first pattern and a second pattern are formed by an aggregate of the stripes, and the stripes of the first and second patterns intersect at right angles. Incorporating the two, making the color reflected from each stripe different, making the hidden pattern composed of the light diffraction structure a hidden pattern that is difficult to distinguish with ordinary visual means, and using a special distinguishing pattern Only clear distinction becomes possible.
[0036]
(Example)
An example of forming a discrimination pattern by a diffractive structure on the surface of a transparent polyester will be described.
A thin metal-deposited glass plate is irradiated with an electron beam having a diameter of 6 μm to form a diffraction grating structural unit having a size of 12 × 24 μm at an angle of 45 ° with respect to one cut surface of the glass.
The formation density of the structural units by the diffraction grating was 2 rows / band, and the units were formed at a pitch of 12 μm in the vertical direction of the band. In the band on the side of connection, the diffraction angle was changed, and two bands were formed alternately. As a result, the stripe density was set to 7 stripes / mm.
In this way, a discriminating pattern on a 45-degree line was prepared to prepare an original plate.
On the other hand, irregularities are reproduced on the surface of a transparent acrylic resin previously applied on a transparent polyester base film having a thickness of 150 μm by a duplicate printing of a discrimination pattern by the light diffraction structure prepared from the above-described original. An optical diffraction structure was produced. A protective layer was applied to the transparent resin on the base film on which the optical diffraction structure was duplicated by coating, and cut into a predetermined size.
The frame was attached so that the cut discrimination pattern forming film was flat.
By placing the discriminator on the surface of the light diffraction structure in which the hidden pattern thermally transferred to the surface of the high-quality paper is incorporated, and visually recognizing the second pattern corresponding to the hidden pattern, the discrimination can be made by ordinary visual means. Hidden patterns could not be determined.
[0037]
【The invention's effect】
The following effects can be obtained by the method for determining a hidden pattern of an optical diffraction structure of the present invention.
1) According to the first aspect of the present invention, a hidden pattern composed of fine stripes, which is difficult to distinguish, is hidden by forming a stripe pattern parallel to the stripes of the hidden pattern on a transparent base material and confirming it. The pattern can be easily determined.
2) As in the invention according to claim 2, any one of a parallel line, a halftone dot, and a diffraction grating having the same pitch and the same line width as the hidden pattern as the discrimination pattern is any one of photoengraving, etching, printing, and transfer. By using the method described above, an inexpensive and highly accurate discriminating tool can be provided.
3) As in the third aspect of the invention, the discrimination pattern is formed by a diffraction grating and has the same diffraction angle and pitch as the stripes constituting the hidden pattern, thereby preventing forgery of the discriminating tool and preventing the hidden pattern from being forged. The distinction can be made more clearly.
4) As described in the fourth and fifth aspects of the present invention, the colored portion is made of a transmissive material, so that a material other than black is used for the colored portion, and the width of the colored portion is made smaller than the width of the transmissive portion. This makes it possible to determine the hidden pattern in a bright state.
5) As in the invention according to claim 6, by setting the number of stripes in which two bands are connected to each other to be 5 lines / mm or more, the thickness of one band by the diffraction grating constituting the stripes is 100 μm. Even if the color of each stripe is differentiated by the invention according to claim 2, since the thickness of each stripe is fine, it looks like a uniform diffraction image in a normal visual recognition state. The existence of the discrimination pattern can be made more difficult.
[Brief description of the drawings]
FIG. 1 is a view for explaining a method of determining a hidden pattern by a light diffraction structure using a determination tool. FIG. 2 is a view for explaining an example of a printed matter on which a light diffraction structure having a hidden pattern is transferred. FIG. 3 is an enlarged view of a hidden pattern partial area in FIG. 2; FIG. 4 is an explanatory view of various discrimination patterns; FIG. 6 is a diagram in which a hidden pattern is discriminated by holding the discrimination pattern over the hidden pattern shown in FIG. 2 [FIG. 7] A diagram for explaining a modification of FIG. 6 [FIG. FIG. 9 is a diagram in which the hidden pattern shown in FIG. 8 is discriminated. FIG. 10 is a diagram for explaining an aggregate of two pairs of bands. FIG. 11 is a diagram for explaining the density of stripes. FIG. 12 It is a diagram for explaining an example of forming diffraction grating.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Hidden pattern discriminator 2 Optical diffraction structure 3 Printed matter 4 Hidden pattern partial area 5 First surface pattern 6 Second surface pattern 11 First pattern installation angle 12 Second pattern installation angle 13 Left and right of visual recognition means A line parallel to the line connecting the eyes (horizontal line)
14 Line indicating the diffraction grating formation angle (α) 10.5 Angle of the discrimination pattern with the horizontal line (45 degrees)
Angle between the discrimination pattern of 160,000 lines and the horizontal line (135 degrees)
17 Angle (45 degrees) between the fringe discrimination pattern by the diffraction grating and the horizontal line
18 Angle formed by the halftone dot discrimination pattern with the horizontal line (135 degrees)
21, 31 First pattern 22, 32 Second pattern 100 Protective layer 101 Optical diffraction structure, hidden pattern 102 Adhesive layer 103 Transparent base material 210, 220 Band 230 One pair of bands (stripe)
2100 Constituent units a, b, c, d of diffraction grating Various discrimination patterns

Claims (6)

A method of determining a hidden pattern by a determination pattern formed on the surface of a transparent film,
The hidden pattern is composed of a diffraction grating, and a pattern is formed by incorporating a first pattern and a second pattern formed of fine stripes by the diffraction grating into N surface patterns forming a design. In the light diffraction structure to be formed, the light diffraction structure forming the pattern is divided into meshes, and each mesh is constituted by N + 1 pixels corresponding to the pattern. ,
The method for determining a hidden pattern using a light diffraction structure, wherein the determination pattern is a stripe pattern formed in parallel with the stripes forming the hidden pattern. In the discrimination pattern, any one of a line, a halftone dot, and a diffraction grating having the same pitch and the same line width as the stripes of the hidden pattern is formed by any one of photoengraving, etching, printing, and transfer. 2. The method according to claim 1, wherein the hidden pattern is determined by the light diffraction structure. 3. The method according to claim 2, wherein the discrimination pattern based on the diffraction grating is formed at the same diffraction angle and pitch as the stripes forming the hidden pattern. 3. The method according to claim 2, wherein a colored portion of the discrimination pattern based on the parallel lines and the halftone dots is formed of a transmissive material. 3. The light according to claim 2, wherein in the discrimination pattern based on the parallel lines and the halftone dots, the width of the colored portion is formed to be narrower than that of the transmission portion, and the colored portion is formed of a material other than black. Hidden pattern discrimination method by diffraction structure. 4. The method according to claim 3, wherein the density of the stripes formed in the discrimination pattern is 5 stripes / mm or more.

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