JP2003344632A - Method for discriminating hidden pattern by optical diffraction structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a hidden pattern incorporated into an optical diffraction structure is faintly viewed dependent on the viewing angle, in checking the forged article by a confirmation pattern. <P>SOLUTION: In the method for discriminating the hidden pattern by a discrimination pattern formed on the surface of a transparent film, the hidden pattern is the pattern by the optical diffraction structure in which the total region formed by a grating is divided into a plurality of discriminable partial regions. At least one region of the plurality of partial regions is composed of two patterns which cannot be discriminated. Each of the two patterns is composed of fine stripes arranged parallel each other. The discrimination pattern is formed parallel to the stripes constituting either of the two patterns. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of discriminating a hidden pattern by a light diffractive structure which is difficult to discriminate in a normal visual state.

[0002]

2. Description of the Related Art In recent years, forgery cases of high-value bills and gift certificates by color copying machines have frequently occurred. For this reason, high-value banknotes and gift certificates have small dots and fine lines that cannot be read by the sensors of color copiers as part of the design.
It is incorporated in a design designed with the same reflection density. As a result, when trying to copy these high-value banknotes and gift certificates with a color copier, the scanner of the copier missed out small dots and fine lines, and the part was white, and it was determined that it was a copy product. .

In addition, a method of discriminating a copy product is also practiced by providing a glittering metal portion in a part of the design of the printed matter. Such a metal portion can reduce incident light to 10
The copy machine reproduces this part in black to reflect 0%. As an example, for example, gold thread is sewn on the surface layer of paper to perform copy check.

In addition, a metal vapor deposition process is performed on the uneven surface of the light diffractive structure duplicated with a transparent resin to thermally transfer it to a part of the printing area to prevent copying by a copying machine. This light diffractive structure is used as a means for preventing counterfeiting due to copying by the reflection effect of the metal surface, while preventing forgery of the heat-transferred printed matter itself. The light diffractive structure is often used as a means for preventing forgery of cash vouchers because it requires high manufacturing technology. However, improvements in manufacturing technology have made it possible to manufacture a light diffractive structure that is close to the real thing at first glance. In order to check such a counterfeit product, a technique is disclosed in which a hidden pattern that is difficult to discriminate is incorporated in the light diffractive structure, and the authenticity is discriminated by the discrimination pattern formed on the discriminating tool. There is a problem that the pattern itself is slightly visible depending on the viewing angle.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides a method for discriminating a hidden pattern which has a great effect of preventing forgery and is very difficult to discriminate visually by a visual means.

[0006]

In order to achieve the above object, the invention according to claim 1 of the method for discriminating a hidden pattern by the light diffractive structure of the present invention is formed on the surface of a transparent film. A method for discriminating a hidden pattern by a discrimination pattern, wherein the hidden pattern is divided into a plurality of partial regions in which the entire region formed by a diffraction grating can be discriminated, and in the partial region, at least one region Is composed of two patterns that cannot be distinguished, and the two patterns are patterns of an optical diffraction structure characterized by being composed of fine stripes arranged in parallel with each other. It is characterized in that it is a striped pattern formed in parallel with the strips that make up one of the two patterns.

The invention described in claim 2 is the same as claim 1
In the invention described in the above, the discriminating pattern is any one of lines, halftone dots, and diffraction gratings having the same pitch and the same line width as the stripes of the hidden pattern, any one of photoengraving, etching, printing, and transfer. It is characterized by being formed by.

The invention described in claim 3 is the same as that of claim 2.
In the invention described in (1), the discrimination pattern by the diffraction grating is formed at the same diffraction angle and pitch as the stripes forming the hidden pattern.

The invention according to claim 4 is the same as claim 2
In the invention described in (3), the discrimination pattern by lines and halftone dots is characterized in that the colored portion is formed of a transparent material.

The invention described in claim 5 is the same as claim 2
In the invention described in (1), the discrimination pattern by lines and halftone dots is characterized in that the width of the colored portion is formed narrower than the width of the transparent portion, and the colored portion is formed of a material other than black. is there.

The invention according to claim 6 is the same as claim 3
In the invention described in (3), the density of the stripes formed in the discrimination pattern is 5 stripes / mm or more.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A hidden pattern discriminating method according to the present invention will be described below with reference to the drawings. FIG. 1 is a diagram for explaining a method of discriminating a hidden pattern of a light diffraction structure using a discriminating tool, FIG.
5 is a diagram 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 the hidden pattern region of FIG. 2, FIG. 4 is an explanatory diagram of various determination patterns, and FIG. 6A and 6B are explanatory views of an example of a layer configuration by a cross section of a discriminating tool for discriminating a hidden pattern;
Is a diagram in which the hidden pattern is discriminated by holding the discriminating pattern over the hidden pattern shown in FIG. 2, FIG. 7 is a diagram for explaining the modification of FIG. 6, and FIG. 8 is a Chinese character for the hidden pattern. FIG. 9 is a diagram in which the hidden pattern shown in FIG. 8 is discriminated, FIG. 10 is a diagram for describing an assembly of two bands forming a pair, and FIG. 11 is a diagram illustrating stripe density. FIG. 12 and FIG. 12 are diagrams for explaining an example of the diffraction grating formed in the band.

In many of the anti-counterfeiting media using the light diffractive structure, a light diffractive structure containing a hidden pattern for restraining counterfeiting or copying is formed at a predetermined position of the printed matter. As a method of formation, an extremely thin resin having irregularities is fused by heat to a predetermined size and is formed on a printed matter such as paper with a heat-reactive adhesive. In rare cases, the light-diffractive structure is formed on the base film and punched out to a predetermined size, and is formed on a printed material together with the base film by an adhesive material or an adhesive.

[0014] Examples of printed matter that cannot be forged or copied include banknotes, gift certificates, admission tickets, gift certificates, bills, and checks. These printed materials include a method that cannot be duplicated unless they also have a special technique in printing itself, and are double protected against misuse by forgery and copying.

In FIG. 1, the light diffractive structure 2 is an adhesive 2.
It is formed on the surface of the printed matter 3 through 3. The light diffractive structure 2 is formed on the base film and is adhered to the printed matter as it is, or only the light diffractive structure formed in a resin thin curtain is transferred to the printed matter by a thermal transfer method or the like. It may have been. When discriminating a hidden pattern incorporated in the light diffractive structure invisible, when the hidden pattern discriminating tool (hereinafter referred to as discriminating tool) 1 is brought close to the printed matter 3 at a predetermined angle, the hidden pattern is formed. It is displayed on the discrimination tool 1 in a moire state. When the hidden pattern displayed on the discriminating tool 1 is a predetermined pattern, the printed matter is determined to be a legitimate product (genuine product) supplied from the correct supplier. The discriminator is such that the light applied to the hidden pattern (2) of the printed matter passes through the discriminator 1,
In order to reach the "eyes" of the observer, a discriminative pattern is formed on the transparent base substrate. Also,
Since the discriminating tool is frequently used, a discriminating tool in which the base material is fixed with a strong frame material is often used. The frame member has a handle or the like to prevent the transparent base material of the discriminating tool 1 from being soiled with fingerprints or oil.

When the hidden pattern is discriminated, the hidden pattern discriminating tool 1 is discriminated so as to come close to the printed matter 3 on which the light diffraction structure 2 is formed. The hidden pattern can be discriminated from the state of close contact to a certain distance, but since the moire phenomenon is used, the light diffraction structure 2
Therefore, it is difficult to determine that the distance of the discriminating tool 1 is too large. In addition, since the light that causes the hidden pattern (2) and the discriminant pattern to be generated by the discriminant tool 1 is light that is incident on the discriminant tool 1 from the direction of the "eyes" shown in FIG. Is preferably highly transparent, and a pattern is formed so that incident light is not blocked by the discrimination pattern formed on the base material.

In FIG. 2, the light diffraction structure 2 is formed on the lower right side of the printed matter 3. The light diffractive structure 2 is composed of a hidden pattern area 4 and other partial areas, and the hidden pattern area 4 is composed of a second pattern 22 and a first pattern 21 of the background thereof. In the case of banknotes, face images of historically renowned leaders and people of cultural merits, buildings that symbolize the country, ruins, etc. are designed in the central area.

In the embodiment of FIG. 2, the second pattern 2
2, the alphabet "H" is incorporated as a hidden pattern. The second pattern 22 is incorporated so as to be indistinguishable in a normal visual recognition state, and can be confirmed only by a special confirmation pattern. Therefore, the second pattern 22, the hidden pattern, is incorporated into the first pattern in a state that is extremely difficult to duplicate. When such a hidden pattern is used in a practical state, it is clear that the entire area is a counterfeit checking means when the second pattern 22 is incorporated into the simple first pattern 21 and used. In many cases, some design such as a hologram is provided as a partial region in the entire region, and the region of the first pattern 21 is provided in a form of harmony, and the second pattern 22 is incorporated.

The hidden pattern area 4 will be described with reference to FIG. In the present embodiment, the light diffraction structure 2 is composed of the first pattern 21 and the second pattern 22, and the second pattern 22 is incorporated as a hidden pattern in the first pattern 21. It is in a state. The second pattern 22 is incorporated so that it cannot be discriminated in a normal visual recognition state, and cannot be discriminated unless it is based on a special discrimination pattern. Therefore, the second pattern 22, i.e. the hidden pattern, is incorporated into the first pattern 21 in a state that is very difficult to duplicate.

The first pattern 21 and the second pattern 22 are composed of a plurality of fine stripes formed of a light diffraction structure. In FIG. 3, when the lower end of the printed matter 3 is placed in a horizontal state, the first pattern 21 corresponds to a line 13 parallel to a line connecting the left and right eyes of the observer (hereinafter referred to as a horizontal line). The angle 11 formed by the stripes constituting the pattern 21 is incorporated so as to be 45 degrees, and the second pattern 22 which is a hidden pattern is incorporated so as to be 135 degrees. 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 135 degrees, and the angle 12 formed by the second pattern may be 45 degrees. Also, 45
The hiding effect does not change even if the angle of 135 degrees changes by plus or minus 5 degrees.

In the above description, the first pattern 21 and the second pattern 21
It can be seen that the patterns 22 of No. 1 are incorporated so that the stripes forming each pattern are 90 degrees, but when the allowable angle that does not change the hiding effect is included, 90 degrees plus or minus 1
It turns out that it is sufficient to incorporate it within the range of 0 degree.

Although not shown, the second pattern may be bordered by stripes having a cycle shifted by a half cycle from the cycle of the stripes forming the pattern. The edging has an effect of facilitating discrimination when discriminating the second pattern.

An 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 discrimination image by the hidden pattern. FIG. 4a shows a fringe angle 1 with respect to the horizontal line.
Reference numeral 5 is a discrimination pattern based on lines of 45 degrees. The line is
A transparent strip and a colored strip are connected as a pair.
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 that has passed through the discriminating tool, so the width of the colored strip formed on the discriminating tool is made narrower than the width of the transparent strip,
Try to let in more light. Further, 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.

FIG. 4b shows the fringe angle 1 with respect to the horizontal.
6 is a discrimination pattern based on the 135-degree line. The content of the discrimination pattern conforms to that of FIG.

FIG. 4c shows the fringe angle 1 with respect to the horizontal.
Reference numeral 7 is a discrimination pattern by a 45-degree diffraction grating. Regarding the pattern formation by the diffraction grating, FIG. 10, FIG.
Details will be described in the description of FIG.

FIG. 4d shows the fringe angle 1 with respect to the horizontal.
Reference numeral 8 is a discrimination pattern based on halftone dots of 135 degrees. A halftone dot is composed of a transparent portion and a colored portion which are independent of each other, or a point where two portions are connected in a chain shape, and a line connecting the transparent portions (a chain shape) and a colored portion The (chain-like) lines connecting the parts are formed in pairs. This pair of bands is formed at an angle of 135 degrees. The configuration of the halftone dots and the transparent portion is based on the diagram a.

FIG. 5 is a cross-sectional view of the discriminating tool having the discriminating pattern shown in FIG. 4C, taken along the band in which the diffraction grating is formed. In the discriminating tool, a transparent adhesive layer 102 and a light diffraction structure layer 101 are formed on the surface of a transparent base material 103 made of synthetic resin or the like. Light diffraction structure layer 10
A transparent reflection layer may be provided on the adhesive 1 side. A protective layer is provided on the outermost surface of the light diffraction structure layer 101 to protect the light diffraction structure from abrasion. In addition, the transparent substrate 103
Is made of polyethylene terephthalate (hereinafter referred to as polyester) having a thickness of 100 to 250 μm, acrylic or other plastic, and the acrylic resin protective layer 100 is preliminarily provided via a vinyl acetate or acrylic thermoplastic adhesive (102). The coated light diffractive structure is thermally transferred. As another manufacturing method, the light diffractive structure may be molded with a resin such as acrylic on the surface of the polyester treated with the adhesive by the matrix of the light diffractive structure. Also in this case, a protective layer is provided on the outermost surface.

A method for discriminating the hidden pattern by the light diffractive structure with the discriminating tool will be described with reference to FIGS. 6, 7, 8 and 9. The discrimination pattern used here is shown in FIG.
The pattern shown in FIG. In FIG. 6, the bottom of the discrimination pattern of FIG. 4A is aligned 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. , Shows an image (discrimination pattern) displayed on the discriminating tool when the discriminating tool is brought into close contact with the surface of the light diffraction structure. In the state of FIG. 2, the hidden pattern “H” which cannot be discriminated clearly appears.

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 deformed pattern due to moire as shown in FIG. 7 appears. It returns to the discrimination pattern as shown in FIG. 6 in the pitch cycle.

In FIGS. 6 and 7, the hidden pattern (22) of the alphabet “H” is discriminated, but in FIG. 8 and FIG.
The hidden pattern (32) of kanji and "genuine" is determined. As shown in FIG. 8, the second pattern 32 is incorporated as a hidden pattern in the first pattern 31. In the state of FIG. 8, the first pattern 32 cannot be discriminated, but the second pattern 32 can be discriminated only by using the discrimination pattern by the discriminating tool.

Next, an example of the case where the discrimination pattern formed on the discriminating tool is a fringe formed by a diffraction grating will be described with reference to FIG. The stripes (a pair of bands) 230 are different from the band 210 in which the light diffraction structure is formed and the band 220 in which the light diffraction structure having a different diffraction angle or pitch is formed with respect to the band 220.
The two bands are connected to each other. Obi 21
The stripe is displayed as 0 to the left,
This indicates that the diffraction grating that constitutes the light diffraction structure is formed at an angle that rises to the left with respect to the band length direction. Further, in the band 220, although the stripes are displayed in a right upward direction, it means that the diffraction grating forming the light diffraction structure is formed in a right upward direction in the longitudinal direction of the band.

As described above, two bands formed by the diffraction grating with different diffraction angles or pitches form a pair to form a fringe, and a first pattern and a second pattern are formed. There is. In order to enhance the concealment effect, the density of the strips forming the stripes may be set to 5 or more in 1 mm, as shown in FIG. It was proved to be preferable by the inventor's experiment. The upper limit number is related to the width and length of the pits forming the diffraction grating and is not particularly limited by the inventor.

With reference to FIG. 12, the stripes formed by the diffraction grating will be described. When the section A of the band 210 forming the stripe is enlarged, it is as shown on the right side of FIG. 12, and a plurality of diffraction grating structural units 2100 are formed inside the band 210. These structural units 2100 are regularly arranged at the same diffraction angle and the same pitch for one band. For example, although the bands 210 and 220 have the same pitch of the constituent units of the formed diffraction grating, the bands 21 and 220 have the same pitch.
In the case of 0, the bands are arranged at an angle of α (14) with respect to the length direction of the band, whereas the bands 220 are arranged at an angle of β (not shown) with respect to the length direction of the band. Has been done.

As described above, when the characteristics of the pair of bands are changed, there are a method of changing the formation angle (diffraction angle) of the structural unit 2100 with respect to the bands 210 and 220, and a method of changing the pitch. For example, even if the diffraction grating formed in the band 220 has an angle similar to the diffraction angle of the band 210 shown in FIG. 12, the number of pits formed for a given length is changed,
The concealing effect of the second pattern can also be enhanced by making the band 210 different from the band 210 and connecting the band 210 and the band 220 to each other. As an example of setting the pitch of the structural units of the diffraction grating or the setting of 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 belt 220, the structural unit 210
The pitch of 0 is b, and the diffraction angle is α. On the contrary, 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 structural units 2100 is a and the diffraction angle is β. In this way, the diffraction angle of the diffraction grating and the pitch of 2
When one element is changed to form a stripe, one of the elements is made the same and the other element is changed. The same effect can be obtained by changing the two elements.

Stripes are formed by the band in which the diffraction grating is formed in this way, and the first pattern and the second pattern are formed by the aggregate of the stripes.
Hidden pattern composed of a light diffractive structure by making a pattern of the above, incorporating both the first pattern and the second pattern so that the stripes intersect at a right angle, and making a difference in the color reflected from each stripe. It is possible to make a clear distinction only by using a hidden pattern that is difficult to distinguish by a normal visual means and using a special distinguishing pattern.

(Example) An example of forming a discrimination pattern by a diffractive structure on the surface of transparent polyester will be described. A glass plate on which a thin metal has been vapor-deposited is irradiated with an electron beam having a diameter of 6 μm, and 45
A diffraction grating structure unit having a size of 12 × 24 μm is formed at an angle of degrees. The formation density of the structural unit by the diffraction grating is
Two rows / strips were formed with a pitch of 12 μm in the vertical direction of the strip. The band on the connecting side is formed by changing the diffraction angle, 2
Two bands are formed alternately, resulting in a stripe density of 7 stripes /
It was set to be mm. In this way, a discrimination pattern on a line having stripes of 45 degrees was prepared to prepare an original plate. On the other hand, 1
On a transparent acrylic resin surface pre-applied on a 50 μm thick transparent polyester base film,
The unevenness was reproduced by the duplication of the discrimination pattern by the light diffractive structure produced from the above-mentioned original plate, and the light diffractive structure was produced. The transparent resin on the base film on which the light-diffracting structure was duplicated was coated with a protective layer and cut into a predetermined size. The frame was attached so that the cut discrimination pattern forming film was in a flat state. Place the above-mentioned discriminating tool on the surface of the light diffractive structure in which the hidden pattern thermally transferred to the surface of the high-quality paper is placed, and the second pattern corresponding to the hidden pattern is visually recognized. It was possible to identify the hidden pattern that could not be obtained.

[0037]

The following effects can be obtained by the method of discriminating the hidden pattern of the light diffraction structure of the present invention. 1) As in the invention described in claim 1, for a hidden pattern that is formed of fine stripes and is difficult to distinguish, a hidden pattern is formed by forming a striped pattern parallel to the stripes of the hidden pattern on a transparent base material and concealing the hidden pattern. The pattern can be easily discriminated. 2) As in the invention according to claim 2, any one of lines, halftone dots and diffraction grating having the same pitch and the same line width as the hidden pattern as the discrimination pattern is any of photoengraving, etching, printing and transfer. Since it is formed by the above method, it is possible to provide an inexpensive and highly accurate discriminating tool. 3) As in the invention according to claim 3, the discrimination pattern is formed by a diffraction grating, and the discrimination pattern is formed with the same diffraction angle and pitch as the stripes forming the hidden pattern, whereby the discrimination tool is prevented from being counterfeited and the hidden pattern is formed. It can be distinguished more clearly. 4) As in the invention according to claims 4 and 5, by forming the colored portion with a transparent material, a material other than black is used for the colored portion, and the width of the colored portion is narrower than the width of the transparent portion. By doing so, it becomes possible to distinguish 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 5 or more, the thickness of one band by the diffraction grating forming the stripes is 100 μm.
Even if the respective stripes have different colors according to the invention described in claim 2, the stripes per one are fine, so that a uniform diffractive image appears in a normal visual state. The existence of the discrimination pattern can be made more difficult to discriminate.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a method of discriminating a hidden pattern formed by a light diffraction structure using a discriminating tool.

FIG. 2 is a diagram 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 the hidden pattern area in FIG.

FIG. 4 is an explanatory diagram of various discrimination patterns.

FIG. 5 is an explanatory diagram of an example of a layer configuration by a cross section of a discriminating tool for discriminating a hidden pattern.

FIG. 6 is a diagram in which a hidden pattern is discriminated by holding a discrimination pattern over the hidden pattern shown in FIG.

FIG. 7 is a diagram for explaining a modification of FIG.

FIG. 8 is an explanatory diagram when the hidden pattern is kanji.

9 is a diagram in which the hidden pattern shown in FIG. 8 is discriminated.

FIG. 10 is a diagram for explaining an assembly of two bands forming a pair.

FIG. 11 is a diagram for explaining the density of stripes.

FIG. 12 is a diagram for explaining an example of a diffraction grating formed in a band.

[Explanation of symbols]

1 Hidden Pattern Discriminating Tool 2 Light Diffraction Structure 3 Printed Material 4 Hidden Pattern Area 11 First Pattern Incorporating Angle 12 Second Pattern Incorporating Angle 13 Line (horizontal line) parallel to the line connecting the left and right eyes of the visual recognition means 14 Line that indicates the diffraction grating formation angle (α) 150,000 The angle formed by the discrimination pattern with the horizontal line (45
The angle formed by the 160,000 line discrimination pattern with the horizontal line (13
(5 degrees) 17 Angle formed by diffraction pattern of fringes with horizontal line (45 degrees) 18 Angle formed by discrimination pattern of halftone dots with horizontal line (13 degrees)
5 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 1 pair of bands (stripes) 2100 Diffraction Lattice structural units a, b, c, d Various discrimination patterns

Continued front page    F-term (reference) 2C005 HA04 HB09 HB10 JA12 JA18                       JA19 JB08 JB09 JB22 JB25                       KA40 KA48 KA51 KA57 LA14                       LA19 LA20 LA24 LA30                 2H049 AA07 AA13 AA31 AA33 AA37                       AA60 AA61 AA65                 3E041 AA01 AA02 AA03 BA14 BA16                       BA20 BB01 DB01

Claims (6)

[Claims] 1. A method for discriminating a hidden pattern by a discrimination pattern formed on a surface of a transparent film, wherein the hidden pattern is divided into a plurality of partial regions capable of discriminating an entire region formed by a diffraction grating. At least one region in the partial region is composed of two patterns that cannot be discriminated, and the two patterns are composed of fine stripes arranged in parallel with each other. A pattern by a light diffractive structure, wherein the discrimination pattern is a striped pattern formed in parallel with a fringe forming one of the two patterns. How to determine the pattern. 2. The discriminating pattern is formed by any one of photolithography, etching, printing and transfer using any one of lines, halftone dots and diffraction grating having the same pitch and the same line width as the stripes of the hidden pattern. The method for discriminating a hidden pattern according to claim 1, wherein the hidden pattern is formed by: 3. The discrimination pattern of the hidden pattern by the light diffraction structure according to claim 2, wherein the discrimination pattern by the diffraction grating is formed at the same diffraction angle and pitch as the stripes forming the hidden pattern. Method. 4. The method of discriminating a hidden pattern by a light diffractive structure according to claim 2, wherein the discriminating pattern based on the lines and halftone dots has a colored portion formed of a transparent material. 5. The discrimination pattern based on the lines and halftone dots is characterized in that the width of the colored portion is narrower than the width of the transparent portion, and the colored portion is made of a material other than black. Two
A method for discriminating a hidden pattern by the light diffraction structure according to. 6. The method for discriminating a hidden pattern by a light diffractive structure according to claim 3, wherein the density of the stripes formed on the discrimination pattern is 5 stripes / mm or more.