JP5516065B2 - Authenticity judgment method - Google Patents

Description

  The present invention relates to an anti-counterfeiting technique that secures an article to be secured, and provides a novel anti-counterfeiting technique.

  As is well known, such anti-counterfeiting technology is used for various articles. For example, a bank note, a bond, a gift certificate, a check such as a check, or a securities. It is also used for various certificates such as credit cards, ID cards, and official documents, and important documents. In recent years, it has been applied to various products and their packaging materials to ensure that the products are authentic. Needless to say, if these items are inspected and proper anti-counterfeiting measures have been taken, it is determined that the item is genuine, and anti-counterfeiting measures have not been taken or are improper. Is determined to be a non-authentic article.

  Such forgery prevention means is generally divided into an overt technique and a covert technique.

  Overt technology is a technology that anyone can recognize as anti-counterfeiting technology and enable authenticity determination. For example, anti-counterfeiting means using a diffraction structure or multilayer interference film whose color or pattern changes depending on the viewing angle can be exemplified. (Patent Document 1). These anti-counterfeiting means using diffractive structures and multilayer interference films change in color and pattern depending on the viewing angle, so no special detector is required, and no skill is required. I can recognize it. For this reason, for example, when a general consumer purchases a product, it can be determined whether or not the product is genuine. On the other hand, since its existence is obvious for a malicious person, it is easy to be targeted for forgery or forgery.

  The covert technique is a technique that cannot be recognized without a special detector or skill. For example, anti-counterfeiting means (Patent Document 2) in which a retardation film is arranged in a pattern on a part of a light reflection film. It can be illustrated. With this forgery prevention means, the presence of the retardation film itself cannot be recognized. Therefore, when the polarizing film is superposed on the retardation film as a detector and the polarizing film is rotated in the plane, the lightness and darkness change in the shape of the retardation film with the rotation. Therefore, if such a phenomenon can be observed, it can be determined that the article is genuine, and if it cannot be observed, it can be determined that the article is a non-genuine counterfeit product or a fake product. The anti-counterfeiting means using the covert technology cannot be recognized as such unless it has a special detector or skill, and for example, it is difficult for general consumers to make a judgment at the store. On the other hand, since it is not clear to a malicious person, it is difficult to grasp it as an object of forgery or forgery.

  There are various covert techniques besides anti-counterfeiting means in which a phase difference film is arranged in a pattern on a part of a reflection film. For example, it is printed using a fluorescent ink that develops color when irradiated with ultraviolet rays. In this case, the existence itself cannot be recognized without an ultraviolet irradiation device.

  A forgery prevention technique using the overt technique and the covert technique in a superimposed manner is also known. For example, Patent Document 3 discloses a forgery prevention medium in which a light reflection film is provided on an uneven surface constituting a diffraction grating, and a phase difference film is arranged in a pattern on a part of the light reflection film. In this technique, the light reflecting film has a function of reflecting and diffracting incident light to form a diffraction image, and a function of changing light and darkness to the pattern shape of the retardation film through a polarizing film superimposed thereon.

JP 2009-063944 A JP 2006-142599 A JP 2006-043978 A

  An object of the present invention is to provide an unprecedented covert technique based on a novel technical principle.

  In the anti-counterfeit medium according to the present invention, when a polarizing film is stacked thereon and the polarizing film is rotated in a plane, the color changes with the rotation. For this reason, when this phenomenon can be observed, it can be determined that the article is genuine, and if it cannot be observed, it can be determined that the article is a non-genuine counterfeit or forged product.

  The present invention relates to a forgery prevention technique using a dichroic sheet in which the color of reflected light and the color of transmitted light are different, and a reflective polarizer that selectively reflects light having a polarization axis in a specific direction. It is.

  The dichroic sheet is generally a sheet formed by laminating a number of transparent layers having an optical level film thickness. When light is incident on this dichroic sheet, the incident light enters the interior of the dichroic sheet, except for the surface reflected light reflected on the surface, and is reflected and refracted at the boundary surface between the transparent layers inside. repeat. As a result of interference between the multiple reflected lights, light having a specific wavelength is selectively emitted to the incident side, and light having the remaining wavelength component is emitted to the opposite side. That is, when white light is incident on the dichroic sheet, light having a specific wavelength is selectively reflected from the white light. For this reason, the reflected light is colored in a specific color.

  The remaining light, that is, light obtained by removing the reflected light component from the white incident light is transmitted through the dichroic sheet. For this reason, this transmitted light is also colored. The color of the reflected light and the color of the transmitted light are different from each other and generally have a complementary color relationship.

  The wavelength and color of reflected light and the wavelength and color of transmitted light all depend on the design of the dichroic sheet. For example, a dichroic sheet that colors reflected light orange and transmits light light blue is known.

  Therefore, when a reflective polarizer is disposed on the back surface of the dichroic sheet, light having a polarization axis in a specific direction among the transmitted light is selectively reflected. In the above example, the light is light blue. This light blue colored polarized light is transmitted through the dichroic sheet again and emitted. The emitted polarized light is light blue as it is.

  For this reason, when white light is incident on a laminated body in which a reflective polarizer is disposed on the back surface of the dichroic sheet and the reflected light is observed, the reflected light to be observed is light obtained by combining the following three components. That is, the composite reflected light is reflected by the surface reflected light reflected by the surface of the dichroic sheet, the reflected light of the dichroic sheet that has been multiple-reflected inside the dichroic sheet, and the reflective polarizer. It contains three components of reflected polarized light. Each of these three components is colored in a specific color. In the above example, the surface reflected light component is white, the reflected light component of the dichroic sheet is orange, and the reflected light component by the reflective polarizer is light blue. For this reason, the synthetic reflection light has a color in which light blue is mixed with orange.

  Next, by observing the synthetic reflected light through the polarizing film, it is possible to separate these light components. That is, since the reflected light component by the reflective polarizer is polarized light, this component can be removed by arranging the polarizing film. In this case, the observed light is light obtained by synthesizing the surface reflected light and the reflected light of the dichroic sheet, and has an orange color in the above example.

  Since the ratio of removing the reflected light component by the reflective polarizer depends on the crossing angle between the polarization axis of this reflected light component and the transmission axis of the polarizing film, it is possible to change this crossing angle by rotating the polarizing film. The removal ratio of the reflected light component by the reflective polarizer can be continuously changed. Since the color of the combined reflected light depends on the removal ratio, the color of the combined reflected light also changes continuously. For example, when the crossing angle between the polarization axis of the reflected light component and the transmission axis of the polarizing film is 0 degree or 180 degrees, the reflected light component by the reflective polarizer is transmitted through the polarizing film without being removed. In the above-described example, the color of the combined reflected light is a color in which light blue is mixed with orange. Further, at 90 degrees, the reflected light component by the reflective polarizer is completely removed. The color of the synthetic reflected light is orange. That is, in this example, the color changes continuously from a color in which light blue is mixed with orange to orange. The period of the crossing angle is 180 degrees.

  Note that the polarizing film does not need to be in close contact with the dichroic sheet and overlapped. Also, the observer does not need to observe close to the dichroic sheet. Even if a polarizing film is arranged at a position away from the dichroic sheet and observed from a distance, the presence or absence of a color change can be clearly recognized.

  The invention described in claim 1 is made on the basis of such a technical principle, and a dichroic sheet in which the color of reflected light and the color of transmitted light are different from each other, and a polarization axis in a specific direction. The anti-counterfeit sheet is formed by laminating a reflective polarizer that selectively reflects the light that it has.

  As apparent from the technical principle described above, when white light is incident on the anti-counterfeit sheet and the reflected light (synthetic reflected light) is observed through the polarizing film, the color is reflected by the reflective polarizer. It depends on the crossing angle between the polarization axis of the light component and the transmission axis of the polarizing film. And the color changes by rotating a polarizing film and changing a crossing angle. For this reason, when the change of the color by rotation of a polarizing film can be observed, it can be judged that the forgery prevention sheet is authentic. Further, an article to which the anti-counterfeit sheet is attached is also authentic. On the other hand, if this phenomenon cannot be observed, the article is a non-genuine counterfeit or counterfeit.

  Next, the invention according to claim 2 is characterized in that the anti-counterfeit sheet is specified by the wavelength of the dichroic sheet, and the dichroic sheet in which the wavelength of the reflected light is different from the wavelength of the transmitted light, The anti-counterfeit sheet is formed by laminating a reflective polarizer that selectively reflects light having a polarization axis in the direction.

  By the way, the dichroic sheet is a sheet formed by laminating a large number of transparent layers having an optical level film thickness. As such a sheet, for example, a sheet in which a plurality of inorganic thin film layers are laminated on a transparent sheet serving as a support is known. These thin film layers can be formed by a vapor deposition method such as a vacuum evaporation method or a sputtering method. A dichroic sheet constituted by laminating a number of transparent resin layers is also known. Each of these is configured by laminating a large number of layers of transparent materials having an optical level film thickness, and reflection and refraction are repeated at the boundary surface between these multiple layers of transparent material layers, and thus repeated. The multiple reflected lights are combined to generate specific colored light, which is reflected or transmitted.

On the other hand, a sheet formed by arranging a polymer substance having a helical molecular structure is also known as a dichroic sheet. A typical example of such a polymer substance is a cholesteric liquid crystal. In this dichroic sheet, a structural unit repeated based on the helical molecular structure has the role of the transparent material layer. That is, the light incident on the dichroic sheet is repeatedly reflected and refracted between the structural unit and the structural unit, and the multiple reflected light thus repeated is synthesized to generate specific colored light, This is reflected or transmitted.

  In the forgery prevention sheet according to the present invention, any of these dichroic sheets can be used. The invention described in claims 3 to 4 clarifies this point. In the invention described in claim 3, the dichroic sheet is formed by laminating a plurality of layers of a transparent material having a film thickness of an optical level. The anti-counterfeit sheet according to claim 1 or 2, wherein the dichroic sheet is a sheet formed by orienting helical molecules. The anti-counterfeit sheet according to claim 1 or 2.

  In these dichroic sheets, by controlling the number of the transparent material layers, the refractive index and the film thickness, or by controlling the helical pitch of the helical molecules, depending on the angle with respect to the normal line of this sheet. It can be configured to have different colors. For example, it is a dichroic sheet that looks orange when the reflected light is observed from the normal direction of the sheet and appears green when the reflected light is observed from an angle of 50 to 60 degrees with respect to the normal. . The invention according to claim 5 clarifies that this sheet can be used, and the invention according to claim 5 is characterized in that the color of the dichroic sheet differs depending on the angle of the sheet with respect to the normal line. Item 5. The forgery prevention sheet according to any one of Items 1 to 4.

  Next, in this anti-counterfeit sheet, a retardation layer can be disposed between the dichroic sheet and the reflective polarizer. The retardation layer is smaller than the reflective polarizer and can be arranged in a pattern such as a letter shape.

  The retardation layer separates light incident on the retardation layer into ordinary light and extraordinary light. Both ordinary light and extraordinary light are linearly polarized light, and their polarization axes are orthogonal to each other. In the retardation layer, the speed of ordinary light and the speed of extraordinary light are different. Therefore, the phase difference between the ordinary light and the extraordinary light transmitted through the retardation layer is the same as that when the light enters the retardation layer. It is different from the phase difference. For example, when normal light and extraordinary light having the same phase are incident on a phase difference layer (half wavelength plate) having a phase difference of ½ wavelength with respect to the design wavelength, the phase difference layer is transmitted. Ordinary light and extraordinary light have a phase difference of ½ wavelength. For this reason, when linearly polarized light having a polarization axis intersecting at an angle of 45 degrees with respect to the fast axis and slow axis of the half-wave plate is incident, the linearly polarized light is ordinary light and extraordinary light having the same intensity. And a half-wave phase difference is produced between the two, and the half-wave plate is emitted. The combined light of ordinary light and extraordinary light emitted in this way is linearly polarized light, and its polarization axis is orthogonal to the polarization axis of linearly polarized light incident on the half-wave plate. Thus, when linearly polarized light is incident on the half-wave plate, its polarization axis can be rotated.

  Therefore, when a half-wave plate is disposed between the dichroic sheet and the reflective polarizer, the polarization axis of the linearly polarized light reflected by the reflective polarizer is rotated by the half-wave plate. Therefore, when the half-wave plate is arranged in a pattern such as letters, the polarization axis of linearly polarized light that has passed through the pattern-like half-wave plate and the portion without the pattern-like half-wave plate The polarization axes of the transmitted linearly polarized light are different from each other. And since this both linearly polarized light permeate | transmits a dichroic sheet | seat and is observed by an observer through a polarizing film, the linearly polarized light and pattern-shaped 1/2 wavelength plate which permeate | transmitted the pattern shape 1/2 wavelength plate. Either one of the linearly polarized light that has passed through the part without the light is blocked by the polarizing film. For this reason, it can observe in a different color in the part by which the pattern-like 1/2 wavelength plate is arrange | positioned, and the part which is not arrange | positioned.

Invention of Claim 6 was made | formed based on such a technical reason, Any one of Claims 1-5 provided with a phase difference layer between the said dichroic sheet and the said reflection type polarizer. The anti-counterfeit sheet according to the above. As is apparent from the above description, it is desirable that the retardation layer has a pattern shape smaller than that of the reflective polarizer. The retardation layer preferably has a half-wave retardation. In addition, it is desirable to dispose the retardation layer so that the fast axis and slow axis of the retardation layer intersect with the polarization axis of the reflected light from the reflective polarizer at an angle of 45 degrees.

  Next, the anti-counterfeit sheet can be fixed to an article using an adhesive layer, and can be used as an anti-counterfeit means for ensuring the authenticity of the article thus fixed. For convenience when fixing to an article, an adhesive layer can be provided on the reflective polarizer of the anti-counterfeit sheet to form a label, and the anti-counterfeit sheet can be peeled from the transfer substrate for transfer. It can be a sheet. The invention according to claims 7 to 8 provides such a label or transfer sheet, and the invention according to claim 7 is a reflection type of the anti-counterfeit sheet according to any one of claims 1 to 6. An anti-counterfeit label having an adhesive layer on a polarizer, and the invention according to claim 8 is a transfer substrate, and a transfer layer that can be peeled off from the transfer substrate and transferred to a transfer object. The transfer layer is a forgery-preventing transfer sheet comprising the anti-counterfeit sheet according to any one of claims 1 to 6 and an adhesive layer that adheres to an object to be transferred. . Moreover, invention of Claim 9 is a forgery prevention article provided with the forgery prevention sheet in any one of Claims 1-6.

  Next, the invention according to claim 10 relates to a method for determining the authenticity of the forgery prevention sheet. As is clear from the above description, it is authentic when the presence of the anti-counterfeit sheet of the present invention can be confirmed, and is unauthentic when it cannot be confirmed. That is, the invention according to claim 10 observes the color of the reflected light from the anti-counterfeit sheet through the polarizing film, and observes the angle between the polarizing film and the anti-counterfeit sheet to change the angle. This is a true / false determination method in which the anti-counterfeit sheet is determined to be authentic when the color change accompanying the image can be observed, and is determined to be unauthentic when the color change cannot be observed.

  As described above, according to the anti-counterfeit sheet of the present invention, the color changes by rotating the polarizing film. When this color can be observed, it is authentic, and when it cannot be observed, it is not authentic. In this way, it is possible to determine the presence or absence of forgery / forgery.

Sectional drawing which shows the example of the forgery prevention sheet comprised from two layers of a dichroic sheet and a reflection type polarizer An explanatory perspective view for explaining a case where polarized light is obliquely incident on the forgery prevention sheet Sectional drawing of an anti-counterfeit sheet having a retardation layer between a dichroic sheet and a reflective polarizer Cross section of label using anti-counterfeit sheet Cross section of transfer sheet using anti-counterfeit sheet The perspective view for demonstrating the method of performing authenticity determination of the articles | goods which fixed the forgery prevention sheet based on this invention using the determination apparatus.

The anti-counterfeit sheet according to the present invention includes a dichroic sheet and a reflective polarizer as essential components. Both can be laminated using, for example, an optically isotropic transparent adhesive. In addition, although other layers may be laminated, it is necessary that light can be transmitted between the dichroic sheet and the reflective polarizer. One or both of the dichroic sheet and the reflective polarizer may be provided in a pattern. For example, a character, a symbol, or a decorative pattern. Thus, by providing in the pattern shape or decoration pattern shape which has a specific meaning, it can be made difficult to recognize that this is a forgery prevention means.

  FIG. 1 is a cross-sectional view illustrating an example of an anti-counterfeit sheet 1 including two layers of a dichroic sheet 11 and a reflective polarizer 12. The illustration of the adhesive is omitted.

  When the dichroic sheet 11 is incident on the dichroic sheet 11, the wavelength of the reflected light and the wavelength of the transmitted light are different. If attention is paid to the color, it can be said that the color of the reflected light is different from the color of the transmitted light.

  As such a dichroic sheet 11, a sheet constituted by laminating a plurality of layers of a transparent material having an optical level film thickness is known. For example, multiple inorganic thin film layers are vacuum-deposited on a transparent support. In addition, a sheet formed by laminating a plurality of transparent resin layers having an optical level film thickness is also known. For example, “MLF-16.5”, “MLF-13.0” from Teijin Limited. ”And“ MLF-19.0 ”. Any of these can be used as a dichroic sheet according to the present invention.

  Further, as the dichroic sheet 11, a sheet formed by orienting helical molecules is also known. A typical example is a cholesteric liquid crystal. As described above, the cholesteric liquid crystal has a property (selective reflectivity) that strongly reflects light in a specific wavelength band of incident light due to its helical structure. When the average refractive index of the cholesteric liquid crystal material is nm, the spiral pitch is P, the ordinary optical axis refractive index is no, and the extraordinary optical axis refractive index is ne, the wavelength band center wavelength λs of the reflected light is expressed by the following equation (1). The wavelength bandwidth Δλ of the reflected light is expressed by the following equation (2) where the birefringence is Δn.

λs = nm × P (1)
Δλ = Δn × P / nm (2)
Here, nm = (no + ne) / 2, and Δn = ne−no.

  The aligned cholesteric liquid crystal material is formed, for example, by first forming an alignment film on a substrate and then applying a low molecular weight curable liquid crystal compound on the alignment film to form a coating film. It can be formed by aligning a liquid crystal compound and then crosslinking and curing with light or heat.

  By the way, these dichroic sheets 11 may have different colors depending on the angle with respect to the normal of the sheet. For example, in the above-mentioned MLF-16.5 manufactured by Teijin Ltd., the transmitted light in the vertical direction looks light blue, and the reflected light looks orange. In addition, when tilted so as to be viewed from a steep angle with respect to the surface, the transmitted light looks magenta and the reflected light looks green. Also, in the case of a sheet configured by arranging helical molecules, the apparent frequency increases when tilted with respect to the helical axis, so the center frequency λs changes in the short wavelength direction, and the wavelength band The width Δλ becomes narrow. Therefore, when the viewing angle is tilted from the spiral axis, the color changes to the short wavelength side.

The cholesteric liquid crystal also has circular polarization selectivity, which is a property of reflecting only one of right circular polarization and left circular polarization and transmitting the other. Therefore, for example, when observing a cholesteric liquid crystal that reflects right-handed circularly polarized light, the verification film shields light reflected from the cholesteric liquid crystal to be observed when viewed through a circular polarizing filter that shields right-handed circularly polarized light on a transparent film. Looks black. Circular polarizing filters include a method of forming a cholesteric liquid crystal with right-handed rotation and left-handed rotation on a transparent film, and a method of forming a nematic liquid crystal with an appropriate retardation for a transmissive polarizer. In this way, the presence or absence of the cholesteric liquid crystal itself can be verified by confirming whether the light reflected by the cholesteric liquid crystal is circularly polarized light.

  Next, the reflective polarizer 12 selectively reflects light having a polarization axis in a specific direction. Such a reflective polarizer 12 is preferably in the form of a film. For example, a wire grid polarizer can be used. A reflective polarizer having a multilayer thin film structure can also be used. A reflective polarizer having such a multilayer thin film structure is commercially available, for example, as a DBEF series polarizing film from 3M. In addition, as the reflective polarizer 12, an absorption polarizer provided with a reflective layer on the back surface may be used as the reflective polarizer. For example, a PVA-iodine type film or a dichroic dye type film in which iodine is absorbed in a stretched film made of PVA is used as an absorption type polarizer, and a metal foil or a metal vapor deposition film is disposed on the back surface thereof, thereby reflecting the polarizer. It is also possible. Also, a DBEF reflective polarizing film (manufactured by 3M) can be used.

  As described above, the anti-counterfeit sheet 1 allows light to be incident on the anti-counterfeit sheet 1 through a polarizing film, and the polarizing film is rotated about the normal line of the anti-counterfeit sheet 1. The color and wavelength of the reflected light change. The incident light may be incident from the normal direction of the anti-counterfeit sheet 1, but is preferably incident from a direction inclined with respect to the normal line of the anti-counterfeit sheet 1 in order to make the color change clear. More preferably, it is at or near the Brewster angle. Since the Brewster angle when entering the dichroic sheet 11 from the air is usually in the range of 50 to 60 degrees, it is desirable that the incident angle be 50 to 60 degrees.

  Next, FIG. 2 is an explanatory perspective view for explaining a case where polarized light is obliquely incident on the forgery prevention sheet 1. In the present invention, the angle parallel to the surface of the anti-counterfeit sheet 1 is called a “horizontal plane” because it is necessary to distinguish between the angle with respect to the normal line and the rotation angle around the normal line. The surface defined by the normal line of the forgery prevention sheet 1 and the incident light is referred to as an “incident surface”. In FIG. 2, a plane including the x axis and the y axis orthogonal to each other is a horizontal plane. Further, the rotation angle around the normal line as an axis is referred to as “horizontal plane angle”.

  The polarization axis of p-polarized light is parallel to the incident plane, but the angle between the polarization axis and the horizontal plane depends on the incident angle. On the other hand, the polarization axis of s-polarized light is perpendicular to the plane of incidence but parallel to the horizontal plane. Such linearly polarized light whose polarization axis is parallel to the horizontal plane may be referred to as “horizontal polarized light”.

  Next, with reference to FIG. 2, the case where the above-mentioned MLF-16.5 manufactured by Teijin Ltd. is used as the dichroic sheet 11 will be described as an example. FIG. 2 shows a case where the polarization axis of the reflected light reflected from the reflective polarizer 12 is in the x-axis direction.

  First, a case where the light Sa is incident obliquely will be described. As shown in the figure, the light Sa is in a plane whose traveling direction is defined by the y-axis and the z-axis. The incident angle is in the range of 50 to 60 degrees.

  The reflected light Sa ′ emitted from the forgery prevention sheet 1 in response to the incident light Sa is a combination of three components. That is, first, the first component is surface reflected light reflected by the surface of the dichroic sheet 11. Since the incident angle is in the range of 50 to 60 degrees, this surface reflected light is s-polarized light, and its polarization axis is in the x direction. That is, it is horizontal polarized light whose polarization axis is parallel to the horizontal plane. When the incident angle does not exactly coincide with the Brewster angle, p-polarized light is slightly mixed in the surface reflected light. The polarization axis of p-polarized light does not coincide with the x direction and includes those having a polarization axis in the y direction or the z direction. In any case, the color of the surface reflected light is white.

  Next, the second component of the reflected light Sa ′ is a light component (internally reflected light) emitted to the incident side after multiple reflection inside the dichroic sheet 11. This internally reflected light also has the same polarization axis as the surface reflected light. That is, the polarization axis in the x direction. The internally reflected light also contains a small amount of polarized light having a polarization axis in the y direction or the z axis direction. The color of these internally reflected lights is green when the dichroic sheet 11 is MLF-16.5 manufactured by Teijin Limited.

  The third component of the reflected light Sa ′ is transmitted through the dichroic sheet 11 and reflected by the reflective polarizer 12, and then transmitted again through the dichroic sheet 11 (reflected). Light reflected by the mold polarizer 12). The polarization axis of this light component is in the x direction according to the reflective polarizer 12. The color is magenta.

  The reflected light Sa 'obtained by combining these three components has a color in which magenta of reflected light from the reflective polarizer 12 is mixed with green of internally reflected light.

  Therefore, the color when the reflected light Sa ′ is observed through the analyzer using the polarizing film as an analyzer will be described. First, if the analyzer is arranged so that the transmission axis is oriented in the y-axis direction, all the three components are blocked. However, as described above, the surface reflected light is slightly mixed with p-polarized light, and the internally reflected light is also slightly mixed with polarized light having a polarization axis in the y-direction or z-axis direction. Observed through the analyzer. The color is green of the internally reflected light.

  Next, when the analyzer is arranged so that the transmission axis thereof is oriented in the x-axis direction, all three components of the reflected light Sa 'are transmitted through the analyzer. Its color is a beige like green mixed with magenta.

  Note that when the transmission axis of the analyzer is in a direction intersecting both the x-axis and the y-axis, the color between them is observed.

  For this reason, the incident light Sa is slanted in a plane defined by the polarization axis of reflected light from the reflective polarizer 12 (in this example, the x-axis direction) and the normal line of the anti-counterfeit sheet 1 (z-axis direction). When the reflected light Sa ′ is observed through the analyzer when it is incident, the color of the reflected light Sa ′ is determined according to the horizontal plane angle of the analyzer's transmission axis (rotational angle around the normal line). It can be observed differently. When the analyzer is rotated about the normal line of the anti-counterfeit sheet 1, the color continuously changes from a beige-like color in which magenta is mixed with green to green. The period is 180 degrees.

  Next, the case where light Sb whose traveling direction is in a plane defined by the x-axis and the z-axis is incident will be described. The polarization axis of the reflected light reflected from the reflective polarizer 12 is the x-axis direction.

  Also in this case, the reflected light Sb 'emitted from the forgery prevention sheet 1 in response to the incident light Sb is a combination of three components. That is, the light reflected by the surface reflection light, the internal reflection light, and the reflection type polarizer 12.

  The main component of the surface reflected light is s-polarized light, and its polarization axis is in the y direction. However, p-polarized light is slightly mixed. The polarization axis of p-polarized light does not coincide with the y-direction, and those having a polarization axis in the x-direction or the z-direction are included. The color is white.

  The main component of the internally reflected light is linearly polarized light having a polarization axis in the y direction in the same manner as the surface reflected light. This internally reflected light also contains a small amount of polarized light having a polarization axis in the x direction or the z axis direction. The color is green.

  Next, the polarization axis of the light reflected by the reflective polarizer 12 is in the x direction according to the reflective polarizer 12. The color is magenta.

  Therefore, when the analyzer is first arranged so that the transmission axis is directed in the y-axis direction, the reflected light from the reflective polarizer 12 is blocked out of the three components, and the surface reflected light and the internally reflected light are transmitted. For this reason, the observed color is the green color of the internally reflected light.

  Next, when the analyzer is arranged so that the transmission axis is oriented in the x-axis direction, the reflected light from the reflective polarizer 12 is transmitted among the three components. On the other hand, surface reflection light and internal reflection light are blocked. However, as described above, the surface reflected light is slightly mixed with p-polarized light, and the internally reflected light is also slightly mixed with polarized light having a polarization axis in the y-direction or z-axis direction. Observed through the analyzer. The color is a color in which magenta of reflected light from the reflective polarizer 12 is slightly mixed with green of internally reflected light.

  When the analyzer is rotated with the normal line of the anti-counterfeit sheet 1 as an axis, the color continuously changes from a color in which magenta is slightly mixed with green to green. The period is 180 degrees.

  As apparent from the above description, the reflected light Sa ′ and Sb ′ of the obliquely incident light is observed through the analyzer regardless of the traveling direction of the incident light Sa and Sb, and the analyzer is prevented from forgery. When the sheet 1 is rotated about the normal of the sheet 1, the color changes continuously.

  Next, the anti-counterfeit sheet 1 of the present invention can have other layers. For example, a retardation layer. Further, other forgery prevention means can be provided together. In addition, an adhesive layer can be provided for the convenience of fixing to an article.

  The retardation layer can be disposed between the dichroic sheet and the reflective polarizer. The retardation layer is desirably provided in a pattern of characters and symbols. Alternatively, it is desirable to divide the boundary surface between the dichroic sheet and the reflective polarizer into a plurality of regions and dispose a retardation layer having a different phase difference for each region. In addition, the retardation layer has a phase difference of ½ wavelength with respect to the design wavelength, with the main wavelength of the wavelength components in the reflected light from the reflective polarizer 12 being the design wavelength (1 / 2 wavelength plate). In this case, the polarization axis of the linearly polarized light reflected by the reflective polarizer is rotated by the half-wave plate. Therefore, when the half-wave plate is arranged in a pattern such as letters, the polarization axis of linearly polarized light that has passed through the pattern-like half-wave plate and the portion without the pattern-like half-wave plate The polarization axes of the transmitted linearly polarized light are different from each other. And this both linearly polarized light is observed by the observer, after permeate | transmitting a dichroic sheet. This pattern cannot be recognized when observed without going through an analyzer composed of a polarizing film. On the other hand, when observed through an analyzer, either the linearly polarized light transmitted through the patterned half-wave plate or the linearly polarized light transmitted through the portion without the patterned half-wave plate is blocked by the polarizing film. Therefore, it is possible to observe different colors in the portion where the pattern-shaped half-wave plate is disposed and the portion where the pattern-shaped half-wave plate is not disposed.

For example, if the pattern area of the retardation layer is composed of specific characters and a plain background, and there are deviations in the two types of area areas showing the contrast, reflection by the reflective polarizer in the positive state is observed when viewed through the analyzer. Although it is dominant and most of the light is bright, in the negative state, it can be configured such that the reflected light is blocked by the transmissive polarizer and most of the light is dark. And since the color by the dichroic sheet 11 can be observed clearly when the surrounding is dark, when the area area is biased in this way, the color can be observed more clearly, and by the rotation of the analyzer Color changes can be clearly recognized.

  FIG. 3 is a cross-sectional view of an anti-counterfeit sheet having such a retardation layer 13. The retardation layer 13 is provided in a pattern, and is configured so that the surface of the forgery prevention sheet 1 is flush with the periphery surrounded by the adhesive layer 14. For this reason, although the phase difference layer 13 is configured in a pattern, the surface of the anti-counterfeit sheet 1 is not uneven, and the presence of the pattern phase difference layer 13 cannot be recognized.

  The retardation layer 13 can be composed of an aligned liquid crystal material. For example, an alignment film is first formed on the dichroic sheet 11 or the reflective polarizer 12, and then a nematic liquid crystal material is applied on the alignment film to form a film, and the liquid crystal material is aligned. . Then, the retardation layer can be formed by curing the liquid crystal material and fixing the alignment state.

  The alignment film can be formed, for example, by forming a film of a synthetic resin material such as polyimide and then rubbing the surface of the film to give linear irregularities. In addition, the surface of the coating is divided into a plurality of regions, and a portion of the plurality of regions is rubbed in a state of being covered with a mask material. The unevenness may be imparted. In any case, the liquid crystal material applied to the region provided with the linear irregularities is aligned along the linear irregularities.

  In addition, the alignment film can be formed using, for example, an optical interference action. For example, a photosensitive resin is applied on an arbitrary support to form a film, and laser light is irradiated from two directions to cause the laser light to interfere on the photosensitive resin film. At this time, the interference fringes are recorded in the form of irregularities on the surface of the photosensitive resin. The photosensitive resin in which the interference fringes are recorded in the form of irregularities is used as the original plate. On the other hand, a thermoplastic resin film is formed on the light reflecting film, and the original plate is hot-pressed on the film to transfer the irregularities of the original plate. When the liquid crystal material is applied to the thermoplastic resin film having the irregularities in this way, the liquid crystal material is aligned along the irregularities. In addition, it is also possible to draw the surface of the electron beam curable resin with an electron beam to form the unevenness instead of forming the unevenness by causing the laser beam to interfere on the photosensitive resin film. By this method, it is also possible to give unevenness to a partial region.

  It is also possible to form an alignment film using a photoalignment agent. The photo-alignment agent is a compound having a group in which the light absorption ability varies depending on the direction of the electric vector of polarization, and an alignment film can be formed by irradiating the coating film of this photo-alignment agent with linearly polarized light. Since the degree of orientation varies depending on the amount of energy of the linearly polarized light to be irradiated, the coating film surface of the photoalignment agent is divided into a number of regions, and high energy linearly polarized light is selectively selected in some of these many regions. , The liquid crystal material applied to this region can be aligned, and a phase difference can be generated in the light transmitted through the liquid crystal material. In this case, the liquid crystal material applied to the portion that has not been irradiated with the linearly polarized light is not aligned, and therefore no phase difference is generated. As the photo-alignment agent, compounds having a group causing a photoisomerization reaction such as azobenzene, a group causing a photodimerization reaction such as a cinnamoyl group, a coumarin group or a chalcone group, or a group causing a photocrosslinking reaction such as a benzophenone group are known. For example, it is commercially available from DIC Corporation under the name of photoalignment agent.

Next, a method for forming a film of a liquid crystal material having a different phase difference for each region will be described. In this method, a nematic liquid crystal compound that exhibits thermotropic liquid crystallinity and can be polymerized or crosslinked by light is used. And a coating material is produced by mixing this liquid crystal compound with a solvent, a chiral agent and a photopolymerization initiator. In addition, a thermal polymerization initiator, a sensitizer, a chain transfer agent, a polyfunctional monomer or oligomer, a resin, a surfactant, a storage stabilizer, an adhesion improver, and other necessary materials can be mixed in the paint. Examples of such a liquid crystal compound include alkylcyanobiphenyl, alkoxybiphenyl, alkylterphenyl, and derivatives thereof.

  Then, by coating and drying the coating material on the alignment film, a liquid crystal film aligned along the unevenness can be obtained. Then, the specific region of the coating is irradiated with ultraviolet rays to cure the coating in the irradiated region, and the orientation state is fixed. As will be described below, this region has a higher degree of orientation and therefore a larger phase difference than the other regions.

  Next, the entire coating film is heated to loosen the alignment state of the uncured region, and in this state, ultraviolet rays are irradiated again to cure the film in the irradiated region, and the alignment state is fixed. Since the relaxed alignment state is fixed in this region, the region has a relatively small phase difference.

  It is also possible to form a film of a liquid crystal material having a different phase difference for each region using the photo-alignment agent. That is, the coating film surface of the photo-alignment agent is divided into a large number of regions, and a relatively high energy linearly polarized light is irradiated to some of the regions, and a relatively low energy linearly polarized light is irradiated to other regions. Next, if a liquid crystal material is applied to the surface, the layer of this liquid crystal material has a relatively high phase difference in the region irradiated with high-energy linearly polarized light and compared in the region irradiated with low-energy linearly polarized light. Low phase difference.

  In addition, it is possible to align the film along the plane of polarization by irradiating the film of photosensitive liquid crystal material with polarized light. That is, by irradiating the polarized film of the nematic liquid crystal material mixed with the chiral agent and the photopolymerization initiator with linearly polarized light, the liquid crystal material contained in the film is aligned along the polarization plane of the irradiated light, and Harden. Therefore, when this method is adopted, an alignment film is not required, a film of a liquid crystal material is formed directly on a base material or a light reflecting film, and the liquid crystal material in this film is aligned to form a retardation layer. Can be formed. Since the degree of orientation changes according to the degree of polarization of the linearly polarized light to be irradiated, the phase difference of the retardation layer can also be controlled. Further, by irradiating in a pattern, it is possible to orient the region corresponding to this pattern.

  Other examples of anti-counterfeiting means include diffractive structures whose colors and patterns change depending on the viewing angle, anti-counterfeiting means using a multilayer interference film, and printed layers containing fluorescent ink that develops color when irradiated with ultraviolet rays. These anti-counterfeiting means can be disposed between the dichroic sheet and the reflective polarizer, but do not interfere with light transmission between the dichroic sheet and the reflective polarizer. Thus, it is desirable to provide in a pattern.

  Next, FIG. 4 is a cross-sectional view of a label using the anti-counterfeit sheet 1, that is, the label is formed by providing an adhesive layer 2 for the convenience of bonding and fixing to an article. The adhesive layer 2 is desirably provided on the reflective polarizer 12 of the anti-counterfeit sheet 1, but when the article to be fixed is transparent, the adhesive layer 2 is provided on the dichroic sheet 11. Then, the adhesive layer 2 may be adhered and fixed to the article. In this case, the authenticity is determined by the reflected light that has been transmitted through and reflected by the transparent article. Any adhesive can be used as the adhesive layer 2, and either a pressure sensitive adhesive or a heat sensitive adhesive may be used.

FIG. 5 shows a transfer sheet using the anti-counterfeit sheet 1. This transfer sheet is configured by releasably laminating a transfer base material 31 and a transfer layer 32, and the transfer layer 32 is a portion that moves to an article (transfer object). This is the part that is peeled off and removed. The transfer layer 32 includes an adhesive layer 2 that adheres to the transfer target body and the anti-counterfeit sheet 1, and is bonded and fixed to the transfer target body by the adhesive layer 2. As shown in the figure, a release layer 33 may be disposed between the transfer base material 31 and the transfer layer 32 to enhance the peelability between the transfer base material 31 and the transfer layer 32. The release layer 33 may remain on the surface of the transfer target when the transfer base material 31 is transferred and peeled off, or may be removed together with the transfer base material 31. When remaining on the surface of the transfer object, the release layer 33 also serves as a protective layer for protecting the surface of the anti-counterfeit sheet 1 from physical damage and chemical damage. It is desirable that the anti-counterfeit sheet 1 is disposed so that the dichroic sheet 11 faces the transfer substrate 31 and the adhesive layer 2 is provided on the reflective polarizer 12. When the transfer target is transparent, the reflective polarizer 12 may be disposed so as to face the transfer substrate 31, and the adhesive layer 2 may be provided on the dichroic sheet 11. Any adhesive can be used as the adhesive layer 2, and either a pressure sensitive adhesive or a heat sensitive adhesive may be used. The transfer substrate 31 and the release layer 33 are both known.

  Next, FIG. 6 is a perspective view showing a method for performing authenticity determination of an article to which the anti-counterfeit sheet 1 according to the present invention is fixed using the determination device 4. In this example, a sheet-like article is used as the article A. For example, a bank note, a bond, a gift certificate, a check such as a check, or a securities. The color determination device 4 is provided with a mounting table 41 on which the sheet-like article A is mounted, and a light source 42 that irradiates light at an incident angle of 50 to 60 degrees with respect to the surface of the mounting table 41 is provided. Yes. A polarizing film 43 is disposed on the optical path of the reflected light from the surface of the sheet-like article A. The periphery of the polarizing film 43 is fixed to a frame 44, and the frame 44 is configured to be rotatable about a normal to the surface of the mounting table 41 as a rotation axis. As the frame 44 rotates, the polarizing film 43 also rotates. The frame 44 can be manually rotated, or can be rotated at a low speed by a rotation mechanism such as a built-in motor.

  A method for determining the authenticity of the sheet-like article A using the determination device 4 will be apparent. That is, the sheet-like article A is placed on the placing table 41, the light source 42 is turned on, and light is incident on the anti-counterfeit sheet 1 of the sheet-like article A at an incident angle of 50 to 60 degrees. Then, the reflected light is observed through the polarizing film 43. This observation is possible with the naked eye. Next, the polarizing film 43 is rotated by rotating the frame 44, and the crossing angle between the polarization axis of the reflected light by the reflective polarizer 12 and the transmission axis of the polarizing film 43 is changed, and the color change is observed. To do. If the color and the change as designed of the forgery prevention sheet 1 can be observed, it can be determined to be authentic. Moreover, if the color as designed and its change cannot be observed, it can be determined that the color is not authentic.

  Examples of the present invention will be described below.

(Example)
On a polycarbonate film, aluminum is formed in a linear concavo-convex structure with a pitch of about 100 to 200 nanometers and a depth of about 100 to 300 nanometers formed by UV resin and a quartz mold, and 20 to 50 nanometers of aluminum. A wire grid type reflective polarizer having the effect of reflecting linearly polarized light by vapor deposition was prepared.

  As the dichroic sheet, MLF-16.5 manufactured by Teijin Limited was used. A patterned retardation layer was formed on this surface. The method for forming this patterned retardation layer is as follows.

That is, first, a photo-alignment agent IA-01 (manufactured by DIC Corporation) is coated on MLF-16.5 at a thickness of 0.1 μm using a microgravure coating method, and linearly polarized light having a wavelength of 365 nm is used. The entire surface was exposed with a dose of 1 J / cm ² . Next, the linearly polarized light was subjected to pattern exposure with a dose of 1 J / cm ² through a photomask so that the alignment performance of the exposed region was different from that of the other regions. Then, UV curable liquid crystal UCL-008 (manufactured by DIC Corporation) was applied to the entire coated surface with a thickness of 1.5 μm, and this liquid crystal was aligned by heating with hot air for 1 minute. At this time, the orientation degree of the liquid crystal in the pattern exposure region is different from the orientation degree of the liquid crystal in other regions. Next, exposure was performed at an illuminance of 0.5 mJ / cm ² under a nitrogen gas atmosphere to cure the liquid crystal film, and the retardation of each region was fixed to form a retardation layer. This retardation layer has a phase difference of ½ wavelength between the patterned exposure region and the surrounding region.

  And using the adhesive agent, the said reflective polarizer and the dichroic sheet | seat with a pattern phase difference layer were bonded together, and the color change sheet | seat was manufactured. At this time, the patterned retardation layer was disposed between the reflective polarizer and the dichroic sheet.

  Hold this color change sheet horizontally, and arrange the polarizing film so as to shield the horizontally polarized light (linearly polarized light whose polarization axis is parallel to the surface of the anti-counterfeit sheet) from the reflected light from this color change sheet. When observing from the angle of 50 to 60 degrees with respect to the normal of the surface of the color change sheet through the polarizing film, the pattern pattern subjected to pattern exposure with a photomask in the overall dark green color It was confirmed from a distance. By rotating the polarizing film by 90 degrees, the negative / positive pattern of the pattern was reversed, and the overall color changed from green to beige like mixed magenta.

  The present invention can be used for applications such as tickets and passports that require authentication. For example, if the determination object is created by using this sheet as the base material of the determination object such as a ticket or passport, or by sticking this sheet to the determination object as a seal or transfer sheet, the authenticity determination For example, the person who performs the determination can confirm the color change by using a determination device as shown in FIG.

DESCRIPTION OF SYMBOLS 1 Counterfeit prevention sheet 11 Dichroic sheet 12 Reflective polarizer 13 Retardation layer 14 Adhesive layer 2 Adhesive layer 31 Transfer base material 32 Transfer layer 33 Peeling layer 4 Judgment device 41 Mounting stand 42 Light source 43 Polarizing film (analyzer) )
44 Frame A Article Sa Incident light Sa 'Reflected light Sb Incident light Sb' Reflected light

Claims (1)

A forgery-preventing sheet comprising a dichroic sheet in which the color of reflected light and the color of transmitted light are different from each other and a reflective polarizer that selectively reflects light having a polarization axis in a specific direction The true / false judgment method of
Light is incident on the anti-counterfeit sheet through the polarizing film at the Brewster angle,
When the color of the reflected light from the anti-counterfeit sheet is observed through the polarizing film, and the angle between the polarizing film and the anti-counterfeit sheet is observed, and a change in color associated with the angle change can be observed. An authenticity determination method in which the anti-counterfeit sheet is determined to be authentic, and when the color change cannot be observed, it is determined to be non-authentic.

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