JP2009237101A - Security device and labelled article - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a birefringent layer made of a solidified liquid crystal material, or a laminate including this layer from being removed from an article without being broken down after a security device is stuck to the article. <P>SOLUTION: A security device 10 has a multi-layered structure of three or more layer including a birefringent layer 13 made of the solidified liquid crystal material, a contact pattern 16 having one principal surface brought into contact with a part of the birefringent layer 13, and an adjacent layer 12 having a part brought into contact with the other principal surface of the contact pattern 16 and having another part brought into contact with the birefringent layer 13. In the multi-layered structure, a contact part including the one part of the birefringent layer 13 and the another part of the adjacent layer 12, out of a plurality of contact parts each of which consists of two layers being in contact with each other, has a lower adhesion strength between two layers than those of the other contact parts. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a forgery prevention technique.

  In order to prevent forgery, a liquid crystal material may be used. For example, Patent Document 1 describes a security device including a birefringent layer made of a solidified cholesteric liquid crystal material. Patent Document 2 describes a security device including a birefringent layer made of a solidified nematic liquid crystal material.

  The anti-counterfeit technology using the solidified liquid crystal material is excellent in the effect of preventing forgery. In addition, a security device to which this forgery prevention technology is applied can achieve high identification and design.

However, the inventors of the present invention have found that the anti-counterfeiting technology has room for improvement in the following points when inventing the present invention. That is, the birefringent layer made of a solidified liquid crystal material has low interlayer adhesion strength with other layers included in the security device. Therefore, the birefringent layer or a laminate including the birefringent layer may be removed from the article without causing the destruction thereof after the security device is attached to the article. In this case, there is a possibility that fraud such as forgery of a security device using the same may be performed.
Japanese Patent Laid-Open No. 11-42875 JP 2003-251643 A

  It is an object of the present invention to remove a birefringent layer made of a solidified liquid crystal material or a laminate including the same from the article without causing the destruction thereof after the security device is attached to the article. It is to prevent.

  According to the first aspect of the present invention, a birefringent layer made of a solidified liquid crystal material, an adhesive pattern in which one main surface is in contact with a part of the birefringent layer, and a part of the adhesive pattern. It has a multilayer structure of three or more layers including an adjacent layer that is in contact with the other main surface and another part is in contact with the birefringent layer, and each of the two layers in contact with each other in the multilayer structure. Among the plurality of contact portions, the contact portion including the birefringent layer and the adjacent layer has a lower interlayer adhesion strength between the two layers compared to the remaining contact portions. A security device is provided.

  According to a second aspect of the present invention, there is provided a labeled article comprising the security device according to the first aspect and an article supporting the security device.

  According to the present invention, a birefringent layer made of a solidified liquid crystal material or a laminate including the same is prevented from being removed from an article without causing the destruction thereof after the security device is attached to the article. It becomes possible to do.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same referential mark is attached | subjected to the component which exhibits the same or similar function through all the drawings, and the overlapping description is abbreviate | omitted.

  FIG. 1 is a plan view schematically showing a security device according to the first aspect of the present invention. 2 is a cross-sectional view taken along line II-II of the security device shown in FIG.

  In FIG. 1, the security device 10 is observed from the display surface side. In FIGS. 1 and 2, directions parallel to the display surface and orthogonal to each other are defined as an X direction and a Y direction, and a direction perpendicular to the display surface is defined as a Z direction.

  The security device 10 shown in FIGS. 1 and 2 is an adhesive label that is supported on an article to be confirmed to be genuine. This security device 10 has a multilayer structure of three or more layers. Specifically, the security device 10 includes a base material 11, an alignment layer 12, a birefringent layer 13, a reflective layer 14, an adhesive layer 15, and an adhesive pattern 16. The front surface of the security device 10 is a surface on the base material 11 side.

  The base material 11 has optical transparency, and is typically colorless and transparent or colored and transparent. The base material 11 is, for example, a film or sheet made of a resin having optical transparency. As this resin, for example, polyethylene terephthalate (hereinafter referred to as PET), triacetyl cellulose, polycarbonate, polyester, polyacetal, polystyrene, or epoxy resin can be used.

  The substrate 11 may have a single layer structure or a multilayer structure. The substrate 11 may have birefringence, but preferably does not have birefringence so as not to affect the display.

  The alignment layer 12 covers the back surface of the substrate 11. Here, the alignment layer 12 is an adjacent layer partly in contact with the adhesive pattern 16 and the other part in contact with part of the birefringent layer 13.

  The alignment layer 12 is a light transmissive layer. Typically, the alignment layer 12 is transparent and optically isotropic. The alignment layer 12 gives scattering properties to transmitted light and / or reflected light by emitting polarized transmitted light and reflected light when incident incident light having polarization is incident. It may be.

  The alignment layer 12 is non-adhesive. As a material of the alignment layer 12, for example, a resin can be used. Examples of the resin include acrylic resin, epoxy resin, vinyl chloride resin, styrene resin, cellulose resin, acetal resin, polyamide resin, polyimide resin, olefin resin, polycarbonate resin, polyether resin, polyester resin, phenol resin, or melamine resin. Can be used.

  The adhesive pattern 16 covers a part of the alignment layer 12. Here, the adhesive pattern 16 is non-adhesive. The adhesive pattern 16 serves to prevent delamination from occurring on both sides of the adhesive pattern 16 when the security device 10 is to be peeled from the article to which it is attached.

  The material of the adhesive pattern 16 is appropriately selected according to the material of the adjacent layer, here the alignment layer 12. That is, the material of the adhesive pattern 16 is such that the contact portion between the adhesive pattern 16 and the adjacent layer and the contact portion between the adhesive pattern 16 and the birefringent layer 13 are more in comparison with the adjacent layer and the birefringent layer 13. Choose to have high interlayer adhesion strength. For example, when an acrylic resin, an epoxy resin, or a vinyl chloride resin is used as the material of the alignment layer 12, a urethane resin can be used as the material of the adhesive pattern 16. Alternatively, when an acrylic resin is used as the material of the alignment layer 12, a vinyl chloride-vinyl acetate copolymer may be used as the material of the adhesive pattern 16. Alternatively, when the alignment layer 12 is non-adhesive, an adhesive resin may be used as the material of the adhesive pattern 16.

  The surface exposed from the adhesive pattern 16 in the surface of the adhesive pattern 16 and the surface of the alignment layer 12 constitutes the ground for the birefringent layer 13. This base surface includes regions Aa to Ac. Each of the areas Aa and Ab is circular. The region Ac surrounds the regions Aa and Ab. Each of the regions Aa to Ac may have other shapes.

  Hereinafter, portions of the security device 10 corresponding to the areas Aa to Ac are referred to as display units 100a to 100c, respectively. Further, portions of the birefringent layer 13 corresponding to the regions Aa to Ac are referred to as portions 130a to 130c, respectively.

  Each of the regions Aa and Ab is provided with a plurality of grooves that are aligned in the length direction and are adjacent to each other in a direction intersecting the length direction. The grooves provided in the region Aa and the grooves provided in the region Ab are different from each other in the length direction. Here, as an example, the length direction of the groove provided in the region Aa is parallel to the X direction, and the length direction of the groove provided in the region Ab is parallel to the Y direction. Here, as an example, the portion corresponding to the region Aa and the portion corresponding to the region Ab in the alignment layer 12 are the same except that the dimensions and the length direction of the grooves are different.

  Various structures can be adopted for the regions Aa and Ab. For example, each of the regions Aa and Ab can employ a structure in which a plurality of grooves are arranged in parallel in the width direction at equal intervals.

  In each of the regions Aa and Ab, these grooves may not be parallel to each other. However, the closer these grooves are in parallel, the easier it is for the long axes of the mesogens to be aligned in each part of the birefringent layer 13 corresponding to the regions Aa and Ab. The angle formed by these grooves is, for example, 5 ° or less, preferably 3 ° or less.

  In each of the regions Aa and Ab, these grooves may be arranged vertically and horizontally. The lengths of the grooves may be equal to each other or different from each other. Further, the distance between adjacent grooves in the length direction may be uniform or non-uniform. Furthermore, the distance between adjacent grooves in the width direction may be uniform or non-uniform.

  For example, in each of the areas Aa and Ab, grooves having the same length may be arranged vertically and horizontally. By making the grooves substantially parallel and appropriately setting the pitch, the diffraction grating can be constituted by these grooves.

  Alternatively, grooves of various lengths may be randomly arranged in each of the regions Aa and Ab. In this case, a unidirectional diffusion pattern can be formed with these grooves. Note that this unidirectional diffusion pattern has a larger light diffusion capacity in a plane perpendicular to the groove length direction than that in a plane parallel to the Z direction and the groove length direction. This is a pattern showing diffusion characteristics, that is, light scattering anisotropy. Here, as an example, it is assumed that the grooves provided in each of the regions Aa and Ab constitute a diffraction grating.

  The region Ac is a region where no groove is provided. The region Ac can be omitted.

  The relief structure of the lower ground can be formed by, for example, a method of recording a hologram pattern using a two-beam interference method on a photosensitive resin material or a method of drawing a pattern by an electron beam. Alternatively, as is done in the manufacture of surface relief holograms, it can be formed by pressing a mold provided with fine linear projections onto the resin. For example, in this relief structure, an alignment layer 12 and an adhesive pattern 16 each made of a thermoplastic resin are formed in this order on a substrate 11, and an original plate provided with linear protrusions on the surface thereof, It is obtained by a method of pressing while applying heat, that is, a hot embossing method. Alternatively, it is also possible to use a method in which an ultraviolet curable resin is applied onto the substrate 11 and the ultraviolet curable resin is cured by irradiating the substrate 11 with ultraviolet rays while pressing the original plate on the substrate 11 and then removing the original plate. It is.

  Usually, a reverse plate is manufactured by transferring the concavo-convex structure of the original plate, and a duplicate plate is manufactured by transferring the concavo-convex structure of the reverse plate. Then, if necessary, a reversal plate is manufactured using the copy plate as an original plate, and the uneven structure of the reversal plate is transferred to further manufacture a copy plate. In actual production, a copy obtained in this way is usually used.

  According to these methods, it is possible to form a plurality of regions in which at least one of the length direction, pitch, depth, width, and length of the grooves is different in one plane.

  The original plate can be obtained, for example, by performing electroforming of a mother die obtained by a method of recording a hologram pattern using a two-beam interference method, a method of drawing a pattern by an electron beam, or a method of cutting by a cutting tool. It is done. When the above-mentioned diversity is not given to the lower ground, grooves may be formed by rubbing.

  The depth of these grooves is, for example, in the range of 0.05 μm to 1 μm, and typically in the range of 0.1 μm to 1 μm. The length of the groove is, for example, in the range of 0.1 μm to 1 μm, and typically in the range of 0.5 μm to 1 μm. The pitch of the grooves is, for example, 0.1 μm or more, and typically 0.75 μm or more. The pitch of the grooves is, for example, 10 μm or less, and typically 2 μm or less. In order to orient mesogens with a high degree of order, it is advantageous that the pitch of the grooves is small.

  The region Aa and the region Ab may be further different in at least one of the pitch, width, and depth of the grooves provided in them. When at least one of the pitch, width, and depth of the groove is further different between the region Aa and the region Ab, the length direction of the groove provided in the region Aa and the region Ab may be the same. . Alternatively, one of the areas Aa and Ab may be omitted.

  The birefringent layer 13 is formed on the base surface. The birefringent layer 13 covers the regions Aa to Ac. The main surface of the birefringent layer 13 facing the substrate 11 is provided with a relief structure corresponding to the groove.

  The birefringent layer 13 is formed by solidifying a liquid crystal material. Typically, the birefringent layer 13 is a polymer birefringent layer formed by curing a polymerizable liquid crystal material having fluidity with ultraviolet rays or heat. This liquid crystal material is, for example, a nematic liquid crystal material.

  Of the birefringent layer 13, the portion 130 a covering the region Aa, the portion 130 b covering the region Ab, and the portion 130 c covering the region Ac have a mesogen orientation structure and / or orientation direction. Are different from each other. In the portion 130a of the birefringent layer 13 covering the region Aa, the orientation direction of the mesogen is substantially parallel to the length direction of the groove provided in the region Aa. In the portion 130b of the birefringent layer 13 covering the region Ab, the orientation direction of the mesogen is substantially parallel to the length direction of the groove provided in the region Ab. That is, in this example, the mesogen is oriented in the X direction in the portion 130a of the birefringent layer 13 that covers the region Aa. In the portion 130b of the birefringent layer 13 that covers the region Ab, the mesogen is oriented in the Y direction.

These portions 130a and 130b of the birefringent layer 13 are birefringent because the mesogens are oriented. Since the mesogen the birefringent portion 130a is oriented in the X direction, the refractive index for X-direction is the extraordinary ray refraction index n _e, the refractive index in the Y direction is the ordinary index n _o. Since the refractive index n _e is greater than the refractive index n _o, the slow axis of the birefringent portion 130a is parallel to the X direction, fast axis is parallel to the Y direction. The slow axis of the birefringent portion 130b is parallel to the Y direction, and the fast axis is parallel to the X direction.

  In the portion 130c of the birefringent layer 13 that covers the region Ac, the mesogen is typically not oriented or oriented as high as the birefringent portions 130a and 130b. . Here, as an example, it is assumed that the mesogen is not oriented in the portion 130c. That is, this portion 130c is assumed to be optically isotropic. In the portion 130c, for example, the mesogen can be aligned with a relatively high degree of order by performing an alignment process such as a rubbing process on the region Ac.

  The birefringent layer 13 can be formed by the following method, for example. First, a nematic liquid crystal material having photopolymerizability is applied on the base surface. The liquid crystal material is then irradiated with ultraviolet light to cause their polymerization. Thereby, the birefringent layer 13 in which the direction of the major axis of the mesogen is fixed can be obtained. As a material for the birefringent layer 13, a cholesteric liquid crystal material or a smectic liquid crystal material may be used.

  The reflective layer 14 covers the birefringent layer 13. The reflective layer 14 is a metal layer obtained by a vapor deposition method such as a vacuum evaporation method and a sputtering method, for example.

  A light transmissive layer having a relief structure on the surface may be interposed between the reflective layer 14 and the birefringent layer 13. When such a light transmission layer is provided, a diffraction structure such as a diffraction grating and a hologram or a light scattering structure can be formed on the surface of the reflection layer 14 facing the birefringence layer 13. As the material of the light transmission layer, for example, the materials described above for the adhesive pattern 16 can be used.

  Instead of using a metal layer as the reflective layer 14, a single-layer or multilayer dielectric layer may be used. In this case, the light transmission layer may or may not be interposed between the reflective layer 14 and the birefringent layer 13. A multilayer dielectric layer, that is, a dielectric multilayer film is obtained by alternately depositing a high refractive index material such as zinc sulfide and a low refractive index material such as magnesium fluoride.

  Instead of using a metal layer as the reflective layer 14, a layer made of a mixture containing a light transmitting resin and metal particles may be used.

  Examples of the light transmissive resin include natural rubber, acrylic resin, polyolefin, polyether, epoxy resin, polyvinyl chloride, chloroprene rubber, silicone resin, nitrile rubber, phenol resin, polyamide, polyimide, polyurethane, polyvinyl acetate, polystyrene. , Polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl butyral, polybenzimidazole, methacrylic resin, melamine resin, melamine resin, resorcinol resin, or a mixture containing one or more thereof can be used.

  The metal particles are made of a metal or an alloy. As this metal or alloy, for example, aluminum, platinum, gold, silver, copper, titanium, bismuth, germanium, indium, tin, or an alloy containing one or more thereof can be used. Among these, aluminum has a high reflectance over the entire visible region, infrared region, and near-ultraviolet region. Moreover, aluminum is highly resistant to oxidation. Therefore, it is preferable to use aluminum particles as the metal particles.

  When irradiated with polarized light, the reflective layer 14 made of a mixture containing a light-transmitting resin and metal particles reflects this polarized light while substantially maintaining the polarization. That is, the reflective layer 14 can function in substantially the same manner as a metal layer obtained by a vapor deposition method such as a vacuum deposition method and a sputtering method.

  In addition, in this case, compared with the case where a metal layer is used as the reflective layer 14, the contact portion between the birefringent layer 13 and the reflective layer 14 and / or the contact portion between the reflective layer 14 and the adhesive layer 15 is more suitable. High interlayer adhesion strength can be achieved. That is, in this case, as compared with the case where a metal layer is used as the reflective layer 14, peeling at the interface between the birefringent layer 13 and the reflective layer 14 and / or the interface between the reflective layer 14 and the adhesive layer 15 is less likely to occur. can do.

  In addition, metals such as aluminum are soluble in an alkaline solution. Therefore, when a metal layer is used as the reflective layer 14, the metal may be dissolved from the end face. On the other hand, when a layer made of a mixture containing a light transmitting resin and metal particles is used as the reflective layer 14, dissolution of the metal particles is prevented by the resin. That is, the reflective layer 14 made of a mixture containing a light transmissive resin and metal particles is unlikely to deteriorate.

  Moreover, the light scattering ability of the reflective layer 14 made of a mixture containing a light transmissive resin and metal particles changes when, for example, at least one of the particle size, shape, and content of the metal particles is changed.

  Instead of using a metal layer as the reflective layer 14, a layer made of a mixture containing the above light-transmitting resin and non-metal particles may be used. In this case, the interface between the birefringent layer 13 and the reflective layer 14 and / or the reflective layer 14 is used in the same manner as when a layer made of a mixture containing a light-transmitting resin and nonmetallic particles is used as the reflective layer 14. Peeling at the interface with the adhesive layer 15 can be made difficult to occur. In this case, higher light scattering can be achieved as compared with the case where a layer made of a mixture containing a light-transmitting resin and metal particles is used as the reflective layer 14. As a material for the non-metallic particles, for example, an inorganic material such as silica or an organic material such as an acrylic resin can be used.

  The adhesive layer 15 covers the reflective layer 14. The adhesive layer 15 is used for attaching the security device 10 to an article. As a material for the adhesive layer 15, for example, a resin that can be used as an adhesive such as a heat-sensitive adhesive and a pressure-sensitive adhesive can be used.

  In this security device 10, the contact portion between the birefringent layer 13 and the alignment layer 12, which is the adjacent layer, out of a plurality of contact portions each composed of two layers in contact with each other, is compared with the remaining contact portions. Interlayer adhesion strength is lower. That is, the contact portion between the birefringent layer 13 and the alignment layer 12 includes a contact portion between the base material 11 and the alignment layer 12, a contact portion between the alignment layer 12 and the adhesive pattern 16, and an adhesive pattern 16 and birefringence. Compared with the contact portion with the layer 13, the contact portion between the birefringent layer 13 and the reflective layer 14, and the contact portion between the reflective layer 14 and the adhesive layer 15, the interlayer adhesion strength is lower.

  Moreover, although the adhesive strength with respect to a certain article | item of the adhesive layer 15 is dependent on the material which comprises the surface of the article | item, normally high adhesive strength can be achieved on the surface which should adhere the security device 10 to. Material is selected. Accordingly, the interlayer adhesive strength at the contact portion between the birefringent layer 13 and the alignment layer 12 is lower than the adhesive strength of the adhesive layer 15 to the article to which the security device 10 is attached.

  In general, a birefringent layer made of a solidified liquid crystal material has low adhesion to other layers. Therefore, a multilayer structure including such a birefringent layer tends to cause delamination at the interface between the birefringent layer and a layer adjacent thereto. In the security device 10, by providing the adhesive pattern 16, delamination between the birefringent layer 13 and the alignment layer 12 at the position of the adhesive pattern 16 is difficult to occur.

  Next, an image that appears when the security device 10 is irradiated with white light and observed with the naked eye will be described. Here, as an example, it is assumed that the alignment layer 12 and the adhesive pattern 16 are optically equivalent. As described above, here, as an example, the reflective layer 14 is made of a mixture containing a light-transmitting resin and metal particles, and has a light scattering property. White light is light composed of non-polarized light having all wavelengths in the visible region.

FIG. 3 is a plan view showing an example of an image displayed by the security device shown in FIGS. 1 and 2.
When the security device 10 is irradiated with white light from substantially the front direction and observed with the naked eye from the front, the display units 100a to 100c are impossible or difficult to distinguish from each other as shown in FIG. This will be described in more detail.

  White light as illumination light incident on the display unit 100a is transmitted through the substrate 11 shown in FIG. Part of the white light transmitted through the substrate 11 passes through the alignment layer 12 and the adhesive pattern 16 in this order and enters the base surface. The remainder of the white light that has passed through the substrate 11 passes through the alignment layer 12 and enters the base surface without entering the adhesive pattern 16.

  The grooves provided in the region Aa constitute a diffraction grating. Accordingly, a part of these incident lights enters the birefringent portion 130a as diffracted light.

  The diffracted light that has passed through the birefringent portion 130 a is reflected by the reflective layer 14. Since the reflective layer 14 has light scattering properties, the reflected light is scattered light.

  This scattered light is transmitted through the birefringent portion 130a. In the region Aa, a diffraction grating is provided. In addition to the reflected light from the reflective layer 14 being scattered light, the incident angle of illumination light varies in a normal environment. Therefore, the reflected light from the reflective layer 14 passes through the adhesive pattern 16 and the alignment layer 12 in this order as scattered light, or passes through the alignment layer 12 and then passes through the substrate 11. An observer perceives the scattered light as display light. Therefore, the display unit 100a looks silvery white.

  As described above, the alignment layer 16 and the adhesive pattern 16 are optically equivalent. Therefore, the part corresponding to the adhesive pattern 16 in the display unit 100a and the other part appear to be the same color.

  The display part 100b and the display part 100a differ only in the length direction of the groove | channel which comprises the diffraction grating except the planar shape. As is clear from the above description, when the display unit 100a is observed with the naked eye, the diffraction grating does not affect the display color or brightness. Therefore, the display unit 100b also looks silvery white.

  The display unit 100c is different from the display unit 100a only in that no groove is provided on the base surface and mesogens are not oriented except for the planar shape. As is clear from the above description, when the display unit 100a is observed with the naked eye, the diffraction grating does not affect the display color or brightness. Therefore, the display unit 100c also looks silvery white.

  In this manner, the display units 100a to 100c appear silver white. The display units 100a to 100c have substantially the same brightness. Accordingly, when the security device 10 is irradiated with white light and observed with the naked eye from the front, the display units 100a to 100c are impossible or difficult to distinguish from each other as shown in FIG.

  When the security device 10 is irradiated with white light and observed with the naked eye, the display colors of the display units 100a to 100c remain silver white even when the observation angle is changed. Further, even if the security device 10 is rotated around the normal line while the observation angle is inclined, the display colors of the display units 100a to 100c remain silver white.

  Next, an image seen when the security device 10 is observed through a polarizer will be described. Here, as an example, a linearly polarizing film is used as the polarizer.

  FIG. 4 is a plan view schematically showing an example of an image that can be observed when the security device shown in FIGS. 1 and 2 and a linearly polarizing film are overlapped.

  In FIG. 4, when the security device 10 and the absorption linear polarizing film 50 shown in FIGS. 1 and 2 are viewed from the polarizing film 50 side, the transmission axis of the polarizing film 50 is in the X direction. In order to make an angle of 45 ° counterclockwise. When such an arrangement is adopted and this is observed from the front, as shown in FIG. 4, the display units 100a and 100b are easily discriminated from the display unit 100c and cannot be discriminated from each other. is there. This will be described in more detail.

  When the linearly polarizing film 50 is irradiated with white light as illumination light, the linearly polarizing film 50 transmits linearly polarized light having a polarization plane parallel to its transmission axis (vibration plane of the electric field vector) and polarized light perpendicular to the transmission axis. Absorbs linearly polarized light having a surface.

  The linearly polarized light incident on the display unit 100a is transmitted through the substrate 11 shown in FIG. Part of the linearly polarized light that has passed through the substrate 11 passes through the alignment layer 12 and the adhesive pattern 16 in this order, and enters the base surface. The remaining portion of the linearly polarized light that has passed through the substrate 11 passes through the alignment layer 12 and enters the base surface without entering the adhesive pattern 16.

  The grooves provided in the region Aa constitute a diffraction grating. Therefore, a part of these linearly polarized light enters the birefringent portion 130a as diffracted light.

  In the birefringent portion 130a, the mesogenic group is oriented substantially parallel to the X direction. That is, when viewed from the polarizing film 50 side, the slow axis of the birefringent portion 130 a is parallel to the direction rotated 45 ° clockwise relative to the transmission axis of the polarizing film 50. Since this incident light is scattered light, it includes a light component that travels in the front direction and a light component that travels in the oblique direction. Therefore, for example, the previous linearly polarized light is converted into circularly polarized light, elliptically polarized light, or linearly polarized light according to the birefringence of the birefringent portion 130a and the optical path length. Here, only the left circularly polarized light and the left elliptical polarized light among the light emitted from the birefringent portion 130a will be described.

  These left circularly polarized light and left elliptically polarized light are reflected by the reflective layer 14. The left circularly polarized light and the left elliptically polarized light are respectively converted into right circularly polarized light and right elliptically polarized light by being reflected by the reflective layer 14. Moreover, since the reflective layer 14 has light scattering properties, this reflected light is scattered light.

The right circularly polarized light and the right elliptically polarized light as the scattered light are incident on the birefringent portion 130a. Since this incident light is scattered light, it includes a light component traveling in the front direction and a light component traveling in an oblique direction. Of the light component traveling in the front direction, the right circularly polarized light having the specific wavelength λ ₀ is converted into linearly polarized light whose polarization plane is perpendicular to the transmission axis of the polarizing film 50 by transmitting through the birefringent portion 130a. The Then, the remaining light component is converted into left elliptically polarized light, left circularly polarized light, right elliptical polarized light, or circularly polarized light by transmitting through the birefringent portion 130a.

  A part of the reflected light from the reflection layer 14 emitted from the birefringent portion 130a passes through the adhesive pattern 16, the alignment layer 12, and the substrate 11 in this order. The remainder of the reflected light from the reflective layer 14 emitted from the birefringent portion 130a passes through the alignment layer 12 and the substrate 11 in this order. Although a diffraction grating is provided on the back surface of the alignment layer 12, in addition to the reflected light from the reflective layer 14 being scattered light, the incident angle of illumination light varies in a normal environment. Therefore, the reflected light from the reflective layer 14 is emitted from the substrate 11 as scattered light.

  As is clear from this, when focusing only on the light component having a polarization plane parallel to the transmission axis of the polarizing film 50, the intensity of the light component emitted by the display unit 100a relative to the intensity of the light component incident on the display unit 100a. This ratio has a wavelength dependency. In other words, the ratio of the intensity of display light emitted from the polarizing film 50 to the intensity of illumination light incident on the polarizing film 50 has wavelength dependency. Therefore, the display unit 101 appears colored. The reason why the display unit 100a appears to be colored will be described later with reference to mathematical expressions.

  The display unit 100b and the display unit 100a differ from each other only in that the length directions of the grooves constituting the diffraction grating are different by 90 ° except for the planar shape. Therefore, the display unit 100b behaves in the same manner as described for the display unit 100a except that the rotation direction of the polarization plane of circularly polarized light or elliptically polarized light is reversed. Therefore, the display unit 100b looks colored in the same manner as the display unit 100a.

  The display unit 100c is different from the display unit 100a only in that the display unit 100c does not include the adhesive pattern 16 except for the planar shape, the groove is not provided in the alignment layer 12, and the mesogen is not aligned. Yes. Therefore, the light emitted from the display unit 100 c is ideally transmitted through the polarizing film 50 without being absorbed by the polarizing film 50. Therefore, the display unit 100c looks silvery white.

  Thus, the display units 100a and 100b appear colored, and the display unit 100c appears silvery white. The display units 100a and 100b have substantially the same brightness. Therefore, when the polarizing film 50 is superimposed on the security device 10 and irradiated with white light and observed from the front, the display units 100a and 100b can be easily distinguished from the display unit 100c as shown in FIG. , Discrimination from each other is impossible or difficult.

Here, the reason why the display unit 100a appears to be colored will be described with reference to mathematical expressions. Incidentally, birefringent portion 130a is directed to act as a quarter wave plate for light of a wavelength lambda _0.

It can be considered that the linearly polarized light having the wavelength λ ₀ emitted from the polarizing film 50 in the normal direction is the sum of the linearly polarized light component whose polarization plane is perpendicular to the X direction and the linearly polarized light component whose polarization plane is perpendicular to the Y direction. it can. As described above, the refractive index in the X-direction of the birefringent portion 130a is extraordinary refractive index n _e, the refractive index in the Y direction is the ordinary index n _o. Accordingly, birefringent portion 130a is in these linearly polarized light component, providing a phase difference of lambda _0/4 in each of the forward path and the backward path. That is, birefringent portion 130a provides a phase difference of lambda _0/2 in total of these linearly polarized light components. Therefore, the light having the wavelength λ ₀ emitted from the display unit 100 a in the normal direction cannot pass through the polarizing film 50.

By the way, the retardation Re depends on the thickness d of the birefringent layer and its birefringence Δn, as shown in the following equation (1).
Re = Δn × d (1)
Here, a Δn = n _e -n _o.

A pair of linearly polarizing films face each other so that their transmission axes are orthogonal to each other, and a birefringent layer is interposed between them so that the optical axis forms an angle θ with respect to the transmission axis of the linearly polarizing film. When one linearly polarizing film is illuminated with light having a wavelength λ from its normal direction, the intensity of light incident on the birefringent layer is I _0, and the intensity of light transmitted through the other linearly polarizing film is I The strength I can be expressed by the following equation (2).
I = I ₀ × sin ² (2θ) × sin ² (Re × π / λ) (2)
The birefringence Δn has wavelength dependence, and the birefringence Δn and the wavelength n are not in a proportional relationship. Therefore, as is clear from equation (2), the spectrum of transmitted light has a different profile from the spectrum of incident light.

  Thus, when the birefringent layer is sandwiched between a pair of linearly polarizing films, transmitted light having a spectrum profile different from that of incident light can be obtained. Similarly, when the birefringent layer is sandwiched between the linearly polarizing film and the reflective layer, reflected light having a spectrum profile different from that of the incident light can be obtained. For this reason, the display unit 100a appears colored.

FIG. 5 is a perspective view showing another example of an image displayed by the security device shown in FIGS. 1 and 2.
As shown in FIG. 5, when the observation direction is tilted in a plane perpendicular to the X direction from the state shown in FIG. 4, the display colors of the display units 100a and 100b change to different colors. As a result, the display units 100a and 100b can be easily distinguished from each other. For example, if the display units 100a and 100b look orange when observed from the normal direction, the display unit 100a changes to red by tilting the observation direction in a plane perpendicular to the X direction. The part 100b changes to green. The reason for the color change that occurs in the display units 100a and 100b will be described below.

When the observation angle θ is tilted, the effective birefringence Δn ′ of the birefringent layer changes from the birefringence Δn, and the effective film of the birefringent layer shown in the following equation (3): The thickness d ′ is larger than twice the actual film thickness d of the birefringent layer.
d ′ = 2d / cos θ (3)
That is, the retardation Re shown in the above equation (1) changes according to the observation angle, and therefore the intensity I shown in the above equation (2) changes. As a result, the spectrum profile of the display light changes according to the observation angle.

  The birefringence Δn ′ depends on the incident angle of the illumination light and the angle formed by the projection onto the main surface of the birefringent layer that is parallel to the propagation direction of the illumination light with respect to the optical axis of the birefringent layer. To do. Specifically, the birefringence Δn ′ of the birefringent portion 130a does not change even when the observation direction is tilted in a plane perpendicular to the X direction because the optical axis is parallel to the X direction. On the other hand, the birefringence Δn ′ of the birefringent portion 130b changes as the observation direction is tilted in a plane perpendicular to the X direction because its optical axis is parallel to the Y direction.

  As described above, when the display unit 100a is tilted in the plane perpendicular to the X direction, the display unit 100a causes a color change due to an effective change in the film thickness d '. On the other hand, when the viewing direction is tilted in a plane perpendicular to the X direction, the display unit 100b changes color due to an effective change in film thickness d ′ and an effective change in birefringence Δn ′. Produce. Therefore, when the observation direction is tilted in a plane perpendicular to the X direction, the display colors of the display units 100a and 100b change to different colors, and as a result, the display units 100a and 100b can be easily distinguished from each other. Become.

  FIG. 6 is a perspective view showing still another example of an image displayed by the security device shown in FIGS. 1 and 2.

  FIG. 6 shows an image that can be observed when the security device 10 is rotated 90 ° around the normal line while the security device 10 is overlapped with the polarizing film 50 from the state shown in FIG.

  When the display units 100a and 100b change the rotation angle, the effective grating constant of the diffraction grating changes. When the security device 10 is rotated 90 ° around the normal line together with the polarizing film 50 while the observation direction is oblique, the display color is switched between the display unit 100a and the display unit 100b. Note that the color change described with reference to FIG. 6 also occurs when only the security device 10 is rotated 90 ° around its normal from the state shown in FIG.

  The security device 10 can be used in a variety of labeled articles.

FIG. 7 is a plan view schematically showing an example of a labeled article.
This labeled article is an ID (identification) card. The labeled article includes a security device 10 and an article 30 that supports the security device 10.

  The article 30 is a card. This article 30 includes a card substrate 31 and printing layers 32a and 32b. The card base 31 is made of plastic, for example. The print layers 32 a and 32 b are formed on the card base 31. The security device 10 is affixed to the card substrate 31.

  The ID card includes the security device 10 described above. Therefore, forgery of this ID card is difficult. In addition, since the ID card includes the security device 10, it is easy to determine an article whose authenticity is unknown between genuine and non-authentic. Moreover, since this ID card further includes the print layers 32a and 32b in addition to the security device 10, it is possible to adopt a counterfeit prevention measure using them.

  In addition, although the ID card is illustrated as the labeled article in FIG. 7, the labeled article is not limited to this. For example, the labeled article may be other cards such as an IC (integrated circuit) card, a magnetic card, and a wireless card. Alternatively, the labeled article may be securities such as gift certificates and stock certificates. Alternatively, the labeled article may be a bill, a deposit, or a savings passbook. Thus, the security device 10 can be applied to various printed materials.

  Moreover, the labeled article may not be a printed material. That is, the security device 10 may be supported on an article that does not include a printed layer. For example, the security device 10 may be supported by a luxury product such as a work of art.

  When the security device 10 is to be peeled from the article 30, the security device 10 is broken as described below.

FIG. 8 is a cross-sectional view schematically illustrating an example of a destroyed security device.
As described with reference to FIG. 1 and FIG. 2, in this security device 10, the contact portions of the adjacent layer and the birefringent layer 13 remain among the plurality of contact portions each composed of two layers in contact with each other. Interlayer adhesion strength is lower compared to the contact portion. In this example, the contact portion between the alignment layer 12 and the birefringent layer 13 has a lower interlayer adhesion strength than the remaining contact portions.

  Therefore, when the security device 10 is peeled from the article 30, delamination occurs at the interface between the alignment layer 12 and the birefringent layer 13. That is, when the security device 10 is to be peeled from the article 30, the security device 10 is destroyed. The security device 10 that has caused such destruction can easily recognize that an illegal act has been performed.

At this time, with the previous delamination, for example, the birefringent layer 13 and the reflective layer 14 may be broken along the contour of the adhesive pattern 16 as shown in FIG. The security device 10 having such a breakage can more easily recognize that an illegal act has been performed.
Therefore, the security device 10 achieves a high anti-counterfeit effect.

Various modifications can be made to the security device 10 shown in FIGS. 1 and 2.
FIG. 9 is a cross-sectional view schematically showing a modification of the security device shown in FIGS. 1 and 2. The security device 10 shown in FIG. 9 is the same as the security device 10 described with reference to FIGS. 1 to 6 except that the adhesive pattern 16 is interposed between the birefringent layer 13 and the reflective layer 14. It is the same.

  In the security device 10, the reflective layer 14 is an adjacent layer. That is, of the plurality of contact portions each composed of two layers in contact with each other, the contact portion between the reflective layer 14 and the birefringent layer 13 has a lower interlayer adhesion strength than the remaining contact portions.

  Therefore, the labeled article formed by attaching the security device 10 to the article 30 causes delamination at the interface between the reflective layer 14 and the birefringent layer 13 when the security device 10 is peeled from the article 30. With this delamination, for example, the reflective layer 14 can be broken along the contour of the adhesive pattern 16.

  FIG. 10 is a cross-sectional view schematically showing another modification of the security device shown in FIGS. 1 and 2. The security device 10 shown in FIG. 10 is the same as the security device 10 described with reference to FIGS. 1 to 6 except that the following configuration is adopted.

  That is, in this security device 10, the length direction of the groove is made equal in the region Aa and the region Ab, and the height of the base surface with respect to the base material 11 corresponds to the portion corresponding to the region Aa of the alignment layer 12 and the region Ab. Different from part. In other words, the birefringent portion 130a and the birefringent portion 130b have the same mesogen orientation direction, and the birefringent portion 130a and the birefringent portion 130b have different retardations.

  When such a structure is employed, the display units 100a and 100b appear to have the same color when observed with the naked eye even if the scattering ability of the reflective layer 13 is small. And when observing through the polarizing film 50, the display parts 100a and 100b can be easily distinguished from each other.

  Further, in the labeled article formed by attaching the security device 10 to the article 30, when the security device 10 is to be peeled from the article 30, the orientation layer 12 and the birefringence are the same as described with reference to FIG. Delamination occurs at the interface with the conductive layer 13. And with this delamination, the birefringent layer 13 and the reflective layer 14 can be broken along the contour of the adhesive pattern 16.

  FIG. 11 is a cross-sectional view schematically showing still another modification of the security device shown in FIGS. 1 and 2. FIG. 12 is a cross-sectional view schematically illustrating another example of a destroyed security device.

  The security device 10 shown in FIG. 11 is the same as the security device 10 described with reference to FIGS. 1 to 6 except that the following configuration is adopted.

  That is, in the security device 10, the reflective layer 14 is omitted. The security device 10 further includes a colored layer 17. According to this security device 10, a transmissive display is possible.

  The colored layer 17 is interposed between the birefringent layer 13 and the adhesive layer 15. The colored layer 17 faces the region Ab. When the colored layer 17 is provided, the design of the security device 10 can be improved.

  Further, in the labeled article formed by attaching the security device 10 to the article 30, when the security device 10 is to be peeled off from the article 30, for example, as described with reference to FIG. Delamination occurs at the interface with the birefringent layer 13. And along with this delamination, for example, the fracture shown in FIG. 12 may occur.

  When the colored layer 17 is interposed between the adhesive pattern 16 and the adhesive layer 15 and the colored layer 17 includes a part facing the adhesive pattern 16 and a part not facing the adhesive pattern 16, The colored layer 17 can be broken. In this case, only a part of the colored layer 17 remains on the peeled security device 10. Therefore, the security device 10 that has caused such destruction can relatively easily recognize that an illegal act has been performed.

  In addition, when performing a transmissive display, the article to which the security device 10 is attached needs to include a light transmission part. The light transmissive portion may be optically anisotropic, but is typically optically isotropic.

  Examples of the material of the light transmitting portion include acrylic resin, urethane resin, epoxy resin, vinyl chloride resin, styrene resin, cellulose resin, acetal resin, polyamide resin, polyimide resin, olefin resin, polycarbonate resin, polyether resin, polyester. Resins, phenolic resins or melamine resins can be used. An inorganic material such as glass and quartz may be used as the material for the light transmission portion.

  Instead of using a nematic liquid crystal material as the liquid crystal material, a cholesteric liquid crystal material may be used. When a cholesteric liquid crystal material is used, display utilizing selective reflectivity and circular polarization selectivity is possible.

Selective reflectivity is a property in which a cholesteric liquid crystal material strongly reflects light in a specific wavelength band of incident light. The central wavelength λ _{s of the} wavelength band in which the cholesteric liquid crystal material causes selective reflection and the wavelength band width Δλ in which the cholesteric liquid crystal material causes selective reflection are represented by the following equations (4), where the average refractive index of the cholesteric liquid crystal material is nm. ) And (5).

λ _s = nm × P (4)
Δλ = Δn × P / nm (5)
Here, the average refractive index nm is ^{_{1/2 [(n o 2 + n}} e 2) / 2], Δn is n _e -n _o.

As is clear from equations (4) and (5), the center wavelength λ _s and the wavelength bandwidth Δλ depend on the helical pitch P. Therefore, reflected light with high color purity can be obtained by appropriately setting the helical pitch P.

Equations (4) and (5) are applicable when light is irradiated from a direction parallel to the helical axis of the helical structure formed by the mesogen. When the incident direction of light is inclined with respect to the spiral axis, the apparent spiral pitch P increases. As a result, the center wavelength λ _s shifts to the short wavelength side, and the wavelength band width Δλ becomes narrow. Accordingly, when the angle formed by the observation direction and the spiral axis is increased, the display color is shifted to the short wavelength side.

  The circularly polarized light selectivity is a property that the cholesteric liquid crystal material reflects only one of the right circularly polarized light and the left circularly polarized light and transmits the other. For example, when the spiral structure formed by the mesogen of the cholesteric liquid crystal material is clockwise, the cholesteric liquid crystal material reflects only the right circularly polarized light and transmits the left circularly polarized light. The reflected light at this time is right circularly polarized light.

  As described above, when a cholesteric liquid crystal material is used instead of a nematic liquid crystal material as a liquid crystal material, selective reflection and circular polarization selectivity can be used for display. For example, in the security device 10 described with reference to FIG. 11, if a cholesteric liquid crystal material is used as the liquid crystal material, it is possible to determine authenticity using the difference between the color of transmitted light and the color of reflected light. That is, in this case, it is not necessary to use a polarizer for authenticity determination. In the security device 10 described with reference to FIG. 11, when a cholesteric liquid crystal material is used as the liquid crystal material, authenticity determination may be performed using a polarizer.

  When a cholesteric liquid crystal material is used, the helical pitch P is, for example, in the visible light range. Generally, when the helical pitch P is in the range of 380 nm to 780 nm, it is possible to make a true / false determination by visual observation. In general, when the helical pitch P is in the range of 400 nm to 700 nm, it is easy to determine the authenticity by visual observation.

  When a cholesteric liquid crystal material is used, the birefringent layer 13 may have a single layer structure or a multilayer structure. In the latter case, by stacking a plurality of layers having different helical pitches P, it is possible to express a color tone that cannot be expressed by, for example, a single layer structure when observed with the naked eye. When observed using a circular polarizer, different colors are displayed depending on the characteristics of the circular polarizer, for example, the design wavelength of the circularly polarized light transmitted by the circular polarizer and the rotation direction of the electric field vector. Is possible.

  When a cholesteric liquid crystal material is used, the birefringent layer 13 may include a birefringent portion that selectively reflects right circularly polarized light and a birefringent portion that selectively reflects left circularly polarized light. When the spiral pitch P in the former and the spiral pitch P in the latter are equal to each other, it is impossible or difficult to distinguish the display portions corresponding to these birefringent portions from each other with the naked eye. In this case, the display units corresponding to these birefringent portions can be easily discriminated from each other by observing them using a circular polarizer.

  Further, when a cholesteric liquid crystal material is used, the multilayer structure may include a black layer or a colored layer. By providing a black layer or a colored layer, a clear image can be obtained.

The top view which shows roughly the security device which concerns on the 1st aspect of this invention. Sectional drawing along the II-II line of the security device shown in FIG. The top view which shows an example of the image which the security device shown in FIG.1 and FIG.2 displays. The top view which shows roughly an example of the image which can be observed when the security device shown in FIG.1 and FIG.2 and a linearly polarizing film are piled up. The perspective view which shows the other example of the image which the security device shown in FIG.1 and FIG.2 displays. The perspective view which shows the further another example of the image which the security device shown in FIG.1 and FIG.2 displays. The top view which shows an example of a labeled article schematically. Sectional drawing which shows an example of the destroyed security device roughly. Sectional drawing which shows roughly the modification of the security device shown in FIG.1 and FIG.2. Sectional drawing which shows schematically the other modification of the security device shown in FIG.1 and FIG.2. Sectional drawing which shows schematically the further another modification of the security device shown in FIG.1 and FIG.2. Sectional drawing which shows the other example of the destroyed security device roughly.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Security device, 11 ... Base material, 12 ... Orientation layer, 13 ... Birefringent layer, 14 ... Reflective layer, 15 ... Adhesive layer, 16 ... Adhesion pattern, 17 ... Colored layer, 30 ... Article, 31 ... Card Substrate, 32a ... printed layer, 32b ... printed layer, 100a ... display unit, 100b ... display unit, 100c ... display unit, Aa ... region, Ab ... region, Ac ... region, 130a ... portion, 130b ... portion, 130c ... portion.

Claims (6)

  A birefringent layer made of a solidified liquid crystal material, an adhesive pattern in which one main surface is in contact with a part of the birefringent layer, a part in contact with the other main surface of the adhesive pattern, and the other Part of which has a multilayer structure of three or more layers including an adjacent layer in contact with the birefringent layer, and in the multilayer structure, a plurality of contact portions each consisting of two layers in contact with each other, The security device, wherein the contact portion including the birefringent layer and the adjacent layer has a lower interlayer adhesion strength between the two layers compared to the remaining contact portion.   The security device according to claim 1, wherein the multilayer structure includes a reflective layer.   The security device according to claim 2, wherein the reflective layer is made of a mixture containing a light transmissive resin and metal particles.   The security device according to claim 1, wherein the multilayer structure includes a black layer or a colored layer.   The security device according to any one of claims 1 to 4, wherein the multilayer structure includes an adhesive layer for attaching the security device to an article.   An article with a label comprising the security device according to any one of claims 1 to 5 and an article that supports the security device.

Images