JP2015225333A - Forgery prevention medium and transfer sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a forgery prevention medium and a transfer sheet having a latent image as a high resolution image that can be formed by an on-demand system and can be recognized by use of a polarizing plate 66.SOLUTION: The forgery prevention medium includes an optical anisotropic layer and a high-reflectance perpendicular magnetization layer having a magnetic Kerr effect, in which an image is drawn in the high-reflectance perpendicular magnetization layer by irradiation heating with laser light 71 while applying a magnetic field so as to change a magnetization direction of a part where the image is drawn in the high-reflectance perpendicular magnetization layer, and changes in the magnetization direction can be visually recognized as a black-and-white image through a polarizing plate 66.

Description

  The present invention relates to a forgery prevention medium capable of recording personal information such as a face image for personal authentication as a latent image.

  Passports and ID cards often have face images for visual information authentication. Many of these facial images still use photographic paper overseas. However, there is a risk of tampering with photographic paper.

  For this reason, there is a strong tendency to digitize face images and reproduce them on authentication media. As a reproduction method, there are a thermal transfer method using a transfer ribbon in which a transfer layer is formed with a sublimation dye or a resin in which a pigment is dispersed, or a laser engrave method in which an image is formed by irradiating an authentication medium with a laser.

  These formed images has the advantage that possible anyone authentication anywhere because it can be authenticated visually. However, for the purpose of further improving the security, a latent image technique has been proposed in which formation information cannot be recognized by normal visual observation but can be recognized by using a filter.

  An example of the latent image technology is one using liquid crystal. First, an image-formed layer with an orientation pattern is prepared in advance on a substrate. Next, when a polymer liquid crystal material is applied to this alignment pattern and placed under appropriate conditions, the major axis of the liquid crystal is aligned in the direction of the alignment pattern. Various liquid crystal coating methods have been proposed. For example, there is a method using an ink jet (Patent Document 1).

  As a technique capable of forming a plurality of latent images, a method has been proposed in which contrast is increased by providing regularity in the alignment direction and a plurality of latent images can be formed (Patent Document 2).

  The point common to these techniques is that a layer in which an orientation pattern is formed in advance is necessary. In order to form a complicated pattern, it is necessary to expose a plurality of masks while precisely aligning them to create an alignment pattern, which complicates the process.

  Although complicated processes are effective because they themselves become security, on the other hand, there is a need to incorporate information on demand in recent years, and it is difficult to form images on demand with this method. It cannot be denied that there is a downside in terms of dealing with on-demand.

  As a method for incorporating on-demand information, there is a method often used in a pigment dispersion type ink ribbon, and there is a method of forming an image by transferring a medium in a dot pattern. When the ink ribbon is brought into contact with the transfer object and heat is applied, the heated portion of the ribbon is transferred to the transfer object. In recent years, there is a tendency to apply heat locally to form a high-definition image.

  FIG. 1 shows an outline of transcription. In the local heating method, when the heat generating element 11 is instantaneously heated by passing a current in a pulsed manner while the transfer medium 12 and the transfer target 13 are in contact with the micro heat generating element 11 having a size of 100 μm or less, the transfer medium The transfer layer is partially heated, and this portion 15 is transferred to the transfer target. The transfer head normally used for transfer has several hundred or more minute heating elements arranged in a line, and each heating element is heated in accordance with information on the image to be formed to form an image on the transfer body.

  Even if the size of the minute heating element is 50 μm, depending on the thickness of the transfer medium, the thermal responsiveness and the sharpness of the transfer layer, transfer may not be possible unless the size is larger than the heating resistor. As shown in FIG. 2, when the transfer medium is thick, heat is transferred to the surroundings by heat conduction from the medium substrate side until the necessary amount of heat reaches the transfer target, so that the region 24 larger than the size of the superheated body. Becomes a transferable area.

  In addition, aluminum, which is often used as a reflective material, has poor sharpness, so it is very difficult to transfer a set size that is transferred by controlling the temperature of the resistor.

  Latent image media using liquid crystals tend to be thicker than thermal transfer media, and the liquid crystals themselves are not sharp. In addition, since aluminum is often used, it is very difficult to form a high-resolution image by transferring a medium having a latent image structure. It is difficult to claim improved security for images with low resolution.

JP 2010-282153 A JP 2009-258151 A

  In view of the above problems, an object of the present invention is to provide an anti-counterfeit medium fake and transfer sheet having a latent image that can be formed on demand and can be recognized by using a polarizing plate as a high-resolution image. To do.

As a means for solving the above problems, the invention according to claim 1 is an anti-counterfeit medium having an optically anisotropic layer and a high-reflectivity perpendicular magnetization layer having a magnetic Kerr effect,
Drawing on the high reflectivity perpendicular magnetization layer by laser irradiation heating while applying a magnetic field, changing the magnetization direction of the drawn portion of the high reflectivity perpendicular magnetization layer,
The anti-counterfeit medium is characterized in that the change in the magnetization direction is visible as a black and white image by passing through a polarizing plate.

  The invention according to claim 2 is a transfer sheet, wherein a release layer, a forgery prevention medium according to claim 1 and an adhesive layer are sequentially laminated on a film substrate.

  The reflective layer of the latent image medium using liquid crystal is made of a magnetic Kerr effect material suitable for the latent image configuration, this medium is irradiated with a focused laser and heated locally, and an external magnetic field is applied to control the magnetic field direction. By doing so, it becomes possible to control the polarization direction to form a latent image on demand, and the latent image can be confirmed using a polarizing plate without using a large apparatus.

It is explanatory drawing of the outline | summary of thermal transfer. It is explanatory drawing of the outline | summary of a thermal transfer when using a thick transfer medium. It is explanatory drawing of a latent image. It is explanatory drawing of a magnetic Kerr effect. It is description of the method of changing a magnetic field direction locally. It is explanatory drawing of the method of reading the information which changed the polarization direction with the magnetic field direction. It is explanatory drawing of the method of forming an image in a latent image by the magnetic Kerr effect.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. The mechanism by which the latent image is established will be described. As shown in FIG. 3, the latent image is not visible with natural light, but can only be seen with polarized light. When the light 35 whose polarization direction is the same as the alignment direction of the liquid crystal is irradiated, it is reflected by the reflection layer 33 without being affected by the polarization plane in the liquid crystal alignment layer 32, passes through as it is, passes through the polarizing plate 31, and this portion looks bright.

  However, when the angle formed by the polarization method and the alignment direction is 45 degrees, the aligned liquid crystal alignment layer 32 exhibits the same effect as the ¼λ plate, so that it rotates 45 degrees when it reaches the reflection layer 33, and further the liquid crystal alignment layer At the time of exiting from 32, it further rotates by 45 degrees, so it differs from the original polarization direction by 90 degrees and cannot pass through the polarizing plate 31, so this part looks dark.

  As described above, the latent image formation utilizes the fact that the polarization direction of the reflected light 42 is different depending on the polarization direction and the orientation direction of the incident light 41. Therefore, if the polarization direction can be controlled by a method other than orientation, it is possible to form an image other than the image by orientation.

  There is a method of using the magnetic Kerr effect as a means of changing the polarization direction. This is a phenomenon in which the polarization direction rotates when polarized light is reflected by a certain kind of magnetic material 43. This phenomenon occurs in two ways, as shown in FIGS. 4a and 4b, between the direction of the magnetic field and the polarization, but FIG. 4a is more commonly used in applications where the plane of polarization is manipulated.

  Each of the magnetic bodies 43 has a unique Curie temperature. When the temperature exceeds this temperature, the direction of the magnetic field of the microscopic magnetic body in the material varies and the magnetic properties disappear. When an external magnetic field is applied above the Curie temperature, the magnetic field direction of the microscopic magnetic material in the material aligns with the magnetic field direction. In this state, cooling to the Curie temperature or lower keeps the state of the magnetic field aligned by the external magnetic field.

  There are magneto-optical disks (MO, MD, etc.) that use this principle. A conceptual diagram of these drive devices is shown in FIG. Laser light 52 is condensed and irradiated by a lens 53 onto a rotating disk, and heated locally. Then, the heated portion 511 where the disk is heated becomes equal to or higher than the Curie temperature. When the external magnetic field 54 is immediately applied in this state and the magnetic direction is recorded, the magnetic field distribution can be digitally distributed in the magnetic field such as the heating unit 512 to record information.

  If the polarizing plate 66 is set so that when the laser beam 61 for reading is irradiated on the recorded disk surface, the polarized light is transmitted through the reflecting surface having the original magnetic field distribution, the reflected light 62 is reflected by the polarizing plate unless otherwise operated. 66, but when the magnetic direction of the disk surface changes, the polarization state of the reflected light changes in the magnetic body 65, so that the reflected light 64 cannot pass through the polarizing plate. In this way, a digital signal can be read.

  This principle is applied to the reflection layer of the latent image medium so that the reflection layer is made of a magnetic material. If there is no particular operation, the image is the same as an ordinary latent image medium, so that an image according to the orientation pattern is obtained. However, when this medium is partially heated to a temperature above the Curie temperature, an external magnetic field is applied to this part and then cooled as it is, the magnetic field state of this part changes, so that the polarized light rotated by the liquid crystal layer is different from the magnetic reflecting layer. Rotate further with reflection.

  Therefore, the brightly displayed portion before changing the magnetic field state of the magnetic material becomes dark due to the rotating action of the magnetic field. On the contrary, a dark place before the magnetic field changes changes due to the rotating action. If such a method is used, a latent image can be formed on demand.

  For example, if the medium is heated to the Curie temperature or higher and laser light is condensed and irradiated by a lens like an optical disk, the laser spot becomes a dot for image formation. According to wave optics, the theoretical spot size of single wavelength light is half the wavelength. However, it is difficult to realize this size effectively, and since the diameter is actually about 1 μm, it is possible to form an image with dots of this size.

  The magneto-optical disk drive rotates the disk at 6000 rpm and records information at intervals of several tens of μm. Therefore, it is considered that the dot formation speed of about 100 MHz has been reached, and image formation is possible at a very high speed. is there.

  Next, an embodiment of the present invention will be described with reference to FIG. The image forming apparatus includes a heating laser 71, a condensing lens 72, a lens position sweeping mechanism, a drawing unit including a coil 73, and a sweeping unit for changing the two-dimensional relative position of the drawing unit and the latent image medium 74. The light emitted from the laser 71 is incident on the lens 72, condensed, and irradiated onto the latent image medium 74.

  Image information that has been subjected to image processing so as to be suitable for a latent image is input to the image forming apparatus. The apparatus moves the drawing unit from the edge of the medium, irradiates the laser 71 at a place necessary for image formation with the previous image information, and simultaneously forms a magnetic field by causing a current to flow through the coil of the magnetic field generator 73 to form the magnetic field of the medium reflection layer. Change direction. The sweep unit operates the drawing unit so as to perform such an operation on the entire surface of the latent image medium 74 to form an image.

  Since the magneto-optical disk is a polycarbonate disk, the distance between the disk and the condenser lens can be made constant to some extent. Since the latent image medium is usually formed on a film, the medium is not always within the focal length of the lens focal point due to distortion of the film or the like. Therefore, it is preferable that a distance detection mechanism and a lens position correction mechanism are provided so that the distance between the lens and the medium irradiation point is constant.

  By this mechanism, it is always monitored whether the condenser lens focus is on the medium, and the lens position is adjusted as needed. As a means of confirming whether the focal point is on the medium, the focal point of the condensing lens can be adjusted by placing a minute distance sensor next to the lens, or by providing the condensing lens with an autofocus mechanism so that the load of the medium pattern is in focus. There are also ways to make it fit the medium.

<High reflectivity perpendicular magnetization layer>
Desirable properties as a reflective material include 1) high reflectivity, 2) strong coercivity, and 3) high Curie temperature. If the reflectance is low, the entire image becomes dark and the contrast is low, and if the holding power is low, the formed image cannot be maintained for a long time. If the Curie temperature is low, the holding power is low. For example, if the Curie temperature is stored at a high temperature, such as in an automobile room directly under the sun, the Curie temperature may be exceeded and image holding may not be possible. Also, the car rotation angle is not necessarily large. For example, in the latent image configuration described in Patent Document 2, the appearance of the latent image changes every 22.5 degrees. Therefore, it does not make sense if the Kerr rotation angle is not less than this.

  In the example of Patent Document 2, since the period is 22.5 degrees, if approximately half of this is a guide, there is USbTe with a Kerr rotation angle of 9 degrees as a reflective material. However, since this material has a low Curie temperature, a BiMn-based reflective material provided with an intermediate layer aiming at the Kerr rotation angle enhancement effect is taken as an example of a reflective layer configuration desirable for the present invention. Several research results have been published for this reflective material system. When a reflective layer having a total thickness of less than 100 nm is formed in the order of Bi and Mn, the Kerr rotation angle becomes about 2.5 degrees.

  There is also a report that a rotation angle of 3.5 degrees can be obtained when Nd is further formed thereon. As an example, “Mn1.27-XBiNdx thin film magnetic properties” Satoshi Matsuda, Takeshi Muzuka, Bulletin of Faculty of Education, Chiba University p54, 2006 can be mentioned.

  As a method for forming the reflective layer, vapor deposition, ion plating, etc. are generally used. The reflective layer formed in this way is annealed at several hundred degrees, and further, a magnetic field of 10 kOe can be written to align the magnetization direction. By performing so-called initialization, a high reflectivity perpendicular magnetization reflective layer is obtained. Since a Kerr rotation angle of 3.5 degrees is not sufficient, a multilayer reflective layer having an effect of enhancing the rotation angle is formed as an intermediate layer. It is possible to enhance the rotation angle by multiple reflection at this intermediate layer. In 2011 “Research and Development of Ultra-Realistic Communication Technology Using Innovative 3D Video Technology” and “Problem A Device Technology for Innovative 3D Video Display” R & D Objectives / Results and Future Research Plan Therefore, when the Si-N layer is formed as an intermediate layer of about 40 nm, it is said that a rotation angle of about 4 times can be obtained. If such a layer is formed, the apparent rotation angle can be enhanced to 10 degrees or more.

  When enhancing the Kerr rotation angle by the intermediate layer, the reflectance generally decreases when the degree of enhancement is large. Since the degree of lowering depends on the material used, it is necessary to set the intermediate layer thickness in consideration of the balance with the reflectance while determining the required rotation angle.

<Optically anisotropic layer>
The formation of the optically anisotropic layer will be described using Patent Document 2 as an example. In Patent Document 2, there are four regions with different orientation directions, and an image is formed by skillfully arranging these regions. Examples of the alignment direction setting method include photo-alignment and rubbing alignment, and a phase difference layer is formed by arranging a liquid crystal substance on the optically anisotropic layer formed by image alignment and image formation. The retardation layer is preferably set so that the retardation is ½ of the design wavelength.

  Usually, a wavelength in the green region where human visibility is high is often applied as the set wavelength, but there are cases where it is set to a wavelength with lower visibility depending on the purpose.

<Forgery prevention medium>
A high reflectivity perpendicular magnetization layer having a magnetic Kerr effect and an optically anisotropic layer were sequentially laminated on the card substrate, and a face photograph was drawn on the high reflectivity perpendicular magnetization layer by laser irradiation while applying a magnetic field. Although the drawn face photograph cannot be seen as it is, a black and white face can be recognized by observing with a polarizing film.

<Preparation of transfer sheet>
A transfer sheet is prepared by providing a release layer on a film substrate, an optically anisotropic layer, a highly reflective perpendicular magnetization layer having a magnetic Kerr effect, an adhesive layer, and a release paper. After being attached to the card substrate, a face photograph was drawn on the high-reflectivity perpendicular magnetization layer by laser irradiation while applying a magnetic field. Although the drawn face photograph cannot be seen as it is, a black and white face can be recognized by observing with a polarizing film.

DESCRIPTION OF SYMBOLS 11 ... Heat generating body 12 ... Transfer medium 13 ... Transfer medium 14 ... Heating area 15 ... Transfer part 21 ... Heat generating body 22 ... Transfer medium 23 ... Transfer medium 24 ... heating region 25 ... transfer part 31 ... polarizing plate 32 ... liquid crystal alignment layer 33 ... reflective layer 34 ... incident natural light 35 ... incident polarized light 36 ... alignment layer Transmitted light 37 ... Reflected light 38 ... Alignment layer transmitted light 39 ... Transmitted light 3a ... Alignment layer transmitted light 3b ... Reflected light 3c ... Alignment layer transmitted light 3d ... Transmitted light 41 ... Incident light 42 ... Reflected light 43 ... Magnetic body 44 ... Magnetic body 51 ... Magnetic body 52 ... Laser light 53 ... Lens 511 ... Heating unit 512 ... -Heating part 54 ... External magnetic field 61 ... Laser light (incident light)
62 ... reflected light 63 ... magnetic material 64 ... reflected light 65 ... magnetic material 66 ... polarizing plate 71 ... laser 72 ... condensing lens 73 ... magnetic field generator 74 ... Latent image medium 75 ... Moving direction of 2-axis stage

Claims (2)

An anti-counterfeit medium having an optically anisotropic layer and a high-reflectance perpendicular magnetization layer having a magnetic Kerr effect, wherein the high-reflectance perpendicular magnetization layer is drawn by laser irradiation heating while applying a magnetic field, and the high-reflection Change the magnetization direction of the drawn portion of the perpendicular magnetic layer,
An anti-counterfeit medium characterized in that the change in the magnetization direction is visible as a black and white image by passing through a polarizing plate.   A transfer sheet, wherein a release layer, the anti-counterfeit medium according to claim 1 and an adhesive layer are sequentially laminated on a film substrate.

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