JP2009139766A - Polarized latent image laminate and medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarized latent image laminate which is highly durable and has high visibility of a latent image. <P>SOLUTION: The polarized latent image laminate is characterized in that a polarized latent image device made of a phase shifter and/or polarizer is disposed on at least part between two sheets of stretched polymer films which are laminated such that stretched directions vertically cross each other. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a polarization latent image laminate and a medium using the same.

  Conventionally, authentication methods such as cards and passports, and securities media such as gift certificates and stock certificates have been used by attaching a device that is difficult to forge and visually or using a verification tool. Yes.

  In recent years, the distribution of counterfeit products has become a problem, and in order to prevent such distribution, the use of technology equivalent to securities is increasing.

  The anti-counterfeiting technology includes (1) a so-called overt technique in which a general user can recognize that the anti-counterfeiting technique can be determined, and (2) a so-called covert technique in which only a specific user knows the existence of the anti-counterfeit technology and can determine the authenticity Divided.

  Typical examples of the overt technique include a diffractive structure forming body such as a hologram, and a multilayer interference film such as an optically variable ink (abbreviated as OVI). Typical examples of the covert technique include fluorescent printing and line latent images. Both occupy important positions and are usually commercialized by a combination of these.

Also proposed are devices that change the optical axis of the phaser using a pattern, devices that change the optical axis of the phaser using a pattern and a polarizer, and devices that change the optical axis of the polarizer using a pattern. ing.
Special table 2001-525080 gazette

  However, since the device is a thin coating film on at least one side, it is difficult to improve light resistance, abrasion resistance, and the like. Even when covered with a stretched film, the stretched film is weak against the tearing force in the stretching direction, and the durability is lowered. Further, since it has birefringence, it is difficult to combine with a polarization latent image device.

  An object of the present invention is to provide a polarized latent image laminate having high resistance and high visibility of a latent image, and a medium using the same.

  The invention according to claim 1 is characterized in that a polarization latent image device comprising a phase retarder and / or a polarizer is provided at least in part between two stretched polymer films laminated with their stretching directions orthogonal to each other. A polarization latent image laminate.

  The invention according to claim 2 is the polarization latent image laminate according to claim 1, wherein a reflective layer is provided in a lower layer of the polarization latent image device.

  The invention according to claim 3 is the polarization latent image laminate according to claim 2, wherein a diffractive structure is formed in the reflective layer.

  According to a fourth aspect of the present invention, the polarization latent image device comprises a liquid crystal molecule or dichroic dye aligned at a first angle, and a liquid crystal molecule or dichroic dye aligned at a second angle. The polarization latent image laminate according to claim 1, wherein the polarization latent image laminate is provided.

  The invention according to claim 5 is characterized in that the liquid crystal molecules or dichroic molecules of the polarization latent image device are aligned by a rubbing alignment method, a photo alignment method, or an emboss alignment method. This is a polarization latent image laminate.

  The invention according to claim 6 is a medium comprising at least a part of the polarization latent image laminate according to any one of claims 1 to 5.

  In the polarization latent image laminate of the present invention, the polarization latent image device is sandwiched between stretched polymer films whose stretching directions are orthogonal from both sides, so that it is difficult to tear from any direction and the resistance can be improved, and the phase difference is canceled out. Therefore, the visibility of the latent image can be improved.

  The term phase shifter as used in the present invention refers to an element that changes the relative phase difference between the x and y components of an electric field to produce the above phase difference. Examples of phase retarders include oriented liquid crystals and liquid crystal polymers; extruded unstretched films such as PP, PE, PET, PPS, and PEN films; uniaxially stretched films; biaxially stretched films; and the like; inorganic crystals such as calcite and quartz Can be mentioned.

  In the present invention, the term “polarizer” is a general term for devices having dichroism. As an example, an absorption polarizer obtained by impregnating PVA with iodine or a dichroic dye and stretched and aligned, or an absorption polarizer obtained by aligning a dichroic dye on an alignment film, or cholesteric liquid crystal with λ / 4 reflective polarizer combined with a phase retarder, reflective polarizer with a birefringent multilayer film (manufactured by 3M), prism polarizer formed into a lenticular lens with a Brewster angle, and diffraction grating for birefringent material A birefringent diffractive polarizer formed in a shape, a diffractive polarizer in which grooves of a diffractive structure are formed deeply, and the like can be used. In addition, any element that can separate or extract a specific polarization component by reflected light or transmitted light can be used as a polarizer in the present invention.

  The polarization latent image device referred to in the present invention is a patterned birefringent layer or a combination thereof with a polarizer, a birefringent layer patterned with a slow axis in two or more directions, or a combination thereof and a polarizer, Examples include a patterned polarizer obtained by patterning a polarizer with two or more optical axes.

  The slow axis is the axis that has a small refractive index and a relatively high speed of light in the phaser, and is called the fast axis, whereas the axis that has a small refractive index and a relatively slow speed of light. It points to.

  Pattern birefringent layers can be formed by printing liquid crystal in a pattern, partially aligning liquid crystal, pasting a birefringent stretched film in a pattern, or birefringent stretched film. There is a method of partially destroying birefringence by giving a physical or chemical stimulus partially.

  There are gravure printing, flexographic printing, offset printing, and the like as a method for printing the liquid crystal in a pattern. In order to control the alignment direction of the liquid crystal, a rubbing alignment method, a photo alignment method, an emboss alignment method, or the like can be used.

  The photo-alignment method is a method that irradiates the film on the substrate with light having anisotropy such as polarized light, and induces rearrangement of molecules in the film or anisotropic chemical reaction. This makes use of the fact that liquid crystal molecules are aligned. Photoalignment mechanisms include photoisomerization of azobenzene derivatives, photodimerization and crosslinking of derivatives such as cinnamic acid ester, coumarin, chalcone and benzophenone, and photolysis of polyimide and the like.

  The rubbing method is a method of rubbing an alignment film produced by applying a polymer solution on a substrate with a cloth, which utilizes the property that the properties of the alignment film surface change in the rubbing direction and liquid crystal molecules are aligned in this direction. It is. For the alignment film, polyimide, PVA, or the like is used.

  The emboss alignment method is a method in which fine grooves are embossed by embossing on a substrate, and the liquid crystal is aligned along the grooves.

  In order to partially align the liquid crystal, a method of forming a patterned birefringent layer by forming a patterned alignment film by applying a mask during the formation of the alignment film and coating the liquid crystal on the entire surface Can be given.

  A birefringent layer or polarizer patterned with two or more optical axes can be produced by coating a liquid crystal or a dichroic dye on an alignment film formed so as to be aligned in two or more directions.

  In order to form the alignment film so that the liquid crystal or the dichroic dye is aligned in two or more directions, a photo alignment method, a rubbing alignment method, or an emboss alignment method can be used.

  When using the photo-alignment method, pattern exposure through a photomask with polarized light in an appropriate wavelength band or non-polarized light from an oblique direction, and exposure by changing the direction to process the unexposed area An alignment film that aligns the liquid crystal or the dichroic dye beyond the direction can be formed.

  When the rubbing alignment method is used, the entire surface of the aligning agent applied on the substrate is rubbed with a cloth, partially masked, rubbed with the cloth again after changing the direction, and then the mask is removed to remove 2 An alignment film that is aligned in the direction or more can be formed.

  In the emboss alignment method, liquid crystals or dichroic dyes can be aligned in two or more directions by forming fine grooves in two or more directions.

  As a method for forming these alignment agents on the substrate, known methods such as a gravure coating method, a micro gravure coating method, and a melt extrusion method can be used.

  The liquid crystal or dichroic dye applied on the alignment film may be a polymer having orientation or a monomer having a reactive functional group such as an acrylic group. As a method for forming a liquid crystal or a dichroic dye on the alignment film, a known method such as a gravure coating method or a micro gravure coating method can be used. The orientation of the coated liquid crystal or dichroic dye can be promoted by heat treatment. The liquid crystal or dichroic dye monomer having a reactive functional group is cured by electron beam, ultraviolet light or heat after alignment.

  A birefringent layer or polarizer patterned with a slow axis in two or more directions can be used such that the alignment film itself has birefringence or polarization dichroism by the photo-alignment method or rubbing method. It doesn't matter.

The birefringent material is a material having a transparent birefringence. Birefringence means that the refractive index of a substance varies depending on the optical axis direction. When light is incident on a substance having birefringence, an extraordinary ray e (refractive index: _ne ) and an ordinary ray o (refractive index: n). _o ) a phenomenon in which a phase difference occurs.

  This difference in refractive index between extraordinary rays and ordinary rays is called birefringence Δn and is expressed by the following equation.

Δn ₌ n e -n _o
Further, the phase difference value δ is proportional to the layer thickness d passing through the birefringent material and is expressed by the following equation.

δ = Δn · d
That is, the phase difference value is proportional to the film thickness. Further, when a reflective layer is used, the phase difference value is doubled because the birefringent material passes twice before and after reflection.

  When the phase difference value is half of the wavelength λ of transmitted light (λ / 2), when the angle between the slow axis of the birefringent material and the polarization plane of the polarized light is θ, it has the property of rotating the polarization plane by 2θ. Therefore, when θ = 45 °, the polarization plane rotates 90 °.

  When a retardation film having a retardation value of λ / 4 is formed on the reflective layer and a polarizing film is overlaid, when the angle formed by the transmission optical axis of the polarizing film and the slow axis of the retardation film is 45 °, Since the light transmitted through the film cannot be transmitted when it rotates 90 ° and returns to the polarizing film, it becomes a dark part. In addition, when the angle formed by the transmission optical axis of the polarizing film and the slow axis of the phase shifter is 0 °, the light transmitted through the polarizing film returns as it is and can be transmitted.

  In addition, as a property of the birefringent material, when passing through two layers whose slow axis directions are parallel, the phase difference values are integrated, and when the slow axis direction is two layers perpendicular, the phase difference values cancel each other.

  When polarized light is transmitted through a birefringent material, the phase difference value δ of the birefringent material and the angle formed by the optical axis of the transmitted polarized light and the slow axis of the birefringent layer And the state of the transmitted polarized light changes.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is an exploded perspective view showing an example of a polarization latent image laminate according to the present invention. As shown in FIG. 1, the polarization latent image device (13) is disposed between two polymer films (11) and (12). Polymer films (11) and (12) are stretched polymer films. FIG. 1 shows the polymer film (11) and (12) and the optical axis direction (14) of the polarization latent image device (13). FIG. 2 is a plan view of the polarization latent image laminate of FIG.

  As the polymer films (11, 12), resin films such as PET, PP, PE, TAC, and PEN can be used. A polarizing latent image device (13) is laminated between these films to form a polarizing latent image laminate (FIG. 1). As for the thickness of the polymer film to be used, 12-200 micrometers is desirable.

  The polymer films (11, 12) can be used regardless of stretching or non-stretching. Since the polymer film exists on both sides of the polarization latent image device, the chemical resistance and the wear resistance are remarkably improved. Light resistance can be improved by using a polymer film in which an ultraviolet absorber is kneaded.

  A polymer film is preferred because a stretched film is tougher. However, there are drawbacks when using a stretched film. The first drawback is that it is easy to tear in the stretching direction. The second drawback is that it has birefringence with the stretching direction as the optical axis. The present invention provides means for solving these drawbacks by bonding the two polymer films with the stretching directions orthogonal to each other.

  As a result of bonding with the stretching directions orthogonal to each other, when a tearing force is applied, any of the polymer films is not in the stretching direction and is not easily torn. Further, when the stretching directions of the two polymer films are orthogonal, the phase difference cancels out, so that the high contrast can be maintained without greatly deviating the design of the birefringent polarization latent image device.

A reflective layer can be provided if necessary. The reflective layer may be provided on the outside of the two polymer films. As the reflective layer, a metal or a high refractive index ceramic can be used. As the metal, in addition to metals such as Al, Sn, Ag, Cr, Ni, and Au, alloys such as Inconel, bronze, and aluminum bronze can be used. As the ceramic, a high refractive index material such as TiO ₂ , ZnS, or Fe ₂ O ₃ can be used. These materials are formed on a substrate with a thickness of about 10 nm to 100 nm using vapor deposition, sputtering, ion plating, or the like. Moreover, metal foil and a ceramic board can be used as a base material. You may transfer what was formed in another base material by the said method.

  Since the reflective layer is transparent when the reflective layer is a half mirror or ceramic, it can be colored on the back side in order to prevent disturbance due to the background and increase the visibility of the latent image. The coloring may be a pattern or the entire surface. Existing printing and coating methods can be used for the colored layer.

  The reflective layer may be provided in a pattern. Examples of the method of providing the pattern include pasta processing, washing sea light processing, and laser processing.

  The reflective layer may be provided with a diffractive structure. The diffraction structure image is an image formed by a diffraction structure, and a hologram and a diffraction grating can be used as the diffraction structure.

  The hologram is a relief type master plate made of a fine uneven pattern by an optical photographing method, and then a nickel press plate is produced by duplicating the uneven pattern from the master plate by an electroplating method, and Mass replication is performed by a method in which the press plate is heated and pressed onto a layer on which a hologram is formed. This type of hologram is called a relief hologram.

  Different from holograms that shoot such actual ones, diffraction gratings use multiple simple diffraction gratings in small areas as pixels, grating images, dot matrices (pixelgrams, etc.) It represents an image called. An image using such a diffraction grating is mass-replicated in the same manner as a relief hologram.

  When it is difficult to form a diffractive structure on the substrate, a diffractive structure forming layer can be provided. The diffractive structure may be formed before the reflective layer is formed, the reflective layer may be formed so that the shape follows the diffractive structure, or the diffractive structure may be formed directly on the reflective layer.

  FIG. 3 is an exploded perspective view of the polarization latent image laminate according to one embodiment of the present invention. As shown in FIG. 3, a polarization latent image device (23) is formed on one stretched polypropylene (PP) substrate (21), and a diffraction structure forming layer (25) is formed on the other PP substrate (22). Is formed. The two PP substrates are arranged so that the surface on which the polarization latent image device (23) is formed faces the surface of the PP substrate (22) on which the diffraction structure forming layer (25) is not formed. Has been. Furthermore, two PP base materials are arrange | positioned so that both optical axis directions may orthogonally cross. The optical axis direction (24) of PP base material (21) and a polarization | polarized-light latent image device (23) is shown. In addition, the optical axis direction of PP base material (22) is not shown.

  FIG. 4 is a plan view of the polarization latent image laminate of FIG. An image (28) is formed on the PP substrate (22).

  FIG. 5 is a sectional view taken along line X-X ′ of FIG. 4. The surface of the PP base material (21) where the polarization latent image device is formed and the surface of the PP base material (22) where the diffractive structure forming layer (25) is not formed are opposed to each other, and the adhesive layer (26 ) Is provided. Further, a protective layer (27) is formed on the surface of the diffractive structure forming layer (25).

  6 and 7 are views in which a verification tool (19) is superimposed on the polarization latent image device (13) portion of the polarization latent image laminate according to the present invention.

  When the polarization latent image devices (13, 23) in these polarization latent image laminates are observed with normal visual inspection without passing through a verification tool, the optical axis direction of the birefringent layer or the polarizer is determined by the human eye. The latent image cannot be seen because it cannot be distinguished. Therefore, it appears as a normal transparent polymer film or reflective layer or diffraction structure image.

  However, in the case of visual recognition through the verification tool (19), which is a polarizing film, or visual recognition sandwiched between the polarizing films, the polarized light passing through the polarizing latent image devices (13) and (23) Since the polarization state is changed by the polarizer or the polarizer and the transmittance of the polarizer on the viewing side is different, a latent image appears. As a result, the authenticity of the security medium can be determined.

  Further, depending on the design of the polarization latent image device, depending on the angle formed by the optical axis of the verification tool and the polarization latent image device, the latent image can be switched between positive (FIG. 6) and negative (FIG. 7).

[Production of latent image device forming film]
A transparent uniaxially stretched polypropylene film with a thickness of λ / 2 having a thickness of 50 μm and kneaded with UV absorber is coated with 10 μm of polypropylene resin melted by an extrusion method, and the liquid crystal molecules are at an angle of 45 °. Then, it was placed on a cooling roll having a fine concavo-convex structure for orientation with a pattern so as to form and cooled and fixed. An ultraviolet curable liquid crystal UCL-008 (manufactured by Dainippon Ink Manufacturing Co., Ltd.) with Δn = 0.18 at 550 nm was formed on the obtained film with a film thickness that would have a phase difference of λ / 4, A portion is applied by gravure printing in stripes, dried by heating in a drying oven at 65 ° C. for 60 seconds, irradiated with 0.5 J / cm ² ultraviolet rays using an ultraviolet lamp in a nitrogen gas atmosphere, cured, and latent A film on which an image device was formed was obtained.

[Production of hologram film]
A uniaxially stretched polypropylene film having a retardation value of λ / 2 with a thickness of 50 μm and kneaded with an ultraviolet absorber is coated with 10 μm of a polypropylene resin melted by an extrusion method. They were held and molded and cooled and fixed. An Al layer is formed on the surface on which the hologram (diffraction structure) is formed with a film thickness of 50 nm using a vacuum deposition method to form a diffraction structure formation layer, and a protective layer is coated with a one-component urethane resin to protect the surface. Formed. A chlorinated polypropylene having a glass transition temperature (Tg) of 50 ° C. was applied as an adhesive layer on the opposite side of the hologram by a gravure coating method with a dry film thickness of 2 μm to obtain a hologram film.

[Preparation of polarization latent image laminate]
The latent image device forming surface of the film on which the latent image device was formed and the adhesive layer surface of the hologram film were laminated at 100 ° C. so that the stretching direction (optical axis direction) of each film was orthogonal. A pattern was printed on the front and back using offset printing and intaglio printing on portions other than the latent image device to obtain a polarized latent image laminate.

[Effect of polarization latent image laminate]
In normal visual inspection without using a verification tool, both the front and back sides look like a hologram-formed medium, but when viewed through the verification tool from the latent image device forming film side, a latent image with high contrast appeared. This medium was highly resistant to tearing from any direction.

  These results show that by arranging the stretched films to be orthogonal to each other, the orthogonal phase differences cancel each other, the latent image by the liquid crystal functions as designed, and the polymer film in a direction that is difficult to tear is easy to tear This was due to the effect of covering the polymer film.

It is a disassembled perspective view of the polarizing latent image laminated body by this invention. FIG. 2 is a plan view of the polarization latent image laminate in FIG. 1. It is a disassembled perspective view of the polarizing latent image laminated body in the Example by this invention. FIG. 4 is a plan view of the polarization latent image laminate of FIG. 3. It is sectional drawing which follows X-X 'of FIG. It is the figure which piled up the verification tool on the polarizing latent image laminated body by this invention. It is the figure which piled up the verification tool on the polarization | polarized-light latent image laminated body by this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11, 12 ... Polymer film, 13, 23 ... Polarization latent image device, 14, 24 ... Optical axis direction, 19 ... Verification tool, 21, 22 ... PP base material, 25 ... Diffraction structure formation layer, 26 ... Adhesion layer, 27 ... protective layer, 28 ... image.

Claims (6)

  A polarizing latent image laminate comprising a polarizing latent image device comprising a phase retarder and / or a polarizer at least partially between two stretched polymer films laminated with their stretching directions orthogonal to each other.   The polarizing latent image laminate according to claim 1, further comprising a reflective layer in a lower layer of the polarizing latent image device.   The polarizing latent image laminate according to claim 2, wherein a diffractive structure is formed in the reflective layer.   The polarization latent image device comprises a liquid crystal molecule or dichroic dye aligned at a first angle and a liquid crystal molecule or dichroic dye aligned at a second angle. The polarization latent image laminate according to any one of 1 to 3.   The polarizing latent image laminate according to claim 4, wherein liquid crystal molecules or dichroic molecules of the polarizing latent image device are aligned by a rubbing alignment method, a photo alignment method, or an emboss alignment method.   A medium comprising at least a part of the polarization latent image laminate according to claim 1.

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