JP4773930B2 - Biaxially stretched multilayer laminated film and identification medium - Google Patents

Description

  The present invention relates to a biaxially stretched multi-layer laminated film, and more specifically, planar objects such as packages in which products are packed, passports, cards, banknotes, cash vouchers, securities, certificates, gift certificates, pictures, tickets, public competition voting tickets, etc. The present invention relates to a biaxially stretched multilayer laminated film that can be suitably used as an identification medium for identifying the authenticity of an object or various three-dimensional objects, for example, an anti-counterfeit seal.

  Multilayer laminated films that exhibit selective wavelength reflectivity due to optical interference have been known. First, the basic principle of a multilayer laminated film exhibiting selective wavelength reflectivity due to optical interference will be described. FIG. 1 is a diagram illustrating a state in which light incident on a multilayer laminated film is selectively reflected by each layer. When white light is incident on a multilayer laminated film, the light is reflected, absorbed, and transmitted according to its wavelength. Especially, the reflected light interferes with each other due to the optical path difference of reflection in each layer, and only light in a specific wavelength region is reflected. There is a nature of being reflected. This is called a selective reflection effect. The reflection wavelength and the reflectance can be obtained by the following equations.

Formula 1 λ = 2 × (nA · dA · cos θ + nB · dB · cos θ)
Formula 2 R = (nA / nB-1) ² / (nA / nB + 1) ²
Here, λ: reflection wavelength, nA: A layer refractive index, nB: B layer refractive index, θ: reflection angle, dA: A layer film thickness, dB: B layer film thickness, R: reflectance.
This selective reflection wavelength region can be arbitrarily set depending on the refractive index and film thickness of the material such as a polymer forming each layer, the number of layers, and the like.

  Further, as is clear from the above formula, the multilayer laminated film has a feature that the color changes depending on the viewing angle. This is because when the incident light is oblique, the film thicknesses dA and dB are apparently reduced, so that the center wavelength λ shifts to the short wavelength side. This phenomenon can also be explained as follows. That is, incident light is reflected due to the difference in refractive index at each interface of the multilayer laminated film, and the reflected light interferes with each other according to the optical path difference. This optical path difference becomes smaller as it is incident and reflected from an angle close to parallel to the surface. Therefore, as the multilayer laminated film is viewed from a direction more parallel to the surface, the optical path difference between the reflected lights reflected at each interface becomes smaller, and the wavelengths that interfere and strengthen each other shift to the shorter wavelength side. According to this principle, when the multilayer laminated film is gradually tilted from the state of being viewed from the front, it is observed that the light that interferes and strengthens shifts to the short wavelength side.

  For example, the reflection color of a multilayer laminated film that turns red when observing normal incident light (that is, when viewed from the front) is orange, yellow, as the viewing angle increases (that is, the multilayer thin film is tilted) Observed to change in order of green, blue-green, and blue (color shift).

  By the way, conventionally, as a method for preventing forgery of a card or a certificate, for example, a technique of applying a hologram or applying special ink to the surface of an object is known. (For example, Unexamined-Japanese-Patent No. 2001-315243). In holograms, identification is performed by visually confirming that the pattern changes depending on the viewing angle or viewing angle. In addition, special inks include fluorescent inks and magnetic inks. When these inks are used, they are not different from normal inks by visual observation, but they can be hidden by irradiating ultraviolet rays or detecting them with a magnetic sensor. The object can be identified by the information. In addition, as an identification medium for an object, a film having a reflection characteristic that selectively reflects light depending on a viewing angle is used. As a method for preventing forgery of cards and certificates, an example using cholesteric liquid crystal ink or film is used. Is well known. (For example, Japanese Patent No. 3244278)

  However, in order to obtain high discriminability only by the hologram, a high-cost technique is required, and there are cases where it cannot be used depending on the type of the object. In addition, fluorescent inks and magnetic inks are easily obtained because similar products are easy to obtain, and the identification device is large and requires a power source. Further, the cholesteric liquid crystal used as a raw material for the identification medium of the object is high in cost, and the manufacturing cost of the identification medium is high, so that it is not suitable for use in a product with a low unit price.

  As a method for solving the above problems, a method using selective wavelength reflectivity by optical interference using the above-mentioned multilayer laminated film has been proposed (Japanese Patent Laid-Open No. 2005-59332, International Publication No. 04 / 024439 pamphlet). However, the above-described film has a problem in that since the reflection is seen in the visible light, the background pattern is colored and the visibility is lowered.

  In addition, in Japanese translations of PCT publication No. 2002-509041, the example which uses a colorless and transparent multilayer laminated film is proposed, but this is a film which reflects infrared rays, and a reflection wavelength shifts to a visible light region by a viewing angle. There is a problem that the film can be designed only in the long wavelength region of visible light.

JP 2001-315243 A Japanese Patent No. 3244278 JP 2005-59332 A International Publication No. 04/024439 Pamphlet Special table 2002-509041 gazette

  The present invention is colorless and transparent, and reflects so that only the P-polarized component of incident light can be visually recognized at a specific viewing angle, while the S-polarized component does not reflect so much as to be visible and appears colorless and transparent. It is an object of the present invention to provide a multilayer laminated film that exhibits selective reflectivity of light depending on the viewing angle and polarization.

  Furthermore, it is an object of the present invention to provide an identification medium for an object that cannot be easily counterfeited, can easily and reliably identify authenticity, and can be manufactured at a low manufacturing cost. To do.

  As a result of various investigations, the present inventors have laminated a thermoplastic resin having negative intrinsic birefringence and a thermoplastic resin different from the thermoplastic resin, and matched the in-plane refractive index after stretching, while in the thickness direction. By providing a sufficient refractive index difference, the reflected light can be visually recognized only in the P-polarized light and the S-polarized light is substantially transparent at a specific viewing angle while being substantially transparent at the front incidence. The present inventors have found that a biaxially stretched multi-layer laminated film can be prepared and have reached the present invention.

  That is, the present invention provides a first layer made of a crystalline thermoplastic resin having a negative intrinsic birefringence having a thickness in the range of 0.05 to 0.5 μm, and a thickness in the range of 0.05 to 0.5 μm. A multilayer laminated film in which 100 layers or more of the second layers made of the thermoplastic resin are alternately laminated, and the reflectance peak height for incident light from a plane perpendicular to the film surface is 5% or less. The reflectance peak height is 5% or less for S-polarized light among the light incident on the film at an angle of 60 °, and P of the light incident on the film at an angle of 60 °. A biaxially stretched multilayer laminate film having a reflectance peak height of 20% or more with respect to polarized light.

According to the present invention, it is colorless and transparent, and reflects so that only the P-polarized component of the incident light can be visually recognized at a specific viewing angle, while the S-polarized component does not reflect so much as to be visible and appears colorless and transparent. It is possible to provide a multilayer laminated film that exhibits selective reflectivity of light depending on viewing angle and polarization.
Further, it is possible to provide an identification medium that cannot be easily counterfeited, can be easily and reliably identified as authentic, and can be manufactured at a low manufacturing cost.

[optical properties]
The biaxially stretched multilayer laminated film of the present invention has a reflectance peak height of 5% or less with respect to incident light from a plane perpendicular to the film surface. If the reflectance peak height exceeds 5%, the color of the light reflected from the film is visually recognized, so that the hue changes when printing or the like is applied to the base.

  The biaxially stretched multilayer laminated film of the present invention has a reflectance peak height of 5% or less for S-polarized light, which is incident at an angle of 60 ° with respect to the film surface, and 60 ° with respect to the film surface. Of the light incident at an angle, the height of the reflectance peak for P-polarized light is 20% or more. Having this characteristic is essential in the present invention, and it can be used as an identification medium by having this property. Specifically, the authenticity of the object to which the identification medium is attached can be identified by observing the identification medium through the polarizing plate. Of the light incident at an angle of 60 ° with respect to the film surface, if the reflectance peak height with S polarization exceeds 5%, the hue is visually recognized, and the light incident at an angle of 60 ° with respect to the film surface. If the reflectance peak height for the P-polarized component is less than 20%, sufficient hue is not visually recognized.

  Here, P-polarized light represents a polarized light component including a vibration component parallel to the plane including the incident angle and the reflection angle, and S-polarized light includes a polarized light component including a vibration component perpendicular to the surface including the incident angle and the reflection angle. Represents. The height of the reflectance peak is the difference between the baseline and the peak when the reflectance for each wavelength is measured.

  The biaxially stretched multilayer laminated film of the present invention has a transmittance of 85% or more from the viewpoint of ensuring transparency. If the transmittance is less than 85%, the transparency of the film is impaired, so that the visibility of a pattern or the like printed on the base is lowered.

[Layer structure]
The biaxially stretched multilayer laminated film of the present invention has a first layer made of a crystalline thermoplastic resin having a negative intrinsic birefringence having a thickness in the range of 0.05 to 0.5 μm, and a thickness of 0.05. It takes the structure which laminated | stacked 100 layers or more alternately with the 2nd layer which consists of a thermoplastic resin in the range of -0.5 micrometer.

[First layer]
The crystalline thermoplastic resin having negative intrinsic birefringence constituting the first layer in the present invention has a negative intrinsic birefringence value calculated from the dielectric constant distribution with the molecular chain direction of the polymer as an axis. It is a crystalline thermoplastic resin. Examples of the polymer satisfying the above include syndiotactic polystyrene, isotactic polystyrene, polyethylene-1,4-naphthalenedicarboxylate and copolymers thereof.

[Second layer]
As the thermoplastic resin constituting the second layer in the present invention, one that can be adjusted to the in-plane refractive index after stretching of the crystalline thermoplastic resin constituting the first layer is used.

As a method of matching the refractive index of the thermoplastic resin of the second layer with the in-plane refractive index of the first layer,
1) A crystalline thermoplastic resin having positive intrinsic birefringence is used as the thermoplastic resin of the second layer, and the in-plane refractive index after stretching is after stretching of the crystalline thermoplastic resin of the first layer. To match the in-plane refractive index of
2) A method of matching an in-plane refractive index after stretching of the crystalline thermoplastic resin of the first layer using an amorphous resin as the thermoplastic resin of the second layer,
3) A method of using a crystalline thermoplastic resin as the thermoplastic resin of the second layer and making it isotropic after the stretching step can be used.

  When the above-described first method is used, a combination of syndiotactic polystyrene as the first layer and polyamide having no aromatic ring as the second layer can be given. An example of this polyamide is nylon 6.

  In the case of using the second method described above, the crystalline thermoplastic resin constituting the first layer is used as the thermoplastic resin constituting the second layer so that anisotropy due to orientation is not expressed in the stretching step. It is preferable to use an amorphous thermoplastic resin having a glass transition temperature that is 20 ° C. or more lower than the glass transition temperature. When the glass transition temperature difference is less than 20 ° C., the thermoplastic resin constituting the second layer is oriented during stretching, or the birefringence of the first layer is not exhibited. Examples of preferred combinations include a combination of syndiotactic polystyrene as the first layer and copolymerized polyethylene terephthalate as the second layer, and syndiotactic polystyrene as the first layer and copolymerized polythene as the second layer. A combination with butylene terephthalate can be mentioned.

  When using the third method described above, a method is used in which the second layer is isotropic by setting the temperature of the crystallization step after stretching to a temperature near the melting point of the thermoplastic resin constituting the second layer. be able to. As the thermoplastic resin constituting the second layer, it is preferable to use a crystalline thermoplastic resin having a melting point 20 ° C. to 50 ° C. lower than the melting point of the crystalline thermoplastic resin constituting the first layer. If the melting point difference is less than 20 ° C., isotropic orientation cannot be realized, and if it is lower than 50 ° C., fluidization occurs in the crystallization step, and a homogeneous film cannot be obtained. As the thermoplastic resin of the second layer, for example, a copolyester can be used. Specifically, for example, copolyethylene terephthalate, copolyethyleneethylene terephthalate, copolyethylene naphthalene dicarboxylate is used. Can do. As the copolymer component, for example, isophthalic acid can be used.

[Film forming method]
The biaxially stretched multilayer laminated film of the present invention can be produced by alternately laminating 100 layers or more of the above-mentioned first layer resin and second layer resin and stretching them. Hereinafter, an example of the manufacturing method will be described in detail. The first polyester supplied from the first extruder and the second polyester supplied from the second extruder are alternately laminated in a molten state to form at least 100 layers to form a multilayer unstretched sheet. By casting this on a rotating drum, an unstretched multilayer laminated film is obtained. The unstretched multilayer laminated film thus obtained is stretched in the biaxial direction (the direction along the film surface) in the width direction perpendicular to the film forming direction. The stretching temperature is in the range of the glass transition temperature (Tg) to Tg + 50 ° C. of the first polyester. The stretching area ratio is preferably 5 to 50 times. The larger the draw ratio, the smaller the variation in the plane direction in the individual layers of the first layer and the second layer due to the thinning by stretching, and the light interference of the biaxially stretched multilayer laminated film becomes uniform in the plane direction. Therefore, the draw ratio is preferably large in this range. The stretching method may be either sequential biaxial stretching or simultaneous biaxial stretching. If necessary, heat setting may be further performed.

Hereinafter, the present invention will be further described with reference to examples.
In addition, the physical property and characteristic in an Example were measured or evaluated by the following method.

(1) Glass transition temperature (Tg) and melting point About 10 mg of sample, DSC (TA Instruments make, brand name: DSC2920) is used, and 20 degreeC / min. The glass transition temperature and the melting point were measured at a temperature increase rate of.

(2) Layer thickness A sample was cut into a triangle, fixed in an embedded capsule, and then embedded in an epoxy resin. And the embedded sample was cut | disconnected along the film forming direction and thickness direction with the microtome (ULTRACUT-S, manufacturer: Reichert), and it was set as the thin film slice | slice of thickness 50nm. The obtained thin film slices were observed and photographed at an accelerating voltage of 100 kV using a transmission electron microscope (manufacturer: JEOL Ltd., trade name: JEM2010), and the thickness of each layer was measured from the photograph.

(3) Reflectance for P-polarized light and S-polarized light at front incidence and 60 ° Using a spectrophotometer (manufactured by Shimadzu Corp., MPC-3100), a polarizing filter for visible light is installed between the film and the light source, and from a wavelength of 400 nm Spectral transmittance was measured over a range of 800 nm. Similarly, the spectral transmittance of the near-infrared polarizing filter between the film and the light source was measured over a wavelength range of 800 nm to 1600 nm.
The measurement at 60 ° incidence was performed by tilting the sample by 60 ° with respect to the optical path. At this time, the component parallel to the plane including the transmission axis, the incident angle, and the reflection angle in the polarizing filter was defined as the P-polarized light component.
The spectral reflectance was calculated from the following formula because the absorption of the film was sufficiently small to be negligible. Among the reflectances measured for each wavelength, the maximum reflectance was defined as the maximum reflectance, and the wavelength was defined as the maximum reflectance wavelength. The difference between the maximum reflectance and the baseline was taken as the maximum reflectance peak height.
Spectral reflectance (%) = 100 (%)-Spectral transmittance (%)

(4) Total light transmittance The total light transmittance was measured using the haze measuring device (NDH-20) by Nippon Denshoku Industries Co., Ltd.

(5) Characteristic evaluation as identification medium
An identification medium was prepared by applying an acrylic adhesive layer on the obtained multilayer stretched film. The identification medium thus manufactured was attached to an object having a white surface, and the identification medium was observed and evaluated with a simple judgment device. The simple discriminator has a polarizing filter for visible light whose transmission axis is aligned in the vertical direction and a polarizing filter for visible light whose transmission axis is aligned in the horizontal direction, and can be easily carried in the shape of a card made of cardboard. It is a means for authenticity identification. Using this simple determiner, it was illuminated with a 30 W fluorescent lamp from above 45 °, observed through a simple determiner from the direction perpendicular to the film and from the direction 60 ° to the film surface, and the hue was observed. Here, the case where the transmission axis of the polarizing filter is parallel to the plane including the incident angle and the reflection angle is P-polarized light, and the case where it is perpendicular is S-polarized light.
FIG. 2 is a schematic diagram of a cross section in which the identification medium is observed with a simple determination device. FIG. 3 shows the arrangement of the visible light polarizing filter with the transmission axis aligned in the vertical direction and the visible light polarizing filter with the transmission axis aligned in the horizontal direction in the simple determination device.

(6) Appearance Ten A4-size sample films were prepared, and each sample film was layered on white plain paper, and the color spots of the transmitted color in the sample film were visually evaluated under illumination of 30 lux. . In addition, 10 A4 size sample films were prepared, and the back surface of each sample film was colored with a black spray, and then the reflected color spots in the sample film were visually observed under 30 lux illumination. Evaluation was made according to the following criteria.
○: No visible hue spots Δ: Slight hue spots confirmed X: Clear hue spots confirmed

[Example 1]
A syndiotactic polystyrene having a melt index of 30 (made by Idemitsu Petrochemical Co., Ltd .: XAREC300ZC: “300ZC”) is prepared as the crystalline thermoplastic resin of the first layer, and 0.65 as the thermoplastic resin of the second layer. Polyethylene terephthalate-2,6-naphthalenedicarboxylic acid copolymer (2,6-naphthalenedicarboxylic acid content 10 mol%, referred to as “NDC10PET”) was prepared.

  Then, the crystalline thermoplastic resin of the first layer and the thermoplastic resin of the second layer are each dried at 170 ° C. for 3 hours, then supplied to the first and second extruders, heated to 290 ° C. and melted In this state, after the first layer of the crystalline thermoplastic resin is branched into 251 layers and the second layer of the thermoplastic resin is branched into 250 layers, the first layer and the second layer are alternately laminated. Using a multi-layer feed block device, a molten material in a laminated state is formed, and the laminated state is maintained and cast on a casting drum. The ratio of the extrusion amount is 50% of the crystalline thermoplastic resin of the first layer. The thermoplastic resin of the second layer was adjusted to 50%, and a total of 501 unstretched multilayer laminated films in which the first layer and the second layer were alternately laminated were prepared. This multilayer unstretched film is stretched 4.0 times in the film forming direction at a temperature of 110 ° C., then stretched 4.0 times in the width direction at a temperature of 110 ° C., and heat-set at 230 ° C. for 3 seconds. A biaxially stretched multilayer laminated film was obtained. The properties of the film thus obtained were evaluated by the method described above, and the results are shown in Tables 1 and 2. In the identification medium using this biaxially stretched multilayer laminated film, coloring is not confirmed in the observation from the vertical direction, and in the observation from the 60 degree direction, the coloring is confirmed from the window for the P-polarized component, and for the S-polarized component. No coloring was observed from the window. This identification medium can determine the authenticity of an object by such a simple method.

[Example 2]
The crystalline thermoplastic resin of the first layer is a copolymer syndiotactic polystyrene having a melt index of 14 (manufactured by Idemitsu Petrochemical Co., Ltd .: XAREC142AE: “142AE”), and the thermoplastic resin of the second layer is an intrinsic viscosity ( Orthobutylphenol, 35 ° C.) 1.0 polybutylene terephthalate-isophthalate copolymer (isophthalic acid content 32 mol%, referred to as “IA32PBT”), and the production conditions were changed as shown in Table 1, In the same manner as in Example 1, a biaxially stretched multilayer laminated film was obtained. The properties of the film thus obtained were evaluated by the method described above, and the results are shown in Table 2. In the identification medium using this biaxially stretched multilayer laminated film, coloring is not confirmed in the observation from the vertical direction, and in the observation from the 60 degree direction, the coloring is confirmed from the window for the P-polarized component, and for the S-polarized component. No coloring was observed from the window. This identification medium can determine the authenticity of an object by such a simple method.

[Example 3]
Except that the thermoplastic resin of the second layer is nylon 6 (trade name “Nylon 6 Brite”: “Ny-6” made by Teijin DuPont Nylon) and the production conditions are changed as shown in Table 1, In the same manner as in Example 1, a biaxially stretched multilayer laminated film was obtained. The properties of the film thus obtained were evaluated by the method described above, and the results are shown in Table 2. In the identification medium using this biaxially stretched multilayer laminated film, coloring is not confirmed in the observation from the vertical direction, and in the observation from the 60 degree direction, the coloring is confirmed from the window for the P-polarized component, and for the S-polarized component. No coloring was observed from the window. This identification medium can determine the authenticity of an object by such a simple method.

[Comparative Example 1]
The crystalline thermoplastic resin of the first layer is polyethylene terephthalate (referred to as “PET”) having an intrinsic viscosity (orthochlorophenol, 35 ° C.) of 0.64, and the thermoplastic resin of the second layer is intrinsic viscosity (orthochlorophenol). 35 ° C.) 0.68 polyethylene terephthalate-isophthalate copolymer (isophthalic acid content 12 mol%, referred to as “IA12PET”), except that the production conditions were changed as shown in Table 1, and Example 1 Similarly, a biaxially stretched multilayer laminated film was obtained. The properties of the film thus obtained were evaluated by the method described above, and the results are shown in Table 2.

[Comparative Example 2]
A biaxially stretched multilayer laminated film was obtained in the same manner as in Comparative Example 1 except that the production conditions were changed as shown in Table 1. The properties of the film thus obtained were evaluated by the method described above, and the results are shown in Table 2.

[Comparative Example 3]
The crystalline thermoplastic resin of the first layer is a syndiotactic polystyrene having a melt index of 30 (made by Idemitsu Petrochemical Co., Ltd .: XAREC300ZC: “300ZC”), and the thermoplastic resin of the second layer is an intrinsic viscosity (orthochlorophenol, 35 ° C.) A biaxially oriented multilayer laminated film in the same manner as in Example 1 except that polyethylene 2,6 naphthalene dicarboxylate (referred to as “PEN”) of 0.62 was used and the production conditions were changed as shown in Table 1. Obtained. The properties of the film thus obtained were evaluated by the method described above, and the results are shown in Table 2.

  The present invention is the authenticity of flat objects such as packages, passports, cards, banknotes, cash vouchers, securities, certificates, gift certificates, pictures, tickets, public competition voting tickets, etc. It can be suitably used as an identification medium for identifying.

It is a figure which shows a mode that the light which injected into the multilayer thin film is selectively reflected by each layer. It is a schematic diagram of the cross section which has observed the identification medium with the simple determination device. It is a figure which shows the mode of arrangement | positioning of the polarizing filter for visible light which matched the transmission axis to the vertical direction in the simple determination device, and the polarizing filter for visible light which adjusted the transmission axis to the horizontal direction.

Claims (2)

  A first layer made of a crystalline thermoplastic resin having a negative intrinsic birefringence having a thickness in the range of 0.05 to 0.5 μm; and a thermoplastic resin having a thickness in the range of 0.05 to 0.5 μm A multilayer laminated film in which 100 or more layers are alternately laminated, and the reflectance peak height with respect to incident light from a plane perpendicular to the film surface is 5% or less, and The reflectance peak height is 5% or less for S-polarized light among the light incident at an angle of 60 °, and for P-polarized light among the light incident at an angle of 60 ° to the film. A biaxially stretched multilayer laminate film having a reflectance peak height of 20% or more.   An identification medium using the biaxially stretched laminated film according to claim 1.

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