Structural color film, anti-counterfeiting medium, information recording medium, and authenticity determination method

Abstract

To provide a structural color film, an anti-counterfeiting medium, an information recording medium, and an authenticity determining method using the structural color film, which can exhibit an excellent eye-catching property, instant recognition of an authenticity determining area, allow easy visual recognition of color tone changes, reduce variation in the recognition of hue changes among determiners, and have a high security level.SOLUTION: The structural color film achieves 10 or greater delta ΔE*ab in color space L*a*b* when measured under the conditions of incident angle α=reflection angle β=15° and incident angle α=reflection angle β=30°.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a structural color film, a counterfeit prevention medium, an information recording medium, and an authenticity determination method. [Background technology]

[0002] Structural color materials exhibit vivid colors and angular dependence, meaning that color changes depending on the viewing angle. This makes them difficult to replicate, and they are used as an anti-counterfeiting technology. In recent years, the distribution of counterfeit and counterfeit goods has expanded globally, and the damage they cause has become more diverse and complex. As the level of technology in counterfeit goods increases, it is important to select technology with security levels and functionality that match the risk of the product in order to prevent them. Counterfeiting prevention technologies can be broadly categorized by their authenticity determination method: overt functions, which allow visual detection; covert functions, which require simple tools; and forensic functions, which require specialized analysis.

[0003] The overt function of pearl ink and other inks has the advantage of allowing for easy and rapid authentication. However, since the perception of color change varies depending on the examiner, the information obtained for authenticity determination is limited to "whether or not there is a change in color tone depending on the observation angle," resulting in a limited amount of information. Furthermore, in anti-counterfeiting technology with an overt function, the part to be judged must be instantly recognizable (highly eye-catching) in order to quickly determine authenticity.

[0004] Patent Document 1 describes a technology in which a metallic paint composition containing a scale-like aluminum pigment is applied to a substrate, and then a multicolor paint composition containing a luster pigment and capable of producing a structural color is applied to the resulting coating, thereby producing a structural color with large color changes. However, although the coating film described in Patent Document 1 was able to visually recognize the color change, it was not very eye-catching, and the hue change was unclear, leading to significant variations in how the color change was perceived by the judge. This resulted in problems such as the ease with which counterfeit products could be produced and a low security level. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-5481 Summary of the Invention [Problem to be solved by the invention]

[0006] The problem to be solved by the present invention is to provide a structural color film, a counterfeit prevention medium, an information recording medium, and an authenticity determination method using the structural color film, which have excellent eye-catching properties, allow instant recognition of the authenticity determination site, allow easy visual recognition of color tone changes, and show little variation in the recognition of hue changes depending on the determiner, and have a high level of security. [Means for solving the problem]

[0007] That is, the present invention relates to a structural color film having a ΔE*ab in the L*a*b* color space of 10 or more when measured under the conditions of an incident angle α = a reflection angle β = 15° and an incident angle α = a reflection angle β = 30°.

[0008] The present invention also relates to the structural color film, which has a hue difference ΔH of 10 or more when measured under the condition of incident angle α = reflection angle β = 15° and the condition of incident angle α = reflection angle β = 30°.

[0009] The present invention also relates to the structural color film, wherein the ratio (C* / L*) of chroma C* to lightness L* at an incident angle α=reflection angle β=15° is 0.5 or more.

[0010] The present invention also relates to the structural color film described above, which comprises an alternately repeating structure of A layers and B layers having different refractive indices, and the coefficient of variation representing the repeat accuracy of the alternately repeating structure is 10% or less.

[0011] The present invention also relates to the structural color film described above, which has a heat-sensitive function.

[0012] The present invention also relates to the structural color film described above, which is formed by printing.

[0013] The present invention also relates to a counterfeit prevention device having the structural color film.

[0014] The present invention also relates to an information recording medium having the structural color film.

[0015] The present invention also relates to a method for determining authenticity using the structural color film.

[0016] The present invention also relates to a method for determining authenticity, which includes the steps of observing the structural color film from at least two different angles, assuming that the structural color film is genuine, and determining the authenticity based on the observation results from the at least two different angles.

[0017] The present invention also relates to the above-mentioned method for determining authenticity, wherein the step of observing the structural color film at at least two different angles includes measuring a reflectance spectrum. [Effects of the Invention]

[0018] The present invention provides a structural color film, a medium for preventing counterfeiting, an information recording medium, and an authentication method using the film, which have excellent eye-catching properties, allow instant recognition of the authenticity determination site, allow easy visual recognition of the color tone change, and have a high level of security with little variation in the recognition of the hue change depending on the examiner. DETAILED DESCRIPTION OF THE INVENTION

[0019] <Structural color film> The structural color film of the present invention is characterized in that ΔE*ab in the L*a*b* color space when measured under the conditions of incident angle α = reflection angle β = 15° and incident angle α = reflection angle β = 30° is 10 or more. The value of ΔEa*b* is preferably 12 or more, more preferably 15 or more, even more preferably 17 or more, and particularly preferably 20 or more. When the structural color film of the present invention exhibits the above ΔEa*b*, it has excellent eye-catching properties, the color tone changes easily when visually observed at different angles, and the variation in perception of the hue change is suppressed. The elements constituting the present invention will be described in detail below.

[0020] (structural color layer) The structural color film of the present invention may be a structural color layer in which the entire structural color film exhibits a structural color, or may be a laminate in which a structural color layer is formed on a substrate. Examples of the structural color layer include colloidal crystals, laminated structures, cholesteric liquid crystals, volume holograms, and diffraction gratings, and colloidal crystals, laminated structures, and cholesteric liquid crystals are particularly preferred because of their large color change. Furthermore, since structural colors can be expressed regardless of the polarization state of incident light, it is preferable that the structural color layer of the present invention has an ordered structure in which layers A and B, which have different refractive indices, are alternately repeated. In particular, if the structural color layer is a colloidal crystal, the ratio of chroma C* to lightness L* becomes high, and the layer exhibits outstanding chroma and excellent eye-catching properties, which is preferable.

[0021] [Alternating repeat structure] Examples of components constituting the A layer and B layer include air, water, inorganic materials such as titanium dioxide, zinc oxide, zirconium oxide, and silicon dioxide, and resin materials such as polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, high-density polyethylene, medium-density polyethylene, low-density polyethylene, ethylene-vinyl acetate copolymer, polypropylene, polyacetal, polymethyl methacrylate, styrene-acrylic copolymer, acrylic copolymer, cellulose acetate, polycarbonate, polyester, polyamide, polyurethane, fluorine-based resin, and silicone resin. Two or more of these materials may be mixed in each layer, and other components may also be contained. It is preferable that at least one of the components constituting the layers A and B is a resin material, since it is easy to handle and can form a precise alternating repeat structure. In addition, when the structural color layer in the present invention is a colloidal crystal, it is preferable that the layer A is made of resin fine particles and the layer B is made of air.

[0022] [Thermal function] The structural color film of the present invention preferably has a heat-sensitive function. In the present invention, having a heat-sensitive function means that when heat-treated at a temperature of 150 to 200° C., the absolute value of the difference in chromaticity a* (|Δa*|) or the absolute value of the difference in chromaticity b* (|Δb*|) before and after heat treatment is 5 or more. The above values ​​are based on chromaticity in the L*a*b* color space measured under the condition of incident angle α = reflection angle β = 15°.

[0023] The heat-sensitive function can be exemplified by the fading of structural colors, which can be advantageously utilized in security applications. When the structural color layer is colloidal crystals, Layer A is resin microparticles, and Layer B is air, the ordered arrangement structure of the colloidal crystal layer is disrupted by heat treatment, causing the color of the colloidal crystal layer to fade and resulting in a clear color change. Therefore, when the structural color layer of the present invention is colloidal crystals, Layer A is resin microparticles, and Layer B is air, it can be particularly advantageously used as a heat-sensitive recording medium. Furthermore, by partially heating the film, the heated areas fade while the non-heated areas maintain their structural color, making it possible to use the film as a counterfeit prevention medium or information recording medium with a higher level of security.

[0024] When fading of the structural color occurs due to heat treatment, after subjecting the structural color film to a heat treatment method described below, the chromaticity in the L*a*b* color space measured under the condition of incident angle α = reflection angle β = 15° preferably satisfies |a*|<10 or |b*|<10, more preferably satisfies |a*|<10 and |b*|<10, even more preferably satisfies |a*|<9 and |b*|<9, and particularly preferably satisfies |a*|<8 and |b*|<8.

[0025] Examples of heat treatment methods include a method in which a thermal printer is used to apply heat to the laminate by applying a thermal head thereto; a method in which laser light is irradiated to cause the coloring material in the colloidal crystal layer to absorb the light and heat the adjacent resin microparticles; a method in which laser light is irradiated to cause the resin microparticles that make up the colloidal crystal to absorb the light and heat the laminate; oven heating, microwave heating, and boiling. Thermal recording using a laser is preferred because it allows for image formation without damaging the substrate or the unheated areas. Furthermore, it is preferable to use an infrared laser because it has minimal adverse effects on the substrate. Examples of infrared laser markers include CO2 laser markers (wavelength 10600nm), YVO4 laser marker (wavelength 1064nm), YAG laser marker laser marker (wavelength 1064 nm), fiber laser marker (wavelength 1090 nm), etc. can be done. The heating temperature in the case of thermal head, oven heating, or boiling treatment is preferably in the range of 100 to 200°C, more preferably in the range of 150 to 200°C, taking into consideration thermal damage to the substrate.

[0026] [Average spacing of alternating repeat structures] In the present invention, the interval between the alternately repeated structures of A layer and B layer is the average thickness of each layer when the structural color layer has a laminated structure, and is the average particle diameter of the constituent particles when the structural color layer is a colloidal crystal. The average spacing between the repeating structures is preferably 100 to 400 nm, more preferably 150 to 350 nm, even more preferably 170 to 330 nm, still more preferably 190 to 320 nm, and particularly preferably 230 to 310 nm. When the average spacing between the repeating structures is within the above range, a clear color change occurs in the visible range when the observation angle is changed, making the color change easily recognizable. In addition, variation in the perception of the hue change is reduced.

[0027] [Coefficient of variation] The coefficient of variation of the alternating refractive index repeating structure in the structural color layer of the present invention, which indicates the repeatability, is preferably 10% or less, more preferably 9% or less, even more preferably 8% or less, even more preferably 7% or less, and particularly preferably 6% or less. A coefficient of variation of 10% or less is excellent in eye-catching properties, and the color change is large depending on the observation angle, resulting in vivid color development and making the color change easily recognizable. In addition, variation in the perception of hue change is reduced. The coefficient of variation, which indicates repeatability, corresponds to the variation (coefficient of variation) in film thickness of each layer in the case of a multilayer structure, and corresponds to the variation in particle size of the particles in the case of colloidal crystals, for example.

[0028] [Refractive index difference] The refractive index difference Δη between the A layer and the B layer that form the structural color layer of the structural color film of the present invention is preferably 0.1 or more, more preferably 0.2 or more, and even more preferably 0.4 or more. By having a refractive index difference Δη of 0.1 or more, the color development of the structural color film becomes vivid and has excellent eye-catching properties. In addition, since the angle dependency is also emphasized, color changes can be easily recognized and variations in the recognition of hue changes are suppressed.

[0029] (Hue difference ΔH) Furthermore, the structural color film of the present invention preferably has a hue difference ΔH of 10 or more, more preferably 15 or more, and even more preferably 20 or more, when measured under the condition of incident angle α = reflection angle β = 15° and the condition of incident angle α = reflection angle β = 30°. A hue difference of 10 or more is preferable because it allows the hue change to be easily recognized and also reduces variations in the recognition of the hue change when the observation angle is changed.

[0030] (Saturation C* / Lightness L*) Furthermore, the structural color film of the present invention preferably has a ratio (C* / L*) of chroma C* to lightness L* at an incident angle α = reflection angle β = 15° of 0.5 or more, more preferably 0.6 or more, even more preferably 0.8 or more, and particularly preferably 1.0 or more. When the ratio of the saturation C* to the lightness L* is 0.5 or more, the color exhibits outstanding saturation and is therefore highly eye-catching.

[0031] (Saturation difference ΔC) The structural color film of the present invention preferably has an absolute value |ΔC| of the saturation difference when measured under the condition of incident angle α = reflection angle β = 15° and the condition of incident angle α = reflection angle β = 30°, which is 5 or more, more preferably 7 or more, and even more preferably 10 or more. A saturation difference of 5 or more is preferable because it allows the hue change to be easily recognized and also reduces variations in the recognition of the hue change when the observation angle is changed. Furthermore, it is preferable that the saturation difference ΔC is greater than 0. When ΔC is greater than 0, a glossy feeling is felt, and therefore the change in hue can be easily recognized.

[0032] <Method of manufacturing structural color film> The method for producing the structural color film is not particularly limited, but it can be produced, for example, by the following method.

[0033] (Method of manufacturing a structural color layer with a laminated structure) For example, when the structural color layer forming the structural color film of the present invention has a laminated structure, it can be produced by the following steps 1 to 3. Step 1) A step of applying a resin composition containing a resin constituting layer A onto a substrate, drying it as necessary, and curing it by irradiation with active energy rays such as ultraviolet rays to form layer A having a thickness of 100 to 400 nm. Step 2) A step of applying a resin composition containing a resin constituting layer B onto layer A formed in step 1, and drying and curing the composition by irradiation with active energy rays such as ultraviolet rays as necessary to form layer B having a thickness of 100 to 400 nm. Step 3) A step of applying a resin composition containing the resin that constitutes the A layer onto the B layer formed in step 2, and drying it as necessary, and curing it by irradiating it with active energy rays such as ultraviolet rays, to form an A layer having a thickness of 100 to 400 nm. Steps 2 and 3 are repeated to create a laminated structure.

[0034] (Method of manufacturing a structural color layer of colloidal crystal) For example, when the structural color layer forming the structural color film of the present invention is a colloidal crystal, it can be produced by the following steps. Step 1) A step of applying a composition for colloidal crystals containing particles that will form layer A onto a substrate, and drying as necessary, to form a colloidal crystal layer having a thickness of 0.5 to 100 μm.

[0035] In the method for producing the structural color layer of the colloidal crystal, when the B layer is made of a material other than air, it is preferable to form the B layer by the following steps in addition to the step 1. Step 2) A step of applying a resin composition containing a resin constituting layer B onto the colloidal crystal layer formed in step 1, and drying it as necessary to form layer B between the colloidal crystal particles.

[0036] Furthermore, when a composition for colloidal crystals containing core-shell resin microparticles whose cores are made of a resin that forms layer A and whose shells are made of a resin that forms layer B is used, a colloidal crystal layer can be formed in which layer B is made of a resin that forms the shell of the core-shell resin microparticles, for example, by the following process. Step 1) A step of applying a composition for colloidal crystals containing core-shell resin microparticles, the core of which is a resin that forms layer A and the shell of which is a resin that forms layer B, onto a substrate, and drying as necessary to form a colloidal crystal layer having a thickness of 0.5 to 100 μm. Step 2) A step in which the shell of the colloidal crystal layer is fluidized by heat treatment to fill the voids, forming a colloidal crystal composed of particles made of resin that forms layer A and gaps between particles made of resin that forms layer B.

[0037] <Counterfeiting prevention media> The structural color film of the present invention has the advantage that the color change can be easily recognized by the naked eye and there is little variation in the recognition of the hue change depending on the judge. Furthermore, it can be used for applications of a covert function that provides high security by instrumental measurement to prevent counterfeiting.

[0038] <Information recording media> The structural color film of the present invention has the feature that the color change can be easily recognized by visual inspection and there is little variation in the recognition of the hue change depending on the judge, which allows it to be used as an information recording medium that provides multiple information.

[0039] <Authenticity determination method> The structural color film of the present invention has the advantage that the color change can be easily recognized visually and there is little variation in the recognition of the hue change depending on the judge, thereby providing a simple, quick, and highly secure method for authenticating.

[0040] The authenticity determination using the structural color film of the present invention preferably includes the steps of observing the structural color film of the present invention at at least two different angles, assuming that the structural color film is genuine, and determining the authenticity based on the observation results at the at least two different angles. The observation may be performed visually or using an instrument such as a spectrophotometer or a colorimeter.

[0041] When the observation is performed visually, for example, the authenticity of the film to be observed can be determined by recording the color change when the genuine structural color film is observed from two different specific angles and comparing it with the color change when the film to be observed is observed in the same way.

[0042] When the observation is carried out using a spectrophotometer, a colorimeter, or other such instrument, values ​​such as L, a, b, ΔEab, ΔH, and ΔC are calculated and recorded based on the reflectance spectrum data measured at at least two different angles for a genuine structural color film. Then, by comparing these values ​​with the same values ​​measured for the film to be observed, the authenticity of the film to be observed can be determined. [Example]

[0043] The present invention will be described in more detail below with reference to examples, but the following examples do not limit the scope of the present invention. Unless otherwise specified, "parts" and "%" mean "parts by mass" and "% by mass", respectively. Furthermore, blank spaces in the tables indicate that no ingredients are blended.

[0044] <Average spacing and coefficient of variation of alternating repeat structures> The average spacing and coefficient of variation of the alternating repeating structure were determined by using a scanning electron microscope (SEM) (JEOL Ltd.'s "JSM-7800F") to observe cross-sectional images of the structural color film at a magnification of 15,000x, and inputting the images into image processing software (Mitani Corporation's "Winroof") to calculate the following values ​​corresponding to the spacing and coefficient of variation of the repeating structure according to the structure of the structural color layer.

[0045] (When the structural color layer has a laminated structure) Average spacing of alternating repeat structure: Average thickness of each layer Ave S Coefficient of variation of alternating repeat structure: Coefficient of variation of film thickness of each layer Ave C The coefficient of variation (CV value) was calculated according to the following formula using the values ​​obtained by the above measurement method. Coefficient of variation of film thickness (%) = (σ S / D S) x 100 σ S : Standard deviation of film thickness D S :Average film thickness

[0046] (When the structural color layer is a colloidal crystal) Average spacing of alternating repeating structures: Coefficient of variation of the equivalent circle diameter of each particle Coefficient of variation of alternating repeat structure: Coefficient of variation of the equivalent circle diameter of each particle

[0047] Coefficient of variation of equivalent circle diameter (%) = (σ C / D C ) x 100 σ C : Standard deviation of equivalent circle diameter D C : Average value of equivalent circle diameter [The equivalent circle diameter is the diameter of a perfect circle that corresponds to the geometric area recognized as a particle.]

[0048] <Weight average molecular weight> The weight-average molecular weight was measured by gel permeation chromatography (GPC) using a polystyrene-equivalent value. More specifically, the dried resin was dissolved in tetrahydrofuran to prepare a 0.2% solution, and the weight-average molecular weight was measured using the following equipment and measurement conditions. For resins that were insoluble due to high molecular weight and difficult to measure, the weight-average molecular weight was considered to be 1 million or more. Apparatus: HLC-8320-GPC system (Tosoh Corporation) Column: TSKgel-SuperMultiporeHZ-M0021488 4.6mm I.D. x 15cm x 3 (molecular weight measurement range: 2,000 to approximately 2,000,000) Elution solvent: tetrahydrofuran Standard material: Polystyrene (Tosoh Corporation) Flow rate: 0.6 mL / min, amount of sample solution used: 10 μL, column temperature: 40°C.

[0049] <Color evaluation> The reflectance spectrum of the structural color film was measured using a UV-Vis-NIR spectrophotometer (JASCO V-770D) at wavelengths ranging from 350 to 850 nm under the conditions of an incident angle α = reflection angle β = 15° and an incident angle α = incident angle β = 30°. The lightness L* and chromaticity a* and b* in the L*a*b* color space were determined from the obtained reflectance spectrum using JASCO color evaluation software. Furthermore, the chroma C*, ΔL*, Δa, Δb*, ΔC*, ΔE*ab, ΔH, and C* / L* were calculated from the determined L*, a*, and b* values ​​using the following formula:

[0050] (formula) JPEG0007797955000001.jpg100146

[0051] <Manufacturing of resins for laminate structures> [Manufacturing Example 1] A reaction vessel equipped with a stirrer, thermometer, and reflux condenser was charged with 250.0 parts of cyclohexanone, 70.0 parts of dipentaerythritol hexaacrylate (DPHA) / dipentaerythritol pentaacrylate (DPPA) mixture (manufactured by Toagosei Co., Ltd., product name: "Aronix M402", number average molecular weight 650), 30.0 parts of styrene, 3.6 parts of ethyl bromoisobutyrate, and 4.7 parts of pentamethyldiethylenetriamine. After heating to 65 ° C while blowing in nitrogen, 2.0 parts of copper chloride was added to initiate polymerization. After 20 minutes from the start of polymerization, the flask was cooled, and 0.2 parts of p-toluenesulfonic acid monohydrate was added and stirred at room temperature for 3 hours. 1.6 parts of Kyoward 500SH (Kyowa Chemical Co., Ltd.) was added as a metal adsorbent, and the mixture was stirred at room temperature for 3 hours. The adsorbent was then filtered using a Kiriyama funnel to obtain a polyfunctional acrylate resin (styrene-acrylic resin) solution with a solids content of 29%. The resulting styrene-acrylic resin had a number-average molecular weight (Mn) of 9600 and a weight-average molecular weight (Mw) of 109,000.

[0052] [Manufacturing Example 2] A polyfunctional acrylate resin (fluorine-based acrylic resin) solution with a solid content of 29% was obtained by the same procedure as in Production Example 1, except that 2,2,3,3,3-pentafluoropropyl acrylate was used instead of styrene. The number-average molecular weight (Mn) of the obtained fluorine-based acrylic resin was 9,200, and the weight-average molecular weight (Mw) was 101,000.

[0053] <Production of Resin Dispersion for Colloidal Crystals> [Manufacturing Example 3] A reaction vessel equipped with a stirrer, thermometer, and reflux condenser was charged with 391.0 parts of ion-exchanged water, 89.0 parts of styrene, 10.0 parts of methyl methacrylate, and 1.0 part of sodium p-styrenesulfonate. The internal temperature was raised to 80°C and the atmosphere was thoroughly purged with nitrogen. Then, 12.0 parts of a 5% aqueous solution of ammonium persulfate was added as an initiator and the reaction was continued for 4 hours to obtain an aqueous dispersion of styrene-acrylic resin. The solids content was adjusted to 20%.

[0054] [Manufacturing Example 4] A reactor equipped with a stirrer, thermometer, dropping funnel, and reflux condenser was charged with 273.7 parts of ion-exchanged water, 62.3 parts of styrene, 7.0 parts of methyl methacrylate, and 0.7 parts of sodium p-styrenesulfonate. The internal temperature was raised to 70°C and thoroughly purged with nitrogen. After this, 8.4 parts of a 5% aqueous solution of ammonium persulfate was added as an initiator and the first-stage reaction was carried out for 4 hours. Next, 29.1 parts of 2,2,3,3,3-pentafluoropropyl acrylate, 0.9 parts of acrylic acid, 1.5 parts of a 20% aqueous solution of Aqualon KH-10, and 11.8 parts of ion-exchanged water were mixed and stirred to prepare an emulsion of ethylenically unsaturated monomers. After the first-stage reaction, the emulsion and 1.0 parts of a 5% aqueous solution of potassium persulfate were added dropwise over 2 hours to further the reaction, yielding a dispersion of core-shell resin microparticles with a styrene-acrylic resin core and a fluorinated acrylic resin shell. The solids content was adjusted to 20%.

[0055] [Manufacturing Example 5] A reaction vessel equipped with a stirrer, thermometer, and reflux condenser was charged with 391.0 parts of ion-exchanged water, 89.0 parts of styrene, 10.0 parts of methyl methacrylate, and 1.0 part of sodium p-styrenesulfonate. The internal temperature was raised to 70°C and the atmosphere was thoroughly purged with nitrogen. Then, 12.0 parts of a 5% aqueous solution of potassium persulfate was added as an initiator and reacted for 30 minutes. The internal temperature was then raised to 80°C and the reaction continued for 4 hours, yielding an aqueous dispersion of styrene-acrylic resin. The solids content was adjusted to 20%.

[0056] <Production of Resin Composition for Laminate Structure> [Manufacturing Example 6] A composition prepared by adding 2.0 parts of Irgacure 184 as a photopolymerization initiator to 100 parts of the polyfunctional acrylate resin solution synthesized in Production Example 1 was diluted with methyl ethyl ketone to prepare an active energy ray-curable resin composition with a solids content of 20%.

[0057] [Manufacturing Example 7] An active energy ray-curable resin composition having a solids content of 20% was prepared by the same procedure as in Production Example 6, except that the polyfunctional acrylate resin solution synthesized in Production Example 2 was used instead of the polyfunctional acrylate synthesized in Production Example 1.

[0058] <Production of Resin Composition for Colloidal Crystals> [Manufacturing Example 8] A composition for colloidal crystals was prepared by adding 1.0 part of Emulgen 1108 manufactured by Kao and 2.5 parts of surface-modified carbon black BONJET BLACK CW-1 manufactured by Orient Chemical Industries to 100 parts of the aqueous dispersion of resin microparticles of Production Example 3 and stirring the mixture.

[0059] [Manufacturing Example 9] A composition for colloidal crystals was prepared in the same manner as in Production Example 8, except that the resin fine particles were changed to those obtained in Production Example 4.

[0060] [Manufacturing Example 10] A composition for colloidal crystals was prepared in the same manner as in Production Example 8, except that the resin fine particles were changed to those obtained in Production Example 5.

[0061] <Preparation of structural color film> [Example 1] 0.2 mL of the active energy ray-curable resin composition of Production Example 6 was dropped onto a biaxially oriented polypropylene (OPP) film (Futamura FOR, thickness 20 μm) and spin-coated at 5000 rpm for 20 seconds. After that, the solvent was dried and removed at 100°C for 2 minutes, and then the film was exposed to ultraviolet light of 400 mJ / cm using a high-pressure mercury lamp. 2 The coating layer was cured by irradiation with light at 1000 V for 1 hour to form a layer A having a thickness of about 200 nm. Subsequently, the active energy ray-curable resin composition of Production Example 7 was spin-coated on the layer A under the same conditions, followed by drying and curing, to form a layer B having a thickness of about 200 nm on the layer A. The formation of layers A and B was repeated alternately to obtain a structural color film with a thickness of 50 μm, consisting of an alternating repeat structure of layers A and B. The average spacing of the repeat structure of the structural color film was 200.1 nm, with a coefficient of variation of 6.7%. Furthermore, the color evaluation results were ΔE*ab of 14.2, ΔH of 11.4, ΔC* of -8.8, and C* / L* of 0.7.

[0062] [Examples 2 and 3] In Example 2, the thickness of each of the A layer and the B layer was changed to about 250 nm, and in Example 3, the thickness of each of the A layer and the B layer was changed to about 300 nm. Except for this, structural color films were prepared in the same manner as in Example 1. The cross-sectional observation results and chromaticity data of the prepared structural color films are summarized in Table 1.

[0063] [Example 4] The resin composition for colloidal crystals from Production Example 8 was applied to a biaxially oriented polypropylene (OPP) film (Futamura FOR, 20 μm thick) using a bar coater to a thickness of 9.0 μm after drying, and the film was dried at 40°C for 5 minutes to obtain a structural color film with a colloidal crystal structural color layer. The average spacing of the repeating structures in the resulting structural color film was 202.3 nm, with a coefficient of variation of 5.3%. Furthermore, the color evaluation results were ΔE*ab of 11.4, ΔH of 0.4, ΔC* of 11.4, and C* / L* of 1.4.

[0064] [Examples 5 and 6] A structural color film in which the structural color layer was a colloidal crystal was obtained in the same manner as in Example 4, except that the composition was changed as shown in Table 1. The cross-sectional observation results and chromaticity data of the prepared structural color film are summarized in Table 1. In Example 5, after drying at 40°C for 5 minutes, an additional heating step at 80°C for 5 minutes was carried out to obtain a structural color film of colloidal crystals in which layer A is made of particles made of styrene acrylic resin and layer B is made of fluorine-based acrylic resin with interparticle spaces.

[0065] [Comparative Manufacturing Example 1] A reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, and dropping device was charged with 50 parts of ethylene glycol monoethyl ether acetate, stirred, and heated to 135°C. The following monomer / polymerization initiator mixture was then added dropwise over 3 hours to the reaction vessel, which was maintained at the same temperature. After the addition, the mixture was aged for 1 hour. A mixture consisting of 10 parts of ethylene glycol monoethyl ether acetate and 0.6 parts of 2,2'-azobis(2-methylpropionitrile) was then added dropwise over 1 hour and 30 minutes while maintaining the temperature, and the mixture was aged for another 2 hours. The ethylene glycol monoethyl ether acetate was then distilled off under reduced pressure to yield a hydroxyl-containing acrylic resin with a weight-average molecular weight of 36,000 and a resin solids content of 65% by mass.

[0066] [Comparative Manufacturing Example 2] A metallic paint (organic solvent-based paint) with a solids content of approximately 25% was prepared by blending 15 parts of aluminum paste GX-180 (a flake aluminum pigment manufactured by Asahi Kasei Metals Corporation) with 100 parts (solids content) of resin components consisting of 75 parts of the hydroxyl group-containing acrylic resin obtained in Comparative Production Example 1 and 25 parts of U-BAN 28-60 (trade name, butyl etherified melamine resin, manufactured by Mitsui Chemicals, Inc.), stirring and mixing, and diluting to a viscosity appropriate for painting.

[0067] [Comparative Manufacturing Example 3] 5 parts of the lustrous pigment Helicone HC Scarabeus (cholesteric liquid crystal polymer, manufactured by Wacker GmbH) were blended and stirred to 100 parts (solids content) of resin components consisting of 75 parts of the hydroxyl group-containing acrylic resin obtained in Comparative Production Example 1 and 25 parts of U-Van 28-60 (trade name, butyl etherified melamine resin, manufactured by Mitsui Chemicals, Inc.), and the mixture was diluted to a viscosity appropriate for painting to prepare a multi-color paint (organic solvent-based paint) with a solids content of approximately 25%.

[0068] [Comparative Example 1] (Preparation of substrate) A degreased and zinc phosphate-treated steel plate (JIS G3141, size 400 × 300 × 0.8 mm) was electrodeposited with the cationic electrodeposition paint "Elecron 9400HB" (product name: manufactured by Kansai Paint Co., Ltd., which uses an epoxy resin polyamine-based cationic resin and a blocked polyisocyanate compound as a curing agent) to a film thickness of 20 μm based on the cured coating, and heated at 170°C for 20 minutes to crosslink and cure, thereby obtaining an electrodeposition coating.

[0069] The resulting electrodeposited coating surface was coated with the intermediate coating paint "Lugabeke Intermediate Coat Gray" (product name: manufactured by Kansai Paint Co., Ltd., polyester resin / melamine resin system, organic solvent type) using an air spray to a film thickness of 30 μm based on the cured coating film, and heated at 140°C for 30 minutes to crosslink and cure.The coated plate with the intermediate coating film formed was used as the substrate. (coating) Using an REA gun, the metallic paint of Comparative Production Example 2 was applied to a 10 μm cured film at a booth temperature of 25°C and humidity of 75%, and left at room temperature for 15 minutes. Next, the multicolor paint of Comparative Production Example 3 was applied to a 10 μm cured film at a booth temperature of 25°C and humidity of 75%, and then a clear paint (Lugabe Clear, Kansai Paint, product name, acrylic resin / amino resin system, organic solvent type) was applied to the uncured coating surface using a mini-bell type rotary electrostatic applicator at a booth temperature of 25°C and humidity of 75%, to a 25-35 μm cured film. After leaving the coating at room temperature for 15 minutes, the coating was heated at 140°C for 30 minutes in a hot air circulating drying oven to simultaneously dry and cure the multi-layer coating, yielding a structural color film. The structural color film did not have a regular structural color layer. The color evaluation results were ΔE*ab 9.6, ΔH 8.2, ΔC* 4.3, and C* / L* 0.32.

[0070] <Evaluation of structural color films> [Heat-sensitive function] The structural color film was attached to a piece of A4-sized white paper with tape, and a 2 cm x 2 cm square was heated from the structural color layer side to form an image using a thermal printer equipped with a thermal head (Brother Industries, Ltd., PocketJet PJ-673) with the density set to 5. It was confirmed that the film was heated to 150°C or higher using a Thermo Label (registered trademark) manufactured by Niyu Giken Kogyo Co., Ltd. The reflectance spectra of the heated image-formed area were measured before and after the heat treatment under the conditions of an incident angle α = reflection angle β = 15° in the wavelength range of 350 to 850 mm. The chromaticity a* and b* in the L*a*b* color space were calculated for the obtained reflectance spectra using color evaluation software manufactured by JASCO Corporation, and evaluated as follows. The results are shown in Table 1. Yes: │Δa*│ or │Δb*│ is 5 or more (thermal function available) None: │Δa*│ and │Δb*│ are less than 5 (no thermal function)

[0071] Furthermore, the structural color film obtained was evaluated by 20 randomly selected panelists as follows. The results are shown in Table 1.

[0072] [Eye-catching] The structural color film was cut into a 1cm x 1cm square and pasted anywhere on an A4-sized piece of black construction paper. The eye-catching ability of the structural color film was evaluated as follows when the black construction paper with the structural color film was observed indoors. S: More than 15 out of 20 panelists were able to instantly identify the position of the structural color film (very good). A: More than 10 but less than 15 out of 20 panelists were able to instantly identify the position of the structural color film (good). B: More than 15 but less than 10 out of 20 panelists were able to instantly identify the position of the structural color film (usable). C: More than 15 but less than 10 out of 20 panelists were able to instantly identify the position of the structural color film (unusable).

[0073] [Easy recognition of color change] The structural color film thus produced was visually inspected for color change when observed from the front and at an angle of 15°, and the recognizability of the color change of the structural color film was evaluated as follows. S: 15 or more out of 20 panelists recognized a color change (very good). A: More than 10 but less than 15 out of 20 panelists recognized the color change (good). B: More than 15 but less than 10 out of 20 panelists recognized the color change (usable). C: More than 15 but less than 10 out of 20 panelists recognized a color change (unusable).

[0074] [Variation in hue change recognition] When the structural color film was observed from the front and from a 30° angle, participants were asked to select from the following nine colors to indicate the color that the structural color film displayed, and were then evaluated as follows: Color options: white, black, blue, light blue, green, yellow-green, yellow, orange, red S: More than 15 out of 20 panelists recognized the same change (very good). A: More than 10 but less than 15 out of 20 panelists recognized the same change (good). B: More than 15 but less than 10 out of 20 panelists recognized the same change (usable). C: More than 15 but less than 10 out of 20 panelists recognized the same change (unusable).

[0075] [Table 1]

[0076] The structural color film of the present invention has excellent eye-catching properties, and the change in color tone can be easily recognized visually, and there was little variation in the recognition of the change in color tone depending on the judge. On the other hand, the laminates of the comparative examples showed large variations in the recognizability of color changes and in the recognition of hue changes, and did not reach a practical level.

Claims

1. ΔE*ab in the L*a*b* color space when measured under the condition of incident angle α = reflection angle β = 15° and the condition of incident angle α = reflection angle β = 30° is 10 or more, A structural color film comprising an alternating repeat structure of A layers and B layers having different refractive indices, wherein the coefficient of variation representing the repeat accuracy of the alternating repeat structure is 10% or less.

2. 2. The structural color film according to claim 1, wherein the hue difference ΔH measured under the condition of incident angle α = reflection angle β = 15° and the condition of incident angle α = reflection angle β = 30° is 10 or more.

3. 3. The structural color film according to claim 1, wherein the ratio of chroma C* to lightness L* (C* / L*) at an incident angle α = a reflection angle β = 15° is 0.5 or more.

4. The structural color film according to claim 1 or 2, which has a heat-sensitive function.

5. The structural color film according to claim 1 or 2, which is formed by printing.

6. A counterfeit prevention device comprising the structural color film according to claim 1 or 2.

7. An information recording medium comprising the structural color film according to claim 1 or 2.

8. A method for determining authenticity, comprising using the structural color film according to claim 1 or 2.

9. A method for determining authenticity, comprising the steps of observing the structural color film described in claim 1 or 2 at at least two different angles, assuming that the structural color film is genuine, and determining the authenticity based on the observation results at the at least two different angles.

10. The authentication method according to claim 9 , wherein the step of observing the structural color film at at least two different angles includes measuring a reflectance spectrum.

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