A structural color material that changes color according to light source characteristics and its preparation method

Abstract

This invention provides a structural color material that changes color according to light source characteristics and its preparation method. The structural color material of this invention is prepared by a method comprising the following steps: a black light-absorbing substance is uniformly mixed with a submicron monodisperse polymer microsphere emulsion, and then uniformly mixed with a gel solution to obtain a mixed dispersion. The mixed dispersion is then spray-dried to obtain the structural color material that changes color according to light source characteristics. The refractive index of the submicron monodisperse polymer microsphere emulsion is less than the refractive index of the gel colloidal particles in the gel solution. This invention is based on the combination of submicron-sized polymer microspheres with a lower refractive index and a gel substance with a higher refractive index to form a periodic structure with controllable refractive index. Due to the periodic structure of the spherical disordered assembly and its spherical scattering characteristics of the light source, this material will produce a color response to different light source spectra, realizing a structural color material that is easy to prepare and has highly controllable color.

Description

Technical Field

[0001] This invention relates to the field of optical anti-counterfeiting technology, and in particular to a structural color material that changes color according to the characteristics of a light source and its preparation method. Background Technology

[0002] The rampant counterfeiting of substandard products and the specific demands for aesthetically pleasing printed materials have placed higher requirements on anti-counterfeiting materials and printing technologies. Optical anti-counterfeiting is a key supporting technology for modern commodity identification and other economic transactions, and it also plays a crucial role in protecting high-value-added goods and building an information-based economy. Traditional technologies such as temperature-sensitive and optically variable inks suffer from problems such as easily counterfeited markings, weak identification capabilities, and low barriers to entry, thus urgently requiring innovative anti-counterfeiting technologies.

[0003] For the industrial application of special optical anti-counterfeiting inks, the optical scattering phenomenon based on submicron-scale microsphere composite structures can achieve special optical anti-counterfeiting applications, such as color-changing with light source characteristics, which is not available in conventional anti-counterfeiting materials. While the use of polymer microsphere structural colors for anti-counterfeiting applications is not uncommon, they generally do not possess the effect of color-changing with light source characteristics, and their anti-counterfeiting properties are mostly based on color changes in response to external factors (e.g., CN110766119B, Liu P, Chang W, Ju L, Chu L, Xie Z, Chen J, Yang J. ACS Appl. Nano). Mater. 2019, 2(9), 5752-5760. Wetting response; CN112835279B, temperature response; CN113416450B, magnetic field response; CN114834172A, light response, etc.); It is also relatively complicated in anti-counterfeiting identification applications, such as needing to input optical microscope images that have been memorized and learned by artificial intelligence for identification (CN110569948B, CN113506508B, He Xueying. Responsive angle-independent structural color anti-counterfeiting label [D]. Hebei Normal University, 2020.), and needing to identify based on changes in reflectance spectrum (CN110766119B), etc. A structural color material for inkjet printing (Wu S, Liu B, Su X, Zhang SJ Phys Chem Lett. 2017, 8(13), 2835-2841, etc.) can achieve invisible optical anti-counterfeiting without external stimulation, but it has intrinsic color and contains heavy metal elements; a structural color material prepared by combining polymer submicron microspheres and melanin colloidal nanoparticles with strong light absorption (Hou J, Li M, Song Y. Angew ChemInt Ed Engl. 2018, 57(10): 2544-2553. Hu Z, Bradshaw N, Vanthournout B. Chem. Mater. 2021, 33(16): 6433-6442, etc.) is well applied to inkjet printing, but it does not have the effect of changing color with the characteristics of the light source.

[0004] Therefore, developing a colored, environmentally friendly ink with intrinsic structural color that can generate color difference through light scattering during scanning and copying is of significant application value for inks that change color with light source characteristics in special optics and for industries based on such applications. Summary of the Invention

[0005] The purpose of this invention is to overcome the deficiency of existing structural color materials that change color with the characteristics of a light source, and to provide a new structural color material that can change color with the characteristics of a light source. Based on submicron-sized polymer microspheres with low refractive index (<1.5) combined with gel materials with high refractive index (>1.8), a periodic structure with controllable refractive index is formed, realizing a structural color material that is easy to prepare and has highly controllable color.

[0006] Another object of the present invention is to provide a method for preparing the structural color material that changes color with the characteristics of the light source.

[0007] Another objective of this invention is to provide the application of the structural color material that changes color with the characteristics of the light source in the field of anti-counterfeiting.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A method for preparing a structural color material that changes color according to the characteristics of a light source includes the following steps:

[0010] After the black light-absorbing material is uniformly mixed with the submicron monodisperse polymer microsphere emulsion, it is then uniformly mixed with the gel solution to obtain a mixed dispersion. The mixed dispersion is then spray-dried to obtain the structural color material that changes color with the characteristics of the light source.

[0011] Wherein, the refractive index of the submicron monodisperse polymer microsphere emulsion is less than the refractive index of the gel colloidal particles in the gel solution.

[0012] This invention is based on submicron-sized polymer microspheres with low refractive index combined with gel material with high refractive index to form a periodic structure with controllable refractive index. Due to the periodic structure of the spherical disordered assembly and its spherical scattering characteristics of the light source, the material will produce a color response to different light source spectra, thus realizing a structural color material that is easy to prepare and has highly controllable color.

[0013] By designing a low-refractive-index polymer emulsion system, submicron-sized monodisperse polymer microsphere emulsions are mixed with a certain proportion of black light-absorbing material. This enhances the saturation of the physical structural color without compromising the overall stability and brightness of the structural color. Further mixing with a hydrolysate that can form a high-refractive-index gel enhances the system's light scattering properties, giving it a color-changing characteristic that changes with the light source, while maintaining system stability and preventing aggregation. Finally, spray drying forms a powder that fixes the disordered assembly structure of the submicron polymer microspheres and gel in the system, while also preventing the ordered stacking of submicron polymer microspheres and thus avoiding Bragg diffraction.

[0014] The inventors of this invention also discovered through research that the black light-absorbing substance must be fully combined with the colloidal microspheres through electrostatic interaction before the addition of the gel hydrolysate in order to enhance the saturation of the structural color. If it is added after the addition of the gel hydrolysate, it will lead to a weakening of the light scattering characteristics of the system, and the system will be dark overall with an indistinct intrinsic structural color.

[0015] Preferably, the refractive index of the submicron monodisperse polymer microsphere emulsion is <1.5.

[0016] Preferably, the refractive index of the gel particles in the gel solution is >1.8.

[0017] Choosing a refractive index within the above range is beneficial for further improving the color difference of structural color materials under different light sources, which is conducive to anti-counterfeiting applications.

[0018] Preferably, the gel solution is a hydrolysis product of one or a mixture of two of the following: an inorganic salt of ammonium ions and an organic chelate of ammonium ions, in an acidic solution.

[0019] Optionally, the inorganic salt of the ammonium ion includes, but is not limited to, at least one of ammonium paratungstate and ammonium zirconium carbonate; the organic chelate of the ammonium ion includes, but is not limited to, di(2-hydroxypropionic acid)-diammonium hydroxide titanium.

[0020] In this invention, the gel solution is prepared by a method comprising the following steps: adding at least one of ammonium paratungstate solution, diammonium di(2-hydroxypropionic acid) hydroxide solution, and ammonium zirconium carbonate solution to an aqueous solution of an acid, and stirring vigorously until clear and transparent to obtain a gel hydrolysate. The acid can be a commonly used inorganic acid in the art, including but not limited to at least one of hydrochloric acid, sulfuric acid, and nitric acid.

[0021] The concentration of the acid in the aqueous solution is 5–10 mmol / L; the mass ratio of the aqueous solution of the acid to the gel-forming substance (i.e., a mixture of one or two of the following: an inorganic salt of ammonium ions and an organic chelate of ammonium ions) is 2–4:1.

[0022] Preferably, in the submicron monodisperse polymer microsphere emulsion, the average particle size of the polymer microspheres is 100–600 nm.

[0023] Optionally, the polymer microspheres may be silicon-containing polymer microspheres, fluoropolymer microspheres, or a mixture of both. The silicon-containing polymer microspheres include, but are not limited to, at least one of poly(trimethylsiloxane) methacrylate microspheres and poly(triisopropylsiloxane) methacrylate microspheres. The fluoropolymer microspheres include, but are not limited to, at least one of poly(hexafluoroisopropyl) acrylate microspheres, poly(perfluorobutyl ethyl) acrylate microspheres, poly(perfluorohexyl) acrylate microspheres, and poly(dodecylfluoroheptyl) methacrylate microspheres.

[0024] Optionally, the black light-absorbing material includes, but is not limited to, at least one of carbon black, carbon nanotubes, graphene, and polydopamine.

[0025] Preferably, the solid content in the gel solution is 5-10 wt%.

[0026] Preferably, in the submicron monodisperse polymer microsphere emulsion, the polymer microspheres account for 5-15% of the total mass.

[0027] Preferably, in the mixed dispersion, the mass ratio of polymer microspheres, black light-absorbing material, and gel colloidal particles in the gel solution is: polymer microspheres: black light-absorbing material: gel colloidal particles in the gel solution = 1:(0.01~0.05):(0.3~1).

[0028] To further improve the dispersion effect, the black light-absorbing substance was first ultrasonically dispersed in water to prepare a black light-absorbing substance dispersion. Then, this dispersion was added to a submicron-sized monodisperse colloidal microsphere emulsion that had been ultrasonically dispersed, and ultrasonic dispersion continued. Finally, the dispersion was slowly added to the prepared gel solution while stirring. Good dispersibility helps ensure the morphological integrity of the polymer microspheres and colloidal particles in the system, as well as the overall uniformity and stability of the system, resulting in a structural color material with more prominent color-changing properties.

[0029] Preferably, the spray drying temperature is 120–170°C. Within this temperature range, the sprayed powder is evenly dispersed, less prone to agglomeration, and can produce structural color materials with stable and excellent performance.

[0030] The structural color material that changes color with the characteristics of the light source and is prepared by the above method is also protected by this invention.

[0031] This invention also protects the application of the structural color material that changes color with the characteristics of the light source in the field of anti-counterfeiting.

[0032] Specifically, the application involves spraying or coating the structural color material, which changes color with the characteristics of the light source, onto a clean substrate surface to prepare a coating. The prepared coating displays significantly different colors under different light sources (e.g., sunlight, indoor diffused light, cold light-emitting diodes, warm light-emitting diodes, incandescent lamps, or fluorescent tubes).

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] This invention utilizes submicron-sized polymer microspheres with low refractive index combined with a gel material with high refractive index to form a periodic structure with controllable refractive index. Due to the spherical scattering characteristics of the periodic structure of the spherical disordered assembly, the material exhibits color responses to different light source spectra, realizing a structural color material that is easy to prepare and has highly controllable color. By selecting polymer microspheres and gel materials with different particle sizes and compositions, as well as specific preparation methods, different structural color characteristics can be obtained, and the structural color of the composite material can be continuously controlled according to actual needs.

[0035] The preparation method of the present invention is simple and convenient to operate, uses inexpensive and readily available raw materials, requires no expensive instruments, has low cost, is suitable for industrial preparation, is suitable for a variety of uses, and has great practical application value.

[0036] The structural color material prepared by this invention overcomes the problems of easy counterfeiting of anti-counterfeiting marks and low technical identification and threshold of traditional optical anti-counterfeiting technologies such as temperature-sensitive and photochromic inks. The color of the structural color material can be changed simply by changing the light source, and it has a large color difference. It is convenient to prevent counterfeiting, difficult to imitate, and has a wide range of applications. It has important application value and broad application prospects in industries such as polymer coatings and office printing. Attached Figure Description

[0037] Figure 1 This is a scanning electron microscope image of the structural color material that changes color with the characteristics of the light source prepared in Example 1;

[0038] Figure 2 for Figure 1 A magnified view of a portion of the image;

[0039] Figure 3 This is a scanning electron microscope image of the structural color material that changes color with the characteristics of the light source prepared in Example 3;

[0040] Figure 4 for Figure 3 A magnified view of a portion of the image. Detailed Implementation

[0041] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to specific embodiments and accompanying drawings. However, the embodiments do not limit the invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in this invention are conventional reagents, methods, and equipment in this technical field. Unless otherwise specified, all reagents and materials used in this invention are commercially available.

[0042] Example 1

[0043] This embodiment provides a structural color material that changes color according to the characteristics of a light source, which is prepared according to a method including the following steps:

[0044] (1) Polyhexafluoroisopropylacrylic acid microspheres with an average particle size of 200 nm were prepared into a polymer microsphere emulsion with a mass fraction of 5% (the refractive index of the microspheres is 1.38). The microspheres were placed in an ultrasonic disperser and ultrasonically dispersed. A carbon black aqueous solution with a mass fraction of 0.5% was added to the emulsion, which was 10% of the mass of the microsphere emulsion. That is, the mass ratio of polymer microspheres to carbon black was 1:0.01. The ultrasonic dispersion was continued until the mixture was uniformly dispersed.

[0045] (2) At room temperature (about 25°C) and under stirring conditions, the prepared gel solution (the refractive index of the gel colloidal particles obtained after drying is 1.95) is slowly added to the mixture obtained in step (1), and then ultrasonically dispersed and mixed evenly to obtain a mixed dispersion. Finally, the mixed dispersion is spray-dried at 145°C using a spray dryer to obtain the structural color material that changes color with the characteristics of the light source.

[0046] The gel solution is prepared by adding ammonium paratungstate to a 5 mmol / L dilute hydrochloric acid aqueous solution and stirring thoroughly at room temperature until it is clear, transparent and does not separate into layers, thus obtaining a gel solution with a dry weight mass fraction of 10%.

[0047] In the mixed dispersion, the mass ratio of polymer microspheres, black light-absorbing material, and gel colloidal particles in the gel solution is: polymer microspheres: black light-absorbing material: gel colloidal particles in the gel solution = 1:0.01:0.8.

[0048] The scanning electron microscope image of the structured color material that changes color with the characteristics of the light source is as follows: Figure 1 and Figure 2 ( Figure 2 for Figure 1 As shown in the enlarged view (of the part), from Figure 2 As can be seen, monodisperse polymer microspheres with a diameter of 200 nm are encapsulated by a gel substance (the outline of the spheres is only the raised part of the surface), and the 200 nm microspheres further form... Figure 1 Aggregates with a diameter of 2-7 micrometers.

[0049] Example 2

[0050] This embodiment provides a structural color material that changes color according to the characteristics of a light source, which is prepared according to a method including the following steps:

[0051] (1) Poly(trimethylsilyl methacrylate) microspheres with an average particle size of 200 nm were prepared into a microsphere emulsion with a mass fraction of 5% (refractive index of 1.4), and ultrasonically dispersed in an ultrasonic disperser. A carbon nanotube aqueous solution with a mass fraction of 0.2% was added to the mixture, which was 10% of the mass of the microsphere emulsion, i.e. the ratio of colloidal microspheres to carbon nanotubes was 1:0.01. The dispersion was continued until a uniform mixture was obtained.

[0052] (2) At room temperature (about 25°C) and under stirring conditions, the prepared gel solution (the refractive index of the gel colloidal particles obtained after drying is 2) is slowly added to the mixture obtained in step (1). Then, after ultrasonic dispersion and uniform mixing, a mixed dispersion is obtained. Finally, the mixed dispersion is spray-dried at 145°C using a spray dryer to obtain the structural color material that changes color with the characteristics of the light source.

[0053] The gel solution is prepared by adding di(2-hydroxypropionic acid)-diammonium dihydrochloride titanium to a 5 mmol / L dilute hydrochloric acid aqueous solution and stirring thoroughly at room temperature until it is clear, transparent and does not separate into layers, thus obtaining a gel solution with a dry weight mass fraction of 10%.

[0054] In the mixed dispersion, the mass ratio of polymer microspheres, black light-absorbing material, and gel colloidal particles in the gel solution is: polymer microspheres: black light-absorbing material: gel colloidal particles in the gel solution = 1:0.01:1.

[0055] Example 3

[0056] This embodiment provides a structural color material that changes color according to the characteristics of a light source, which is prepared according to a method including the following steps:

[0057] (1) Prepare a microsphere emulsion with a mass fraction of 5% (refractive index 1.42) of polyisopropyl silicone acrylate microspheres with an average particle size of 200 nm. Place it in an ultrasonic disperser for ultrasonic dispersion. Add a 0.5% (mass fraction) aqueous solution of graphene oxide to the mixture, which is 10% of the mass of the microsphere emulsion, i.e. the ratio of colloidal microspheres to graphene oxide is 1:0.01. Continue until the mixture is uniformly dispersed.

[0058] (2) At room temperature (about 25°C) and under stirring conditions, the prepared gel solution (the refractive index of the gel colloidal particles obtained after drying is 1.95) is slowly added to the mixture obtained in step (1), and then ultrasonically dispersed and mixed evenly to obtain a mixed dispersion. Finally, the mixed dispersion is spray-dried at 145°C using a spray dryer to obtain the structural color material that changes color with the characteristics of the light source.

[0059] The gel solution is prepared by adding ammonium zirconium carbonate to a 5 mmol / L dilute hydrochloric acid aqueous solution and stirring thoroughly at room temperature until it is clear, transparent and does not separate into layers, thus obtaining a gel solution with a dry weight mass fraction of 10%.

[0060] In the mixed dispersion, the mass ratio of polymer microspheres, black light-absorbing material, and gel colloidal particles in the gel solution is: polymer microspheres: black light-absorbing material: gel colloidal particles in the gel solution = 1:0.01:1.

[0061] The scanning electron microscope image of the structured color material that changes color with the characteristics of the light source is as follows: Figure 3 and Figure 4 ( Figure 4 for Figure 3 As shown in the enlarged view (of the part), from Figure 4 It can be seen that monodisperse polymer microspheres with a diameter of 200 nm are encapsulated by a gel substance (the outline of the spheres is only the raised part of the surface), and the 200 nm microspheres further form... Figure 3 Aggregates with a diameter of 1-8 micrometers.

[0062] Example 4

[0063] This embodiment provides a structural color material that changes color according to the characteristics of a light source, which is prepared according to a method including the following steps:

[0064] (1) Poly(perfluorobutyl ethyl acrylate) microspheres with an average particle size of 300 nm were prepared into a microsphere emulsion with a mass fraction of 5% (refractive index of 1.37), and ultrasonically dispersed in an ultrasonic disperser. A polydopamine aqueous solution with a mass fraction of 0.5% was added to the mixture, which was 10% of the mass of the microsphere emulsion, i.e. the ratio of colloidal microspheres to carbon nanotubes was 1:0.01. The dispersion was continued until a uniform mixture was obtained.

[0065] (2) At room temperature (about 25°C) and under stirring conditions, the prepared gel solution (the refractive index of the gel colloidal particles obtained after drying is 1.95) is slowly added to the mixture obtained in step (1), and then ultrasonically dispersed and mixed evenly to obtain a mixed dispersion. Finally, the mixed dispersion is spray-dried at 145°C using a spray dryer to obtain the structural color material that changes color with the characteristics of the light source.

[0066] The gel solution is prepared by adding ammonium paratungstate to a 5 mmol / L dilute hydrochloric acid aqueous solution and stirring thoroughly at room temperature until it is clear, transparent and does not separate into layers, thus obtaining a gel solution with a dry weight mass fraction of 10%.

[0067] In the mixed dispersion, the mass ratio of polymer microspheres, black light-absorbing material, and gel colloidal particles in the gel solution is: polymer microspheres: black light-absorbing material: gel colloidal particles in the gel solution = 1:0.01:1.

[0068] Example 5

[0069] This embodiment provides a structural color material that changes color according to the characteristics of a light source, which is prepared according to a method including the following steps:

[0070] (1) Prepare a microsphere emulsion with a mass fraction of 5% (refractive index 1.35) of polyperfluorohexyl acrylate microspheres with an average particle size of 400 nm. Place it in an ultrasonic disperser for ultrasonic dispersion. Add a carbon black aqueous solution with a mass fraction of 0.5% to the emulsion, which is 10% of the mass of the microsphere emulsion, i.e. the ratio of colloidal microspheres to carbon black is 1:0.01. Continue until the dispersion is uniform to obtain a mixture.

[0071] (2) At room temperature (about 25°C) and under stirring conditions, the prepared gel solution (the refractive index of the gel colloidal particles obtained after drying is 1.95) is slowly added to the mixture obtained in step (1), and then ultrasonically dispersed and mixed evenly to obtain a mixed dispersion. Finally, the mixed dispersion is spray-dried at 160°C using a spray dryer to obtain the structural color material that changes color with the characteristics of the light source.

[0072] The gel solution is prepared by adding ammonium paratungstate to a 5 mmol / L dilute hydrochloric acid aqueous solution and stirring thoroughly at room temperature until it is clear, transparent and does not separate into layers, thus obtaining a gel solution with a dry weight mass fraction of 10%.

[0073] In the mixed dispersion, the mass ratio of polymer microspheres, black light-absorbing material, and gel colloidal particles in the gel solution is: polymer microspheres: black light-absorbing material: gel colloidal particles in the gel solution = 1:0.01:1.

[0074] Example 6

[0075] This embodiment provides a structural color material that changes color according to the characteristics of a light source, which is prepared according to a method including the following steps:

[0076] (1) Poly(dodecyl fluoroheptyl methacrylate) with an average particle size of 100 nm was prepared into a microsphere emulsion with a mass fraction of 5% (refractive index of 1.33), and ultrasonically dispersed in an ultrasonic disperser. A carbon black aqueous solution with a mass fraction of 0.5% was added to the mixture, which was 50% of the mass of the microsphere emulsion, i.e. the ratio of colloidal microspheres to carbon black was 1:0.05. The dispersion was continued until a uniform mixture was obtained.

[0077] (2) At room temperature (about 25°C) and under stirring conditions, the prepared gel solution (the refractive index of the gel colloidal particles obtained after drying is 1.95) is slowly added to the mixture obtained in step (1), and then ultrasonically dispersed and mixed evenly to obtain a mixed dispersion. Finally, the mixed dispersion is spray-dried at 145°C using a spray dryer to obtain the structural color material that changes color with the characteristics of the light source.

[0078] The gel solution is prepared by adding ammonium paratungstate to a 10 mmol / L dilute hydrochloric acid aqueous solution and stirring thoroughly at room temperature until it is clear, transparent and does not separate into layers, thus obtaining a gel solution with a dry weight mass fraction of 10%.

[0079] In the mixed dispersion, the mass ratio of polymer microspheres, black light-absorbing material, and gel colloidal particles in the gel solution is: polymer microspheres: black light-absorbing material: gel colloidal particles in the gel solution = 1:0.01:1.

[0080] Example 7

[0081] This embodiment provides a structural color material that changes color according to the characteristics of a light source, which is prepared according to a method including the following steps:

[0082] (1) Poly(trimethylsilyl methacrylate) microspheres with an average particle size of 600 nm were prepared into a microsphere emulsion with a mass fraction of 15% (refractive index 1.38), and ultrasonically dispersed in an ultrasonic disperser. A carbon black aqueous solution with a mass fraction of 0.5% was added to the mixture, which was 20% of the mass of the microsphere emulsion, i.e. the ratio of colloidal microspheres to carbon black was 1:0.02. The dispersion was continued until a uniform mixture was obtained.

[0083] (2) At room temperature (about 25°C) and under stirring conditions, the prepared gel solution (the refractive index of the gel colloidal particles obtained after drying is 2) is slowly added to the mixture obtained in step (1). Then, after ultrasonic dispersion and uniform mixing, a mixed dispersion is obtained. Finally, the mixed dispersion is spray-dried at 145°C using a spray dryer to obtain the structural color material that changes color with the characteristics of the light source.

[0084] The gel solution is prepared by adding di(2-hydroxypropionic acid)-diammonium dihydrochloride titanium to a 5 mmol / L dilute hydrochloric acid aqueous solution and stirring thoroughly at room temperature until it is clear, transparent and does not separate into layers, thus obtaining a gel solution with a dry weight mass fraction of 10%.

[0085] In the mixed dispersion, the mass ratio of polymer microspheres, black light-absorbing material, and gel colloidal particles in the gel solution is: polymer microspheres: black light-absorbing material: gel colloidal particles in the gel solution = 1:0.01:1.2.

[0086] Comparative Example 1

[0087] This comparative example provides a structural color material, which is prepared in a manner that is basically the same as that in Example 1, except that in step (2), it is not mixed with the gel solution and is directly spray-dried.

[0088] Comparative Example 2

[0089] This comparative example provides a structural color material, and the preparation method is basically the same as that in Example 1, except that: in step (1), no black light-absorbing substance is added to the polymer microsphere emulsion.

[0090] Comparative Example 3

[0091] This comparative example provides a structural color material, and the preparation method is basically the same as that in Example 1, except that in step (1), micron-sized polyhexafluoroisopropylacrylic acid microspheres with an average particle size of 1 μm are used instead of submicron-sized polyhexafluoroisopropylacrylic acid microspheres.

[0092] Comparative Example 4

[0093] This comparative example provides a structural color material, the preparation method of which is basically the same as that of Example 1, except that the concentrations of the polymer microsphere emulsion and the colloidal solution are changed so that the refractive index of the polymer microsphere emulsion (e.g., refractive index 1.8) is greater than the refractive index of the colloidal solution (e.g., refractive index 1.5), while other parameters (e.g., the mass ratio of each component in the system) remain unchanged.

[0094] Performance testing

[0095] The anti-counterfeiting performance of the structural color materials obtained in the above embodiments and comparative examples was characterized. The specific test items, test methods, and results are as follows:

[0096] The structural color materials prepared in the above examples and comparative examples were mixed with a polyurethane-based UV-curable binder at a mass fraction of 10%. After coating and curing, a coating with a thickness of 20 μm was obtained. The coating was then irradiated with different light sources, with a light intensity of 500 mW / cm². 2 Image analysis was performed on the red, green and blue components of the coating surface under different light sources, and the color change characteristics with light source features are shown in Table 1.

[0097] Table 1. Image test results of structural color materials obtained from the examples and comparative examples.

[0098]

[0099] The results above show that:

[0100] The structural color material prepared according to the embodiments of the present invention can change to different colors depending on different light sources.

[0101] In the structural color material of Comparative Example 1, no gel material forms a microstructure with a fixed refractive index. After the gaps between the polymer microspheres are filled by the binder, the coating loses its specific periodic refractive index structure and only appears as a light gray color. Therefore, it does not have the characteristic of changing color with the characteristics of the light source.

[0102] In the structural color material of Comparative Example 2, there is no carbon black to absorb scattered light, so the structural color of the coating is masked by background scattering and only appears as a light white color. Therefore, it does not have the characteristic of changing color with the characteristics of the light source.

[0103] In the structural color material of Comparative Example 3, micron-sized polyhexafluoroisopropylacrylic acid microspheres with larger particle size were used. The coating did not have a specific visible light scattering ability and only showed a light gray state. Therefore, it did not have the characteristic of changing color with the characteristics of the light source.

[0104] In the structural color material of Comparative Example 4, the refractive index of the colloidal solution is lower than that of the submicron-sized polymer microspheres. The light source passing through the gaps between the polymer microspheres is refracted by the polymer microspheres with a larger refractive index, and the intensity of the scattered light source is weak. Therefore, although there is a certain color difference under different light sources, ΔE is below 3.5, and the color difference value is small.

[0105] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a structural color material that changes color according to the characteristics of a light source, characterized in that, Includes the following steps: After the black light-absorbing material is uniformly mixed with the submicron monodisperse polymer microsphere emulsion, it is then uniformly mixed with the gel solution to obtain a mixed dispersion. The mixed dispersion is then spray-dried to obtain the structural color material that changes color with the characteristics of the light source. Wherein, the refractive index of the submicron monodisperse polymer microsphere emulsion is less than the refractive index of the gel colloidal particles in the gel solution; The black light-absorbing material includes at least one of carbon black, carbon nanotubes, graphene, and polydopamine; In the submicron monodisperse polymer microsphere emulsion, the average particle size of the polymer microspheres is 100-600 nm; the polymer microspheres include at least one of silicon-containing polymer microspheres and fluoropolymer microspheres; the silicon-containing polymer microspheres include one of poly(trimethylsiloxane methacrylate) microspheres and poly(triisopropylsiloxane methacrylate) microspheres; the fluoropolymer microspheres include at least one of poly(hexafluoroisopropyl acrylate) microspheres, poly(perfluorobutyl ethyl acrylate) microspheres, poly(perfluorohexyl acrylate) microspheres, and poly(dodecylfluoroheptyl methacrylate) microspheres. The gel solution is a hydrolysis product of one or a mixture of two of the following: an inorganic salt of ammonium ions and an organic chelate of ammonium ions, in an acidic solution.

2. The method for preparing structural color materials that change color with light source characteristics according to claim 1, characterized in that, The inorganic salt of the ammonium ion includes at least one of ammonium paratungstate and ammonium zirconium carbonate; the organic chelate of the ammonium ion includes di(2-hydroxypropionic acid)-diammonium hydroxide titanium.

3. The method for preparing a structural color material that changes color according to the characteristics of a light source according to claim 1, characterized in that, The refractive index of the submicron monodisperse polymer microsphere emulsion is <1.5; the refractive index of the gel colloidal particles in the gel solution is >1.

8.

4. The method for preparing a structural color material that changes color with light source characteristics according to claim 1, characterized in that, Includes at least one of the following features: 1) The solid content of the gel solution is 5-10%; 2) In the submicron monodisperse polymer microsphere emulsion, the polymer microspheres account for 5-15% of the total mass; 3) In the mixed dispersion, the mass ratio of polymer microspheres, black light-absorbing material, and gel colloidal particles in the gel solution is: polymer microspheres: black light-absorbing material: gel colloidal particles = 1: (0.01~0.05): (0.3~1).

5. A structural color material that changes color according to the characteristics of a light source, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 4.

6. The application of the structural color material that changes color with the characteristics of the light source as described in claim 5 in the field of anti-counterfeiting.

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