Magnetic photonic crystal pigment powder as well as preparation method and application thereof

Abstract

The invention relates to the technical field of optical materials, in particular to magnetic photonic crystal pigment powder as well as a preparation method and application thereof. The magnetic photonic crystal pigment powder is prepared from the following raw materials in parts by weight: 1 to 15 parts of superparamagnetic ferroferric oxide, 50 to 70 parts of nano microspheres, 15 to 50 parts of acrylate reactants, 0.1 to 3 parts of a photoinitiator and 50 to 120 parts of a solvent, the superparamagnetic ferroferric oxide is magnetic ferroferric oxide of which the surface is modified by a nonionic surfactant. The preparation method comprises the following steps: synthesizing non-ionic surfactant modified ferroferric oxide nanoparticles by a coprecipitation method, dispersing the non-ionic surfactant modified ferroferric oxide nanoparticles in a photonic crystal coating liquid, and carrying out coating, normalizing, photocuring and crushing processes to prepare the colorful magnetic photonic crystal pigment powder, the preparation method of the pigment powder is simple, convenient, low in cost, green and environment-friendly, and the preparation method is suitable for industrial production. The anti-counterfeit label is expected to be widely applied to various application scenes such as decoration and anti-counterfeit labels.

Description

Technical Field

[0001] This invention relates to the field of optical materials technology, and in particular to a magnetic photonic crystal pigment powder, its preparation method, and its application. Background Technology

[0002] Compared to traditional dyes, structural colors derived from oriented alignment exhibit significant advantages in multiple dimensions. Firstly, the formation of structural colors stems from a series of physical effects such as interference, scattering, or diffraction between incident light and micro / nano structures. The color presentation depends solely on the ordered arrangement of the photonic crystals. As long as this structure remains intact, its color can remain stable for a long time, unlike organic dyes which are easily oxidized or decomposed by environmental factors, thus achieving a durable coloring effect. Secondly, traditional dyes often contain certain toxic components, easily polluting the surrounding environment during their production and actual use, posing an ecological hazard. Structural colors, however, require no added chemical pigments, eliminating pollution problems caused by dye use at the source, demonstrating superior environmental protection characteristics, and providing an ideal choice for green and sustainable development. Thirdly, structural colors can exhibit a unique iridescent effect; that is, the same object can display different color effects as the angle of incident light or the direction of observation changes, creating a unique visual effect.

[0003] Magnetic pearlescent pigments can produce dynamic optical effects through the reflection, refraction, and interference of light. As the viewing angle changes, the color and brightness gradually shift, effectively enhancing the visual depth. They are well-suited for processing techniques such as spraying, printing, and injection molding, and are therefore widely used in the decorative field. Chinese invention patent application CN112626892A utilizes magnetic pearlescent pigments on umbrella fabrics, combined with composite coating technology. Under an external magnetic field, the pigments are oriented within the coating, enhancing the pattern's depth and creating a 3D effect, making the umbrella's appearance more three-dimensional and richer. Chinese invention patent application CN118108981A coats magnetic pearlescent pigments with an oil-based coupling agent, facilitating uniform dispersion in photocurable resins. During 3D printing, the orientation and distribution of the magnetic filler are modified by controlling the magnetic field, resulting in a rich variety of model colors. However, the coating material, uniformity, and thickness of the magnetic pearlescent powder have extremely high requirements, making the production process complex. Furthermore, the particles are prone to agglomeration due to magnetic forces, requiring the addition of dispersants or special treatments, which limits the color range of the magnetic pearlescent powder.

[0004] Magnetic photonic crystals can balance the attractive force of an external magnetic field through electrostatic interactions or repulsive forces generated by steric hindrance. Adjusting the magnetic field can change the equilibrium spacing of the photonic crystal structure, allowing for precise and rapid color control. Chinese invention patent application CN115260528A synthesized a porous magnetic hydrogel in which magnetic particles maintain a certain degree of fluidity within the hydrogel structure and can self-assemble into a photonic crystal under an external magnetic field, exhibiting the ability to instantly change color and display repeating colors. However, the production equipment and raw materials for this magnetic photonic crystal are expensive, the reaction scale is small, and the arrangement structure of the magnetic photonic crystal may be destroyed after strong external forces or prolonged use, thus limiting its practical applications.

[0005] Against this backdrop, the preparation of a magnetic photonic crystal pigment powder with excellent physical properties and a wide color rendering range using a low-cost, high-volume, and environmentally friendly method has become a pressing technical problem to be solved in this field. Summary of the Invention

[0006] To address the aforementioned technical issues, this invention optimizes the pigment powder. First, nonionic surfactant-modified iron oxide nanoparticles are synthesized via a co-precipitation method and dispersed in a photonic crystal coating solution. Then, the nanoparticles undergo coating, conditioning, photocuring, and pulverization processes sequentially to obtain stable and richly colored magnetic photonic crystal pigment powder. This pigment powder preparation method is simple, low-cost, and environmentally friendly, and can be repeatedly synthesized in large quantities, making it promising for widespread application in various scenarios such as decoration and anti-counterfeiting labels.

[0007] The first aspect of the present invention provides a magnetic photonic crystal pigment powder, wherein the raw materials for preparing the magnetic photonic crystal pigment powder include, by weight: 1-15 parts of superparamagnetic iron oxide, 50-70 parts of nanospheres, 15-50 parts of acrylate reactants, 0.1-3 parts of photoinitiator, and 50-120 parts of solvent.

[0008] To ensure color development and stability, based on the total amount of raw materials used in the preparation of the magnetic photonic crystal pigment powder excluding solvent, the mass fraction of the superparamagnetic iron oxide is 1-15 wt%; examples include 1 wt%, 2 wt%, 2.5 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, and 15 wt%.

[0009] Optionally, the superparamagnetic iron oxide is magnetic iron oxide with a surface modified by a nonionic surfactant.

[0010] The nonionic surfactants may include polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, fatty acid polyoxyethylene ester, sorbitan fatty acid ester (Span type), polyoxyethylene sorbitan fatty acid ester (Tween type), alkyl polyglycoside, glycerol fatty acid ester, polyoxyethylene polyoxypropylene block copolymer, etc.

[0011] Optionally, the nonionic surfactant includes one or more combinations of polyethylene glycol, polyvinyl alcohol, and polyvinylpyrrolidone.

[0012] To further improve the film-forming properties and magnetic responsiveness of the pigment powder, the nonionic surfactant may optionally be polyvinyl alcohol.

[0013] Optionally, the nanospheres are selected from at least one of organic polymer microspheres, inorganic microspheres, or organic polymer-inorganic composite microspheres.

[0014] Optionally, the average particle size of the nanospheres is 80-400 nm, and the PDI (polydispersity index) is less than 0.15.

[0015] Optionally, the organic polymer microspheres may include one or more combinations of polystyrene (PS) microspheres, polymethyl methacrylate (PMMA) microspheres, polylactic acid (PLA) microspheres, polyethylene (PE) microspheres, polypropylene (PP) microspheres, polycarbonate (PC) microspheres, polyurethane (PU) microspheres, polypyrrole microspheres, and polyaniline microspheres.

[0016] Further optionally, the organic polymer microspheres include polystyrene-polymethyl methacrylate (PS-PMMA) composite microspheres with a core-shell structure.

[0017] The inorganic microspheres may include one or more of the following: silicon dioxide, titanium dioxide, iron tetroxide, ferric oxide, zinc sulfide, zinc oxide, aluminum oxide, and calcium carbonate.

[0018] Optionally, the inorganic microspheres include one or more of the following: silicon dioxide, titanium dioxide, iron tetroxide, and zinc sulfide.

[0019] The acrylate reactants may include acrylate monomers, methacrylate monomers, or other photocurable acrylic oligomers.

[0020] Optionally, the acrylate reactants include, but are not limited to, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate, n-pentyl methacrylate, neopentyl methacrylate, tert-pentyl methacrylate, n-hexyl methacrylate, 2-ethylbutyl methacrylate, cyclohexyl methacrylate, n-heptyl methacrylate, n-octyl methacrylate, and 2-ethylbutyl methacrylate. Ethylhexyl acrylate, nonyl acrylate, decyl acrylate, dodecyl acrylate, tridecyl acrylate, tetradecyl acrylate, hexadecyl acrylate, octadecyl acrylate, dodecyl acrylate, norbornyl acrylate, isobornyl acrylate, borneol acrylate, menthyl acrylate, octahydroindene acrylate, adamantyl acrylate, dimethyl adamantyl acrylate, phenyl acrylate, 2-ethylphenyl acrylate, indene acrylate, toluene acrylate, benzyl acrylate, acryloylmorpholine, N-hydroxyethylacrylamide, dimethylacrylamide, diethylacrylamide, isopropylacrylamide The following are at least one of the following: N-vinylcaprolactam, (ethoxy)phenol acrylate, benzyl acrylate, tetrahydrofurfuryl acrylate, cyclotrimethylolpropane formal acrylate, 4-tert-butylcyclohexyl acrylate, ethoxyethoxyethyl acrylate, diethoxyphenol acrylate, 1,6-hexanediol diacrylate, dipropylene glycol diacrylate, dipropylene glycol diacrylate, diethylene glycol diacrylate, dipropoxyneopentyl glycol diacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, triethoxytrimethylolpropane triacrylate, hexaethoxytrimethylolpropane triacrylate, nonethoxytrimethylolpropane triacrylate, pentadecylethoxytrimethylolpropane triacrylate, tripropoxytrimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, and dipentaerythritol hexaacrylate, or oligomers thereof.

[0021] Optionally, the acrylate reactants are composed of 1,6-hexanediol diacrylate and pentaerythritol triacrylate, with a weight ratio of 1:(0.5-3).

[0022] The photoinitiator may include free radical photoinitiators, cationic photoinitiators, or anionic photoinitiators; it may be a free radical photoinitiator. The free radical photoinitiator generates free radicals upon absorbing light energy, initiating free radical polymerization of the photocurable reactant. Free radical photoinitiators may include one or more combinations of benzoin or its derivatives, benzoyl or its derivatives, acetophenone or its derivatives, α-hydroxy ketone derivatives, α-amino ketone derivatives, benzoylcarbamates, acylphosphine oxides, benzophenone or its derivatives, thioxanthone or its derivatives, and anthraquinone or its derivatives.

[0023] Optionally, the photoinitiator is 2,4,6-trimethylbenzoyl-diphenylphosphine oxide.

[0024] Optionally, the magnetic photonic crystal pigment powder has an average particle size of 30-1000 μm.

[0025] A second aspect of this invention provides a method for preparing magnetic photonic crystal pigment powder; the preparation steps of the magnetic photonic crystal pigment powder include: S1. Preparation of superparamagnetic iron oxide; S2. Mix the superparamagnetic iron oxide, nanospheres, acrylate reactants, photoinitiator, and solvent to obtain a magnetic photonic crystal coating solution; S3. The magnetic photonic crystal coating liquid is sequentially subjected to coating, regularization and photocuring treatments to obtain a magnetic photonic crystal film. After crushing, the powder is collected and sieved to obtain magnetic photonic crystal pigment powder.

[0026] Optionally, the preparation steps of the superparamagnetic iron oxide include: Ferrous and ferrous salts were mixed, heated in a water bath, and alkali solution was added under an inert gas atmosphere. The mixture was kept warm and aged to produce iron(III) oxide. A nonionic surfactant was added to carry out a surface modification reaction. After the reaction was completed, the product was ultrasonically washed, and the supernatant was poured off after magnetic adsorption to obtain superparamagnetic iron(III) oxide.

[0027] Optionally, the iron salt may include ferric chloride, ferric sulfate, ferric nitrate, ferric acetate, etc.

[0028] Optionally, the ferrous salt may include ferrous chloride, ferrous sulfate, ferrous nitrate, ferrous acetate, etc.

[0029] Optionally, the molar ratio of the ferric salt to the ferrous salt is (1.5-2.2):1; examples include 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2.0:1, 2.1:1, and 2.2:1.

[0030] Optionally, the water bath heating temperature is 30-80℃.

[0031] The alkaline solution may include potassium hydroxide aqueous solution, sodium hydroxide aqueous solution, ammonia water, etc.; optionally, the alkaline solution is sodium hydroxide aqueous solution.

[0032] Optionally, the molar ratio of sodium hydroxide to ferrous salt in the alkaline solution is (8-12):1; examples include 8:1, 9:1, 10:1, 11:1, and 12:1.

[0033] Optionally, the heat preservation and aging time is 15-60 minutes; examples include 15 minutes, 30 minutes, 45 minutes, and 60 minutes.

[0034] Optionally, the mass ratio of the nonionic surfactant to the iron oxide is (0.01-5):1; examples include 0.01:1, 0.1:1, 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, and 5:1.

[0035] Optionally, the surface modification reaction is carried out at a temperature of 60-90℃ and for a reaction time of 30-240 min.

[0036] Optionally, step S2 includes: first, mixing nanospheres, acrylate reactants, photoinitiator, and 50-80 wt% of solvent to obtain a photonic crystal coating solution; then, mixing the superparamagnetic iron oxide with the remaining solvent, slowly dripping it into the photonic crystal coating solution, and dispersing it at high speed to obtain a magnetic photonic crystal coating solution.

[0037] Optionally, step S3 specifically includes: coating the magnetic photonic crystal coating liquid onto the substrate surface and drying it; performing a regularization treatment to make the nanospheres three-dimensionally ordered; then performing a photocuring treatment to obtain a magnetic photonic crystal film; pulverizing the magnetic photonic crystal film; collecting and sieving it to obtain magnetic photonic crystal pigment powder of the target particle size.

[0038] Optionally, the drying temperature is 60-150℃, and can be listed as 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, and 150℃.

[0039] In some embodiments, the pulverized magnetic photonic crystal pigment powder presents as irregular flakes with a diameter of 1-1000 μm, and more preferably 100-600 μm.

[0040] A third aspect of the present invention provides an application of magnetic photonic crystal pigment powder; the magnetic photonic crystal pigment powder is applied in the fields of decorative materials, anti-counterfeiting labels or display elements.

[0041] In some embodiments, the magnetic photonic crystal pigment body is used in the preparation of color-developing thin films.

[0042] Beneficial effects: This invention provides a magnetic photonic crystal pigment powder, its preparation method, and its application, which has the following advantages: (1) The present invention introduces superparamagnetic iron oxide nanoparticles into the formulation system of pigment powder, which improves the film-forming properties and magnetic responsiveness of pigment powder without affecting the three-dimensional photonic crystal structure arrangement of nanospheres. (2) The present invention further uses a co-precipitation method to synthesize nonionic surfactant-modified iron oxide nanoparticles. Under alkaline conditions, superparamagnetic iron oxide nanoparticles are prepared by using a specific molar ratio of iron ions and ferrous ions. This preparation process has a fast reaction rate, mild conditions, and high yield. (3) In the process of synthesizing superparamagnetic iron oxide nanoparticles, the present invention introduces nonionic surfactants to modify the surface of iron oxide nanoparticles in situ, which effectively inhibits the aggregation of nanoparticles and enables them to be well dispersed in the photonic crystal coating solution, thereby significantly improving the dispersion stability and storage stability of the coating solution system. (4) The superparamagnetic iron oxide nanoparticles introduced in this invention provide a black base for photonic crystal pigments, which can effectively absorb stray light and improve the contrast and color saturation of structural colors. (5) The pigment powder provided by the present invention can be flipped, moved and oriented under the action of a magnetic field. By changing the direction and distribution of the magnetic field, the pattern and color effect can be customized, which broadens the application scenarios of photonic crystal pigment powder and provides a new idea for the preparation of color-changing materials in the fields of anti-counterfeiting labels, decorative coatings and functional displays. Attached Figure Description

[0043] Figure 1 Microscopic images of magnetic photonic crystal pigment powders in Examples 1-5; Figure 1 In the examples, a represents Example 1, b represents Example 2, c represents Example 3, d represents Example 4, and e represents Example 5; Figure 2 Optical images of magnetic photonic crystal pigment powders in Examples 2, 4, and 5, and samples in Comparative Examples 1-3; Figure 2 In the examples, a is Example 2, b is Example 4, c is Example 5, d is Comparative Example 1, e is Comparative Example 2, and f is Comparative Example 3; Figure 3 Optical images of colorimetric thin films in Application Examples 1-4; Figure 3 In the example, a is application example 1, b is application example 2, c is application example 3, and d is application example 4. Detailed Implementation

[0044] Note: Unless otherwise specified, the solvent of the solutions involved in this invention is water; the PS-PMMA microspheres are self-made by our company (the preparation method is based on Chinese invention patent CN105949379A); the other raw materials used are commercially available, including but not limited to suppliers such as McLean, Aladdin, Xilong Chemical Reagent Factory, and Changxing Chemical Industry (Guangdong) Co., Ltd.

[0045] Example 1 This embodiment provides a magnetic photonic crystal pigment powder and its preparation method; the raw materials for preparing the magnetic photonic crystal pigment powder include, by weight, 2.6 parts of superparamagnetic iron oxide, 60 parts of nanospheres, 40 parts of acrylate reactants, 1 part of photoinitiator, and 100 parts of solvent.

[0046] The superparamagnetic iron oxide is magnetic iron oxide whose surface has been modified with a nonionic surfactant.

[0047] The nonionic surfactant is polyvinyl alcohol, derived from Aladdin, with product number P139535.

[0048] The nanospheres are organic polymer microspheres, specifically PS-PMMA microspheres; the average particle size of the nanospheres is 250 nm, the PDI (polydispersity index) is less than 0.15, and they are sourced from Guangzhou Guangyu Metamaterials Co., Ltd.

[0049] The acrylate reactants are 1,6-hexanediol diacrylate and pentaerythritol triacrylate in a weight ratio of 1:1.

[0050] The photoinitiator is 2,4,6-trimethylbenzoyl-diphenylphosphine oxide.

[0051] A second aspect of this invention provides a method for preparing magnetic photonic crystal pigment powder; the preparation steps of the magnetic photonic crystal pigment powder include: S1. Preparation of superparamagnetic iron(III) oxide: 7.8 g FeCl3 and 4.8 g FeCl2·4H2O were ultrasonically dissolved in 40.0 g of purified water, transferred to a three-necked flask, heated in a water bath to 40 °C, and stirred rapidly; 8.0 g NaOH was dissolved in 40.0 g of purified water, and the resulting NaOH aqueous solution was added to the three-necked flask and aged at 40 °C for 30 min to generate iron(III) oxide; 10.0 g polyvinyl alcohol was dissolved in 70.0 g of purified water to obtain a hydrophilic surfactant solution, which was added to the three-necked flask, and the reaction temperature was raised to 80 °C for surface modification reaction. During the reaction, a condenser was used to condense the reflux water vapor and continuously introduce N2, and the reaction was kept at this temperature for 2 hours; after the reaction, the product was ultrasonically washed with deionized water, the supernatant was poured off after magnetic adsorption, and the washing was repeated twice to obtain polyvinyl alcohol-modified superparamagnetic iron(III) oxide; S2. First, mix nanospheres, acrylate reactants, photoinitiator and 75 parts of solvent to obtain a photonic crystal coating solution; mix polyvinyl alcohol modified paramagnetic iron oxide with 25 parts of solvent and slowly drop it into the photonic crystal coating solution, disperse it at high speed to obtain a magnetic photonic crystal coating solution; S3. The magnetic photonic crystal coating liquid is coated onto the surface of a PET substrate and dried at 80°C to obtain a coating (the mass fraction of superparamagnetic iron oxide in the coating is 2.5%). The coating is then subjected to a regularization treatment to ensure that the nanospheres are arranged in a three-dimensional order (specifically, a bending shear regularization treatment is performed, referring to step (b) of Chinese Patent CN103534079B). Then, a photocuring treatment is performed (the photocuring conditions are: photocuring wavelength 365nm, photocuring energy 1000mJ / cm²). 2 The magnetic photonic crystal film was obtained; the magnetic photonic crystal film was peeled off from the PET substrate, crushed using a crusher, and collected and sieved to obtain magnetic photonic crystal pigment powder of the target particle size.

[0052] Example 2 This embodiment provides a magnetic photonic crystal pigment powder and its preparation method, with the specific implementation method being the same as in Embodiment 1; the difference is that the amount of superparamagnetic iron oxide added is 5.3 parts by weight, and the mass fraction of superparamagnetic iron oxide in the coating prepared in step S3 is 5%.

[0053] Example 3 This embodiment provides a magnetic photonic crystal pigment powder and its preparation method, with the specific implementation method being the same as in Embodiment 1; the difference is that the amount of superparamagnetic iron oxide added is 11.2 parts by weight, and the mass fraction of superparamagnetic iron oxide in the coating prepared in step S3 is 10%.

[0054] Example 4 This embodiment provides a magnetic photonic crystal pigment powder and its preparation method, with the specific implementation method being the same as in Embodiment 2; the difference is that the average particle size of the PS-PMMA microspheres is 220 nm.

[0055] Example 5 This embodiment provides a magnetic photonic crystal pigment powder and its preparation method, with the specific implementation method being the same as in Embodiment 2; the difference is that the average particle size of the PS-PMMA microspheres is 190 nm.

[0056] Comparative Example 1 Guangzhou Guangyu Ultramaterials Co., Ltd.'s red photonic crystal pigment product T80-134 (excluding iron tetroxide).

[0057] Comparative Example 2 Guangzhou Guangyu Ultramaterials Co., Ltd.'s green photonic crystal pigment product T80-406 (excluding iron tetroxide).

[0058] Comparative Example 3 Guangzhou Guangyu Supermaterials Co., Ltd.'s blue photonic crystal pigment product T80-607 (excluding iron tetroxide).

[0059] Application Example 1 The magnetic photonic crystal pigment powder obtained in Example 2 was dispersed in UV-curing adhesive (Lankel L-6211) at an addition amount of 5 wt%, and then coated onto the surface of a PET substrate. A bar magnet was placed under the PET substrate, and after magnetic attraction for 2 minutes, it was photocured for 1 minute under UV light irradiation (photocuring wavelength 365 nm, photocuring energy 1000 mJ / cm). 2 ), to obtain a red-green colored film ( Figure 3 a).

[0060] Application Example 2 The magnetic photonic crystal pigment powder obtained in Example 4 was dispersed in UV-curing adhesive (Lankel L-6211) at an addition amount of 5 wt%, and then coated onto the surface of a PET substrate. A bar magnet was placed under the PET substrate, and after magnetic attraction for 2 minutes, it was photocured for 1 minute under UV light irradiation (curing wavelength 365 nm, curing energy 1000 mJ / cm²). 2 A green-blue colored thin film was prepared. Figure 3 b).

[0061] Application Example 3 The magnetic photonic crystal pigment powder obtained in Example 5 was dispersed in UV-curing adhesive (Lankel L-6211) at an addition amount of 5 wt%, and then coated onto the surface of a PET substrate. A bar magnet was placed under the PET substrate, and after magnetic attraction for 2 minutes, it was photocured for 1 minute under UV light irradiation (photocuring wavelength 365 nm, photocuring energy 1000 mJ / cm). 2 A blue color-developing film was prepared. Figure 3 c).

[0062] Application Example 4 The specific implementation method is the same as in Application Example 2; the difference is that the bar magnet is replaced with a circular magnet to obtain a green-blue color-developing film. Figure 3 d).

[0063] Performance testing 1. Pigment powder properties The magnetic photonic crystal pigment powder samples from Examples 1-5 and Comparative Examples 1-3 were observed. The sample results are shown in the figure. Figure 1 , Figure 2 ; Figure 1 The letters a and e in the examples correspond to Examples 1-5, respectively. Figure 2 The af in the examples correspond to Examples 2, 4, 5 and Comparative Examples 1-3, respectively.

[0064] like Figure 1 As shown, Examples 1-5 successfully synthesized pigment powders of different colors with a high proportion of colored area, proving that the pigment powders possessed good physical properties and stability during the crushing process, effectively avoiding the destruction of the nanosphere assembly structure. The pigment powders in Examples 1-5 were all irregularly shaped flakes with particle diameters between 100-600 μm, and contained a small number of black spots. Comparing Examples 1-3, it can be seen that, under unchanged conditions, with the increase of the iron(III) oxide content, the black spots in the magnetic photonic crystal pigment powder became larger and more numerous. Simultaneously, the increased iron(III) oxide content also led to the destruction of the nanosphere assembly structure, resulting in a poorer color rendering effect. To ensure color rendering and stability, the iron(III) oxide content in the pigment powder needs to be maintained within a moderate range.

[0065] like Figure 2 As shown, currently commercially available pigment powders (Comparative Examples 1-3) exist in light-colored substrates, resulting in low structural color contrast and relatively weak color rendering effect. However, the magnetic photonic crystal pigment powder of this invention improves the absorption rate of stray light by adding black iron oxide, effectively enhancing the structural color contrast of the product.

[0066] 2. Properties of color-developing films The colorimetric films from Application Examples 1-4 were photographed and observed; the results are shown below. Figure 3 ; Figure 3 The "ad" in the examples correspond to application examples 1-4.

[0067] like Figure 3 As shown, outside the magnetic field region, the pigment powder exhibits a uniformly dispersed state with random orientation. Due to the angular-chromatic nature of photonic crystals, the structural color of some pigment powders outside the magnetic field region undergoes a blue shift, resulting in each pigment powder exhibiting a different structural color. In the magnetic field region, the powder aggregates more highly and aligns oriented along the magnetic field lines, causing the structural color of the pigment powders standing upright along the magnetic field lines to exhibit a blue shift. Figure 3 As shown in application example 1, the structural color of the pigment powder shifts from red to blue and then to green. Figure 3 As shown in examples b and d, the structural color of the pigment powder shifts from green to blue to blue in Examples 2 and 4. Figure 3 The structural color of the pigment powder in Application Example 3 (shown in c) did not change significantly, mainly because its structural color continued to shift to the ultraviolet region, making it undetectable to the naked eye. Meanwhile, it was found that in Application Examples 2 and 4, the generated patterns and colors could be controlled by changing the magnetic field, successfully preparing thin films with color-developing patterns, which can further broaden the application scenarios of photonic crystal pigment powders.

[0068] In summary, by introducing iron(III) oxide modified with a nonionic surfactant, the embodiments of this invention effectively endow pigment powder with magnetic responsive characteristics, enabling it to achieve directional aggregation, alignment, or flipping under the influence of a magnetic field, thereby obtaining diverse color rendering effects such as angle-dependent color variation. Simultaneously, iron(III) oxide also possesses stray light absorption capabilities, further enhancing the color purity and visual depth of the pigment. In contrast, the pigment systems in the three comparative proportions, which did not contain iron(III) oxide, not only failed to achieve magnetic field-induced aggregation and flipping behavior, but their color rendering effects were also significantly inferior to those of the embodiments of this invention, thus strongly demonstrating the crucial role of iron(III) oxide in the technical effectiveness of this invention.

Claims

1. A magnetic photonic crystal pigment powder, characterized by, The raw materials for preparing the magnetic photonic crystal pigment powder by weight parts include: superparamagnetic ferroferric oxide 1-15 parts, nano microspheres 50-70 parts, acrylate reactant 15-50 parts, photoinitiator 0.1-3 parts, and solvent 50-120 parts; The superparamagnetic ferroferric oxide is a magnetic ferroferric oxide with surface modified by a non-ionic surfactant.

2. The magnetic photonic crystal pigment powder according to claim 1, wherein The non-ionic surfactant includes a combination of one or more of polyethylene glycol, polyvinyl alcohol, and polyvinylpyrrolidone.

3. The magnetic photonic crystal pigment powder according to claim 1, wherein The nano microspheres are selected from at least one of organic polymer microspheres, inorganic microspheres, or organic polymer-inorganic composite microspheres.

4. The magnetic photonic crystal pigment powder according to claim 1, wherein The nano microspheres have an average particle size of 80-400 nm and a PDI less than 0.

15.

5. The magnetic photonic crystal pigment powder according to claim 1, wherein The total amount of the raw materials for preparing the magnetic photonic crystal pigment powder, except the solvent, is the basis, and the mass fraction of the superparamagnetic ferroferric oxide is 1-15 wt%.

6. The magnetic photonic crystal pigment powder according to claim 1, wherein The preparation steps of the superparamagnetic ferroferric oxide include: Mixing a ferric salt and a ferrous salt, heating in a water bath, adding a lye in an inert gas atmosphere, incubating and aging to generate ferroferric oxide; Adding a non-ionic surfactant for surface modification reaction, washing the product after the reaction to obtain the superparamagnetic ferroferric oxide.

7. The magnetic photonic crystal pigment powder according to claim 6, wherein The molar ratio of the ferric salt to the ferrous salt is (1.5-2.2):

1.

8. The magnetic photonic crystal pigment powder according to claim 6, wherein, The mass ratio of the non-ionic surfactant to the ferroferric oxide is (0.01-5):

1.

9. A method for producing the magnetic photonic crystal pigment powder according to any one of claims 1 to 8, characterized by, The preparation steps of the magnetic photonic crystal pigment powder include: Preparing the superparamagnetic ferroferric oxide; Mixing the superparamagnetic ferroferric oxide, nano microspheres, acrylate reactant, photoinitiator, and solvent to obtain a magnetic photonic crystal coating liquid; The magnetic photonic crystal coating liquid is sequentially subjected to coating, regularization, and photocuring treatment to obtain a magnetic photonic crystal film, which is crushed to obtain the magnetic photonic crystal pigment powder.

10. Use of the magnetic photonic crystal pigment powder according to any one of claims 1 to 8, characterized in that, The magnetic photonic crystal pigment powder is applied in the fields of decorative materials, anti-fake labels, or display elements.

Images