A method for preparing a structural color coating

Abstract

The application discloses a preparation method of a structural color coating, which is an organic gel-nanoparticle cluster composite coating composed of an organic polymer gel and monodisperse nanoparticle clusters; the specific steps are as follows: after organic polymer gel prepolymer, a curing agent, light-absorbing material and monodisperse nanoparticle clusters are uniformly stirred and mixed, the mixture is coated on a substrate, and then a structural color coating is obtained through solidification and crosslinking. The coating has good mechanical stability, chemical stability and washing resistance, and presents uniform and bright angle-independent structural color. The preparation process of the coating is simple, and no VOC (volatile organic compound) is discharged into the atmosphere during the solidification and film formation process, so that the coating is green and environment-friendly. The structural color coating can be widely applied to decoration and protection of surfaces of substrates such as metal, plastic, glass and cloth.

Description

Technical Field

[0001] This invention relates to a method for preparing a structural color coating, and more particularly to a method for preparing an organic gel-nanoparticle cluster composite coating with angle-independent structural color. Background Technology

[0002] Photonic crystals, as optical materials with periodic and ordered micro / nano structures, can selectively control photon propagation, producing stable and vibrant structural colors. This structure-driven color avoids the problems of photo-oxidation and photo-bleaching common in chemical dyes. Simultaneously, structural colors avoid the environmental pollution caused by chemical dyeing, showing broad application prospects in fields such as pattern printing, optical displays, and sensing. Colloidal photonic crystals are a class of optical microstructure materials formed by the self-assembly of monodisperse colloidal particles. Compared to photonic crystals constructed through machining and laser etching, colloidal photonic crystals have attracted widespread attention in many fields, especially in color-related fields, due to their versatility, controllability, low cost, and ease of functional modification. Researchers have long been dedicated to developing brightly colored colloidal photonic crystal coatings for decorative fabrics, automobiles, and buildings.

[0003] The weak particle-particle and particle-substrate interactions in colloidal photonic crystal structures result in poor mechanical stability and easy detachment of the prepared structural color coatings, severely hindering their practical application. Furthermore, these structural color coatings are highly susceptible to environmental influences; liquid wetting and mechanical friction can cause damage and discoloration. To address the problems of poor mechanical stability and limited application of structural color coatings, researchers have made considerable efforts. For example, patent CN107201690 B discloses a method for preparing structural color coatings using functionalized polystyrene or polymethyl methacrylate monodisperse colloidal particles as building blocks. By introducing functional groups such as carboxyl, amino, and hydroxyl groups onto the particle surface during the synthesis process, the assembly forces between particles are enhanced, thereby achieving structurally stable, large-area, crack-free structural color coatings. However, due to limitations in synthesis methods and processes, this method is difficult to scale up. In addition, pure particle-based coatings cannot withstand high-intensity washing and friction, limiting their further applications. Patent CN 104725919 B discloses a method for preparing a hydrophobic structural color coating. It uses a cationic hydrophobic agent to coat a photonic crystal film assembled from anionic monodisperse nanoparticles. Under the protection of the hydrophobic coating, the colloidal photonic crystal coating is protected from external environmental damage. While this method achieves a structural color coating with bright colors and stable mechanical properties, it often requires multiple steps, has many limitations, and is time-consuming and labor-intensive. Furthermore, due to the asymmetry of the assembled structure, the constructed structural color coating exhibits an iridescent effect. Patent CN 114958182A discloses a method for preparing a structural color coating using waterborne polyurethane as an auxiliary film-forming component. It uses a flexible long-chain polymer with abundant functional groups as an auxiliary film-forming component. Through crosslinking and coating of colloidal particles, the mechanical stability of the structural color coating is significantly improved. However, the flexible long chains disrupt the ordered assembly of the colloidal particles, causing them to tend to assemble into a long-range disordered but short-range ordered amorphous photonic structure. This amorphous photonic structure often produces a large amount of incoherent light scattering, resulting in a whitish structural color and low color saturation.

[0004] Therefore, considering practical applications, improving the overall performance of the structural color coating while maintaining the high orderliness of the colloidal photonic crystal assembly structure, and developing a colloidal photonic crystal coating with bright non-iridescent structural color, stable mechanical properties and good washability remains a huge challenge. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a structural color coating. The coating prepared by this method exhibits good mechanical stability, chemical stability, and washability, and can be widely used for decoration and protection of substrates such as metals, plastics, glass, and fabrics. This invention provides an organic gel-nanoparticle composite coating that exhibits uniform and bright, angle-independent structural color. The preparation method of this coating is simple, requires no special post-treatment, and the coating does not emit VOCs into the atmosphere during the curing process, meeting the requirements of green and sustainable development.

[0006] This invention is mainly achieved through the following technical solution: a method for preparing a structural color coating, the specific steps of which are as follows:

[0007] a. Preparation of monodisperse nanoparticle clusters: The solvent in the monodisperse nanoparticle dispersion was rapidly removed using a spray drying device, resulting in spherical monodisperse nanoparticle clusters with a micron-scale distribution; among which,

[0008] The parameters of the spray drying equipment are set as follows: inlet temperature of 100-130℃, peristaltic pump feed rate of 10-30mL / h, and air flow rate of 30-50L / h.

[0009] b. Preparation of the organic gel-nanoparticle cluster prepolymer: The organic polymer gel prepolymer, curing agent, light-absorbing material, and monodisperse nanoparticle clusters are thoroughly mixed at room temperature to obtain a homogeneous organic gel-nanoparticle cluster prepolymer. The mass ratio of the organic polymer gel prepolymer, curing agent, light-absorbing material, and monodisperse nanoparticle clusters is 1:(0.1-0.3):(0.001-0.003):

[0010] (0.2-0.5); wherein the organic polymer gel prepolymer is one of polyurethane prepolymer, epoxy resin prepolymer or polydimethylsiloxane prepolymer; under the action of the corresponding curing agent, cross-linking and curing can be achieved;

[0011] c. Substrate surface treatment: The substrate is ultrasonically washed in an ethanol bath to remove dust, oil and small organic molecules from the surface, and then dried at room temperature to obtain a clean substrate.

[0012] d. The prepared organic gel-nanoparticle prepolymer is coated onto the surface of the treated substrate and allowed to cure statically to obtain a coating with angle-independent structural color, wherein the coating thickness is 200-500μm.

[0013] Preferably, the nanoparticles in the monodisperse nanoparticle dispersion described in step a are one of polystyrene nanoparticles, polymethyl methacrylate nanoparticles, or silica nanoparticles; the particles in the monodisperse nanoparticle dispersion maintain a high degree of monodispersity in the solvent, and the aggregation degree index (PDI value) is 0.001-0.05.

[0014] Preferably, the nanoparticles in the monodisperse nanoparticle dispersion in step a have a particle size of 180-350 nm. The submicron particle size ensures that the structural color of the coating is adjustable throughout the visible light range, and the mass fraction of the nanoparticles is 10%-20%. The solvent in the monodisperse nanoparticle dispersion in step a is one or a mixture of water and ethanol.

[0015] Preferably, the monodisperse nanoparticle clusters described in step a maintain a highly spherical morphology, with the cluster size distributed in the micrometer scale range of 1-10 μm.

[0016] Preferably, the curing agent mentioned in step b is the corresponding curing agent of the organic polymer gel prepolymer, wherein the curing agent of the polyurethane prepolymer is one of diisocyanate-based urethane or diisocyanate-based urea; the curing agent of the epoxy resin prepolymer is one of ethylenediamine, hexamethylenediamine, diethylenetriamine or triethylenetetramine; and the curing agent of the polydimethylsiloxane prepolymer is diphenylurethane.

[0017] The light-absorbing material mentioned in step b is preferably one or a mixture of two or more of the following: nano-carbon black, carbon nanotubes, carbon dots, or dopamine particles. Black light-absorbing substances can effectively eliminate ambient light and incoherent scattered light, which is beneficial for enhancing the saturation of the coating's structural color.

[0018] The preferred stirring speed in step b is 200-300 rpm, and the stirring time is 40-80 min.

[0019] Preferably, the substrate mentioned in step c is one of metal, plastic or glass; the ultrasonic cleaning power mentioned in step c is 500-1000W and the time is 10-30min.

[0020] The preferred coating method described in step d is one of scraping, rolling, or brushing.

[0021] The preferred curing time in step d is 6-12 hours, and the curing temperature is 30-60℃.

[0022] The present invention discloses a method for preparing a structural color coating. A further technical solution of the method is that the prepared structural color coating has a bright, angle-independent structural color, the coating is uniform and has good mechanical stability, chemical stability and washability. The adhesion of the coating can reach level 1 or above (GB / T9286-1998) according to experiments. At the same time, the coating is not completely damaged or exposed after being washed 1600-1800 times by a washing machine.

[0023] Beneficial effects:

[0024] 1. The structural color coating prepared by this invention has good mechanical stability, chemical stability and washability, and can be widely used for decoration and protection of substrates such as metal, plastic and glass.

[0025] 2. The present invention provides a method for preparing a structural color coating. The entire preparation process is simple, highly compatible, and requires no special post-treatment. Furthermore, the coating does not emit VOCs into the atmosphere during the curing and film formation process, thus meeting the requirements of green and sustainable development.

[0026] 3. The structural color coating prepared by this invention presents a color generated by the structure, which will not cause problems of photo-oxidation and photo-bleaching. At the same time, the structural color also avoids the environmental pollution caused by chemical dyeing, making it green and environmentally friendly.

[0027] 4. The structural color coating prepared by the present invention has the structural color angle independence derived from the isotropic spherical symmetry structure of monodisperse nanoparticle clusters. The long-range ordered and short-range ordered lattice structure in the particle clusters ensures the brightness and saturation of the structural color. Attached Figure Description

[0028] Figure 1 SEM image of the monodisperse nanoparticle clusters prepared in Example 1;

[0029] Figure 2 Optical images and reflection spectra of the blue structural color coating prepared in Example 1;

[0030] Figure 3 SEM image of the blue structural color coating prepared in Example 1;

[0031] Figure 4 Optical images of the blue structural color coating prepared in Example 1 at different bending angles;

[0032] Figure 5 The test results for (a) chemical stability, (b) mechanical stability, and (c) scrub resistance of the blue structural color coating prepared in Example 1 are shown.

[0033] Figure 6Optical images and reflection spectra of the green structural color coating prepared in Example 2;

[0034] Figure 7 Optical images and reflection spectra of the red structural color coating prepared in Example 3. Detailed Implementation

[0035] The present invention is illustrated below with specific embodiments, but the present invention is not limited to the following examples. The purpose of these examples is only to provide a better understanding of the present invention and not to limit the scope of protection of the present invention.

[0036] Example 1

[0037] The inlet temperature, peristaltic pump feed rate, and air velocity of the spray dryer were set to 130℃, 10mL / h, and 30L / h, respectively. After the parameters of the equipment stabilized, an ethanol dispersion of silica nanoparticles with a particle size of 180nm, a PDI value of 0.02, and a mass fraction of 20% was introduced. Under the action of the high-temperature airflow, the solvent in the dispersion was rapidly removed, and the silica nanoparticles spontaneously assembled into spherical monodisperse nanoparticle clusters. As can be seen from the SEM image in Figure (1), the spherical monodisperse nanoparticle clusters are assembled from silica nanoparticles arranged in a long-range ordered and short-range ordered lattice structure, and the cluster size is distributed in the micrometer scale range of 1-8μm. Weigh 10g of polydimethylsiloxane prepolymer, 1g of diphenylcarbamate curing agent, 0.01g of nano-carbon black, and 5g of pre-prepared monodisperse silica nanoparticle clusters into a 50mL beaker using an analytical balance. Stir continuously at 200rpm for 80min at room temperature to obtain a uniform organic gel-nanoparticle cluster prepolymer. Place the purchased plastic substrate in an ethanol bath ultrasonic cleaner with a power of 500W and ultrasonically clean for 10 minutes to remove dust, oil, and small organic molecules from the substrate surface. Dry at room temperature for later use. Apply the prepared organic gel-nanoparticle cluster prepolymer to the surface of the treated plastic substrate by scraping. The coating thickness is 300μm. Then, cure at 30℃ for 12h to obtain a structural color coating. The coating exhibits a blue structural color as shown in Figure (2). As can be seen from the SEM image, the coating contains spherical nanoparticle clusters of different sizes and monodisperse nanoparticles arranged in an orderly manner within the clusters, as shown in Figure (3). Based on the isotropic optical properties and highly ordered assembly structure of spherical nanoparticle clusters, the prepared structural color coating exhibits saturated and bright colors and angle-independent characteristics, as shown in Figure (4). After immersion in solutions of different pH values ​​for 48 consecutive hours, the morphology, structure, and color of the coating remained intact, demonstrating good chemical stability, as shown in Figure (5a). Experimental measurements showed that the coating possesses good mechanical stability, with adhesion reaching grade 0 (GB / T9286-1998), as shown in Figure (5b). Furthermore, the coating exhibits good washability; after 1800 cycles of washing with a washing machine, the coating remained intact without complete damage or exposure of the substrate, as shown in Figure (5c).

[0038] Example 2

[0039] The inlet temperature, peristaltic pump feed rate, and air flow rate of the spray dryer were set to 120℃, 25mL / h, and 40L / h, respectively. After the equipment parameters stabilized, an alcohol-water dispersion of polystyrene nanoparticles with a particle size of 250nm, a PDI value of 0.001, and a mass fraction of 10% was introduced. Under the action of the high-temperature airflow, the solvent in the dispersion was rapidly removed, and the polystyrene nanoparticles spontaneously assembled into spherical monodisperse nanoparticle clusters, with cluster sizes distributed in the micrometer scale range of 2-10μm. 10g of polyurethane prepolymer, 2g of diisocyanate-based urethane curing agent, 0.01g of carbon nanotubes, 0.01g of carbon dots, and 3g of the pre-prepared monodisperse polystyrene nanoparticle clusters were weighed into a 50mL beaker and continuously stirred at 200rpm for 60min at room temperature to obtain a homogeneous organic gel-nanoparticle cluster prepolymer. The purchased glass substrate was placed in an 800W ethanol bath ultrasonic cleaner and ultrasonically cleaned for 20 minutes to remove dust, oil, and small organic molecules from the substrate surface. It was then dried at room temperature for later use. The prepared organic gel-nanoparticle cluster prepolymer was coated onto the treated glass substrate surface by brushing, with a coating thickness of 200μm. It was then cured at 40℃ for 8 hours to obtain a structural color coating, which exhibited a green structural color as shown in Figure (6). Experimental results showed that the coating had good mechanical stability and the adhesion of the coating reached level 1 (GB / T9286-1998). At the same time, the coating had good scrubbing resistance. After 1600 cycles of scrubbing, the coating was not completely damaged or exposed.

[0040] Example 3

[0041] The inlet temperature, peristaltic pump feed rate, and air flow rate of the spray dryer were set to 100℃, 30mL / h, and 50L / h, respectively. After the equipment parameters stabilized, an aqueous dispersion of polymethyl methacrylate (PMMA) nanoparticles with a particle size of 350 nm, a PDI value of 0.05, and a mass fraction of 20% was introduced. Under the action of the high-temperature airflow, the solvent in the dispersion was rapidly removed, and the PMMA nanoparticles spontaneously assembled into spherical monodisperse nanoparticle clusters with cluster sizes ranging from 1 to 7 μm. 10 g of epoxy resin prepolymer, 3 g of ethylenediamine curing agent, 0.02 g of carbon dots, 0.01 g of dopamine particles, and 2 g of the pre-prepared monodisperse PMMA nanoparticle clusters were weighed into a 50 mL beaker and continuously stirred at 300 rpm for 40 min at room temperature to obtain a homogeneous organic gel-nanoparticle cluster prepolymer. The purchased iron sheet substrate was placed in an ethanol bath ultrasonic cleaner with a power of 1000W and ultrasonically cleaned for 30 minutes to remove dust, oil, and small organic molecules from the substrate surface. It was then dried at room temperature for later use. The prepared organic gel-nanoparticle cluster prepolymer was coated onto the treated iron sheet substrate surface by roller coating, with a coating thickness of 500μm. It was then cured at 60℃ for 6 hours to obtain a structural color coating, which exhibits a red structural color as shown in Figure (7). Experimental results showed that the coating has good mechanical stability and the adhesion of the coating can reach level 1 (GB / T9286-1998). At the same time, the coating has good scrubbing resistance. After 1700 cycles of scrubbing, the coating was not completely damaged or exposed.

Claims

1. A method for preparing a structural color coating, the specific steps of which are as follows: a. Preparation of monodisperse nanoparticle clusters: The solvent in the monodisperse nanoparticle dispersion was rapidly removed using a spray dryer, resulting in spherical monodisperse nanoparticle clusters with a micron-scale distribution; among which, The parameters of the spray drying equipment are set as follows: inlet temperature of 100-130℃, peristaltic pump feed rate of 10-30mL / h, and air flow rate of 30-50L / h. b. Preparation of organic gel-nanoparticle cluster prepolymer: The organic polymer gel prepolymer, curing agent, light-absorbing material, and monodisperse nanoparticle clusters are thoroughly stirred and mixed to obtain a uniform organic gel-nanoparticle cluster prepolymer, wherein the mass ratio of the organic polymer gel prepolymer, curing agent, light-absorbing material, and monodisperse nanoparticle clusters is 1:(0.1-0.3):(0.001-0.003):(0.2-0.5); wherein the organic polymer gel prepolymer is one of polyurethane prepolymer, epoxy resin prepolymer, or polydimethylsiloxane prepolymer; c. Substrate surface treatment: The substrate is placed in an ethanol bath for ultrasonic cleaning to remove dust, oil and small organic molecules from the surface. After drying, a clean substrate is obtained. d. The prepared organic gel-nanoparticle prepolymer is coated onto the surface of the treated substrate and allowed to cure statically to obtain a coating with angle-independent structural color, wherein the coating thickness is 200-500μm.

2. The preparation method according to claim 1, characterized in that... The nanoparticles in the monodisperse nanoparticle dispersion mentioned in step a are one of polystyrene nanoparticles, polymethyl methacrylate nanoparticles, or silica nanoparticles; the aggregation degree index (PDI) of the monodisperse nanoparticle dispersion is 0.001-0.

05.

3. The preparation method according to claim 1, characterized in that... The nanoparticles in the monodisperse nanoparticle dispersion described in step a have a particle size of 180-350 nm and a mass fraction of 10%-20%; the solvent in the monodisperse nanoparticle dispersion described in step a is one or a mixture of water and ethanol.

4. The preparation method according to claim 1, characterized in that... The monodisperse nanoparticle clusters described in step a maintain a highly spherical morphology, with cluster sizes distributed in the micrometer scale range of 1-10 μm.

5. The preparation method according to claim 1, characterized in that... The curing agent mentioned in step b is the corresponding curing agent for the organic polymer gel prepolymer. Specifically, the curing agent for the polyurethane prepolymer is one of diisocyanate-based urethane or diisocyanate-based urea; the curing agent for the epoxy resin prepolymer is one of ethylenediamine, hexamethylenediamine, diethylenetriamine or triethylenetetramine; and the curing agent for the polydimethylsiloxane prepolymer is diphenylcarbamate.

6. The preparation method according to claim 1, characterized in that... The light-absorbing material mentioned in step b is one or a mixture of two or more of the following: carbon nanofibers, carbon nanotubes, carbon dots, or dopamine particles.

7. The preparation method according to claim 1, characterized in that... The stirring speed in step b is 200-300 rpm, and the stirring time is 40-80 min.

8. The preparation method according to claim 1, characterized in that... The substrate mentioned in step c is one of metal, plastic or glass; the ultrasonic cleaning power mentioned in step c is 500-1000W and the time is 10-30min.

9. The preparation method according to claim 1, characterized in that... The coating method described in step d is one of scraping, rolling, or brushing.

10. The preparation method according to claim 1, characterized in that... The curing time mentioned in step d is 6-12 hours, and the curing temperature is 30-60℃.

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