Reversible color-changing microcapsule high-temperature-resistant paint and preparation method thereof

Abstract

The present application relates to the technical field of high polymer materials, and particularly relates to a reversible color-changing microcapsule high-temperature-resistant coating and a preparation method thereof, which comprises the following components in mass ratio: inorganic polysiloxane resin 30%-40%, hydroxyl acrylic resin 10%-20%, additive 2%-5%, solvent 5%-15%, white corundum 5%-10%, silicon powder 10%-15%, and reversible color-changing microcapsule pigment 5%-15%; the reversible color-changing microcapsule pigment is synthesized by core material and wall material, and through the synergistic design of organic-inorganic hybrid wall material (methyl polysiloxane prepolymer, acrylic prepolymer and nano silicon dioxide composite) and core material phase change medium (glyceryl stearate), the problems such as insufficient high-temperature resistance of traditional thermochromic coating, slow color-changing response and poor mechanical stability of microcapsules are effectively solved.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a reversibly color-changing microcapsule high-temperature resistant coating and its preparation method. Background Technology

[0002] Thermochromic materials are a class of functional materials that can reversibly change color with temperature. The color changes when the temperature rises or falls, and the color can be automatically restored after the temperature returns to the initial range. The core is that temperature triggers a reversible change in the molecular structure, crystal form or phase state of the material, thereby changing its light absorption / reflection characteristics.

[0003] There are three main technical paths for existing thermochromic materials: one is organic leuco dye system, which achieves color change through hydrogen bonding and phase change of dye-developer-solvent, with rich colors and fast response; the second is inorganic oxide (such as VO2), which relies on crystal phase change to regulate optical properties, with good stability and high temperature resistance; the third is liquid crystal type, which generates interference colors through changes in molecular arrangement, with high precision.

[0004] The current technical problems are: 1. Organic materials have insufficient high temperature resistance, are prone to photodegradation, and have short cycle life; 2. Inorganic materials have high transition temperatures, limited color tones, and slow color change response; 3. Liquid crystals are expensive, difficult to process, and most systems cannot balance response speed, durability, and environmental adaptability.

[0005] To address the issues of traditional color-changing materials being prone to degradation, weathering, and migration, reversible color-changing microcapsule pigments have emerged. These pigments are composite pigments formed by encapsulating thermo- or photo-induced reversible color-changing core systems (such as organic leuco dyes and liquid crystals) within a micron-sized (1-100μm) polymer shell using microcapsule technology. The core is a micro-nano structure of "color-changing core + protective shell," which combines color-changing function with material stability.

[0006] For example, the invention patent with patent application number 202410601494.2 specifically discloses a high-temperature resistant color-changing microcapsule and its preparation method and application. It specifically discloses the hybrid coating of nano-SiO2+ polymer prepolymer, which forms a dense shell through covalent bonding, solving the problems of microcapsule anti-rupture and high temperature resistance. However, the temperature it can withstand is only 200℃+, which does not meet the application requirements of extreme environments.

[0007] Furthermore, the invention patent with patent application number 202211370350.8 specifically discloses a silica hybrid modified epoxy resin wall material-coated thermochromic microcapsules, which adopts an inorganic reinforcing material (silica / polysilsesquioxane) + polymer shell (polysulfone / melamine-formaldehyde) one-step organic / inorganic hybrid coating; the core material contains leucochromic agent, color developer, and temperature-regulating solvent, and the nano-inorganic silicon-based filler is doped into the hybrid shell to achieve interfacial covalent bonding (different from hydrogen bond adsorption), which significantly improves the compactness and rupture resistance of the microcapsules. However, the use of formaldehyde resin as the shell component poses a risk of formaldehyde residue, has poor environmental performance, and does not meet the current development requirements of low-toxicity, formaldehyde-free, and green materials.

[0008] Furthermore, for example, the invention patent with patent application number 202410005020.1 specifically discloses a high-durability thermotropic reversible color-changing microcapsule based on multiple Pickering emulsions and its preparation method. It uses 5-30nm nano-SiO2 modification to participate in interfacial cross-linking, forming a three-dimensional network to reinforce the shell and improve its crack resistance. However, only strengthening the crack resistance of the three-dimensional network of the outer shell without structural design for the color-changing core material's resistance to migration, degradation, and weathering still results in problems such as core material leakage, color-changing failure, and poor resistance to environmental aging after long-term use. Summary of the Invention

[0009] To address the above problems, this invention provides a reversible color-changing microcapsule high-temperature resistant coating and its preparation method. Through the synergistic design of organic-inorganic hybrid wall material (methyl polysiloxane prepolymer, acrylic prepolymer and nano silica composite) and core material phase change medium (glyceryl stearate), it effectively solves the problems of insufficient high-temperature resistance, slow color change response and poor mechanical stability of traditional thermochromic coatings.

[0010] To achieve the above objectives, the present invention provides the following technical solution: By weight percentage, it comprises the following components: 30%-40% inorganic polysiloxane resin, 10%-20% hydroxyl acrylic resin, 2%-5% additives, 5%-15% solvent, 5%-10% white corundum, 10%-15% silica powder, and 5%-15% reversible color-changing microcapsule pigment; The reversible color-changing microcapsule pigment is synthesized by encapsulating a core material and a wall material. The diameter of the reversible color-changing microcapsule pigment is 3-10 μm. By mass percentage, the core material includes 0.5%-1% crystal violet lactone, 3%-5% bisphenol A, 10%-15% cetyl alcohol, and 5%-10% glyceryl stearate. The wall material includes 40%-50% methyl polysiloxane prepolymer, 25%-30% acrylic prepolymer, 8%-15% nano silica, and 2%-5% styrene oligomer.

[0011] As an improvement, the solvent is composed of xylene and methyl ethyl ketone mixed in a mass ratio of 3:1.

[0012] As an improvement, the additive is composed of coupling agent, leveling agent, anti-settling agent and composite light stabilizer mixed in a mass ratio of 1:2:3:6.

[0013] As an improvement, the white corundum, silica powder and reversible color-changing microcapsule pigment are composed in a mass ratio of 3:5:5.

[0014] As an improvement, the core material of the reversible color-changing microcapsule pigment is composed of crystal violet lactone, bisphenol A, cetyl alcohol and glyceryl stearate in a mass ratio of 1:5:15:10.

[0015] As an improvement, the wall material is composed of methyl polysiloxane, acrylic resin prepolymer, nano silica and styrene oligomer in a mass ratio of 11:6:1.5:1.

[0016] As an improvement, the silica comprises hydrophobic silica and hydrophilic silica, wherein the hydrophobic silica and hydrophilic silica are composed in a mass ratio of 1:2, and the particle size is in the range of 5-10 μm. As an improvement, the microcapsule structure of the reversible color-changing pigment was obtained by the W / O / W multiple emulsion method.

[0017] As an improvement, the method for synthesizing the microcapsule structure of reversible color-changing pigments includes the following steps: Crystal violet lactone, bisphenol A, cetyl alcohol and glyceryl stearate were mixed and dispersed at 60°C, and then hydrophobically modified nano-SiO2 (accounting for 0.5%-1.5% of the total amount of nano-silica) was added and ultrasonically emulsified to form a stable W / O type Pickering emulsion. The emulsion was dispersed in an aqueous phase containing hydrophilic nano-TiO2 (accounting for 0.3%-0.8% of the total nano-silica) and subjected to high-speed shearing to form a W / O / W multi-emulsion; After mixing phenyl / methyl polysiloxane prepolymer with acrylic resin prepolymer, styrene oligomer (used to improve the film-forming properties of wall materials and enhance the stability of microcapsule structures) is added. The mixture is stirred until dissolved, and then slowly dripped into the aforementioned W / O / W type multi-layer emulsion, controlling the dripping rate at 1-2 drops / second. After the dripping is complete, the system temperature is raised to 80℃, the rotation speed is adjusted to 1500 rpm, and the mixture is stirred at a constant temperature for 2-3 hours to polymerize the prepolymer at the emulsion interface, forming a nanoparticle-resin composite wall material.

[0018] After the polymerization reaction is completed, the reaction system is cooled to room temperature, vacuum filtered, and the filter cake is washed 3-4 times alternately with deionized water and anhydrous ethanol to remove unreacted monomers and impurities. Then the filter cake is placed in a vacuum drying oven at 60℃ and dried for 24 hours. After drying, it is sieved through a standard sieve to obtain reversible color-changing microcapsule pigment powder with a particle size of 2-10μm.

[0019] Furthermore, the present invention also provides a method for preparing a reversibly color-changing microcapsule high-temperature resistant coating as described in any one of the above claims, comprising the following steps: S1, under medium-speed stirring, inorganic polysiloxane / acrylic resin as base, solvent is added and stirred continuously to obtain mixture A; S2, under medium-speed stirring, white corundum, silica powder and reversible color-changing microcapsule pigment are added to the mixture A in step S1 in sequence, and stirring is continued until uniformly dispersed to obtain mixture B; S3, add the grinding media to the mixture from step S2, and grind it in a vibrating mill or sand mill to obtain a finely ground material; S4. Stir at high speed, add additives, and continue stirring until uniform and free of particles to obtain a reversible color-changing high-temperature resistant coating.

[0020] The preparation method according to claim 9 is characterized in that: In step S1, the medium speed is 500-800 rpm, and the stirring time is 10 min. In step S2, the medium speed is 500-800 rpm, and the stirring time is 20 min. In step S3, the grinding medium is glass beads with a diameter of 0.2 mm, which account for 70% of the mass ratio of the mixture, the grinding time is 40 min, and the fineness of the ground material is less than or equal to 30 micrometers; In step S4, the high rotation speed is 1000-1200 rpm and the duration is 10 min.

[0021] The present invention also provides an application of a reversible color-changing microcapsule high-temperature resistant coating. Based on the above-mentioned coating, the coating is applied to the surface of the object to be coated, with a thickness of about 50-60 micrometers, and dried for 24 hours.

[0022] The beneficial effects of this invention are as follows: This invention utilizes the high-temperature barrier effect of the "organic-inorganic hybrid" wall material, combined with the high-temperature stability synergy of the "phase change medium + color development system" core material, and the high-temperature resistance stability of the coating matrix "inorganic polysiloxane + hydroxy acrylic acid", which significantly improves the high-temperature resistance of the coating and can maintain the stability of reversible color change for a long time in high-temperature environments. This invention significantly shortens the color change response time by using the wide temperature range coverage of the core material “phase change medium compounding”, combined with the rapid response mechanism of the color development system “precise ratio”, and the response efficiency improvement of microcapsule “particle size control”, to achieve a rapid and sensitive temperature-sensitive color development effect, and to achieve a wide range of color changes in the high temperature range of 200-300℃. This invention strengthens the wall material structure through "covalent cross-linking" rather than "physical blending", optimizes the density of nano-silica through "hydrophilic and hydrophobic compounding", and achieves anti-breakage synergy of "inorganic rigid particles + organic tough chains", thereby obtaining covalent cross-linking between nano-silica and prepolymer, enhancing the density and anti-breakage ability of the microcapsule structure, and ensuring long-term reliability. This invention endows the coating with excellent adhesion and stain resistance through a resin matrix compound system. Combined with composite light stabilizers and low solvent formulation, it further expands the coating's resistance to ultraviolet aging and environmental friendliness. It is suitable for dynamic high-temperature scenarios such as building exterior walls, industrial equipment and automotive coatings, achieving a synergistic improvement in functionality and durability.

[0023] In summary, this invention has advantages such as high temperature resistance, rapid response, and strong stability, and is particularly suitable for the field of high temperature resistant coating materials technology that are resistant to high temperatures, have fast color recovery, good durability, and reversible color change. Attached Figure Description

[0024] Figure 1 Images of reversible color-changing microcapsule pigments observed using a scanning electron microscope (SEM); Figure 2 A set of photographs depicting the color-changing properties of reversibly color-changing microcapsule high-temperature resistant coatings; Figure 3 Schematic diagram of the preparation method of reversible color-changing microcapsules; Figure 4 A schematic diagram of the preparation process of reversibly color-changing microcapsule high-temperature resistant coating. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0027] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0028] Example 1: like Figure 2 , 4 As shown, a reversible color-changing microcapsule high-temperature resistant coating comprises, by weight percentage, the following components: 30%-40% inorganic polysiloxane resin, 10%-20% hydroxyl acrylic resin, 2%-5% additives, 5%-15% solvent, 5%-10% white corundum, 10%-15% silica powder, and 5%-15% reversible color-changing microcapsule pigment; The reversible color-changing microcapsule pigment is synthesized by encapsulating a core material and a wall material. The diameter of the reversible color-changing microcapsule pigment is 3-10 μm. By mass percentage, the core material includes 0.5%-1% crystal violet lactone, 3%-5% bisphenol A, 10%-15% cetyl alcohol and 5%-10% glyceryl stearate. The wall material includes 40%-50% methyl polysiloxane prepolymer, 25%-30% acrylic prepolymer, 8%-15% nano silica and 2%-5% styrene oligomer.

[0029] The solvent is composed of xylene and methyl ethyl ketone in a mass ratio of 3:1.

[0030] The additive is composed of coupling agent, leveling agent, anti-settling agent and composite light stabilizer mixed in a mass ratio of 1:2:3:6.

[0031] The white corundum, silica powder, and reversible color-changing microcapsule pigment are composed of a mass ratio of 3:5:5.

[0032] The core material of the reversible color-changing microcapsule pigment is composed of crystal violet lactone, bisphenol A, cetyl alcohol and glyceryl stearate in a mass ratio of 1:5:15:10.

[0033] The wall material is composed of methyl polysiloxane, acrylic resin prepolymer, nano silica and styrene oligomer in a mass ratio of 11:6:1.5:1.

[0034] The silica comprises hydrophobic silica and hydrophilic silica, which are composed of hydrophobic silica and hydrophilic silica in a mass ratio of 1:2, and the particle size is in the range of 5-10 μm.

[0035] The microcapsule structure of the reversible color-changing pigment was obtained by the W / O / W multiple emulsion method.

[0036] Specifically, the method for synthesizing the microcapsule structure of reversible color-changing pigments includes the following steps: Crystal violet lactone, bisphenol A, cetyl alcohol and glyceryl stearate were mixed and dispersed at 60°C, and then hydrophobically modified nano-SiO2 (accounting for 0.5%-1.5% of the total amount of nano-silica) was added and ultrasonically emulsified to form a stable W / O type Pickering emulsion. The emulsion was dispersed in an aqueous phase containing hydrophilic nano-TiO2 (accounting for 0.3%-0.8% of the total nano-silica) and subjected to high-speed shearing to form a W / O / W multi-emulsion; After mixing phenyl / methyl polysiloxane prepolymer with acrylic resin prepolymer, styrene oligomer (used to improve the film-forming properties of wall materials and enhance the stability of microcapsule structures) is added. The mixture is stirred until dissolved, and then slowly dripped into the aforementioned W / O / W type multi-layer emulsion, controlling the dripping rate at 1-2 drops / second. After the dripping is complete, the system temperature is raised to 80℃, the rotation speed is adjusted to 1500 rpm, and the mixture is stirred at a constant temperature for 2-3 hours to polymerize the prepolymer at the emulsion interface, forming a nanoparticle-resin composite wall material.

[0037] After the polymerization reaction is completed, the reaction system is cooled to room temperature, vacuum filtered, and the filter cake is washed 3-4 times alternately with deionized water and anhydrous ethanol to remove unreacted monomers and impurities. Then the filter cake is placed in a vacuum drying oven at 60℃ and dried for 24 hours. After drying, it is sieved through a standard sieve to obtain reversible color-changing microcapsule pigment powder with a particle size of 2-10μm.

[0038] Example 2: like Figure 1 , Figure 3 As shown, the method for preparing the reversibly color-changing microcapsule high-temperature resistant coating described in Example 1 of the present invention, as described in Example 2, includes the following steps: S1, under medium-speed stirring, inorganic polysiloxane / acrylic resin as base, solvent is added and stirred continuously to obtain mixture A; S2, under medium-speed stirring, white corundum, silica powder and reversible color-changing microcapsule pigment are added to the mixture A in step S1 in sequence, and stirring is continued until uniformly dispersed to obtain mixture B; S3, add the grinding media to the mixture from step S2, and grind it in a vibrating mill or sand mill to obtain a finely ground material; S4. Stir at high speed, add additives, and continue stirring until uniform and free of particles to obtain a reversible color-changing high-temperature resistant coating.

[0039] The preparation method according to claim 9 is characterized in that: In step S1, the medium speed is 500-800 rpm, and the stirring time is 10 min. In step S2, the medium speed is 500-800 rpm, and the stirring time is 20 min. In step S3, the grinding medium is glass beads with a diameter of 0.2 mm, which account for 70% of the mass ratio of the mixture, the grinding time is 40 min, and the fineness of the ground material is less than or equal to 30 micrometers; In step S4, the high rotation speed is 1000-1200 rpm and the duration is 10 min.

[0040] Preparation Example 1: The coating provided in this preparation example comprises the components shown in Table 1 by mass ratio. The increased content of microcapsules and the higher content of nano-silica in the wall material further optimize the phase transformation efficiency of the core material (glyceryl stearate). Furthermore, reducing the polysiloxane resin / hydroxyl acrylic resin ratio results in a decrease in coating hardness but an increase in flexibility. The increased proportion of flexible segments in the hydroxyl acrylic resin alleviates the rigid structure of the high-content inorganic resin, but slightly reduces the temperature resistance from 300°C to 250°C. After baking at 300°C for 24 hours, slight peeling of the coating film was observed, and the cross-cut adhesion was rated at level 1.

[0041] Preparation Example 2: This preparation example provides a reversible color-changing microcapsule high-temperature resistant coating, the components of which, by mass ratio, are shown in Table 1. In this preparation example, the high ratio of polysiloxane resin / hydroxyl acrylic resin enhances temperature resistance, but insufficient hydroxyl acrylic resin leads to decreased coating flexibility and a cross-cut adhesion grade of 1.

[0042] Preparation Example 3: The organic-inorganic hybrid waterborne coating prepared in this example, capable of withstanding temperatures up to 700°C, comprises the components listed in Table 1 by mass ratio. This preparation represents the optimal formulation; the paint achieves rapid color response after 24 hours at 300°C and completes rapid recoloring upon cooling to room temperature. The paint surface remained intact during the adhesion test, and no cracks appeared after the test. Adhesion to stainless steel surfaces reached grade 0; specific values ​​and other performance indicators are supplemented in Table 4, such as impact resistance, temperature resistance, weather resistance, and salt spray resistance.

[0043] Comparative Example 1: The coatings provided in this comparative example are shown in Table 1. The wall material in this comparative example did not contain nano-silica; it only used methyl polysiloxane and acrylic prepolymer. Its temperature resistance decreased to 150℃, its scrub resistance was only 5000 cycles, and its cross-cut adhesion was grade 4. Insufficient number of silica groups caused chain segment decomposition of the wall material at high temperatures, leading to core material leakage (color change performance decreased by 50% after 500 hours).

[0044] Comparative Example 2: The coatings provided in this comparative example are shown in Table 1. In this comparative example, the microcapsule content is increased to 15%, but the wall material uses only a single polysiloxane, which leads to a decrease in the mechanical strength of the microcapsules, an increase in the breakage rate (>30%) during high-speed dispersion, and a reduction in the effective color development component. The cross-cut adhesion is grade 5.

[0045] Comparative Example 3: The coatings provided in this comparative example are shown in Table 1. No light stabilizer was added in this comparative example. The composite light stabilizer inhibits the photo-oxidation of the resin matrix through a dual action of free radical capture and ultraviolet absorption. In the absence of light stabilizer, the microcapsule wall material is attacked by ultraviolet light, resulting in microcracks and volatilization of the phase change medium in the core material. After 500 hours of QUV testing, the coating chalked, and the cross-cut adhesion was grade 5.

[0046] Table 1. Components of the coatings in Comparative Examples 1-3 and Preparation Examples 1-3 In Comparative Examples 1-3 and Preparation Examples 1-3, the solvent is composed of xylene and methyl ethyl ketone in a mass ratio of 3:1. In some embodiments, the additives are composed of coupling agent, leveling agent, anti-settling agent, and composite light stabilizer in a mass ratio of 1:2:3:6. The white corundum, silica powder, and reversible color-changing microcapsule pigment are composed in a mass ratio of 3:5:5. In some embodiments, the thermochromic system of the core material is composed of crystal violet lactone, bisphenol A, cetyl alcohol, and glyceryl stearate in a mass ratio of 1:5:15:10. In some embodiments, the wall material is composed of methyl polysiloxane, acrylic resin prepolymer, and nano-silica in a mass ratio of 9:5:1, and the core-to-wall ratio must be maintained in the range of 1:2-1:3. In some embodiments, the silica comprises hydrophobic silica and hydrophilic silica in a mass ratio of 1:2, with a particle size in the range of 5-20 μm.

[0047] Table 2 Coverage Method Table 2 above provides examples of application scenarios and methods for reversible color-changing microcapsule high-temperature resistant coatings.

[0048] The coatings obtained in Preparation Examples 1-3 and Comparative Examples 1-3 were tested for impact resistance, temperature resistance, weather resistance, and salt spray resistance, according to the standards GB / T 9286, GB / T 1732, GB / T 1771, and GB / T 1735, respectively. The test results are shown in Table 3-5 below: Table 3. Comparison of temperature response sensitivity tests between the comparative example and the embodiment at 300℃ (24h) Table 4. Comparison of temperature response sensitivity test results between the comparative example and the preparation example after 10 cycles at 300℃ (24h). Table 5. Comparison of various performance tests for comparative examples and embodiments The reversible color-changing microcapsule pigments and reversible color-changing coatings provided in Preparation Examples 1-3 have a color-changing range of 290-300℃. Figure 1 SEM image of the reversible color-changing microcapsule pigment prepared in Example 3, wherein the reversible color-changing microcapsule pigment is spherical; Figure 2The comparison of the reversible color-changing high-temperature resistant coatings prepared in Comparative Examples 1-3 and Preparation Examples 1-3 before and after color change is shown. This reversible color-changing material exhibits significant color-changing effects, appearing deep blue at room temperature and turning white upon reaching the color-changing temperature. The color gradually transitions from deep blue to white as the temperature increases. Table 3-5 shows that Preparation Example 1 demonstrates the best overall performance. Comparative Example 1, due to the lack of silica in the wall material, suffers from insufficient strength of the microcapsule wall material, leading to wall material rupture after high-temperature cycling, unstable color-changing temperature, and a 50% decrease in color-changing performance under weathering test conditions. Comparative Example 2 suffers from increased coating viscosity and uneven dispersion due to excessive microcapsules, resulting in decreased mechanical strength of the shell-core structure and increased rupture rate. The initial color-changing temperature decreases to 250℃, but the color-changing time shortens to 5.5s, due to excessively high local concentrations. Comparative Example 3 suffers from prolonged recoloring time due to the lack of a composite light stabilizer, leading to high-temperature oxidation of styrene oligomers and surface cracking of the coating.

[0049] In Preparation Example 1, the increased proportion of polysiloxane resin enhanced temperature resistance, but insufficient hydroxyl acrylic resin led to a decrease in coating flexibility. Preparation Example 2 exhibited similar properties to Preparation Example 3, but at a higher cost, making it more suitable for high-end, rapid-response applications. Combining the above information with Tables 3, 4, and 5, it can be seen that the ratio of polysiloxane resin to hydroxyl acrylic resin determines the adhesion, impact resistance, stain resistance, and salt spray resistance of the topcoat. The synergistic effect of the chemical bonds and physical anchoring of the two resins allows for the simultaneous establishment of a dense layer and a strong interface.

[0050] The excellent core-to-wall ratio of microencapsulated pigments endows them with outstanding stability under long-term high-temperature environments, enabling rapid and sensitive response to color change / recoloration, and achieving wide-range color change within a high-temperature range of 200-300℃. This coating can be widely used in real-time temperature monitoring of high-temperature equipment (such as petrochemical pipelines and aerospace components), smart labels, and fire early warning systems, combining functionality and durability to meet the dual requirements of industry for intelligent and reliable materials.

[0051] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A reversibly color-changing microcapsule high-temperature resistant coating, characterized in that: By weight percentage, it comprises the following components: 30%-40% inorganic polysiloxane resin, 10%-20% hydroxyl acrylic resin, 2%-5% additives, 5%-15% solvent, 5%-10% white corundum, 10%-15% silica powder, and 5%-15% reversible color-changing microcapsule pigment; The reversible color-changing microcapsule pigment is synthesized by encapsulating a core material and a wall material. The diameter of the reversible color-changing microcapsule pigment is 3-10 μm. By mass percentage, the core material includes 0.5%-1% crystal violet lactone, 3%-5% bisphenol A, 10%-15% cetyl alcohol, and 5%-10% glyceryl stearate. The wall material includes 40%-50% methyl polysiloxane prepolymer, 25%-30% acrylic prepolymer, 8%-15% nano silica, and 2%-5% styrene oligomer. The reversible color-changing microcapsule high-temperature resistant coating according to claim 1 is characterized in that: The solvent is composed of xylene and methyl ethyl ketone in a mass ratio of 3:

1.

2. The reversibly color-changing microcapsule high-temperature resistant coating according to claim 1, characterized in that: The additive is composed of coupling agent, leveling agent, anti-settling agent and composite light stabilizer mixed in a mass ratio of 1:2:3:

6.

3. The reversibly color-changing microcapsule high-temperature resistant coating according to claim 1, characterized in that: The white corundum, silica powder, and reversible color-changing microcapsule pigment are composed of a mass ratio of 3:5:

5.

4. The reversible color-changing microcapsule pigment according to claim 1, characterized in that: The core material of the reversible color-changing microcapsule pigment is composed of crystal violet lactone, bisphenol A, cetyl alcohol and glyceryl stearate in a mass ratio of 1:5:15:

10.

5. The reversible color-changing microcapsule pigment according to claim 1, characterized in that: The wall material of the reversible color-changing microcapsule pigment is composed of methyl polysiloxane, acrylic resin prepolymer, nano silica and styrene oligomer in a mass ratio of 11:6:1.5:

1. The nano-silica comprises hydrophobic silica and hydrophilic silica, which are composed of hydrophobic silica and hydrophilic silica in a mass ratio of 1:2, and the particle size is in the range of 5-10 μm.

6. The reversibly color-changing microcapsule high-temperature resistant coating according to claim 1, characterized in that: The reversible color-changing microcapsule pigments were obtained by the W / O / W multiple emulsion method.

7. The reversibly color-changing microcapsule high-temperature resistant coating according to claim 7, characterized in that, The method for synthesizing the microcapsule structure of reversible color-changing pigments includes the following steps: Crystal violet lactone, bisphenol A, cetyl alcohol and glyceryl stearate were mixed and dispersed at 60°C, and then hydrophobically modified nano-SiO2 (accounting for 0.5%-1.5% of the total amount of nano-silica) was added and ultrasonically emulsified to form a stable W / O type Pickering emulsion. The emulsion was dispersed in an aqueous phase containing hydrophilic nano-TiO2 (accounting for 0.3%-0.8% of the total nano-silica) and subjected to high-speed shearing to form a W / O / W multi-emulsion; After mixing phenyl / methyl polysiloxane prepolymer with acrylic resin prepolymer, styrene oligomer (used to improve the film-forming properties of wall materials and enhance the stability of microcapsule structures) is added. The mixture is stirred until dissolved, and then slowly dripped into the aforementioned W / O / W type multi-layer emulsion, controlling the dripping rate to 1-2 drops / second. After the dripping is complete, the system temperature is raised to 80℃, the rotation speed is adjusted to 1500 rpm, and the mixture is stirred at a constant temperature for 2-3 hours to polymerize the prepolymer at the emulsion interface, forming a nanoparticle-resin composite wall material. After the polymerization reaction is completed, the reaction system is cooled to room temperature, vacuum filtered, and the filter cake is washed 3-4 times alternately with deionized water and anhydrous ethanol to remove unreacted monomers and impurities. Then the filter cake is placed in a vacuum drying oven at 60℃ and dried for 24 hours. After drying, it is sieved through a standard sieve to obtain reversible color-changing microcapsule pigment powder with a particle size of 2-10μm.

8. A method for preparing a reversibly color-changing microcapsule high-temperature resistant coating according to any one of claims 1-8, characterized in that, Includes the following steps: S1, under medium-speed stirring, inorganic polysiloxane / acrylic resin as base, solvent is added and stirred continuously to obtain mixture A; S2, under medium-speed stirring, white corundum, silica powder and reversible color-changing microcapsule pigment are added to the mixture A in step S1 in sequence, and stirring is continued until uniformly dispersed to obtain mixture B; S3, add the grinding media to the mixture from step S2, and grind it in a vibrating mill or sand mill to obtain a finely ground material; S4. Stir at high speed, add additives, and continue stirring until uniform and free of particles to obtain a reversible color-changing high-temperature resistant coating.

9. The preparation method according to claim 9, characterized in that: In step S1, the medium speed is 500-800 rpm, and the stirring time is 10 min. In step S2, the medium speed is 500-800 rpm, and the stirring time is 20 min. In step S3, the grinding medium is glass beads with a diameter of 0.2 mm, which account for 70% of the mass ratio of the mixture, the grinding time is 40 min, and the fineness of the ground material is less than or equal to 30 micrometers; In step S4, the high rotation speed is 1000-1200 rpm and the duration is 10 min. A reversibly color-changing microcapsule high-temperature resistant coating and its preparation method Technical Field This invention relates to the field of polymer materials technology, and in particular to a reversibly color-changing microcapsule high-temperature resistant coating and its preparation method. Background Technology Thermochromic materials are a class of functional materials that can reversibly change color with temperature. The color changes when the temperature rises or falls, and the color can be automatically restored after the temperature returns to the initial range. The core is that temperature triggers a reversible change in the molecular structure, crystal form or phase state of the material, thereby changing its light absorption / reflection characteristics. There are three main technical paths for existing thermochromic materials: one is organic leuco dye system, which achieves color change through hydrogen bonding and phase change of dye-developer-solvent, with rich colors and fast response; the second is inorganic oxide (such as VO2), which relies on crystal phase change to regulate optical properties, with good stability and high temperature resistance; the third is liquid crystal type, which generates interference colors through changes in molecular arrangement, with high precision. The current technical problems are:

1. Organic materials have insufficient high temperature resistance, are prone to photodegradation, and have short cycle life; 2. Inorganic materials have high transition temperatures, limited color tones, and slow color change response; 3. Liquid crystals are expensive, difficult to process, and most systems cannot balance response speed, durability, and environmental adaptability. To address the issues of traditional color-changing materials being prone to degradation, weathering, and migration, reversible color-changing microcapsule pigments have emerged. These pigments are composite pigments formed by encapsulating thermo- or photo-induced reversible color-changing core systems (such as organic leuco dyes and liquid crystals) within a micron-sized (1-100μm) polymer shell using microcapsule technology. The core is a micro-nano structure of "color-changing core + protective shell," which combines color-changing function with material stability. For example, the invention patent with patent application number 202410601494.2 specifically discloses... A high-temperature resistant color-changing microcapsule, its preparation method and application are disclosed. Specifically, the microcapsule is coated with a nano-SiO2+ polymer prepolymer hybrid. A dense shell is formed by covalent bonding, which solves the problems of microcapsule rupture resistance and high temperature resistance. However, the temperature resistance is only 200℃+, which does not meet the application requirements of extreme environments. Furthermore, the invention patent with patent application number 202211370350.8 specifically discloses a silica hybrid modified epoxy resin wall material-coated thermochromic microcapsules, which adopts an inorganic reinforcing material (silica / polysilsesquioxane) + polymer shell (polysulfone / melamine-formaldehyde) one-step organic / inorganic hybrid coating; the core material contains leucochromic agent, color developer, and temperature-regulating solvent, and the nano-inorganic silicon-based filler is doped into the hybrid shell to achieve interfacial covalent bonding (different from hydrogen bond adsorption), which significantly improves the compactness and rupture resistance of the microcapsules. However, the use of formaldehyde resin as the shell component poses a risk of formaldehyde residue, has poor environmental performance, and does not meet the current development requirements of low-toxicity, formaldehyde-free, and green materials. Furthermore, for example, the invention patent with patent application number 202410005020.1 specifically discloses a high-durability thermotropic reversible color-changing microcapsule based on multiple Pickering emulsions and its preparation method. It uses 5-30nm nano-SiO2 modification to participate in interfacial cross-linking, forming a three-dimensional network to reinforce the shell and improve its crack resistance. However, only strengthening the crack resistance of the three-dimensional network of the outer shell without structural design for the color-changing core material's resistance to migration, degradation, and weathering still results in problems such as core material leakage, color-changing failure, and poor resistance to environmental aging after long-term use. Summary of the Invention To address the above problems, this invention provides a reversible color-changing microcapsule high-temperature resistant coating and its preparation method. Through the synergistic design of organic-inorganic hybrid wall material (methyl polysiloxane prepolymer, acrylic prepolymer and nano silica composite) and core material phase change medium (glyceryl stearate), it effectively solves the problems of insufficient high-temperature resistance, slow color change response and poor mechanical stability of traditional thermochromic coatings. To achieve the above objectives, the present invention provides the following technical solution: By weight percentage, it comprises the following components: 30%-40% inorganic polysiloxane resin, 10%-20% hydroxyl acrylic resin, 2%-5% additives, 5%-15% solvent, 5%-10% white corundum, 10%-15% silica powder, and 5%-15% reversible color-changing microcapsule pigment; The reversible color-changing microcapsule pigment is synthesized by encapsulating a core material and a wall material. The diameter of the reversible color-changing microcapsule pigment is 3-10 μm. By mass percentage, the core material includes 0.5%-1% crystal violet lactone, 3%-5% bisphenol A, 10%-15% cetyl alcohol, and 5%-10% glyceryl stearate. The wall material includes 40%-50% methyl polysiloxane prepolymer, 25%-30% acrylic prepolymer, 8%-15% nano silica, and 2%-5% styrene oligomer. As an improvement, the solvent is composed of xylene and methyl ethyl ketone mixed in a mass ratio of 3:

1. As an improvement, the additive is composed of coupling agent, leveling agent, anti-settling agent and composite light stabilizer mixed in a mass ratio of 1:2:3:

6. As an improvement, the white corundum, silica powder and reversible color-changing microcapsule pigment are composed in a mass ratio of 3:5:

5. As an improvement, the core material of the reversible color-changing microcapsule pigment is composed of crystal violet lactone, bisphenol A, cetyl alcohol and glyceryl stearate in a mass ratio of 1:5:15:

10. As an improvement, the wall material is composed of methyl polysiloxane, acrylic resin prepolymer, nano silica and styrene oligomer in a mass ratio of 11:6:1.5:

1. As an improvement, the silica comprises hydrophobic silica and hydrophilic silica, wherein the hydrophobic silica and hydrophilic silica are composed in a mass ratio of 1:2, and the particle size is in the range of 5-10 μm. As an improvement, the microcapsule structure of the reversible color-changing pigment was obtained by the W / O / W multiple emulsion method. As an improvement, the method for synthesizing the microcapsule structure of reversible color-changing pigments includes the following steps: Crystal violet lactone, bisphenol A, cetyl alcohol and glyceryl stearate were mixed and dispersed at 60°C, and then hydrophobically modified nano-SiO2 (accounting for 0.5%-1.5% of the total amount of nano-silica) was added and ultrasonically emulsified to form a stable W / O type Pickering emulsion. The emulsion was dispersed in an aqueous phase containing hydrophilic nano-TiO2 (accounting for 0.3%-0.8% of the total nano-silica) and subjected to high-speed shearing to form a W / O / W multi-emulsion; After mixing phenyl / methyl polysiloxane prepolymer with acrylic resin prepolymer, styrene oligomer (used to improve the film-forming properties of wall materials and enhance the stability of microcapsule structures) is added. The mixture is stirred until dissolved, and then slowly dripped into the aforementioned W / O / W type multi-layer emulsion, controlling the dripping rate to 1-2 drops / second. After the dripping is complete, the system temperature is raised to 80℃, the rotation speed is adjusted to 1500 rpm, and the mixture is stirred at a constant temperature for 2-3 hours to polymerize the prepolymer at the emulsion interface, forming a nanoparticle-resin composite wall material. After the polymerization reaction is completed, the reaction system is cooled to room temperature, vacuum filtered, and the filter cake is washed 3-4 times alternately with deionized water and anhydrous ethanol to remove unreacted monomers and impurities. Then the filter cake is placed in a vacuum drying oven at 60℃ and dried for 24 hours. After drying, it is sieved through a standard sieve to obtain reversible color-changing microcapsule pigment powder with a particle size of 2-10μm. Furthermore, the present invention also provides a method for preparing a reversibly color-changing microcapsule high-temperature resistant coating as described in any one of the above claims, comprising the following steps: S1, under medium-speed stirring, inorganic polysiloxane / acrylic resin as base, solvent is added and stirred continuously to obtain mixture A; S2, under medium-speed stirring, white corundum, silica powder and reversible color-changing microcapsule pigment are added to the mixture A in step S1 in sequence, and stirring is continued until uniformly dispersed to obtain mixture B; S3, add the grinding media to the mixture from step S2, and grind it in a vibrating mill or sand mill to obtain a finely ground material; S4. Stir at high speed, add additives, and continue stirring until uniform and free of particles to obtain a reversible color-changing high-temperature resistant coating. The preparation method according to claim 9 is characterized in that: In step S1, the medium speed is 500-800 rpm, and the stirring time is 10 min. In step S2, the medium speed is 500-800 rpm, and the stirring time is 20 min. In step S3, the grinding medium is glass beads with a diameter of 0.2 mm, which account for 70% of the mass ratio of the mixture, the grinding time is 40 min, and the fineness of the ground material is less than or equal to 30 micrometers; In step S4, the high rotation speed is 1000-1200 rpm and the duration is 10 min.

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