Preparation method of diffuse reflection coating

Abstract

The present invention relates to the field of chemical industry. A method for preparing a diffuse reflection coating comprises the following steps: step 1, electrostatically spraying a first coating on the inner wall of an integrating sphere to form a first coating, wherein the first coating comprises 20 parts of metal microbeads and 2 parts of sodium bicarbonate; step 2, heating the integrating sphere after the first coating is half dry and before it is completely dry to decompose the sodium bicarbonate; step 3, rolling a second coating on the first coating to form a second coating, wherein the second coating comprises 20 parts of hollow glass microbeads and 10 parts of self-repairing microcapsules. Water and carbon dioxide are produced during the decomposition of sodium bicarbonate. Among them, carbon dioxide is beneficial to improving the diffuse reflection effect and increasing the bonding strength between the second coating and the first coating. Among them, water can avoid the problem of easy cracking and falling off caused by the first coating drying too quickly.

Description

Technical Field

[0001] The present invention relates to the field of chemical industry, and in particular to a method for preparing a diffuse reflection coating. Background Art

[0002] An integrating sphere is a hollow sphere with an inner wall coated with a white diffuse reflective material. It is also called a photometric sphere or a luminous flux sphere. The reflectivity of the inner wall coating is one of the most important quality indicators of an integrating sphere, so it is necessary to develop products with coatings with high reflectivity. Summary of the Invention

[0003] The object of the present invention is to provide a method for preparing a diffuse reflective coating, wherein the coating prepared by the method has a high diffuse reflectivity.

[0004] A method for preparing a diffuse reflection coating comprises the following steps:

[0005] Step 1: electrostatically spray a first coating on the inner wall of the integrating sphere to form a first coating layer, wherein the first coating layer comprises the following raw materials in the following weight ratio: 5 parts of acrylic emulsion, 10 parts of polyurethane-modified acrylic emulsion, 5 parts of aqueous fluorocarbon emulsion, 2 parts of polyvinyl alcohol, 80 parts of deionized water, 100 parts of barium sulfate, 20 parts of metal microbeads, 0.5 parts of wetting and dispersing agent, 0.8 parts of defoaming agent, 0.2 parts of thickener, and 2 parts of sodium bicarbonate;

[0006] Step 2: After the first coating is half dry but before it is completely dry, heat the integrating sphere to decompose the sodium bicarbonate;

[0007] Step 3: Roll-coat the second coating on the first coating to form a second coating. The second coating includes the following raw materials in the following weight ratio: 2 parts of acrylic emulsion, 10 parts of polyurethane-modified acrylic emulsion, 10 parts of water-based fluorocarbon emulsion, 2 parts of polyvinyl alcohol, 80 parts of deionized water, 100 parts of barium sulfate, 0.5 parts of wetting and dispersing agent, 0.8 parts of defoaming agent, 0.2 parts of thickener, 20 parts of hollow glass microspheres, and 10 parts of self-repairing microcapsules.

[0008] Beneficial Effects: 1. The decomposition of sodium bicarbonate produces water and carbon dioxide. The carbon dioxide impacts the first coating. The portions of the carbon dioxide that do not penetrate the first coating form air bubbles, which improve diffuse reflection. The portions that penetrate the first coating form relatively uniform micropores, with tiny burrs forming at the edges of the pores. These micropores and burrs help strengthen the bond between the second and first coatings. The water produced by the decomposition enters the first coating and slowly evaporates, allowing the moisture content of the first coating to be used to assess the extent of sodium bicarbonate decomposition. Furthermore, the water prolongs the drying time of the first coating, thereby preventing cracking and peeling caused by rapid drying. 2. The first coating contains metal microbeads. In addition to abrading the materials and accelerating mixing during mixing, the metal microbeads, once formed into a coating, have the following unexpected technical benefits: a. The metal microbeads have excellent thermal conductivity. When heating the integrating sphere, they effectively transfer heat from the sphere, resulting in more uniform heating of the first coating. b. The bonding strength at the metal microbeads is different from the bonding strength at other locations, so it plays a guiding role and provides a path when the carbon dioxide breaks through the first coating. c. The metal microbeads have good electrical conductivity and can effectively control the thickness of the first coating during the electrostatic spraying process. 3. Self-repairing microcapsules are added to the second coating. When the second coating is damaged by mechanical scratches, cracks, etc., it can be repaired by the self-repairing microcapsules. 4. Those skilled in the art generally believe that sodium bicarbonate decomposes to produce carbon dioxide, making the first coating rough, and the defoaming agent eliminates bubbles in the mixture, making the first coating smoother. Therefore, the two have opposite effects, and the first coating should not contain a defoaming agent. The present invention overcomes this technical prejudice. The defoaming agent eliminates bubbles of inconsistent shape and size in the mixture, making the thickness of the first coating more consistent and more uniform. After coating, the sodium bicarbonate reacts and regenerates bubbles with relatively uniform distribution, relatively consistent shape and size. Not only are the two not contradictory, but the defoaming agent also has the effect of promoting uniform bubbles and relatively consistent shape and size. 5. This invention utilizes a combination of acrylic emulsion, polyurethane-modified acrylic emulsion, water-based fluorocarbon emulsion, and polyvinyl alcohol to effectively enhance the strength, aging resistance, and diffuse reflectivity of the resulting coating. Synergistic effects exist between the raw materials, as demonstrated by: a) excellent film-forming ability, even with a high filler content, enabling the formation of a complete, continuous, and durable coating on the substrate; and b) the crystallization and microscopic incompatibility of the resin groups enhances diffuse reflectivity.

[0009] Preferably, the shell material of the self-healing microcapsules is polyurea, and the core material of the self-healing microcapsules includes a siloxane prepolymer and a platinum catalyst. The present invention selects the materials of the self-healing microcapsules so that upon rupture of the polyurea, the siloxane prepolymer and platinum catalyst in the core material are simultaneously released into the damaged area, reacting to form a three-dimensional cross-linked polysiloxane elastomer with high flexibility and adhesion, which can tightly bond with the original coating.

[0010] Further preferably, the metal microbeads are made of platinum. The present invention selects a material for the metal microbeads so that they act as catalysts after the self-repairing microcapsules rupture, effectively resolving the problem of the platinum catalyst in the self-repairing microcapsules having difficulty flowing into the first coating, thereby improving the repair effect within the first coating and at the interface between the first and second coatings.

[0011] Preferably, the particle size of the metal microbeads is larger than that of the hollow glass microbeads. The present invention selects the particle size of the microbeads so that the depressions formed after the metal microbeads on the first coating fall off can accommodate the hollow glass microbeads, effectively improving the uniformity of the distribution of the hollow glass microbeads in the second coating.

[0012] Preferably, the integrating sphere is constructed from two joined hemispheres. The roller used to roll-apply the second coating is semicircular in shape, pressed against the first coating layer, with the central axis of the roller coinciding with the central axis of the hemisphere. The roller rotates clockwise about its central axis, while the hemisphere rotates counterclockwise. First, the present invention aligns the shapes of the roller and hemisphere, effectively improving the efficiency and uniformity of roll-coating. Second, the roller and hemisphere rotate in opposite directions, increasing their relative speed, further enhancing the efficiency and effectiveness of roll-coating.

[0013] Preferably, the roller is removed after the coating is completed, and the hemisphere continues to rotate about the central axis until the second coating is at least half dry. In the present invention, the continued rotation of the hemisphere after the coating is completed can make the second coating more evenly distributed and at the same time, make the second coating more closely bonded to the first coating. DETAILED DESCRIPTION

[0014] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below.

[0015] The preparation method of the diffuse reflection coating comprises the following steps: Step 1, electrostatically spraying a first coating on the inner wall of an integrating sphere to form a first coating. The first coating comprises sodium bicarbonate. Step 2, after the first coating is half dry and before it is completely dry, heating the integrating sphere to decompose the sodium bicarbonate. Preferably, the outer wall of the integrating sphere is covered with a heating wire, and the integrating sphere is heated by the heating wire. The heating wire coating method has the advantages of being relatively easy to set up and remove, and relatively uniform heating. The heating wire can be directly spirally wound on the outer wall of the integrating sphere. Water and carbon dioxide are produced during the decomposition of sodium bicarbonate. Among them, the carbon dioxide impacts the first coating, and the part that does not break through the first coating will cause the first coating to form air bubbles. The air bubbles are conducive to improving the diffuse reflection effect. The part that breaks through the first coating will form relatively uniform micropores on the first coating, and form tiny burrs at the edges of the micropores. The micropores and tiny burrs are conducive to improving the bonding strength between the second coating and the first coating. The water produced by decomposition will enter the first coating and then slowly evaporate. Therefore, the moisture content of the first coating can be used to help determine the degree of sodium bicarbonate decomposition. In addition, water will prolong the drying time of the first coating, thereby preventing the first coating from drying too quickly and causing cracking and peeling. Step 3: Roll the second coating over the first coating to form a second coating.

[0016] According to the above preparation method, the diffuse reflective coatings were differentiated according to the raw material components and component weight ratios in the following embodiments to prepare diffuse reflective coatings.

[0017] Specific Example 1: The first coating comprises the following raw materials in the following weight ratios: 5 parts acrylic emulsion, 10 parts polyurethane-modified acrylic emulsion, 5 parts aqueous fluorocarbon emulsion, 2 parts polyvinyl alcohol, 80 parts deionized water, 100 parts barium sulfate, 20 parts metal microbeads, 0.5 parts wetting and dispersing agent, 0.8 parts defoaming agent, 0.2 parts thickener, and 2 parts sodium bicarbonate. The second coating comprises the following raw materials in the following weight ratios: 2 parts acrylic emulsion, 10 parts polyurethane-modified acrylic emulsion, 10 parts aqueous fluorocarbon emulsion, 2 parts polyvinyl alcohol, 80 parts deionized water, 100 parts barium sulfate, 0.5 parts wetting and dispersing agent, 0.8 parts defoaming agent, 0.2 parts thickener, 20 parts hollow glass microbeads, and 10 parts self-repairing microcapsules.

[0018] Specific Example 2: The first coating comprises the following raw materials in the following weight ratios: 5 parts acrylic emulsion, 10 parts polyurethane-modified acrylic emulsion, 5 parts aqueous fluorocarbon emulsion, 2 parts polyvinyl alcohol, 80 parts deionized water, 100 parts barium sulfate, 20 parts metal microbeads, 0.5 parts wetting and dispersing agent, 0.8 parts defoaming agent, and 0.2 parts thickener. The second coating comprises the following raw materials in the following weight ratios: 2 parts acrylic emulsion, 10 parts polyurethane-modified acrylic emulsion, 10 parts aqueous fluorocarbon emulsion, 2 parts polyvinyl alcohol, 80 parts deionized water, 100 parts barium sulfate, 0.5 parts wetting and dispersing agent, 0.8 parts defoaming agent, 0.2 parts thickener, 20 parts hollow glass microbeads, and 10 parts self-repairing microcapsules.

[0019] Specific Example 3: The first coating comprises the following raw materials in the following weight ratios: 5 parts acrylic emulsion, 10 parts polyurethane-modified acrylic emulsion, 5 parts aqueous fluorocarbon emulsion, 2 parts polyvinyl alcohol, 80 parts deionized water, 100 parts barium sulfate, 0.5 parts wetting and dispersing agent, 0.8 parts defoaming agent, 0.2 parts thickener, and 2 parts sodium bicarbonate. The second coating comprises the following raw materials in the following weight ratios: 2 parts acrylic emulsion, 10 parts polyurethane-modified acrylic emulsion, 10 parts aqueous fluorocarbon emulsion, 2 parts polyvinyl alcohol, 80 parts deionized water, 100 parts barium sulfate, 0.5 parts wetting and dispersing agent, 0.8 parts defoaming agent, 0.2 parts thickener, 20 parts hollow glass microspheres, and 10 parts self-repairing microcapsules.

[0020] Specific Example 4: The first coating comprises the following raw materials in the following weight ratios: 5 parts acrylic emulsion, 10 parts polyurethane-modified acrylic emulsion, 5 parts aqueous fluorocarbon emulsion, 2 parts polyvinyl alcohol, 80 parts deionized water, 100 parts barium sulfate, 20 parts metal microbeads, 0.5 parts wetting and dispersing agent, 0.8 parts defoaming agent, 0.2 parts thickener, and 10 parts sodium bicarbonate. The second coating comprises the following raw materials in the following weight ratios: 2 parts acrylic emulsion, 10 parts polyurethane-modified acrylic emulsion, 10 parts aqueous fluorocarbon emulsion, 2 parts polyvinyl alcohol, 80 parts deionized water, 100 parts barium sulfate, 0.5 parts wetting and dispersing agent, 0.8 parts defoaming agent, 0.2 parts thickener, 20 parts hollow glass microbeads, and 10 parts self-repairing microcapsules.

[0021] Specific Example 5: The first coating comprises the following raw materials in the following weight ratios: 5 parts acrylic emulsion, 10 parts polyurethane-modified acrylic emulsion, 5 parts aqueous fluorocarbon emulsion, 2 parts polyvinyl alcohol, 80 parts deionized water, 100 parts barium sulfate, 20 parts metal microbeads, 0.5 parts wetting and dispersing agent, 0.8 parts defoaming agent, 0.2 parts thickener, and 2 parts sodium bicarbonate. The second coating comprises the following raw materials in the following weight ratios: 2 parts acrylic emulsion, 10 parts polyurethane-modified acrylic emulsion, 10 parts aqueous fluorocarbon emulsion, 2 parts polyvinyl alcohol, 80 parts deionized water, 100 parts barium sulfate, 0.5 parts wetting and dispersing agent, 0.8 parts defoaming agent, 0.2 parts thickener, and 20 parts hollow glass microbeads.

[0022] Specific embodiment 6: The first coating and the second coating are made of the same material and both include the following raw materials in the following weight ratio: 5 parts of acrylic emulsion, 10 parts of polyurethane modified acrylic emulsion, 5 parts of aqueous fluorocarbon emulsion, 2 parts of polyvinyl alcohol, 80 parts of deionized water, 100 parts of barium sulfate, 0.5 parts of wetting and dispersing agent, 0.8 parts of defoaming agent, 0.2 parts of thickener, and 2 parts of sodium bicarbonate.

[0023] Specific embodiment 7: The first coating and the second coating are made of the same material and both include the following raw materials in the following weight ratio: 2 parts of acrylic emulsion, 10 parts of polyurethane modified acrylic emulsion, 10 parts of aqueous fluorocarbon emulsion, 2 parts of polyvinyl alcohol, 80 parts of deionized water, 100 parts of barium sulfate, 0.5 parts of wetting dispersant, 0.8 parts of defoaming agent, 0.2 parts of thickener, 20 parts of hollow glass microspheres, and 10 parts of self-repairing microcapsules.

[0024] Among the above materials, the acrylic emulsion preferably has a solid content of 35%. The polyurethane-modified acrylic emulsion has a solid content of 35%. The water-based fluorocarbon emulsion has a solid content of 45% and a fluorine content of 10-15%. The water-based fluorocarbon emulsion preferably has a fluorine content of 10%, but the higher the fluorine content, the better. The higher the fluorine content, the poorer the filler coating ability, which can cause filler precipitation. Therefore, the selection of the fluorine content of the water-based fluorocarbon emulsion and the amount added in the formulation are also important. Polyvinyl alcohol is preferably 1000 mesh polyvinyl alcohol that is soluble in cold water. It provides good interfacial activity, allows for more uniform mixing between the raw materials, and improves the leveling properties of the coating. Barium sulfate is preferably a mixture of 1250 mesh and 3000 mesh in a ratio of 2:1. Hollow glass microspheres preferably have a particle size of 100-150 mesh and are aggregated and stacked with barium sulfate to provide a moderately rough and continuous surface. The roughness is jointly affected by the barium sulfate and the hollow microspheres, and the accumulation of fillers of different particle sizes can form a stable structure. In the experiment: When using barium sulfate alone, the surface roughness is not enough and powder will fall off. This is because the particle size is too fine and the filler amount is too high, resulting in poor resin bonding effect. However, after adding hollow glass microbeads with larger particle size, a skeleton is formed, and the barium sulfate and resin are evenly dispersed and connected together. On the surface, the surface is rough and continuous, and no powder will fall off.

[0025] In the above embodiments, the acrylic emulsion used was Dow PRIMAL NW-5118 acrylic emulsion. The polyurethane-modified acrylic emulsion used was Wacker VAEVINNAPAS EZ3066 propylene. The water-based fluorocarbon emulsion used was Zhejiang Juhua JF-4DCD concentrated dispersion. The polyvinyl alcohol used was polyvinyl alcohol 2488 PVA powder.

[0026] The coatings of the above embodiments were coated on an integrating sphere, wherein the thickness of the first coating and the thickness of the second coating were each 0.3 mm, to obtain a diffuse reflective coating. The diffuse reflective coating was then tested for diffuse reflectivity (using an illuminometer, GB / T5700-2023). After exposure to a halogen lamp for approximately 152 hours, the reflectivity loss was measured.

[0027] The diffuse reflectivity of the diffuse reflective coating obtained in Specific Example 1 was 98%, and the reflectivity loss rate was 0.8%. The diffuse reflectivity of the diffuse reflective coating obtained in Specific Example 2 was 94%, and the reflectivity loss rate was 1.18%. The diffuse reflectivity of the diffuse reflective coating obtained in Specific Example 3 was 95%, and the reflectivity loss rate was 1.2%. The diffuse reflectivity of the diffuse reflective coating obtained in Specific Example 4 was 90%, and the reflectivity loss rate was 1.5%. The diffuse reflectivity of the diffuse reflective coating obtained in Specific Example 5 was 95%, and the reflectivity loss rate was 1.2%. The diffuse reflectivity of the diffuse reflective coating obtained in Specific Example 6 was 96%, and the reflectivity loss rate was 1.8%. The diffuse reflectivity of the diffuse reflective coating obtained in Specific Example 7 was 97%, and the reflectivity loss rate was 1%.

[0028] The above test results show the following: 1. Specific Example 1 achieved the best test results. 2. Adding too little sodium bicarbonate (Specific Example 2) or too much (Specific Example 4) is not conducive to improving diffuse reflectivity and controlling reflectivity loss. 3. Adding metal microbeads (comparing Specific Example 1 and Specific Example 3) is beneficial for improving diffuse reflectivity and reflectivity loss. 4. Adding self-healing microcapsules helps maintain reflectivity loss. 5. The double-coating method (Specific Example 1) is superior to the single-coating method (Specific Examples 6 and 7).

[0029] The preparation method of the first coating in Specific Example 1 is as follows: Step 1. Add polyvinyl alcohol to 60°C deionized water and stir at 300 rpm to dissolve. Then, while continuing to stir at 300 rpm, first add a wetting dispersant and a defoamer, then add metal microbeads, and disperse evenly at 500 rpm to obtain Mixture 1. Step 2. Add an acrylic emulsion, a polyurethane-modified acrylic emulsion, barium sulfate, and an aqueous fluorocarbon emulsion to Mixture 1 in sequence, and stir evenly at 300 rpm to obtain Mixture 2. Step 3. Add a thickener and a defoamer to Mixture 2, stir at 100 rpm for 30 minutes, and filter through a 100-mesh sieve to obtain Mixture 3. Step 4. Add sodium bicarbonate to Mixture 3 and stir at low speed until uniformly mixed, controlling the temperature of the mixture to be no higher than 30°C, to obtain the first coating. Preferably, the metal microbeads are made of platinum. The present invention selects the material of the metal microbeads. The selected metal microbeads act as catalysts after the self-repairing microcapsules are broken, which can effectively solve the problem that the platinum catalyst in the self-repairing microcapsules is difficult to flow into the first coating, thereby improving the repair effect in the first coating and at the junction of the first coating and the second coating.

[0030] The preparation method of the second coating in Specific Example 1 is as follows: Step 1: Add polyvinyl alcohol to 60°C deionized water and stir at 300 rpm to dissolve. Then, while continuing to stir at 300 rpm, first add a wetting dispersant and a defoamer, then add hollow glass microspheres, and disperse evenly at 500 rpm to obtain Mixture 1. Step 2: Add an acrylic emulsion, a polyurethane-modified acrylic emulsion, barium sulfate, and an aqueous fluorocarbon emulsion to Mixture 1 in sequence, and stir at 300 rpm to obtain Mixture 2. Step 3: Add a thickener and a defoamer to Mixture 2, stir at 100 rpm for 30 minutes, and filter through a 100-mesh sieve to obtain Mixture 3. Step 4: Lower the temperature of Mixture 3 to below 10°C, add self-healing microcapsules to Mixture 3, and stir at low speed until mixed evenly to obtain the second coating. This preparation method optimizes the timing of adding the self-healing microcapsules. By lowering the temperature to below 10°C and using low stirring speed, rupture of the self-healing microcapsules can be effectively avoided.

[0031] Preferably, the shell material of the self-healing microcapsules is polyurea, and the core material comprises a siloxane prepolymer and a platinum catalyst. The preparation method for the self-healing microcapsules includes step 1: mixing the siloxane prepolymer and the platinum catalyst as an oil phase; step 2: dispersing the oil phase in an aqueous phase containing an emulsifier (Span-80) to form an oil-in-water emulsion; step 3: adding diisocyanate (HDI) and diamine (EDA) to carry out interfacial polymerization to form a polyurea shell; and step 4: collecting by centrifugation and drying to obtain the self-healing microcapsules. The preferred mass percentage of the platinum catalyst is 10%.

[0032] Preferably, the particle size of the metal microbeads is larger than that of the hollow glass microbeads. Thus, the depressions formed after the metal microbeads on the first coating fall off can accommodate the hollow glass microbeads, effectively improving the distribution uniformity of the hollow glass microbeads in the second coating.

[0033] Yes, the integrating sphere is constructed from two joined hemispheres. The roller used to roll-apply the second coating is semicircular and presses against the first coating. The central axis of the roller coincides with the central axis of the hemisphere. The roller rotates clockwise around its central axis, while the hemisphere rotates counterclockwise. First, the shape of the roller and hemisphere match, effectively improving the efficiency and uniformity of the roll-apply process. Second, the roller and hemisphere rotate in opposite directions, increasing their relative speed, further enhancing the efficiency and effectiveness of the roll-apply process.

[0034] Preferably, the roller is removed after the coating is completed, and the hemisphere continues to rotate about the central axis until the second coating is at least half dry. In the present invention, the continued rotation of the hemisphere after the coating is completed can make the second coating more evenly distributed and at the same time, make the second coating more closely bonded to the first coating.

Claims

1. A method for preparing a diffuse reflective coating, characterized in that: The steps include: Step 1: electrostatically spray a first coating on the inner wall of the integrating sphere to form a first coating layer, wherein the first coating layer comprises the following raw materials in the following weight ratio: 5 parts of acrylic emulsion, 10 parts of polyurethane-modified acrylic emulsion, 5 parts of aqueous fluorocarbon emulsion, 2 parts of polyvinyl alcohol, 80 parts of deionized water, 100 parts of barium sulfate, 20 parts of metal microbeads, 0.5 parts of wetting and dispersing agent, 0.8 parts of defoaming agent, 0.2 parts of thickener, and 2 parts of sodium bicarbonate; Step 2: After the first coating is half dry but before it is completely dry, heat the integrating sphere to decompose the sodium bicarbonate; Step 3: Roll-coat the second coating on the first coating to form a second coating. The second coating includes the following raw materials in the following weight ratio: 2 parts of acrylic emulsion, 10 parts of polyurethane-modified acrylic emulsion, 10 parts of water-based fluorocarbon emulsion, 2 parts of polyvinyl alcohol, 80 parts of deionized water, 100 parts of barium sulfate, 0.5 parts of wetting and dispersing agent, 0.8 parts of defoaming agent, 0.2 parts of thickener, 20 parts of hollow glass microspheres, and 10 parts of self-repairing microcapsules.

2. The method for preparing a diffuse reflective coating according to claim 1, wherein: The shell material of the self-repairing microcapsule is polyurea, and the core material of the self-repairing microcapsule includes silicone prepolymer and platinum catalyst.

3. The method for preparing a diffuse reflective coating according to claim 2, wherein: The material of the metal microbeads is platinum.

4. The method for preparing a diffuse reflective coating according to claim 1, wherein: The particle size of the metal microspheres is larger than that of the hollow glass microspheres.

5. The method for preparing a diffuse reflective coating according to any one of claims 1 to 4, characterized in that: The integrating sphere is made up of two hemispheres spliced together. The roller used to roll on the second coating is semicircular and presses against the first coating. The central axis of the roller coincides with the central axis of the hemisphere. The roller rotates clockwise around the central axis, and the hemisphere rotates counterclockwise around the central axis. The roller is removed after the coating is completed, and the hemisphere continues to rotate around the central axis until the second coating is at least half dry.

6. The method for preparing a diffuse reflective coating according to any one of claims 1 to 4, characterized in that: The preparation method of the first coating comprises the following steps: step 1, adding polyvinyl alcohol to deionized water at 60° C., stirring and dissolving at a speed of 300 rpm, then, while continuing to stir at a speed of 300 rpm, first adding a wetting dispersant and a defoaming agent, then adding metal microbeads, and dispersing evenly at a speed of 500 rpm to obtain a mixture 1; step 2, adding an acrylic emulsion, a polyurethane-modified acrylic emulsion, barium sulfate, and an aqueous fluorocarbon emulsion to the mixture 1 in sequence, and stirring evenly at a speed of 300 rpm to obtain a mixture 2; step 3, adding a thickener and a defoaming agent to the mixture 2, stirring at a speed of 100 rpm for 30 minutes, and filtering through a 100-mesh sieve to obtain a mixture 3; step 4, adding sodium bicarbonate to the mixture 3, stirring at a low speed until the mixture is evenly mixed, and controlling the temperature of the mixture to be no higher than 30° C. to obtain the first coating.

7. The method for preparing a diffuse reflective coating according to any one of claims 1 to 4, characterized in that: The preparation method of the second coating comprises the following steps: step 1, adding polyvinyl alcohol to deionized water at 60°C, stirring and dissolving at a speed of 300 rpm, then, while continuing to stir at a speed of 300 rpm, first adding a wetting dispersant and a defoaming agent, and then adding hollow glass microbeads, and dispersing evenly at a speed of 500 rpm to obtain a mixture 1; step 2, adding acrylic emulsion, polyurethane-modified acrylic emulsion, barium sulfate, and aqueous fluorocarbon emulsion to the mixture 1 in sequence, and stirring evenly at a speed of 300 rpm to obtain a mixture 2; step 3, adding a thickener and a defoaming agent to the mixture 2, stirring at a speed of 100 rpm for 30 minutes, and filtering through a 100-mesh sieve to obtain a mixture 3; step 4, reducing the temperature of the mixture 3 to below 10°C, adding self-repairing microcapsules to the mixture 3, and stirring at a low speed until the mixture is evenly mixed to obtain the second coating.

8. The method for preparing a diffuse reflective coating according to any one of claims 1 to 4, characterized in that: The preparation method of the self-healing microcapsules comprises the following steps: step 1, mixing a siloxane prepolymer and a platinum catalyst as an oil phase; step 2, dispersing the oil phase in an emulsifier-containing water phase to form an oil-in-water emulsion; step 3, adding diisocyanate and diamine to carry out interfacial polymerization to form a polyurea shell layer; and step 4, collecting by centrifugation and drying to obtain the self-healing microcapsules.