Preparation method of diffuse reflection coating

Abstract

The invention relates to the field of chemical engineering. The preparation method of the diffuse reflection coating comprises the following steps that 1, a first coating is electrostatically sprayed to the inner wall of an integrating sphere to form a first coating, and the first coating comprises 20 parts of metal microbeads and 2 parts of sodium bicarbonate; 2, after the first coating is half-dried and before the first coating is completely dried, heating the integrating sphere to decompose sodium bicarbonate; 3, the first coating is coated with a second coating in a rolling mode, a second coating is formed, and the second coating comprises 20 parts of hollow glass beads and 10 parts of self-repairing microcapsules. Water and carbon dioxide can be generated in the decomposition process of sodium bicarbonate. Wherein the carbon dioxide is beneficial to improving the diffuse reflection effect and improving the bonding strength of the second coating and the first coating. Wherein the water can avoid the problem that the first coating is easy to crack and fall off due to the fact that the first coating is dried too fast.

Description

Technical Field

[0001] The present invention relates to the chemical industry field, and particularly to a preparation method of a diffuse reflection coating. Background Art

[0002] An integrating sphere is a cavity sphere with an inner wall coated with a white diffuse reflection material, also known as a photometric sphere, a luminous flux sphere, etc. The reflectivity of the inner wall coating of the integrating sphere is one of the most important quality indicators of the integrating sphere. Therefore, it is necessary to develop a coating product with a high reflectivity. Summary of the Invention

[0003] The purpose of the present invention is to provide a preparation method of a diffuse reflection coating, and the coating prepared by this method has a high diffuse reflectivity.

[0004] The preparation method of the diffuse reflection coating comprises the following steps: Step 1: Electrostatically spray a first coating material on the inner wall of the integrating sphere to form a first coating. The first coating material comprises 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 part of wetting and dispersing agent, 0.8 part of defoaming agent, 0.2 part of thickening agent, and 2 parts of sodium bicarbonate; Step 2: Heat the integrating sphere after the first coating is semi-dry and before it is completely dry to decompose the sodium bicarbonate; Step 3: Roll-coat a second coating material on the first coating to form a second coating. The second coating material comprises 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 part of wetting and dispersing agent, 0.8 part of defoaming agent, 0.2 part of thickening agent, 20 parts of hollow glass microspheres, and 10 parts of self-healing microcapsules.

[0005] Beneficial effects: 1. During the decomposition of sodium bicarbonate, water and carbon dioxide are produced. Among them, the carbon dioxide impacts the first coating. The part that does not break through the first coating will cause air bubbles to form in the first coating, and the air bubbles are beneficial to improving the diffuse reflection effect. The part that breaks through the first coating will form relatively uniform micropores on the first coating and tiny burrs at the edges of the micropores. The micropores and tiny burrs are beneficial to improving the bonding strength between the second coating and the first coating. Among them, the water produced by decomposition will enter the first coating and then slowly volatilize. Therefore, the moisture content of the first coating can be used to assist in judging the decomposition degree of sodium bicarbonate. In addition, the water will prolong the drying time of the first coating, thus avoiding the problems of easy cracking and peeling caused by the first coating drying too fast. 2. The first coating contains metal microbeads. In addition to the effect of grinding materials and accelerating mixing when mixing, after being made into a coating, it has the following unexpected technical effects: a. The metal microbeads have good heat conduction effects. When heating the integrating sphere, they can effectively conduct the heat on the integrating sphere, so that the first coating is heated more evenly. b. The bonding strength at the position of the metal microbeads is different from that at other positions. Therefore, when carbon dioxide breaks through the first coating, it plays a role in guiding and providing a path. c. The metal microbeads have good electrical conductivity. During the electrostatic spraying process, they can effectively control the thickness of the first coating. 3. Self-healing microcapsules are added to the second coating. When the second coating is damaged due to mechanical scratches, cracks, etc., it can be repaired through the self-healing 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 the bubbles in the mixture, making the first coating smoother. Therefore, the effects of the two are opposite, and the first coating should not contain a defoaming agent. The present invention overcomes this technical prejudice. The defoaming agent eliminates the bubbles with inconsistent shapes and sizes in the mixture, making the thickness consistency and uniformity of the first coating higher when coated. After coating, sodium bicarbonate reacts to regenerate bubbles with relatively uniform distribution, relatively consistent shapes and sizes. The two are not contradictory, and the defoaming agent has the effect of promoting the uniformity and relatively consistent shapes and sizes of the bubbles. 5. The present invention adopts the compounding scheme of acrylic emulsion, polyurethane-modified acrylic emulsion, water-based fluorocarbon emulsion, and polyvinyl alcohol, effectively improving the strength, aging resistance, and diffuse reflectivity of the formed coating. There is a synergistic effect between the raw materials. The synergistic effect is reflected in: a. In the case of a high filler ratio, there is still good film-forming ability, and a complete, continuous, and durable coating can be formed on the substrate; b. The crystallization and microscopic incompatibility of the resin groups can improve the diffuse reflectivity.

[0006] Preferably, the shell material of the self-healing microcapsules is polyurea, and the core material of the self-healing microcapsules includes a silicone pre-polymer and a platinum catalyst. In the present invention, the material of the self-healing microcapsules is selected. After the polyurea ruptures, the silicone pre-polymer and the platinum catalyst in the core material are simultaneously released into the damaged area, and react to form a three-dimensional cross-linked polysiloxane elastomer, which has high flexibility and adhesion and can be tightly combined with the original coating.

[0007] More preferably, the material of the metal microbeads is platinum. In the present invention, the material of the metal microbeads is selected. After the self-healing microcapsules rupture, the selected metal microbeads act as a catalyst, which can effectively solve the problem that the platinum catalyst in the self-healing microcapsules is difficult to flow into the first coating, thereby improving the repair effect at the junction of the first coating and the second coating and inside the first coating.

[0008] Preferably, the particle size of the metal microbeads is larger than that of the hollow glass microbeads. In the present invention, the particle size of the microbeads is selected. The depression formed after the metal microbeads on the first coating fall off can accommodate the hollow glass microbeads, which can effectively improve the distribution uniformity of the hollow glass microbeads in the second coating.

[0009] Preferably, after the first coating is completely dry, first use a magnet to absorb the metal microbeads on the surface of the first coating, then use high-pressure air with a pressure of 0.5 MPa - 0.8 MPa to impact the surface of the first coating, and finally roll-coat the second coating. By adding a magnetic attraction step in the present invention, the metal microbeads with insufficient adhesion on the surface of the first coating can be effectively sucked out. On the one hand, the amount of platinum used can be reduced, thereby reducing costs. On the other hand, the number of depressions on the surface of the first coating can be increased. By adding a high-pressure air impact step in the present invention, on the one hand, the metal microbeads with insufficient adhesion on the surface of the first coating and the dust and impurities on the surface can be blown out, so that the adhesion between the first coating and the second coating is higher. On the other hand, the surface temperature of the first coating can be reduced, and the shape and orientation of the micro burrs can be fixed, so as to ensure that the micro burrs can better embed into the second coating. In addition, the order of magnetic attraction and high-pressure air blowing in the present invention is selected. First, magnetic attraction makes the micro burrs face outward, and then air blowing makes the micro burrs tilt or produce a barb structure. Compared with the method of first high-pressure air blowing and then magnetic attraction, the orientation of the micro burrs can be more diversified.

[0010] More preferably, the magnet is spherical, and the outer surface of the magnet is densely covered with depressions opening outward. Thus, these depressions are used to accommodate the adsorbed metal microbeads.

[0011] Preferably, the integrating sphere is formed by splicing two hemispheres. The roller for rolling the second coating is semi-circular in shape. The roller 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. First, the present invention makes the shapes of the roller and the hemisphere match, which can effectively improve the efficiency and uniformity of rolling coating. Second, the roller and the hemisphere of the present invention rotate in opposite directions, thereby increasing the relative speed between the two, which is conducive to improving the efficiency and effect of rolling coating.

[0012] Preferably, the roller is removed after the rolling coating is completed, and the hemisphere continues to rotate around the central axis until the second coating is at least semi-dry. After the rolling coating is completed, the present invention uses the continuous rotation of the hemisphere to make the distribution of the second coating more uniform. At the same time, the combination of the second coating and the first coating can be made more compact. Specific embodiments

[0013] In order to make the technical means, creative features, achieved purposes and effects of the present invention easy to understand, the present invention will be further described below.

[0014] A method for preparing a diffuse reflection coating includes the following steps: Step 1: Electrostatically spray a first coating on the inner wall of the integrating sphere to form a first coating. The first coating includes sodium bicarbonate. Step 2: After the first coating is semi-dry and before it is completely dry, heat the integrating sphere to decompose sodium bicarbonate. Preferably, an electric heating wire is covered on the outer wall of the integrating sphere, and the integrating sphere is heated through the electric heating wire. The way of covering the electric heating wire has the advantages of being relatively easy to set and remove, and relatively uniform heating. The electric heating wire can be directly spirally wound on the outer wall of the integrating sphere. During the decomposition of sodium bicarbonate, water and carbon dioxide are generated. Among them, carbon dioxide impacts the first coating. The part that does not break through the first coating will form air bubbles in the first coating. The air bubbles are beneficial 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 beneficial to improving the bonding strength between the second coating and the first coating. Among them, the decomposed water will enter the first coating and then slowly volatilize. Therefore, the moisture content of the first coating can be used to assist in judging the decomposition degree of sodium bicarbonate. In addition, water will prolong the drying time of the first coating, thus avoiding the problems of easy cracking and peeling caused by the first coating drying too fast. Step 3: Roll a second coating on the first coating to form a second coating.

[0015] According to the above preparation method, the diffuse reflection coatings are prepared by differentiating the raw material components and the component weight ratios in the following respective embodiments.

[0016] Specific Embodiment 1: The first coating comprises raw materials in the following weight ratios: 5 parts of acrylic emulsion, 10 parts of polyurethane-modified acrylic emulsion, 5 parts of waterborne fluorocarbon emulsion, 2 parts of polyvinyl alcohol, 80 parts of deionized water, 100 parts of barium sulfate, 20 parts of metal microbeads, 0.5 part of wetting and dispersing agent, 0.8 part of defoaming agent, 0.2 part of thickening agent, and 2 parts of sodium bicarbonate. The second coating comprises raw materials in the following weight ratios: 2 parts of acrylic emulsion, 10 parts of polyurethane-modified acrylic emulsion, 10 parts of waterborne fluorocarbon emulsion, 2 parts of polyvinyl alcohol, 80 parts of deionized water, 100 parts of barium sulfate, 0.5 part of wetting and dispersing agent, 0.8 part of defoaming agent, 0.2 part of thickening agent, 20 parts of hollow glass microspheres, and 10 parts of self-healing microcapsules.

[0017] Specific Embodiment 2: The first coating comprises raw materials in the following weight ratios: 5 parts of acrylic emulsion, 10 parts of polyurethane-modified acrylic emulsion, 5 parts of waterborne fluorocarbon emulsion, 2 parts of polyvinyl alcohol, 80 parts of deionized water, 100 parts of barium sulfate, 20 parts of metal microbeads, 0.5 part of wetting and dispersing agent, 0.8 part of defoaming agent, 0.2 part of thickening agent. The second coating comprises raw materials in the following weight ratios: 2 parts of acrylic emulsion, 10 parts of polyurethane-modified acrylic emulsion, 10 parts of waterborne fluorocarbon emulsion, 2 parts of polyvinyl alcohol, 80 parts of deionized water, 100 parts of barium sulfate, 0.5 part of wetting and dispersing agent, 0.8 part of defoaming agent, 0.2 part of thickening agent, 20 parts of hollow glass microspheres, and 10 parts of self-healing microcapsules.

[0018] Specific Embodiment 3: The first coating comprises raw materials in the following weight ratios: 5 parts of acrylic emulsion, 10 parts of polyurethane-modified acrylic emulsion, 5 parts of waterborne fluorocarbon emulsion, 2 parts of polyvinyl alcohol, 80 parts of deionized water, 100 parts of barium sulfate, 0.5 part of wetting and dispersing agent, 0.8 part of defoaming agent, 0.2 part of thickening agent, and 2 parts of sodium bicarbonate. The second coating comprises raw materials in the following weight ratios: 2 parts of acrylic emulsion, 10 parts of polyurethane-modified acrylic emulsion, 10 parts of waterborne fluorocarbon emulsion, 2 parts of polyvinyl alcohol, 80 parts of deionized water, 100 parts of barium sulfate, 0.5 part of wetting and dispersing agent, 0.8 part of defoaming agent, 0.2 part of thickening agent, 20 parts of hollow glass microspheres, and 10 parts of self-healing microcapsules.

[0019] Specific Embodiment 4: The first coating comprises raw materials in the following weight ratios: 5 parts of acrylic emulsion, 10 parts of polyurethane-modified acrylic emulsion, 5 parts of waterborne fluorocarbon emulsion, 2 parts of polyvinyl alcohol, 80 parts of deionized water, 100 parts of barium sulfate, 20 parts of metal microbeads, 0.5 part of wetting and dispersing agent, 0.8 part of defoaming agent, 0.2 part of thickening agent, and 10 parts of sodium bicarbonate. The second coating comprises raw materials in the following weight ratios: 2 parts of acrylic emulsion, 10 parts of polyurethane-modified acrylic emulsion, 10 parts of waterborne fluorocarbon emulsion, 2 parts of polyvinyl alcohol, 80 parts of deionized water, 100 parts of barium sulfate, 0.5 part of wetting and dispersing agent, 0.8 part of defoaming agent, 0.2 part of thickening agent, 20 parts of hollow glass microspheres, and 10 parts of self-healing microcapsules.

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

[0021] Specific Example 6: The first coating and the second coating are made of the same material and both comprise raw materials in the following weight ratio: 5 parts of acrylic emulsion, 10 parts of polyurethane-modified acrylic emulsion, 5 parts of waterborne fluorocarbon emulsion, 2 parts of polyvinyl alcohol, 80 parts of deionized water, 100 parts of barium sulfate, 0.5 part of wetting and dispersing agent, 0.8 part of defoaming agent, 0.2 part of thickening agent, and 2 parts of sodium bicarbonate.

[0022] Specific Example 7: The first coating and the second coating are made of the same material and both comprise raw materials in the following weight ratio: 2 parts of acrylic emulsion, 10 parts of polyurethane-modified acrylic emulsion, 10 parts of waterborne fluorocarbon emulsion, 2 parts of polyvinyl alcohol, 80 parts of deionized water, 100 parts of barium sulfate, 0.5 part of wetting and dispersing agent, 0.8 part of defoaming agent, 0.2 part of thickening agent, 20 parts of hollow glass microspheres, and 10 parts of self-healing microcapsules.

[0023] In each of the above embodiments, if the composition contains metal microbeads, after the first coating is completely dry, first use a magnet to attract the metal microbeads on the surface of the first coating, then use high-pressure air with a pressure of 0.5 MPa - 0.8 MPa to impact the surface of the first coating, and finally roll-coat the second coating. If the composition does not contain metal microbeads, directly roll-coat the second coating after the first coating is completely dry. By adding a magnetic attraction step, the present invention can effectively suck out the metal microbeads with insufficient adhesion on the surface of the first coating. On the one hand, the amount of metal microbeads used can be reduced, thereby reducing costs. On the other hand, the number of depressions on the surface of the first coating can be increased. By adding a high-pressure air impact step, on the one hand, the metal microbeads with insufficient adhesion on the surface of the first coating and the dust and impurities on the surface can be blown out, so that the adhesion between the first coating and the second coating is higher. On the other hand, the surface temperature of the first coating can be reduced, so that the shape and orientation of the micro burrs are fixed, and then it is ensured that the micro burrs are better embedded in the second coating. In addition, the present invention selects the order of magnetic attraction and high-pressure air blowing. First, magnetic attraction makes the micro burrs face outward, and then air blowing makes the micro burrs inclined or generate a barb structure. Compared with the method of first high-pressure air blowing and then magnetic attraction, the orientation of the micro burrs can be more diversified. The magnet can be made into a spherical shape, and the outer surface of the magnet is preferably densely covered with depressions opening outward, so as to use these depressions to accommodate the adsorbed metal microbeads. The magnet can also be made into a hemispherical shape, fixed on the support arm, and the magnet is driven to rotate by the support arm.

[0024] Among the above-mentioned various materials, preferably, the solid content of the acrylic emulsion is 35%. The solid content of the polyurethane-modified acrylic emulsion is 35%. The solid content of the waterborne fluorocarbon emulsion is 45% and the fluorine content is 10 - 15%. The waterborne fluorocarbon emulsion preferably has a fluorine content of 10%, and it is not that the higher the fluorine content, the better. The higher the fluorine content, the worse the coating ability for the filler, which will cause the filler to precipitate. Therefore, the selection of the fluorine content of the waterborne fluorocarbon emulsion and its addition amount in the formula are also very important. Polyvinyl alcohol is preferably 1000-mesh polyvinyl alcohol that can be dissolved in cold water, which provides good interfacial activity, makes the mixing of the preparation raw materials more uniform, and the leveling property of the coating is higher. Barium sulfate is preferably a 2:1 mixture of 1250-mesh and 3000-mesh. The 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, where the roughness is affected by both barium sulfate and hollow glass microspheres. The stacking of fillers with different particle sizes can form a stable structure. In the experiment: when only barium sulfate is used, the surface roughness is insufficient and powder falling occurs, which is due to too fine particle size and too high filler content, and the resin bonding effect is poor. However, after adding larger particle size hollow glass microspheres, a skeleton is formed, and barium sulfate and resin are evenly dispersed and connected together, and the surface looks rough and continuous, and there is no powder falling.

[0025] In the above embodiments, the acrylic emulsion uses Dow PRIMAL NW-5118 acrylic emulsion. The polyurethane-modified acrylic emulsion uses Wacker VAEVINNAPAS EZ3066 propylene. The waterborne fluorocarbon emulsion uses Zhejiang Juhua JF-4DCD concentrated dispersion. Polyvinyl alcohol is selected as polyvinyl alcohol 2488PVA powder.

[0026] Coat the coatings of the above embodiments on an integrating sphere. Among them, the thickness of the first coating and the second coating is 0.3 mm each to obtain a diffuse reflection coating. Then, perform a diffuse reflectance test on the diffuse reflection coating (test using an illuminometer, GB / T5700-2023). Then, after exposure under a halogen lamp for about 152 hours, test the reflectance loss.

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

[0028] It can be seen from the above test results that: 1. The test effect of Specific Example 1 is the best. 2. Too little addition amount of sodium bicarbonate (Specific Example 2) and too large addition amount (Specific Example 4) are not conducive to the improvement of diffuse reflectance and the control of reflectance loss rate. 3. The addition of metal microspheres (comparing Specific Example 1 and Specific Example 3) is beneficial to improving diffuse reflectance and reflectance loss rate. 4. The addition of self-healing microcapsules is beneficial to ensuring the reflectance loss rate. 5. The double-coating method (Specific Example 1) is superior to the single-coating method (Specific Example 6 and Specific Example 7).

[0029] Preparation method of the first coating in Specific Embodiment 1: Step 1. Add polyvinyl alcohol into deionized water at 60 °C, stir and dissolve at a speed of 300 rpm. Then, while continuing to stir at a speed of 300 rpm, first add a wetting dispersant and an antifoaming agent, and then add metal microbeads, and disperse evenly at a speed of 500 rpm to obtain Mixture 1. Step 2. Add acrylic emulsion, polyurethane-modified acrylic emulsion, barium sulfate, and water-based fluorocarbon emulsion into Mixture 1 in sequence, and stir evenly at a speed of 300 rpm to obtain Mixture 2. Step 3. Add a thickening agent and an antifoaming agent into Mixture 2, stir at a speed of 100 rpm for 30 min, and then filter through a 100-mesh sieve to obtain Mixture 3. Step 4. Add sodium bicarbonate into Mixture 3, stir at a low speed until evenly mixed, and control the temperature of the mixture not to be higher than 30 °C to obtain the first coating. Preferably, the material of the metal microbeads is platinum. The present invention selects the material of the metal microbeads. After the self-healing microcapsules are ruptured, the selected metal microbeads play the role of a catalyst, which can effectively solve the problem that the platinum catalyst in the self-healing microcapsules is difficult to flow into the first coating, thereby improving the repair effect at the junction of the first coating and between the first coating and the second coating.

[0030] Preparation method of the second coating in Specific Embodiment 1: Step 1. Add polyvinyl alcohol into deionized water at 60 °C, stir and dissolve at a speed of 300 rpm. Then, while continuing to stir at a speed of 300 rpm, first add a wetting dispersant and an antifoaming agent, and then add hollow glass microbeads, and disperse evenly at a speed of 500 rpm to obtain Mixture 1. Step 2. Add acrylic emulsion, polyurethane-modified acrylic emulsion, barium sulfate, and water-based fluorocarbon emulsion into Mixture 1 in sequence, and stir evenly at a speed of 300 rpm to obtain Mixture 2. Step 3. Add a thickening agent and an antifoaming agent into Mixture 2, stir at a speed of 100 rpm for 30 min, and then filter through a 100-mesh sieve to obtain Mixture 3. Step 4. Lower the temperature of Mixture 3 below 10 °C, add self-healing microcapsules into Mixture 3, and stir at a low speed until evenly mixed to obtain the second coating. This preparation method optimizes the addition timing of the self-healing microcapsules. By lowering the temperature below 10 °C and selecting low-speed stirring, the 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 of the self-healing microcapsules includes a silicone prepolymer and a platinum catalyst. The preparation method of the self-healing microcapsules includes Step 1, mixing the silicone prepolymer and the platinum catalyst as the oil phase; Step 2, dispersing the oil phase in the water phase containing an emulsifier (Span-80) to form an oil-in-water emulsion; Step 3, adding diisocyanate (HDI) and diamine (EDA) for interfacial polymerization to form a polyurea shell layer; Step 4, centrifugally collecting and drying to obtain the self-healing microcapsules. The mass percentage of the platinum catalyst is preferably 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, which can effectively improve the distribution uniformity of the hollow glass microbeads in the second coating.

[0033] It is possible that the integrating sphere is composed of two hemispheres spliced together, the roller for roll-coating the second coating is in a semi-circular arc shape, the roller 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. First, the present invention makes the shapes of the roller and the hemisphere match, which can effectively improve the efficiency and uniformity of roll-coating. Second, the roller and the hemisphere of the present invention rotate in opposite directions, thereby increasing the relative speed between the two, which is conducive to improving the efficiency and effect of roll-coating.

[0034] Preferably, the roller is removed after the roll-coating is completed, and the hemisphere continues to rotate around the central axis until the second coating is at least semi-dry. After the roll-coating is completed, the present invention uses the continuous rotation of the hemisphere to make the distribution of the second coating more uniform. At the same time, the combination of the second coating and the first coating can be made more compact.

Claims

1. A method for preparing a diffuse reflection 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, wherein the first coating comprises the following raw materials in weight ratio: 5 parts of acrylic emulsion, 10 parts of polyurethane-modified acrylic emulsion, 5 parts of water-based 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 and before it is completely dry, heat the integrating sphere to decompose the sodium bicarbonate; Step three, roll-coat the second coating on the first coating to form a second coating, wherein the second coating comprises 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-healing microcapsules.

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

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

4. The method for preparing a diffuse reflective coating according to claim 1, characterized in that: 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 claim 1, characterized in that: After the first coating is completely dry, use a magnet to absorb the metal beads on the surface of the first coating, then use 0.5MPa-0.8MPa high-pressure gas to impact the surface of the first coating, and finally roll on the second coating.

6. The method for preparing a diffuse reflective coating according to claim 5, characterized in that: The magnet is in a spherical shape, and the outer surface of the magnet is densely covered with depressions opening outward.

7. The method for preparing a diffuse reflective coating according to any one of claims 1 to 6, characterized in that: The integrating sphere is composed of two hemispheres. The roller used for rolling the second coating is in the shape of a semicircular arc. The roller is pressed 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 rolling is completed, and the hemisphere continues to rotate around the central axis until the second coating is at least half dry.

8. The method for preparing a diffuse reflective coating according to any one of claims 1 to 6, characterized in that: The preparation method of the first coating comprises the following steps: step 1, adding polyvinyl alcohol into deionized water at 60°C, stirring at 300 rpm to dissolve, then, while continuing to stir at 300 rpm, first adding a wetting dispersant and a defoaming agent, then adding metal microbeads, and dispersing evenly at 500 rpm to obtain a mixture 1; step 2, adding acrylic emulsion, polyurethane-modified acrylic emulsion, barium sulfate, and aqueous fluorocarbon emulsion into the mixture 1 in sequence, stirring evenly at 300 rpm to obtain a mixture 2; step 3, adding a thickener and a defoaming agent into the mixture 2, stirring at 100 rpm for 30 minutes, and filtering through a 100-mesh sieve to obtain a mixture 3; step 4, adding sodium bicarbonate into 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.

9. The method for preparing a diffuse reflective coating according to any one of claims 1 to 6, characterized in that: The preparation method of the second coating comprises the following steps: step 1, adding polyvinyl alcohol into deionized water at 60°C, stirring at 300 rpm to dissolve, then, while continuing to stir at 300 rpm, first adding a wetting dispersant and a defoaming agent, and then adding hollow glass microbeads, and dispersing evenly at 500 rpm to obtain a mixture 1; step 2, adding acrylic emulsion, polyurethane-modified acrylic emulsion, barium sulfate, and aqueous fluorocarbon emulsion into mixture 1 in sequence, and stirring evenly at 300 rpm to obtain a mixture 2; step 3, adding a thickener and a defoaming agent into mixture 2, stirring at 100 rpm for 30 minutes, and filtering through a 100-mesh sieve to obtain a mixture 3; step 4, reducing the temperature of mixture 3 to below 10°C, adding self-repairing microcapsules into mixture 3, and stirring at a low speed until the mixture is evenly mixed to obtain a second coating.

10. The method for preparing a diffuse reflective coating according to any one of claims 1 to 6, 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 aqueous phase containing an emulsifier to form an oil-in-water emulsion; step 3, adding diisocyanate and diamine for interfacial polymerization to form a polyurea shell layer; step 4, collecting by centrifugation, and obtaining the self-healing microcapsules after drying.