Thermal insulation coating and preparation method thereof

Abstract

The application provides a kind of thermal insulation coating and preparation method thereof, belong to coating composition technical field, including the following preparation steps: water phase A is dropped into oil phase A, emulsification, into water bath, stirring reaction, cooling, after separation, dispersed in water phase B, add to oil phase B, heating stirring reaction, add demulsifier demulsification, centrifugation, washing, drying, obtain double-shell microspheres;Add PBA, IPDI, DMPA and catalyst to react, cooling, add triethylamine, add deionized water under high speed shearing, obtain water-based polyurethane dispersion, add chain extender to react, then add MMA, BA and KPS, heating reaction, cooling, filtration, obtain composite resin emulsion;Double-shell microspheres, deionized water and auxiliary agent are pre-dispersed, add composite resin emulsion, stirring dispersion, obtain finished coating.The thermal insulation coating provided by the application can realize efficient heat insulation while having good thermal insulation effect.

Description

Technical Field

[0001] This invention relates to the field of coating composition technology, specifically to a heat-insulating coating and its preparation method. Background Technology

[0002] Building energy conservation is a crucial global issue, and energy-saving retrofitting of building envelopes is a key component. Wall coatings, due to their ease of application and relatively low cost, have become a widely used technology for building energy conservation, especially in the renovation of existing buildings. Currently, energy-saving coatings on the market are mainly developing along two technical paths: one is reflective heat-insulating coatings that focus on increasing solar reflectivity, and the other is phase-change temperature-regulating coatings that attempt to impart thermal regulation capabilities to walls by introducing phase-change materials. However, both technical paths have some drawbacks and cannot meet the urgent need for high-performance energy-saving coatings.

[0003] For reflective heat-insulating coatings that primarily reflect solar radiation, the main technical bottleneck lies in the limitation of their function and the seasonality of their application. These coatings effectively reflect the near-infrared portion of sunlight by adding high-refractive-index pigments, such as rutile titanium dioxide, and reflective fillers, thereby blocking heat and reducing the temperature inside buildings in summer. However, their energy-saving effect is heavily dependent on solar irradiance. On cloudy days, at night, or in winter when solar radiation is weak, the effect significantly diminishes or even disappears. Furthermore, the high reflectivity alone, while blocking excess heat in summer, also blocks beneficial solar radiation in winter, and fails to provide sufficient thermal resistance to reduce indoor heat loss, thus failing to achieve the desired insulation effect.

[0004] To overcome the seasonal limitations of reflective coatings, current research attempts to introduce phase change materials (PCMs) into coating systems. PCMs can absorb or release a large amount of latent heat near their phase change temperature, theoretically mitigating indoor temperature fluctuations and achieving a heat preservation effect. However, the engineering application of this technology faces three core challenges: poor encapsulation reliability, weak compatibility with coating systems, and insufficient long-term stability. Most methods directly microencapsulate PCMs and physically blend them with the coating base material. However, the wall material of general PCM microcapsules lacks sufficient mechanical strength, making them prone to breakage during high-speed dispersion, brushing shearing, and long-term use. This leads to PCM leakage, resulting not only in loss of temperature regulation function but also damage to the integrity of the coating.

[0005] Therefore, there is an urgent need to provide a heat-insulating coating and its preparation method to solve the above problems.

[0006] Furthermore, if the thermal insulation performance of the coating can be guaranteed, and its self-healing properties can be increased to improve the self-healing effect of micro-cracks in the coating, this will further enhance its market application prospects. Summary of the Invention

[0007] In view of this, the present invention provides a heat-insulating coating and its preparation method, which can achieve efficient heat insulation while having a good heat preservation effect.

[0008] To achieve the above objectives, the specific solution of the present invention is as follows: a method for preparing a heat-insulating coating, comprising the following preparation steps:

[0009] S1. Under heating and high-speed shearing, aqueous phase A is dropped into oil phase A, emulsified, transferred to a water bath, stirred and reacted, cooled, separated, dispersed in aqueous phase B, added to oil phase B under heating and high-speed shearing, heated and stirred and reacted, demulsifier was added to demulsify, centrifuged, washed, dried, and obtained bishell microspheres.

[0010] S2. Add PBA, IPDI, DMPA and catalyst to react, cool down, add triethylamine, add deionized water under high-speed shear to obtain an aqueous polyurethane dispersion, add chain extender to react, then add MMA, BA and KPS, heat up to react, cool, filter to obtain a composite resin emulsion.

[0011] S3. Pre-disperse the double-shell microspheres, deionized water and additives, add the composite resin emulsion, stir and disperse to obtain the finished coating;

[0012] The aqueous phase A is obtained by mixing deionized water, tetraethyl orthosilicate and ammonia; the oil phase A is obtained by mixing phase change material with Span-80 and heating to melt; the aqueous phase B is obtained by mixing deionized water, tetrabutyl titanate and acetylacetone, and adding acetic acid to adjust; the oil phase B is obtained by mixing paraffin wax with Span-80.

[0013] This invention employs a two-step dual emulsion method to construct a double-shell microsphere with a phase change material as the core material, a silica shell layer coated on the surface of the core material as the inner shell using interfacial reaction, and a titanium dioxide shell layer coated on the surface as the outer shell. Phase change materials (PCCs) reversibly absorb / release a large amount of latent heat through solid-liquid phase transitions, enhancing the thermal insulation properties of coatings. The dense silica inner shell itself possesses excellent thermal insulation properties, and its nanoporous structure efficiently blocks heat conduction. It can also encapsulate the PCC, preventing leakage that could lead to PCC performance degradation or even damage to the coating structure and performance. The titanium dioxide outer shell, deposited in situ on the inner shell surface, enhances solar reflection and acts as a phonon scattering center. Furthermore, the silica inner shell, the mesoporous titanium dioxide outer shell, and the tiny gaps between the inner and outer shells work together to provide excellent thermal resistance, significantly reducing the overall thermal conductivity of the coating. Thus, the double-shell microspheres possess both excellent thermal insulation and temperature regulation functions, as well as superior thermal insulation and reflection capabilities. They also effectively seal the PCC to ensure its stable performance, resulting in superior thermal insulation and heat preservation effects for the coating.

[0014] In this process, an initial emulsion is formed by dripping aqueous phase A into oil phase A and emulsifying it. Then, a reaction is carried out where tetraethyl orthosilicate (TEOS) hydrolyzes and condenses at the oil-water interface, forming a dense silica inner shell around the phase change material, resulting in SiO2 phase change microcapsules. These microcapsules are dispersed in aqueous phase B and then added to oil phase B to form a (W / O) / W dual emulsion. The reaction is then heated. However, TBOT hydrolyzes extremely rapidly, easily generating a large amount of titanium dioxide precipitate instantaneously, rather than being deposited controllably at the microsphere interface. Ultimately, a mixture of SiO2 phase change microcapsules and TiO2 particles is formed. In contrast, the present invention uses acetylacetone (AcAc) to pre-chelate tetrabutyl titanate (TBOT), which effectively avoids the violent hydrolysis of TBOT, allowing it to migrate to the outer surface of the silica inner shell and deposit there. This achieves controlled interfacial deposition rather than explosive precipitation, promoting the formation of a complete and uniform mesoporous titanium dioxide outer shell. Finally, the double-shell microspheres are obtained by washing. The entire preparation process does not require high-temperature calcination, and the silica inner shell and titanium dioxide outer shell are constructed simultaneously under relatively mild reaction conditions.

[0015] Furthermore, by adding a chain extender to the waterborne polyurethane (WPU) dispersion and reacting it, followed by emulsion copolymerization with acrylate monomers, a composite resin emulsion is obtained. This emulsion is then stirred and dispersed with bi-shell microspheres, allowing the microspheres to be uniformly dispersed in the composite resin emulsion and bonded into a film, resulting in a better bonding effect. The mesoporous titanium dioxide shell of the bi-shell microspheres has both high reflectivity and stability, which can reduce the risk of photocatalytic degradation of the resin and thus improve the overall stability.

[0016] Preferably, in step S3, tungsten bronze nanopowder, double-shell microspheres, deionized water, and additives are added for pre-dispersion; the chain extender is UPy chain extender, and it is prepared by the following method: 2-amino-4-hydroxy-6-methylpyrimidine is dissolved in anhydrous tetrahydrofuran, excess IPDI and catalyst mixture is added dropwise, after reaction, it is transferred to pre-cooled diethyl ether to precipitate, filtered, dissolved again in anhydrous tetrahydrofuran, a small amount of deionized water is added dropwise, the reaction is heated, quenched, and then transferred to pre-cooled diethyl ether to precipitate, filtered, and dried to obtain the final product.

[0017] This invention prepares the UPy chain extender by first reacting the UPy monomer 2-amino-4-hydroxy-6-methylpyrimidine with excess IPDI to ensure the formation of a single-terminal NCO UPy precursor. A small amount of water is then added for controlled hydrolysis, converting it into the target single-terminal amine group, avoiding excessive hydrolysis or side reactions. The preparation of the waterborne polyurethane dispersion involves synthesizing an NCO-terminated prepolymer using PBA, IPDI, and DMPA. Triethylamine is added to neutralize the carboxyl groups, followed by reaction with the UPy chain extender (single-terminal amine group). The amine group reacts rapidly with NCO without byproducts. The UPy supramolecular unit is introduced as a crosslinking agent into the waterborne polyurethane resin network, enabling the UPy unit to be efficiently and stably chemically anchored to the polymer chain and improving the coating's mechanical strength. Then, MMA, BA monomers, and an initiator are added for free radical emulsion copolymerization, allowing the UPy unit to exist stably in the composite resin emulsion as side chains or inter-chain dynamic crosslinking points. The dynamic bonds of UPy can reversibly dissociate and recombine under heat, endowing the coating with self-healing capabilities.

[0018] By incorporating tungsten bronze nanomaterials, which have strong absorption in the near-infrared portion of the solar spectrum, the energy is efficiently converted into heat energy, thus providing a key energy source for the photothermal triggering self-healing of UPy dynamic bonds. When triggered by photothermal action, hydrogen bonds dissociate, allowing chain segment movement to repair cracks. After the temperature decreases, hydrogen bonds recombine, restoring the coating strength. This allows the coating to repair itself using only sunlight without external heating, effectively reducing cracks in the coating, achieving self-healing, and improving the crack resistance and impermeability of the coating, making it suitable for protection in complex service environments.

[0019] In addition, the formed dynamic network allows the bishell microspheres to have a certain displacement when subjected to stress, avoiding stress concentration that could lead to coating cracking, and also improves the bonding effect between the bishell microspheres and the resin, resulting in a stronger overall bonding force of the coating.

[0020] Preferably, in the preparation of the UPy chain extender, 2-amino-4-hydroxy-6-methylpyrimidine is dissolved in anhydrous tetrahydrofuran under a dry nitrogen atmosphere, cooled to 0-5°C in an ice bath, and an excess of IPDI and catalyst mixture is slowly added dropwise while controlling the temperature to <10°C. The mixture is then reacted at room temperature for 18 hours, transferred to pre-cooled diethyl ether to precipitate, filtered, and the intermediate is obtained. This intermediate is dissolved in anhydrous tetrahydrofuran, a small amount of deionized water is added dropwise under an ice bath, the temperature is raised to 40°C, and the reaction is carried out for 6 hours. Methanol is added to quench the reaction, and the mixture is then transferred to pre-cooled diethyl ether to precipitate, filtered, and vacuum dried at 40°C to obtain the final product.

[0021] By precipitating the reaction solution in pre-cooled diethyl ether, excess IPDI can be removed using the pre-cooled diethyl ether, improving the controllability of subsequent reactions. By quenching any remaining -NCO groups with methanol, precipitating again with pre-cooled diethyl ether, filtering, and vacuum drying, a pale yellow solid powder, UPy chain extender, can be obtained.

[0022] Optionally, the chain extender is 1,4-butanediol.

[0023] When 1,4-butanediol is used as a chain extender, it also undergoes addition polymerization with the -NCO group at the end of the prepolymer to obtain a composite resin emulsion. 1,4-Butanediol has good water solubility and is easier to mix evenly in an aqueous dispersion system. The urethane bond formed is a permanent chemical bond, resulting in a more stable resin structure and good emulsion storage stability.

[0024] Preferably, the ammonia concentration in the aqueous phase A is 28 wt%; the oil phase A is made by mixing a phase change material with Span-80 and heating it to 60°C to melt; the phase change material is paraffin or dodecanol, and the phase change temperature is 23-25°C; the aqueous phase B also contains 1.0-1.4 parts by mass of hexadecyltrimethylammonium bromide, which is mixed with deionized water, tetrabutyl titanate and acetylacetone, and the pH is adjusted to 3-4 with acetic acid. At the same time, in step S1, a demulsifier is added to demulsify, and after centrifugation, Soxhlet extraction is performed for 24 hours using an ethanol solution containing 1 wt% hydrochloric acid during the washing process.

[0025] In preparing the titanium dioxide shell of the double-shell microspheres, acetylacetone (AcAc) was used as a chelating agent to pre-complex with tetrabutyl titanate (TBOT). Then, in a dual emulsion system, the complex AcAc-TBOT underwent slow hydrolysis and condensation. At the same time, the Span-80 (oil-soluble surfactant) molecules present in the system guided the assembly around the generated titanium dioxide inorganic material, so that the titanium dioxide inorganic framework gradually formed around the surfactant micelles. Then, acetone and ethanol were used for washing to remove the organic surfactant, leaving the mesoporous structure composed of the titanium dioxide inorganic framework.

[0026] By adding hexadecyltrimethylammonium bromide (CTAB) as a mesoporous template agent, the formation of titanium dioxide mesopores can be further promoted, resulting in bishell microspheres with a more ordered mesoporous structure. In subsequent washing, the template agent can be easily and gently removed by Soxhlet extraction with an ethanol solution containing 1% hydrochloric acid for 24 hours.

[0027] Preferably, in step S1, aqueous phase A is dropped into oil phase A under heating at 60-62℃ and high-speed shearing at 9000-10000 rpm, emulsified for 5-6 minutes to form a primary emulsion, transferred to a water bath at 48-53℃, and stirred at 300-350 rpm for 4-4.5 hours. After cooling to room temperature, the mixture is centrifuged, washed with ethanol, and dispersed in aqueous phase B. Under shearing at 45-48℃ and 7500-8500 rpm, the mixture is added to oil phase B to form a double emulsion, transferred to a water bath at 45-50℃, and stirred slowly at 200 rpm for 12-15 hours. A demulsifier is added to break the emulsion, the product is collected by centrifugation, washed three times alternately with ethanol and acetone, and dried under vacuum at 40℃ to obtain double-shelled microspheres.

[0028] By employing the above two-step dual emulsion interface stabilization method, a silica inner shell and a titanium dioxide outer shell can be constructed simultaneously under mild conditions, while also avoiding severe hydrolysis of TBOT.

[0029] Preferably, in step S2, PBA (Mn=1000), IPDI, dimethylolpropionic acid, and a catalyst are added to a dry reactor and reacted at 80°C. The temperature is then lowered to 40°C, and triethylamine is added for neutralization. Deionized water is added under high-speed shear at 8000 rpm to obtain an aqueous polyurethane dispersion. A chain extender is added, and the reaction is carried out at 45°C for 30 minutes. MMA, BA, and KPS are added, and the temperature is raised to 70-75°C for 4-5 hours. The mixture is then cooled to room temperature and filtered to obtain a composite resin emulsion.

[0030] Preferably, in step S3, the double-shell microspheres, deionized water and additives are pre-dispersed for 20 minutes under low-speed stirring at 350-400 rpm, and then the composite resin emulsion is added, the speed is increased to 600-650 rpm, and the mixture is dispersed for 15-25 minutes to obtain the finished coating.

[0031] Preferably, the catalyst is DBTDL; the demulsifier is acetone; and the additives include wetting and dispersing agent BYK-190, defoamer TEgO 810, and leveling agent BYK-333.

[0032] The present invention also provides a heat insulation coating, which is prepared by the above-mentioned heat insulation coating preparation method and comprises the following components in parts by weight: 20-26 parts of double-shell microspheres, 18-24 parts of deionized water, 2-2.7 parts of additives and 55-70 parts of composite resin emulsion.

[0033] The bishell microspheres comprise the following raw materials in parts by weight: 130-170 parts deionized water, 5-6.5 parts tetraethyl orthosilicate, 0.5-0.7 parts 28wt% ammonia, 10-15 parts phase change material, 2.3-2.9 parts Span-80, 3-4 parts tetrabutyl titanate, 1.5-2 parts acetylacetone, and 200-250 parts liquid paraffin;

[0034] The composite resin emulsion comprises the following raw materials in parts by weight: 20-25 parts PBA, 8-10 parts IPDI, 2-3 parts DMPA, 0.02-0.04 parts catalyst, 1.5-2.0 parts triethylamine, 60-75 parts deionized water, 1-2.5 parts chain extender, 10-15 parts MMA, 6-12 parts BA and 0.2-0.3 parts KPS.

[0035] Preferably, it further includes 1.5-2 parts of tungsten bronze nanoparticles; the chain extender is UPy chain extender, comprising the following raw materials in parts by weight: 5.0-6.5 parts of 2-amino-4-hydroxy-6-methylpyrimidine, 60-65 parts of anhydrous tetrahydrofuran, 10-13 parts of isophorone diisocyanate, 0.05-0.1 parts of catalyst, 40-50 parts of anhydrous tetrahydrofuran, 0.5-0.6 parts of deionized water and 2-2.5 parts of methanol.

[0036] Preferably, the bishell microspheres further include 0.1-1.4 parts of hexadecyltrimethylammonium bromide.

[0037] Preferably, the additives include 1-1.5 parts of wetting and dispersing agent BYK-190, 0.5-0.6 parts of defoamer TEgO 810 and 0.5-0.6 parts of leveling agent BYK-333.

[0038] By using the above-mentioned raw materials and optimizing their dosage, the resulting coating can achieve efficient heat insulation and heat preservation without the need for complex and diverse filler materials.

[0039] In the application, PBA is polybutylene adipate, IPDI is isophorone diisocyanate, DMPA is dimethylolpropionic acid, DBTDL is dibutyltin dilaurate, MMA is methyl methacrylate, BA is butyl acrylate, and KPS is potassium persulfate.

[0040] The above-described technical solution of the present invention has at least the following beneficial effects:

[0041] This invention constructs a double-shell microsphere by using a phase change material as the core material, coating the core material surface with a silica shell as the inner shell through interfacial reaction, and then coating it with a titanium dioxide shell as the outer shell. This double-shell microsphere integrates heat storage, heat insulation, and light reflection functions, with the phase change material as the heat storage core material, the dense silica inner shell as the sealing and heat insulation layer, and the mesoporous titanium dioxide outer shell as the light reflection layer. Furthermore, the combined effect of the inner and outer shells provides excellent thermal resistance, significantly reducing the overall thermal conductivity of the coating. This allows the coating to achieve excellent and efficient heat insulation and heat preservation effects without the need for multiple functional fillers.

[0042] This invention prepares double-shell microspheres using a dual emulsion method, effectively encapsulating phase change materials and solving leakage problems. It utilizes acetylacetone (AcAc) to pre-chelate tetrabutyl titanate (TBOT), effectively avoiding violent hydrolysis of TBOT and enabling it to migrate to the outer surface of the silica inner shell and deposit there. This achieves controlled interfacial deposition rather than explosive precipitation, promoting the formation of a complete and uniform mesoporous titanium dioxide outer shell. Finally, the double-shell microspheres are obtained by washing. The entire preparation process does not require high-temperature calcination, and the silica inner shell and titanium dioxide outer shell are constructed simultaneously under relatively mild reaction conditions.

[0043] This invention prepares a composite resin emulsion, which is then stirred and dispersed with bi-shell microspheres, allowing the microspheres to be uniformly dispersed in the composite resin emulsion and bonded into a film, resulting in a better bonding effect. The mesoporous titanium dioxide shell of the bi-shell microspheres has both high reflectivity and stability, which can reduce the risk of photocatalytic degradation of the resin and improve the overall stability. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. The described embodiments are some embodiments of the present invention, and all other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0045] Preparation Example 1

[0046] Take 30 parts of deionized water, add 5 parts of tetraethyl orthosilicate (TEOS) and 0.5 parts of 28wt% ammonia water and mix well to form aqueous phase A; take 15 parts of phase change material dodecanol (melting point 24℃) and mix with 0.3 parts of Span-80, heat to 60℃ to melt, and form oil phase A; take 100 parts of deionized water, add 3 parts of tetrabutyl titanate (TBOT) and 1.5 parts of acetylacetone (AcAc), and adjust the pH to 3 with acetic acid to form aqueous phase B; take 200 parts of liquid paraffin and mix with 2 parts of Span-80 to form oil phase B.

[0047] Under high-speed shearing at 60℃ and 9000rpm, aqueous phase A was dropped into oil phase A and emulsified for 6 minutes to form a W / O primary emulsion. The emulsion was then transferred to a 48℃ water bath and stirred at 300rpm for 4.5 hours. After cooling to room temperature, the emulsion was centrifuged and washed with ethanol to obtain SiO2 phase change microcapsules. These microcapsules were redispersed in aqueous phase B and added to oil phase B under shearing at 45℃ and 7500rpm to form a (W / O) / W double emulsion. The emulsion was then transferred to a 50℃ water bath and stirred slowly at 200rpm for 12 hours. After the reaction was completed, 100 parts of acetone were added as a demulsifier to break the emulsion. The product was collected by centrifugation, washed three times alternately with ethanol and acetone, and dried under vacuum at 40℃ to obtain bishell microspheres.

[0048] Preparation Example 2

[0049] Take 40 parts of deionized water, add 6.5 parts of tetraethyl orthosilicate (TEOS) and 0.7 parts of 28 wt% ammonia water and mix well to form aqueous phase A; take 13 parts of phase change material paraffin (melting point 23℃) and mix with 0.4 parts of Span-80, heat to 60℃ to melt, and form oil phase A; take 130 parts of deionized water, add 4 parts of tetrabutyl titanate (TBOT), 2 parts of acetylacetone (AcAc), and 1.4 parts of cetyltrimethylammonium bromide (CTAB), and adjust the pH to 4 with acetic acid to form aqueous phase B; take 250 parts of liquid paraffin and mix with 2.5 parts of Span-80 to form oil phase B.

[0050] Under high-speed shearing at 62℃ and 10000rpm, aqueous phase A was dropped into oil phase A and emulsified for 5 minutes to form a W / O primary emulsion. The emulsion was then transferred to a 53℃ water bath and stirred at 350rpm for 4 hours. After cooling to room temperature, the emulsion was centrifuged and washed with ethanol to obtain SiO2 phase change microcapsules. These microcapsules were redispersed in aqueous phase B and added to oil phase B under shearing at 48℃ and 8500rpm to form a (W / O) / W double emulsion. The emulsion was then transferred to a 45℃ water bath and stirred slowly at 200rpm for 15 hours. After the reaction was completed, 180 parts of acetone were added to break the emulsion. The product was collected by centrifugation and washed three times alternately with ethanol and acetone. The product was then extracted with an ethanol solution containing 1wt% hydrochloric acid for 24 hours to completely remove the template agent. The product was then vacuum dried at 40℃ to obtain bishell microspheres.

[0051] Preparation Example 3

[0052] Take 35 parts of deionized water, add 6 parts of tetraethyl orthosilicate (TEOS) and 0.6 parts of 28 wt% ammonia water and mix well to form aqueous phase A; take 12 parts of phase change material paraffin (melting point 25℃) and mix with 0.3 parts of Span-80, heat to 60℃ to melt, and form oil phase A; take 115 parts of deionized water, add 3.5 parts of tetrabutyl titanate (TBOT) and 1.8 parts of acetylacetone (AcAc), and 1.0 part of cetyltrimethylammonium bromide (CTAB), and adjust the pH to 3 with acetic acid to form aqueous phase B; take 230 parts of liquid paraffin and mix with 2.3 parts of Span-80 to form oil phase B.

[0053] Under high-speed shearing at 60℃ and 10000rpm, aqueous phase A was dropped into oil phase A and emulsified for 5 minutes to form a W / O primary emulsion. The emulsion was then transferred to a 50℃ water bath and stirred at 350rpm for 4 hours. After cooling to room temperature, the emulsion was centrifuged and washed with ethanol to obtain SiO2 phase change microcapsules. These microcapsules were redispersed in aqueous phase B and added to oil phase B under shearing at 45℃ and 8000rpm to form a (W / O) / W double emulsion. The emulsion was then transferred to a 46℃ water bath and stirred slowly at 200rpm for 13 hours. After the reaction was completed, 150 parts of acetone were added to break the emulsion. The product was collected by centrifugation and washed three times alternately with ethanol and acetone. The product was then extracted with an ethanol solution containing 1wt% hydrochloric acid for 24 hours to completely remove the template agent. The product was then vacuum dried at 40℃ to obtain bishell microspheres.

[0054] Example 1

[0055] In a dry reactor, 20 parts of polybutylene adipate (PBA, Mn=1000), 8 parts of IPDI, 2 parts of dimethylolpropionic acid (DMPA), and 0.02 parts of catalyst DBTDL were added. The reaction was carried out at 80°C until the isocyanate group (-NCO) content reached the theoretical value. The temperature was then lowered to 40°C, and 1.5 parts of triethylamine were added to neutralize the carboxyl groups. Under high-speed shearing at 8000 rpm, 60 parts of deionized water were added to obtain an aqueous polyurethane (WPU) dispersion. 1 part of chain extender 1,4-butanediol was added, and the reaction was carried out at 45°C for 30 minutes. 10 parts of methyl methacrylate (MMA), 12 parts of butyl acrylate (BA), and 0.2 parts of potassium persulfate (KPS) were added, and the temperature was raised to 70°C and reacted for 5 hours. The mixture was then cooled to room temperature and filtered to obtain a composite resin emulsion.

[0056] Under low-speed stirring at 350 rpm, 20 parts of bishell microspheres, 18 parts of deionized water, 1 part of wetting and dispersing agent (BYK-190), 0.5 parts of defoamer (TEgO 810), and 0.5 parts of leveling agent (BYK-333) were pre-dispersed for 20 minutes. Then, 55 parts of composite resin emulsion were slowly added, the speed was increased to 600 rpm, and the mixture was dispersed for 15 minutes to obtain the finished coating.

[0057] The double-shelled microspheres were prepared in Preparation Example 1.

[0058] Example 2

[0059] Under dry nitrogen protection, 5.0 parts of 2-amino-4-hydroxy-6-methylpyrimidine were dissolved in 60 parts of anhydrous tetrahydrofuran (THF), and cooled to 5°C in an ice bath. A mixture of 10 parts of isophorone diisocyanate (IPDI) and 0.05 parts of the catalyst dibutyltin dilaurate (DBTDL) was slowly added dropwise, with the temperature controlled below 10°C throughout. After the addition was complete, the reaction was carried out at room temperature for 18 hours. Then, the mixture was transferred to 350 parts of pre-cooled diethyl ether (-20°C) to precipitate, filtered, and the UPy-NCO intermediate was obtained. This intermediate was dissolved in 40 parts of anhydrous THF, and 0.5 parts of deionized water were slowly added dropwise in an ice bath. The temperature was then raised to 40°C and the reaction was carried out for 6 hours. The reaction was quenched with 2 parts of methanol, and the mixture was then transferred to 320 parts of pre-cooled diethyl ether (-20°C) to precipitate, filtered, and dried under vacuum at 40°C to obtain a pale yellow powdery UPy chain extender.

[0060] In a dry reactor, 25 parts of polybutylene adipate (PBA, Mn=1000), 10 parts of IPDI, 3 parts of dimethylolpropionic acid (DMPA), and 0.04 parts of catalyst DBTDL were added. The reaction was carried out at 80°C until the isocyanate group (-NCO) content reached the theoretical value. The temperature was then lowered to 40°C, and 2.0 parts of triethylamine were added to neutralize the carboxyl groups. Under high-speed shearing at 8000 rpm, 75 parts of deionized water were added to obtain an aqueous polyurethane (WPU) dispersion. 2.5 parts of UPy chain extender were added, and the reaction was carried out at 45°C for 30 minutes. 15 parts of methyl methacrylate (MMA), 6 parts of butyl acrylate (BA), and 0.3 parts of potassium persulfate (KPS) were added, and the temperature was raised to 75°C and reacted for 5 hours. The mixture was then cooled to room temperature and filtered to obtain a composite resin emulsion.

[0061] Under low stirring at 400 rpm, 26 parts of bishell microspheres and 2 parts of tungsten bronze nanoparticles (Cs) were mixed. 0.33 WO3 (CAS No. 189619-69-0), 24 parts deionized water, 1.5 parts wetting and dispersing agent (BYK-190), 0.6 parts defoamer (TEgO 810), and 0.6 parts leveling agent (BYK-333) were pre-dispersed for 20 minutes. Then, 70 parts of composite resin emulsion were slowly added, the rotation speed was increased to 650 rpm, and the mixture was dispersed for 25 minutes to obtain the finished coating.

[0062] The double-shelled microspheres were prepared in Preparation Example 2.

[0063] Example 3

[0064] Under dry nitrogen protection, 6 parts of 2-amino-4-hydroxy-6-methylpyrimidine were dissolved in 62 parts of anhydrous tetrahydrofuran (THF), and cooled to 2°C in an ice bath. A mixture of 12 parts of isophorone diisocyanate (IPDI) and 0.08 parts of the catalyst dibutyltin dilaurate (DBTDL) was slowly added dropwise, with the temperature controlled below 10°C throughout. After the addition was complete, the reaction was carried out at room temperature for 18 hours. The mixture was then transferred to 500 parts of pre-cooled diethyl ether (-20°C) to precipitate, filtered, and the UPy-NCO intermediate was obtained. This intermediate was dissolved in 45 parts of anhydrous THF, and 0.6 parts of deionized water were slowly added dropwise in an ice bath. The temperature was then raised to 40°C and the reaction was carried out for 6 hours. The reaction was quenched with 2.5 parts of methanol, and the mixture was then transferred to 400 parts of pre-cooled diethyl ether (-20°C) to precipitate, filtered, and dried under vacuum at 40°C to obtain a pale yellow powdery UPy chain extender.

[0065] In a dry reactor, 22 parts of polybutylene adipate (PBA, Mn=1000), 9 parts of IPDI, 2 parts of dimethylolpropionic acid (DMPA), and 0.03 parts of catalyst DBTDL were added. The reaction was carried out at 80°C until the isocyanate group (-NCO) content reached the theoretical value. The temperature was then lowered to 40°C, and 1.5 parts of triethylamine were added to neutralize the carboxyl groups. Under high-speed shearing at 8000 rpm, 65 parts of deionized water were added to obtain an aqueous polyurethane (WPU) dispersion. 2.0 parts of UPy chain extender were added, and the reaction was carried out at 45°C for 30 minutes. 12 parts of methyl methacrylate (MMA), 10 parts of butyl acrylate (BA), and 0.3 parts of potassium persulfate (KPS) were added, and the temperature was raised to 72°C and reacted for 4.5 hours. The mixture was then cooled to room temperature and filtered to obtain a composite resin emulsion.

[0066] Under low stirring at 350 rpm, 22 parts of bishelled microspheres and 1.8 parts of tungsten bronze nanoparticles (Cs) were mixed. 0.33 WO3 (CAS No. 189619-69-0), 20 parts deionized water, 1.2 parts wetting and dispersing agent (BYK-190), 0.6 parts defoamer (TEgO 810), and 0.6 parts leveling agent (BYK-333) were pre-dispersed for 20 minutes. Then, 65 parts of composite resin emulsion were slowly added, the rotation speed was increased to 600 rpm, and the mixture was dispersed for 25 minutes to obtain the finished coating.

[0067] The double-shelled microspheres were prepared in Preparation Example 3.

[0068] Example 4

[0069] Under dry nitrogen protection, 5.5 parts of 2-amino-4-hydroxy-6-methylpyrimidine were dissolved in 60 parts of anhydrous tetrahydrofuran (THF), and cooled to 1°C in an ice bath. A mixture of 12 parts of isophorone diisocyanate (IPDI) and 0.06 parts of the catalyst dibutyltin dilaurate (DBTDL) was slowly added dropwise, with the temperature controlled below 10°C throughout. After the addition was complete, the reaction was carried out at room temperature for 18 hours. The mixture was then transferred to 500 parts of pre-cooled diethyl ether (-20°C) to precipitate, filtered, and the UPy-NCO intermediate was obtained. This intermediate was dissolved in 45 parts of anhydrous THF, and 0.6 parts of deionized water were slowly added dropwise in an ice bath. The temperature was then raised to 40°C and the reaction was carried out for 6 hours. The reaction was quenched with 2.5 parts of methanol, and the mixture was then transferred to 400 parts of pre-cooled diethyl ether (-20°C) to precipitate, filtered, and dried under vacuum at 40°C to obtain a pale yellow powdery UPy chain extender.

[0070] In a dry reactor, 23 parts of polybutylene adipate (PBA, Mn=1000), 9 parts of IPDI, 3 parts of dimethylolpropionic acid (DMPA), and 0.03 parts of catalyst DBTDL were added. The reaction was carried out at 80°C until the isocyanate group (-NCO) content reached the theoretical value. The temperature was then lowered to 40°C, and 1.6 parts of triethylamine were added to neutralize the carboxyl groups. Under high-speed shearing at 8000 rpm, 65 parts of deionized water were added to obtain an aqueous polyurethane (WPU) dispersion. 2.0 parts of UPy chain extender were added, and the reaction was carried out at 45°C for 30 minutes. 12 parts of methyl methacrylate (MMA), 11 parts of butyl acrylate (BA), and 0.3 parts of potassium persulfate (KPS) were added, and the temperature was raised to 72°C and reacted for 4.5 hours. The mixture was then cooled to room temperature and filtered to obtain a composite resin emulsion.

[0071] Under low stirring at 350 rpm, 24 parts of bishelled microspheres and 1.8 parts of tungsten bronze nanoparticles (Cs) were mixed. 0.33 The mixture of WO3 (CAS No. 189619-69-0), 20 parts deionized water, 1.2 parts wetting and dispersing agent (BYK-190), 0.5 parts defoamer (TEgO 810), and 0.6 parts leveling agent (BYK-333) was pre-dispersed for 20 minutes. Then, 65 parts of composite resin emulsion were slowly added, the rotation speed was increased to 600 rpm, and the mixture was dispersed for 25 minutes to obtain the finished coating.

[0072] The double-shelled microspheres were prepared in Preparation Example 3.

[0073] Example 5

[0074] Under dry nitrogen protection, 5.5 parts of 2-amino-4-hydroxy-6-methylpyrimidine were dissolved in 60 parts of anhydrous tetrahydrofuran (THF), and cooled to 1°C in an ice bath. A mixture of 11 parts of isophorone diisocyanate (IPDI) and 0.05 parts of the catalyst dibutyltin dilaurate (DBTDL) was slowly added dropwise, with the temperature controlled below 10°C throughout. After the addition was complete, the reaction was carried out at room temperature for 18 hours. The mixture was then transferred to 500 parts of pre-cooled diethyl ether (-20°C) to precipitate, filtered, and the UPy-NCO intermediate was obtained. This intermediate was dissolved in 45 parts of anhydrous THF, and 0.6 parts of deionized water were slowly added dropwise in an ice bath. The temperature was then raised to 40°C and the reaction was carried out for 6 hours. The reaction was quenched with 2.5 parts of methanol, and the mixture was then transferred to 400 parts of pre-cooled diethyl ether (-20°C) to precipitate, filtered, and dried under vacuum at 40°C to obtain a pale yellow powdery UPy chain extender.

[0075] In a dry reactor, 22 parts of polybutylene adipate (PBA, Mn=1000), 9 parts of IPDI, 3 parts of dimethylolpropionic acid (DMPA), and 0.03 parts of catalyst DBTDL were added. The reaction was carried out at 80°C until the isocyanate group (-NCO) content reached the theoretical value. The temperature was then lowered to 40°C, and 1.6 parts of triethylamine were added to neutralize the carboxyl groups. Under high-speed shearing at 8000 rpm, 65 parts of deionized water were added to obtain an aqueous polyurethane (WPU) dispersion. 2.0 parts of UPy chain extender were added, and the reaction was carried out at 45°C for 30 minutes. 11 parts of methyl methacrylate (MMA), 11 parts of butyl acrylate (BA), and 0.2 parts of potassium persulfate (KPS) were added, and the temperature was raised to 72°C and reacted for 4.5 hours. The mixture was then cooled to room temperature and filtered to obtain a composite resin emulsion.

[0076] Under low stirring at 350 rpm, 22 parts of bishelled microspheres and 1.6 parts of tungsten bronze nanoparticles (Cs) were mixed. 0.33 WO3 (CAS No. 189619-69-0), 20 parts deionized water, 1.2 parts wetting and dispersing agent (BYK-190), 0.5 parts defoamer (TEgO 810), and 0.5 parts leveling agent (BYK-333) were pre-dispersed for 20 minutes. Then, 64 parts of composite resin emulsion were slowly added, the rotation speed was increased to 600 rpm, and the mixture was dispersed for 25 minutes to obtain the finished coating.

[0077] The double-shelled microspheres were prepared in Preparation Example 3.

[0078] The present invention also includes the following comparative examples.

[0079] Comparative Example 1

[0080] Compared with Example 4, the only difference is that double-shelled microspheres were not prepared. Instead, a mixture of silica nanoparticles and titanium dioxide nanoparticles in a 1:1 mass ratio was used to replace an equal amount of double-shelled microspheres. All other preparation steps and materials were the same, resulting in the finished coating.

[0081] Comparative Example 2

[0082] Compared with Example 4, the only difference is that no titanium dioxide shell was deposited. All other preparation steps are the same. After obtaining the SiO2 phase change microcapsules, the subsequent washing and drying steps are carried out directly to obtain silica microspheres, which are used instead of double-shell microspheres for subsequent preparation steps to obtain the finished coating.

[0083] Comparative Example 3

[0084] Compared with Example 4, the only difference is that acetylacetone was not added to the aqueous phase B. All other preparation steps and materials are the same, resulting in the finished coating.

[0085] Performance testing

[0086] Cement mortar substrates with dimensions of 200mm×200mm×5mm were prepared and coated with the coatings obtained in Examples 1-5 and Comparative Examples 1-3, respectively. The dry film thickness was controlled at 1.0±0.1mm. The substrates were cured for 7 days. Uncoated cement mortar substrates were set up as blank substrate control samples. Then, the following tests were conducted on thermal insulation performance, optical performance and self-healing performance.

[0087] (I) Thermal Insulation Performance Test: The thermal insulation performance test was conducted in accordance with standard GB / T 25261-2018 "Reflective Thermal Insulation Coatings for Buildings". Simulated sunlight was used, with the coated surface of each substrate facing a 500W / m² direction. 2 A full-spectrum xenon lamp light source was used at a fixed distance for 90 minutes of continuous irradiation. The temperature at the center point on the back of the substrate was monitored and recorded using thermocouples. The summarized data results are shown in Table 1 below.

[0088] (II) Optical Performance Testing: The solar reflectance optical performance was tested in accordance with the standard GB / T 25261-2018 "Architectural Reflective Thermal Insulation Coatings". An ultraviolet-visible-near-infrared spectrophotometer equipped with an integrating sphere was used. Each coating sample was placed at the test port, and the reflectance of the coating in the 300-2500 nm solar spectrum range was measured. The solar reflectance (TSR) was calculated by weighted averaging according to the solar radiation spectral energy distribution. The test results are summarized in Table 1.

[0089] (III) Self-healing performance test: The industry-standard scratch repair rate method was adopted. A regular scratch of approximately 30 mm in length and 20 μm in width was made on the coating surface using a sharp blade, and its initial width W0 was measured. Then, the cement mortar substrate being tested was placed under simulated sunlight of 0.8 kW / m 2 Under photothermal triggering conditions for 4 hours, samples were taken, and the scratch morphology was observed and the residual scratch width W was measured under a super depth-of-field microscope. t Then calculate the repair rate (%) = (W0 - W tThe experimental results are summarized as follows: ) / W0×100%, and the results are shown in Table 1 below.

[0090] (iv) Thermal conductivity test: The thermal conductivity was tested according to standard GB / T 10294-2008 "Determination of steady-state thermal resistance and related properties of thermal insulation materials - protective hot plate method". The coatings obtained in Examples 1-5 and Comparative Examples 1-3 were coated onto flat thin plates, dried, and then peeled off to prepare solid homogeneous coating thin plate samples with uniform thickness, flat surface, and a size of 300mm×300mm. The thickness was measured at multiple points and the average thickness d was recorded. A protective hot plate thermal conductivity meter was used, with the hot plate temperature set at 35℃ and the cold plate temperature at 15℃. The temperature difference ΔT=20K was recorded. After the system heat flow stabilized, the steady-state heat flow rate Q was recorded. The effective heat transfer area of ​​the coating thin plate sample perpendicular to the heat flow direction, i.e., the area A of the central measuring area of ​​the hot plate of the thermal conductivity meter, was measured and recorded. The thermal conductivity λ value of the coating was calculated according to the formula λ=Q×d / (A×ΔT), with the unit being W / (m·K). The summarized data results are shown in Table 1.

[0091] Table 1

[0092] The data in the table above clearly show that after 90 minutes of irradiation, the back temperature of the uncoated blank substrate reached 53.5℃, while the back temperature of the substrate coated with the heat-insulating coatings obtained in Examples 1-5 of this invention was below 40℃. Furthermore, the thermal conductivity λ of the coatings obtained in these examples is all below 0.041, indicating a strong ability to block heat conduction. This effectively blocks heat in hot weather and prevents excessive heat loss in cold weather. Therefore, the coatings obtained in these examples have excellent heat preservation, insulation, and heat buffering effects, achieving superior heat insulation performance. Moreover, the solar reflectance (TSR) of the coatings obtained in these examples can reach between 0.881 and 0.892, demonstrating strong reflectivity and the ability to effectively block heat under strong irradiation.

[0093] The data obtained from the coating in Comparative Example 1 showed that the substrate back temperature was still as high as 48.5℃. Although this was lower than the back temperature of the blank substrate, indicating a certain heat insulation effect, it was far inferior to the substrate back temperature of Example 4, which was only 38.6℃. This shows that the double-shell microspheres containing phase change materials can effectively insulate and buffer heat. Furthermore, Comparative Example 1 had a high thermal conductivity and a weak ability to block heat conduction, resulting in poor overall heat insulation performance. Although the substrate back temperature and thermal conductivity of Comparative Example 2 were much better than those of Comparative Example 1, they were still significantly lower than those of Example 4. This indicates that even if SiO2 phase change microcapsules were prepared, the lack of a double-shell structure of silicon dioxide and titanium dioxide significantly reduced the heat insulation and heat preservation effect. Compared to Example 4, Comparative Example 3 showed an increase in substrate back temperature and a decrease in thermal conductivity. This was mainly due to the lack of acetylacetone, which prevented the pre-chelation of tetrabutyl titanate, leading to severe hydrolysis and the instantaneous generation of a large amount of titanium dioxide precipitate. Instead of controllable deposition at the microsphere interface, a mixture of SiO2 phase change microcapsules and titanium dioxide particles was formed, failing to form a complete titanium dioxide shell and thus affecting the thermal insulation performance. Furthermore, the coatings obtained in Comparative Examples 1-3 also had relatively low solar reflectance (TSR).

[0094] Furthermore, the coatings obtained in Examples 2-5 and Comparative Examples 1-3 of this invention all exhibited a high repair rate for cracks under 4 hours of light exposure, while Example 1, lacking UPy chain extender, did not possess self-healing properties.

[0095] In summary, the coatings obtained in the embodiments of the present invention all have excellent thermal insulation properties, and by adding UPy chain extender to prepare composite resin emulsions as needed, coatings with self-healing properties can be obtained.

[0096] The above are preferred embodiments of the present invention. For those skilled in the art, any improvements and modifications made without departing from the principle of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a heat-insulating coating, characterized in that: The preparation steps include the following: S1. Under heating and high-speed shearing, aqueous phase A is dropped into oil phase A, emulsified, transferred to a water bath, stirred and reacted, cooled, separated, dispersed in aqueous phase B, added to oil phase B under heating and high-speed shearing, heated and stirred and reacted, demulsifier was added to demulsify, centrifuged, washed, dried, and obtained bishell microspheres. S2. Add PBA, IPDI, DMPA and catalyst to react, cool down, add triethylamine, add deionized water under high-speed shear to obtain an aqueous polyurethane dispersion, add chain extender to react, then add MMA, BA and KPS, heat up to react, cool, filter to obtain a composite resin emulsion. S3. Pre-disperse the double-shell microspheres, deionized water and additives, add the composite resin emulsion, stir and disperse to obtain the finished coating; The aqueous phase A is obtained by mixing deionized water, tetraethyl orthosilicate, and ammonia; the oil phase A is obtained by mixing phase change material with Span-80 and heating to melt; the aqueous phase B is obtained by mixing deionized water, tetrabutyl titanate, and acetylacetone, and adding acetic acid to adjust the mixture; the oil phase B is obtained by mixing paraffin wax with Span-80. The chain extender is an UPy chain extender, and it is prepared by the following method: 2-amino-4-hydroxy-6-methylpyrimidine is dissolved in anhydrous tetrahydrofuran, excess IPDI and catalyst are added dropwise, after reaction, the mixture is transferred to pre-cooled diethyl ether to precipitate, filtered, dissolved again in anhydrous tetrahydrofuran, a small amount of deionized water is added dropwise, the reaction is heated, quenched, and then transferred to pre-cooled diethyl ether to precipitate, filtered and dried to obtain the final product.

2. The method for preparing a heat-insulating coating according to claim 1, characterized in that: In step S3, tungsten bronze nanopowder, double-shell microspheres, deionized water, and additives are added for pre-dispersion.

3. The method for preparing a heat-insulating coating according to claim 2, characterized in that: In the preparation of the UPy chain extender, 2-amino-4-hydroxy-6-methylpyrimidine is dissolved in anhydrous tetrahydrofuran under a dry nitrogen atmosphere and cooled to 0-5°C in an ice bath. An excess mixture of IPDI and catalyst is slowly added dropwise while controlling the temperature to <10°C. The mixture is then reacted at room temperature for 18 hours. The product is transferred to pre-cooled diethyl ether to precipitate, filtered, and the intermediate is obtained. This intermediate is dissolved in anhydrous tetrahydrofuran, and a small amount of deionized water is added dropwise under an ice bath. The temperature is raised to 40°C and reacted for 6 hours. Methanol is added to quench the reaction, and the product is then transferred to pre-cooled diethyl ether to precipitate, filtered, and dried under vacuum at 40°C to obtain the final product.

4. The method for preparing a heat-insulating coating according to claim 1, characterized in that: The ammonia concentration in aqueous phase A is 28 wt%; the oil phase A is made by mixing a phase change material with Span-80 and heating it to 60°C to melt; the phase change material is paraffin or dodecanol, and the phase change temperature is 23-25°C; 1.0-1.4 parts by mass of hexadecyltrimethylammonium bromide are added to aqueous phase B, and it is mixed with deionized water, tetrabutyl titanate and acetylacetone, and the pH is adjusted to 3-4 with acetic acid. At the same time, in step S1, a demulsifier is added to demulsify, and after centrifugation, Soxhlet extraction is performed for 24 hours using an ethanol solution containing 1 wt% hydrochloric acid during the washing process.

5. The method for preparing a heat-insulating coating according to claim 1, characterized in that: In step S1, aqueous phase A is dropped into oil phase A under heating at 60-62℃ and high-speed shearing at 9000-10000 rpm, emulsified for 5-6 minutes to form a primary emulsion, transferred to a water bath at 48-53℃, and stirred at 300-350 rpm for 4-4.5 hours. After cooling to room temperature, it is centrifuged, washed with ethanol, and dispersed in aqueous phase B. Under shearing at 45-48℃ and 7500-8500 rpm, it is added to oil phase B to form a double emulsion, transferred to a water bath at 45-50℃, and stirred slowly at 200 rpm for 12-15 hours. A demulsifier is added to demulsify, the product is collected by centrifugation, washed three times alternately with ethanol and acetone, and dried under vacuum at 40℃ to obtain bi-shell microspheres.

6. The method for preparing a heat-insulating coating according to claim 1, characterized in that: In step S2, PBA (Mn=1000), IPDI, dimethylolpropionic acid, and a catalyst are added to a dry reactor and reacted at 80°C. The temperature is then lowered to 40°C, and triethylamine is added for neutralization. Deionized water is added under high-speed shear at 8000 rpm to obtain an aqueous polyurethane dispersion. A chain extender is added, and the reaction is carried out at 45°C for 30 minutes. MMA, BA, and KPS are added, and the temperature is raised to 70-75°C for 4-5 hours. The mixture is then cooled to room temperature and filtered to obtain a composite resin emulsion.

7. The method for preparing a heat-insulating coating according to claim 1, characterized in that: In step S3, the double-shell microspheres, deionized water and additives are pre-dispersed for 20 minutes under low-speed stirring at 350-400 rpm. Then, the composite resin emulsion is added, the speed is increased to 600-650 rpm, and the mixture is dispersed for 15-25 minutes to obtain the finished coating.

8. The method for preparing a heat-insulating coating according to claim 1, characterized in that: The catalyst is DBTDL; the demulsifier is acetone; the additives include wetting and dispersing agent BYK-190, defoamer TEgO 810 and leveling agent BYK-333.

9. A heat-insulating coating, characterized in that: The heat-insulating coating is prepared by the method described in any one of claims 1-8, comprising the following components in parts by weight: 20-26 parts of double-shell microspheres, 18-24 parts of deionized water, 2-2.7 parts of additives and 55-70 parts of composite resin emulsion. The bishell microspheres comprise the following raw materials in parts by weight: 130-170 parts deionized water, 5-6.5 parts tetraethyl orthosilicate, 0.5-0.7 parts 28wt% ammonia, 10-15 parts phase change material, 2.3-2.9 parts Span-80, 3-4 parts tetrabutyl titanate, 1.5-2 parts acetylacetone, and 200-250 parts liquid paraffin; The composite resin emulsion comprises the following raw materials in parts by weight: 20-25 parts PBA, 8-10 parts IPDI, 2-3 parts DMPA, 0.02-0.04 parts catalyst, 1.5-2.0 parts triethylamine, 60-75 parts deionized water, 1-2.5 parts chain extender, 10-15 parts MMA, 6-12 parts BA and 0.2-0.3 parts KPS.

10. The heat-insulating coating according to claim 9, characterized in that: It also includes 1.5-2 parts of tungsten bronze nanoparticles; the chain extender is UPy chain extender, comprising the following raw materials in parts by weight: 5.0-6.5 parts of 2-amino-4-hydroxy-6-methylpyrimidine, 60-65 parts of anhydrous tetrahydrofuran, 10-13 parts of isophorone diisocyanate, 0.05-0.1 parts of catalyst, 40-50 parts of anhydrous tetrahydrofuran, 0.5-0.6 parts of deionized water and 2-2.5 parts of methanol; The bishell microspheres also include 0.1-1.4 parts of hexadecyltrimethylammonium bromide; The additives include 1-1.5 parts of wetting and dispersing agent BYK-190, 0.5-0.6 parts of defoamer TEgO 810, and 0.5-0.6 parts of leveling agent BYK-333.

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