Radiation cooling paint, coating, preparation method and application

Abstract

The invention discloses a radiation cooling coating, a coating, a preparation method and application, and the coating comprises the following components in parts by mass: 8-15 parts of P (VDF-HFP) resin; 3-5 parts of first fluorocarbon resin; 0.3 to 0.5 part of a curing agent; 85-92 parts of a first solvent; 7 to 13 parts of a non-solvent; wherein the first solvent comprises at least three small molecule compound solutions with different boiling points; the absolute value of the boiling point difference between any different small molecule compound solutions is greater than or equal to 20 DEG C and less than or equal to 180 DEG C. The volatilization speeds of different small molecule compounds in the first solvent are different, so that a multi-stage pore structure can be constructed through volatilization induced phase separation at different time nodes, the coating has sufficient time to permeate and wet a bottom layer base material, the mechanical embedding effect between two layers is improved, the adhesive force is improved, and the service life of the coating is prolonged. And the adhesion effect of the coating on the base material is indirectly improved.

Description

Technical Field

[0001] This application belongs to the field of coating technology, specifically relating to a radiation cooling coating, coating method and application. Background Technology

[0002] Passive radiation cooling (PRC) is a technology that effectively mitigates the greenhouse effect and urban heat island effect by reflecting sunlight and releasing heat into space through atmospheric windows. Polyvinylidene fluoride-hexafluoroethylene copolymer (P(VDF-HFP)) can be used as a radiation cooling material due to its unique molecular structure and tunable physical morphology. However, even though P(VDF-HFP) possesses excellent film-forming properties, mechanical properties, chemical stability, and weather resistance, its poor adhesion to the substrate limits its application in coatings. Acetone is a good solvent for P(VDF-HFP) and has a relatively fast evaporation rate, making it a preferred solvent for evaporation-induced phase separation methods. However, excessively rapid evaporation of acetone can generate significant shrinkage stress within the coating, easily leading to the coating detaching from the substrate surface. Summary of the Invention

[0003] Purpose of the invention: This application provides a radiation cooling coating, a coating layer and a preparation method, while solving the problem of poor adhesion between P(VDF-HFP) and the substrate when used as a coating.

[0004] In some embodiments, a radiation cooling coating, by parts by weight, comprises: 8-15 parts of P(VDF-HFP) resin; 3-5 parts of the first fluorocarbon resin; 0.3 to 0.5 parts of curing agent; 85-92 parts of the first solvent; 7-13 parts of non-solvent; The first solvent is used to mix with the P(VDF-HFP) resin to form a P(VDF-HFP) resin solution; wherein the first solvent comprises at least three small molecule compound solutions with different boiling points; the absolute value of the boiling point difference between any two different small molecule compound solutions is greater than or equal to 20°C and less than or equal to 180°C.

[0005] In some embodiments, the first solvent comprises a first compound solution, a second compound solution, and a third compound solution; wherein the boiling point of the first compound solution is T1°C, the boiling point of the second compound solution is T2°C, and the boiling point of the third compound solution is T3°C, and the mixed solvent further satisfies at least one of the following characteristics: a) T1 < T2 < T3; b) 39℃≤T1≤66℃; c) 70℃≤T2≤120℃; d) 130℃≤T3≤210℃.

[0006] In some embodiments, the mass ratio of the first compound solution, the second compound solution, and the third compound solution is 3~6 : 2~5 : 2.

[0007] In some embodiments, the first compound is selected from at least one of acetone, tetrahydrofuran, and dichloromethane; and / or The second compound is selected from at least one of butanone, methyl isobutyl ketone, sec-butyl acetate, and 1-methoxy-2-propanol; and / or The third compound is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, γ-butyrolactone, and dimethylcyclohexylamine.

[0008] In some embodiments, the number average molecular weight of the first fluorocarbon resin is 5000-50000; the solid content of the first fluorocarbon resin is 50-55%. The number-average molecular weight of the P(VDF-HFP) resin is 50,000 to 300,000. The curing agent is selected from any one of hexamethylene diisocyanate, isophorone diisocyanate, naphthalene diisocyanate, toluene diisocyanate, and diphenylmethane diisocyanate; The non-solvent is selected from deionized water.

[0009] In some embodiments, a method for preparing a radiation cooling coating is also provided, comprising the following steps: Take the corresponding mass parts of P(VDF-HFP) resin, non-solvent and first solvent and mix them. Stir until P(VDF-HFP) resin is fully dissolved to obtain P(VDF-HFP) resin solution. Take the corresponding mass parts of the first fluorocarbon resin and the curing agent, mix them, and add them dropwise to the P(VDF-HFP) resin solution. Stop adding the mixture as soon as the mixed solution changes from clear and transparent to turbid. Continue stirring until the whole solution is homogeneous and stable to obtain the radiation cooling coating. The first solvent is composed of a first compound solution, a second compound solution, and a third compound solution.

[0010] In some embodiments, a radiation cooling coating is also provided, comprising a substrate and a first coating disposed on the substrate; wherein the first coating comprises the radiation cooling paint, or the first coating is obtained by coating the radiation cooling paint prepared by the method onto the surface of the substrate.

[0011] In some embodiments, the radiation cooling coating further includes a second coating located between the first coating and the substrate and connected to both the first coating and the substrate; wherein the second coating is composed of a second fluorocarbon resin, the second fluorocarbon resin having a solid content of 30-55%, a number-average molecular weight of 5000-50000, and a fluorine content greater than 20%. In some embodiments, the first coating has a plurality of pores, which are formed by the evaporation of a first compound solution, a second compound solution, and a third compound solution in the first solvent; Wherein, the pore size of the pores formed after the first compound solution evaporates is 150~400 nm; The pore size formed after the second compound solution evaporates is 400~1100 nm; The pore size formed after the third compound solution evaporates is 1100~2500 nm.

[0012] In some embodiments, the application of the radiation cooling coating to building, wire and cable, and automotive / ship surfaces is also provided.

[0013] Beneficial Effects: Compared with existing technologies, the radiation cooling coating provided in this application improves upon the drawback of rapid evaporation of a single solvent component leading to film defects by including at least three small molecule compound solutions with different boiling points in the first solvent. When the absolute value of the boiling point difference between any two different small molecule compound solutions is greater than or equal to 20°C and less than or equal to 180°C, the different small molecule compounds in the first solvent evaporate at different rates. This allows for the construction of a multi-level porous structure through evaporation-induced phase separation at different time points. This provides the coating with sufficient time to penetrate and wet the underlying substrate, enhancing the mechanical interlocking between the two layers and improving adhesion, thereby indirectly improving the coating's adhesion to the substrate. The coating's pot life is significantly extended, maintaining stable quality during long-term application, and the resulting film has a smoother and defect-free appearance.

[0014] The radiative cooling coating provided in this application also includes a second coating composed of a second fluorocarbon resin, which compensates for the potential lack of adhesion in the first coating. The first solvent in the first coating and the solvent of the first fluorocarbon resin can fully redissolve the second fluorocarbon resin in the second coating, promoting the untangling of polymer molecular chains between the two coatings and enhancing the bonding force between them. Finally, the compatibility between the first fluorocarbon resin in the first coating and the second coating is further improved. Simultaneously, the resulting coating exhibits a hierarchical porous structure due to the gradient evaporation of the first solvent; the pore structure with different pore sizes can almost completely cover the entire solar radiation band, thus improving the coating's reflectivity. Furthermore, the second fluorocarbon resin in the second coating reinforces the emissivity of the first coating; the two work synergistically to further enhance the coating's outdoor radiative cooling capability. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Figure 1 This is a schematic diagram of the structure of the radiation cooling coating provided in this embodiment; Figure 2 A digital photograph of the coating applied to an aluminum substrate (7.5 cm * 15 cm * 0.1 cm) provided in this embodiment; Figure 3 This is a schematic diagram illustrating the adhesion effect of the first coating applied to the bottom substrate under different conditions provided in this embodiment; Figure 4 The solar reflectance (a) and emissivity (b) curves of the radiation cooling coating provided in this embodiment; Figure 5 The flowchart for the preparation of the radiation cooling coating and the cooling mechanism diagram provided in this embodiment; Figure 6 Fourier transform infrared (FTIR) curves of P(VDF-HFP) resin and fluorocarbon resin provided in this embodiment; Figure 7 This is a schematic diagram of holes with different diameters formed in the first coating provided in this embodiment; Reference numerals in the attached figures: 101 - first coating, 102 - second coating, 103 - substrate, 104 - hole. Detailed Implementation

[0016] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0017] In the description of this application, it should be understood that the terms "upper," "lower," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. In the description of this application, "a plurality of" means two or more, and "at least one" can mean one, two, or more, unless otherwise expressly specified.

[0018] The applicant discovered that passive radiative cooling (PRC), as a zero-energy, zero-carbon cooling technology, significantly reduces the use of compression cooling systems (such as air conditioning) by reflecting sunlight (0.28-2.5 μm) and emitting heat into space through atmospheric transparent windows (8-13 μm), thereby mitigating the greenhouse effect and urban heat island effect. P(VDF-HFP), as a promising candidate in the field of radiative cooling materials, derives its advantages not from a single property, but from the perfect combination of its unique molecular structure and tunable physical form.

[0019] However, it is rarely used in the coating field. Even though P(VDF-HFP) has excellent film-forming properties, mechanical properties, chemical stability, and weather resistance, its poor adhesion to the substrate limits its application in coatings. Acetone, as a good solvent for P(VDF-HFP) and with a relatively fast evaporation rate, is often used as the preferred solvent in evaporation-induced phase separation. However, the rapid evaporation of acetone causes huge shrinkage forces within the coating, leading to the coating peeling off from the substrate.

[0020] Therefore, based on the above problems, a new system needs to be developed that can improve the adhesion of P(VDF-HFP) to the substrate while constructing a porous structure, so that it can be used as a radiation cooling coating for applications such as outdoor buildings, wire and cable, and automobiles and ships.

[0021] This embodiment provides a radiation cooling coating, comprising, by weight: 8-15 parts of P(VDF-HFP) resin; 3-5 parts of a first fluorocarbon resin; 0.3-0.5 parts of a curing agent; 85-92 parts of a first solvent; and 7-13 parts of a non-solvent. The first solvent is used to mix with the P(VDF-HFP) resin to form a P(VDF-HFP) resin solution. The first solvent comprises at least three small molecule compound solutions with different boiling points. The absolute value of the boiling point difference between any two different small molecule compound solutions is greater than or equal to 20°C and less than or equal to 180°C.

[0022] Understandably, the P(VDF-HFP) resin has excellent film-forming properties, providing the main framework for the first coating and supporting the porous structure formed by subsequent phase separation; the first fluorocarbon resin has very low surface energy and can improve the leveling properties of the coating itself. In a multi-solvent system, it can undergo certain surface migration with the gradient evaporation of the solvent, further optimizing the surface properties of the coating and reducing defects; the isocyanate curing agent can further react with the fluorocarbon resin to form a cross-linked network structure, thereby enhancing the mechanical strength of the first coating; the use of a mixture of good solvents with significant differences in boiling point as the first solvent creates a solvent environment that changes dynamically and non-linearly over time. This allows the components within the solvent system to undergo dynamic recombination first, and then synergize with non-solvents to induce a more complex phase separation structure. Furthermore, as the low surface tension solvent evaporates rapidly, the solution containing medium and high boiling point solvents can still maintain a certain degree of fluidity, which can "repair" the local unevenness that may be caused by rapid evaporation and allow the polymer solution and the substrate to have more sufficient contact and interaction time. When the boiling point difference is ≥20℃, it ensures that different solvent components have a clear order of evaporation. When the boiling point difference is ≤180℃, it can prevent the boiling point difference from being too large, which would result in the earliest evaporating solvent having almost no residue in the later stages. This ensures that multiple solvent components coexist and their proportions change continuously throughout the evaporation process, forming a multi-stage solubility inflection point, while also preventing the coating with an excessively high boiling point from having an excessively long pot life.

[0023] In some embodiments, it is further preferred that the absolute value of the boiling point difference between any two different small molecule compound solutions is greater than or equal to 20°C and less than or equal to 160°C; more preferably, the absolute value of the boiling point difference between any two different small molecule compound solutions is greater than or equal to 20°C and less than or equal to 100°C.

[0024] In some embodiments, the first solvent consists of a first compound solution, a second compound solution, and a third compound solution. It is understood that the first compound solution evaporates rapidly first, initially shaping the coating surface, preventing sagging, and the sharp increase in the concentration of P(VDF-HFP) solution forms the earliest polymer-rich and polymer-poor phase regions, inducing initial nucleation for liquid-liquid phase separation. The second compound solution, acting as a "transition" solvent, continues to maintain a certain fluidity of the coating after the first compound solution evaporates, alleviating drying stress and causing a continuous, non-linear shift in the solubility parameter of the solution system. The phase separation process is "relayed" and accelerated, allowing the early-formed phase regions to continue growing and merging, providing a sufficient time window for phase separation. The third compound solution evaporates last, and since the non-solvent (water) in the formulation itself does not dissolve P(VDF-HFP), its relative concentration reaches its highest level in the later stages of evaporation, providing the final and strongest driving force for phase separation. This ensures that liquid-liquid phase separation is fully carried out, allowing the polymer to completely precipitate and solidify, and ultimately supporting the pore structure during the drying stage, preventing collapse and "locking."

[0025] In some embodiments, the boiling point of the first compound solution is T1℃, the boiling point of the second compound solution is T2℃, and the boiling point of the third compound solution is T3℃, with the mixed solvent further satisfying: T1 < T2 < T3. When the above range is met, it ensures a clear order of evaporation for the different solvent components. The first compound solution (e.g., acetone) evaporates first in large quantities. As it is a good solvent for P(VDF-HFP), its rapid departure causes the solution's solubility for P(VDF-HFP) to decrease significantly for the first time, thus inducing the initial nucleation of liquid-liquid phase separation (forming the earliest polymer-rich and polymer-poor phase regions). After the first compound solution evaporates, the second compound solution (e.g., butanone) begins to dominate the evaporation process. At this point, very little of the first compound solution remains, and the concentration of P(VDF-HFP) further increases. The solubility parameter of the solution system continuously and non-linearly shifts, and the phase separation process is "relayed" and accelerated, causing the early-formed phase regions to continue to grow and merge. Finally, the third compound solution (e.g., DMF) evaporates slowly. Meanwhile, the non-solvents (such as water) in the formulation do not dissolve P(VDF-HFP), and their relative concentration reaches its highest level in the later stage of volatilization, providing the final and strongest driving force for phase separation, enabling the polymer to completely precipitate and solidify, and "locking" the porous structure formed in the early stage.

[0026] In some embodiments, the mixed solvent further satisfies: 39℃ ≤ T1 ≤ 66℃. For example, the boiling point T1℃ of the first compound solution can be any one or a range between any two of the following values: 39℃, 40℃, 41℃, 42℃, 43℃, 44℃, 45℃, 46℃, 47℃, 48℃, 49℃, 50℃, 51℃, 52℃, 53℃, 54℃, 55℃, 56℃, 57℃, 58℃, 59℃, 60℃, 61℃, 62℃, 63℃, 64℃, 65℃, and 66℃. The first compound solution evaporates fastest in the first solvent, responsible for the initial rapid drying of the solvent, allowing the coating surface to initially set and preventing sagging.

[0027] In some embodiments, the mixed solvent further satisfies: 70℃ ≤ T2 ≤ 120℃. For example, the boiling point T2℃ of the second compound solution can be any one or a range between any two of the following values: 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, and 120℃. The second compound solution has a moderate evaporation rate in the first solvent, acting as a "transition" solvent. After the first compound solution evaporates, it continues to maintain a certain degree of fluidity in the coating, reducing drying stress and providing a time window for phase separation.

[0028] In some embodiments, the mixed solvent further satisfies: 130℃ ≤ T3 ≤ 210℃. For example, the boiling point T3℃ of the third compound solution can be any one or a range between any two of the following values: 130℃, 135℃, 140℃, 145℃, 150℃, 151℃, 152℃, 153℃, 154℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, 195℃, 200℃, 205℃, and 210℃. The third compound solution has the slowest evaporation in the first solvent, which maximizes the delay of non-solvent (water) intrusion throughout the evaporation process, ensuring sufficient liquid-liquid phase separation and ultimately supporting the pore structure during the drying stage to prevent collapse.

[0029] In some embodiments, the first compound is selected from at least one of acetone (boiling point 56.5°C), tetrahydrofuran (boiling point 66°C), and dichloromethane (boiling point 39.8°C).

[0030] In some embodiments, the second compound is selected from at least one of butanone (boiling point 79.6°C), methyl isobutyl ketone (116.5°C), sec-butyl acetate (boiling point 111~112°C), and 1-methoxy-2-propanol (boiling point 118.54°C).

[0031] In some embodiments, the third compound is selected from at least one of N,N-dimethylformamide (boiling point 153°C), N,N-dimethylacetamide (boiling point 116.1°C), N-methylpyrrolidone (boiling point 202°C), dimethyl sulfoxide (boiling point 189°C), and dimethylcyclohexylamine (boiling point 149~150°C).

[0032] In some embodiments, the number average molecular weight of the first fluorocarbon resin is 5000 to 50000. The solid content of the first fluorocarbon resin is 50% to 55%, and the solvent is butyl acetate. Preferably, the solid content of the first fluorocarbon resin is 55%.

[0033] In some embodiments, the number average molecular weight of the P(VDF-HFP) resin is 50,000 to 300,000.

[0034] It should be noted that the term "number-average molecular weight" refers to the statistical average of the molecular weights of all polymer molecules based on their number of molecules. The first fluorocarbon resin within the above molecular weight range exhibits relatively good compatibility with P(VDF-HFP) resin and solvents, and may exist in a near-molecular-scale dispersion within the P(VDF-HFP)-rich phase without disrupting the P(VDF-HFP) molecular framework, thus playing a role in interfacial modification. Simultaneously, due to its short chain segments and rapid movement, it quickly diffuses to the surface and bottom during phase separation, optimizing surface morphology, enhancing substrate wettability, and improving weather resistance. Within this molecular weight range, the compatibility window of P(VDF-HFP) resin with solvents / other polymers is narrower, making phase separation more likely (i.e., easier to precipitate from solution). Furthermore, the larger molecular weight polymer framework exhibits higher strength and toughness, better supporting the porous structure and preventing collapse. Moreover, phase separation facilitates the formation of larger and more irregular primary phase regions. Under the subsequent action of the first solvent and non-solvent, secondary phase separation may occur within these large phase regions, thus more easily forming a hierarchical porous structure.

[0035] In some embodiments, the curing agent is selected from any one of hexamethylene diisocyanate, isophorone diisocyanate, naphthalene diisocyanate, toluene diisocyanate, and diphenylmethane diisocyanate. The curing agent is used to undergo a cross-linking curing reaction with the fluorocarbon resin, and is preferably an isocyanate curing agent, which has polyisocyanate groups that can react with the hydroxyl groups on the side chains of the fluorocarbon resin to form a cross-linked network structure, thereby greatly enhancing the mechanical strength of the first coating.

[0036] In some embodiments, the non-solvent is selected from deionized water. The purpose of adding the non-solvent to the system is to initiate liquid-liquid phase separation. In this embodiment, the addition of non-solvent water causes the originally homogeneous and stable polymer solution to enter a thermodynamically unstable state. As the mixed solvent rapidly evaporates, the non-solvent gradually begins to disrupt the solvation between the mixed solvent and the polymer chains in the system, thereby causing liquid-liquid phase separation in the polymer system, forming two coexisting liquid phases: a polymer-rich phase and a polymer-depleted phase. The polymer-rich phase has a high polymer concentration and high viscosity, and will eventually solidify into the film framework; the polymer-depleted phase has a low polymer concentration and mainly contains both solvent and non-solvent, and will eventually form a porous structure.

[0037] In some embodiments, this embodiment provides a method for preparing a radiation cooling coating, comprising the following steps: Take the corresponding mass parts of P(VDF-HFP) resin, non-solvent and first solvent and mix them. Stir until P(VDF-HFP) resin is fully dissolved to obtain P(VDF-HFP) resin solution. Take the corresponding mass parts of the first fluorocarbon resin and the curing agent, mix them, and add them dropwise to the P(VDF-HFP) resin solution. Stop adding the mixture as soon as the mixed solution changes from clear and transparent to turbid. Continue stirring until the whole solution is homogeneous and stable to obtain the radiation cooling coating. The first solvent is composed of a first compound solution, a second compound solution, and a third compound solution.

[0038] Specifically, by mass, the specific part ranges of each component include: 8-15 parts of P(VDF-HFP) resin; 3-5 parts of the first fluorocarbon resin; 0.3-0.5 parts of curing agent; 85-92 parts of the first solvent; and 7-13 parts of non-solvent water.

[0039] In some embodiments, in the above preparation method, the first solvent is composed of a first compound solution, a second compound solution, and a third compound solution.

[0040] In some embodiments, the mass ratio of the first compound solution, the second compound solution, and the third compound solution in the first solvent is 3~6 : 2~5 : 2.

[0041] Understandably, the preparation method of this application, through a carefully designed multi-boiling-point gradient solvent system, upgrades the simple solution evaporation-phase separation process into a controlled, multi-stage thermodynamic and kinetic process. This allows for independent control of the thermodynamic threshold and kinetic rate of phase separation, forming a hierarchical porous structure combining macropores, mesopores, and micropores. The core driving force of this method is the sequential evaporation of the solvent itself, a process primarily dominated by the coating's own temperature, significantly reducing sensitivity to external environmental disturbances and resulting in excellent process stability and reproducibility. In this method, the role of "non-solvents" is weakened or becomes a later auxiliary process; the main phase separation is driven by changes in the internal solvent composition, making it easier to form a uniform coating with a continuous structure from the surface to the interior. This ensures the formation of uniform coatings with excellent adhesion on various substrates. The viscosity, rheology, and wettability of the coating produced by this method can be precisely adjusted like conventional coatings. This makes it perfectly compatible with almost all industrial coating processes, such as blade coating, spin coating, spray coating, roller coating, and even slot extrusion, without sacrificing coating performance for "phase separation" characteristics.

[0042] In some embodiments, this embodiment also provides a radiation cooling coating, see [link to relevant documentation]. Figure 1 The coating comprises a first coating 101, a second coating 102, and a substrate 103. The second coating 102 is located between and connected to both the first coating 101 and the substrate 103. The first coating 101 is formed from the aforementioned radiation cooling coating, and the second coating 102 is formed from a second fluorocarbon resin. The solid content of the second fluorocarbon resin is 30-55%, and the diluent is selected from at least one of butyl acetate, ethyl acetate, propylene glycol methyl ether acetate, and xylene. The number average molecular weight of the second fluorocarbon resin is 5000-50000, and the fluorine content is greater than 20%. It should be noted that the purpose of setting the solid content of the second fluorocarbon resin to 30-55% is to control the viscosity of the resin, ensuring that the coating surface does not develop defects or unevenness due to excessively high or low resin viscosity during the coating process.

[0043] In some embodiments, the solid content of the second fluorocarbon resin is less than the solid content of the first fluorocarbon resin.

[0044] In some embodiments, the substrate may be made of materials such as metal, ceramic, plastic, glass, rubber, or wood. Aluminum plate substrate is preferred.

[0045] In some embodiments, see further. Figure 1The first coating 101 has multiple pores 104, formed by the evaporation of a first compound solution, a second compound solution, and a third compound solution in a first solvent. The pore size formed after the evaporation of the first compound solution is 150–400 nm; the pore size formed after the evaporation of the second compound solution is 400–1100 nm; and the pore size formed after the evaporation of the third compound solution is 1100–2500 nm. See further details. Figure 7 The prepared coating contains different pores within the above-mentioned pore size range, which further proves that the volatilization of different solutions in the first solvent can form pores in the coating.

[0046] Understandably, see further. Figure 5 The radiation-cooling coating of this embodiment exhibits the synergistic benefits of a multi-level porous structure. The multi-scale pores form a hierarchical scattering network: large pores primarily scatter long wavelengths, while small pores primarily scatter short wavelengths, thus achieving efficient and broad-spectrum Mie scattering across the entire solar spectrum (250-2500 nm), resulting in extremely high solar reflectivity (>90%). The large pores provide the main framework and through-channels, while the small pores fill the framework, allowing the coating to maintain high porosity (efficient heat insulation and scattering) while exhibiting superior mechanical strength and structural stability compared to structures with single pore sizes. See also... Figure 6 P(VDF-HFP) resin itself has strong infrared emitting groups (CF bonds) in the 8-13 μm atmospheric transparency window. The hierarchical porous structure, especially the micropores, greatly increases the internal surface area in contact with air, allowing heat inside the coating to be emitted more effectively through these surfaces in the form of infrared radiation, thereby enhancing the emissivity in the mid-infrared band (>0.90).

[0047] In some embodiments, the radiation cooling coating of this embodiment can be applied to the surfaces of buildings, wires and cables, and automobiles and ships.

[0048] It should be noted that the raw material information used in the following embodiments and comparative examples is as follows: P(VDF-HFP) resin is commercially available, with a melt index of 4.3, and is available in granules.

[0049] The first fluorocarbon resin is commercially available, brand name: HLR-Si, liquid, solid content: 55%, hydroxyl content: 1.5%, fluorine content ≥26%; the number average molecular weight of the first fluorocarbon resin is 20000.

[0050] Second fluorocarbon resin: According to the solvent requirements, at least one of butyl acetate, xylene, propylene glycol methyl ether acetate, and ethyl acetate shall be selected and directly mixed with the first fluorocarbon resin to prepare a second fluorocarbon resin with a solid content of 35%; the number average molecular weight of the second fluorocarbon resin shall be 20,000.

[0051] The curing agent is one of the following: hexamethylene diisocyanate, isophorone diisocyanate, naphthalene diisocyanate, toluene diisocyanate, and diphenylmethane diisocyanate, and is directly mixed with fluorocarbon resin without solvent dilution.

[0052] Examples 1-9 Table 1

[0053] Table 1 provides the specific components and quantities of the radiation cooling coatings in Examples 1-9. The specific composition of the first solvent in Examples 1-9 is shown in Table 2.

[0054] Table 2

[0055] As can be seen from Table 2, in each embodiment, the absolute value of the boiling point difference between any two compound solutions satisfies the range of greater than or equal to 20°C and less than or equal to 180°C.

[0056] Taking Example 1 as an example, the specific preparation process of the radiation cooling coating is as follows: (1) Prepare a mixed solution of acetone / butanone / N,N-dimethylformamide (DMF) according to the proportions in Table 2, and then weigh the corresponding parts of P (VDF-HFP) and deionized water according to Table 1 and add them to the mixed solution; (2) Place the mixed solution in a water bath at 55°C and heat and stir magnetically for 5-6 h (rotation speed of about 400 rmp / min) until P(VDF-HFP) is fully dissolved and the solution is homogeneous and stable without premature phase separation; (3) The first fluorocarbon resin and the isocyanate curing agent were directly mixed according to Table 1 to obtain the first fluorocarbon resin mixed solution; (4) Remove the P(VDF-HFP) mixture from the water bath and place it at room temperature for high-speed magnetic stirring (1000 rpm / min). During stirring, slowly add the previously prepared first fluorocarbon resin solution containing the curing agent dropwise to the solution. Stop adding the solution as soon as the P(VDF-HFP) mixture begins to change from clear and transparent to slightly turbid. Then continue stirring with a magnetic stirrer for 1-1.5 h until the entire solution is uniform and stable to obtain the coating.

[0057] The preparation methods for Examples 2-9 are the same as those for Example 1, except that the corresponding components in Tables 1 and 2 need to be replaced.

[0058] The coating obtained in Example 1 was used to prepare a radiation cooling coating. The specific preparation process is as follows: (1) First, prepare a second fluorocarbon resin with a solid content of 30%-55%. Apply the prepared second fluorocarbon resin to the substrate with a scraper (thickness adjustable). After the coating is left at room temperature for a period of time until it is dry, put it in an oven at 80°C to allow the solvent to evaporate completely. Finally, a single-layer transparent second coating is obtained. (2) The coating obtained in Example 1 was also applied to the second coating, which had completely evaporated, by scraping. The sample was placed in a constant temperature and humidity environment and left to stand for 24 h to allow the phases to separate completely. Then the sample was placed in an oven at 80°C and baked for 2-4 h to allow the coating to fully cure. Finally, a double-layer radiation cooling coating with a micro-nano porous structure was obtained.

[0059] Similarly, radiation cooling coatings were prepared from the coatings obtained in Examples 2-9 in the same manner as described above.

[0060] Comparative Example 1 A radiation cooling coating is provided, and the specific preparation process is as follows: (1) Prepare a single acetone solution according to Example 1 (the first solvent has only a single component), and then weigh the corresponding parts of P(VDF-HFP) and water according to Example 1 and add them to the mixed solution; (2) Place the mixed solution in a water bath at 55 °C and heat and stir magnetically for 5-6 h (rotation speed of about 400 rmp / min) until P(VDF-HFP) is fully dissolved and the solution is homogeneous and stable without premature phase separation; (3) The first fluorocarbon resin and the isocyanate curing agent were directly mixed according to the proportions of Example 1 to obtain a first fluorocarbon resin mixed solution; (4) Remove the P(VDF-HFP) mixture from the water bath and place it at room temperature for high-speed magnetic stirring (1000 rpm / min). During stirring, slowly add the previously prepared first fluorocarbon resin solution containing the curing agent dropwise to the solution. Stop adding the solution as soon as the P(VDF-HFP) mixture begins to change from clear and transparent to slightly turbid. Then continue stirring with a magnetic stirrer for 1-1.5 h until the entire solution is uniform and stable to obtain the coating.

[0061] Comparative Example 2 The preparation method of Comparative Example 2 is the same as that of Comparative Example 1, except that the single acetone solution in step (1) is replaced with a mixed solution of acetone / butanone, and the ratio is the same as that of Example 1.

[0062] Comparative Example 3 The preparation method of Comparative Example 3 is the same as that of Comparative Example 1, except that the single acetone solution in step (1) is replaced with a mixed solution of dichloromethane / acetone / tetrahydrofuran (the ratio is the same as in Example 1). The boiling points of the solvents are 39.6℃, 56.5℃, and 66℃, respectively. The difference between the boiling points of adjacent solvents is less than 20℃, which does not meet the boiling point difference range.

[0063] Comparative Example 4 The preparation method of Comparative Example 4 is the same as that of Comparative Example 1, except that: the single acetone solution in step (1) is replaced with a mixed solution of acetone / butanone / N,N-dimethylformamide (the ratio is the same as in Example 1); the preparation of the first fluorocarbon resin mixed solution in step (3) is not carried out and the mixed solution of the first fluorocarbon resin and curing agent is not added in step (4).

[0064] Comparative Example 5 The preparation method of Comparative Example 5 is the same as that of Comparative Example 1, except that the preparation of the first fluorocarbon resin mixed solution in step (3) is not carried out and the mixed solution of the first fluorocarbon resin and curing agent is not added in step (4).

[0065] Comparative Example 6 The preparation method of Comparative Example 6 is the same as that of Comparative Example 1, except that the single acetone solution in step (1) is replaced with a mixed solution of acetone / butanone / N,N-dimethylformamide (the ratio is the same as in Example 1) and no non-solvent water is added to the mixed solution.

[0066] The coating obtained in Comparative Example 1 was used to prepare a radiation cooling coating. The specific preparation process is as follows: (1) First, prepare a second fluorocarbon resin with a concentration of 30%-55%. Apply the prepared fluorocarbon resin to the substrate with a scraper (thickness adjustable). After the coating is left at room temperature for a period of time until it is dry, put it into an oven at 80°C to allow the solvent to evaporate completely. Finally, a single-layer transparent second coating is obtained. (2) The coating obtained in Comparative Example 1 was also applied to the fully volatilized fluorocarbon resin coating by scraping. The sample was placed in a constant temperature and humidity environment and left to stand for 24 h to allow the phases to separate completely. Then the sample was placed in an oven at 80℃ and baked for 2-4 h to allow the coating to fully cure. Finally, a double-layer radiation cooling coating with a micro-nano porous structure was obtained.

[0067] Similarly, radiation-cooled coatings were prepared from the coatings obtained in Comparative Examples 2-6 using the same method described above. The performance results of each coating are shown in Table 3.

[0068] Table 3

[0069]

[0070] As shown in Table 3, in Examples 1-9, since only the component content, solvent type, and curing agent type in the coating were adjusted without affecting the core design concept, the coatings in Examples 1-9 all have a long service life and a smooth, defect-free appearance. Because the mixed solvents all contain fast, medium, and slow volatile compound solvents, the coatings in Examples 1-9 all exhibit excellent emissivity, chemical resistance, media resistance, and weather resistance. This is mainly attributed to the excellent performance of P(VDF-HFP) and fluorocarbon resin itself. In contrast, Examples 1, 6, and 9 have a higher proportion of the first compound solution than other example groups, so they are more likely to form smaller pores during phase separation. Therefore, their reflectivity is higher than that of other examples. When the proportion of the first compound solution is higher, the volatilization stress during phase separation is greater, so their adhesion is only level 1, slightly lower than that of other example groups. The outdoor cooling effect varies slightly in Examples 1-9 because the reflectivity and emissivity of the coating must be considered comprehensively, but overall, the cooling effect is more than 10°C lower than the ambient temperature.

[0071] Besides the comparison between the examples, a comparison of Comparative Examples 1, 2, and 3 with the examples shows that the mixed solvents in Comparative Examples 1, 2, and 3 did not meet the core evaporation design, resulting in excessively rapid solvent evaporation and a short pot life. The instantaneous evaporation caused excessive stress on the coating, leading to shrinkage and curling of the coating surface, and an adhesion rating of only 4. Furthermore, the lack of controlled evaporation rate resulted in the absence of a multi-level porous structure within the coating, resulting in low reflectivity. These defects in adhesion and appearance also significantly affected its resistance to chemical media, weathering, and temperature differences. Comparative Example 4, compared to the examples, did not contain fluorocarbon resin or a curing agent, which mainly affected the coating's adhesion. Therefore, Comparative Example 4's adhesion rating was only 2, lower than the examples, and there was a small amount of peeling in terms of chemical media resistance and weathering resistance, but other overall performance was consistent with the examples. Comparative Example 5, compared to the examples... Comparative Example 5 does not meet the core design concept of the mixed solution and does not contain fluorocarbon resin and curing agent. Therefore, it has all the defects of Comparative Examples 1-4, including appearance shrinkage and curling, low reflectivity, the worst adhesion (level 5), insufficient weather resistance, and coating cracking after temperature difference test. It is the worst among the comparative examples. Compared with the examples, Comparative Example 6 does not contain non-solvent water. This mainly affects the porosity of the coating. Without the addition of non-solvent water, the coating can only induce phase separation from trace amounts of water in the air. This makes it difficult for liquid-liquid phase separation to occur in the coating. As a result, the coating may have almost no pore structure after complete evaporation. Therefore, the reflectivity of Comparative Example 6 is extremely low, resulting in almost no cooling effect under sunlight. However, it has a smooth appearance, excellent adhesion, and its resistance to chemical media, weather resistance, and temperature difference resistance are basically the same as those of the examples.

[0072] In summary, the first solvent in the mixture affects the appearance, adhesion, and reflectivity of the coating because it influences the core driving force in the phase separation process; the first fluorocarbon resin and the curing agent mainly affect the adhesion of the coating to the substrate or between the second fluorocarbon resin; finally, the non-solvent water mainly affects the porosity inside the coating, which is the core key to whether the coating can have high reflectivity.

[0073] See further Figure 2 This is a schematic diagram of the radiation cooling coating obtained using the coating from Example 1 applied to an aluminum substrate. It can be seen that the coating provided in this embodiment can be well coated on the substrate surface, ensuring the overall integrity and stability of the coating.

[0074] See Figure 3 The coatings prepared in Comparative Example 1 and Example 1 were prepared and applied respectively. It can be seen that the first coating of Comparative Example 1, after being directly applied to the substrate under the evaporation of acetone alone, showed obvious peeling and poor adhesion. However, after using Example 1, the first coating, after being directly applied to the substrate under the evaporation of mixed solvent, showed only a small amount of peeling at the cut compared to the coating with evaporation of acetone alone, and the overall adhesion was significantly improved. It is worth noting that when the first coating (mixed solvent) was applied to the second fluorocarbon resin, the coating did not peel off after the adhesion test, indicating that the coating of this example has a significantly improved adhesion effect and can solve the problem of poor adhesion between P(VDF-HFP) and the substrate when used as a coating.

[0075] The coating prepared using the coating from Example 1 was tested for emissivity and reflectivity. The reflectivity test was conducted according to ASTM E903 standard using a UV-Vis-NIR spectrophotometer equipped with an integrating sphere. After 100% and 0% baseline calibration to eliminate systematic errors, the sample was continuously scanned in the solar spectrum range of 280 nm to 2500 nm. The measured spectral reflectivity data was weighted and integrated using the AM1.5 standard solar irradiance distribution to calculate the accurate average solar reflectivity. The emissivity test was conducted using a Fourier transform infrared spectrometer (FTIR) with an infrared integrating sphere or a specular reflection accessory, according to ASTM E408 standard, to measure the normal spectral emissivity of the coating in the 2.5–25 μm band. For opaque coatings, the spectral emissivity can be indirectly derived using Kirchhoff's laws. Figure 4 Test results show that the multi-level porous structure enables the coating to achieve extremely high solar reflectivity (>90%) through the synergistic scattering effect of multi-scale pores. Through the intrinsic infrared absorption characteristics of P(VDF-HFP) material and the huge internal surface area given by the porous structure, the coating has extremely high mid-infrared emissivity (>90%).

[0076] The above provides a detailed description of the radiation cooling coating, coating method, and application of the embodiments of this application, and uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the technical solutions and core ideas of this application. Those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A radiation cooling coating, characterized in that, By weight, including: 8-15 parts of P(VDF-HFP) resin; 3-5 parts of the first fluorocarbon resin; 0.3 to 0.5 parts of curing agent; 85-92 parts of the first solvent; 7-13 parts of non-solvent; The first solvent is used to mix with the P(VDF-HFP) resin to form a P(VDF-HFP) resin solution; wherein the first solvent comprises at least three small molecule compound solutions with different boiling points; the absolute value of the boiling point difference between any two different small molecule compound solutions is greater than or equal to 20°C and less than or equal to 180°C.

2. The radiation cooling coating according to claim 1, characterized in that, The first solvent is composed of a first compound solution, a second compound solution, and a third compound solution; wherein the boiling point of the first compound solution is T1℃, the boiling point of the second compound solution is T2℃, and the boiling point of the third compound solution is T3℃, and the mixed solvent further satisfies at least one of the following characteristics: a) T1 < T2 < T3; b) 39℃≤T1≤66℃; c) 70℃≤T2≤120℃; d) 130℃≤T3≤210℃.

3. The radiation cooling coating according to claim 2, characterized in that, The mass ratio of the first compound solution, the second compound solution, and the third compound solution is 3~6 : 2~5 :

2.

4. The radiation cooling coating according to claim 2, characterized in that, The first compound is selected from at least one of acetone, tetrahydrofuran, and dichloromethane; and / or The second compound is selected from at least one of butanone, methyl isobutyl ketone, sec-butyl acetate, and 1-methoxy-2-propanol; and / or The third compound is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, γ-butyrolactone, and dimethylcyclohexylamine.

5. The radiation cooling coating according to claim 1, characterized in that, The number average molecular weight of the first fluorocarbon resin is 5000~50000; the solid content of the first fluorocarbon resin is 50~55%; The number-average molecular weight of the P(VDF-HFP) resin is 50,000 to 300,000. The curing agent is selected from any one of hexamethylene diisocyanate, isophorone diisocyanate, naphthalene diisocyanate, toluene diisocyanate, and diphenylmethane diisocyanate; The non-solvent is selected from deionized water.

6. The method for preparing the radiation cooling coating according to any one of claims 1 to 5, characterized in that, Includes the following steps: Take the corresponding mass parts of P(VDF-HFP) resin, non-solvent and first solvent and mix them. Stir until P(VDF-HFP) resin is fully dissolved to obtain P(VDF-HFP) resin solution. Take the corresponding mass parts of the first fluorocarbon resin and the curing agent, mix them, and add them dropwise to the P(VDF-HFP) resin solution. Stop adding the mixture as soon as the mixed solution changes from clear and transparent to turbid. Continue stirring until the whole solution is homogeneous and stable to obtain the radiation cooling coating. The first solvent is composed of a first compound solution, a second compound solution, and a third compound solution.

7. A radiation cooling coating, characterized in that, The coating comprises a substrate and a first coating disposed on the substrate; wherein the first coating comprises a radiation cooling coating according to any one of claims 1-5, or the first coating is obtained by coating a radiation cooling coating prepared by the method of claim 6 onto the surface of the substrate.

8. The radiation cooling coating according to claim 7, characterized in that, It also includes a second coating, which is located between the first coating and the substrate and is connected to the first coating and the substrate respectively; wherein the second coating is composed of a second fluorocarbon resin, the solid content of the second fluorocarbon resin is 30~55%; the number average molecular weight of the second fluorocarbon resin is 5000~50000, and the fluorine content is greater than 20%.

9. A radiation cooling coating according to claim 7, characterized in that, The first coating has a plurality of pores, which are formed by the evaporation of a first compound solution, a second compound solution, and a third compound solution in the first solvent; Wherein, the pore size of the pores formed after the first compound solution evaporates is 150~400 nm; The pore size formed after the second compound solution evaporates is 400~1100 nm; The pore size formed after the third compound solution evaporates is 1100~2500 nm.

10. Application of the radiation cooling coating of any one of claims 7-9 on building, wire and cable, and automotive / ship surfaces.

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