Multilayer gradient super-hydrophobic radiation refrigeration coating for container as well as preparation method and application of multilayer gradient super-hydrophobic radiation refrigeration coating

Abstract

The invention belongs to the technical field of functional coating materials of logistics equipment, and discloses a multilayer gradient super-hydrophobic radiation refrigeration coating for a container and a preparation method and application thereof.The coating comprises an infrared emission layer, a reflection isolation layer and a super-hydrophobic protection layer which are sequentially connected from inside to outside, the infrared emission layer can be tightly attached to the outer surface of the container. The coating is of a PDMS-based adhesive layer / core-shell reflecting layer / cold spraying hydrophobic layer sandwich layer structure, a porous PDMS shell layer is prepared through a spray drying method, physical isolation of reflecting and hydrophobic functions is achieved, and stability and durability optimization in a dynamic transportation environment is achieved. The coating is an innovative super-hydrophobic radiation refrigeration coating with a three-layer structure, the problem of mutual exclusion of reflection and hydrophobic functions is solved, the interlayer stability is improved, and the infrared emissivity is enhanced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of functional coating materials for logistics equipment, in particular to a container super-hydrophobic radiation refrigeration coating based on gradient and dynamic coupling verification of core-shell microspheres, a preparation method and application thereof. BACKGROUND

[0002] Super-hydrophobic radiation refrigeration coating is a new technology field aiming to achieve passive cooling without external energy through high solar reflectance and high infrared emissivity. The development of this field mainly relies on the combination of polymer matrix and inorganic fillers, combined with micro-nano rough structure to build super-hydrophobic surface. However, the existing technology faces significant bottlenecks: the reflective layer and the hydrophobic layer are functionally exclusive, the reflective layer and the hydrophobic layer diffuse due to solvent miscibility, forming a blurred gradient (interlayer thickness deviation ± 30%), reducing infrared emission efficiency (from 96% to 82%), and traditional scraping or spraying process causes blurred interlayer interface, reducing refrigeration efficiency. The fundamental contradiction of existing super-hydrophobic radiation refrigeration coating technology lies in the physical conflict between optical performance and surface energy. In order to achieve high solar reflectance, large particle size inorganic nano-filler is used in traditional technology, but its smooth surface is difficult to build a hydrophobic micro-nano structure; while super-hydrophobicity depends on nano-scale roughness, but nano-particles will embed into the reflective layer pores, and the high surface energy of nano-particles will cause agglomeration, further reducing the optical uniformity, resulting in a 15-20% decrease in light scattering efficiency.

[0003] In a dynamic environment, the above defects will trigger a chain reaction: interlayer blur further triggers thermal stress concentration, micro-crack propagation eventually leads to a decrease in refrigeration performance. In summary, the existing super-hydrophobic radiation refrigeration coating has essential defects in the three dimensions of material physical property conflict, interlayer structure stability, and dynamic environment durability.

[0004] After searching, the following two patent publications related to the present patent application were found: 1. Chinese patent publication CN115449268B discloses a radiation refrigeration double-layer structure: the bottom layer uses PVDF flexible film to provide ductility, and the functional layer uses PDMS mixed with multi-walled carbon nanotubes / graphite powder / titanium nitride, which has the functions of conductivity, photothermal, and hydrophobicity. However, it has the following defects: The conductive filler (carbon nanotubes, graphite powder) used absorbs visible light, which reduces reflectivity; the PVDF bottom layer has no infrared emission function, which reduces the overall refrigeration efficiency; the coupling of hydrophobicity and photothermal function leads to a decrease in hydrophobic stability at high temperature. The interlayer interface is blurred by scraping process, which is easy to peel off in dynamic environment.

[0005] 2. Chinese patent publication CN120484543A discloses a daytime radiation refrigeration structure coating and a preparation method. Zinc oxide arrays and graphene oxide are grown in situ on the surface of a substrate through a hydrothermal reaction. Barium sulfate particles are directionally scattered on titanium dioxide particles. The actual cooling is 8.7℃. There is no cracking in the cyclic thermal shock. The thermal stability and long-term stability of the coating are improved.

[0006] However, it has the following defects: The zinc oxide array only slows down heat conduction through physical blocking, and cannot actively dissipate heat energy. The physical mixing of barium sulfate / titanium dioxide can cause the particles to settle during large-scale production, resulting in uneven interfaces. Only static thermal cycling (-40℃~80℃) is tested, and the wind load / vibration coupling effect is not verified.

[0007] By comparison, the present patent application is essentially different from the above-mentioned patent publication. SUMMARY

[0008] The present application aims to overcome the shortcomings of the prior art and provide a container super-hydrophobic radiation refrigeration coating based on core-shell microsphere gradient and dynamic coupling verification, a preparation method and application.

[0009] The technical solution adopted by the present application to solve its technical problems is: A multilayer gradient super-hydrophobic radiation refrigeration coating for containers, characterized in that the container super-hydrophobic radiation refrigeration coating comprises an infrared emission layer, a reflective isolation layer and a super-hydrophobic protective layer connected in sequence from the inside out. The infrared emission layer can be tightly arranged on the outer surface of the container.

[0010] Application of the radiation refrigeration coating as described above in radiation refrigeration.

[0011] The preparation method of the radiation refrigeration coating as described above, the method comprising the following steps: First, a polydimethylsiloxane (PDMS) based glue layer is constructed as an infrared emission layer. Second, barium sulfate@PDMS core-shell microspheres or ZrO2@PDMS core-shell microspheres are dispersed in ethanol and then sprayed on the glue layer to form a porous reflective interface, obtaining a reflective isolation layer. Finally, the super-hydrophobic protective layer uses organosilicon resin modified silica aerogel powder or fluorinated SiO2 particles, which are deposited by cold spraying process and self-assembled into micro-nano structures at room temperature to obtain the radiation refrigeration coating, ensuring the hydrophobic stability.

[0012] Further, the PDMS-based adhesive layer is prepared by mixing the PDMS precursor and the crosslinking agent in a mass ratio of 10:1 and adding 200 nm hollow silica microspheres, and a ladder process is used in the curing process to form a high-crosslinking elastomer, i.e., pre-curing at 50°C for 1 hour, and post-curing at 80°C for 2 hours, to obtain the PDMS-based adhesive layer.

[0013] Further, the core of the BaSO4@PDMS core-shell microspheres is 500 nm, and the shell is 100 nm; or the thickness of the BaSO4@PDMS core-shell microspheres dispersed in ethanol sprayed on the adhesive layer is 50 μm; or the pre-drying temperature is 60°C.

[0014] Further, the particle size of the organosilicon resin modified silica aerogel powder is 1-5 μm; or the pressure of the cold spraying process is 0.2 MPa.

[0015] Further, the specific steps are as follows: Step one: preparation of the PDMS-based adhesive layer First, the polydimethylsiloxane (PDMS) precursor and the PDMS crosslinking agent are mixed in a mass ratio of 10:1, mechanically stirred at 500 rpm for 10 min until homogeneous, and then SiO2 is added and dispersed by ultrasonic wave at 40 kHz for 15 min to eliminate agglomeration; then, n-heptane diluent is added; uniform speed is scraped on the surface of the container, forming a wet film thickness of 210 μm and a dry film thickness of 200±10 μm; after coating, ladder curing is performed: 50°C hot air curing for 1 h to form an elastic network of the prepolymer, and then heating to 80°C for 2 h to complete crosslinking, obtaining the PDMS-based adhesive layer; Step two: preparation of the reflective isolation layer BaSO4@PDMS core-shell microspheres are prepared, BaSO4 microspheres are mixed with anhydrous ethanol, and are placed in a ball mill with ZrO2 grinding balls for dispersion for 24 h until the particle size distribution of the slurry is uniform; a high-pressure airless spray gun is used, the pressure is set to 0.3 MPa, and the gun is sprayed uniformly at a distance of 25 cm from the PDMS-based adhesive layer, forming a wet film thickness of 55 μm. After spraying, it is immediately transferred into a 60°C hot air oven for drying for 10 min, and the film layer is required to be free of sagging and cracking, obtaining BaSO4@PDMS; wherein, Step three: preparation of the super-hydrophobic protective layer Take SiO2 aerogel powder, add 5wt% silicone resin modifier, react at 60℃ for 4h, obtain hydrophobic modified aerogel powder, contact angle >156°; use supersonic cold spraying system, nitrogen as carrier gas, gas pressure 0.2MPa, powder flow rate 10g / min, spray deposition at 15cm from the BaSO4@PDMS container surface in RH<45% environment, form a 20±2μm thick protective layer; after deposition, room temperature standing for 24h, self-assembly of aerogel powder into micro-nano structure, obtain SiO2@BaSO4@PDMS coating, obtain multi-layer gradient super-hydrophobic radiation refrigeration coating for container.

[0016] Further, the ratio of polydimethylsiloxane PDMS precursor: SiO2: n-heptane in step one is 18:6:40; or, the diameter d of SiO2 in step one is 200nm; Or, the mass ratio of BaSO4 microspheres: anhydrous ethanol in step two is 1:4; or, the nozzle diameter of high-pressure airless spray gun in step two is 0.5mm; Or, the SiO2 aerogel powder in step three is 30nm SiO2 aerogel powder.

[0017] Further, in step one, the polydimethylsiloxane PDMS precursor is mixed with the PDMS crosslinking agent at a mass ratio of 10:1, and after homogenization by mechanical stirring at 500 rpm for 10 min, 5% PMMA microspheres, poly(methyl methacrylate), with an average particle size of 1μm, are added relative to the mass fraction of the PDMS precursor, and then SiO2 is added.

[0018] The preparation method as described above is applied in radiation refrigeration.

[0019] The advantages and positive effects obtained by the present application are: 1. Three-layer structure synergistic optimization: the coating of the present application is a sandwich layer structure of PDMS-based glue layer / core-shell reflective layer / cold sprayed hydrophobic layer, the porous PDMS shell layer is prepared by spray drying method, realizing the physical isolation of reflection and hydrophobic function, and realizing the optimization of stability and durability in dynamic transportation environment. The coating of the present application is an innovative three-layer structure super-hydrophobic radiation refrigeration coating, which solves the mutual exclusion of reflection-hydrophobic function, improves the interlayer stability and enhances the infrared emissivity.

[0020] 2. Cold spraying process innovation: develop 0.2MPa supersonic cold spraying technology, realize the room temperature precise deposition and self-assembly of resinized SiO2 aerogel, form hierarchical micro-nano structure, contact angle up to 156°. Compared with electrostatic spraying, it avoids the loss of PDMS elasticity caused by high temperature.

[0021] 3. Gradient interface design: In the present application, the elasticity of the PDMS layer is enhanced by hollow SiO2 microspheres, combined with a step curing process (50℃ / 1h→80℃ / 2h), and the thermal conductivity is reduced to 0.08 W / m·K.

[0022] 4. Wind tunnel three-factor coupling test method: In the present application, the dynamic stability of the coating is verified by simultaneous loading of 120km / h wind load + 5% salt spray + -40℃~80℃ temperature variation. The reflectivity and emissivity of the super-hydrophobic radiation cooling coating remain unchanged before and after testing. The functional failure problem of the container under high-speed transportation (120km / h), salt spray corrosion and temperature difference alternation (-40℃~80℃) is solved, and the effect of reducing the surface temperature of the container is achieved.

[0023] 5. Infrared emission and stability are enhanced. Hollow SiO2 microspheres (cavity diameter 200nm) enhance the emissivity of 8-13μm band to 96.5% through cavity resonance effect, which is 20% higher than traditional coating (without cavity structure, emissivity ≈80%). In the present application, the infrared emissivity of the container surface is as high as 96.5%, the traditional container coating emissivity is almost 50%, the solar reflectivity of the container is as high as 95%, and the solar reflectivity of the traditional container coating is 80-85%. In outdoor measurement, the coating can achieve a cooling amplitude of 5-16 ℃ on the surface of the container at noon when the ambient temperature is 35℃. After 10 times of sandpaper rubbing test, the contact angle still remains 156.5°, indicating that the durability is significantly enhanced, and the contact angle of the traditional container is <120°.

[0024] 6. The method of the present application separates each layer function by physical separation, avoids filler coverage, and simultaneously utilizes the cavity resonance effect of hollow silica microspheres to significantly enhance the infrared emissivity of 8-13μm band. The spectral properties of the three-layer structure super-hydrophobic radiation cooling coating are shown in Figure 1 and Figure 2 The reflectivity in the visible light band (0.4-0.8μm) is 0.94, and the emissivity in the atmospheric window band (8-13μm) is 0.96. The excellent spectral performance lays a foundation for the later refrigeration efficiency and cooling effect. The thermodynamic experiments of the core-shell microsphere super-hydrophobic radiation cooling coating prepared in the present application and three kinds of traditional container coatings are carried out outdoors, and the surface temperature fluctuation of the container is shown in Figure 4 Compared with traditional coatings, the present application can reduce the surface temperature of the container by 5-16 ℃, wherein the solar intensity q solar = 800 W / m 2 . BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is the reflectivity diagram of the hydrophobic radiation cooling coating prepared in Example 1 of the present application in the solar light band; Figure 2The emissivity diagram of the hydrophobic radiative cooling coating prepared in Example 1 of the present application in the blackbody radiation band; Figure 3 The thermal stability test diagram of the water transport radiative cooling coating prepared in Example 1 of the present application under extreme conditions; wherein there is no significant difference in the reflectivity of the water transport radiative cooling coating in the visible light band and the emissivity in the atmospheric window band before and after the test; Figure 4 The comparison diagram of the surface temperature reduction of the hydrophobic radiative cooling coating prepared in Example 1 of the present application and the traditional coating on the container. The present application can reduce the surface temperature of the container by 5-16 DEG C compared with the traditional coating. DETAILED DESCRIPTION

[0026] The present application is further described below in conjunction with examples, which are descriptive rather than limiting, and cannot limit the protection scope of the present application.

[0027] The various experimental operations involved in the specific embodiments are all conventional techniques in the art, and the parts not specially noted in the text can be implemented by referring to various commonly used tool books, scientific and technical literature or related instructions, manuals, etc. before the application date of the present application.

[0028] A multilayer gradient super-hydrophobic radiative cooling coating for containers, characterized in that the super-hydrophobic radiative cooling coating for containers comprises an infrared emission layer, a reflective isolation layer and a super-hydrophobic protective layer which are sequentially connected from inside to outside, and the infrared emission layer can be closely arranged on the outer surface of the container.

[0029] Application of the radiative cooling coating as described above in radiative cooling.

[0030] Preparation method of the radiative cooling coating as described above, the method comprising the following steps: First, a polydimethylsiloxane (PDMS) based glue layer is constructed as an infrared emission layer; Second, barium sulfate@PDMS core-shell microspheres or ZrO2@PDMS core-shell microspheres are dispersed in ethanol and then sprayed on the glue layer, and pre-dried to form a porous reflective interface to obtain a reflective isolation layer; Finally, the super-hydrophobic protective layer adopts organosilicon resin modified silica aerogel powder or fluorinated SiO2 particles, which are deposited by cold spraying process and self-assembled into micro-nano structures at room temperature to obtain the radiative cooling coating, ensuring the hydrophobic stability.

[0031] Preferably, the PDMS-based adhesive layer is prepared by mixing the PDMS precursor and the crosslinking agent in a mass ratio of 10:1 and adding 200 nm hollow silica microspheres, and a step process is used in the curing process, i.e., pre-curing at 50°C for 1 hour, and then post-curing at 80°C for 2 hours, to form a highly crosslinked elastomer, i.e., the PDMS-based adhesive layer.

[0032] Preferably, the core of the BaSO4@PDMS core-shell microspheres is 500 nm, and the shell is 100 nm; or the thickness of the BaSO4@PDMS core-shell microspheres dispersed in ethanol sprayed on the adhesive layer is 50 μm; or the pre-drying temperature is 60°C.

[0033] Preferably, the particle size of the organosilicon resin modified silica aerogel powder is 1-5 μm; or the pressure of the cold spraying process is 0.2 MPa.

[0034] Preferably, the specific steps are as follows: Step one: preparation of the PDMS-based adhesive layer First, the polydimethylsiloxane (PDMS) precursor and the PDMS crosslinking agent are mixed in a mass ratio of 10:1, and stirred at 500 rpm for 10 min until homogeneous, and then SiO2 is added and dispersed by ultrasonic wave at 40 kHz for 15 min to eliminate agglomeration; then, n-heptane diluent is added; and the mixture is uniformly scraped and coated on the surface of the container to form a wet film with a thickness of 210 μm and a dry film thickness of 200±10 μm; after coating, a step curing is performed: pre-polymer forms an elastic network by hot air curing at 50°C for 1 h, and then the temperature is increased to 80°C for 2 h to complete the crosslinking, and the PDMS-based adhesive layer is obtained; Step two: preparation of the reflective isolation layer BaSO4@PDMS core-shell microspheres are prepared by mixing BaSO4 microspheres with anhydrous ethanol, and then placing them in a ball mill with ZrO2 grinding balls for dispersion for 24 h until the particle size distribution of the slurry is uniform; a high-pressure airless spray gun is used, and the pressure is set to 0.3 MPa, and the gun is sprayed uniformly at a distance of 25 cm from the PDMS-based adhesive layer to form a wet film with a thickness of 55 μm. After spraying, it is immediately transferred to a hot air oven at 60°C for drying for 10 min, and the film layer is required to be free of sagging and cracking, and BaSO4@PDMS is obtained; wherein, Step three: preparation of the super-hydrophobic protective layer SiO2 aerogel powder was mixed with 5wt% organosilicon resin modifier and reacted at 60℃ for 4 hours to obtain hydrophobic modified aerogel powder with a contact angle >156°. Using a supersonic cold spraying system with nitrogen as the carrier gas at a pressure of 0.2MPa and a powder flow rate of 10g / min, the powder was sprayed at a distance of 15cm from the surface of a container coated with BaSO4@PDMS under an environment with a relative humidity of RH <45% to form a protective layer with a thickness of 20±2μm. After deposition, the aerogel powder was allowed to stand at room temperature for 24 hours to self-assemble into a micro-nano structure, thus obtaining the SiO2@BaSO4@PDMS coating, which is a multilayer gradient superhydrophobic radiation cooling coating for containers.

[0035] Preferably, in step one, the ratio of polydimethylsiloxane PDMS matrix: SiO2: n-heptane (g:g:ml) is 18:6:40; or, in step one, the diameter of SiO2 is d = 200nm. Alternatively, in step two, the mass ratio of BaSO4 microspheres to anhydrous ethanol is 1:4; or, in step two, the nozzle diameter of the high-pressure airless spray gun is 0.5 mm. Alternatively, the SiO2 aerogel powder in step three can be 30nm SiO2 aerogel powder.

[0036] Preferably, in step one, the polydimethylsiloxane PDMS matrix and PDMS crosslinking agent are mixed at a mass ratio of 10:1, and mechanically stirred at 500 rpm for 10 min until homogeneous. Then, PMMA microspheres with an average particle size of 1 μm and a mass fraction of 5% relative to the PDMS matrix are added. Finally, SiO2 is added.

[0037] The application of the preparation method described above in radiation refrigeration.

[0038] Specifically, the relevant preparation and testing methods are as follows: Example 1 A method for preparing a superhydrophobic radiation-cooling coating for shipping containers based on core-shell microsphere gradient and dynamic coupling verification includes the following steps: Step 1: Preparation of PDMS base adhesive layer First, 180g of polydimethylsiloxane (PDMS) matrix and 18g of PDMS crosslinking agent were mixed at a mass ratio of 10:1 and mechanically stirred at 500rpm for 10min until homogeneous. Then, 60g of SiO2 (d = 200nm) was added, and the mixture was ultrasonically dispersed at 40kHz for 15min to eliminate agglomeration. Subsequently, 400ml of n-heptane diluent was added. The mixture was uniformly coated onto the surface of a container model to form a wet film thickness of 210μm (dry film thickness 200±10μm). After coating, a stepped curing process was performed: hot air curing at 50℃ for 1h to allow the prepolymer to form an elastic network, followed by curing at 80℃ for 2h to complete crosslinking, resulting in the PDMS base adhesive.

[0039] Step two: Preparation of reflective isolation layer BaSO4@PDMS core-shell microspheres were prepared. 20 g of BaSO4 microspheres were mixed with 80 g of anhydrous ethanol and placed in a ball mill with ZrO2 grinding balls for dispersion for 24 h until the slurry particle size distribution was uniform. A high-pressure airless spray gun (nozzle diameter 0.5 mm) was used, with a pressure of 0.3 MPa, and uniform spraying was performed at a distance of 25 cm from the PDMS-based primer layer, forming a wet film thickness of 55 μm. After spraying, it was immediately transferred to a 60°C hot air oven for drying for 10 min, and the film layer was required to be free of sagging and cracking, and BaSO4@PDMS was obtained.

[0040] Step three: Preparation of super-hydrophobic protective layer 30 nm SiO2 aerogel powder was taken and 5 wt% organosilicon resin modifier was added, and the mixture was reacted at 60°C for 4 h to obtain hydrophobically modified aerogel powder (contact angle > 156°). An ultrasonic cold spraying system was used, with nitrogen as the carrier gas (pressure 0.2 MPa) and a powder flow rate of 10 g / min, and the system was used to spray and deposit at a distance of 15 cm from the surface of the BaSO4@PDMS container, forming a protective layer with a thickness of 20±2 μm in an environment with a relative humidity RH < 45%. After deposition, the system was allowed to stand at room temperature for 24 h to allow the aerogel powder to self-assemble into a micro-nano structure, and a SiO2@BaSO4@PDMS container was obtained.

[0041] Comparative Example 1 A method for preparing a container super-hydrophobic radiation refrigeration coating based on core-shell microsphere gradient and dynamic coupling verification, steps one and two are the same as in Example 1, the difference is that in step three, instead of using an ultrasonic cold spraying system for spraying, a conventional thermal spraying process is used. The thermal spraying gun process parameters are a pressure of 0.5 MPa and a nozzle temperature of 60°C, and the carrier gas is compressed air. The 60°C spraying temperature causes the aerogel powder to melt and lose the hierarchical roughness; the peeling force between the protective layer and the reflective layer in the salt spray test is only 0.8 MPa (3.2 MPa in Example 1), and the interface is oxidized due to the thermal spraying.

[0042] Comparative Example 2 A preparation method of a container super-hydrophobic radiative cooling coating based on core-shell microsphere gradient and dynamic coupling verification, the steps are the same as in Example 1, the difference is only that in step three, the SiO2 aerogel powder is replaced by ordinary nano titanium dioxide (TiO2), and a final mass concentration of 2 wt% fluorosilane is added for surface hydrophobic modification. TiO2 has strong absorption in the ultraviolet light part, resulting in a loss of 6.4% in solar light reflection. The emissivity of the super-hydrophobic radiative cooling coating in the solar light band is 84.4%, making it difficult to achieve cooling effect. At the same time, after modifying TiO2 with fluorosilane, the water contact angle of the material is 120°, which does not meet the super-hydrophobic standard due to the high residual rate of TiO2 surface hydroxyl (-OH). In addition, in the dynamic environment verification test, cracks appear on the surface of the coating due to the mismatch between the rigidity (elastic modulus 5 GPa) of TiO2 and PDMS (0.5 MPa).

[0043] As shown in Figure 1 , the average reflectivity of the coating of Example 1 in the visible light band of 0.4-0.8 μm is 0.94, and the reflectivity at 550 nm wavelength is 0.95, close to the ideal reflector. Its reflectivity is much higher than that of Comparative Example 2 (0.84) and traditional coating (0.4-0.8). This is due to the gradient design of the core-shell microspheres (BaSO4@PDMS), which effectively avoids the scattering loss caused by the embedding of nano-filler. The present application solves the problem of functional exclusion by physically isolating the reflective layer and the hydrophobic layer, and the reflectivity is improved by 15.7% (i.e. from 0.83 to 0.94) compared with the traditional coating.

[0044] Figure 2 The emissivity graph of the super-hydrophobic radiative cooling coating prepared for Example 1 in the blackbody radiation band, the average emissivity of the coating of Example 1 in the atmospheric window band of 8-13 μm is 0.96, and the emissivity at 10 μm wavelength is 0.97, which is highly consistent with the blackbody radiation curve. Mainly due to the cavity resonance effect of hollow SiO2 microspheres. The emissivity of Comparative Example 1 decays to 0.85, because the interdiffusion between the layers destroys the vibration of the infrared active group (such as Si-O bond). The emissivity of Comparative Example 2 is only 0.82 (because TiO2 has no cavity structure), and the emissivity of the traditional coating (metal-based) is almost less than 20%.

[0045] Figure 4 The cooling comparison chart of the hydrophobic radiative cooling coating prepared in Example 1 of the present application and the traditional coating on the surface of the container. Traditional coating 1-Comparative Example uses a matching system of epoxy zinc-rich primer and polyurethane topcoat, traditional coating 2-Comparative Example is an acrylic polyurethane topcoat, and traditional coating 3-Comparative Example is a chlorinated rubber anticorrosive topcoat. Its characteristics of high thermal conductivity (>0.8 W / m·K), low emissivity (<0.2), and weak reflection (<80%) result in a container surface temperature 10-20℃ higher than the environment. As shown in Figure 4The measured data show that the ambient temperature is about 35℃ at the peak period of solar radiation (intensity > 800 W / m²) at 12:00 noon. At this time, the surface temperature of the coating of Example 1 of the present application is only 41℃, which is about 6℃ higher than the ambient temperature (ΔT) (ΔT≈6℃), which is significantly lower than all the comparative examples. Due to the inherent defects of high thermal conductivity and low emissivity, the three traditional coatings show serious heat accumulation: the surface temperature of traditional coating 1 (zinc-rich epoxy + polyurethane) is as high as 45.2℃ (ΔT≈10.2℃); the surface temperature of traditional coating 2 (acrylic polyurethane) is 50.6℃ (ΔT≈15.6℃); and the surface temperature of traditional coating 3 (chlorinated rubber) is 56.6℃ (ΔT≈21.6℃). As can be seen, the temperature difference between the coating of the present application and the traditional coating at the peak temperature reaches 4.2℃ to 15.6℃, which directly verifies the effectiveness of the radiation cooling mechanism, and fundamentally overcomes the technical bottleneck of traditional sacrificial coatings in heat management, providing an innovative and efficient solution to the high temperature problem of containers.

[0046] At the same time, by comparing Example 1, Comparative Example 1 and Comparative Example 2, it can be seen that the ultrasonic cold spraying system and the SiO2 aerogel powder in the method of the present application have a synergistic effect, which can synergistically improve the related properties of the container super-hydrophobic radiation cooling coating prepared, especially the “30nm SiO2 aerogel powder” and the “use of an ultrasonic cold spraying system, with nitrogen as the carrier gas (gas pressure of 0.2MPa), powder flow rate of 10g / min, in an environment with relative humidity RH<45%” two conditions have a synergistic effect, which can synergistically improve the related properties of the container super-hydrophobic radiation cooling coating prepared.

[0047] Example 2 To verify the dynamic stability of the super-hydrophobic radiation cooling coating in the extreme transportation environment of the container, the present application designs a multi-stress coupling accelerated aging test scheme. The test platform integrates a humidity adjustable incubator, an oven (20℃-100℃), and a shaking table (5-2000Hz) to test the SiO2@BaSO4@PDMS container for 720 hours. A single cycle of 72 hours includes four stages: 0-12h of 5% NaCl salt spray (35℃) and 100Hz random vibration; 12-24h of-10℃ to 50℃ temperature change (10℃ / min) superimposed with 100km / h wind speed; 24-48h of 50mm / h rain and 120km / h wind load with 100Hz constant frequency vibration; 48-72h of maintaining 80℃ high temperature and 95%RH high humidity with 60km / h wind speed. After 10 cycles, the spectral properties of the SiO2@BaSO4@PDMS core-shell microsphere super-hydrophobic radiation cooling coating are as follows: Figure 3As shown, the reflectivity is 0.94 and the infrared emissivity is 0.96, which are not significantly different from those before the test. This indicates that the coating has excellent cooling performance. The results confirm that the coating can still meet the long-term protection and cooling performance requirements of the surface functional coating for shipping containers under the combined effects of multiple factors such as 120km / h wind load, salt spray corrosion, severe temperature change and mechanical vibration.

[0048] in addition, Figure 3 The image shows the thermal stability test results of the superhydrophobic radiation-cooling coating prepared in Example 1 under extreme conditions. After 720 hours of multi-stress coupling testing (salt spray, temperature change, wind load, vibration), the reflectivity and emissivity of the coating in Example 1 showed no significant difference (p>0.05), with reflectivity remaining at 0.94 and emissivity at 0.96, demonstrating stable interlayer bonding. In contrast, the reflectivity of Comparative Example 1 decreased from 0.88 to 0.77 after the test due to interface oxidation caused by thermal spraying; the emissivity of the coating in Comparative Example 2 decreased from 0.82 to 0.70 due to microcracks caused by CTE mismatch between TiO2 and PDMS. Therefore, the stepped curing process (50℃ / 1h→80℃ / 2h) and the core-shell microsphere design effectively resist dynamic environmental stress, with a performance degradation rate <0.03, far lower than that of the Comparative Example (>0.1).

[0049] Meanwhile, by comparing Example 1, Comparative Example 1, and Comparative Example 2, it can be seen that the supersonic cold spraying system and the SiO2 aerogel powder in the method of the present invention have a synergistic effect, which can synergistically improve the relevant properties of the prepared superhydrophobic radiation cooling coating for containers. In particular, the two conditions of "30nm SiO2 aerogel powder" and "using a supersonic cold spraying system with nitrogen as the carrier gas (pressure of 0.2MPa), powder flow rate of 10g / min, and relative humidity RH < 45%" have a synergistic effect, which can synergistically improve the relevant properties of the prepared superhydrophobic radiation cooling coating for containers.

[0050] Example 3: ZrO2@PDMS reflective coating suitable for high UV environments This embodiment utilizes a wide-bandgap ZrO2 material to construct a core-shell microsphere reflective layer, effectively suppressing material degradation and performance decline caused by ultraviolet radiation. The preparation steps in this embodiment are basically the same as in Example 1, except that the material of the reflective isolation layer in step two is replaced with ZrO2@PDMS core-shell microspheres.

[0051] The specific steps are as follows: Preparation of the reflective isolation layer: ZrO2 microspheres with an average particle size of 500nm are mixed with PDMS prepolymer at a mass ratio of 1:1, an appropriate amount of anhydrous ethanol is added as a dispersion medium, and the mixture is placed in a ball mill and continuously ball-milled with ZrO2 grinding balls for 24 hours to form core-shell structured microspheres ZrO2@PDMS with ZrO2 as the core and PDMS as the shell; The raw materials, proportions, and process parameters for Step 1 (preparation of PDMS base adhesive layer) and Step 3 (preparation of superhydrophobic protective layer) are exactly the same as those in Example 1.

[0052] To verify its resistance to ultraviolet aging, the coating of this embodiment was placed in an ultraviolet aging test chamber to simulate high-intensity ultraviolet radiation (wavelength 340nm, intensity 0.68W / m). 2 The coating was continuously irradiated for 336 hours. The test results are shown in Table 1: the solar reflectance of the coating in this embodiment remained at 0.93 after UV aging, indicating strong UV stability.

[0053] Table 1

[0054] Example 4: Base coat coating with added PMMA microspheres to enhance infrared emission This embodiment introduces PMMA microspheres as a pore-forming agent into the PDMS base adhesive. After dissolution and precipitation, a porous structure is formed to enhance its infrared emissivity in the 8-13μm atmospheric window, making it particularly suitable for static storage containers with extremely high requirements for refrigeration efficiency but relatively low requirements for mechanical wear resistance. The difference between this embodiment and Example 1 is that PMMA microspheres are added in the preparation of the PDMS base adhesive layer in step one. The specific steps are as follows: Preparation of PDMS base adhesive layer: Based on step one of Example 1, when mixing the PDMS matrix, crosslinking agent, and hollow SiO2 microspheres, PMMA microspheres (polymethyl methacrylate) (average particle size 1μm) equivalent to 5% of the PDMS mass fraction are added, and uniform dispersion is ensured; Step curing and pore formation: In the subsequent step curing process (pre-curing at 50℃ for 1 hour, followed by curing at 80℃ for 2 hours), the PMMA microspheres are partially dissolved by n-heptane diluent and subsequently precipitated, forming a porous structure with a porosity of approximately 40% inside the base adhesive layer.

[0055] The specific steps are as follows: First, the raw materials are mixed and dispersed. PDMS matrix and crosslinking agent are weighed at a mass ratio of 10:1 and placed in a mixing container. PMMA microspheres (polymethyl methacrylate, average particle size 1 μm) with a mass fraction of 5% relative to the PDMS matrix are added. Hollow SiO2 microspheres with the amount specified in the steps of Example 1 are added at the same time. Then, n-heptane diluent with a mass ratio of 3-5% of the total volume of the mixture is added. The mixture is first stirred at 1500 rpm for 10 minutes with a mechanical stirrer, and then ultrasonically treated with a power of 200W for 5 minutes to ensure that the microspheres are uniformly dispersed and there are no obvious agglomerates in the system. Subsequently, stepped curing and pore formation were carried out. In the pre-curing stage, the mixed system was placed at 50°C for 1 hour to allow PDMS to initially cross-link and form a network skeleton. At the same time, n-heptane began to penetrate and partially swell the PMMA microspheres. In the post-curing stage, the temperature was increased to 80°C at a rate of 1-2°C / min and cured for another 2 hours. During this process, n-heptane was heated and volatilized, causing the PMMA microspheres to precipitate from the swollen state and form pores. Finally, a porous structure with a porosity of about 40% was formed inside the base adhesive layer.

[0056] In summary, as shown in Table 2, the present invention (i.e., the superhydrophobic radiation cooling coating for containers prepared in Example 1, and all subsequent tests used the superhydrophobic radiation cooling coating for containers prepared in Example 1) can reduce the surface temperature of containers by 5-16 °C compared to traditional coatings.

[0057] The infrared emissivity of the container surface is as high as 96.5%, while the emissivity of traditional container coatings is almost 20%.

[0058] The solar reflectivity of shipping containers can reach up to 95%, while the solar reflectivity of traditional shipping container coatings is 40-80%.

[0059] In outdoor testing, the coating achieved a temperature reduction of 5-16°C on the container surface at a midday ambient temperature of 35°C.

[0060] After 10 sandpaper abrasion tests, the contact angle remained at 156.5°, indicating significantly enhanced durability, compared to the contact angle of traditional containers which is <120°.

[0061] Table 2 Comparison of spectral characteristics and cooling effect between the coating of the present invention and the conventional coating.

[0062] As shown in Table 3, although the initial cost of the coating of this invention is slightly higher (250-350 / box), its superior durability results in zero maintenance costs for 5 years, compared to 800-1200 / box for traditional coatings. More importantly, it can save up to $500 / box of refrigeration energy consumption annually in cold chain applications. This demonstrates that by significantly reducing long-term maintenance costs and energy consumption, this invention provides a comprehensive economic advantage far exceeding that of traditional coatings throughout its entire life cycle, highlighting its technological innovation value and market competitiveness.

[0063] Table 3. Comparison of the total life cycle cost of the coating of this invention and conventional coatings.

[0064] Although embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations, and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the scope of the invention is not limited to the contents disclosed in the embodiments.

Claims

1. A multilayer gradient superhydrophobic radiative refrigeration coating for containers, characterized by: The container super-hydrophobic radiative cooling coating comprises an infrared emission layer, a reflective isolation layer and a super-hydrophobic protective layer arranged in sequence from inside to outside, and the infrared emission layer can be tightly arranged on the outer surface of the container.

2. Application of the radiative cooling coating in claim 1 in radiative cooling.

3. The method of producing a radiative cooling coating of claim 1, wherein: The method comprises the following steps: First, a polydimethylsiloxane (PDMS) based adhesive layer is constructed as the infrared emission layer; Second, barium sulfate@PDMS core-shell microspheres or ZrO2@PDMS core-shell microspheres are dispersed in ethanol and then sprayed on the adhesive layer and pre-dried to form a porous reflective interface to obtain the reflective isolation layer; Finally, the super-hydrophobic protective layer adopts silicone resin modified silica aerogel powder or fluorinated SiO2 particles, which are deposited by cold spraying process and self-assembled into micro-nano structures at room temperature to obtain the radiative cooling coating, ensuring the hydrophobic stability.

4. The method of claim 3, wherein: In the preparation of the PDMS based adhesive layer, the PDMS parent and the crosslinking agent are mixed in a mass ratio of 10:1, and 200 nm hollow silica microspheres are added, and a ladder process is used in the curing process to form a high crosslinking elastomer, i.e., pre-curing at 50°C for 1 hour, and post-curing at 80°C for 2 hours, to obtain the PDMS based adhesive layer.

5. The method of claim 3, wherein: The core of the barium sulfate@PDMS core-shell microspheres is 500 nm, and the shell is 100 nm; or the thickness of the barium sulfate@PDMS core-shell microspheres dispersed in ethanol sprayed on the adhesive layer is 50 μm; or the pre-drying temperature is 60°C.

6. The method of claim 3, wherein: The particle size of the silicone resin modified silica aerogel powder is 1-5 μm; or the pressure of the cold spraying process is 0.2 MPa.

7. The method of manufacture according to any one of claims 3 to 6, wherein: The specific steps are as follows: Step one: preparation of the PDMS based adhesive layer First, the polydimethylsiloxane (PDMS) parent and the PDMS crosslinking agent are mixed in a mass ratio of 10:1, and stirred at 500 rpm for 10 min until homogeneous, and then SiO2 is added and dispersed by ultrasonic wave at 40 kHz for 15 min to eliminate agglomeration; then, n-heptane diluent is added; uniform speed is scraped on the surface of the container to form a wet film with a thickness of 210 μm and a dry film thickness of 200±10 μm; after coating, ladder curing is performed: 50°C hot air curing for 1 h to make the prepolymer form an elastic network, and then the temperature is raised to 80°C for 2 h to complete the crosslinking, obtaining the PDMS based adhesive layer; Step two: preparation of the reflective isolation layer BaSO4@PDMS core-shell microspheres are prepared, BaSO4 microspheres are mixed with anhydrous ethanol, and are placed in a ball mill with ZrO2 grinding balls for dispersion for 24 h until the slurry particle size distribution is uniform; a high-pressure airless spray gun is used, the pressure is set to 0.3 MPa, and the gun is uniformly sprayed at a distance of 25 cm from the PDMS based adhesive layer to form a wet film with a thickness of 55 μm. After spraying, it is immediately transferred to a 60°C hot air oven for drying for 10 min, and the film layer is required to be free of sagging and cracking, obtaining BaSO4@PDMS; wherein, Step three: preparation of the super-hydrophobic protective layer Take SiO2 aerogel powder, add 5wt% silicone resin modifier, react at 60℃ for 4h, obtain hydrophobic modified aerogel powder, contact angle >156°; use supersonic cold spray system, nitrogen as carrier gas, gas pressure 0.2MPa, powder flow rate 10g / min, spray deposition at 15cm from the BaSO4@PDMS container surface coated with, in the relative humidity RH <45% environment, form a protective layer thickness of 20±2μm; after deposition, room temperature standing for 24h, so that the aerogel powder self-assembly into micro-nano structure, get SiO2@BaSO4@PDMS coating, namely the container with multilayer gradient super-hydrophobic radiation refrigeration coating.

8. The method of claim 7, wherein: The ratio of polydimethylsiloxane PDMS precursor: SiO2: n-heptane in step one is 18:6:40; or, the diameter of SiO2 in step one is d = 200nm; Or, the mass ratio of BaSO4 microspheres: anhydrous ethanol in step two is 1:4; or, the nozzle diameter of high-pressure airless spray gun in step two is 0.5mm; Or, the SiO2 aerogel powder in step three is 30nm SiO2 aerogel powder.

9. The method of claim 7, wherein: In step one, mix polydimethylsiloxane PDMS precursor and PDMS crosslinking agent with a mass ratio of 10:1, mechanically stir at 500 rpm for 10min until homogeneous, then add 5% PMMA microspheres, polymethyl methacrylate, with an average particle size of 1μm, relative to the mass fraction of PDMS precursor, and then add SiO2.

10. The use of the preparation method according to any one of claims 3 to 9 in radiation refrigeration.

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