Porous radiation refrigeration film layer structure with heat directional transmission function and preparation method of porous radiation refrigeration film layer structure

Abstract

The invention relates to the technical field of radiation refrigeration materials, in particular to a porous radiation refrigeration film layer structure with a heat directional transmission function and a preparation method thereof, and the porous radiation refrigeration film layer structure comprises a blocking layer, a radiation layer and a reflecting layer which are sequentially arranged from inside to outside; the barrier layer is a graded porous membrane which is made of a high polymer material and has atmospheric window wave band absorption capability; the radiation layer is a graded porous membrane formed by a high polymer material with atmospheric window wave band absorption capability and radiation refrigeration filler which is randomly and uniformly distributed; the heat conductivity coefficient of the radiation refrigeration filler exceeds 50 W / m.K, and the radiation refrigeration filler has emissivity exceeding 85% in an atmospheric window. The reflecting layer is a graded porous film formed by a high polymer material with atmospheric window wave band absorption capability and randomly and uniformly distributed pigments and fillers; the porous radiation refrigeration film layer structure has a good heat directional transmission function, and the passive refrigeration effect is outstanding.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of radiation refrigeration materials, and particularly relates to a porous radiation refrigeration film layer structure with heat directional transmission function and a preparation method thereof. BACKGROUND

[0002] Radiation refrigeration technology is to use selective radiation refrigeration materials to dissipate the heat on the surface of an object in the form of mid-infrared electromagnetic waves through the atmospheric transparent window (8-13 μm) to the low-temperature outer space, so as to achieve passive cooling without energy consumption. In recent years, radiation refrigeration technology has attracted widespread attention in the fields of building energy saving, electronic device heat dissipation, and transportation tools.

[0003] When the sun is directly shining, the increase of the temperature on the surface of an object depends on the absorption of sunlight by the object (the heat is mainly concentrated in visible light and near-infrared rays). In order to reduce the temperature on the surface of an object, it is necessary to not only reduce the absorption of sunlight, but also to radiate the absorbed heat to the outer space. Although the existing single-layer radiation refrigeration film has the above two functions, it often has low reflectivity and radiance, and cannot achieve high-efficiency refrigeration effect.

[0004] The prior art such as patent No. CN 117382272A discloses a double-layer radiation refrigeration film, which comprises a radiation layer and a heat-blocking layer. The radiation layer radiates the absorbed heat to the outer space in the form of infrared rays, and the heat-blocking layer prevents the heat on the surface layer from being transmitted to the object. The prior art such as patent No. CN 119958135A discloses a four-layer radiation refrigeration film, which comprises a surface coating layer composed of super-hydrophobic coating for providing anti-fouling and self-cleaning functions; a top layer composed of titanium dioxide nanoparticles with high solar reflectivity; a middle layer which is a polytetrafluoroethylene layer with a hierarchical porous structure, providing thermal insulation and high-efficiency mid-infrared emission; and a bottom layer composed of graphene oxide, having high thermal conductivity to promote heat transfer. As can be seen from the existing disclosed patents, in order to reduce the absorption of sunlight by the multi-layer radiation refrigeration film and improve the refrigeration effect, the surface layer of the multi-layer film is often a coating layer with high solar reflectivity. However, the radiation refrigeration film with a surface layer having high solar reflectivity is more likely to cause light pollution. In order to reduce the light pollution caused by the radiation refrigeration film, a non-white or colored coating layer can be selected as the surface layer of the multi-layer radiation refrigeration film, but this will lead to an increase in the solar absorption rate and accumulation of heat on the surface layer.

[0005] It is very important to quickly conduct the heat absorbed by the surface layer and radiate it to the outer space through the atmospheric window. Therefore, it is of great significance to provide a multi-layer refrigeration film that can meet the high-efficiency radiation refrigeration of a white or non-white surface layer. SUMMARY

[0006] In order to solve the above technical problems, a porous radiative cooling film layer structure with heat directional transmission function and a preparation method thereof are provided. The porous radiative cooling film layer structure has good heat directional transmission function and prominent passive cooling effect.

[0007] In order to achieve the above purpose, the present application realizes the following technical solutions:

[0008] The porous radiative cooling film layer structure with heat directional transmission function comprises a barrier layer, a radiative layer and a reflective layer arranged in sequence from inside to outside.

[0009] The barrier layer is a hierarchical porous film formed by a high molecular material with atmospheric window band absorption capability;

[0010] The radiative layer is a hierarchical porous film formed by a high molecular material with atmospheric window band absorption capability and randomly and uniformly distributed radiative cooling fillers; the thermal conductivity of the radiative cooling fillers is more than 50 W / m·K and the emissivity in the atmospheric window is more than 85%; the emissivity of the radiative layer in the atmospheric window is more than 95%;

[0011] The reflective layer is a hierarchical porous film formed by a high molecular material with atmospheric window band absorption capability and randomly and uniformly distributed color fillers, and the reflective layer can be a white reflective layer or a colored reflective layer;

[0012] The heat gathered in the reflective layer can be directionally transmitted to the radiative layer through the radiative cooling fillers in the radiative layer.

[0013] Further, the high molecular material with atmospheric window band absorption capability is selected from polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) and / or polymethyl methacrylate (PMMA) to provide thermal insulation and high-efficiency mid-infrared emission;

[0014] The radiative cooling fillers are selected from one or more of ZnO, SiC, BN, AlN, Si3N4, graphene and derivatives thereof;

[0015] The color fillers are selected from one or more of white inorganic fillers, black inorganic fillers and colored inorganic fillers, the white inorganic fillers are selected from one or more of BaSO4, ZnO, Al2O3, TiO2, ZrO2 and AlPO4, the black inorganic fillers are selected from spinel structure Cu-Cr composite (such as CN114621604A), and the colored inorganic fillers are selected from one or more of iron-based pigments (such as iron red and iron yellow) and chromium-based pigments (such as chromium green, cobalt-chromium blue and cobalt-chromium green).

[0016] Further, the porosity of the barrier layer is 80%-90%, the pore size is 2-10 microns, and the thickness of the barrier layer is 1000-2000 microns;

[0017] The porosity of the radiation layer is in the range of 0%-85%, the pore size is 50 nanometers-5 microns, and the thickness of the radiation layer is 1000-5000 microns;

[0018] The porosity of the reflection layer is 50%-80%, the pore size is 50 nanometers-5 microns, and the thickness of the reflection layer is 500-2000 microns.

[0019] Further, the proportion of the radiation cooling filler in the radiation layer is 1%-70%, and the proportion of the color filler in the reflection layer is in the range of 0%-70%.

[0020] Preferably, the proportion of the radiation cooling filler in the radiation layer is 20%-60%, and the proportion of the color filler in the reflection layer is 5%-50%.

[0021] The preparation method of the porous radiation cooling film layer structure with the heat directional transmission function comprises the following steps:

[0022] S1, coating a barrier slurry on a substrate, and obtaining a barrier layer on the substrate after volatilization and drying;

[0023] The barrier slurry comprises the following uniformly mixed materials: a polymer material with atmospheric window waveband absorption capability, a good solvent for dissolving the polymer material, and a poor solvent which can at least partially mutually dissolve with the good solvent;

[0024] S2, coating a radiation cooling slurry on the barrier layer, and obtaining a radiation layer on the barrier layer after volatilization and drying;

[0025] The radiation cooling slurry comprises the following uniformly mixed materials: a radiation cooling filler, a polymer material with atmospheric window waveband absorption capability, a good solvent for dissolving the polymer material, and a poor solvent which can at least partially mutually dissolve with the good solvent;

[0026] S3, coating a reflection slurry on the radiation layer, and obtaining a reflection layer on the radiation layer after volatilization and drying; the porous radiation cooling film layer structure with the heat directional transmission function is obtained by peeling off or not peeling off from the substrate;

[0027] The reflection slurry comprises the following uniformly mixed materials: a color filler, a polymer material with atmospheric window waveband absorption capability, a good solvent for dissolving the polymer material, and a poor solvent which can at least partially mutually dissolve with the good solvent;

[0028] The selection of the polymer material, the good solvent and the poor solvent in the material composition of the three-layer material can be the same or different. The good solvent forms a polymer film during the drying process, and the poor solvent causes the formation of a hierarchical porous structure during the film forming process.

[0029] Further, the mass ratio of the polymer material having atmospheric window band absorption capacity, the good solvent and the poor solvent in the barrier slurry is 1:8.5-11.5:0.8-1.2.

[0030] The mass ratio of the polymer material having atmospheric window band absorption capacity, the good solvent and the poor solvent in the radiation refrigeration slurry is 1:8.5-11.5:0-1.2.

[0031] The mass ratio of the polymer material having atmospheric window band absorption capacity, the good solvent and the poor solvent in the reflective slurry is 1:8.5-11.5:0.8-1.2.

[0032] Preferably, the mass ratio of the polymer material having atmospheric window band absorption capacity, the good solvent and the poor solvent in the barrier slurry is 1:10-11:0.8-1.1.

[0033] The mass ratio of the polymer material having atmospheric window band absorption capacity, the good solvent and the poor solvent in the radiation refrigeration slurry is 1:10-11:0.8-1.1.

[0034] The mass ratio of the polymer material having atmospheric window band absorption capacity, the good solvent and the poor solvent in the reflective slurry is 1:10-11:0.8-1.1.

[0035] Further, the good solvent is selected from one or more of acetone, ethyl acetate, toluene and vinyl acetate; and the poor solvent is selected from water and / or ethanol.

[0036] Beneficial technical effects:

[0037] The reflective film of the surface layer is white or colored, that is, has a reflective or semi-reflective effect, which expands the application range of the radiation refrigeration film; the inorganic filler with high thermal conductivity and high emissivity is added to the intermediate radiation layer, so that the heat absorbed by the reflective film of the surface layer is directionally transmitted to the radiation layer, the radiation layer can concentrate the heat absorbed from the surface layer in the intermediate layer, and the heat is efficiently radiated to outer space by using the high emissivity of the layer, thereby achieving passive refrigeration effect; the barrier layer of the inner layer hinders the transmission of heat to the inside of the object.

[0038] The film layer structure of the present application realizes the high efficiency characteristics of solar light reflection and medium infrared radiation through the combination of multiple functional film layers. The reflective layer with surface reflection or semi-reflection effect can be white or colored, which increases the decoration of the overall film layer structure; when the surface reflective layer is white, the solar light reflectivity is high and the heat absorption is low; when the surface reflective layer is colored, although there is a certain absorption effect on solar light, the intermediate radiation layer has a high radiation rate on the atmospheric window, the high thermal conductive inorganic particles in the intermediate radiation layer directionally transmit the heat absorbed by the surface reflective layer to the intermediate radiation layer, and the high radiation rate of the layer on the atmospheric window is used to realize the high efficiency heat dissipation performance, and the inner barrier layer hinders the heat transfer of the intermediate layer to the inside of the object through hierarchical porous. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 SEM image of the porous radiation refrigeration film layer structure with heat directional transmission function of Example 1; wherein (a) is the SEM image of the cross section of the film layer structure, (b) is the surface SEM image of the surface reflective layer, (c) is the surface SEM image of the bottom barrier layer, and (d) is the surface SEM image of the intermediate radiation layer;

[0040] Figure 2 Working principle diagram of the porous radiation refrigeration film layer structure with heat directional transmission function of the present application;

[0041] Figure 3 Spectral reflectivity of the porous radiation refrigeration film layer structure with heat directional transmission function of Example 1; the surface layer of the structure of Example 1 is a white reflective layer;

[0042] Figure 4 Schematic diagram and device diagram of daytime radiation refrigeration test; wherein (a) is a schematic diagram, and (b) is a device diagram;

[0043] Figure 5 Illumination intensity and wind speed on the day of daytime radiation refrigeration; wherein (a) is the curve of illumination intensity changing with time, and (b) is the curve of wind speed changing with time;

[0044] Figure 6 Daytime cooling effect diagram of the porous radiation refrigeration film layer structure with heat directional transmission function of Example 1;

[0045] Figure 7 Radiation refrigeration efficiency of the porous radiation refrigeration film layer structure with heat directional transmission function of Example 1;

[0046] Figure 8 Spectral reflectivity of the porous radiation refrigeration film layer structure with heat directional transmission function of Example 2; the surface layer of the structure of Example 2 is a gray semi-reflective layer;

[0047] Figure 9The daytime cooling effect diagram of the porous radiative cooling film layer structure with heat directional transmission function of Example 2;

[0048] Figure 10 The radiative cooling efficiency of the porous radiative cooling film layer structure with heat directional transmission function of Example 2. DETAILED DESCRIPTION

[0049] The technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the embodiments of the present application and the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative, but not as any limitation on the present application and its application or use. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application.

[0050] Unless otherwise specifically indicated, the numerical values set forth in these embodiments do not limit the scope of the present application. Techniques, methods known to those of ordinary skill in the relevant art can not be discussed in detail, but should be considered part of the specification where appropriate. In all examples shown and discussed herein, any specific value should be interpreted as merely exemplary, and not as a limitation. Thus, other examples of the exemplary embodiments can have different values.

[0051] It should be noted that, for example, the values expressed as "in the range of a-b", "between a-b" do not include the end point values a and b; the values expressed as "a-b", "is a-b", "a-b" include the end point values a and b.

[0052] The experimental methods in the following embodiments without specific conditions are generally determined according to the national standard; if there is no corresponding national standard, they are carried out according to the general standard requirements or general methods.

[0053] Example 1

[0054] The porous radiative cooling film layer structure with heat directional transmission function comprises a barrier layer, a radiative layer and a reflective layer arranged in turn from inside to outside;

[0055] The barrier layer is a hierarchical porous membrane formed by PVDF-HFP;

[0056] The radiative layer is a hierarchical porous membrane formed by PVDF-HFP and SiC; the amount of SiC in this layer is 20% of the mass of PVDF-HFP;

[0057] The reflective layer is a hierarchical porous membrane formed by PVDF-HFP and AlPO4; the amount of AlPO4 in the layer is 30% of the mass of PVDF-HFP;

[0058] The preparation method of the porous radiative cooling film layer structure with heat directional transmission function comprises the following steps:

[0059] S1, preparing a barrier slurry: mixing PVDF-HFP, acetone (a good solvent), and water (a poor solvent) in a mass ratio of 1:10.5:0.9, dissolving at 55°C for 2h, and forming a uniformly mixed barrier slurry;

[0060] The barrier slurry is coated on the surface of the aluminum substrate using a film applicator, and the coating thickness is 1500 microns. After drying at 30°C for 3h, a hierarchical porous membrane is formed during the solvent evaporation process. After evaporation and drying, a barrier layer with a hierarchical porous structure is obtained on the aluminum substrate, and the film thickness is 1500 microns. The SEM image of the surface morphology of the barrier layer is shown in (c) of Figure 1 ;

[0061] S2, preparing a radiative cooling slurry: mixing SiC (average particle size 0.5 microns), PVDF-HFP, acetone (a good solvent), and water (a poor solvent) in a mass ratio of 0.2:1:10.5:0.9, dissolving at 55°C for 2h, and forming a uniformly mixed and dispersed radiative cooling slurry;

[0062] The radiative cooling slurry is coated on the barrier layer using a film applicator, and the coating thickness is 1000 microns. After drying at 30°C for 3h, a hierarchical porous membrane is formed during the solvent evaporation process. After evaporation and drying, a radiative layer with a hierarchical porous structure is obtained on the barrier layer, and the film thickness is 1000 microns. The SEM image of the surface morphology of the radiative layer is shown in (d) of Figure 1 ;

[0063] S3, preparing a reflective slurry: mixing white pigment AlPO4 (average particle size 2 microns), PVDF-HFP, acetone (a good solvent), and water (a poor solvent) in a mass ratio of 0.3:1:10.5:0.9, dissolving at 55°C for 2h, and forming a uniformly mixed and dispersed reflective slurry;

[0064] The reflective slurry is coated on the radiative layer using a film applicator, and the coating thickness is 500 microns. After drying at 30°C for 3h, a hierarchical porous membrane is formed during the solvent evaporation process. After evaporation and drying, a reflective layer with a hierarchical porous structure is obtained on the radiative layer, and the film thickness is 500 microns. The SEM image of the surface morphology of the reflective layer is shown in (b) of Figure 1 ;

[0065] Thus, the porous radiative cooling film layer structure with heat directional transmission function is obtained, the SEM image of the layer structure cross section is shown in (a) of Figure 1 , and the schematic diagram of the working principle is shown in Figure 2 .

[0066] The spectral reflectivity of the film layer structure obtained in this case is tested in the solar and infrared light bands, and the results are shown in Figure 3 , and it can be seen from Figure 3 that the average reflectivity of the film layer structure obtained in this case to sunlight (0.2-2.5 μm) is 94%, and the average emissivity in the atmospheric window (8-13 μm) is 98%.

[0067] The daytime cooling test of the film layer structure obtained in this case is carried out, and the schematic diagram and device diagram of the test are shown in Figure 4 . Polystyrene foam with low thermal conductivity is used as thermal insulation material, which is used as the external support frame of the device, and aluminum foil is covered outside the device as an incident light reflector, which is used as a thermal barrier for surrounding heat conduction to reduce the interference of outdoor solar radiation. Because the device is filled with foam, the heat exchange between the inside of the device and the environment can be reduced. A shelf made of natural fibers is placed at the bottom of the device to reduce the contact area between the device and the test film layer. The aluminum plate coated with the film layer of the product in this case is placed on the top of the device. In order to minimize the influence of the thermal convection of the surrounding environment on the measurement results of the radiative cooling, a layer of highly transparent polyethylene (PE) film is covered on the foam box to eliminate the thermal convection of unpredictable or unstable air flow. In order to ensure the accuracy of the temperature measurement of the film layer, a thermocouple is fixed at the bottom of the film layer to measure the temperature of the film layer. The radiative cooling effect of the film layer is evaluated by real-time temperature. The experiment was carried out on the roof platform of a seven-story building in Jingdezhen (North Latitude 29.3°, East Longitude 117.3°) on April 3, 2025 (09:00-17:00), and the test site was open with no high-rise buildings around to ensure that the test environment was not disturbed by the thermal radiation of adjacent buildings. The meteorological conditions during the test were stable, with an ambient temperature of 12-25℃, a relative humidity maintained at a low level and a small fluctuation. The solar radiation monitoring data are shown in (a) of Figure 5 , and the wind speed monitoring results are shown in (b) of Figure 5 (<2 m / s), which ensures the reliability of the test data. The daytime cooling test results are shown in Figure 6 , and it can be seen from Figure 6 that the film layer structure of this case can achieve an average cooling effect of 6℃ (maximum 12.2℃) compared with the surface temperature of the object without covering the film.

[0068] The cooling power of the film layer structure obtained in this case is calculated according to formula 1-1:

[0069] P cooling= P rad - P sun - P atm - P cond+conv (1-1)

[0070] P in formula 1-1 rad is the power of the radiation of the radiator outward, P rad = ε atm · σ · T 4 , wherein: ε atm is the emissivity of the atmospheric window waveband; σ is the Stefan-Boltzmann constant (5.67 x 10 -8 W / (m 2 · K 4 )); T is the temperature of the radiator (assuming 25℃, i.e. 298K);

[0071] P in formula 1-1 sun is the power of the solar absorption radiation, P sun = (1- R sun ) x I sun , wherein: R sun is the solar reflectivity (0.80); I sun is the solar irradiance (1000 W / m 2 );

[0072] P in formula 1-1 atm is the atmospheric radiation power, P atm = 150 W / m 2 ;

[0073] P in formula 1-1 cond+conv is the non-radiative heat exchange power, P cond+conv = h · (T- T amb ), wherein: h is the non-radiative heat exchange coefficient (0.5 W / (m 2 · K)); T is the temperature of the radiator (298K); T amb is the ambient temperature (298K), since T = T amb , so P cond+conv = 0 W / m 2 .

[0074] The cooling power corresponding to the surface temperature of the radiator in this case is shown in Figure 7 , as can be seen from Figure 7 , the radiation refrigeration power of the film layer structure in this case is 218.2 W / m 2 , and the refrigeration effect is excellent.

[0075] Example Two

[0076] The porous radiation refrigeration film layer structure with heat directional transmission function comprises a barrier layer, a radiation layer and a reflection layer arranged in sequence from inside to outside.

[0077] The barrier layer is a hierarchical porous film formed by PMMA.

[0078] The radiation layer is a hierarchical porous film formed by PMMA and BN; the amount of BN in the layer is 30% of the mass of PMMA.

[0079] The reflection layer is a hierarchical porous film formed by PMMA and CuCr2O4; the amount of CuCr2O4 in the layer is 5% of the mass of PMMA.

[0080] The preparation method of the porous radiation refrigeration film layer structure with heat directional transmission function comprises the following steps:

[0081] S1, preparing barrier slurry: mixing PMMA, vinyl acetate (good solvent) and ethanol (poor solvent) according to a mass ratio of 1:10:1, dissolving at 65 DEG C for 2.5 h to form uniformly mixed barrier slurry;

[0082] The barrier slurry is coated on the surface of the aluminum substrate by using a film applicator, the coating thickness is 1000 microns, and the solvent forms a hierarchical porous film during volatilization, and a barrier layer with a hierarchical porous structure is obtained on the aluminum substrate after volatilization and drying, and the film thickness is 1000 microns;

[0083] S2, preparing radiation refrigeration slurry: mixing BN (average particle size 1 micron), PMMA, vinyl acetate (good solvent) and ethanol (poor solvent) according to a mass ratio of 0.3:1:10:1, dissolving at 65 DEG C for 2.5 h to form uniformly mixed radiation refrigeration slurry;

[0084] The radiation refrigeration slurry is coated on the barrier layer by using a film applicator, the coating thickness is 1000 microns, and the solvent forms a hierarchical porous film during volatilization, and a radiation layer with a hierarchical porous structure is obtained on the barrier layer after volatilization and drying, and the film thickness is 1000 microns;

[0085] S3, preparing reflection slurry: mixing black pigment CuCr2O4 (average particle size 0.5 microns), PMMA, vinyl acetate (good solvent) and ethanol (poor solvent) according to a mass ratio of 0.05:1:11:0.8, dissolving at 60 DEG C for 3 h to form uniformly mixed reflection slurry;

[0086] The reflective slurry is coated on the radiation layer by using a film doctor, the coating thickness is 500 microns, dried at 30°C for 2h, and the solvent is volatilized to form a hierarchical porous film. After volatilization and drying, a reflective layer with a hierarchical porous structure is obtained on the radiation layer, and the film thickness is 500 microns.

[0087] Thus, a porous radiation refrigeration film layer structure with heat directional transmission function is obtained.

[0088] The film layer structure obtained in this case is tested for spectral reflectivity in the solar light band and the infrared light band, and the results are shown in Figure 8 , it can be seen from Figure 8 that the average reflectivity of the radiation refrigeration film obtained in this case to sunlight (0.2-2.5 μm) is 85%, and the average radiation rate in the atmospheric window (8-13 μm) is 95%.

[0089] The film layer structure obtained in this case is tested for daytime cooling, and the testing process is shown in Example 1. The daytime cooling test results are shown in Figure 9 , it can be seen from Figure 9 that the film layer structure of this case can achieve an average cooling effect of 3°C (maximum 6.2°C) compared with the surface temperature of the object without covering the film.

[0090] The film layer structure obtained in this case is calculated for refrigeration power, and the calculation method is shown in Example 1. The cooling power corresponding to the surface temperature of the radiator is shown in Figure 10 , it can be seen from Figure 10 that the radiation refrigeration power of the film layer structure of this case is 83.7 W / m 2 , and the refrigeration effect is good.

[0091] Comparative Example 1

[0092] The preparation process and related parameters of this comparative case are the same as those of Example 1, except that no color filler is added to the reflective layer, which is a pure PVDF-HFP film; and no SiC filler is added to the radiation layer, which is also a pure PVDF-HFP film. That is, the three layers of this case are all PVDF-HFP porous films, i.e. all three layers are barrier layers.

[0093] Comparative Example 2

[0094] The preparation process and related parameters of this comparative case are the same as those of Example 1, except that no SiC filler is added to the radiation layer, which is a pure PVDF-HFP film, and the barrier layer and the reflective layer are the same as those of Example 1. That is, this case is provided with two barrier layers and a reflective layer from inside to outside.

[0095] Comparative Example 3

[0096] The preparation process and related parameters of the comparative case are the same as Example 1, except that no color filler is added to the reflective layer, which is a pure PVDF-HFP film, and the barrier layer and the radiation layer are the same as Example 1. That is, the structure of this case is to set the radiation layer between the two barrier layers.

[0097] Comparative Example 4

[0098] The preparation process of this comparative case is: AlPO4, SiC, PVDF-HFP, acetone, water are mixed in a mass ratio of 0.3:0.2:1:10.5:0.9, dissolved and mixed at 55°C for 2h, forming a uniformly mixed slurry, which is coated onto the surface of the aluminum substrate using a doctor blade, and after drying treatment, a single layer of blended porous film with the same total thickness as Example 1 is obtained. The related preparation process parameters not shown are consistent with Example 1.

[0099] Comparative Example 5

[0100] The preparation process and related parameters of this comparative case are the same as Example 1, except that the radiation layer is first prepared on the surface of the aluminum substrate, then the barrier layer is prepared on the radiation layer, and finally the reflective layer of the surface layer is prepared. That is, the layer structure of this case is radiation layer, barrier layer, and reflective layer from inside to outside.

[0101] Comparative Example 6

[0102] The preparation process and related parameters of this comparative case are the same as Example 2, except that no BN filler is added to the radiation layer. That is, this case is sequentially provided with two barrier layers and a reflective layer from inside to outside.

[0103] Comparative Example 7

[0104] The preparation process of this comparative case is: CuCr2O4, PMMA, vinyl acetate, ethanol are mixed in a mass ratio of 0.05:1:11:0.8, dissolved and mixed at 60°C for 3h, forming a uniformly mixed slurry, which is coated onto the surface of the aluminum substrate using a doctor blade, and after drying treatment, a single layer of blended porous film with the same total thickness as Example 2 is obtained. The related preparation process parameters not shown are consistent with Example 2.

[0105] Test Example

[0106] The film layer structure of the above examples and comparative examples is tested, and the test results are shown in Table 1.

[0107] Table 1 Performance of each case structure

[0108]

[0109] As shown in Table 1, the average solar reflectivity of the film layer structure of the embodiment one of the present application reaches 94%, the atmospheric window radiation reaches 98%, the cooling effect of 6℃ (maximum 12.2℃) can be realized, and the refrigeration power reaches 218.3W / m 2 The average solar reflectivity of the film layer structure of the embodiment two of the present application reaches 85%, the atmospheric window radiation reaches 95%, the cooling effect of 3℃ (maximum 6.2℃) can be realized, and the refrigeration power reaches 83.7W / m 2 .

[0110] The comparative example 1 with three layers of barrier layer design cannot effectively radiate the heat flow, resulting in poor refrigeration effect; the comparative example 2 with two layers of barrier layer and a surface reflection layer design has high solar reflectivity, but the part of heat flow penetrating the surface layer is absorbed and cannot be effectively radiated through the porous structure and the radiation effect of PVDF-HFP, so the average atmospheric window radiation and the refrigeration effect are relatively poor compared with the embodiment one; the comparative example 3 with a radiation layer between the two layers of barrier layer has slightly poor solar reflectivity of the surface layer and slightly poor refrigeration effect compared with the embodiment one; the comparative example 4 with the filler and the polymer forming a single layer of porous film has the worst refrigeration effect; the comparative example 5 with the radiation layer and the barrier layer exchanged positions has the same solar reflectivity due to the existence of the reflection layer, but the heat is transferred to the inner layer due to the ineffective radiation of the heat after being transferred to the middle barrier layer, and the heat is partially accumulated and transferred to the object due to the existence of the high thermal conductivity filler in the inner layer, resulting in poor refrigeration effect.

[0111] The above is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited to this, any skilled person in the art can make equivalent replacement or change according to the technical solution and the inventive concept of the present application within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. A porous radiative cooling film layer structure with heat directional transmission function, characterized in that, The barrier layer, the radiation layer and the reflection layer are sequentially arranged from inside to outside. The barrier layer is a hierarchical porous membrane formed by a high polymer material with atmospheric window band absorption capacity. The radiation layer is a hierarchical porous membrane formed by a high polymer material with atmospheric window band absorption capacity and randomly and uniformly distributed radiation refrigeration fillers; the thermal conductivity of the radiation refrigeration fillers is more than 50 W / m·K and the emissivity in the atmospheric window is more than 85%; the emissivity of the radiation layer in the atmospheric window is more than 95%. The reflection layer is a hierarchical porous membrane formed by a high polymer material with atmospheric window band absorption capacity and randomly and uniformly distributed color fillers. The heat gathered in the reflection layer can be directionally transmitted to the radiation layer through the radiation refrigeration fillers in the radiation layer.

2. The porous radiative cooling film layer structure with heat direction transmission function according to claim 1, wherein, The high polymer material with atmospheric window band absorption capacity is selected from polyvinylidene fluoride-hexafluoropropylene and / or polymethyl methacrylate. The radiation refrigeration fillers are selected from one or more of ZnO, SiC, BN, AlN, Si3N4, graphene and derivatives thereof. The color fillers are selected from one or more of white inorganic fillers, black inorganic fillers and colored inorganic fillers; the white inorganic fillers are selected from one or more of BaSO4, ZnO, Al2O3, TiO2, ZrO2 and AlPO4; the black inorganic fillers are selected from spinel structure Cu-Cr compound; and the colored inorganic fillers are selected from one or more of iron-based pigments and chromium-based pigments.

3. The porous radiative cooling film layer structure with heat direction transmission function according to claim 2, characterized in that, The porosity of the barrier layer is 80%-90% and the pore size is 2-10 microns; the thickness of the barrier layer is 1000-2000 microns; The porosity of the radiation layer is in the range of 0%-85% and the pore size is 50 nanometers-5 microns; the thickness of the radiation layer is 1000-5000 microns; The porosity of the reflection layer is 50%-80% and the pore size is 50 nanometers-5 microns; the thickness of the reflection layer is 500-2000 microns.

4. The porous radiative cooling film layer structure with heat direction transmission function according to any one of claims 1-3, characterized in that, The proportion of the radiation refrigeration fillers in the radiation layer is 1%-70%; and the proportion of the color fillers in the reflection layer is in the range of 0%-70%.

5. The porous radiative cooling film layer structure with heat direction transmission function according to claim 4, characterized in that, The proportion of the radiation refrigeration fillers in the radiation layer is 20%-60%; and the proportion of the color fillers in the reflection layer is 5%-50%.

6. A preparation method of a porous radiation refrigeration film layer structure with heat directional transmission function, suitable for preparing the film layer structure according to any one of claims 1-5, comprising the following steps: S1, coating a barrier slurry on a substrate, and obtaining a barrier layer on the substrate after volatilization and drying; The barrier slurry comprises the following uniformly mixed materials: a high polymer material with atmospheric window band absorption capacity, a good solvent for dissolving the high polymer material, and a poor solvent which can at least partially mutually dissolve with the good solvent; S2, coating a radiation refrigeration slurry on the barrier layer, and obtaining a radiation layer on the barrier layer after volatilization and drying; The radiation refrigeration slurry comprises uniformly mixed materials: radiation refrigeration fillers, polymer materials with atmospheric window band absorption capacity, good solvents for dissolving the polymer materials, and poor solvents which can at least partially dissolve the good solvents; S3, coating a reflective slurry on the radiation layer, and obtaining a reflective layer on the radiation layer after volatilization and drying; thus obtaining a porous radiation refrigeration film layer structure with heat directional transmission function; The reflective slurry comprises uniformly mixed materials: pigments and fillers, polymer materials with atmospheric window band absorption capacity, good solvents for dissolving the polymer materials, and poor solvents which can at least partially dissolve the good solvents.

7. The method for preparing a porous radiative cooling film structure with directional heat transfer function according to claim 6, characterized in that, The mass ratio of the polymer materials with atmospheric window band absorption capacity, the good solvents, and the poor solvents in the barrier slurry is 1:8.5-11.5:0.8-1.2; The mass ratio of the polymer materials with atmospheric window band absorption capacity, the good solvents, and the poor solvents in the radiation refrigeration slurry is 1:8.5-11.5:0-1.2; The mass ratio of the polymer materials with atmospheric window band absorption capacity, the good solvents, and the poor solvents in the reflective slurry is 1:8.5-11.5:0.8-1.

2.

8. The method for preparing a porous radiative cooling film structure with directional heat transfer function according to claim 7, characterized in that, The mass ratio of the polymer materials with atmospheric window band absorption capacity, the good solvents, and the poor solvents in the barrier slurry is 1:10-11:0.8-1.1; The mass ratio of the polymer materials with atmospheric window band absorption capacity, the good solvents, and the poor solvents in the radiation refrigeration slurry is 1:10-11:0.8-1.1; The mass ratio of the polymer materials with atmospheric window band absorption capacity, the good solvents, and the poor solvents in the reflective slurry is 1:10-11:0.8-1.

1.

9. The method for preparing a porous radiative cooling film structure with directional heat transfer function according to claim 6, characterized in that, The good solvents are selected from one or more of acetone, ethyl acetate, toluene, and vinyl acetate; and the poor solvents are selected from water and / or ethanol.

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