Optical radiation cooling film with gradient multilayer structure and preparation method thereof

Abstract

The invention discloses an optical radiation cooling film with a gradient multi-layer structure and a preparation method thereof, and relates to the technical field of radiation cooling, the film comprises high refractive index layers and low refractive index layers which are alternately stacked along the same direction; the high-refractive-index layer and the low-refractive-index layer form a micro-nano laminated structure; the high-refractive-index layer is obtained by selecting a high-refractive-index polymer, introducing a high-refractive-index filler or increasing the refractive index through a two-way stretching process; the low-refractive-index layer is obtained by selecting a low-refractive-index polymer, selecting a low-refractive-index filler or introducing a pore structure to reduce the refractive index; the optical radiation cooling film is of a multi-layer structure with layer thicknesses distributed in a gradient mode. The optical radiation cooling film can achieve more efficient sunlight reflection.

Description

Technical Field

[0001] The present application relates to the field of radiation cooling technology, and in particular to an optical radiation cooling film with a gradient multilayer structure and a preparation method thereof. Background Art

[0002] In recent years, with the intensification of global climate change, the high energy consumption and environmental impact of traditional refrigeration technology have attracted widespread attention. According to statistics, traditional refrigeration technology consumes about 13% of the world's energy and emits nearly 1 billion tons of carbon dioxide, exacerbating environmental problems such as extreme weather and rising sea levels. Therefore, the development of low-energy or even zero-energy refrigeration technology is of great significance to alleviating environmental problems.

[0003] Passive Daytime Radiative Cooling is a zero-energy cooling strategy that achieves efficient cooling by reflecting solar radiation (wavelength range of 0.3-2.5μm) and radiating heat to outer space (temperature of about 3K) through the atmospheric transparent window (wavelength range of 8-13μm). Passive daytime radiative cooling technology has a wide range of application potentials in buildings, vehicles, food preservation and other cooling scenarios, and has therefore received great attention from academia and industry in recent years.

[0004] Polymer materials are considered to be ideal for passive daytime radiative cooling due to their low absorptivity of the solar spectrum and infrared absorption and emission properties caused by functional group vibrations. However, polymers are usually transparent to sunlight and cannot directly achieve efficient sunlight reflection. To solve this problem, special structural design of polymers is usually required, such as additional metal reflective layers, porous structures, and metamaterial designs. However, the above methods involve complex manufacturing processes and are costly, making it difficult to meet the requirements of rapid large-scale production in industry. Therefore, the development of a low-cost, easy-to-scale radiative cooling film has become the key to promoting its industrial application.

[0005] One-dimensional photonic crystals are multilayer film structures composed of alternating high-refractive index and low-refractive index materials. By precisely designing the thickness and refractive index of each layer, strong reflection of sunlight of a specific wavelength can be achieved. This designed structure can be quickly mass-produced through microlayer co-extrusion technology to meet the needs of industrial applications. However, due to the small difference in refractive index between polymer materials (usually Δn<0.2), the reflection bandwidth of existing polymer-based one-dimensional photonic crystals is narrow (less than 100nm), making it difficult to achieve efficient reflection in a wide band (0.3-2.5μm). To achieve broadband and strong reflection, it is necessary to precisely construct a microlayer structure consisting of hundreds to thousands of layers, with a single layer thickness of nanometers and a gradient distribution of layer thickness. In addition, further increasing the refractive index difference between high / low refractive index layers can reduce the number of layers required and simplify the structural design.

[0006] However, there is currently no relevant technology that can successfully design and prepare gradient multilayer radiative cooling films that can efficiently reflect the entire solar spectrum. Therefore, the preparation of gradient multilayer radiative cooling films through gradient microlayer co-extrusion technology can achieve low-cost, high-efficiency large-scale production and has broad industrial application prospects. Summary of the invention

[0007] The purpose of the present application is to provide an optical radiation cooling film with a gradient multilayer structure and a preparation method thereof, which can be used for efficient radiation cooling.

[0008] To achieve the above objectives, this application provides the following solutions:

[0009] In the first aspect, the present application provides an optical radiation cooling film with a gradient multilayer structure, comprising high refractive index layers and low refractive index layers alternately stacked in the same direction; the high refractive index layers and the low refractive index layers constitute a micro-nano stacked structure; the high refractive index layers are obtained by selecting high refractive index polymers, introducing high refractive index fillers or increasing the refractive index through a biaxial stretching process; the low refractive index layers are obtained by selecting low refractive index polymers, introducing low refractive index fillers or lowering the refractive index through an introduction of a pore structure; the optical radiation cooling film is a multilayer structure with a gradient distribution of layer thickness.

[0010] Optionally, the gradient multilayer structure is prepared by a stacking system comprising a non-uniform stacker; the non-uniform stacker has two fishtail channels, wherein the width of the first fishtail channel is different from that of the second fishtail channel, and the height of the first fishtail channel is the same as that of the second fishtail channel.

[0011] Optionally, when the stacked structure with an initial number of layers of m in the gradient multilayer structure flows through n non-uniform layer stackers in sequence, a gradient structure with a number of layers of m×2n is formed.

[0012] Optionally, the gradient multilayer structure is prepared by a high-layer distributor, and the high-layer distributor is provided with a plurality of slit channels, and the volume of each slit channel gradually changes according to a linear or exponential law; different slit channels are used to transport high and low refractive index materials respectively.

[0013] Optionally, the high refractive index polymer is at least one of polycarbonate, polystyrene, nylon-6, nylon-66, polybutylene terephthalate, polyethylene terephthalate, polyethylene naphthalate, polylactic acid and polyethylene terephthalate-1,4-cyclohexanedimethanol.

[0014] Optionally, the high refractive index filler is at least one of titanium dioxide, aluminum oxide, zinc oxide, barium silicate, calcium silicate and zinc sulfide.

[0015] Optionally, the low refractive index polymer is at least one of fluoropolymer, polymethyl methacrylate, methyl methacrylate copolymer, ethylene terephthalate copolymer, ethylene naphthalate copolymer, ethylene terephthalate copolymer, polyethylene and polypropylene.

[0016] Optionally, the low refractive index filler is at least one of silicon dioxide, borosilicate, quartz, calcium fluoride, magnesium fluoride, aluminum fluoride, bauxite, and sodium chloride.

[0017] In a second aspect, the present application provides a method for preparing an optical radiation cooling film having a gradient multilayer structure, comprising the following steps:

[0018] Put high refractive index material A and low refractive index material B into extruder and medium for melting and plasticization respectively;

[0019] After the two melts are merged by a confluence device, they pass through a number of homogeneous layer stackers and gradient layer stackers connected in series to form a gradient multilayer melt flow with a layer thickness gradient distribution;

[0020] The gradient multilayer melt flow with controlled layer thickness gradient distribution flows through the die, cooling and pulling device and stretching device in sequence to obtain a gradient multilayer radiation cooling film.

[0021] In a third aspect, the present application provides a method for preparing an optical radiation cooling film having a gradient multilayer structure, comprising the following steps:

[0022] The high refractive index material A and the low refractive index material B are respectively put into separate extruders and melt-plasticized, and are superimposed into a gradient multi-layer melt flow in a high-layer gradient distributor;

[0023] The gradient multilayer melt flow flows through a die, a cooling and pulling device and a stretching device in sequence to obtain a gradient multilayer radiation cooling film.

[0024] According to the specific embodiments provided in this application, this application discloses the following technical effects:

[0025] The present application provides an optical radiation cooling film with a gradient multilayer structure and a preparation method thereof, the optical radiation cooling film comprising a high refractive index layer and a low refractive index layer alternately stacked in the same direction; the high refractive index layer and the low refractive index layer constitute a micro-nano stacked structure; the high refractive index layer is obtained by selecting a high refractive index polymer, selecting a high refractive index filler or by a biaxial stretching process to increase the refractive index; the low refractive index layer is obtained by selecting a low refractive index polymer, selecting a low refractive index filler or by introducing a pore structure to reduce the refractive index; the optical radiation cooling film is a gradient multilayer structure. The film of the present application adopts a gradient multilayer structure, which allows light to undergo multiple reflections and interferences inside the film, thereby enhancing the reflection effect of sunlight. By precisely controlling the refractive index and thickness of each layer, light of a specific wavelength can form constructive interference inside the film, thereby achieving efficient reflection. Secondly, the alternating stacking of high refractive index layers and low refractive index layers is also a key factor in achieving efficient reflection. The high refractive index layer increases its refractive index by selecting high refractive index polymers, high refractive index fillers or through a biaxial stretching process, while the low refractive index layer decreases its refractive index by selecting low refractive index polymers, low refractive index fillers or by introducing a pore structure, thereby further increasing the difference in refractive index at the interface and further enhancing the reflection effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 This is an electron microscope image of a medium-gradient multilayer radiation cooling film provided in one embodiment of the present application.

[0028] Figure 2 A schematic diagram of a non-uniformly layered stacker structure for preparing a gradient multilayer structure provided in one embodiment of the present application.

[0029] Figure 3 A schematic diagram of a high-layer distributor structure for preparing a gradient multi-layer structure provided in one embodiment of the present application.

[0030] Figure 4 A schematic diagram of a process for preparing a gradient multilayer radiation cooling film with 32*n layers of alternating A / B layers provided in one embodiment of the present application.

[0031] Figure 5A schematic diagram of a gradient structure design for preparing a gradient multilayer radiation cooling film provided in one embodiment of the present application.

[0032] Figure 6 The reflectivity of the gradient multilayer radiation cooling film provided in one embodiment of the present application.

[0033] Figure 7 The emissivity of a gradient multilayer radiative cooling film provided in one embodiment of the present application.

[0034] Figure 8 This is a stress-strain curve of a gradient multilayer radiation cooling film tensile test provided in an embodiment of the present application.

[0035] Fig. 9 This is the actual outdoor cooling effect of the gradient multi-layer radiation cooling film provided in one embodiment of the present application.

[0036] Fig.10 A flow chart of a process for preparing a gradient multilayer radiation cooling film with A / B alternating multiple layers based on a non-uniform layer stacker provided in one embodiment of the present application.

[0037] Fig.11 A flow chart of a process for preparing a gradient multilayer radiation cooling film with A / B as alternating multiple layers and C as a protective layer based on a non-uniform layer stacker provided in one embodiment of the present application.

[0038] Fig.12 A flow chart of a process for preparing a gradient multilayer radiation cooling film with alternating multiple layers of A / B based on a high layer distributor provided in one embodiment of the present application. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0040] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0041] Embodiment 1

[0042] The present embodiment provides an optical radiation cooling film with a gradient multilayer structure, comprising high refractive index layers and low refractive index layers alternately stacked in the same direction; the high refractive index layers and the low refractive index layers constitute a micro-nano stacked structure; the high refractive index layers are obtained by selecting high refractive index polymers, selecting high refractive index fillers or increasing the refractive index through a biaxial stretching process; the low refractive index layers are obtained by selecting low refractive index polymers, selecting low refractive index fillers or lowering the refractive index through the introduction of a pore structure; the optical radiation cooling film is a gradient multilayer structure.

[0043] Among them, the film forms a micro-nano stacked structure by alternately arranging materials with different refractive indices along the thickness direction, which can be used as a one-dimensional photonic crystal to achieve strong reflection of light in a specific band. In addition, the gradient layer thickness distribution can broaden the width of the reflection band. The film has excellent solar weighted reflectivity (≥0.8) for vertically incident sunlight with a wavelength in the range of 350nm to 2500nm, thereby achieving excellent solar radiation reflection performance. The film also has excellent flexibility, mechanical strength and anti-aging properties. It can be produced at low cost and on a large scale through gradient microlayer co-extrusion technology, and is suitable for construction, automotive, medical packaging and other fields. This technology can provide an effective solution for addressing global climate change and promoting the widespread application of zero-energy refrigeration technology.

[0044] In some embodiments, the high refractive layer can be realized by directly selecting a high refractive index polymer (such as at least one of polycarbonate, polystyrene, nylon-6, nylon-66, polyethylene terephthalate, polyethylene terephthalate, polyethylene naphthalate, polylactic acid, and polyethylene terephthalate-1,4-cyclohexane dimethanol), or adding a high refractive index filler to increase the refractive index (such as at least one of titanium dioxide, aluminum oxide, zinc oxide, barium silicate, calcium silicate, and zinc sulfide). Or the refractive index can be increased by biaxial stretching. The low refractive index layer can be realized by directly selecting a low refractive index polymer (such as at least one of a fluorine-containing polymer, polymethyl methacrylate, methyl methacrylate copolymer, ethylene terephthalate copolymer, ethylene naphthalate copolymer, ethylene terephthalate copolymer, polyethylene, and polypropylene), or adding a low refractive index filler (such as silicon dioxide, borosilicate, quartz, calcium fluoride, magnesium fluoride, aluminum fluoride, bauxite, and sodium chloride), or introducing a pore structure to reduce the refractive index.

[0045] Among them, the optical radiation cooling film can increase the refractive index difference through biaxial stretching. The high refractive index layer constituting the gradient multilayer structure can be made of crystalline polymer, and the low refractive index layer can be made of amorphous polymer. The biaxial stretching process further increases the in-plane refractive index of the high refractive index material, while the refractive index of the amorphous polymer remains unchanged during the stretching process, thereby further increasing the refractive difference between the materials.

[0046] Specifically, the gradient multilayer structure can be realized by connecting a series of uniform layer stackers and non-uniform layer stackers in series to achieve gradient layer thickness control, such as Figure 2 As shown, the non-uniform stacker is provided with a first fishtail channel A and a second fishtail channel B. The two fishtail channels occupy different volumes of space and are arranged in an overpass-like staggered manner. The inlets of the two channels are arranged in parallel on the left and right and the outlets are arranged in parallel on the top and bottom. At the inlet end, the widths of the two channels A and B are different but the heights are the same. At the outlet end, the widths of the two channels A and B are the same. The volume of space occupied by the channel A is V A , the volume of space occupied by channel B is V B , the volume ratio of the two channels R = V A / V B The entrance width, height and exit width, height of channel A are W respectively. A ,H,W,H A , the entrance width, height and exit width, height of channel B are W respectively B ,H,W,H B , where W = W A +W B ,H=H A +H B .

[0047] The gradient multilayer structure can also be realized by connecting a series of uniform layer stackers and non-uniform layer stackers in series to achieve gradient layer thickness control. Specifically, when the initial layer stack with m layers (m≥2) flows through the non-uniform layer stacker ( Figure 2 ), it is cut into two layer stacks A and B with different widths at the inlet end, and the two are widened and thinned when flowing forward in their respective channels, and re-converge and overlap in the thickness direction at the outlet end to form a layer stack C containing layer stacks A and B, wherein the thickness ratio of the internal layer stack A to the layer stack B is R, and the number of layers in the layer stack C is 2m. Further, when an initial layer stack with m layers (m≥2) flows through n non-uniform stackers with different R values ​​connected in series, a layer stack with m×2 layers can be formed. n , and has 2 n The micro-nano stacked structure with layer stacking thickness distribution, preferably, when n non-uniform stackers are connected in series according to their R values ​​from small to large, 2 n Gradient control of layer stack thickness.

[0048] The implementation method of the gradient multi-layer structure can be: to achieve layer thickness gradient control through a high layer number distributor, such as Figure 3 As shown, the distributor is specifically provided with hundreds or thousands of slit channels, and the volume of the slit channels changes gradually in sequence. Materials from different feeding devices are gathered into a gradient micro-nano stacked structure through the slit units with gradually changing volumes.

[0049] The number of layers of the prepared multilayer radiation cooling film is in the range of 8-2048 layers, preferably 128-1536 layers; the thickness of a single layer in the gradient multilayer structure is in the range of 15-20000 nanometers, preferably 30-16000 nanometers, and particularly preferably 50-10000 nanometers; the thickness gradient ratio of the thinnest and thickest layers is in the range of 1-10, preferably 1.5-8, and particularly preferably 2-6 ( Figure 5 ).

[0050] The multilayer radiation cooling film may be an integrated multilayer film having high reflectivity in the range of 300-2500 nm, such as Figure 6 As shown in (a) in FIG. 1 , it can also be a composite film of multiple multilayer thin films that reflect light of different wavelength bands, such as Figure 6 As shown in (b), the composite film can be assembled by hot pressing, cold pressing, adhesive bonding, and surface chemical cross-linking.

[0051] In some embodiments, the internal structure of the radiation cooling film may be composed of a micro-nano stacked structure, and upper and lower protective layers may be added as needed to prevent the gradient multilayer structure from being damaged during processing. Functional fillers may also be added to the protective layer as a functional layer to provide additional functions such as anti-ultraviolet, increase or decrease reflection, barrier, antibacterial / antiviral, self-cleaning, electromagnetic shielding, and anti-counterfeiting.

[0052] In some embodiments, the optical radiation cooling film has excellent reflectivity in the solar band (300nm-2500nm) and high emissivity in the atmospheric transparent window (8-13um). Figure 7 ), which can achieve excellent radiation cooling performance ( Fig. 9 ) and has excellent mechanical properties ( Figure 8 ), suitable for many fields such as construction, automotive, medical packaging, etc.

[0053] In an exemplary embodiment, this embodiment provides a method for preparing an optical radiation cooling film with a gradient multilayer structure, comprising the following steps:

[0054] Put high refractive index material A and low refractive index material B into extruder and medium for melting and plasticization respectively;

[0055] After the two melts are merged by a confluence device, they pass through a number of homogeneous layer stackers and gradient layer stackers connected in series to form a gradient multilayer melt flow with a layer thickness gradient distribution;

[0056] The gradient multilayer melt flow with controlled layer thickness gradient distribution flows through the die, cooling and pulling device and stretching device in sequence to obtain a gradient multilayer radiation cooling film.

[0057] In an exemplary embodiment, this embodiment provides a method for preparing an optical radiation cooling film with a gradient multilayer structure, comprising the following steps:

[0058] The high refractive index material A and the low refractive index material B are respectively put into separate extruders and melt-plasticized, and are superimposed into a gradient multi-layer melt flow in a high-layer gradient distributor;

[0059] The gradient multilayer melt flow flows through a die, a cooling and pulling device and a stretching device in sequence to obtain a gradient multilayer radiation cooling film.

[0060] Specifically, according to Figure 2 The layer multiplier working principle diagram shown, or Figure 3 The working principle diagram of the high-layer distributor shown in the figure completes the material preparation in the embodiment. This application demonstrates the preparation methods of the following six examples, as follows:

[0061] Example 1:

[0062] according to Figure 2 and Figure 4 The optical radiation cooling film with a gradient multilayer structure comprises the following raw materials:

[0063] High refractive index material A: polyethylene terephthalate (PET) material.

[0064] Low refractive index material B: polymethyl methacrylate (PMMA) material.

[0065] The preparation of a gradient multilayer radiation cooling film comprises the following steps:

[0066] The PET and PMMA materials were placed in a forced air drying oven for drying.

[0067] use Fig.10 and Fig.11 The preparation is carried out according to the flow chart shown in the figure. The materials from the two extruders A and B pass through a merger to form an initial 2-layer structure, and then flow through four 1:1 uniform layer stackers connected in series in sequence to form an initial 32-layer uniform layer stack. The 32-layer melt stack flows through five non-uniform layer stackers 1 (0.92 / 1), non-uniform layer stacker 2 (0.85 / 1), non-uniform layer stacker 3 (0.72 / 1), non-uniform layer stacker 4 (0.51 / 1), and non-uniform layer stacker 5 (0.26 / 1) with increasing segmentation ratios to form 32 layer thickness distributions, each with 32 layers of layer thickness distribution, a total of 1024 layers of gradient micro-nano stacking structure, and a gradient multilayer radiative cooling film is prepared after biaxial stretching.

[0068] The temperature settings of extruder #1 barrel zone 1, zone 2, zone 3, zone 4 and the front end zone of the merger are 260℃, 270℃, 270℃, 270℃, 270℃, respectively, and the speed is 60r / min; the temperature settings of extruder #2 barrel zone 1, zone 2, zone 3, zone 4 and the front end zone of the merger are 220℃, 230℃, 265℃, 265℃, 265℃, respectively, and the speed is 65r / min; the temperature settings of the merger zone, layer multiplier zone and die head zone are 270℃, 275℃, 275℃, 255℃ respectively.

[0069] Add the pre-baked polyethylene terephthalate (PET) and polymethyl methacrylate (PMMA) materials into extruders #1 and #2 respectively to form films. The prepared film has 32 layer thickness distributions after biaxial stretching, and each layer thickness distribution has 32 layers, with a total of 1024 layers of gradient micro-nano laminated structures, such as Figure 8 As shown, the layer thickness gradient is Figure 4 The weighted reflectivity of the prepared radiation cooling film in the 300nm-2500nm band is 95% ( Figure 6 (a) in the figure), and the emissivity in the atmospheric transparent window (8-13um) is 93% ( Figure 7 ), with excellent mechanical properties ( Figure 8 ), in outdoor cooling tests, it can achieve a sub-ambient cooling effect of an average of 3.2 degrees Celsius at night and an average of 8.8 degrees Celsius during the day ( Fig. 9 ).

[0070] Example 2:

[0071] according to Figure 2 and Figure 4 As shown, a gradient multilayer radiation cooling film comprises the following raw materials:

[0072] High refractive index material A: polyethylene terephthalate (PET) material.

[0073] Low refractive index material B: polymethyl methacrylate (PMMA) material.

[0074] Protective layer C: polymethyl methacrylate (PMMA) material

[0075] according to Fig.11 The process flow chart of preparing a gradient multilayer radiation cooling film comprises the following steps:

[0076] The PET and PMMA materials were placed in a forced air drying oven for drying.

[0077] use Fig.11The preparation is carried out according to the flow chart shown in the figure. Four uniform layer multipliers and 2, 3, 4, 5, and 6 gradient layer multipliers are connected in series at the confluence of the two extruders, and then a protective layer confluence, a casting die, and a traction device are installed in sequence after the layer multipliers. The series connection of four uniform layer multipliers and 2, 3, 4, 5, and 6 gradient layer multipliers can achieve a film with a gradient multilayer structure of 128, 256, 512, 1024, and 2048 layers. After biaxial stretching, gradient multilayer radiation cooling films with different numbers of layers can be prepared.

[0078] The temperature settings of the barrel zone 1, zone 2, zone 3, zone 4 and the front end zone of the confluence of extruder #1 are 260℃, 270℃, 270℃, 270℃, 270℃, and the speed is 60r / min; the temperature settings of the barrel zone 1, zone 2, zone 3, zone 4 and the front end zone of the confluence of extruder #2 are 220℃, 230℃, 265℃, 265℃, 270℃, and the speed is 65r / min; the temperature settings of the barrel zone 1, zone 2, zone 3, zone 4 and the front end zone of the confluence of extruder #3 are 230℃, 250℃, 260℃, 260℃, 270℃, and the speed is 30r / min; the temperature settings of the confluence zone, layer multiplier zone and die head zone are 270℃, 275℃, 275℃, 255℃, respectively.

[0079] Pre-baked polyethylene terephthalate (PET) and polymethyl methacrylate (PMMA) materials were added to extruders #1 and #2 respectively to form films. The prepared films were gradient multilayer radiation cooling films with 128, 256, 512, 1024, and 2048 layer structures.

[0080] Example 3:

[0081] A gradient multilayer radiation cooling film, comprising the following raw materials:

[0082] High refractive index material A: polyethylene naphthalate (PEN) material.

[0083] Low refractive index material B: polyvinylidene fluoride (PVDF) material.

[0084] according to Fig.12 The process flow chart of preparing a gradient multilayer radiation cooling film comprises the following steps:

[0085] The PEN and PVDF materials were placed in a forced air drying oven for drying.

[0086] according to Fig.12 The preparation is carried out according to the flow chart shown in the figure. The melt A and melt B extruded by the two extruders are superimposed in a high-layer distributor to form a gradient multi-layer melt flow, and then flow through the die, cooling and traction device, and biaxial stretching device in sequence.

[0087] By installing high-layer distributors with different numbers of branch channels, the prepared film can have a gradient multilayer structure of 128, 256, 512, 1024, and 2048 layers. After biaxial stretching, gradient multilayer radiation cooling films with different numbers of layers can be prepared.

[0088] The temperature settings of the first, second, third and fourth zones of the barrel of extruder #1 are 265℃, 275℃, 275℃ and 275℃ respectively, and the speed is 60r / min; the temperature settings of the first, second, third and fourth zones of the barrel of extruder #2 are 230℃, 240℃, 270℃ and 270℃ respectively, and the speed is 65r / min; the temperature settings of the high-layer distributor and die head zone are 275℃ and 260℃ respectively.

[0089] Pre-baked polyethylene naphthalate (PEN) and polyvinylidene fluoride (PVDF) materials were added to extruders #1 and #2 respectively to form films. The prepared films were gradient multilayer radiation cooling films with 128, 256, 512, 1024, and 2048 layer structures.

[0090] Example 4:

[0091] according to Figure 2 and Figure 4 As shown, a gradient multilayer radiation cooling film comprises the following raw materials:

[0092] High refractive index material A: polystyrene (PS) material.

[0093] Low refractive index material B: polycarbonate (PC) material.

[0094] The preparation of a gradient multilayer radiation cooling film comprises the following steps:

[0095] Put the PS and PC materials in a forced air drying oven to dry. Connect 4 uniform layer multipliers and 2, 3, 4, 5, and 6 gradient layer multipliers in series at the confluence of the two extruders, and then connect the die and traction device in sequence after the layer multipliers.

[0096] By connecting 4 uniformly layered multipliers and 2, 3, 4, 5, and 6 gradient layer multipliers in series, the prepared film can have a gradient multilayer structure of 128, 256, 512, 1024, and 2048 layers. After biaxial stretching, gradient multilayer radiation cooling films with different numbers of layers can be prepared.

[0097] The temperature settings of extruder #1 barrel zone 1, zone 2, zone 3, zone 4 and the front end zone of the merger are: 255℃, 265℃, 265℃, 265℃, 265℃, respectively, and the speed is 60r / min; the temperature settings of extruder #2 barrel zone 1, zone 2, zone 3, zone 4 and the front end zone of the merger are: 230℃, 240℃, 260℃, 260℃, 260℃, respectively, and the speed is 65r / min; the temperature settings of the merger zone, layer multiplier zone and die head zone are: 270℃, 275℃, 275℃, 255℃ respectively.

[0098] Pre-baked polystyrene (PS) and polycarbonate (PC) materials were added to extruders #1 and #2 respectively to form films. The prepared films were gradient multilayer radiation cooling films with 128, 256, 512, 1024, and 2048 layer structures.

[0099] Example 5:

[0100] according to Figure 2 and Figure 4 As shown, a gradient multilayer radiation cooling film comprises the following raw materials:

[0101] High refractive index material A: 70% polyethylene terephthalate (PET) / 30% titanium dioxide (TiO 2 )materials.

[0102] Low refractive index material B: polycarbonate (PC) material.

[0103] The preparation of a gradient multilayer radiation cooling film comprises the following steps:

[0104] 70% PET / 30% TiO 2 The PC material is placed in a forced air drying oven for drying. Four uniform layer multipliers and 2, 3, 4, 5, and 6 gradient layer multipliers are connected in series at the confluence of the two extruders, and then the casting die and the traction device are connected in sequence after the layer multipliers.

[0105] By connecting 4 uniformly layered multipliers and 2, 3, 4, 5, and 6 gradient layer multipliers in series, the prepared film can have a gradient multilayer structure of 128, 256, 512, 1024, and 2048 layers.

[0106] The temperature settings of extruder #1 barrel zone 1, zone 2, zone 3, zone 4 and the front end zone of the merger are: 255℃, 265℃, 265℃, 265℃, 265℃, respectively, and the speed is 60r / min; the temperature settings of extruder #2 barrel zone 1, zone 2, zone 3, zone 4 and the front end zone of the merger are: 230℃, 240℃, 260℃, 260℃, 260℃, respectively, and the speed is 65r / min; the temperature settings of the merger zone, layer multiplier zone and die head zone are: 270℃, 275℃, 275℃, 255℃ respectively.

[0107] Add the pre-baked 70% polyethylene terephthalate (PET) / 30% titanium dioxide (TiO 2 ) and polycarbonate (PC) materials to prepare films. The prepared films are gradient multilayer radiation cooling films with 128, 256, 512, 1024, 2048 layer structures.

[0108] Example 6:

[0109] according to Figure 2 and Figure 4 As shown, a gradient multilayer radiation cooling film comprises the following raw materials:

[0110] High refractive index material A: polyethylene terephthalate (PET) material.

[0111] Low refractive index material B: 70% polyethylene terephthalate (PET) / 30% poly-4-methylpentene-1 (TPX) material.

[0112] The preparation of a gradient multilayer radiation cooling film comprises the following steps:

[0113] PET and 70% PET / 30% TPX materials were placed in a forced air drying oven for drying. Four uniform layer multipliers and 2, 3, 4, 5, and 6 gradient layer multipliers were connected in series at the confluence of the two extruders, and then the casting die and the traction device were connected in sequence after the layer multipliers.

[0114] By connecting 4 uniformly layered multipliers and 2, 3, 4, 5, and 6 gradient layer multipliers in series, the prepared film can have a gradient multilayer structure of 128, 256, 512, 1024, and 2048 layers. In the subsequent stretching process, PET and TPX debond at the interface to produce a porous structure, and finally a radiation cooling film is obtained.

[0115] The temperature settings of extruder #1 barrel zone 1, zone 2, zone 3, zone 4 and the front end zone of the merger are: 255℃, 265℃, 265℃, 265℃, 265℃, respectively, and the speed is 60r / min; the temperature settings of extruder #2 barrel zone 1, zone 2, zone 3, zone 4 and the front end zone of the merger are: 230℃, 240℃, 260℃, 260℃, 260℃, respectively, and the speed is 65r / min; the temperature settings of the merger zone, layer multiplier zone and die head zone are: 270℃, 275℃, 275℃, 255℃ respectively.

[0116] Pre-baked polyethylene terephthalate (PET) material and 70% polyethylene terephthalate (PET) / 30% poly-4-methylpentene-1 (TPX) material were added to extruders #1 and #2, respectively, to form films. The prepared films were gradient multilayer radiation cooling films with 128, 256, 512, 1024, and 2048 layer structures.

[0117] In summary, this application has the following technical effects:

[0118] 1) The multilayer radiative cooling film provided in this application is a film material that is composed of hundreds to thousands of layers of materials alternately stacked together. Its unique gradient micro-nano layer structure design can accurately control the thickness and refractive index difference of each layer, thereby achieving more efficient sunlight reflection. By adjusting the layer thickness gradient ratio, it can meet the needs of different applications, such as reflecting solar radiation in different bands, and improve the adaptability and functionality of the film.

[0119] 2) The multilayer radiative cooling film provided by the present application can realize large-scale production of multilayer films through gradient microlayer co-extrusion technology. This technology can not only reduce production costs, but also quickly manufacture large-area films to meet the needs of industrial production. At the same time, the precise design of the microlayer structure enables the film to efficiently reflect sunlight in a wide band, with high production efficiency and economic benefits.

[0120] 3) The multilayer radiative cooling film provided in this application not only has excellent solar reflection performance, but also has good flexibility, mechanical strength and anti-aging performance. These characteristics enable the film to maintain its performance during long-term use and is suitable for various extreme environments and long-term use scenarios.

[0121] 4) The biaxial stretching process used in the preparation of the multilayer radiative cooling film provided in this application can not only increase the refractive index difference between high and low refractive index materials, thereby further increasing the reflection peak width and intensity, but also the biaxial stretching process can also improve the mechanical properties of the material, ensuring its optimal performance in different application fields.

[0122] 5) The film design provided in this application introduces upper and lower protective layers, which can reduce the damage to the layer structure caused by the wall shear of the mold during the extrusion process, ensure the regularity and gradient ratio of the layer structure, and have significant advantages in widening the width of the reflection band to achieve high solar reflectivity.

[0123] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0124] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. An optical radiation cooling film with a gradient multilayer structure, characterized in that: It comprises high refractive index layers and low refractive index layers alternately stacked in the same direction; the high refractive index layers and the low refractive index layers constitute a micro-nano stacked structure; the high refractive index layers are obtained by selecting high refractive index polymers, introducing high refractive index fillers or increasing the refractive index through a biaxial stretching process; the low refractive index layers are obtained by selecting low refractive index polymers, selecting low refractive index fillers or lowering the refractive index through the introduction of a pore structure; the optical radiation cooling film is a multilayer structure with a gradient distribution of layer thickness.

2. The optical radiation cooling film with a gradient multilayer structure according to claim 1, characterized in that: The gradient multilayer structure is prepared by a stacking system including a non-uniform stacker; the non-uniform stacker has two fishtail channels, wherein the inlet widths of the first fishtail channel and the second fishtail channel are different, and the inlet heights of the first fishtail channel and the second fishtail channel are the same.

3. The optical radiation cooling film with a gradient multilayer structure according to claim 2, characterized in that: When the stacked structure with an initial number of layers of m in the gradient multilayer structure flows through n non-uniform layer stackers in sequence, a gradient structure with a number of layers of m×2n is formed.

4. The optical radiation cooling film with a gradient multilayer structure according to claim 1, characterized in that: The gradient multilayer structure is prepared by a high-layer distributor, and the high-layer distributor is provided with a plurality of slit channels, and the volume of each slit channel gradually changes according to a linear or exponential law; different slit channels are used to transport high and low refractive index materials respectively.

5. The optical radiation cooling film with a gradient multilayer structure according to claim 1, characterized in that: The high refractive index polymer is at least one of polycarbonate, polystyrene, nylon-6, nylon-66, polybutylene terephthalate, polyethylene terephthalate, polyethylene naphthalate, polylactic acid and polyethylene terephthalate-1,4-cyclohexanedimethanol.

6. The optical radiation cooling film with a gradient multilayer structure according to claim 1, characterized in that: The high refractive index filler is at least one of titanium dioxide, aluminum oxide, zinc oxide, barium silicate, calcium silicate and zinc sulfide.

7. The optical radiation cooling film with a gradient multilayer structure according to claim 1, characterized in that: The low refractive index polymer is at least one of fluoropolymer, polymethyl methacrylate, methyl methacrylate copolymer, ethylene terephthalate copolymer, ethylene naphthalate copolymer, ethylene terephthalate copolymer, polyethylene and polypropylene.

8. The optical radiation cooling film with a gradient multilayer structure according to claim 1, characterized in that: The low refractive index filler is at least one of silicon dioxide, borosilicate, quartz, calcium fluoride, magnesium fluoride, aluminum fluoride, bauxite, and sodium chloride.

9. A method for preparing an optical radiation cooling film with a gradient multilayer structure according to any one of claims 1 to 8, characterized in that: The following steps are involved: Put high refractive index material A and low refractive index material B into the extruder for melting and plasticization respectively; After the two melts are merged by a confluence device, they pass through a number of homogeneous layer stackers and gradient layer stackers connected in series to form a gradient multilayer melt flow with a layer thickness gradient distribution; The gradient multilayer melt flow with controlled layer thickness gradient distribution flows through the die, cooling and pulling device and stretching device in sequence to obtain a gradient multilayer radiation cooling film.

10. A method for preparing an optical radiation cooling film with a gradient multilayer structure according to any one of claims 1 to 8, characterized in that: The following steps are involved: The high refractive index material A and the low refractive index material B are respectively put into separate extruders and melt-plasticized, and are superimposed into a gradient multi-layer melt flow in a high-layer gradient distributor; The gradient multilayer melt flow flows through a die, a cooling and pulling device and a stretching device in sequence to obtain a gradient multilayer radiation cooling film.

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