Dual-band refrigeration film for plant growth and preparation method thereof

Abstract

The present invention provides a dual-band refrigeration film for plant growth and its preparation method. The refrigeration film comprises an encapsulation layer, a coating layer, and a substrate layer, arranged sequentially from the outside inward. The encapsulation layer is a high-emission polymer film layer. The coating layer comprises at least four layers, each 1-300 nm thick, stacked in sequence. The film layers include a metal film layer, an oxide film layer, and a fluoride film layer, and the metal film layer cannot be the outermost layer. The film layers are arranged alternately according to their refractive index. While ensuring normal plant growth, the refrigeration film of the present invention can achieve maximum cooling power, reduce plant leaf temperature, and reduce plant transpiration rate, thus solving the traditional agricultural problems of summer plant overheating and water shortage.

Description

Technical Field

[0001] The present invention relates to the technical field of refrigeration films, and in particular to a dual-band refrigeration film for plant growth and a preparation method thereof. Background Art

[0002] With the global population increase, rapid industrialization, and increasing urbanization, the effective crop and forestry planting areas are rapidly shrinking, leading to increasingly severe food shortages and desertification. To address food shortages, in addition to increasing per-acre yields, finding new land for cultivation is a more effective and convenient approach. Therefore, the development and utilization of land in extreme regions has become crucial. Furthermore, the increasing global warming problem has led to annual increases in global average temperatures and frequent high temperatures, making summer planting particularly difficult. Summer planting significantly increases water consumption, which runs counter to the ideal of water conservation. To reduce water consumption, cooling systems such as air conditioners can be used for cooling. However, cooling systems, such as air conditioners, are not only energy-intensive and economically costly, but also generate greenhouse gas emissions that affect plant growth, making this approach unacceptable to traditional agriculture. Therefore, research is underway to develop a passive, energy-free thin film that can provide a suitable temperature and humidity environment for plant growth in summer. This could effectively reduce the use of active cooling devices and the significant water consumption, lowering economic costs and aligning with green principles.

[0003] For any object on the surface of the earth, the energy transfer it receives during the day is calculated as: P net =P rad -P atm -P solar -P non-radiative , where P net Refers to the cooling power obtained by the object, P rad Refers to the radiation power of an object to the environment, P atm Refers to the radiation power of the environment to the object, P solar Refers to the incident power of sunlight, P non-radiative Refers to the convection conduction power. From the above formula, we can see that in order to obtain the highest cooling power possible, it is necessary to atm 、P solar and P non-radiative Effective regulation, where P solar It accounts for the largest proportion, so it is of great significance to effectively regulate the solar spectrum and reduce its incident energy accordingly.

[0004] At present, scientists have done a lot of work on the effective regulation of the solar spectrum to achieve the cooling effect. The first category is the research and development of radiative cooling materials. In 2014, a foreign research group achieved a 97% reflection in the sunlight band (the range of sunlight reaching the surface is 0.2-2.5μm) through the design of SiO2 / HfO2 multilayer photonic crystals. At the same time, the heat was highly emitted in the form of mid-infrared (8-13μm) electromagnetic waves, achieving a daytime cooling effect of 4.9℃ and a heat dissipation rate of 40W / m for the first time. 2 Subsequently, other researchers used different methods to achieve polymer-based daytime radiant cooling films, which rapidly reduced production costs and simplified the process, facilitating large-scale production and application. The second type is transparent cooling films, which have been widely used in the automotive industry. Compared to radiant cooling materials, transparent cooling films transmit visible light (0.4-0.7μm) while reflecting near-infrared light (0.7-2.5μm) that produces thermal effects as much as possible. This minimizes energy input without affecting people's normal vision, achieving the purpose of cooling.

[0005] Although both of the above methods have played an effective role in regulating sunlight, considering that plant photosynthesis is generally based on red light of 0.6-0.7μm and blue-green light of 0.4-0.5μm (light of 0.5-0.6μm is not needed by plants, but it will generate heat), the required materials cannot fully reflect sunlight like traditional radiative cooling materials, nor do they need to be fully transparent in a wide band of 0.4-0.7μm like transparent cooling films. It can be seen that the two current cooling materials have limitations when applied to the field of plant cultivation. Therefore, designing a cooling material that only allows light in the 0.4-0.5μm and 0.6-0.7μm bands required for plant photosynthesis to pass through, while reflecting light in other bands; at the same time, it emits heat in the form of mid-infrared electromagnetic waves, that is, to obtain maximum cooling power while meeting the normal growth of plants, is an urgent problem to be solved.

[0006] In view of this, it is necessary to design an improved dual-band refrigeration film for plant growth and a preparation method thereof to solve the above problems. Summary of the Invention

[0007] The object of the present invention is to provide a dual-band refrigeration film for plant growth and a preparation method thereof. By arranging a metal film layer and an oxide film layer and a fluoride film layer alternately stacked with different refractive indices, and controlling the thickness and positional relationship of the different film layers, a transmittance of more than 70% in the 0.4-0.5μm and 0.6-0.7μm bands and a reflectivity of more than 70% in the 0.5-0.6μm and 0.7-2.5μm bands are achieved. In addition, by stacking a high-emission polymer film layer on the coating layer, heat can be transferred to outer space in the form of mid-infrared (8-13μm) electromagnetic waves with an emissivity of more than 90%, thereby cooling the object.

[0008] To achieve the above-mentioned purpose of the invention, the present invention provides a dual-band refrigeration film for plant growth, comprising an encapsulation layer, a coating layer and a substrate layer arranged in sequence from the outside to the inside; the encapsulation layer is a high-molecular polymer film layer with high emissivity; the coating layer comprises at least 4 film layers with a thickness of 1-300 nm stacked in sequence, the film layers comprising a metal film layer, an oxide film layer and a fluoride film layer, and the metal film layer cannot be arranged in the outermost layer; the film layers are arranged alternately according to the size of the refractive index; when sunlight is incident, it can achieve transmission of light in the 0.4-0.5μm and 0.6-0.7μm bands and reflection of light in other bands, and at the same time, heat is highly emitted in the form of mid-infrared electromagnetic waves.

[0009] As a further improvement of the present invention, the coating layer includes 4-12 stacked film layers.

[0010] As a further improvement of the present invention, the thickness of the metal film layer is 1-50 nm; the thickness of the oxide film layer is 10-300 nm; and the thickness of the fluoride film layer is 10-200 nm.

[0011] As a further improvement of the present invention, the metal film layer includes one of aluminum, silver, and gold; the oxide film layer includes one of titanium dioxide, silicon dioxide, hafnium dioxide, and zinc oxide; and the fluoride film layer includes one of magnesium difluoride, calcium difluoride, barium difluoride, and aluminum trifluoride.

[0012] As a further improvement of the present invention, the high molecular polymer film layer includes one of PDMS, PET, and PEO; and has a thickness of 10-500 μm.

[0013] As a further improvement of the present invention, a glue layer is provided between the encapsulation layer and the coating layer, and the glue layer is a high-transparency OCA optical glue with a thickness of 1-30 μm.

[0014] As a further improvement of the present invention, the substrate layer is a high molecular polymer film or inorganic glass with a thickness of 0.1-1.5 mm; the high molecular polymer film is one of PET, PMMA, and PDMS, and the inorganic glass is silica glass.

[0015] As a further improvement of the present invention, the dual-band cooling film for plant growth has a transmittance of 70% for light in the 0.4-0.5μm and 0.6-0.7μm bands, and a reflectivity of more than 70% for light in the 0.5-0.6μm and 0.7-2.5μm bands, while heat achieves a 90% emissivity in the form of mid-infrared electromagnetic waves.

[0016] To achieve the above-mentioned object of the invention, the present invention further provides a method for preparing the above-mentioned dual-band refrigeration film for plant growth, comprising the following steps:

[0017] S1. Laminating corresponding film layers on the substrate layer in a predetermined order using a coating technology to form a coating layer on the substrate layer;

[0018] S2. Coating an optical adhesive on the coating layer obtained in step S1, and forming an adhesive layer on the coating layer after heat treatment;

[0019] S3. A composite encapsulation layer is formed on the adhesive layer obtained in step S2 to obtain a dual-band refrigeration film for plant growth;

[0020] The coating layer includes at least 4 film layers with a thickness of 1-300 nm stacked in sequence, the film layers include a metal film layer, an oxide film layer and a fluoride film layer, and the metal film layer cannot be arranged in the outermost layer; the film layers are arranged alternately according to the refractive index; the encapsulation layer is a high molecular polymer film layer with high emissivity characteristics.

[0021] As a further improvement of the present invention, in step S1, the coating technology includes one or more methods of electron beam evaporation, resistive thermal evaporation, and magnetron sputtering coating.

[0022] The beneficial effects of the present invention are:

[0023] (1) The present invention arranges a metal film layer, an oxide film layer and a fluoride film layer on a substrate layer, and the film layers are arranged alternately according to the size of the refractive index, and at the same time controls the thickness and position relationship of different film layers. By utilizing the difference in thickness and refractive index of each film layer, the present invention realizes fine control of each band of the solar spectrum, so that sunlight is reflected and refracted between different film layers. These reflected and refracted light rays interfere with each other to varying degrees. Through the superposition or attenuation of light rays, the transmission of light in the 0.4-0.5μm and 0.6-0.7μm bands and the reflection of light in other bands are finally achieved. Only the light required by plants is transmitted, while light in other bands is reflected, which not only avoids the damage to plants caused by excess light, but also reduces the heat generated by other light rays. At the same time, the present invention also stacks a high-emission polymer film layer on the coating layer. First, the polymer with a special structure absorbs heat during energy level transition and converts it into mid-infrared (8-13μm) electromagnetic waves, which are then transmitted to outer space to achieve cooling of the object. Secondly, the synergistic effect of the encapsulation layer and the coating layer is used to further achieve selective transmission and reflection of sunlight. Under the condition of normal incidence of sunlight, this refrigeration film can only pass the light required for plant growth, reducing the total energy incident. Under the premise of meeting the normal growth of plants, it can obtain maximum cooling power, reduce the temperature of plant leaves, and reduce the transpiration rate of plants. This solves the problems of overheating and water shortage of plants in traditional agriculture in summer. It can be applied to products such as plant greenhouses or greenhouses. While not affecting the normal growth of plants, it effectively reduces the temperature of the chamber and improves plant survival rate and yield.

[0024] (2) The cooling film prepared by the present invention has a transmittance of more than 70% in the 0.4-0.5μm and 0.6-0.7μm bands, and a reflectivity of more than 70% in the 0.5-0.6μm and 0.7-2.5μm bands; at the same time, the cooling film can transfer heat to space in the form of mid-infrared (8-13μm) electromagnetic waves with an emissivity of more than 90%, and at noon 900W / m 2 Under high-energy sunlight, the film reduces the temperature by 5-10°C compared to traditional transparent greenhouses and commercial transparent cooling films, achieving excellent radiant cooling. It boasts excellent minimum effective energy transmission and maximum energy output, resulting in superior radiant cooling. This cooling film significantly reduces water consumption, saving nearly 20% compared to traditional greenhouse films. It also reduces electricity consumption in summer greenhouses, increasing crop yields. The cooling film produced by this invention is an energy-free, high-performance, and environmentally friendly passive cooling device. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic structural diagram of the dual-band refrigeration film for plant growth according to the present invention.

[0026] Figure 2 This is a characterization diagram of the spectral transmittance of the substrate layer in the solar light band of Example 1 of the present invention.

[0027] Figure 3 This is a characterization diagram of the solar light band spectral transmittance of the dual-band refrigeration film for plant growth prepared in Example 1 of the present invention.

[0028] Figure 4 This is a characterization diagram of the mid-infrared band spectral emissivity of the dual-band refrigeration film for plant growth prepared in Example 1 of the present invention.

[0029] Figure 5 Schematic diagram of the structure of the device used to test the cooling performance of materials.

[0030] Figure 6 Temperature curves of different film materials.

[0031] Figure 7 This is a characterization diagram of the solar light band spectral transmittance of the dual-band refrigeration film for plant growth prepared in Example 2 of the present invention.

[0032] Figure 8 This is a characterization diagram of the solar light band spectral transmittance of the dual-band refrigeration film for plant growth prepared in Comparative Example 1 of the present invention.

[0033] Figure 9 This is a characterization diagram of the spectral transmittance of the dual-band refrigeration film for plant growth prepared in Comparative Example 2 of the present invention in the sunlight band.

[0034] Reference numerals

[0035] 1-Encapsulation layer; 2-Glue layer; 3-Coating layer; 4-Substrate layer; 5-Film to be tested; 6-Thermocouple; 7-Plant; 8-Foam. DETAILED DESCRIPTION

[0036] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] It should also be noted here that, in order to avoid obscuring the present invention due to unnecessary details, only structures and / or processing steps closely related to the solutions of the present invention are shown in the drawings, while other details that are not closely related to the present invention are omitted.

[0038] In addition, it should be noted that the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0039] See also Figure 1 As shown, the present invention provides a dual-band refrigeration film for plant growth, comprising an encapsulation layer 1, a coating layer 3 and a substrate layer 4 arranged in sequence from the outside to the inside. The encapsulation layer 1 is a high-molecular polymer film layer with high emissivity; the coating layer 3 comprises at least four film layers with a thickness of 1-300 nm stacked in sequence, specifically, the film layers include metal film layers, oxide film layers and fluoride film layers, and the metal film layer cannot be arranged in the outermost layer; the film layers are arranged alternately according to the refractive index, and the refractive index difference between adjacent film layers is greater than 0.5. With such an arrangement, when sunlight is incident, under the synergistic effect of the encapsulation layer 1 and the coating layer 3, the transmission of light in the 0.4-0.5μm and 0.6-0.7μm bands and the reflection of light in other bands can be achieved, and at the same time, heat is highly emitted in the form of mid-infrared electromagnetic waves.

[0040] The encapsulation layer 1 satisfies the requirements of high transmittance in the solar wavelength band and high emissivity in the mid-infrared region. Preferably, the polymer film layer comprises one of PDMS (polydimethylsiloxane), PET (polyethylene terephthalate), and PEO (polyethylene oxide), with a thickness of 10-500 μm. These highly emissive polymers absorb heat during energy level transitions and convert it into mid-infrared (8-13 μm) electromagnetic waves, which are then transmitted to outer space, thereby cooling the object.

[0041] Preferably, the coating layer 3 includes 4-12 stacked film layers, wherein the metal film layer includes one of aluminum, silver, and gold, with a thickness of 1-50nm; the oxide film layer includes one of titanium dioxide, silicon dioxide, hafnium dioxide, and zinc oxide, with a thickness of 10-300nm; and the fluoride film layer includes one of magnesium difluoride, calcium difluoride, barium difluoride, and aluminum trifluoride, with a thickness of 10-200nm. The film layers are arranged alternately according to the refractive index, with high refractive index film layers and low refractive index film layers arranged alternately. The metal film layer is intercalated or located at the bottom layer, but cannot be located at the top layer. This is mainly because the metal film layer has high reflectivity. If it is located at the top layer, it will easily be oxidized, resulting in changes in its optical properties, thereby failing to achieve effective transmission of sunlight. When sunlight passes through encapsulation layer 1 and hits coating layer 3, it reflects and refracts between the different layers, depending on the thickness and refractive index. These reflected and refracted rays interfere with each other to varying degrees, superimposing or attenuating the light. Ultimately, light in the 0.4-0.5μm and 0.6-0.7μm bands is transmitted, while light in other bands is reflected. This allows only the light needed by the plants to be transmitted, while light in other bands is reflected. This prevents damage to the plants from excess light and reduces the heat generated by other light.

[0042] In some embodiments, an adhesive layer 2 is provided between the encapsulation layer 1 and the coating layer 3. Adhesive layer 2 is a highly transparent OCA optical adhesive. OCA optical adhesive is a specialty adhesive that is colorless and transparent, has a light transmittance exceeding 90%, exhibits excellent bonding strength, and can be cured at room or moderate temperatures. This arrangement allows light to pass through adhesive layer 2 with minimal attenuation, thereby maintaining the performance of the dual-band cooling film for plant growth prepared by the present invention.

[0043] Substrate layer 4 can be made of either a rigid substrate such as quartz glass or a flexible substrate. It primarily serves as a support, so it must meet certain mechanical strength requirements. More importantly, it must possess optical properties with high transmittance across the solar spectrum to ensure effective light penetration. Substrate layer 4 has a thickness of 0.1-1.5 mm. Rigid substrates are made of inorganic glass, preferably silica glass; flexible substrates are made of a polymer film, preferably polyethylene terephthalate (PET), polymethyl methacrylate (PMMA), or polydimethylsiloxane (PDMS).

[0044] The present invention also provides a method for preparing the dual-band refrigeration film for plant growth, comprising the following steps:

[0045] S1. Preparation of coating layer

[0046] A suitable substrate layer 4 is selected, and corresponding film layers are stacked on the substrate 4 in a predetermined order using a coating technique. That is, a first film layer is first formed on the substrate layer 4 using a coating technique, and then a second film layer is formed on the formed first film layer using a coating technique. This process is repeated until the required last film layer is coated to form a planar photonic crystal, and finally a coating layer 3 is formed on the substrate layer 4.

[0047] The coating technology includes one or more methods of electron beam evaporation, resistive thermal evaporation, and magnetron sputtering coating.

[0048] The coating layer 3 includes at least four film layers with a thickness of 1-300 nm stacked in sequence, including metal film layers, oxide film layers and fluoride film layers, and the metal film layer cannot be set in the outermost layer; the film layers are alternately arranged according to the refractive index, and the refractive index difference between adjacent film layers is greater than 0.5; different high refractive index film layer materials can replace each other, and different low refractive index film layer materials can also replace each other.

[0049] In the entire preparation process, cleaning the surface of the substrate layer 4 is of vital importance. The present invention strictly follows the traditional "three-step method" for cleaning, which involves soaking in acetone and ultrasonically for 10 minutes, then replacing it with ethanol and ultrasonically soaking for 10 minutes, and finally soaking it in water and ultrasonically soaking for 10 minutes to remove all the oil and impurities on the surface of the substrate layer 4 and obtain a clean and smooth surface. Next, copper glue is used to fix the substrate layer 4 in the center of the substrate to improve the fit between the substrate layer 4 and the substrate to increase thermal conductivity, while also preventing the substrate layer 4 from curling and causing sample unevenness. Then, normal coating operations are carried out, the source materials are replaced, and the coating materials used are placed in different crucibles respectively. The samples are placed, and the hatch is closed and vacuumed. When the vacuum degree reaches 5x10 -4 When the pressure drops below 5 Pa, set the substrate speed to 15 rpm, open the electron gun and gun baffle for pre-sputtering, and observe and adjust the current through the crystal oscillator to control the coating rate until the coating rate reading stabilizes at 5 A / s. Open the substrate baffle to proceed with coating. During the coating process, constantly observe the crystal oscillator reading and fine-tune the current to stabilize it. After the first layer is deposited, replace the crucible for sputtering and begin depositing the second layer. Repeat this process until all layers are deposited. Release the vacuum and remove the sample to complete the preparation of coating layer 3.

[0050] S2. Preparation of the Substrate

[0051] Optical adhesive is coated on the coating layer 3 obtained in step S1, and after heat treatment, an adhesive layer 2 is formed on the coating layer 3. The heat treatment temperature is 40°C, and the thickness of the obtained adhesive layer 2 is 1-30 μm.

[0052] S3. Preparation of dual-band refrigeration membrane for plant growth

[0053] A packaging layer 1 with a thickness of 10-500 μm is compounded on the adhesive layer 2 obtained in step S2 to obtain a dual-band refrigeration film for plant growth.

[0054] The resulting dual-band cooling film for plant growth has a transmittance of 70% for light in the 0.4-0.5μm and 0.6-0.7μm bands, and a reflectivity of over 70% for light in the 0.5-0.6μm and 0.7-2.5μm bands. At the same time, heat is emissive at 90% in the form of mid-infrared electromagnetic waves.

[0055] The present invention is described in detail below through a number of embodiments:

[0056] Example 1

[0057] A method for preparing a dual-band refrigeration film for plant growth comprises the following steps:

[0058] S1. Preparation of coating layer

[0059] 1mm thick SiO2 glass was selected as the substrate layer 4, and the substrate layer 4 was characterized for its transmittance in the sunlight band. The results are as follows: Figure 2 As shown, the substrate layer 4 can achieve a transmittance higher than 90% in the sunlight band and has good light transmittance.

[0060] Place one side of the SiO2 glass upward, load TiO2, MgF2, Ag, HfO2 and SiO2 targets into the electron beam chamber, and use electron beam evaporation technology to stack a 190nm thick TiO2 film layer, a 70nm thick MgF2 film layer, a 140nm thick TiO2 film layer, a 70nm thick MgF2 film layer, a 10nm thick Ag film layer, a 207nm thick HfO2 film layer, a 53nm thick MgF2 film layer, an 88nm thick TiO2 film layer, a 7nm thick Ag film layer, a 25nm thick HfO2 film layer and a 100nm thick SiO2 film layer on the SiO2 glass in sequence to form a coating layer 3 on the substrate layer 4, break the vacuum and take out the sample.

[0061] S2. Preparation of the Substrate

[0062] An acrylic pressure-sensitive adhesive is coated on the topmost coating layer of the coating layer 3 obtained in step S1 and dried to obtain an adhesive layer, i.e., an adhesive layer 2 is formed on the coating layer 3. The adhesive is LOCTITE DURO-TAK 8063 solvent-based acrylic adhesive from Henkel, Germany.

[0063] S3. Preparation of dual-band refrigeration membrane for plant growth

[0064] A 300 μm thick PDMS encapsulation layer 1 is compounded on the adhesive layer 2 obtained in step S2 to obtain a dual-band refrigeration film for plant growth.

[0065] The dual-band cooling film for plant growth was characterized for its solar band transmittance. The results are as follows: Figure 3 As shown. Figure 3 It can be seen that the cooling film has a transmittance of more than 70% in the 0.4-0.5μm and 0.6-0.7μm bands, and a reflectivity of more than 70% in the 0.5-0.6μm and 0.7-2.5μm bands. It can be seen that the cooling film basically only transmits the light needed by plants, and basically reflects all the light that plants do not need.

[0066] The dual-band cooling film for plant growth was characterized for its spectral emissivity in the mid-infrared band. The results are as follows: Figure 4 As shown. Figure 4 It can be seen that the cooling film can transfer heat to outer space in the form of mid-infrared (8-13μm) electromagnetic waves with an emissivity of more than 90%, thereby cooling objects.

[0067] Depend on Figure 3and Figure 4 It can be seen that the cooling film has excellent minimum effective energy transmittance and highest energy output, thereby achieving excellent radiative cooling effect.

[0068] In order to study the cooling effect of the dual-band refrigeration film for plant growth prepared in Example 1 of the present invention, the following Figure 5 Measurements were performed using the apparatus shown. Reference numeral 5 represents the film to be tested; 6 represents a thermocouple; 7 represents a plant; and 5 represents foam. Plant 7 was placed in an open-lid box made of acrylic glass, insulated on all sides and at the bottom with foam 8. Film to be tested 5 was placed on top of the box, and thermocouple 6 was placed between plant 7 and film to be tested 5 for temperature measurement.

[0069] The films to be tested 5 are respectively the dual-band refrigeration film for plant growth prepared in Example 1 of the present invention, the commercial transparent heat-insulating film and the PE film. 2 The temperature curve under sunlight irradiation is as follows Figure 6 As shown. Figure 6 It can be seen that (1) the dual-band cooling film for plant growth prepared in Example 1 of the present invention basically maintains the ambient temperature at 25-30°C, which is a temperature suitable for plant growth; (2) the commercial transparent insulation film causes the ambient temperature to rise; and (3) under the action of the PE film, the ambient temperature rises to 35°C and even exceeds 40°C, which is far beyond the maximum temperature tolerated by plants. It can be seen that the cooling film prepared in the present invention does have a relatively good cooling effect and can meet the normal growth requirements of plants.

[0070] Examples 2-4

[0071] A method for preparing a dual-band refrigeration film for plant growth. Compared with Example 1, the difference is that the number of coating layers is reduced, but the spectral effect is still the same. The specific film layers and structures are shown in Table 1. The rest are roughly the same as Example 1 and will not be repeated here.

[0072] Table 1 Film structure of the dual-band refrigeration film for plant growth prepared in Examples 2-4

[0073] Example 2 (9-layer structure) Example 3 (6-layer structure) Example 4 (4-layer structure) <![CDATA[200nm SiO2]]> <![CDATA[100nm TiO2]]> <![CDATA[90nm HfO2]]> <![CDATA[80nm HfO2]]> <![CDATA[70nm SiO2]]> <![CDATA[80nm MgF2]]> <![CDATA[50nm SiO2]]> <![CDATA[220nm HfO2]]> <![CDATA[211nm TiO2]]> <![CDATA[240nm TiO2]]> 17nm Ag 17nm Ag 17nm Ag <![CDATA[120nm MgF2]]> Substrate layer 4 <![CDATA[100nm MgF2]]> <![CDATA[100nm HfO2]]> <![CDATA[120nm TiO2]]> Substrate layer 4 <![CDATA[150nm SiO2]]> <![CDATA[90nm TiO2]]> Substrate layer 4

[0074] The refrigeration film prepared in Example 2 was characterized for its transmittance in the solar band. The results are as follows: Figure 7 As shown. Figure 7It can be seen that the transmittance of the cooling film of Example 2 in the 0.4-0.5μm and 0.6-0.7μm bands, and the reflectance in the 0.5-0.6μm and 0.7-2.5μm bands are basically similar to those of Example 1. Similarly, the transmittance of the cooling films prepared in Examples 3-4 in the solar wavelength band was characterized, and the spectral effects (i.e., reflection and absorption of light in different wavelength bands) were also similar to those of Example 1. The corresponding cooling effects of the cooling films prepared in Examples 2-4 were also similar to those of Example 1.

[0075] Comparative Example 1

[0076] A method for preparing a dual-band refrigeration film for plant growth, compared with Example 1, differs in that the 10nm thick Ag film layer in the coating layer 3 is removed, and a 190nm thick TiO2 film layer, a 70nm thick MgF2 film layer, a 140nm thick TiO2 film layer, a 70nm thick MgF2 film layer, a 207nm thick TiO2 film layer, a 53nm thick MgF2 film layer, an 88nm thick TiO2 film layer, a 7nm thick Ag film layer, a 25nm thick TiO2 film layer and a 100nm thick SiO2 film layer are sequentially stacked on the SiO2 glass. The rest is roughly the same as in Example 1 and will not be repeated here.

[0077] The refrigeration film prepared in Comparative Example 1 was characterized for its transmittance in the solar band. The results are as follows: Figure 8 As shown. Figure 8 It can be seen that the spectral structure has completely deviated from the pre-constructed structure, with the transmittance in the 0.4-0.5μm band significantly reduced, and the reflectivity in the 0.5-0.6μm and 0.7-2.5μm bands also significantly reduced, allowing more light in the 0.5-0.6μm and 0.7-2.5μm bands to pass through, seriously affecting the dual transmission peaks and near-infrared light blocking effect, indicating that the role of the Ag film layer is crucial. This may be because without the presence of the Ag film layer, the reflection and refraction of light between the different film layers are affected, which in turn affects the interference effect between different light rays, resulting in poor performance of the final prepared refrigeration film.

[0078] Comparative Example 2

[0079] A method for preparing a dual-band refrigeration film for plant growth, compared with Example 1, differs in that the order of the first TiO2 film layer and the second MgF2 film layer is swapped, and a 70nm thick MgF2 film layer, a 190nm thick TiO2 film layer, a 140nm thick TiO2 film layer, a 70nm thick MgF2 film layer, a 10nm thick Ag film layer, a 207nm thick HfO2 film layer, a 53nm thick MgF2 film layer, an 88nm thick TiO2 film layer, a 7nm thick Ag film layer, a 25nm thick HfO2 film layer and a 100nm thick SiO2 film layer are stacked on the SiO2 glass in sequence. The rest is substantially the same as in Example 1 and will not be repeated here.

[0080] The refrigeration film prepared in Comparative Example 2 was characterized for its transmittance in the solar band. The results are as follows: Figure 9 As shown. Figure 9 As can be seen, the peak position shifts to the right, resulting in a weakened intensity, which seriously affects the peak position and intensity of the dual transmission peak. In fact, it is impossible to transmit dual bands, but the entire visible light band is transmitted. This shows that the order of film layers is crucial and needs to be placed in an alternating order of refractive index. At the same time, there are strict requirements for the thickness of the film layers (if a 190nm thick TiO2 film layer and a 140nm thick TiO2 film layer are considered as the same layer, the thickness exceeds the standard).

[0081] In summary, the present invention provides a dual-band refrigeration film for plant growth and a preparation method thereof. By arranging a metal film layer, an oxide film layer and a fluoride film layer on a substrate layer, and the film layers are alternately arranged according to the refractive index, while controlling the thickness and position relationship of different film layers, and utilizing the difference in thickness and refractive index of each film layer, a transmittance of more than 70% in the 0.4-0.5μm and 0.6-0.7μm bands and a reflectivity of more than 70% in the 0.5-0.6μm and 0.7-2.5μm bands are achieved; the present invention also stacks a high-emission polymer film layer with high emissivity characteristics on the coating layer, which can transfer heat to outer space in the form of mid-infrared (8-13μm) electromagnetic waves with an emissivity of more than 90%, thereby achieving cooling of objects.

[0082] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A dual-band refrigeration film for plant growth, characterized by: It includes an encapsulation layer, a coating layer and a substrate layer arranged in sequence from the outside to the inside; the encapsulation layer is a high molecular polymer film layer with high emissivity; the coating layer includes at least 4 film layers with a thickness of 1-300nm stacked in sequence, the film layers include a metal film layer, an oxide film layer and a fluoride film layer, and the metal film layer cannot be arranged in the outermost layer; the film layers are arranged alternately according to the size of the refractive index; when sunlight is incident, the dual-band refrigeration film for plant growth has a transmittance of 70% for light in the 0.4-0.5μm and 0.6-0.7μm bands, and a reflectivity of more than 70% for light in the 0.5-0.6μm and 0.7-2.5μm bands, and at the same time, heat achieves an emissivity of 90% in the form of mid-infrared electromagnetic waves.

2. The dual-band refrigeration film for plant growth according to claim 1, characterized in that: The coating layer includes 4 to 12 stacked film layers.

3. The dual-band refrigeration film for plant growth according to claim 1, characterized in that: The thickness of the metal film layer is 1-50 nm; the thickness of the oxide film layer is 10-300 nm; and the thickness of the fluoride film layer is 10-200 nm.

4. The dual-band refrigeration film for plant growth according to claim 3, characterized in that: The metal film layer includes one of aluminum, silver, and gold; the oxide film layer includes one of titanium dioxide, silicon dioxide, hafnium dioxide, and zinc oxide; and the fluoride film layer includes one of magnesium difluoride, calcium difluoride, barium difluoride, and aluminum trifluoride.

5. The dual-band refrigeration film for plant growth according to claim 1, characterized in that: The high molecular polymer film layer includes one of PDMS, PET and PEO; and has a thickness of 10-500 μm.

6. The dual-band refrigeration film for plant growth according to claim 1, characterized in that: An adhesive layer is provided between the packaging layer and the coating layer. The adhesive layer is a high-transparency OCA optical adhesive with a thickness of 1-30 μm.

7. The dual-band refrigeration film for plant growth according to claim 1, characterized in that: The substrate layer is a high molecular polymer film or inorganic glass with a thickness of 0.1-1.5 mm; the high molecular polymer film is one of PET, PMMA, and PDMS, and the inorganic glass is silica glass.

8. A method for preparing a dual-band refrigeration film for plant growth according to any one of claims 1 to 7, characterized in that: The steps include: S1. Laminating corresponding film layers on the substrate layer in a predetermined order using a coating technology to form a coating layer on the substrate layer; S2. Coating an optical adhesive on the coating layer obtained in step S1, and forming an adhesive layer on the coating layer after heat treatment; S3. A composite encapsulation layer is formed on the adhesive layer obtained in step S2 to obtain a dual-band refrigeration film for plant growth; The coating layer includes at least 4 film layers with a thickness of 1-300 nm stacked in sequence, the film layers include a metal film layer, an oxide film layer and a fluoride film layer, and the metal film layer cannot be arranged in the outermost layer; the film layers are arranged alternately according to the refractive index; the encapsulation layer is a high molecular polymer film layer with high emissivity characteristics.

9. The method for preparing a dual-band refrigeration film for plant growth according to claim 8, characterized in that: In step S1 , the coating technology includes one or more methods of electron beam evaporation, resistive thermal evaporation, and magnetron sputtering.

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