Photovoltaic reflective film and preparation method thereof

Abstract

The present invention relates to the technical field of reflective film and discloses a reflective film for photovoltaic use and a preparation method thereof. The present invention prepares a four-layer composite structure, namely a protective layer, a reflective layer, a base layer, and an adhesive layer. Each layer is bonded together by a hot pressing composite process. Each layer has insulating properties. In addition, a modified EVA adhesive layer is used as a bottom functional layer, which has both strong adhesiveness and insulating properties. The prepared reflective film has excellent insulating properties, weather resistance, and high reflectivity, and has great application value in the field of photovoltaic reflective film.

Description

Technical Field

[0001] The present invention relates to the technical field of reflective films, in particular to a reflective film for photovoltaic use and a preparation method thereof. Background Art

[0002] In solar photovoltaic power generation systems, reflective film is a key auxiliary component, reflecting sunlight onto the light-receiving surface of photovoltaic modules, thereby improving the utilization rate of solar energy. With the growing global demand for renewable energy, the photovoltaic industry is placing increasing demands on reflective film for its performance, including high reflectivity, weather resistance, flexibility, ease of installation, and excellent insulation. Insulation is crucial in photovoltaic systems, effectively preventing the risk of electrical leakage and ensuring safe system operation. This is particularly true in complex environments such as humid and dusty environments, where it prevents electrical failures and enhances the stability and safety of photovoltaic systems.

[0003] Currently, the most commonly used reflective sheeting includes aluminum-based, glass-based, and polymer-based reflective sheeting. Although aluminum-based reflective sheeting has a high initial reflectivity, it is susceptible to oxidation and corrosion after long-term exposure to outdoor environments, resulting in a decrease in reflectivity. Its lack of flexibility makes it difficult to adapt to complex curved surfaces. Furthermore, aluminum is inherently conductive, which poses a risk of electrical leakage when used in photovoltaic systems and fails to meet insulation requirements. While glass-based reflective sheeting offers some insulation properties, it is heavy, which increases installation costs and difficulty. Its high brittleness makes it susceptible to breakage during transportation and use, and its overall structure is cumbersome, limiting its application in distributed photovoltaic systems. Furthermore, improper edge treatment of glass-based reflective sheeting can lead to a decrease in insulation performance. Polymer-based reflective sheeting has a weak bond with the substrate, making it prone to delamination. It also has poor UV resistance, resulting in a significant decrease in reflective performance after long-term use. The addition of conductive fillers or metal particles to some polymer-based reflective sheets can compromise insulation performance. Even without these additives, their structural design lacks specific consideration for insulation optimization, making it difficult to ensure insulation reliability in complex environments. Summary of the Invention

[0004] This invention addresses the problems of existing reflective film, such as rapid reflectivity decay, poor weather resistance, insufficient flexibility, inconvenient installation, and poor insulation. This solution designs a multi-layer composite reflective film, including a base layer, a reflective layer, a protective layer, and an adhesive layer. Each layer is made of materials with excellent insulation properties. The structural design ensures that the metal reflective coating is completely encapsulated, preventing the formation of conductive paths. This achieves an integrated combination of high reflectivity, weather resistance, flexibility, and insulation, resolving the multiple issues of existing reflective film. The resulting photovoltaic reflective film exhibits excellent weather resistance and high reflectivity.

[0005] To achieve the above-mentioned purpose, the present invention provides the following technical solutions:

[0006] A photovoltaic reflective film, the photovoltaic reflective film comprising the following four layers: a protective layer, a reflective layer, a base layer, and an adhesive layer, wherein each layer is bonded together by a hot pressing composite process to obtain the photovoltaic reflective film;

[0007] The bonding layer is a modified EVA film, and its preparation method is as follows:

[0008] EVA, maleic anhydride, tetrasalicylic aldehyde gemini quaternary ammonium salt and dicumyl peroxide are added into a Haake rheometer at 170-180° C., extruded and cooled to obtain modified EVA; and then placed in a film blowing machine to be blown into a film to obtain a modified EVA film.

[0009] Preferably, the mass ratio of the EVA, maleic anhydride, tetrasalicylicaldehyde gemini quaternary ammonium salt, and dicumyl peroxide is 100:1-2:3-5:0.1-0.3.

[0010] Preferably, the protective layer is a thin film composited with a high-refractive-index matrix resin and nano-oxide particles. The high-refractive-index matrix resin is polymethyl methacrylate (PMMA), and the nano-oxide particles are either titanium dioxide or zirconium dioxide. Nano-titanium dioxide and zirconium dioxide have UV resistance and can effectively block ultraviolet rays. PMMA is an excellent insulating material with good wear resistance and insulation properties. Both the high-refractive-index resin matrix and the nano-oxide are insulating materials. The coating process uniformly applies the protective layer to the surface of the reflective layer, forming a sealed insulating layer that prevents external moisture, dust, and other factors from affecting the reflective layer while also preventing current from intruding from above. This creates a multifunctional layer that combines light transmission, diffuse reflection, and insulation protection. The nano-titanium dioxide and zirconium dioxide particles, through the light scattering effect (Mie scattering), convert direct light into multi-angle diffuse light, ensuring uniform light incidence on the microstructured prism array or deflected plane structure of the reflective layer. This particularly enhances the utilization of low-angle incident light (such as morning and evening sunlight). The diffuse reflection effect is controlled by particle size (10-50nm can avoid severe light absorption), and the diffuse reflectivity is increased by 20%-30% in the wavelength range of 300-1100nm, reducing the "hot spot effect" on the surface of photovoltaic modules (efficiency attenuation caused by local strong light).

[0011] Preferably, the reflective layer comprises a metal reflective coating. The metal reflective coating is prepared by depositing a 50-150 μm thick aluminum or silver coating on the surface of the PET insulating material using a magnetron sputtering process. Although aluminum and silver are conductive metals, the coating is extremely thin and completely encapsulated by the upper and lower insulating layers (base layer and protective layer), eliminating exposed points. This prevents the formation of conductive pathways and ensures overall insulation. The PET insulating material has a planar structure or a microstructured prism array structure. The microstructured prism array is prepared by forming a triangular prism array with a height of 5-20 μm and a vertex angle of 90-150° on the surface of the base layer through a compression molding process, with a prism pitch of 20-100 μm. When sunlight enters the microstructured prism array, the prisms refract and reflect, converging the light onto the metal reflective coating. After reflection from the metal coating, the light is emitted at a specific angle, achieving efficient reflection of the sunlight. During this process, the reflective film remains insulated as a whole because the metal coating is wrapped by the insulating layer.

[0012] Preferably, the base layer is one of a polyethylene terephthalate (PET) film and a polyimide (PI) film.

[0013] Preferably, the preparation method of the tetrasalicylic aldehyde gemini quaternary ammonium salt is:

[0014] (1) Disalicylaldehyde diethylenetriamine Schiff base and 1,4-dibromo-2-butene are added to a 20% by mass sodium hydroxide aqueous solution, stirred and dispersed, and reacted at 80-90°C for 5-8 hours. After the reaction is completed, rotary evaporation is performed, and ethanol is added thereto, filtered, and rotary evaporation is performed to obtain an intermediate product A, wherein the molar ratio of disalicylaldehyde diethylenetriamine Schiff base and 1,4-dibromo-2-butene is 2-2.4:1. In this reaction, by controlling the molar ratio, the secondary amine contained in the disalicylaldehyde diethylenetriamine Schiff base is substituted with the bromine in 1,4-dibromo-2-butene to obtain the intermediate product A. The reaction route is as follows:

[0015] ;

[0016] (2) 3-chloro-1-propanol, isocyanate propyl triethoxysilane, and dibutyltin dilaurate are added to a flask, heated to 40-50°C, stirred and reacted for 3-5 hours. After the reaction is completed, the mixture is distilled under reduced pressure and dried to obtain an intermediate product B, wherein the molar ratio of 3-chloro-1-propanol, isocyanate propyl triethoxysilane, and dibutyltin dilaurate is 1:1-1.2:0.001-0.003. Under the catalytic reaction of dibutyltin dilaurate, 3-chloro-1-propanol and isocyanate propyl triethoxysilane react to obtain an intermediate product B, that is, a carbamate group is introduced into the intermediate product B, which is a group with strong polarity and can generate hydrogen bonds with the surface of the photovoltaic substrate, and synergistically increase the bonding effect with the siloxane structure. The reaction route is:

[0017] ;

[0018] (3) Add intermediate product A and intermediate product B to isopropanol solvent, add 20% by mass sodium hydroxide aqueous solution thereto, adjust the pH to 9-10, react at 75-85°C for 10-14h, and after the reaction, distill under reduced pressure, wash with ethanol, and dry to obtain tetrasalicylic aldehyde-based gemini quaternary ammonium salt, wherein the molar ratio of intermediate product A to intermediate product B is 1:2-2.2. In this reaction, the tertiary amine structure in intermediate product A and the chlorine atom in intermediate product B are used to undergo quaternization reaction to obtain tetrasalicylic aldehyde-based gemini quaternary ammonium salt. The product contains antibacterial structures such as salicylaldehyde, Schiff base and gemini quaternary ammonium salt structure (the antibacterial performance of the gemini quaternary ammonium salt structure is better than that of the monoquaternary ammonium salt structure). The reaction route is:

[0019] .

[0020] Beneficial technical effects of the present invention:

[0021] (1) The present invention prepares a four-layer composite structure, each layer has insulating properties, ensuring that the metal coating is wrapped by the insulating layer, achieving the unity of high reflection and insulation, and using the EVA adhesive layer as the bottom functional layer, which has both strong bonding and insulating functions.

[0022] (2) Both the base layer and the protective layer are made of highly insulating materials. Although the metal coating of the reflective layer is a conductive material, it is completely enclosed by the two insulating layers above and below, leaving no exposure, thus avoiding the risk of leakage. After testing, the insulation resistance of this reflective film is ≥ (test voltage 1000V DC), meeting the stringent insulation performance requirements of photovoltaic systems, effectively preventing electrical failures and improving system safety. It is particularly suitable for complex environments such as humid and dusty environments.

[0023] (3) The present invention improves the antibacterial performance of the reflective film by utilizing the antibacterial properties of Schiff base structure, salicylaldehyde structure and gemini quaternary ammonium salt, thereby increasing the service life of the reflective film, and introduces polar structures (such as carbamate, hydroxyl and quaternary ammonium salt structures) into the adhesive layer, i.e. the modified EVA film, to generate hydrogen bonds with the surface of the photovoltaic substrate, thereby increasing the bonding performance between the reflective film and the substrate.

[0024] (4) The modified EVA adhesive layer allows the reflective film to be directly attached to the edge of the photovoltaic module or the reflective area of ​​the bracket without the need for additional adhesives, which simplifies the installation process, reduces construction costs, and improves the fit for curved surfaces and special-shaped substrates (such as curved brackets). During the bending process, the modified EVA layer maintains adhesion through elastic deformation, avoiding structural damage caused by traditional mechanical fixing methods.

[0025] (5) The base layer and the modified EVA adhesive layer form a double-layer insulation structure of "high insulation substrate + insulating adhesive layer", which can effectively prevent moisture from penetrating into the metal plating of the reflective layer, especially in a humid environment, and prevent the formation of leakage paths.

[0026] (6) The modified EVA layer and the protective layer (anti-UV PMMA coating) form upper and lower weathering protection. After 1000 hours of humidity and heat test (85℃ / 85% RH), the interlayer peel strength retention rate is ≥90%, which is significantly better than the structure without adhesive layer (retention rate ≤70%). BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The present invention is a schematic diagram of a reflective film structure, comprising a protective layer (1), a reflective layer (2), a base layer (3) and an adhesive layer (4) arranged in sequence from top to bottom, wherein the reflective layer has a planar structure.

[0028] Figure 2 This is a schematic diagram of the reflective layer structure, A is the microstructure prism array, and B is the metal reflective coating. DETAILED DESCRIPTION

[0029] Preparation method of disalicylicaldehyde diethylenetriamine Schiff base: 0.06 mol of salicylaldehyde and ethanol are added to a flask, and then 0.01 mol of calcium chloride catalyst is added thereto. At 85°C, 0.03 mol of diethylenetriamine is added thereto and the reaction is carried out for 7 hours. After the reaction is completed, the mixture is cooled, concentrated, and recrystallized to obtain disalicylicaldehyde diethylenetriamine Schiff base. The reaction route is as follows:

[0030] .

[0031] Fabrication of the microstructured prism array: A triangular prism array with a height of 20 μm and a vertex angle of 100° is formed on the substrate surface through a compression molding process. The prism spacing is 100 μm. This structure is made of PET insulating material, which is inherently insulating.

[0032] Preparation of the metal reflective coating: A 100nm thick aluminum coating is deposited on the surface of the microstructured prism array using a magnetron sputtering process. Although aluminum is a conductive metal material, the coating is extremely thin and is completely wrapped by the upper and lower insulating layers (base layer and protective layer) with no exposed points, thus avoiding the formation of a conductive path and ensuring overall insulation.

[0033] Example 1

[0034] (1) Add 10 mmol of disalicyclic aldehyde diethylenetriamine Schiff base and 5 mmol of 1,4-dibromo-2-butene to a 20% by mass sodium hydroxide aqueous solution, stir and disperse, and react at 85°C for 8 h. After the reaction is completed, evaporate the mixture by rotary evaporation, add ethanol, filter, and evaporate the mixture by rotary evaporation to obtain intermediate product A.

[0035] (2) Add 20 mmol of 3-chloro-1-propanol, 22 mmol of isocyanatepropyltriethoxysilane, and 0.02 mmol of dibutyltin dilaurate into a flask, heat to 45°C, and stir to react for 3 hours. After the reaction is completed, distill under reduced pressure and dry to obtain intermediate product B.

[0036] (3) 10 mmol of intermediate product A and 20 mmol of intermediate product B were added to isopropanol solvent, and a 20% by mass sodium hydroxide aqueous solution was added thereto, and the pH was adjusted to 10. The mixture was reacted at 80°C for 10 h. After the reaction was completed, the mixture was distilled under reduced pressure, washed with ethanol, and dried to obtain tetrasalicylic aldehyde gemini quaternary ammonium salt.

[0037] (4) 100 g of EVA, 1 g of maleic anhydride, 3 g of tetrasalicylic aldehyde gemini quaternary ammonium salt, and 0.1 g of diisopropylbenzene peroxide were added to a Haake rheometer at 170 °C, extruded, and cooled to obtain a modified EVA; the modified EVA was then placed in a film blowing machine and blown into a film to obtain a modified EVA film.

[0038] Example 2

[0039] (1) Add 12 mmol of disalicyclic aldehyde diethylenetriamine Schiff base and 5 mmol of 1,4-dibromo-2-butene to a 20% by mass sodium hydroxide aqueous solution, stir and disperse, and react at 80°C for 7 h. After the reaction is completed, evaporate the mixture by rotary evaporation, add ethanol, filter, and evaporate the mixture by rotary evaporation to obtain intermediate product A.

[0040] (2) Add 20 mmol of 3-chloro-1-propanol, 20 mmol of isocyanatepropyltriethoxysilane, and 0.06 mmol of dibutyltin dilaurate into a flask, heat to 40°C, and stir to react for 5 hours. After the reaction is completed, distill under reduced pressure and dry to obtain intermediate product B.

[0041] (3) 10 mmol of intermediate product A and 22 mmol of intermediate product B were added to isopropanol solvent, and a 20% by mass sodium hydroxide aqueous solution was added thereto, and the pH was adjusted to 9. The mixture was reacted at 75°C for 14 h. After the reaction was completed, the mixture was distilled under reduced pressure, washed with ethanol, and dried to obtain tetrasalicylic aldehyde gemini quaternary ammonium salt.

[0042] (4) 100 g of EVA, 1 g of maleic anhydride, 4 g of tetrasalicylic aldehyde gemini quaternary ammonium salt, and 0.2 g of diisopropylbenzene peroxide were added to a Haake rheometer at 180 °C, extruded, and cooled to obtain a modified EVA; the modified EVA was then placed in a film blowing machine and blown into a film to obtain a modified EVA film.

[0043] Example 3

[0044] (1) 11 mmol of disalicyclic aldehyde diethylenetriamine Schiff base and 5 mmol of 1,4-dibromo-2-butene were added to a 20% by mass sodium hydroxide aqueous solution, stirred and dispersed, and reacted at 90°C for 5 h. After the reaction was completed, the mixture was rotary evaporated, and ethanol was added thereto. The mixture was filtered and rotary evaporated to obtain intermediate product A.

[0045] (2) Add 20 mmol of 3-chloro-1-propanol, 24 mmol of isocyanatepropyltriethoxysilane, and 0.04 mmol of dibutyltin dilaurate into a flask, heat to 50°C, and stir to react for 4 hours. After the reaction is completed, distill under reduced pressure and dry to obtain intermediate product B.

[0046] (3) 10 mmol of intermediate product A and 22 mmol of intermediate product B were added to isopropanol solvent, and a 20% by mass sodium hydroxide aqueous solution was added thereto. The pH was adjusted to 9, and the mixture was reacted at 85°C for 12 h. After the reaction was completed, the mixture was distilled under reduced pressure, washed with ethanol, and dried to obtain tetrasalicylic aldehyde gemini quaternary ammonium salt.

[0047] (4) 100 g of EVA, 2 g of maleic anhydride, 5 g of tetrasalicylic aldehyde gemini quaternary ammonium salt, and 0.3 g of diisopropylbenzene peroxide were added to a Haake rheometer at 175 °C, extruded, and cooled to obtain a modified EVA; the modified EVA was then placed in a film blowing machine and blown into a film to obtain a modified EVA film.

[0048] The modified EVA was evenly coated on a 100×20mm metal iron sheet, and a PE sheet of the same width was attached to the hot melt adhesive. After cooling, the sheet was placed on a flat vulcanizer at 70°C and 2MPa, hot pressed for 2h, and kept at room temperature for 24h. The hot melt adhesive peel strength was tested according to GB / T2792-1998.

[0049] The antibacterial properties of the film were tested with reference to QB / T2591-2003, and the test bacteria was Escherichia coli.

[0050] Table 1:

[0051] Peel strength (MPa) Antibacterial rate (%) Example 1 2.36 97.6 Example 2 2.39 99.7 Example 3 2.41 99.9 Comparative Example 1 1.92 -

[0052] Comparative Example 1 is an EVA hot melt adhesive to which no tetrasalicylicaldehyde gemini quaternary ammonium salt is added.

[0053] The greater the peel strength, the better the bonding effect. As can be seen from the table, the bonding layer of the present invention has excellent bonding effect and antibacterial performance.

[0054] Example 4-6:

[0055] According to the following layer structure, each layer is bonded together by a hot pressing composite process, thereby preparing Examples 4-6 of the photovoltaic reflective film of the present invention.

[0056] protective layer reflective layer grassroots Adhesive layer Example 4 Mixed film of polymethyl methacrylate and titanium dioxide Microstructure prism array and metal reflective coating polyethylene terephthalate EVA film of Example 1 Example 5 Mixed film of polymethyl methacrylate and titanium dioxide Microstructure prism array and metal reflective coating polyimide EVA film of Example 1 Example 6 Mixed film of polymethyl methacrylate and zirconium dioxide Microstructure prism array and metal reflective coating polyethylene terephthalate EVA film of Example 1

[0057] Use UV high temperature and high humidity aging test chamber to test weather resistance.

[0058] Table 2:

[0059] UV45kw / h (wet) UV75kw / h (wet) UV120kw / h (dry) UV240kw / h (dry) Example 4 1.8 2.2 1.2 2.1 Example 5 2.2 1.8 1.4 2.3 Example 6 2.1 1.4 2.4 2.4

[0060] As shown in Table 2, the UV resistance Δb of the composite prepared by the present invention is ≤3 in both UV wet heat and UV dry heat, and has excellent weather resistance.

[0061] Use a spectrophotometer to test reflectance.

[0062] Test the insulation using an insulation resistance tester.

[0063] The flexibility was tested using an electronic universal testing machine.

[0064] Table 3:

[0065] Reflectivity (%) Resistance (Ω) Elongation (%) Example 4 91.53 9.58×10^10 194.1 Example 5 91.16 9.97×10^10 177.2 Example 6 91.29 1.24×10^11 184.6

[0066] The reflective film of the present invention has a high reflectivity, which is greater than 90%, a resistance greater than 10^9Ω, and an elongation greater than 50%, so it has excellent insulation performance and flexibility.

Claims

1. A photovoltaic reflective film, characterized in that: The photovoltaic reflective film is composed of the following four layers: a protective layer, a reflective layer, a base layer, and an adhesive layer. Each layer is bonded together by a hot pressing composite process to prepare the photovoltaic reflective film. The bonding layer is a modified EVA film, and its preparation method is as follows: Add EVA, maleic anhydride, tetrasalicylic aldehyde gemini quaternary ammonium salt, and dicumyl peroxide into a Haake rheometer at 170-180° C., extrude, and cool to obtain modified EVA; then place the modified EVA in a film blowing machine and blow it into a film to obtain a modified EVA film; The preparation method of the tetrasalicylic aldehyde gemini quaternary ammonium salt is as follows: (1) Disalicyclic aldehyde diethylenetriamine Schiff base and 1,4-dibromo-2-butene were added to a 20% by mass sodium hydroxide aqueous solution, stirred and dispersed, and reacted at 80-90°C for 5-8 hours. After the reaction was completed, the mixture was rotary evaporated, and ethanol was added thereto, filtered, and rotary evaporated to obtain intermediate product A; (2) Add 3-chloro-1-propanol, isocyanate propyltriethoxysilane, and dibutyltin dilaurate into a flask, heat to 40-50°C, stir and react for 3-5 hours. After the reaction is completed, distill under reduced pressure and dry to obtain intermediate product B; (3) Add intermediate product A and intermediate product B to isopropanol solvent, add 20% by mass sodium hydroxide aqueous solution, adjust the pH to 9-10, react at 75-85°C for 10-14 hours, and after the reaction is completed, distill under reduced pressure, wash with ethanol, and dry to obtain tetrasalicylic aldehyde gemini quaternary ammonium salt.

2. The photovoltaic reflective film according to claim 1, characterized in that: The protective layer is a film formed by compounding a high-refractive-index matrix resin and nano-oxide particles. The high-refractive-index matrix resin is polymethyl methacrylate, and the nano-oxide particles are one of titanium dioxide and zirconium dioxide.

3. The photovoltaic reflective film according to claim 1, characterized in that: The reflective layer is composed of a metal reflective coating. The metal reflective coating is prepared by depositing a layer of aluminum or silver with a thickness of 50-150 μm on the surface of a PET insulating material using a magnetron sputtering process. The PET insulating material has a planar structure or a microstructured prism array structure. The microstructured prism array is prepared by forming a triangular prism array with a height of 5-20 μm and a vertex angle of 90-150° on the surface of a base layer through a compression molding process. The prism spacing is 20-100 μm.

4. The photovoltaic reflective film according to claim 1, characterized in that: The base layer is one of a polyethylene terephthalate (PET) film and a polyimide (PI) film.

5. The photovoltaic reflective film according to claim 1, characterized in that: The mass ratio of the EVA, maleic anhydride, tetrasalicylicaldehyde gemini quaternary ammonium salt, and dicumyl peroxide is 100:1-2:3-5:0.1-0.

3.

6. The photovoltaic reflective film according to claim 1, characterized in that: In the above (1), the molar ratio of disalicylicaldehyde diethylenetriamine Schiff base and 1,4-dibromo-2-butene is 2-2.4:

1.

7. The photovoltaic reflective film according to claim 1, characterized in that: In the above (2), the molar ratio of 3-chloro-1-propanol, isocyanatepropyltriethoxysilane and dibutyltin dilaurate is 1:1-1.2:0.001-0.

003.

8. The photovoltaic reflective film according to claim 1, characterized in that: In the above (3), the molar ratio of intermediate product A to intermediate product B is 1:2-2.2.

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