Photovoltaic composite frame and preparation method thereof

Abstract

The application provides a photovoltaic composite frame and a preparation method thereof. The photovoltaic composite frame comprises a frame body and cellulose nanofiber modified polyurethane resin and reinforcing fibers filled in the frame body; and the material of the frame body is a continuous filament mat. The application can make up for the short board of the composite frame in the transverse mechanics, greatly improve the mechanical properties of the composite frame outdoors, and effectively protect the photovoltaic module from being damaged by the harsh environment.

Description

Technical Field

[0001] This invention relates to a composite material molding process, and more particularly to a photovoltaic composite frame and its preparation method. Background Technology

[0002] With the continuous growth of global energy demand and calls for environmental protection, photovoltaic (PV) power generation technology has a very broad application prospect in energy production. In the future, PV power generation will become an important part of global energy supply, providing clean, reliable, and economical electricity to residents and businesses around the world. PV power generation mainly uses the photovoltaic effect of PV modules to generate electricity. PV modules are the key to power generation. PV modules are composed of PV cells, encapsulant film, glass, frames, junction boxes, etc. Among these, the frame accounts for a relatively high proportion of the module cost. Furthermore, aluminum alloy frames on the market are prone to acid corrosion and tearing damage in harsh weather conditions such as strong winds. Their mechanical properties cannot meet the requirements to protect PV modules from damage in harsh environments.

[0003] Currently, over 90% of photovoltaic modules on the market are assembled using aluminum alloy frames, while about 10% use fiberglass polyurethane composite frames to protect the photovoltaic modules.

[0004] Existing photovoltaic modules use aluminum alloy frames, which are extremely susceptible to corrosion at sea or in areas with high acid rain or salt spray. They are also prone to tearing and breakage in extreme weather. About 10% of the market uses fiberglass-polyurethane composite frames, which are made by mixing and curing fiberglass, polyurethane resin, and fiberglass felt at high temperatures. Their advantage lies in high longitudinal mechanical strength, but their disadvantage is very low transverse tensile and flexural strength. This is because the fiberglass felt and polyurethane resin provide the transverse force. The felt used in composite panel frames on the market is chopped fiberglass mat, which is made by cutting fiberglass filaments into 20mm lengths, laying them randomly and evenly, and then weaving them together with longitudinal and transverse polyester threads. Due to its structure, the transverse tensile and flexural forces are very low. Furthermore, the relatively low strength of the polyurethane resin itself also contributes to the low transverse mechanical strength. Summary of the Invention

[0005] To overcome the aforementioned problems in the prior art, this invention provides a photovoltaic composite frame and its preparation method. This invention prepares a composite frame by using continuous filament felt and cellulose nanofibers modified polyurethane resin, which compensates for the composite frame's weakness in lateral mechanical properties, greatly improving its outdoor mechanical performance and effectively protecting photovoltaic modules from damage by harsh environments.

[0006] The first aspect of the present invention provides a photovoltaic composite frame, the photovoltaic composite frame comprising a frame body and cellulose nanofiber modified polyurethane resin and reinforcing fibers filled in the frame body; the material of the frame body is continuous filament felt.

[0007] In one or more embodiments, the filament in the continuous filament felt is glass fiber filament, rock fiber filament, or carbon fiber filament.

[0008] In one or more embodiments, the filaments of the continuous filament felt are in the form of an outward figure-eight, an inward figure-eight, a ring, a wave, or a spiral.

[0009] In one or more embodiments, the continuous filament mat is obtained by heating and curing continuous fiber filaments.

[0010] In one or more embodiments, the boundaries of the continuous filament felt are provided with polyester filaments or polylactic acid fibers.

[0011] In one or more embodiments, in the cellulose nanofiber modified polyurethane resin, the cellulose nanofibers have a diameter of 50-100 nm and an aspect ratio of 100-500.

[0012] In one or more embodiments, the cellulose nanofibers modified polyurethane resin have an elastic modulus of 10-20 GPa and a tensile strength of 500 MPa-1 GPa.

[0013] In one or more embodiments, the polyurethane resin is formed by a polycondensation reaction of a polyol and a polyisocyanate.

[0014] In one or more embodiments, the mass ratio of polyol to polyisocyanate is 1:(0.5-1.5).

[0015] In one or more embodiments, the mass ratio of polyurethane resin to cellulose nanofibers in the cellulose nanofiber modified polyurethane resin is 1:(0.01-0.06).

[0016] In one or more embodiments, the viscosity of the polyurethane resin is 700-900 mPa·s.

[0017] In one or more embodiments, the cellulose nanofiber modified polyurethane resin is prepared by mixing cellulose nanofibers and polyurethane resin.

[0018] In one or more embodiments, the reinforcing fiber is glass fiber, basalt fiber, or carbon fiber.

[0019] In one or more embodiments, based on 100 parts by weight, the continuous filament mat accounts for 1%-5%; the reinforcing fiber accounts for 75%-85%; and the cellulose nanofiber modified polyurethane resin accounts for 15%-25%.

[0020] In one or more embodiments, the surface of the frame body further comprises a weather-resistant coating, the material of which is selected from waterborne polyurethane and / or FEVE fluorocarbon resin.

[0021] A second aspect of the present invention provides a method for preparing a photovoltaic composite frame as described in any embodiment herein, the method comprising the following steps:

[0022] Reinforcing fibers and continuous filament felt are passed through a mold with a customized cross-section to obtain a structure with continuous filament felt as the frame body and reinforcing fibers filling the frame body; polyurethane and cellulose nanofibers are injected above the mold; the mold is then subjected to high temperature and pressure curing and shaping; and finally, the profile is pulled and cooled by a traction machine.

[0023] In one or more embodiments, polyurethane is replaced with polyols and polyisocyanates injected above the mold.

[0024] In one or more embodiments, the process conditions for high-temperature and high-pressure curing are: temperature of 170°C to 180°C; pressure of 400-600 Bar; and curing time of 3 to 5 minutes.

[0025] In one or more embodiments, the method further includes the step of applying a weather-resistant coating to the surface of the frame body after traction cooling.

[0026] A third aspect of the present invention provides a photovoltaic module comprising a substrate and a photovoltaic composite frame as described in any embodiment herein, sealed to the side of the substrate, wherein the substrate comprises: a panel, a face film, a cell, a back film, and a back sheet.

[0027] A fourth aspect of the present invention provides the application of continuous filament mat in the preparation of photovoltaic composite frames with improved transverse mechanical properties.

[0028] The fifth aspect of this invention provides the application of cellulose nanofiber modified polyurethane resin in the preparation of photovoltaic composite frames with improved transverse and longitudinal mechanical properties. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the preparation of the continuous filament felt in Example 1.

[0030] Figure 2 This is a schematic diagram showing the distribution of each component in the photovoltaic composite frame of Example 1.

[0031] Figure 3This is a flowchart illustrating the fabrication process of the photovoltaic composite frame in Example 1.

[0032] Explanation of reference numerals in the attached figures:

[0033] 1 is polyester yarn, 2 is glass fiber filament, 3 is binder, I is continuous filament mat, II is glass fiber, III is cellulose nanofiber modified polyurethane resin, and IV is water-based polyurethane coating. Detailed Implementation

[0034] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0035] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0036] In this document, the terms “contains,” “includes,” “containing,” and similar terms encompass the meanings of “basically composed of” and “composed of.” For example, when this document discloses “A contains B and C,” “A is basically composed of B and C” and “A is composed of B and C” should be considered as having been disclosed in this document.

[0037] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0038] Unless otherwise specified, percentages refer to mass percentages and proportions refer to mass ratios in this article.

[0039] In this document, when describing embodiments or examples, it should be understood that it is not intended to limit the invention to those embodiments or examples. Rather, all alternatives, modifications, and equivalents of the methods and materials described herein are covered within the scope defined by the claims.

[0040] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0041] The present invention provides a photovoltaic composite frame, which includes a frame body and cellulose nanofiber modified polyurethane resin and reinforcing fibers filled in the frame body; the material of the frame body is continuous filament felt.

[0042] Continuous filament felt

[0043] The filament in the continuous filament mat of the present invention can be one or more of glass fiber filament, rock fiber filament, and carbon fiber.

[0044] In some embodiments, the continuous filament mat comprises filaments and an adhesive. The adhesive may be selected from those conventionally used in the art to produce continuous filament mats, such as polyester emulsions or polyester powder emulsion blends.

[0045] Continuous filament mats can be obtained by heating and curing continuous filament fibers.

[0046] In some implementations, the method for preparing continuous filament mat may include the following steps: laying continuous filaments flat on a mesh belt, then shaping the filaments into a specific form such as an outward figure-eight, inward figure-eight, ring, wave, or spiral to obtain a felt blank; uniformly spraying an adhesive onto the felt blank, and then heating and curing it to form a continuous filament mat. Continuous filament mat is far superior to chopped strand mat in reinforcing composite materials because the fibers in the continuous filament mat are continuous.

[0047] In some implementations, continuous fiber filaments can be obtained by drawing molten liquid into filaments. Typically, the obtained continuous fiber filaments can be divided into several bundles using a bundle splitter.

[0048] In some implementations, the raw filament bundle can be wound around the guide roller and then enter the filament polishing mechanism. The filament polishing mechanism moves in a reciprocating cycle along a certain trajectory, such as an outward figure-eight shape, to form a raw filament felt with a certain shape, such as an outward figure-eight shape.

[0049] In some implementations, the raw filament felt is pre-dried. Pre-drying can be carried out in an oven. The pre-drying temperature can be 160-200°C.

[0050] In some implementations, the adhesive can be evenly sprayed onto the pre-dried felt blank using a powdering device or a curtain-type device with suction function.

[0051] In some implementations, the width of the felt blank is 10-100cm.

[0052] In some implementations, polyester threads are arranged at the boundaries of the felt blank to provide support and address issues such as burrs at the edges. The polyester threads are made of polyester filament or polylactic acid (PLA) fiber. The addition of polyester threads allows for better bonding between the original felt layers, reduces the impact of surface texture on the composite border, and also provides some reinforcement of the transverse tensile strength.

[0053] In some implementations, the felt blank with adhesive is conveyed by a conveyor belt to a curing oven for drying and curing. The curing temperature can be 80°C to 250°C.

[0054] After heat curing, the felt blank can be cooled, smoothed, and rolled up. Cooling can be achieved by using water as the cooling medium and a metal roller rotating at a linear speed of 5-25 m / min to cool the felt. Smoothing can be achieved by applying a pressure of 1000-10000 N / 2 m to the felt using a rotating metal roller.

[0055] In some implementations, the basis weight of the continuous filament mat can be 100-500 g / m². 2 .

[0056] Cellulose nanofiber modified polyurethane resin

[0057] In this invention, cellulose nanofiber modified polyurethane resin can be prepared by mixing cellulose nanofibers and polyurethane resin. In some embodiments, the mass ratio of polyurethane resin to cellulose nanofibers can be 1:(0.01-0.06), such as 1:(0.01-0.03) or 1:(0.04-0.06).

[0058] In some embodiments, the cellulose nanofibers have a diameter of 50-100 nm and an aspect ratio of 100-500. In some embodiments, the elastic modulus of the cellulose nanofibers is 10-20 GPa, and the tensile strength is 500 MPa-1 GPa. Cellulose nanofibers are semi-rigid linear polymer compounds with a large number of hydroxyl groups between their molecules. Polyurethane resin molecular chains exhibit molecular chain entanglement and hydrogen bonding. After modification with cellulose nanofibers, entanglement and hydrogen bonding occur between the nanofibers and polyurethane molecular chains, forming a three-dimensional spatial network structure. This structure possesses high mechanical strength and can significantly improve the mechanical properties of polyurethane.

[0059] In some embodiments, the polyurethane can be formed by a polycondensation reaction of a polyol and a polyisocyanate. In some embodiments, the polyol can be a polyether polyol. In some embodiments, the polyisocyanate can be a diisocyanate, such as toluene diisocyanate. In some embodiments, the mass ratio of the polyol to the polyisocyanate can be in the range of 1:(0.5-1.5), for example, 1:1, 3:2, or 2:3. In some embodiments, the viscosity of the polyurethane can be 700-900 mPa·s.

[0060] In some embodiments, obtaining cellulose nanofiber modified polyurethane resin includes the following steps: mixing polyol, polyisocyanate and cellulose nanofiber.

[0061] Photovoltaic composite frame

[0062] The photovoltaic composite frame of the present invention includes a frame body and cellulose nanofiber modified polyurethane resin and glass reinforcing fiber filled in the frame body; the material of the frame body is glass fiber continuous filament mat.

[0063] In this invention, the reinforcing fiber can be glass fiber, basalt fiber, or carbon fiber.

[0064] In this invention, based on 100 parts by weight, the proportion of continuous filament mat is 1%-5%; the proportion of reinforcing fiber is 75%-85%; and the proportion of cellulose nanofiber modified polyurethane resin is 15%-25%.

[0065] In some embodiments, the surface of the frame body may also contain a weather-resistant coating. The material of the weather-resistant coating may be selected from waterborne polyurethane and / or FEVE fluorocarbon resin. Fluoroethylene-vinyl ether copolymer is simply referred to as FEVE fluorocarbon resin.

[0066] The photovoltaic composite frame of this invention can be prepared by pultrusion molding of cellulose nanofiber modified polyurethane resin, reinforcing fibers and continuous virgin mat.

[0067] In some embodiments, the method for preparing the photovoltaic composite frame of the present invention includes the following steps:

[0068] Reinforcing fibers and continuous filament felt are passed through a mold with a customized cross-section to obtain a structure with continuous filament felt as the frame body and reinforcing fibers filling the frame body. Polyurethane and cellulose nanofibers are injected above the mold. The mold is then subjected to high temperature and pressure curing and shaping, which mixes the polyurethane and cellulose nanofibers to obtain cellulose nanofiber modified polyurethane resin. The cellulose nanofiber modified polyurethane resin and the reinforcing fibers are filled together in the frame body made of continuous filament felt. The profile is then pulled and cooled by a traction machine.

[0069] In some implementations, polyols and polyisocyanates are injected above the mold instead of polyurethane. The polyols and polyisocyanates undergo a polycondensation reaction to form polyurethane.

[0070] In some embodiments, a release agent is also injected above the mold. The release agent may be a perfluoroalkyl acrylate or a solvent-based silicone oil. The content of the release agent may be 0.06-0.2% of the cellulose nanofiber modified polyurethane resin.

[0071] In some embodiments, an antioxidant is also injected above the mold. The antioxidant prevents the polyurethane from oxidizing. The antioxidant can be di-tert-butyl-p-cresol and / or di-tert-butylphenol. The antioxidant content can be 0.06-0.2% of the cellulose nanofiber modified polyurethane resin.

[0072] In some implementations, the high-temperature pressure curing temperature is 170-180°C. The high-temperature pressure curing time is 3-5 minutes. The high-temperature pressure curing pressure is 400-600 Bar.

[0073] In some implementations, after high-temperature and high-pressure curing and shaping, the photovoltaic composite frame can be subjected to traction cooling. Cooling can be carried out at room temperature. After cooling, it can be sawn to customized dimensions. A weather-resistant coating can be applied to the sawn frame. The coating method is not particularly limited; an example is spraying the surface of the frame.

[0074] photovoltaic modules

[0075] The present invention also provides a photovoltaic module, which includes a substrate and a photovoltaic composite frame as described herein, sealed to the side of the substrate, wherein the substrate includes: a panel, a face film, a cell, a back film, and a back sheet.

[0076] The panels, face film, backsheet, and backing film of the aforementioned photovoltaic modules can adopt the corresponding structures of existing photovoltaic modules, such as tempered glass panels, EVA or PVB films, and backsheet films.

[0077] The photovoltaic module provided by this invention can be manufactured in the following manner:

[0078] The panel, backing film, battery cell, top adhesive film, and panel are stacked in sequence and then vacuum hot-pressed to form a substrate; the four sides of the substrate are covered with the photovoltaic composite frame described in this article to obtain a photovoltaic module.

[0079] The beneficial effects of this invention are:

[0080] This invention improves the structure of the fiber felt by optimizing its transverse and longitudinal structures, fundamentally enhancing the transverse tensile and flexural strength of the composite frame material. Furthermore, it modifies polyurethane resin with cellulose nanofibers, significantly increasing its strength, which also contributes to improving the transverse tensile and flexural strength of the composite frame material. By preparing the composite frame using the structurally improved fiber felt and the cellulose nanofiber-modified polyurethane resin, the weakness of the composite frame in transverse mechanical properties can be compensated for, greatly improving its outdoor mechanical performance and effectively protecting the photovoltaic modules from damage by harsh environments.

[0081] The present invention will be described below by way of specific embodiments. It should be understood that these embodiments are merely illustrative and are not intended to limit the scope of the invention. The methods, reagents, and materials used in the embodiments are conventional methods, reagents, and materials in the art, unless otherwise stated. The raw material compounds in the embodiments are all commercially available.

[0082] Preparation Example 1

[0083] Preparation of continuous filament mat: Molten glass is melted in a high-temperature melting furnace, flows out through a precious metal perforator, and is drawn into continuous fiber filaments. After being coated with a sizing agent by an oiling roller, the fiber filaments are divided into several bundles by a bundle splitter. The filament bundles are wound around guide rollers and enter a filament-striking mechanism. Under the reciprocating motion of the filament-striking mechanism in an outward figure-eight pattern, the filament bundles are thrown onto a moving conveyor belt below, forming a filament mat covering the entire width of the conveyor belt. The filament mat is continuously conveyed into an oven at 180℃ for pre-drying. Then, a curtain-type device with a suction function is used to evenly spray polyester emulsion or a polyester powder emulsion mixed binder onto the felt blank. The width of the felt blank is controlled at 30cm. Polyester threads are arranged at the boundary of the felt blank. The felt blank with adhesive is conveyed by a conveyor belt at a speed of 10 m / min to a 200℃ curing oven for drying and curing. Water at 20℃ is used as the cooling medium, and the felt is cooled by metal rollers rotating at a linear speed of 15 m / min. A pair of rotating metal rollers apply a pressure of 5000 N / 2 m to smooth the felt before winding. The basis weight of the continuous filament felt is controlled at 300 g / m². 2 The resulting continuous filament felt (I) is as follows: Figure 1 As shown, 1 is polyester yarn, 2 is glass fiber filament, and 3 is adhesive.

[0084] Example 1

[0085] Reinforcing fibers and continuous filament mat are passed through a mold with a customized cross-section to obtain a structure in which continuous filament mat forms the frame body and reinforcing fibers fill the frame body. Polyether polyol, toluene diisocyanate (TDI), cellulose nanofibers, perfluoroalkyl acrylate as a release agent, and di-tert-butyl-p-cresol as an antioxidant are injected above the mold; wherein the mass ratio of polyether polyol to toluene diisocyanate (TDI) is 1:1, and the viscosity of the synthesized polyurethane is between 800 mPa·s; the cellulose nanofibers have a diameter of 70 nm, an aspect ratio of 300, an elastic modulus of 13 GPa, and a tensile strength of 700 MPa. The content of cellulose nanofibers is 3% of the synthesized cellulose nanofiber modified polyurethane resin; the content of the release agent is 1% of the cellulose nanofiber modified polyurethane resin; and the content of the antioxidant is 1% of the cellulose nanofiber modified polyurethane resin.

[0086] The mixture is cured and shaped under high temperature and pressure within a mold (180℃, 5 min, 500 Bar), resulting in a mixture of polyurethane and cellulose nanofibers to obtain cellulose nanofiber-modified polyurethane resin. This cellulose nanofiber-modified polyurethane resin, along with reinforcing fibers, is then filled into a frame body made of continuous filament felt. The resin is then pulled and cooled to room temperature using a traction machine, and then sawn to the customized dimensions. The final step involves spraying with water-based polyurethane paint to complete the preparation. The preparation process is as follows: Figure 3 As shown.

[0087] The resulting photovoltaic composite frame is as follows Figure 2 As shown, Ⅰ is continuous filament mat, Ⅱ is glass fiber, and Ⅲ is cellulose nanofiber modified polyurethane resin. The mass percentage of glass fiber is 76%, the mass percentage of cellulose nanofiber modified polyurethane resin is 20%, and the mass percentage of continuous filament mat is 4%.

[0088] Example 2

[0089] The other conditions in this embodiment are the same as those in Embodiment 1, except that the mass of the cellulose nanofibers in this embodiment is 0.1% of the synthesized cellulose nanofiber modified polyurethane resin.

[0090] Example 3

[0091] The other conditions in this embodiment are the same as those in Embodiment 1, except that the mass of the cellulose nanofibers in this embodiment is 0.6% of the synthesized cellulose nanofiber modified polyurethane resin.

[0092] Example 4

[0093] The conditions in this embodiment are the same as those in Embodiment 1, except that the mass ratio of polyether polyol to toluene diisocyanate (TDI) in this embodiment is 3:2.

[0094] Example 5

[0095] The conditions in this embodiment are the same as those in Embodiment 1, except that the mass ratio of polyether polyol to toluene diisocyanate (TDI) in this embodiment is 2:3.

[0096] Comparative Example 1

[0097] Comparative Example 1 and Example 1 are the same in all other conditions, except that the original continuous filament mat in Comparative Example 1 is replaced with glass fiber chopped strand mat commonly found in the market. It is made by cutting glass fiber filaments into 30mm lengths, laying them out randomly and evenly, and then weaving them with transverse and longitudinal polyester threads. The mass fraction is 4%.

[0098] Comparative Example 2

[0099] Comparative Example 2 and Example 1 were subject to the same conditions, except that there was no cellulose nanofiber content in Comparative Example 2.

[0100] Test Example 1

[0101] Mechanical property testing: Following the national standard GB / T1447-2005 for tensile testing of fiber-reinforced plastics, sheets were prepared according to Examples 1-5 and Comparative Examples 1-2. The sheet dimensions were 150mm*10mm*2mm. These sheets were used to test transverse tensile strength, transverse flexural strength, longitudinal tensile strength, and longitudinal flexural strength. The tensile speed of the universal tensile testing machine was 50mm / min. The test results are shown in Table 1.

[0102] Table 1. Comparison of mechanical data of sheets prepared according to national standards after different embodiments.

[0103]

[0104] As shown in Table 1, Example 1 has significantly higher transverse tensile strength and transverse bending strength than Comparative Example 1, indicating that continuous filament felt can greatly improve the transverse mechanical properties of the composite material, which is significantly higher than that of chopped strand mat commonly found in the market. As for the longitudinal mechanical data, there is little change. This is because 90% of the force in the longitudinal mechanical properties comes from the 75-85% glass fiber content. Therefore, continuous filament felt can effectively improve the transverse mechanical properties of the composite material.

[0105] Example 1 showed higher tensile and flexural strengths in both the transverse and longitudinal directions than Comparative Example 2, indicating that cellulose nanofiber modified polyurethane resin can simultaneously improve the transverse and longitudinal mechanical properties of the composite material.

Claims

1. A photovoltaic composite frame, characterized in that, The photovoltaic composite frame includes a frame body and cellulose nanofiber modified polyurethane resin and reinforcing fibers filled within the frame body; the material of the frame body is continuous filament felt.

2. The photovoltaic composite frame as described in claim 1, characterized in that, The photovoltaic composite frame has one or more of the following characteristics: The filaments in the continuous filament felt are glass fiber filaments, rock fiber filaments, or carbon fibers; The raw filaments of the continuous filament felt are in the form of an outer figure-eight, an inner figure-eight, a ring, a wave, or a spiral; The continuous filament mat is obtained by heating and curing continuous fiber filaments; and The boundaries of the continuous filament felt are provided with polyester filaments or polylactic acid fibers.

3. The photovoltaic composite frame as described in claim 1, characterized in that, The photovoltaic composite frame has one or more of the following characteristics: In cellulose nanofiber modified polyurethane resin, the diameter of the cellulose nanofiber is 50-100 nm and the aspect ratio is 100-500. The elastic modulus of cellulose nanofibers is 10-20 GPa, and the tensile strength is 500 MPa-1 GPa. Polyurethane resin is formed by polycondensation reaction of polyol and polyisocyanate, with a mass ratio of polyol to polyisocyanate of 1:(0.5-1.5). In cellulose nanofiber modified polyurethane resin, the mass ratio of polyurethane resin to cellulose nanofibers is 1:(0.01-0.06); and Cellulose nanofiber modified polyurethane resin is prepared by mixing cellulose nanofibers and polyurethane resin.

4. The photovoltaic composite frame as described in claim 1, characterized in that, The reinforcing fiber is glass fiber, basalt fiber, or carbon fiber.

5. The photovoltaic composite frame as described in claim 1, characterized in that, Based on 100 parts by weight, the continuous filament mat accounts for 1%-5%; the reinforcing fiber accounts for 75%-85%; and the cellulose nanofiber modified polyurethane resin accounts for 15%-25%.

6. The photovoltaic composite frame as described in claim 1, characterized in that, The surface of the frame body also contains a weather-resistant coating, the material of which is selected from waterborne polyurethane and / or FEVE fluorocarbon resin.

7. A method for preparing a photovoltaic composite frame as described in any one of claims 1-6, characterized in that, The method includes the following steps: Reinforcing fibers and continuous filament felt are passed through a mold with a customized cross-section to obtain a structure with continuous filament felt as the frame body and reinforcing fibers filling the frame body. Polyurethane and cellulose nanofibers are injected above the mold. The mold is then subjected to high temperature and pressure curing and shaping, which mixes the polyurethane and cellulose nanofibers to obtain cellulose nanofiber modified polyurethane resin. The cellulose nanofiber modified polyurethane resin and the reinforcing fibers are filled together in the frame body made of continuous filament felt. The profile is then pulled and cooled by a traction machine.

8. The method as described in claim 7, characterized in that, The process conditions for high-temperature and high-pressure curing and shaping are as follows: temperature 170℃~180℃; pressure 400-600Bar; shaping time 3min~5min. The method further includes the step of applying a weather-resistant coating to the surface of the frame body after traction cooling.

9. A photovoltaic module, characterized in that, It includes a substrate and a photovoltaic composite frame as described in any one of claims 1-6 sealed to the side of the substrate, wherein the substrate includes: a panel, a face film, a cell, a back film, and a back sheet.

10. Selected from the following applications: Application of continuous filament mat in the preparation of photovoltaic composite frames with improved transverse mechanical properties; Application of cellulose nanofiber modified polyurethane resin in the preparation of photovoltaic composite frames with improved transverse and longitudinal mechanical properties.

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