Photovoltaic back sheet composite film and preparation method thereof

Abstract

The present application discloses a photovoltaic backplane composite film and a preparation method thereof, wherein the photovoltaic backplane composite film comprises a first composite layer, a second composite layer and a third composite layer, and the preparation raw material of the second composite layer comprises a supporting filler, and the supporting filler is any one of Zn / Co‑ZIF, Zn / Cu‑ZIF or Zn / Ag‑ZIF. The photovoltaic backplane composite film of the present application can effectively improve the water vapor permeability and stability of the photovoltaic backplane film, can maintain the stability of quality in a low-temperature and high-temperature cycle environment, helps to provide protection in outdoor environments, and prolongs the service life of photovoltaic modules.

Description

Technical Field

[0001] The present application relates to the field of photovoltaic modules, and in particular to a photovoltaic backplane composite film and a preparation method thereof. Background Art

[0002] Photovoltaic power generation is a process that uses solar photons to convert into electrical energy through the photovoltaic effect in semiconductor materials. It has many advantages, such as clean and environmental protection, renewable energy, energy security and economic benefits. Photovoltaic power generation uses solar energy to generate electricity. It does not produce any pollutants in the process, is harmless to the environment, and significantly reduces environmental damage and pollution. Solar energy is a renewable energy source with huge reserves and can be used continuously. The photovoltaic power generation system does not need to consume the earth's limited resources during its life cycle, which is in line with the concept of sustainable development and green energy. In addition, the photovoltaic power generation system has the characteristics of distributed energy, which can be developed and used on-site, reducing the burden of energy transmission and avoiding the geographical limitations and potential safety hazards of traditional energy supply. With the continuous development of photovoltaic technology and the continuous reduction of costs, the price of photovoltaic power generation has the advantage of competing with the price of traditional energy. In areas with abundant light resources, photovoltaic power generation can even become the main source of electricity supply.

[0003] From an environmental protection perspective, it has become a trend to use PET film instead of fluorine-free film in photovoltaic backsheets. PET material is currently the most widely used backsheet substrate, with excellent insulation and mechanical properties. Many patented technologies are dedicated to using polyolefin materials to replace the fluorine film protective layer to prepare fluorine-free but PET-containing polyolefin backsheets, in order to reduce the environmental pollution problem of fluorine film and improve the environmental friendliness of photovoltaic backsheets. Fluorine-free photovoltaic backsheets do not contain fluorine elements, which is more in line with the current national requirements for ecology and environmental protection. This substitution not only helps to reduce the environmental emissions of fluorides, but also reduces costs to a certain extent while maintaining the performance of the backsheet.

[0004] Although PET film is widely used due to its environmental advantages, it also has some disadvantages. First, the support strength of PET film may not be as good as some other materials, which may affect the overall mechanical properties of photovoltaic backsheets. Second, the water vapor transmission rate of PET film is relatively low, which means that it does not perform as well as some other materials in blocking water vapor, which may affect the long-term stability and efficiency of photovoltaic modules. Therefore, PET film needs to be modified during the design and manufacturing process to improve its performance and meet the strict requirements of photovoltaic backsheets. For example, the water barrier properties and mechanical strength of PET film can be improved by adding specific additives or adopting composite structures. Summary of the invention

[0005] The purpose of the present application is to provide a photovoltaic backplane composite film with greater stability.

[0006] To achieve the above objectives, the technical solution adopted in the present application is: to provide a photovoltaic backplane composite film, including a first composite layer, a second composite layer and a third composite layer, the preparation raw materials of the second composite layer include a supporting filler, and the supporting filler is any one of Zn / Co-ZIF, Zn / Cu-ZIF or Zn / Ag-ZIF.

[0007] As a preferred method, the supporting filler is prepared by dissolving zinc salt and a second metal salt in a solution, and slowly mixing them with a 2-methylimidazole solution, stirring and then standing, centrifuging, washing and drying the product to obtain the supporting filler, wherein the second metal salt is any one of a cobalt salt, a copper salt or a silver salt.

[0008] As a preference, the added amount of the supporting filler is 0.2% to 1.2% of the total mass of the second composite layer.

[0009] As another preference, the raw materials for preparing the second composite layer include: white pigment, the supporting filler, antioxidant, other additives and PET.

[0010] As another preference, the raw materials for preparing the first composite layer include infrared reflective filler and sodium alginate.

[0011] As another preferred embodiment, the raw materials for preparing the first composite layer include: white pigment, antioxidant, anti-hydrolysis agent, the infrared reflective filler, the sodium alginate and PET.

[0012] As another preference, the raw materials for preparing the third composite layer include: white pigment, other additives, EVA and PET.

[0013] As another preference, the supporting filler is Zn / Ag-ZIF, and the added amount of the supporting filler is 0.6 wt %.

[0014] Provided is a method for preparing a photovoltaic backplane composite film, comprising the following preparation steps: S1: dissolving a zinc salt and a second metal salt in a solution to obtain a first solution, mixing the first solution with a 2-methylimidazole solution, stirring the reaction for a period of time and then standing, separating, washing and drying the product to obtain the supporting filler, wherein the second metal salt is a cobalt salt, a copper salt or a silver salt; S2: mixing a white pigment, an antioxidant, an anti-hydrolysis agent, sodium alginate, an infrared reflective filler and PET, adding the mixture to a screw extruder, extruding, melting and plasticizing to obtain a first composite layer; mixing the white pigment, the supporting filler, other additives and the PET, adding the mixture to a screw extruder, extruding, melting and plasticizing to obtain a second composite layer; mixing the white pigment, the other additives, EVA and the PET, adding the mixture to a screw extruder, extruding, melting and plasticizing to obtain a third composite layer; S3: molding the first composite layer, the second composite layer and the third composite layer through a three-layer co-extrusion casting machine to obtain the photovoltaic backplane composite film.

[0015] Further preferably, the S2 step is specifically as follows: 0.2% to 0.8% of the white pigment, 0.2% to 0.8% of the antioxidant, 0.2% to 0.8% of the anti-hydrolysis agent, 0.5% to 1% of the sodium alginate, 1% to 5% of the infrared reflective filler and the remainder of the PET masterbatch are mixed and added to a screw extruder, and the first composite layer is obtained after extrusion, melt and plasticization; 0.2% to 1% of the white pigment, 0.2% to 1.2% of the supporting filler, 1% to 3% of the other additives and the remainder of the PET masterbatch are mixed and added to a screw extruder, and the second composite layer is obtained after extrusion, melt and plasticization; 0.2% to 1% of the white pigment, 0.2% to 1% of the other additives, 40% to 50% of the EVA masterbatch and the remainder of the PET masterbatch are mixed and added to a screw extruder, and the third composite layer is obtained after extrusion, melt and plasticization.

[0016] Compared with the prior art, the beneficial effects of this application are:

[0017] (1) The present application uses a triple structure of the first composite layer, the second composite layer and the third composite layer to make the photovoltaic backsheet composite film have infrared reflectivity, water vapor resistance and stability, and can be used for a long time;

[0018] (2) The present application adds a supporting filler to the second composite layer, which is beneficial to improving the water vapor resistance and stability of the photovoltaic backsheet composite film, and can maintain better product properties in low-temperature and high-temperature cycle tests;

[0019] (3) The third composite layer of the present application uses a mixed material of EVA and PET, which can increase the interlayer viscosity and prevent the layers from falling off. DETAILED DESCRIPTION

[0020] Below, the present application is further described in conjunction with specific implementation methods. It should be noted that, under the premise of no conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0021] The terms "including" and "having" and any variations thereof in the specification and claims of this application are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products or apparatuses.

[0022] The present application provides a photovoltaic backplane composite film, including a first composite layer, a second composite layer and a third composite layer, and the three layers of materials are all white. The photovoltaic backplane composite film of the present application is white, and in the downstream assembly process, a surface layer can be superimposed on the basis of the photovoltaic backplane composite film of the present application, so that the photovoltaic backplane component presents the required color.

[0023] In the photovoltaic backplane composite film of the present application, the main substrate of the first composite layer is PET, the second composite layer is a PET material with uniformly dispersed supporting fillers, and the main substrate of the third composite layer is a composite material of PET and EVA, wherein the supporting filler is ZIF-8 with a bimetallic skeleton structure, including Zn / Co-ZIF, Zn / Cu-ZIF or Zn / Ag-ZIF.

[0024] ZIF-8, the full name of which is Zeolitic Imidazolate Framework-8, is a kind of zeolite imidazolate framework material composed of zinc ions (Zn 2+ ) and 2-methylimidazole (2-MiM) coordinated metal organic framework (MOFs) materials. With its unique pore structure, high specific surface area, regular pore structure and adjustable pore size, it has shown broad application prospects in many fields.

[0025] ZIF-8 exhibits a strong adsorption capacity for water pollutants, especially for water pollutants, and can produce a synergistic effect when combined with other materials, making the catalytic adsorption stronger and more targeted on pollutants. In addition, ZIF-8 has made significant progress in the application research of adsorption separation, catalysis, biomedicine and other fields. Its derivative materials have shown broad application potential in heavy metal adsorption, nuclear pollution control, radioactive iodine capture, antibiotic adsorption, oil-water separation, dye degradation and water environment monitoring. In the biomedical field, ZIF-8 is used in cancer treatment, antibacterial, biosensor and biocatalysis. In summary, ZIF-8 plays an important role in many fields such as environmental governance and biomedicine due to its unique physical and chemical properties.

[0026] Bimetallic ZIF-8 is a metal-organic framework (MOFs) material, which is usually formed by integrating two different metal ions, such as zinc (Zn) and cobalt (Co), into the structure of ZIF-8. This structure not only inherits the advantages of ZIF-8 itself, such as high specific surface area, ordered pore structure, high crystallinity, multi-metal sites, and strong thermal and chemical stability, but also brings some additional advantages through the synergistic effect of bimetallic. For example, the pore size and specific surface area of ​​bimetallic ZIF-8 can be adjusted by changing the ratio of metal ions, which provides flexibility for tailoring its properties to suit specific applications. In water treatment, bimetallic ZIF-8 has shown great potential due to its strong adsorption effect on water pollutants, especially in the removal of copper ions and dyes. In general, bimetallic ZIF-8 enhances its functionality and application range by combining the characteristics of two metals, making it have broader application prospects in catalysis, adsorption, sensors and environmental governance.

[0027] In some embodiments, the added amount of the supporting filler is 0.2% to 1.2% of the total mass of the second composite layer.

[0028] The present application provides a method for preparing a supporting filler, comprising the following preparation steps: slowly mixing a mixed solution of a zinc salt and a second metal salt with a 2-methylimidazole solution, stirring and then standing, centrifuging, washing and drying the product to obtain the supporting filler of the present application, wherein the second metal salt is any one of a cobalt salt, a copper salt or a silver salt, to prepare Zn / Co-ZIF, Zn / Cu-ZIF or Zn / Ag-ZIF respectively.

[0029] In some embodiments, the materials used to prepare the second composite layer include: white pigment, supporting filler, antioxidant, other additives and PET.

[0030] In the photovoltaic backplane composite film prepared in the present application, adding supporting fillers to the second composite layer can effectively improve the water vapor permeability and stability of the photovoltaic backplane film, can maintain stable quality in a low-temperature and high-temperature cycle environment, help provide protection in outdoor environments, and extend the service life of photovoltaic modules.

[0031] The applicant found that adding supporting fillers to the second composite layer can improve the stability of the photovoltaic backplane film, but at the same time, the photovoltaic backplane is prone to heat up, the adhesion between layers is not strong, and it is easy to peel off. Therefore, it is necessary to design the first composite layer and the third composite layer in a targeted manner.

[0032] The raw materials for preparing the first composite layer of the present application include: white pigment, antioxidant, anti-hydrolysis agent, infrared reflective filler, sodium alginate and PET.

[0033] Sodium alginate is a natural polysaccharide extracted from brown algae with unique gel properties. It can react with calcium ions to form a stable gel-like substance, which makes it widely used in the food industry to make products such as jelly and soft candy. Another important role of sodium alginate is as an emulsifier and stabilizer, which can help maintain the texture of food and extend the shelf life. In cosmetics and personal care products, sodium alginate is also used to improve the texture and stability of products. Due to its natural origin and environmental protection characteristics, sodium alginate is increasingly valued in the fields of modern green chemistry and sustainable development.

[0034] Infrared reflective fillers can be metal oxides such as aluminum oxide, titanium oxide, zirconium oxide, etc., or graphite, magnesium fluoride, titanium dioxide, barium sulfate, etc. Infrared reflective fillers are relatively mature materials. When added to polyester film, they can effectively reflect infrared light and reduce the temperature rise caused by the material absorbing infrared light.

[0035] The raw materials for preparing the third composite layer of the present application include EVA and PET.

[0036] Through the multi-layer compounding of the first composite layer, the second composite layer and the third composite layer of the present application, a photovoltaic backplane composite film with infrared reflectivity, good stability and resistance to water vapor permeability can be obtained. It is not easy to tear the glass and has a longer service life in harsh environments such as outdoors.

[0037] The present application provides a method for preparing a photovoltaic backsheet composite film, comprising the following preparation steps:

[0038] S1: dissolving a zinc salt and a second metal salt in a solution to obtain a first solution, mixing the first solution with a 2-methylimidazole solution, stirring the solution for a period of time and then standing the solution, centrifuging, washing and drying the product to obtain a supporting filler, wherein the second metal salt is a copper salt, a silver salt or a cobalt salt;

[0039] S2: white pigment, antioxidant, anti-hydrolysis agent, sodium alginate, infrared reflective filler and PET are mixed and added into a screw extruder, and the first composite layer is obtained after extrusion, melting and plasticization;

[0040] The white pigment, supporting filler, other additives and PET are mixed and added into a screw extruder, and the second composite layer is obtained after extrusion, melting and plasticization;

[0041] The white pigment, other additives, EVA and PET are mixed and added into a screw extruder, and the third composite layer is obtained after extrusion, melting and plasticization;

[0042] S3: The first composite layer, the second composite layer and the third composite layer are formed by a three-layer co-extrusion casting machine to obtain a photovoltaic backplane composite film of the present application.

[0043] In some embodiments, the raw materials for preparing the first composite layer include: 0.2% to 0.8% white pigment, 0.2% to 0.8% antioxidant, 0.2% to 0.8% anti-hydrolysis agent, 0.5% to 1% sodium alginate, 1% to 5% infrared reflective filler and the balance PET masterbatch;

[0044] The raw materials for preparing the second composite layer include: 0.2%~1% white pigment, 0.2%~1.2% supporting filler, 1%~3% other additives and the balance PET masterbatch;

[0045] The raw materials for preparing the third composite layer include: 0.2%~1% white pigment, 0.2%~1% other additives, 40%~50% EVA masterbatch and the balance PET masterbatch.

[0046] Example 1

[0047] A photovoltaic backplane composite film is prepared, including the following preparation method:

[0048] S1: 30 g of 2-methylimidazole and 0.18 g of triethylamine were dissolved in 500 mL of deionized water to obtain a first solution, and 70 g of anhydrous zinc acetate and 10 g of cobalt nitrate hexahydrate were dissolved in another 500 mL of deionized water to obtain a second solution; the second solution was slowly added to the first solution while the first solution was stirred, and the stirring was maintained for 4 h at a stirring speed of 600 r / min, and then the mixed solution was allowed to stand at room temperature for 10 h, the product was centrifuged and washed once with methanol and deionized water, and dried to obtain Zn / Co-ZIF material as a supporting filler;

[0049] S2: 0.5% white pigment, 0.5% antioxidant, 0.5% anti-hydrolysis agent, 0.5% sodium alginate, 2% infrared reflective filler and the remaining PET masterbatch are mixed uniformly in a high-speed mixer, and the uniformly mixed filler is added into a screw extruder, and extruded at a temperature of 220 ° C and a rotation speed of 15 r / min to melt and plasticize to obtain a first composite layer;

[0050] 1% white pigment, 0.6% supporting filler, 1.2% other additives and the remaining PET masterbatch were mixed evenly in a high-speed mixer, and the mixed filler was added into a screw extruder, and extruded and melted at a temperature of 220 ° C and a rotation speed of 15 r / min to obtain a second composite layer;

[0051] 1% white pigment, 1% other additives, 49% EVA masterbatch and 49% PET masterbatch were mixed evenly in a high-speed mixer, and the evenly mixed filler was added into a screw extruder, and extruded and melted at a temperature of 220 ° C and a rotation speed of 15 r / min to obtain a third composite layer;

[0052] S3: The first composite layer, the second composite layer and the third composite layer are formed by a three-layer co-extrusion casting machine to obtain a photovoltaic backplane composite film of the present application.

[0053] Example 2

[0054] The cobalt salt in step S1 is replaced by silver salt to prepare Zn / Ag-ZIF material as a supporting filler. The other preparation steps are consistent with the preparation steps in Example 1.

[0055] Example 3

[0056] The cobalt salt in step S1 is replaced with copper salt to prepare Zn / Cu-ZIF material as a supporting filler. The other preparation steps are consistent with the preparation steps in Example 1.

[0057] Example 4

[0058] The addition amount of the supporting filler in step S2 is adjusted to 0.8%, and the other preparation steps are consistent with the preparation steps in Example 1.

[0059] Example 5

[0060] The addition amount of the supporting filler in step S2 is adjusted to 1%, and the other preparation steps are consistent with the preparation steps in Example 1.

[0061] Comparative Example 1

[0062] No supporting filler is prepared, and no supporting filler is added in step S2. The other preparation steps are consistent with the preparation steps in Example 1.

[0063] Comparative Example 2

[0064] When preparing the first composite layer in step S2, no infrared reflective filler is added, and the other preparation steps are consistent with the preparation steps in Example 1.

[0065] Comparative Example 3

[0066] When preparing the first composite layer in step S2, no sodium alginate is added, and the other preparation steps are consistent with the preparation steps in Example 1.

[0067] Comparative Example 4

[0068] In step S1, ZIF-8 is synthesized using zinc salt and 2-methylimidazole, and added to the second composite membrane as a comparative filler instead of a supporting filler. The preparation of other membrane layers is consistent with the preparation steps in Example 1.

[0069] Performance Testing

[0070] 1. Water vapor transmission rate test: The test was conducted according to the method described in GB / T 26253-2010. The test conditions were: 38° C. and 90% relative humidity. The test results of each embodiment and each comparative example are recorded in Table 1.

[0071] 2. Peel strength test: The photovoltaic backsheet composite films prepared in each embodiment and each comparative example were subjected to 120°C, 80% humidity, and 150 KWh / m 2 The back sheet after accelerated aging was subjected to accelerated aging for 48 h in accordance with the provisions of GB / T 2790-1995 for the peel strength test of the PVF-PET interface and the PET-EVA interface, with the unit of N / cm. The test results of each embodiment and each comparative example are recorded in Table 1.

[0072] 3. Infrared reflectivity test: According to the technical specification CQC3308-2013 of China Quality Certification Center, a spectrophotometer with an integrating sphere is used for measurement. The diameter of the integrating sphere must be greater than 90 mm. The reflectivity is tested within a wavelength range of 380 nm to 1100 nm. The specific steps include cutting three samples of 100 mm × 100 mm from the composite film and testing them with a spectrophotometer. The test results of each embodiment and each comparative example are recorded in Table 1.

[0073] 4. Hot and cold cycle test: According to the standard GB / T 31034-2014, each photovoltaic backsheet composite film prepared in the embodiment and the comparative example was tested, and 10 parallel samples were set in each group. The test conditions were -40°C~85°C, 8h / cycle, 400 cycles, and the number of samples M with delamination, blistering, discoloration, cracks, and sticky adhesive layer after hot and cold cycles was observed and recorded in Table 1.

[0074] Table 1 Performance test results of various embodiments and comparative examples

[0075]

[0076] Analyzing the water vapor permeability and hot and cold cycle test results in Table 1, the photovoltaic backplane composite film prepared in each embodiment can significantly improve the water vapor resistance and stability of the photovoltaic backplane composite film by adding supporting fillers in the second composite layer, which is beneficial for the photovoltaic backplane composite film to maintain stable properties in harsh environments such as outdoors and extend the service life of photovoltaic modules.

[0077] From the interlayer peeling strength data and infrared light reflectivity data, it can be seen that if only supporting fillers are added to the second composite layer, its infrared light reflection ability is insufficient, and the photovoltaic backplane composite film easily absorbs infrared light and causes the temperature to rise. Moreover, after adding supporting fillers, the interlayer peeling strength is low, and the film layers are easy to separate, resulting in damage to the photovoltaic modules.

[0078] Adding infrared reflective filler and sodium alginate to the first composite layer can significantly improve the shortcomings of poor infrared reflection intensity and low peeling strength, and can prepare a photovoltaic backplane composite film with good stability.

[0079] The above describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited by the above embodiments, and the above embodiments and the specification only describe the principles of the present application. The present application may have various changes and improvements without departing from the spirit and scope of the present application, and these changes and improvements fall within the scope of the present application for which protection is sought. The scope of protection claimed by the present application is defined by the attached claims and their equivalents.

Claims

1. A photovoltaic backsheet composite film, characterized in that: It comprises a first composite layer, a second composite layer and a third composite layer, wherein the raw material for preparing the second composite layer comprises a supporting filler, and the supporting filler is any one of Zn / Co-ZIF, Zn / Cu-ZIF or Zn / Ag-ZIF.

2. The photovoltaic backsheet composite film according to claim 1, characterized in that: The supporting filler is prepared by dissolving a zinc salt and a second metal salt in a solution, and slowly mixing them with a 2-methylimidazole solution, stirring and then standing, centrifuging, washing and drying the product to obtain the supporting filler, wherein the second metal salt is any one of a cobalt salt, a copper salt or a silver salt.

3. The photovoltaic backsheet composite film according to claim 1, characterized in that: The added amount of the supporting filler is 0.2% to 1.2% of the total mass of the second composite layer.

4. The photovoltaic backsheet composite film according to claim 3, characterized in that: The raw materials for preparing the second composite layer include: white pigment, the supporting filler, antioxidant, other additives and PET.

5. The photovoltaic backsheet composite film according to claim 4, characterized in that: The raw materials for preparing the first composite layer include infrared reflective filler and sodium alginate.

6. The photovoltaic backsheet composite film according to claim 5, characterized in that: The raw materials for preparing the first composite layer include: white pigment, antioxidant, anti-hydrolysis agent, the infrared reflective filler, sodium alginate and PET.

7. The photovoltaic backsheet composite film according to claim 6, characterized in that: The raw materials for preparing the third composite layer include: white pigment, other additives, EVA and PET.

8. The photovoltaic backsheet composite film according to claim 3, characterized in that: The supporting filler is Zn / Ag-ZIF, and the added amount of the supporting filler is 0.6 wt %.

9. A method for preparing a photovoltaic backsheet composite film, characterized in that: The method comprises the following preparation steps: S1: dissolving a zinc salt and a second metal salt in a solution to obtain a first solution, mixing the first solution with a 2-methylimidazole solution, stirring and reacting for a period of time, and then standing, separating, washing and drying the product to obtain a supporting filler, wherein the second metal salt is a cobalt salt, a copper salt or a silver salt; S2: white pigment, antioxidant, anti-hydrolysis agent, sodium alginate, infrared reflective filler and PET are mixed and added into a screw extruder, and the first composite layer is obtained after extrusion, melting and plasticization; white pigment, the supporting filler, other additives and PET are mixed and added into a screw extruder, and the second composite layer is obtained after extrusion, melting and plasticization; white pigment, other additives, EVA and PET are mixed and added into a screw extruder, and the third composite layer is obtained after extrusion, melting and plasticization; S3: forming the first composite layer, the second composite layer and the third composite layer through a three-layer co-extrusion casting machine to obtain the photovoltaic backplane composite film.

10. The preparation method according to claim 9, characterized in that: The S2 step is specifically as follows: 0.2% to 0.8% of the white pigment, 0.2% to 0.8% of the antioxidant, 0.2% to 0.8% of the anti-hydrolysis agent, 0.5% to 1% of the sodium alginate, 1% to 5% of the infrared reflective filler and the remainder of the PET are mixed and added to a screw extruder, and the first composite layer is obtained after extrusion, melting and plasticization; 0.2% to 1% of the white pigment, 0.2% to 1.2% of the supporting filler, 1% to 3% of the other additives and the remainder of the PET are mixed and added to a screw extruder, and the second composite layer is obtained after extrusion, melting and plasticization; 0.2% to 1% of the white pigment, 0.2% to 1% of the other additives, 40% to 50% of the EVA and the remainder of the PET are mixed and added to a screw extruder, and the third composite layer is obtained after extrusion, melting and plasticization.

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