High-adhesion low-gram-weight co-extrusion adhesive film as well as preparation method and application thereof

Abstract

The invention relates to the technical field of photovoltaic packaging adhesive films, and discloses a high-adhesion low-gram-weight co-extrusion adhesive film and a preparation method and application thereof. The co-extrusion adhesive film is formed by co-extrusion casting of an upper EVA layer, a POE layer and a lower EVA layer. The total gram weight of the co-extrusion adhesive film is 300-400 g / m < 2 >, and the gram weight of the POE layer is 60-120 g / m < 2 >; each of the upper EVA layer and the lower EVA layer comprises EVA matrix resin, a cross-linking agent, a silane coupling agent with double bonds and a titanate modified anti-corrosion additive in specific parts by weight; the POE layer comprises POE matrix resin, POE bifunctional modified resin double-grafted by a silane coupling agent and an assistant cross-linking agent, and a cross-linking agent in specific parts by weight. The co-extrusion adhesive film has the advantages of low gram weight, low cost, light weight, high adhesion, aging and yellowing resistance, high temperature and high humidity resistance and the like, has no abnormity in the lamination process, and can improve the reliability and efficiency of the flexible photovoltaic module.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic encapsulation film technology, specifically to a co-extruded film with high adhesion and low basis weight, its preparation method, and its application. Background Technology

[0002] Solar photovoltaic (PV) modules encapsulate series-and-parallel solar cells within a double-layered photovoltaic glass panel (or between a photovoltaic glass panel on one side and a photovoltaic backsheet on the other) using photovoltaic encapsulation films. With advancements in encapsulation materials and processes, PV modules are trending towards lighter weights, reducing the load on the support system and adapting to more scenarios and application environments. Currently, there are various types of photovoltaic encapsulation films, such as EVA films, POE films, EPE co-extruded films, and white films (e.g., white EVA films) or black high-reflectivity films, applicable to different environments and usage scenarios to improve the power generation efficiency of PV modules. However, with the reduction in the weight of PV modules and changes in encapsulation materials, the reliability of the PV modules themselves faces higher requirements.

[0003] To meet the standard production requirements of photovoltaic modules and the performance demands of encapsulation materials, the basis weight of photovoltaic encapsulation films can reach 400-500 g / m². 2 Traditional photovoltaic (PV) encapsulation films have a high basis weight, which increases costs and limits their application scenarios, failing to meet the encapsulation needs of more PV modules (such as lightweight flexible PV modules). Lighter film basis weight, on the other hand, can reduce the overall weight of PV modules, alleviating the burden of transportation and installation. Simultaneously, lighter film basis weight can improve the light transmittance of PV modules, increase the light absorption capacity of PV cells, and improve photoelectric conversion efficiency.

[0004] However, there is often a trade-off between lightweight and high adhesion properties in co-extruded films. Interfacial interactions between layers can also degrade film performance, leading to poor adhesion, resistance to aging and yellowing (such as PCT aging and damp heat aging), and crosslinking properties. Furthermore, co-extruded films are prone to appearance defects such as lamination snowflakes and bubbles (as shown in publication number CN116970351A). Therefore, developing a low-basis-weight co-extruded film that combines lightweight and high adhesion properties is crucial for improving the performance and reducing the cost of photovoltaic modules. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a co-extruded film with high adhesion and low basis weight, as well as its preparation method and application. While reducing the basis weight of the co-extruded film, the co-extruded film also has excellent adhesion, resistance to aging and yellowing (such as resistance to PCT aging and yellowing, and resistance to damp heat aging and yellowing) and crosslinking performance, and can greatly reduce the phenomenon of lamination snowflake bubbles.

[0006] Based on this, the present invention discloses a co-extruded film with high adhesion and low basis weight, which is formed by co-extrusion casting of an upper EVA layer, a POE layer and a lower EVA layer, wherein the POE layer is located between the upper EVA layer and the lower EVA layer; the total basis weight of the co-extruded film is 300-400 g / m³. 2 The basis weight of the POE layer is 60-120 g / m². 2 ; Both the upper and lower EVA layers comprise the following raw materials in parts by weight: 100-120 parts EVA matrix resin, 2.8-3.5 parts crosslinking agent, 0.5-0.8 parts silane coupling agent with double bonds, and 0.1-0.2 parts titanate modified anti-corrosion additive. The POE layer comprises the following raw materials in parts by weight: 100-120 parts of POE matrix resin, 15-20 parts of POE bifunctional modified resin grafted with silane coupling agent and co-crosslinking agent, and 2.5-4 parts of crosslinking agent.

[0007] By employing co-extrusion technology, the thickness of the POE layer sandwiched between two EVA layers is reduced. Furthermore, the raw material formulations for both the EVA and POE layers are improved, and the thickness of the EVA layer is also optimized to match the thinned POE layer. This reduces the total basis weight of the EPE co-extruded film while simultaneously improving its adhesion, resistance to aging and yellowing (such as PCT aging and damp heat aging), and crosslinking properties. For example, the EPE film of this invention exhibits an adhesion strength of 120-200 N / cm with a photovoltaic glass panel and 60-120 N / cm with a photovoltaic backsheet. While meeting the current requirements for conventional photovoltaic encapsulation films, it demonstrates high adhesion capabilities in both double-glass and single-glass photovoltaic module encapsulation. Moreover, no abnormal phenomena occur during the lamination process. Therefore, the co-extruded film of this invention meets the lightweight requirements of photovoltaic modules (especially flexible photovoltaic modules) while also possessing high comprehensive performance in areas such as adhesion, and reduces the risk of abnormal lamination of the EPE co-extruded film.

[0008] Preferably, a low-basis-weight co-extruded film with uniform thickness and a smooth surface is prepared by controlling the POE layer thickness and the overall basis weight of the co-extruded film. The total basis weight of the co-extruded film is 300-360 g / m³. 2 To meet a wider range of application scenarios and achieve a balance between lightweight design and co-extruded film performance, the thicknesses of the POE and EVA layers are adjusted in real time.

[0009] Preferably, the silane coupling agent with double bonds is one or a mixture of several of γ-methacryloyloxypropyltrimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, vinyltriperoxytert-butylsilane, vinyltriacetoxysilane, and vinyltris(β-methoxyethoxy)silane. This silane coupling agent with double bonds can be copolymerized with vinyl acetate, acrylic acid, or methacrylic acid monomers to synthesize silane-modified polymers that can be crosslinked and cured at room temperature, for use in adhesives and sealants, providing excellent adhesion, water resistance, corrosion resistance, weather resistance, and scratch resistance.

[0010] Preferably, the titanate-modified anti-corrosion additive is a blend of titanate-modified magnesium hydroxide microparticles and polyethylene-polyvinyl acetate copolymer, or a blend of titanate-modified magnesium oxide and polyethylene-polyvinyl acetate copolymer. Acetic acid produced during film aging, as well as moisture under humid and hot conditions, can cause corrosion of the solder ribbons connecting to the battery cells, blackening of the battery cells, and delamination of the film. This titanate-modified anti-corrosion additive can act as an acid-absorbing component, adsorbing CH3COOH and H2O, which can significantly slow down the chemical corrosion of the battery cells. Titanate modification can improve hydrophobicity and interfacial bonding. The modified particles can be granulated using a twin-screw extrusion method to improve compatibility and achieve uniform dispersion. Furthermore, magnesium oxide or magnesium hydroxide, as an inorganic filler, can ensure the shrinkage rate of the film.

[0011] More preferably, the preparation process of the titanate-modified anti-corrosion additive includes: The filler, magnesium oxide or magnesium hydroxide, is dried at 110-120℃ for 2-4 hours to remove moisture, yielding the dried filler. The titanate coupling agent is diluted with 1-3 times its weight of anhydrous ethanol or toluene, with the titanate coupling agent accounting for 1-2% of the filler weight, to obtain a diluted mixed solution. The dried filler is preheated to 80-110℃ while stirring at 400-500 rpm / min. The diluted mixed solution is then slowly added by dripping or spraying, and the mixture is continuously stirred and mixed for 10-20 minutes. Titanate coupling agent is uniformly coated on the filler surface; then, EVA resin is added for premixing, with the amount of EVA resin added being 2-5 times the weight of the filler; in a screw extruder, melt blending is carried out at a processing temperature of 80-100℃, the screw speed is controlled at 10-20 rpm / min, the feeding speed is 5-10 rpm / min, and vacuum degassing is turned on to remove moisture and volatiles; the extruded melt is then processed by water-cooled string pelletizing or underwater pelletizing to produce uniform titaniumate modified anti-corrosion additive particles.

[0012] Preferably, the crosslinking agent in both the upper and lower EVA layers comprises 1-1.5 parts of a main crosslinking agent and 1.8-2 parts of a co-crosslinking agent; The upper EVA layer and the lower EVA layer also include the following raw materials in parts by weight: 0.1-0.2 parts of antioxidant and 0.1-0.2 parts of light stabilizer.

[0013] Preferably, the preparation process of the POE bifunctional modified resin grafted with silane coupling agent and co-crosslinking agent includes: pre-mixing POE resin, silane coupling agent, co-crosslinking agent, and initiator thoroughly using a one-step melt grafting method, wherein the silane coupling agent, co-crosslinking agent, and initiator account for 1-2%, 1-2%, and 0.1-0.2% of the POE resin mass, respectively; then, carrying out the grafting reaction using a screw extruder at a melting temperature of 160-220℃, with the melt uniformly dispersed and reacted under shearing action at a shearing temperature of 80-100℃ and a shearing speed of 800-1000 rpm / min; the completely reacted melt is extruded, water-cooled, and pelletized to obtain the finished product. To improve the bonding strength, crosslinking degree, and light transmittance between the POE layer and the EVA layer, modifying agents with enhanced functions are generally added to the POE layer. However, polar additives repel each other and migrate outward in the non-polar POE layer, reducing the interlayer adhesion between the POE layer and the EVA layer. When using a POE bifunctional modified resin with silane coupling agent and co-crosslinking agent grafted together, the easily migratable additives are grafted onto the POE segments, causing them to undergo chemical crosslinking in advance, improving compatibility, reducing additive precipitation, and forming a three-dimensional crosslinked network structure inside the POE layer, thereby improving the mechanical properties of the POE layer and enhancing properties such as interlayer adhesion.

[0014] Preferably, the crosslinking agent in the POE layer comprises 1-2 parts of a primary crosslinking agent and 1.5-2 parts of a secondary crosslinking agent; The POE layer also includes the following raw materials in parts by weight: 0.5-0.8 parts of silane coupling agent and 0.1-0.2 parts of light stabilizer.

[0015] This invention also discloses a method for preparing a co-extruded film with high adhesion and low basis weight, comprising the following preparation steps: S1. Mix all the raw materials of the POE layer to obtain semi-finished material A; and mix all the raw materials of the upper EVA layer and the lower EVA layer to obtain semi-finished material B1 and semi-finished material B2 respectively. S2. Using EPE co-extrusion, semi-finished material B1, semi-finished material A and semi-finished material B2 are melt-co-extruded, cast and cooled to form a film, thus obtaining a co-extruded film.

[0016] This invention also discloses the application of a high-adhesion, low-basis-weight co-extruded film. The high-adhesion, low-basis-weight co-extruded film described above is used as an encapsulation material in flexible photovoltaic modules, so that the flexible photovoltaic modules meet the application performance of basic battery modules while also having the advantages of lightweight, low cost, and qualified shrinkage rate. After lamination, there are no bubbles or delamination.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects: The co-extruded film of the present invention achieves a low basis weight by controlling the basis weight ratio of the EVA layer and the POE layer, as well as the total basis weight of the co-extruded film. Furthermore, by optimizing the raw material formulations of the EVA and POE layers (adding a special silane coupling agent with double bonds to increase adhesion to the EVA layer, along with an appropriate amount of titanate-modified anti-corrosion additive, and adding a high-adhesion, crosslinkable POE bifunctional modified resin grafted with both silane coupling agent and crosslinking aid to the POE layer), the degree of crosslinking, peel strength to photovoltaic backsheets and photovoltaic glass, yellowing index after 48 hours of PCT aging, yellowing index after high-temperature and high-humidity aging, and the appearance of the photovoltaic module are all effectively improved.

[0018] Therefore, the co-extruded film of this invention, while possessing the advantage of low basis weight, also features high adhesion, resistance to aging and yellowing (such as resistance to PCT aging and yellowing, and resistance to damp heat aging), and crosslinking performance, and can significantly reduce lamination snowflake bubble phenomenon. Thus, photovoltaic modules encapsulated using the co-extruded film of this invention meet the comprehensive requirements of low cost, lightweight, and high performance. The product performance conforms to the application standards of EPE co-extruded films and can be used in flexible photovoltaic modules, broadening its application scenarios in the photovoltaic field. Detailed Implementation

[0019] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to specific embodiments.

[0020] The following EVA matrix resin was purchased from Zhejiang Petrochemical Co., Ltd.; POE matrix resin was purchased from Wanhua Chemical Group Co., Ltd.; main crosslinking agent was purchased from Arkema; ​​co-crosslinking agent was purchased from Changxing Chemical Industry Co., Ltd.; silane coupling agent was purchased from Shandong Silicon Science New Materials Co., Ltd.; and light stabilizer was purchased from Jiangsu Bost Chemical Technology Co., Ltd.

[0021] Example 1 This embodiment describes a method for preparing a high-adhesion, low-basis-weight co-extruded film, comprising the following preparation steps: (1) Mix 100 parts (by weight, the same below) of POE matrix resin, 20 parts of high-adhesion-crosslinkable POE bifunctional modified resin double-grafted with silane coupling agent and co-crosslinking agent, 1 part of main crosslinking agent tert-butyl peroxycarbonate-2-ethylhexyl ester, 1.5 parts of crosslinking agent mixture of triallyl isocyanate and 0.1 parts of 1,6-hexanediol diacrylate, 0.5 parts of silane coupling agent γ-methacryloyloxypropyltrimethoxysilane, and 0.1 parts of light stabilizer sebacic acid bis-2,2,6,6-tetramethylpiperidinol ester to obtain semi-finished product material A of POE layer.

[0022] The specific preparation process of the high-adhesion-crosslinkable POE bifunctional modified resin with dual grafting of silane coupling agent and co-crosslinking agent includes: using a one-step melt grafting method to fully mix Dow PV8688 POE resin, silane coupling agent KH-570, co-crosslinking agent triallyl cyanurate, and initiator 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (silane coupling agent, co-crosslinking agent, and initiator account for 1.5%, 1.5%, and 0.15% of the POE resin mass, respectively), and then using a twin-screw extruder to carry out the grafting reaction at a melting temperature of 200℃. The melt is uniformly dispersed and reacted under strong shear (shear temperature of 95℃ and shear speed of 800 rpm / min). The completely reacted melt is extruded, water-cooled, and pelletized to obtain the finished product.

[0023] 100 parts of EVA matrix resin, 1 part of the main crosslinking agent tert-butyl peroxycarbonate-2-ethylhexyl ester, 1 part of the crosslinking agent triallyl cyanurate and 0.8 parts of propane trimethylol ester, 0.5 parts of the silane coupling agent γ-methacryloyloxypropyltrimethoxysilane with double bonds to increase adhesion, 0.1 parts of the light stabilizer bis-2,2,6,6-tetramethylpiperidinol sebacate, 0.1 parts of the antioxidant 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate n-octadecyl alcohol ester, and 0.1 parts of titanate modified anti-corrosion additive were mixed to obtain the semi-finished product material B of EVA layer.

[0024] The titanate-modified anti-corrosion additive is a blend of titanate-modified magnesium hydroxide particles and polyethylene-polyvinyl acetate copolymer, and its specific preparation process includes: Magnesium hydroxide was dried in an oven at 120°C for 3 hours to completely remove moisture. The titanate coupling agent (2% of the filler weight) was diluted with an appropriate amount of anhydrous ethanol (twice the weight of the filler, where the filler refers to magnesium hydroxide) to obtain a diluted mixed solution. The dried filler (magnesium hydroxide) was added to a high-speed mixer, and stirring was started (stirring speed 500 rpm / min) and preheated to 90°C. The diluted mixed solution was slowly added via spraying, and stirring was continued for 20 minutes to ensure uniform coating with the titanate coupling agent. The filler (magnesium hydroxide) is applied to the surface; then, polyethylene-polyvinyl acetate copolymer (EVA) resin (addition amount is 4 times that of the filler) is added for premixing; in a twin-screw extruder, melt blending is carried out at a processing temperature of 85°C, and the screw speed and feed rate need to be properly controlled (screw speed is 20 rpm / min, feed rate is 7 rpm / min), and vacuum degassing is turned on to remove moisture and volatiles; finally, the extruded melt is processed by water-cooled string pelletizing to produce uniform titanate modified anti-corrosion additive granules.

[0025] (2) Using EPE co-extrusion, one layer of semi-finished material A and two layers of semi-finished material B are respectively put into the corresponding mixing tank, and melt co-extrusion is carried out at a set temperature of 85°C. The extrusion speed is 30 m / min. After casting and cooling, a high-adhesion, low-basis-weight co-extruded film (EPE co-extruded film) with the structure of EVA layer + POE layer + EPE layer is obtained in this embodiment. The total basis weight of the co-extruded film is 360 g / m. 2 The basis weight of the POE layer is 60 g / m². 2 The basis weight of the EVA layer is 300 g / m³. 2 .

[0026] Examples 2-6 Examples 2-6 describe a co-extruded film with high adhesion and low basis weight and its preparation method. Referring to Example 1, the difference between Examples 2-6 and Example 1 is that the basis weight of the EVA layer is different. The specific sample basis weights are shown in Table 1.

[0027] Examples 7-10 Examples 7-10 describe a co-extruded film with high adhesion and low basis weight, and its preparation method. Referring to Example 1, the difference between Examples 7-10 and Example 1 is that the basis weight of the POE layer is different. The specific sample basis weights are shown in Table 1.

[0028] Examples 11-14 Examples 11-14 describe a co-extruded film with high adhesion and low basis weight, and its preparation method. Referring to Example 1, the difference between Examples 11-14 and Example 1 is that the total basis weight of the same EPE co-extruded film is different for the EVA layer and the POE layer. The specific sample basis weights are shown in Table 1.

[0029] Table 1

[0030] In Table 1, Examples 2, 3, 1, and 4-6 all have a POE layer basis weight set to 60 g / m². 2 The basis weight of the EVA layer shows a gradient decreasing trend; in Examples 7, 8, 1, and 9-10, the basis weight of the EVA layer was set to 300 g / m³. 2 The basis weight of the POE layer shows a gradient decreasing trend; the total basis weight of the EPE co-extruded films in Examples 1 and 11-14 was all set to 360 g / m³. 2 The basis weights of the POE layer and the EVA layer show a complementary increasing and decreasing gradient trend.

[0031] Performance testing The co-extruded films obtained in Examples 1-14 and Comparative Examples 1-2 were subjected to the following performance tests, and the test results are shown in Table 2 below: 1. Crosslinking degree (xylene method): Tested according to the testing requirements specified in Clause 5.5.3 of GB / T 29848-2018 "Ethylene-vinyl acetate copolymer (EVA) film for photovoltaic module encapsulation".

[0032] 2. Adhesion strength test between the adhesive film and the photovoltaic glass panel: according to GB / T 2790 The test was conducted in accordance with the 1995 standard "Test Method for 180° Peel Strength of Adhesives". The 180° peel test specimen method was used, and the peel force between the photovoltaic glass and the adhesive film was measured on a tensile tester at a tensile speed of (100±10) mm / min.

[0033] 3. Visual inspection (first visual inspection): Check for air bubbles after lamination between the adhesive film and the photovoltaic glass.

[0034] 4. Adhesion strength test between adhesive film and photovoltaic backsheet: The test shall be conducted in accordance with the provisions of GB / T 2790-1995 "Adhesives 180° Peel Strength Test Method". The 180° peel test method shall be used, and the peel force between the adhesive film and the photovoltaic backsheet shall be measured on a tensile tester at a tensile speed of (100±10) mm / min.

[0035] 5. PCT Aging Test: Prepare test samples according to the test conditions for the adhesion strength between the adhesive film and the photovoltaic glass panel and between the photovoltaic backsheet. For double-glass samples: cut the front and back adhesive films to 7cm × 18cm size. Place them into the preheated laminator from bottom to top in the following order: photovoltaic glass (20cm × 8cm) / front adhesive film / back adhesive film / photovoltaic glass (20cm × 8cm). After lamination and curing, the adhesive film inside the sample should be free of air bubbles. The test method is as follows: a) Place the prepared samples into the PCT aging chamber and set the test conditions according to JESD22-A102-C: temperature 121℃ ±0.5℃, relative humidity 99%-100%, test time: 24h, 48h; b) After the test, the sample was taken out and conditioned for 4 hours at a temperature of (23±2)℃ and a relative humidity of (50±5)% before a visual inspection (second visual inspection). c) Test the peel strength of the encapsulant film / photovoltaic glass of the double-glass sample and the yellowing index ΔYI.

[0036] 6. High temperature and high humidity aging test: Take two pieces of the adhesive film to be tested, each measuring 15cm × 25cm, and prepare three double-glass laminate samples, each measuring 15cm × 25cm. The test method is as follows: a) Place the prepared sample in a constant humidity and heat test chamber and set the test conditions according to IEC 61215-2:2021, 4.13: temperature 85℃±2℃, relative humidity 85%±5%; b) After the test, the sample was taken out and conditioned for 4 hours under the conditions of (23±2)℃ temperature and (50±5)% relative humidity, and then a visual inspection was carried out (third visual inspection). c) Test the yellowing index ΔYI of the double-glass sample.

[0037] 7. After performing test 2 above, conduct a visual inspection (fourth visual inspection) to observe whether there is any residual adhesive film on the photovoltaic glass on the POE layer side after the adhesive film separates from the photovoltaic glass. If there is no residue, it indicates that the interlayer adhesion between the EVA layer and the POE layer is high, and vice versa.

[0038] 8. Verification of snowflake bubbles in small photovoltaic modules: Prepare and laminate small photovoltaic modules according to the lamination appearance requirements specified in IEC 61215-1:2021. Perform a visual inspection on the periphery and edges of the photovoltaic modules (fifth visual inspection) to observe whether dendritic snowflake bubbles appear around the periphery of the small photovoltaic modules.

[0039] Table 2

[0040] Based on the basis weight distribution in Table 1 and the performance test results in Table 2, in Examples 1-14 of the present invention, by controlling the basis weight ratio of the EVA layer and the POE layer, as well as the total basis weight of the EPE co-extruded film, the total basis weight of the EPE co-extruded film after co-extrusion casting is controlled at 300-400 g / m³. 2 (Preferred size: 300-360g / m³) 2This yields a low-basis-weight EPE co-extruded film, with the POE layer having a basis weight of 60-120 g / m². 2 .

[0041] Furthermore, by optimizing the raw material formulations in the EVA and POE layers (adding a special silane coupling agent with double bonds to increase adhesion to the EVA layer, along with an appropriate amount of titanate-modified anti-corrosion additive, and adding a high-adhesion, crosslinkable POE bifunctional modified resin with silane coupling agent and crosslinking aid to the POE layer), the various properties of the low-basis-weight EPE co-extruded film (as shown in Table 2) are all excellent: the degree of crosslinking, peel strength to photovoltaic backsheet and photovoltaic glass, yellowing index after PCT aging for 48 hours, yellowing index after high temperature and high humidity aging, and appearance of photovoltaic modules of the low-basis-weight EPE co-extruded films in Examples 1-14 are all significantly better than those in Comparative Examples 1-2. For example, its initial peel strength with photovoltaic glass can reach over 166 N / cm, and its initial peel strength with photovoltaic backsheet can reach over 80 N / cm. After PCT aging for 48 hours, its peel strength with photovoltaic glass can still reach over 30 N / cm. The yellowing index after PCT aging for 48 hours can be as low as 1.36, and the yellowing index after high temperature and high humidity aging can be as low as 1.73, meeting the usage requirements of encapsulation film for photovoltaic cells. Furthermore, no abnormal phenomena occur after lamination, and there are no snowflake bubbles in the photovoltaic modules.

[0042] This is mainly because: the POE layer incorporates a highly adhesive, crosslinkable, bifunctional modified POE resin grafted with both silane coupling agents and co-crosslinking agents. The grafted resin forms a more complete three-dimensional network structure, reducing the migration and precipitation of additives in the POE layer and making the crosslinking reaction during lamination more stable. Therefore, the crosslinking degree of the low-basis-weight EPE co-extruded film prepared by this invention is above 80%, and no snowflake bubbles are generated in the small photovoltaic module lamination test results. Simultaneously, the addition of titanate-modified anti-corrosion additives to the EVA layer enhances the compatibility between the additives and the resin within the EVA layer, ensuring high adhesion and stability of the EVA layer. The thicker the EVA layer, the more difficult it is for the POE layer additives to migrate out, thus maintaining a high peel strength between the co-extruded film and the photovoltaic glass. In the casting extrusion process, the tight bonding between the EVA and POE layers allows the low-basis-weight EPE co-extruded film to possess the advantages of both, as well as superior aging resistance and adaptability to extreme environments with high temperature and humidity.

[0043] In summary, the co-extruded film of this invention, while possessing the advantage of low basis weight, also features high adhesion, resistance to aging and yellowing (such as resistance to PCT aging and yellowing, and resistance to damp heat aging), and excellent crosslinking performance, and can significantly reduce lamination snowflake bubble phenomenon. Thus, photovoltaic modules encapsulated using the co-extruded film of this invention meet the comprehensive requirements of low cost, lightweight, and high performance. The product's performance conforms to the application standards of EPE co-extruded films and can be used in flexible photovoltaic modules, broadening its application scenarios in the photovoltaic field.

[0044] Although preferred embodiments of the present invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of the present invention.

[0045] The technical solution provided by the present invention has been described in detail above. Specific examples have been used to illustrate the principle and implementation of the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation and application scope based on the idea of ​​the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A co-extruded film with high adhesion and low basis weight, characterized in that, It is formed by co-extrusion casting of an upper EVA layer, a POE layer, and a lower EVA layer, with the POE layer located between the upper and lower EVA layers; the total basis weight of the co-extruded film is 300-400 g / m³. 2 The basis weight of the POE layer is 60-120 g / m². 2 ; Both the upper and lower EVA layers comprise the following raw materials in parts by weight: 100-120 parts EVA matrix resin, 2.8-3.5 parts crosslinking agent, 0.5-0.8 parts silane coupling agent with double bonds, and 0.1-0.2 parts titanate modified anti-corrosion additive. The POE layer comprises the following raw materials in parts by weight: 100-120 parts of POE matrix resin, 15-20 parts of POE bifunctional modified resin grafted with silane coupling agent and co-crosslinking agent, and 2.5-4 parts of crosslinking agent.

2. The co-extruded film with high adhesion and low basis weight according to claim 1, characterized in that, The total basis weight of the co-extruded film is 300-360 g / m³. 2 .

3. The co-extruded film with high adhesion and low basis weight according to claim 1, characterized in that, The silane coupling agent with double bonds is one or a mixture of several of γ-methacryloyloxypropyltrimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, vinyltriperoxytert-butylsilane, vinyltriacetoxysilane, and vinyltri(β-methoxyethoxy)silane.

4. The co-extruded film with high adhesion and low basis weight according to claim 1, characterized in that, The titanate-modified anti-corrosion additive is a blend of titanate-modified magnesium hydroxide particles and polyethylene-polyvinyl acetate copolymer, or a blend of titanate-modified magnesium oxide and polyethylene-polyvinyl acetate copolymer.

5. The co-extruded film with high adhesion and low basis weight according to claim 4, characterized in that, The preparation process of the titanate-modified anti-corrosion additive includes: Moisture is removed from the magnesium oxide or magnesium hydroxide filler to obtain dried filler. The titanate coupling agent is diluted with 1-3 times the weight of the filler in anhydrous ethanol or toluene, and the titanate coupling agent accounts for 1-2% of the weight of the filler to obtain a diluted mixed solution. The dried filler is preheated to 80-110℃ with stirring at 400-500 rpm / min. The diluted mixed solution is slowly added by dripping or spraying, and stirring is continued for 10-20 minutes to ensure that the titanate coupling agent is uniformly coated on the surface of the filler. Subsequently, EVA resin is added for premixing, and the amount of EVA resin added is 2-5 times the weight of the filler. The mixture is melt-blended at a processing temperature of 80-100℃, and vacuum degassing is performed to remove moisture and volatiles. The extruded melt is then granulated by water-cooled strip cutting or underwater pelletizing to produce uniform titanate modified anti-corrosion additive particles.

6. A co-extruded film with high adhesion and low basis weight according to any one of claims 1-5, characterized in that, The crosslinking agents in both the upper and lower EVA layers comprise 1-1.5 parts of a primary crosslinking agent and 1.8-2 parts of a secondary crosslinking agent. The upper EVA layer and the lower EVA layer also include the following raw materials in parts by weight: 0.1-0.2 parts of antioxidant and 0.1-0.2 parts of light stabilizer.

7. A co-extruded film with high adhesion and low basis weight according to any one of claims 1-5, characterized in that, The preparation process of the POE bifunctional modified resin grafted with silane coupling agent and co-crosslinking agent includes: pre-mixing POE resin, silane coupling agent, co-crosslinking agent and initiator thoroughly using a one-step melt grafting method, wherein the silane coupling agent, co-crosslinking agent and initiator account for 1-2%, 1-2% and 0.1-0.2% of the POE resin mass, respectively; then carrying out the grafting reaction using a screw extruder at a melting temperature of 160-220℃, the melt is uniformly dispersed and reacted under shear action, the shear temperature is 80-100℃ and the shear speed is 800-1000 rpm / min, and the completely reacted melt is extruded, water-cooled and pelletized to obtain the finished product.

8. A co-extruded film with high adhesion and low basis weight according to any one of claims 1-5, characterized in that, The crosslinking agent in the POE layer includes 1-2 parts of a primary crosslinking agent and 1.5-2 parts of a secondary crosslinking agent; The POE layer also includes the following raw materials in parts by weight: 0.5-0.8 parts of silane coupling agent and 0.1-0.2 parts of light stabilizer.

9. A method for preparing a high-adhesion, low-basis-weight co-extruded film according to any one of claims 1-8, characterized in that, The preparation steps include the following: S1. Mix all the raw materials of the POE layer to obtain semi-finished material A; and mix all the raw materials of the upper EVA layer and the lower EVA layer to obtain semi-finished material B1 and semi-finished material B2 respectively. S2. Using EPE co-extrusion, semi-finished material B1, semi-finished material A and semi-finished material B2 are melt-co-extruded, cast and cooled to form a film, thus obtaining a co-extruded film.

10. The application of a co-extruded film with high adhesion and low basis weight, characterized in that, The co-extruded film with high adhesion and low basis weight as described in any one of claims 1-8 is used as an encapsulation material in flexible photovoltaic modules.

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