Coating compositions, methods for their preparation, photovoltaic backsheet and photovoltaic module

Abstract

The present application relates to the technical field of solar cells, and specifically includes a coating composition and a preparation method thereof, a photovoltaic back sheet and a photovoltaic module. The coating composition comprises a first composition and a second composition, the first composition comprises a fluorine-containing acrylic resin, and the second composition comprises a curing agent. The fluorine-containing acrylic resin is obtained by polymerization of a first monomer, a second monomer and a third monomer. The first monomer comprises an acrylate monomer, the second monomer comprises a fluorine-containing acrylic monomer, and the third monomer comprises a high steric hindrance-containing acrylic monomer. The curing agent comprises a first curing agent and a second curing agent. The first curing agent comprises an aliphatic isocyanate, and the second curing agent comprises an alicyclic isocyanate. The coating composition prepared by the present application has good ultraviolet resistance, hydrolysis resistance and alcoholysis resistance. The coating obtained by coating the coating composition and the desoxime type silica gel have excellent interfacial adhesion and weather resistance.

Description

Technical Field

[0001] This invention belongs to the field of solar cell technology, specifically relating to a coating composition and its preparation method, a photovoltaic backsheet, and a photovoltaic module. Background Technology

[0002] The structure of a solar cell module consists of glass, EVA, solar cells, and a backsheet. The backsheet, located on the outermost layer of the module, is a crucial component, providing not only long-term effective encapsulation but also protection against environmental factors such as moisture, ultraviolet radiation, and sandstorms. Therefore, the backsheet must possess excellent resistance to moisture and heat, corrosion, ultraviolet radiation, high temperatures, impact, and sandstorms. Currently, commonly used double-sided fluorinated solar cell backsheet structures include double-sided composite (TPT / KPK), single-sided composite (TPC / KPC), and double-sided coated (CPC). Due to raw material monopolies, the price of TPT / KPK film remains high. In recent years, the shortage of PVDF raw materials has led to a continuous rise in the price of KPC / KPC film, resulting in high prices for backsheets with adhesive-coated fluorinated film structures on the outer layer, which contradicts the continuous need for cost reduction in photovoltaic power generation. Double-sided coated backsheets (CPC) offer high reliability and moderate cost, gradually gaining market acceptance and becoming the mainstream backsheet product in the photovoltaic industry.

[0003] The double-sided coated backplate (CPC) is connected to the aluminum alloy frame by silicone sealant. Therefore, the weather-resistant layer and the silicone sealant of the double-sided coated backplate (CPC) should have good adhesion, UV resistance, solvent resistance, acid and alkali resistance, salt spray resistance, stain resistance and wind and sand resistance.

[0004] Currently, the weather-resistant layer of double-sided coated backsheets (CPC) is mainly obtained by cold-blending fluoropolymers with hydroxyl acrylic resins or polyester resins and then curing them with isocyanates. However, due to the high price of fluoropolymers, acrylic resins are increasingly used to improve efficiency and reduce costs. Different acrylic resin structures have varying compatibility with FEVE resins, and poorly compatible resins are prone to phase separation after cold blending, leading to chalking of the weather-resistant coating after harsh UV aging. Meanwhile, the aforementioned silicone sealants are usually ketoxime-free silicone sealants. While ketoxime-free silicone sealants have advantages such as fast cross-linking speed and high adhesive strength, in actual use, the ketoximes released from them corrode the weather-resistant layer, promoting the hydrolysis and alcoholysis of ester bonds under humid and hot conditions, thus destroying the cross-linked structure of the weather-resistant layer.

[0005] Therefore, there is an urgent need for a coating mixture with good UV resistance, hydrolysis resistance, and alcoholysis resistance, so that the prepared coating and silicone have excellent interfacial adhesion and weather resistance. Summary of the Invention

[0006] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, the object of this invention is to provide a coating composition and its preparation method, a photovoltaic backsheet, and a photovoltaic module. The coating composition prepared in this application exhibits good UV resistance, hydrolysis resistance, and alcoholysis resistance. The coating obtained by applying the coating composition and the silicone exhibit excellent interfacial adhesion and weather resistance.

[0007] In one aspect of the invention, a coating composition is provided. According to an embodiment of the invention, it comprises: a first composition and a second composition, the first composition comprising a fluorinated acrylic resin, and the second composition comprising a curing agent, wherein the fluorinated acrylic resin is obtained by polymerization of a first monomer, a second monomer, and a third monomer.

[0008] Wherein, the first monomer includes acrylate monomers, the second monomer includes fluorinated acrylic monomers, and the third monomer includes acrylic monomers with high steric hindrance.

[0009] The curing agent includes a first curing agent and a second curing agent, wherein the first curing agent includes an aliphatic isocyanate and the second curing agent includes an alicyclic isocyanate.

[0010] According to embodiments of the present invention, a coating composition is prepared by polymerizing a first monomer, a second monomer, and a third monomer to obtain a fluorinated acrylic resin. The addition of the second monomer improves the UV resistance of the coating composition and ensures good adhesion between the prepared coating and the base film, while also maintaining a low surface energy in the coating. The addition of the third monomer introduces sterically hindered crosslinking sites into the prepared fluorinated acrylic resin. When the fluorinated acrylic resin reacts with the curing agent, it significantly improves the hydrolysis and alcoholysis resistance of the coating composition. Simultaneously, the combined use of aliphatic and alicyclic isocyanates enhances the coating composition's adaptability to coating processes, further improving its hydrolysis and alcoholysis resistance. Furthermore, the addition of alicyclic isocyanates increases the coating hardness. Therefore, the coating composition prepared in this application exhibits excellent UV resistance, hydrolysis resistance, and alcoholysis resistance. The coating obtained using this composition and silicone exhibit excellent interfacial adhesion and weather resistance.

[0011] In addition, the coating composition according to the above embodiments of the present invention may also have the following additional technical features:

[0012] In some embodiments of the present invention, the first monomer includes at least one selected from methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, acrylic acid, methacrylic acid, methyl methacrylate, ethyl methacrylate, β-hydroxyethyl methacrylate, and β-hydroxyethyl acrylate.

[0013] In some embodiments of the present invention, the second monomer includes at least one of trifluoroethyl acrylate, trifluoroethyl methacrylate, hexafluorobutyl acrylate, hexafluorobutyl methacrylate, and perfluorodecyl acrylate.

[0014] In some embodiments of the present invention, the third monomer includes at least one of β-hydroxypropyl methacrylate, glycidyl methacrylate, β-hydroxypropyl acrylate, 2-acrylamido-2-methylpropanesulfonic acid, and isobornyl methacrylate.

[0015] In some embodiments of the present invention, the weight-average molecular weight of the fluorinated acrylic resin is 25,000-60,000, and the hydroxyl value of the fluorinated acrylic resin is 50 mg KOH / g-120 mg KOH / g.

[0016] In some embodiments of the present invention, the aliphatic isocyanate includes at least one of hexamethylene diisocyanate trimer, hexamethylene diisocyanate dimer, and hexamethylene diisocyanate biuret.

[0017] In some embodiments of the present invention, the alicyclic isocyanate includes at least one of isophorone diisocyanate trimer, isophorone diisocyanate trimer, and hydrogenated dimethyl diisocyanate trimer.

[0018] In some embodiments of the present invention, the ratio of the total amount of ester groups in the aliphatic isocyanate to the total amount of hydroxyl groups in the fluorinated acrylic resin is (0.4-0.7):1.

[0019] In some embodiments of the present invention, the ratio of the total amount of ester groups in the alicyclic isocyanate to the total amount of hydroxyl groups in the fluorinated acrylic resin is (0.2-0.4):1.

[0020] In some embodiments of the present invention, the first composition further comprises: a solvent, a filler, a dispersant, and a leveling agent.

[0021] In some embodiments of the present invention, the solvent includes at least one of butyl acetate, xylene, and propylene glycol methyl ether acetate.

[0022] In some embodiments of the present invention, the filler includes at least one of organic fillers and inorganic fillers.

[0023] In some embodiments of the present invention, the dispersant comprises at least one of a polyester polyamide containing acidic groups, a modified acrylate polymer, and a modified polyurethane.

[0024] In some embodiments of the present invention, the leveling agent includes at least one of silicone, acrylate copolymers, and fluorinated polyacrylates.

[0025] In some embodiments of the present invention, the second composition further comprises a diluent, said diluent comprising at least one of ethyl acetate, butyl acetate, and butanone.

[0026] In a second aspect, the present invention provides a method for preparing the coating composition described in the above embodiments. According to embodiments of the present invention, the method includes:

[0027] (1) The first monomer, the second monomer, the third monomer and the initiator are introduced into a solvent to carry out a polymerization reaction to obtain a fluorinated acrylic resin mixture;

[0028] (2) Add the first curing agent and the second curing agent to the fluorinated acrylic resin mixture to obtain a coating composition.

[0029] In addition, the method according to the above embodiments of the present invention may also have the following additional technical features:

[0030] In some embodiments of the present invention, in step (1), the first monomer, the second monomer, and the third monomer are mixed in a molar ratio of (30-75):(10-40):(15-30), and an initiator is added and heated to obtain the fluorinated acrylic resin.

[0031] In some embodiments of the present invention, step (1) further includes: mixing the fluorinated acrylic resin mixture obtained by polymerization with filler, dispersant and leveling agent to obtain the fluorinated acrylic resin mixture.

[0032] In a third aspect, the present invention provides a photovoltaic backsheet. According to embodiments of the invention, it comprises: a substrate layer; an adhesive layer and a weather-resistant layer, the adhesive layer and the weather-resistant layer being located on opposite sides of the substrate layer, and the adhesive layer and the weather-resistant layer being obtained by curing at least one of the coating compositions described in the embodiments above. This significantly improves the stability and weather resistance of the photovoltaic backsheet, which is beneficial for large-scale applications.

[0033] In a fourth aspect, the present invention provides a photovoltaic module. According to an embodiment of the present invention, the photovoltaic module includes the photovoltaic backsheet described in the above embodiments. Therefore, the photovoltaic module possesses all the features and advantages of the aforementioned photovoltaic backsheet, which will not be repeated here.

[0034] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0035] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0036] Figure 1 This is a flowchart of a method for preparing the coating composition of the above embodiment according to one embodiment of the present invention. Detailed Implementation

[0037] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0038] In one aspect of the present invention, a coating composition is provided. According to an embodiment of the present invention, the coating composition comprises: a first composition and a second composition, the first composition comprising a fluorinated acrylic resin, the second composition comprising a curing agent, the fluorinated acrylic resin being obtained by polymerization of a first monomer, a second monomer, and a third monomer, wherein the first monomer comprises an acrylate monomer, the second monomer comprises a fluorinated acrylic monomer, the third monomer comprises an acrylic monomer with high steric hindrance, and the curing agent comprises a first curing agent and a second curing agent, the first curing agent comprising an aliphatic isocyanate, and the second curing agent comprising an alicyclic isocyanate. Therefore, the coating composition prepared according to this application has good UV resistance, hydrolysis resistance, and alcoholysis resistance, and the coating obtained by applying the coating composition to silicone exhibits excellent interfacial adhesion and weather resistance.

[0039] The following provides a detailed explanation of how the above-mentioned coating composition can achieve the aforementioned technical effects:

[0040] In this application, by adding a second and a third monomer to carry out the polymerization reaction, the steric hindrance of the reaction sites of the fluoroacrylic resin can be significantly improved, thereby enhancing the hydrolysis and alcoholysis resistance of the coating prepared by the coating composition. At the same time, by adding the second monomer, due to the strong electronegativity of the F atom, the F atom will form hydrogen bonds with -OH, promoting the electronic polarization of the -OH at the larger reaction sites, making it easier to react chemically with -NCO, and increasing the curing reaction rate of the coating composition. This can not only improve the UV resistance of the coating composition, but also ensure that the prepared coating and the base film have good adhesion and the coating has a low surface energy. The coating composition is obtained by crosslinking the coating containing fluoroacrylic resin with aliphatic isocyanate and alicyclic isocyanate. Using aliphatic isocyanate and alicyclic isocyanate together as curing agents can not only make the coating have good coating process adaptability, but also further improve the hydrolysis and alcoholysis resistance of the coating. In addition, by adding alicyclic isocyanate, the hardness of the coating can also be increased. Therefore, the coating composition prepared in this application has good UV resistance, hydrolysis resistance and alcoholysis resistance, and the coating obtained by applying the coating composition and the silicone have excellent interfacial adhesion and weather resistance.

[0041] It should be noted that the aforementioned silicone includes, but is not limited to, deketoxime type silicone.

[0042] In embodiments of the present invention, the first monomer includes, but is not limited to, at least one of methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, acrylic acid, methacrylic acid, methyl methacrylate, ethyl methacrylate, β-hydroxyethyl methacrylate, and β-hydroxyethyl acrylate. Therefore, the prepared coating composition can be further guaranteed to have good UV resistance, hydrolysis resistance, and alcoholysis resistance, and the coating obtained by applying the coating composition and the silicone exhibit excellent interfacial adhesion and weather resistance.

[0043] According to a specific embodiment of the present invention, the first monomer has a Tg of 25-40℃ and an acid value of less than 5mgKOH / g. Therefore, it can be further ensured that the prepared coating composition has good UV resistance, hydrolysis resistance and alcoholysis resistance. The coating obtained by applying the coating composition and the silicone have excellent interfacial adhesion and weather resistance.

[0044] In embodiments of the present invention, the second monomer includes, but is not limited to, at least one of trifluoroethyl acrylate, trifluoroethyl methacrylate, hexafluorobutyl acrylate, hexafluorobutyl methacrylate, and perfluorodecyl acrylate. This further ensures that the prepared coating composition exhibits good UV resistance, hydrolysis resistance, and alcoholysis resistance, and that the coating obtained by applying the coating composition and the silicone exhibit excellent interfacial adhesion and weather resistance.

[0045] In embodiments of the present invention, the third monomer includes, but is not limited to, at least one of β-hydroxypropyl methacrylate, glycidyl methacrylate, β-hydroxypropyl acrylate, 2-acrylamido-2-methylpropanesulfonic acid, and isobornyl methacrylate. This further ensures that the prepared coating composition exhibits good UV resistance, hydrolysis resistance, and alcoholysis resistance, and that the coating obtained by applying the coating composition and the silicone exhibit excellent interfacial adhesion and weather resistance.

[0046] In embodiments of the present invention, the initiator includes, but is not limited to, at least one of azo initiators and peroxide initiators. This further ensures that the prepared coating composition exhibits good UV resistance, hydrolysis resistance, and alcoholysis resistance, and that the coating obtained by applying the coating composition and the silicone exhibit excellent interfacial adhesion and weather resistance.

[0047] According to another specific embodiment of the present invention, the aliphatic isocyanate includes, but is not limited to, at least one of hexamethylene diisocyanate trimer, hexamethylene diisocyanate dimer, and hexamethylene diisocyanate biuret; similarly, the alicyclic isocyanate includes at least one of isophorone diisocyanate trimer, isophorone diisocyanate dimer, and hydrogenated phenylenediamine diisocyanate trimer. Therefore, the prepared coating composition can be further guaranteed to have good UV resistance, hydrolysis resistance, and alcoholysis resistance, and the coating obtained by applying the coating composition and the silicone exhibit excellent interfacial adhesion and weather resistance.

[0048] According to another specific embodiment of the present invention, the ratio of the total amount of ester groups in the aliphatic isocyanate to the total amount of hydroxyl groups in the fluorinated acrylic resin is (0.4-0.7):1. Therefore, controlling the ratio of the total amount of ester groups in the aliphatic isocyanate to the total amount of hydroxyl groups in the fluorinated acrylic resin within the above range further improves the coating's resistance to alcoholysis and also further improves the adhesion between the coating and PET. The inventors have found that if the ratio of the total amount of ester groups in the aliphatic isocyanate to the total amount of hydroxyl groups in the fluorinated acrylic resin is too large, the proportion of sterically hindered -NCO is too low, which reduces the coating's resistance to hydrolysis and alcoholysis. Conversely, if the ratio of the total amount of ester groups in the aliphatic isocyanate to the total amount of hydroxyl groups in the fluorinated acrylic resin is too small, the proportion of sterically hindered -NCO is too high, resulting in a slow crosslinking and curing speed between the fluorinated acrylic resin and the aliphatic isocyanate after a rapid coating process, leading to poor crosslinking and curing effects.

[0049] According to another specific embodiment of the present invention, the ratio of the total ester groups in the alicyclic isocyanate to the total hydroxyl groups in the fluorinated acrylic resin is (0.2-0.4):1. Therefore, controlling the ratio of the total ester groups in the alicyclic isocyanate to the total hydroxyl groups in the fluorinated acrylic resin within the above range further improves the coating's resistance to alcoholysis and also further improves the adhesion between the coating and PET. The inventors have found that if the ratio of the total ester groups in the alicyclic isocyanate to the total hydroxyl groups in the fluorinated acrylic resin is too large, the proportion of sterically hindered -NCO is too high, resulting in a slower crosslinking and curing speed between the fluorinated acrylic resin and the alicyclic isocyanate after a rapid coating process, leading to a poorer crosslinking and curing effect. Conversely, if the ratio of the total ester groups in the alicyclic isocyanate to the total hydroxyl groups in the fluorinated acrylic resin is too small, the proportion of sterically hindered -NCO is too low, which reduces the coating's resistance to hydrolysis and alcoholysis.

[0050] According to another specific embodiment of the present invention, the first composition further includes: a solvent, a filler, a dispersant, and a leveling agent. Thus, by adding a filler (such as titanium dioxide), the high hiding power of the coating composition can be significantly improved, and the weather-resistant layer obtained after coating has good coloring power and adhesion. By adding a dispersant, the filler (such as titanium dioxide particles) can be uniformly dispersed in the coating composition, improving the stability and flowability of the filler (such as titanium dioxide particles). By adding a leveling agent, the coating composition can be promoted to form a smooth, uniform coating film during the drying and film-forming process.

[0051] In embodiments of the present invention, the solvent includes, but is not limited to, at least one of butyl acetate, xylene, and propylene glycol methyl ether acetate, thereby allowing the first composition and the second composition to be better present in the solvent.

[0052] In embodiments of the present invention, the filler includes at least one of organic fillers and inorganic fillers. The organic filler includes, but is not limited to, at least one of organosilicon micropowder, polymethyl methacrylate micropowder, and polyamide wax powder; preferably, the polyamide wax powder has a particle size of 2-10 micrometers. The inorganic filler includes at least one of rutile titanium dioxide, barium sulfate, and calcium carbonate. The particle size of the inorganic filler is 20-400 nanometers, which helps to improve the stability of the grinding fineness of the inorganic filler, thereby providing a better shielding effect against ultraviolet light.

[0053] In embodiments of the present invention, the dispersant includes at least one of a polyester polyamide containing acidic groups, a modified acrylate polymer, and a modified polyurethane, thereby enabling materials such as fluorinated acrylates to be better dispersed in the solvent.

[0054] In embodiments of the present invention, the leveling agent includes at least one of silicone, acrylate copolymers and fluorinated polyacrylates, thereby reducing the surface tension of the coating compound and eliminating the surface tension gradient of the wet film.

[0055] According to another specific embodiment of the present invention, the second composition further comprises a diluent, said diluent including at least one selected from ethyl acetate, butyl acetate, and butanone. This reduces the viscosity of the fluorinated acrylic resin system, allowing for better mixing of the fluorinated acrylic resin with other components.

[0056] According to a specific embodiment of the present invention, the weight-average molecular weight of the fluorinated acrylic resin is 25,000-60,000, and the hydroxyl value of the fluorinated acrylic resin is 50 mg KOH / g-120 mg KOH / g. Therefore, if the weight-average molecular weight of the fluorinated acrylic resin is too high, the viscosity of the fluorinated acrylic resin will be too high, making the coating difficult to apply. If the weight-average molecular weight of the fluorinated acrylic resin is too low, the adhesion between the coating composition and the substrate and EVA will be too low. If the hydroxyl value of the fluorinated acrylic resin is too high, the crosslinking density of the coating obtained by applying the coating compound will be too high, easily leading to brittleness of the coating. If the hydroxyl value of the fluorinated acrylic resin is too low, the crosslinking density of the coating obtained by applying the coating compound will be too low, easily leading to hydrolysis or alcoholysis.

[0057] In a second aspect, the present invention provides a method for preparing a coating composition, as detailed in the appendix. Figure 1 The preparation method includes the following steps:

[0058] S100: A mixture of fluorinated acrylic resins obtained by polymerizing the first monomer, the second monomer, and the third monomer.

[0059] In this step, the first monomer, the second monomer, the third monomer, and the initiator are introduced into a solvent to carry out a polymerization reaction to obtain a fluorinated acrylic resin mixture.

[0060] According to a specific embodiment of the present invention, step S100 further includes: mixing the polymerized fluorinated acrylic resin mixture with filler, dispersant and leveling agent to obtain the fluorinated acrylic resin mixture.

[0061] According to another specific embodiment of the present invention, in step S100, a solvent is further added. The amount of solvent can be adjusted according to the actual situation to obtain a coating composition that is more suitable for different application scenarios.

[0062] According to another specific embodiment of the present invention, the first monomer, the second monomer, and the third monomer are mixed in a molar ratio of (30-75):(10-40):(15-30), and an initiator is added. The mixture is then heated to obtain the fluorinated acrylic resin. This further improves the UV resistance, adhesion, hydrolysis resistance, and alcoholysis resistance of the coating composition. The inventors have found that if the molar percentage of the second monomer is too high, there are too many fluorinated branches in the fluorinated acrylic resin chain, resulting in excessively low surface tension of the coating and consequently poor adhesion between the coating and PET. If the molar percentage of the second monomer is too low, there are too few fluorinated branches in the fluorinated acrylic resin chain, and the electronic polarization of the F atoms on the -OH branches is severely weakened, which is not conducive to the rapid crosslinking of -OH and -NCO. Simultaneously, the fluorinated segments cannot effectively encapsulate the acrylic resin backbone, resulting in poor UV resistance of the obtained coating. If the molar percentage of the third monomer is too high, the steric hindrance of the crosslinking points in the acrylic resin will be too large, resulting in a slow crosslinking reaction between the first monomer and the isocyanate composition, a poor crosslinking and curing effect, and no practical production value. If the molar percentage of the third monomer is too low, the steric hindrance of the crosslinking points in the first monomer will be too small, resulting in poor hydrolysis and alcoholysis resistance of the crosslinked urethane bonds.

[0063] According to another specific embodiment of the present invention, the polymerization reaction temperature is 60-140°C. Therefore, controlling the polymerization reaction temperature within the above range is beneficial for the polymerization of the first monomer, the second monomer, and the third monomer, thereby obtaining a fluorinated acrylic resin.

[0064] According to yet another specific embodiment of the present invention, the polymerization reaction occurs under an inert atmosphere.

[0065] According to another specific embodiment of the present invention, the method for introducing the first monomer, the second monomer, the third monomer, and the initiator into the solvent includes, but is not limited to, slow dropwise addition. The rate of slow dropwise addition is not particularly limited, and those skilled in the art can choose according to the actual situation.

[0066] S200: Adding the first and second curing agents to a fluorinated acrylic resin mixture to obtain a coating composition.

[0067] In this step, aliphatic isocyanate and alicyclic isocyanate are used together as curing agents. The above-mentioned fluorinated acrylic resin mixture and the above-mentioned curing agents are mixed and a crosslinking reaction occurs to obtain a coating composition.

[0068] According to another specific embodiment of the present invention, in step S200, a solvent is further added. The amount of solvent can be adjusted according to the actual situation to obtain a coating composition that is more suitable for different application scenarios.

[0069] In a third aspect, the present invention provides a photovoltaic backsheet. According to embodiments of the invention, it comprises: a substrate layer; an adhesive layer and a weather-resistant layer, the adhesive layer and the weather-resistant layer being located on opposite sides of the substrate layer, and the adhesive layer and the weather-resistant layer being obtained by curing at least one of the coating compositions described in the embodiments above. This significantly improves the stability and weather resistance of the photovoltaic backsheet, which is beneficial for large-scale applications.

[0070] According to a specific embodiment of the present invention, the thickness of the weather-resistant layer is 15 micrometers to 30 micrometers, the thickness of the adhesive layer is 15 micrometers to 30 micrometers, and the thickness of the substrate layer is 150 micrometers to 300 micrometers. This can further improve the stability and weather resistance of the photovoltaic backsheet, which is beneficial for large-scale application.

[0071] In embodiments of the present invention, the substrate layer is a polyester film. The materials of the polyester film include, but are not limited to, at least one of polyethylene terephthalate (PET) resin, polybutylene terephthalate (PBT) resin, or polyethylene terephthalate (PEN) resin.

[0072] In a fourth aspect, the present invention provides a photovoltaic module. According to an embodiment of the present invention, the photovoltaic module includes the photovoltaic backsheet described in the above embodiments. Therefore, the photovoltaic module possesses all the features and advantages of the aforementioned photovoltaic backsheet, which will not be repeated here.

[0073] The embodiments of the present invention are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. In addition, unless otherwise specified, all reagents used in the following embodiments are commercially available or can be synthesized according to the methods described herein or known to others. For reaction conditions not listed, they are also readily available to those skilled in the art.

[0074] Example 1

[0075] This embodiment provides a method for preparing a coating composition, the specific steps of which are as follows:

[0076] (1) Weigh the first monomer, the second monomer, the third monomer, the solvent and the initiator (by weight);

[0077]

[0078]

[0079] (2) Under heat preservation and inert atmosphere, the first monomer, the second monomer, the third monomer, the solvent and the initiator are slowly added dropwise to the solvent to carry out the polymerization reaction. After the dropwise addition is completed, the heat preservation is continued for 3 hours to obtain fluorinated acrylic resin; the heat preservation temperature is 100℃.

[0080] (3) Grind 40g of fluorinated acrylic resin, 55g of butyl acetate, 0.4g of polyester polyamide (dispersant) containing acidic groups and 19.2g of titanium dioxide. Then, physically disperse and mix the ground particles with 2g of polyamide wax powder, 0.5g of acrylate copolymer (leveling agent) and an appropriate amount of butyl acetate to obtain the first mixture.

[0081] (4) Add 1.65g of the first curing agent (Bayer 3390) and 1.35g of the second curing agent (Bayer Z4470) to the first mixture, and add an appropriate amount of solvent to obtain a coating mixture.

[0082] Example 2

[0083] This embodiment provides a method for preparing a coating composition. The only difference between this embodiment and Embodiment 1 is that:

[0084] (1) Weigh the first monomer, the second monomer, the third monomer, the solvent and the initiator (by weight);

[0085]

[0086] The rest of the content is consistent with the description in the embodiments.

[0087] Example 3

[0088] This embodiment provides a method for preparing a coating composition. The only difference between this embodiment and Embodiment 1 is that:

[0089] (1) Weigh the first monomer, the second monomer, the third monomer, the solvent and the initiator (by weight);

[0090]

[0091]

[0092] The rest of the content is consistent with the description in the embodiments.

[0093] Example 4

[0094] This embodiment provides a method for preparing a coating composition. The only difference between this embodiment and Embodiment 1 is that:

[0095] (1) Weigh the first monomer, the second monomer, the third monomer, the solvent and the initiator (by weight);

[0096]

[0097] The rest of the content is consistent with the description in the embodiments.

[0098] Example 5

[0099] This embodiment provides a method for preparing a coating composition. The only difference between this embodiment and Embodiment 1 is that:

[0100] (4) Add 1.1g of the first curing agent (Bayer 3390) and 1.8g of the second curing agent (Bayer Z4470) to the first mixture, and add an appropriate amount of solvent to obtain a coating mixture.

[0101] The rest of the content is consistent with the description in the embodiments.

[0102] Example 6

[0103] This embodiment provides a method for preparing a coating composition. The only difference between this embodiment and Embodiment 1 is that:

[0104] (4) Add 1.9g of the first curing agent (Bayer 3390) and 0.9g of the second curing agent (Bayer Z4470) to the first mixture, and add an appropriate amount of solvent to obtain a coating mixture.

[0105] The rest of the content is consistent with the description in the embodiments.

[0106] Comparative Example 1

[0107] This comparative example provides a method for preparing a coating composition. The only difference between this comparative example and Example 1 is that:

[0108] (1) Weigh the first monomer, the second monomer, the third monomer, the solvent and the initiator (by weight);

[0109]

[0110] The rest of the content is consistent with the description in the embodiments.

[0111] Comparative Example 2

[0112] This comparative example provides a method for preparing a coating composition. The only difference between this comparative example and Example 1 is that:

[0113] (1) Weigh the first monomer, the second monomer, the third monomer, the solvent and the initiator (by weight);

[0114]

[0115] The rest of the content is consistent with the description in the embodiments.

[0116] Comparative Example 3

[0117] This comparative example provides a method for preparing a coating composition. The only difference between this comparative example and Example 1 is that:

[0118] (4) Add 2.2g of the first curing agent (Bayer 3390) and 0.45g of the second curing agent (Bayer Z4470) to the first mixture, and add an appropriate amount of solvent to obtain a coating mixture.

[0119] The rest of the content is consistent with the description in the embodiments.

[0120] Comparative Example 4

[0121] This comparative example provides a method for preparing a coating composition. The only difference between this comparative example and Example 1 is that:

[0122] (4) Add 0.825g of the first curing agent (Bayer 3390) and 2.7g of the second curing agent (Bayer Z4470) to the first mixture, and add an appropriate amount of solvent to obtain a coating mixture.

[0123] The rest of the content is consistent with the description in the embodiments.

[0124] Comparative Example 5

[0125] Take 30g of commercially available acrylic resin, 10g of Changxing 41011 fluororesin, 55g of butyl acetate, 19.2g of titanium dioxide, and 0.4g of polyester polyamide containing acidic groups (dispersant). Grind for 1 hour and then add to butyl acetate solvent. Then add 2g of polyamide wax powder and 0.5g of acrylate copolymer (leveling agent) to butyl acetate solvent to obtain the first coating composition. Add 3.79g of Bayer 3390 and an appropriate amount of butyl acetate solvent to the first coating composition to obtain a coating mixture.

[0126] Test procedure: (1) Coat one side of the PET with the coating mixture prepared in the above example or comparative example, dry at 150°C for 2 min to obtain a weather-resistant layer with a bonding thickness of 15 micrometers; coat the other side of the PET with fluorocarbon coating to obtain a bonding layer with a dry thickness of 5 micrometers, and cure at 50°C for 3 days to obtain a test sample, and test the performance of the above test sample: (2) Cut two test samples with a width of 15 mm, and bond the two test samples together with a deketoxime type silicone sealant with a thickness of 3 mm. After curing at 30°C-RH85% for no less than 3 days, test and PCT aging are performed.

[0127] Testing standards:

[0128] 1. Compatibility test with deketoxime type silicone sealant:

[0129] Tested according to GB / T 29595-2013 "Silicone Rubber Sealants for Photovoltaic Modules";

[0130] 2. Solvent resistance test:

[0131] Tested according to GB / T 23989-2009 "Resistance of Coatings to Solvents - Test Method";

[0132] 3. Adhesion test:

[0133] Tested according to standard GB / T 9286-1998;

[0134] 4. Yellow Index Test:

[0135] Tested according to national standard GB / T11186.2-1989 "Test Method for Coating Color";

[0136] 5. Gloss test:

[0137] According to the national standard GB / T9754-2007 "Determination of 20°, 60° and 85° specular gloss of paint films without metallic pigments".

[0138] Table 1 Test results of embodiments and comparative examples of the present invention

[0139]

[0140]

[0141] Note: Peel strength after matching with silicone mainly reflects the hydrolysis and alcoholysis resistance of the coating composition; initial adhesion level mainly reflects the adhesion between the coating and PET; ethanol wiping resistance mainly reflects the cross-linking and curing effect of fluorinated acrylic resin and curing agent; QUV300kwh mainly reflects the UV resistance of the coating composition.

[0142] A comparison of Examples 1-4 with Comparative Examples 1-2 shows that if the molar percentage of the second monomer is too high, the adhesion between the coating and PET will deteriorate; if the molar percentage of the second monomer is too low, the UV resistance of the resulting coating will deteriorate. If the molar percentage of the third monomer is too high, the steric hindrance of the crosslinking points in the acrylic resin will be too large, resulting in a slow crosslinking reaction between the first monomer and the isocyanate composition and a poor crosslinking curing effect. If the molar percentage of the third monomer is too low, the crosslinked urethane bonds will have poor hydrolysis resistance and alcohol and alkali resistance.

[0143] As can be seen from the comparison of Examples 1, 5-6 and Comparative Examples 3-4, if the ratio of the total amount of ester groups in the above-mentioned aliphatic isocyanate to the total amount of hydroxyl groups in the fluorinated acrylic resin is too large, or if the ratio of the total amount of ester groups in the alicyclic isocyanate to the total amount of hydroxyl groups in the fluorinated acrylic resin is too small, the proportion of sterically hindered -NCO is too low, which will reduce the coating's resistance to hydrolysis and alcoholysis. If the ratio of the total amount of ester groups in the above-mentioned aliphatic isocyanate to the total amount of hydroxyl groups in the fluorinated acrylic resin is too small, or if the ratio of the total amount of ester groups in the alicyclic isocyanate to the total amount of hydroxyl groups in the fluorinated acrylic resin is too large, the proportion of sterically hindered -NCO is too high, and the crosslinking and curing speed of the fluorinated acrylic resin and aliphatic isocyanate is slow after the rapid coating process, resulting in a poor crosslinking and curing effect.

[0144] As can be seen from the comparison between Examples 1-6 and Comparative Example 5, the coating composition prepared in this example has good UV resistance, hydrolysis resistance and alcoholysis resistance. The coating obtained by coating with the coating composition and the deketoxime type silica gel have excellent interfacial adhesion and weather resistance.

[0145] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A coating composition, characterized in that, include: A first composition and a second composition, the first composition comprising a fluorinated acrylic resin, and the second composition comprising a curing agent, wherein the fluorinated acrylic resin is obtained by polymerization of a first monomer, a second monomer, and a third monomer. The first monomer includes at least one of methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, isopropyl methacrylate, acrylic acid, methacrylic acid, methyl methacrylate, ethyl methacrylate, styrene, β-hydroxyethyl methacrylate, and β-hydroxyethyl acrylate; the second monomer includes a fluorinated acrylic monomer; and the third monomer includes an acrylic monomer with high steric hindrance. The third monomer includes at least one of β-hydroxypropyl methacrylate, glycidyl methacrylate, β-hydroxypropyl acrylate, 2-acrylamido-2-methylpropanesulfonic acid, and isobornyl methacrylate. The molar ratio of the first monomer, the second monomer, and the third monomer is (30-75):(10-40):(15-30); The curing agent includes a first curing agent and a second curing agent, wherein the first curing agent includes an aliphatic isocyanate and the second curing agent includes an alicyclic isocyanate. The ratio of the total ester groups in the aliphatic isocyanate to the total hydroxyl groups in the fluorinated acrylic resin is (0.4-0.7):1; The ratio of the total ester groups in the alicyclic isocyanate to the total hydroxyl groups in the fluorinated acrylic resin is (0.2-0.4):

1.

2. The coating composition according to claim 1, characterized in that, The second monomer includes at least one of trifluoroethyl acrylate, trifluoroethyl methacrylate, hexafluorobutyl acrylate, hexafluorobutyl methacrylate, and perfluorodecyl acrylate.

3. The coating composition according to claim 1, characterized in that, The fluorinated acrylic resin has a weight-average molecular weight of 25,000-60,000 and a hydroxyl value of 50 mg KOH / g-120 mg KOH / g.

4. The coating composition according to any one of claims 1-3, characterized in that, The aliphatic isocyanate includes at least one of hexamethylene diisocyanate trimer, hexamethylene diisocyanate dimer, and hexamethylene diisocyanate biuret; And / or, the alicyclic isocyanate includes at least one of isophorone diisocyanate trimer, isophorone diisocyanate trimer, and hydrogenated dimethyl diisocyanate trimer.

5. The coating composition according to claim 1, characterized in that, The first composition further comprises at least one of a solvent, a filler, a dispersant, and a leveling agent, and the first composition satisfies at least one of the following conditions: The solvent includes at least one of butyl acetate, xylene, and propylene glycol methyl ether acetate; The filler includes at least one of organic fillers and inorganic fillers; The dispersant includes at least one of polyester polyamide containing acidic groups, modified acrylate polymer, and modified polyurethane; The leveling agent includes at least one of silicone, acrylate copolymer, and fluorinated polyacrylate.

6. The coating composition according to claim 1, characterized in that, The second composition further comprises a diluent, said diluent comprising at least one of ethyl acetate, butyl acetate, and butanone.

7. A method for preparing the coating composition according to any one of claims 1-6, characterized in that, include: (1) The first monomer, the second monomer, the third monomer and the initiator are introduced into a solvent to carry out a polymerization reaction to obtain a fluorinated acrylic resin mixture; (2) Add the first curing agent and the second curing agent to the fluorinated acrylic resin mixture to obtain a coating composition.

8. The method according to claim 7, characterized in that, In step (1), the first monomer, the second monomer and the third monomer are mixed in a molar ratio of (30-75):(10-40):(15-30), and an initiator is added and heated to obtain the fluorinated acrylic resin; And / or, step (1) further includes: mixing the fluorinated acrylic resin mixture obtained by polymerization with fillers, dispersants and leveling agents to obtain a fluorinated acrylic resin mixture.

9. A photovoltaic backsheet, characterized in that, include: Substrate layer; An adhesive layer and a weather-resistant layer, wherein the adhesive layer and the weather-resistant layer are located on opposite sides of the substrate layer, and at least one of the adhesive layer and the weather-resistant layer is cured from a coating composition according to any one of claims 1-6, or a coating composition prepared by the method according to any one of claims 7-8.

10. A photovoltaic module, characterized in that, include: The photovoltaic backsheet as described in claim 9.

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