Photovoltaic backboard coating and preparation method thereof

Abstract

The invention relates to a photovoltaic backboard coating and a preparation method thereof, and belongs to the technical field of photovoltaic panels. The preparation method of the photovoltaic backboard coating comprises the following steps: placing isocyanate and an organic solvent in a reaction kettle, preheating in an inert gas atmosphere, adding a catalyst, uniformly mixing, adding polyol, stirring for reaction, and carrying out rotary evaporation after the reaction is finished to obtain a prepolymer; and stirring and mixing the prepolymer, the modified silicon dioxide, a reaction monomer, a pigment and a photoinitiator to obtain a coating, coating the surface of the photovoltaic back plate with the coating, and performing UV curing to obtain the photovoltaic back plate. According to the prepared flame-retardant compound, flame-retardant elements P, S and N and a Schiff base structure are introduced, the flame-retardant performance of a coating is remarkably improved, chemical bonding is formed through carbon-carbon double bonds and hydroxyl of the flame-retardant compound, the stability of a core-shell structure is remarkably improved, and then the mechanical property and flame-retardant stability of the coating are remarkably improved.

Description

Technical Field

[0001] This invention belongs to the technical field of photovoltaic panels, and relates to a photovoltaic backsheet coating and its preparation method. Background Technology

[0002] Solar photovoltaic (PV) panels, represented by backsheets, are located on the back of PV modules and serve to support and protect the solar cells. In practical applications, PV modules may experience bulging, overheating, or even burn-through or fire due to material defects, system design factors, or obstruction from foreign objects. This can lead to incalculable economic losses and environmental damage. Therefore, it is necessary to improve the flame retardancy and heat resistance of PV panels.

[0003] Traditional flame retardant coatings, using flame retardants such as halogenated flame retardants, while exhibiting good flame retardancy, release large amounts of toxic fumes and gases, posing significant risks to the environment and human health. Inorganic flame retardant additives, however, can enhance the flame retardant effect of coatings. Due to their cost-effectiveness, ease of processing, and environmental advantages, inorganic flame retardant additives have been widely used in industrial production. However, some problems have also emerged during their use. For example, when excessive amounts of magnesium hydroxide inorganic flame retardant are used, its compatibility with the polymer matrix becomes poor. These problems often severely affect the mechanical properties of photovoltaic backsheet coatings, thereby damaging the overall performance of the coating.

[0004] Phosphorus-based flame retardants possess excellent flame retardant properties and stability, and are more environmentally friendly. Therefore, adding phosphorus-based flame retardants to epoxy resin systems is currently an ideal and widely used halogen-free flame retardant method. The flame retardant mechanism of phosphorus-based flame retardants encompasses two levels: First, the condensed-phase flame retardant effect, when heated and burned in a high-temperature environment, the phosphorus-containing flame retardant decomposes to form substances such as phosphoric acid and polyphosphoric acid, promoting the dehydration and carbonization of the organic resin. At the same time, the high-viscosity substances produced by combustion cover the surface of the substrate, isolating oxygen and heat, and protecting the interior of the organic resin; Second, the gas-phase flame retardant effect, where active free radicals in the gas phase are captured by PO· produced by the phosphorus-based flame retardant, thereby interrupting the combustion chain reaction. Summary of the Invention

[0005] The purpose of this invention is to provide a photovoltaic backsheet coating and its preparation method. This invention uses a flame-retardant composite prepared by 2-amino-6-hydroxybenzothiazole, phenylphosphodichloro, and citral to introduce P, S, and N flame-retardant elements and a Schiff base structure, which significantly improves the flame-retardant performance of the coating. Moreover, the carbon-carbon double bonds and hydroxyl groups of the flame-retardant composite can participate in the reaction of the monomer raw materials in the organic system. This chemical bonding method also significantly improves the stability of the core-shell structure, thereby significantly improving the mechanical properties and flame-retardant stability of the coating.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for preparing a photovoltaic backsheet coating includes the following steps:

[0008] 1) Place isocyanate and organic solvent in a reaction vessel, preheat under an inert gas atmosphere, add catalyst and mix well, add polyol and stir to react, and after the reaction is completed, perform rotary evaporation to obtain prepolymer;

[0009] 2) The coating is prepared by stirring and mixing the prepolymer, modified silica, reactive monomer, pigment and photoinitiator. The coating is then applied to the surface of the photovoltaic backsheet and cured by UV curing.

[0010] As a preferred embodiment of the present invention, the inert gas atmosphere in step 1) is a nitrogen gas atmosphere, the preheating is to raise the temperature to 50-60°C, and the stirring reaction temperature is 60-70°C and the reaction time is 4-5 hours.

[0011] As a preferred embodiment of the present invention, the isocyanate in step 1) is isophorone diisocyanate, the organic solvent is one or more of ethyl acetate, butyl acetate and methyl acetate, the catalyst is one or more of dibutyltin laurate, dioctyltin dilaurate, stannous octoate, di(dodecyl sulfide)dibutyltin, di(dodecyl sulfide)dioctyltin, di(dodecyl sulfide)dimethyltin, dibutyltin diacetate, dibutyltin dimercaptoacetate, di-n-butyltin oxide, dimethyltin dinedecanoate, dioctyltin dinedecanoate, dioctyltin dimercaptoacetate and dimethyltin dioleate, and the polyol is polytetrahydrofuran with a molecular weight of 2000.

[0012] As a preferred embodiment of the present invention, the mass ratio of isocyanate, organic solvent, catalyst and polyol in step 1) is 80-100:60-80:0.03-0.05:40-48.

[0013] As a preferred embodiment of the present invention, the reactive monomer in step 2) is composed of methacrylate, 2-methacrylate-4-hydroxybutyl ester and flame retardant compound in a mass ratio of 26-32:0.8-1.2:3.5-4.2; the mass ratio of the prepolymer, modified silica, reactive monomer, pigment and photoinitiator is 30-40:8-9:80-100:13-16:2.5-3.0.

[0014] As a preferred embodiment of the present invention, the pigments selected are titanium dioxide, carbon black, or iron oxide pigments. Titanium dioxide, primarily rutile, possesses high hiding power, excellent weather resistance, and chemical stability. It reflects ultraviolet light, protecting the coating substrate from aging, while also providing a white base. Iron oxide pigments, including iron oxide red, iron yellow, and iron black, exhibit strong weather resistance and corrosion resistance, stable color, and good compatibility with the coating system. Carbon black is used for the black backing plate, providing strong light-blocking properties and absorbing excess ultraviolet light, while also improving the coating's anti-aging performance. However, its usage must be controlled to avoid affecting the coating's insulation. Titanium dioxide is used in both this embodiment and the comparative example.

[0015] As a preferred embodiment of the present invention, the photoinitiator in step 2) is one or more combinations of 2-hydroxy-2-methyl-1-phenyl-1-propanone, 1-hydroxycyclohexylphenyl ketone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide and α-hydroxyalkylphenyl ketone.

[0016] As a preferred technical solution of the present invention, the stirring and mixing in step 2) is to stir at 30-40℃ for 30-40 minutes.

[0017] This invention discloses a method for preparing the flame-retardant composite, comprising the following steps:

[0018] A1. 2-Amino-6-hydroxybenzothiazole, triethylamine and dichloromethane were placed in a reaction vessel and mixed. Under an inert gas atmosphere, phenylphosphodichloride solution was slowly added. After heating and stirring, the mixture was filtered, the filtrate was washed, and the organic phase was dried with anhydrous sodium sulfate to obtain the intermediate.

[0019] A2. The intermediate and ethyl acetate are mixed in a reaction vessel. Under an inert gas atmosphere, citral is added and stirred at a constant temperature. The solvent is removed by rotary evaporation to obtain the final product.

[0020] As a preferred embodiment of the present invention, the inert gas in the inert gas atmosphere in step A1 is nitrogen, the washing is performed by washing three times with saturated brine, the heating and stirring temperature is 25-30°C and the time is 4-6 hours, the mass ratio of 2-amino-6-hydroxybenzothiazole, triethylamine, dichloromethane and phenylphosphodichloro solution is 8-10:6.5-7.5:90-100:30-38, and the phenylphosphodichloro and anhydrous dichloromethane are mixed in a mass ratio of 6.5-7.0:25-30.

[0021] As a preferred technical solution of the present invention, the flame retardant properties of 2-amino-6-hydroxybenzothiazole mainly depend on the N and S elements in the molecule: N decomposes at high temperature to produce inert gas to dilute combustible gas, S captures active free radicals in the combustion chain reaction, and its benzothiazole heterocyclic structure can promote the formation of a preliminary char layer during pyrolysis. Its heterocyclic structure can slightly enhance the rigidity of the resin molecular chain and improve the hardness of the coating.

[0022] As a preferred technical solution of the present invention, the flame retardant properties of phenylphosphine dichloride are mainly due to the condensation phase effect of the P element, which can catalyze the pyrolysis of the resin to form a carbon layer to block heat and oxygen. Its rigid benzene ring structure can effectively enhance the coating's impact resistance and tensile strength.

[0023] As a preferred embodiment of the present invention, the inert gas in the inert gas atmosphere in step A2 is nitrogen, the temperature of the constant temperature stirring is 40-50℃ and the time is 8-10h, and the mass ratio of the intermediate, ethyl acetate and citral is 10-12:70-80:2.2-3.0.

[0024] This invention discloses a method for preparing the modified silica, comprising the following steps: mixing fumed silica and anhydrous ethanol, adding a silane coupling agent, sonicating at 300-500W for 30-40 minutes, then stirring at a constant temperature of 50-60℃ for 3-4 hours, filtering to obtain the solid, washing three times with pure ethanol, and vacuum drying at 80℃ to constant weight to obtain the modified silica. The modified silica is obtained by modifying fumed silica with vinyltriethoxysilane through a specific process, enabling it to undergo a crosslinking reaction with the resin matrix via the vinyl functional groups in the silane coupling agent. This crosslinking effect not only significantly improves the mechanical strength of the coating, making it more resistant to deformation under external forces, but also greatly enhances the coating's weather resistance and anti-aging ability, allowing it to maintain stable performance even after prolonged exposure to harsh environmental conditions. Furthermore, the effective dispersibility of the modified silica avoids its agglomeration in the coating, thereby ensuring the uniformity of the coating, resulting in a smooth and flat surface and superior overall performance.

[0025] As a preferred embodiment of the present invention, the mass ratio of the fumed silica, anhydrous ethanol and silane coupling agent is 18-20:50-60:5.5-6.5, the silane coupling agent is one or more of vinyltriethoxysilane, methacryloxypropyltrimethoxysilane and vinyltrimethoxysilane, and the particle size of the fumed silica is 10-20 nm.

[0026] This invention discloses a photovoltaic backsheet coating prepared by the above-described preparation method.

[0027] The beneficial effects of this invention are:

[0028] 1. The present invention prepares a flame-retardant composite by 2-amino-6-hydroxybenzothiazole, phenylphosphodichloro and citral, and introduces P, S and N flame-retardant elements and Schiff base structure, which significantly improves the flame-retardant performance of the coating. Moreover, the carbon-carbon double bond of the flame-retardant composite participates in the polymerization reaction of the monomers, and the hydroxyl group of 2-methacrylate-4-hydroxybutyl ester reacts with the isocyanate. This chemical bonding method also significantly improves the stability of the core-shell structure, thereby significantly improving the mechanical properties and flame-retardant stability of the coating.

[0029] 2. The present invention uses specific raw material ratios and process conditions to make the prepared photovoltaic backsheet coating have excellent adhesion, which can adhere tightly to the surface of the photovoltaic backsheet and is not easy to fall off, thus effectively extending the service life of the photovoltaic backsheet.

[0030] Instruction manual illustrations

[0031] Figure 1 The infrared spectrum of the flame-retardant composite of Example 2 is shown. Detailed Implementation

[0032] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with embodiments, is provided below.

[0033] Example 1

[0034] The preparation method of the modified silica includes the following steps: fumed silica and anhydrous ethanol are mixed, a silane coupling agent is added and ultrasonically sonicated at 300W power for 30 minutes, then stirred at 50℃ for 3 hours, the solid is filtered and taken, washed 3 times with pure ethanol, and dried under vacuum at 80℃ to constant weight to obtain modified silica.

[0035] In the preparation of modified silica, the mass ratio of fumed silica, anhydrous ethanol and silane coupling agent is 18:50:5.5, the silane coupling agent is vinyltriethoxysilane, and the particle size of the fumed silica is 10 nm.

[0036] The preparation method of the flame retardant composite includes the following steps:

[0037] A1. 2-Amino-6-hydroxybenzothiazole, triethylamine and dichloromethane were placed in a reaction vessel and mixed. Phenylphosphoryl dichloride solution was slowly added under a nitrogen atmosphere. The mixture was heated and stirred at 25°C for 4 hours and then filtered. The filtrate was washed three times with saturated brine and the organic phase was dried with anhydrous sodium sulfate to obtain the intermediate.

[0038] In step A1, the mass ratio of 2-amino-6-hydroxybenzothiazole, triethylamine, dichloromethane, and phenylphosphodichloride solution is 8:6.5:90:30, and the phenylphosphodichloride and anhydrous dichloromethane are mixed in a mass ratio of 6.5:25.

[0039] A2. The intermediate and ethyl acetate were placed in a reaction vessel and mixed. Citral was added under a nitrogen atmosphere and stirred at 40°C for 8 hours. The solvent was removed by rotary evaporation to obtain the final product.

[0040] The mass ratio of the intermediate, ethyl acetate and citral in step A2 is 10:70:2.2.

[0041] A method for preparing a photovoltaic backsheet coating includes the following steps:

[0042] 1) Place isocyanate and organic solvent in a reaction vessel, heat to 50°C under a nitrogen atmosphere, add catalyst and mix well, add polyol and stir at 60°C for 4 hours, after the reaction is completed, rotary evaporate to obtain prepolymer;

[0043] The isocyanate mentioned in step 1) is isophorone diisocyanate, the organic solvent is ethyl acetate, the catalyst is dioctyltin dilaurate, and the polyol is polytetrahydrofuran with a molecular weight of 2000; the mass ratio of the isocyanate, organic solvent, catalyst and polyol is 80:60:0.03:40.

[0044] 2) After stirring the prepolymer, modified silica, reactive monomer, pigment and photoinitiator at 30°C for 30 min, the resulting coating is applied to the surface of the photovoltaic backsheet and UV cured to complete the preparation.

[0045] The reactive monomers in step 2) are composed of methacrylate, 2-methacrylate-4-hydroxybutyl ester and flame retardant complex in a mass ratio of 26:0.8:3.5; the mass ratio of the prepolymer, modified silica, reactive monomers, pigment and photoinitiator is 30:8:80:13:2.5, and the photoinitiator is 2-hydroxy-2-methyl-1-phenyl-1-propanone.

[0046] Example 2

[0047] The preparation method of the modified silica includes the following steps: fumed silica and anhydrous ethanol are mixed, a silane coupling agent is added and ultrasonically sonicated at 365W power for 35 minutes, then stirred at 53℃ for 3.5 hours, the solid is filtered and washed three times with pure ethanol, and then vacuum dried at 80℃ to constant weight to obtain modified silica.

[0048] In the preparation of modified silica, the mass ratio of fumed silica, anhydrous ethanol and silane coupling agent is 18.5:55:5.8, the silane coupling agent is vinyltriethoxysilane, and the particle size of the fumed silica is 15 nm.

[0049] The preparation method of the flame retardant composite includes the following steps:

[0050] A1. 2-Amino-6-hydroxybenzothiazole, triethylamine and dichloromethane were placed in a reaction vessel and mixed. Under a nitrogen atmosphere, phenylphosphodichloro solution was slowly added. The mixture was heated and stirred at 27°C for 4.5 h and then filtered. The filtrate was washed three times with saturated brine and the organic phase was dried with anhydrous sodium sulfate to obtain the intermediate.

[0051] In step A1, the mass ratio of 2-amino-6-hydroxybenzothiazole, triethylamine, dichloromethane, and phenylphosphodichloride solution is 8.5:6.8:95:35, and the phenylphosphodichloride and anhydrous dichloromethane are mixed in a mass ratio of 6.6:26.

[0052] A2. The intermediate and ethyl acetate were mixed in a reaction vessel. Citral was added under a nitrogen atmosphere and stirred at 43°C for 8.5 hours. The solvent was removed by rotary evaporation to obtain the final product.

[0053] The mass ratio of the intermediate, ethyl acetate and citral in step A2 is 10.5:75:2.5.

[0054] Depend on Figure 1 It can be seen that at 1250cm -1 1070cm -1 The characteristic peak at 1651 cm⁻¹ is mainly attributed to P=O and PO bonds. Compared to the intermediate, the infrared value in the product is higher at 1651 cm⁻¹. -1 The appearance of a new characteristic peak is attributed to the Schiff base bond generated by the Schiff base reaction between the intermediate and citral, indicating that the flame retardant complex contains P element and Schiff base bond, proving that the flame retardant complex was successfully synthesized.

[0055] A method for preparing a photovoltaic backsheet coating includes the following steps:

[0056] 1) Place isocyanate and organic solvent in a reaction vessel, heat to 53°C under a nitrogen atmosphere, add catalyst and mix well, add polyol and stir at 63°C for 4.5 h, after the reaction is completed, rotary evaporate to obtain prepolymer;

[0057] The isocyanate mentioned in step 1) is isophorone diisocyanate, the organic solvent is ethyl acetate, the catalyst is dioctyltin dilaurate, and the polyol is polytetrahydrofuran with a molecular weight of 2000; the mass ratio of the isocyanate, organic solvent, catalyst and polyol is 87:65:0.035:43.

[0058] 2) After stirring the prepolymer, modified silica, reactive monomer, pigment and photoinitiator at 33°C for 33 min, the resulting coating is applied to the surface of the photovoltaic backsheet and UV cured to complete the preparation.

[0059] The reactive monomers in step 2) are composed of methacrylate, 2-methacrylate-4-hydroxybutyl ester and flame retardant complex in a mass ratio of 28:0.9:3.6; the mass ratio of the prepolymer, modified silica, reactive monomers, pigment and photoinitiator is 34:8:87:14:2.6, and the photoinitiator is 2-hydroxy-2-methyl-1-phenyl-1-propanone.

[0060] Example 3

[0061] The preparation method of the modified silica includes the following steps: fumed silica and anhydrous ethanol are mixed, a silane coupling agent is added and ultrasonically sonicated at 435W power for 38 minutes, then stirred at 57℃ for 3.8 hours, the solid is filtered and washed 3 times with pure ethanol, and dried under vacuum at 80℃ to constant weight to obtain modified silica.

[0062] In the preparation of modified silica, the mass ratio of fumed silica, anhydrous ethanol and silane coupling agent is 19.5:58:6.2, the silane coupling agent is vinyltriethoxysilane, and the particle size of the fumed silica is 15 nm.

[0063] The preparation method of the flame retardant composite includes the following steps:

[0064] A1. 2-Amino-6-hydroxybenzothiazole, triethylamine and dichloromethane were placed in a reaction vessel and mixed. Phenylphosphoryl dichloride solution was slowly added under a nitrogen atmosphere. The mixture was heated and stirred at 28°C for 5.5 h and then filtered. The filtrate was washed three times with saturated brine and the organic phase was dried with anhydrous sodium sulfate to obtain the intermediate.

[0065] In step A1, the mass ratio of 2-amino-6-hydroxybenzothiazole, triethylamine, dichloromethane, and phenylphosphodichloride solution is 9.5:7.2:95:35, and the phenylphosphodichloride and anhydrous dichloromethane are mixed in a mass ratio of 6.8:28.

[0066] A2. The intermediate and ethyl acetate were placed in a reaction vessel and mixed. Citral was added under a nitrogen atmosphere and stirred at 46°C for 9.5 hours. The solvent was removed by rotary evaporation to obtain the final product.

[0067] The mass ratio of the intermediate, ethyl acetate and citral in step A2 is 11.5:78:2.8.

[0068] A method for preparing a photovoltaic backsheet coating includes the following steps:

[0069] 1) Place isocyanate and organic solvent in a reaction vessel, heat to 56°C under a nitrogen atmosphere, add catalyst and mix well, add polyol and stir at 66°C for 4.8 h, after the reaction is completed, rotary evaporate to obtain prepolymer;

[0070] The isocyanate mentioned in step 1) is isophorone diisocyanate, the organic solvent is ethyl acetate, the catalyst is dioctyltin dilaurate, and the polyol is polytetrahydrofuran with a molecular weight of 2000; the mass ratio of the isocyanate, organic solvent, catalyst and polyol is 95:74:0.04:45.

[0071] 2) After stirring the prepolymer, modified silica, reactive monomer, pigment and photoinitiator at 37°C for 38 min, the resulting coating is applied to the surface of the photovoltaic backsheet and UV cured to complete the preparation.

[0072] The reactive monomers in step 2) are composed of methacrylate, 2-methacrylate-4-hydroxybutyl ester and flame retardant complex in a mass ratio of 30:1.1:4; the mass ratio of the prepolymer, modified silica, reactive monomers, pigment and photoinitiator is 38:8.3:95:14:2.8, and the photoinitiator is 2-hydroxy-2-methyl-1-phenyl-1-propanone.

[0073] Example 4

[0074] The preparation method of the modified silica includes the following steps: fumed silica and anhydrous ethanol are mixed, a silane coupling agent is added and ultrasonically sonicated at 500W power for 40 minutes, then stirred at 60℃ for 4 hours, the solid is filtered and taken, washed 3 times with pure ethanol, and dried under vacuum at 80℃ to constant weight to obtain modified silica.

[0075] In the preparation of modified silica, the mass ratio of fumed silica, anhydrous ethanol and silane coupling agent is 20:60:6.5, the silane coupling agent is vinyltriethoxysilane, and the particle size of the fumed silica is 20 nm.

[0076] The preparation method of the flame retardant composite includes the following steps:

[0077] A1. 2-Amino-6-hydroxybenzothiazole, triethylamine and dichloromethane were placed in a reaction vessel and mixed. Phenylphosphoryl dichloride solution was slowly added under a nitrogen atmosphere. The mixture was heated and stirred at 30°C for 6 hours and then filtered. The filtrate was washed three times with saturated brine and the organic phase was dried with anhydrous sodium sulfate to obtain the intermediate.

[0078] In step A1, the mass ratio of 2-amino-6-hydroxybenzothiazole, triethylamine, dichloromethane, and phenylphosphoryl dichloride solution is 10:7.5:100:38, and the phenylphosphoryl dichloride and anhydrous dichloromethane are mixed in a mass ratio of 7.0:30.

[0079] A2. The intermediate and ethyl acetate were mixed in a reaction vessel. Citral was added under a nitrogen atmosphere and stirred at 50°C for 10 hours. The solvent was removed by rotary evaporation to obtain the final product.

[0080] The mass ratio of the intermediate, ethyl acetate and citral in step A2 is 12:80:3.0.

[0081] A method for preparing a photovoltaic backsheet coating includes the following steps:

[0082] 1) Place isocyanate and organic solvent in a reaction vessel, heat to 60°C under a nitrogen atmosphere, add catalyst and mix well, add polyol and stir at 70°C for 5 hours, after the reaction is completed, rotary evaporate to obtain prepolymer;

[0083] The isocyanate mentioned in step 1) is isophorone diisocyanate, the organic solvent is ethyl acetate, the catalyst is dioctyltin dilaurate, and the polyol is polytetrahydrofuran with a molecular weight of 2000; the mass ratio of the isocyanate, organic solvent, catalyst and polyol is 100:80:0.05:48.

[0084] 2) After stirring the prepolymer, modified silica, reactive monomer, pigment and photoinitiator at 40°C for 40 min, the resulting coating is applied to the surface of the photovoltaic backsheet and UV cured to complete the preparation.

[0085] The reactive monomers in step 2) are composed of methacrylate, 2-methacrylate-4-hydroxybutyl ester and flame retardant complex in a mass ratio of 32:1.2:4.2; the mass ratio of the prepolymer, modified silica, reactive monomers, pigments and photoinitiators is 40:8.5:100:15:3.0, and the photoinitiator is 2-hydroxy-2-methyl-1-phenyl-1-propanone.

[0086] Example 5

[0087] The preparation method of the modified silica includes the following steps: fumed silica and anhydrous ethanol are mixed, a silane coupling agent is added and ultrasonically sonicated at 365W power for 35 minutes, then stirred at 53℃ for 3.5 hours, the solid is filtered and washed three times with pure ethanol, and then vacuum dried at 80℃ to constant weight to obtain modified silica.

[0088] In the preparation of modified silica, the mass ratio of fumed silica, anhydrous ethanol and silane coupling agent is 18.5:55:5.8, the silane coupling agent is vinyltriethoxysilane, and the particle size of the fumed silica is 15 nm.

[0089] The preparation method of the flame retardant composite includes the following steps:

[0090] A1. 2-Amino-6-hydroxybenzothiazole, triethylamine and dichloromethane were placed in a reaction vessel and mixed. Phenylphosphoryl dichloride solution was slowly added under a nitrogen atmosphere. The mixture was heated and stirred at 28°C for 5 hours and then filtered. The filtrate was washed three times with saturated brine and the organic phase was dried with anhydrous sodium sulfate to obtain the intermediate.

[0091] In step A1, the mass ratio of 2-amino-6-hydroxybenzothiazole, triethylamine, dichloromethane, and phenylphosphoryl dichloride solution is 9:6.8:95:36, and the phenylphosphoryl dichloride and anhydrous dichloromethane are mixed in a mass ratio of 6.6:26.

[0092] A2. The intermediate and ethyl acetate were placed in a reaction vessel and mixed. Citral was added under a nitrogen atmosphere and stirred at 45°C for 9 hours. The solvent was removed by rotary evaporation to obtain the final product.

[0093] The mass ratio of the intermediate, ethyl acetate and citral in step A2 is 10.5:75:2.5.

[0094] A method for preparing a photovoltaic backsheet coating includes the following steps:

[0095] 1) Place isocyanate and organic solvent in a reaction vessel, heat to 56°C under a nitrogen atmosphere, add catalyst and mix well, add polyol and stir at 65°C for 4.5 h, after the reaction is completed, rotary evaporate to obtain prepolymer;

[0096] The isocyanate mentioned in step 1) is isophorone diisocyanate, the organic solvent is butyl acetate, the catalyst is stannous octoate, and the polyol is polytetrahydrofuran with a molecular weight of 2000; the mass ratio of the isocyanate, organic solvent, catalyst and polyol is 90:70:0.04:45.

[0097] 2) After stirring the prepolymer, modified silica, reactive monomer, pigment and photoinitiator at 36°C for 35 min, the resulting coating is applied to the surface of the photovoltaic backsheet and UV cured to complete the preparation.

[0098] The reactive monomers in step 2) are composed of methacrylate, 2-methacrylate-4-hydroxybutyl ester and flame retardant complex in a mass ratio of 30:1:3.8; the mass ratio of the prepolymer, modified silica, reactive monomers, pigment and photoinitiator is 36:9:90:16:2.8, and the photoinitiator is 2-hydroxy-2-methyl-1-phenyl-1-propanone.

[0099] Comparative Example 1

[0100] Compared with Example 2, Comparative Example 1 differs in that methacrylate is used instead of 2-methacrylate-4-hydroxybutyl ester, while the other components, preparation steps and parameters are the same.

[0101] Comparative Example 2

[0102] Compared with Example 2, Comparative Example 2 differs in that methacrylate is used instead of the flame retardant compound, while the other components, preparation steps and parameters are the same.

[0103] Comparative Example 3

[0104] Compared with Example 2, Comparative Example 3 differs in that step A1 is omitted, and step A2 uses 2-amino-6-hydroxybenzothiazole instead of the intermediate. The remaining components, preparation steps and parameters are the same.

[0105] Comparative Example 4

[0106] Compared with Example 2, Comparative Example 4 differs in that o-aminophenol is used instead of 2-amino-6-hydroxybenzothiazole, while the other components, preparation steps and parameters are the same.

[0107] The coatings prepared in Examples 1-5 and Comparative Examples 1-4 were subjected to the following performance tests after UV curing at 365nm. The test results are shown in Table 1.

[0108] Vertical flammability rating test: based on UL-94;

[0109] Limiting oxygen index test: according to GB / T 2406.2-2009;

[0110] Impact strength test: according to GB / T 1843-2021;

[0111] Table 1. Test results of flame retardant and mechanical properties

[0112]

[0113] As can be seen from the test results in Table 1, compared with Comparative Examples 1-4, the coatings prepared by the present invention in Examples 1-5 have excellent flame retardant properties and mechanical properties.

[0114] Comparative Example 1, lacking 2-methacrylate-4-hydroxybutyl ester, lost its hydroxyl group bonding with isocyanate, resulting in decreased mechanical properties. However, the flame-retardant complex was retained, ensuring the synergistic flame-retardant effect of PNS, indicating that hydroxyl groups significantly influence mechanical properties, while flame-retardant performance decreased slightly. Comparative Example 2, lacking the flame-retardant complex and the PNS-Schiff base flame-retardant system, experienced a significant deterioration in flame-retardant performance. The loss of its double bond cross-linking effect also led to a comprehensive decline in mechanical properties, verifying that the flame-retardant complex is the core of the synergistic effect between flame retardancy and mechanical properties. Comparative Example 3, lacking phosphorus due to the absence of the A1 step, retained only NS flame retardancy. The lack of synergistic effect weakened flame-retardant performance, and the incomplete intermediate structure resulted in reduced cross-linking density and worsened mechanical properties, demonstrating that phosphorus is crucial for condensed-phase flame retardancy and cross-linking rigidity. Comparative Example 4, replacing 2-amino-6-hydroxybenzothiazole with o-aminophenol, lacked the thiazole structure and sulfur, retaining only PN flame retardancy. This resulted in decreased flame-retardant performance, and the loss of molecular chain rigidity due to the benzothiazole heterocycle indicated that sulfur can enhance gas-phase flame retardancy and molecular chain rigidity.

[0115] This invention utilizes the N and S elements provided by the thiazole structure of 2-amino-6-hydroxybenzothiazole to form a P / N / S ternary synergistic flame retardant system with the P element of phenylphosphodichloro. Combined with the Schiff base structure's self-crosslinking reaction at high temperatures, this forms a nitrogen-containing six-membered ring structure, imparting superior charring properties to the coating and significantly improving its thermal stability and flame retardant performance. Furthermore, the rigid thiazole structure of 2-amino-6-hydroxybenzothiazole and the rigid benzene ring structure of phenylphosphodichloro synergistically enhance the coating's hardness and tensile strength. Secondly, the intermediate introduces carbon-carbon double bonds through reaction with citral, ultimately participating in the polymerization of the reactant monomers. Meanwhile, the hydroxyl groups of 2-methacrylate-4-hydroxybutyl ester form chemical bonds with the isocyanate prepolymer. Together, they anchor the flame-retardant composite containing PNS-Schiff base in the resin matrix through chemical bonds. By improving the interfacial bonding force between the flame-retardant composite and the resin matrix, the mechanical properties of the coating are improved, while preventing the migration and loss of flame retardant and ensuring its uniform distribution in the coating. This results in a stable and long-lasting flame-retardant effect. This combination of "multi-element synergistic flame retardancy and chemical bonding" far exceeds the effect of a single flame-retardant element or physical addition, achieving a synergistic improvement in both flame-retardant and mechanical properties.

[0116] In summary, the photovoltaic panel coating prepared by this invention has excellent flame retardant properties, good impact mechanical properties and substrate adhesion. It can also prevent flame retardant migration through chemical bonding, improve weather resistance and anti-aging properties with the help of modified silica, and ensure film formation by relying on suitable solvents and catalysts, thus comprehensively meeting the functional requirements of photovoltaic backsheets for long-term outdoor use.

[0117] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any indirect modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a photovoltaic backsheet coating, characterized in that, The preparation method includes the following steps: 1) Place isocyanate and organic solvent in a reaction vessel, preheat under an inert gas atmosphere, add catalyst and mix well, add polyol and stir to react, and after the reaction is completed, perform rotary evaporation to obtain prepolymer; 2) The coating is prepared by stirring and mixing the prepolymer, modified silica, reactive monomer, pigment and photoinitiator, and then applying it to the surface of the photovoltaic backsheet and UV curing it. The preparation method of the flame-retardant composite includes the following steps: A1. 2-Amino-6-hydroxybenzothiazole, triethylamine and dichloromethane were placed in a reaction vessel and mixed. Under an inert gas atmosphere, phenylphosphodichloride solution was slowly added. After heating and stirring, the mixture was filtered, the filtrate was washed, and the organic phase was dried with anhydrous sodium sulfate to obtain the intermediate. A2. The intermediate and ethyl acetate are mixed in a reaction vessel. Under an inert gas atmosphere, citral is added and stirred at a constant temperature. The solvent is removed by rotary evaporation to obtain the final product.

2. The method for preparing a photovoltaic backsheet coating according to claim 1, characterized in that: Step 1) The inert gas atmosphere is a nitrogen gas atmosphere, the preheating is to raise the temperature to 50-60℃, the stirring reaction temperature is 60-70℃ and the reaction time is 4-5h, and the mass ratio of isocyanate, organic solvent, catalyst and polyol is 80-100:60-80:0.03-0.05:40-48.

3. The method for preparing a photovoltaic backsheet coating according to claim 1, characterized in that: Step 1) The isocyanate is isophorone diisocyanate, and the polyol is polytetrahydrofuran with a molecular weight of 2000.

4. The method for preparing a photovoltaic backsheet coating according to claim 1, characterized in that: Step 1) The organic solvent is one or more of ethyl acetate, butyl acetate, and methyl acetate, and the catalyst is one or more of dibutyltin laurate, dioctyltin dilaurate, stannous octoate, di(dodecyl sulfide)dibutyltin, di(dodecyl sulfide)dioctyltin, di(dodecyl sulfide)dimethyltin, dibutyltin diacetate, dibutyltin dimercaptoacetate, di-n-butyltin oxide, dimethyltin dineodecanate, dioctyltin dineodecanate, dioctyltin dimercaptoacetate, and dimethyltin dioleate.

5. The method for preparing a photovoltaic backsheet coating according to claim 1, characterized in that: Step 2) involves stirring at 30-40°C for 30-40 minutes. The reactant monomers consist of methacrylate, 2-methacrylate-4-hydroxybutyl ester, and the flame retardant complex in a mass ratio of 26-32: The composition is 0.8-1.2:3.5-4.2; the mass ratio of the prepolymer, modified silica, reactive monomer, pigment and photoinitiator is 30-40:8-9:80-100:13-16:2.5-3.0, and the photoinitiator is one or more combinations of 2-hydroxy-2-methyl-1-phenyl-1-propanone, 1-hydroxycyclohexylphenyl ketone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide and α-hydroxyalkyl benzophenone.

6. The method for preparing a photovoltaic backsheet coating according to claim 1, characterized in that: In step A1, the inert gas in the inert gas atmosphere is nitrogen. The washing is performed three times with saturated brine. The heating and stirring temperature is 25-30°C and the time is 4-6 hours. The mass ratio of the 2-amino-6-hydroxybenzothiazole, triethylamine, dichloromethane, and phenylphosphodichloro solution is 8-10:6.5-7.5:90-100:30-38. The phenylphosphodichloro and anhydrous dichloromethane are mixed in a mass ratio of 6.5-7.0:25-30.

7. The method for preparing a photovoltaic backsheet coating according to claim 1, characterized in that: The inert gas in the inert gas atmosphere mentioned in step A2 is nitrogen, the constant temperature stirring temperature is 40-50℃ and the time is 8-10h, and the mass ratio of the intermediate, ethyl acetate and citral is 10-12:70-80:2.2-3.

0.

8. The method for preparing a photovoltaic backsheet coating according to claim 1, characterized in that: The method for preparing the modified silica includes the following steps: mixing fumed silica and anhydrous ethanol, adding a silane coupling agent, sonicating at 300-500W power for 30-40 minutes, then stirring at a constant temperature of 50-60℃ for 3-4 hours, filtering to obtain the solid, rinsing three times with pure ethanol, and drying under vacuum at 80℃ to constant weight to obtain the modified silica.

9. The method for preparing a photovoltaic backsheet coating according to claim 8, characterized in that: The mass ratio of the fumed silica, anhydrous ethanol, and silane coupling agent is 18-20:50-60:5.5-6.5, the silane coupling agent is one or more of vinyltriethoxysilane, methacryloxypropyltrimethoxysilane, and vinyltrimethoxysilane, and the particle size of the fumed silica is 10-20 nm.

10. A photovoltaic backsheet coating prepared by any one of claims 1 to 9.

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