A solvent-free adhesive for a solar cell backsheet and a preparation method thereof

Abstract

The present invention relates to an adhesive applicable to PO / PET and PVDF / PET for solar cell backsheets, specifically a solvent-free adhesive for solar cell backsheets and a preparation method thereof. It consists of two components, a main agent and a curing agent. The main agent is a copolymerized polyester polyol, and the curing agent is a polyurethane prepolymer capped with isocyanate formed by the reaction of a polyol and an isocyanate; wherein, the molar ratio of the isocyanate group in the curing agent to the hydroxyl group in the main agent is 1.2 - 1.8:1. For the solar cell backsheet prepared using this adhesive, after normal state and PCT aging for 96 hours, both the PO / PET and PVDF / PET layers have high peel strength, with almost no yellowing, and can fully meet the application performance requirements of the adhesive for solar backsheets.

Description

Technical Field

[0001] The invention relates to an adhesive suitable for PO / PET and PVDF / PET solar cell back panels, in particular to a solvent-free adhesive for solar cell back panels and a preparation method thereof. Background Art

[0002] Solar cell backsheets are a crucial component of photovoltaic power generation equipment, serving primarily as electrical insulation, moisture barrier, and solar cell protection. Located on the back of a solar panel, they provide electrical insulation, moisture barrier, and protection for the cells. Currently, solar cell backsheets are categorized into two types: composite and coated. Composite backsheets combine multiple layers of materials with different functions using adhesives. Typically, the outer protective layer uses PVDF for excellent weather resistance, the base film uses PET for strength, and the inner layer uses PO or EVA for cushioning. Coated backsheets utilize a fluorocarbon coating applied to the substrate surface, using a fluorine-containing coating to provide weather resistance.

[0003] Currently, the adhesives used to bond the various layers of solar cell backsheets are all solvent-based. These adhesives carry the risk of fire or explosion during storage and use. The evaporation of the solvent can also cause harm to users and pollute the environment. Furthermore, after coating, solvent-based adhesives must be dried before lamination. This time-consuming drying process severely limits production efficiency, and subsequent solvent recovery or disposal also incurs costs.

[0004] Solvent-free adhesives, however, are safer during storage and use because they contain no solvents. They also eliminate the need for drying and solvent recovery, significantly increasing production line speeds and reducing lamination costs. With increasing environmental awareness among domestic companies and the need for national policy, solvent-free adhesives are poised to offer a new bonding solution. Summary of the Invention

[0005] The present invention aims to provide a solvent-free solar cell backsheet adhesive having improved moisture and heat resistance, so that the adhesive can withstand PCT (Pressure Cooker Test) aging for 96 hours or double 85 aging for 3000 hours, and a preparation method thereof.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions:

[0007] A solvent-free adhesive for solar cell backsheets consists of two components: a main agent and a curing agent. The main agent is a copolymerized polyester polyol, and the curing agent is an isocyanate-terminated polyurethane prepolymer generated by the reaction of the polyol and isocyanate. The molar ratio of the isocyanate group in the curing agent to the hydroxyl group in the main agent is 1.2-1.8:1.

[0008] When the molar ratio of isocyanate groups to hydroxyl groups is too large, the remaining isocyanate groups will continue to react with water, generating carbon dioxide gas, which affects the water resistance and high-temperature resistance of the adhesive. When the molar ratio of isocyanate groups to hydroxyl groups is too small, the adhesive cures incompletely, affecting the bonding performance and resulting in a small interlayer peeling strength.

[0009] The polyol is a copolymerized polyester polyol and a polyether polyol with a water content of less than 400 ppm. Among them, the copolymerized polyester polyol used in the main agent and the curing agent has a molecular weight of 500-4000 and an aliphatic cyclic structure in the structural unit. Preferably, it is 700-2500 and has an aliphatic cyclic structure in the structural unit. When the polyether polyol used in the curing agent has a molecular weight of 500-4000, preferably 700-2500. If the polyol molecule is too small, the required curing time is longer and the mechanical properties after curing are poor. If the polyol molecular weight is too large, the viscosity of the finished adhesive will be too high, making it difficult to achieve application.

[0010] The copolymerized polyester polyol is prepared by mixing polybasic acid monomers and polyol monomers, slowly heating to 220-230 °C, filling with nitrogen for protection, carrying out an esterification reaction and discharging water. When the amount of water discharged reaches the theoretical amount of water discharged, it is determined that the esterification reaction is over. Continue to heat up to make the system temperature reach 230-240 °C, and keep the vacuum degree at -0.09 to -0.1 MPa for 2-4 h to obtain a copolymerized polyester polyol with a water content of less than 400 ppm.

[0011] The above-mentioned alcohol-acid ratio is 1.2-1.6:1.

[0012] The polyester polyol needs to be measured for acid value and hydroxyl value, and the molecular weight of the polyester polyol is calculated using the following formula.

[0013]

[0014] Among them, the measurement method of the amount of hydroxyl substance is carried out according to the measurement method of hydroxyl value in HG / T 2709-95 polyester polyol, and the measurement method of the amount of acid value substance is carried out according to the measurement method of acid value in HG / T 2708-95 polyester polyol. If the monomers for preparing the polyester polyol are all dibasic acids and diols, the functionality of the polyester polyol is 2.

[0015] The polybasic acid monomer is selected from one or more of 1,2-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic anhydride (hexahydrophthalic anhydride), 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 1,6-hexanedioic acid, 1,9-nonanedioic acid, 1,10-decanedioic acid; wherein the alicyclic polybasic acid structural unit needs to reach more than 20 wt% of the total mass of the polyester polyol, preferably more than 30 wt%, which can exhibit more excellent high-temperature resistance and hydrolysis resistance and can maintain good adhesion ability under high temperature and high humidity.

[0016] The polyol monomer is selected from one or more of 1,2-cyclohexanediol, 1,3-cyclohexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, 3-methyl-1,5-pentanediol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), trimethylolpropane.

[0017] The main agent is obtained by heating one or more copolymerized polyester polyols with a water content of 400 ppm or less to 60-80 °C, adding an auxiliary agent under nitrogen protection, and mixing evenly to obtain the main agent component.

[0018] Among them, the water content is measured by a Karl Fischer moisture meter. If the measured value is greater than 400 ppm, the polyol needs to be dehydrated pretreated. The pretreatment method is to add the copolymerized polyester polyol into the reaction vessel, heat it to 100-120 °C and maintain the vacuum degree of -0.09 to -0.1 MPa. Measure the water content at intervals until the water content is below 400 ppm.

[0019] The auxiliary agent is an antioxidant, a hydrolysis-resistant agent, a light stabilizer and a silane coupling agent. Among them, the antioxidant, the hydrolysis-resistant agent, the light stabilizer and the silane coupling agent account for 0.02-0.5 wt%, 0.1-2 wt%, 0.1-2 wt%, 0.02-0.5 wt% of the mass of the copolymerized polyester polyol respectively.

[0020] The antioxidant mainly includes phenolic antioxidants, and its mechanism of action is to capture free radicals generated during the decomposition of organic substances to prevent subsequent free radical chain reactions, thereby effectively controlling the degradation and yellowing of organic molecule. In the present invention, the addition of the antioxidant can improve the heat oxidation and light oxidation resistance of the adhesive. It can be selected from BASF's commercially available products IRGANOX 1010, IRGANOX 1076, IRGANOX 1098, IRGANOX 245, IRGANOX 1330, IRGANOX3114, and can be used in combination with other types of antioxidants, such as IRGAFOS 168, IRGAFOS 38, IRGAFOS 126, IRGANOXPS 802, etc.

[0021] The anti-hydrolytic agent mainly includes carbodiimide anti-hydrolytic agents, which mainly act on the carboxyl groups generated by hydrolysis, generating cross-links while inhibiting the hydrolysis promoting effect of carboxyl groups. One or more of the commercially available products from RheinChemie, such as Stabaxol 1LF, Stabaxol MTC, Stabaxol P, Stabaxol P200, the commercially available products from Nisshinbo, such as CARBODILITE V-02B, CARBODILITE V-05, and the commercially available products from Shanghai Langyi New Materials, such as HyMax 220 and HyMax 1010 can be selected.

[0022] The main functions of the light stabilizer include converting harmful ultraviolet rays and capturing free radicals activated by light. One or more of the commercially available products from BASF, such as Chimassorb 81, Chimassorb 944, Chimassorb2020, Tinuvin 326, Tinuvin328, Tinuvin 329, Tinuvin 234, Tinuvin 360, Tinuvin 1577FF, Tinuvin 1600, Uvinul4050FF can be selected.

[0023] The silane coupling agent includes, but is not limited to, one or more of vinyltris(β-methoxyethoxy)silane, vinyltriethoxysilane, vinyltrimethoxysilane, γ-(meth)acryloxypropyltrimethoxysilane, γ-(meth)acryloxypropyltriethoxysilane, γ-(meth)acryloxypropyldimethoxymethylsilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, β-(3,4-epoxycyclohexyl)methyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltriethoxysilane, β-(3,4-epoxycyclohexyl)methyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, N-β-(aminoethyl)-γ-aminopropylmethyldiethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, N-phenyl-γ-aminopropyltriethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane.

[0024] The curing agent is prepared by adding one or more polyether polyols or copolymeric polyester polyols with a water content of 400 ppm or less into a reaction vessel, heating to 60 - 80°C, adding isocyanate under nitrogen protection, heating to 80 - 100°C and maintaining for 0.5 - 4 h, then adding a catalyst and continuing the reaction until the content of isocyanate groups in the system no longer decreases, obtaining the curing agent component; wherein, the mass ratio of polyol to isocyanate is 0.5 - 2:1, and the dosage of the catalyst is 0.02 wt% - 0.1 wt% of the total mass of the raw materials (polyol and isocyanate).

[0025] When the addition amount of isocyanate is too small, the viscosity of the curing agent component will be too large, affecting the product application process; when the addition amount of isocyanate is too large, the molecular weight of the curing agent component is small, the curing time required in actual application is long, and the mechanical properties after curing are poor.

[0026] Among them, the amount of isocyanate groups is determined according to the method for determining the content of isocyanate groups in polyurethane prepolymers in GB / T 29493.6 - 2013.

[0027] The polyether polyols used in the curing agent are selected from one or more of polyethylene glycol, polytetrahydrofuran diol, and hydroxyl-terminated polybutadiene.

[0028] The isocyanates in the curing agent component are selected from one or more of isophorone diisocyanate, isophorone diisocyanate trimer, hexamethylene diisocyanate, hexamethylene diisocyanate trimer, and hydrogenated diphenylmethane diisocyanate.

[0029] In the curing agent component, the catalyst is selected from one or more of stannous octoate, dibutyltin diacetate, dibutyltin dilaurate, dioctyltin dilaurate, and stannous chloride.

[0030] A preparation method of the solvent-free adhesive for solar cell backsheets described above, which involves mixing the main agent and the curing agent described above; wherein, the molar ratio of the isocyanate group in the curing agent to the hydroxyl group in the main agent is 1.2 - 1.8:1.

[0031] An application of the solvent-free adhesive for solar cell backsheets described above, where the solvent-free adhesive is applicable to solar cell backsheets that can withstand PCT accelerated aging (121°C, saturated humidity) for 96 hours. The advantages of the present invention are as follows:

[0032] The adhesive of the present invention consists of two parts: the main agent and the curing agent. Among them, the curing agent is mainly composed of a copolymerized polyester polyol capped with isocyanate and a mixture of polyether polyols; the main agent is mainly composed of a copolymerized polyester polyol and additives.

[0033] Generally speaking, there is a relatively large amount of polyester component in the main structure of this adhesive. In the synthesis of the copolymerized polyester, monomers containing an alicyclic structure are used, and the remaining components contain more side chains, which can strengthen the rigidity of the main structure of the adhesive while protecting the ester group and reducing the hydrolysis rate. When it is used on solar cell backsheets, after normal state and PCT aging for 96 hours, both the PO / PET and PVDF / PET layer interfaces have relatively high peel strengths, with almost no yellowing, which can fully meet the application performance requirements of adhesives for high-performance solar backsheets. Detailed implementation manners

[0034] The present invention is further described through the following specific implementation manners. It should be noted that the following examples cannot be used as the basis for limiting the protection scope of the present invention, and are only for facilitating the understanding of the technical solution of the present invention.

[0035] Example 1

[0036] Preparation of copolymerized polyester polyol P-1: Add 745.62 g of 1,2-cyclohexanedicarboxylic acid, 111.69 g of adipic acid, and 352.56 g of 2,2-dimethyl-1,3-propanediol (neopentyl glycol) into a reaction vessel, displace nitrogen three times, mix and slowly heat up to 220°C. After the esterification reaction is completed, continue to heat up to make the internal temperature of the reaction vessel reach 235°C, and keep the vacuum degree at 30 kPa for 2.5 h to obtain copolymerized polyester polyol P-1 with a number average molecular weight of 825.

[0037] Example 2

[0038] Preparation of Copolyester Polyol P-2: Add 745.62 g of 1,2-cyclohexanedicarboxylic acid, 143.82 g of 1,9-nonanedioic acid, and 352.56 g of 2,2-dimethyl-1,3-propanediol (neopentyl glycol) into a reaction vessel. Replace nitrogen three times, mix and slowly heat up to 220 °C. After the esterification reaction is completed, continue to heat up to make the internal temperature of the reaction vessel reach 235 °C, and maintain a vacuum of 30 kPa for 2.5 h to obtain copolyester polyol P-2 with a number average molecular weight of 997.

[0039] Example 3

[0040] Preparation of Copolyester Polyol P-3: Add 745.62 g of 1,2-cyclohexanedicarboxylic acid, 154.53 g of 1,10-decanedioic acid, and 352.56 g of 2,2-dimethyl-1,3-propanediol (neopentyl glycol) into a reaction vessel. Replace nitrogen three times, mix and slowly heat up to 220 °C. After the esterification reaction is completed, continue to heat up to make the internal temperature of the reaction vessel reach 235 °C, and maintain a vacuum of 30 kPa for 2.5 h to obtain copolyester polyol P-3 with a number average molecular weight of 1031.

[0041] Example 4

[0042] Preparation of Copolyester Polyol P-4: Add 745.62 g of 1,2-cyclohexanedicarboxylic acid, 143.82 g of 1,9-nonanedioic acid, 282.05 g of 2,2-dimethyl-1,3-propanediol (neopentyl glycol), and 98.99 g of 3-methyl-1,5-pentanediol into a reaction vessel. Replace nitrogen three times, mix and slowly heat up to 220 °C. After the esterification reaction is completed, continue to heat up to make the internal temperature of the reaction vessel reach 235 °C, and maintain a vacuum of 30 kPa for 2.5 h to obtain copolyester polyol P-4 with a number average molecular weight of 876.

[0043] Example 5

[0044] Preparation of Copolyester Polyol P-5: Add 372.81 g of 1,2-cyclohexanedicarboxylic acid, 372.81 g of 1,4-cyclohexanedicarboxylic acid, 143.82 g of 1,9-nonanedioic acid, 282.05 g of 2,2-dimethyl-1,3-propanediol (neopentyl glycol), and 98.99 g of 3-methyl-1,5-pentanediol into a reaction vessel. Replace nitrogen three times, mix and slowly heat up to 220 °C. After the esterification reaction is completed, continue to heat up to make the internal temperature of the reaction vessel reach 240 °C, and maintain a vacuum of 30 kPa for 3 h to obtain copolyester polyol P-5 with a number average molecular weight of 1105.

[0045] Example 6

[0046] Preparation of Copolyester Polyol P-6: 372.30 g of adipic acid, 479.4 g of azelaic acid, 390.53 g of 1,4-cyclohexanedimethanol, and 61.02 g of 2-methyl-1,3-propanediol were added to a reaction vessel. Nitrogen was replaced three times, and the mixture was slowly heated to 220 °C. After the esterification reaction was completed, the temperature was further raised to make the internal temperature of the reaction vessel reach 240 °C, and the reaction was carried out at a vacuum degree of 30 kPa for 3 h to obtain copolyester polyol P-6 with a number average molecular weight of 1004.

[0047] Example 7

[0048] Preparation of Copolyester Polyol P-7: 372.30 g of adipic acid, 479.4 g of azelaic acid, 235.94 g of 1,4-cyclohexanediol, and 113.88 g of 3-methyl-1,5-pentanediol were added to a reaction vessel. Nitrogen was replaced three times, and the mixture was slowly heated to 220 °C. After the esterification reaction was completed, the temperature was further raised to make the internal temperature of the reaction vessel reach 240 °C, and the reaction was carried out at a vacuum degree of 30 kPa for 3 h to obtain copolyester polyol P-7 with a number average molecular weight of 967.

[0049] Example 8

[0050] Preparation of Solvent-Free Adhesive Main Agent A-1: 240 g of copolyester polyol P-1, 3 g of silane coupling agent γ-glycidoxypropyltrimethoxysilane, 0.05 g of antioxidant IRGANOX 1010, 2 g of hydrolysis inhibitor Carbodilite V-02B, and 0.1 g of light stabilizer Chimassorb 2020 were added to a reaction vessel. The mixture was heated to 90 °C to melt the raw materials, and stirring was started at 120 rpm to make the raw materials mix evenly to obtain solvent-free adhesive main agent A-1.

[0051] According to the preparation process of this example, solvent-free adhesive main agents A-2 to A-7 can be obtained. According to the above description, only the copolyester polyol P-1 is sequentially replaced with the different copolyester polyols (P-2 to P-7) prepared corresponding to Examples 2-6 above. Among them, copolyester polyol P-2 is added to solvent-free adhesive main agent A-2, and so on.

[0052] Example 9

[0053] Preparation of curing agent S-1: Add 300 g of copolymerized polyester polyol P-1 and 510 g of polypropylene glycol (molecular weight 1000) into a reaction kettle. Heat to 70 - 80 °C to melt the raw materials, start stirring at 120 rpm to mix the raw materials evenly, add 697 g of isophorone diisocyanate, slowly raise the temperature of the reaction kettle to 90 °C, after reacting at a constant temperature for 1 h, add 0.75 g of dibutyltin dilaurate as a catalyst, and then maintain the reaction temperature at 95 °C for 1 h to obtain curing agent S-1. The isocyanate group content of curing agent S-1 is measured to be 9.27%.

[0054] Example 10

[0055] Preparation of curing agent S-2: Add 300 g of copolymerized polyester polyol P-1 and 510 g of polypropylene glycol (molecular weight 1000) into a reaction kettle. Heat to 70 - 80 °C to melt the raw materials, start stirring at 120 rpm to mix the raw materials evenly, add 697 g of isophorone diisocyanate, slowly raise the temperature of the reaction kettle to 90 °C, after reacting at a constant temperature for 1 h, add 0.75 g of dibutyltin dilaurate as a catalyst, and then maintain the reaction temperature at 95 °C for 1 h, add 75 g of hexamethylene diisocyanate trimer to obtain curing agent S-2. The isocyanate group content of curing agent S-2 is measured to be 10.26%.

[0056] Preheat different main agents and different curing agents to 60 °C according to the records in the following table, mix them evenly according to the ratio of 1.4:1 of the isocyanate group content in the curing agent and the hydroxyl group content in the main agent, and coat them on the PET substrate. Preheat the laminating machine to 60 °C, and use a pressure of 0.6 MPa to laminate the PVDF film and the PO film with the PET respectively, and cure at 60 °C for 144 h. After curing, the thickness of the adhesive film is measured to be in the range of 5 - 10 μm.

[0057] Peel strength test: According to the standard of the 180° peel strength test method for adhesives - flexible materials to rigid materials in GB-T 2790-1995, cut the composite film sample into a strip shape of 15 mm × 200 mm, symmetrically clamp the unbonded ends of the materials on both sides of the measured adhesive layer between the upper and lower holders of a universal testing machine, ensure that there is no slippage at the clamping part, that is, the applied tensile force is evenly distributed on the width of the specimen, start the testing machine, and separate the upper and lower holders at a rate of 100 mm / min, and the interlayer peel strength of the corresponding material is given by the testing machine.

[0058] Due to the low body strength of the PVDF film, the peel strength cannot be effectively measured. The adhesion performance of PVDF / PET is measured according to the method described in GB / T 1720-79(89) Determination of film adhesion.

[0059] PCT Accelerated Aging Test: Place the composite film in a PCT accelerated aging test chamber, keep the chamber connected to the outside, heat it up to 100°C at a rate of 10°C / min, close the exhaust valve, and continue heating to 121°C. At this time, the absolute pressure inside the chamber is about 2.3 atm. Start timing when the temperature reaches 121°C, keep it at 121 ± 0.5°C and 2.3 ± 0.1 atm for 48 h / 96 h, then take out the composite film and place it for 24 h until the moisture evaporates completely, and then test the interfacial peel strength by the above-mentioned peel strength test method.

[0060] The test data are shown in the following table:

[0061]

[0062] From the interfacial peel strength test results in the above table, the solvent-free two-component solar cell backsheet adhesive prepared by the present invention has good bonding performance for both PO / PET and PVDF / PET. The interfacial peel strength in the normal state is ≥ 9 N / cm, and after 96 h of PCT accelerated aging, the interfacial peel strength is ≥ 4 N / cm, still having good bonding performance, indicating that the adhesive's hydrolysis resistance and damp heat resistance can meet the requirements of high-performance solar cell backsheets.

[0063] Yellowing Resistance Test: For the samples after PCT aging, measure the yellow edge index Δb of the backsheet according to the provisions of GB / T 3979-2008 and GB / T7921-2008. After measurement, the color difference values of all the above samples are < 2, and there is almost no obvious yellowing, indicating that the product has good yellowing resistance.

[0064] The above are only some of the more preferred embodiments of the present invention, and the scope of the rights protection of the present invention includes but is not limited to this. Those skilled in the art of this professional field can easily think of changes or substitutions within the information disclosed by the present invention, which should be covered by the protection scope of the present invention. The specific protection scope shall be subject to the content covered in the claims.

Claims

1. A solvent-free adhesive for a solar cell backsheet, characterized in that, It consists of two components, namely the main agent and the curing agent. The ratio of the content of isocyanate groups in the curing agent to the content of hydroxyl groups in the main agent is 1.4:1; The curing agent is prepared as follows: 300 g of copolymerized polyester polyol P-1, 510 g of polypropylene glycol with a molecular weight of 1000 are added to a reaction kettle. The raw materials are melted by heating to 70 - 80 °C, and stirring is started at 120 rpm to mix the raw materials evenly. Then 697 g of isophorone diisocyanate is added. The reaction kettle is slowly heated to 90 °C, and after reacting at a constant temperature for 1 h, 0.75 g of dibutyltin dilaurate as a catalyst is added. Then the reaction temperature is maintained at 95 °C for 1 h to obtain the curing agent; The main agent is 240 g of copolymerized polyester polyol P-6 or P-7, 3 g of silane coupling agent γ-glycidoxypropyltrimethoxysilane, 0.05 g of antioxidant IRGANOX 1010, 2 g of anti-hydrolysis agent Carbodilite V-02B, and 0.1 g of light stabilizer Chimassorb 2020 are added to a reaction vessel. The raw materials are melted by heating to 90 °C, and stirring is started at 120 rpm to mix the raw materials evenly to obtain the main agent of the solvent-free adhesive; Copolymerized polyester polyol P-6 is prepared by adding 372.30 g of adipic acid, 479.4 g of azelaic acid, 390.53 g of 1,4-cyclohexanedimethanol, and 61.02 g of 2-methyl-1,3-propanediol to a reaction vessel. Nitrogen is replaced three times, and the mixture is slowly heated to 220 °C. After the esterification reaction is completed, the temperature is further increased to make the internal temperature of the reaction vessel reach 240 °C, and the reaction is carried out at a vacuum degree of 30 kPa for 3 h to obtain copolymerized polyester polyol P-6 with a number average molecular weight of 1004; Copolymerized polyester polyol P-7 is prepared by adding 372.30 g of adipic acid, 479.4 g of azelaic acid, 235.94 g of 1,4-cyclohexanediol, and 113.88 g of 3-methyl-1,5-pentanediol to a reaction vessel. Nitrogen is replaced three times, and the mixture is slowly heated to 220 °C. After the esterification reaction is completed, the temperature is further increased to make the internal temperature of the reaction vessel reach 240 °C, and the reaction is carried out at a vacuum degree of 30 kPa for 3 h to obtain copolymerized polyester polyol P-7 with a number average molecular weight of 967; Copolymerized polyester polyol P-1 is prepared by adding 745.62 g of 1,2-cyclohexanedicarboxylic acid, 111.69 g of adipic acid, and 352.56 g of 2,2-dimethyl-1,3-propanediol to a reaction vessel. Nitrogen is replaced three times, and the mixture is slowly heated to 220 °C. After the esterification reaction is completed, the temperature is further increased to make the internal temperature of the reaction vessel reach 235 °C, and the reaction is carried out at a vacuum degree of 30 kPa for 2.5 h to obtain copolymerized polyester polyol P-1.

2. The preparation method of the solvent-free adhesive for the solar cell backplane according to claim 1, characterized in that: Mix the above-mentioned main agent and curing agent; among them, the molar ratio of isocyanate groups in the curing agent to hydroxyl groups in the main agent is 1.4:

1.

3. Use of the solvent-free adhesive for a solar cell backsheet according to claim 1, characterized in that: The said solvent-free adhesive is applicable to the solar cell backplane that can withstand PCT accelerated aging for 96 hours; the aging conditions are 121 °C and saturated humidity.

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